CA1248705A

CA1248705A - Electroless copper bath and process

Info

Publication number: CA1248705A
Application number: CA000474448A
Authority: CA
Inventors: Donald A. Arcilesi; Oscar E. Roberto
Original assignee: OMI International Corp
Current assignee: OMI International Corp
Priority date: 1984-02-17
Filing date: 1985-02-15
Publication date: 1989-01-17
Also published as: GB8503104D0; JPH0218387B2; GB2154250A; DE3504150A1; DE3504150C2; FR2559788B1; JPS60194081A; GB2154250B; FR2559788A1

Abstract

ABSTRACT OF THE DISCLOSURE

An aqueous alkaline electroless copper plating solution and process for depositing adherent uniform copper deposits on a substrate. The solution contains copper ions in an amount sufficient to deposit copper, a reducing agent in an amount sufficient to reduce the copper ions present to the metallic state, hydroxyl ions to provide a pH on the alkaline side and a composite complexing agent comprising an amine compound selected from the group consisting of ethylenediaminetetraacetic acid and N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine and a hydroxy acid selected from the group consisting of gluconic acid and glucoheptonoic acid as well as the bath soluble and compatible salts and partial salts thereof as well as mixtures thereof in which the hydroxy acid compound is present relative to the amine compound at a mol ratio of about 0.1 to about 3:1. The synergistic effect of the use of the controlled combination of complexing agents provides for bath stability and commercially acceptable plating rates of adherent, ductile bright copper deposits over a broad range of temperatures, pH and processing conditions.

Description

7~

Case ~o. U-11,042 ~IPRaVED E~T.FXS C~PPER ~

Back~round of the Invention The present invention broadly relates to an improved ccmposition and process for prcducing electr~less or catalytic copper deposits on substrates, and par~icularly, nonconductive substrates such as various plastics which have ~een subjected to various pretreatments to render the nonconductive substrate receptive to the copper deposit. Electroless ccpper plating baths of the types heretofore k~own conventionally comprise an agueous alkaline solution containing oopper ions, a complexing agent for the copper ions to prevent precipitation thereof, a reducing agent for reducing the oopper ions to the m~tallic state, a pH regulator, a stabilizing agent, a rate co~troller and optionally, but preferably, wetting agents to imprcve coverage and distribution of the oopper deposit.
The increased use of decorative plated trLm components on automobiles has provided impetus for further research and development efforts to improve prior art electroless copper plating solutions tu reduce their cost and simplify their maintenan oe and oontr~l, to increase ~heir stability and t~ provide uniform, ~aherent copper deposits at commercially acceptable deposition rates. The present inNention achieves the foregoing ~nefits and cbjectives by employing a controlled oo~binatiGn of ccmplexing ag~nts pro~id~ng a s~nergistic effect whereby a substantial reduction , ~

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in the quantity of oomplexing agent required is achieved providing for significant savings in the cost of make-up and replenishment of such electroless copper baths. Additionally, the present invention enables uperation of the bath under commercial conditions at a lower pH level thereby reducing the quantity of the alkaline pH control agent necessary which in turn substantially reduces the degradation reaction of the alkaline agent such as caustic and the reducing agent such as formaldehyde providin~ for a significant reduction in the consumption of reducing agent. Still a further advantage of the bath of the present invention resides in the use of higher than normal rocm temperatures enabling the bath to be operated at a temperature up to about 150F to achieve t~e desired bath activity for aut~catalytically dep~siting copper. Such higher te~perature enables the bath to be ccoled to akout r temperature during periods of nonuse such as during shutdcwn over weekends at which temperature the b~th is of comp~ratively lcw activity enhancing its stability and inhibiting autocatalytic deocmposition during periods of nsnuse. At such higher operating temperatures, evaporation of the bath normally also occurs providing volumetric spaoe in the plating tank for the additian of replenishing chemicals as is ne oe ssary during normal operation due to oonsumption and drag-out of the oonstituents. In oontrast, electroless copper plating baths of the types heretofore known adap~ed tD operate at rocm temperature have frequently req~LL~ed the removal of some of t~e ~ .
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operating solution to provide volumetric space for replenishment which not only wastes valuable solution but has also presented a waste disposal problem. The Lmproved ccmposition of the present invention has been found to also enable a substantial reduction, and in some instances a co~plete elimination of the need of rate controllers such as cyanide and iodide ccnpounds conventionally employed in prior art electroless copper baths thereby further simplifying control and replenishment of the bath and a cost reduction in the materials required.

