We have recently seen a failure of an assembly in a humidity chamber.  There
were two things observed.  First, on an external layer, power traces (+25V) were
very close to ground traces (~20 mils), and an apparent electrical bridge caused
a short and a burned the area.   Secondly, other areas of the board appeared to
have white residue and broken down soldermask bridging between connector pins.
Some of these areas took up a number of pins (thumb print size).

I vaguely remember and issue where assemblies that were not thoroughly cleaned
could leave residuals (chlorides?) and that when subjected to a humid
environment could break down soldermask.  I also believe that humid chlorides
can crystallize and can be influenced by electrical potentials between pins -
causing shorts.  However, that's where my memory breaks down.

Can anybody provide some clarity on potential reasons for soldermask to
breakdown in a humidity chamber?

Thank you,

                Anders P. Pedersen                         * 407-729-2143 (ph)
        Harris Aerospace                                   * 407-729-2097 (fax)
        P.O. Box 94000, MS22-4842                  * [log in to unmask]
        Melbourne, FL 32902                        http://www.harris.com/

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