Evaluating the degradation of thermal interface materials in liquid immersion cooling systems using ultrasonic methods

Immersion cooling systems for data centers provide improved energy efficiency. However, the mechanisms of degradation of thermal interface materials (TIMs) over time and their interactions with coolant fluids have not been thoroughly studied, and there are no current nondestructive/noninvasive degradation monitoring methods. While high-frequency ultrasonics and scanning acoustic microscopy are ubiquitous in metrology and defect detection for electronic packaging, the ability to characterize with these modalities has been underutilized. This presentation will discuss the use of ultrasonic nondestructive evaluation to detect changes in the material properties of coolant fluids and TIMs. For this purpose, combinations of various commercially available coolants and TIMs were degraded and evaluated under simulated immersion cooling conditions (in accordance with JESD22-A103C test standard). Due to the limited quantities and various form factors of the TIMs and coolants, creative experimental solutions were implemented in the ultrasonic data collection process. The relative changes in sound wave speed and attenuation in coolant fluids and TIMs were used to quantify the changes in material properties, which reveal important information about the compatibility between coolants and TIMs. This demonstrates that ultrasonic nondestructive evaluation can be leveraged to periodically or continuously monitor degradation.