US3914162A - Compositions and process for the electrodeposition of metals - Google Patents

Abstract

An electrically conductive medium for the electrodeposition of metals comprises an aqueous solution of (a) a metal ion, (b) a carboxy alkylene amino di(methylene phosphonic acid) and optionally, (c) 1-hydroxy alkylidene-1,1-diphosphonic acid.

Description

United States Patent 1191 Kowalski 51* Oct. 21, 1975 1 COMPOSITIONS AND PROCESS FOR THE [56] References Cited ELECTRODEPOSITION OF METALS UNITED STATES PATENTS [75] Inventor: Xavier Kowalski, St. Louis, Mo. 2,673,214 3/1954 Bersworth et al 260/5025 2,961,311 11/1960 Bersworth et a1 1. 260/5015 X [73] Asslgnee' clmpalw Lows 3,293,176 12/1966 White 260/5025 X [*1 Notice: The portion of the term of this Z1323 fichieferm 32 aynes g g?? 5 3 3,617,343 11/1971 Kandler 117/47 R as e almfi 3,706,635 12/1972 Kowalski 204/46 22 i J 25 1973 OTHER PUBLICATIONS [21] Appl. No.: 373,051 H. Koretzky, IBM Tech. Disclosure Bulletin, Vol. 9, [44] Published under the Trial Voluntary Protest 1634 Apnl 1967 Program on January 28, 1975 as document no. B 373,051. Primary ExaminerG. L. Kaplan Attorney, Agent, or FirmThomas B. Leslie [52] US. Cl 204/46 G; 204/43 R; 204/44; 204/46 R; 204/48; 204/49; 204/50 R; 204/51; 204/52 R; 204/55 R; 260/5025 [57] ABSTRACT 2 6 [51] CL C251) 3/04 C251) g ga i An electrically conductive medium for the electrode. [581 Field Of Search 204/45-55, Position of metals comprises an aqueous wlutlo of (a) a metal ion, (b) a carboxy alkylene amino di(- methylene phosphonic acid) and optionally, (c) 1- hydroxy alkylidene-1,l-diph0sphonic acid.

10 Claims, N0 Drawings COMPOSITIONS AND PROCESS FOR THE ELECTRODEPOSITION OF METALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the electrodeposition or electroplating of metals. More particularly, the present invention relates to the composition of the electroplating bath from which the metal is deposited.

2. Description of the Prior Art The electrodeposition of metals from aqueous solutions of metal ions is an old art. The typical electroplating system consists of an electroplating bath and two or more electrodes. The cathode of the electrode system is the object to be plated. The anode may be carbon or a solid piece of the metal to be plated upon the cathode. A solid metal anode is consumed in the electroplating process and provides a constant source of metal ions to the plating bath.

Metal ions are maintained in solution in the electroplating bath by forming salts or metal complexes. Some of the most popular plating compositions utilize inorganic metal cyanides, and cadmium, brass, copper, silver and zinc can all be plated from cyanide baths.

Electroplatingbaths comprising aqueous alkaline solution of metal cyanides have several disadvantages. Such baths often tend to produce relatively dull and uneven coatings of the plated metal. The use of metal cyanide solutions can also be hazardous since if the pH of the electroplating medium should drop to neutral or below there is a danger of poisonous hydrogen cyanide gas being produced. Also, the use of metal cyanides presents a disposal problem due to their toxicity, and removing cyanides from waste baths prior to disposal is an expensive undertaking.

The prior art has suggested certain techniques for improving the performance of cyanide plating baths or for even eliminating cyanide from the bath. US. Pat. No. 2,195,409 claims to improve the performance of metal cyanide baths by the addition of a nuclear alkyl derivative of an aromatic sulfonic acid of the benzene series. The presence of this material is reported to eliminate pitting, uneven thicknesses and the formation of pinholes in the metal plate, and also improve brightness and uniformity of deposits.

