Daan,
I don't think the problem is with moisture, but with the surface condition
of the plastic ICs.  We have the same problem occasionally our plastic ICs
and we prebake before coating.  Many of the plastic ICs are injection
molded and you have residual release agents on the surface which cause
de-wetting.  You may also have the material thinned down too much and it
all runs off.  As a remedy, you can either pre-apply the coating by hand to
the surface of these problem ICs and cure the material, or you can touch up
afterward.

Doug Pauls
Rockwell Collins




"d. terstegge" <[log in to unmask]>@ipc.org> on 08/14/2002
07:28:39 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
       to "d. terstegge" <[log in to unmask]>

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Subject:    [TN] Conformal coating on top of plastic IC's


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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