Dear KP Chan

Blow out of PHT solder joints is not only a question of the copper
thickness but also of the moisture contents of the board and, very
important, of the quality of the drilled hole. If the PCB manufacturer is
using the drills too long or if he's feeding too much while drilling (
price pressure ) you will find ripped out glass fibres causing hollow
sections as well as glass fibres reaching out of the drilled walls. Both
cause a porous copper plating of the holes no matter how thick the final
plating is especially because the first process step of plating, where the
walls of the holes are covered electroless with a layer of copper in order
to make galvanic plating possible, will not cover all these irregularities.
Give me your Fax number. I can send you a 3-D graph where the average
amount of voids in a solder joint vs. the average copper thickness and the
number of not metallized glass fibres after the electroless copper plating
is shown.

Best regards

Guenter Grossmann
Federal Institute of Technology
Reliability Laboratory
Zurich


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