Simulation of Effect of Current Stressing on Reliability of Solder Joints with Cu-Pillar Bumps

Authors: Y. Li, Q. S. Zhang, H. Z. Huang, B. Y. Wu

Abstract:

The mechanism behind the electromigration and thermomigration failure in flip-chip solder joints with Cu-pillar bumps was investigated in this paper through using finite element method. Hot spot and the current crowding occurrs in the upper corner of copper column instead of solders of the common solder ball. The simulation results show that the change in thermal gradient is noticeable, which might greatly affect the reliability of solder joints with Cu-pillar bumps under current stressing. When the average applied current density is increased from 1×104 A/cm2 to 3×104 A/cm2 in solders, the thermal gradient would increase from 74 K/cm to 901 K/cm at an ambient temperature of 25°C. The force from thermal gradient of 901 K/cm can nearly induce thermomigration by itself. With the increase in applied current, the thermal gradient is growing. It is proposed that thermomigration likely causes a serious reliability issue for Cu column based interconnects.

Keywords: Simulation, Cu-pillar bumps, Electromigration, Thermomigration.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1332506

References:

[1] J. H. Lau, Flip Chip Technology , New York: McGraw-Hill, 1995, pp. 28.
[2] J. W. Nah, J. O. Suh, and K. N. Tu, "Electromigration in flip chip solder joints having a thick Cu column bumpand a shallow solder interconnect," J. Appl. Phys., 2006, 100: 123513.
[3] C. Y. Liu, C. Chen, and K. N. Tu, "Electromigration in Sn-Pb solder strips as a function of alloy composition," J. Appl. Phys., 2000, 88: 5703.
[4] C. Chen, and S. W. Liang, "Electromigration issues in lead-free solder joints, J. Mater. Sci. - Mater Electron.," 2007, 18: 259-268.
[5] B. Y. Wu, Y. C. Chan, and H. W. Zhong, "Study of the thermal stress in a Pb-free half-bump solder jointunder current stressing," Appl. Phys. Lett., 2007, 90: 232112.
[6] S. H. Chiu, T. L. Shao, and C. Chen, "Infrared microscopy of hot spots induced by Joule heating in flip-chip SnAg solder joints under accelerated electromigration", Appl. Phys. Lett., 2006, 88: 022110.
[7] S.W. Liang, T. L. Shao, C. Chen, E. C. C. Yeh, and K. N. Tu, "Relieving current crowding effect in flip-chip solder joints during current stressing," J. Mater. Res., 2006, 21(1): 137-146.
[8] P. G. Shewmon, Diffusion in Solids, Warrendale, PA: TMS, 1989, Chap. 7.
[9] D. V. Ragone, Thermodynamics of Materials, New York: Wiley, 1995,Vol. 2, Chap. 8.
[10] F. Y. Ouyang, K. N. Tu, Y. S. Lai, and A. M. Gusak, "Effect of entropy production on microstructure change in eutectic SnPb flip chip soider joints by thermigration," Appl. Phys. Lett., 2006, 89: 221906 .
[11] Y. C. Hsu, T. L. Shao, C. J. Yang, and C. Chen, "Electromigration study in SnAg3.8 Cu0.7 solder joints on Ti/Cr-Cu/Cu under-bump metallization," J. Electron. Mater, 2003, 132: 1222.
[12] B. Y. Wu, and Y. C. Chan, "Electric current effect on microstructure of ball grid array solder joint," J. Alloys Compd. , 2005, 39: 237.