Investigation On Microstructure And Reliability Of Lead-Free Solder/Cu Interconnection Interface

The solder joints in packaging not only play the role of mechanical connection,but also the current channel,so its reliability is crucial.Nowadays,because electronic products are developing towards miniaturization,the size of solder joints is getting smaller and smaller.As the number of solder joints per unit area is increasing,higher requirements wre put forward for microelectronic packaging technology.Sn-Pb eutectic alloy with excellent performance and low cost has been widely used in welding field in the past decades.However,lead has adverse effects on human body and environment.Thus,it is of great significance to develop high reliability lead-free solder.Two kind of novel composite solders were prepared by adding Mo and Ag nanoparticles in Sn58Bi solder by mechanically mixing,respectively.The intermetallic compounds（IMC）of Sn58Bi/Cu solder joint thickened due to atomic diffusion reaction during aging process.However,the growth rate of IMC layer has reduced due to the Mo nanoparticles addition during isothermal aging.The reason is that Mo nanoparticles could hinder the diffusion behavior of atoms.The addition of Ag nanoparticles has the similar inhibition effect on the growth of IMC layer in Sn58Bi solder/Cu solder joints during isothermal aging.In addition,the Sn58Bi composite solder with2.0%Ag nanoparticles added has finer microstructure compared with Sn58Bi solder.The growth rate of IMC layer in Sn58Bi composite solder decreased during temperature cycling.In the hardness test,the hardness of composite solder with Ag nanoparticles added was significantly enhanced.Sn3Ag0.5Cu solder paste was reflowed for 2,5,10,15 and 20 minutes at 240℃on the Cu substrate,respectively.The size statistics for the Cu₆Sn₅ compounds were carried out basing on a large number of SEM images.The effect of reflow time on the growth of interfacial Cu₆Sn₅grain was analyzed,and the growth mechanism of the IMC layer in the solder joint during reflow process was studied.The hardness of Sn3Ag0.5Cu solder alloy decreased with the increased of the reflow time.Temperature cycling tests were carried out for Sn3Ag0.5Cu/Cu solder joints with different cooling methods.The crack formation mechanism and damage fracture behavior of solder joints subjected to cyclic thermal stress were studied.