Highly reliable hard soldered QCW laser diode stack packaging platform

We describe the performance and reliability of multi-bar diode stacks assembled with hard solder attachment of the laser diode bar to the conduction-cooled package substrate. The primary stack package design is based on a modular platform that makes use of common piece parts to incorporate anywhere from 2-7 bars, operating at peak powers of 80W/bar to 200W/bar. In assembling monolithic type diode stack packages, it is typical to use a soft solder material such as indium for P-side bar attachment into the package. Due to its low melting point and low yield stress, indium can provide a solder joint that transfers low stress to the laser bar. However, during CW and QCW operation, indium is prone to migration that can cause device failure due to a number of well-known mechanisms. This shortcoming of soft-solder bar attachment can limit the number of shots the stack delivers over its operating life. By replacing the soft solder typically used for P-side attachment with a hard solder, it is possible to greatly reduce or eliminate certain failure modes, thereby increasing the operating life of the part. We demonstrate lifetime of > 1E9 shots at 80 W/bar, 250 us/40 Hz pulses, and 50C package operating temperature.