Thermal characterization of thermal interface material bondlines

Minimizing the thermal resistance of thermal interface material (TIM) bondlines is of interest to the electronics industry. The thermal interface material class examined in this study comprises epoxy based adhesives in which conductive filler particles are suspended. When used to assemble a thin bondline (on the order of two hundred microns or less) the apparent thermal conductivity of the bondline has been shown to be less than the bulk thermal conductivity value of the TIM. This deviation is often attributed to inefficient heat transport at the interface between substrate and TIM due to thermophysical mismatches combined with bondline defects including voiding, delamination, and heterogeneous filler distribution in the TIM. Our study focuses on: understanding how various process parameters affect thermal performance and bondline micro structure, and application of standard physics models to understand and optimize TIM bondlines. To this end, we have fabricated TIM bondlines using various TIM materials while systematically varying the process parameters. We employ two different techniques for characterizing the lumped thermal resistance of these bondlines: a micro Fourier apparatus which uses Pt thin film thermometers and a flash diffusivity system coupled to a finite difference parameter estimation algorithm. Our micro Fourier apparatus also includes arrays of Pt thin film thermometers which allow for direct observation of the spatial variations in the temperature. The correlation between these temperature variations and the micro structure of the bondline is studied.