Non-destructive structural analysis of the heat conducting path in power electronics and solid state lighting by thermal transient testing

Abstract

Thermal transient testing is a tool for examining structural details of a heat conducting path composed of heat conduction and heat convection sections. Using the change of inherent heat in electronics, temperature transients provide a characterisation technique where using x-ray or acoustic microscopy would be troublesome and time-consuming. A complete toolkit for the accurate dynamic characterisation of subassemblies and cooling mounts is described in the paper. After giving the theoretical background, it is shown that the methodology can directly generate a valid and detailed structural equivalent from a single transient measurement. The descriptive thermal functions such as time constants and structure functions are demonstrated in practical examples, the capability of the structure functions for validating cooling concepts and detecting assembly problems is shown. Recognising the fact that systems with multiple energy transport such as electric energy converted to heat and light exhibit special features; the concept of structure functions has been modified for applications in solid state lighting.