Boundary-dependent circuit model for the transient behavior of a thermal stack in power modules

An accurate circuit model for transient behavior is necessary for transient thermal design and coupled electro-thermal simulation of complete power electronics system including semiconductor devices, thermal packages, and heat exchangers. Conventional thermal models of a power module are usually independent of boundary conditions, rendering these models ineffective in predicting the transient temperature of the thermal stacks as a function of heat-transfer coefficients. Thus, the paper presents an RC circuit model in which the thermal resistances and capacitances depend on the material properties and dimensions of the thermal layers, as well as the heat-transfer coefficient of the boundary. Only steady-state FEM simulation is needed to extract the model parameters. The boundary-dependent thermal model has been verified by simulation and experiment, which confirms that it is more accurate than the widely used thermal model based on assumption of 45° heat spreading.