What is Thermal Grease? Complete Guide to Thermal Paste, Its Types and How It Works

Thermal grease - also called thermal paste, thermal compound, or heat sink compound - is a paste-like thermally conductive silicone material used to improve heat transfer between two contacting surfaces. If you have ever asked "what is thermal grease?", this guide answers the question in depth and explains how to select the right thermal paste for electronics manufacturing.

Definition: What Is Thermal Grease?

Thermal grease is a soft, paste-like interface material made of silicone oil as the base fluid and highly thermally conductive fillers such as alumina, zinc oxide, boron nitride and aluminum nitride. It is applied between a heat source (CPU, GPU, IGBT, LED, power module) and a heat sink to fill microscopic air gaps that exist even on apparently flat machined surfaces.

Air is a poor heat conductor. By replacing air with a material whose thermal conductivity is far higher, thermal grease dramatically reduces contact thermal resistance and keeps components cooler.

How Does Thermal Grease Work?

No surface is perfectly flat. Under a microscope, metal surfaces show valleys and peaks of several microns. When two surfaces are pressed together, air pockets remain trapped, blocking heat flow. Thermal grease flows into these micro-gaps under mounting pressure, creating continuous heat paths from the component to the heat sink.

Main Types of Thermal Grease

• Silicone-based thermal grease - the most common type, with excellent temperature resistance from -50°C to 200°C or higher;
• Non-curing thermal paste - remains soft for years, easy to rework, widely used in EV battery and power electronics;
• Curing thermal compounds - cross-link after application for higher reliability in vibration environments;
• Electrically insulating thermal grease - ceramic-filled, safe for exposed circuits;
• Silver or metal-filled conductive grease - highest conductivity, used only where electrical insulation is not required.

Key Performance Parameters

• Thermal conductivity (W/m·K) - from 1.0 W/m·K to 6.0 W/m·K across the Hanast HN100-HN600 series;
• Thermal impedance (°C·cm²/W) - depends on the applied layer thickness (BLT);
• Viscosity - determines dispensing method and wetting;
• Density and specific gravity - typical 1.6-2.6 g/cm³;
• Breakdown voltage - insulation safety for non-conductive grades;
• Operating temperature range - from -50°C to 200-300°C depending on formula;
• Shelf life and durability - resistance to dry-out, pump-out and oil separation.

Typical Applications

Thermal grease is used wherever heat must be moved efficiently: CPU and GPU coolers, graphics cards, notebook cooling modules, IGBT modules, switching power supplies, LED lamps and drivers, automotive electronics, EV battery thermal management, 5G base stations and industrial inverters.

How to Apply Thermal Grease

1. Clean both surfaces with isopropyl alcohol and let them dry;
2. Apply a thin, even layer - dispensing, screen printing or stencil printing for mass production;
3. Assemble with the correct mounting pressure;
4. Verify coverage after disassembly during process qualification.

Thermal Grease vs Thermal Pad: Which One to Choose?

Compared with pre-formed thermal pads, thermal grease achieves a thinner bond line and lower thermal impedance, which is why high-power CPUs, GPUs and IGBT modules use grease. Thermal pads are faster to assemble and easier to rework, making them popular for mass-produced consumer electronics. Many designs combine both: grease on the main die and pads on surrounding low-power components.

Hanast HN Series Thermal Grease at a Glance

FAQ

Is thermal grease electrically conductive?

Standard ceramic-filled thermal grease is electrically insulating. Only special silver or metal-filled grades are conductive, and they must be used carefully to avoid short circuits.

How often should thermal grease be replaced?

High-quality non-curing silicone grease can last 5-8 years in normal electronics use. In high-temperature or high-vibration applications, periodic inspection is recommended.

Does more thermal grease mean better cooling?

No. A thick layer increases thermal resistance. The best result comes from the thinnest possible layer that still fills the surface gaps.

Conclusion

Thermal grease is one of the most cost-effective reliability components in electronics. Choosing the correct thermal paste - by conductivity, viscosity, insulation and durability - directly affects product temperature, lifetime and warranty cost. For bulk supply of thermally conductive silicone grease with consistent quality, contact Hanast to request samples and technical data.