Steve,

Sounds /looks like your previous supplier did not use
a vacuum chamber to help remove air from the via holes. I have personally
evaluated the CB100 and
Emerson & Cumming Eccobond 56C which are both conductive silver via fills
and it is not an easy process. I eventually used a via fill from Lackwerke
Peters(non-conductive) since conductive fill was not required, which was
much more user friendly but still required a vacuum chamber to insure no
voids in vias.

Tony Steinke
AIT-Atlanta Inc.

----- Original Message -----
From: "Steve Gregory" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, March 22, 2004 9:44 AM
Subject: Re: [TN] Plugged Via bubble


> 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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