Power QFN device bump ball lift issue study

Abstract

Power QFN device had CSR(Current Sense Ratio-Mirror cell Mosfet current to Main mosfet current Ratio. Mirror cell current is proportional to main mosfet, used for monitor main mosfet current) issue on TC500 or application. Failure analysis verified that it was caused by bump ball lift issue. XPS (X-ray Photoelectron Spectroscopy) Analysis verified the pad contamination caused the bump ball lift issue. After further analysis, the contamination was from solder paste out-gassing during Die bonding process. Finally, the contamination was reduced by die bond oven improvement and forming gas/exhaust parameters optimization and passed all reliability test.