Research Of Magnetic Field Effects On Microstructures And Mechanical Properties Of Lead-free Solder Joints

Electronic products will be affected by many factors when they work in the multi-coupling conditions. With applications continue to expand, the magnetic field has become one of the service environment factors. Magnetic field mainly comes from two aspects: the applied magnetic field and electronic products own magnetic field generated by electromagnetic induction. Many studies of the solder joints failure under the conditions of electric, force and thermal conditions have been reported, while the effect of magnetic field is few reported. Under magnetic field, the microstructures of solder joints are changed, which affects solder joints reliability and reduce life time of electronic devices. Thus, it is necessary to study the impact of magnetic field or magnetic field and other conditions on the microstructure of the solder joints.This paper researched low silver lead-free Sn-0.3Ag-0.7Cu solder and 1wt.% Fe and 0.6wt.% Ni doped composite solder heated from 293 k to 573 K with 10k/min of heating rate and then cooled to 293 k with50k/min cooling rate in the single magnetic field condition, comparing to non-magnetific condition. Scanning electron microscopy was used to observe the morphology, size and distribution of the intermetallic compound, and the average thickness of IMC layer was calculated. The grain orientation of Sn was observed by EBSD. In addition,the experimental platform was built to simulate the magnetoelectric coupling environment. As the base plate, the copper was filled with Sn-0.3Ag-0.7Cu solder to form 1mm×1mm solder joint. While applying a constant current of 20 A, the current density would be controlled at 0.2×104A/cm2.Experimenttime was 2days, 5days and 10 days, As a contrast experiment, another group had no magnetic field. Paperless recorder was used to measure the voltage at both ends of the solder joints, by means of Ohm's law calculating solder joint resistance. The shear strength of the solder joint was calculated by the tensile testing machine.The results show that the IMC layers of the solder joint were affected by the magnetic field, and the shape of the solder joint was changed from scallop shape into needle shape, with single magnetic field condition. The average thickness of IMC layer was changed. Along the magnetic field lines direction, the IMC layer became thicker and against the magnetic field lines direction, the IMC layer became thinner. The growth of the grain orientation of the solder matrix ? –Sn was affected to grow in the direction of the magnetic field. Adding Fe powder and Ni powder, magnetic field made intermetallic compounds more easily nucleate and more uniform distribution. With the magnetoelectric coupling condition, electromigration was obvious and the polarization was serious for the existence of the magnetic field. The microstructure of the solder joint increased and the conductivity decreased. Under magnetic field, the shear strength of the solder joint was reduced and the mechanical properties decreased. Under the condition of the magnetic field, the solder joints microstructures had new changes, which affected the reliability of the solder joints...