Flexible PCBs require different design rules than rigid boards. The polyimide substrate, adhesive layers, and coverlay all affect what’s achievable. Here’s what we can manufacture.
Layer Count and Thickness
| Parameter | Standard | Advanced |
|---|---|---|
| Layer count | 1–4 layers | 5–8 layers |
| Board thickness (without stiffener) | 0.05–0.5mm | 0.5–0.8mm |
| Thickness tolerance (single layer) | ±0.05mm | ±0.03mm |
| Thickness tolerance (multilayer <0.3mm) | ±0.05mm | ±0.03mm |
| Thickness tolerance (multilayer 0.3–0.8mm) | ±0.1mm | ±10% |
Bend Radius Requirements
The minimum bend radius depends on your layer count and whether the flex will bend repeatedly:
| Configuration | Minimum Bend Radius |
|---|---|
| Single layer (static bend) | 3–6× board thickness |
| Double layer (static bend) | 6–10× board thickness |
| Multilayer (static bend) | 10–15× board thickness |
| Dynamic bend (repeated flexing) | 20–40× board thickness |
Dynamic bend applications require single-layer construction for reliability.
Line Width and Spacing
Achievable trace geometries depend on copper weight:
| Copper Weight | Standard (width/space) | Advanced (width/space) |
|---|---|---|
| 12–18μm (⅓–½oz) | 3.0/3.2 mil | 2.8/2.7 mil |
| 35μm (1oz) | 4.0/4.0 mil | 3.5/3.5 mil |
| 70μm (2oz) | 6.0/6.5 mil | 5.0/6.0 mil |
| 105μm (3oz) | 10/13 mil | 9.5/12.5 mil |
Note: Loop lines (traces that return to the same point) require approximately double the width/space.
Materials
Base Materials (FCCL)
Adhesive-based:
- Shengyi SF305: PI 0.5–2 mil, Cu ⅓–1oz
- Panasonic R-F775: PI 1–3 mil, Cu ½–1oz
- Taiflex MHK: PI 1–2 mil, Cu ⅓–1oz
Adhesiveless:
- DuPont Pyralux AP: PI 1–3 mil (standard), 4 mil (advanced), Cu ½–2oz
- Taiflex MHK: PI 1–2 mil, Cu ⅓–1oz
Coverlay
- Shengyi SF305C
- Taiflex FHK
Stiffeners
- PI stiffener: 3–9 mil thickness
- FR4 stiffener: Available with ±0.1mm tolerance
Drilling and Holes
| Parameter | Standard | Advanced |
|---|---|---|
| Minimum mechanical drill | 6 mil (0.15mm) | 4 mil (0.1mm) |
| Via-to-conductor clearance (<4 layer) | 6 mil | 5 mil |
| Via-to-conductor clearance (4–6 layer) | 8 mil | 7 mil |
| Via-to-conductor clearance (7–8 layer) | 12 mil | 10 mil |
Surface Finishes
Available finishes for flex PCBs:
- HASL – Hot air solder leveling
- ENIG – Electroless nickel immersion gold (Ni: 3–6μm, Au: 0.05–0.1μm)
- ENEPIG – Electroless nickel electroless palladium immersion gold
- Electrolytic gold – Soft or hard gold options
- Immersion silver – 0.2–0.4μm thickness
- OSP – Organic solderability preservative
- Immersion tin – Advanced capability only
Mixed finishes (ENIG+OSP, ENIG+gold finger) are also available.
Board Size
| Parameter | Standard | Advanced |
|---|---|---|
| Minimum size (without bridge) | 5×10mm | 4×8mm |
| Minimum size (with bridge) | 10×10mm | 8×8mm |
| Maximum size | 9×14 inch | 9×23 inch |
Impedance Control
| Type | Standard Tolerance | Advanced Tolerance |
|---|---|---|
| Single-ended ≤50Ω | ±5Ω | ±3Ω |
| Single-ended >50Ω | ±10% | ±8% |
| Differential ≤50Ω | ±5Ω | ±4Ω |
| Differential >50Ω | ±10% | ±8% |
Solder Mask
- Colors: Green standard, others available
- Minimum solder dam: 4 mil (green), 8 mil on large copper areas
- Minimum clearance: 3 mil (2.5 mil for specific areas)
- Coverlay bridge minimum: 8 mil
Related Articles
- Multilayer PCB Capabilities – Rigid PCB specifications for comparison
- PCB Materials and Laminates Guide – Material properties and selection
- PCB Designer’s Tips – Design guidelines for manufacturability
Need help with a flex PCB design? Request a quote – our engineers can review your design for manufacturability and recommend the best construction.