Core Function of Thermal Grease: Heat Transfer, Gap Filling and Reliability Explained

The core function of thermal grease is to transfer heat efficiently from electronic components to heat sinks by filling microscopic air gaps between two solid surfaces. While it looks simple, this paste-like thermally conductive compound plays a decisive role in the operating temperature, performance and service life of power electronics.

Why Do Electronic Components Need Thermal Grease?

All semiconductor devices - CPUs, GPUs, IGBT modules, MOSFETs, LED chips and power resistors - generate heat during operation. If that heat is not removed, junction temperature rises, efficiency drops, and reliability falls. Heat sinks remove heat, but the interface between the component and the heat sink is the bottleneck. Thermal grease solves exactly this problem.

The Three Core Functions

1. Filling Micro-Gaps

Machined metal surfaces look smooth but contain valleys up to several tens of microns deep. Thermal grease conforms to these irregularities and expels trapped air, creating continuous heat paths.

2. Reducing Contact Thermal Resistance

Air has very low thermal conductivity (~0.026 W/m·K). Thermal grease with 1.0-6.0 W/m·K conductivity (Hanast HN100-HN600) replaces air at the interface, dramatically lowering contact thermal resistance and the temperature rise of the component.

3. Stabilizing Long-Term Thermal Performance

Quality silicone thermal grease resists pump-out, dry-out and oil separation, so the thermal path remains stable for years even under thermal cycling and vibration.

Where Thermal Grease Is Indispensable

• PC and server cooling: CPU, GPU, chipset and VRM;
• Power electronics: IGBT, rectifier and inverter modules;
• LED lighting: COB modules, LED drivers and lamp housings;
• Automotive: EV battery packs, motor controllers and onboard chargers;
• Telecom: 5G base station power amplifiers and remote radio units;
• Industrial: welding machines, UPS and frequency converters.

Thermal Grease vs Other Thermal Interface Materials

How to Judge If Thermal Grease Works Well

1. Measure component temperature before and after application;
2. Check coverage: after disassembly the grease layer should cover the whole die area thinly and evenly;
3. Run thermal cycling and vibration tests to confirm stability;
4. Verify the grease does not harden, crack or bleed oil over time.

What Happens Without Thermal Grease?

Without thermal grease, a typical CPU or IGBT running at 80-100 W may run 15-30°C hotter, leading to thermal throttling, higher fan noise, faster aging of electrolytic capacitors and, in extreme cases, premature failure. The cost of one tube of thermal paste is negligible compared with the warranty cost of a returned product, which makes thermal grease one of the highest-return investments in thermal design.

How to Select Thermal Grease for Your Product

For a new design, first calculate the allowable temperature rise and required thermal impedance, then choose a grease with sufficient thermal conductivity and a viscosity that matches your dispensing equipment. High-power modules with heat flux above 10 W/cm² usually need 3.0 W/m·K or higher; LED drivers, adapters and consumer devices perform well with 1.0 W/m·K grades. Always request the technical data sheet and run a temperature verification with your real assembly.

FAQ

Does thermal grease dry out?

Low-quality grease can dry out over years of high-temperature operation. Premium silicone-based grease with low oil separation maintains performance for 5-8 years in typical electronics.

Can I reuse a heat sink after removing the old grease?

Yes. Clean both surfaces thoroughly with isopropyl alcohol, reapply a fresh thin layer, and remount with the correct torque.

Conclusion

The core function of thermal grease is simple but critical: move heat across the interface reliably. Whether you manufacture LED drivers, EV battery systems, power supplies or industrial electronics, selecting a thermal paste with the right conductivity, viscosity and durability protects your products from overheating and premature failure. Contact Hanast for free samples of thermally conductive silicone grease and expert selection support.