Daan
Now is covering 1 mm of epoxy with 0.05 mm of epoxy or other material
going to make any difference? If, under a given set of conditions, it
takes humidity exposure of 1 year for the IC to be damaged without the
top covered, it will take 1 year and 18 days if it were covered. A
conformal coating is designed to delay problems due to loss of
electrical insulation and to protect it from dust, etc. It is next to
useless as a pure humidity-proofing. This is why, as a general rule, you
must remove hygroscopic contaminants (ionic or otherwise) before
applying a coating.
However, by definition, a conformal coating should conform to the
contours of an assembly, and that does not mean skipping some areas
without a very good reason (e.g., contacts). In that respect, your
client is right, even if there is no good technical reason.
Brian
"d. terstegge" wrote:
>
> Dear Technetters,
>
> We've just finished our first few boards with Humiseal 1B31 conformal
> coating, applied with a selective spraycoating machine, and we asked the
> customer to inspect the products.
> He commented that some areas on top of the IC's were not covered
> completely, which is required (so he says) because these are plastic
> components which may absorb moisture if left uncovered.
>
> I'm not gonne argue about this with the customer, but still I'm
> interested to hear from you wether the fact that the IC's are plastic is
> indeed a reason to require them to be completely covered with coating.
> As far as my knowledge goes the problem with plastic IC's and moisture
> is limited to the soldering process only, but I may be wrong.....
> Anyone can comment ?
>
> Daan Terstegge
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
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