GB2109013A

GB2109013A - Metallic impurity control for electroless copper plating

Info

Publication number: GB2109013A
Application number: GB08230180A
Authority: GB
Inventors: Donald Alan Arcilesi
Original assignee: Occidental Chemical Corp
Current assignee: Occidental Chemical Corp
Priority date: 1981-10-23
Filing date: 1982-10-22
Publication date: 1983-05-25
Also published as: CA1184359A; SE8205982D0; BE894789A; DE3238921A1; AU544591B2; SE8205982L; IT1197434B; IT8249324A0; DE3238921C2; AU8915282A

Abstract

In a process for electroless copper plating comprising contacting a substrate with a solution comprising a source of copper, a complexing agent, a reducing agent and a pH adjuster, an amount of a hydroxy compound effective to complex metallic impurities is present in the solution. A stabilizer and a rate controller may also be present. Sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose, and glucose are among the preferred hydroxy compounds. The solution has been found to be relatively stable, easy to control and of versatile use.

Description

SPECIFICATION Metallic impurity control for electroless copper plating A variety of methods have heretofore been used or proposed for use in applying metallic platings to all or portions of the surfaces of polymeric plastics parts. Such processes conventionally comprise a plurality of sequential pre-treatment steps to render the plastics substrate receptive to the application of electroless plating whereafter the plated part can be processed through conventional electroplating operations to apply one or a plurality of supplemental metallic platings over all or selected portions of the plastic substrate.Conventionally, the pretreatment steps employed include a cleaning or series of cleaning steps, if necessary, to remove surface films or contaminating substances, followed thereafter by an aqueous acidic etching step employing a hexavalent chromium solution to render the plastics hydrophilic and create bonding sites to achieve a desired surface roughness or texture enhancing a mechanical interlock between the substrate and the metallic plating to be applied thereover. The etched substrate is then subjected to one or a plurality of rinse treatments to extract and remove any residual hexavalent chromium ions on the surfaces of the substrate which may also include a neutralization step including reducing agents to substantially convert any residual hexavalent chromium ions to the trivalent state.The rinsed etched substrate is thereafter typically subjected to an activation treatment in an aqueous acidic solution containing a tin-palladium complex to form active sites on the surface of the substrate followed by one or more rinsing steps after which the activated surface is typically subjected to an accelerating treatment in an aqueous solution to extract any residual tin constituents or compounds on the surface of the substrate and thereby expose active catalytic sites. The accelerated plastics part is again water rinsed and thereafter is subjected to an electroless plating operation of any of the types known in the art to apply a metallic plate such as copper, nickel, or cobalt over all or certain selected areas thereof whereafter the part is rinsed and thereafter is subjected to conventional electroplating operations.

Typical of such plastics plating processes are those described in United States Patent Nos.

3,011,920; 3,329,512; 3,532,518; 3,622,370; 3,961,109; 3,962,497; and 4,204,013; to which reference is made for further details of the process, and the disclosures of which are hereby incorporated by reference. The present invention is believed to be applicable to processes of the foregoing type and is specifically directed to a method and composition for metallic impurity control in electroless copper plating which can yield benefits and advantages heretofore unattainable in accordance with prior art practices.

In a conventional electroless copper plating bath, the various components of the plating bath are aqueous concentrates, and include such basic components as copper concentrate, a metal solubilizer or complexer, a reducing agent, and a pH adjuster. In addition, a stabilizer and a rate controller may also be used. Most of the early electroless copper processes used cupric sulphate as the source of metal ions. However, more recent processes employ cupric chloride, which is more soluble than copper sulphate. Due to the high alkalinity of present state-of-the-art autocatalytic copper baths, a complexer is needed to prevent the precipitation of copper as its hydroxide.

Substituted aliphatic amine chelating agents such as ethylenediaminetetraacetic acid tetrasodium salt (Na4EDTA) have been found to be effective over relatively broad pH and temperature ranges, and therefore, have allowed the plating rate to be varied. This in turn permits the thickness of the deposit to be varied over a constant period of time without jeopardizing bath stability. Formaldehyde (such as a 37 percent solution stabilized with 10 percent methanol) is believed to be the major reducing agent used in high volume production.

