Ken:

There are many factors to consider. We normally use Silicone Coating
(Dow-Corning 2577) and on occasion we have had to use a polyurethane
(Conethane CE-1155).

First off, all spray guns, measuring cups, Zahn cups, stirrers, etc. must be
dedicated for silicone coating.

When we switch from silicone to the poly, we strip down all table tops, turn
tables and even spray booth walls to totally eliminate all loose particles
of silicone. The silicone basically forms a white snow flake like appearance
on all surfaces.It is important to eliminate these loose particles. I have
seen a single speck of silicone stick to a board surface and cause a
non-wetted area around the speck approx. 1/8" diameter. It requires a lot of
work to srcub down the affected area so that the poly material would stick.
It is not unusual for our conformal coat operator to spend 4 - 6 hours in
site preparation for using polyurethane in a silicone environment. I can't
say the reverse is true because when we spray the poly material, it is a
limited amount, therefore site preparation for going back to silicone is
minimal.

Bill Kasprzak
Moog Inc.

> -----Original Message-----
> From: Ken Bloomquist [SMTP:[log in to unmask]]
> Sent: Friday, May 19, 2000 9:37 AM
> To:   [log in to unmask]
> Subject:      [TN] Silicone Confromal Coating
>
> Hi TechNet,
>
> We have a customer that wants us to spray Silicone confromal coating on
> their boards. We currently spray polyurethane and acrylic.
>
> My question is: Is there any problem adding Silicone to our process? What
> art the things we need to consider in adding this process?
>
> Thanks,
>
> Ken Bloomquist
>
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