# SolderlessPCB: Reusing Electronic Components in PCB Prototyping through
Detachable 3D Printed Housings

Zeyu Yan  University of Maryland, College ParkCollege ParkMDUSA20895
<EMAIL_ADDRESS>,  Jiasheng Li  University of Maryland, College ParkCollege
ParkMDUSA20895<EMAIL_ADDRESS>,  Zining Zhang  University of Maryland, College
ParkCollege ParkMDUSA20895<EMAIL_ADDRESS>and  Huaishu Peng  University of
Maryland, College ParkCollege ParkMDUSA20895<EMAIL_ADDRESS>
(2024)

###### Abstract.

The iterative prototyping process for printed circuit boards (PCBs) frequently
employs surface-mounted device (SMD) components, which are often discarded
rather than reused due to the challenges associated with desoldering, leading
to unnecessary electronic waste. This paper introduces SolderlessPCB, a
collection of techniques for solder-free PCB prototyping, specifically
designed to promote the recycling and reuse of electronic components. Central
to this approach are custom 3D-printable housings that allow SMD components to
be mounted onto PCBs without soldering. We detail the design of SolderlessPCB
and the experiments conducted to evaluate its design parameters, electrical
performance, and durability. To illustrate the potential for reusing SMD
components with SolderlessPCB, we discuss two scenarios: the reuse of
components from earlier design iterations and from obsolete prototypes. We
also provide examples demonstrating that SolderlessPCB can handle high-current
applications and is suitable for high-speed data transmission. The paper
concludes by discussing the limitations of our approach and suggesting future
directions to overcome these challenges.

PCB prototyping, Sustainability, Reuse, Electronic Component, Soldering

††journalyear: 2024††copyright: rightsretained††conference: Proceedings of the
CHI Conference on Human Factors in Computing Systems; May 11–16, 2024;
Honolulu, HI, USA††booktitle: Proceedings of the CHI Conference on Human
Factors in Computing Systems (CHI ’24), May 11–16, 2024, Honolulu, HI,
USA††doi: 10.1145/3613904.3642765††isbn: 979-8-4007-0330-0/24/05††ccs: Social
and professional topics Sustainability††ccs: Hardware Printed circuit
boards††ccs: Human-centered computing Systems and tools for interaction design

Figure 1. Bristlebot design iterations using SolderlessPCB: the initial design
is assembled using a SolderlessPCB housing; the updated design is assembled
into the final prototype by reusing SMD components harvested from the initial
prototype.

Figure 1 illustrates the iterative design process for the Bristlebot. Users
start with an initial design and assemble it using a solderless PCB housing.
Then, they update its design and reuse some SMD (Surface-Mount Device)
components from the initial prototype.

##  1\. Introduction

Circuit prototyping is a key step in both product design and research. The
process often involves multiple rounds of iteration and testing, beginning
with circuit validation using breadboards and breakout boards, and later
transitioning to custom printed circuit boards (PCBs).

The two stages of circuit prototyping have distinct differences. Breadboard
circuitry allows engineers and designers to quickly assemble a circuit by
inserting through-hole components and jumper wires into a standardized
baseboard. It offers the flexibility to easily modify the circuit by
reconnecting different parts or replacing electronic components if mistakes
are identified.

In contrast, PCB prototyping is less flexible. Since it usually occurs closer
to the final stages of the design process, the form factor of the circuit
becomes critical. As a result, the electronic components used in PCB
prototyping are often surface-mounted (SMD) with small footprints, requiring
assembly through a semi-permanent bonding method—soldering. As such, PCB
prototyping boards are often one-off creations. When errors are identified
during prototyping, or when a PCB assembly is no longer needed, these PCB
boards are often not disassembled like with breadboard prototyping. Instead,
new PCBs are produced and assembled with an entirely new suite of electronic
components. The components on the old prototyping boards, even though they
mostly function perfectly, are not reused or salvaged, leading to unnecessary
e-waste.

This paper explores an alternative approach to traditional PCB prototyping,
aimed at promoting the reuse of still-functional SMD components. The key to
our idea is a set of 3D-printable housings that can mechanically mount SMD
components onto custom PCBs. This eliminates the need for soldering and
desoldering during PCB assembly, thereby allowing designers and engineers the
flexibility to interchange SMD components similarly to how they would with
through-hole components in breadboard prototyping. This approach enables the
reuse or replacement of SMD components, while also allowing the exploration of
the comparably small form factor of custom PCBs. We call our prototyping
technique SolderlessPCB.

In the remainder of the paper, we first report on a formative interview
exploring how designers and engineers currently conduct circuit prototyping.
The design implications drawn from the interview guide our work on
SolderlessPCB. We detail the key design considerations and the fabrication
method for the 3D-printable housings. We then present a series of experiments
on resistance, impedance reproducibility, and high-frequency signal loss in
circuits made with SolderlessPCB. These experiments characterize the
electrical performance and stability of our approach. To contextualize
SolderlessPCB, we present two scenarios in which it can encourage the reuse of
electronic components during prototyping, accompanied by three additional
examples: a mug heater, a mini game console with an OLED display, and an FTDI
code-uploading module, showcasing the applicability of our method. We conclude
with a discussion on the limitations of our approach and our thoughts on
future research directions.

##  2\. Related Work

###  2.1. Sustainability in HCI: Making and Prototyping

Sustainable Interaction Design(SID) (Blevis, 2007) highlights the importance
of considering environmental impacts and human behaviors in designing
interaction technologies, particularly regarding the material outcomes of
physical making. Subsequent works (e.g., (Knowles et al., 2016; Wei et al.,
2019; Blevis et al., 2017)) have explored the impact of various design
paradigms on sustainability. In particular, prior efforts have demonstrated
methods to reduce the environmental impact of waste generated during the
design process by utilizing decomposable and recyclable materials (Song et
al., 2022; Karana et al., 2018; Rivera et al., 2023; Buechley et al., 2023) or
bio-materials (Bell et al., 2023; Koelle et al., 2022; Guridi et al., 2023;
Jin et al., 2016; Bell et al., 2022a). However, materials with unique
properties are often not easily replaceable with eco-friendly alternatives,
which may require special fabrication processes (Pataranutaporn et al., 2018)
or certain levels of manual manipulations (Vasquez and Vega, 2019b; Lazaro
Vasquez et al., 2022; Bell et al., 2022b).

Besides using alternative materials, much research has explored the concepts
of repairing and repurposing wasted materials, or “unmake” artifacts that are
beyond their design lifespan (Jackson and Kang, 2014; Dew and Rosner, 2019; Lu
et al., 2023; Maestri and Wakkary, 2011; Song and Paulos, 2021; Kumar et al.,
2021; Kim and Paulos, 2011). For example, FabricatINK (Hanton et al., 2022)
has proposed making personal, bespoke displays using electronic ink from
upcycled E-Readers. Unfabricate (Wu and Devendorf, 2020) has demonstrated
design practices for reclaiming and reusing materials in the context of smart
textiles.

Recently, HCI researchers have also argued that the design iteration during
the prototyping process should also be viewed from a sustainability
perspective (Lazaro Vasquez et al., 2020; Yan et al., 2023). As most
prototyping processes involve multiple iterations, modules and materials are
often integrated into the interim results but are rarely reused or recovered
(Yan et al., 2023). In other words, their lifespan is as short as the duration
of the testing process for each prototyping iteration. In this research, we
examine the prototyping process of PCBs and propose a suite of techniques
aimed at reusing the electronic components involved. We hope this research
will spark discussions revolving around reuse and recycling during electronic
design iterations.

###  2.2. Supporting the Reuse of Electronics

Research on sustainability in electronics, especially PCBs, extends across
multiple domains and encompasses various stages of the PCB lifecycle.

A common set of industrial approaches for recycling electronics involves
extracting raw materials from PCB scrap. Both chemical and mechanical
techniques are employed to reclaim valuable materials, including refractory
metals and elements from the platinum group, found in standard PCB waste (Hsu
et al., 2019; Maurice et al., 2021). New recycling methods are also being
developed to extract valuable materials from several more specific types of
semiconductors, such as ICs and LEDs (Zhan et al., 2020; Bradwell et al.,
2011). However, these methods have yet to demonstrate generalizability across
a wide range of components.

Besides extracting raw materials from discarded PCBs, various research efforts
have explored new materials that can make functional PCBs more sustainable.
For example, several works have shown that paper (Cheng et al., 2020; Kawahara
et al., 2013; Wang et al., 2018), wood (Ishii et al., 2021), and water-soluble
materials (Bharath et al., 2020; Jiva, 2023; Cheng et al., 2023; Groeger and
Steimle, 2018) can all serve as circuit substrates, which can be easily
recycled after their lifecycle. Similarly, transient electronics, utilizing
novel composite materials, can be engineered to actively or passively degrade
into the environment (Yin et al., 2014; Huang et al., 2014; Vasquez and Vega,
2019a; Song and Paulos, 2023).

From a systems perspective, HCI researchers have explored alternative methods
to encourage the reuse of electronic components. For example, CurveBoards (Zhu
et al., 2020) has proposed a custom-shaped breadboard design that is versatile
for rapid prototyping, enabling the reuse of through-hole components. Shorter
et al. (Shorter et al., 2014) have demonstrated methods that utilize
conductive everyday objects, such as binder clips, to create circuits that can
be easily disassembled, albeit with limitations on the resolution and size of
the resulting circuits. ecoEDA (Lu et al., 2023) has demonstrated how
interactive circuit design software, by integrating early-stage suggestions
for utilizing recyclable electronic components from stock PCBs, can facilitate
the reuse of electronics throughout the design process. Like ecoEDA, our work
also aim to encourage the reuse of electronic components during the PCB
prototyping stage. However, our focus is on simplifying the assembly and
disassembly of SMD components through the use of a non-soldered mounting
method.

###  2.3. Circuit Assembly and Disassembly

While recent HCI research has explored the use of CO2 and fiber lasers to
facilitate the soldering and assembly of PCBs (Nisser et al., 2021; Yan et
al., 2022), the removal and desoldering of electronic components from PCBs
remains time-consuming and energy-intensive (Hao et al., 2020).

In the industry, heating methods such as infrared, solder baths, and hot
fluids are often used for desoldering (Maurice et al., 2021), but they require
expensive equipment and are neither environmentally friendly nor safe for
health (Ni et al., 2014; Wang et al., 2011). Other works have examined the use
of conductive epoxy, rather than solder paste, as a method for circuit
assembly (Aradhana et al., 2020). However, while epoxy does not require the
high melting temperatures as with soldered PCBs, it is still difficult to
remove without damaging the components.

Our work introduces a new mounting method for PCB assembly, thus entirely
eliminates the need of soldering, reduce the risk of damaging SMD components
and facilitate solder-free replacement and reuse of these components.

##  3\. Understanding the Current PCB Prototyping Practice

To better understand current practices and challenges in PCB prototyping, we
conducted semi-structured interviews with experienced PCB designers.

