A simple analytic method for converting standardized IC-package thermal resistances (&thetas;ja, &thetas;jc) into a two-resistor model (&thetas;jb, &thetas;jt)

A typical data-sheets of an IC package supplied by a manufacturer, include two standardized thermal resistances, junction-to-ambient resistance θ_ja and junction-to-case resistance θ_jc. It is well known that these two parameters are not applicable in thermal analysis of practical systems. Large errors can be encountered in predicting the die temperature. In recent years, the concept of “compact model” was introduced. It predicts die temperatures to a higher level of accuracy. The simplest is a two-resistor model with junction-to-board and junction-to-top as thermal resistors (θ_jb and θ_jt respectively). There are a number of methods for the creation of this model. Unfortunately, they requires information that is considered proprietary by the manufacturer. In this paper, we propose a novel approach that overcomes this difficulty. The two resistors are evaluated based solely on the manufacturer data-sheet. The method, named PERIMA, is a simple analytic algorithm, which is easy-to-use. The standard test methods for measuring the thermal resistances θ_ja and θ_jc are analytically re-constructed and the unknown resistors θ_jb and θ_jt are derived. PERIMA was applied successfully for representative types of IC packages. The results compare very well with available data found in the literature, θ_jb with less than 20% and θ_jt in a range of 10% to 40%