I am working with an epoxy based solder resist to fill signal holes.
The material conforms to IPC-SM-840(B).  If it helps, the material is
Hysol SR 1000.

What I am seeing on routine thermal testing (cyclic -40C to 150C) is
that these plugs are shrinking? causing pull-away of the copper from the
drilled epoxy thru hole.  Nothing is wrong with the thickness or quality
of the copper walls, and on occasion barrel cracking is noticed, and
sometimes these plugs seem to squeeze a few mils out of the hole.

Note that no other hole type produced these results including solder
filled and open holes.

Also note that I see zero evidence of outgassing.

I NEED SOME ADVICE TECHNET!

What is the root cause of the problem?

Is this material meant to be subjected to this testing?

The data sheet I have states that the material only shrinks 0.65% so why
is the hole shrinking 2mil off each edge?

Is the adhesion of an epoxy strong enough to collapse a PTH?


I thank all in advance for every snippet of information possible toward
addressing the questions.  I have run these tests on over 10,000 boards
and never saw anything like it.

(Disclaimer:  I have no evidence that Hysol SR1000 is the root cause,
but welcome input from others who might have witnessed similar
observations with other materials.)

Thank you,
The Condor

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