GB2167447A - Cyanide free copper plating process - Google Patents

Abstract

Copper plate is applied by electrolysing an electrolyte containing copper ions chelated with a complexing agent e.g. organo-phosphonate, a buffering agent, hydroxyl and/or hydrogen ions to provide pH 6-10.5, using a combination of a bath soluble copper anode and an insoluble nickel-iron (10-40%) alloy anode to provide a copper anode to nickel-iron anode surface area ratio of 1:2 to 4:1. The combination of anodes in controlled anode surface ratios achieves the desired oxidizing medium for maintaining plating conditions and for achieving copper.

Description

GB 2 167447 A 1

SPECIFICATION

Cyanide-Free Copper Plating Process and Alloy Anode The use of cyanide salts in copper plating electrolytes 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 replacements for the well-known and conventional commercially 5 employed cyanide counterparts For example, U S Patent No 3,475,293 discloses the use of certain diphosphonates for electroplating 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 agents for the metal ions in the bath; U S Patent No 3,833,486 discloses the use of water soluble phosphonate chelating 10 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 of the types disclosed in U S Patents 3,475,293,3,706,634 and 3,706,635.

1 5 While the electrolytes and processes disclosed in the aforementioned United States patents have 1 5 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, 20 chromium plating solutions and zinc metal ions introduced into the electrolyte during conventional commercial practice Still another problem is the hazardous nature of strong oxidizing agents employed in certain of such prior art electrolytes.

The present invention overcomes or mitigates many of the problems and disadvantages associated with prior art cyanide-free copper plating solutions by providing a process employing an electrolyte which 25 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 O 015 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 30 chromium plating solutions and zinc metal ions as normally introduced into a plating bath in a commercial practice, 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 35 of cupric ions, an organo-phosphonate chelating agent, a buffering agent, hydroxyl and/or hydrogen ions to provide a p H from mildly acid to moderately alkaline, and optionally but preferably, a wetting agent The copper ions may be introduced by a bath soluble and compatible copper salt, to provide a cupric ion concentration in an amount sufficient to electrodeposit copper, and generally ranging from as low as about 3 to as high as about 50 grams per litre (g/l) under selected conditions The organo-phosphonate chelating 40 agent is a compound selected from 1-hydroxy-ethylidene-1, 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) (ATMP) 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 present in an amount of at least about 30 percent by weight of the mixture, as well as the bath soluble and 45 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 The concentration of the organo-phosphonate chelating agent will range in relationship to the specific amount of copper ions present in the bath and is usually controlled to provide an 50 excess of the chelating agent relative to the 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 as a buffering agent which is present in 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 55 acidic (p H 6) to moderately alkaline (p H 10 5) with a p H of about 9 to about 10 being usually preferred The bath may optionally and preferably further contain a bath soluble and compatible wetting agent present in an amount up to about 0 25 g/l.

In accordance with the process aspects of the present invention, the cyanide-free electrolyte as hereinabove described is employed for electrodepositing a fine-grained ductile, adherent copper strike on 60 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 insoluble ferrite anode is employed to provide a copper anode to ferrite anode surface area ratio of about 1 2 tn about GB 2 167 447 A 2 1:6 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 order to deposit the desired thickness of copper on the cathodic substrate e The bath can be operated at a temperature of from about 100 'to about 160 'F ( 38 " to 71 "C) with temperatures of about 110 to about 140 'F ( 43 ' to 600 C) being preferred The particular temperature 5 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 per square foot (ASF) 0 11 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 prior to immersion in the electrolyte In the 10 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 of the 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 1 5 plating and rinsing operations 15 In accordance with a further process aspect of the present invention, the cyanide-free electrolyte as hereinabove described is employed for electro-depositing a fine-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 insoluble 20 nickel-iron anode is employed to provide a copper anode to nickel-iron alloy anode surface area ratio of about 1:2 to 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 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 160 'F ( 370 to 710 C) with temperatures of about 1100 to about 140 'F ( 430 to 60 C) being 25 preferred The particular temperature 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 per square foot (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 30 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 of the electrolyte will vary depending upon the type of basis 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 35 The present invention further provides a novel nickel-iron insoluble anode which is employed in the process in conjunction with a soluble copper anode in controlled anode surface ratios thereby achieving the desired oxidizing medium for maintaining appropriate plating conditions and for achieving copper electrodeposits of the desired characteristics The insoluble nickel-iron alloy anode is preferably of a composite construction comprising a conductive core having an adherent nickel-iron alloy electrodeposit 40 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 metals such as copper, aluminium, iron and other conductive alloys of which copper itself comprises the preferred core material The nickel-iron alloy coating or plating on the core is further characterized as being substantially non-porous and may be as thin as 1 to 2 mils ( 25 4 to 50 8 microns) thick 45 For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the preferred embodiments and the accompanying drawings, in which:- Figure 1 is a schematic perspective view partly in section illustrating a plating receptacle suitable for use in the practice of the present process; 50 Figure 2 is a side elevational view of an insoluble nickel-iron alloy anode employed in the practice of the process of the present invention; and Figure 3 is a magnified transverse cross-sectional view of the anode shown in Figure 2 and taken substantially along the line 3-3 thereof.

