material compatiability study should not be done at production level.  Why
you are doing it on the populated board? If you done the work at front (in
the design stage as part of material selection), you should not see the need
to do it at production level.
Why?
                               jk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Edward Mines
Sent: Thursday, December 16, 2004 1:33 PM
To: [log in to unmask]
Subject: [TN] solder mask/conformal coating compatability


To the best of my knowledge there is no written standard for solder
mask/conformal coating compatability, but I have heard instances where poor
adhesion of conformal coating to the solder mask was preceived as a problem.
It's a dirty little secret that not all conformal coatings adhere to all
solder masks; I've seen some that peel right off, no matter how clean the
underling solder mask is.

At one time Enthione had a flier listing the "compatability" of popular
conformal coatings to their solder masks. THer criteria that they used to
judge this was vague. I don't know if it's still available.

HumiSeal tried to develop a correlation between the surface tensions of
conformal coatings and solder masks to predict adhesion but was
unsuccessful.

1B31S - a goosed up version of 1B31-  has improved adhesion to some problem
solder masks, but there are still some solder masks where 1B31S will  peel
right off.

Doug Pauls is correct that cleaning problems are sometimes mistaken for
incompatabilty of solder masks to conformal coating. Frequently this was
solder mask batch related, sometimes process, sometimes the chemistry of the
batch itself.

Somewhere IPC (IPC-CC-830?) calls out an adhesion test for conformal coating
to solder masks. The test cuts a grid larger than 1" X 1" into the coating
with a $100 plus apparatus and then trys to lift off coating squares with
tape. That test is  operator dependent (subjective) and it's hard to find a
1" square area free of components on most boards.



Edward Mines BEChE, MEChE
238 Willard Dr.
Hewlett, NY  11557
516 205-6523
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