Approaches on compact component thermal models and a few related topics

Abstract

This paper introduces the FEM Condensation Method that generates compact component thermal models (CCTM). CCTMs have become popular among component suppliers and printed circuit board (PCB) designers because they provide comprehensive, environmentally independent thermal characteristics of component packages. The DELPHI method generates the resistor type of component thermal networks by minimizing the differences in temperature and heat flux results with respect to the validated 3-D finite element method (FEM) models on a number of given boundary conditions. It is a valuable method for engineers who have only FEM thermal analysis tools. However, this method is a 1-D simplification of 3-D FEM models, and the structures of resistor networks are subject to engineers' intuitions. All of these can result in significant errors. On the other hand, component thermal characteristics are determined by component internal structures and materials, which are built-in the validated 3-D FEM models. The FEM Condensation Method directly condenses the 3-D FEM models to CCTMs by mathematic manipulations with only a few simple assumptions on temperature distribution at junction and surface nodes. No guess-works on thermal network structures and no simplifications on 3-D FEM models are involved. The method requires no thermal analysis and does not need application of heat sources and boundary conditions. This paper also discusses the relationship between conductance matrices and the corresponding resistance matrices, their physical meanings, and conversion from resistor networks to the corresponding conductance matrices.