A cyanide-free electrolyte suitable for use in the practice of the present invention contains as its 55 essential constituents, copper ions, an organo-phosphonate complexing agent in an amount sufficient to complex the 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 p H of about 6 to 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 60 bath soluble and compatible copper salts such as sulphate, carbonates, oxides hydroxides, and the like Of the foregoing copper sulphate in the form of a pentahydrate (CU 504 5 H 20) is preferred The copper ions are present in the bath within the range of about 3 up to about 50 g/l, typically from around 5 to about 20 g/l.

For example, when plating steel substrates, copper ion concentrations of about 15 up to about 50 g/l are employed to achieve a high rate of copper electrodeposition In such instances in which the copper ion 65 GB 2 167 447 A 3 concentration is above about 20 g/l, it has been found by experimentation that electrified 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 at the time of bath immersion to achieve an adherent deposit.

During use of the electrolyte, a replenishment of the copper ions consumed during the electrodeposition 5 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 due to precipitation Preferably, the complexing salt comprises an alkali metal such as sodium, potassium lithium and mixtures thereof of which potassium 10 constitutes the preferred metal The complexing agent is present in the bath in consideration of the specific concentration of copper ions present.

The specific organo-phosphorus ligand suitable for use in accordance with the practice of the present invention comprises a compound selected from 1 -hydroxyethylidene-1, 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 15 phosphonic acid) (ATMP) 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 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 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 20 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 of the foregoing types which can be satisfactorily employed in the practice of the present invention include Dequest 2010 (HEDP), Dequest 2000 (ATMP) and Dequest 2041 (EDTMP) available from Monsanto Company The word 'Dequest' is a trade mark 25 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 up to a concentration of about 500 g/l corresponding to a copper ion concentration of about 50 g/l, with intermediate concentrations proportionately scaled in consideration of corresponding intermediate concentrates of copper ions When a mixture of HEDP and ATMP is employed, preferably comprising about 70 percent HEDP and 30 percent by 30 weight ATMP, it has been discovered that 14 g/l HEDP and 6 g/l ATMP are satisfactory at a copper ion content of 3 g/l while 225 g/l HEDP and 97 g/l ATMP are satisfactory at a copper ion bath concentration of 50 g/l Corresponding adjustments in the concentrations 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 35 employed, preferably comprising about 50 percent by weight of each compound, it has been discovered that 9 g/l HEDP and 10 g/l EDTMP are satisfactory at a copper ion concentration of about 3 g/l while 145 g/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 ion concentrations It will also be appreciated that alternative mixtures of chelating agents within the 40 ranges specified will require proportionate adjustments in concentration of total chelating agent present in relation to copper ion concentration in consideration of the foregoing concentration relationships which can be readily calculated and confirmed by routine testing to provide optimum performance for any given conditions in further consideration of the specific examples hereinafter set forth.

A third desirable constituent of the copper electrolyte comprises a bath soluble and compatible 45 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 p H 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 of the aforementioned buffering agents has further been observed, 50 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 of the 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 as the sodium salt, preferably about 10 to about 55 g/l Concentrations of the buffering agent below the recommended minimum concentrations will result in p H fluctuations whereas concentrations above the maximum range specified do not appear to have any adverse effects on the operation of the electrolyte.

