Effect of Ni barrier layer thickness on IMCs evolution in Ф5μm Cu/Ni/Sn pillar bumps

Abstract

Uniform 5μm diameter Cu/Ni/Sn micro-bump array has been fabricated by multilayer electrodeposition, and the effect of Ni barrier thickness (0μm, 0.42μm, 0.67μm, 1.12μm) on microstructure evolution and growth behaviors of Intermetallic Compounds (IMCs) have been studied through SEM and EDS. It has been found that the thicker the Ni layer, the slower the rate of IMCs growth. The diffusion coefficient of Cu/Ni/Sn system with 0μm, 0.42μm, 1.12μm Ni is calculated to be 7.46×10−17m2s−1, 5.51×10−17m2s−1, and 1.71×10−17m2s−1 for total IMCs, respectively. In the Sn/0.42μm Ni/Cu system, (Cu,Ni) 6 Sn 5 is formed firstly. After the consumption of Ni layer, the growth behavior of Cu 6 Sn 5 and Cu 3 Sn is similar to that of the Sn/Cu system; In the Sn/1.12μm Ni/Cu system, 1.12μm Ni barrier layer can form Ni3Sn4 preventing Cu atoms from diffusing into Sn phase and there is almost no formation of (Cu,Ni) 6 Sn 5 .