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Chromium Copper Step Phasing

IP.com Disclosure Number: IPCOM000088848D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Dalal, HM: AUTHOR [+2]

Abstract

In Cr-Cu-Au ball-limiting metallurgy, the bond between the Cr and Cu is achieved by codepositing Cr and Cu during evaporation. During subsequent heat cycles the Pb-In solder deposited on the Cr-Cu-Au forms intermetallics with the Cu which, along with the Au, gets dispersed in the solder pad. This brings the solder in direct contact with the phased Cr-Cu.

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Chromium Copper Step Phasing

In Cr-Cu-Au ball-limiting metallurgy, the bond between the Cr and Cu is achieved by codepositing Cr and Cu during evaporation. During subsequent heat cycles the Pb-In solder deposited on the Cr-Cu-Au forms intermetallics with the Cu which, along with the Au, gets dispersed in the solder pad. This brings the solder in direct contact with the phased Cr-Cu.

Costly multichip substrates put a new demand on chips, namely, the ability to withstand multiple heat cycles required as part of module engineering changes, chip rework, etc. Thus, the leaching of Cu from the phased Cr-Cu region is greatly enhanced. This article presents a Cr-Cu phasing structure better suited to a multiple heat cycle environment.

Mechanical interlocking which occurs during Cr-Cu co-evaporation is the mechanism by which adhesion is obtained between Cr and the remaining metallization. Therefore, structures which are Cr rich with some Cu dispersed in it or vice-versa are of poor quality. Thus, effective phasing can be defined as that part of the total phasing during which the rates of Cr and Cu evaporation are within 2:1.

It is difficult to achieve this condition. While the deposition rate of subliming Cr can be well-controlled between 2-4Angstrom/second with resistance or radiation type heating, the rate of Cu evaporation, by resistance or radiation heating source, cannot be controlled below about 10Angstroms/second. The required phasing can be simply obtained by the s...