Corrosion prevention for CAC component

Corrosion prevention of CAC components

Field of invention

This invention relates generally to printed circuit boards and, more particularly, to components for making printed circuit boards and other articles.

Background of the invention

U.S. Patent Nos. 5,153,050, 5, 674, 596, and 5, 942, 315 (both issued to Johnston) disclose the use of the assembly for the manufacture of items such as printed circuit boards. The assembly consists of at least one copper foil which, when formed into a printed circuit board, constitutes the functional component of the panel, i.e., the conductive path. The other components of the assembly are an aluminum substrate sheet that constitutes a disposable component in the finished printed circuit board. One of the surfaces of the copper sheet and the aluminum sheet is substantially uncontaminated, and the interface can be joined to each other.

A flexible adhesive strip joins the uncontaminated surface boundaries of the sheets and defines a substantially uncontaminated central region within the edge of the sheet and is joined at the interface. The aluminum substrate provides copper foil strength, making it easier to handle.

The assembly may consist of two pieces of copper foil that form the functional elements of the separator in the printed circuit board, and a piece of aluminum that forms the disposable element. The inner surface of each of the copper sheets is substantially uncontaminated with the two surfaces of the aluminum sheet, and is engageable with each other at the aluminum back interface.

It has been found that components of the foregoing type can be effectively applied to the manufacture of printed circuit boards, but in some lamination processes, the aluminum reacts with copper, causing copper staining and fading. It is generally believed that the reason for the copper dyeing is the result of electrolytic corrosion, or the result of oxidation of the aluminum and then reaction with the copper. In either case, for some laminators, such copper dyeing would render the formed laminate unusable.

The present invention provides a CAC type assembly having an aluminum substrate sheet and a coating on the aluminum substrate sheet to prevent dyeing and fading of the copper foil during the lamination process.

General theory of invention

According to the present invention, an assembly for manufacturing an article such as a printed circuit board is provided. The component consists of a copper foil and an aluminum substrate which form a functional component in the finished printed circuit board, and the aluminum substrate constitutes a disposable component. The aluminum surface has a coating on it. One of the surfaces of the copper sheet and the coating on the aluminum sheet of the substrate are substantially uncontaminated, and the interface can be joined to each other. A flexible adhesive bonds the uncontaminated surface boundaries of the sheets together and defines a substantially uncontaminated central zone within the edge of the sheet and is unbonded at the interface.

It is an object of the present invention to provide a copper/aluminum/copper assembly that is less prone to copper staining and/or corrosion.

Another object of the present invention is to provide a copper/aluminum/copper assembly as described above having a coated aluminum support substrate to avoid the aforementioned dyeing and/or corrosion problems.

Another object of the present invention is to provide a copper/aluminum/copper assembly as described above, wherein when the aluminum support substrate is separated from the assembly, the coating thereon is preferably not transferred, contaminated or remains on the copper.

These and other objects will be apparent from the following description of the preferred embodiments and the appended claims.

The invention adopts a physical form in which specific parts and parts are arranged, in the specification DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments thereof will be described in detail, and the components thereof will be described in the accompanying drawings, wherein: FIG. 1 is an enlarged cross-sectional view of a specific embodiment of the assembly for manufacturing a printed circuit board, which specifically shows the features of the present invention. Figure 2 is another embodiment of the invention; Figure 3 is a plan view of a component made in accordance with one of these specific embodiments; and Figure 4 is a plan view of the assembly made in accordance with one of these specific embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The present invention is intended to be illustrative of preferred embodiments of the present invention and is not intended to be limiting. FIG. 1 shows a component 10 (also known as CAC, which is copper/aluminum/copper). Cross section of the head word). The assembly 10 is comprised of a metal substrate 12 having a surface 12_i, surface 12_iThe protective layer 14 is coated thereon. Surface 12_iBasically uncontaminated. The metal substrate 12 is preferably formed of industrial grade aluminum having a thickness of between about 0.010 and about 0.020 inches. Metal substrate 12 can be made from aluminum having a thickness of between about 0.001 inches and about 0.125 inches, depending on its end use.

