Study of Cu wire bonding on NiPdAu pad of fine pitch low k C55nm technology for high temperature automotive application

Abstract

Cu wires are increasingly used instead of gold wire and gradually become a mainstream in micro-electronic package interconnection, especially in fine pitch and low k wafer technology. The advantages of Cu wire over gold wire are well known for its high thermal conductivity, great electrical property and low cost. For Cu wires on Automobile devices application, especially with wafer technology keep scaling down, pitch finer and dielectric (k) lower, it is hard to endure high temperature stress (4000TC and 4000HTB at 150°C). In the area of fine pitch wire bond reliability of an IC product, Au wire on Al pad is known to have ball bond failure after prolong thermal aging at elevated temperature, due to diffusion of Au during intermetallic phase transformation, resulted in excessive Al precipitation and Kirkendall void formation, and Cu wire on Al pad will cause excessive Al push-out and risk to damage under layer sensitive structures. This papers presents recent studies on NiPdAu pad with bare Cu wire and Pd Cu wire on BGA package for low k and fine pitch C55 device, also paralleling with Pd Cu wire on Al pad in the same device, the result show on OPM package, there are better wire bonding performance and reliability result and no pad metal push out. In this study, in order to achieve high temperature automotive reliability effect equivalent to 150 deg C for 4000hrs for NiPdAu pad and Al pad, wire bonded units were subjected to thermal aging at 225 deg C in nitrogen environment 26hrs for Cu wire which were calculated based on the respective diffusion rate.