The term “packaging” applied to diode-laser bars refers to mounting a diode-laser bar on some sort of cooling base or heat-sink. This base may be a relatively massive base providing a “conductively cooled package” (CCP). For higher power operation, the base may be water-cooled, for example by a micro-channel arrangement. Typically the diode-laser bar is soldered “p-side down” onto an insulating sub-mount. The sub-mount, in turn, is soldered to the heat-sink.
Packaging involves a number of compromises and trade-offs. As the materials of the bar, sub-mount, heat-sink, and solder have different thermal properties, particularly the coefficient-of-thermal-expansion (CTE), there is invariably a trade-off between thermal performance and CTE-matching (or mismatching). Indium (In) soldered bars on copper (Cu) perform well thermally, i.e., tolerate some CTE mismatch, but soft solders such as the indium solder can be unreliable. One hard solder that is essentially completely reliable is an 80:20 gold-tin (Au—Sn) solder. This solder however cannot tolerate any CTE mismatch between the soldered components.
There is a need for a diode-laser bar packaging arrangement that will provide effective CTE-matching using high thermal-conductivity materials, Preferably the packaging arrangement should be capable of being water-cooled.