3D Finite Element Simulation For Solder Joint Electromigration In IC Chip

Electromigration of semiconductor integrated circuits is an important aspect of IC reliability. With the rapid development of large-scale integrated circuits, electromigration becomes one of the major failure mechanisms in semiconductor industry. In order to improve the reliability of large-scale integrated circuits, the mechanism of the electromigration degradation of life must be further investigated for improving IC interconnect and packaging reliability. Study of electromigration in lead-free solder joint is the new direction of the solder joint reliability in a wafer-level flip chip package, it becomes the particularly interesting problem in the interconnects and bumping structure of a IC packaging. Since electromigration in solder joint and its related interconnects involves complicated multiple-physics problems, fully investigation of it in both theory and experiment is very necessary. This paper studies the three dimensional finite element algorithms for electromigration in solder joint and related interconnects of an IC chip, which includes electromigration void formation and time to failure mechanism.First, summary and discussion of the basic theory of electromigration theory is presented. Electromigration consists of three parts: electronic migration, thermomigration and stress migration. The expressions of these three parts and the corresponding time-depending divergences are investigated. The relationship of electromigration time-to-failure and electromigration divergence as well as the related solder materials' physical parameters is studied. Second, based on the finite element code ANSYS sub-model technology, the electromigration coupled field analysis and algorithm are studied. The direct and in-direct coupling method for electromigration is developed with ANSYS APDL procedures. This paper also develops the local reconstruction algorithm for stress migration and its divergence. The electromigration induced void generation algorithm and time to failure life prediction methodology are fully developed.Finally, as a application of above electromigration studies, a CSP (Chip Scale Package) solder joint and its interconnect structure are modeled and simulated with different electromigration parameters. The simulation results have showed that the methodology and algorithm for electromigration studied in this paper are reliable and effective. The simulation results agree with the experimental results^[52] of K.N. Tu in UC LA, USA.