Electro-thermal simulation of multi-channel power devices on PCB with SPICE

In this paper we will present an efficient method allowing thermal modeling, simulation and design of a multichannel power semiconductor device on Printed circuit board (PCB). The method starts with a finite element discretization of the heat equation at the continuous field level. In a second step, the resulting large set of differential equations is approximated by a reduced-order model by means of the well-known Arnoldi algorithm. Next, the reduced-order thermal model is represented by an electrical equivalent network allowing SPICE simulation. The new approach allows to simultaneously evaluate the temperature of the semiconductor junctions and of the PCB track underneath the semiconductor device. The entire model generation procedure was automated and is now available for use with the software tool ANSYS/Workbench. This allows the development of a set of thermal SPICE models of different devices and different PCB design layouts. We will demonstrate the method by performing an electro-thermal analysis of Freescale´s new eXtreme Switch devices. These devices typically consist of 4 high-side MOSFET switches with associated drive-diagnostic- and protection circuitry integrated in a power quad flat no-lead (PQFN) package. A typical application demonstrates the validity of the followed approach.