Study On The Interfacial Thermal Resistance Of Thermal Interface Materials

The increasing power density of electronic equipment leads to challenges in thermal management.Due to their small size,electronic devices usually transfer their internal heat out through the installation of heat dissipation substrates,heat sink and other components.In this process,there are multiple interfaces for heat transfer.Discrete point contact between rough solid surfaces leads to the existence of interfacial thermal resistance,which seriously affects the heat transfer through interface and the heat dissipation of equipment.Thermal interface material(TIM)can effectively reduce interfacial thermal resistance and enhance heat transfer efficiency by increasing the actual contact area by filling the gap between the solid contact surfaces.When TIM fills the contact surfaces,air could be trapped in the gap.Theoretical studies on interfacial thermal resistance often ignore the influence of trapped air,while experimental studies are mostly carried out in vacuum.There is a lack of relevant studies on the influence of trapped air on interfacial thermal resistance.In this paper,a testing system was built to measure the interfacial thermal resistance of TIM applied in vacuum and air,and analyze the influence of trapped air and related factors.The steady-state difference method was used to measure the thermal conductivity of the heat flow meter,which was close to the value measured by the thermal conductivity analyzer LFA 467.The reliability of the test system was verified and the heat loss of the whole system was analyzed.Three kinds of thermal grease were selected as TIM,and copper substrate was used as the contact interface.The thermal conductivity of several TIM was measured,which was similar to that measured by the hot disk method.The average value was taken for subsequent calculation.In the experiment of studying the influence of trapped air on interfacial thermal resistance,the vacuum and air samples with different thermal grease and different copper substrate roughness were prepared by using the method of control variable,and their interfacial thermal resistance was measured.The results showed that the interfacial thermal resistance of vacuum group was smaller than air group for different thermal grease,indicating that the application of thermal grease in the vacuum environment can indeed enhance its wettability and make it better fill the gap leading to effectively reduce of interfacial thermal resistance.Among them,the difference between vacuum and air groups of ShinEtsu X-23-7762 with moderate viscosity was the largest,reaching 24%.The value for ShinEtsu X-23-7783 D and Dow corning TC-5688 were 15% and 14% respectively.It is found that the influence of trapped air on interfacial thermal resistance becomes larger with increasing interface roughness.For smooth surfaces,trapped air can be ignored,but when the interface roughness is large,its influence must be considered.In this experiment,with increasing interface roughness of copper substrate,the difference of interfacial thermal resistance between vacuum and air groups of ShinEtsu X-23-7762 increased from 6% to 24%.After proving the influence of trapped air on interfacial thermal resistance,two methods of surface treatment were applied to copper substrate: surface oxidation treatment and the application of dimethyl silicone oil.The results show that surface oxidation treatment can improve the wettability of the contact interface and reduce interfacial thermal resistance.The use of silicone oil can enhance the effect of thermal grease with high viscosity and poor fluidity.