###  3.1. Method

We recruited five participants (four male, one female, aged 26-42) through
local makerspaces’ email lists and social media platforms. All participants
have at least five years of experience in PCB design and prototyping. We
visited their labs and makerspaces to conduct in-person, semi-structured
interviews. During these interviews, we asked about their general practices of
circuit prototyping, as well as their approaches to handling used electronic
components. This included both the validation of circuit designs (e.g., using
a breadboard) and the process of making PCB prototypes. Each interview lasted
between 60 and 90 minutes. Participants who successfully completed our
interviews were compensated at a rate of $15 per hour. The interviews were
audio-recorded and transcribed for analysis. Thematic analysis (Braun and
Clarke, 2006) was conducted individually by two investigators and unified
through discussion to derive proper findings. In the rest of this section, we
present the key findings from the interviews, which informed the design of
SolderlessPCB.

###  3.2. Findings

####  3.2.1. Circuit validation with breadboarding

While all interviewees prototype circuit boards for various objectives,
including research, robotic product development, and personal projects, they
reported an inevitable circuit validation phase to gain confidence in their
circuit diagram. According to the interviewees, breadboarding is the most
commonly used technique to conduct circuit validation, as it allows for easy
modifications when necessary. By the end of this phase, over 60% of the
components are stored for future use. This includes larger components that are
placed on the breadboard with DIP packages, such as breakout modules,
transducers, and microphones, as well as through-hole components like
transistors and LEDs. One participant stated, “The nature of my projects is
more or less related, so a lot of components will be reused between projects
for breadboards.” Additionally, apart from small components like resistors and
capacitors, which are difficult to have their pins straightened after use,
people agree that it is easy and efficient to recycle these components from
the breadboard for future use.

####  3.2.2. PCB prototyping and assembly

After the circuit diagram has been verified, PCBs are made and assembled for
long-term use. According to the interviewees, PCBs are either outsourced or
made in-house using CNC machines, laser cutters, or chemical etching
processes. All of them revealed that more than 80% of the components used in
these PCB assemblies are SMD components. Two of the interviewees had
experience ordering PCB assemblies with components pre-installed by the
manufacturer. However, due to differences in cost-effectiveness and lead time
between ordering pre-assembled boards and bare PCBs, they ultimately converged
their decision with the rest of the interviewees. They chose to make or
purchase bare PCB boards and components separately and conduct PCB assembly
themselves using soldering irons, heat guns, or reflow ovens.

Despite their experience working with SMD components, none of the interviewees
chose to desolder them for reuse between iterations or projects, except in the
case of expensive or hard-to-find components. Interviewees highlighted several
challenges in reusing SMD components. For example, one interviewee mentioned,
“Many components have plastic housing or plastic parts in their packaging.
When desoldering them using a heat gun, it is easy to mess them up, and the
components end up not being usable anyway.” Besides the desoldering
techniques, cleaning the leftover solder also presents challenges. “Sometimes,
it’s hard to make sure all pins are properly cleaned after desoldering, so
when using components like that, it is hard to solder them again,” said a
circuit designer with eight years of PCB prototyping experience. Reportedly,
less than 15% of components in PCB assemblies get desoldered and reused.

###  3.3. Design Implications

The interviews confirmed that the low incentive for recycling electronic
components during PCB prototyping is largely due to the extensive effort
required to desolder components from existing PCBs. We argue that the tedious
and unreliable process could be significantly alleviated if the assembly
process did not require soldering the components onto the PCB in the first
place.

Inspired by the principles of commonly used breadboards (Adafruit, 2022) and
conventional in-circuit testing methods (Buckroyd, 2015), we propose
assembling SMD components onto PCBs by applying external pressure to the
conductive pads. Ideally, the agent applying this pressure would eliminate the
need for solder, thereby facilitating a smoother and less cumbersome
disassembly process, which in turn makes it easier to reuse and recycle SMD
components. In the following sections, we detail our method of solder-free PCB
assembly.

##  4\. SolderlessPCB

We develop SolderlessPCB, a novel rapid PCB prototyping technique that
facilitates easy assembly and disassembly of PCBs as well as the reuse of SMD
components.

Figure 2 illustrates the exploded view of a PCB assembly made with
SolderlessPCB. As shown in the figure, the key to our approach is a custom
3D-printable housing that secures small SMD components to a PCB. The housing
includes custom cavities sized to fit the SMD components and positioned to
align with their locations on the PCB. End-users can place all the SMD
components inside these cavities and then directly bolt the entire housing to
the PCB all at once. The housing firmly presses the SMD components against the
PCB, forming the electrical connection with its internal tab structures, which
also compensate for any height differences among the components. With this
technique, the PCB assembly process becomes solder-free. In turn, the process
for reusing electronic components from assembled PCBs will involve only the
unscrewing of the bolts and nuts to release the SMD components from the board.

In the remainder of Section 4, we document the detailed designs of
SolderlessPCB, which include: 1) the housing anchoring mechanism; 2) the
cavity design for various types of electronic components; and 3) the
fabrication and design workflow for creating a SolderlessPCB prototype.

Figure 2. SolderlessPCB: a) rendering of an exploded view of a SolderlessPCB
assembly. b) a photo of a SolderlessPCB assembly.

Figure 2: This figure contains two images labeled ’a’ and ’b’, illustrating
the exploded view of SolderlessPCB. Image ’a’ shows the exploded view of a
SolderlessPCB assembly. The 3D-printable housing on the top part, the SMD
components in the middle, and the PCB at the bottom. Image ’b’ shows the
assembled PCB using SolderlessPCB approach.

###  4.1. Housing Anchoring and Pressure Generation

The key to a successful SolderlessPCB assembly is establishing a reliable
electrical connection between the electronic components and the FR-4 PCB
baseboard. To maintain such a connection, the custom housing needs to exert
sufficient pressure to keep the electronic components pressed against the
baseboard. We explored two sets of housing anchoring mechanisms: snap-fit and
screw bolting.

####  4.1.1. Snap-fit

Snap-fit anchoring consists of four or more custom clips located at the four
corners and along the edges of a housing, as shown in Figure 3. These clips
are designed with groove heights that exactly match the thickness of an FR-4
baseboard. As a result, the housing can achieve a tight fit with a baseboard
without requiring any additional manual process beyond simply pressing them
together.

Figure 3. Snap-fit housing PCB assembly with zoomed-in view.

Figure 3: This figure shows the snip-fit design of the housing. The clips
achieve with the FR-4 baseboard.

While snap-fit is the easiest assembly method, our experiments have shown that
this anchoring mechanism does not provide uniform electrical connections
across the entire area of a PCB. Because the downward force is primarily
generated through clipping, components situated closer to the edges receive
greater force than those nearer to the center of the baseboard. Although
allocating more slots for snap-fit mechanisms would improve the overall
pressure generated, it’s important to note that these slots take up a
considerable amount of circuit board area to accommodate the compliant snap-
fit tabs. Each slot occupies around $9\text{\,}{\mathrm{mm}}^{2}$ of area. As
a result, snap-fit housing will either severely interfere with PCB design and
routing, or not provide reliable electrical connections across the board
unless the prototyping board is sufficiently small. Due to this major
reliability issue, we will not recommend this design overall.

####  4.1.2. Screw bolting

Our second approach uses bolts and nuts with diameters as small as
$1\text{\,}\mathrm{mm}$ to serve as the primary hardware for attaching the
housing to the PCB baseboard, as shown in Figure 4. While bolting requires
additional manual assembly effort, it allows us to distribute fixture
hardware, and thus the downward force, evenly across the entire area of a PCB,
regardless of their size. Since each bolt occupies only
$0.8\text{\,}{\mathrm{mm}}^{2}$ of area per hole on the board, its footprint
does not significantly interfere with circuit trace routing. To ensure optimal
pressure generation without damaging the housing, we apply a torque of
$0.01\text{\,}\mathrm{N}\text{\,}\mathrm{m}$ to each of the nuts. Unless
otherwise specified, all the examples in the paper are based on the screw
bolting mechanism.

Figure 4. SolderlessPCB assembly using bolts.

Figure 4: This figure shows a SolderlessPCB using bolts.

###  4.2. Cavity Design

In addition to generating sufficient downward force, the housing must also
accommodate a variety of SMD components with different packages and reliably
hold them in place mechanically. Common SMD components include: 1) two-
terminal components with regulated package standards, such as resistors,
capacitors, and LEDs; 2) integrated circuits (ICs) with standardized packages,
such as microcontrollers, IMUs and transistors; and 3) non-standard SMD
components like battery holders, terminal connectors, and various specialized
sensors. We design different types of cavities for each type of component to
optimize housing performance. We document these designs in detail below.

####  4.2.1. Two-terminal components

Two-terminal components are among the most commonly seen SMD components. They
come in a series of numerically ordered package designs, with their dimensions
in length and width measured in hundredths of an inch. Packages sized 0603,
0805, and 1206 are commonly used for PCB prototyping.

Due to their small size, these two-terminal components often have a degree of
height variance. While this tolerance does not affect their performance, as
they are designed to be soldered onto PCBs, it can pose a challenge for
solderless assembly. Inconsistent height tolerances can affect the pressure
applied during assembly. For example, if a component is slightly lower than
its expected design height, it may not receive enough pressure to establish a
reliable contact with the baseboard. Conversely, if the component is taller
than expected, the housing may bend away from the PCB in that area. This could
potentially allow neighboring components more vertical movement, resulting in
loose connections.

Figure 5. Flexible tab structure accommodating two-terminal components: a) a
0805 component with a housing cavity featuring flexible tabs, b) an exploded
view illustration of the housing, a two-terminal component, and the PCB, c) an
illustration of the housing pressing the component onto the PCB using flexible
tabs.

Figure 5: This figure contains three images labeled in ’a’, ’b’, and ’c’
showing the flexible tab structure accommodating two-terminal components.
Image ’a’ shows a 0805 component being placed in its housing cavity featuring
flexible tabs. Image ’b’ shows an exploded view illustration of the housing, a
two-terminal component and PCB. Image ’c’ shows the housing is pressing the
component onto the PCB with flexible tabs.

We propose a cubic cavity design with a pair of flexible tabs to compensate
for possible height variations caused by manufacturing tolerances (Figure 5).
These flexible tabs are located on the side walls of the cavity, angled at
$30^{\circ}$ towards the PCB baseboard. Upon assembly, the tabs will deform
inward, towards the cavity’s ceiling. Depending on the actual height of each
two-terminal component, they will bend to varying degrees (Figure 5). This
design will ensure adequate pressure between the components and the PCB, while
at the same time absorbing energy through tab deformation to prevent the
housing from bending away from the PCB.

####  4.2.2. Integrated circuits

In addition to two-terminal components, the majority of commonly used ICs for
rapid prototyping are also available in standardized package designs. These
include the Small Outline Integrated Circuit (SOIC), Thin Shrink Small Outline
Package (TSSOP), Thin Quad Flat Package (TQFP), Ball Grid Array (BGA), and
Quad Flat No-Lead Package (QFN). We categorize these package designs into two
main types: Type 1, which includes SOIC, TSSOP, and TQFP, features pins
extending from the plastic enclosure; and Type 2, which includes BGA and QFN,
where pins are exposed only on the bottom of the chips. These two types of
packages present different challenges for cavity design. We address them
separately.

Figure 6. Type 1 IC: a) IC with extended metal pins; b) illustration of
unsettled extended pins when pressure is applied at the center; c)
illustration of all pins complying when the housing structure is pressed
directly upon them.

