Thermal Interface between AI Server Chips and Heat Sinks: Selection of Thermal Grease and Gel
When specifying material between the integrated heat spreader (IHS) of GPUs and CPUs in AI servers and cold plates or heat sinks, thermal conductivity alone shall not be the primary selection criterion. ELAPLUS SIGR 2250 thermal grease may be considered for flat mating surfaces requiring a thin interface under consistent screw‑driven clamping pressure; its published thermal conductivity is 5.1 W/m·K, with microprocessors listed among typical applications. For assemblies prone to warpage, variable gaps, or where automated dispensing and shot‑volume control are preferred, ELAPLUS TCMP 3365 one‑component post‑cure thermal gel can be evaluated against the actual mechanical design. Its published thermal conductivity reaches 6.2 W/m·K with a minimum controllable bond‑line thickness (BLT) of 100 μm. Final material selection must be validated through stack dimensions, assembly pressure and system temperature‑rise testing. Identify the Target Thermal Interface First Inside an AI server, the typical thermal path runs from the package IHS, through the thermal interface material, to a vapour chamber or cold plate, then onward to the heat sink, air duct or liquid cooling loop. This article addresses only the interface between the chip IHS and its adjacent cooling component; the TIM itself is not a substitute for the heat sink. GPUs, CPUs, switch chips and power modules differ in heat flux, clamping scheme and serviceability, even within the same server platform, and may therefore require distinct thermal solutions. Four sets of baseline data should be collected before thermal modelling: contact area and flatness, minimum and maximum assembly gap, clamping force plus tolerance, and intended rework strategy. Preliminary Screening: Grease vs Thermal Gel Construction / Operating Condition Key Evaluation Focus Candidate Grade Validation Boundaries Flat IHS‑to‑cold‑plate interface, thin bond line, stable screw clamping Fill micro‑voids and control excessive squeeze‑out SIGR 2250 thermal grease Shot volume, coverage after compression, interface integrity after thermal cycling…
