Novel low-temperature micro-insert bonding technology for 3D package

In this paper, a novel low-temperature micro-insert bonding technology for 3D package has been reported. Nickel microcone arrays (MCA) fabricated on the bonding pad was used as the under bump metallization (UBM). The bonding temperature is below the melting point of the solder. At certain temperature and pressure, the MCA inserted into the lead-free Sn-Ag-Cu solder bumps to achieve a good adhesion. The bonding of the joint is realized by the mechanical interlocking and the diffusion between the MCA and the solder. The nickel microcone arrays were prepared by directional electrodeposition (DEP) method on the Cu substrates in the solution with inorganic additives. And then hundreds of bumps were bonded on the substrates at different temperatures (150deg-210degC) and different bonding pressure (450, 560, 750 gf/p). Subsequently, ball shear testings were performed to evaluate the mechanical reliability and failure mode of the solder joints. After the shear testings, the microstructures of the fracture interfaces were investigated by SEM.