Method of making a copper on INVAR® composite

Details Method of making a copper on INVAR® composite Method of making a copper on INVAR® composite

2001-08-09

2003-07-08

King, Roy (Department: 1742)

Electrolysis: processes, compositions used therein, and methods

Electrolytic coating

Coating moving substrate

C205S182000, C205S184000, C205S218000, C205S291000, C205S293000

Reexamination Certificate

active

06589413

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a composite for use in forming multilayer printed circuit boards, and more particularly to a copper on INVAR® composite.
BACKGROUND OF THE INVENTION
INVAR® (a registered trademark of Imphy S.A.) is a nickel-iron alloy containing about 36% nickel and 64% iron. It has been known to use copper/INVAR®/copper composite materials in the manufacture of printed circuit boards because of its low thermal coefficient of expansion (TCE). In this respect, copper/INVAR®/copper composite materials are commonly used in printed circuit boards as ground planes, power planes and/or metal cores, hybrid enclosures, heat sinks, and other areas where thermal coefficient of expansion matching is required or beneficial.
Heretofore, copper/INVAR®/copper composite materials were produced by metallurgically bonding two copper layers onto each side of an INVAR® layer. This mechanical process basically required rolling the respective layers together under pressure. A problem with metallurgically bonding a copper layer to an INVAR® layer is the inability of producing composite materials thinner than 2 mil. In addition, the metallurgical properties of the resulting copper/INVAR®/copper composites are not consistent throughout the resulting composite.
The present invention overcomes these and other problems and provides a copper on INVAR® composite that is thinner than copper/INVAR®/copper composites known heretofore, and that has more uniform consistent, metallurgical properties.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided a method of forming a copper on INVAR® composite comprising the steps of:
conveying a generally continuous strip of INVAR® along a path having a plurality of locations;
at a first location, cleaning the strip in an alkaline solution;
at a second location, cleaning the strip in an acid solution;
at a third location, applying a copper strike layer to the strip; and
at a fourth location, electrodepositing copper onto the strike layer.
In accordance with another aspect of the present invention, there is provided a composite for use in forming a multi-layer printed circuit board, comprised of an INVAR® sheet having a thickness of between 0.5 mil and 5 mil; and a layer of electrodeposited copper on at least one side thereof. The copper has a thickness of between 1&mgr; and 50&mgr;. The composite has a thermal coefficient of expansion (TCE) of about 2.8 to 6.0 ppm at temperatures between 0° F. and 200° F.
It is an object of the present invention to provide a copper on INVAR® composite that is thinner than similar composites formed by a metallurgical bonding process.
It is another object of the present invention to provide a composite as described above that has more consistent metallurgical properties than a metallurgically bonded composite.
It is another object of the present invention to provide a composite as described above that has a thermal coefficient of expansion of about 2.8 to 6.0 ppm at temperatures between 0° F. and 200° F.
These and other objects will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.


REFERENCES:
patent: 5011655 (1991-04-01), Mankins
patent: 6190939 (2001-02-01), Burns
F.A. Lowenheim. Electroplating, McGraw-Hill Book Co, New York pp 74-77, 82-83, 88-89, 99-101, 106-111, 194-205, 1978 Month of Publication Not Available.*
Texas Instruments brochure entitled: “Clad Meat Copper Clad Invar,” 1983, 3 pgs. Month of Publication is Not Available.
Texas Instruments brochure entitled: “Copper/Invar/Copper Material Specification/Data Sheet,” Dec. 1987, 4 pages.

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