Evaluation of isothermal and isoflux natural convection coefficient correlations for utilization in electronic package level thermal analysis

A 20-lead heatsink small outline package (20HSOP) was modeled on both an FR4 and aluminum printed circuit board using a solid model finite element simulation tool. Three different correlations (isothermal, single surface isoflux, and dual surface isoflux) were utilized to define the surface convection coefficients of both the package and printed circuit board in a natural convection cooled environment. Solid model temperature results were compared to physical measurements in order to evaluate the usefulness of the individual convection coefficient correlations for package level thermal analysis. Both the experimental and solid model simulation results were also compared to those obtained from an identical computational fluid dynamics (CFD) model of the 20HSOP package. The isothermal convection coefficient correlations provided the most accurate solid model simulation results (within 12%) when using the FR4 thermal characterization test board. The isoflux dual surface convection coefficient correlations provided the most accurate solid model simulation results (within 13%) when using the aluminum thermal characterization test board. Solid model solutions closely matched, and in some cases exceeded, the accuracy of the CFD model. The significance of these results to package level thermal analysis is discussed.