The reasons that affect the thermal conductivity of the thermal gel.

Thermal conductive gel and thermal conductive silicone sheet with the same thermal conductivity, according to the analysis, the thermal conductive effect of thermal conductive gel is better than that of thermal conductive silicone sheet, but in some applications, the effect of thermal conductive gel and thermal conductive silicone sheet with the same thermal conductivity is almost the same, and the preliminary estimation is that there is a problem in application. In this paper, this paper briefly analyzes the reasons that affect the thermal effect of thermal gel.

thermal conductive filler

The thermal conductivity of a thermally conductive gel is first determined by its material composition and internal structure. Among them, the thermal conductive filler plays a central role.

1. Filler type: Alumina has become a common filler for thermal conductivity gel due to its high cost performance and insulation, while high-end fillers such as boron nitride and carbon fiber can improve thermal conductivity, but the cost is too high.

2. Filler morphology: Although the granular filler is conducive to processing, the flake or fibrous filler (such as graphene or carbon nanotubes) can greatly improve the thermal conductivity by forming a thermal network chain. Experiments show that the fiber filler can improve the efficiency of the heat conduction path by more than 30%.

Matrix Materials and Additives

Silicone polymers are commonly used as matrices because of their flexibility and thermal stability, and their viscosity needs to balance fluidity (ease of application) and sag resistance (shape maintenance). Dispersing agent can improve the uniformity of filler distribution and avoid the formation of local thermal resistance. The crosslinking agent affects the strength of the network structure after curing. If the additive is not properly selected, it is easy to cause phase separation or aging cracking.

Apply Smudge Thickness

Many customers do not care about the thickness when using thermal conductivity gel, resulting in the thermal conductivity effect is not as expected. However, the thickness is positively correlated with the thermal resistance. When the coating thickness increases from 0.5mm to 3mm, the thermal resistance may increase several times, causing the customer to misjudge the "insufficient performance" of the material ". It is recommended to apply the thermal conductive gel in a thin layer of 0.1~1mm, and ensure that it is evenly applied to avoid residual air and reduce thermal resistance.

interface effective contact

The thermal gel should completely fill the gap between the heating element and the heat sink. The actual measurement shows that the existence of an air gap (>1μm) at the interface can increase the thermal resistance by more than 50%. When assembling, keep a certain pressure (5-15psi) as far as possible to squeeze out the air bubbles at the interface, increase the effective contact surface, fill the small gaps, and make the thermal conductive gel contact more closely with the heat dissipation material.

Radiator efficiency

Many customers only pay attention to the thermal conductivity of thermally conductive materials, but they have not thought about whether the radiator is suitable. For example, some customers started to use 2 W/m · K thermal conductivity gel on the power supply, and the thermal conductivity effect barely met the requirements. In order to achieve better results, the customer used a 5 W/m · K thermal conductivity gel, but the result was very unexpected. There was no obvious difference in the thermal conductivity effect of the two thermal conductivity gels with large difference in thermal conductivity. After eliminating the reason for the material (because the material has been verified by many customers and there is no problem in application, and the surface of the material is flat and wrinkle-free, indicating good effective contact), we infer that it is because the radiator is small and its maximum efficiency has been exerted when 2 W/m · K thermal conductive gel is used, just like large flow water pipe connecting fine water outlet, when the surface area or fin design of the radiator cannot dissipate heat in time, even if the thermal conductivity of the thermally conductive material is increased from 2 W/m · K to 20 W/m · K, the temperature difference improvement is less than 5%. We recommend that customers use a larger radiator to verify that the thermal conductivity effect is significantly improved. It can be seen that the heat capacity of the radiator needs to match the power of the heat source and the thermal conductivity of the thermal conductivity material.