Optimization of Micropillars Electroplating Bonding Processes and Additives

Abstract

With the increasing interconnect density of electronic components, copper–copper direct bonding technology has garnered increasing attention from researchers. The electroplating bonding method is an efficient copper pillar interconnection technique that can be implemented at room temperature and atmospheric pressure. comsol simulation results show that under convective conditions, the plating layer primarily deposits on the convection exit side of the copper plate. Under weak convection and low current density, the plating exhibits deposition characteristics that conform to the substrate surface. As convection intensity increases, preferential deposition begins to occur, although the overall deposition rate decreases. At this point, when the current density is increased, the deposition pattern predominantly shows preferential deposition; however, excessively high current density can lead to copper deposition in nonbonding areas. Orthogonal experimental results indicate that, within the accelerator bis(3-sulfopropyl) disulfide (SPS)–inhibitor polyethylene glycol (PEG)–leveling agent Jenner Green B (JGB)–chloride ion (Cl−) system, the influence of the four additives on bonding strength follows this order: JGB > Cl− > SPS > PEG. The optimal formulation derived from the orthogonal experiments is SPS 2 ppm, PEG (8000) 150 ppm, JGB 5 ppm, and Cl− 30 ppm, which results in a shear strength of 123.2 MPa. These findings suggest that high-strength copper pillar interconnections can be achieved by adjusting physical parameters such as the electric field, flow field, and additive concentrations.