PCB - Rigid Flex
Description
A rigid-flex PCB combines a rigid PCB and a flexible PCB (Flex) into a single substrate. The rigid portion provides component mounting and structural support, while the flexible portion (PI Kapton) enables bending and folding, replacing connectors and cables. Rigid-flex PCBs combine the rigidity of rigid materials with the flexibility of flexible materials, making them the optimal PCB solution for creating compact, lightweight, and highly reliable products.
Specifications
Layer Structure
• Rigid Area: 2-N Layers (FR-4-based)
• Flex Area: 1-4 Layers (PI-based)
• Overall Structure: Rigid + Flex + Rigid (Multi-Foldable)
Selection Criteria
• Simple Folding/Connection → Flex 1-2 Layers
• High-Speed/High-Density → Flex Multi-Layer + Rigid Multi-Layer
Base Material
Rigid Area
• FR-4 / High-Tg FR-4
• Provides mechanical rigidity and component mounting stability
Flex Area
• Polyimide (PI, Kapton)
• Adhesiveless construction recommended (excellent heat resistance and durability)
Selection Criteria
• Repeated bending and high reliability → Adhesiveless PI
• Cost-conscious and static bending → Adhesive PI
Board Thickness
• Rigid area: 0.8 ~ 1.6 mm (typical)
• Flex area: 0.05 ~ 0.2 mm
• Total thickness depends on stack-up
Thinner for better bending performance, thicker for better rigidity
Copper Type & Weight
• RA Copper (Rolled Copper): Required for Flex Areas, Recommended
• ED Copper (Electrolytic Copper): General for Rigid Areas
• Thickness: 0.5 to 1 oz (Flex), Up to 2 oz (Rigid)
RA Copper is required for repetitive bending areas
Lines & Spaces
• Standard: 75–100 μm
• Minimum: 50 μm (HDI/laser process)
The finer the material, the greater the impact on cost and yield.
Via Specifications
• Through Via (PTH)
• Blind/Buried Via
• Micro Via (Laser Via)
Micro Via is used for high-density, miniaturized designs.
Stack-up design
• Separate signal, power, and ground layers
• Symmetrical structure minimizes warpage
• Impedance control (differential, high-speed signaling)
Critical impact on SI/PI/EMI performance
Protection Layers
• Rigid Area: Solder Mask
• Flex Area: Coverlay (PI + Adhesive)
Coverlay is required for bending sections.
Stiffener
• Materials: FR-4, PI, SUS
• Usage: Connector fastening, ensuring rigidity of component mounting areas
Surface Finish
• ENIG: Excellent flatness, solderability, and reliability (recommended)
• OSP / Im Tin / Im Silver: Select based on application
Bending Radius
• Static bending: 6 to 10 times the thickness
• Dynamic bending: 10 to 20 times the thickness
Risk of cracks and short circuits if radius is not observed
Electrical Test
• 100% BBT inspection
• Open/Short circuit confirmation
• Required for high-reliability products
Technical Data
| Item |
General Specifications |
| Structure |
Rigid + Flex Integration |
| Rigid material |
FR-4 / High-Tg |
| Flex material |
PI (Kapton) |
| Copper Foil |
RA / ED, 0.5~1 oz |
| Line WIdth/Pitch |
75~100 μm |
| Via |
PTH / Blind / Micro |
| Protect |
Solder Mask / Coverlay |
| Surface Finish |
ENIG recommended |
| Test |
BBT transfer |
