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Publication numberUS3625844 A
Publication typeGrant
Publication dateDec 7, 1971
Filing dateJun 5, 1969
Priority dateJun 5, 1969
Publication numberUS 3625844 A, US 3625844A, US-A-3625844, US3625844 A, US3625844A
InventorsMckean Walter A
Original AssigneeCircult Foll Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Stainproofing process and products resulting therefrom
US 3625844 A
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Description  (OCR text may contain errors)

United States Patent Inventor Walter A. McKean 'Colonia, NJ. Appl. No. 830,789 Filed June 5, 1969 Patented Dec. 7, 1971 Assignee Circuit Foil Corporation Bordentown, N .J

STAINPROOFING PROCESS AND PRODUCTS RESULTING THEREFROM 6 Claims, 1 Drawing Fig.

U.S. Cl 204/140, 204/28, 204/56 R Int. Cl. C23b 1/00, C23b 5/58, C23b 9/00 Field of Search 204/ 140, 28, 56

[56] References Cited UNITED STATES PATENTS 1,827,247 10/1931 Mason 204/140 2,450,508 10/1948 Glock 204/28 2,746,915 5/1956 Giesker.. 204/140 3,531,384 9/1970 lnouye 204/56 Primary ExaminerJohn H. Mack Assistant Examiner-T. Tufariello Attorney-Lane, Aitken. Dunner & Ziems ABSTRACT: An electrolytic process for imparting stain resistance to sheet copper comprising rendering the copper sheet cathodic in an electrolytic cell containing an aqueous electrolyte containing about 0.4-0.8 grams/liter of hexavalent chromium ions and subjecting said foil to a current density of about 2-4 amps/ft. for about 6-8 seconds. Products resulting therefrom.

ELECTROLYTE LEVEL PATENTEU DEC 7197:

ELECTROLYTE LEVEL INVENTOR WALTER A. McKEAN BY W ATTORNEYS STAINPROOFING PROCESS AND PRODUCTS RESULTING TI-IEREFROM BACKGROUND OF THE INVENTION One of the problems with which manufacturers of copper foil (both of the electrolytic and rolled variety) are faced is the staining of the copper foil between the time of shipment and the time of use by the ultimate purchaser. This staining results from the exposure of the copper to normal atmospheric and other conditions and, particularly for applications of the copper foil in critical areas such as printed circuitry, is an extremely undesirable characteristic.

In the past, various suggestions have been made for stainproofing copper foil. While a number of the approaches used in the past have served to stainproof such foil, one of the difficulties related to the use of such techniques is that they have created one or more collateral problems negatively affecting the desirability of the treated copper for use in printed circuit applications and the like. Such problems include:

a. a decrease in the bond strength of the stainproofed foil;

b. an increase in the etching resistance of the foil;

0. a decrease in the solvent resistance of the adhesive/treatment interface; and/or d. a decrease in the solderability of the shiny side of the foil.

SUMMARY OF THE INVENTION In accordance with the present invention, a novel stainproofing technique is provided which provides to copper foil a finish having superior tarnish and oxidation resistance but which does not deleteriously affect such foil in any of the manners described above. This technique involves the use of an aqueous electrolyte under critical conditions of hexavalent chromium ion concentration, cathode current density and treatment time.

OBJECTS OF THE INVENTION It is accordingly an important object of the present invention to provide a novel stainproofing technique useful in stainproofing copper foil rendering such foil particularly adapted for use in printed circuit applications.

It is a further important object of the present invention to provide an improved electrolytic stainproofing technique for stainproofing copper foil involving the use of a novel electrolyte bath as well as products resulting therefrom.

These and other important objects and advantages of the present invention will become more apparent as this description proceeds.

DESCRIPTION OF THE DRAWINGS The FIGURE is a front elevation, partly in section, illustrating an electrolytic tank for carrying out the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION As previously noted, the material to be subject to the improved stainproofing treatment of the present invention is sheet copper. While electrodeposited copper foil is preferred (particularly for printed circuit applications), other types of sheet copper (such as rolled foil) may be used.

The preferred method for stainproofing such foil is to use an elongated sheet of such foil and to pass such elongated sheet through an appropriate electrolyte using an apparatus such as is illustrated in the FIGURE. The apparatus illustrated therein comprises a tank containing an electrolyte inlet 12 and electrolyte outlet 14 by means of which electrolyte l6 respectively enters and is withdrawn from tank 10. The positive bus bar 18 is secured to one longitudinal top edge of tank 10 by means of insulating strip 20. Supported on the bus bar 18 and insulating strip 20 by means of copper bars 22 are a plurality of anodes 24. These anodes 24 are shown in the form of thick, insoluble planar lead plates (which may appropriately be also made of stainless steel). A terminal lead 25, adapted to be connected to the positive terminal of a power source (not shown). is connected to the bus bar 18. A support frame 26 is mounted on the tank 10.

