Optimization and reliability evaluation of a laser inner lead bonding process

A series of designed experiments have been performed to determine the process window for laser inner lead bonding (ILB). The parameters studied were power, pulse time and lead contact. Bond pull tests were used as the monitor for these evaluations. The results of the experiments have demonstrated that the laser bonding process is very insensitive to wide variations in the parameters studied. Laser-bonded test devices have been subjected to extended high temperature storage and temperature cycle tests and compared to conventional thermo-compression (TC) bonded devices under the same conditions. By comparison to the TC-bonded devices, laser bonded samples have lower average bond pull failure strength, but exhibit a more uniform strength distribution and a slower rate of decline in bond pull strength over time in either of the stress tests. Cratering, which is a bond pull test failure mode that becomes increasingly significant over time at test for the TC-bonded devices, is almost totally absent from the laser-bonded samples