Browse Prior Art Database

Circuit Module Interconnection

IP.com Disclosure Number: IPCOM000085859D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

DiGiacomo, G: AUTHOR [+2]

Abstract

In some circuit modules the electrical and mechanical connections between a semiconductor chip and a supporting ceramic wafer are made by solder balls. Typically layers of selected metals are located between a solder ball and a conductor on the chip, and between the solder ball and a conductor on the ceramic wafer. For example, a lead-indium solder ball may have a relatively thick layer of nickel and a relatively thin layer of gold for connections to a conductor of the wafer.

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Circuit Module Interconnection

In some circuit modules the electrical and mechanical connections between a semiconductor chip and a supporting ceramic wafer are made by solder balls. Typically layers of selected metals are located between a solder ball and a conductor on the chip, and between the solder ball and a conductor on the ceramic wafer. For example, a lead-indium solder ball may have a relatively thick layer of nickel and a relatively thin layer of gold for connections to a conductor of the wafer.

When the solder and layers of metal are repeatedly heated for replacing chips, electrical failures can occur at this connection. One cause of such a failure is stress that is associated with nickel-indium intermetallics. The density of these intermetallics varies as the nickel diffuses into the solder and the variation in density of the nickel-indium intermetallics causes stresses in the connection.

This problem is avoided in the solder connection shown in the drawing which has only a thin layer of nickel, an additional layer of copper, and a conventional thin layer of gold. The copper layer is formed by evaporation and gold is formed by electroless deposition.

The copper provides a good bond with the nickel and gold. Gold diffuses through the copper and improves the sintering. Also, copper-indium intermetallics mix gradually with the nickel-indium intermetallics and minimize the sharp changes in density that produce stresses. This combination of copper- indium...