Daan -

From your description, the condition is starting to sound more like a
"non-wetting" problem than "de-wetting".  Non-wetting being a situation where
the solder never spreads and wets the pad.  Refer to Dave Hillman's earlier
response which discussed the possibility of gold porosity, which could be the
source of your problem.

A simple test to visually confirm the above would be to do a brief solder dip
test on a section of circuit board using an RMA flux similar to that in your
paste.  If the specimen remains gold plated, you have a pretty good indicator
that the condition is non-wetting.  Another test option might be to heat a
specimen with paste on it on a hot plate where it can be observed under
magnification.  If the solder does not spread when it melts, it is an
indication of non-wetting.

Given that you are receiving boards with this same finish from other
suppliers, and processing them successfully, it would seem that your problems
must originate with the new suppliers processes rather than your own.

Regards - Kelly

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