International Business Machines Corporation

Kenneth Robert Herman

Hormazdyar M Dalal

Kenneth Michael Fallon

Gene J Gaudenzi

Georges Henri Robert

Frederic Robert Pierre

Alexis Bitaillou

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.

Method for forming reflowed solder ball with low melting point metal cap

Reflowed solder ball with low melting point metal cap

Growing community of inventors

Poughkeepsie, NY, United States of America

Kenneth Robert Herman