Size effect on shear performance of microscale ball grid array structure Cu/Sn-3.0Ag-0.5Cu/Cu solder joints under current stressing

Purpose The purpose of this study is to explore the size effect on shear mechanical behavior of microscale ball grid array (BGA) structure Cu/SAC305/Cu solder joints with different heights under current stressing, and to reveal the influence mechanism of current and solder joint’s height on shear performance and fracture behavior. Design/methodology/approach A dynamic mechanical analyzer was used in conjunction with a constant current power supply to conduct shear mechanical testing of solder joints under current stressing with current densities from 6.0 × 103 to 1.1 × 104 A/cm2. Meanwhile, temperature, current density, stress and strain distribution in solder joint are analyzed in combination with finite element simulation to further reveal the evolution mechanism of mechanical behavior of solder joint. Findings This study reveals that the shear size effect in solder joints originates from the weakened constraint effect of the intermetallic compound (IMC)/substrate interface on the solder matrix with increase of joint height. Furthermore, incorporating in situ current stressing demonstrates that greater joint height leads to greater heat accumulation at identical current densities, resulting in monotonic degradation of shear strength with greater joint height. Simultaneously, greater joint height intensifies current crowding and strain mismatch at the solder/IMC interface, promoting interfacial fracture. These findings are rigorously supported by decline-rate trends and a finite element (FE)-validated simulation mechanism chain (including stress triaxiality, temperature, current density and stress/strain fields), establishing quantitative thresholds for interfacial fracture initiation. Originality/value This study extends previous research on shear size effect of solder joints by incorporating in situ current stressing. The coupling influence of joint height and current stressing was revealed by a FE-validated mechanism chain, and relevant quantitative thresholds was established, providing critical data and theoretical support for evaluating the reliability of microscale BGA-structured solder joints under current stressing.