Numerical solution methodology for Compact Thermal Models of electronic packages

Compact Thermal Models (CTMs) are multi-nodal thermal resistor networks which predict the internal thermal response of an electronic package, in various environments, to within an accuracy of 2%. The junction temperature of the package is typically obtained by solving a set of linear algebraic equations wherein the heat transfer to the ambience is modeled by a convection coefficient obtained from hand-book data, assuming identical ambient conditions imposed at all nodal surfaces. In reality, this approach may give misleading results as the ambience at each of the nodal surfaces is different and depends on the cooling fluid flow behavior at that surface. In this work, a methodology is presented where the network equations of the CTMs are coupled with the governing fluid equations solved by computational fluid dynamics (CFD). The CTM+CFD approach predicts a significantly (28%) higher junction temperature as compared to the conventional CTM network solver method, even when the convection coefficient used in the latter is obtained more accurately from CFD, rather than from hand-book correlations. It is likely that the new approach offers a more effective prediction of the package them-tat performance.