Rheology of Thermal Interface Materials Composed of Silicone Gels

A reliable thermal interface material (TIM) typically has a low storage modulus (G') and a tan(δ) less than one; these mechanical properties are crucial for minimizing contact resistance (R
_c
). This paper demonstrates the correlation between storage modulus (G') and the crosslink density of silicone gels. Formulations span between 0.30 and 1.00 hydride to vinyl (H:Vi) ratios for the vinyl terminated and hydride pendent polymers used in the gel. These gels are tailored for TIM applications by adding highly conductive particles to improve thermal conductivity. During this study, when 80 wt% conductive filler was added to gels with a 0.6 H:Vi ratio, the G' increased by 6025%. In order to minimize G', the crosslinker in the formulation was replaced with a chain extender. With this formula substitution, the modulus of the filled gel can be successfully lowered to the original value of the unfilled gel while maintaining the crucial properties of a reliable TIM. In effect, it is possible to independently optimize the thermal conductivity of a TIM while creating a compliant gel that maintains surface contact and minimizes contact resistance.