Coverlay of Flexible PCB - A Comprehensive Introduction in 2022

What is Flexible PCB Coverlay

Coverlay is the protective film of flexible PCBs, which plays the same functions as the solder mask of rigid PCBs:

Insulate the copper foil (RA copper or ED copper) from the air and protect it from oxidation
Cover the bare areas and circuit traces and protect them from soldering
Make preparation for surface finishes to PCB pads
Coverlay is insulating resin, and typical coverlay materials are polyimide (PI) and transparent polyester (PET). It has excellent dielectric properties and abrasion resistance, and flex PCBs can be used in aerospace, defense, medical, and precise electronics fields.

Coverlay includes a PI or PET film and an adhesive layer. The adhesive is brushed on the PI or PET film and then laminated under high temperatures and pressures, and a flexible PCB coverlay is formed.

Flexible PCB PI film coverlay can have a color of yellow, white, or black. PET film coverlay is transparent.

During flexible PCB manufacturing, the coverlay is laminated with copper foil first, and then the other side of the copper is etched to generate circuit traces.

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