GB2133040A - Copper plating bath process and anode therefore - Google Patents

Abstract

The bath comprises copper ions, 1- hydroxyethylidene- 1,1 - diphosphonic acid, optionally together with either aminotri - (methylene phosphoric acid) or ethylene diamine tetro (methylene phosphonic acid) and a buffer (eg a carbonate) and has a pH of 6 to 10.5. The process involves providing an electrolyte having a pH of 6 to 10.5 and comprising copper ions, a complexing agent and a buffer and using as anodes a combination of a copper base soluble anode 16 and a nickel-iron alloy insoluble anode 18 containing from 10 to 40 weight % iron to provide a copper anode to nickel-iron alloy anode surface area ratio of from 1:2 to 4:1. The anode claimed comprises a nickel-iron alloy containing 10 to 40 weight % iron, 0.005 to 0.06 weight % sulphur, balance essentially nickel. <IMAGE>

Description

SPECIFICATION Cyanide-free copper plating process and alloy anode The use of cyanide salts in copper plating electro lytes has become environmentally disfavoured because of ecological considerations. Accordingly, a variety of non-cyanide electrolytes for various metals have heretofore been proposed for use as replace ments for the well-known and conventional commercially employed cyanide counterparts. For example, U.S. Patent No.3,475,293 discloses the use of certain diphosphonatesforelectroplating divalent metal ions; U.S. Patents Nos. 3,706,634 and 3,706,635 disclose the use of combinations of ethylene diamine tetra (methylene phosphonic acid), 1 - hydroxyethylidene - 1, 1 - diphosphonic acid, and aminotri (methylene phosphonic acid) as suitable complexing agentsforthe metal ions in the bath; U.S.Patent No.

3,833,486 discloses the use of water soluble phosphonate chelating agents for metal ions in which the bath further contains at least one strong oxidizing agent; while U.S. Patent No.3,928,147 discloses the use of an organophosphorus chelating agent for pretreatment of zinc die castings prior to electroplating with electrolytes ofthe types disclosed in U.S.

Patents 3,475,293,3,706,634 and 3,706,635.

While the electrolytes and processes disclosed in the aforementioned United States patents have provided satisfactory electrodeposits under carefully controlled conditions, such electrolytes and processes have not received widespread commercial acceptance in view of one or more problems associated with their practice. A primary problem associated with such prior art electrolytes has been inadequate adhesion of the copper deposit to zinc and zinc alloy substrates.

Another such problem relates to the sensitivity of such electrolytes to the presence of contaminants such as cleaners, salts of nickel plating solutions, chromium plating solutions and zinc metal ions introduced into the electrolyte during conventional commercial practice. Still another problem is the harzardous nature of strong oxidizing agents employed in certain of such prior art electrolytes.

The present invention overcomes or mitigates many ofthe problems and disadvantages associated with prior a rt cya nide-free copper plating solutions by providing a process employing an electrolyte which is cyanide-free providing an environmentally manageable system, which will function to produce an adherent copper deposit on conductive substrates including steel, brass and zinc base metals such as zinc die casts and the like; which will efficiently produce ductile, fine-grained copper deposits at thicknesses usually ranging from about 0.01 5 to about 5 mils (0.381 to 127 microns), which is more tolerant of the presence of reasonable concentrations of contaminants such as cleaning compounds, salts of nickel and chromium plating solutions and zinc metal ions as normally introduced into a plating bath in a commercial practivce, and which is of efficient and economical operation. The invention further encompasses a novel insoluble alloy anode employed in the practice of the process.

The benefits and advantages of the present invention are achieved in accordance with the process aspects thereof by employing a cyanide-free aqueous electrolyte containing controlled, effective amounts of cupric ions, an organo-phosphonate chelating agent, a buffering agent, hydroxyl and/or hydrogen ions to provide a pH from mildly acid to moderately alkaline, and optionally but preferably, a wetting agent. The copper ions may be introduced by a bath soluble and compatiblecoppersalt,to provide a cupric ion concentration in an amount sufficientto electrodeposit copper, and generally ranging from as low as about 3to as high as about 50 grams per litre (gill) under selected conditions.The organo-phosphonate chelating agent is a compound selected from 1 - hydroxy ethylidene - 1,1 - diphosphonic acid (HEDP) by itself present in an amount of about 50to about 500 g/l, a mixture of HEDP and aminotro - (methylene phosphonic acid) (ATMP) in which HEDP is present in an amount of at least about 50 percent by weight of the mixture of HEDP and ethylenediaminetetra (methylenephosphonicacid) (EDTMP) in which HEDP is present in an amount of at least about 30 percent by weightofthe mixture, as well as the bath soluble and compatible salts and partial salts thereof.When mixtures of HEDP and ATMP or HEDP and EDTMP are employed as the chelating agent instead of HEDP by itself, a reduction in concentration ofthe chelating agent can be used due to the increased chelating capacity of the ATMP and EDTMP compounds in comparison to that of HEDP. The concentration ofthe organo-phosphonatechelating agentwill range in relationship to the specific amount of copper ions present in the bath and is usually controlled to provide an excess ofthe chelating agent relativetothe copper ions present.

In addition to the foregoing, the bath contains a suitable compound such as alkali metal carbonates, acetates and/or borates as a stabilizing agent as well asa bufferingagentwhich ispresentin an amount usually of at least about 5 up to about 100 g/l with amounts of at least about 20 g/l being required in most instances. The bath further contains hydroxyl and/or hydrogen ions to provide an electrolyte from mildly acidic (pH 6) to moderately alkaline (pH 10.5) with a pH of about 9 to about 10 being usually preferred. The bath may optionally and preferablyfurthercontaina bath soluble and compatible wetting agent present in an amount upto about0.25 g/l.

In accordance with the process aspects of the present invention,the cyanide-free electrolyte as hereinbefore described is employed for electrodepositing afine-grained ductile, adherent copper strike on conductive substrates including ferrous-base substrates such as steel, copper-base substrates such as copper, bronze and brass; and zinc-base substrates including zinc die castings. The substrate to be plated is immersed in the electrolyte as a cathode and a soluble copper anode in combination with an insolu bleferriteanodeisemployedto provide a copper anode to ferrite anode surface area ratio of about 1:2 to about 1:6.The electrolyte is electrolyzed by passage of current between the cathode and anode for a period oftime of about 1 minute to as long as several hours and even days in order to deposit the desired thickness of copper on the cathodic substrate. The bath can be operated at a temperature of from about 1000 to about 1 600F (38" to 71"C) with temperatures of about 11 otto about 140"F (43 to 60"C) being preferred.

The particulartemperature employed will vary depending on the specific bath composition in order to optimize plate characteristics. The bath can be operated at a current density of about 1 to about 80 amperes persquare foot (ASF) 0.1 1 to 8.8 amperes per square decimetre (ASD)), depending on bath composition, employing a cathode to anode ratio usually of about 1:2 to about 1 :6. It has been surprisingly discovered that, uniform, adherent and fine-grained deposits are obtained by electrifying the substrates priorto immersion in the electrolyte. In the case of zinc-base substrates, electrification of the part at a voltage of at least about 3 volts has been found necessary to attain satisfactory adhesion of the copper deposit.The specific operating parameters and composition ofthe electrolyte will vary depending upon the type of basis metal being plated, the desired thickness of the copper plate to the deposited, and time availability in consideration of the other integrated plating and rinsing operations.

In accordance with a further process aspect ofthe present invention, the cyanide-free electrolyte as hereinabove described is employed for electro-depositing afine-grained ductile, adherent copper strike on conductive substrates including ferrous-base substrates such as steel, copper-base substrates such as copper, bronze and brass; and zinc-base substrates including zinc die castings. The substrate to be plated is immersed in the electrolyte as a cathode and a soluble copper anode in combination with an insolu bie nickel-iron anode is employed to provide a copper anode to nickel-iron alloy anode surface area ratio of about 1 :2to about 4:1.The electrolyte is electrolyzed by passage of current between the cathode and anode for a period of time of about 1 minute to as long as several hours and even days in orderto deposit the desired thickness of copper on the cathodic substrate.

