How to distinguish between thermal conductive silicone grease and thermal conductive silicone rubber

Many users often have difficulty distinguishing between thermal grease and thermal conductive silicone rubber, and when purchasing, they don't know how to choose, easily confusing grease with silicone. Although thermal grease and thermal silicone differ by only one character in their names and are both thermal conductive materials, their characteristics are quite different. Improper use can lead to serious consequences.

thermal grease

thermal grease, also known as silicone paste, is a grease-like substance without adhesive properties that does not harden. It is produced using a special formula and is made from a composite of metal oxides with good thermal conductivity and insulating properties and organosiloxanes. The product has excellent thermal conductivity, good electrical insulation, a wide operating temperature range (-60°C to 300°C), good stability, low viscosity, and good workability. The paste is non-toxic, non-corrosive, odorless, non-drying, and non-dissolving. Silicone grease is used for lubrication and can be applied under high loads. It looks similar to butter, and we generally have less contact with it.

The thermal grease we commonly refer to should be called silicone paste, which consists of silicone oil + filler. The filler is finely ground powder, composed of ZnO/Al2O3/boron nitride/silicon carbide/aluminum powder, etc. The silicone oil ensures a certain fluidity, while the filler fills the tiny gaps between the CPU and the heat sink, ensuring thermal conductivity. Due to the low temperature sensitivity of silicone oil, it does not thicken at low temperatures and does not become thinner at high temperatures, and it does not evaporate, so it can be used for a relatively long time. Now some thermal greases use silver or aluminum powder as fillers, utilizing the high thermal conductivity of metals.

Thermal Conductive Silicone Rubber

Thermal conductive silicone rubber is a one-component de-alcoholization type room temperature curing silicone rubber, which has the effect of cooling and bonding for electronic devices. It can cure into a high-hardness elastomer in a short time. After curing, it closely adheres to the contact surface to reduce thermal resistance, thereby facilitating heat conduction between the heat source and the surrounding heat sink, motherboard, metal shell, and housing. It has advantages such as high thermal conductivity, good insulation performance, and ease of use, and has good adhesion to metals including copper, aluminum, stainless steel, etc. The curing form is de-alcoholization, and it does not corrode metal and non-metal surfaces.

Compared to thermal grease, thermal conductive silicone rubber is much lower and once cured, it is difficult to separate the bonded objects. It is generally only used in graphics cards, memory heat sinks. If used on the CPU, it can cause overheating, and it is difficult to remove the heat sink. Pulling down hard may directly damage the CPU or CPU socket. If you pull down the graphics card heat sink bonded with silicone rubber hard, you may pull the display chip off the PCB.

Although silicone grease and silicone rubber differ by only one word in spelling and are both thermal conductive materials, they are entirely different things. Relatively speaking, silicone grease has a wider range of applications and is suitable for almost any cooling condition; while because silicone rubber is difficult to remove once stick it, it is mostly used in situations that require one-time bonding, such as graphics card heat sinks, etc.

In thermal dissipation and heat conduction applications, even two very smooth surfaces in contact with each other will have gaps. The air in these gaps is a poor conductor of heat and will hinder the conduction of heat to the heat sink. thermal grease is a material that can fill these gaps, making the conduction of heat smoother and faster. There are many types of silicone grease on the market now, and different parameters and physical characteristics determine different uses, such as some suitable for CPU heat conduction, some for memory heat conduction, and some for power supply heat conduction. 

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