Greetings all,

We are a fab shop and are looking for a solution to a problem being
experienced by one of our customers.  They have a board which resides in a
somewhat hostile environment
        - steam/salt water vapour
        - board carries 20Amp current
        - susceptible to multiple thermal excursions which put further stress on
the unit
The problem, as one might expect, is that the soldermask is not man enough
for the job.  Some units have exhibited significant solder mask flaking from
the conductors after as little as 4 hours of operation.  FYI, board is
double sided with 3oz base Cu.

The product is currently only in the prototype stage but production volumes
are expected to be in the 100,000-250,000 units annually.  We have proposed
the obvious solution of utilizing a conformal coating post assy but that is
an option they would initially prefer to avoid due to the inherent costs
involved.  They would like us to first exhaust any possibility that the
problem can be averted from the pcb fabrication level.  I should also
mention that the expected lifespan of the unit is a maximum of 1000hrs and
likely only several hundred hours.

Some options that have been discussed are; (in no particular order of
likelihood to succeed of fail!)
        - multiple coating of soldermask
        - micro etch of copper prior to mask application (currently pumice scrub)
        - conductor pacification with oxide alternative.  If this does not provide
additional bite for the mask it may provide additional protection from
corrosion once the mask has pealed off.

Any ideas from the lot of you?  Are there properties to specialty solder
masks which might be beneficial in this application?  Any options to
conformal coating??

Regards
John Parsons

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