US 3615733 A
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United States Patent  Inventors Charles R. Shipley,Jr.
Newton; Lucia 1!. Shipley, Newton; Michael Gulla, Newton; Oleh B. Dutkewych, Medfield, all of Mass.  App]. No. 752,166  Filed Aug. 13, 1968  Patented Oct. 26, 1971  Assignee Shipley Company, Inc.
 ELECTROLESS COPPER PLATING 19 Claims, No Drawings 52 us. Cl 106/1, 117/47, 117/130, 117/160  Int. Cl C23c 3/02  Field ofScar-ch 106/1; l17/130,130E,47 R, 35 S, 213,227,160
 References Cited UNITED STATES PATENTS 3,093,509 6/1963 Wein v 117/213 3,134,690 5/1964 Eriksson 117/213 Primary Examiner- Lorenzo B. Hayes Attorney- Roberts, Cushman & Grover ABSTRACT: An electroless copper plating solution comprising a source of cupric ions, hydroxyl radicals, formaldehyde or a formaldehyde precursor, preferably paraformaldehyde, and a complexing agent for copper; said solution characterized by the addition of a combination of additives comprising an organic silicon compound and a hydrogen inclusion retarding agent and preferably, the combination of the two with at least one member selected from the group consisting of a formaldehyde addition agent and a Group VIII metal salt of the Periodic Chart of the Elements. Copper plate deposited from a solution of this invention is distinguishable from prior art copper deposits by substantially improved bending or tensile properties and a smoother, more highly reflecting appearance. The electroless copper plating solution is capable of providing a rapid rate of copper deposition dependent upon the selection of the complexing agent and the stability of its chelate with copper without sacrifice in tensile or bending properties of the copper deposit.
ELECTROLESS COPPER 'I EIG ,4 herein by reference. Improved properties are obtained by the addition of a silicon compound to an electroless copper solu- BACKGROUND OF THE INVENTION tion where silicon is believed to be the active agent. A major advantage of this system is that the rate of copper deposition m 2 .22.13.a":is:2i.:2;22:32:15.3;.ssgitiizzziztt:3 v t m en es to a metal deposmng composmon and ties is not fully understood but-1s believed to be due, at least in more Pamcularly, to electroless copper platmg sohmon part, to a surface effect resulting in deposition of a smoother capable of providing an electroless copper deposit of improved bending or tensile properties and having a g y 10 depotsit ftlewer structural defects as will be explained in reflective appearance tfdp ser degoziiion solution capable of providing a copper Descnptlon of the plate having substantially improved tensile or bending proper- Electroless copper deposition refers to the chemical plating ties is disc! t osed m copendmg U.S. Pat. application Ser. No. of copper over acme Surfacies by chemlca] means m the 752,250 filed concurrently herewith. Improved properties are absence of an external electric current. Such processes and obtained by the addition of a formaldehyde addition a em composmons useful therefor are known and are in substamlal and/or a salt of a Group VIII metal of the Periodic Chart of the commercial use. They are disclosed in a number of prior art patents, for example, U.S. Pat. Nos. 2,938,805; 3,011,920; El :121: 55 3:31 2 amlxture ofthe twom combination wnh 3,310,430, and 3,383,224.
Known electroless copper deposition solutions generally comprise four ingredients dissolved in water. They are (1) a source of cupric ions, usually a copper salt, such as copper sulfate (2) a reducing agent such as formaldehyde, or preferably, a formaldehyde precursor such as paraformal- I dehyde (3) hydroxide, generally an alkali metal hydroxide and The Subject invention i an illllnlllvelnent 0V6! that usually sodium hydroxide, sufficient to provide the required described in the above-noted 3,310,430 and alkaline solution in which said compositions are effective, and 3,475,136 and p s an electroless c pp r ut n capable (4) a complexing agent for copper sufi'icient to prevent its of depositing an electroless copper plate of improved bending precipitation in alkaline solution. A large number of suitable or tensile properties. The copper solution is characterized by complexing agents are known and described in the abovethe addition of the combination of a silicon compound and a cited patents, and also in U.S. Pat. Nos. 2,874,072; 3,075,856; hydrogen inclusion retarding agent, preferably a cyanide com- 3,1 19,709; 3,075,855 and 3,329,512 all incorporated herein pound and preferably the combination of the two with at least by reference. Known electroless copper solutions of the above one member selected from the group consisting of a formaltype usually provide a plate which if mechanically dense and dehyde addition agent and a salt of Group VIII metal of the strong, is somewhat brittle such that it can withstand only Periodic Chart of the Elements. The addition of the hydrogen limited bending or thermal stress without fracture. This is not inclusion retarding agent to 'a solution containing an organic a substantial disadvantage where the electroless plate is of the silicon compound produces a synergism resulting in substanorder of inillionths of an inch of thickness and is overplated tially increased tensile or bending properties. The further ad- STATEMENT OF THE INVENTION with ductile electrolytic copper. However, where the entire dition of a formaldehyde addition agent or a salt of a Group desired thickness, typically 1 to 3 mils in an electrical applica VIII metal provides a further substantial improvement in protion, is provided by electroless plating, limited ductility is a perties, especially where a combination of the two are used. In serious limitation. addition to the above-noted improvement in ductility proper- One means of improving bending or tensile characteristics ties, electroless copper deposits from the solutions of this inof an electroless copper plate is described in U.S. Pat. No. 4 vention provide the further advantages of excellent laydown Preferred Copper salt 0.002 mole to saturation 0.02 to 0.12 mole. Formaldehyde... 0.05 to 3.5 moles 0.1 to 1 mole.
