Electroplating Characteristics of Eutectic Sn–Cu Ions for Micro-Solder Bump on a Si Chip
Abstract:The fabrication of fine bumps on a Si chip is an important issue due to the trend of smaller sized and multi-functioning electronics. In this study, a Sn–Cu near eutectic solder bump was fabricated by electroplating. A Si wafer was used as a substrate, while layers of the Under Bump Metallization (UBM) of Al/Cu/Ni/Au (400/300/400/20 nm in each) were coated onto the Si wafer by electron beam evaporation. The bumps on the UBM were plated by a direct current, and the bump size was 20×20×10 μm with a 50 μm pitch. Characteristics of the electroplated bumps were examined by XRD, EDS and EPMA. A polarization curve was established to find a potential range of electrodeposition of Sn–Cu. By plating with a reduction current density of 1 A/dm2 for 23 min, a near eutectic Sn–Cu bump was obtained. The bump height increased in current density, namely from 2.25 μm at 0.5 A/dm2 to 6.58 μm at 2 A/dm2 from 10 min of plating. In the electroplated state, a β-Sn and Sn–Cu intermetallic compound (IMC) coexisted in the bumps. Cu3Sn and Ni3Sn4 IMCs were discovered by XRD analysis along the interface between the bump and the UBM.
Document Type: Research Article
Publication date: April 1, 2012
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