For thermal grease, thermal conductivity may not be so important

     As we all know, thermal conductive grease, as a TIM (Thermal Interface Material), is mainly used to fill the gap between solids, increase the contact area, reduce the thermal resistance of the interface, and improve the heat flux.

     There is a very important indicator of the thermal conductivity of grease, which may be the only indicator in our cognitive range. The thermal conductivity, which is expressed in W/m K. The definition is also very simple. When two parallel planes in a substance are 1 meter apart and 1 square meter in area, and their temperatures differ by 1K, the heat transferred from one plane to the other within one second is the thermal conductivity of the substance. The larger the thermal conductivity is, the stronger its thermal conductivity is.

The thermal conductivity of grease depends more on its thermal resistance:

   Gernally speaking ， the thermal conductivity of  grease depends on its interface thermal resistance under actual operating conditions. The interface thermal resistance includes the thermal resistance of grease itself, which is inversely proportional to the thermal conductivity of silicone grease and the area of silicone grease layer, and is proportional to the thickness of silicone grease layer; In addition, there is the contact thermal resistance between silicone grease and the two base materials, which depends partly on the roughness of solid materials, thermal conductivity of silicone grease, wettability, external pressure, etc. The contact thermal resistance can be ignored only when the silicone grease is relatively thick, but as a small tolerance TIM material, the thickness of silicone grease is usually µ m, so the impact of contact thermal resistance exists.

      The thermal conductivity of grease can only determine the thermal resistance of silicone grease, but the overall interface thermal resistance is also related to the contact thermal resistance of the upper and lower surfaces of silicone grease layer. For silicone grease, the contact thermal resistance is related to the external force, surface roughness of substrate material, thermal conductivity and wettability of silicone grease, but not to the thickness. When facing the same substrate material, the same thickness and area, the contact thermal resistance is fixed.