Thermal interface materials for AI chips
Next-generation AI chips consume hundreds to more than a thousand watts over an area of just a few dozen square centimeters. To keep junction temperatures within allowable limits, designers are moving to phase-change thermal interface materials (TIMs) and high-conductivity thermal adhesives instead of conventional thermal grease.
This article summarizes the specifications to consider when selecting a TIM for AI accelerators, GPU servers and edge computing modules, based on the experience of the AMS Vietnam engineering team in advising server board assembly plants.
Why AI chips pose a different thermal challenge
Power density on an AI chip die can exceed 100 W/cm², along with localized hot spots in the compute cores. With large dies and package substrates that warp with temperature, the gap between the chip and the heat spreader lid changes constantly during operation. A TIM therefore not only needs good thermal conductivity but must also fill a varying gap without being squeezed out, a phenomenon commonly known as pump-out.
Phase-change TIMs: as thin as grease, as clean as a pad
Phase-change materials are solid at room temperature, so they are easy to handle and can be pre-applied to the heat sink. When the chip reaches about 45–60°C, the material softens and flows into microscopic gaps, forming a bond line only 20–30 µm thick. Their major advantage is that they do not dry out, do not bleed oil and show little pump-out after thousands of thermal cycles.
High-conductivity thermal adhesives
Where mechanical fixing is required, silicone or epoxy thermal adhesives filled with ceramic, aluminum oxide or boron nitride particles deliver 3–8 W/m·K. Some grades containing metal particles achieve higher values but are electrically conductive and require careful isolation design.
| TIM type | Thermal conductivity | Bond line thickness | Suitable applications |
|---|---|---|---|
| Conventional thermal grease | 1–4 W/m·K | 25–50 µm | Mainstream CPUs |
| Phase-change TIM | 3–8.5 W/m·K | 20–30 µm | GPUs, AI accelerators |
| Curing thermal adhesive | 3–8 W/m·K | 50–150 µm | Heat spreader lids, power modules |
| Liquid gap filler | 2–6 W/m·K | 0.3–3 mm | Memory, on-board VRMs |
Material selection criteria for the production line
- Total thermal resistance at the actual thickness, not just the nominal thermal conductivity.
- Stability after thermal cycling and aging tests at 125–150°C.
- Ease of application: pad placement, stencil printing or machine dispensing.
- Low volatile siloxane content so that optical and electrical contacts are not affected.
The AMS engineering team can help measure the thermal resistance of samples and recommend Shin-Etsu, Henkel or Dow grades suited to your thermal design. Contact AMS Vietnam to receive samples and technical documentation.
