Electrodeposited Sn-TiO₂ Composite Solder And Interface Reaction Of Solder Joints

With the rapid development of electronic packaging technology,the size of package solder joints is also decreasing,but the reliability requirements for soldering joints are getting higher and higher.Studies have shown that the addition of nanoparticles to the solder can improve the reliability of the solder joints,but how to make the nanoparticles evenly distributed in the solder and joints is a common process problem.Therefore,it has been very important to develop a new process to prepare a composite solder with uniform distribution of nanoparticles,and to study the influence of nanoparticles on the growth behavior of IMC at the solder joint interface.In this paper,the Sn-TiO₂ composite solder with uniform distribution of TiO₂ was prepared by electrodeposition method,and the linear solder joints with the spacing of 10?m,20?m and 30?m were prepared,the effects of solder joint spacing and nano-TiO₂ particles addition on the IMC growth behavior of the solder joint interface were investigated.The main conclusions of this paper are as follows:?1?Preparation of pure Sn solder by direct-current,single pulse and double pulse electrodeposition.X-ray diffraction analysis found that the pure Sn solder prepared by the three methods has preferred growth orientations of?101?,?112?and?103?.It was found by electrochemical corrosion tests that the direct-current electrodeposited pure Sn solder had the worst corrosion resistance,and the single-pulse electrodeposited pure Sn solder had good corrosion resistance,and the double-pulse electrodeposited pure Sn solder had the best corrosion resistance.This is because the surface of the direct-electrodeposited pure Sn solder is not flat,the crystal grains are coarse,there is a gap between the crystal grains,and the microstructure of the solder is not dense;the surface of the single-pulse electrodeposition is relatively flat,but the crystal grains are also coarse;and the double-pulse electrodeposited pure Sn solder has the most flat surface,fine grain and dense structure.?2?Preparation of Sn-TiO₂ composite solder.Nano-TiO₂ particles were not found in the direct-electrodeposited composite solder,in the single-pulse electrodeposited composite solder,the nano-TiO₂ particles exist only on the near surface,and the nano-TiO₂ particles in the electrophoresis-pulsed electrodeposited composite solder are evenly distributed.After X-ray diffraction analysis,after adding nano-TiO₂ particles,13 diffraction peaks such as?200?,?101?,?220?,?211?and?112?etc.appeared,indicating that the addition of the nano-TiO₂particles makes the solder preferential growth orientation disappear.The cross-section elemental analysis of the Sn-TiO₂ composite solder shows that when the amount of nano-TiO₂particles added in the solution is 30 g/L,the composite amount of nano-TiO₂ particles in the solder layer is the most,which is 0.32 wt.%.Electrochemical corrosion tests show that the corrosion resistance of Sn-TiO₂ composite solder is worse than that of double-pulse pure Sn solder.This is because the solder grains are coarsened after the addition of nano-TiO₂particles,and the compactness of the solder structure is deteriorated,resulting in corrosion resistance of the solder decline.?3?Effect of solder joint spacing and nano-TiO₂ on the interface reaction of solder joints.During the soldering process,the proportion of IMC in Cu/Sn/Cu and Cu/Sn-TiO₂/Cu solder joints increased with the decrease of solder joint spacing.The growth index of Cu/Sn/Cu and Cu/Sn-TiO₂/Cu solder joints is 1/3<n<1/2 by curve fitting,which indicates that the growth of IMC at solder joint interface is controlled by both grain boundary diffusion and body diffusion during the soldering process,but the growth index n of the Cu/Sn-TiO₂/Cu solder joint interface IMC is smaller than that of the Cu/Sn/Cu solder joint,it indicates that nano-TiO₂ particles have an inhibitory effect on the growth of IMC at the solder joint interface,this is because the nano-TiO₂ particles are adsorbed on the surface of the IMC grains during the soldering process,which reduces the Gibbs free energy of the surface of the IMC grains,moreover,the nano-TiO₂ particles are adsorbed between the IMC grains,which hinders the grain boundary diffusion flux of the Cu atoms,thereby inhibiting the growth of the IMC.