Jim,
        I specifically looked for voids in microBGA's that had microvias in
the pad.  I found voids in every pad with micro vias.  However the voids
were very small.  I'm not entirely convinced the voids I saw were not an
illusion from looking into a via; although I did view the voids and via at
an angle.  (I guess if I really cared, I could cross section a joint and
know for sure).

        Voids in BGA balls can be caused by many factors.  I think microvias
will sometimes get a bum rap because large voids are assumed to come from
the microvia; when in fact the large void may be caused by the paste, reflow
profile or whatever else.  While it may or may not be true that micro vias
cause voids, they are definitely here to stay.

> -----Original Message-----
> From: Jim Kittel [SMTP:[log in to unmask]]
> Sent: Wednesday, January 19, 2000 1:11 PM
> To:   [log in to unmask]
> Subject:      [TN] Pad in Via for Micro BGA's
>
> Tech Netters
>
> I have a question for you on micro BGA's and I don't want this to be
> confused with the recent discussion on via-in-pad which may still be in
> process.
>
> The working draft copy I have of "Design and Assembly Process
> Implementation
> for BGAs" states on page 63 that a 0.1 mm micro via may be placed in the
> BGA
> solder land to allow more space for routing of traces.  They say the only
> noticeable affect is a small dimple.  I seem to remember articles in
> literature about outgassing and large voids in the BGA solder ball
> centered
> over the embedded via.   Could anyone comment on their experience placing
> microvias in BGA solder lands and if they agree with this comment in the
> design guide?
>
>                 Jim Kittel
>
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