Frequently Asked Questions
1) What is CuW?
CuW, or WCu is a pseudo-alloy of copper and tungsten. As copper and tungsten are not mutually soluble, the material is composed of distinct particles of one metal dispersed in a matrix of the other one. The microstructure is therefore rather a metal matrix composite instead of a true alloy.
2) How is CuW mostly made?
There are two formulation processes for CuW.
1. Powder metallurgy: A blending of tungsten, copper or copper oxide and various sintering aids are formed under high pressure and then sintered at high temperatures where the material becomes fully dense.
2. Infiltration: The process of infiltrating copper into a tungsten skeleton. This process is performed under pressure and high temperature.
3) What is the purpose of adding copper to tungsten?
Using Cu to increase electrical and thermal conductivities and W to control CTE (coefficient of thermal expansion).
4) What are the different compositions of CuW?
Commonly used copper tungsten alloy contains 10–50 wt.% of copper, the remaining portion being mostly tungsten. The alloy with less wt.% of copper has higher density, higher hardness and higher resistivity.
5) How is it used in Optoelectronics, power electronics, semiconductor lasers, silicon die, plastic packages, etc applications
As base plates, flange, heat sink, optical bench, laser diode submount, chip carrier, heat spreaders.
6) What’s the difference between CuW and CuMo? Under what circumstanced is CuMo used instead of CuW.
Copper Molybdenum (CuMo) and Copper Tungsten (CuW) are considered thermal management materials because they have CTE values that are compatible with the electronic materials and substrate materials. Both these materials have been used extensively in the military and aerospace industry in hermetic packaging because of the CTE thermal management reliability required in these systems. CuMo is lighter than CuW and is used for weight sensitive applications as a replacement for CuW
7) What is CMC composite? How is CMC made? In what applications are CMC used? How is CuW compared to CMC?
Cu/Mo/Cu laminate. Cu and Mo are laminated at elevated temperatures (or hot rolling). Most CMC’s are used as heat spreaders or flanges.
CuW is a uniform structure. Immediately under the die, there is a uniform CuW. If CMC is used, the die will see pure Cu at microscopic level. Generaly CMC is not used for high reliability applications.
8) What is CPC composite? How is CPC made? In what applications are CPC used? How is CPC compared to CMC and CuW?
CPC: Copper- Pressed CuMo – Copper
It is a sandwich structure with CuMo (typically Mo70Cu30) sandwiched by 2 layers of Cu. The hot lamination process is very similar to that of CMC. CPC has relatively higher thermal conductivity than that of CMC and CuW. Its CTE is anisotropic (X-Y directions are different). Most CPC are used for long and skinny dice (like LDMOS). CuW is a uniform structure. Immediately under the die, there is a uniform CuW. If CPC is used, the die will see pure Cu at microscopic level. Generally CPC is not used for high reliability applications.