Hi Albert! I suspect that you are driving off/volatilizing some type of
ionic contamination with your baking procedure. One method investigating
this is to bake a set of boards at 90 C for 65 minutes, run the omegameter
test and compare results. A temperature of 150 C is high enough to
volatilize a number of different ionic contaminates species. Doesn't such a
high bake temperature result in solderability problems for your pwbs? Good
Luck.

Dave Hillman
Rockwell Collins
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Albert Mok <[log in to unmask]> on 04/14/99 07:48:44 PM

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Subject:  [TN] ionic contamination




Good morning, technetters,

We aer using Alpha 600SMD for detecting the ionic contamination of bare
PCB.  All boards are D.I. rinse and dried prior for the testing.  The
reading come out is about 10ug NaCl/sq.in.  However, when the boards sent
to baking at 110 C for four hours and the boards are tested again, the
reading drop to 3ug NaCl/sq. in.   We do not suspect inadequate baking at
the first time.  We bake the boards at 150 C for 65 mins.  The solder mask
is photoimagable solder mask.

This is not a single case.  Everytime when the contamination is failed,
then bake the boards again, the result turn to positive.  However, if we
prolong the baking time at the first baking, it does have this result
apparently.

Do you have this experience?

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