A simple analytic method for converting standardized IC-package thermal resistances (/spl theta//sub ja/, /spl theta//sub jc/) into a two-resistor model (/spl theta//sub jb,/ /spl theta//sub jt/)

Abstract

A typical data-sheets of an IC package supplied by a manufacturer, include two standardized thermal resistances, junction-to-ambient resistance /spl theta//sub ja/ and junction-to-case resistance /spl theta//sub 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 (/spl theta//sub jb/ and /spl theta//sub 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 /spl theta//sub ja/ and /spl theta//sub jc/ are analytically re-constructed and the unknown resistors /spl theta//sub jb/ and /spl theta//sub 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, /spl theta//sub jb/ with less than 20% and /spl theta//sub jt/ in a range of 10% to 40%.