Figure 6: This figure contains three images labeled in ’a’, ’b’, and ’c’
showing the Type 1 IC. Image ’a’ shows a photo of a Type 1 IC. Image ’b’ shows
an illustration of unsettled extended pins when pressure is applied at the
center. Image ’c’ shows an illustration of all pins complying when the housing
structure is pressed directly upon them.

For Type 1 components, the extended metal pins are generally at the same
height, although there may be some manufacturing tolerance errors. When a
downward force is applied solely to the center of the IC enclosure, as with
the cavity designed for two-terminal components, the pressure will not be
evenly distributed across all the pins of the IC (Figure 6). Pins that are
initially higher than others will not experience the same pressure as the
lower ones and may not sufficiently connect to the baseboard. To account for
potential manufacturing discrepancies, our cavity design for Type 1 ICs
includes additional solid volumes at the top of each row of metal pins. These
structures directly press on the metal pins, rather than applying pressure to
the center of the IC enclosure (Figure 6c). This approach ensures that all
metal pins receive downward force, regardless of their individual height
differences.

For Type 2 components, an exact negative volume is provided in the housing to
accommodate the component, since the exposed metal connectors are not flexible
and therefore do not require height compensation.

However, one challenge for Type 2 components is that the exposed metal
connectors are not always the lowest point of the package design. Therefore,
when pressing downwards, these metal connectors may not make contact with the
baseboard. This can be mitigated by deliberately making the copper pads on the
PCB baseboard taller than the surrounding areas, as illustrated in Figure 7.

Figure 7. Type 2 ICs: a) IC with hidden pins on the bottom (bottom view); b)
illustration of Type 2 ICs working with conductors higher than clearance
areas.

Figure 7: This figure contains two images labeled in ’a’ and ’b’ showing the
Type 2 IC. Image ’a’ shows a photo of two Type 2 ICs with hidden pins on the
bottom. Image ’b’ illustrates Type 2 ICs working with conductors higher than
clearance areas.

For both Type 1 and Type 2 cavities, we employ the bolting technique
introduced in Section 4.1.2 to generate localized downward pressure. A strong
force applied to the corners of the ICs by the bolts may cause local
deformation in the housing structure. This could affect neighboring small two-
terminal components when multiple such components are required for a PCB
design. This issue can be alleviated by carving a groove in the housing
surrounding each component that requires bolting (Figure 8). The groove’s
depth is set so that there is only a $0.3\text{\,}\mathrm{mm}$ thick of
material connecting the component housing to the main housing. The
$0.3\text{\,}\mathrm{mm}$-thick connection will deform to absorb energy and
prevent housing deformation from propagating to the neighboring components.
The entire structure of the 3D housing remains as one piece during printing.

Figure 8. Groove structure: a) around the IC cavity (highlighted), b)
illustration of the side sectional view of grooves surrounding a component.

Figure 8: This figure contains two images labeled in ’a’ and ’b’ showing the
groove structure of the housing. Image ’a’ shows the grooves location around
the IC cavity. Image ’b’ illustrates the side sectional view of grooves
surrounding a component.

####  4.2.3. Custom form factor components

For SMD components that do not come in standard packaging, we individually
design a customized cavity for each one. All these designs are tested for
proper electrical connectivity and are stored in a component library.

###  4.3. Fabrication

All housings are 3D printed with a desktop LCD resin printer (Elegoo, 2020).
Since the cavity design includes miniature tabs that act as a deformable
buffer (Section 4.2.1), the standard resin is too brittle for this purpose.
Following the printing guidelines for flexible resin (Yan and Peng, 2021) and
through experimentation, we empirically found that a mixture of tough UV resin
(Anycubic, 2020) and flexible UV resin (RESIONE, 2020) in a 3:2 weight ratio
produces reliable printing results. This mix allows the detailed tab features
to function as intended.

###  4.4. Design Workflow

The SolderlessPCB housings in our work were designed using Autodesk Fusion
360, which offers integrated PCB design and 3D modeling features. To
facilitate the design process, we developed a custom IC component library that
contains the bolt hole locations and the 3D cavity designs co-existing with
each IC’s symbol and footprint. The library is open-sourced and can be found
at: https://github.com/zyyan20h/solderlessPCB. Below, we briefly explain the
PCB and housing design workflow using the IC component library.

Figure 9. Design workflow: a) import component from the library and build
schematic, b) route the PCB while working with bolt holes linked from the
library footprint, c) push the PCB design to 3D automatically with 3D cavity
models linked from the library, d) use Boolean operation to create cavities in
the housing to accommodate components.

Figure 9: This figure contains four screenshots labeled in ’a’, ’b’, ’c’, and
’d’ showing the SolderlessPCB housings design workflow using Autodesk Fusion
360. Screenshot ’a’ shows the importing component process from the library and
build a schematic. Screenshot ’b’ shows the PCB routing while working with
bolt holes linked from the library footprint. Screenshot ’c’ shows the PCB
design to a 3D model including 3D cavity models linked from the library.
Screenshot ’d’ shows the boolean operation to create cavities in the housing
to accommodate components.

As shown in Figure 9a, the design begins with the standard PCB design
pipeline, from schematic to 2D layout. In this stage, the user completes the
circuit schematic by placing and connecting symbols of electronic components
from our custom IC library onto the canvas. When transitioning from the
schematic design to the PCB design (Figure 9b), the bolt holes associated with
each IC component are automatically rendered on the board design canvas. The
cavity models for each IC are also automatically loaded into the 3D modeling
canvas, as shown in Figure 9c. To create a SolderlessPCB housing, the user
simply extrudes a 3D shape based on the PCB board profile to the height of the
intended housing thickness. A Boolean operation between the extruded shape and
the 3D cavity models of the ICs results in the final housing design, as shown
in Figure 9d. Once the design is finalized, the PCB design file is sent to a
CNC milling machine, and the housing design can be exported and sliced for 3D
printing.

##  5\. Characterization and Validation

In this section, we present a set of experiments to characterize our
SolderlessPCB approach, including design characterization, electrical
validation, and durability testing.

###  5.1. Design Parameter Characterization

####  5.1.1. Bolts allocation

In the IC component library, we have incorporated pre-allocated bolt holes
into each IC footprint, and the same approach can also be extended to two-
terminal components. However, it’s a common practice in PCB design to place
two-terminal components closely together, as illustrated in Figure 10. In such
scenarios, a set of predefined bolt holes for each two-terminal component may
be unnecessary and could simply increase the manual assembly time. Instead, it
is possible for a group of closely placed two-terminal components to share
bolts (Figure 10b). Here, we report on an experiment that determines the
maximum allowable distance between neighboring bolts for a specific thickness
of 3D-printed housing. The results of this experiment can serve as guidelines
for the placement of bolts in two-terminal components that do not have pre-
allocated holes.

Figure 10. Bolt hole allocation for two-terminal components: a) assigning bolt
holes to all closely-spaced two-terminal components may lead to an excess of
bolts, b) achieving the same connection quality using only half the number of
bolts.

Figure 10: This figure contains two illustrations labeled ’a’ and ’b’ showing
the bolt hold allocation for two-terminal components. Illustration ’a’ shows
assigning bolt holes to closely-spaced two-terminal components may lead to an
excess of bolts. Illustration ’b’ shows achieving the same connection quality
using only half the number of bolts.

Figure 11. Bolting distance experiment: a) rendering of the PCB for the
experiment; b) housings in different thicknesses; c) graph showing the maximum
bolting distance versus housing thickness.

Figure 11: This figure contains three images labeled in ’a’, ’b’, and ’c’
showing the bolting distance experiment and results. Image ’a’ illustrates the
experimental PCB design. Image ’b’ shows the photo of sample housings in
different thicknesses. image ’c’ contains a graph showing the maximum bolting
distance versus housing thickness. The maximum distance between bolt holes
monotonically increases with the thickness of the housing.

As shown in Figure 11a, we prepared a $23\text{\,}\mathrm{mm}$ by
$91\text{\,}\mathrm{mm}$ PCB with a pair of bolt holes every
$3\text{\,}\mathrm{mm}$ along the longitudinal axis. Between each pair of bolt
holes, there is space for a 0805 two-terminal component. In total, the PCB can
host 29 0805 SMD resistors. We also prepared nine 3D printed housings the size
of the PCB, with the thickness ranging from $1\text{\,}\mathrm{mm}$ to
$5\text{\,}\mathrm{mm}$, at intervals of $0.5\text{\,}\mathrm{mm}$.

In the experiment, we first placed all 29 0805 0-ohm resistors into one of the
3D printed housings. We then bolted the housing to the PCB, installing one
pair of bolts at the very left end of the PCB, and another pair of bolts
starting from the very right end and moving towards the first pair. While
moving this second pair of bolts, we measured the conductivity of all
resistors located between them and the left pair, until all resistors in
between showed continuous connection. The distance between the two pairs is
the maximum distance between bolts that can ensure reliable conductivity for
the given thickness of the housing.

We repeated the same experiment for all nine housings, with each housing
tested three times. As shown in the graph (Figure 11c), the maximum distance
between bolt holes monotonically increases with the thickness of the housing.
This experiment enables us to determine the maximum distance between bolts for
each housing thickness. For example, for a 3D printed housing with a thickness
of 3 mm, as long as the distance between bolts is less than 27 mm, we can
ensure that the electronic components in between have a reliable connection to
the base PCB. All examples presented in this paper adhere to this design rule.

####  5.1.2. Tab dimensions

For two-terminal components, the flexible tab structure must be sufficiently
pliable to absorb energy, thereby preventing the housing from bending. At the
same time, it must exert enough pressure on the components to ensure good
conductivity without causing breakage. We experimented with different
geometric parameters and converged on the following empirical formula:

$T=t;\alpha=$$;W=0.6\times w;L=0.45\times l;H=t+$0.1\text{\,}\mathrm{mm}$;$

Where $T$ represents tab thickness, $\alpha$ is the tab’s slope angle, $W$ and
$L$ denotes width and length, and $H$ indicates the height with respect to the
housing surface. These parameters are determined by the specifications of a
two-terminal component, where t, w, l represent the rated component thickness,
width, and length, respectively.

Figure 12. Tab dimensions with respect to component.

Figure 12: This figure shows the dimensions with respect to component.

We report that, using the aforementioned parameters and setup, we can reliably
print housings for two-terminal components the size of or larger than the 0603
series. For the 0603 package, the tab has a length of
$0.69\text{\,}\mathrm{mm}$, a width of $0.48\text{\,}\mathrm{mm}$, and a
thickness of $0.45\text{\,}\mathrm{mm}$.

####  5.1.3. IC cavity validation

To validate our housing cavity design for ICs, we developed a simple testing
circuit incorporating ATtiny microcontrollers. We specifically selected three
types of ICs: ATtiny85, ATtiny84A, and ATtiny828, chosen for their identical
architecture, which enables them to run the same testing code. This selection
enables us to test five different yet commonly used SMD packages: the ATtiny85
is available in BGA, SOIC, and TSSOP; the ATtiny84A in a QFN package, and the
ATtiny828 in a TQFP package. Among the five different packages, the TSSOP has
the minimal pitch between pins at $0.6\text{\,}\mathrm{mm}$; the BGA has the
smallest contacting pad area of $0.0625\text{\,}{\mathrm{mm}}^{2}$.

