PCB - Flex

Description

Flex PCBs are printed circuit boards that utilize a flexible substrate that can be bent or folded. They enable 2D and 3D wiring in confined spaces, resulting in miniaturization, weight reduction, and high reliability. They typically use polyimide (PI) as an insulating layer and are designed to maintain electrical performance even under repeated bending conditions. Flex PCBs are a next-generation printed circuit board that offer flexible wiring and high reliability in confined spaces.

Specifications

Base Material
Polyimide (PI): Standard
High heat resistance, high insulation, excellent bending durability
Adhesive / Adhesiveless construction
Adhesiveless offers reduced thickness, heat resistance, and superior reliability (recommended)

Selection Guide
• Repeated bending/high reliability → Adhesiveless PI
• Cost-conscious/simple bending → Adhesive PI

Board Thickness
• Typical range: 0.05–0.2 mm (excluding coverlay)
• Influencing factors: Bending radius, durability, and assembly

Selection Guide
• Small/repetitive bending → Thinner
• Component mounting/rigidity required → Add reinforcement plate

Copper Type & Weight
• RA Copper (Rolled Copper): Ideal for Repetitive Bending (Recommended)
• ED Copper (Electrolytic Copper): Cost-Effective
• Thickness: 0.5 oz to 1 oz (Typical), Up to 2 oz

Selection Guidea
• Repetitive Bending/Dynamic Environments → RA
• Static Bending/Cost-Conscious → ED

Lines & Spaces
• Standard: 75–100 μm
• Minimum: 50 μm (laser process/advanced specifications)

The finer the material, the greater the impact on cost and yield.

Layer Count
• 1~2 Layers (Single/Double Flex)
• Multi-layer Flex: High-end (higher cost)

Consider Rigid-Flex for high-density, high-speed applications

Coverlay
• A protective layer that replaces solder mask
• PI film + adhesive structure
• Protects bend areas and ensures reliability

Coverlay is more essential than solder mask in bending areas

Stiffener
• Materials: FR-4, PI, SUS (stainless steel)
• Usage: Ensuring component mounting rigidity and stabilizing connector connections

Vias and Holes
• PTH / Laser Via
• Drill size limitations exist due to the thin-film structure.

High-density implementation possible with laser vias.

Surface Finish
• ENIG: Excellent flatness, solderability, and reliability (recommended)
• OSP: Low cost, short-term use
• Im Tin / Im Silver: Special applications

Bending Radius
• Static bending: 6-10 times the substrate thickness
• Dynamic bending: 10-20 times the substrate thickness

Failure to comply with the bending radius can lead to cracking and short circuits.

Electrical Test
• BBT 100%: Open/Short Test
• Complete testing is essential for highly reliable products.

Technical Data

Item	General Specifications
Material	Polyimide (PI)
Thickness	0.05~0.2mm
Copper Foil	RA/ED, 0.5~1 oz
Line WIdth/Pitch	75~100 μm (Minimum 50 μm)
Layer	1~2
Protect	Coverlay
Reinforcement	FR-4 / PI / SUS
Surface Finish	ENIG recommended
Test	BBT transfer