Sodium hydroxide (50 percent caustic soda for example) is used to maintain the pH at from about 11 to 13, depending on the specific additive system being used. It is important to control the pH carefully because the ability of formaldehyde to reduce copper increases dramatically with increasing pH.

Because copper is autocatalytic, random copper particles that form in solution would be plated indefinitely if they were not stabilized. An electroless copper stabilizer causes the plating rate at a given copper surface to diminish as plating time increases. Among the reasons for using a stabilizer are to limit metal deposition to the work being plated and to prevent solution decomposition. If no stabilizer were present, copper particles or solid impurities falling to the bottom of the plating tank would be plated.

Furthermore, they would continue to plate in an uncontrolled manner until the solution decomposed due to massive tank plating. Some stabilizers can also improve the lustre and/or ductility of copper deposits.

Electroless copper stabilizers are compounds that cause the formation of non-catalytic thin films on the surface of electroless copper deposits that remain in the solution for extended periods of time. Heterocyclic organic sulphur compounds are believed to be the most widely used electroless copper stabilizers. They have replaced numerous other organic and inorganic sulphur compounds, including colloidal sulphur. Very high molecular weight organic poiymers such as gelatin, hydroxy alkyl starches, cellulose ethers, polyamides, polyvinyl alcohol, and polyalkylene oxides have also been used to encapsulate copper particles.

Rate controllers such as cyanide, iodide, or other related organic compounds reduce the activity of the electroless copper processes. Rate controllers accommodate the stabilizers by significantly retarding the plating rate and thereby allowing them to form noncatalytic coatings over the active plating sites. Rate controllers can also improve the lustre and ductility of copper deposits.

A continuing problem associated with the use of electroless copper plating solutions has been the control and/or elimination of metallic impurities in the electroless copper plating solutions. The foreign metals or impurities that are most often encountered and which have the most deleterious impact on the electroless copper plating process are iron, palladium, and chromium.

Iron ions may be introduced into the subject solutions by "dragging in" from previous preplating solutions, from contaminated chemicals, as well as from other sources such as impurities in additives or substrates. If iron ions are present in an electroless copper solution as impurities, they can form a precipitate (probably ferric oxide and/or ferric hydroxide). The resulting precipitate settles to the bottom of the plating tank and causes copper to plate on the bottom of the tank, as well as in the tank filters. This tank plating causes the bath to become unstable and difficult to control, and also raises the cost of operating the electroless copper process because of increased consumption of materials.If palladium colloids are present in an electroless copper solution as impurities, such as from the tinpalladium activator solution from the activation step, or even from the action of the EDTA complexer, they can cause the solution to spontaneously decompose. If hexavalent chromium is present in an electroless copper solution as an impurity, such as from any residual amounts from the etching step not taken care of by the neutralizing step, such hexavalent chromium can remove palladium catalyst from the surface of the plastic to be plated. When this happens either the plastics material will be slow to become covered with copper or it will not plate at all.

As noted above, it is well known that alkaline electroless copper plating solutions must contain a complexing agent for copper ions. If a copper complexing agent was not present the copper would form insoluble hydroxides and precipitate out of solution. The preferred type of copper complexing agents are substituted alkyl amines such as ethylenediamine tetraacetic acid (EDTA).

Other materials such as glycine; alanine; aspartic acid; glutamic acid; cystine, nitrilodiacetic acid; triethanolamine nitrilotriacetic acid; N-hydroxyethyldiaminetetraacetic acid (HEDTA); N, N, N', N'-tetrakis (2-hydroxypropyl) ethylene diamine; as well as diethylenetriamine pentaacetic acid are also believed to be usable. Of the substituted alkyl amines suitable for use in connection with the present process, EDTA comprises the preferred material including the mono, di, tri and tetra alkali metal salts thereof.

