Effect of squeezing conditions on the particle distribution and bond line thickness of particle filled polymeric thermal interface materials

An experimental study is performed to characterize the effect of squeezing conditions on the particle distribution and bond line thickness of particle filled polymeric thermal interface materials (TIM). Two different commercial particle-filled polymeric TIMs with different particle volume fractions have been used in this study. Rheological properties such as yield stress and viscosity are measured experimentally. Using laser granulometry technique, particle sizes have been measured and are further confirmed by SEM imaging. The TIM is then deposited on circular copper samples and is squeezed with different pressing rates. Analyzing the samples by acoustic microscopy technique shows that at low pressing rates the particle distribution is not uniform and a TIM branching phenomena can be observed. At higher pressing rates, the final thickness of the bond line is approximately 30% higher than low velocity pressing rates. By keeping the load on the sample at the end of the pressing procedure the final BLT will continue to decrease. It can be concluded that the optimum condition of TIM dispense procedure should include a high velocity pressing rate to attain a uniform particle distribution followed by a constant load period to obtain the minimum BLT.