Sherry,

The use of conductive epoxy when sandwiched and compressed between 2
surfaces is a decent conductor, the larger the surface area the better.
When painted across a surface as a conductive path, bridging 2 points some
distance apart, it is quite unreliable. Especially if it has to handle
current (I would define as 10-20 ma or greater) or be exposed to repeated
temperature extremes (I would define as 55C-85C or greater delta).

Since the 2 uBGA pads are adjacent, after removing the component, I would
epoxy a small piece of Cu trace or #36 bare wire or even a flattened little
piece of buss wire in place with minimal epoxy in the center only and cure.
You might even have to flatten a #36 wire which measures about (about .005
inch) in diameter.  After cure, be sure surfaces are solder wet (pads and
wire ends) with micro iron, then reinstall the uBGA using std rework.  You
should end up with a hard solder short with a Cu conductor running through
it.  This will handle current and temp extremes. Just one idea, I'm sure.

Good Luck,
Bruce Misner

> ----------
> From:         Sherry Warner[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Thursday, October 04, 2001 10:22 AM
> To:   [log in to unmask]
> Subject:      [TN] uBGA Rework
>
> Thank you Steve!  Looks like we may be on the right track, hopefully
> we can get a couple more suggestions for the technetters.
>
>
>
>
> Hi Sherry,
>
> I've posted the footprint of your uBGA up on my web page, I took the
> image and made a *.jpg out of it instead of a *.pdf...I called the
> image microBGA footprint.
>
> Go to: http://www.stevezeva.homestead.com/
>
> I had something similar to your problem a couple of years ago...except in
> my
> situation there was a trace running between the two pads. So I had to
> dig a little
> "tunnel" beneath the trace, and connected the two pads with a piece of
> trace
> material. This was on a uBGA as well...
>
> Good Luck!!
>
> -Steve Gregory-
>
>
>
> >Steve,
> >
> >Hope you can help us.  I don't think technet will allow attachments,
> >I know I can't receive them.
> >
> >I attached a pdf file of the package outline data sheet for a uBGA we
> >attached to a FR4 pcb.  Everything worked wonderfully through our
> >reflow process. Then the designer found an error in the board layout.
> >E3 should have been tied to E4 (active) but wasn't, it is a dead pad
> >under the component.   In order to get a temporary fix, the best
> >solution that we can think of is to remove the part, remove the mask
> >between the two pads on the board and apply conductive epoxy.
> >Purchase a micro mini-stencil (5 mil) for paste application and
> >reflow/attach a new component.
> >
> >Still in the learning stage and would welcome suggestions, there
> >hasn't been much BGA use here on-site until recently.
> >
> >Thank you,
> >Sherry
>
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