Selection of the TIM material is critical to ensure the most efficient thermal solution at the critical boundary between the die or lid and the heatsink. Ensuring the bond line thickness (BLT) is optimized and maintained through the products lifetime is also critical for not only beginning of life (BOL) but also end of life (EOL) performance.
Traditionally there is a lot of focus on the thermal conductivity of the material. While that is important, other properties such as adhesion, elongation, and the material's ability to deal with warpage of the system should also be considered. Selecting a material that strikes a balance can often give the best long-term thermal performance.
It is recommended that customers validate their thermal interface material or work with their thermal vendor to validate TIM selection for thermally critical applications. To this end, AMD has published an IEEE paper along with Nokia, Laird, and Shin-Etsu investigating different materials and their performance: https://ieeexplore.ieee.org/document/10013175. With the addition of lidless packaging and the ability for customers to move the BLT from above the package to the die further improves thermal solution efficiency.