The foregoing amines or classes of amines can be further categorized as a compound of the following general formula:

Wherein R, represents an organic radical

in which each x and y is an integer from 1 to 4, and each of R, R2 and R3 represents a hydrogen atom or a radical

in which z is an integer from 1 to 6 and X represents a halogen atom or an -OH, -SO3H, -COOH,-NH2,-CH3 or OCH3 group, or an alkali metal salt of the foregoing.

If EDTA is used as the sole complexing agent in an alkaline electroless copper process, then the deleterious effects from iron, palladium, and chromium, referred to hereinabove occur when the above-referenced contaminating metals are introduced into the plating solution via drag-in from previous preplating solutions, contaminated chemicals, or other sources.

It has now been unexpectedly found that if relatively small quantities of certain hydroxy compounds are added to alkaline electroless copper solutions whose copper ions are complexed with relatively large quantities of substituted alkyl amine complexing agents of the type referred to above, then deleterious effects from contaminating metal ions can be significantly reduced or even possibly completely eliminated. The present invention may be used in processes for applying electroless copper plating to a substrate where the process includes contacting the substrate with a solution which comprises copper, a complexing agent, a reducing agent and a pH adjuster.

According to a first aspect of the present invention, there is provided a process for applying electroless copper plating to a substrate, which process comprises contacting the substrate with a solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

According to a second set aspect of the present invention, there is provided a process for applying electroless copper plating to a substrate, which process comprises contacting the substrate with a solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster, a stabilizer, a rate controller and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

According to a third aspect of the present invention, there is provided an electroless copper plating solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster and an amount of a hydroxy compound effective to complex metallic impurities present in said solution.

According to a fourth aspect of the present invention, there is provided an electroless copper plating solution comprising copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster, a stabilizer, a rate controller and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

According to a fifth aspect of the present invention, there is provided an article whenever plated by a process in accordance with the first or second aspect and/or using a solution in accordance with the third or fourth aspect.

A "hydroxy compound" may be an organic compound having one or more hydroxy groups each attached to a respective carbon atom, it may therefore be a carbohydrate such as sugar.

Hydroxy compounds suitable for use with the present invention include such materials as sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose, and glucose, as well as mixtures thereof. These among other preferred compounds, may be represented by the following general structural formula:

wherein each of RA and RB independently represents a group having one of the following structures:

wherein M represents an alkali metal or ammonium and x is an integer from 1 to 5.

The preferred hydroxy compounds are sodium gluconate, sodium glucoheptonate and sorbitol.

The hydroxy compounds of the present invention should be present in an amount effective to reduce the amount of metallic impurities present in the electroless copper plating solution by forming complexes with such impurities. Hydroxy compound concentrations in the range of from about 0.01 to about 10g/l are suitable in solutions of the present invention, with from about 0.1 to about 1 g/l being preferred. The solutions may be operated in a temperature range of from about 700F to about 1 600F, at pH values of from about 11 to about 13. In this regard, about 10 to about 100gel of the amine complexing agent would be used. About 1 to 4 moles of amine complexing agent are needed for each mole of copper ions.

In the past, materials such as sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, and the like, have been used as complexers in electroless copper plating baths, but they have generally given unacceptably slow plating rates. As noted above, it has unexpectedly been found that relatively small quantities of the above-described hydroxy compounds, when added to alkaline electroless copper solutions whose copper ions are complexed with relatively large quantities of the above-referenced known amine complexing agents, provide a significant reduction or complete elimination of deleterious effects of contaminating metal ions such as iron, palladium, or chromium.

As used herein, the term "copper" is meant to include copper ions, copper salts, and other forms the copper may take in the electroless copper plating solutions used in accordance with the present invention.

Additional benefits and advantages of the present invention will become apparent upon a reading of the detailed description of the preferred embodiments taken in conjunction with the accompanying examples.