Figure 13. IC validation: a) schematic used for IC package validation, b)
example circuit board used for validation (TQFP-32), c) example PCB assembly
(TQFP-32), d) all packages and components used during validation.

Figure 13: This figure contains four images labeled in ’a’, ’b’, ’c’, and ’d’
showing the IC validations. Image ’a’ shows a schematic used for IC package
validation. Image ’b’ shows an example circuit board used for validation
(TQFP-32). Image ’c’ shows an example PCB assembly (TQFP-32). Image ’d’ shows
all packages and components used during validation.

Our testing circuit comprises five LEDs, each connected to one of the five
GPIO pins of the ATtiny ICs. Every LED features a 1206 footprint and is
serially connected to a $100\text{\,}\mathrm{\SIUnitSymbolOhm}$ resistor in a
0805 package. Power is supplied to the circuit through two soldered through-
hole pin headers. To test the housing cavity design, we uploaded code that
controls the sequential flashing of each LED, as shown in Figure 13 and the
accompanying video. We confirmed that all five packages establish reliable
mechanical contact with the PCB baseboards. As a result, they effectively
control the LED blinking, free from any glitches or ghost connections.

###  5.2. Electrical Characterization

As the SolderlessPCB approach alters the method of bonding electronic
components to the PCB board, we conducted three sets of experiments to
understand how it might impact specific circuit electric characteristics.
Specifically, we focused on examining three aspects of a circuit: resistance,
impedance, and high-frequency signal energy loss, as these are critical for
circuits with AC and DC functionalities.

####  5.2.1. Resistance

We measured 177 connection points created by SolderlessPCB across various
packages of SMD components. For each measurement, we produced custom PCB
boards and housings, enabling us to place two measurement probe leads: one at
the IC’s metal lead, and the other at the contacting trace for ICs, or
alternatively, at each side of the contacting traces for two-terminal
components. Figure 14 illustrates our measuring setup. We measured the
resistance using a Keysight 3446SECU digital multimeter and reported an
average resistance of $0.46\text{\,}\mathrm{\SIUnitSymbolOhm}$ with a standard
deviation of $0.139\text{\,}\mathrm{\SIUnitSymbolOhm}$. The extra resistance
should not affect the performance of common DC circuits when the electrical
load is significantly larger than the connection point resistance. Note that
the resistance data does not include connection points for any BGA package due
to the lack of exposed conductors available for direct measurement, however,
all prototypes made with UFBGA-15 package fulfill their functionalities.

Figure 14. Measurement procedure: a) the resistance measured at IC pins, b)
the resistance measured for two-terminal components.

Figure 14: This figure contains two illustrations, labeled in ’a’ and ’b’,
showing the measurement procedure. Illustration ’a’ shows the resistance
measured at ICs with two probes. One probe lead touches the IC’s lead, the
other probe lead touches contacting trace. Illustration ’b’ shows the
resistance measured for two-terminal components.

####  5.2.2. High-frequency signal energy loss

Besides resistance, the quality of the electrical connection also affects
signal transmission power, especially at higher frequencies (Chen, 2013;
Sharawi, 2004).

To understand how SolderlessPCB preserves waveforms across different frequency
ranges, we designed a test PCB equipped with two identical traces sharing the
same input pin header. One trace includes a soldered
$0\text{\,}\mathrm{\SIUnitSymbolOhm}$ resistor, while the other features a
$0\text{\,}\mathrm{\SIUnitSymbolOhm}$ resistor assembled using the
SolderlessPCB approach (Figure 15a). We supplied both a sinusoidal wave and a
quasi-square wave to the common pin header using a Function Generator BK
PRECISION 4053, with frequencies ranging from $100\text{\,}\mathrm{Hz}$ to
$10\text{\,}\mathrm{MHz}$ (the equipment’s maximum frequency). We then output
the waveform from both output terminals and the input terminal as a benchmark,
using an Oscilloscope SIGLENT SDS 1104X-E (Figure 15b, c, and d). The results
indicate no waveform attenuation through either the soldered or solderless
circuit. For example, in the output graphs shown in Figure 15, both
signals–the soldered trace (pink curve) and the solderless trace (blue
curve)–exhibit the same amplitude level as the input signal (yellow curve),
for both the sine wave and the zoomed-in view of the square wave.

Figure 15. Waveform results: a) the PCB used for the waveform experiment, b)
the sinusoidal wave measured from both input and output terminals, c) the
quasi-square wave measured from both input and output terminals, d) zoomed-in
view in the time domain of the quasi-square wave measured from all terminals.

Figure 15: This figure contains four images labeled in ’a’, ’b’, ’c’, and ’d’
showing the waveform experiment setup and results. Image ’a’ shows the PCB
used for the waveform experiment. Image ’b’ shows the results of the
sinusoidal wave measured from both input and output terminals. Image ’c’ shows
the quasi-square wave measured from both input and output terminals. Image ’d’
shows the zoomed-in view in the time domain of the quasi-square wave measured
from all terminals. The results of the waveform show there is no waveform
attenuation through either the soldered or solderless circuit.

To further assess the power loss of the high-frequency signals through
mechanical connection points compared to soldered connections, we measured the
energy loss between input and output signals using two
$0\text{\,}\mathrm{\SIUnitSymbolOhm}$ resistors. Each resistor was assembled
to close the circuit using either a soldered connection or the SolderlessPCB
approach. To minimize energy loss on the trace itself, we redesigned the PCB
with 65 mil traces (Figure 16a). We also used individual input pins for each
trace to prevent uneven splitting of signal energy at a shared input pin. For
accurate power loss data, the test PCB was connected to a Vector Network
Analyzer Keysight E5071C and fed with a pure sinusoidal wave signal within a
range of $100\text{\,}\mathrm{kHz}$ to $5\text{\,}\mathrm{GHz}$. The average
signal energy loss across the full testing frequency was
$-18.96\text{\,}\mathrm{dB}$ for SolderlessPCB and
$-21.61\text{\,}\mathrm{dB}$ for the soldered PCB, with higher frequencies
exhibiting greater energy loss in both cases (Figure 16b).

The results of our experiment show that the SolderlessPCB is comparable to the
soldered PCB even for high-frequency signal transmission.

Figure 16. Signal energy loss for solderless and soldered PCB. a) the PCB used
for the waveform experiment, b) the energy loss curve (dB) in the frequency
domain.

Figure 16: This figure contains two images labeled in ’a’ and ’b’ showing the
experiment setup for the signal energy loss and results. Image ’a’ shows the
experiment setup for the signal energy loss. Image ’b’ shows the graph of the
testing result.

####  5.2.3. Impedance circuit reproducibility

Impedance is crucial in prototyping applications like radio, Bluetooth, and
WiFi antennas, where impedance matching circuits are often developed through
an iterative process (Moore et al., 2022). In such scenarios, minimizing
impedance variance at the connection interfaces between components and the PCB
during assembly and disassembly is preferable. To assess impedance variance
through multiple (dis)assembly iterations with SolderlessPCB, we designed and
fabricated two identical PCBs carrying a pi-network circuit, commonly used for
impedance matching (Lim et al., 2014). We assembled the same set of
components, both soldered and solderless, on these boards. Using a Vector
Network Analyzer Keysight E5071C, we measured the impedance values for both
PCBs across five (dis)assembly iterations. A pure sinusoidal wave signal
ranging from $100\text{\,}\mathrm{kHz}$ to $5\text{\,}\mathrm{GHz}$ was
supplied to the input end. It should be noted that frequencies below
$100\text{\,}\mathrm{kHz}$ were not tested, as they are not relevant for
impedance circuit applications (Chen, 2013; Sharawi, 2004).

We report the results for both the soldered and solderless PCBs, along with
their variances, in Figure 17. As shown in the figure, the impedance variance
for solderless PCBs across different assembly iterations remains on par with
that of the soldered ones. The results indicate that SolderlessPCB can be used
for prototyping impedance matching circuits and other similar applications.

Figure 17. Impedance values between the solderless and soldered PI PCB: a)
rendering of the PCB used in the impedance experiment, b) the PCB connection
and experiment setup, c) the impedance values and variances (Ohm) in the
frequency domain.

Figure 17: This figure contains three images labeled in ’a’, ’b’, and ’c’
showing the experiment setup for the impedance experiment and results. Image
’a’ shows the PCB used in the experiment. Image ’b’ shows the experiment
setup. Image ’c’ shows the graph of the testing result.

###  5.3. Reliability Test

We performed additional tests to understand the reliability of SolderlessPCB.

####  5.3.1. Housing reliability

All prototypes described in Section 5.1 and Section 6, including those with
both IC cavity and tab housings, remained fully functional three months post-
assembly. This demonstrates that our SolderlessPCB methods can be reliably
used for prototyping purposes.

As one potential application of SolderlessPCB is to facilitate the replacement
of defective SMD components with new ones, we further investigated the housing
reliability for component switching. Our focus was specifically on the tab
structures of the two-terminal component housing, which are printed on a sub-
millimeter scale and can be vulnerable to fatigue during the re-installation
of a housing. To test the reliability of the printed tab structures, we
repeatedly assembled and disassembled housings of three 0805
$0\text{\,}\mathrm{\SIUnitSymbolOhm}$ resistors. For each iteration, we
unbolted the housing and took out the resistors, and reassembled them from
scratch. Using the same method as in Section 5.2.1, we measured the resistance
values at the connection points after each assembly. We report the average
resistance value across ten disassembly-assembly iterations in Figure 18. The
resistance value remains consistent for the initial assembly cycles but begins
to increase after the seventh iteration, indicating a failure of the tabs to
exert adequate pressure beyond this point. We conclude that SolderlessPCB can
be reliably used for component switching up to seven times before a new
housing is required.

Figure 18. Resistance at contact pads after each disassembly-assembly
iteration.

Figure 18: This figure shows the experiment results of resistance at contact
pads after each disassembly-assembly iteration.

####  5.3.2. Drop test

We conducted a drop test to investigate the robustness of SolderlessPCB.
Specifically, we dropped the PCB assembly described in Section 5.1.3 from
heights ranging from $0.3\text{\,}\mathrm{m}$ to $2\text{\,}\mathrm{m}$, at
$0.3\text{\,}\mathrm{m}$ intervals. We conducted three drops from each height;
the PCB assembly remained fully functional after the entire series of drop
tests. For an additional stress test, we dropped the same PCB assembly from a
height of $6\text{\,}\mathrm{m}$ three more times. The PCB assembly continued
to function properly. Our accompanying video documented one of these tests.

##  6\. Scenarios and Walkthroughs

In this section, we present two walkthrough examples to demonstrate: 1) how
SolderlessPCB enables designers to create prototypes without soldering; 2) how
it allows for the reuse of old electronic components in new projects; and 3)
how SolderlessPCB aids in iterative prototyping practices by requiring fewer
new electronic components.

###  6.1. From Kitchen Timer to Foosball Scoreboard: Reusing SMD Components
for a New Project

####  6.1.1. Building a timer with the SolderlessPCB approach.

Alex is a maker and a designer. She recently moved to a new apartment and
wanted to take up cooking as a new hobby. While the kitchen was well-equipped,
it lacked one essential tool for Alex: a kitchen timer. Rather than using a
smartphone, which could get greasy during cooking, or purchasing a brand-new
kitchen timer, which might take time to be delivered, Alex decided to build
her own timer using electronic parts she had saved previously.

