Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Reexamination Certificate
1999-07-27
2001-07-31
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
C204S230200, C204S297060, C204S297100, C204S297130, C204SDIG007
Reexamination Certificate
active
06267860
ABSTRACT:
DESCRIPTION
TECHNICAL FIELD
The present invention relates to a method for enhancing the electroplating of an article and especially for electroplating of microelectronic and other precision components. The present invention is particularly concerned with improving the uniformity of plating thicknesses. Moreover, the present invention relates to electroplating apparatus capable of improving the uniformity of plating thicknesses.
BACKGROUND OF INVENTION
Electrolytic plating is widely used for plating of microelectronic and other precision articles. For example, electroplating is widely practiced in the printed circuit industry to add layers of various metals to other conductors. Copper may be plated to increase the thickness of conductors. Layers of nickel and gold are routinely added to copper for protection to prevent oxidation. A great variety of materials, thicknesses and layers are known in the electroplating art.
An important and major concern in electroplating is control of plated thickness distribution. It especially impacts the conventional pattern electroplating of circuits, on printed circuit boards or on semiconductors, where isolated circuits plate thicker than dense circuits.
Plating thickness is also related to the current distribution during the plating operation. Printed circuit or plated feature density also affects the uniformity of the plating in a given region.
One suggestion for improving thickness distribution has been pulse reverse plating. However, this involves significant investments in new rectifiers and cabling, and the use of different plating chemistries than when DC is used.
Attempts to minimize disparity in plating thicknesses have also involved changing the cross-sectional area of plating rack bus bars. However, tailoring the bus bars' geometry is difficult to implement in an actual rack due to the extra bus bar mass that is needed in the lower current regions to reduce the voltage drop between contacts and the design complexity this generates.
It would therefore be desirable to provide for improving the thickness distribution in electroplating.
SUMMARY OF INVENTION
The present invention provides for enhanced electroplating and particularly for improved plating thickness distribution. More particularly, the present invention relates to a method for electroplating one article which comprises providing a resistor between an electrically conductive bus bar and the at least one article to be electroplated. The ratio of the resistance of the resistor to the bus bar resistance between at least two workpiece contact points is at least about 10:1. An electroplating composition is provided in contact with the at least one article to be plated, and a plating current is applied to plate the at least one article.
Another aspect of the present invention relates to electroplating apparatus which comprises a plating tank comprising an electrically conductive bus bar, rack for at least one article to be plated, a resistor located between the bus bar and rack, and a source for supplying current to the plating tank. The ratio of the resistance of the resistor to the bus bar resistance between at least two workpiece contact points is at least about 10:1.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
REFERENCES:
patent: 3531392 (1970-09-01), Schmeiser
patent: 3592754 (1971-07-01), Aihara
patent: 4786384 (1988-11-01), Gerhardt et al.
patent: 4828654 (1989-05-01), Reed
patent: 5024732 (1991-06-01), Hubel
patent: 5759363 (1998-06-01), Rose
Connolly Bove Lodge & Hutz LLP.
Fraley, Esq. Lawrence R.
Gorgos Kathryn
International Business Machines - Corporation
Leader William T.
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