Since the buffering agent and complexing agent are subject to depletion by both decomposition and drag-out, a replenishment of these two chemicals to maintain the electrolyte within appropriate 60 composition limits is necessary during commercial operation This can conveniently be performed on an intermittent or continuous basis 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 p H of from about 6 up to about 10 5 with a p H of about 9 to about 10 being preferred Typically an operating p H of about 9 5 has been found particularly satisfactory 65 GB 2 167447 A 4 The appropriate p H of the electrolyte can be maintained by adding an alkali metal hydroxide to the electrolyte to raise the p H of which potassium hydroxide is preferred In order to reduce the p H within the desired range, a mineral acid or an alkali metal bicarbonate can be employed of which potassium bicarbonate constitutes a preferred material When the operating p H decreases below the recommended level, it has been observed that the electrolyte tends to promote poor adhesion of the copper deposit on the 5 substrate On the other hand, at an operating p H 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 p H 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 p H above about 7 5 to about 10 5 has been found to provide best results 10 In addition to the foregoing constituents, the bath may optionally further contain a wetting agent or surfactant which is bath soluble and compatible with the other constituents therein When such a surfactant is employed, it can be used in concentrations up to about 0 25 g/l with amounts of from about 0 01 to about 0.1 g/l being preferred Typical surfactants suitable for use in the practice of the present invention include polyethylene oxides such as Carbowax 1000, alkyl sulphates such as 2- ethyl hexyl sulfate provided that the 15 bath is carbon filtered to remove degradation products formed during operation, purfluro anionic wetting agents, and the like.

In the practice of the process of the present invention, the electrolyte can be operated at a temperature of from about 1000 to about 160 'F ( 38 ' to 71 'C), preferably from about 110 'to about 140 'F ( 43 to 600 C) with temperatures of about 120 to about 140 'F ( 540 to 60 'C) being typical The specific temperature employed 20 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 about 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 of the copper deposit can be performed in consideration of the other operating parameters of the bath within a time of as little as 1 minute to as long as several hours or even days with 25 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 of the plate desired which will typically range from about 0 015 to about 5 mils ( 0 38 to 127 microns).

The electroplating operation is performed by immersing the conductive substrate to be plated in the electrolyte and connecting the substrate to the cathode of a direct current source It has been found that 30 when the copper ion concentration is above about 20 g/l, it is advantageous, and usually necessary, to electrify the substrate prior to and during immersion in order to 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-basis substrate 35 A combination 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 copper ions falls below the recommended minimum concentration, a reduction in cathode 40 efficiency occurs accompanied by burnt deposits On the other hand, concentrations of copper ions above the recommended maximum range has been observed to adversely affect the 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 of the copper anode at a rate substantially corresponding to the depletion rate of the copper ions by an appropriate adjustment of the copper anode 45 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 1:2 to about 1:6 with a ratio of about 1:3 to about 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 50 surface area of the cathode to the total anode surface area can range from about 1:2 up to about 1:6, preferably about 1:3 to about 1:5 and typically, about 1:4.

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 55 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 Fe 203 and at least one other metal oxide present in an amount of about 10 to 45 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 60 Such ferrite electrodes can be manufactured, for example, by forming a mixture of ferric oxide (Fe 2 03) and one or a mixture of metal oxides selected from the group consisting of Mn O, Ni O, Co O, Cu O, and Zn O to provide a concentration of about 55 to 90 mol percent of the ferric oxide and 10 to 45 percent of one or more of the metal oxides which are mixed in a ball mill The blend is heated for about one to about fifteen hours in air, nitrogen or carbon dioxide at temperatures of about 700 to about 1000 C The heating 65 GB 2167447 A 5 atmosphere may contain hydrogen in an amount up to 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 11000 to about 1450 C in nitrogen or carbon dioxide containing up to about 20 percent by volume of oxygen for a period ranging from about 1 to about 4 hours The resultant sintered body is 5 thereafter slowly cooled in nitrogen or carbon dioxide containing up to about 5 percent by volume of oxygen producing an electrode of the appropriate configuration characterized as having relatively low resistivity, good corrosion resistance and resistance to thermal shock.

It will be appreciated that instead of employing ferric oxide, metal iron or ferrous oxide can be used in preparing the initial blend Additionally, instead of the other metal oxides, compounds of the metals which 10 subsequently produce the corresponding metal oxide upon heating may alternatively be used, such as, for example, the metal carbonate or oxalate compounds Of the foregoing, ferrite anodes comprised predominantly of iron oxide and nickel oxide within the proportions as hereinabove set forth have been found particularly satisfactory for the practice of the present process.

