Earl

With regard to the thickness and strength at where the lead rich area failed,
you will note that this happened with the high purity copper foil (at least
three 9s).  This high purity copper is not seen when produced in a circuit
board plating bath.  The large lead crystals and failure in this area is
something that is often seen in high lead solders that have undergone thermal
aging.   The failure was between the solder and the solder an the
intertermetallic only occurred with the higfh purity copper.  With the normal
circuit board plated foil, failures occurr between the two intermetallic
layers or between the copper and Cu3Sn layer.  As to strength; with the low
purity copper that had been aged extensively, masking tape easily pulled off
the solder.  As copper purity increased the strength increased.  The strength
of the high purity foil solder joint where the failure was in the lead rich
area was roughly 40% of the the failure strength of a fresh joint.

Phil Hinton