Lei Sun

Microstructures and properties of Sn58Bi, Sn35Bi0.3Ag, Sn35Bi1.0Ag solder and solder joints

Microstructures, interface reaction, melting characteristics, tensile property, thermal fatigue behavior and wettability of Sn58Bi, Sn35Bi0.3Ag and Sn35Bi1.0Ag solders were investigated. Only Sn phase and Bi phase like net-type distribute uniformly in the Sn58Bi matrix, Sn35Bi0.3Ag and Sn35Bi1.0Ag solder show the Ag3Sn particles in the Sn matrix around net-like Bi phase, at the solder/Cu solder joints, only Cu6Sn5 intermetallic compound was observed. The liquid phase line temperature of Sn35Bi0.3Ag and Sn35Bi1.0Ag is higher than that of SnBi solder. Sn35Bi1.0Ag solder joints show superiority in mechanical property and fatigue life, which can attribute to the strengthening effect of Ag3Sn particles. Moreover, the wettability of Sn35Bi1.0Ag solder was best of all, and the N2 atmosphere and RMA flux can enhance the wettability obviously, which can provide the reference support of the research of SnBi base solders.

Wettability of SnCuNi-xEu solders and mechanical properties of solder joints

Abstract Wettability balance method was used to investigate the wetting performance of SnCuNi-xEu on Cu substrate, and the mechanical properties and the fracture morphology were studied. The results indicated that the addition of Eu could enhance the properties of solder and solder joints, with the increase of Eu content, tendency of first increase and then decrease could be found in the wetting time, wetting force and the mechanical properties of SnCuNi-xEu, and the optimal content was 0.039%. For SnCuNi-0.039Eu solder joints, the optimum mechanical properties could be found, and the amplitude increased was 20%, with the observation of the fracture morphology, it was found that small dimples could be seen, the toughness fracture for SnCuNi and mixture fracture for SnCuNi-0.039Eu could be demonstrated. And thermal fatigue behavior of SnCuNi solder joints could be enhanced obviously with the 0.039%Eu addition.

Reliability of SnAgCu/SnAgCuCe solder joints with different heights for electronic packaging

Finite element simulation and experiments were used to analyze the reliability of SnAgCu/SnAgCuCe solder joints with different heights. With the increase of height of solder joints, the tensile strength of SnAgCu and SnAgCuCe solder joints drops significantly. With the same height, the tensile strength of SnAgCuCe solder joints show enhanced reliability comparing with that of SnAgCu solder joints. The heights of lead-free solder joints can markedly influence the failure modes of SnAgCu/SnAgCuCe solder joints, three models [intermetallic compound (IMC), solder/IMC, solder] can be demonstrated with the variation of height. Based on finite element methods, it is found the maximum stress concentrated location show a relationship with heights of solder joints, smaller height can keep the high reliability of solder joints.

Reliability of Lead-free Solder Joints in WLCSP Device with Finite Element Simulation and Taguchi Method

Abstract In this paper, we research the thermo-mechanical reliability of lead-free solder joints in WLCSP assembly subjected to an accelerated thermal cyclic loading based on finite element simulation and Taguchi method. Effects of different control factors, including solder materials, height of solder ball, chip thickness and substrates thickness on the reliability of the lead-free solder joints were examined and calculated. The corner solder joint is the most critical solder joints in the assembly, the top surface of the solder joint is the crack propagated location. The optimal design in the WLCSP assembly has the combination of the SnAgCuAl, height of solder ball at 0.25 mm, chip thickness at 0.6 mm, substrate thickness at 1.0 mm. Moreover, the solder materials is the most important factor among the control factors in the WLCSP assembly.

Wettability optimization analysis of lead-free solders with Taguchi method

Abstract In this paper, the wettability of lead-free solders on substrates with fluxes was studied based on reflow process and Taguchi method. Effects of different control factors, including solder materials, fluxes, substrate materials and atmosphere on the wettability of the lead-free solder joints were examined and calculated. Moreover, the effect of rare earth Eu on the wetting of SnAgCu solder was investigated, the effect mechanism was analyzed too. The wettability optimal design in the lead-free solders system has the combination of the SnAgCu-0.04Eu solder, RMA flux, Au/Ni/Cu substrate, and vacuum atmosphere. Moreover, the flux is the most important factor among the control factors in the wettability system.

Dorn Creep Model and Finite Element Simulation of SnAgCu-CNT Solder Joints in FCBGA Device

Abstract With the addition CNTs, the properties of SnAgCu solders and solder joints can be improved remarkably. In this paper, based on the creep testing, the Dorn creep model was used to represent the creep behavior of SnAgCuCNT solder, and the parameters were determined with the fitting analysis. Moreover, the Dorn creep model of SnAgCu and SnAgCuCNT was incorporated into finite element code for calculating the creep strain response of solder joints in FCBGA (Flip Chip Ball Grid Array) device during thermal cycle loading. The results indicated that the CNTs can enhance the creep resistance of SnAgCu solder, which demonstrates the SnAgCuCNT solders can replace the SnAgCu solder in electronic industry for highreliability requirement.

Reliability of Pb-free solder joints in FCBGA using finite element simulation and Taguchi method

Thermo-mechanical reliability of containing Pb and Pb-free solder joints in FCBGA device subjected to an accelerated thermal cyclic loading was investigated based on finite element simulation and Taguchi method. Effects of different control factors on the reliability of the lead-free solder joints were anlyzed and calculated. The corner solder joint is the most critical solder joints in the ball array, the top surface of the solder joint is the crack propagated location. The optimal combination in FCBGA assembly show obvious enhancement effect on fatigue life of solder joints. Moreover, the solder material is the most important factor among the control factors in the FCBGA device.