Yep, been there done that.  We had an assembly that was used in a marine enviroment that was also conformal coated.  We found that the solder mask would (using a peelable not washable) almost adhere to the soldermask and when it was removed the LPI would come up with it and enough surronding adhesion was also affected and then the board would fail the TM-650 tape test (we even used a scotch tape that was half the tensile strength of the tape called out in the TM-650.  We finally used Kapton tape over the mounting holes that we would normally had masked off.  This solved our problem.  It involved a little more labor putting the tape on instead of the mask but it solved the problem.  I also found that if we put the tape on and then surrounded the tape with mask we didn't have any issues with adhesion.  The adhesion loss always started where the pad edge and the soldermask met.  The PCB's passed all testing prior to solder masking.  

Kathy







owever, they had coated some bds and
allowed them to set over the weekend and after washing them off found the
peeling mask. We tape test all boards at our facility per IPC-TM-650
procedure. There has been no evidence of peeling at all. After visiting
with the Customer it seems that the time the Solder Stop is on the bds
(i.e. longer than 2 days) determines whether or not peeling will occur. The
peeling is always on pad openings which are on Copper groundplanes. We have
no evidence of any peeling on pads which are surrounded by FR4. The peeling
is usually limited to an area concentric to the mask opening and extends 5-
30 mils into the surrounding mask. We have run tests at one of our other
facilities consisting of running numerous bds across the wave solder at
different preheat and solder pot temps (we even matched the temperatures
the Customer with the issue is using) with no evidence of peel. The
customer is adding approx 1 cup of water to 1 Gal of Solder Stop to aid in
flow. It was requested not to refer to the Material's manufacturer until we
have additional data. Any suggestions or help you can provide will be
greatly appreciated.
Thanks,
Craig

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