Surface-functionalized Multi-walled Carbon Nanotubes And Silver Nanowires, And Their Epoxy-base Composites

Miniaturization and three-dimensional integration of modern electronic devices make heat dissipation a significant issue to ensure their high performance and structural reliability in the electronics industry. Therefore, there is an urgent need to design epoxy-based underfill materials (EUMs) with high thermal conductivity to dissipate the thermal energy generated by microelectronic chips and cool the electronic devices. However, the poor thermal conductivity of epoxy and the complex packaging process have limited their progress. So far, EUMs still face challenges to meet the stringent requirements for the next-generation electronics in terms of high thermal conductivity (??1 W/mK),high glass transition temperature (Tg?125?), high electrical insulation and low viscosity (< 20 Pa s at 25?).In the present work, in order to obtain uniform dispersion of MWCNTs in epoxy matrix and enhance the interfacial interaction between matrix and MWCNTs, covalent and noncovalent functionalization methods had been taken to produce MWCNTs-iL and AIL-MWCNTs. The effects of functionalized MWCNTs on the rheological properties, thermal conductivity and mechanical properties of epoxy composites were investigated. Furthermore, silica coated AgNWs and hybrid filler system consisting AgNWs and silica nanoparticles also utilized to compound with epoxy matrix to improve the thermal conductivity of epoxy composites.Firstly, ionic liquid-like MWCNTs (MWCNTs-iL) were synthesized by surface grafting reaction with ionic flexible chains and cation-anion process, and then the MWCNTs-iL were compounded with epoxy resins to fabricate epoxy/MWCNTs-iL composites. The rheological results showed that the fluidization of MWCNTs-iL decreased the viscosity of epoxy composites, which is benefit for the underfill processing. Although the dispersion of MWCNTs in epoxy matrix were greatly improved, the damage of the MWCNTs structure by covalent functionalization approach caused the thermal conductivity of samples increased very modestly as a function of MWCNTs-iL contents.Secondly, MWCNTs were successfully noncovalent functionalized with amine-terminated ionic liquid to produce AIL-MWCNTs by n-n and cation-? interaction, then compounded with epoxy resins to fabricate epoxy/AIL-MWCNTs composites. The effect of noncovalent functionalization on the dispersion of MWCNTs in matrix and the effect on rheological, dynamic mechanical, fracture toughness, thermal conductivity and electrical resistivity properties of epoxy/AIL-MWCNTs composites were investigated. The results showed that the amine-terminated ionic liquid enhanced the dispersion of the MWCNTs and the interfacial interaction between MWCNTs and epoxy matrix, thereby improved the dynamic mechanical, fracture toughness and thermal stable properties of the epoxy/AIL-MWCNTs composites. Furthermore, thermal conductivity properties also increased when compared with epoxy/MWCNTs composites which due to the enhanced interfacial interaction without destroy the structure of MWCNTs by noncovalent functionalization.Thirdly, in order to further improve the thermal conductivity of epoxy composites, the core-shell nanostructured AgNWs@SiO2 have been successfully fabricated and used as a novel type of 1D thermal conductive fillers with high aspect ratio to effectively improve the thermal conductivity of epoxy matrix. The silica nanolayer coated on AgNWs provides strong enhancements on dispersion of AgNWs in epoxy matrix and interfacial interaction between AgNWs and epoxy. Especially, the less stiff silica layer acts like a springboard to reduce the phonon propagation barrier, decreasing the thermal interfacial resistance, thereby decreasing their thermal interfacial resistance. Hence, the thermal conductivities of epoxy /AgNWs@SiO2 composites are higher than those of epoxy/AgNWs composites with the same loading. More importantly, due to the silica nanolayer coated on AgNWs, epoxy /AgNWs@SiO2 composites have higher electrical insulation and lower dielectric constants than equivalent epoxy/AgNWs composites. Clearly, the epoxy/AgNWs@SiO2 composite with 4 vol% filler has a thermal conductivity of 1.030 W/mK, Tg of 137.6?, an electrical resistivity of 1.385×1014 ?·cm, a dielectric loss tangent of less than 0.035, and a viscosity of less than 20 Pa·s at 25?, making it a potential candidate for the underfill material in electronic packaging.In the final part, a facile and effective approach by incorporating silica nanoparticles (SNPs) to fabricate high performance epoxy-based electronic packaging materials which are both thermally conductive and electrically insulating was presented. Because of the strong interaction between SNPs and silver nanowires (AgNWs), uniformly dispersed SNPs- modified epoxy was employed to promote the dispersion of AgNWs in epoxy matrix. Further, the enhanced modulus of epoxy matrix by the incorporation of SNPs effectively alleviates the modulus mismatch between stiff AgNWs and epoxy matrix. Compared with epoxy/AgNWs composites without SNPs, the resulting hybrid materials, that is, epoxy /SNP/AgNWs, showed distinct improvements in thermal conductivity without degrading their mechanical properties. Also, the SNPs were absorbed onto the surface of AgNWs forming an electrical insulation layer to disrupt the electron flows between adjacent AgNWs, hence retaining the electrical insulation of epoxy matrix. Finally, this new fabrication method is easily scalable owing to its simple procedure and use of commercial well-dispersed SNPs-modified epoxies.