Microchannel coolers (MCC's) for laser diodes are most commonly constructed of copper or copper alloy. A
disadvantage of the use of these metals is their much higher coefficient of thermal expansion (CTE) compared to GaAs.
This mismatch can result in stress on the devices during soldering or operation. It can also stress the solder joint,
encouraging voiding. One solution is to attach the laser to an MCC made from low CTE material. Suitable examples
are tungsten-copper and molybdenum-copper.
We have fabricated MCC's from these materials and have performed CFD modeling followed by flow, thermal
resistance, and accelerated life tests on the parts. We show that the thermal results can be achieved that compare to
copper MCC's. The erosion resistance of the materials is demonstrated to be higher than copper. Life tests using DI
water flow indicates that superior life can be expected from these MCC's, especially at higher flow rates of 0.5 lpm/0.13
gpm and with lower water quality and elevated temperature. Finally, we show that the dimensional tolerances required
can be obtained with these material combinations.
Wafer-level packaging can result in significant yield improvement, cost savings, and other improvements in function. For power devices, mismatch between coefficients of thermal expansion (CTE's) between the device and the mounting substrate or package can induce stress that reduces reliability. Adapting CTE-matched composite materials to wafer-level packaging schemes would be beneficial. We describe processes and show data for tungsten-copper substrates that meet wafer specifications for form and finish.
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