The bath can be operated at a temperature of from about 100"to about 160"F (37"to 71"C)with tempera tures of about 1100 to about 140"F (43" to 60"C) being preferred. The particulartemperature employed will vary depending on the specific bath composition in order to optimize plate characteristics. The bath can be operated at a current density of about 1 to about 80 amperes persquarefoot(ASF) (0.11 to 8.8 ASD), depending on bath composition, employing a cathode to anode ratio usually of about 1:1 to about 1:6.It has been surprisingly discovered, that uniform, adherent and fine-grained deposits are obtained by electrifying the substrates priorto immersion in the electrolyte. In the case of zinc-base substrates, electrification ofthe part at a voltage of at least about 3 volts has been found necessary to attain satisfactory adhesion of the copper deposit. The specific operating parameters and composition ofthe electrolyte will vary depending upon the type of bases metal being plated, the desired thickness of the copper plate to be deposited, and time availability in consideration of the other integrated plating and rinsing operations.

The present invention further provides a novel nickel-iron insoluble anode which is employed in the process in conjunction with asolublecopperanodein controlled anode surface ratios thereby achieving the desired oxidizing medium for maintaining appropriate plating conditions andfor achieving copper electrodepos tsof the desired characteristics. The insoluble nickel-fron alloy anode is preferably of a composite construction comprising a conductive core having an adherent nickel-iron alloy electrodeposit bonded thereover containing from about 10 percent up to about 40 percent by weight iron in the alloy and from about 0.005 up to about 0.06 percent sulphur.

The core comprises metalssuch-as copperralurni- nium, iron and other conductive alloys ofwhich copper itself comprises the preferred core rnaterial.

The nickel-iron alloy coating or plating on the coreis further characterized as being substantially nonporous and may be as thin as 1 to 2 mils (25.4to 50.8 microns) thick.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, byway of example, to the preferred embodiments and the accompanying drawings, in which: Figure lisa schematic perspective view partly in section illustrating a plating receptacle suitable for use in the practice of the present process; Figure 2 is a side elevational view of an insoluble nickel-iron alloy anode employed in the practice ofthe process of the present invention; and Figure 3 is a magnified transverse cross-sectional view ofthe anode shown in Figure 2 and taken substantially along the line 3-3 thereof.

A cyanide-free electrolyte suitable for use in the practice ofthe present invention contains as its essential consituents, copper ions, an organo-phos phonatecomplexing agent in an amount sufficient to complexthe copper ions present, a stabilizing and buffering agent comprising a bath soluble and compatible carbonate, borate and/or acetate compound, as well as mixtures thereof, a pH of about 6to about 10.5, and optionally, a wetting agent.

The copper ions are introduced during makeup of the electrolyte by employing any one or mixtures of bath solubles and compatible coppersaltssuch as sulphate, carbonates, oxides hydroxides, and the like.

Oftheforegoing, copper sulphate in the form of pentahydrate (CuSO-4.5H2O) is preferred. The copper ions are present in the bath within the range of about 3 upto about 50 g/l,typicallyfrom around5to about 20 g/l. For example, when plating steel substrates, copper ion concentrations of about 15 upto about 50 9/l are employed to achieve a high rate of copper electrodeposition. In such instances in which the copper ion concentration is above about 20 girl, it has been found by experimentationthatelectrified part entry into the bath is preferred to attain satisfactory adhesion. On the other hand, when plating zinc-base substrates such as zinc die castings, for example, copper ion concentrations of about 3.5 to about 10 g/l are preferred and in which instance the part must be electrified atthe time of bath immersion to achieve an adherent deposit. During use ofthe electrolyte, a replenishment of the copper ions consumed during the electrodeposition operation as well as those removed by drag-out is achieved by the progressive dissolution of a copper anode employed in electrolyzing the bath.

The complexing or chelating agent comprises an organo-phosphorus ligand of an alkali metal and alkaline earth metal salt of which calcium is not suitable dueto precipitation. Preferably,thecomplex- ing salteomprisesan alkali metal such as sodium, potassium lithium and mixtures thereof ofwhich potassium constitutes the preferred metal. The complexing agent is present in the bath in consideration of the specific concentration of copper ions present.

Thespecificorgano-phosphorus ligand suitable for use in accorda nce with the practice ofthe present invention comprises a compound selected from 1 hydroxyethylidene -,1 - diphosphonic acid (HEDP) by itself present in an amount of about 50 to about 500 g/l, a mixture of HEDP and aminotri - (methylene phosphonic acid) (ATM P) in which HEDP is present in an amount of at least about 50 percent by weight of the mixture, and a mixture of HEDP and ethylenediamine tetra (Methylene phosphonic acid) (EDTMP) in which HEDP is presentin anamountofat least about 30 percent by weight of the mixture, as well as the bath soluble and compatible salts and partial salts thereof.

When mixtures of HEDP and ATMP or HEDP and EDTMP are employed as the chelating agent instead of HEDP by itself, a reduction in the concentration of the chelating agent can be used due to the increased chelating capacity of the ATMP and EDTMP compounds in comparison to that of HEDP. Commercially available compounds ofthe foregoing types which can be satisfactorily employed in the practice ofthe present invention include Dequest 2010 (HEDP), Dequest 2000 (AMP) and Dequest 2041 (EDTMP) available from. Monsanto Company. The word 'Dequest' isa trade mark.

As previously indicated, the HEDP chelating agent can be employed at a concentration of about 50 g/l corresponding to a copper ion concentration of about 3 g/l upto a concentration of about 500 g/l correspond ing to a copper ion concentration of about 50 g/l, with intermediate concentrations proportionately scaled in consideration of corresponding intermediate concentrations of copper ions. When a mixture of HEDP and ATMP is employed, preferably comprising about70 percent HEDP and 30 percent by weig ht ATMP, it has been discoveredthat 14g/l HEDP and 6 g/l A are satisfactory at a copper ion content of 3 g/l while 225 gll HEDP and 97 g/l ATMP are satisfactory at a copper ion bath concentration of 50 g/l.Corresponding adjustments intheconcentrations of HEDP and ATMP are proportionately made when the copper ion concentration is intermediate of the 3 and 50 g/l limits to provide satisfactory chelation with a slight excess of chelating agent present in the bath. Similarly, when a mixture of HEDP and EDTMP is employed, preferably comprising about 50 percent by weight of each compound, it has been discovered that 9 g/l HEDP and 1 0 gel EDTMP are satisfactory at a copper ion concentration of about3g/l while 145g/l HEDP and 166 g/l EDTMP are satisfactory at a copper ion bath concentration of about 50 g/l with proportionate adjustments in the concentrations of these two constituents in consideration of intermediate copper in concentrations.Itwill also be appreciated that alternative mixtures of chelating agents within the ranges specified will require proportionate adjustments in concentration oftotal chelating agent present in relation to copper ion concentration in consideration ofthe foregoing concentration rela tionshipswhich can be readily calculated and confirmed by routine testing to provide optimum per formanceforanygiven conditions infurtherconsid- eration ofthe specific examples hereinafter set forth.

Athird desirable constituent ofthe copper electrolyte comprises a bath soluble and compatible stabilizing and buffering agent including carbonate compounds, borate compounds, acetate compounds as well as mixtures thereof. Preferably, sodium carbonate and potassium carbonate are employed to stabilize the electrolyte against pH fluctuations and to further serve as a carrier for contaminating metal ions introduced in the bath as a result of drag-in and dissolution of the parts in the electrolyte during the electrodeposition operation. The use ofthe aforementioned buffering agents has further been observed, depending upon the particular chelating agent used, to inhibit the formation of smutty copper deposits and eliminate dark copper deposits in the cathode low current density areas.Ammonium ions have been found undesirable in some instances because of a loss of adhesion ofthe electrodeposit while calcium ions are undesirable because of the tendency to form precipitates in the bath. The concentration of the buffer can broadly range from about 3 up to about 100 g/l calculated asthe sodium salt, preferably about 10 to about 20 g/l. Concentrations of the buffering agent below the recommended minimum concentrations will result in pH fluctuations whereas concentrations above the maximum range specified do not appearto have any adverse effects on the operation of the electrolyte.

Since the buffering agent and complexing agent are subject ot depletion by both decomposition and drag-out, a replenishment of these two chemicals to maintain the electrolyte within appropriate composition limits is necessary during commercial operation.

