Metallic TIM Testing and Selection for Harsh Environment Applications for GaN RF Semiconductors

Summary An important determinant of device reliability is operating temperature control. Maintaining a semiconductor device at or below the maximum rated junction temperature (Tj) is accomplished through careful thermal management design and selection of well-performing thermal interface materials (TIM) that minimize efficiency losses in packaging and between the semiconductor device package and a heat sink or liquid cold plate. Thermal management design is increasingly important in harsh operating environments, especially where higher operating temperatures are specified. Minimizing thermal resistances through each semiconductor package material stack and at the external case or package surface of the device are important aspects of maintaining operating temperatures within specified maximum values. In addition, certain semiconductor devices require an electrical path from the semiconductor case to an external component. Maximizing electrical performance of gallium nitride (GaN) RF semiconductors is critical to system performance, as a primary example. The on-going transition within RF and microwave systems from silicon to GaN devices has increased the need for thermal interface materials which offer both improved thermal performance and electrical conductivity. Additionally, GaN semiconductor die are typically smaller in footprint and, even with equivalent power dissipation values, therefore may operate with higher heat flux values that require greater attention to proper thermal solution design. To address such needs, recently-developed forms of metallic TIM preforms are available for integrated circuits, power semiconductors, and RF devices. Understanding how these materials may be tested and selected for specific application requirements is the subject of this discussion.