Fatigue lifetimes of PBGA solder joints reflowed at different conveyor speeds

The shear cycle fatigue lifetimes of plastic ball grid array (PBGA) solder joints formed using different reflow profiles are studied in this paper. Th e profiles were devised to have the same "heating factor" but to have diffe rent conveyor speeds. The test results show that, by increasing the conveyo r speed during reflow, the shear fatigue lifetime of solder joints can be i mproved substantially. On the other hand, the fatigue lifetime of the test specimens decreased with increasing the cycle displacement amplitude. Heat transmission analysis shows that increasing conveyor speed increases the co oling rate during solder solidification. SEM micrographs reveal that cracks initiated at the acute point near the PCB solder pad, then propagate along the interface of the bulk solder/IMC layer. The test results are ascribed to roughing interface of the bulk solder/IMC of the solder joints that resu lts oil increasing the cooling rate. The frictional sliding mechanism is us ed to explain the test results.