Minimum necessary to maintain copper in solution.. About 1 to 3 times the moles of cupric.
Complexing agent Free hydroxide Suflicient to provide pH 10 or greater Hydrogen inclusion retarding agent.. 1 to 1,000 p.p.m 5 to 500 p.p in
Silicon compound Greater than 1 p.p.m 5 to 250 p.p.m.
Formaldehyde addition agent... To that amount that restricts dcposition.. 0.1 to times the moles of formaldehyde. GroupVIIImetalsa1t. ..5to2,500p.p.m H J0to1,000p.p.rn.
Water To lliter ofso1ution............................ To 1 liter lsolution.
3,310,430 which discloses the addition to a copper plating properties, excellent solderability, and improved smoothness, solution of a water soluble compound of cyanide, vanadium, brightness, and overall appearance. molybdenum, niobium, tungsten, arsenic, antimony, bismuth,
rare earths of the actin ium series and rare earths of the lanthanum series. Certain members of the above group, espe- DESCRIPTION OF THE PREFERRED EMBODIMENTS cially the vanadium compounds, provide significantly improved bending characteristics. The reason for this is not fully understood but is stated in the patent that the agents poison A ypic l l le c pper solution in accordance with the the analyti u fa e so a to promote formation and le of invention will have additives in the following concentration hydrogen gas at the catalytic surface, thereby inhibiting the inranges: clusion of hydrogen in the deposit as it forms. It has been It should be understood thatthe above concentration ranges found that where a complexing agent or bath formulation is are preferred, but not critical. Variation in the ranges are used permitting rapid deposition of copper with rapid evolupossible without departing from the scope of the invention. In tion of hydrogen gas at the surface, the improved ductility or most cases, additives may be added in an amount up to that bending characteristics are frequently sacrificed or lost. amount that poisons the solution.
An alternative means for improving the tensile properties of In the above formulations, any water soluble copper salt an electroless copper deposit while simultaneously improving heretofore used for preparingelectroless copper deposition brightness and other appearance properties as described in solutions may be used. Fog example, the halides, nitrate,
commonly assigned U.S. Pat. No. 3,475,186 incorporated acetate, sulfate and other organic and inorganic acid salts of copper are generally suitable as is known in the art. Copper sulfate is preferred.
Suitable complexing agents for the copper ions include Rochelle salts, the sodium salts (mono, di, tri, and tetrasodium salts) of ethylenediaminetetraacetic acid, nitrilotriacetic acid and its alkali metal salts, triethanolamine, modified ethylenediaminetetraacetic acids such as N-hydroxyethylenediaminetriacetate, hydroxyalkyl substituted-dialkylene triamines such as pentahydroxypropyldiethylenetriamine, sodium salicylate, and sodium tartrate. Other complexing agent for copper ions are disclosed in U.S. Pat. Nos. 2,996,408; 3,075,855; 3,075,856; and 2,938,805.
The preferred class at complexing agents 531155.: described in U.S. Pat. No. 3,329,512 noted above. They include hydroxyalkyl substituted tertiary amines corresponding to one of the following structures:
l ROH ROH where R is an alkyl group having from two to four carbon atoms, R is a lower alkylene radical and n is a positive integer. Examples of these complexing agents include tetrahydroxypropyl ethylene diamine, pentahydroxypropyl diethylene triamine, trihydroxypropylamine triisopropanolamine), trihydroxypropyl hydroxyethyl ethylene diamine, etc. As disclosed in said patent, the aforesaid amines are preferably used in small amounts in combination with other complexing agents and with certain polymers dispersed in solution such as cellulose ethers, hydroxyethyl starch, polyvinyl alcohol, polyvinylpyrrolidone, peptones, gelatin, polyamides and polyacrylamides.
