ProForm: Solder-Free Thermoforming Circuit Assembly

• ProForm is defined as a solder-free electronics assembly method that uses thermoformed PETG encapsulation to mechanically secure surface-mount devices.
• It employs pressure forming and Z-tape stabilization to achieve low-resistance, robust electrical connections under varied operational conditions.
• The method enhances sustainability through component reuse, easy reversibility, and compatibility with substrates ranging from rigid PCBs to flexible and curved surfaces.

Searching arXiv for the exact ProForm paper and close name variants to ground the article in current literature. arXiv search query: ProForm thermoforming solder-free circuit assembly arXiv search query: PoFormer speaker verification pooling transformer ProForm, short for prototyping through thermoforming, is a solder-free circuit assembly method that uses thermoforming to mechanically capture and stabilize surface-mount electronic components on a circuit board or other substrate. Rather than creating semi-permanent solder joints, it uses a thermoformed thermoplastic encapsulation layer to press component leads and pads into reliable electrical contact and physically lock the assembly in place. The resulting circuit is described as immediately functional after forming, while remaining reversible: the plastic can later be cut or removed so that components can be reused or replaced without desoldering (Pourjafarian et al., 28 Jul 2025).

1. Definition, rationale, and design objective

ProForm is framed as a response to two linked problems in electronics prototyping and fabrication: the environmental cost of electronic waste and the practical permanence of soldered assembly. Conventional prototyping is described as still dominated by soldering, which creates semi-permanent joints. Those joints are reliable, but recovering components typically requires manual desoldering, which is labor-intensive, energy-intensive, and often damages parts during removal. The paper cites approximately 62 billion kg of e-waste generated in 2022 as context and presents ProForm as a way to address component disposability and difficulty of disassembly (Pourjafarian et al., 28 Jul 2025).

Conceptually, the method replaces solder with a thermoformed thermoplastic encapsulation layer. Surface-mount devices are first positioned on a PCB or other conductive substrate, then a softened plastic sheet is pressure-formed over them so that it conforms around the components and board. After trimming, the assembly remains mechanically stable and electrically functional. This design also eliminates the need for solder or custom mechanical housings and is presented not only as a sustainability-oriented method but also as a rapid prototyping technique for substrates and form factors that are awkward for conventional solder-based workflows (Pourjafarian et al., 28 Jul 2025).

2. Fabrication sequence and material system

The reported fabrication sequence has four stages. First, the circuit substrate is prepared using standard PCB design tools, with two recommended additions: test points for debugging and troubleshooting, and small vent holes of about $\sim 0.5\ \mathrm{mm}$ to improve air circulation and forming quality. Second, components are placed and stabilized with anisotropic conductive film (3M Z-tape), which both prevents shifting during handling and thermoforming and helps maintain pin-to-pad contact by compensating for small height variations. The paper notes that Z-tape can be applied per component or as larger strips across sections of the PCB, but that it requires uniform compression along the bond line for low contact resistance (Pourjafarian et al., 28 Jul 2025).

The thermoforming step uses pressure forming rather than vacuum forming. In pressure forming, positive air pressure pushes the softened sheet tightly against the mold or board geometry, yielding sharper detail and better conformity. The reported material is PETG (polyethylene terephthalate glycol), selected because it is recyclable, transparent, semi-rigid, strong and lightweight, easy to form at relatively low temperature, and compatible with desktop thermoforming tools. The paper reports 160°C forming temperature, pressure between 55 psi and 63 psi, and notes that pressures above 58 psi gave sharper details and more reliable electrical connections. The total thermoforming cycle is 210 seconds, broken down into a 120 s forming cycle and a 90 s cooling phase. To ensure the plastic wraps around PCB edges, the board must be elevated above the flat bed of the machine, for example with pin headers, spacers, or temporary supports. After forming, excess thermoplastic is removed with scissors or a hot knife (Pourjafarian et al., 28 Jul 2025).

