Electroplated Bonding of Copper Pillar Micro-Bumps Using an Accelerator–Suppressor System

With the continuous advancement of advanced packaging technologies and the growing interconnection density, Cu-Cu bonding has become one of the key directions for future development. As a novel interconnection technology, electroplating bonding enables Cu-Cu interconnection under ambient temperature and pressure, offering significant advantages such as avoiding the formation of intermetallic compounds and eliminating thermal stress. In response to this, this study proposes a new electroplating bonding process for the interconnection of copper pillar micro-bump arrays. The research primarily focuses on the accelerator-suppressor system, where the virgin make-up solution (VMS) is an acidic copper sulfate system, sodium 3,3′-dithiodipropane sulfonate (SPS) is selected as the accelerator, and polyethylene glycol (PEG6000 and PEG10000) of different molecular weights is used as the suppressor. Subsequently, a dual-bump unit model is utilized for finite element simulation of electroplating growth under the accelerator-suppressor system. Finally, electroplating bonding experiments are conducted, and the results show that in both the VMS-SPS-PEG6000 and VMS-SPS-PEG10000 systems, the deposition mode of the electroplated layer is preferential inside-out deposition, which is consistent with the finite element simulation results. Furthermore, the electroplated layers exhibit a deposition profile that is thicker at the sides and thinner in the center. In addition, increasing the current or convective flow accelerates the growth of the electroplated layer, while changes in PEG molecular weight do not affect the growth mode of the electroplated layer.