Ryan,

Did you dig up an old magazine or something?  Butter coat is an old and
probably poor term and how much resin is above the glass depends on the
glass style.  Prepreg coaters typically squeeze excess resin off the glass
as it is pulled through a trough of resin and then past a bar that pumps
resin through the glass.  The meter bars that strip the resin are set to
leave a controlled percentage of resin in and on the glass.

Chuck Brummer
Siemens

-----Original Message-----
From: Ryan Grant [mailto:[log in to unmask]]
Sent: Thursday, January 13, 2005 8:52 AM
To: [log in to unmask]
Subject: [TN] Butter coat


Hi Technetters,

I just learned a new PCB fabrication term today..."butter coat".  It's
supposed to be thin layer of resin between glass cloth bundles and
conductors to assure reliability.  In the few shop audits I've been
through, I've never seen or heard of a "butter coat".  What would the
process look like?  Is the resin pressed and frozen into a sheet that
can be handled or would it be squeegy'd on?  If it is squeegy'd, can
that be performed by hand or must a machine do it?  If a machine must do
it, how do you lay up the brick for the press?  Finally, is this a
standard process that I've just been unaware of?

Thanks,
Ryan

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