We had a similar situation recently on a rigid-flex brd (which were sold to
assy house)
where hand soldering was performed....green soldermask....to a trained eye
it looked like massive delamination.

It was discoloration of soldermask (not soldermask peeling or
lifting)....which could be due to heat, flux interaction...we did not really  figure out the
cause.  It was limited to hand soldering areas only.

X-section proved it (looking with back-light) and also U can scrap  the
soldermask w. X-acto knife and see if the laminate below is really  delaminated.

Our brds were for aerospace...customer bought the brds after X-sections  from
independent lab and report.

Rush
Accurate Engg Inc
_www.accueng.com_ (http://www.accueng.com)
818-768-3919


In a message dated 11/28/2006 9:01:58 AM Pacific Standard Time,
[log in to unmask] writes:

This is  standard FR4 with immersion silver finish.
The standard soldermask  colour we spec is clear, not green.  Allows us to
better see the copper,  and often some inner layer features as well, but if you
aren't used to working  with FR4 with clear soldermask, it can definitely look
a little strange, at  first.
The dark colour seen is due to an inner layer that is  primarily ground plane.
I'm pretty sure that it isn't soldermask  bubbling
We have not yet done any microsectioning.  So far we  have only seen this on
fully populated boards that have experienced some  hand-soldering, and we are
reluctant to sacrifice one, if it can be saved for  production.
I have a blank two-up panel available from each  manufacturer we've used.  We
are planning to run some hand-soldering  tests.  Vary temperatures, one
unbaked and one baked from each panel,  etc.  Any other  ideas?


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