R. Tavangar, L. Weber

A combination of a highly heat conductive metal with high volume fraction of diamond particles results in a material suitable for thermal management applications electronic devices in which high thermal conductivity and low thermal expansion (CTE) are combined. While materials development aims at optimized properties after manufacturing of the materials real improvement in the application will only result if these properties are maintained in service, i.e. after aging and when submitted to thermal cycles. 
In this contribution composites made by gas pressure assisted liquid metal infiltration with pure Al and based on a Ag–Si alloy as matrices combined with diamond particles have been chosen to study the impact of thermal cycling on thermal expansion and thermal conductivity. For the aluminum/diamond composites with reinforcement ranging from 62 to 74 vol.-pct. CTE varies from 3.4 to 7 ppm/K and for the silver/diamond with 62 to 77 vol.-pct a range from 3 to 5.6 ppm/K is covered. In terms of thermal conductivity, while the aluminum composites were all between 680 and 760 W/mK, the Ag-based composites with bimodal particle size distribution and concomitant high diamond volume fraction were all above 950 W/mK after heat treatment while the ones based on monomodal particle size distribution were typically in the range between 800 and 900 W/mK. Thermal fatigue experiments were conducted on both the aluminum and silver-based composite using a custom-made apparatus. The sample were subjected to 1000 thermal cycles between -40 and 140°C with intermittent measurement of the thermal conductivity after 10, 30, 100, 300 and 1000 cycles. The result of this experiment showed an overall reduction in thermal conductivity of up to 15% in both Al- and Ag-based composites the reduction being less pronounced in those systems with bimodal particle distribution.

Diamond-based Metal

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