Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-03-24
2001-05-29
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S626000, C428S901000
Reexamination Certificate
active
06238778
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to printed circuits, and more particularly, to components used in the manufacturing of printed circuit boards and other articles.
BACKGROUND OF THE INVENTION
In the manufacture of printed circuit boards, sheets of copper foil are typically bonded to a dielectric layer of a partially cured epoxy resin containing woven glass fiber (such a dielectric layer is conventionally referred to as a “pre-preg”). In the manufacture of copper clad laminates, sheets of copper foil are typically bonded to another layer of foil. In both processes, the copper foil is etched to produce conductive paths. In such processes, it is extremely important to avoid contamination of the copper foil sheets in that any foreign matter contacting the copper foil, such as resin dust, fiberglass fibers, hair, grease, oil or the like, may result in dots, dents, deposits or pits on the copper foil that can adversely affect the formation of the conductive paths forming the printed circuits.
Copper foil is conventionally formed by an electrodeposition process. Following the production of the copper foil, it is known to secure a metallic substrate to one side of the copper foil to protect that side of the copper foil from contamination during subsequent handling and shipping. The protected side of the copper foil is typically the side used to form the conductive pathways, while the exposed side of the foil is typically the side that is attached to a pre-preg or bonded to another layer of copper foil. The protective metallic substrate remains attached to the copper foil as it is attached to the pre-preg or bonded to the other layer of copper foil. The protective metallic substrate is subsequently removed and discarded (or recycled) to expose the protected, uncontaminated side of the foil for processing to form the conductive pathways.
U.S. Pat. No. 5,153,050 to Johnston discloses a copper/aluminum/copper laminate wherein the shiny side of a copper foil is bonded along its peripheral edges to an aluminum substrate. U.S. Pat. No. 5,674,596 to Johnston further discloses securing copper foil to a metallic substrate, such as a steel or a stainless steel substrate. U.S. Pat. No. 5,512,381 to Konicek et al. discloses securing copper foil to a copper substrate.
Each of the foregoing structures uses a relatively expensive material, e.g., aluminum, stainless steel and copper, to form the disposable, protective substrate. In addition to the cost of such materials, copper and aluminum are relatively soft metals that are susceptible to image transfer during lamination of multi-layer laminates, particularly at high lamination temperatures and pressures. Stainless steel is a stronger metal than copper or aluminum, and possesses the corrosion resistance necessary to avoid contamination of the copper foil sheet. As a result, stainless steel finds advantageous application at higher laminating temperatures and pressures. However, corrosion resistance and higher strength of stainless steel come at a price. Typically, stainless steel sheet is even more expensive than copper and aluminum sheet.
The present invention provides a component for manufacturing printed circuit boards that has a copper foil protected by a metallic substrate, wherein the metallic substrate has the corrosion resistance of stainless steel at a significantly reduced cost.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a component for use in manufacturing articles such as printed circuit boards. The component is comprised of a laminate constructed of a sheet of copper foil that, in a finished printed circuit board, constitutes a functional element, and a sheet of carbon steel having a layer of an inert metal thereon. The sheet of carbon steel constitutes a discardable element. One surface of the copper sheet and the surface of the inert metal layer on the carbon steel sheet are essentially uncontaminated and are engageable with each other at interfaces. The copper sheet is attached to the inert metal layer of the carbon steel sheet at its borders to define substantially uncontaminated central zones inwardly of the edges.
In accordance with another aspect of the present invention, there is provided a sheet of copper foil for manufacturing multi-layer laminates comprising a sheet of copper foil having a thickness greater than about 5 microns. The copper foil has a first surface adapted for adhering to a fiber reinforced polymer layer, and a second surface to be exposed after the first surface is adhered to the fiber reinforced polymer layer. A protective sheet of carbon steel having a thickness of about 0.05 mm to about 2.0 mm is provided. The carbon steel sheet has a layer of chromium with about 0.1 grams/m
2
to about 10 grams/m
2
electrodeposited on its surface. The layer of chromium engages the second surface of the copper sheet and is attached thereto in a manner defining substantially uncontaminated central zones.
It is an object of the present invention to provide a component having a copper sheet for use in manufacturing articles, such as printed circuit boards, and a metallic substrate to protect a surface of the copper sheet before and during a manufacturing process.
It is a further object of the present invention to provide a component as described above wherein the metallic substrate is a relatively low cost, discardable item.
It is a further object of the present invention to provide a component as described above wherein the metallic substrate is formed of carbon steel and has an outer layer of an inert metal thereon for engagement with the copper sheet.
It is a further object of the present invention to provide a component as described above wherein the inert metal is chromium.
It is another object of the present invention to provide a component as described above that is suitable for high temperature processing applications.
A still further object of the present invention is to provide a component as described above wherein the discardable metallic substrate has a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of press plates used in forming laminated circuit boards.
A still further object of the present invention is to provide a component as described above wherein the metallic substrate is dimensioned and used as a press plate in a circuit board forming operation.
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:
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patent: 3595632 (1971-07-01), Ross
patent: 3655349 (1972-04-01), Shah et al.
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patent: 4563399 (1986-01-01), Wright, Jr.
patent: 4770947 (1988-09-01), Flagello et al.
patent: 4863808 (1989-09-01), Sallo
patent: 5153050 (1992-10-01), Johnston
patent: 5320919 (1994-06-01), Azuma et al.
patent: 5496422 (1996-03-01), Morishige et al.
patent: 5512381 (1996-04-01), Konicek et al.
patent: 5674596 (1997-10-01), Johnston
patent: 5686194 (1997-11-01), Shimizu et al.
patent: 5942315 (1999-08-01), Johnston
patent: 6127051 (2000-10-01), Frater
patent: 6129998 (2000-10-01), Frater
Centanni Michael A.
GA-TEK Inc.
Kusner Mark
Lorin Francis J.
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