Crystallographic Orientation Effect on Electromigration in Ni-Sn Microbump

This article addresses the reliability challenges regarding electromigration in developing three-dimensional integrated circuits (3D-ICs). The line-type sandwich structure of Ni/Sn3.5Ag(15 μm)/Ni was used to simulate microbumps to examine the reliability of electromigration in 3D-IC technology. The solder strip of Ni/Sn3.5Ag(15 μm)/Ni was stressed with a current density of 1.0 × 10⁴ A/cm² at 150°C. The current stressing enhanced the reaction between the solder and Ni to form Ni₃Sn₄, which occupied the entire joint and transformed into a Ni/Ni₃Sn₄/Ni structure when the solder was completely consumed. Electron backscatter diffraction was used to analyze the crystallographic characteristics of Sn and Ni₃Sn₄ as related to the electromigration effect. The results indicated that the crystallographic orientation of Sn plays a significant role in the Ni/Sn3.5Ag/Ni, whereas the orientation of Ni₃Sn₄ is the dominant factor of diffusion behavior in the Ni/Ni₃Sn₄/Ni.