Thermal Circuit Models of Microstrip Lines Based on Precise Heat Spreading Angles and Convection Boundary Conditions

In this article, the equivalent thermal circuits of microstrip lines are proposed based on the equivalent spreading angle (ESA) model and convection boundary conditions. Unlike the conventional constant-angle assumption, the ESAs corresponding to the situations of conductor and dielectric losses of microstrip lines are determined precisely by means of the modified parallel-plate model (MPM), which are associated with the geometry and material of the microstrip lines. Furthermore, different kinds of boundary conditions are considered in the thermal circuit models, especially the impact of heat convection condition, which matters in realistic situations. In addition, the thermal circuit models are extended to the case of coupled microstrip lines. The calculated results of the proposed model agree well with those simulated by the multiphysics solver.