The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion coefficient compatible with chip materials while still ensuring the reliability of the power modules. Metal matrix composites, especially copper matrix composites, containing carbon fibers, carbon nanofibers, or diamond are considered very promising as the next generation of thermal-management materials in power electronic packages. These composites exhibit enhanced thermal properties, as compared to pure copper, combined with lower density. This paper presents powder metallurgy and hot uniaxial pressing fabrication techniques for copper/carbon composite materials which promise to be efficient heat-dissipation materials for power electronic modules. Thermal analyses clearly indicate that interfacial treatments are required in these composites to achieve high thermal and thermomechanical properties. Control of interfaces (through a novel reinforcement surface treatment, the addition of a carbide-forming element inside the copper powders, and processing methods), when selected carefully and processed properly, will form the right chemical/mechanical bonding between copper and carbon, enhancing all of the desired thermal and thermomechanical properties while minimizing the deleterious effects. This paper outlines a variety of methods and interfacial materials that achieve these goals.

The lack of robust interphases between carbon and most metals prevent the exploration of the full scope potential of carbon-based metal matrix composites. Here, we demonstrated a scalable and straightforward way to produce strong interphase between copper (Cu) and carbon fibers (CFs) by designing a tailored titanium oxide-carbide coating (TiO y-TiC x) on CFs in a molten salt process. The oxide-carbide composition in the graded layer strongly depends on the coating temperature (800-950 ºC). A coating with a high TiO y content obtained at a low coating temperature (800 ºC) contributes to better molten-Cu wetting and strong adhesion energy between CFs and Cu during a subsequent exposure at 1200 ºC. The Cu wetting angle for the TiO y-TiC x-CF sample obtained at 800 ºC was ~80º ± 5º with a Cu surface coverage of ~50% versus ~115º and ~10% for the TiC x-CF sample made at 950 ºC. The kinetic analysis of the coating process step by step suggests a growth rate limited by the mass-transfer through the coated layer. This method provides a novel approach to improve the thermal conductivity of Cu/C composite for thermal management applications.

Highlights:  Dense Cu/40CF composite are fabricated by low temperature hydrothermal sintering at 265 °C and 250 MPa with 5 wt.% water.  Thermal properties of Cu/40CF composite materials fabricated by low temperature hydrothermal sintering are isotropic 2  Hydrothermal sintering increases thermal conductivity and reduces coefficient of thermal expansion in comparison to uniaxial hot pressing  Hydrothermal sintering improves mechanical hardness of Cu/40CF composite materials in comparison to uniaxial hot pressing

Aluminum matrix composites reinforced with carbon fibers or diamond particles have been fabricated by a powder metallurgy process and characterized for thermal management applications. Al/C composite is a nonreactive system (absence of chemical reaction between the metallic matrix and the ceramic reinforcement) due to the presence of an alumina layer on the surface of the aluminum powder particles. In order to achieve fully dense materials and to enhance the thermo-mechanical properties of the Al/C composite materials, a semi-liquid method has been carried out with the addition of a small amount of Al-Si alloys in the Al matrix. Thermal conductivity and coefficient of thermal expansion were enhanced as compared with Al/C composites without Al-Si alloys and the experimental values were close to the ones predicted by analytical models.

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Developing solder joints capable of withstanding high-power density, hightemperature, and significant thermomechanical stress is essential to further develop electronic devices performances. This study demonstrates an effective route of producing dense, robust, and reliable high-temperature Cu-Sn soldering by modifying the interfacial exchange during a transient liquid phase bonding (TLP) process. Our approach relies thus on altering internal phenomena (diffusion and transport of reactive species) rather than classical external TLP bonding parameters (e.g., time, temperature, and pressure). By adding a Cu3Sn coated layer between Cu and Sn before the TLP process, a fast dissolution of Cu in liquid Sn is achieved, altering undesired Cu6Sn5 scallop grains impingement and promoting their uniform growth within the liquid. A bonding and pore formation mechanism of the solder with or not the Cu3Sn coated layer is proposed based on experimental and theoretical analysis. The developed TLP joint possesses a shear stress resistance of more than 80 MPa with a thermal cycle endurance 2 superior to 1200 (-45 to 180 ºC), making it highly reliable compared to a classical solder joint with shear and thermal cycling resistance of 45 MPa and 500, respectively. The developed approaches provide, thus, an easy, affordable, and scalable method of producing hightemperature and durable Cu-Sn joint for high-power module applications.

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