FCCL

Not all printed circuit boards use rigid CCL. Some are designed to be very flexible or slightly flexible called flex circuits. Flexible copper clad laminate (FCCL) is a core component of flexible printed circuits (FPCs). FCCL comprises layers of copper foil and polyimide, which are used as an electrical conductor and insulator, respectively.

• Single-sided FCCL: with copper foil only on one side
• Double-sided FCCL: with copper foil on both sides

 

 

In-between polyimide and copper foil(s), there is adhesive or not. And FCCLs can be divided into

• Adhesiveless FCCL
• Adhesive FCCL

Both single- and double-sided FCCLs with or without adhesive can be used to fabricate flexible PCBs. Together with rigid CCL and PP, FCCLs can be used to fabricate rigid-flex boards.

 

ED and RA Copper on FCCL

 

The copper foils can be ED (Electro Deposit) Copper or RA (Rolled & Annealed) Copper. The standard ED copper typically has a relatively high profile or rough surface as compared to rolled annealed copper. ED copper tends to lack flexibility and does not promote good signal integrity. RA copper has been used extensively in the flex industry for decades. In complex and multilayer flexible and rigid-flex PCB designs, MADPCB recommends FCCL with RA copper foil.

 

Adhesive-less vs. Adhesive FCCL

 

FCCLs fall into adhesive-less and adhesive categories. What’s adhesive-less FCCL? There is no adhesive in-between the copper and polyimide. It’s obvious to understand when compare our common stock flexible laminates as below charts.

• Thinner PI laminates have better flexible bending capacity
• Thicker PI laminates are more expensive than that of thinner PI laminates
• Adhesiveless FCCL is more expensive than that of adhesive FCCL

 

Considering higher flexibility and lowest CTE (i.e. high dimensional stability), MADPCB suggest to use adhesiveless (or adhesive-less) FCCLs to manufacture

• Rigid-flex PCB
• Multilayer PCB
• HDI PCB
• Impedance controlled PCB
• High density SMDs (with coverlay openings)

 

Considering of low cost and no strict thickness requirements, MADPCB suggest to use adhesive FCCLs to manufacture

• Simple flex circuit
• Single-sided flex circuit
• Double-sided flex circuit

 

Flexible Copper Clad Laminates (FCCLs) in Stock

 

Thicker polyimide thickness in FCCL equal to or more than 4mils, is not commonly used since high material price and less flexibility, and we can combine different thicknesses of FCCL, adhesive, coverlay and bondply to reach your required FPC thickness and desired controlled impedance.

 

 

 

 

 

Basics of FPC Flexibility

 

Flexible printed circuit is widely used in many industry sectors for their unique physical property of flexible bending and extension to let the PCB to be made to fit in the limited of your electronic product or devices, but not make the device to conform with your PCB board when it is not a flexible circuit. The flexible bending will be affected by copper thickness, adhesive thickness, PI (/Kapton) thickness, and coverlay thickness. In many years FPC manufacturing experience, we get some basics as below.

 

• When the copper thicknesses are the same 1oz, the flexible bending with hatching pour is better than that with solid pour.
• When the adhesive-less FCCL are the same, the flexible bending with 1/2oz is better than that with 1oz.
• When one is adhesive FCCL and the other is adhesive-less FCCL. The flexible bending with adhesive-less FCCL is better than that with adhesive FCCL.