Squeeze flow characterization of particle-filled polymeric materials through image correlation

Particle-filled polymeric materials are common choices for thermal interface materials (TIMs). During assembly, TIMs are applied between the surfaces across which heat must be transported. The goal of the present work is to develop a test procedure that is consistent with the length scales characteristic of real thermal interfaces. A mechanical tester (Instron 5848 Micromechanical Tester) is employed with closed-loop capacitive sensor-based control. During the squeeze flow process both direct (capacitive sensor, glass gauge encoder, and load cell) measurements and indirect (large working depth lens, video camera) measurements are made in order to record transient and steady-state loads and displacements. Discrete two-dimensional Fourier transform-based digital image correlation methods are used with microscope images to track surfaces relative to each other. Parameters describing Herschel-Bulkley and Bingham models are extracted using experimental data. Transient measurements are used to determine viscosity and strain-rate index, and the steady-state bond-line thicknesses corresponding to various loads are used to determine the yield stress. Advantages of the testing method include non-destructiveness, relative ease of deployment, and the ability to characterize materials at realistic assembly conditions.