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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.

The PQFN device revealed down bond lift and delamination issues. Based on AES (Auger Electron Spectroscopy), XPS (X-ray Photoelectron Spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy) analysis it was possible to verify that a down bond contamination caused the failure. Cross sections of down bond wire for the failed unit showed a broken heel on the down bond. Furthermore, cracking between molding compound and lead frame was found. It was proven that the delamination caused the down bond lift and the broken heel. FEA (Finite Element Analysis) revealed that the delamination can lead to shear stress increase at the down bond heel.

Power QFN Tiger device failed the down bond open on TC500 or application. Failure analysis verified that it was caused by down bond delamination. Finite Element Analysis modeling was established to analyze the Tiger down bond stress and find out a new position with relative less stress impact as down bond end point. Meanwhile, new bonding model with security loop was applied to down bond to improve the bond-ability and passed all reliability test.

With the popularity of the mobile and handset electronic product, there is a stringent requirement on IC package size, weight and thermal/ mechanical integrity. To be smaller, lighter and faster, traditional IC packaging is undergoing an evolution to achieve further miniaturization. Less than 1.0mm CSP BGA with die to package ratio larger than 0.78 was developed to provide such a miniaturization solution to mobile electronic product manufacturer. A series of packaging challenges were encountered when trying to scale down the traditional BGA packages, DAF (die attach film) heating induced strip warpage and post mold cure strip warpage are two key issues which have great impact on package manufacturability. Frequent substrate alignment alarm during die bonding, missing ball during ball attach process and insufficient sucking vacuum during saw singulation are three key showstoppers in qualifying this package for mass production. Thermal mechanical simulation was conducted to analyze the CTE/modulus mismatch induced mold strip warpage, Substrate was re-designed and new compound were evaluated based on the improvement direction given through simulation analysis. Full auto assembly operation was achieved through process/ material improvement for this low profile CSP BGA package.