PETG thickness	Average resistance	Standard deviation
0.5 mm	$15.8\ \Omega$	$7.39\ \Omega$
1.0 mm	$1.13\ \Omega$	$0.18\ \Omega$
1.5 mm	$0.85\ \Omega$	$0.44\ \Omega$

The thickness study used fifteen zero-ohm resistors total, specifically 1206 size resistors, with five samples per thickness. The paper identifies 1.0 mm PETG as the default because it delivered reliability comparable to 1.5 mm while using less material and lowering cost and recycling burden. It also gives a cost point of 1.08 USD per A4-sized sheet (Pourjafarian et al., 28 Jul 2025).

3. Electrical, thermal, and mechanical performance

The reported electrical characterization emphasizes that thermoforming is functionally central rather than merely protective. Across the zero-ohm resistor tests, the overall average resistance is reported as $1.32\ \Omega$, with standard deviation overall of $0.34\ \Omega$. By package size, the paper reports 1206 at $1.13\ \Omega$ or $15.8\ \Omega$0, and 0603 at $15.8\ \Omega$1 or $15.8\ \Omega$2. A key comparison is that a Z-tape-mounted resistor without thermoforming initially measured 2.2 k$15.8\ \Omega$3 and later failed entirely, which the paper uses to argue that the pressure-formed encapsulation is what makes the electrical contact reliable (Pourjafarian et al., 28 Jul 2025).

For signal integrity, the paper reports tests with sine waves from 100 kHz to 10 MHz using a function generator and oscilloscope, with no observable waveform attenuation in ProFormed circuits, including at 5 Vp-p, 1 MHz, and 10 MHz. For higher-current operation, a circuit based on an AOD452 Power MOSFET driving two DC motors (ZR370-02PM, 500 mA) was toggled with a 50% duty cycle PWM at 0.5 Hz for one hour; current measurements every 15 minutes gave average current = 946 mA and standard deviation = 21 mA. A second test with two type-130 DC motors (1.5–6 V) running continuously for an hour gave average current = 984 mA and standard deviation = 11 mA. The authors conclude that the assembly remained stable under these conditions, while noting that more work is needed for higher currents and longer durations (Pourjafarian et al., 28 Jul 2025).

Mechanical and environmental tests are similarly varied. A ProFormed PCB with an ATtiny85 and six LEDs stayed continuously powered for 152 days and remained fully functional. For water sealing, a PCB encapsulated on both sides with an ATtiny85 MCU, an LED, and a coin cell battery remained fully functional during and after 24 hours of water submersion. In drop testing, a ProFormed PCB was dropped from 50 cm, 100 cm, 150 cm, and 200 cm, with three drops at each height, and remained functional throughout. In the MOSFET and motor test, thermal imaging showed only a 3.7°C temperature increase after one hour of continuous operation; the paper interprets this as no significant overheating, while noting that heat sinks could be added if necessary (Pourjafarian et al., 28 Jul 2025).

4. Supported components, substrates, and geometric scope

The evaluation covers a broad set of standard surface-mount packages. Reported successful component types include SOIC (ATtiny85), TSSOP (ATtiny45), TQFP (ATtiny828), QFN (ATtiny85), SSOP (CD74HC multiplexer), LEDs in 0805, 3014, 3528, and 5050 sizes, and zero-ohm resistors in 0603, 0805, and 1206 packages. The paper reports that the method worked well across these standard SMD components. The explicit failure case is BGA packages, which failed because the pad geometry was too small to provide sufficient conductive contact area for reliable Z-tape adhesion (Pourjafarian et al., 28 Jul 2025).

A major claim of the work is substrate and geometry compatibility. The paper states that ProForm works on traditional rigid PCBs, flexible circuits, paper-based electronics, conductive inkjet and screen-printed circuits, copper foil circuits, laser-etched substrates, non-planar surfaces, curved surfaces, tilted and vertical surfaces, and boards with components on both sides. This suggests that the method is not limited to conventional flat FR-4 assemblies but is intended as a general assembly technique for electronics embedded into objects or unconventional physical forms (Pourjafarian et al., 28 Jul 2025).