According to the present invention, the uncontaminated surface 12 of the aluminum substrate 12 is before or during the lamination process._iIt is preferred to apply the protective layer 14 to avoid the surface of the copper foil 16 and the aluminum substrate 12 12_iInteraction between the two. Aluminum surface 12_iA metal protective layer 14, such as chromium, copper, nickel, silver, gold or alloys thereof, may be applied. The metal protective layer 14 can be applied by any of various deposition methods, such as thermal deposition methods such as arc spray, combustion chemical vapor deposition, electrolytic deposition, electroless plating or vacuum deposition, such as sputtering or chemical vapor deposition. These examples are not intended to be limiting. The minimum thickness of the metal protective layer 14 must avoid the above-mentioned dyeing problem. It is generally believed that the minimum thickness at which dyeing does not occur is about 20 angstroms. Thus, the metal protective layer 14 has a thickness of at least about 20 angstroms.

In accordance with an embodiment of the present invention, the protective layer 14 is formed of an inorganic material, such as an inert decane, which is disclosed in U.S. Patent Nos. 5,622,782 and 5,614,324, the disclosures of each of each of each of each The inert decane material can be applied by dipping, spraying, plasma deposition or knife coating. The inert decane compound is disclosed in the above-mentioned U.S. Patent. The preferred inert decane compound for use in forming the protective layer 14 is propyltrimethoxydecane (PTMO). Thickness is about 2.5μg/dm²The propyltrimethoxydecane (PTMO) protective layer 14 (per square centimeter) provides satisfactory results.

The copper foil 16 is attached to the coated aluminum substrate 12. The copper foil used in the present invention can be fabricated using one of two techniques. The copper foil or the thickness of the copper or copper alloy strip or block is mechanically reduced by a method such as rolling to produce an exercised or rolled copper foil. Copper atoms are electrolytically deposited on a rotating cathode barrel, and then the deposited foil is peeled off from the cathode to produce an electrolytic foil. Electrodeposited copper foil is suitable for use in the present invention.

The copper foil is typically rated from about 0.0002 inches to about 0.02 inches. Copper foil thickness is sometimes expressed in terms of weight, and the foil weight or thickness of the present invention is typically from about 1/8 to about 14 oz per square inch (oz/ft).²). Especially suitable for forming printed circuit boards, the weight is 1/3, 1/2, 1 or 2 oz / ft²Copper foil.

The copper foil obtained by electrolytic deposition has a smooth or shiny (barrel) surface and a rough or matte (copper deposition growth front) surface, which is conventionally known as "base foil" and is known to be capable of processing the base foil without Particles are produced on the glossy side. Such treated foil is referred to as "treated copper foil." "Reversely treated copper foil" conventionally refers to the treatment of copper foil to produce copper particles on the shiny side. The "double treated copper foil" is a treated copper foil which produces particles on both sides of the foil. All of the foregoing types of foils can be used in the present invention.

In a preferred embodiment of the invention, the copper foil 16 is a 1/2 oz. base foil, which means that the foil has 1/2 oz. copper per square inch. This corresponds to a thickness of about 0.0007 inches. In general, 1/2 oz. copper foil is the industry standard for current PC boards. As noted above, other types or weights of copper foil 16 can be used and are still within the scope of the invention.

Copper foil 16 has an outer surface 16_oIt is roughened to make it easier to adhere to the prepreg, which is bonded in the PC board manufacturing method. Inner surface 16 of copper foil 16_iVery clean and uncontaminated, often referred to as "unused." In completing the printed circuit board, the inner surface 16_iA functional component is constructed and etched to form the desired conductive circuit configuration. Protective layer 14 and surface 16_iSurface 12 of bonded aluminum substrate 12_iIt is also basically uncontaminated.

On the bottom surface of the aluminum substrate 12 is a protective layer 14 and a second copper foil sheet 16, which also has an oxidized outer surface 16_oWith "unused" or uncontaminated inner surface 16_i, not shown in Figure 2. The underlying matte surface of the aluminum substrate 12 (with the protective layer 14 thereon) is also as clean and uncontaminated as possible.

