Thermal transient characterization of semiconductor devices with multiple heat sources - Fundamentals for a new thermal standard

The thermal performance of semiconductor devices is most often specified according to JEDEC standards JESD51 1-14 which describe precisely how various steady-state thermal metrics are to be measured. Most of these metrics represent a thermal resistance between the junction of a semiconductor and some reference; e.g. R_th-JA (Junction-to-ambient), R_th-JB (Junction-to-board), or R_th-JC (Junction-to-case). However all of the above thermal metrics characterize the steady-state behaviour and have been designed for semiconductors with a single heat source only. While the extension of a stationary thermal resistance R_th-JX to the corresponding transient thermal impedance Z_th-JX is straightforward the adaptation of existing standards for the characterization of devices with multiple heat sources is far less obvious. This publication gives an overview on the theoretical framework which allows extending the existing thermal metrics in a compliant way.