John,

Your basic choices are (in random order);

1. A 1" thick encapsulation of silicon (it might make 1000 hours)
2. Several  mils of paralyne
3. A "sealed" container
4. Let someone else try to build it

This sounds like a "down hole" board for drilling.

If you figure out something that works a lot of people would be
interested in the answer.

David A. Douthit
Manager
LoCan LLC

John Parsons wrote:

>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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