Are you troubled by choosing solder resist and cover glass when designing flexible circuit boards? The solder mask layer and the cover layer have the same basic insulation function. Do you know the difference between solder mask and cover layer? Can solder resist and cover layer overlap to provide insulation? Do you think the flexible solder mask layer is the same as the rigid printed circuit solder mask layer?

1) Design: Coverlay is actually widely used in flexible circuit boards. Due to the fact that most FPCS require the addition of PI/FR4 reinforcement and EMI shielding layers. However, if there are dense areas with BGA solder pads and solder mask openings, the minimum size and material mesh of the openings will be limited and can be retained between adjacent openings. Below, we will share with you the cladding and solder mask layers covered by FPCB. Firstly, cover the winding layer, and then slightly overlap the solder mask layer to cover the winding layer to prevent any gaps from appearing in the composite layer. This design has higher requirements for our production to ensure the functionality and reliability of your design.

2) Thickness: Why choose to use green soldering flux instead of cover glass? The normal cover glass thickness is 27.5/50um. The thickness of the solder mask layer is 8/12um. Because the customer requires ultra-thin flexible PCBs. Then, we suggest that customers use solder mask instead of cover glass.

3) Color: The most popular cover film color is yellow. We usually have yellow, white, and black cover films in stock. There are various colors available for solder mask, including green, black, white, yellow, etc. Please note that the FPC solder mask layer is completely different from the PCB. The cost of FPC soldering is much higher than that of PCB because FPC soldering has better bending resistance and high temperature resistance than PCB.