Preparation Of Ag/MWCNTs Composites And Their Application To Improve Thermal Conductivity Of Low-temperature Electronic Pastes

In order to improve the service life of high-performance electronic equipment,it is necessary to solve the heat dissipation issue when the equipment is running.As a thermal interface material(TIM)with excellent performance,the low temperature electronic paste can fill the gap between the contact interface of the radiator and the heating device,reduce the contact thermal resistance,and achieve efficient electronic cooling,which is a good choice to solve the heat dissipation issue.Recently,in order to obtain TIM with improved thermal conductivity and good printability,composite materials composed of various particles(such as metals,ceramics,etc.)in an epoxy matrix have been developed,while silver/carbon nanotubes(Ag/MWCNTs)composites are ideal materials to achieve better heat conduction and high thermal conductivity,and have gradually become research hotspots in TIM filed.Compared to metals and ceramics,multi-walled carbon nanotubes(MWCNTs)with one-dimensional architectures have better characteristics in terms of elevated specific surface areas,high tensile strength and toughness,good thermal conductivity,and electrical conductivity.Hence,MWCNTs attracted wide attention in both research and application fields,especially in microelectronics and composites materials.In addition,the metal Ag has good thermal and electrical conductivity,depositing Ag on the surface of MWCNTs could produce a synergistic effect between the two,and further improving the performances of MWCNTs.However,in the research of Ag/MWCNTs composites,it has been difficult to deposit silver nanoparticles(Ag-NPs)with high distribution density,uniform size and good dispersibility on the surface of MWCNTs.At the same time,MWCNTs are easy to agglomerate,it is necessary to improve their dispersibility and reduce entanglement before preparing Ag/MWCNTs composites.This paper introduces two methods for preparing Ag/MWCNTs composites,namely to surface modification of MWCNTs with ammonium bicarbonate(NH₄HCO₃)and iodine(I₂)respectively to improve their surface activity.Then,Ag/MWCNTs composites were prepared by a simple chemical method using different dispersants and reducing agents,and used to modify low temperature electronic paste.The micro-morphology and spectral analysis of Ag/MWCNTs composites indicated that Ag-NPs can be uniformly distributed on the MWCNTs surfaces with high distribution densities prepared by aminating-functional MWCNTs and iodinating MWCNTs.However,by comparison,Ag/MWCNTs composites prepared after iodination of MWCNTs perform better,the silver content in Ag/MWCNTs composites was measured by inductively coupled plasma optical emission spectrometer(ICP-OES)to be about 22.4%.The obtained Ag/MWCNTs composites(1 wt%)was added to the silver-epoxy paste to prepare a modified low temperature electronic paste.Field emission scanning electron microscopy(FESEM),thermal conductivity,resistivity,and thermogravimety(TG)analysis suggested that Ag flakes were better connected by Ag/MWCNTs composites,which improved the thermal conductivity of the paste from about 0.735 to 1.275 W/m K,it has thermal stability and the resistivity value of the paste is reduced,however,more weight loss was observed when Ag/MWCNTs composites were incorporated in the silver-epoxy paste between the temperature range of 25-600°C.Furthermore,the research on the thermal conduction mechanism of low temperature electronic paste shows that after adding Ag/MWCNTs composites to silver-epoxy paste,the paste system has a discontinuous filler network,and Ag-NPs attached to the surface of MWCNTs can promote the interface bonding between MWCNTs and Ag flakes during the curing process,reduce interface thermal resistance,increase the heat conduction path and improve thermal conductivity.Overall,the addition of Ag/MWCNTs composites into the low temperature electronic paste can significantly improve the thermal conductivity of the paste,and Ag/MWCNTs composites have the potential to improve the other performance of low temperature electronic paste.