Low temperature bonding process of high density Cu bumps Array

High density Cu bump array is widely used in advanced packaging technology like Flip Chip and Through Silicone Via technology. We combined Al/Ni multilayer as local heating source and Sn-Ni transient liquid system to study the low temperature Cu bumps bonding. After alignment, the Cu bumps were bonded at one time by rapid heating high to 4K/s and cooled at 2K/s. In Sn0.25Ni group, the interface between Sn and Ni layers disappeared replaced by a large area of network structure of Ni3Sn4. With the Sn/Ni thickness ratio increasing, the diffusion and reaction between Sn and Ni was slowed, and left a very thin layer with the clear stratification appearing again. The bonding shear strength of the four groups were all higher than 100MPa and increased from 107.8MPa to 162.5MPa, attributed to a much denser bonding interface with few defects, and the enhanced staggered effect between increased Ni3Sn4 and residual Sn (or Ni). When the Sn/Ni thickness ratio of increases to Sn1.0Ni, more Sn remained and the interface between Sn and IMC became fragile, leading to the reducing of the shear strength.