Mornin' All!

I'd be interested in an opinion as well about the reliability of voiding in
vias filled with silver epoxy. I got some pictures as well up on my page of
voids in vias. Go to:

http://www.stevezeva.homestead.com and look at "Voids and Voids 2" as well as
Douglas's pictures.

I was wondering about class-3 reliability, if you saw voids like in my
pictures, would you reject the fabs?

A little bit about my pictures. The vendor who made the boards from where
these these cross sections came from, was fired. Not primarily for the voiding, bu
t we actually had a cross section that showed vias with huge copper voids in
the barrel walls. The only reason the boards passed bare board test is because
they were silver filled...to make matters even worse, we had assemblies built
and shipped that had fabs that came from the lot where the cross sections
came from. Everything we built we recalled, and fired the fab shop, because they
could not provide us with any objective evidence that they had done any
process monitoring building these fabs. The cross sections that these pictures came
from were ones that I had done...and it's a long story, but it was just a
fluke that I had them done. Up to that point, we thought everything was going
along okay. We had no reason to doubt anything was wrong.

A little more info about my pictures. The epoxy that was used was a Dupont
CB-100 I believe, I have heard stories that particular epoxy can sometimes be
difficult to work with. Is that true? If so, is there another brand to specify?

It was difficult to find somebody to build this fab. I'm not saying that this
was a easy fab to build either. As you can see in the cross sections, this is
a 10-layer fab, blind vias, via-in-pad, and all vias are silver filled. The
10th layer of the board was sequentially laminated after the vias were epoxy
filled and planarized. As you can also see, that 10th layer is nothing but a
solid copper plane. Laminate material is Polyimide. The board is HASL'ed as
well...try to build that without it becoming a taco.

To make things fun for me, there's 20-mil pitch devices on the board as well
as 0603's.

Ahhhhhh! Such is the life in a contract shop...

-Steve Gregory-



> Technetters,
>
> Do any of you have reliability data or other experience with plugged vias
> that are subsequently plated over?
>
> Steve has been kind enough to agree to post pictures of the "defect" on his
> website.
>
> The micro section photos of the voids in the plug-and-cap vias. These were
> taken at 10X magnification. The voids/bubbles average .005" in diameter,
> almost round. Looking at the photos you can determine approximately how
> large they are by noting that the drill hole diameter is .010 inches drilled
> with a 10-mil drill size.
>
> What potential long-term reliability concerns are there, and is this
> considered acceptable for Class 2 product.
>
>
> Douglas Corbett
> L-3 Communications / Communication Systems - West
> Senior Manufacturing Engineer - Printed Circuit Boards
> (801) 594-3153
>


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