Summary of the Invention The benefits and advantages of the present invention are achieved in accordance with the conposition aspects thereof, ~y an electroless copper plating bath oo~prising an aqueous alkalLne solution containing c~pper ions in an amcunt sufficient to autocatalytically deposit ocpper which usually ranges in a concentration of about O.5 to about 30 grams per liter (g/l), a reducing agent present in an ~cunt sufficient to effect a reduction of the copper ions to the metallic state of which ~ormaldehyde is preferred and can generally be pr~sent in an amount of abo~t 0.1 up to about 40 g/l~ a complex~ng agent presen~ in an amount to oomplex the copper io~s present in the bath and usually present in a mol ratio of oorplexing a~ent to copper ions of from about 1:1 up to about 5:1. The . . :

:

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co~plexlng agent oomprises a nixture of an amine ccmpound selected from the group oonsisting of ethylenediamune-tetra-a oe tic acid tEDTA) and N,N,N',N'-tetrakis (2-hydroxypropyl~
ethylenediamine (THPEDA3 and a hydroxy acid selected from the group consisting of glucanic acid and gluooheptonoic acid as well as the bath soluble and cGmpatible salts and mixtures thereof wherein the hydroxy acid is present in a mol ratio relative to the mols of amune compound of about 0.1 to about 3:1. The bath can further contain a stabilizing agent, preferably a heterocyclic organic sulfide compound present in an a~ount up to about 2.5 g/l, hydroxyl ions to provide a pH of from about 9 up to about 14, and optionally, a rate controller such as cyanide, iodide and derivatives thereof present in an i amount up to about 1 g/l and a ~ath soluble and compatible wetting agent which may be present in an amount up to about 10 g/l.
In accor& n oe with the process asp~cts o~ the present invention, a substrate t~ be oopper plated is immersed in the electroless copper solution maintained at a temperature of about rcom temperature (70F3 u~ to about 150F under agitation for a period of ~ime sufficient tD eff~ct a unifonm, dense and adherent ccpper deposit over the surfa oe s thereof to the desired thickness. If desired, the substrate incorpDra~ing the electroless ccpper deposit thereover can be subjected ~o further oonventional electroplating operations to apply one or 37~

a plurality of overlying electrodeposits thereon to achieve the d~esired physical characteristics and appearance.
Additional benefits and advantages of the present invention will beccme apparont upon a reading of the Desoription of the Preferred ~m~odi~ents taken in c~njunction with the accompanying examples.

Description of the Preferred Embodiments In accordance with the cc~position aspects of the present invention, the aqueous alkaline electroless or autocatalytic copper plating solution contains as its essential constituents, copper ions in an amount sufficient to deposit metallic copper on a substrate, a reducing agent for reducing the copper ions to the metallic state, a oomplexing agent present in an amDunt sufficient to maintain the copper ions in solution in the alkaline ~edium, hydroxyl ions to provide an alkaline pH and optionally, s~abiliæing agents, rate cGntxollers and wetting agents present in amounts sufficient to stabili~e the solution and provide appropriate platin~ actiYity and good wetting and unifonmity of the copper deposit produced.
The oopper ions can be introdu~ed into the aqueous alkaline solution in the form of any kath oluble and compatible oopper salt in which t~e associated anion does not have any deleterious effects on the plating characteristics of the process. Typically, cupric chloride dihydrate and o~pper sulfate pentahydrate can be used as t~e source of the copper ~ 87~S