The process of the present invention may be used with any of the various platable plastic or polymeric plastics including acrylonitrilebutadiene-styrene (ABS), polyaryl ethers, polyphenylene oxide, nylon and the like. Such substrates are typically cleaned and then rinsed in a manner well known in the art (such as employing an aqueous alkali soak solution followed by contact in an organic solvent medium which may comprise either a single-phase system or an aqueous-organic solvent emulsion, followed by a thorough water rinsing), and as typically preferred to in U.S. Patent No. 4,204,013, the teachings of which are hereby incorporated by reference. The part is then subjected to an etching treatment in an aqueous acid solution containing hexavalent chromium ions and acid, such as sulphuric acid, to effect an etching of the surface thereof.The specific concentration of the etching solution, the temperature, and the duration of the treatment will vary depending upon the specific type of plastic substrate and the parameters of the etching step are, accordingly, dictated by procedures well known and practiced in the art.

Following the etching step, the etched polymeric substrate is subjected to one or more cold water rinses and may additionally include a neutralization step employing an aqueous solution containing a reducing agent to effect a reduction of any residual contaminating hexavalent chromium ions to the trivalent state. A typical neutralization treatment is described in United States Patent No. 3,962,497, the teachings of which are incorporated herein by reference. Following neutralization, if employed, the substrate is again water rinsed and thereafter is subjected to an activation treatment employing an aqueous acid solution containing a tinpalladium complex of the various types well kown in the art. A typical one-step activation treatment is described in United States Patent No.

3,011,920 and United States Patent No.

3,532,518, the substance of both of which patents is incorporated herein by reference.

Following the activation treatment, the activated polymeric substrate is subjected to one or a series of separate cold water rinse treatments whereafter it is subjected to acceleration in an aqueous solution in accordance with methods generally well known in the art. A typical acceleration treatment employing an aqueous accelerating solution containing an aqueous soluble compatible substituted alkyl amine is described in United States Patent No. 4,204,013, the teachings of which are incorporated herein by reference. Following acceleration, the part is cold water rinsed and thereafter is subjected to electroless plating in accordance with the method and composition of the present invention, to apply a conductive continuous and adherent metallic plate such as copper over all or selected surface areas thereof.Following the electroless plating step, the part is subjected to one or a plurality of water rinse treatments and is thereafter in condition for conventional electroplating employing normal procedures to apply one or a plurality of overlying metal coatings on the polymeric substrate.

In order to further describe and illustrate process and composition of the present invention, the following examples are provided. It will be understood that these examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as herein described and as set forth in the subjoined claims.

Examples The following electroless copper formulation (hereinafter referred to as "Formulation A") is typical of a conventional eiectroless copper bath of a type to which the present invention may be applied. (Of course, other similar conventional solutions are also suitable herein.) Ethylenedaminetetraacetic acid tetrasodium salt (Na4 EDTA) 40g/l Cupric Chloride (CuC12) 4.2g/l Formaldehyde (HCHO) 3Q/l Sodium hydroxide (NaOH) to pH 12.2 Temperature 14O0F Plating Rate 32 micro inches per 10 minutes Na4EDTA is present as a complexing agent, and is typical of normal production. Of course, other known complexers may be used.Cupric chloride is the source of copper but other water soluble copper salts such as cupic sulphate, cupric nitrate, cupric acetate, or the like are also suitable for use. Formaldehyde is a reducing agent, although other reducing agents such as formaldehyde precursors or derivatives including paraformaldehyde, trioxane, and glyoxal, as well as sodium borohydride, hydrazine, dimethylamine borane, or the like are also suitable for use.

Sodium hydroxide is added as a pH adjuster, although other hydroxides are also suitable to provide similar pH adjustment. The above described solution is normally clear and blue.

Example 1 20mg/l of ferrous ions added as ferrous sulphate and 20mg/l of ferric ions added as ferric chloride, were added as contaminating metal ions to separate portions of the above electroless copper formulation (Formulation A). In each instance, the solution became green and turbid and iron compounds precipitated out of solution.

Example 2 The procedure of Example 1 was repeated but with the addition of 1 g/l sodium gluconate to Formulation A. In each instance, upon the addition of 20mg/l of ferrous or ferric ions, the plating solution remained blue and clear. The plating rate and quality of the plated copper deposit remained unchanged Example 3 The procedure of Example 1 was repeated but with the addition of 1 g/l of sodium glucoheptonate to Formulation A. In each instance, upon the addition of 20mg/l of ferrous orferric ions, the plating solution remained blue and clear. The plating rate and quality of the plated copper deposit remained unchanged.

