4.16 Metal Matrix Composite Thermal Management Materials

Development of composite materials has been driven primarily by their combination of high strengths and stiffnesses combined with low densities. However, increasingly, new generations of composites are being developed based on physical properties, such as high thermal conductivity and low coefficient of thermal expansion (CTE). Heat dissipation, thermal stresses, warpage, cost, and in many cases weight (i.e., mass), are key electronic and photonic (optoelectronic) packaging issues. Heat dissipation limits power levels and affects reliability and performance. Thermal stresses and warpage affect reliability. Semiconductors and ceramics used in electronics and photonics have low CTEs. Copper, aluminum, and conventional polymer composite printed circuit boards (PCBs) have high CTEs, which can cause high thermal stresses under thermal excursions. Most traditional low-CTE materials like Kovar and tungsten/copper, which date from the mid-20th century, have thermal conductivities that are no better than those of aluminum alloys, about 200 W/m K. There are an increasing number of low-CTE metal matrix composite materials with reported thermal conductivities as high as 980 W/m K. Some of these materials are low cost. Others have the potential to be low cost in high-volume production. This chapter provides an overview of advanced metal matrix composite thermal materials, starting with a review of traditional electronic and photonic thermal management and packaging materials for reference.