Direct observation of the effect of solder voids on the current uniformity of power transistors

In this letter, we demonstrate that the degree to which the nonuniformity in the heat sinking affects the current distribution in a power transistor can be quickly, nondestructively, and unambiguously ascertained by observing the bias dependence of the recombination radiation emitted by the transistor. This technique is more sensitive than the more conventional thermal imaging where thermal diffusion tends to wash out the relevant nonuniformities at the low power levels.