A PTH Corner Crack – or Is It?
Drilling may be behind ‘false’ gaps.
The microsection in Figure 1 was taken from the knee of a plated through-hole during board examination. The section shows a gap between the edge of the original copper foil and the through-hole copper plating. This is not a crack in the plating, however. Rather, there is resin smear on the copper foil edge, and the copper plating to the surface of the board and into the through-hole has simply covered the resin, giving the appearance of a crack or the copper folding.
As resin smear is the most likely cause on the edge of the copper foil, a full review of the steps during and after drilling needs to be examined. Test sections taken after panel plating should be considered to demonstrate any improvements in the copper plating adhesion to the edge of the foil. Reference should be made to IPC-A-600 or internal company procurement standards.
Dr. Davide Di Maio is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); defectsdatabase@npl.co.uk.
