Fine pitch Cu wire bonding on thin pad metallization

Abstract

Lan Seng Heng, Loh Lee Jeng, Dennis C.Vborde Cars em Technology Center (CTC) Carsem(M) Sdn. Bhd.Cu wire bonding technology has been introduced in semiconductor manufacturing as early as 1980' s. Several studies were conducted to resolve the issues and challenges it poses during wire bonding process. Currently, Cu wire interconnect is gaining momentum towards mass adoption from semiconductor manufacturers as the industry has realized its cost benefits as compared to Au wire interconnect. This technology has now improved and matured on low I/O and power devices. With this significant turnaround, Cu wire interconnect is no longer foreign even to devices with fine pitch wire bonding application.This paper discusses the issues and challenges encountered during the development and implementation phases of Cu wire bonding on a high pin count MLP device using high density lead frame with fine pitch application and thin aluminum pad top metallization thickness. It covers the optimization done to eliminate the pad crack damage after crater test and pull test, and the investigations of forming gas settings to eliminate the oxidation of Cu wire. This paper also tackles the challenges and improvement activity done during the pre-production stage. The statistical tools and techniques were used extensively during the wire bond process parameters characterization and optimization while other problem solving techniques were explored in order to understand the risk encountered and mitigate its effects. These efforts have yielded favorable results in addressing the problems encountered during the development and implementation phases. To date, Carsem Malaysia has successfully implemented Cu wire bonding with no problem under proven volume production.