More recently it has been suggested to use certain metal complexing agents in cyanide free plating baths. U.S. Pat. No. 3,457,293, for example, suggests the use of certain diphosphonates or monoamino lower alkylene phosphonates in the electroplating of divalent metal ions. US. Pat. No. 3,706,634 and 3,706,635 suggest combinations of ethylene diamine tetra( methylene phosphonic acid), l-hydroxy ethylidene-l l diphosphonic acid, and amino tri(methylene phos phonic acid) as particularly useful complexing compositions. US. Pat. No. 3,617,343 is similarly directed toward a nickel plating system employing certain phosphonic acid compounds. The present invention supplements and improves upon these methods of the prior art by providing certain organophosphorus compounds not taught in the prior art which are useful in electroplating applications.

SUMMARY In accordance with the present invention there is employed as the electroplating bath an aqueous solution comprising (a) a divalent or polyvalent metal ion; (b)

a carboxy alkylene amino di(methylene phosphonic acid) having the structure CH (OM) MOOC (CH N pound having the structure I M O P C PO M wherein M is as above defined and R is an alkyl radical having from 1 to II and preferably from l to 5 carbon atoms. Such electroplating bath compositions are particularly useful in plating divalent metal ions at a pH of about 6.0 to 10.0.

DESCRIPTION OF PREFERRED EMBODIMENTS In the practice of the present invention the metal to be plated in conjunction with the carboxy alkylene amino di(methylene phosphonic acid) compound (hereinafter referred to as carboxy amino phosphonate or CAP) is preferably a divalent transitional metal such as copper. iron, nickel, zinc, cadmium or alloys 5 such as brass. Monoand trivalent metals. however.

such as silver, chromium, and gold, may also be electorplated in conjunction with CAP and are included within the scope of the present invention.

The electroplating bath composition of the present invention is an aqueous solution comprising the metal to be plated, the carboxy amino phosphonate, pH adjusters and optionally one or more additives including brighteners, buffering agents, levelers, and the hydroxy alkylidene diphosphonic acid compound (HAD?) 5 which are intended to improve the performance or life of the bath or the quality of the metal deposit, or to impart other beneficial effect. It is common in the electro' plating art to utilize many and varied additives which are selected according to the particular system being used and on the basis of the skill of the electroplater. The use of such additives in the electroplating bath compositions of the present invention in order to adapt these compositions to individual circumstances are included within the scope of the present invention.

The bath is prepared according to conventional techniques by simply dissolving the desired ingredients into a quantity of water. The water is preferably low in mineral content and may be deionized. The metal to be plated is often added in the form of a water soluble salt such as a metal sulfate, chloride, phosphate, citrate, carbonate or acetate. Carbonate and acetate salts are often preferred because the anions of these salts may be thermally decomposed and thereby removed from the bath when the metal ion is released.

The carboxy amino phosphonate may be added directly to the bath in either the acid or a salt form as defined above. The acid form is generally preferred simply because it does not introduce extraneous metal or ammonium ions into the bath, but the introduction of such anions is usually not detrimental to the electroplating system. While the alkylene radical of the CAP compound may have from 3 to about 1 1 carbon atoms as defined above, the preferred compounds are those having alkylene radicals of from about 3 to 6 carbon atoms. N-(S-carboxypentyl) amino di(methylene phosphonic acid) is one particularly preferred CAP compound. CAP compounds useful in the practice of this invention may be prepared by the method of copending patent application Ser. No. 361,383, filed May 17, 1973, which is commonly assigned with the instant application and is incorporated herein by reference.

The optimum concentration of metal salt and CAP in the electroplating bath will be largely determined by the identity of the metal and metal salt, and by the characteristics of the individual electroplating system. As a rule, the concentrations are limited primarily by the solubilities of the compounds. Generally speaking, there is usually employed sufficient metal salt and CAP to provide from about 1 percent to about 5 percent by weight of metal in solution and to provide a mole ratio of CAP to metal of from about 1:1 to about 5:1. The optimum ratio will again depend to some extent on the metal being plated and the conditions and composition of the electroplating bath but as a general rule at least a slight molar excess of CAP is desirable and it is generally preferred that the mole ratio of CAP to metal ion be within the range of from about 1.2:1 to 2: 1. In most instances, the concentration of complex formed between the metal ion and the CAP should not exceed its solubility at the temperature and pH employed in the electroplating operation.

