Surface chemistry and characteristics based model for the thermal contact resistance of fluidic interstitial thermal interface materials

Microprocessor powers are increasing at a phenomenal rate, which requires v ery small thermal resistance between the die (chip) and the ambient, if the current economical methods of conduction and convection cooling are to be utilized. A typical thermal solution in flip chip technology utilizes two l evels of thermal interface materials: between the die and the heat spreader and between the heat spreader and the heat sink. Phase change materials an d thermal greases are among the most prominent interstitial thermal interfa ce materials (TIM) used in electronic packaging. These TIMs are typically, polymeric matrix loaded with highly conducting filler particles. The dwindl ing thermal budget has necessitated a better understanding of the thermal r esistance of each component of the thermal solution. Thermal conductivity o f these particle-laden materials is better understood than their contact re sistance. A careful review of the literature reveals the lack of analytical models for the prediction of contact resistance of these types of intersti tial materials, which possess fluidic properties. This paper introduces an analytical model for the thermal contact resistance of these types of inter stitial materials. This model is compared with the experimental data obtain ed on the contact resistance of these TIMs. The model, which depends on par ameters such as, surface tension, contact angle, thermal conductivity, roug hness and pressure matches very well with the experimental data at low pres sures and is still within the error bars at higher pressures.