A ferrite anode comprising a sintered mixture of iron oxide and nickel oxide suitable for use in the 15 practice of the present invention is commercially available from TDK, Inc under the designation of F-21.

By the proper proportioning of the copper and ferrite anode surfaces, the chemistry of the electrolyte is maintained with appropriate additions of the complexing and buffering agent and small additions, if necessary, of the copper salt Insufficient ferrite anode surface area results in dull or grainy deposits while an excessive ferrite anode surface area may result in reduced cathode efficiency and progressive depletion 20 of copper anions requiring more frequent replenishment of the electrolyte with copper salts.

Surprisingly, the use of alternative primary insoluble anodes in lieu of the ferrite anode as hereinabove described or the 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 by-products in the bath which result in smutty deposits 25 The insoluble nickel-iron alloy anode employed in controlled combination with the soluble copper anode 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 40 percent by weight iron and the balance essentially nickel,preferably about 15 to about 30 percent iron In accordance with a preferred form of the present invention, the insoluble nickel-iron alloy anode is comprised of an electrically 30 conductive core having an adherent electrodeposit of the nickel-iron alloy over the surfaces thereof of a thickness sufficient to envelop the core material preventing its exposure over prolonged periods of use The nickel-iron alloy deposit or coating is further characterized as being substantially non-porous 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, 35 aluminium and alloys of aluminium, nickel and the like Of the foregoing, a high purity copper core similar 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 of the coating or plating over prolonged periods of time does not adversely affect the operation of the bath in that copper ions are introduced in a manner similar to those introduced by the conventional soluble copper 40 anodes In contrast, when ferrous-base cores are employed, inadvertent exposure of the core to the electrolyte results in a progressive dissolution of iron introducing iron ions into the electrolyte which ultimately adversely effects the quality of the copper deposit produced rendering the process commercially unsatisfactory 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 of the burnt type Moreover, the 45 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 of nickel 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 50 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 art for 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 55 operation The electrolyte for depositing the nickel-iron alloy deposit on the anode core may comprise any of the types 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 60 extremely bright decorative nickel-iron alloy deposit on a conductive substrate simulating that of a conventional bright nickel deposit A very 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 rather than 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 65 GB 2 167 447 A 5 GB 2 167 447 A 6 concentration and types of primary and secondary brighteners employed in the aforementioned United States patents can be varied and reduced in concentration to provide an adherent and ductile nickel-iron plating of the desired alloy composition.

The nickel-iron alloy electrolyte contains organic sulphur compounds to introduce sulphur in the resultant alloy deposit to provide satisfactory operation and which also enhances the adhesion of the plate 5 to the anode core It has been found that sulphur contents in amounts of about 0 005 up to 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 about 0 02 to about 0 03 percent by weight 10 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 acceptable from the standpoint of ease of control, maintenance 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 1 5 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 of the present process in that it rapidly dissolves causing a rapid increase in iron ion concentration rendering the bath inoperative for the reasons previously setforth Similarly, substantially pure nickel anodes have been found unsatisfactory in spite of the fact they are relatively insoluble Substantially pure nickel anodes have been 20 found inadequate for providing the desired oxidizing medium to achieve proper plating performance over prolonged time periods Similarly, nickel-iron alloys devoid of any sulphur have 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 unsatisfactory for sustained commercial operation.

Referring now in detail to the drawing, and as shown in Figure 1 thereof, a typical electroplating 25 arrangement is schematically illustrated suitable for use in the practice of the present invention As shown, the apparatus includes a tank 10 filled with 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 alloy anode 18 are suspended in electrical contact therewith The ratio of the anode surface area of the soluble and insoluble anode or anodes is important to achieve proper operation of the 30 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 up to about 4:1, preferably at ratios of about 1:1 up to about 2:1, the chemistry of the electrolyte is maintained with appropriate additions of the complexing and buffering agents and small additions, if necessary, of the copper salt When the ratio of the copper anode surface area to nickel-iron alloy anode surface area falls below about 1:2, i e when the total 35 copper anode surface area falls below about 33 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, while the process can be operated for short time periods at a copper 40 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 now to Figure 2 of the drawing, the insoluble nickel-iron alloy anode constructed in accordance with a preferred embodiment of the 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 45 preferably is comprised of an inert conductive material such as titanium, for example The elongated bar 20 as best seen in Figure 3 is comprised of a central conductive core 24 which may be of a solid or tubular construction having an adherent outer stratum or plating 26 overlying the entire outer surface thereof The particular configuration of the nickel-iron alloy anode is not critical in achieving satisfactory performance thereof and the shape as well as the cross-sectional configuration can be varied in accordance with known 50 practices to achieve optimum throwing power and uniformity in the characteristics and thickness of the copper electrodeposit consistent with the nature of the substrates being plated.