Figure 19. Kitchen timer example: a) and b) the kitchen timer was fully
assembled without soldering. c) and d) when Alex decided to start a new
project, she was able to fully salvage the SMD components from the old timer
and repurposed them to create the scoreboard.

Figure 19: This figure contains four images labeled in ’a’, ’b’, ’c’, and ’d’
showing the components reuse example. Image ’a’ and ’b’ show the kitchen timer
was fully assembled without soldering. Image ’c’ and ’d’ show a new project
with the SMD components from the old timer and repurposed them to create the
new scoreboard.

Alex’s design was a PCB measuring $90\text{\,}\mathrm{mm}$ by
$50\text{\,}\mathrm{mm}$, featuring the following components: one ATtiny828 IC
in TQFP-32 format, two 8-digit displays, two push buttons, and a battery
holder (Figure 19a). Adhering to the design workflow of SolderlessPCB, Alex
designed the circuit and generated the corresponding 3D housing. She
fabricated the circuit using a desktop CNC machine and printed the housing
with an off-the-shelf resin printer. Figure 19b showcases the completed
assembly, which functions as a 60-minute timer.

####  6.1.2. Reuse electronic components for a foosball scoreboard.

Alex recently received two birthday gifts: a professional kitchen timer and a
mini foosball table—the DIY timer she made earlier was no longer needed.
However, noting all the electronic components in the DIY timer are perfectly
functioning, she decided to reuse and repurpose them to create a digital
scoreboard for the new foosball table.

Thanks to the SolderlessPCB approach, the kitchen timer could be easily
disassembled using just a screwdriver. Alex then designed a new PCB for a
scoreboard, utilizing all the components from the previous project. In the new
design, the two 8-digit displays were positioned on either side, now serving
to display the game scores.

Figure 19d shows that the scoreboard installed on the foosball table. When a
player scores a goal, pressing a button will update the display accordingly.

###  6.2. Design Iteration on a Bristlebot

####  6.2.1. Iteration one: malfunctioning IC

A bristlebot is a tiny robot built from a toothbrush head. With bristles on
its bottom, it can move in arbitrary patterns or follow a predefined
trajectory when vibrating. Alex saw it online and would like to build one as a
toy for her newborn nephew.

Alex tested the circuit with a breadboard first. However, as a breadboard was
too big for a toothbrush head, the finished toy had to have a compact design
using a custom PCB.

Like before, Alex employed the SolderlessPCB approach and manufactured her own
PCB baseboard and 3D-printed housing. Figure 20a shows the first iteration. It
featured an ATtiny84 as the microcontroller and utilized two top-open JST
connectors, one reserved for a vibration motor and the other for a Li-Po
battery.

Alex used a bench power supply to power the circuit for testing.
Unfortunately, the two terminals of the supply were incorrectly connected to
the board, resulting in the small IC on the circuit getting burned. Figure 20b
shows the fried IC.

Figure 20. Bristlebot iterations: a) the first iteration PCB design, b) fried
microcontroller, c) assembly of the second iteration, involving a simple
replacement of the fried IC with a new one, d) the PCB design for the third
iteration incorporating new sensors and actuators, e) assembly of the third
iteration.

Figure 20: This figure contains five images labeled in ’a’, ’b’, ’c’, ’d’, and
’e’ showing the Bristlebot iterations. Image ’a’ shows the first iteration PCB
design. Image ’b’ shows a photo of a fried microcontroller. Image ’c’ shows
the assembly of the second iteration, involving the simple replacement of the
fried IC with a new one. Image ’d’ shows the PCB design for the third
iteration incorporating new sensors and actuators. Image ’e’ shows the
assembly of the third iteration.

####  6.2.2. Iteration two: IC replacement

In most cases, a burned multi-pin IC can pose a problem since it is
challenging to desolder from a PCB and to clean all the pins properly. As a
result, the fried PCB and all its onboard electronic components are often
disposed of directly.

In Alex’s case, however, replacing the IC was much simpler. After
disassembling the housing from the PCB baseboard, Alex popped out the broken
IC. Noticing that the circuit traces were intact, she directly inserted a new
IC into the design. This time, the circuit worked properly, and Alex had a
functioning bristlebot (Figure 20c).

####  6.2.3. Iteration three: upgrading the design with new features

Since the bristlebot lacked the capability to respond to its environment and
was not controllable, Alex embarked on a third design iteration. In this
iteration, she decided to include an ambient light sensor to sense
environmental light as a means to control the bot’s motion. Additional
features like an LED to indicate the bot’s status and a buzzer to make sounds
were also added (Figure 20d). Because these extra components could add weight,
Alex also upgraded the bot from one brush head to two, and with two vibration
motors.

Alex still needed to prepare a new PCB baseboard, but because she used
SolderlessPCB approach, she was able to recycle all the SMD components from
the second iteration. Alex also modified the PCB housing to include a few
additional features, allowing it to clamp directly onto the two brush heads.
The housing now serves two functions: it secures the SMD components to the
PCB, and it also forms part of the bot’s structure. Figure 20e shows the final
design iteration.

###  6.3. Additional Examples

In this section, we showcase three additional example circuits created using
SolderlessPCB, each illustrating different electronic functionalities.

Figure 21. Mug heater made with SolderlessPCB approach: a) the schematic
design for the heater, b) a rendering of the heater PCB, c) a rendering of the
PCB housing that integrated with the heater’s cylinder frame, d) the assembled
heater, e) a mug being heated on the heater, f) the thermal imaging of the
heater surfaces.

Figure 21: This figure contains six images labeled in ’a’, ’b’, ’c’, ’d’, ’e’,
and ’f’ showing a mug heater example and its made process with SolderlessPCB
approach. Image ’a’ shows the schematic design for the heater. Image ’b’ shows
a rendering of the heater PCB. Image ’c’ shows a rendering of the PCB housing
integrated with the heater’s cylinder frame. Image ’d’ shows an illustration
of the assembled heater. Image ’e’ shows a mug being heated on the heater.
Image ’f’ shows a thermal imaging of the heater surfaces with a red heating
area.

####  6.3.1. Mug heater

SolderlessPCB can be used in circuits that deliver higher current beyond those
used in typical logic signaling. Here, we demonstrate a tabletop mug heater
designed to maintain liquid temperature. The mug heater composes a 3D printed
mug base plate, an aluminum topping, and a PCB made using SolderlessPCB
approach. As illustrated in Figures 21a, b, and d, the main component of the
PCB is a $12\text{\,}\mathrm{V}$, $60\text{\,}\mathrm{W}$ heating element.
This element is undervolted and powered by a $7.4\text{\,}\mathrm{V}$,
$2500\text{\,}\mathrm{mA}\text{\,}\mathrm{h}$ Li-Po battery with a 35C rating,
and is controlled through a relay.

The logic circuit is made with an ATtiny84A microcontroller in an SOIC package
and powered by a 2032 coin cell battery. It reads the temperature of the
aluminum and controls the relay accordingly. The PCB housing design is
directly integrated into the cylindrical frame of the mug heater and was
manufactured as a single piece, as shown in Figure 21c. Upon turning on the
device, the aluminum surface of the mug heater quickly reaches
$40\text{\,}\mathrm{\SIUnitSymbolCelsius}$ (as shown in Figure 21e and f)
within 1 minute and then stabilizes at around
$45\text{\,}\mathrm{\SIUnitSymbolCelsius}$. The current draw during heating is
around $3.3\text{\,}\mathrm{A}$.

####  6.3.2. Game console

In this example, we utilized the SolderlessPCB approach to create a mini game
console, where the display data was transmitted through the I2C protocol. The
PCB comprises an ATtiny84A microcontroller, four non-lock push buttons, and a
4-pin SMD JST connector that interfaces with an OLED display (Figure 22a). The
housing of the SolderlessPCB is assembled as part of the game console, with
the top housing holding the OLED display screen while the bottom houses the
circuits and the buttons (Figure 22 b and c). We implemented a snake game
operated on the OLED display through I2C, transmitting data at a rate of
$100\text{\,}\mathrm{kHz}$ with no data loss. The example demonstrates that
SolderlessPCB can be used for prototyping circuits that require fast-speed
data transmission.

Figure 22. Game console: a) rendering of the game console PCB design, b) the
front page of the snake game displayed on the OLED display, c) player gaming
with the console.

Figure 22: This figure contains three images labeled in ’a’, ’b’ and ’c’
showing the design of a game console. Image ’a’ shows a rendering of the game
console PCB design. Image ’b’ shows the front page of the snake game displayed
on the OLED display when the console is on. Image ’c’ shows a player gaming
with the console.

####  6.3.3. FTDI unit

In this example, we show that the SolderlessPCB approach can reliably support
ICs transmitting data at even higher speeds. Future Technology Devices
International (FTDI) modules, which convert USB to serial communication, are
commonly used for code uploading in miniature Arduino boards lacking on-board
UART (universal asynchronous receiver/transmitter) support (Figure 23a). Here,
we built a custom miniature FTDI adapter using SolderlessPCB, with a 28-pin
FTDI232RL IC in an SSOP package and an SMD micro-USB connector. The 3D printed
housing secures both the IC and the USB connector with six bolts (Figure 23b).
The custom FTDI module, made with the SolderlessPCB approach, tolerates
repeated plugging and unplugging of the USB cable, and can communicate with
the USB at the default rate of
$12\text{\,}\mathrm{M}\mathrm{b}\mathrm{p}\mathrm{s}$ and reliably upload code
to an Arduino Pro mini (Figure 23c).

Figure 23. FTDI unit: a) rendering of the PCB design of FTDI unit, b) FTDI
unit assembled and connected to USB, c) FTDI unit successfully uploading code
to an Arduino Pro Mini.

Figure 23: This figure contains three images labeled in ’a’, ’b’ and ’c’
showing a FTDI unit. Image ’a’ shows a rendering of the PCB design of FTDI
unit. Image ’b’ shows the FTDI unit being assembled and connected to USB.
Image ’c’ shows FTDI unit successfully uploading code to an Arduino Pro Mini.

##  7\. discussion

###  7.1. Housing Waste and Alternatives

The key idea of SolderlessPCB is to facilitate the easy swapping of SMD
components on a PCB prototyping board, so that still-functional electronic
components can be salvaged from an old design and reused in the future. While
our method promotes the reuse of a wide range of different SMD components, the
use of resin-based 3D printed housing requires additional material
consumption, which is one limitation of our method.

To mitigate this limitation, we are exploring alternative materials that can
be biodegradable and recyclable, thereby reducing the potential for material
waste from the housing. Specifically, we explored two additional housing
fabrication materials: PLA (Taib et al., 2023), used with FDM 3D printing, and
MDF (Irle et al., 2019), used with CNC milling.

As one example, we replicated the same housing design for the previous kitchen
timer example (Section 6.1.1) using both methods. The kitchen timer PCB
contains six SMD electronic components but no small-scale, two-terminal
electronic components. The PLA housing was 3D printed with a Bambu Lab X1 3D
printer using a 0.2 mm nozzle, while the CNC housing was milled using a Bantam
Tools desktop PCB milling machine. We report that both housings worked with
the timer PCB baseboard without additional changes to the housing design. This
indicates that the SolderlessPCB method could potentially be extended to other
materials for hosting ICs and larger SMD components such as buttons and
displays (Figure 24). However, it should be noted that we were unable to
create the small tabs design for two-terminal components with either FDM 3D
printing or CNC milling, as these tabs require a higher precision than either
of the machines can achieve.

