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

Background: 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. Methods: 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 degrees 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. Significant Findings: 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.