Standard Tungsten Copper Technology
Metal-matrix composites having copper as the continuous matrix phase have been used extensively during the last two decades. The use of a refractory metal such as tungsten (or molybdenum) as reinforcement is favored. Copper/tungsten composites traditionally have been produced using infiltration technology by which parts are produced by copper infiltration of a tungsten preform. The parts are then mechanically ground to final shape.
Processes have been developed recently that are based on powder metallurgy technology that produces net or nearly net-shape parts. A mixture of refractory metal powder and copper-containing powder is milled and agglomerated using spray drying to produce flowable power.
The powder is compacted into green (unfired) parts using conventional uniaxial mechanical or hydraulic dry presses and fired in a hydrogen environment at temperatures that can reach 1450°C. Parts can be machined at this point if special features or surface finish is required. The parts are nickel (Ni) plated and gold (Au) plated for most optoelectronics applications. A die bonded to a ceramic base may be brazed onto the copper composite heat sink. Other users may attach the semiconductor die directly to the WCu mount.
The main advantage of the powder-metallurgy process is the ability to produce parts that are suitable for use with only slight additional processing immediately after firing. Minimal postfiring machining results in considerable cost savings, and most of the precision machining is concentrated in the area where the laser diode is mounted.
Another advantage of the processed WCu is its very fine grain and homogeneous microstructure that allows for the machining of perfectly square, sharp, and defect-free knife edges where edge emitters can be mounted. In contrast, the WCu microstructure manufactured by traditional infiltration technology is characterized by copper pools and very large tungsten grains, which results in machined parts that exhibit a larger number of grain pullouts and pits.