Figure 24. Custom housings in alternative materials: a) PLA housing printed
with an FDM 3D printer, b) MDF housing manufactured with a CNC milling
machine.

Figure 24: This figure contains two images labeled in ’a’ and ’b’ showing the
housing can be made in in alternative materials. Image ’a’ shows a PLA housing
printed with an FDM 3D printer. Image ’b’ shows a MDF housing manufactured
with a CNC milling machine.

###  7.2. Oxidization

Throughout the development of SolderlessPCB, we observed a certain level of
oxidation on the FR-4 surfaces, which could potentially affect the solderless
connection between the oxidized copper and electronic components. To
understand how the assembly process influences material oxidation, we compared
the oxidation levels of two bare FR-4 boards, one handled by an operator with
gloves and the other without. The results show that when there is no direct
skin contact, the FR-4 does not exhibit signs of oxidation even after a month
of daily handling. In contrast, the FR-4 handled with bare hands begins to
oxidize within two weeks. It should be noted that the oxidized prototype
remained functional despite signs of oxidation. However, we recommend wearing
gloves when directly handling the FR-4 PCBs during the assembly process.

###  7.3. Working with Outsourced PCB

So far, all the PCB baseboards discussed in our paper have been fabricated
with FR-4 and machined using a CNC milling machine. To further explore the
applicability of the SolderlessPCB approach, we investigated its compatibility
with outsourced PCBs. We outsourced PCBs for the kitchen timer, featuring a
lead-free HASL (Hot Air Solder Leveling) surface finish. These outsourced PCBs
were then encased in three different materials: DLP-printed resin housing,
CNC-milled MDF housing, and FDM-printed PLA housing. We report that all
housings facilitated reliable connections, as demonstrated in Figure 26b and
c. This suggests that SolderlessPCB can also be utilized with outsourced PCBs,
making it applicable to engineers and designers who may not have the
capability to fabricate PCBs in-house.

Figure 25. SolderlessPCB working with outsourced PCBs: a) an outsourced PCB
with the same layout of the timer example, b) the outsourced PCB working with
FDM 3D-printed housing, c) the outsourced PCB working with CNC-milled MDF
housing.

Figure 25: This figure contains three images labeled in ’a’, ’b’ and ’c’
showing the SolderlessPCB approach working with outsourced PCBs. Image ’a’
shows an outsourced PCB with the same layout of the timer example. Image ’b’
shows the outsourced PCB working with FDM 3D-printed housing. Image ’c’ shows
the outsourced PCB working with CNC-milled MDF housing.

###  7.4. Adding Thickness to PCB Design

Our method requires an additional housing for a PCB prototype, resulting in an
increase in the overall thickness. This is a limitation of our approach when
the thickness of the PCB is a critical design constraint.

However, for certain designs, it is possible to integrate the PCB housing as
part of the overall form factor, mitigating the effect caused by the housing
thickness. For example, in the third iteration of the bristlebot toy (Figure
20c and e), the bot’s PCB housing was directly integrated into the toothbrush
bases with a single print. Similarly, the mug heater and its PCB housing shown
in Figure 21c were also integrated as one piece. We expect future research to
automate this process, suggesting designs that combine the SolderlessPCB
housing and the surrounding 3D-printed cases when necessary.

###  7.5. Assembly Effort

SolderlessPCB eliminates the need for soldering and desoldering of SMD
components; instead, the primary assembly and disassembly efforts involve
screwing and unscrewing the bolts. As anecdotal evidence, we measured the time
it took for the first author to assemble and disassemble the scoreboard
(Figure 19), which has the highest number of bolts (24) among all the examples
presented in the paper. We report that the assembly process took 5 minutes
while disassembly took 3 minutes. It should be noted that the effort required
for manual (dis)assembly may vary among individuals, and our timing represents
just one data point. Generalizing the assembly effort requires further
investigation.

Figure 26. Closely adjacent bolts used in the bristlebot example.

Figure 26: This image shows closely adjacent bolts used in the bristlebot
example.

###  7.6. Design Automation and Software

The main focus of this paper is on a new technique that enables the assembly
of PCBs without soldering. As mentioned in Section 4.4, we have constructed,
and open-sourced a custom Fusion 360 component library to ensure SolderlessPCB
design compatibility with a variety of existing, off-the-shelf SMD components.
This library can be further expanded by the PCB prototyping community.

Looking ahead, we envision opportunities for a more advanced, end-to-end
software pipeline that can optimize housing generation and reduce design
effort for designers. For example, future software could determine the
placement of bolts by holistically considering all SMD components. This
approach could potentially lessen the need for bolts compared to our current
method (Figure 26). As discussed in Section 7.4, another feature of future
software could be the automatic integration of PCB housings into the overall
design form factor when necessary. Finally, we anticipate that future software
may assist in counting the number of old SMD components made possible for
reuse through SolderlessPCB. This may encourage and promote the practice of
reusing electronic components within the community.

###  7.7. Retrofitting Current PCB Prototyping Workflow

As the assembly and disassembly process is the only major difference between
SolderlessPCB and conventional PCB prototyping methods, we expect that
SolderlessPCB can be integrated into the daily PCB prototyping workflow with
minimal effort. To validate this expectation, we plan to conduct a
longitudinal study by deploying SolderlessPCB among electronic designers in
the near future. We anticipate that the qualitative results from this study
will provide insights into how designers can incorporate SolderlessPCB into
their daily routines, and shed light on its potential to facilitate the
recycling and reuse of electronic components in prototyping practices.

##  8\. Conclusion

We have presented SolderlessPCB, a suite of techniques specifically designed
to support PCB prototyping without the need for soldering. We detail the
design and fabrication guidelines, along with parameter characterizations, to
ensure reliable PCB assemblies. We showcase two sets of scenarios and three
additional examples, which demonstrate both the salvage and reuse of SMD
components and the diverse types of circuits that can be realized using
SolderlessPCB. We conclude with discussions on the limitations of our
approach, potential methods to mitigate these limitations, and future research
directions.

###### Acknowledgements.

We thank the Anlage Research Group at the University of Maryland for sharing
access to their measurement equipment, and Jingnan Cai for providing the
necessary training. We also thank the Jagdeep Singh Family Makerspace for
providing access to tools during the development and documentation processes
of this project. ChatGPT is used in this work solely to correct spelling or
grammar errors.

