Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-03-12
2001-07-31
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S624000, C428S675000, C428S676000, C428S209000, C428S343000, C428S458000
Reexamination Certificate
active
06268070
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to printed circuits, and more specifically, to components employed in the manufacturing of printed circuit boards.
BACKGROUND OF THE INVENTION
In recent years, printed circuit components have become widely used in a variety of electronic devices. Of particular interest are multi-layer printed circuit board laminates which have been developed to meet the demand for miniaturization of electronic components and the need for printed circuit boards having a high density of electrical interconnections and circuitry. In the manufacture of printed circuit boards, raw materials, including conductive foils, which are usually copper foils, are secured to opposite sides of a core which is conventionally a reinforced or non-reinforced dielectric. (Throughout this specification, the use of the term “core” is meant to include any one of a variety of core materials, all of which may be reinforced or non-reinforced and may include an epoxy, polyester, polyimide, a polytetrafloroethylene, and in some applications, a core material which includes previously formed printed circuits.)
The process includes one or more etching steps in which the undesired or unwanted copper is removed by etching away portions of the conductive foil from the laminate surface to leave a distinct pattern of conductive lines and formed elements on the surface of the etched laminate. The etched laminate and other laminate materials may then be packaged together to form a multi-layer circuit board package. Additional processing, such as hole drilling and component attaching, will eventually complete the printed circuit board product.
The trend in recent years 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, such as surface-mount components provided on the printed circuit board. This in turn results in a so-called “densely populated” or simply “dense” printed circuit board. A key to providing a densely populated printed circuit board is to produce close and fine circuit patterns on the outer surfaces (i.e., the exposed surfaces) of the resulting multi-layer printed circuit board. The width and spacing of conductive paths on a printed circuit board are generally dictated by the thickness of the copper foil used thereon. For example, if the copper foil has a thickness of 35 &mgr;m (which is a conventional 1-ounce foil used in the manufacture of many printed circuits), exposing the printed circuit board to an etching process for a period of time to remove such a foil thickness will also reduce the width of the side areas of the printed circuit path in approximately the same amount. In other words, because of the original thickness of the copper foil, a printed circuit board must be designed to take into account that an etching process will also eat away the sides of a circuit path (i.e., undercut a masking material). In other words, the thickness of the spacings between adjacent circuit lines is basically limited by the thickness of the copper foil used on the outer surface of the multi-layer printed circuit board.
In summary, to produce “densely populated” printed circuit boards, it is necessary to reduce the thickness of the copper, at least on the outermost surface of the multi-layer printed circuit package.
The thickness of the copper foil sheet is generally limited by the ability of a foil manufacturer to handle and transport such sheets. In this respect, as the thickness of the foil decreases below 35 &mgr;m, the ability to physically handle such foil becomes more difficult.
The present invention overcomes this and other problems and provides an outer surface laminate for forming multi-layer printed circuit boards having an outer copper layer that facilitates finer circuit lines and closer line spacings on multi-layer printed circuit boards.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a laminate for use as a surface laminate in a multi-layer printed circuit board. The laminate is comprised of a film substrate formed of a first polymeric material. At least one layer of a flash metal is applied to a first side of the film substrate. At least one layer of copper is disposed on the layer of flash metal. An adhesive layer formed of a second polymeric material has a first surface that is attached to a second side of the film substrate.
In accordance with another aspect of the present invention, there is provided a multi-layer printed circuit comprised of an inner core and a surface laminate. The inner core is formed of one or more printed circuit laminates, wherein the printed circuit laminates are comprised of a core substrate having a first surface with a strip conductor disposed thereon. The surface laminate is comprised of a film substrate formed of a first polymeric material having at least one layer of flash metal applied to a first side of the film substrate. At least one layer of copper is disposed on the layer of flash metal. An adhesive layer formed of a second polymeric material has a first surface attached to a second side of the film substrate. The adhesive layer has a second surface that is attached to the strip conductor of the inner core.
In accordance with another aspect of the present invention, there is provided a method of forming a multi-layer printed circuit that comprises the steps of:
a) forming an inner core from one or more printed circuit laminates, each of the printed circuit laminates having a core substrate and a first surface with a strip conductor disposed thereon;
b) forming at least one surface laminate comprised of a film substrate formed of a first polymeric material, at least one layer of a flash metal applied to a first side of the film substrate, at least one layer of copper on the layer of flash metal and an adhesive layer formed of a second polymeric material having a first surface and a second surface, the first surface of the adhesive layer being attached to a second side of the film substrate and the second surface being attached to the strip conductor of the inner core; and
c) compressing the inner core and the surface laminate together under conditions of heat and pressure to create a first multi-layer printed circuit.
It is an object of the present invention to provide a flexible laminate for use in forming multi-layer flexible circuits.
Another object of the present invention is to provide an outer surface laminate for a multi-layer printed circuit, wherein the outer surface laminate has an exceptionally thin layer of copper that facilitates fine circuit lines and a “densely populated” circuit surface.
Another object of the present invention is to provide an outer surface laminate as described above that has an exposed copper surface having improved photoresist adhesion properties that further facilitates the creation of fine circuit lines and a “densely populated” circuit surface by an etching process.
Another object of the present invention is to provide an outer surface laminate as described above, wherein one side of the outer surface laminate includes an adhesive layer for attachment to core laminates.
Another object of the present invention is to provide an outer surface laminate as described above, wherein the outer surface laminate is comprised of a polymeric film having a thin layer of copper adhered to one side of the polymeric film and a layer of an adhesive as applied to a second side of the polymeric film.
A still further object of the present invention is to provide an outer surface laminate as described above, wherein the adhesive is a dimensionally stable film of an uncured resin material.
These and other objects and advantages will become apparent from the following description of preferred embodiments of the invention, taken together with the accompanying drawings.
REFERENCES:
patent: 4193849 (1980-03-01), Sato
patent: 4383003 (1983-05-01), Lifshin et al.
patent: 5130192 (1992-07-01), Takabayashi et al.
patent: 5589280 (1996-12
Bergstresser Tad
Poutasse Charles A.
Centanni Michael A.
Gould Electronics Inc.
Jones Deborah
Kusner Mark
Sten Stephen
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