Mike,
the old mil spec. clearly indicated the difference between AR, UR, SR
coating and their usage...I am not sure if similar guideline exist for the
selection of conformal coat for commercial product...I don't think the
selection of any material based on "familiarity or irrational personal
preference" are the common practice...(hopefully, not)...jk
At 11:12 AM 11/26/99 EST, you wrote:
>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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