I don't know why this did not post yesterday...oh well, better late than never.

Phil


Phillip Bavaro <[log in to unmask]> wrote:
Date: Tue, 20 Sep 2005 12:03:06 -0700 (PDT)
From: Phillip Bavaro <[log in to unmask]>
Subject: Re: [TN] BGA Adpater board
To: TechNet E-Mail Forum <[log in to unmask]>,
Dwight Mattix <[log in to unmask]>

Thank Dwight.

The daughter card methods listed so far are all feasible methods.   It is best when building the daughtercards in panel form with extras to ensure the yield.  Our designers typically only needed a few to work with so we would buy three or four arrays (16 each).

The one that caused us some real concern was when they wanted other components as well to go on the daughtercard and it's envelope was larger than the original part being replaced and not symetrical.

We ended up having to use tooling fixtures to place it and standoff spacers (dummy 0201s) to keep the non-symetrical daughtercard from tilting, but it worked the first time and saved design from having to wait months to try their change out.

Winslow Automation provided the preforms for the solderballs, we assembled them, but they do not have preforms for the 0.5 mm pitch.  We also assembled daughtercards with only prescreen paste bumps on the bottomside instead of solderballs.

Keep the daughtercard limited to the original footprint make sure the center of mass does not get moved and you should have no problems with the pick and placement.

The other tricky aspect is when they want to do this to already asssembled motherboards, as opposed to new motherboard builds, but then it is really just a matter of checking the placement before reflowing using the xray.

Hope this helps.

Phil

Dwight Mattix <[log in to unmask]> wrote:
We've done it (do it) with much success at .8 and 1mm. With
limited/qualified success at .5mm. Typically we've pre-assembled to bottom
of BGA and then placed as one unit on the motherboard. Phil Bavaro is a
great resource for this application.

dw



> > Folks,
> >
> > We have a requirement to design a daughterboard that will be soldered
>to
> > the motherboard in place of BGA devices. This means that BGA balls are
> > required (on the secondary side) of the daughterboard so it can be
> > soldered to the existing BGA pattern(s) on the motherboard, as if it
> > were just another BGA. I've not heard of this being done before so I'm
> > hoping others may be able to provide some insight in regards to
> > feasability and process.
> >
> > Thanks Much!
> >
> > Rick
> >
> >
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