We found that success in wetting plastic packages very much depends on
the conformal coating material.  Assuming the packages are clean and
free of oil and mold release, wetting is a function of the surface
tension of the coating material and the critical free energy of the
substrate.  Some coating products have the appropriate surface tension
for plastic substrates, some do not. Talk with your coating manufacturer
and try various products.  Do not assume that what worked elsewhere will
work on plastic.   Some plastics have very low critical surface free
energies - in the range of 18-40 dyn/cm.  Ask your coating manufacturers
if they can tell you the surface tension of their coating products.  The
lower the better.   If the surface tension of the coating is less than
the critical free energy of the solid, complete wetting will occur; but
if the surface tension is greater, partial non wetting can result.

Call me and I can tell you the name of the product performed best in our
application.


        Mary Davis
        Sr. Material & Process Engineer
        Product & Process Analysis Lab

        Raytheon Systems Company
        Naval and Maritime Systems
        KW 281, MK4C08
        6500 Harbour Heights Parkway
        Mukilteo, WA 98275-4862
        425.356.3311
        425.356-3185 fax

> -----Original Message-----
> From: Paul Stolar [SMTP:[log in to unmask]]
> Sent: Monday, October 12, 1998 7:09 AM
> To:   [log in to unmask]
> Subject:      [TN] Confomal coating adhesion
>
>      Does anyone have any good experience at improving conformal
> coating
>      adhesion to plastic packaging?
>
>      Is it a cleanliness issue, or is it inherent in materials?
>
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