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INFLUENCE OF SOLDER JOINT CONFIGURATION ON ELECTROMIGRATION BEHAVIOR AND MICROSTRUCTURAL EVOLUTION OF Cu/Sn-58Bi/Cu MICROSCALE JOINTS |
YUE Wu, QIN Hongbo, ZHOU Minbo, MA Xiao, ZHANG Xinping |
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 |
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Cite this article:
YUE Wu, QIN Hongbo, ZHOU Minbo, MA Xiao, ZHANG Xinping. INFLUENCE OF SOLDER JOINT CONFIGURATION ON ELECTROMIGRATION BEHAVIOR AND MICROSTRUCTURAL EVOLUTION OF Cu/Sn-58Bi/Cu MICROSCALE JOINTS. Acta Metall Sin, 2012, 48(6): 678-686.
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Abstract With the increasing miniaturization of electronic devices and systems, the pitch size and dimension of solder interconnects become smaller, accordingly the current density in solder interconnects gets higher and this results in severe electromigration (EM) effect that may deteriorate the performance of solder interconnects. The studies on flip chip interconnects have shown that the configurable change of solder joints can significantly affect the electromigration behavior. In this study, the microscale Cu/Sn-58Bi/Cu joints with different geometrical configurations, i.e., right angle-type and line-type solder joints, were designed and the electromigration behavior of joints under a direct current of a density 1.5×104 A/cm2 were investigated by SEM observation, microanalysis based on focused ion beam (FIB) and finite element simulation. The focus was placed on clarifying the influence of the solder joint configuration on the electromigration mechanism of the joint in terms of atomic diffusion distance, microregional resistance change and the change of phases in anode and cathode. Results showed that for both types of solder joints after current stressing for 112 and 224 h, Bi migrated to the anode side and congregated there, while Sn tended to enrich near the cathode side; in particular for the right angle-type solder joint the microscale hillocks and microcracks occurred at the anode side caused by the compressive stress which was attributed to Bi congregation and the consequent volume expansion of the phase, while the microscale concave valleys and microcracks appeared at the cathode side caused by the tensile stress, and it was worth noticing that the phenomenon above happened non-uniformly along the interface in right angle-type joint. The microanalysis results revealed that the diffusion velocity of Bi atoms was faster than that of Sn under current stressing in the solder joint. Furthermore, observations and finite element simulation results showed that for the solder joint with an asymmetrical configuration like the right angle-type solder joint the electrons flowed toward the bottom corner of the joint where the resistance was smaller and thus the current crowding effect occurred, and this was the primary factor for causing the severe electromigration.
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Received: 27 February 2012
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