Mark

If your SMD's are desoldering you are going over the melting point of the
solder. Well that's trivial I know. The question is, where in the soldering
operation you pump enough energy into the board in order to increase this
temperature. This can only be answered, if you measure the temperature-
time behaviour of the boards during soldering. I assume that passing faster
through the waves could ease the problem. Another approach I've seen is
installing a van that blows cool air on the top side of the board. ( Nice
job for a lab. technician). But without seeing the Temp.-time profile and
the solder machine it's quite difficult to give a sophisticated advise.

Blowholes are almost certain caused by pinholes in the plating of the
trough holes. These pinholes are usually caused by glass fibres reaching
out the drilled walls if the drills are pressed too fast through the PCB or
if they are used too long. Whether there are any fibres can be seen with
mircrosections where you see whether the surface of the walls of the holes
was excessively rough before plating. Another reason is the plating process
where the first plating ( don't know the correct expression in English ) is
too thin, thus leaving free glass fibres uncovered. This again can be see
in microsection. Be only sure the the sections are not just set in the
directions on the glass fibres but also 45° to this direction.

Best regards

Guenter Grossmann


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