How to produce a FPC without adhesive?

It is well known that FPC is soft, light, thin, flexible, and it has been widely used in Smart wearable device, Digital related, LCD monitors, etc.

The traditional FPC board material is mainly based on the five-layer stack up of coverlay/adhesive/copper/adhesive/PI film (like below picture), and the adhesive is mainly Epoxy/Acrylic, but the heat resistance and dimensional stability of the adhesive are not good, and the temperature of long-term use is limited to 100-200C, which makes the field of Flex PCB limited.

How can we give pre-sale advice to customers when they have strict requirements for heat resistance and dimension?

Today I’d like to share some suggestions with you/as well as 《Flexible PCB Materials》

1. Change base material to adhesiveless material. There are two types of base material for FPC, adhesive material and adhesiveless material, normally we will use adhesive material since the price is lower than adhesiveless material, but if the customer has high bending requirements or the customer requires no adhesive on the board, so we will use adhesiveless material.
2. No coverlay or use solder mask instead of coverlay. The purpose of the coverlay is to protect the copper foil from oxidation, but all coverlay have adhesive. If the customer doesn't want adhesive on the flex circuit, there are two options. Option A is No coverlay, copper will oxidize in the absence of a coverlay. Option B is use solder mask instead of coverlay, solder mask in FR4 PCB and coverlay in FPC have the same effect, solder mask can also be used for FPC, but FPC requires special ink since the FPC needs to bend, and only slight bending is allowed to prevent the ink from breaking.
3. Use ENIG or OSP surface treatment on whole copper foil. If your FPC can not accept copper oxidation and requires a good flexibility, then the second tip above is not suitable for you. In this case you can choose not to use coverlay and surface treatment on whole copper foil, normally we will use ENIG or OSP, OSP will be cheaper than ENIG, it depends on your choice.

If you have more questions about our design suggestions, please feel free to contact us at sales@bestfpc.com