Pad Cratering and Pin Pull Strength for Large BGA and Connectors — How Are They Correlated?

Pad cratering is a prevalent failure mode in the PCB assembly especially for large BGA components in halogen-free and lead-free soldering process. To characterize the pad cratering of a PCBA, one can use copper peel, ball shear, ball pull and pin pull methods in which the samples are not directly taken from the field electronic assemblies. Most of them need component removal by desoldering and then reballing and pin soldering. This paper lays out an innovative direct pin pull test using a BGA connector which can reveal the true defective pad. The pad cratering characterization was conducted by the Dye & Pull method. The assembled boards have endured thermal cycling up to 2000 cycles and/or bending up to a PCB strain of 500ue. Several thousand pins of BGA connectors have been pulled using a Dage tester and pad cratering scores have been recorded. The results show that pin pull strength doesn't necessarily correlate with the pad cratering but only correlates in the average trend. Detailed studies have performed using FEA which give a good direction for pad cratering improvements.