Abstract
Thin film Au(80)Sn(20) solder layer ( about 0.8um~2um of thickness ) was utilized for flip-chip bonding. For different optoelectronic devices, we tried several bonding parameters – reflow temperature, reflow arm z-position, solder thickness on chip or substrate or both – to get the optimized condition. From the results of shear force tests, we believed that thin film solder layer could provide acceptable shear strength. The flip-chip bonded 1.55um laser diode showed excellent L-I(CW) and I-V characteristics compared to pre-bonded bare chip. To verify its thermal stability, it was tested by thermal shock test. After 500 thermal cycles, the characteristics of bonded chips show no noticeable degradation. So it is believed that using thin film solder layer could obtain both acceptable mechanical strength and good thermal stability. We also tested the flip-chip bonded PIN photodiode utilizing its p-type diffusion window as bonding interface. Under higher reflow temperature ( 310℃), it showed lower contact resistance because of sufficient interdiffusion between Au and AuSn, but the dark current became larger due to the induced stress during reflow. Under lower reflow temperature (290℃), the dark current was close to that of pre-bonded bare chip, while the contact resistance became larger. In summary, the thin film flip-chip bonding technique showed good feasibility for integration of optoelectronic devices and silicon substrates.