For high-power chips, servers and optical modules, thermal interface materials (TIMs) play a vital role in thermal management. Many hardware engineers prioritize thermal conductivity only, which is a common misunderstanding.

Thermal conductivity describes the intrinsic heat transfer property of the material. Contact thermal resistance actually determines the real cooling performance. Microscopic gaps exist between PCB and heat sinks. Thermal materials must deform to fill gaps and displace trapped air. Air has extremely low thermal conductivity; even a thin air layer greatly increases total thermal resistance.

Five critical factors should be evaluated together:

1. Gap tolerance: Soft thermal pads with high compressibility are recommended for variable gaps. Thermal gel or phase-change materials fit fixed narrow gaps.

2. Electrical insulation requirements: Power modules require fillers like boron nitride with high dielectric strength and low ionic contamination.

3. Silicone bleeding risk: Non-silicone TIMs are mandatory for optical modules and precision cameras to prevent lens contamination.

4. Long-term aging performance: Thermal cycling and humidity tests verify hardness stability and prevent cracking or hardening over time.

5. Assembly pressure: The pressure available from mechanical structures defines material thickness and hardness selection.

For AI server GPU and HBM high-power applications, thermal material selection should be considered at the early design phase, instead of after mechanical design finalization. Early collaboration reduces risks of overheating and reliability issues and shortens development cycles.