Understanding Criticality of Thermal Performance in Thermal Interface Material Applications

Thermal interface material (TIM) is used in between a heat generating component (e.g., microelectronic packaging) and a heat spreading component (e.g., heatsink or cooling plate) to create an effective path for the heat (Phonon) to travel. Standard heatsink and heat generating component surfaces are generally uneven and rough. Actual metal to metal contact is no more than 10%. These surface imperfections allow air to get trapped in between the two surfaces. Air, being a thermal insulator, prevents the heat from dissipating and thus the device/system fails to maintain the required operating temperature to meet the reliability and functionality needed. Replacing the air with the “right” thermal interface material is the focus of this research. TIM is a composite of thermally conductive fillers dispersed in a polymer matrix. A higher filler loading causes a higher bulk conductivity. Common practice among design engineers is to utilize output from thermal modelling & simulation to specify a TIM with a certain thermal conductivity to meet the system’s thermal needs. What many engineers miss is the impact of thermal boundary resistance that could have significant effect on the overall thermal management of the design. This paper discusses how to characterize thermal performance of TIM beyond the bulk thermal conductivity. Boundary/interfacial thermal resistance and impedance will be explored as a function of TIM wetting ability, bond line thickness and surface conditions. This paper will discuss the importance of thermal conductivity, thermal resistance/impedance in a real application scenario.