Preparation And Heat Transfer Performance Of The Thermal Interface Materials With Property Of Thermal Expansion During Phase Change Process

The development of technology, manufacturing and packaging, brings smaller size, more integrated chip and at the same time higher input power of electronics. The contact between two surfaces established on the touch salient points on the surfaces, caused the decrease of real contact area, which results in thermal contact resistance(TCR). TCR, one of the most important parameters for the cooling the cooling performance, determines the running status of some key apparatus, as a consequence its research for the solution to the cooling problem of high heat flux is of great significance. What’s more, the contact issues between substrate and heat sink keeps being the bottleneck in the channel of heat conduction. Now, thermal interface materials(TIM) mainly consist of phase change materials and elastic materials, such as conductive adhesive, thermal grease and thermal gasket, whose research idea apparently has been adding particles with high thermal conductivity into elastic materials to greatly promote their thermal performance. According to the above, we adopted low-melting alloy(LMA) as substrate with the addition of particles with thermal expansion property.In this study, peritectoid, peritectic and eutectic points of BiInSn Alloy were taken as substrate,at the same time filling in with a certain amount of Sb expanding when heated as a guidance for improving the exposure atmosphere. Characterized by ESEM, XPS, XRD, and DSC, their internal structure, phases included and thermal properties were identified. The results showed that the micro structure and phases of BiInSn alloy changed after adding some Sb. Moreover, though the melting points of these new materials increased by 1～3℃, as well as the melting enthalpy, they were still functioned as phase change TIM with low melting point to buffer the heat delivered from the chip. More importantly, Sb dissolved into each phase, and then with other expansion elements in the material forming the expansion network in the TIM.The alloy composed by the eutectic point of BiInSn alloy and Sb had grain refinement, dendritic structure so that phase separation were avoided. Herein, the eutectic point was chosen as backing material. With the characterization of XRD, it showed that, intermetallic compound InSb, BiIn and Bi3In5 generated in the alloy gradually rose with the increase of the content of Sb. But compared with the alloys containing 1% and 1.5%(wt) Sb, The characteristic peaks of the former compounds in the alloy involving 0.55%(wt) Sb appeared to be very weak. In addition, just a extra endothermic peak and a slightly rise in melting point showed up in the alloy with 0.55%(wt) Sb when comparing with the eutectic point of BiInSn alloy. The expansion rate of the alloy measured by the self-designed device come to the maximum when its content of Sb is 0.55%(wt).The heat transfer performance of those alloys sandwiched in two slippery ceramic substrates was taken theoretical and experimental research, and it turned out that, increasing the real contact area between two slippery ceramic substrates is more effective than just lower their surface roughness by mechanical means. The TCR of the above samples like sandwiches was detected by hot disk, and it comes out that TCR decreased at least 80% after the materials liquefied, and dropped then hovered up with the growing of the additive amount of Sb, reaching the lowest at 0.55%(wt)Sb.Through the above analysis, four formulas of TIM with the property of phase change expansion at various temperature-level were obtained. Applying one of them to the LED lamp, it can obviously improve the effect of heat transfer.