Mounting of high power laser diodes on diamond heatsinks

Abstract
This work describes the mounting of commercial 1 W laser diodes soldered on chemical vapor deposition (CVD) diamond heatsinks using Au(80)Sn(20)-solder. With a standard heatsink metallization, the laser diode suffers under high stress. This can be seen in the power-current characteristic and the spectrum as well as in the near and farfield beam pattern, With a modification of the heatsink metallization layer, it was possible to obtain a reproducible mounting process. We compare the electrical and optical characterization of the typical standard heatsink metallization with the modified metallization. So we are able to qualify the mechanical stress in the laser diode. For a better understanding of the modified metallization SEM and EDX analyses are performed. For the quantification of the stress an analytical model is used to compute the maximal shear, tensile, and peel stress. Furthermore, the quality of the bond interface is investigated with high resolution X-ray microscopy. No voids are found. Additionally, the results of a standard burn-in and the first accelerated aging tests to prove the reliability are presented.