The electroplating bath is generally operated within a pH range of from about 6 to 12. The optimum pH will depend to a great extent upon the identity of the metal being plated, the presence of extraneous anions within the system and the composition and physical nature of the cathode being plated. Since pH is easily adjusted by the addition of alkaline materials such as alkali metal hydroxides, or acid materials such as mineral acids, it is a relatively simple matter to adjust the pH in either direction until optimum plating characteristics are achieved. As a general rule it is often found that lower pH values, that is within the range of from about 6 to 8, give better results in the practice of this invention than higher pH levels although exceptions to this rule may be found.

The use of the HADP compound (c) as defined above, is found to enhance the performance of the electroplating bath, particularly with respect to the plating copper. HADP compounds useful in the practice of the present invention may be prepared according to the method of U.S. Pat. No. 3,551,480. A particularly preferred HADP compound is l-hydroxy ethylidene-1,l-diphosphonic acid (HEDP). A combination of CAP and HADP is particularly effective to produce bright, uniform, and tightly adhering deposits of copper on brass and steel by electroplating at a pH of about 8.0. The concentration of HADP used in the composition of this invention is sufficient to provide a mole ratio of HADP to metal of from about 0.5:1 to about 5:], although from about 1:1 to about 2:1 is preferred.

While the aforegoing description is directed primarily to the composition of the electroplating bath, the

present invention further provides a process for the electrodeposition ofa divalent or trivalent metal which comprises the steps of electrolyzing an aqueous solution of a metal complex consisting of any of the metal ions hereinbefore described, a CAP compound, and any of the optional additives hereinbefore described. By the process of this invention, metals such as copper, iron, nickel, zinc and cadmium may be electrically deposited upon a cathode such as steel, aluminum, brass, zinc and the like.

During the electrodeposition process, the electroplating bath is maintained at a temperature within the range of the freezing point to boiling point of the bath, generally within a range of from about 30C. to about C. For reasons of current efficiencies it has been found preferable to maintain the temperature of the electroplating bath within the range from about 50C. to about 80C.

The amount of current employed in the electrodeposition may vary widely, depending upon the particular metal being plated, the temperature of the bath and whether or not the bath is agitated during the electroplating process. In general, the amount of current employed will be sufficient to provide a current density of from about 1 to 300 amperes per square foot of electrode surface. Ordinarily when the electroplating bath is quiescent or unagitated, the current density will be in the range of from about 5 to amperes per square foot, while when the electroplating bath is agitated current densities up to about 300 amperes per square foot may be utilized. The optimum or preferred current density for any particular electroplating situation will depend upon the individual characteristics of the operation and is readily determined by employing conventional electroplating techniques.

The time required to electroplate or to electrically deposit the metal will vary with the kind of metal, the current density, and bath composition and concentration, as well as upon the thickness of the plate or deposit desired. Generally, the greater the current density, the shorter will be the time required to produce a metal deposit or plate of a given thickness.

In accordance with a preferred embodiment of the present invention, copper is electrically deposited upon a wide variety of base metals or substrates such as zinc, iron, brass, steel, aluminum and the like. This preferred process comprises passing an electric current, at a density in the range of from about 5 to about 150 amperes per square foot of cathode surface, through an aqueous solution containing divalent copper ions and CAP or CAP HADP and having a pH in the range of from about 6.0 to about 10.0 and preferably 6.0 to 8.0. The concentration of copper in the electroplating bath composition is preferably from about 1% to about 5 percent by weight, based on the weight of the solution. The temperature of the solution is preferably maintained within the range of from about 50C. to about 70C. during the electroplating operation.

