Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-09-16
2001-10-02
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S607000, C174S256000
Reexamination Certificate
active
06296949
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
A basic component of a printed circuit board is a dielectric layer having a sheet of copper foil bonded thereto. Through a subtractive process that includes one or more etching steps, portions of the copper foil are etched away to leave a distinct pattern of conductive lines and formed elements on the surface of the dielectric layer. Multi-layer printed circuit boards are formed by stacking and joining two or more of the aforementioned dielectric layers having printed circuits thereon.
In recent years, the trend has been to reduce the size of electronic components and provide printed circuit boards having multi-chip modules, etc. This results in a need to increase the number of components, i.e., surface mount components, provided on a printed circuit board. A key to providing a densely populated circuit board is to produce close and fine circuit patterns from the copper. The width and spacing of conductive paths on the printed circuit board are generally dictated by the thickness of the copper on the dielectric layer. For example, if the copper has a thickness of 35 &mgr;m (which is a conventional 1-ounce copper used in manufacturing many printed circuits), exposing the printed circuit board to an etching process for a period of time to remove such a copper thickness will also reduce the width of the side areas of the printed circuit path in approximately the same amount. In other words, the width of the spacing between adjacent circuit lines is basically determined by the thickness of the copper foil on the dielectric layer, as well as the narrowness of the line to be formed. In this respect, as the thickness of the foil decreases below 35 &mgr;m, the ability to physically handle such foil becomes more difficult. There is a minimum thickness of a copper foil sheet that is determined by the ability of the foil manufacturer to handle and transport such sheets. Hence, there is also a limit on achieving close and fine circuit patterns from copper sheets.
In recent years, it has been proposed to use copper-coated polyimides in forming printed circuits. The thickness of the copper on polyimide is generally significantly less than the thickness of traditional copper foil sheet. The thinner copper on the polyimide allows for finer and more closely spaced circuit lines in that the thinness of the copper layer reduces the etching time required to remove unwanted copper. In this respect, it is possible to use copper clad polyimide wherein the copper has a thickness as low as 0.1 &mgr;m (1,000 Å). The thinner copper on the polyimide also finds advantageous application in a semi-additive process. In a semi-additive process, the copper is masked to define a circuit pattern, and copper is plated onto the exposed pattern to build up a circuit. The mask material is removed and a “flash etch” removes the base copper on the polyimide leaving the built-up circuit on the polyimide. Thus, copper on polyimide finds advantageous application in both subtractive and semi-additive processes for forming printed circuits.
As with conventional copper foil, it is important to maintain the surface of the copper on the polyimide free from contamination. It is also important not to bend or flex the polyimide in such a way that cracks may form in the copper layer. In this respect, it is preferable to maintain a copper coated polyimide sheet in a flat planer orientation, i.e. the orientation that will be used within a printed circuit.
The present invention provides a method of protecting the exposed copper layer on a copper-coated polyimide from surface contamination and from undesirable flexing of the laminate.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided a component for use in manufacturing a printed circuit. The component is comprised of a laminate that in a finished printed circuit constitutes a functional element, and a planar layer of metal that constitutes a discardable element. The laminate is comprised of a film substrate formed of a first polymeric material, with at least one layer of a tie metal applied to a first side of the film substrate, and at least one layer of copper on the at least one layer of a tie metal. The layer of copper has an essentially uncontaminated exposed surface facing away from the at least one layer of tie metal. The planar layer of metal has an essentially uncontaminated surface that is inert to copper. The laminate is attached to the planar layer of metal at its borders, with the essentially uncontaminated, exposed surface of the at least one copper layer engaging the essentially uncontaminated surface of the planar layer of metal to define a substantially uncontaminated central zone inwardly of the edges of the sheet that is un-joined at the interfaces.
It is an object of the present invention to provide a component having a copper layer for use in manufacturing articles such as printed circuit boards, and a planar layer of metal to protect the surface of the copper layer before and during the manufacturing process.
It is another object of the present invention to provide a component as described above wherein the planar layer of metal is comprised of aluminum.
It is another object of the present invention to provide a component as described above wherein the copper layer has a thickness significantly less than conventional foil sheet.
It is another object of the present invention to provide a component as described above wherein the copper layer finds advantageous application in subtractive and semi-additive circuit forming processes.
It is another object of the present invention to provide a component as described above wherein the copper layer has a uniform thickness and a smooth interface that facilitates good etching, as well as good electrical properties in the resulting circuit.
It is another object of the present invention to provide a component as described above wherein the polymeric layer is dimensionally stable, has a uniform thickness, has good electrical properties and is lasable.
It is another object of the present invention to provide a component as described above wherein the planar layer of metal has sufficient thickness to maintain the laminate in the general planar shape.
These and other objects will become apparent from the following description of the embodiment taken together with the accompanying drawings and the appended claims.
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Bergstresser Tad
Poutasse Charles A.
Centanni Michael A.
GA-TEK Inc.
Jones Deborah
Kusner Mark
Savage Jason
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