Sam

In through hole technology very often defects in the copper plating of the
hole walls are the reason for voids in the solder joints. These defects
have their origin in a rough surface of the walls after drilling. If the
holes are drilled with too much feed or if the drills are used too long and
thus are not sharp again glass fibres will reach out of the drilled wall
and will not be covered with copper in the plating process leaving an
opening. Additionally chemicals from the galvanic plating process will
remain in the holes. Through the openings in the copper plating gas will
enter into the molten solder causing voids. If you want to verify this
source of the voids you have to make microsections trough the solder joints
where you might see the irregular shape of the metallisation indicating the
poor quality of the wall after drilling.

Best regards

Guenter

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