## References

  * (1)
  * Adafruit (2022) Adafruit. 2022.  _Half Sized Premium Breadboard_.  https://www.adafruit.com/product/64
  * Anycubic (2020) Anycubic. 2020.  Anycubic UV Tough Resin.  https://www.anycubic.com/products/anycubic-uv-tough-resin?variant=40893986603170
  * Aradhana et al. (2020) Ruchi Aradhana, Smita Mohanty, and Sanjay Kumar Nayak. 2020.  A review on epoxy-based electrically conductive adhesives.  _International Journal of Adhesion and Adhesives_ 99 (2020), 102596.  https://doi.org/10.1016/j.ijadhadh.2020.102596
  * Bell et al. (2022a) Fiona Bell, Latifa Al Naimi, Ella McQuaid, and Mirela Alistar. 2022a.  Designing with Alganyl. In _Sixteenth International Conference on Tangible, Embedded, and Embodied Interaction_ (Daejeon, Republic of Korea) _(TEI ’22)_. Association for Computing Machinery, New York, NY, USA, Article 2, 14 pages.  https://doi.org/10.1145/3490149.3501308
  * Bell et al. (2023) Fiona Bell, Derrek Chow, Hyelin Choi, and Mirela Alistar. 2023.  SCOBY BREASTPLATE: SLOWLY GROWING A MICROBIAL INTERFACE. In _Proceedings of the Seventeenth International Conference on Tangible, Embedded, and Embodied Interaction_ (Warsaw, Poland) _(TEI ’23)_. Association for Computing Machinery, New York, NY, USA, Article 34, 15 pages.  https://doi.org/10.1145/3569009.3572805
  * Bell et al. (2022b) Fiona Bell, Netta Ofer, and Mirela Alistar. 2022b.  ReClaym our Compost: Biodegradable Clay for Intimate Making. In _Proceedings of the 2022 CHI Conference on Human Factors in Computing Systems_ _(CHI ’22)_. Association for Computing Machinery, New York, NY, USA, Article 454, 15 pages.  https://doi.org/10.1145/3491102.3517711
  * Bharath et al. (2020) Kurki N. Bharath, Puttegowda Madhu, Thyavihalli G. Y. Gowda, Akarsh Verma, Mavinkere R. Sanjay, and Suchart Siengchin. 2020.  A novel approach for development of printed circuit board from biofiber based composites.  _Polymer Composites_ 41, 11 (2020), 4550–4558.  https://doi.org/10.1002/pc.25732
  * Blevis (2007) Eli Blevis. 2007.  Sustainable Interaction Design: Invention & Disposal, Renewal & Reuse. In _Proceedings of the SIGCHI Conference on Human Factors in Computing Systems_ (San Jose, California, USA) _(CHI ’07)_. Association for Computing Machinery, New York, NY, USA, 503–512.  https://doi.org/10.1145/1240624.1240705
  * Blevis et al. (2017) Eli Blevis, Chris Preist, Daniel Schien, and Priscilla Ho. 2017.  Further Connecting Sustainable Interaction Design with Sustainable Digital Infrastructure Design. In _Proceedings of the 2017 Workshop on Computing Within Limits_ (Santa Barbara, California, USA) _(LIMITS ’17)_. Association for Computing Machinery, New York, NY, USA, 71–83.  https://doi.org/10.1145/3080556.3080568
  * Bradwell et al. (2011) David J. Bradwell, Sebastian Osswald, Weifeng Wei, Salvador A. Barriga, Gerbrand Ceder, and Donald R. Sadoway. 2011.  Recycling ZnTe, CdTe, and Other Compound Semiconductors by Ambipolar Electrolysis.  _Journal of the American Chemical Society_ 133, 49 (2011), 19971–19975.  https://doi.org/10.1021/ja208577j
  * Braun and Clarke (2006) Virginia Braun and Victoria Clarke. 2006.  Using thematic analysis in psychology.  _Qualitative Research in Psychology_ 3, 2 (2006), 77–101.  https://doi.org/10.1191/1478088706qp063oa
  * Buckroyd (2015) Allen Buckroyd. 2015.  _In–Circuit Testing_.  Butterworth-Heinemann.  https://books.google.com/books?id=GD8BvwEACAAJ
  * Buechley et al. (2023) Leah Buechley, Ruby Ta, and Alyssa Johnson. 2023.  3D Printable Play-Dough. In _Extended Abstracts of the 2023 CHI Conference on Human Factors in Computing Systems_ _(CHI EA ’23)_. Association for Computing Machinery, New York, NY, USA, Article 428, 4 pages.  https://doi.org/10.1145/3544549.3583927
  * Chen (2013) Albert Chen. 2013.  Why Signal Always Be Loss in a High Speed High Frequency Transmission Line.  _concern_ 1, 4 (2013), 8GHz.  https://www.circuitinsight.com/pdf/signal_loss_high_speed_high_frequency_ipc.pdf
  * Cheng et al. (2020) Tingyu Cheng, Koya Narumi, Youngwook Do, Yang Zhang, Tung D. Ta, Takuya Sasatani, Eric Markvicka, Yoshihiro Kawahara, Lining Yao, Gregory D. Abowd, and HyunJoo Oh. 2020.  Silver Tape: Inkjet-Printed Circuits Peeled-and-Transferred on Versatile Substrates.  _Proc. ACM Interact. Mob. Wearable Ubiquitous Technol._ 4, 1, Article 6 (mar 2020), 17 pages.  https://doi.org/10.1145/3381013
  * Cheng et al. (2023) Tingyu Cheng, Taylor Tabb, Jung Wook Park, Eric M Gallo, Aditi Maheshwari, Gregory D. Abowd, Hyunjoo Oh, and Andreea Danielescu. 2023.  Functional Destruction: Utilizing Sustainable Materials’ Physical Transiency for Electronics Applications. In _Proceedings of the 2023 CHI Conference on Human Factors in Computing Systems_ _(CHI ’23)_. Association for Computing Machinery, New York, NY, USA, Article 366, 16 pages.  https://doi.org/10.1145/3544548.3580811
  * Dew and Rosner (2019) Kristin N. Dew and Daniela K. Rosner. 2019.  Designing with Waste: A Situated Inquiry into the Material Excess of Making. In _Proceedings of the 2019 on Designing Interactive Systems Conference_ (San Diego, CA, USA) _(DIS ’19)_. Association for Computing Machinery, New York, NY, USA, 1307–1319.  https://doi.org/10.1145/3322276.3322320
  * Elegoo (2020) Elegoo. 2020.  Elegoo Mars LCD-SLA 3D Printer.  http://en.godsaid3d.com/?attachment_id=17671
  * Groeger and Steimle (2018) Daniel Groeger and Jürgen Steimle. 2018.  ObjectSkin: Augmenting Everyday Objects with Hydroprinted Touch Sensors and Displays.  _Proc. ACM Interact. Mob. Wearable Ubiquitous Technol._ 1, 4, Article 134 (2018), 23 pages.  https://doi.org/10.1145/3161165
  * Guridi et al. (2023) Sofía Guridi, Emmi Pouta, Ari Hokkanen, and Aayush Jaiswal. 2023.  LIGHT TISSUE: Development of Cellulose-Based Optical Textile Sensors. In _Proceedings of the Seventeenth International Conference on Tangible, Embedded, and Embodied Interaction_ (Warsaw, Poland) _(TEI ’23)_. Association for Computing Machinery, New York, NY, USA, Article 27, 14 pages.  https://doi.org/10.1145/3569009.3572798
  * Hanton et al. (2022) Ollie Hanton, Zichao Shen, Mike Fraser, and Anne Roudaut. 2022.  FabricatINK: Personal Fabrication of Bespoke Displays Using Electronic Ink from Upcycled E Readers. In _Proceedings of the 2022 CHI Conference on Human Factors in Computing Systems_ (New Orleans, LA, USA) _(CHI ’22)_. Association for Computing Machinery, New York, NY, USA, Article 173, 15 pages.  https://doi.org/10.1145/3491102.3501844
  * Hao et al. (2020) Juanjuan Hao, Yishu Wang, Yufeng Wu, and Fu Guo. 2020.  Metal recovery from waste printed circuit boards: A review for current status and perspectives.  _Resources, Conservation and Recycling_ 157 (2020), 104787.  https://doi.org/10.1016/j.resconrec.2020.104787
  * Hsu et al. (2019) Emily Hsu, Katayun Barmak, Alan C. West, and Ah-Hyung A. Park. 2019.  Advancements in the treatment and processing of electronic waste with sustainability: a review of metal extraction and recovery technologies.  _Green Chem._ 21 (2019), 919–936.  Issue 5. https://doi.org/10.1039/C8GC03688H
  * Huang et al. (2014) Xian Huang, Yuhao Liu, Suk-Won Hwang, Seung-Kyun Kang, Dwipayan Patnaik, Jonathan Fajardo Cortes, and John A. Rogers. 2014.  Biodegradable Materials for Multilayer Transient Printed Circuit Boards.  _Advanced Materials_ 26, 43 (2014), 7371–7377.  https://doi.org/10.1002/adma.201403164 arXiv:https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201403164
  * Irle et al. (2019) Mark Irle, François Privat, Laetitia Couret, Christophe Belloncle, Gérard Déroubaix, Estelle Bonnin, and Bernard Cathala. 2019.  Advanced recycling of post-consumer solid wood and MDF.  _Wood Material Science & Engineering_ 14, 1 (2019), 19–23.  https://doi.org/10.1080/17480272.2018.1427144
  * Ishii et al. (2021) Ayaka Ishii, Kunihiro Kato, Kaori Ikematsu, Yoshihiro Kawahara, and Itiro Siio. 2021.  Fabricating Wooden Circuit Boards by Laser Beam Machining. In _Adjunct Proceedings of the 34th Annual ACM Symposium on User Interface Software and Technology_ (Virtual Event, USA) _(UIST ’21 Adjunct)_. Association for Computing Machinery, New York, NY, USA, 109–111.  https://doi.org/10.1145/3474349.3480191
  * Jackson and Kang (2014) Steven J. Jackson and Laewoo Kang. 2014.  Breakdown, Obsolescence and Reuse: HCI and the Art of Repair. In _Proceedings of the SIGCHI Conference on Human Factors in Computing Systems_ (Toronto, Ontario, Canada) _(CHI ’14)_. Association for Computing Machinery, New York, NY, USA, 449–458.  https://doi.org/10.1145/2556288.2557332
  * Jin et al. (2016) Jungho Jin, Daewon Lee, Hyeon-Gyun Im, Yun Cheol Han, Eun Gyo Jeong, Marco Rolandi, Kyung Cheol Choi, and Byeong-Soo Bae. 2016.  Chitin nanofiber transparent paper for flexible green electronics.  _Advanced Materials_ 28, 26 (2016), 5169–5175.  https://doi.org/10.1002/adma.201600336
  * Jiva (2023) Jiva. 2023.  The World’s First Fully Recyclable Printed Circuit Board Laminate.  https://www.jivamaterials.com/.
  * Karana et al. (2018) Elvin Karana, Davine Blauwhoff, Erik-Jan Hultink, and Serena Camere. 2018.  When the Material Grows: A Case Study on Designing (with) Mycelium-based Materials.  _International Journal of Design_ 12, 2 (2018), 119 – 136.  https://www.ijdesign.org/index.php/IJDesign/article/viewFile/2918/817
  * Kawahara et al. (2013) Yoshihiro Kawahara, Steve Hodges, Benjamin S. Cook, Cheng Zhang, and Gregory D. Abowd. 2013.  Instant Inkjet Circuits: Lab-Based Inkjet Printing to Support Rapid Prototyping of UbiComp Devices. In _Proceedings of the 2013 ACM International Joint Conference on Pervasive and Ubiquitous Computing_ (Zurich, Switzerland) _(UbiComp ’13)_. Association for Computing Machinery, New York, NY, USA, 363–372.  https://doi.org/10.1145/2493432.2493486
  * Kim and Paulos (2011) Sunyoung Kim and Eric Paulos. 2011.  Practices in the Creative Reuse of E-Waste. In _Proceedings of the SIGCHI Conference on Human Factors in Computing Systems_ (Vancouver, BC, Canada) _(CHI ’11)_. Association for Computing Machinery, New York, NY, USA, 2395–2404.  https://doi.org/10.1145/1978942.1979292
  * Knowles et al. (2016) Bran Knowles, Adrian K. Clear, Samuel Mann, Eli Blevis, and Maria Håkansson. 2016.  Design Patterns, Principles, and Strategies for Sustainable HCI. In _Proceedings of the 2016 CHI Conference Extended Abstracts on Human Factors in Computing Systems_ (San Jose, California, USA) _(CHI EA ’16)_. Association for Computing Machinery, New York, NY, USA, 3581–3588.  https://doi.org/10.1145/2851581.2856497
  * Koelle et al. (2022) Marion Koelle, Madalina Nicolae, Aditya Shekhar Nittala, Marc Teyssier, and Jürgen Steimle. 2022.  Prototyping Soft Devices with Interactive Bioplastics. In _Proceedings of the 35th Annual ACM Symposium on User Interface Software and Technology_ (Bend, OR, USA) _(UIST ’22)_. Association for Computing Machinery, New York, NY, USA, Article 19, 16 pages.  https://doi.org/10.1145/3526113.3545623
  * Kumar et al. (2021) A. Kumar, K. Kumari, R. Sadasivam, and M. Goswami. 2021.  Development of a 3D printer–scanner hybrid from e-waste.  _International Journal of Environmental Science and Technology_ 19, 3 (2021), 1447–1456.  https://doi.org/10.1007/s13762-021-03131-6
