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J.L. Johnson, “Metal Injection Molding (MIM) of Thermal Management Materials in Electronics,” Handbook of Metal Injection Molding, Second Edition, D.F. Heaney (ed.), Woodhead Publishing, Duxford, UK, 2019, pp. 461-498.

 

Abstract

    This chapter begins with an overview of heat dissipation in electronics and the need for thermal management materials. Methods of measuring thermal properties are reviewed. The characteristics and preparation of suitable powders for MIM Cu, W–Cu, and Mo–Cu are discussed. Examples of binders and mixing techniques for preparing injection molding feedstock from these powders are described. Specific issues with molding Cu, W–Cu, and Mo–Cu feedstocks into heat sink components are discussed. Processing conditions for debinding and sintering or infiltrating such components are described with a special focus on densification and control of the oxygen content, microstructure, and dimensions. Factors affecting the thermal properties, such as impurities and porosity, are discussed. Examples of MIM heat sink components are provided.

 

Conclusions

    High thermal conductivity materials, Cu, W–Cu, and Mo–Cu can be processed by metal injection molding. Copper can be solid-state sintered to near full density, but care is needed to avoid hydrogen swelling. Near full density can be achieved for W–Cu and Mo–Cu by either liquid-phase sintering or infiltration. The commercial availability of composite W–Cu powders with excellent sintering behavior makes liquid-phase sintering preferable for W–Cu. Because of the poor molding characteristics of fine Mo powders and their poor densification during liquid-phase sintering, infiltration techniques are recommended for Mo–Cu. With proper powder selection and good control of sintering cycles and impurities, thermal properties close to model predictions can be achieved. Metal injection molding allows fabrication of heat sink geometries that are difficult to produce with other metal-working technologies. Novel structures, such as a heat pipe with a high conductivity casing surrounding a porous wick, can be directly fabricated into complex shapes.