Kaye: Most of all the new generation LPI soldermasks have pretty much the
same numbers regarding moisture absorption i.e. they are not orders of
magnitude apart. The biggest issue is making sure they are properly
proportioned and cured, everybody wants to cut the cure cycle.
This reminds me of one of our design engineers. We had a polyamide board,
which has a tendency to absorb moisture, and he wanted to apply soldermask
normally over the surface of the board and also around all the exposed
routed edges and NPT holes. He was convinced that moisture was "pouring" in
thru these exposed areas. He wanted to "seal" the board with soldermask by
painting in mask on all these exposed areas. A processing nightmare.
I would be the first to agree that moisture can propagate from exposed
edges. However, thank God testing revealed any moisture penetration was
minimal and with PROPER design it was not necessary.
If your design is that sensitive you will not be able to limit moisture
absorption by trying to use soldermask as a poorman's conformal coat. It
will not effectively "encase" the board.
Perhaps our design fellow left Fluke is now working for Keithly.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: Kaye Clayo [mailto:[log in to unmask]]
Sent: Friday, July 11, 2003 8:38 AM
To: [log in to unmask]
Subject: [TN] Low moisture absorbing soldermask
Dear Technet:
I have just been asked if there is a soldermask that has a low moisture
absorption property.
We have a pcboard that uses Taconics TLC material, which is absorbing
moisture, and the engineer
would like to "encase" the board with a low moisture absorbing soldermask to
solve this problem.
Does anyone know of anything that will work, or another way around this
problem?
The engineer also asked me if anyone knew how to relate IPC-TM-650 2.6.2.1
"Water Absorption, Metal Clad Plastic Laminates"
to real life. What he means is, how does this test method, which dunks a
pcboard into distilled water for 24 hours, relate to
70% humidity at 23C.
Thank you for your help.
Kaye Clayo
Sr. P. C. Board Designer
Keithley Instruments, Inc.
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