During what process is the Solder Mask blistering? Wave solder, Reflow? 
 What temperatures are the boards seeing?  Is the LPI properly cured?
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From: TechNet-request
To: TechNet
Subject: Soldermask
Date: Friday, June 21, 1996 14:24

We are having problems with LPI soldermask when plugging via holes. On many
occasions we get blistering of the LPI mask on and around the vias. Any help
in resolving this problem would be appreciated.