Mechanical Behaviors of Soft Elastomers Filled with LowMelting Alloys

Soft elastomers with mechanical properties similar to biological tissues have shown encouraging potential in applications of biomedical devices and stretchable electronics.With the ability to enhance electric and thermal conductivity,embedding low melting alloys into soft elastomer matrix has received considerable attention in recent years.However,the mechanical properties,especially the fatigue behaviors of these soft composites,have not been extensively investigated.Here,we fabricate two silicone elastomers filled with eutectic gallium-indium,a liquid metal alloy,which has a melting temperature around room temperature.The cyclic loading–unloading tests are first performed on the composites with low melting alloys in either solid or fluid state.The results show that the modulus and energy dissipation density of the composite increase with the ratio of the alloys when the deformation temperature is below the melting temperature,while these properties decrease with the ratio of alloys when they are in the fluid state.In contrast,the failure strain shows an opposite trend.Mechanical tests are further performed on specimens with a precut to measure the fracture energy and fatigue threshold.It is demonstrated that both fracture energy and fatigue threshold are significantly enhanced in the presence of low melting alloys regardless of their states.Finally,we apply a continuum damage model to describe the Mullins effect of the soft composites observed in the loading–unloading cycles,which further reveals the change of mechanical properties with deformation for different compositions of soft composites.

Thermal Performance of Low-Melting-Temperature Alloy Thermal Interface Materials

Thermal resistance of low-melting-temperature alloy （LMTA） thermal interface materials （TIMs） was measured by laser flash method before and after different stages of heating. The results showed that the thermal performance of the LMTA TIMs was degraded during the heating process. It is suggested that the degradation may mainly be attributed to the interfacial reaction between the Cu and the molten LMTAs. Due to the fast growth rate of intermetallic compound （IMC） at the solid-liquid interface, a thick brittle IMC is layer formed at the interface, which makes cracks easy to initiate and expand. Otherwise, the losses of indium and tin contents in the LMTA during the interfacial reaction will make the melting point of the TIM layer increase, and so, the TIM layer will not melt at the operating temperature.

Research progress on solder thermal interface materials

Down to the road of miniaturization and high power density,the heat dissipation is becoming one of the critical factors restricting further development of advanced microelectronic devices.Traditional polymer-based thermal interface materials(TIMs) are not competitive for the high efficiency thermal management,mainly due to their low intrinsic thermal conductivity and high interface thermal resistance.Solder-based TIM is one of the best candidates for the next generation of thermal interface materials.This paper conducts a perspective review of the state of the art of solder TIM,including low melting alloy solder TIM,composite solder TIM and nanostructured solder TIM.The microstructure,process parameters,thermal performance and reliability of different TIMs are summarized and analyzed.The future trends of advanced TIMs are discussed.