The Construction Of Segregated Structure And Thermal Conductivity Of Polymer/Low-Melting-Point Alloy Composites

With the development of high power,miniaturization and integration of electric devices,the amount of heat generated during operation increases dramatically.However,excessively high temperature affects the service life and efficiency of electronic devices.Therefore,the effective heat dissipation of electronic devices has been an urgent problem to be solved in the field of electronic packaging.Adding thermally conductive fillers to polymers to prepare polymer-based composites is a widely adopted method.However,the addition of a large amount of fillers inevitably cause processing problems and deterioration of mechanical properties while improving the heat dissipation.Therefore,the construction of continuous thermal conduction paths with low filler filling through microstructure design of filler particles in polymer is the hotspot of current research.In this paper,the low-melting-point alloy(LMPA)as fillers,which were added into the thermoplastic matrix(polyetherimide)and thermosetting matrix(epoxy resin)to construct the segregated network respectively.With the aid of the solid-liquid transition of the alloy during processing,the fluidity of the inorganic filler in the polymer matrix was improved.Besides,the thermal conductivity of the composites was greatly improved due to the microscopic continuous network of the alloy was constructed.The research not only broadened the application of LMPA,but also provided an effective reference for the preparation of high-performance thermal conductive materials.1.Polyetherimide(PEI)microspheres were prepared by water vapor induced phase separation method,and then LMPA(SnBiCu)alloy was introduced into the PEI matrix to obtain the PEI/SnBiCu composites by hot-pressing.The tensile test showed that the addition of alloy enhanced the mechanical properties of the composites,suggesting a good combination of PEI matrix and alloy particles.Scanning electron microscopy(SEM)images showed that the PEI microspheres in the composites were separated by alloy particles.Besides,the alloy particles were interconnected to form a continuous network structure as the content increases of alloy.This special segregated structure provided a path for heat transmission,and phonons could efficiently transmit along the alloy particles.Therefore,the thermal conductivity of the PEI/SnBiCu composites with the addition of 50 vol%alloy was greatly improved to 1.26 W m-1 K-1.Furthermore,the research also focused on the effect of the processing temperature,the type of alloy and the size of PEI microspheres on the segregated network structure and thermal conductivity of the composites.2.Using epoxy resin as the matrix,the micro-design of the segregated structure of the LMPA(SnBi58)in the thermosetting polymer matrix was realized.LMPA endowed the epoxy resin good thermal conductivity,and simultaneously enhanced electromagn--etic interference shielding(EMI)performance.Cross-linked epoxy microspheres(CEMs)were firstly synthesized by precipitation polymerization,and then the CEMs were physically mixed with SnBi58 alloy.Finally,the segregated EP/SnBiss composites were prepared via hot-pressing technique.Because of the alloy acts as a "metal binder"during the hot-pressing process,which overcame the difficulty of constructing segregated network microstructure in thermosetting by the hot-pressing.In addition,the mechanical tensile test showed that the addition of alloy significantly improved the mechanical properties of the composites.SEM results showed that with high alloy content in the composites,a continuous structure surrounding the epoxy microspheres was formed between the alloy particles.The alloy network formation beneficial to the transmission of phonons,so the EP/SnBi58 composites with 50 vol%alloy presented a satisfactory thermal conductivity of 1.6 W m-1 K-1.In addition,the alloy has high conductivity,the excellent conductivity and the formation of the segregated structure in the composites significantly improved the EMI performance of the composites at X-band frequency(8.2-12.5 GHz),which reached 72 dB at 10 GHz.In short,the EP/SnBi58 composites has broad application prospects in the field of thermal management and EMI materials in the future.