ions. The conoe ntration of the copper ions can generally range from as lcw as about 0.5 to as high as about 30 g/l with concentrations of fram about 1 to about 5 g/l being preferred.
Higher con oe ntrations of oopper ions are required when the bath is operated at or about room temperature to prGvide for a satisfactory rate of copper deposition whereas lower concentrations such as about 0.5 g/l can be employed when the temperature of the bath is at an elevated te~perature such as frcm about 140F to about 150F.
In additio~ to the copper ions, ~he aqueous alkaline solution contains a reducing agent present in an a~cunt sufficient to redu oe the cupric ions to the metallic state for deposition on the surfa oe of the substrate being plated. For 1 this purpose, formaldehyde oomprises a preferred material li although paraformaldehyde can also be satisfactorily employed.
In addition to the foregoin3, hypophosphite and hydrazine as well as derivatives thereof have heretofore been us~d or proposed for use as reducing agents but are generally not as effective as fol~ ldehyde it æ lf. The oonoentration of the reducing agent will vary in relationship to the copper ion o~ncentration present in the bath and may range fram as low as akout 0.1 up to about 40 g/l calculated on a weight equivalent ' basis as formaldehyde with amDunts of about 1 to about 5 g/l l;
being preferred.
In addition to the ccpper ions and xe~ucLng agent, the aqueous aIkaline solution further oontaLns a- controlled 7~

mixture of an organic complexing agent to naintain the ccpper ions in solution which otherwise would precipitate as copper hydroxide in the alkaline medium. The total complexing agent is controlled in concentration to provide at least about 1 mol of complex m g agent per mDl of copper ions present with mol ratios of ccmplexing agent to copper ions as high as about 5:1 being feasible. Preferably the ccmple,Ying ~gent is controlled at a mol ratio of about 1.3:1 to a~out 3.5:1 with a mol ratio of about 1.7:1 being typical.
It has been discovered that a synergistic effect in the complexing characteristics and in the activity and stability of the bath are achieved when the complexing agent comprises a contrDlled muxture of an amine oompound selected from the group consisting of ethylenediaminetetraacetic acid (EDTA) and N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine (THPEDA) and an organic hydroxy acid selected from the group consisting of gluconic acid and glucoheptonDic acid and mixtures thereof in ad~ition to the bath sDluble and ccmpatible salts of the foregDing. Ihe mDl ratio of the hydroxy acid to EDrA may range from 0.1 to ab~ut 3:1. The particular mol ratio will depend somewhat on the type of amune compound e~ployed in combination with the hydroxy acid ccmpound. For ~xample, wh~n IHPEDA co~prises the amine compound, the gluconi~ acid and/or gluooheptonoic acid can be present in a mDl ratio relative to the amone oompo~Dnd within a range of about 0.11:1 up to about

2.45:1, with mol ratios of abcut 0.2:1 to abYut 1~1 being , :

preferred and with a mol ratio of about 0.25:1 being optimum.
On the other hand, when the amLne compound comprises EDTA, the gluconic acid and/or glucoheptonoic acid can be present m a mol ratio of about 0.25:1 up to about 3:1, preferably at a mol ratio of about 0.6:1 ~o about 2:1 with a mol ratio of about 1.3:1 being optim~. The controlled mixture of co~plexing agents can conveniently be introduced in the bath in the form of the alkali metal neutralized salts thereof which avoids any significant acidification of the bath and a reduction in its pH
in comparison to that which occurs when the acid form of the complexing agents are added. The sodium salts are particularly satisfactory for this purpose.
By employing the specific controlled muxture of the two complexing agents as hereinabove set forth in the proportions indicated, a substantial reduction in the quantity of complexing agent can be achieved and wherein the tw~ types of complexing agents are individually present in an amcunt insufficient ky itself to complex all of the copper ions present.
The electroless copper solution is on the aIkaline side and contains hydm xyl ions in an amount to provide a pH
ranging from about 9 up to about 14, with a pH range of about 10.5 ~o akout 12.5 being preferredO Typically, a pH of abDut 11.5 can be satisfactorily used which provides for a commercially satisfacb~ry copper deposition rate while at the same time requiring a lo~er hydroxyl ion oonoentration which , .

