Study of a gel thermal interface material with micron-size particles

The assembly by squeezing flow and the thermal resistance of a thin layer of a gel composite thermal interface material (TIM) with micron-sized alumina particles in a curing silicone resin is studied. The thin layer is formed before curing by squeezing flow between the plates to be bonded. Thin layers (10 microns) are achieved with reasonable squeezing flow pressure (20 psi), resulting in low unit-area thermal resistance for this class of TIM. The assembly process is studied using a lubrication model for the squeezing flow of a Bingham fluid between square plates. The squeezing model predicts the time history of the layer thickness reasonably well, given the temporal profile of the squeezing force, the initial gap, the plate form error and the steady-shearing viscosity. The thermal resistance of cured layers is measured with samples of varying thickness. The observed linear relationship between thermal resistance and layer thickness is interpreted in terms of the bulk effective thermal conductivity and the wall region thermal resistance. There is significant sample-to-sample variation in both of these parameters, which may imply the existence of layer defects. The effective bulk thermal conductivity is compared to predictions from theoretical models in the literature