The demonstrated applications reflect that breadth. The paper includes a smart cupboard switch whose parts were later reused in a hydration tracker, an interactive wristband on a concave curved surface, smart glasses with UV sensing, an interactive greeting card on paper, a pen holder with a digital clock, and a waterproof thermometer designed for liquid submersion. These examples are used to show that the electronics can become part of the form factor rather than being added as a separate enclosed module (Pourjafarian et al., 28 Jul 2025).

5. Reversibility, repairability, and sustainability framing

Reversibility is central to the method. To recover components, the thermoplastic layer can be removed with scissors, a hot knife, or a laser cutter, after which the components are fully accessible for reuse. To replace a single component, the reported procedure is to cut only around that component, replace it, and thermoform again. The paper further reports that the same component can survive ten thermforming/disassembly cycles with no measurable electrical degradation in a multiplexer test: a CD74HC multiplexer in SSOP package was repeatedly re-thermoformed and tested with a 1 MHz, 3.5 Vp-p sinusoidal signal, and the output waveforms remained unchanged across cycles (Pourjafarian et al., 28 Jul 2025).

The sustainability argument is developed in specifically circular terms. The authors explicitly state that ProForm was designed to address component disposability and difficulty of disassembly. They argue that the environmental cost of semiconductor components is much larger than the cost of the PETG encapsulation layer, and they note that thermoforming is relatively low-energy compared with solder reflow or industrial rework. The paper also states that PETG waste can be reclaimed with desktop recycling systems. In this framing, ProForm aims to make circuit construction a build–test–open–reuse–rebuild process rather than a one-way assembly process (Pourjafarian et al., 28 Jul 2025).

The paper also attributes several practical advantages over soldering to this reversibility: component reuse without desoldering damage, simpler repair by local trimming rather than full board rework, encapsulation against dust, corrosion, and moisture, waterproofing when both sides are formed and sealed, integration into objects without a separate enclosure, and support for reused components from old prototypes or other devices. These claims position reversibility as both an environmental and an engineering property (Pourjafarian et al., 28 Jul 2025).

6. Limitations, open constraints, and terminological context

The paper is explicit about design constraints. It states that surface preparation matters and that pads must be clean, flat, and aligned. Through-hole components are not natively supported, and current prototypes often still require soldered headers and wires. PETG adds rigidity, which can reduce flexibility in paper or soft substrates. Larger boards may need better pressure uniformity, and the maximum tested pressure of 63 psi may still be insufficient for severely misaligned or deformed leads. Because direct access to traces is limited after forming, debugging requires planning, test points, or selective cutting. The authors also experimented with alternatives to Z-tape, including glycerin and carbon- and silver-based conductive greases; these showed some promise but had drawbacks, especially in small packages or dense layouts where spreading could cause shorts (Pourjafarian et al., 28 Jul 2025).

In current arXiv usage, the exact name “ProForm” denotes this thermoforming-based, solder-free electronics assembly method. It should be distinguished from unrelated names that are superficially similar, including the speaker-verification pooling transformer PoFormer (Ma et al., 2021), the parallel descendants of the symbolic manipulation system FORM, namely ParFORM and TFORM (Tentyukov et al., 2010), the shallow parallel transformer architecture ParaFormer (Wang et al., 17 Oct 2025), the prescriptive-optimization framework PolyFormer (Wen et al., 9 Mar 2026), and exercise-form systems such as FormCoach (Zuo et al., 10 Aug 2025). This naming proximity does not indicate a shared technical lineage. Within the cited literature, ProForm is specifically the use of PETG encapsulation plus conductive film-based component stabilization to create circuit assemblies that are electrically reliable, mechanically robust, reusable, reparable, and compatible with rigid, flexible, paper-based, and curved substrates (Pourjafarian et al., 28 Jul 2025).