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redu oe s the tendency of reaction and degradation of the formaldehyde reducin,g agent reguiiring lower replenis~ment thereiof and further economy in the operation of the process.
m e pH of ~he copper electroless solution can be naintained within the foregoing ranige by the addition of any alkali metal hydroxide of which sodium hydroxide itself constitutes a preferred material.
In addition to the foregoing constituents, it is also oontemplated that the electroless copper bath can contain a stabilizing agent of any of the various types known in the art to inhibit the spontaneous oopper deposition on catalytic particles formed in the bath during the plating operation which rapidly depletes the solution of copper ions. A variety of oompounds hhve heretofore been used or proposed for this purpose of which 2-mercaptobenzothiiazole has been in widespread use. Alternative stabilizing agents heretofore used or proposed for use include 2.5-dimercapto-1,3,4-thiodizole, 8-nercaptopurine, o-phenanthroline~ 1-phenyl-5-mercapt~tetra-zole, 2,2-dipyridyl, 2-(2-pyridyl)-benzimidazole, benzothiazole-thioetherpolyethyleneglyool, thiazoles, isothiazoles, thiozines, ben~otriazole, diazole, Imidazole, guanidine, pyrimidine,2,2'-biquinoline, 2,9~dimethylphenanthro-line and 4,7_diphenyl-1,10-phenanthrolLne. Such stabilizing agents can optionally and preferably be employed in an ~maunt up to abcut 2.5 g/l with ooncentrations of about O.0001 to about 0.5 g/l being u~ually preferred.

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7~5 ~ hile the novel ccmbination of complexing agents has been found to obviate the necessity of incorporating rate controllers in the bath of the types conventionally required, it is oontemplated, under certain conditions, that rate controlling agents such as cyanide, iodide, or derivative compounds thereof can be incorporated in the electroless oopper plating bath in 3m~unts usuall~ up to about 1 g/l. Such rate controllers accomnodate the stabilizers by reta~ding the plating rate of the bath. It has also been found that t~e use of such rate controllers in relatively ~small prDportions improves the lustre and ductility of the copper deposit. When employed, such rate controllers can be u~ed in amounts up to about 1 g/l with amounts of from about 1 pQm up to a~bout 200 ppm being m~re typical.
Optionally, and preferably, the electroless copper plating bath further contains small controlled a~ou~ts of bath soluble and compatible wetting agents to enhance uniformity of ooverage of the copper plate on the substrate. Wetting agents of the general types which can be satisfactorily used are those oonventionally emplcyed in electroless ccpQer plat mg baths amD~3 which are PlurDnic P85, available fro~ B~SF CDrporation, cc~prisLng a ~Dnionic block copol~mer of ethylene oxide and pro~ylene oxi~e; Gafac RE 610, available f~ GAF Corporation~
an anionic phosphate ester, or the like are typical~ ~kien .

:

-7~5 emplo,yed, such ~etting agents can be incorporated in amDunts up to about 10 g/l while amounts of abcut 0.1 to about 3 g/l are re ~ypical and preferred.
In accordance with the proc~ss aspects of the present invention, an aqueous alkaline electrolyte of the com~osition as hereinbefore described is formed and is heated to an operating temperature of from about room te~QeratUre l60F) up to about 160F, and preferably from about 80 to a~aut 150F.
S~bstrates to be copper plated are subjected to appropriate clean mg treatments, if ne oe ssary, to remove surfa oe contaminants therefrom. In the case of nonoonductive substrates such as plastics, for example, a preliminary pre-treatment of the nonconductive substrate is p~rformed including a tin-palladium oo~plex treating solution to forn active sites on the surfaces thereof usually followed by an accelerating treatment whereafter t~e pretreated plastic is susceptible for autocatalytic copper deposition. As a ge~eral rule, the plating rate of the solution can ~e adjusted ~o meet any desired oommercial situation by varying the con oentration of ccpper ions, reducing agent, tenperature, pH and co~plexing agent ooncentration to attain the desired result. In~reasing copper ion oonoentration, re~ucing agent conoentration, increasing temperatule and pH and reducing oomplexiny agent conoentration all contribute tcward an increased rate of deposition of ospper. Generally speaking, a copper deposition rate of about at least 20 microinches in 10 minutes is ~2~1~7~

considered oommercially satisfactory. ~gitation of the solution also increases plating rate and can be attained by air agitation, cath~de rod agitation or other mechanical agitating ~ar s.
In order to further illustrate the present invention, the following examples are provided. It will be understc3d that the examples are provided for illustrative purposes and are not intended to be limit m g of the sccpe of the present invention as herein described and as set forth in the subjoined claims.

