Investigation on electro-optical performance of aluminium indium gallium phosphate light emitting diode with cracked substrate

Die crack in light emitting diode (LED) is a major concern that affects the LED performance. Experiments were conducted to examine the cracked germanium (Ge) substrate of aluminium indium gallium phosphate (AlInGaP) die for its reliability performance. The dies were indented at 60, 100 and 140 g-Force (gF) bond force. These dies were packaged on a stable LED package and underwent power and temperature cycles (PTC) test for about 1000 cycles. Forward voltage characteristics of good and cracked die shows no abnormalities. However, leakage current of the crack die units has higher leakage current compared to units without crack. Dies indented at 140 gF were cross-sectioned using Focus Ion Beam (FIB) and were checked using Scanning Electron Microscope (SEM). The result shows that the cracks appear at the surface level on the backside of the substrate. It could be, concluded that the crack at Ge substrate did not propagate much inside the substrate throughout the 1000 cycles PTC test. The force is not high enough to cause further crack propagation.