Development of Electrolyte with Enhanced Corrosion Resistance for Sn Electroplating on Multi-Layer Ceramic Capacitors

Abstract

Capacitors not only store and release electricity but selectively conduct alternating current. Among the various types of capacitors, multi-layer ceramic capacitors (MLCCs) have been widely used in automotive, smartphone, and wearable devices because of their compact size and high capacitance capabilities. In this study, we have developed an electrolyte for tin electroplating on multi-layer ceramic capacitors (MLCCs) to address the barium leaching issue at the termination points of the MLCCs. This issue has been effectively mitigated by introducing NaHSO<sub>4</sub> into the conventional tin plating electrolyte as a corrosion inhibitor. This addition facilitates a rapid reaction between the dissolved barium ions and NaHSO<sub>4</sub>, resulting in the formation of a thin passivation layer on the surface of the MLCC. The BaSO<sub>4</sub> passivation layer effectively prohibits excessive leaching of barium ions from the glass in MLCCs, thereby maintaining chip insulation resistance and preventing crack formation. However, the chemical reaction of NaHSO<sub>4</sub> and the formation of the passivation layer can lead to the generation of tin hydroxide precipitates due to pH fluctuations. To address this issue, we increase the amount of complexing agent from 100 g/L to 130 g/L. This adjustment enhanced the ability of tin ions to form stronger complexes, thereby enabling stable electrodeposition on the termination of MLCC. Consequently, the final electrolyte for Sn electroplating (denoted as LW-3) simultaneously achieves corrosion resistance and practical working efficiency, resulting in a uniform 5.4 μmthick tin plating layer with outstanding solderability, and high temperature/humidity stability.