In order to guide a sheet of copper 28 to be stainproofed, two upper electrically connected idler rollers identified by the numbers 30 and 32 are mounted on and are in electrical contact with the support frame 26, and a polyvinyl chloride idler roll 34 is rotatably mounted on a stainless steel bar 36 which, in turn, is connected to the supporting frame 26 at its upper end. By virtue of the electrical contact between rollers 30 and 32 and support frame 26, and by connecting the latter to the negative terminal of a power source (not shown), copper sheet 28 may be rendered cathodic.

The continuous sheet of copper 28 which is to be stainproofed is shown fed from a supply spool 38 mounted on the support frame 26, over the first upper idler 32 and into the electrolytic bath 16. The continuous sheet 28 is guided into and out of the electrolyte 16 in serpentine fashion by means of the idler roller 34 at the bottom of the tank 10 and the upper idler roller 30. As the stainproofed sheet 28 emerges from the electrolytic tank 10, it passes by a pair of nozzle elements 40 and 42 which are connected to a source of wash solution (not shown) to pennit the sheet 28 to be spray washed on both sides. The stainproofed sheet of copper is then fed across idler roller 44, past a squeegee device 46 which removes any excess material, past a pair of infrared lamps and an idler roller 52, 48 and 50 to dry the stainproofed material and finally to the take-up roll 54 which is provided with a suitable drive mechanism (not shown)-which provides the necessary force to draw the sheet of copper 28 through the system.

By passing the copper foil through the system in the manner indicated, the matte and shiny surfaces of the foil will receive an electrochemical treatment and will have. stain resistance imparted thereto.

As will be apparent, electrolytic tank 10 can be enlarged and additional anodes 24 added to increase the amount of exposure of the moving sheet of foil to electrolytic treatment, though for the purpose of the present invention, a 3-anode system is quite adequate to expose the foil to the critical treatment time mentioned below.

The electrolyte employed in the present invention is an aqueous electrolyte containing hexavalent chromium ions which is preferably substantially free of any impurities. Such an electrolyte may conveniently be formed by dissolving chromium trioxide (CrO in water to form chromic acid. This aqueous solution must contain 0.4-0.6 grams/liter of hexavalent chromium ions (determined as CrO As the copper foil passes through the electrolyte, it should be subjected to a cathode current density of about 2-4 amps/ft. for about 6-8 seconds.

When foil is subject to conditioning as set forth above, the foil has a remarkable degree of resistance to oxidation and tarnishing as measured by several accelerated staining procedures (immersion in a sulfide test solution and a humidity exposure test), while not suffering any of the disadvantages previously noted as being associated with prior art techniques.

The particular hexavalent chromium ion concentration, cathode current density and exposure time are critical in the carrying out of the process of the present invention. More specifically, when hexavalent chromium ion concentrations, cathode current densities and exposure times below the aforementioned lower limits are used, adequate stain protection is not provided to the copper foil; similarly, the use of hexavalent chromium ion concentrations, cathode current densities and exposure times above the aforementioned upper limits hinders etching of the foil in printed circuit applications.

In a specific example of the process of the present invention, one ounce copper foil (which had been previously electrochemically treated to improve bond strength) was passed in serpentine fashion in the manner indicated above past insoluble lead anodes in an aqueous chromic acid electrolyte containing 0.5 grams/ liter of hexavalent chromium ions (determined as CrO The electrolyte was at a temperature of 25 C., the cathode current density was 3 amps/ft. and the copper was immersed in the electrolyte for 7 seconds. The resulting copper foil has excellent stain resistance as measured by a standard sulfide stain resistance test and passes a standard etchability test employed for printed circuit applications.

The standard sulfide stain resistance test involves the immersion of the foil in a filtered solution of 5 grams/liter of Zonax Oxidizing Salt (a proprietary material produced by W. Canning Co. in Birmingham, England which is likely an ammonium polysulfide compound) in distilled water. The solution is maintained at room temperature without agitation.

Stain resistance is proportional to the time after immersion that an overall black film is produced on the shiny surface of the foil. Untreated foil will stain in less than 5 seconds, ordinary prior art stainproofed foil in 15 to 30 seconds, while foil stainproofed in accordance with the process of the present invention may last over 5 minutes without staining.

The standard etching test described above is as follows:

A. Solutions I. Etch solution (5 percent ferric chloride in water) a standard 42 B. ferric chloride etch solution such as Hunt's RCE in the ratio of 1 part concentrate plus 7 parts water.

2. Post-etch cleaning solution 10 percent by volume of concentrated hydrochloric acid in water.

B. Procedure Immerse the sample to be tested in the 5 percent etch solution at room temperature and without agitation for 60 seconds. Remove from the etch and place in the 10% hydrochloric acid solution for 60 seconds. Remove and wash in running water. Dry and examine.

A properly etched specimen will exhibit a uniform matte surface of a reddish pink color. Non-etchability shows shiny streaks or areas in the immersed portion. Extreme cases of etch resistance appear indistinguishable from the unetched areas.

