Barrier properties of thin Au/Ni–P under bump metallization for Sn–3.5Ag solder
Date of Issue2004
School of Materials Science and Engineering
Electroless Ni–P with a thin layer of immersion gold has been considered as a promising under bump metallization (UBM) for low-cost flip–chip technology. However, the presence of P in electroless Ni–P causes complicated interfacial reactions, which affect the reliability of solder joint. In this work, barrier properties of thin Au/Ni–P UBM between Cu substrate and Sn–3.5Ag solder were investigated during annealing at 160, 180, and 200 °C in terms of IMC formation. Multilayer Sn–3.5Ag/Au/Ni–P/Cu sample was prepared by electroless chemical plating and solder reflow for the investigation. Annealing results showed that electroless Ni–P acts as a good barrier for Sn diffusion at 160 and 180 °C. However, it fails to protect the Cu substrate from reacting with Sn at 200 °C. The reason is that the electroless Ni–P layer starts converting into a ternary Ni–Sn–P layer at 200 °C. Complete conversion of the Ni–P layer into Ni–Sn–P, results in the formation of two Cu–Sn intermetallics, Cu6Sn5 and Cu3Sn, at the Ni–Sn–P/Cu interface and the formation of (NixCu1−x)6Sn5 intermetallic at the Ni3Sn4/Ni–Sn–P interface.
DRNTU::Engineering::Materials::Microelectronics and semiconductor materials
Surface and coatings technology
© 2004 Elsevier B.V. This is the author created version of a work that has been peer reviewed and accepted for publication by Surface and Coatings Technology, Elsevier B.V. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1016/j.surfcoat.2004.10.085 ].