Stable Gold Bump Solder Connections

Abstract

A metallic interconnect structure (200) for connecting a gold bump (205) and a copper pad (212), as used for example in semiconductor flip-chip assembly. A first region (207) of binary AuSn₂ intermetallic is adjacent to the gold bump. A region (208) of binary AuSn₄ intermetallic is adjacent to the first AuSn₂ region. Then, a region (209) of binary gold-tin solid solution is adjacent to the AuSn₄ region, and a second region (210) of binary AuSn₂ intermetallic is adjacent to the solid solution region. The second AuSn₂ region is adjacent to a nickel layer (213) (preferred thickness about 0.08 μm), which covers the copper pad. The nickel layer insures that the gold/tin intermetallics and solutions remain substantially free of copper and thus avoid ternary compounds, providing stabilized gold bump/solder connections.

Description

FIELD OF THE INVENTION[0001]The present invention is related in general to the field of metallurgical systems with application to electronic systems and semiconductor devices, and more specifically to stable gold bump solder connections.DESCRIPTION OF THE RELATED ART[0002]The growing popularity of flip-chip assembly in the fabrication process flow of silicon integrated circuit (IC) devices is driven by several facts. First, the electrical performance of the semiconductor devices can be improved when the parasitic inductances correlated with conventional wire bonding interconnection techniques are reduced. Second, flip-chip assembly provides higher interconnection densities between chip and package than wire bonding. Third, flip-chip assembly consumes less silicon “real estate” than wire bonding, and thus helps to conserve silicon area and reduce device cost. And fourth, the fabrication cost can be reduced, when concurrent gang-bonding techniques are employed rather than consecutive ...

AI Technical Summary

Benefits of technology

[0013]These regions and their sequential structure remain intact even when the solder reflow cycle is repeated several more times (for example five times or more). Since substantially no copper can diffuse throug

Problems solved by technology

Because of the brittleness of these compounds and the direct contact of the intermetallics with the aluminum pad on the chip side, the joints frequently fail reliability tests such as the mechanical drop test by cracking at the bump/chip interface.

For chips which have the gold bumps positi

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