Is Your Thermal Grease Drying Out? The Problem May Be the Base Silicone Oil-Iota

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News > Dynamic industry > Is Your Thermal Grease Drying Out? The Problem May Be the Base Silicone Oil

Is Your Thermal Grease Drying Out? The Problem May Be the Base Silicone Oil

In CPUs, GPUs, power electronics, and EV systems, thermal grease plays a critical role in transferring heat between chips and heat sinks.

But after long-term operation, many engineers find that the grease becomes dry, hard, or even suffers from pump-out, causing thermal resistance to increase significantly.

In many cases, the real problem isn't the thermal filler—it's the base silicone oil.

Why Does Thermal Grease Fail?

Thermal grease is mainly made of thermally conductive fillers (such as aluminum oxide or boron nitride) and a silicone oil carrier.

When operating at high temperatures for long periods, conventional dimethyl silicone oil can gradually lose its low-molecular-weight components through evaporation.

This leads to:

Thermal grease becoming dry and hard
Filler particles agglomerating
Poor contact with the heat source
Increased thermal resistance

Another common issue is the pump-out effect.

During repeated heating and cooling cycles, chips and heat sinks expand and contract differently. Low-viscosity silicone oil can gradually migrate out of the interface, leaving the center dry while oil accumulates around the edges.

The Solution: Phenyl Silicone Oil

More high-end thermal interface materials (TIMs) now use phenyl silicone oil instead of conventional PDMS.

Key advantages include:

Excellent thermal and oxidation stability
Extremely low volatility
Better resistance to oil migration and pump-out
Improved compatibility with thermal fillers
Stable viscosity from -40°C to 200°C

These properties help thermal grease maintain long-term performance, even under continuous high-temperature operation.

How to Choose the Right Phenyl Silicone Oil

When selecting a phenyl silicone oil for thermal grease, pay attention to these key properties:

Volatility: Less than 0.1% (200°C / 24 h) for long service life.
Phenyl content: Around 5–20% for the best balance of thermal stability and compatibility.
Viscosity: Typically 100–1000 cSt, depending on filler loading and anti-pump-out requirements.
Appearance: Clear and transparent for high electrical insulation performance.

Conclusion

Dry thermal grease is not simply an aging issue—it is often a material selection issue.

While conventional PDMS is economical, its higher volatility and lower resistance to migration make it less suitable for today's high-power electronic devices.

Using low-volatility phenyl silicone oil can significantly reduce pump-out, extend the service life of thermal grease, and provide more reliable long-term thermal management.

If you're looking for low-volatility phenyl silicone oil or technical support for thermal grease formulations, we're here to help.

Website: www.siliconeoil.net
E-mail: zyf@siliconeoil.cn

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