Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-04-01
2001-12-18
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S901000, C174S257000
Reexamination Certificate
active
06331347
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method for forming a gold plating electrode, a substrate based on the gold plating electrode forming method, and a wire bonding method utilizing the gold plating electrode forming method.
2. Prior Art
According to conventional technologies, it has been well known that gold plating is used to form an electrode on a glass epoxy substrate and thus formed electrode is electrically connect with a chip through bonding of a wire. In this case, gold plating must provide sufficient bondability, such as bonding strength, to a ball formed at a distal end of the wire.
From numerous experiences, it has been conventionally believed that the thickness of a gold layer formed by the gold plating needs to be as thick as 300 nanometer or more. To this end, it was usual to utilize the electro plating or electroless reduction plating to form a gold layer being sufficiently thick.
However, as well known to artisans, it takes an extremely long time until a growing gold layer reaches a required thickness when the gold layer is formed by the electro plating or electroless substitution plating, and the manufacturing cost must be expensive.
SUMMARY OF THE INVENTION
Accordingly, in view of above-described problems encountered in the prior art, a principal object of the present invention-is to provide a method for forming a novel and excellent gold plating electrode assuring sufficient bondability without requiring long processing time and expensive manufacturing costs, and to provide a substrate based on the above gold plating electrode forming method, and a wire bonding method utilizing this gold plating electrode forming method.
In order to accomplish this and other related objects, a first aspect of the present invention provides a novel and excellent method for forming a gold plating electrode comprising: a step of forming a circuit pattern on a substrate; a step of forming a nickel-containing barrier metal layer at a portion where an electrode of the circuit pattern is formed; a step of forming a gold layer on the barrier metal layer by plating; a step of heating the substrate to cause nickel contained in the gold layer to move toward a surface zone of the gold layer to deposit nickel compound in the surface zone of the gold layer, thereby enhancing the fineness of a remaining part of the gold layer at at least an inside zone immediately below the surface zone; and a step of removing the surface zone containing the nickel compound off the gold layer so as to expose a purified surface of the inside zone of the gold layer.
According to features of the preferred embodiments, the surface zone containing the nickel compound is removed off by etching. It is preferable that the surface zone containing the nickel compound is removed off by a thickness of 3 to 10 nanometer. The substrate is heated at a temperature of 150 to 200 centigrade for 5 to 60 minutes. The gold layer is formed by plating so as to have a thickness in the range of 5 to 100 nanometer.
A second aspect of the present invention provides a substrate comprising: a circuit pattern formed on a surface of the substrate; a nickel-containing barrier metal layer formed at a portion where an electrode of the circuit pattern is formed; a gold layer formed on-the barrier metal layer by plating, wherein the substrate is heated up to cause nickel contained in the gold layer to move toward a surface zone of the gold layer to deposit nickel compound in the surface zone of the gold layer so that the fineness of a remaining part of the gold layer is enhanced at at least an inside zone immediately below the surface zone, and the surface zone containing the nickel compound is removed off sd as to expose a purified surface of the inside zone of the gold layer.
Furthermore, a third aspect of the present invention provides a wire bonding method comprising: a step of forming a circuit pattern on a substrate, forming a nickel-containing barrier metal layer at a portion where an electrode of the circuit pattern is formed, and forming a gold layer on the barrier metal layer by plating, thereby forming an electrode on the substrate; a step of heating the substrate to cause nickel contained in the gold layer to move toward a surface zone of the gold layer to deposit nickel compound in the surface zone of the gold layer, thereby enhancing the fineness of a remaining part of the gold layer at at least an inside zone immediately below the surface zone; a step of removing the surface zone containing the nickel compound off the gold layer by etching to expose a purified surface of the inside zone of the gold layer; a step of applying an adhesive material on the substrate and die bonding a chip on the adhesive material; and a step of connecting an electrode of the chip to the electrode of the substrate via an electrically conductive wire.
According to this novel and excellent gold plating electrode method. A circuit pattern, which is preferably a copper foil, is formed on a substrate. Next, a nickel-containing barrier metal layer is formed on the copper foil. Then, a gold layer is formed on the barrier metal layer by plating. Thereafter, the substrate is heated up to cause nickel contained in the gold layer to move or shift toward a surface zone of the gold layer, so that nickel compound can be deposited or collected in the surface zone of the gold layer and, as a result, the fineness of the remaining part of the gold layer can be enhanced at at least the inside zone immediately below the surface zone.
Through experiments conducted by an inventor of the present application, it was confirmed that nickel had surely moved from the barrier metal layer into the gold layer even immediately after the gold layer was formed by plating. Furthermore, it was confirmed that heating the substrate promoted or impelled the nickel in the gold layer to move into and deposit as nickel compound in the surface zone, enhancing the fineness of the gold layer at least the inside zone immediately below the surface zone to be sufficiently high to assure a satisfactory bondability to the wire. Accordingly, by removing the nickel compound crowded in the surface zone off the gold layer, it becomes possible to form an excellent gold electrode having high fineness and assuring a satisfactory bondability to the wire.
REFERENCES:
patent: 3781596 (1973-12-01), Galli et al.
patent: 4016050 (1977-04-01), Lesh et al.
patent: 4068022 (1978-01-01), Glick
patent: 5232873 (1993-08-01), Geva et al.
patent: 5242861 (1993-09-01), Inaba
patent: 5302492 (1994-04-01), Ott et al.
patent: 5635764 (1997-06-01), Fujikawa et al.
patent: 5652434 (1997-07-01), Nakamura et al.
patent: 5767008 (1998-06-01), Haji
patent: 5909633 (1999-06-01), Haji et al.
patent: 0089559 (1983-09-01), None
patent: 0203423 (1986-12-01), None
Connolly Bove & Lodge & Hutz LLP
Lam Cathy
Matsushita Electric Industrial Co. Ltd
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