This can conveniently be performed on an intermittent or continuous bases in response to an analysis of bath composition by adding the two constituents separately or in admixture in appropriate proportions.

The electrolyte is adjusted to provide a pH of from about6 upto about 10.5 with a pH of about 9 to about 10 being preferred. Typically an operating pH of about 9.5 has been found particularly satisfactory. The appropriate pH of the electrolyte can be maintained by adding an alkali metal hydroxide to the electrolyte to raise the pH of which potassium hydroxide is preferred. In orderto reduce the pH within the desired range, a mineral acid oran alkali metal bicarbonate can be employed of which potassium bicarbonate consti tuts a preferred material. When the operating pH decreases below the recommended level, it has been observed thatthe electrolyte tends to promote poor adhesion of the copper deposit on the substrate.On the other hand, at an operating pH above the recommended range, it has been observed in some instances, that the copper deposit becomes grainy and of a burnt characteristic. It has been found that at a pH of below about 7.5 down to about 6, satisfactory adhesion and deposit appearance can be obtained on copper and copper alloy substrates. However,when plating ferrous and zinc base substrates, a pH above about7.5to about 10.5 has been found to provide best results.

In addition to the foregoing constituents, the bath may optionallyfurther contain a wetting agent or surfactantwhich is bath soluble and compatible with the otherconstituentstherein. When such a surfactant is employed, it can be used in concentrations upto about0.25g/lwith amounts of from about 0.01 to about 0.1 g/l being preferred. Typical surfactants suitable for use in the practice ofthe present invention include polyethylene oxides such as Carbowax 1000, alkyl sulphates such as 2 - ethyl hexyl sulfate provided that the bath is carbon filtered to remove degradation products formed during operation, purfluro anionic wetting agents, and the like.

In the practice ofthe process of the present invention, the electrolyte can be operated at a temperature of from about 1000 to about 1 600F (38 to 71"C), preferablyfrom about 1100 to about 140"F (43" to 60"C) with temperatures of about 1200 to about 140"F (54" to 60"C) being typical.The specific temperature employed will vary depending on bath composition such as will become apparent in the specific examples subsequently to be described.The bath can operate at a cathode current density of from abot 1 to about 80 ASF (0.1 to 8.8 ASD) with a current density of about 5 to about 25 ASF (0.55 to 2.75 ASD) being preferred.

The electrodeposition ofthe copper deposit can be performed in consideration ofthe other operating parameters ofthe bath within a time of as little as 1 minute to as long as several hours or even dayswith plating times of about 2 minutes to about 30 minutes being more usual for strike deposits. The specific time of electrodeposition will vary depending upon the thickness ofthe plate desired which will typically rangefrom about 0.015to about 5 mils (0.38to 127 microns).

The electroplating operation is performed by immersing the conductive substrate to be plated in the elctrolyte and connecting the substrate to the cathode of a direct current source. It has been found that when the copper ion concentration is above about 20 g/l, it is advantageous, and usually necessary, to electrify the substrate priorto and during immersion in orderto achieve good adherence of the copper plate on ferrous-base substrates. In the case of zinc-base substrates, it has been found essential at all copper ion bath concentrations to electrify the zinc-base substrate priorto and during entry into the bath at a minimum potential of about 3 volts to achieve satisfactory adhesion of the copper plate on the zinc-bases substrate.

Acombination of anodes are employed for electrolyzing the bath and effecting the deposition of a copper plating on the cathode. The combination of anodes includes a copper anode of any of the types well known in the art such as an oxygen-free high purity copper anode which is soluble and replenishes the copper ions consumed from the bath by electrodeposition and drag-out It has been observed that when the concentration of copperfalls belowthe recommended minimum concentration, a reduction in cathode efficiency occurs accompanied by burnt deposits. On the other hand, concentrations of copper ions above the recommended maximum range has been observed to adversely affectthe adhesion of the copper deposit.While replenishment of copper ions can be effected by the addition of copper salts to the electrolyte, it is preferred to effect replenishment by dissolution ofthe copper anode at a rate substantially corresponding to the depletion rate ofthe copper ions by an appropriate adjustment ofthe copper anode surface relative to the insoluble anode surface, which insoluble anode may be a ferrite anode or a nickel-iron alloy anode. The specific copper anode surface area to ferrite anode surface area ratio can range from about 1 :2toabout 1 :6with a ratio of about 1 :3about 1:5 being preferred and a ratio of about 1:4 being typical.

The specific anode surface area to nickel-iron alloy anode surface area ratio can range from about 1:2 up to about 4: 1, with a ratio of about 1 :1 to about 2:1 being preferred. Moreover, the ratio of the surface area of the cathode to the total anode surface area can range from about 1:2 up to about 1 :6, preferably about 1 :3to about 1:5 :Sandtypically,aboutl:4.

The insoluble ferrite anode employed in controlled combination with the soluble copper anode may comprise an integral or composite anode construction in which the ferrite sections thereof comprise a sintered mixture of iron oxides and at least one other metal oxide to produce a sintered body having a spinnel crystalline structure. Particularly satisfactory ferrite anode materials comprise a mixture of metal oxides containing about 55 to about 90 mol percent of iron oxide calculated as Fe2O3 and at least one other metal oxide present in an amount of about 10to45 mol percent of metals selected from the group consisting of manganese, nickel, cobalt, copper, zinc and mixtures thereof. The sintered body is a solid solution in which the iron atoms are present in both the ferric and ferrous forms.

Such ferrite electrodes can be manufactured, for example, by forming a mixture offerricoxide (Fe2O3) and one or a mixture of metal oxides selected from the group consisting of MnO, NiO, CoO, CuO,and ZnO to provide a concentration of about 55 to 90 mol percent ofthe ferric oxide and 10 to 45 percent of one or more ofthe metal oxides which are mixed in a ball mill. The blend is heatedforaboutoneto aboutfifteen hours in air, nitrogen or carbon dioxide attemperatures of about 7000 to about 1000 C. The heating atmosphere may contain hydrogen in an amountupto about 10 percent in nitrogen gas. After cooling, the mixture is pulverized to obtain a fine powder which is thereafter formed into a shaped body of the desired configuration such as by compression molding or extrusion.

The shaped body is thereafter heated at a temperature of about 11 000to about 1450"C in nitrogen or carbon dioxide containing up to about20 percentby volume of oxygen for a period ranging from about 1 to about 4 hours. The resultant sintered body is thereafter slowly cooled in nitrogen or carbon dioxide containing up to about 5 percent by volume of oxygen producing an electrode ofthe appropriate configuration characte rized as having relatively low resistivity, good corro sion resistance and resistance to thermal shock.

It will be appreciated that instead of employing ferric oxide, metal iron orferros oxide can be used in preparing the initial blend. Additionally, instead of the other metal oxides, compounds of the metals which subsequently produce the corresponding metal oxide upon heating may alternatively be used, such as, for example, the metal carbonate or oxalate compounds.

Oftheforegoingferrite anodes comprised predomi nantly of iron oxide and nickel oxide within the proportions as hereinbefore set forth have been found particularly satisfactoryforthe practice ofthe present process.

Aferrite anode comprising a sintered mixture of iron oxide and nickel oxidesuitableforuse in the practice of the present invention is commercially available from TDK, Inc. underthe designation of F-21.

By the proper proportioning ofthe copper and ferrite anode surfaces, the chemistry of the electrolyte is maintained with appropriate additions ofthe complexing and buffering agent and small additions, if necessary, ofthe copper salt Insufficientferrite surface area results in dull or grainy deposits while an excessive ferrite anode surface area may result in reduced cathode efficiency and progressive depletion of copper anions requiring more frequent replenishmentofthe electrolyte with copper salts.

Surprisingly, the use of alternative primary insoluble anodes in lieu of the ferrite anode as hereinabove described orthe nickel-iron alloy anodes as hereinafter described does not provide satisfactory deposits For example, insoluble graphite primary anodes have been found to deteriorate producing harmful byproducts in the bath which result in smutty deposits.