During an electroplating operation, a substrate orworkpiece 28 to 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 sufficient to deposit the 55 desired thickness of copper on the substrate.

While the replenishment of the complexing agent during operation of the electrolyte is usually done employing a neutralized alkali metal salt thereof to avoid a drastic reduction in the operating p H of the electrolyte, it is contemplated that the acid form of the complexor can be used for original or new bath makeup by first dissolving the acid form complexor in waterfollowed by the addition of a base such as 60 potassium hydroxide to increase the p H 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 orderto further illustrate the process and novel anode of the present invention, the following specific examples are provided It will be understood that the examples as hereinafter set forth are provided for GB 2 167 447 A 7 illustrative purposes and are not intended to be limiting of the scope of this invention as herein disclosed and as set forth in the subjoined claims.

EXAMPLE 1

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 5 water, about 60 to about 72 g/l of copper sulphate pentahydrate ( 15 to 18 g/l copper ions) under agitation.

Following the complete dissolution of the copper sulphate salt, about 81 to about 87 g/l of a complexing agent is dissolved comprising the neutralized potassium salt of a 30 percent by weight aminotri (methylene-phosphonic acid) (ATMP) and 70 percent by weight of 1hydroxyethylidene-1, 1-diphosphonic acid (HEDP) The p H of the solution is adjusted employing a 50 percent aqueous solution of potassium 10 hydroxide to provide a p H 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 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 ferrite anode are immersed while suspended from an anode bar to provide a ferrite anode surface area to copper anode surface area of about 4:1 15 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 electrolyte for periods of about 2 to 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 of about 1:2 to about 1:6 The bath is maintained within a p H of about 8 5 to 9 5 and the solution is 20 vigorously agitated by air agitation Substantially uniform grain-refined, ductile adherent copper strile deposits are obtained.

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

EXAMPLE 2 25

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 30

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 g/l 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-hydroxy ethylidene-1,1, diphosphonic acid is added The p H of the solution is adjusted employing a 50 percent 35 aqueous solution of potassium hydroxide to above p H 8 0 Thereafter, from about 5 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 130 'Fto 1400 F ( 54 to 600 C) and a combination of an oxygen-free high purity copper anode and ferrite anode is immersed in the bath while suspended from an anode bar to provide a ferrite anode surface area to copper surface area of about 4:1 40 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 1:6 The bath is maintained within a p H of about 8 5 to 10 2 and the solution is vigorously agitated by air agitation Uniform, fine-grained, ductile and adherent copper strike deposits are 45 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 prior to and during immersion in the 50 electrolyte, to provide adherent, fine-grained, ductile copper deposits.

EXAMPLE 5

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 g/l to about 88 g/l of copper sulfate pentahydrate ( 13 5 to 22 g/l of copper ions) under 55 agitation Following the complete dissolution of the copper sulphate salt, about 100 to about 122 g/l of 1-hydroxy-ethylidene-1,1, diphosphonic acid are added The p H of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a p H of about 8 0 Thereafter from about 15 to 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 1500 F ( 54 to 660 C) and a combination of an oxygen-free high 60 GB 2 167 447 A 8 purity copper anode and ferrite anode is immersed while suspended from an anode bar to 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 preferably air agitation is employed to provide efficiency and throwing power of the process Steel and brass substrates are electroplated in the foregoing electrolyte for periods of 2 to 60 minutes at a cathode current density of 5 about 10 to 30 ASF ( 1 1 to 3 3 ASD) and at a cathode to anode surface area ratio of about 1:2 to about 1:6.

