Reference Standard for Plasma Etching or Scrubbing on Flex Ckts

I am having coating adhesion problem with flex circuits. The cover plate material is KAPTON or Poly imide. The conformal coating material used is humiseal 2A64. The boards are cleaned, measuring less than 4 microgram Nacl per sq in. against acceptable value of 10.6 max.

The flex circuit is dipped twice , followed by one spray. There is 15-20 minutes bake between each dip. There is clear evidence of dewetting after first dip and 2nd dip. The spray coat is unable to make all uniform coating- especially areas which had dewetting. Fluoroscence is weak to Nil where dewetting occured. That requires lengthly manual touch up work. Most of the dewetting is on edges of the board.

We are interested in roughtening up the surface - providing Matt Finish in place of Glossy Finish. We did scrubbed few samples and observed marked improvement in adhesion of coating to surface.

Any one who can suggest IPC Standard, Military Standard or any other industrial standard where this process step is specified as controlled process ?

Our customer is Mil Standard, IPC and J-STD user and is concerned with where Plasma etch is controlled process ?

Any help on this will be highly appreciated.

Regards

Ashok Dhawan Solectron Winnipeg (204) 631 7208

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