Thermal diagnostic of power transistor at increased junction temperatures

Infrared (IR) thermography in power-cycling experiments was combined in reliability studies of an RF power amplifier, operating at elevated junction temperatures. A powercycling technique (adjusted to reach high junction temperatures) was used as a life acceleration method. Several sets of IR measurements were performed for various working conditions to correlate the device power and the maximum junction temperatures. Finite element (FE) simulations in combination with traditional failure analysis methods were employed to examine main failure causes. IR thermography was used for experimental validation of temperature distributions obtained by the simulations. Furthermore, the validated FE model has been extended to achieve stress distribution and reliability predictions via selection of the most risky areas. The entire procedure can provide reliable, evaluated information of the governing thermal resistances and enable optimizing the required cooling arrangement.