The rate of copper deposition is, to some extent, dependent upon the selection of the complexing agent. Complexing agents such as pentahydroxypropyldiethylenetriamine provide a fast rate of copper deposition, usually in excess of 1.0 mils per hour. Though the copper solutions of this invention provide copper deposits from solutions containing any of the known complexing agents for copper ions, they are particularly well adapted for copper solutions having complexing agents that provide a rapid rate of copper deposition.
The silicon additive is one that is soluble in the copper solution and comprises the organic silicon compounds disclosed in the above-noted Pat. No. 3,475,186. It should be noted that many silicon compounds are not fully soluble in aqueous alkaline solutions and many are considered insoluble. However, the silicon, for purposes of the present invention, is required in solution in parts per million and silicon compounds termed insoluble in aqueous solution usually are soluble to the extent of a few parts per million and suitable for purposes of the present invention. For those silicon compounds considered insoluble in water, it is desirable to dissolve the compound in a solvent, such as alcohol, and add the solution to the electroless copper solution with agitation to form a dispersion or an emulsion. An excess of the silicon compound will be required to provide the necessary concentration of silicon compound in solution.
Exemplary of the silicon compound within the scope of the invention are the silanes, such as silane itself, disilane, tetramethylsilane, trimethylethylsilane, tetraethylsilane, tetraphenylsilane, dimethyldichlorosilane, etc., and low to intermediate molecular weight polysiloxanes such as silicone fluids, gums, and resins substituted with methyl, ethyl, vinyl, penyl, chloro, bromo, methoxy, hydroxy, etc. Other suitable organic silicon compounds are disclosed in the above-noted U.S. Pat. No. 3,475,186.
The polysiloxanes are the least soluble silicon compounds in basic copper solution, but are preferred because they provide the greatest increase in ductility and also enhance appearance by yielding a finer grained, more highly reflecting copper deposit. Of the polysiloxanes, the silicon fluids are most preferred. The solid polysiloxanes are preferably dissolved in a solvent such as alcohol and added to the copper solution.
The hydrogen inclusion retarding agent is of the same class disclosed in the above-noted U.S. Pat. No. 3,310,430 and includes simple and complex compounds which comprise one or more compounds or cyanide, vanadium, molybdenum, niobium, tungsten, rhenium, arsenic, antimony, bismuth, actinium, lanthanum, rare earths of both the lanthanum and actinium series and mixtures of the foregoing.
Preferred are those compounds which consist of or comprise elements of the type described which have at least two oxidation states. In this preferred group are compounds comprising vanadium, niobium, molybdenum, tungsten, rhenium, arsenic, antimony, bismuth, cerium, praseodymium, neodymium, samarium, europium, terbium, uranium, and mixtures of the foregoing. These elements are preferably added to the electroless copper plating baths in a form such that the element is at its most stable valence state. VAnadium and cyanide compound such as alkali metal cyanides exemplified by sodium cyanide and potassium cyanide as disclosed in the above-noted U.S. Pat. No. 3,310,430 are the most preferred hydrogen inclusion retarding agents. Where cyanide is selected as the hydrogen inclusion retarding agent, it may appear twice in the formulation dependent upon the selection of the remaining additives.
The hydrogen inclusion retarding agent is added to the bath, preferably as a soluble salt. For example, molybdenum may be supplied as molybdic trioxide as well as water soluble organic and inorganic acid salts of molybdenum, as for example alkali and alkaline earth metal, or ammonium molybdates. Suitable sources of tungsten, molybdenum, rhenium and arsenic are the oxides of such elements, as well as organic and inorganic acid water soluble salts of such elements, e.g., the tungstates, vanadates, arsenates, and rhenates of the metals of Groups l-A and II-A of the Periodic Chart of the Elements, and ammonium. Preferred for use are the sodium, potassium, and ammonium salts. Sources of antimony, bismuth, lanthanum, actinium, and rare earths are the oxides of such elements and water soluble organic and inorganic acid salts of such elements, including the sulfates, nitrates, halides, acetates, and the like. The function of the hydrogen inclusion retarding agent is not fully understood, but it is reported that it tends to poison the catalytic surface so as to promote the formation and release of hydrogen gas to the catalytic surface on which copper is depositing electrolessly, thereby inhibiting the inclusion of hydrogen in the deposit as it forms.
