CMOS COMPATIBLE ELECTROLESS PLATING PROCESS FOR UNDER BUMP METALLIZATION
Authors: Shigeo Hashimoto and Don Gudeczauskas, et al. Company: C. Uyemura & Co., Ltd. and Uyemura International Corporation Date Published: 10/13/2008
IWLPC (Wafer-Level Packaging)
Abstract: A CMOS compatible electroless plating process for Under Bump Metallization was compared with a conventional non-CMOS compatible process. The basic plating process consisted of depositing ENEPIG (Electroless Nickel – Electroless Palladium – Immersion Gold) onto the Al-Cu wafer pads. Testing was performed on the deposits including GD-OES (Glow Discharge Optical Emission Spectroscopy), bump shear testing for adhesion, ball pull testing for solder joint reliability, and wire bond testing. Results showed that mobile ions present in the pre-treatment process left no detectable mobile ions (Na, K) on the deposit structure and presumably will not affect chip performance. Mobile ions present in the electroless nickel solution, however, did result in mobile ions being present at the Al-Ni interface which may negatively affect performance. Little to no mobile ions were deposited from the electroless palladium step. The non-CMOS compatible immersion gold process did result in mobile ions being present in the gold deposit.