Topic:
Motherboard failure - suspect run or joint...


I agree that the broken or fractured run is a possibility.  I'm leaning
toward the cold solder joint just because of the nature of the
manufacturing process.  The fact that you were able to induce the failure
using the freon is a real plus.  You've closed in on it.  Now you'll need
to do like the other fellow said and break out the magnifying glass and
find that cold solder joint (or fractured run).  A cold solder joint will
look dull grey most likely.  A good solder joint is uniform in shape and is
shiny.  A cold solder joint is often non-uniform and dull grey.  If you
look real closely, you can see hairline fractures, "wrinkles", or pits in a
cold solder joint - depending upon the power of the lense you're using.  If
you do identify a cold solder joint, it will need to be retouched.  If you
haven't done this before, you might want to get some advice first about how
to do this properly.  A real simple job can turn into a real nightmare if
you're not careful.

There is the possibility, however, that on the multi-layer board, there was
not good flow all the way through on one or more of the joints you're
looking at.  It could be virtually impossible to find the culprit in this
case - the solder joint may be fine on the surface but still have
incomplete flow through.  You'd have to reflow everything in the area
you've been able to induce the failure in.  In doing so you might make an
intermittent problem worse if the solder flow is not good all the way
through on all the joints.  It can be difficult to get solder to flow all
the way through properly on a multi-layer board because the combined
surface area of each layer that is electrically connected to that lead can
act as a big heat sink.  This doesn't apply to surface mounts, flat packs,
etc, of course.  That's a whole other ball of wax.

Good Luck!

Joan Rapier

            PCBUILD maintains many useful files for download
              on our web site - visit our download page at:
                     http://nospin.com/pc/files.html