Polycarbonate Flexible PCBs is Optically-Clear Circuits for Illuminated, Form-In-Place, and Smart-Surface Electronics
What Is a Polycarbonate PCB?
A polycarbonate PCB (PC PCB) is a flexible printed-circuit board that replaces the traditional polyimide or polyester dielectric with an optically clear, bis-phenol-A polycarbonate film. The laminate is typically:
- RA copper 9–18 µm (rolled-annealed for ductility)
- Polycarbonate core 50–125 µm (εʀ ≈ 2.9, Df ≈ 0.010)
- Optional acrylic or epoxy tie-coat for high-bond interfaces
The result is a transparent, thermo-formable circuit that can be back-lit, vacuum-formed, or directly insert-moulded into three-dimensional plastic parts.
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Key Advantages of Polycarbonate Flex
Optical clarity (> 85 % transmittance)
Perfect for light guides, illuminated logos, HUD masks
High tear strength & impact resistance
Survives thermo-forming and snap-fit assembly
Mid-range thermal window (service ≈ 120 °C)
Higher than polyester, suitable for most interior automotive trim
Form-in-place capability
Vacuum-form or high-pressure form into 3-D curvatures without white-stress lines
Low dielectric constant (εʀ ≈ 2.9)
Lower capacitive loading for GHz-range antennas & NFC
Limitations to Keep in Mind
| Limitation | Design Implication |
| Reflow incompatible (softens > 140 °C) | Use low-temp Sn-Bi solder (< 180 °C) or conductive epoxy; avoid Pb-free reflow |
| Moisture uptake slightly higher than PI | Bake 2 h @ 80 °C before adhesive lamination |
| Copper-to-PC adhesion weaker than PI | Mandatory O₂ plasma or silane primer before seed copper |
Typical Applications
| Segment | Example Use-Cases |
| Automotive interiors | Ambient-lit trim, capacitive slider on centre console, seat-belt warning logo |
| Smart glass & glazing | Transparent antennas, de-fog heater grids, electrochromic bus bars |
| Medical disposables | Illuminated diagnostics strips, transparent bio-sensors with optical read-out |
| Wearable devices | Curved smart rings, see-through display interconnects |
| Consumer lighting | Edge-lit acrylic panels with embedded current drivers |
Polycarbonate PCB Manufacturing Flow
| Step | Process Highlight | Critical Control |
| Film preparation | De-dust, bake 80 °C/2 h | Moisture < 0.07 % |
| Surface activation | O₂ plasma 60 s (200 W) | Contact angle < 35° |
| Seed layer deposition | 0.1 µm Pd/Sn catalyst + Cu flash | Peel > 1.0 N cm⁻¹ |
| Copper build-up | 9–18 µm DC plate, 1.5 A dm⁻² | Uniformity ±8 % |
| Imaging & etch | LDI 90 µm min line / space | Undercut < 15 µm |
| Coverlay lamination | 25 µm PC + UV-curing acrylic | Bondline void < 1 % AOI |
| Thermo-form / vacuum-form | 155 °C, vacuum 0.85 bar, 20 s | Draw-ratio ≤ 1.6 : 1 |
| Low-temp soldering | Sn42 Bi57 Ag1 paste, 175 °C peak | ΔT ≤ 3 °C across panel |
| Final inspection | 100 % flying-probe, visual trans-illumination | No haze, crack, or rainbow stress |
Design Guidelines (Engineer’s Quick Sheet)
| Rule | Recommended Value |
| Min trace / gap | 90 / 90 µm (ED Cu); 70 / 70 µm (RA 9 µm) |
| Copper density balance | ≤ 30 % mismatch per 25 mm² area |
| Bend radius (static fold) | ≥ 8 × total thickness |
| Trace routing in bends | No vias; serpentine for strain relief |
| Component land | Add 100 µm solder-mask dam; teardrop pads |
| Thermo-form draw | Avoid copper in high-strain (> 3 %) areas or use hatched pattern |
| Finish options | Imm Ag ≤ 2 µm, OSP, low-temp SnBi; ENIG not recommended (heat) |
Optics tip: Enlarge solder-mask openings +0.15 mm to avoid light leakage shadows.
Reliability Test Suite for PC Flex
| Test | Spec | Typical Result |
| Thermal cycling −40 ↔ 85 °C, 500 cycles | IPC-TM-650 2.6.7.2 | ΔR < 5 % |
| Dynamic bend R = 20 mm, 10 000 cycles | IPC-6013 3.4.2 | No open / short |
| Humidity 85 °C / 85 % RH, 168 h | IPC-TM-650 2.6.3.5 | IR > 100 MΩ |
| Light ageing 500 h @ UV-A 340 nm | ASTM G154 | ΔTransmittance < 5 % |
Cost Drivers & Optimization
| Driver | Impact | Mitigation |
| Optical-grade PC film | +25 % over commodity PI | Use 75 µm film if stiffness allows |
| Vacuum-form tooling | US$ 1 000–3 000 | Combine multiple parts per shot |
| Low-temp alloy paste | +US$ 0.02/component | Consolidate component types |
| Silane primer step | +5 % process time | Required only on double-sided copper |
Support All Types of PCB Fabrication
Biggest PCB Manufacturers
FAQ
Q 1. Can polycarbonate PCBs go through standard SMT reflow?
No. PC softens above ~150 °C. Use low-temperature Sn42 Bi57 Ag1 reflow (peak ≤ 180 °C) or anisotropic conductive film.
Q 2. How transparent are finished PC flex circuits?
With 9 µm RA copper and clear acrylic coverlay the assembly maintains > 80 % light transmittance; ideal for back-lit graphics.
Q 3. Are PC flex boards UL-rated?
Yes—HighPCB offers UL 94 V-2 and V-0 polycarbonate grades; specify your flammability target when quoting.
Q 4. Maximum size you can thermo-form?
Single-shot vacuum-form up to 400 × 500 mm; larger panels supplied flat for customer forming.
