Good morning everyone.

Today we have a situation where we have our "Lore and Legend" of
business (or "that's the way we've always done it") versus what a vendor
will supply.  Now let my unscramble this for you.  We make systems that
use high voltage coils encapsulated in epoxy.  Our practice for many
years is to not accept any voids (that we could see on the surface) in
the finished encapsulated item.  Generally we can achieve this by
pouring the epoxy into the mold while it is at roughing pressure or
under low vacuum.  If there was a void we never accepted the unit even
if it was patched because of a concern about punch through because of a
poor bond, dirt or other "conductive" gunk possible trapped under the
patch.  We won't go into the waste generated or process control here,
that's a separate discussion.

We now have a unit that is being potted by an outside vendor.  One unit
came in with a visibly patched void.  We rejected it because of our
undocumented culture of "no voids".  The outside vendor says they will
not guarantee void free potting.  So now we can either eat the cost of
this unit or use it.

What is a generally accepted practice for encapsulation or potting
regarding visible voids and patching?
Do you flat out reject it or do you consider the application and the
location of the void/patch?

I'd appreciate your views as we will be meeting on this subject and I'd
like to have some external opinions as reference when discussing the
merits of accepting repaired voids.

Thanks in advance,

Phil Nutting

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