Polyimide Flexible PCB Is The Gold-Standard Material for High-Temperature, High-Reliability, and High-Density Flex Circuits
Why Choose Polyimide?
Exceptional thermal window — Tg > 360 °C
Survives 6 × lead-free reflow cycles at 260 °C with zero delamination
Low dielectric loss (εʀ ≈ 3.4, Df ≈ 0.008)
Clean 10 Gb/s eye-diagrams over 200 mm flex length
Outstanding dynamic bend life
≥ 10 million cycles @ radius 10 × thickness with 12 µm RA copper
Chemical & radiation resistance
Compatible with sterilisation gases, fuels, and space radiation
Adhesiveless variants available
Thinner stack-ups, tighter impedance tolerance (±8 %)
Polyimide’s property mix makes it the default choice for mission-critical applications where PET and PC flex films cannot survive.
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Material Options
| Grade | Copper Type | Core Thickness | Key Feature | Typical Use |
| Standard PI | RA 12 µm | 25, 50 µm | Cost-balanced | Consumer cameras, laptops |
| Adhesiveless PI | RA 12 / 18 µm | 25 µm | Best HDI & impedance | 5 G RF, USB4, PCIe Gen 5 |
| Ultra-thin PI | RA 9 µm | 12.5 µm | Foldable phones | Wearables, medical implants |
| Low-CTE PI (HF) | RA 18 µm | 50 µm | Dimensional stab. | Satellite phased arrays |
highpcb is one of the largest Flex PCB manufacturing company in China, Click on the link for more information.
Typical Applications
- Mobile & imaging: Folded camera modules, hinge flex in foldable phones.
- Data & RF: 10 Gb/s USB-C cable replacement, 6–40 GHz antennas.
- Medical: Catheter pull-wire flex, intracardiac endoscope lighting strips (autoclavable).
- Aerospace: Solar-array harness, CubeSat bus, SAR radar triggers.
- Automotive: Air-bag spiral cables, HUD light guides, e-motor sensor flex.
Stack-Up Examples
1 Single-Sided PI Flex (Entry-Level LED Strip)
White overlay ink
Imm Ag finish
Cu 18 µm (rolled-annealed)
Adhesive 15 µm (low-temp epoxy)
Polyimide 50 µm core
White PET backer (optional)
2 Double-Sided Adhesiveless PI (10 Gb/s Differential Pair)
ENIG 0.05 µm Au
Coverlay 12.5 µm PI + 12.5 µm epoxy
Cu 18 µm — Signal +
Polyimide 25 µm
Cu 18 µm — Signal –
Coverlay 12.5 µm PI + 12.5 µm epoxy
Impedance 100 Ω ± 8 % with 100 µm trace / 100 µm gap.
Manufacturing Flow & Critical Controls
| Step | Parameter | Typical Spec |
| Surface clean | Wet acid + DI rinse | Contact angle < 30° |
| Copper imaging | LDI, SAP or subtractive | Line/space ≥ 60 µm (SAP 35 µm) |
| Etch | CuCl₂ for ED, Na₂S₂O₈ for RA | Undercut < 12 µm |
| Coverlay lamination | 190 °C, 1.8 MPa, 60 min | Void < 1 % AOI |
| Stiffener attach | FR-4/Al/Steel, 170 °C press | Alignment ± 75 µm |
| PTH & microvia | Laser Ø 0.10–0.15 mm | Cu fill void < 5 % |
| Surface finish | ENIG/ENEPIG/OSP | Ni 3–5 µm, Au 0.05 µm |
| Dynamic bend test | R = 10 × t, 1 M cycles | No crack, ΔR < 5 % |
Design Guidelines
| Rule | Value / Note |
| Trace / space (single-oz) | 60 µm / 60 µm standard LDI; 40 µm possible (SAP) |
| Min laser microvia | Ø 0.10 mm; land Ø 0.20 mm |
| Bend radius | Static ≥ 6 × t, Dynamic ≥ 10 × t |
| Copper thickness in bend | ≤ 18 µm; avoid 35 µm in dynamic areas |
| Pad design in hinge | Teardrop + anchor spur, relieved mask |
| Plane hatching in bend | 50 % diamond or 0.5 mm slots |
| Coverlay opening | +0.10 mm beyond pad all round |
| Impedance tolerance | ± 8 % diff pair, ± 10 % single-ended |
Bend-life tip: Route traces perpendicular to the bend axis for at least 2 mm before the hinge to reduce copper work-hardening.
Reliability Tests (HighPCB Class 2/3 Baseline)
| Test | Method | Spec |
| Thermal shock −55 ↔ 125 °C, 500 cycles | JESD22-A104 | No delam, ΔR < 5 % |
| Dynamic bend R = 10 t, 1 M cycles | IPC-6013 3.4.2 | No open / short |
| IST (IST-2.6.26) | 35 A/mm², 25 ↔ 145 °C | ΔR < 5 % after 250 cycles |
| Moisture 85 °C/85 % RH, 168 h | IPC-TM-650 2.6.3.5 | IR > 1 GΩ |
| Solder float 260 °C, 10 s × 3 | IPC-TM-650 2.4.13 | No blister, no pad-lift |
Cost Drivers & How to Optimise
| Driver | Cost Impact | Optimisation |
| Adhesiveless PI core | +15 % | Use standard PI if reflow ≤ 240 °C |
| Microvia count | +US$ 4–6 / 1000 vias | Fan-out to larger vias outside hinge |
| ENEPIG finish | ×1.25 vs ENIG | Choose ENIG unless Al wire-bonding |
| Double-sided stiffeners | +US$ 25 per panel setup | Limit stiffener to actual BGA footprint |
| Gold finger bevel | +US$ 0.02 /finger | Use 20° bevel (cheaper) vs 45° |
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Support All Types of PCB Fabrication
Biggest PCB Manufacturers
Why Source Polyimide Flex from HighPCB?
- ISO 7 clean-room LDI—60 µm lines standard; 40 µm HDI option.
- Adhesiveless PI in stock—25 µm & 50 µm for tight impedance control.
- Laser microvia & via-fill—void rate < 2 %, stack ≤ 2 levels.
- 48-h DFM + fold simulation—strain map & impedance report with every quote.
- 5-day prototypes (1-layer), 7-day 2-layer, 10-day stiffener-assembled builds.
- Value-add: stiffener lamination, selective ENEPIG, low-temp reflow, 100 % dynamic bend testing.
Need a flex that shrugs off heat, vibration, and millions of bends?
Request your instant polyimide flexible PCB quotation from HighPCB today—our engineers will craft the optimal stack-up and process flow to bring your high-reliability design to life.
FAQ
Q1. Can polyimide flex go through autoclave sterilisation?
Yes. PI withstands 134 °C saturated steam cycles with no delamination (class II medical devices).
Q2. What copper weight supports 3 A continuous on flex?
18 µm copper, 2 mm width, PI 50 µm core yields < 25 °C temperature rise at 3 A.
Q3. Maximum roll length you can supply?
Roll-to-roll PI up to 30 m continuous; sheet-fed panels up to 510 × 610 mm.
Q4. Do I need stiffeners under every BGA?
Only under fine-pitch (< 0.8 mm) or heavy packages. Thin FR-4 (0.2–0.3 mm) stiffeners keep coplanarity < 0.08 mm.