The bath is maintained within a p H of about 8 5 to 10 2 Uniform, finegrained, ductile and adherent copper deposits are obtained.

The foregoing electrolyte is also suitable for copper plating steel and brass work pieces in a barrel plating operation 10 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 g/l to about 100 g/l of copper sulphate pentahydrate ( 13 5 to 25 g/l of copper ions) under 1 5 agitation Following the complete dissolution of the copper sulphate salt, about 43 5 g/l to 52 g/l of 15 1 -hydroxyethylidene-1,1 diphosphonic acid (HEDP) and 100 to 122 g/l of ethylene diamine tetra (methylene phosphonic acid) (EDTMP) are added The p H of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a p H of 8 0 Thereafter from about 10 to 25 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 from about 130 'to about 140 'F ( 54 to 60 'C) and a combination of 20 oxygen-free high purity copper anode and a ferrite anode is immersed while suspended from an anode bar to provide a ferrite anode surface area to copper surface area ratio 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) at a cathode current 25 density of about 10 to 40 ASF ( 1 1 to 4 4 ASD) and at a cathode to anode surface area ratio of about 1:2 to about 1:6 The bath is maintained within the p H range of 8 5 to 10 2 Uniform,fine-grained, ductile and adherent copper deposits are obtained.

The foregoing electrolyte is also suitable for copper plating steel and brass parts in a barrel plating operation 30 It will be appreciated that it is not essential to the satisfactory practice of the process and composition of the present invention to prepare the 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 of the potassium salt to provide the desired concentration of the complexing agent Typically, the acid form of the complexing agent can be first neutralized 35 employing a 50 percent aqueous solution of potassium hydroxide providing a concentrate having a p H of about 8.

GB 2 167 447 A 9 EXAMPLE 7

A composite nickel-iron alloy anode comprising an electrodeposited nickeliron alloy on a solid copper core is prepared employing an electrolyte of the following composition:

Optimum Range Ni 2 56 g/l 35 100 g/l 5 Fe" and Fe 3 4 g/l 1-10 g/I Ni SO 46 H 2 Ol 150 g/l 50-300 g/l Ni CI 2 l 6 H 20 l 100 g/I 30-150 g/l H 3 803 45 g/l 30-Saturation Sodium Gluconate 20 g/l 5 100 g/l 10 Sodium Saccharin 2 5 g/l 0-10 g/l Sodium Allyl Sulphonate 4 0 g/l 0 5-15 g/l Wetting Agent 0 2 g/l 0 05-1 0 g/l p H 2 9 2 5-4 0 1 5 Agitation: Air, Cathode Bar or Still 15 Temperature 1350 F ( 570 C) 100-1600 F ( 38 -710 C) Cathode Current Density 40 ASF ( 4 4 ASD) 5-100 ASF ( 0 55-11 ASD) Anodes: Iron and Nickel The wetting agent employed includes low foaming type wetting agents such as sodium octyl sulphate when employing air agitation and relatively high foaming wetting agents such as sodium lauryl sulphate 20 when employing cathode bar agitation or still baths Sodium gluconate in the electrolyte composition comprises a complexing agent for the ferric ions and alternative satisfactory complexing agents or mixtures thereof can be employed for this purpose including citrates, tartrates, glucoheptonates, salicylates, ascorbates or the like.

Alternative complexing agents which can be satisfactorily employed include those as described in the 25 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 30 balance essentially nickel using cathode bar agitation When air agitation is employed, the iron concentration in the electrodeposit will increase to about 30 percent by weight When no agitation is employed, the iron concentration in the electrodeposit will decrease to about 15 percent by weight In accordance with a preferred practice of the present invention, cathode bar or mild air agitation is employed in that the electrodeposit is more uniform in both composition as well as in appearance 35 In the formulation of suitable nickel-iron electrolytes, the ratio of nickel ions to iron ions is perhaps the single most important factor 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 40 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 for forming a composite nickel-iron alloy anode and is subjected to a conventional pre-treatment prior to plating in the aforementioned electrolyte The pretreatment can 45 typically comprise an alkaline soak treatment for a period of about 1 to about 3 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 5 to 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 GB 2 167 447 A 1 O thereafter immersed in the aforementioned nickel-iron electrolyte and is electroplated for a period of i to about 2 hours at an average cathode current density of about 40 amperes per square foot (ASF) ( 4 4 ASD) whereafter the composite anode is withdrawn, cold water rinsed and dried The nickel-iron alloy electrodeposit is of a thickness of about 2 to about 4 mils ( 50 8 to 102 microns) and contains about 20 % iron by weight and about 0 025 percent sulphur by weight In the fabrication of such nickel-iron alloy anodes, the 5 electrodeposition of the nickel-iron alloy electrodeposit can usually range from about 0 5 mils ( 12 7 microns) up to about 10 mils ( 254 microns) or even thickerto achieve satisfactory operation The important criteria of the electrodeposit is that it is substantially nonporous and is adherent to the core and is further characterized as being of good ductility and of relatively low stress The conditions as set forth in Example 1 provide a nickel-iron electrodeposit possessed of the foregoing desirable properties 10 EXAMPLE 8

