ABSTRACT
The expression of the governing heat transfer relations in the form of thermal resistances greatly simplifies the first-order thermal analysis of electronic systems. In the thermal control of radio frequency (RF) devices, it is necessary to provide an acceptable microclimate for a diversity of devices and packages that vary widely in size, power dissipation, and sensitivity to temperature. In microelectronic, microwave, and RF components, the levels of integration and device density on the chips, as well as frequencies of operation, continue to increase. In early microelectronic systems, catastrophic failure was primarily functional and thought to result from changes in the bias voltage, thermal runaway produced by regenerative heating, and dopant migration, all occurring at elevated transistor junction temperatures. Thermal stress generation in packaging materials and structures is exacerbated by power transients, as well as by the periodically varying environmental temperatures, experienced by most electronic systems, during both qualification tests and actual operation.