EXA~LE 1 An aqueous alkaline electroless copper solution is prepared by dissolving in water cupric chloride to ~rcvide a copper ion ~oncentration of about 2 g/l (0.032 mol), EDI~ tetra sodium salt in an amount of about 9 g/l ~0.023 mol), sodium glucoheptonate dihydrate in an amount of about 9 g/l (0.032 mDl), formaldehyde as a reducing agent in an amount to pravide a formaldehyde o~ncentration of abaut 3 g/l, sodium hydr3xide to adjust the pH of the soluticn to about 11~6 and a sul~ur conta~Ing stabiliz1ng agent such as 2-mer ~ okhiazole in an amount of ab3ut 0~05 tD about 10 pFm. Ihe bath is a oorresponding to a turncver of about five to ten times of the copper ion 03ncentration ~ reple m shment of the original copper oon oentration a~d the other bath CDnStitUentS. Th2 aged bath oonta ms a mDl ratio of gluoo ~ onate to ECIA of abcut ~L2~B7~5 1.4:1 with a total complexor to oopper ion mDl ratio of about 1.7:1.
The bath at a temperature of about 60C (140F) in the presence of air agitation is employed for depositing copper on test panels producing a bright, smcoth, unifonm pink copper deposit at a plating rate of about 45 microinc~es in 10 minutes. The bath is stable.

An aged aqueous alkaline electroless copper solution is prepared identical to that as previously described in Example 1 with the exception that no complexing agent is added.
TD separate portions of the oomplex-free aged sollltion, selected amounts and combinations of the EDIA and glucoheptonate complexors are added and the sta~ility of the result~ng solution under typical operating conditions is cbserved. Tb sample A, 0.032 mol EDTA is added and the bath is observed to be unstable. Tb a separate sample Bp a combination of 0.023 mol ED~A and 0.014 mDl glucoheptonate is added providIng a mDl ratio of gluoDheptonate to EDrR of about 0.6~
The ocpper deposit is semi-lustrous and provi~es a plating rate of akout 60 micrDinches in 10 minutes.
I3 sample C, a nixture of 0.021 mDl gluoDheptonate an~ 0.016:1 mol ED~A is added providing a relative mDl ratio of gluoDheptonate to EDIA of about 1.3:1. The resultant elect~Dless o~pper solution provides a pink copper deposit at . i ~8~

deposition rate of about 56 micxoinches in 10 munutes. me bath is stable.
To sample D, a mixture of 0.028 m~l glucoheptDnate and 0.008 m~l EDTA is added provid mg a mol ratio of glucoheptonate to EDTA of about 3.5:1. Ihe bath is unstable and produ oe s a copper d~position rate at about 34 ~icroinches in 10 minutes.
~ D sample E, 0.035 m~l glucoheptonate is added without any EDrA. The bath provides a copper deposition rate of about 16 microinches in 10 minutes. The bath is unstable and decomposes.
The foregoing tests indicate that the use of substantially equal mDlar amounts of EDrA or glucoheptonate by themselves d~es not provide a stable aqueous aL~aline electroless oopper solution. When employing a ocmbination of glucoheptonate and EDTA within the mDlar ratios as hereinabuve specified, namely, from about 0.1:1 to about 3:1 and preferably frcm about 0.6:1 to about 2:1 mDls gluosheptonate to EDI~, satisfactory ocpper deposits are obtained with relative ba~h stability.

EX~MPLE 3 An aged aqueous alkaline electr~less oop2er s~lution oontains abGut 2 g/l ~0.032 mDl) ocpper ions, about 9 g/l (0.023 mDl) EDr~ about 5.3 g/l (0.021 mDl) gluoonate providing a mol ratio of gl~oonate to EDT~ of about 0.9:1, about 3 g/l 7~5 formaldehyde and sufficient scdium hydroxide to provide a p~ oE
a~out 11.6. The bath further contains a sulfur stabilizing compound such as 2-mexcapkobenzothiazole in an am~unt up to about 0.25 ppm.
m e solution is at a temperature of abcut 60C
(140F) and is subject to air agitation. A bright pink copper deposit is obtained on test panel surfa oe s at a plating rate of about 37 microinches in 10 minutes.

E~2~PLE 4 An aged aqueous alkaline electroless c~pper solution oontains 2 g/1 (0.032 mol~ copper ions, about 8 g/l ~0.027 m~l) THPEDA, about 2 g/l (0.007 mol) sodium glucoheptonate dihydrate to provide a glucoheptonate to ~.IPEDA ~Dl ratio of about 0.26:1, about 3 g/l formaldehyde and sufficient sodium hydroxide to pr~vide a pH of about 12.2.
The solution is at a temperature of abGut 60C
(140F) and is subject to air agitation. A bright, smcokh, pink oopper deposit is obtained on test panel surfaces at a platiLng rate of about 140 microinches in 10 minutes.

