Rolf

Are you sure it's whisker growth? I had some similar cases in my lab for
analysis. Microsections showed badly burned internal layers usually with a
clear path of destruction leading from a through hole component to the
ground plane. The reason was always delamination of the internal layers.
Usually due to a rough drilling action, in one occasion due to entrapped
air. If delamination occurs ( the gap between the layers can be so small
that you need 600x magnification to make it visible ) the chemicals of the
copper plating process can enter the delamination thus leaving hygroscopic
residues when drying or in can even happen, that the glass fibres of the
PCB are metallised or a combination of both. In sevice the residues will
absorb humidity and build up a cunductive path. It's not easy to find the
defects. I had good results in using a Infrared microscope, applying power
with a power source with limited current. The shorts where clearly visible
as hot spots after the power was applied for some time. Microsections at
the spot showed the metallised fibres or the residues.

Best regards

Guenter Grossmann



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