The insoluble nickel-iron alloy anode employed in controlled combination with the soluble cepperanode may be of an integral or composite construction providing at least an exterior surface stratum which is comprised of a nickel-iron alloy containing from about 10 percent up to about 40t percent by weigiNtiron and the balance essentially nickel, preferably about 15 to about 30 percent iron. ln accordance with a preferred form ofthe present invention, the insoluble nickel-iron alloy anode is comprised of an electrically conductive core having an adherent electrodepositofthe nickeliron alloy over the surfaces thereof of a thickness sufficientto envelop the core material preventing its exposure over prolonged periods of use.The nickeliron alloy deposit or coating is further characterized as being substantially nonporous effectively sealing the internal core from exposure to the electrolyte. In such composite anode constructions, the core material may comprise metals such as copper, alloys of copper, ferrous-base cores including iron and steel, aluminium and alloys of aluminium, nickel andthe like.Oftheforegoing,a high puritycoppercoresimilar to the copper anode employed in conjunction with the insoluble nickel-iron anode is preferred since inadvertent exposure of the core as a result of damage or as a result of progressive dissolution ofthe coating or plating over prolonged periods of time does not adversely affect the operation of the bath in that copper ions are introduced ion a mannersimilarto those introduced by the conventional soluble copper anodes. In contrast, when ferrous-base cores are employed, inadvertent exposure ofthe core to the electrolyte results in a progressive dissolution of iron introducing iron into the electrolyte which ultimately adversely effects the quality ofthe copper deposit produced rendering the process commercially insatisfactory.It has been observed that concentrations of iron ions in the electrolyte in excess of about 325 ppm are detrimental and tend to produce dull, grainy copper deposits ofthe burnt type. Moreover, the contaminating iron ions cannot be readily removed in view of the complexing agent in the electrolyte which complexes such contaminating iron ions very strongly. While cores comprised of nickel or alloys ofnickel can also be satisfactorily employed, their lower electrical conductivity and relatively higher cost renders them less desirable than copper cores.

In accordance with a preferred practice of the present invention, the insoluble nickel-iron alloy anode is produced by electrodepositing a nickel-iron alloy plate on a conductive core which has been subjected to appropriate preplating steps to render the substrate receptive to the electrodeposition of a nickel-iron alloy in accordance with conventional preplate practices well known in the artfor metal substrates. When an aluminium or aluminium alloy core is employed preplate steps such as zincate, bronze alloy or anodizing are employed in accordance with well-known practices to render the core receptive to the nickel-iron plating operation.The electrolyte for depositing the nickel-iron alloy deposit on the anode core may comprise any ofthetypes well known in the art such as described, for example, in United States Patents Nos. 3,806,429; 3,974,044 and 4,179,343 which are assigned to the same assignee as the present invention and the teachings of which are incorporated herein by reference. It will be appreciated that the compositions and processes as described in the aforementioned United States patent are primarily intended for producing an extremely bright decorative nickel-iron alloy deposit on a conductive substrate simulating that of a conventional bright nickel deposit.

Avery bright levelled nickel-iron deposit is not essential to the satisfactory operation of the insoluble nickel-iron alloy anode of the present invention in that the alloy deposit is of a functional ratherthan a decorative plating and accordingly, semi-bright, satin and even relatively dull nickel-iron electrodeposits can be employed. In view of the foregoing, the particular concentration and types of primary and secondary brighteners employed in the aforementioned United States patents can be varies and reduced in concentration to provide an adherent and ductile nickel-iron plating ofthe desired alloy composition.

The nickel-iron alloy electrolyte contains organic sulphur compounds to introduce sulphur in the resultant alloy deposit to provide satisfactory opera tionandwhich alsoenhancesthe adhesion ofthe plate to the anode core. It has been found that sulphur contents in amounts of about 0.005 upto about 0.06 percent by weight preferably about 0.01 to about 0.04 percent by weight, in the nickel-iron alloy deposit is necessary to provide satisfactory performance as an insoluble anode in the practice of the present process.

Typically, the sulphur content in the nickel-iron alloy electrodeposit is abut 0.02 to about 0.03 percent by weight.

It has been found that the composition of the alloy is important in attaining the appropriate oxidizing medium in the copper electrolyte to provide a copper electroplating process which is commercially accept able from the standpoint of ease of control, mainte nance and replenishment and in the quality of the copper plate produced. While iron concentrations of about 10 percent to about 40 percent by weight have been found satisfactory, particularly satisfactory results are obtained at iron concentrations of about 15 to about 30 percent iron, especially of about 20 to about 25 percent iron with the balance essentially nickel.

Surprisingly, an anode consisting essentially of pure iron will not work in the practice ofthe present process in that it rapidly dissolves causing a rapid increase in iron ion concentration rendering the bath inoperative forthe reasons previously set forth. Similarly, substantially pure nickel anodes have been found unsatisfactory in spite of the factthey are relatively insoluble.

Substantially pure nickel anodes have been found inadequate for providing the desired oxidizing medium to achieve proper plating performance over prolonged time periods. Similarly, nickel-iron alloys devoid of anysulphurhave been found unsatisfactory after relatively short periods of use such as about 8 hours. On the other hand, sulphur contents in excess of about 0.06 percent in the nickel-iron alloy are unsatisfactoryfor sustained commercial operation.

Referring now in detail to the drawing, and as shown in Figure 1 thereof, a typical electroplating arrangement is schematically illustrated suitable for use in the practice ofthe present invention. As shown, the apparatus includes a tank lOfilledwith the cyanide-free alkaline copper electrolyte 12 and having an anodically charged bus bar 14 disposed thereabove from which a pair of soluble copper anodes 16 and an insoluble nickel-iron alloyanode 18aresuspended in electrical contact therewith. The ratio ofthe anode surface area ofthe soluble and insoluble anode or anodes is importantto achieve proper operation ofthe bath during sustained commercial operation.By appropriate proportioning of the copper anode surface area and nickel-iron alloy anode surface area within a range of about 1:2 upto about preferably at ratios of about 1:1 upto about 2:1 ,the chemistry of the electrolyte is maintained with appropriate additions ofthe complexing and buffering agents and small additions, if necessary, of the copper salt. When the ratio of the copper anode surface area to nickeliron alloy anode surface area falls below about 1 :2, i.e.

when the total copper anode surface area falls below about33 percent of the total anode surface area, the copper anode has been observed to tend to polarize in which condition it remains conductive but no longer dissolves at the desired rate resulting in dull and grainy copper deposits. This also necessitates increased replenishment of copper ions by the addition of soluble salts which is associated with the formation of degradation products in the bath. Accordingly, whilethe process can be operated for shorttime periods at a copper anode surface area to nickel-iron alloy anode surface area ratio of less than about 1 :2, such operation is not commercially practical over prolonged time periods.

Referring nowto Figure 2 ofthe drawing, the insoluble nickel-iron alloy anode constructed in accordance with a preferred embodiment ofthe present invention is of a composite construction comprising an elongated bar 20 securely connected at its upper end to a hook-shaped member 22 which preferably is comprised of an inert conductive mate rial such as titanium, for example. The elongated bar 20 as best seen in figure3 is comprised of a central conductive core 24which maybe of a solid ortubufar construction having an adherent outer stratum or plating 26 overlying the entire outer surface thereof.

The particular configuration ofthenickel-iron alloy anode is not critical in achieving satisfactory perform ance thereof and the shape as well as the crosssectional configuration can be varied in accordance with known practices to achieve optimum throwing power and uniformity in the characteristics and thickness of the copper electrodeposit consistent with the nature ofthe substrates being plated.

During an electroplating operation, a substrate or workpiece 28to be copper plated is immersed in the electrolyte 12 in the tank 10 of Figure 1 generally supported from a suitable cathodically charged bus bar 30 and current is passed between the anode and the substrate for a period of time sufficientto deposit the desired thickness of copper on the substrate.

While the replenishment of the complexing agent during operation ofthe electrolyte is usually done employing a neutralized alkali metal saltthereofto avoid a drastic reduction in the operating pH ofthe electrolyte, it is contemplated that the acid form of the complexorcan be used for original or new bath makeup byfirst dissolving the acid form complexor in waterfollowed bytheaddition of a base such as potassium hydroxide to increase the pH to a level above about 8. Thereafter, the buffering agent can be added to the preliminary solution in which a neutralization of the complexor has been accomplished in situ.

In ordertofurther illustrate the process and novel anode of the present invention, the following specific examples are provided. It will be understood that the examples as hereinaftersetforth are provided for illustrative purposes and are not intended to be limiting of the scope ofthis invention as herein disclosed and as setforth in the subjoined claims.

