Research On Preparation And Properties Of Electrically Conductive Adhesives Based On Silver Coated Copper Powder

Electrically conductive adhesives?ECAs?,which usually consist of conductive fillers and polymeric resin,are proposed to replace the traditional tin lead solder,in order to develop high-density,thin separation,low defect ratio,fine-pitch and environmentally friendly microelectronics.However,there are still several disadvantages in the existing conductive fillers which are commercially available,such as the high resistivity for carbon filler,high oxidation for copper filler,high costs and migration phenomenon for silver filler,etc.Herein,silver-coated copper powders,to solve the problems,were proposed as conductive fillers,supplemented by the modification of resin to improve the performance of ECAs.The main research contents are as follows:1.Copper powders were synthesized by chemical reduction and electrolytical method,respectively.Thanks to the high overlap rate of dendritic morphology,the dendritic copper obtained by electrolytic method exhibited lower volume resistivity than the spherical one prepared by reduction in the same experimental condition.In addition,high pressure hydrothermal method was carried out to improve the oxidation resistance of copper powders,by the diffusion and convection in copper ions to repair the defect lattice.Therefore,the oxidation resistance of copper powder is improved,as well as the conductivity of ECAs.2.Silver plating on copper powder substrate was carried out by chemical reduction.The effects of pretreatment method,including reaction temperature?80°C,70°C,60°C,25°C?,solution concentration(0.5 mol·L^-1,0.1 mol·L^-1,0.05 mol·L^-1,0.025 mol·L^-1)and dropping speed(8 mL·min^-1,3 mL·min^-1)on silver-coated copper powders were investigated.The optimal preparation process was obtained after the fully characterization of products,including SEM,XRD,EDS,four-point probe,etc.The resulting metal powder showed the best properties under the condition of dripping 0.05 mol L^-1 silver-ammonia solution into the reaction mixture at the rate of 8 mL min^-1 at 25°C and following with a secondary silver plating.3.The resin substrate was modified by different strategies.Carboxylated-terminated liquid acrylonitrile rubber?CTBN?was used to modify the epoxy resin?EP?,in this research,epoxy E-44,for its shortage of brittle quality after curing.The different adding methods?chemical copolymerization and physical blending modification?,as well as the effect of CTBN addition?30%,25%,20%,15%,10%,0%?has been tested.As a result,the chemical prepolymer addition strategy worked better overall,and resulted the best value of impact strength as 31.2889 J·cm^-2,the tensile strength as 38.24 MPa and the elongation at break as 26.42%under the condition of 20%CTBN addition.Moreover,the optimized curing conditions were obtained by differential thermal analysis?DSC?:preheating at 40°C for 0.5 h to remove the small molecules,following with pre-polymerizing at 80°C for 1 h,and formal curing at 160°C for 1 h.4.The effect of coupling agent and surface additive were also investaged.The experimental results indicated that the best performance EACs was obtained with the recipe of 2%KH550,1.925%glutaric acid,and 82.5%filler,with the minimum volume resistivity as 0.912×10^-4?·cm and thermal conductivity as 1.92 W·mk^-1.