At 07:05 PM 1/17/97 -0500, you wrote:
>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.



Have you checked the holes prior to thermal testing. When the mask material
is screened on it has a solvent thinner mixed in. When the mask is thermally
cured the solvent out-gasses and the plug naturally gets smaller. After the
plug is cured I can't think of any reason it would shrink outside of the
normal thermal expansion. Also, you state that nothing is wrong with the
thickness or quality of the copper walls. Thickness of plating should not be
confused with quality. Barrel cracking is a quality problem.


>
>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 know that SR-1000 is considered a great mask for adhesion over copper. (I
wish I could get all the photoimageable soldermasks to adhere as well). But,
I imagine that the root cause must be in the quality of the plating since
you mentioned barrel cracks. If you are also seeing it on holes that do not
exhibit cracks, it may also be caused by the type of hole desmear process
used or electroless copper vs. direct plate (some say you sacrifice plating
adhesion to the hole wall when using certain types of direct plate
processes. This would simply indicate that the adhesion of the mask to the
copper is greater than the adhesion to the hole wall. One other potential
problem area is the laminate itself. You say the copper is pulling away from
the holewall. It may be that your laminate is not completely cured and the
laminate is pulling away from the hole wall. This is termed resin recession
and is sometimes difficult to tell from pullaway on a microsection. You
might try measuring the barrel width to the drill diameter. If they match
and if the laminate to laminate measurement is larger than the drill size,
you may be dealing with resin recession. It is a subtle difference and the
microsection has to be ground to the center of the hole to get a good reading.

Anyway thats my $.02
David Arivett
Cuplex Inc.


>
>
>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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