Electro-Migration Failure Map for Snag/Cu(Ni) Pad Micro-Flip-Chip Solder Joint(2/3)

Nowadays, reliability issues are become more important for flip-chip package and 3D IC package due to the size shrinkage of the solder joint. We find that the dissolution of the Cu-pad is the major reason which makes the reliability issues become more important. According to our previous study, we realize that the electro-migration resistance of the solder joint can be improved by doping Ag into lead-free solders. In order to study the cathode Cu-pad dissolution under EM test in detail, we deign an experiment to study the Cu-pad dissolution without electro-migration. However, we find that the Cu-pad dissolution rate is faster in Sn(Ag) solder than in pure Sn solder. Thus, we consider that the details of the Cu-pad dissolution mechanism should be studied more carefully with the pitch size of solder bumps become smaller and smaller. And also the effect of Ag in the Sn(Ag) that affect the dissolution mechanism of Cu. According to the importance of Ni as a good diffusion barrier, we should also consider the dissolution mechanism of Ni into the solder. In this proposed three-years project, we will first study on the mechanism of Cu-pad dissolution into the small pitch size of bump. Also, study the Cu dissolution mechanism with different preferred-oriented Cu-pad. And the effect of different Ag content of lead-free solders on the Cu dissolution mechanism. In addition, we study how does the size shrinkage (different ratio of Cu-pad/solder volume: 1×10-6, 1×10-4, 1×10-2, and 1) affect the mechanism of Cu-pad dissolution. Finally, the EM effect on the Cu (or Ni) dissolved into different Ag-doped solders. The final goal is to build an EM failure map for the micro-flip-chip SnAg solder joints, which can be used to enhance the reliability of flip-chip solder joints.