Hi Russ,
While the PWB material between layers 5 & 6 may have a problem, this is not
likely. The likely problem is the uncontrolled hand soldering operation. This
operation is very dependent upon the operator, the PWB construction, and the
type of component being soldered (heat sinking). I have heard of hand
soldering operations performed with irons in excess of 410C! Depending of the
polymer glass transition temperature, that might be a delta-T of 285C above
Tg. The excessive compressive hoop stresses on the PTH barrel together with
the land rotation of the lands near the surface produce loading conditions
for which the materials ionvolved are not designed.
If you like to get more in-depth background on this, I will be giving a
workshop "Design, Manufacturing and Reliability Issues of
Small-Diameter/High-Aspect-Ratio Plated-Through-Holes and Vias" the
IPCWorks'97 on October 5.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]