No experience with water soluble mask, but we had same experience with
peelable latex mask. We switched from synthetic latex to natural latex. This
gave us some relief. There should be a thread in the archives. We did not do
an exhaustive study or anything. I think the cause of the problem was partly
a do to variation in the LPI (cure process result) and partly due to the
fact that latex masks contain ammonia. If I recall someone suggested that
natural latex contained less ammonia than synthetic latex. I tried it and it
helped. I am not speaking as an authority only from experience.

 Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Craig Ropp
Sent: Friday, March 09, 2001 1:56 PM
To: [log in to unmask]
Subject: [TN] Solder Stop affecting LPISM adhesion of pad openings on
Copper Groundplanes


Has anyone had any experience with Solder Stop (water soluble mask)
affecting LPI adhesion around pad openings on Groundplanes. Typically
adhesion issues almost always relate back to inadequate surface prep during
the board manufacturing process. I had to "see it to believe it". We have
reviewed every step of the process and cannot find any disconnects. We have
only one Customer experiencing this problem. They have used the same Solder
Stop for approx 5-6 yrs. At 1st it was believed that the peeling didn't
occur until after Wave Solder. However, they had coated some bds and
allowed them to set over the weekend and after washing them off found the
peeling mask. We tape test all boards at our facility per IPC-TM-650
procedure. There has been no evidence of peeling at all. After visiting
with the Customer it seems that the time the Solder Stop is on the bds
(i.e. longer than 2 days) determines whether or not peeling will occur. The
peeling is always on pad openings which are on Copper groundplanes. We have
no evidence of any peeling on pads which are surrounded by FR4. The peeling
is usually limited to an area concentric to the mask opening and extends 5-
30 mils into the surrounding mask. We have run tests at one of our other
facilities consisting of running numerous bds across the wave solder at
different preheat and solder pot temps (we even matched the temperatures
the Customer with the issue is using) with no evidence of peel. The
customer is adding approx 1 cup of water to 1 Gal of Solder Stop to aid in
flow. It was requested not to refer to the Material's manufacturer until we
have additional data. Any suggestions or help you can provide will be
greatly appreciated.
Thanks,
Craig

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