EXAMPLE 1 Acyanide-free aqueous alkaline electrolyte suitable for depositing a copper strike on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water, about 60 to about 72 g/l of copper sulphate pentahydrate (15 to 18 g/l copper ions) under agitation. Followingthe complete dissolution ofthecopper sulphate salt, about 81 to about 87 g/l of a complexing agent is dissolved comprising the neutralized potas sìum salt of a 30 percentbyweightaminotri (methylene - phosphonic acid) (ATMP) and 70 percent byweightof 1 - hydroxyethylidene - 1, 1 di phosphonic acid (HEDP). The pH of the solution is adjusted employing a 50 percent aqueous solution of potas sium hydroxide to provide a pH of about 8.5.

Thereafter from about 15 to about 25 g/l of potassium carbonate is added and the solution is agitated until complete dissolution occurs. The solution isthereafter heated to an operating temperature of from about 1100 to about 140"F (43 to 60"C) and a combination of an oxygen-free, high purity copper anode and a ferrite anode are immersed while suspended from an anode bar to provide a ferrite anode surface area to copper anodesurfaceareaofabout4:1.

While agitation is not critical, some agitation such as mechanical, cathode rod and preferably air agitation is employed to provide for improved efficiency and throwing power of the plating process. Steel and brass test panelsare electroplated in the foregoing electrolyte for periods of about 2 to 20 minutes at a cathode currentdensityofabout5to 10ASF(0.55to 1.1 ASD) and at a cathode to anodesurfacearea ratio of about 1 :2to about 1:6. The bath is maintained within a pH of about86 to 9.5 and the solution is vigorously agitated by air agitation. substantially uniform grain-refined, ductile adherent copper strike deposits are obtained.

The foregoing electrolyte is also suitable for copper plating steel and brass parts in a barrel plating operation.

EXAMPLE2 An electrolyte is prepared identical to that described in Example 1. Zinc test panels are satisfactorily plated employing the same operating parameters as described in Example 1 with the exception that the test panels are electrified at a minimum voltage of 3 volts prior to and during immersion in the electrolyte to provide adherent, grain-refined ductile copper strike deposits EXAMPLE 3 A cyanide-free aqueous alkaline electrolyte suitable for depositing a copper strike on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water about 25 gil to 35 g/l of copper sulphate pentahydrate (6.25 to 8.75 g/l copper ion) under agitation.Following the complete dissolution of the copper sulphate salt, about 62.5 g/l to about 78.5 g/l of 1 - hydroxyethylidene - 1,1, diphosphonic acid is added.The pH ofthe solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to above pH 8.0. Thereafter, from about 15 to about 20 g/l of sodium carbonate is added and the solution is agitated until complete dissolution occurs.The solution is thereafter heated to an operating temperature offrom about 1300to 1400F (54" to 600C) and a combination of an oxygen-free high purity copper anode and ferrite anode is immersed in the bath while suspendedfrom an anode barto provideaferrite anode surface area to copper surface area of about 4:1 Air agitation is employed to reduce burning and to improve throwing power of the process steel and brass panels or parts are electroplated in the foregoing electrolyte for periods of about 2 to 20 minutes at cathode current densities of about 20 to 30 ASF (2.2 to 3.3 ASD) and at a cathode to anode surface area ratio of about 1::2 to about 1 The bath is maintained within a pH of about 8.5 to 10.2 and the solution is vigorosly agitated by air agitation. Uniform, finegrained, ductile and adherent copper strike deposits are obtained.

EXAMPLE 4 An electrolyte is prepared identical to that described in Example 3. Zinc test panels or parts are satisfactorily plated employing the same operating parameters described in Example 3 with the exception that the cathode (work) are electrified at a minimum voltage of 3 volts priorto and during immersion in the electrolyte, to provide adherent, fine-g rained, ductile copper deposits.

EXAMPLE 5 A cyan ide-free aqueous alkaline electrolyte suitable for depositing a copper deposit on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water, about 55 g/l to about 88 g/l of copper sulfate pentahydrate (13.5 to 22 g/l of copper ions) under agitation. following the complete dissolution of the copper sulphate salt, about 100 to about 122 gil of 1 - hydroxyethylidene - 1,1, diphosphonic acid are added. The pH of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a pH of about 8.0. Thereafter from about 15 to 25 g/l of sodium carbonate is added and the solution is agitated until complete dissolution occurs.The solution is thereafter heated to about 130" to 150"F (54 to 66"C) and a combination of an oxygen-free high purity copper anode and ferrite anode is immersed while suspended from an anode barto provide a ferrite anode surface area to copper anode surface area ratio of about 4:1.

While agitation is not critical, some agitation such as mechanical, cathode rod and preferablyairagitation is employed to provide efficiency and throwing power of the process. Steel and brass substrates are electroplated in theforegoing ectrolytefor periods of 2to 60 minutes at a cathode current density of about 10 to 30 ASF (1.1 to 3.3 ASD) and at a cathode to anode surface area ratio of about 1 :2to about 1:6. The bath is maintained within a pH of about 8.5 to 10.2. Uniform, fine-grained, ductile and adherent copper deposits are obtained.

The foregoing electrolyte is also suitableforcopper plating steel and brass work pieces in a barrel plating operation.

EXAMPLE 6 A cyanide-free aqueous alkaline electrolyte suitable for depositing a copper deposit on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water, about 55 gll to about 100 g/l of copper sulphate pentahydrate (13.5 to 25 g/l of copper ions) under agitation. following the complete dissolution of the copper sulphate salt, about 43.5 git to 52 gn of 1 hydroxyethylidene- 1,1 diphosphonic acid (HEDP) and 100 to 122 g/l of ethylene diamine tetra (methylene phosphonic acid) (EDTMP) are added. The pH of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a pH of 8.0. Thereafter from about 10 to 25 g/i of sodium carbonate is added and the solution is agitated until complete dissolution occurs. The solution is thereafter heated to an operating temperature from about 130 to about 140"F (54 to 60"C) and a combination of oxygen-free high purity copper anode and a ferrite anode is immersed while suspended from an anode barto provide a ferrite anode surface area to copper surface area ration of about 4:1.

While agitation is not critical, some agitation such as mechanical, cathode rod and preferably air agitation is employed. Steel and brass test panels or parts are electroplated in the foregoing electrolyte for periods of 2 minutes to several days (depending on thickness of copper required) ata cathode current density of about 10 to 40ASF (1.1 to4.4ASD)andata cathode to anode surface area ratio of about 1:2 to about 1:6. The bath is maintained within the pH range of 8.5 to 10.2. Uniform, fine-grained, ductile and adherent copper deposits are obtained.

The foregoing electrolyte is also suitableforcopper plating steel and brass parts in a barrel plating operation.

Itwill be appreciated that it is not essential tothe satisfactory practice ofthe process and composition ofthe present invention to preparethe copper electrolytes in the specific sequence and employing the specific ingredients disclosed. For example, the complexing agent or mixture of complexing agents can be introduced in the form of an aqueous concentrate ofthe potassium salt to provide the desired concentration ofthe complexing agent.

typically, the acid form of the complexing agent can be first neutralized employing a 50 percent aqueous solution of potassium hydroxide providing a concentrate having a pH of about8.

EXAMPLE 7 A composite nickel-iron alloyanode comprising an electrodeposited nickel-iron ally̲on à solid copper core is prepared employing an electrolytcof the following composition: cgtirmzi Range Uni 2 56 g/l 35-100 g/l Fe+2 and Foe 3 4 g/l 1-10 g/l NiSO4[6H2O] 150 g/l 50-300 g/l NiC12[6H20] lOO g/l 30-150 g/l H3BO3 45 g/l 30 - Saturation Sodium Qconate 20 g/l 5-100 g/l Sodium Saccharin 2.5 g/l 0-10 g/l SodiumAUyl Sulphonate 4.0 g/l 0.5-15 g/l Wetting Agent 0.2 g/l 0.05-1.0 g/l pH 2.9 2.5-4.0 Agitation Air, Cathode Bar or Still T:< rature 135 F (570C) 100-160 'F (380-710C) Cathode Current Density 40 ASFt4.4ASD) 5-100 ASF (0. 5S-llSS0) Anodes Iron and Nickel The wetting agent employed includes lowfoaming type wetting agents such as sodium octyl sulphate when employing air agitation and relatively high foaming wetting agents such as sodium lauryl sulphate when employing cathode bar agitation or still baths. Sodium gluconate in the electrolyte composition comprises a complexing agentforthe ferric ions and alternative satisfactory complexing agents or mixturesthereofcan be be employedforthis purpose including citrates, tartrates, glucoheptonates, salicylates, ascorbates orthe like.