The formaldehyde addition agent for purposes of this invention is one that may be added to solution in amounts sufficient to undergo reaction with formaldehyde to form a relatively unstable formaldehyde adduct. Reactions of this nature and formaldehyde, addition agents are well known in the art and described in various publications, such as Formaldehyde J. Frederick Walker, Reinhold Publishing Company, Third Edition 1964, pages 219 to 221, included herein by reference. Preferred addition agents are sulfites, bisulfites, and phosphites of a metal cation that does not codeposit with copper and preferably an alkali metal cation. Preferred formaldehyde addition agents are sodium sulfite, potassium bisulfite and sodium phosphite.
The formaldehyde addition agent and formaldehyde or preferably, paraformaldehyde are reacted with each other to form the adduct prior to addition to the remaining components of the copper solution.
The Group VIII metal salts include water-soluble inorganic salts of iron, cobalt, nickel, rutenium, rhodium, palladium, osmium, iridium, and platinum, salts of iron, nickel and platinum being most preferred and slats of palladium being least preferred due to solution stability problems caused by palladium. Suitable salts include phosphates, nitrates, halides,
and acetates of the above metals. A wetting agent may be added to solution in accordance with art recognized procedures.
The baths may be used at widely varying temperatures, e.g., at least room temperature and preferably up to 140 F. As temperature is increased, it is customary to find an increase in the rate of plating. Temperature is not highly critical, and within the usual operating ranges, excellent, bright deposits of electroless copper having excellent tensile or bending properties are obtained. Preferably, the bath is used without agitation.
In using the-electroless copper solution to plate metal, the surface to be plated should be catalytically active and free of grease and contaminating material. Where a nonmetallic surface is to be plated, the surface area to receive the deposit must first be sensitized to render it catalytically active as by the well-known treatment with an acidic aqueous solution of stannous chloride followed by treatment with a dilute aqueous acidic solution of palladium chloride. Alternatively, extremely good sensitization of nonmetallic surfaces is achieved by contact with an acidic colloidal formulation formed by the admixture of stannous chloride and a precious metal chloride, preferably palladium chloride, the stannous chloride being present in stoichiometric excess based upon the amount of precious metal chloride.
The invention will be better understood by reference to the following examples where all parts were plated using the following procedure:
a. Cut a phenolic substrate to a size of 2 inches X 2 inches.
b. Scrub part clean using an abrasive cleaner.
c. Rinse in cold water.
d. Immerse in a solution of a wetting agent identified as Shipley Conditioner 1159 at room temperature for l to 3 minutes.
e. Rinse in cold water.
f. Immerse in a colloidal stannic acid-palladium catalyst (identified as Cuposit Catalyst 6F) maintained at room temperature for i to 5 minutes.
g. Rinse in cold water.
h. Immerse in Cuposit Accelerator 19 or a mild perchloric acid solution maintained at room temperature for 3 to 10 minutes.
i. Rinse in cold water.
j. Immerse in electroless copper solution maintained at between 110 and 130 F. for a period sufficient to provide a deposit of desired thickness not to exceed 3 hours.
k. Dry parts and examine deposit for appearance and ductility. Ductility is determined by peeling a copper deposit from the substrate and bending through 180 in one direction, creasing at the fold, then returning it to its original position with pressing along the crease to flatten it. This cycle constitutes one bend. The procedure is repeated until the sample breaks at the crease. A sample unable to withstand at least to bend is considered brittle.
EXAMPLES l-20 CuS0,-$l-I,0 8.0 g. Paraformaldehyde 7.5 g. NaOH(25% solution by wt.) 50.0 ml. tetrahydroxypropylethylene diamine 12.0 g. triisopropanolamine 2.0 g.
Water to l liter of solution The above formulation, with various additives was used to deposit electroless copper. Additive composition and deposit properties are set forth in the following table:
0 deposit electroless copper.
Additive Deposit Deposit eoncenappearthickness Ductility Ex. No. Additives tratiou ance (in. 10- (bends) 1 Control Poor 0.50 Brittle. ;0p.p.m do 0.29 yDo. p.p.m-- 0.37 10 p.p.m..} 0. as Britt 250 p.p.m. Fair 0.87 -56.