As stated above, the electroplating solutions of the present invention can contain known brighteners, buffers, and leveling agents and other additives commonly used in electroplating operations. Boric acid and its salts are compatible buffers for many formulas of the invention, and selenites and arsenites are useful brighteners for copper plating baths while aldehydes and ketones are useful for zinc plating. Other additives which may be employed in the electroplating solutions of the present invention include those disclosed in the 39th Annual Edition of Metal Finishing Guidebook Directory, 1973, published by Metals and Plastics Publications, Inc., 99 Kinderkamack Road, Westwook, NJ.

tent agitation. The results of these tests are set forth in Table I and particular attention is directed to the column designated Brightness Rating which provides the basic criteria for an evaluation of the electroplating ef- Certain preferred embodiments of the present inven- 5 fects on an overall basis.

TABLE I Test Additive/ Brightness No. pH Additive Cu Ratio Cathode Rating Remarks on Brightness l 6.0 CAP 2:l Brass Good Dark heavy copper deposit. 2 8.0 CAP 2:l Brass Poor Dark burn. 3 10.0 CAP 221 Brass Poor Dark burn. 4 6.0 CAP 81. 2:1 Brass Fair-Good Dark heavy copper deposit.

HEDP lzl 5 8.0 CAP & 2:l (a) Brass Very Good Very bright, good cover.

HEDP 1:] (b) Steel Very Good Very bright, good cover and copper adhesion. 6 10.0 CAP & 2:] Steel Fair Dark burn.

HEDP lzl 7 6.0 HEDP 2:] Brass Fair Foggy, smudged. S 8.0 HEDP 2:l Brass Poor Smudged, Streaky, spotted. 9 10.0 HEDP 2:l (a) Brass Good Bright, smudged.

(b) Steel Good Bright, smudged. good copper adhesion.

CAP N-(S-carboxypentyl) amino dimethylene phosphoric acid HEDP l-hydroxy ethylidene-l.l-diphosphonic acid tion concerning the electrodeposition of copper are illustrated by the following Example which is not limiting of the invention. All parts and percentages are by weight unless otherwise specified.

EXAMPLE Eleven tests were conducted to illustrate the performance of CAP alone and a combination of CAP and HEDP as compared to HEDP alone in the electrodeposition of copper from an electroplating solution con taining these additives.

The plating solutions identified as Test Nos. 1-9 in Table I were individually prepared in deionized water by dissolving measured amounts of CAP and/or HEDP and copper sulfate to provide 2 percent copper and the molar ratio of CAP/HEDP/Cu indicated in Table I. The pH of each solution was adjusted to the desired value of 6.0, 8.0, or 10.0 by the addition of potassium hydroxide. When necessary to dissolve the copper sulfate, the solution was heated up to 80C. and stirred vigorously for an additional minutes. The solutions were cooled, if necessary, to the plating temperature of 70C. and transferred to a Hull Cell". The particular additive utilized, the additive of copper mole ratio and the percent copper in solution are all shown in Table I.

The Hull Cell is constructed substantially as the electrolysis cell described in US. Pat. No. 2,149,344. This type of Hull Cell is standard equipment for the evaluation of electroplating solutions by the subjective determination of brightness rating" as based on the width of the brightness range, uniformity of brightness, and the presence or absence of smudges, stains and discoloration. In addition, the effectiveness of the bath is also evaluated on the basis of adhesion of plated metal to the cathode. The particular cathodes utilized in this test were brass or steel as indicated in Table l and were each 5 X 3 /4 inches in size. The anode utilized in these tests was made of copper and was 2% X 2% inches in size. The Hull Cell utilized in this test had a capacity of 1,000 milliliters.

Each test was conducted for a period of two minutes at a constant current of two amperes and with intermit- Tests Nos. 4-6 in Table 1 illustrate the advantage gained by utilizing HEDP in combination with CAP. A particular advantage, is noted at pH of 8.0 (Test No. 5) where a Brightness Rating of very good" was registered for plating on both brass and steel cathodes. It was also observed that copper adhesion on steel was very good under the conditions of this test. Test No. 5 accordingly represents a particularly preferred embodiment of the present invention.

Tests Nos. 7-9 are controls illustrating the results obtained with HEDP alone under similar electroplating conditions. It is observed that HEDP performs best at the higher pH of 10.0, but the quality of the plate is still inferior to that obtained with the combination of CAP and HEDP.