Example 4 The procedure of Example 1 was repeated but with the addition of 1 g/l of sorbitol to Formulation A. In each instance, upon the addition of 20mg/l of ferrous or ferric ions, the plating solution remained blue and clear. The plating rate and quality of the plated copper deposit remained unchanged.

Example 5 Platable plastic which was activated was totally covered with a thin film of copper after being immersed in the above-specified electroless copper formulation (Formulation A) for about 8 seconds. The appearance of the deposits after about 1 0 minutes of plating was smooth, lustrous, and pink. After 8mg/l of hexavalent chromium ions were added as contaminating metal ions to the above-specified electroless copper formulation (Formulation A), and an activated platable plastic was immersed therein, only 75% of the plastic surface was covered even after 10 minutes of plating and the deposits had a dark bronze appearance.

The above procedure was repeated with the addition of 1 g/l of sorbitol to Formulation A. Even after the addition of 8mg/l of hexavalent chromium, 98% of the plastic surface became covered with a lustrous pink copper coating.

Example 6 1 Omg of palladium chloride (PdCI2) was added as a contaminat to 1 litre of the state-of-the-art electroless copper formulation specified above (Formulation A). The palladium caused copper metal to be chemically reduced out of solution.

The above procedure was repeated with the addition of 1 g/l of sodium glucoheptonate to Formulation A. Even after the addition of 1 Omg/l of palladium chloride, added via aqueous concentrate, the electroless copper solution remained stable. No copper was reduced out of solution.

Example 7 Additional electroless copper plating solutions comprising copper, a substituted alkyl amine complexing agent, a reducing agent, and a pH adjuster are prepared containing a hydroxy compound present in an amount so as to be effective to complex metallic impurities present in said solution. Hydroxy compounds corresponding to the general structural formula referred to above and present in an amount of from about 0.01 to about 1 Og/l, with the substituted alkyl amine complexing agent present in an amount of from about 10 to about 100gel are used.Upon the addition of iron ions, palladium, or hexavalent chromium into separate portions of the solutions as contaminating ions or metallic impurities, all of the solutions remains clear, and the plating rate and quality of the plated copper deposit are the same as without any of the above-referenced metallic impurities present in the solutions.

When the foregoing examples are repeated using other conventional electroless copper solutions, similar results are obtained. Such other electroless copper solutions contain N, N, N', N'tekrakis (2-hydroxypropyl) ethylene diamine as the amine complexing agent instead of Na4EDTA, and further contain rate controllers, including sodium cyanide, cyanide and organic derivatives of cyanide, iodide and iodide derivatives, nitrogen containing heterocyclics such as bipyridyls, phenanthrolines, and the like; and stabilizer, including organic and inorganic sulphur compounds, colloidal sulphur, very high molecular weight organic polymers, such as gelatin, hydroxy alkyl starches, polyamides, polyvinyl alcohol, polyalkylene oxides and the like.

As evidenced by the above-referenced examples, it should be apparent that the use of the process and composition of the present invention can provide both stability and plated plastics of high quality. Impurities are controlled thereby substantially eliminating skip-plating and precipitation, as well as substantially eliminating subsequent plating on electro-plating tanks and in solution filters.

Among the specific advantages of the present invention, in addition to and in accordance with those described hereinabove, is that iron ions will be complexed thereby preventing them from precipitating out of solution, which in turn prevents solution decomposition due to particle nucleation. Palladium will also be complexed thereby preventing it from catalyzing the decomposition of the copper solution. Similarly, hexavalent chromium ions will also be complexed thereby preventing them from removing palladium catalyst from the surface of the plastic by oxidation, which in turn prevents skip-plating or islands of unplated plastic.

While it will be apparent that the invention herein disclosed is well calculated to achieve the benefits and advantages as hereinabove set forth, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the spirit thereof.

