Analytical and FEM simulations of the thermal spreading effect in LED modules and IR thermography validation

Abstract

Thermal management is a key issue in LED packaging. To keep the LED junction temperature as low as possible, one has to address the spreading effect from a localised heat source into a bigger substrate as it is the case in the Chip On Board configuration (COB). We performed a benchmark of the existing analytical models for the spreading effect and derived a new model that allows a better prediction of the thermal resistance in such LED COB modules. This new analytical model, implemented in a Scilab application, was first assessed in different cases with the Finite Element Method (FEM) software Ansys <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> . Besides, IR thermography was performed on different kind of modules allowing a direct comparison with the analytical and FEM predictions. In addition to correctly fit the the predictions, IR thermography measurements enabled to give rise to the important thermal effect of the die attach material used to bond the LED to the substrate. We demonstrated that AuSn solder exhibit higher performances than other low melting point solders and Ag-based adhesive.