Polymer Matrix Composite Thermal Materials

Abstract

Development of composite materials has been driven primarily by their excellent structural properties, such as high strengths, high stiffnesses, and low densities. However, there are many applications for which thermal conductivity is also an important design requirement. This includes some structures, mechanical systems, and electronics and photonics (optoelectronics). Monolithic polymers, and reinforcements made from glass and other oxides are considered thermal insulators for most engineering applications. Carbon fibers made from polyacrylonitrile (PAN) precursors have relatively low thermal conductivities, and polymer matrix composites (PMCs) using these reinforcements do not meet conductive heat dissipation requirements of many applications. However, several types of carbonaceous reinforcements, including some fibers made from pitch precursors, have thermal conductivities that are higher than that of aluminum, a thermally conductive structural material. In addition, some ceramics and metals are used as particulate reinforcements. A new generation of composite materials is being developed based on physical properties, especially high thermal conductivity and, in some applications, low and tailorable coefficient of thermal expansion (CTE). Heat dissipation, thermal stresses, warpage, cost, and in many cases weight (i.e., mass), are important in electronics and photonics (e.g., lasers, light-emitting diodes). Heat dissipation limits power levels and affects reliability and performance. Thermal stresses and warpage affect reliability. Semiconductors and ceramics used in microelectronics 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 significant limitations. There are an increasing number of PMC materials that are being used in a variety of applications. 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 thermally conductive PMC materials for structural and mechanical systems and electronic/photonic applications.