Study On The Mechanical And Electrical Properties Of Cu-Cu Interconnect Based On The Nanocopper Pastes

In microelectronic packaging field,the traditional lead-alloy solder is fail to meet the demand from the decreasing size of electronic devices,increasing packaging density and heat dissipation because of its overgrowth intermetallic component,electromigration and size effect.However,the Cu-Cu bonding based on the nanocopper paste(NCP)is believed to be one of promising solutions.In this paper,the influences of different organic solution systems and processing parameters on the Cu-Cu bonding were studied.The phenolic-resin(PF)was added to the nanocopper paste to enhance the mechanical property of Cu-Cu bonding.The main content and conclusion are as follow:The influence of organic solution systems on the Cu-Cu bonding was studied by testing different Cu-Cu bonding,which was obtained by using different NCPs.The results suggest that in low temperature(e.g.240 ?C)process,the shear strength of Cu-Cu bonding increases first and then decreases when the volatile point of solution system is rising.However,in the relative high temperature(e.g.300 ?C)processing,the shear strength of Cu-Cu bonding increases with the increase of volatile point of solution system.Because the organic solution systems with high volatile point can prevent copper nanoparticles from oxidation,but remain organic coating would hinder the sintering between copper nanoparticles.However,little organic matter remains in Cu-Cu bonding at high temperature,hence the higher shear strength.The influences of reflow conditions(reflow temperature,reflow time and atmosphere)on the shear strength of Cu-Cu bonding were studied by orthogonal experiment.The range analysis method was adopted to obtain the optimized parameters and the analysis of variance was utilized to determine the significance level of each parameter.The data shows that the reflow temperature affects the shear strength of CuCu bonding most,however,reflow time and atmosphere do not reach statistical significance.The parameters are optimized when reflow temperature is 340 ?C,reflow time is 15 min and atmosphere is nitrogen.The condition of atmosphere has an interaction with reflow temperature and reflow time.The effects of addition of phenolic resin(PF)on electrical conductivity and joining strength of Cu-Cu bonding were investigated by adding various content of PF into NCPs.The results show that the increase of shear strength depended on the additive amount of PF.Moderate PF enhanced the strength for it filled the void and coated the bonding.Electrical conductivity of the joint was reduced with the addition of PF.however,PF also prevented Cu nanoparticles from oxidation and therefore 2 wt% PF barely changed the whole electrical resistivity.The excess addition of PF hindered the sintering between Cu nanoparticles,which lead to the decreasing in both shear strength and electrical conductivity.