Alternative complexing agents which can be satis factorily employed includethose as described in the aforementioned United States Patents 3,806,429; 3,974,044 and 4,179,343 the substance of which is incorporated herein by reference. The anodes employed in the nickel-iron electroplating process are in the form of individual slabs or chips of iron and nickel in separate baskets.

The composition of the nickel-iron electrolyte in accordance with the optimum composition as set forth in the foregoing table produces a nickel-iron alloy deposit containing approximately 20 percent iron and the balance essentially nickel using cathode bar agitation. When air agitation is employed, the iron concentration in the electrodepositwill increase to about 30 percent by weight. When no agitation is employed, the iron concentration in the electrodepositwill decrease to about 15 percent by weight. In accordance with a preferred practice ofthe present invention, cathode bar or mild air agitation is employed in thatthe electrodeposit is more uniform in both composition as well as in appearance.

In theformulation of suitable nickel-iron electrolytes, the ratio of nickel ions to iron ions is perhaps the single most importantfactor in determining the composition of the final alloy electrodeposit In accordance with the optimum formulation, a nickel to iron ratio of about 14:1 employing cathode bar agitation provides an iron concentration in the alloy electrodeposit of about 20 percent by weight. At a higher nickel to iron ion ratio, a lower iron concentration in the deposit is produced whereas at a lower nickel: iron ratio, a higher iron concentration in the alloy is produced. In either event, the electrolyte and the conditions of operation are controlled so as to provide a nickel-iron alloy deposit containing from about 15 percent up to about 30 percent by weight iron.

An elongate copper core is employed forforming a composite nickel-iron alloy anode and is subjected to a conventional pre-treatment prior to plating in the aforementioned electrolyte. The pretreatment can typically comprise an alkaline soaktreatmentfora period of about 1 to about3 minutes followed by a cathodic electrocleaning step for a period of about 1 to about 2 minutes followed by a cold water rinse. The rinsed copper core is thereafter subjected to a soak treatment in a Sto 10 percent sulphuric acid solution for a period of about 15 to about 30 seconds followed by a cold water rinse.The pretreated copper core is thereafter immersed in the aforementioned nickeliron electrolyte and is electroplated for a period of 1 to about 2 hours at an average cathode current density of about 40 amperes per square foot (ASF) (4.4ASD) whereafterthe composite anode is withdrawn, cold water rinsed and dried. The nickel-iron alloy electrodeposit is of a thickness of about 2 to about4 mils (50.8 to 102 microns) and contains about 20% iron by weight and about 0.025 percent sulphur by weight. In thefabrication of such nickel-iron alloy anodes, the electrodeposition ofthe nickel-iron alloy electrodeposit can usually range from about O.5mils(12.7 microns) upto about 10 mils (254 microns) or even thicker two achieve satisfactory operation.The important criteria ofthe electrodeposit is that it is substan tiallynonporousand is adherenttothecore and is further characterized as being of good ductility and of relatively low stress. The conditions as setforth in Example 1 provide a nickel-iron electrodeposit possessed of the foregoing desirable properties.

EXAMPLE 8 A composite nickel-iron alloy anode comprising an electrodeposited nickel-iron alloy on a solid steel core is prepared employing the same procedure as set forth in Example 7 with the exception that the steel core during the pretreatment priorto plating is subjected to an anodicelectrocleaning step instead of a cathodic electrocleaning step and is subsequently subjected to a soak treatment employing a more concentrated sulfuric acid solution at about 25 percent concentration for a similar time period as described in Example 7.

The resultant composite anode has a nickel-iron electrodeposit of the same characteristics as obtained in Example 7.

EXAMPLE 9 A cyanide-free aqueous alkaline electrolyte suit ablefordepositing a copper strike on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water about 25 g/l to 35 g/l ofcoppersulfate pentahydrate (6.25 to 8.75 g/l copper ion) under agitation. Following the complete dissolution of the copper sulphate salt, abot 76.1 g/l to about 84.8 g/l of 1 - hydroxy ethylidene - 1,1, diphosphonic acid is added. The pH ofthe solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to above pH 8.0. Thereafter, from about 15 to about 20 g/l of sodium carbonate is added and the solution is agitated until complete dissolution occurs.The solution is thereafter heated to an operating temperature of from about 1300to 1400F (54 to 60"C) and a combination of an oxygen-free high purity copper anode and a nickel-iron alloy anode as obtained in accordance with Example 7 is immersed in the bath while suspended from an anode barto provide a copper anode surface area to nickel-iron alloy anode surface area of about 2:1.

Air agitation is employed to reduce burning and to improve throwing power ofthe process. Steel and brass panels or parts are electroplated in the fore going electrolyte for periods of about 2 to 20 minutes at cathode current densities of about 15 to 20 ASF (1.65to2.2ASD) and ata cathode to anode surface area ratio of about 1 to about 1:6. The bath is maintained within a pH of about 9.5 to 10.2 and the solution is vigorously agitated by air agitation.

Uniform,fine-grained,ductile and adherent copper strike deposits are obtained.

EXAMPLE 10 A cyanide-free aqueous alkaline electrolyte suit able for depositing a copper deposit on ferrous-base substrates such as steel and on copper-base subs trates such as brass is prepared by dissolving in deionized water, about 55 gll to about 88 g/l of copper sulphate pentahydrate (13.5to 22 gll of copper ions) under agitation. Following the complete dissolution ofthe copper sulphate salt, about 107.9 to about 147 g/l of 1 - hydroxy - ethylidene - 1,1, diphosphonic acid are added. The pH of the solution is adjusted employing a 50 percent aqueous solution of potas sium hydroxide to provide a pH of about 8.0.

Thereafter from about 15 to 25 g/l of sodium carbonate is added and the solution is agitated until complete dissolution occurs. The solution is thereaf ter heated to about 130" to 150"F (54" to 66"C) and a combination of an oxygen-free high purity copper anode and nickel-iron alloy anode is immersed while suspended from an anode barto provide a copper anode surface area to nickel-iron alloy anode surface area ratio of about 1:1.

While agitation is not crucial, some agitation such as mechanical, cathode rod and preferably air agitation is employed to provide efficiency and throwing power ofthe process. Steel and brass substrates are electroplated in the foregoing electrolyte for periods of 2 to 60 minutes at a cathode current density of about 10 to 30 ASF (1.1 to 3.3ASD) and at a cathode to anode surface area ratio of about 1 :2to about 1:6. The bath is maintained within a pH of about 9.5 to 10.2.

Uniform, fine-grained, ductile and adherent copper deposits are obtained.

The foregoing process is also suitable for copper plating steel and brass work pieces in a barrel plating operation.

EXAMPLE 11 The process as described in Example 9 is repeated for depositing a copper strike on ferrous-base subs trates with the exception that a composite nickel-iron alloy anode is employed atthe same copper to nickel-iron alloy anode surface ratio but containing only 11 percent by weight iron and 0.02 percent sulphurA uniform,fine-grained, ductile and adherent copper deposit is obtained.

EXAMPLE 12 The process of Example 11 is repeated except that a composite nickel-iron alloy anode is employed con taining 11 percent by weight iron and 0.067 percent sulphur. The resultant copper deposit is unacceptable comprising a grainy, reddish deposit believed to be caused bythe excessive sulfur content in the nickeliron alloy ofthe anode.

EXAMPLE 13 The process of Example 10 is repeated with the exception that a composite nickel-iron alloy anode is employed in which the alloy contains 32 percent by weight iron and 0.02 percent sulphurAn acceptable uniform,fine-grained, ductile and adherent copper electrodeposit is obtained.

EXAMPLE 14 The process of Example 13 is repeated with the exception that a composite nickel-iron alloy anode is employed containing about 32 percent by weight iron and sulphur at a concentration of 0.088 percent. An unacceptable grainy, reddish-brown copper deposit is obtained.

