Preparation Of Sn-based Composite Bumps By Electroplating And Reliability Study Of Hourglass Type Interconnecting Joints

With the development of miniaturization and high integration of electronic products,the hourglass-type solder joint interconnection technology was attracting great interest due to its advantages of greatly increasing the number of I/O ports by shortening the size and pitch of solder joints and improving the electromigration performance.However,due to the unique geometry and the excessive growth of the interface intermetallic compound of the hourglass solder joint,the mechanical properties of the solder joint were poor and a serious reliability problem easily occured.In order to adapt to the trend of miniaturization of electronic products,the excellent reliability hourglass-type solder joint using new preparation methods and materials was necessery.In this paper,the hourglass-type Sn-Ag₃Sn nanoparticles and Sn-Ag composite solder joints were fabricated by composite electroplating method and controlling the thickness of coating.The effects of Ag₃Sn nanoparticles and Ag addition on the melting properties and wettability of the composite coatings were investigated.During the test of thermal aging process at 150?and the high-low temperature cycling at-45?-150?,the effects of Ag₃Sn nanoparticles and Ag addition on the growth of the intermetallic compounds and the shear strength of the composite solder joints were investigated.Besides,the influence of the shape of joint on the growth and shear strength of the intermetallic compounds in the different thermal service conditions were also discussed.The results showed that the addition of Ag₃Sn nanoparticles and Ag can improve the surface morphology of composite coating,decrease the melting temperature and improve the wettability of the solder.When 0.4⁰.8 wt.%Ag₃Sn nanoparticles were added,the melting temperature of the solder decreased obviously.With the increase of the Ag content,the melting temperature of the solder decreased and the wetting properties of the solder increased.The reduction effect of the melting temperature with the addition of Ag₃Sn nanoparticles was better than the addition of the Ag element,while the wetting performance with the addition of Ag elements was better than the addition of Ag₃Sn nanoparticles.During the thermal aging process at 150?,the appropriate addition of Ag₃Sn nanoparticles can suppressed the growth of intermetallic compound layer of the hourglass-type solder joint,and improved the shear strength of the solder joint.When the amount of Ag₃Sn nanoparticles is 0.8 wt.%,the thinkness and the growth rate constant of the intermetallic compound were the smallest,and the shear strength was the biggest,which had good aging reliability.The effect of Ag₃Sn nanoparticles on the growth of intermetallic compounds was investigated by adsorption theory.The thickness and growth rate of the interface intermetallic compound increased with the increase of Ag content.The thickness of the intermetallic compound of the Ag₃Sn composite solder joint was smaller than the Ag composite solder joint.The deterioration of the mechanical properties of the solder joint caused by the excessive growth of the brittle phase was weakened.Thus,the shear strength of the Ag₃Sn composite solder joint was bigger than the Ag composite solder joint.During the high-low temperature cycling,the intermetallic compound thickness increased with the increase of the number of cycles.With the increase of Ag₃Sn nanoparticles,the thickness and growth rate of the interface intermetallic compounds decreased first and then increased,and the shear strength of solder joints increased and then decreased.The thickness and growth rate of the interface intermetallic compound and the shear strength of the joint increased with the addition of the Ag content.When the amount of Ag₃Sn nanoparticles was 0.8 wt.%,the thickness of the interface intermetallic compound was the lowest,and the shear strength of the interface was the highest,which had good reliability of high and low temperature cycling.The results of the properties of different shape of solder joints showed that the shape of joint has little effect on the growth of interfacial IMC layer,and the shear strength of barrel-type joint was larger than that of hourglass-type joint.But the addition of 0.8 wt.%Ag₃Sn nanoparticles could greatly improve the reliability of hourglass-type solder joints,and had higher thermal reliability than barrel-type Sn solder joint.