Synergistic effects of additives on impurity residues in high-speed copper electrodeposition and voiding propensity in solder joints

•Co-deposition of organic additives results in impurity residues in electroplated Cu.•Voids form at interface between solder and impurity-doped Cu during annealing.•Competitive adsorption between suppressor and accelerator molecules reduces impurities and voids.•Formulation of organic additives dominates competitive adsorption effect.•Effective formulation of organic additives varies with plating current density. Copper electroplating is an important technology used to construct the interconnects/conductors in microelectronic industry. Functional additives such as suppressor and accelerator is crucial to formulate the plating solution. Co-deposition of additive molecules with reduced Cu atoms inevitably occurs, resulting in the impurity residues in the Cu deposits. When the Cu deposit joins with Sn-based alloy to form solder joints, the impurity residues deteriorate the joints mechanically due to void formation. In this study, chloride ion (Cl−), polyethylene glycol (PEG), and bis,(3-sulfopropyl)disulfide (SPS) are used as the additives to fabricate the Cu deposits. The solder joints constructed by joining solder alloy to electroplated Cu were thermally annealed at 200 °C to investigate the voiding propensity at the joint interface. Plating current density is increased from 4 A/dm2 to 16 A/dm2 to explore the impurity effects in high-speed Cu electrodeposition. The results show that the interplay between suppressor (PEG+Cl−) and accelerator (SPS) produces a synergy of competitive adsorption that can potentially suppress the impurity residues and void formation. Nonetheless, the synergy of competitive adsorption is current density dependent. For high-speed Cu electroplating (16 A/dm2), the suppression of impurity residues and void formation needs careful reformulation of additives to elaborate effective synergy. [Display omitted]