EXAMPLE 15 The process of Example 13 is repeated with the exception that a composite nickel-iron alloy anode is employed containing 60 percent by weight iron and 0.02 percent sulphurAn acceptable grainy, brittle copper deposit is obtained which is believed due to the high iron content in the nickel-iron alloy anode.

EXAMPLE 16 The process of Example 13 is repeated with the exception that a nickel-iron alloy anode is employed containing about 25 percent iron byweightand 0.02 percentsulphurAn acceptable uniform,fine-grained, ductile and adherent copper deposit is obtained.

EXAMPLE 17 A cyanide-free aqueous alkaline electrolyte suit able for depositing a copper strike on ferrous-base substrates such as steel and on copper-base substrates such as brass is prepared by dissolving in deionized water, about 60 to about 72 g/l of copper sulphatepentahydrate (15 to 18 g/l copper ions) under agitation. Following the complete dissolution ofthe copper sulphate salt, about 81 to about 87 g/l of a complexing agent is dissolved comprising the neutralized potassium saltofa 30 percent by weight aminotri (methylene-phosphonic acid) (ATMP) and 70 percentbyweightofl -hydroxyethylidene- 1,1 diphosphonicacid (HEDP).The pH ofthesolution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a pH of about 8.5.

Thereafterfrom about 15 to about 25 g/l of sodium borate is added and the solution is agitated until complete dissolution occurs. The solution is thereafter heated to an operating temperature of from about 1100 to about 140"F (43 to 60"C) and a combination of an oxygen-free, high purity copper anode and a composite nickel-iron alloy anode containing 25 percent by weight iron and 0.02 percent by weight sulphur are immersed while suspended from an anode barto provide a copper anode surface area to nickel-iron alloy anode surface area ratio of about 1:1.

While agitation is not critical, some agitation such as mechanical, cathode rod and preferably air agitation is employed to provide for improved efficiency and throwing power of the plating process. Steel and brass test panels are electroplated in the foregoing electrolytefor periods of about 2to 20 minutes at a cathode current density of about 5 to 10 ASF (0.55 to 1.1 ASD) and at a cathode to anode surface area ratio ofabout 1 :2to about 1 The bath is maintained within a pH of about7.5to 9.5 and the solution is vigorously agitated by air agitation. Susbstantially uniform grain-refined, ductile adherent copper strike deposits are obtained.

Theforegoing process is also suitable for copper plating steel and brass parts in a barrel plating operation.

EXAMPLE 18 An electrolyte is prepared identical to that described in Example 17 except that about 15to about 25 g/l of potassium carbonate was employed in place of sodium borate as a buffering agent. Zinc test panels are satisfactorily plated employing the same operating parameters as described in Example 17 with the exception that the test panels are electrified at a minimum voltage of 3 volts priorto and during immersion in the electrolyteto-provide adherent, grain-refined ductile copper strike deposits.

Claims (61)

1. An aqueous cyanide-free electrolyte for electrodepositing a grain refined ductile and adherent copper plate on a conductive substrate comprising an aqueous alkaline solution containing copper ions present in an amount sufficient to electrodeposit copper, a complexing agent present in an amount sufficient to chelate the copper ions present, said complexing agent comprising a compound selected from 1 - hydroxyethylidene -1,1 - diphosphonic acid, a mixture of 1 - hydroxyethylidene - 1,1 - diphosphonicacid andaminotri-(methylenephosphonicacid) in which said 1 - hydroxyethylidene - 1,1 - diphosphonic acid is present in an amount of at least about 50 percent byweight ofthe mixture; and a mixture of 1 hydroxyethylidene - 1,1 - diphosphonic acid and ethylenediaminetetro (methylene phosphonic acid) in which said 1 - hydroxyethylidene - 1,1 - diphosphonic acid is present in an amount of at least about 30 percent by weight of the mixture, as well as the bath soluble and compatible salts and partial salts thereof, a bath soluble and compatiblestabilizercompound present in an amount sufficient to stabilize the pH of the electrolyte, and hydrogen and/or hydroxyl ions present in an amountto provide a pH of from 6to 10.5.

2. An electrolyte as claimed in Claim 1,wherein the stabilizer comprises a carbonate compound.

3. An electrolyte as claimed in Claim 1 or2, wherein hydroxyl ions are present in an amount to provide a pH of from 7.5 to 10.5.

4. An electrolyte as claimed in Claim 1,2 or 3, in which said copper ions are present in an amount of from 3 to 50 g/l.

5. An electrolyte as claimed in any one of Claims 1 to 4, which said copper ions are present in an amount offrom 15to 50 g/l.

6. An electrolyte as claimed in any one of Claims 1 to 5, in which said copper ions are present in an amount of from 3,5 to 10 girl.

7. An electrolyte as claimed in any one of Claims 1 to 6, in which hydroxyl ions are present in an amount ot provide a pH of from 9.5 to 10.

8. An eleetrolyte as claimed in any one of Claims 1 to 7, further including a bath soluble and compatible wetting agent present in an amount up to 0.25 g/l.

9. An electrolyte as claimed in any one of Claims 1 to7furtherincluding a bath soluble and compatible wetting agent present in an amount of from 0.01 to 0.1 9/l.

10. An electrolyte as claimed in any one of Claims f to 9, which said stabilizer comprises one or more alkali metal and alkaline earth metal carbonate or bicarbonate compounds.

11 An electrolyte as claimed in any one of Claims 1 to 9, ín which said stabilizer comprises one or more alkali metal carbonate or bicarbonate compounds.

12. Anelectrolyte as claimed in any one of Claims 1 to 9, in whichthestabilizercomprises potassium bicarbonate.

13. An electrolyte as claimed in any one of Claims 1 to 12, in which said stabilizer is present in an amount offrom 3 to 100 g/l calculated on a weight equivalent basis as sodium carbonate.

14. An electrolyte as claimed in any one of Claims 1 to 12, in which said stabilizer is present in an amount of from 10 to 20 gll calculated on a weight equivalent bases as sodium carbonate.

15. An electrolyte as claimed in any one of Claims 1 to 14, in which said complexing agent comprises 1 hydroxyethylidene -1,1 - diphosphonic acid present inan amountoffrom50to500g/l.

16. The electrolyte as claimed in any one of Claims 1 to 15, in which said complexing agent comprises a mixture containing 70 percent by weight 1 - hydroxyethylidene - 1,1 - diphosphonic acid and 30 percent by weight aminotri - (methylene phosphonic acid) or a bath soluble and compatible salt or partial salt thereof, said mixture being present in an amount of about 20 to about322 g/l.

17. An electrolyte asclaimed in anyoneofClaims 1 to 16, in which said complexing agentcomprisesa mixture containing about 50 percent byweight 1 hydroxyethylidene - 1,1 - diphosphonic acid and about 50 percent by weight ethylene diamine tetra (methylene phosphonicacid) or a bath soluble and compatible saltthereof, ora combination thereof, said mixture being present in an amount of from 1 9to from311 g/l.

18. A processforelectrodepositing a grain refined ductile and adherent copper strike on a conductive substrate which comprises the steps of providing an aqueous alkaline cyanide-free electrolyte of a composition as claimed in any one of Claims 1 to 17, controlling the temperature of or said electrolyte be- tween 1000 and 160'F (38' and 71 0C), immersing a conductive substrate to be plated as a cathode in said electrolyte, immersing a combination of a copperbase soluble anode and a ferrite insoluble anode in said electrolyte to provide a copper anode to ferrite anode surface area ratio of from 1::2 to 1 passing current between said anodes and said cathode for a period of time sufficient to deposit copper on said satbstrate to the desired thickness.

19. A process as claimed in Claim 18, in which the step of controlling the temperature of said electrolyte is performed to provide atemperature of from 1 100F to 1409F (43 to 60'C).

20. A process as claimed in Claim 18 or 19 in which the step of controlling the temperature of said electrolyte is performed to provide a temperature of from 1200to 140 F (49 to 60 C).

