In a message dated 11/26/1999 5:38:58 AM Pacific Standard Time,
[log in to unmask] writes:

> I am dismayed at the suggestion of changing the coating after all, it is a
> permanent product to do a permanent job -- not a temporary product to do a
> temporary job. Further, silicone does not stick to other silicone so
> easily -- usually not at all.

My experience has been, frankly, that many times one coating is specified
over another due to familiarity or irrational personal preference. Unless
there is some engineering criterion that dictates the use of one coating type
over another, it may be the course of fiscal wisdom to evaluate whether the
properties of silicone coating may suffice while eliminating the problem of
contamination.

The issue of silicone sticking to silicone is more complex than "usually not
at all." In our experience this varies from product to product and the nature
of the silicone (resinous vs. RTV). I can say with certainty that Humiseal
1C49, properly applied, does in fact eliminate the dewetting, fisheye (and
presumably adhesion, although it's tough to quantify) problems involved in
the Kapton-type tape residue on the boards we are currently coating with this
problem.

And I will also say that, in my experience, the Humiseal urethanes and
acrylics tend to react less to this silicone residue than other brands of
coating we also use on around 1000 boards a day.


Mike Moninger
Thermospray Company, Inc.
www.thermospray.com

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