Pending the genuine guru's here is my offering:
This was a
big debate a good few years back when the VPR v IR debate was at its
peak.
(Basically the then current VPR systems put a lot of heat in the PWA's
giving slow cool
down, gave big structure, so they claimed an advantage for
this). So somewhere in the
archives there will be reams of argument and
counter argument. I seem to recall it was all
knocked on the head by
Nokia? IVF?, some one Scandinavian anyway, who did a series of
tests
and found that small or large when made, all solder microstructures tended to
the
same size in a short while so it made no difference. This was in
accordance with industry
pre- perception /built in wisdom and the whole
distraction was nicely ended/died away.
That was on solder joints
as formed. There are certainly some more quantifiable advantages
to be had in
certain forms of solder supply -preforms, ribbons etc - by making from
chill
cast or rapidly cooled material, but this relates to non formation of
intermetallics and
ribbon ductility, easing production issues for the user.
The advantages are slightly less
than the hype, but real, and most people do
this as a norm now.
Mike Fenner
----- Original Message -----
Sent: 01 February 2000 23:24
Subject: [TN] Strength of Solder
Joints
Technet,
I have recently
read in an article that the most favourable type of solder joint is formed
from rapid cooling of the solder.
I am a bit confused
with this as I have always been under the impression that rapid cooling of
metals results in tight compact grain structures (very hard, but brittle).
This is in contrast to slow cooling that forms long grain structures
resulting in a stronger and tougher material (which I would have thought is
what would be ideal for a solder joint - good shock resistance).
Regards....
Clayton
Gardner
Engineering Manager