We have a board with a safety relay on it that is exhibiting moisture inside the relay case after we process it (aqueous process). After numerous discussions with the relay vendor and several rounds of testing various epoxies for sealing the case to the base of the relay, the vendor is indicating they believe our wave solder process is heating the part too much, causing expansion of the air inside and subsequent breaking of the seal. I believe our wave solder profile is fairly standard and was developed to ensure that all solder fillets on the top-side meet IPC-610 Class 3 standards.  I'm hoping some of you wave solder gurus can tell me if we're way off base with our profiles.  We currently aim to acheive 90-100 C on the topside of the board prior the board entering the wave.  This gives us the wetting we're looking for as well as reduces the level of thermal shock on bottom side components.  Is this temperature in line with what's being done in wave soldering? Is there something I should be looking at to reduce this topside temperature without sacrificing solder wetting?  

As an added note, we ran around 70,000 of these units without much evidence of this problem occurring. Our process has not changed other than to move to a new building. The vendor did change epoxy but tests with both the old and the new epoxy yield similar failure rates.

Thanks in advance.

Rick Thompson

Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
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