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September 2006

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Subject:
From:
Kevin Glidden <[log in to unmask]>
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Date:
Tue, 26 Sep 2006 12:26:29 -0400
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Question for the PCB fabricators...

One of our PCB suppliers is asking us to accept PCBs with a "minor" issue.
The problem is described as this: The panels were under-developed and some
residual solder mask was left over.  To eliminate this, the panels were put
through a second pass to ensure all residual solder mask was removed.  The
result is some overdevelopment of the solder mask.  Then, this apparently
resulted in an "undercut" along the demarcation lines.  They say during a
tape test, very small traces of mask from the undercuts comes off.  The mask
is still present between all features and is adhered to the PCB.   But, it
is over-developed and has undercuts.  They say that while it does not pass
the tape adhesion test, it is of no detriment to the PCB quality or
performance.

My question is if over-developed soldermask maintains the same properties as
normally developed soldermask?  When I asked about this, they said the
properties of the mask are determined by the initial (pre-developing) cure
and the final (post-developing cure), and the over-development does not
affect the properties.  True?

In case "it depends", these PCBs are used in avionics power supplies.

Thanks in advance!

Kevin

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