发明授权
- 专利标题: Method for forming reflowed solder ball with low melting point metal cap
- 专利标题(中): 用低熔点金属帽形成回流焊球的方法
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申请号: US08476475申请日: 1995-06-07
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公开(公告)号: US06344234B1公开(公告)日: 2002-02-05
- 发明人: Hormazdyar Minocher Dalal , Alexis Bitaillou , Kenneth Michael Fallon , Gene Joseph Gaudenzi , Kenneth Robert Herman , Frederic Pierre , Georges Robert
- 申请人: Hormazdyar Minocher Dalal , Alexis Bitaillou , Kenneth Michael Fallon , Gene Joseph Gaudenzi , Kenneth Robert Herman , Frederic Pierre , Georges Robert
- 主分类号: B05D512
- IPC分类号: B05D512
摘要:
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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