Terminal Reaction Behaviors in Micro Bumps: Comparison of Ti and Cr Adhesion Layers

In this research, the terminal reaction of the Ti adhesion layer with Sn/Cu IMCs is discussed through thermal aging, which Ti is fully attached to Sn/Cu IMCs. The samples are first fabricated by electroplating Cu and Sn sequentially on the Ti adhesion layer to form micro bumps and then underwent thermal aging at 200 °C to observe the evolution between layers. After thermal aging from 0 h to 72 h, the micro bumps all transform into intermetallic structures (IMCs), yet they all attach well with the Ti adhesion layer. Moreover, the difference in diffusion rate between Cu and Sn will lead to some voids during aging. These voids will progress to the center of the bump through the depletion of the Cu layer, but they do not affect the attachment between the IMCs and the adhesion layer. To conclude, using Ti as an adhesion layer shows better adhesive behavior with IMCs than using Cr.