21. A process as claimed in Claim 18,19 or 20, in which the step of passing current between said anodes and said cathode is performed to provide a cathode current density of from 1 to 80 ASF (0.11 to

8.8 ASD).

22. A process as claimed in any one of Claims 18 to 21 in which the step of passing current between said anodes and said cathode is performed to provide a cathode current density offrom 5 to 25 ASF (0.55 to

2.75 ASD).

23. A process as claimed in any one of Claims 18 to 22 including the further step of maintaining the pH of said electrolyte within a range of from 9.5 to 10.

24. A process as claimed in any one of Claims 18 to 23 including the further step of maintaining the copper anode to ferrite anode surface area ratio between 1 :3and 1:5.

25. A process as claimed in any one of Claims 18 to 23, including the further steps of maintaining the copper anode to ferrite anode surface area ratio at 1:4.

26. A process as claimed in any one of Claims 18 to 24, in which the step of passing current is controlled to provide a copper deposit on said substrate of an average thickness of from 0.015 to 5 mils (0.38 to 127 microns).

27. A process as claimed in any one of Claims 18 to 26 in which the step of passing current is controlled for a period of time offrom 1 minute to 1 hour.

28. A process as claimed in any one of Claims 18 to 26 in which the step of passing current is controlled for a time of from 2 to 30 minutes.

29. A process as claimed in any one of Claims 18 to 28 including the further step of replenishing said complexing agent and said stabilizerto maintain said bath constituents within the desired operating range.

30. A process as claimed in any one of Claims 18 to 29 includingthefurther step of controlling the cathode to anode surface area ratio between 1:2 and :6.

31. A process as claimed in any one of Claims 18 to 30 including the further step of controlling the cathode to anode surface area ratio between 1:3 and 1:5.

32. A process as claimed in any one of Claims 18 to 30 including the further step of controlling the cathode to anode surface area ratio at 1:4.

33. A process for electrodepositing a grain refined ductile and adherent copper strike on a ferrous-base conductive substrate which comprises the steps of providing an aqueous alkaline cyanide-free electro lyte of a composition as claimed in any one of Claims 1 to 17, controlling the copper ion concentration within a range of about 1 5 to about 50 g/l, controlling the temperature of said electrolyte between 1000 and 160"F (38 and 71 C), immersing a ferrous-base conductivesubstrateto be plated asa cathode in said electrolyte, immersing a combination of a copper base soluble anode and a ferrite insoluble anode in said electrolyte to provide a copper anode to ferrite anodesurfacearea ratio of from 1 :2to 1 :6, passing current between said anodes and said cathodefora period oftime sufficient to deposit copper on said ferrous-base substrate to the desired thickness.

34. A process as claimed in Claim 33 including the further step of electrifying said ferrous-base substrate priorto and during the step of immersing said substrate in said electrolyte.

35. A process for electrodepositing a grain refined ductile and adherent copper strike on a zinc-base conductive substrate which comprises the steps of providing an aqueous alkaline cyanide-free electrolyte of a composition as claimed in Claim 3, controlling the temperatu re of said electrolyte between 100" and 160"F (388 and 71 C), cathodically electrifying said conductive zinc-base substrate at a voltage of at least about3 volts and immersing the electrified said substrate in said electrolyte, immersing a combination of a copper-base soluble anode and a ferrite insoluble anode in said electrolyte to provide a copper anode to ferrite anode surface area ratio of from 1 :2to 1 ::6, passing current between said anodes and said zinc-base substrate for a period of time sufficient to deposit copper on said substrate to the desired thickness.

36. A process for electrodepositing a grain refined ductile and adherent copper plate on a conductive substrate which comprises the steps of providing an aqueous cyanide-free electrolyte containing copper ions present in an amount sufficient to electrodepositcopper, a complexing agent present in an amount sufficient to chelatethe copper ions present, a bath soluble and compatible buffering agent present in an amount sufficient to stabilize the pH ofthe electrolyte, and hydroxyl and/or hydrogen ions present in an amountto provide a pH from 6to 10.5; immersing a conductive substrate to be plated as a cathode in said electrolyte, immersing a combination of a copper base soluble anode and a nickel-iron alloy insoluble anode containing from 10 percentto 40 percent by weight iron in said electrolyte to provide a copper anode to nickel-iron alloy anode surface area ratio of from 1 :2to 4:1, and passing current between said anodes and said cathodefora period of time sufficientto deposit copper on said substrate to the desired thickness.

37. A process as claimed in Claim 36 including the further step of controlling the temperature ofthe electrolyte within a range of from 1000 to 1600F (38" to 71'C).

38. A process as claimed in Claim 36 including the further step of controlling the temperature ofthe electrolyte within a range offrom 1 100to 1400F (43" to 60 C).

39. A process as claimed in Claim 36 including the further step of controlling the temperature ofthe electrolyte within a range offrom 1200 to 140"F (49" to 60 C).

40. A process as claimed in Claim 36,37 or38 in which the copper anode to nickel iron alloy anode surface area ratio is controlled within a range offrom 1:1to2:1.

41. A process as claimed in Calim 36,37 or 38 including the further step of controlling the cathode surface area to anode surface area ratio between 1:1 and 1:6.

42. A process as claimed in Claim 36,37 or 38, includingthefurtherstep of controlling the cathode surface area to anode surface area ratio between 1:3 and 1:5.

43. A process as claimed in Claim 36,37 or 38 including the furtherstep of controlling the cathode surface area to anode surface area ratio at 1:4.

44. A process as claimed in any one of Claims 36 to 43 in which the step of passing current between said anodes and said cathode is performed to provide an average current density offrom 1 to 80 ASF (0.11 to 8.8 ASD).

45. A process as claimed in any one of Claims 36 to 43, in which the step of passing current between said anodes and said cathode is performed to provide an average cathode current density of from 5 to 25 ASF (0.55 to 2.75 ASD).

46. A process as claimed in any one of Claims 36 to 45, including the further step of controlling the concentration of said hydroxyl ions to provide a pH of from 9 to 10.

47. A process as claimed in any one of Claims 36 to 46, including the further step of electrifying said conductive substrate cathodically priorto and during the step of immersing said substrate in said electrolyte.

48. A process as claimed in Claim 47, in which the electrification of said conductive substrate is per formed ata voltage of at least3 volts priorto and during the step of immersing said substrate in said electrolyte.

49. A process as claimed in any one of Claims 36 to 48, in which said nickel-iron alloy insoluble anode contains from 15 percent to 30 percent by weight iron.

50. Aprocess as claimed in any one of Claims 36 to 48 in which said nickel iron alloy anode contains from 20 percentto 25 percent by weight iron.

51. A process as claimed in any one of Claims 36 to 50 in which said nickel-ironalloyanodefurther contains from 0.005 to 0.06 percent sulphur.

52. A process as claimed in any one of Claims 36 to 50 in which said nickel-iron alloy anode further contains from 0.01 to 0.04 percent sulphur.

53. An anode suitable for use in electro-depositing copperfrom am aqueous cyanide-free electrolyte on a conductive substrate comprising nickel-iron alloy containing from 10 to 40 percent by weight iron, from 0.005 to 0.06 percent by weight sulphu rwith the balance essentially nickel.

54. An anode as claimed in Claim 53, comprising an electrically conductive core having an adherent, substantially non-porous plate on at least a portion of the exteriorsurface ofthe core,the plate being of a thickness of at least 1 mil (25 microns).

55. An anode as claimed in Claim 53 or 54 in which said nickel-iron alloycontainsfrom 15to30 percent byweight iron and from 0.01 to 0.04 percent by weight sulphur.

56. An anode as claimed in Claim 53,54 or 55, in which said nickel-iron alloy containsfrom 20to25 percent by weight iron and from 0.02 to 0.03 percent by weight sulphur.

57. An anode as claimed in Claim 54, wherein the core comprises copper, an alloy of copper, a ferrous base material, aluminium, an aluminium alloy or nickel.

58. An electrolyte substantially as hereinbefore described with reference to any one of the Examples.

59. A process for electrodepositing copper sub stantially as herein described with reference to any one ofthe Examples.

60. An anode comprising a nickel-iron alloy sub stantiallyas herein described.

61. An article plated by a process as claimed in any one of Claims 18to 52 and 59 and/or using an electrolyte as claimed in any one of Claim 1 to 17 and 58 and/or using an anode as claimed in any one of Claims 53 to 57 and 60.