Lou,
Every chemical vendor probably has an oxide treatment that they would
recommend for solder mask adhesion. Usually, they recommend
red/bronze oxide versions. But, like your 33% less filling oxide,
they do require time, process control, etc.
Equipment manufacturers would recommend scrubbing as being sufficient
for solder mask adhesion, with pumice being the preferred option. A
"good" pumice scrubber carries a significant price tag. Also, some
pumice scrubbers tend to self destruct.(Keep in mind price versus
cost, you get what you pay for, etc.)
As a former chemical salesman, I recommend going with a proprietary
oxide treatment. (Enthone-OMI, MacDermid, Shipley, etc.) However, I
would also get inputs from your LPI vendor on his recommendations.
(LPIs should not present a particular adhesion problem IF your boards
are clean prior to the solder mask process.)
As a former quality manager, I recommend pumice scrubbing of the
copper surfaces prior to solder mask application. It seems to be more
consistent and less of a headache for the lab guys. (I've never been
a maintenance guy though, so take this with a grain of salt.)
As a current engineer working with buyers of circuit boards, I don't
care as long as the solder mask stays on the board. Solder mask
adhesion has not been an issue with the board shops we use.
In summary: Weigh the options, pick the vendor (equipment or chemical)
you trust to support you the best, and go for it.
Regards,
Jamie Baumgart
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