Thermal Spreading Resistance for Square and Rectangular Entities

A systematic study was performed using numerical modeling to understand the effects of thermal spreading resistance on the total resistance from junction to ambient for square and rectangular entities. Simultaneously, a literature survey was conducted to understand effects of thermal spreading resistance on circular, square and rectangular heat sources and heat spreading plates. Simulation from numerical model (Flotherm) was then compared with results from analytical solution derived by Lee and Ellison for square and rectangular heat sources respectively as a benchmarking process for the numerical model. The model presumes a heat source on a large cooling plate beneath which has a constant heat transfer coefficient on the sink side. Numerical simulations were performed for steady-state conditions with different range of dimensions for source to plate edge length ratio and dimensionless thickness. Results for dimensionless spreading resistance as a function of relative contact size, plate thickness and Biot number were derived using Flotherm and compared with the analytical models mentioned above. Results show that numerical modeling using software like Flotherm can offer excellent results within acceptable percentage difference when compared to analytical solutions