Fluxless die bonding for optoelectronics

Two new approaches are described for epi-down die bonding of diode lasers. The first approach, based on an acetic acid vapor flux, eliminates complications associated with the use of liquid flux in optoelectronic packaging. Based on this approach, InGaAsP/InP laser arrays were soldered onto silicon substrates. These laser arrays, which were passively aligned to single-mode optical fibers on the silicon substrate, had thermal impedances comparable to those obtained using conventional liquid flux. The second approach, called bridged die bonding, is proposed as a technique for reducing stress associated with epi-down bonding of diode lasers with hard solders. Bridged die bonding seeks to minimize bonding stress by avoiding contact of the laser active region with the hard solder. Thermal modeling indicates that the bridged die bonding approach, which uses a solder pattern with an air gap, can provide a thermal impedance comparable to conventional soldering techniques