Thermal Conductivity And Structure Of Sninbi Low Melting Thermal Interface Material

Today's electronic products are becoming smaller, run faster, do more and generate more heat. Although there are many ways to achieve the heat dissipation of electronic apparatus, the contact surface contains a combination of surface roughness and surface non-flatness. Thus, cooling channels reduce in the case of decreasing of actual contact points, therefore, the interface thermal resistance and contact resistance increase accordingly. When the power of electronics is small, the thermal contact resistance can be ignored. While the power of electronics is up to a certain value, the contact resistance becomes a problem. The quality of thermal interface materials determines the quality of electronics. The main thermal interface materials in the market are thermal grease, thermal gel, and phase change materials. These thermal interface materials are made of the polymer matrix and appropriate additives.In this paper, three low melting point alloys with the component in mass percent of 17Sn26In57Bi,17Sn51In32Bi and 27Sn44.9In28.1Bi were chosen to investigate properties of the thermal conductivity and structure of these alloys. The basic properties were measured by using DSC and flash method. Flash method, XRD and SEM were employed to evaluate the heat transfer performance and interface structure between SnInBi alloy and copper.Research results show that the thermal conductivity of high Bi alloy (17Sn26In57Bi) is relatively low, while that of alloy (27Sn44.9In28.1Bi) with minimum Bi content is higher.The thermal conductivity of low melting alloys in our investigation is higher than polymer materials, and the thermal interface resistance is lower. The thermal conductivity decrease when the solid-liquid reaction takes places between alloys and copper, which may related to the formation of intermetallic compound at the interface.17Sn26In57Bi alloy is verified to be composed of BiIn, Bi and Sn phases. During the interface reaction with copper, Flat Cu6(Sn, In)5 phase forms in the side next to copper, between Cu6(Sn, In)5 and 17Sn26In57Bi alloy is branched Cu9(In, Sn)4 intermetallic compounds. Interface reaction rate is faster, Bi segregation phenomenon is obviously observed at the interface.17Sn51In32Bi alloy is composed of BiIn2 and InSn4 phases. Flat Cu6(Sn, In)5 forms at the interface. Interface reaction is slow. No Bi segregation or phase transition phenomenon was found in this experiment, this result suggests that the heat transfer property is steady during the solid-liquid reaction.BiIn2 and InSn4 were identified to be the two component phases in 27Sn44.9In28.1Bi alloy. During the interface reaction with copper, branched Cu6(Sn, In)5 forms at the interface. The interface reaction rate is in between that of 17 Sn26In57Bi and 17 Sn51In32Bi alloys. Bi segregation is obvious near the interface. After a longer time solid-liquid reaction at high temperature, BiIn2 and InSn4 phases in the alloy transform into BiIn and Bi phases.