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Lead Free Micro-Ball Bumping for Flip Chip and Wafer Level Packaging at Nippon Steel
Keywords: Microball, Flip Chip , Bumping
The Micro-ball Wafer Bumping Technology had been originally developed that could be used for high-density LSI assembly, specifically for flip chip interconnection and wafer level packages. This method using lead free micro-balls of the size 150 um in diameter or less has been brought into practice to fabricate the wafer level packages for the various mobile electronic devices. The Micro-ball bumping method has the advantages in adjusting the optimum material combinations of joints: almost all types of solder materials could be used to form bumps, when considering the combination with the pad materials of chips or boards for the long term reliability. The bump interconnection with various lead free materials of Sn-3.5Ag, Sn-3.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu etc. were evaluated for the drop shock and thermal cycle reliabilty. The joints with Sn-1.2Ag-0.5Cu containing a small amount of Ni(LF35) exhibited outstanding high drop shock reliability in particular. In this paper will be also described the productivity and the bumping yield of the micro-ball bumping method.
Kohei Tatsumi, General Manager
Nippon Steel Corporation Advanced Technology Research Lab.
Futtsu-City, Chiba 293-8511,

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