  * Lazaro Vasquez et al. (2022) Eldy S. Lazaro Vasquez, Netta Ofer, Shanel Wu, Mary Etta West, Mirela Alistar, and Laura Devendorf. 2022.  Exploring Biofoam as a Material for Tangible Interaction. In _Proceedings of the 2022 ACM Designing Interactive Systems Conference_ _(DIS ’22)_. Association for Computing Machinery, New York, NY, USA, 1525–1539.  https://doi.org/10.1145/3532106.3533494
  * Lazaro Vasquez et al. (2020) Eldy S. Lazaro Vasquez, Hao-Chuan Wang, and Katia Vega. 2020.  Introducing the Sustainable Prototyping Life Cycle for Digital Fabrication to Designers. In _Proceedings of the 2020 ACM Designing Interactive Systems Conference_ (Eindhoven, Netherlands) _(DIS ’20)_. Association for Computing Machinery, New York, NY, USA, 1301–1312.  https://doi.org/10.1145/3357236.3395510
  * Lim et al. (2014) Yongseok Lim, Hoyoung Tang, Seungok Lim, and Jongsun Park. 2014.  An Adaptive Impedance-Matching Network Based on a Novel Capacitor Matrix for Wireless Power Transfer.  _IEEE Transactions on Power Electronics_ 29, 8 (2014), 4403–4413.  https://doi.org/10.1109/TPEL.2013.2292596
  * Lu et al. (2023) Jasmine Lu, Beza Desta, K. D. Wu, Romain Nith, Joyce E Passananti, and Pedro Lopes. 2023.  EcoEDA: Recycling E-Waste During Electronics Design. In _Proceedings of the 36th Annual ACM Symposium on User Interface Software and Technology_ _(UIST ’23)_. Association for Computing Machinery, New York, NY, USA, Article 30, 14 pages.  https://doi.org/10.1145/3586183.3606745
  * Maestri and Wakkary (2011) Leah Maestri and Ron Wakkary. 2011.  Understanding repair as a creative process of everyday design. In _Proceedings of the 8th ACM Conference on Creativity and Cognition_ (Atlanta, Georgia, USA) _(C &C ’11)_. Association for Computing Machinery, New York, NY, USA, 81–90.  https://doi.org/10.1145/2069618.2069633
  * Maurice et al. (2021) Ange A. Maurice, Khang Ngoc Dinh, Nicolas M. Charpentier, Andrea Brambilla, and Jean-Christophe P. Gabriel. 2021.  Dismantling of Printed Circuit Boards Enabling Electronic Components Sorting and Their Subsequent Treatment Open Improved Elemental Sustainability Opportunities.  _Sustainability_ 13, 18 (2021).  https://doi.org/10.3390/su131810357
  * Moore et al. (2022) Gregory E. Moore, James D. Rosenthal, Joshua R. Smith, and Matthew S. Reynolds. 2022.  Adaptive Wireless Power Transfer and Backscatter Communication for Perpetual Operation of Wireless Brain–Computer Interfaces.  _Proc. IEEE_ 110, 1 (2022), 89–106.  https://doi.org/10.1109/JPROC.2021.3130059
  * Ni et al. (2014) Wenqing Ni, Yue Huang, Xiaoling Wang, Jingwen Zhang, and Kusheng Wu. 2014.  Associations of neonatal lead, cadmium, chromium and nickel co-exposure with DNA oxidative damage in an electronic waste recycling town.  _Science of The Total Environment_ 472 (2014), 354–362.  https://doi.org/10.1016/j.scitotenv.2013.11.032
  * Nisser et al. (2021) Martin Nisser, Christina Chen Liao, Yuchen Chai, Aradhana Adhikari, Steve Hodges, and Stefanie Mueller. 2021.  LaserFactory: A Laser Cutter-Based Electromechanical Assembly and Fabrication Platform to Make Functional Devices & Robots. In _Proceedings of the 2021 CHI Conference on Human Factors in Computing Systems_ (Yokohama, Japan) _(CHI ’21)_. Association for Computing Machinery, New York, NY, USA, Article 663, 15 pages.  https://doi.org/10.1145/3411764.3445692
  * Pataranutaporn et al. (2018) Pat Pataranutaporn, Jaime Sanchez De La Vega, Abhik Chowdhury, Audrey Ng, and Galina Mihaleva. 2018.  Toward Growable Robot : Exploring and Integrating Flexible – Biological Matter with Electronics. In _2018 International Flexible Electronics Technology Conference (IFETC)_. 1–4.  https://doi.org/10.1109/IFETC.2018.8584034
  * RESIONE (2020) RESIONE. 2020.  RESIONE F39/F69 Material Datasheet.  https://www.resione.com/products/f39-white-flexible-rubber-like-3d-printer-resin-1kg-1
  * Rivera et al. (2023) Michael L. Rivera, S. Sandra Bae, and Scott E. Hudson. 2023.  Designing a Sustainable Material for 3D Printing with Spent Coffee Grounds. In _Proceedings of the 2023 ACM Designing Interactive Systems Conference_ (Pittsburgh, PA, USA) _(DIS ’23)_. Association for Computing Machinery, New York, NY, USA, 294–311.  https://doi.org/10.1145/3563657.3595983
  * Sharawi (2004) Mohammad S Sharawi. 2004.  Practical issues in high speed PCB design.  _IEEE Potentials_ 23, 2 (2004), 24–27.  https://doi.org/10.1109/MP.2004.1289994
  * Shorter et al. (2014) Michael Shorter, Jon Rogers, and John McGhee. 2014.  Practical Notes on Paper Circuits. In _Proceedings of the 2014 Conference on Designing Interactive Systems_ (Vancouver, BC, Canada) _(DIS ’14)_. Association for Computing Machinery, New York, NY, USA, 483–492.  https://doi.org/10.1145/2598510.2602965
  * Song et al. (2022) Katherine W Song, Aditi Maheshwari, Eric M Gallo, Andreea Danielescu, and Eric Paulos. 2022.  Towards Decomposable Interactive Systems: Design of a Backyard-Degradable Wireless Heating Interface. In _Proceedings of the 2022 CHI Conference on Human Factors in Computing Systems_ (New Orleans, LA, USA) _(CHI ’22)_. Association for Computing Machinery, New York, NY, USA, Article 100, 12 pages.  https://doi.org/10.1145/3491102.3502007
  * Song and Paulos (2021) Katherine W Song and Eric Paulos. 2021.  Unmaking: Enabling and Celebrating the Creative Material of Failure, Destruction, Decay, and Deformation. In _Proceedings of the 2021 CHI Conference on Human Factors in Computing Systems_ _(CHI ’21)_. Association for Computing Machinery, New York, NY, USA, Article 429, 12 pages.  https://doi.org/10.1145/3411764.3445529
  * Song and Paulos (2023) Katherine Wei Song and Eric Paulos. 2023.  Vim: Customizable, Decomposable Electrical Energy Storage. In _Proceedings of the 2023 CHI Conference on Human Factors in Computing Systems_ _(CHI ’23)_. Association for Computing Machinery, New York, NY, USA, Article 180, 18 pages.  https://doi.org/10.1145/3544548.3581110
  * Taib et al. (2023) Nur-Azzah Afifah Binti Taib, Md Rezaur Rahman, Durul Huda, Kuok King Kuok, Sinin Hamdan, Muhammad Khusairy Bin Bakri, Muhammad Rafiq Mirza Bin Julaihi, and Afrasyab Khan. 2023.  A review on poly lactic acid (PLA) as a biodegradable polymer.  _Polymer Bulletin_ 80, 2 (2023), 1179–1213.  https://doi.org/10.1007/s00289-022-04160-y
  * Vasquez and Vega (2019a) Eldy S. Lazaro Vasquez and Katia Vega. 2019a.  From plastic to biomaterials: prototyping DIY electronics with mycelium. In _Adjunct Proceedings of the 2019 ACM International Joint Conference on Pervasive and Ubiquitous Computing and Proceedings of the 2019 ACM International Symposium on Wearable Computers_ (London, United Kingdom) _(UbiComp/ISWC ’19 Adjunct)_. Association for Computing Machinery, New York, NY, USA, 308–311.  https://doi.org/10.1145/3341162.3343808
  * Vasquez and Vega (2019b) Eldy S. Lazaro Vasquez and Katia Vega. 2019b.  Myco-Accessories: Sustainable Wearables with Biodegradable Materials. In _Proceedings of the 2019 ACM International Symposium on Wearable Computers_ (London, United Kingdom) _(ISWC ’19)_. Association for Computing Machinery, New York, NY, USA, 306–311.  https://doi.org/10.1145/3341163.3346938
  * Wang et al. (2018) Guanyun Wang, Tingyu Cheng, Youngwook Do, Humphrey Yang, Ye Tao, Jianzhe Gu, Byoungkwon An, and Lining Yao. 2018.  Printed Paper Actuator: A Low-Cost Reversible Actuation and Sensing Method for Shape Changing Interfaces. In _Proceedings of the 2018 CHI Conference on Human Factors in Computing Systems_ (Montreal QC, Canada) _(CHI ’18)_. Association for Computing Machinery, New York, NY, USA, 1–12.  https://doi.org/10.1145/3173574.3174143
  * Wang et al. (2011) Hongmei Wang, Mei Han, Suwen Yang, Yanqing Chen, Qian Liu, and Shen Ke. 2011.  Urinary heavy metal levels and relevant factors among people exposed to e-waste dismantling.  _Environment International_ 37, 1 (2011), 80–85.  https://doi.org/10.1016/j.envint.2010.07.005
  * Wei et al. (2019) Huaxin Wei, Jeffrey C. F. Ho, Kenny K. N. Chow, Shunying An Blevis, and Eli Blevis. 2019.  Should Do, Can Do, Can Know: Sustainability and Other Reflections on One Hundred and One Interaction Design Projects. In _Proceedings of the Fifth Workshop on Computing within Limits_ (Lappeenranta, Finland) _(LIMITS ’19)_. Association for Computing Machinery, New York, NY, USA, Article 6, 18 pages.  https://doi.org/10.1145/3338103.3338109
  * Wu and Devendorf (2020) Shanel Wu and Laura Devendorf. 2020.  Unfabricate: Designing Smart Textiles for Disassembly. In _Proceedings of the 2020 CHI Conference on Human Factors in Computing Systems_ (Honolulu, HI, USA) _(CHI ’20)_. Association for Computing Machinery, New York, NY, USA, 1–14.  https://doi.org/10.1145/3313831.3376227
  * Yan et al. (2023) Zeyu Yan, Tingyu Cheng, Jasmine Lu, Pedro Lopes, and Huaishu Peng. 2023.  Future Paradigms for Sustainable Making. In _Adjunct Proceedings of the 36th Annual ACM Symposium on User Interface Software and Technology_ _(UIST ’23 Adjunct)_. Association for Computing Machinery, New York, NY, USA, Article 109, 3 pages.  https://doi.org/10.1145/3586182.3617433
  * Yan and Peng (2021) Zeyu Yan and Huaishu Peng. 2021.  FabHydro: Printing Interactive Hydraulic Devices with an Affordable SLA 3D Printer. In _The 34th Annual ACM Symposium on User Interface Software and Technology_ (Virtual Event, USA) _(UIST ’21)_. Association for Computing Machinery, New York, NY, USA, 298–311.  https://doi.org/10.1145/3472749.3474751
  * Yan et al. (2022) Zeyu Yan, Anup Sathya, Sahra Yusuf, Jyh-Ming Lien, and Huaishu Peng. 2022.  Fibercuit: Prototyping High-Resolution Flexible and Kirigami Circuits with a Fiber Laser Engraver. In _Proceedings of the 35th Annual ACM Symposium on User Interface Software and Technology_ (Bend, OR, USA) _(UIST ’22)_. Association for Computing Machinery, New York, NY, USA, Article 12, 13 pages.  https://doi.org/10.1145/3526113.3545652
  * Yin et al. (2014) Lan Yin, Huanyu Cheng, Shimin Mao, Richard Haasch, Yuhao Liu, Xu Xie, Suk-Won Hwang, Harshvardhan Jain, Seung-Kyun Kang, Yewang Su, Rui Li, Yonggang Huang, and John A. Rogers. 2014.  Dissolvable Metals for Transient Electronics.  _Advanced Functional Materials_ 24, 5 (2014), 645–658.  https://doi.org/10.1002/adfm.201301847
  * Zhan et al. (2020) Lu Zhan, Yongliang Zhang, Zahoor Ahmad, and Zhenming Xu. 2020.  Novel Recycle Technology for Recovering Gallium Arsenide from Scraped Integrated Circuits.  _ACS Sustainable Chemistry & Engineering_ 8, 7 (2020), 2874–2882.  https://doi.org/10.1021/acssuschemeng.9b07006
  * Zhu et al. (2020) Junyi Zhu, Lotta-Gili Blumberg, Yunyi Zhu, Martin Nisser, Ethan Levi Carlson, Xin Wen, Kevin Shum, Jessica Ayeley Quaye, and Stefanie Mueller. 2020.  CurveBoards: Integrating Breadboards into Physical Objects to Prototype Function in the Context of Form. In _Proceedings of the 2020 CHI Conference on Human Factors in Computing Systems_ (Honolulu, HI, USA) _(CHI ’20)_. Association for Computing Machinery, New York, NY, USA, 1–13.  https://doi.org/10.1145/3313831.3376617