Ed, try baking one of the stained boards at 220F for an hour.
If the staining disappears or is reduced markedly, the problem was moisture
absorption into the mask during the hot rinse after soldering.   The
appearance is common at hot air solder level when the LPI has not been UV
cured as part of the mask cure.  You can also decrease it by letting the
boards cool some before the post soldering wash.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ed Hare
Sent: May 23, 2001 1:12 PM
To: [log in to unmask]
Subject: [TN] Discoloration of LPI solder mask


Dear Technetters,

Thanks in advance for any insight you can offer on this issue ...

The issue is discoloration of LPI solder mask (ENPLATE DSR-3241 (MD)) that
corresponds to areas that were selectively wave soldered I believe using OA
flux.  There are pictures at the link below ...

http:\\www.eskimo.com\~ehare\EH_516

The discoloration does not map with ground planes or other internal
circuitry in the PWB.

What might cause this type of discoloration?

Thanks,
Ed Hare
SEM Lab, Inc.

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