無電解ニッケルめっきによるアルミニウム電極上へのバンプ形成

抄録

Flip chip (FC) bonding and chip size packaging (CSP) have progressed along with the development of surface mounting manufacturing technology. Micro bumps must be formed to connect the circuits and electrodes on semiconductor chips. Aluminum alloy has generally been used for circuits or electrodes in semiconductors.
Electroplating and electroless plating have been used to form the metal bumps on aluminum electrodes. A zincate method has been adopted as a pretreatment step as part of the electroless plating process. However, aluminum is attacked by the high alkaline zincate bath. Therefore, this research investigated the use of direct nickel plating on aluminum and the formation of nickel bumps without the zincate method. This study involved application of direct nickel plating on the aluminum pads of the semiconductor chips. As a result, deposition behavior on the signal and the ground pads differd and uniform bumps were not formed. This phenomenon is thought to be due to the potential difference in the signal and the ground pads. Uniform bump formation on aluminum pads can be achieved by increasing the load factor and reducing the DO (Dissolved Oxygen) level in the electroless nickel bath. Nickel bumps with a uniform and smooth surface can be formed on the signal and the ground pads by the optimization of the reactivity of electroless plating. Furthermore, uniform gold plating on the nickel bumps has also been achieved.