A composite nickel-iron alloy anode comprising an electrodeposited nickeliron 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 prior to plating is subjected to an anodic electrocleaning step instead of a 1 5 cathodic electrocleaning step and is subsequently subjected to a soak treatment employing a more 1 5 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 20

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 g/l to 35 g/l of copper sulfate pentahydrate ( 6 25 to 8 75 g/l copper ion) under agitation.

Following the complete dissolution of the copper sulphate salt, about 76 1 g/l to about 84 8 g/l of 1-hydroxy ethylidene-1,1, diphosphonic acid is added The p H of the solution is adjusted employing a 50 percent 25 aqueous solution of potassium hydroxide to above p H 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 1300 F to 1400 F ( 540 to 600 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 bar to provide a copper anode surface 30 area to nickel-iron alloy anode surface area of about 2:1.

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 15 to 20 ASF ( 1 65 to 2 2 ASD) and at a cathode to anode surface area ratio of about 1:2 to about 1:6 The bath is maintained within a p H of about 9 5 to 10 2 and the solution is 35 vigorously agitated by air agitation Uniform, fine-grained, ductile and adherent copper strike deposits are obtained.

EXAMPLE 10

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 40 water, about 55 g/l to about 88 g/l of coppersulphate pentahydrate ( 13 5 to 22 g/l of copper ions) under agitation Following the complete dissolution of the copper sulphate salt, about 107 9 to about 147 g/l of 1-hydroxy-ethylidene-1,1, diphosphonic acid are added The p H of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a p H 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 45 solution is thereafter heated to about 130 to 150 F ( 540 to 660 C) and a combination of an oxygen-free high purity copper anode and nickel-iron alloy anode is immersed while suspended from an anode bar to 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 efficiency and throwing power of the process Steel and brass substrates 50 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 3 ASD) and at a cathode to anode surface area ratio of about 1:2 to about 1:6.

The bath is maintained within a p H of about 9 5 to 10 2 Uniform, finegrained, 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 55 operation.

EXAMPLE 11

The process as described in Example 9 is repeated for depositing a copper strike on ferrous-base substrates with the exception that a composite nickel-iron alloy anode is employed at the same copper to nickel-iron alloy anode surface ratio but containing only 11 percent by weight ironand 0 02 percent sulphur 60 A uniform, fine-grained, ductile and adherent copper deposit is obtained.

GB 2 167 447 A 11 EXAMPLE 12

The process of Example 11 is repeated except that a composite nickel-iron alloy anode is employed containing 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 by the excessive sulfur content in the nickel-iron alloy of the anode 5 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 sulphur An acceptable uniform, fine-grained, ductile and adherent copper electrodeposit is obtained.

EXAMPLE 14 10

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 1 5 employed containing 60 percent by weight iron and 0 02 percent sulphur An unacceptable 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 nickeliron alloy anode is employed containing about 25 percent iron by weight and 0 02 percent sulphur An acceptable uniform, fine-grained, 20 ductile and adherent copper deposit is obtained.