E~E ~
An aged aqueous alkaline electroless copper solution oontaLns about 5 g/l (0~08 ~ol) copper ions, about 15 g/l (0.05 mol3 T~PEDA, abcut 7.5 g/l ~n .02 mol) ED~, about 3.75 g/l (0.013 ~ol) ~odium glucoheptonate dihydrat~ providiny a mol ~L291~7~i ratio of gluooheptonate to the two amlne ccmpounds present of about 0.18:1, about 5 g/l formaldehyde and sodium hydroxide to provide a pH of about 12.2.
The solution is at a temperature of about 60C
(140F) and is subject to air agitation. A bright, pink oopper deposit is obtained on test panel ~urfaces at a plating rate of about 123 microinches in 10 minutes.

~ hile it will be apparent that the preferred emtodlments of the invention di~closed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is sus oe ptib}e to modification, variation and change without departing from the proper soope or fair meaning of the subjoined claims.

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Claims

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

1. In an aqueous alkaline electroless copper plating solution containing copper ions in an amount sufficient to deposit copper, a reducing agent, hydroxyl ions sufficient to provide a pH on the alkaline side, the improvement comprising a complexing agent present in an amount sufficient to complex the copper ions present and comprising a mixture of an amine compound selected from the group consisting of ethylenediaminetetraacetic acid and N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine and a hydroxy acid compound selected from the group consisting of gluconic acid and glucoheptonoic acid as well as the bath soluble and compatible salts and partial salts thereof as well as mixtures thereof in which said hydroxy acid and said amine compound are present in the mixture at a mol ratio of about 0.1 to about 3:1.

2. An aqueous alkaline electroless copper plating solution as defined in claim 1 in which said hydroxyl ions are present in an amount to provide a pH of from about 9 to about 14.

3. An aqueous alkaline electroless copper plating solution as defined in claim 1 in which said hydroxyl ions are present in an amount to provide a pH of from about 10.5 to about 12.5.

4. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises ethylenediaminetetraacetic acid and said hydroxy acid compound is present in an amount to provide a mol ratio of hydroxy acid compound to amine compound of about 0.25:1 to about 3:1.

5. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises ethylenediaminetetraacetic acid and said hydroxy acid compound is present in an amount to provide a mol ratio of hydroxy acid compound to amine compound of about 0.6:1 to about 2:1.

6. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises ethylenediaminetetraacetic acid and said hydroxy acid compound is present in an amount to provide a mol ratio of about 1.3:1.

7. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine and said hydroxy acid compound is present in an amount to provide a mol ratio of hydroxy acid compound to amine compound of from about 0.11:1 to about 2.45:1.

8. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine and said hydroxy acid compound is present in an amount to provide a mol ratio of hydroxy acid compound to amine compound of from about 0.2:1 to about 1:1.

9. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said amine compound comprises N,N,N',N'-tetrakis (2-hydroxypropyl) ethylenediamine and said hydroxy acid compound is present in an amount to provide a mol ratio of about 0.2.

10. The aqueous alkaline electroless copper plating solution as defined in claim 1 in which said complexing agent and said copper ions are present to provide a mol ratio of complexing agent to copper ions of about 1:1 to about 5:1.

11. The aqueous alkaline electroless copper plating solution as defined in claim 1 further including a stabilizing agent present in an amount up to about 2.5 g/l.

12. The aqueous alkaline electroless copper plating solution as defined in claim 1 further including a rate controller present in an amount up to about 1 g/1.

13. The aqueous alkaline electroless topper plating solution as defined in claim 1 further including a wetting agent present in an amount up to about 10 g/l.

14. A process for depositing a copper plating on a conductive substrate which comprises the steps of immersing the substrate in an aqueous alkaline electroless copper plating solution as defined in claim 1, controlling the temperature of said solution within a range of about 60° up to about 160°F, and continuing the immersion of said substrate until a desired thickness of copper has been deposited thereon.