Invention Grant
- Patent Title: Method for forming reflowed solder ball with low melting point metal cap
- Patent Title (中): 用低熔点金属帽形成回流焊球的方法
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Application No.: US08476475Application Date: 1995-06-07
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Publication No.: US06344234B1Publication Date: 2002-02-05
- Inventor: Hormazdyar Minocher Dalal , Alexis Bitaillou , Kenneth Michael Fallon , Gene Joseph Gaudenzi , Kenneth Robert Herman , Frederic Pierre , Georges Robert
- Applicant: Hormazdyar Minocher Dalal , Alexis Bitaillou , Kenneth Michael Fallon , Gene Joseph Gaudenzi , Kenneth Robert Herman , Frederic Pierre , Georges Robert
- Main IPC: B05D512
- IPC: B05D512

Abstract:
A method and structure for a solder interconnection, using solder balls for making a low temperature chip attachment directly to any of the higher levels of packaging substrate is disclosed. After a solder ball has been formed using standard methods it is reflowed to give the solder ball a smooth surface. A layer of low melting point metal, such as, bismuth, indium or tin, preferably, pure tin, is deposited on the top of the solder balls. This structure results in localizing of the eutectic alloy, formed upon subsequent low temperature joining cycle, to the top of the high melting solder ball even after multiple low temperature reflow cycles. This method does not need tinning of the substrate to which the chip is to be joined, which makes this method economical. It has also been noticed that whenever temperature is raised slightly above the eutectic temperature, the structure always forms a liquid fillet around the joint with copper wires. This liquid fillet formation results in substantial thermal fatigue life improvement for reduced stress at interface; and secondly, provides an easy means to remove chip for the purpose of chip burn-in, replacement or field repairs.
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