THERMAL CHARACTERIZATION OF A PLCC - EXPANDED RJC METHODOLOGY

The R(jc) thermal characterization technique is commonly used for determining the maximum temperature a given chip will experience when operating in a specified environment. As such, R(jc) provides a simple, inherent figure-of-merit that is also readily adaptable to the numerical analysis of virtually any packaging design or type. Unfortunately, R(jc) is strictly valid only for an isothermal package surface and, when significant temperature variations am encountered, the use of the reported value of R(jc) can lead to substantial errors in chip temperature. In a previous study, it was proposed to extend the use of the junction-to-case thermal resistance to nonisothermal packages by defining an appropriately weighted, average surface temperature based on numerically derived ''thermal influence'' coefficients for each package surface (or segment) of interest. The present paper applies the expanded R(jc) methodology to an actual PLCC package. Experimental data and the results of an extensive three-dimensional thermal simulation are used to establish the values of 11 sensitivity coefficients, which make it possible to determine the weighted average case temperature. The variations in the sensitivity coefficients and the accuracy of the chip temperature predictions, with the number of data sets used to determine the coefficients, are also examined.