EXAMPLE 17

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 60 to about 72 g/l of copper sulphate pentahydrate ( 15 to 18 g/l copper ions) under agitation 25 Following the complete dissolution of the copper sulphate salt, about 81 to about 87 g/l of a complexing agent is dissolved comprising the neutralized potassium salt of a 30 percent by weight aminotri (methylene-phosphonic acid) (ATMP) and 70 percent by weight of 1- hydroxyethylidene-1, 1-diphosphonic acid (HEDP) The p H of the solution is adjusted employing a 50 percent aqueous solution of potassium hydroxide to provide a p H of about 8 5 Thereafter from about 15 to about 25 g/l of sodium borate is added 30 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 bar to provide a copper anode surface area to nickel-iron alloy anode surface area ratio of about 1:1 35 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 electrolyte for periods of about 2 to 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 of about 1:2 to about 1:6 The bath is maintained within a p H of about 7 5 to 9 5 and the solution is 40 vigorously agitated by air agitation Substantially uniform grain-refined, ductile adherent copper strike deposits are obtained.

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

EXAMPLE 18 45

An electrolyte is prepared identical to that described in Example 17 except that about 15 to about 25 g/l of potassium carbonate was employed in place of sodium borate and 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 prior to and during immersion in the electrolyte to provide adherent, grain-refined ductile copper strike deposits 50

Claims (1)

1 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 electrodeposit copper, a complexing agent present in an amount sufficient to chelate the copper ions present, a bath soluble and compatible buffering agent present in an 55 amount sufficient to stabilize the p H of the electrolyte, and hydroxyl and/or hydrogen ions present in an amount to provide a p H from 6 to 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 percent to 40 percent by weight iron in said electrolyte to provide a copper anode G 1 B 2 167 447 A 12 to nickel-iron alloy anode surface area ratio of from 1:2 to 4:1, and passing current between said anodes and said cathode for a period of time sufficient to deposit copper on said substrate to the desired thickness.

2 A process as claimed in Claim 1 including the further step of controlling the temperature of the electrolyte within a range of from 100 Q to 160 IF ( 380 to 710 C).

3 A process as claimed in Claim 1 including the further step of controlling the temperature of the 5 electrolyte within a range of from 11 Oc to 1400 F ( 43 ' to 600 C).

4 A process as claimed in Claim 1 including the further step of controlling the temperature of the electrolyte within a range of from 120 'to 140 TF ( 490 to 60 TC).

A process as claimed in Claim 1, 2 or 3 in which the copper anode to nickel iron alloy anode surface 1 o area ratio is controlled within a range of from 1:1 to 2:1 10 6 A process as claimed in Claim 1, 2 or 3 including the further step of controlling the cathode surface area to anode surface area ratio between 1:1 and 1:6.

7 A process as claimed in Claim 1, 2 or 3 including the further step of controlling the cathode surface area to anode surface area ratio between 1:3 and 1:5.

8 A process as claimed in Claim 1, 2 or 3 including the further step of controlling the cathode surface 1 5 area to anode surface area ratio at 1:4.

9 A process as claimed in any one of Claims 1 to 8 in which the step of passing current between said anodes and said cathode is performed to provide an average current density of from 1 to 80 ASF ( 0 11 to 8 8 ASD).

10 A process as claimed in any one of Claims 1 to 8, in which the step of passing current between said 20 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).

11 A process as claimed in any one of Claims 1 to 10, including the further step of controlling the concentration of said hydroxyl ions to provide a p H of from 9 to 10.

12 A process as claimed in any one of Claims 1 to 11, including the further step of electrifying said 25 conductive substrate cathodically prior to and during the step of immersing said substrate in said electrolyte.

13 A process as claimed in Claim 12, in which the electrification of said conductive substrate is performed at a voltage of at least 3 volts prior to and during the step of immersing said substrate in said electrolyte 30 14 A process as claimed in any one of Claims 1 to 13, in which said nickel-iron alloy insoluble anode contains from 15 percent to 30 percent by weight iron.

A process as claimed in any one of Claims 1 to 13, in which said nickel iron alloy anode contains from 20 percent to 25 percent by weight iron.

16 A process as claimed in any one of Claims 1 to 15, in which said nickel-iron alloy anode further 35 contains from 0 005 to 0 06 percent sulphur.

17 A process as claimed in any one of Claims 1 to 15, in which said nickel-iron alloy anode further contains from 0 01 to 0 04 percent sulphur.

18 A process substantially as herein described with reference to any one of the examples.

19 An article whenever plated by a process as claimed in any preceding claim 40 Printed for Her Majesty's Stationery Office by Courier Press, Leamington Spa 5/1986 Demand No 8817356.

Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A 1 AY, from which copies may be obtained.