Electroless deposition of Nickel-Palladium-Gold for high reliability and power application: Cost and performance progress

Abstract

Electroless deposited metal stacks of Nickel-Palladium-Gold (ENEPIG) or Nickel-Palladium (ENEP) are frequently used in modern advanced packaging technologies. Main application for this metal stack is the under bump or pad metallization (fig1.). The surface of this specific metal stack allows for reliable wire bonding including thick Copper wire bonding as well as for soldering on the die. This technology has been successfully adopted by automobile suppliers as well as power chip manufacturers. Recently it has been introduced for housing redistribution layers of Copper (see fig. 2). In this paper we are presenting the latest improvements over the entire ENEP(IG) process leading to a substantial Cost of Ownership (CoO) reduction. Improvements span chemistry control, manufacturing process, the plating process itself and tool layout. We are discussing how this has been achieved and how strong this is influencing the cost for the overall process steps. Different tool concepts for the ENEPIG process will be discussed, with a focus on benefits of specific spray pre-treatment as this is a key enabler for fine line applications.