Heat Sinks

Abstract

THERMAL MANAGEMENT is one of the critical aspects of packaging design. To ensure reliable operation of electronic and microwave components. junction tempera­ tures must be kept within specified limits. As a rule, the problem is one of cooling, because failure rates increase dramatically with increasing temperature. For every 10 �C (18 °F) increase in temperature, silicon and gallium arsenide lifetime drops by a factor of 2.5 to 3. Heat sinks, also called cold plates, are commonly used to transport heat dissipated by devices to a heat ex­ -_ changer or to spread it over a larger smface area to facilitate cooling by radiation or convection. To minimize thermal imped­ ance, the heat sink typically is adhesively bonded or soldered to the component it supports, which generally is one or more devices, a ceramic substrate supporting the devices, or a multilayer printed wiring board (PWB). Another critical packaging design prob­ lem is minimizing thermal stresses in the assembly. Thermal stresses can cause me­ chanical failures of devices, circuit solder joints, substrates, or the adhesive or solder used to hold the assembly together. Failure