6 F13514 200 p.p.m....do 0.34 SF1138 200 p.p.m....do 0.46
20 g./l Poor 0.43 Brittle. 8 d 0.46 Do. 00p.p.m do 0.09 Do. 300 p.p.m. do 0.36 D0. 300 p.p.m. do 0.25 Do.
p.p.m. 300 }Poor 0. 32 10 p.p.m.. 300 p.pm. Poor 0.40 7 p.p.m. 30g. Poor 0.44
' 0. 50 p 0 43 I6 ZOO I p.p.m. }(iood 0.40 1. 200 p.p.m. 7p.p.m. Good"... 0.32 1%. 300 p.p m- 200 p.p.m. NaHSO: 20 g.ll Good..." 0.43 2. NaCN 7 p.p.m
(l) F-l-3514 A silicone fluid believed to be a dimethylpolysiloxane-ethylene glycol copolymer available from the General Electric Company. X
(2) SF-l 138 A silicone fluid believed to be a dimethylpolysiloxane-polyalkyleneoxide copolymer available from the General Electric Company.
In the above examples, a deposit was considered poor if it was dark in color and powdery. A fair deposit was one lighter in color, though powdery in appearance. A good deposit was one having a fine grained metallic copper appearance.
The improvements in tensile or bending properties using the preferred electroless copper solutions of the present invention are readily apparent by reference to the above examples. Examples 2 to 12 illustrate the use of a single additive. The only single additives showing observable improvement in properties are the silicon and vanadium compounds. Combination of a silicon compound with a cyanide gives greater improvement. Significantly greater improvements are obtained by the combination of a silicon compound, a cyanide compound, and a member selected from the group of a formaldehyde addition agent and a metal salt of a Group VIII metal (Examples 19 to 20).
EXAMPLES 21 to 25 CuSo,'5H,0 8.0 g. Formaldehyde 7.5 g. NaOH(25% solution) 50.0 ml. Sodium/potassium tartrate 40.0 g.
Water to 1 liter ofsolution The above formulation, with various additives, is used to Additive compositions and deposits properties are set forth in the following table:
Copper solutions of this invention find utility for all purposes for which electroless copper solutions have heretofore been used including both decorative and industrial applications. They are especially useful for the formation of printed circuit boards where the deposits act as a ductile conductor and as a ductile connector plated onto the walls of throughholes. The formation of a printed circuit board having through-holes is illustrated in the following example.
EXAMPLE 26 a. Sandblast one side of a phenolic substrate leaving the second surface smooth.
b. Drill through-holes at desired locations.
c. Silk screen a reverse image of a printed circuit pattern onto the roughened surface of the phenolic substrate using an epoxy resin.
d. Immerse in a colloidal palladium sensitizing solution maintainedatroom temperature for a period of five minutes.
e. Immerse in a stripping solution comprising 10 grams of copper chloride, 100 grams of 37 percent hydrochloric acid, and water to one liter. Maintain solution at room temperature and immerse for 6 minutes.
f. Deposit electroless copper of example 25 with copper deposition taking place on the walls of the through-holes and on the roughened surfaces in the image pattern. No copper deposition takes place on the epoxy resist nor on the smooth surfaces of the plastic laminate.
The mechanism by which copper deposits from the solution of this invention differs from that of the above-referenced U.S. Pat. No. 3,310,430 where hydrogen inclusion retarding agents alone are used to improve ductility. Though neither mechanism is fully understood, a different mechanism is suggested by the observation that the Group VIII metal cation codeposits with copper, to some extent, in the absence of a hydrogen inclusion retarding agent but codeposition is lessened when a hydrogen inclusion retarding agent is in solution. This is shown by the following examples:
The copper deposits of the above examples were analyzed. In example 27 containing both vanadium and nickel compounds in solution, only 0.00088 percent nickel was found in the deposit. Omission of the vanadium compound in example 28 results in a copper deposit containing 0.100 percent nickel. This indicates that the vanadium somehow retarded the codeposition of nickel.
It should be understood that various changes may be made in the embodiments described above without departing from the spirit and scope of the invention as defined by the following claims:
1. In an aqueous eleetroless copper plating solution comprising a source of cupric ions, hydroxyl radicals, a source of formaldehyde and sufficient complexing agent to render said cupric ions soluble in alkaline solution, the improvement comprising an additive in the solution of a combination of an organic silicon compound and a hydrogen inclusion retarding agent, said organic silicon compound and said hydrogen inclusion retarding agent being present in combined amounts insufficient to prevent copper deposition and each of said organic silicon compound and said hydrogen inclusion retarding agent being present in solution in an amount of at least one part per million parts of solution.