Figure 3 illustrates another embodiment of the invention. 3 shows that the aluminum substrate 12 has the copper foil 16 on only one side. Specific embodiments of the invention may be utilized as desired by the circuit board manufacturer in designing and completing the circuit board. This is identical to the embodiment of Figure 1 except that there is only one layer of copper foil 16. The copper foil 16 constitutes a functional component for completing the printed circuit board, and the aluminum substrate 12 constitutes a disposable component.

Referring next to Figure 4, the surface 16 of the copper foil 16 of the laminate assembly 10 or CAC is observed._oGoing up, and peeling back from a vertex.

Assembly 10 of Figure 4 includes an industrial grade aluminum aluminum substrate 12 having a thickness from about 0.010 to about 0.015 inches. A protective layer 14 is stacked on the aluminum substrate 12. One of the copper foil sheets 16 on the protective layer 14, in the exemplary embodiment, is 1/2 oz. copper, i.e., has a thickness of about 0.0007 inches. The peeling apex exposes the inner surface or "unused" surface of the copper foil 16 and the metal substrate 12 having the protective layer 14.

In the particular embodiment shown, the strip of flexible adhesive 20 extends at or near the boundary of the aluminum substrate 12 along the periphery of the assembly 10, the uncontaminated surface of the copper and aluminum 16_iWith 12_iThe boundaries are combined. Of course, it will be apparent to those skilled in the art that the aluminum substrate 12 and the copper foil 16 can be joined by means other than adhesives and still be suitable for use in the present invention. Since the contact surface is "unused" or at least physically clean as possible, the adhesive 20 creates a substantially uncontaminated central zone CZ inside the edge of the sheet. The central zone interface is not joined.

The strip of adhesive 20 is located in the adhesive coating zone defined by the dashed line 22 and the edge of the component CAC. The zone is from about 0.10 to 1.0 inch depending on the final product requirements and the size of the aluminum and copper sheets used. Adhesive strips or strips having a width from about 0.060 to about 0.090 inches have been found to meet the requirements, but may range from about 0.010 to 0.500 inches, depending on the size of the laminated sheet, from about 0.0005 to about 0.005 inches thick. Inches. A thickness of 0.0005 to 0.002 has been found to meet the demand. In these figures, the central zone CZ is defined by the more internal boundary line 24 from the adhesive coating zone line 22.

Thus, the strip 26 of flexible adhesive 20 seals the copper and aluminum layers before and during the manufacturing process to prevent dust from prepreg or intrusion from any other contaminants that may form in the air, such as particles, fingerprints, and the like. .

Although the CAC assembly configuration has been described with reference to a single copper foil 16 on one side of the aluminum substrate 12, the invention is equally applicable to the specific embodiment shown in Figures 1 and 2. That is, the copper foil 16 can be fixed to both surfaces of the aluminum substrate 12. In the finished product, the two copper foil sheets 16 form the functional components of the individual PC boards, and the single aluminum substrate constitutes a disposable element.

In the configuration of Figure 1, one of the surfaces of each of the copper foil sheets 16 and the surface of the aluminum substrate 12 are substantially "unused" surfaces and are not contaminated. Uncontaminated surface of copper foil 16_iUncontaminated surface 12 of aluminum substrate 12_iOpposite, a substantially uncontaminated central zone is thus defined inside the edge of the sheet opposite the aluminum substrate 12. A barrier or protective layer 14 is applied to the aluminum substrate 12, and any kind of copper foil 16 can be adhered thereto without the problem that the aluminum substrate 12 causes the copper foil 16 to be dyed before or during the lamination process.

The foregoing description is a particular embodiment of the invention. It is to be understood that the specific embodiments are intended to be illustrative only, and that those skilled in the art can make various alternatives and modifications without departing from the spirit and scope of the invention. All such modifications and alternatives are intended to be included within the scope of the invention.

Schematic description

10. . . Component

12,12i. . . Metal substrate

14. . . The protective layer

16,16_i. . . Copper foil

20. . . Flexible adhesive

twenty two. . . dotted line

twenty four. . . borderline

26. . . band