We do not use the type of solder mask as you, however; I have seen low pre cure 
temps or time leave mask in holes and high temps or time leave mask on surface 
copper.  This has been seen on all types of LPI's.  We also found that solder 
mask loves to lock on tin/lead residue, this might be something else to check.

______________________________ Reply Separator _________________________________
Subject: Solder Mask Residue
Author:  <[log in to unmask]> at INTERNET
Date:    7/15/97 6:30 AM


Dear Sir,
     
We are one of the PCB manufacturer in the Philippines. Since last Feb., we 
have encountered a serious problems with solder mask residue on hole edge. 
We have been using Tamura DSR-2200 with open screen. Some people said 
Tamura has very poor developing ability. We've been trying to solve this 
problems as changing the pre-curing condition from 80 degrees, 30 min. to 
70 degrees, 20 min. and increased the pressure of developing zone. However, 
we still have the same problems and make us difficult to solve it because 
it is on-off problems, in other words, sometimes O.K. but sometimes it 
happend. Basically, I have the questions as below.
1. Why is it on-off problems, but not continue?
2. Why only on hole edge, but not on the other areas like SMD pads, hole 
wall?(sometimes we were able to find the residue right after developing, 
but the most of cases, we only were able to find it after HASL as a exposed 
copper on hold edge)
Please help me with some advice if you have any ideas on this problem. 
Thanks for your cooperation!
     
Truly yours,
     
Sonny Jee
     
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