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"Improvement of C-4 Chip Soldering Process"

IP.com Disclosure Number: IPCOM000037888D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Seraphim, DP: AUTHOR [+4]

Abstract

In the fabrication of circuits on organic films such as polyimide, copper pads are provided for attachment of a semiconductor chip or other such electronic device. One of the major problems in chip joining by C-4 soldering process is the oxidation of the copper pads. It is very difficult to prevent the oxidation because of the trace oxygen (few ppm) and water vapor from the environment of the furnace where chip joining occurs.

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"Improvement of C-4 Chip Soldering Process"

In the fabrication of circuits on organic films such as polyimide, copper pads are provided for attachment of a semiconductor chip or other such electronic device. One of the major problems in chip joining by C-4 soldering process is the oxidation of the copper pads. It is very difficult to prevent the oxidation because of the trace oxygen (few ppm) and water vapor from the environment of the furnace where chip joining occurs.

A two-step process is described to: 1) provide a very clean active copper surface and 2) to protect the copper by depositing gold on it. Step 1 can be achieved by plasma cleaning, reactive ion etching or laser beam of the pad area. Step 2 is done by immersion gold coating of copper pads.

The gold solution has the following composition:

Gold (1) cyanide, AuCN ............... 2.4 g/L

Gold as metal, Au .................... 2.1 g/L

Potassium cyanide, KCN ............... 12 g/L

The gold solution provides a Cu-Au exchange reaction and is self limiting. The coatings are very thin, about 0.025 micron, and relatively pore free.

Disclosed anonymously.

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