Claims

1. A process for applying electroless copper plating to a substrate, which process comprises contacting the substrate with a solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

2. A process according to Claim 1, in which at least one hydroxy compound is present, the or each compound being a compound having the following general structural formula:

wherein M represents an alkali metal of ammonium and xis an integer from 1 to 5.

3. A process according to Claim 1 or 2, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose or glucose.

4. A process according to Claim 1 or 2 in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate or sorbitol.

5. A process according to any one of Claims 1 to 4, in which the hydroxy compound(s) is/are present in a total amount of from about 0.01 to about 10g/l.

6. A process according to Claim 5, in which the hydroxy compound(s) is/are present in a total amount of from about 0.1 to about 1 g/l.

7. A process according to any one of Claims 2 to 6, in which the substituted alkyl amine complexing agent is present in an amount of from about 10 to 100g/l.

8. A process for applying electroless copper plating to a substrate, which process comprises contacting the substrate with a solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster, a stabilizer, a rate controller and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

9. A process according to Claim 8, in which at least one hydroxy compound is present, the or each hydroxy compound being a compound having the following general structural formula:

wherein M represents an alkali metal of ammonium and x is an integer of from 1 to 5.

10. A process according to Claim 8 or 9, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose or glucose.

11. A process according to Claim 8 or 9, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate or sorbitol.

12. A process according to any one of Claims 8 to 11, in which the hydroxy compound(s) is/are present in an amount of from about 0.01 to about log/r.

13. A process according to Claim 12 in which the hydroxy compound(s) is/are present in a total amount of from about 0.1 to about 1 g/l.

14. A process according to any of Claims 8 to 13, in which the substituted alkyl amine complexing agent is present in an amount of from about 10 to about 100g/l.

1 5. An electroless copper plating solution comprising a source of copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster and an amount of hydroxy compound effective to complex metallic impurities present in said solution.

1 6. A solution according to Claim 15, in which at least one hydroxy compound is present, the or each hydroxy compound being a compound having the following general structural formula:

wherein M represents an alkali metal or ammonium and x is an integer from 1 to 5

1 7. A solution according to Claims 1 5 or 16, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose or glucose.

18. A solution according to Claim 15 or 16, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate or sorbitol.

19. A solution according to any one of Claims 1 5 to 18, in which the hydroxy compound(s) is/are present in a total amount of from about 10g/l.

20. A solution according to Claim 19, in which the hydroxy compound(s) is/are present in a total amount of from about 0.1 to 1 g/l.

21. A solution according to any one of Claims 1 5 to 20, in which the substituted alkyl amine complexing agent is present in an amount of from about 10 to about 1 00g/l.

22. An electroless copper plating solution comprising copper, a substituted alkyl amine complexing agent, a reducing agent, a pH adjuster, a stabilizer, a rate controller and an amount of a hydroxy compound effective to complex metallic impurities present in the solution.

23. A solution according to Claim 22, in which at least one hydroxy compound is present, the or each hydroxy compound being a compound having the following general structural formula:

wherein M represents an alkali metal or ammonium and x is an integer of from 1 to 5.

24. A solution according to Claim 22 or 23, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate, sorbitol, mannitol, glycerol, fructose or glucose.

25. A solution according to Claim 22 or 23, in which the or each hydroxy compound is sodium gluconate, sodium glucoheptonate or sorbitol.

26. A solution according to any one of Claims 22 to 25, in which the hydroxy compound(s) is/are present in an amount of from about 0.01 to about 1 Og/l.

27. A solution according to Claim 26 in which hydroxy compound(s) is/are present in an amount of from about 0.1 to about 1 g/l.

28. A solution according to any one of Claims 22 to 27, the substituted alkyl amine complexing agent is present in an amount of from about 1 0 to about 100g/l.

29. A process for applying electroless copper plating to a substrate in accordance with Claim 1 substantially as described with reference to any one of Examples 2 to 7.

30. A solution in accordance with Claim 1 5 substantially as described with reference to any one of Examples 2 to 7.

31. An article whenever plated using a process according to any one of Claims 1 to 14 and 29 and/or using a solution according to any one of Claims 1 5 to 28 and 30.