This test applies only to the shiny surface of electrodeposited foil.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. An electrolytic process of imparting stain resistance to sheet copper comprising rendering said copper sheet cathodic in an electrolytic cell containing an electrolyte comprised of an aqueous solution containing about 0.4 to 0.6 grams/liter hexavalent chromium ions (determined as CrO and subjecting said sheet copper to a current density of about 2 to 4 amps/ft. for about 6 to 8 seconds.

2. A process as defined in claim 1 wherein said copper is copper foil.

3. A process as defined in claim 1 wherein said electrolyte is substantially free of impurities.

4. A process as defined in claim 1 wherein said electrolyte contains dissolved chromium trioxide.

5. The product of the process of claim 2.

6. The product of the process of claim 1.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1827247 *Oct 18, 1927Oct 13, 1931Western Electric CoMethod of protecting metal surfaces
US2450508 *Mar 29, 1948Oct 5, 1948Crown Cork & Seal CoTin plate treatment
US2746915 *Oct 15, 1951May 22, 1956Autoyre Company IncElectrolytic metal treatment and article
US3531384 *Dec 26, 1967Sep 29, 1970Okada HideyaProcess of treating surfaces of metallic articles
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3853716 *Sep 8, 1972Dec 10, 1974Yates IndustriesElectrolytic copper stainproofing process
US4071417 *Jun 29, 1977Jan 31, 1978Bell Telephone Laboratories, IncorporatedProcess for decreasing the porosity of gold
US4077851 *Mar 4, 1977Mar 7, 1978Bell Telephone Laboratories, IncorporatedPatterned chromate film process
US4077852 *Feb 9, 1977Mar 7, 1978Bell Telephone Laboratories, IncorporatedSelective gold plating
US4082620 *Apr 29, 1977Apr 4, 1978Bell Telephone Laboratories, IncorporatedProcess for chromating metallic surfaces
US4387006 *Jul 8, 1981Jun 7, 1983Fukuda Metal Foil & Powder Co., Ltd.Roughness, zinc chromate electrodeposition
US4647315 *Jul 1, 1985Mar 3, 1987Olin CorporationChromic acid, phosphoric acid
US4952285 *Dec 22, 1989Aug 28, 1990Olin CorporationUsing mixture of chromic and sulfuric acid
US4961828 *Apr 5, 1989Oct 9, 1990Olin CorporationPretreating with chromic acid solution before forming copper or copper oxide dendrites or nodules on surface
US5022968 *Sep 20, 1990Jun 11, 1991Olin CorporationOxidation resistance; removable with dilute hydrochloric or sulfuric acid
US5057193 *Dec 22, 1989Oct 15, 1991Olin CorporationAnti-tarnish treatment of metal foil
US5071520 *Oct 30, 1989Dec 10, 1991Olin CorporationMethod of treating metal foil to improve peel strength
US5098796 *Mar 25, 1991Mar 24, 1992Olin CorporationChromium-zinc anti-tarnish coating on copper foil
US5164235 *Mar 6, 1990Nov 17, 1992Olin CorporationTreating copper with chromium and zinc ions
US5215646 *May 6, 1992Jun 1, 1993Circuit Foil Usa, Inc.Low profile copper foil and process and apparatus for making bondable metal foils
US5230932 *Mar 20, 1992Jul 27, 1993Olin CorporationChromium-zinc anti-tarnish coating for copper foil
US5250363 *Oct 26, 1992Oct 5, 1993Olin CorporationChromium-zinc anti-tarnish coating for copper foil having a dark color
US5332486 *Jan 29, 1993Jul 26, 1994Gould Electronics Inc.Anti-oxidant coatings for copper foils
US5356527 *Aug 9, 1991Oct 18, 1994Olin CorporationRinsing in aqueous buffer solution of alkali metal or alkaline earth metal phosphates or borates maintained at specified pH
US5447619 *Nov 24, 1993Sep 5, 1995Circuit Foil Usa, Inc.Oxidation resistant chromate coating and metallic zinc
US5989727 *Mar 4, 1998Nov 23, 1999Circuit Foil U.S.A., Inc.Electrolytic copper foil having a modified shiny side
US6145468 *Oct 19, 1998Nov 14, 2000Woog; Manfred J.Silver indicator methods and test kit
US6270889Dec 23, 1998Aug 7, 2001Mitsui Mining & Smelting Co., Ltd.For making printed wiring boards
US6538211Dec 13, 2001Mar 25, 2003World Properties, Inc.Multi-layer circuits and methods of manufacture thereof
US6544664 *May 24, 2000Apr 8, 2003Mitsui Mining & Smelting Co., Ltd.Copper foil for printed wiring board
US6652962May 27, 1999Nov 25, 2003Mitsui Mining & Smelting Co. Ltd.Resin-coated composite foil, production and use thereof
EP0930811A1 *Jan 15, 1999Jul 21, 1999MITSUI MINING & SMELTING CO., LTD.Composite copper foil, process for preparing the same, and copper-clad laminate and printed wiring board using the same
Classifications
U.S. Classification205/704, 205/283, 205/142
International ClassificationH05K3/28, C25D11/38, C25D11/00
Cooperative ClassificationH05K3/282, C25D11/38
European ClassificationC25D11/38, H05K3/28C