2. The copper plating solution of claim 1 containing as an additional additive at least one member selected from the group consisting of a formaldehyde addition agent in an amount of at least 01 moles per mole of formaldehyde in solution to that amount that prevents deposition of copper and a salt of a Group VIII metal of the Periodic Chart of the Elements in an amount of at least five parts per million parts of solution, said Group VIII metal salt having an anion noninterferin g with said solution.
3. In an aqueous electroless copper plating-solution comprising a source of cupric ions, hydroxyl radicals, formaldehyde and sufficient complexing agent to render said cupric ions soluble in alkaline solution, the improvement comprising an additive in the solution of an organic silicon compound, a solution-soluble alkali metal cyanide compound, and at least one of a formaldehyde addition agent selected from the group of alkali metal sulfites, bisulfites and phosphites and solution soluble salts of a Group VIII metal selected from the group of iron, nickel and platinum, said salts of a Group VIII metal having an anion noninterfering with said electroless copper solution, said organic silicon compound and said alkali metal cyanide being present in solution in combined amount insufficient to prevent copper deposition, each of said organic silicon compound and said alkali metal cyanide being present in solution in an amount of at least one part per million parts of solution, said formaldehyde addition agent being in an amount of about 0.1 moles per mole of formaldehyde to that amount that prevents copper deposition and said Group VIII metal salt being present in an amount of at least five parts per million parts of solution.
4. The copper plating solution of claim 3 having as additives the silicon compound, the cyanide compound, the formaldehyde addition agent and the Group VIII metal salt.
5. The copper solution of claim 4 where the silicon compound is a silicone fluid.
6. The copper solution of claim 5 where the Group VIII metal salt is selected from the group consisting of NiSO,, Fe (SO )X and H PtCl 7. The copper solution of claim 3 where the formaldehyde addition agent is selected from the group' consisting of Na,so,, NaI-ISO and Na I-IPO '5H,O.
8. The copper solution of claim 5 where the cyanide compound is sodium cyanide.
9. In an aqueous electroless copper plating solution comprising a source of cupric ions, hydroxyl radicals, a source of formaldehyde and sufficient complexing agent to render said cupric ions soluble in alkaline solution, the improvement comprising an additive in the solution of a combination of an organic silicon compound and a hydrogen inclusion retarding agent selected from the group consisting of a water soluble cyanide compound, vanadium, molybdenum, niobium, tungsten, rhenium, arsenic, antimony, bismuth, rare earths of the actinum series, rare earths of the lanthanum series and mixtures of the foregoing, said organic silicon compound and said hydrogen inclusion retarding agent being present in a combined amount insufficient to prevent copper deposition and said organic silicon compound and said hydrogen inclusion retarding agent being present in solution in an amount of at least lpart per million parts of solution.
10. The copper plating solution of claim 9 containing as an additional additive at least one member selected from the group consisting of a formaldehyde addition agent in an amount of at least 0.1 moles per mole of formaldehyde in solution to that amount that prevents copper deposition and a salt of a Group VIII metal of the Periodic Chart of the Elements in an amount of at least five parts per million parts of solution, said formaldehyde addition agent being selected from the group consisting of metal salts of a member selected from the group consisting of sulfites, bisulfites and phosphites, and said salt of a Group VIII metal being selected from the group consisting of salts of platnium, iron and nickel and having an anion noninterfering with said electroless copper plating solution.
11. The copper solution of claim 10 having as additives, the
copper salt 0.02 to 0.12 rnoles formaldehyde 0.1 to 1 moles complexing agent i to 3 times the moles of cupric ion free hydroxide 0.] to 03 moles hydrogen inclusion 5 to 250 ppm retarding agent silicon compound 5 to 250 ppm.
fonnaldehyde addition 0.] to 1 times the moles agent formaldehyde Group VIII metal salt 30 to 1,000 ppm.
Water to 1 liter ofsolution 15. The copper solution of claim 10 where the organic-silicon compound is selected from the group consisting of silanes and polysiloxanes.
1 6. The copper solution of claim 15 where the silicon compound is a polysiloxane.
17. The copper solution of claim 10 where the silicon compound is added to the copper solution by dissolution in a solvent and addition of the solution to the copper solution.
18. The copper solution of claim 9 where the hydrogen inclusion retarding agent is an alkali metal cyanide.
19. The copper solution of claim 18 where the alkali metal cyanide compound is sodium cyanide