With further reference to the date in Table I, it is observed that the combination of CAP and HEDP gives at least fair results over the entire pH range, and that at a pH of 8.0, the combination gives significantly better results than can be obtained with either component alone regardless of pH.

Although the invention has been illustrated by reference to the electrodeposition of copper utilizing the method and compositions of this invention, the present invention is not limited thereto but is also useful in electrodepositiong other metals electrodepositing other cathode materials as hereinabove described. Ac-

cordingly, the present invention is not to be limited except as defined in the claims appended hereto.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A process for the electrodeposition of divalent and polyvalent metal ions which comprises the steps of electrolyzing an aqueous solution comprising a. a divalent or polyvalent metal ion,

b. a carboxy amino phosphonic acid compound of the structure CH PO M MOOC (CH N CH PO M I and wherein M is hydrogen, alkali metal, ammonium, alkyl ammonium, or amine, n is an integer of from 3 to about 11 and R is a C, alkyl radical; the concentration of (a) in said aqueous solution being from about 1 percent to 5 percent; the molar ratio of (a):(b) being from about 1:1 to 1:5; and the molar ratio (a):(c) being from about 2:1 to 1:5; the pH of said aqueous solution being from about 6.0 to 10.0, and the temperature of said aqueous solution being from about 30 to 90C.

2. A process of claim 1, wherein (b) is CH POM MOOC (CH N 6. An electroplating bath composition comprising an aqueous solution of a. a divalent or polyvalent metal ion,

b. a carboxy amino phosphonic acid compound of the structure CH POM 5 MOOC (CH n CH PO M and c. a l-hydroxy alkylidene-l,l-diphosphonic acid compound of the structure C PO MOP- 32 cu PO M MOOC (CH 8. A composition of claim 7 wherein R is CH 9. A composition of claim 8 wherein said metal ion (a) is copper,

10. A composition of claim 6 wherein said metal ion (a) is selected from the group consisting of copper, iron, nickel, zinc, and cadmium, silver, chromium and gold.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 0 PATENT NO. 3,914,162

DATED 3 October 21 1975 INVENTOMS) I Xavier Kowalski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown beiow:

Col. 5, line 4, "Westwook, N.J. should read 1 Westwood, N.J.

Col. 6, line 27, "brightness" should read brightness Col. 6, line 45, "date" should read data Col. 6, line 55, "electrodepositiong other metals electrodepositing other cathode materials as hereinabove described." should read electrodepositing other metals upon other cathode materials as hereinabove described Col. 8, line 25, Claim 7, "A composition of claim 1" should read a A composition of claim 6 Engned and Sealed this sixth [SEAL] D y of Aprll1976 Arrest:

RUTH 3 2:3" c. MARSHALL DANN a Commissioner oflarents and Trademark

Claims (10)

1. A PROCESS FOR THE ELETRODEPOSITION OF DIVALENT AND POLYVALENT METAL IONS WHICH COMPRISES THE STEPS OF ELEDTROLYZING AN AQUEOUS SOLUTION COMPRISING A. A DIVALENT OR POLYVALENT METAL ION, B. A CARBOXY AMINO PHOSPHONIC ACID COMPOUND OF THE STRUCTURE

2. A process of claim 1, wherein (b) is

3. A process of claim 1 wherein R is -CH3.

4. A process of claim 3 wherein said metal ion (a) is copper and the pH of said aqueous solution is about 8.0.

5. A process of claim 1, wherein said metal ion (a) is selected from the group consisting of copper, iron, nickel, zinc, and cadmium, brass, silver, chromium and gold.

6. An electroplating bath composition comprising an aqueous solution of a. a divalent or polyvalent metal ion, b. a carboxy amino phosphonic acid compound of the structure

7. A composition of claim 1 wherein (b) is

8. A composition of claim 7 wherein R is CH3.

9. A composition of claim 8 wherein said metal ion (a) is copper.

10. A composition of claim 6 wherein said metal ion (a) is selected from the group consisting of copper, iron, nickel, zinc, and cadmium, brass, silver, chromium and gold.