Study On The Electromigration Behavior And Inhibition Mechanism Of SnBi Solder

With the development of miniaturization and multi-function of electronic products, the size of solder joint is decreasing and the density of current through the solder joint is increasing sharply. Significant electromigration in solder joint occurred and it has seriously affected the reliability of solder joint. Sn Bi solder has many advantages such as low-melting point, superior yield strength and comparable solder ability. However, the application of Sn Bi solder is limited by bulky Bi-rich precipitate which lead to crack propagation. It is important to investigate the electromigation in the Sn Bi solder. The influence of electromigration on microstructure, interfacial IMC and mechanical properties the Sn Bi solder miro-interconnection joint is studied. The Al2O3 and Ce particles were added into Sn Bi solder to study the effect on electromigation resistance of Sn Bi solder.When the electromigration is 240 h, cracks were occurred in cathode interfacial,and a coarse Bi-rich zone was formed. This is due to the diffusion of the Bi atom from anode to cathode, which make the void and crack formed near the cathode. When the conduction time is increased, the temperature is rising in the solder joint. This is leading to the many Bi atom accumulated near the anode and Bi-rich zone appeared.When the conduction time is more than 240 h, the increase rate of the IMC thickness is more and more quicker. The reason is that the crack is occurred in the cathode, which leading to the current density and atom migration rate is increased sharply.The electromigration resistance of Sn Bi solder is improved by adding Al2O3 particles. The microstructure of Sn Bi solder joint is uniform and fine. The change on the thickness of IMC is little. In addition, There is no Bi-rich phase and crack formed.This is probably that the path of Bi atom is blocked by the Al2O3 particles and the migration rate is reduced.The Microstructure and properties of Sn Bi-0.5%Ce are improved by adding Ce particle. The joint occurred fracture when when conduction time is 330 h. The thickness of IMC is changed with the when conduction time increased.The morphology of IMC change from scallop of shell to lamellar, and some bar like IMC grow into solder. The IMC thickness little change compared to Sn Bi solder joint.When the conduction time of Sn58 Bi solder joint is increasing, the microhardness of the area near cathode interface is increasing, and the microhardness of the area near anode interface is decreasing. This is because a largenumber of Bi atoms transfer from cathode to anode causes empty and Sn-rich phase and thereby leading to hardness decrease. Meanwhile, massive Sn-rich phase formed near the anode is hard and brittle phases which ultimately results in anode hardness increasing.The UTS of Sn Bi, Sn Bi-0.5% Al2O3 and Sn Bi-0.5%Ce solders are 12 MPa,33MPa and 19 MPa when conduction time is 200 h, respectively. The UTS and elongation of Sn Bi-0.5% Al2O3 and Sn Bi-0.5% Ce are improved by adding the particles. In addition, Sn Bi solder exhibited cleavage appearance in the fracture surface. However, the microscopic fracture of Sn Bi-0.5% Al2O3 and Sn Bi-0.5%Ce solders is composed of tearing-mark and exhibited the better ductility.The electromigration resistance of Sn Bi solder is improved by adding Al2O3 and Ce particles, and the resistance of Sn Bi-0.5% Al2O3 solder is more better when compared to that of Sn Bi-0.5%Ce solder.