PLATING BATH AND METHOD FOR ELECTROPLATING TIN AND/OR LEAD

Abstract: A tin and/or lead electroplating bath is free from fluoride or fluoborate ions and comprises (A) a bath-soluble metal salt which is a stannous salt, a lead salt, or a mixture of stannous and lead salts; (B) an alkane sulphonic acid or alkanol sulphonic acid; (C) a nonionic, cationic or amphoteric surfactant; (D) a primary brightening agent which is an aromatic aldehyde, an acetophenone or a carbonyl compound of the formula: Ar-CH=CH-CO-CH₃ (III) in which Ar is a substituted or unsubstituted phenyl, na­ phthyl, pyridyl, thiophenyl or furyl group; and (E) a secondary brightening agent which is a lower ali­ phatic aldehyde or a substituted olefin of the formula: in which R₁ is a carboxy, carboxamide, alkali metal car­ boxylate, ammonium carboxylate, amine carboxylate or allyl carboxylate group; and R₂, R₃ and R₄ are each independently hydrogen or lower alkyl groups.

Description: This invention relates to the electrodeposition of tin, lead, or tin-lead alloys, and particularly to a plating bath which is free of fluorborates and which deposits smooth, level and bright tin and/or lead coatings. Aqueous acidic plating baths for depositing tin and/or lead coatings on substrates are known, and most of these baths contain, in addition to water-soluble tin and/or lead salts, fluoborates, fluosilicates, sulphates, sulphamates, etc. Plating baths containg fluoborate have been used widely to permit high-speed, uniform metal plating of tin, lead or tin-lead alloys. However, baths containing fluoborates are generally quite corrosive and toxic requiring special equipment which is expensive and presents difficulties in operation, including the disposal of waste water. In addition to the basic ingredients, there have been suggested improvements in tin and/or lead plating baths by including additives which will improve on the brightness of the deposit obtained from such baths. For example, in US-A-3,875,029, the use of naphthalene monocarboxaldehyde either alone or in combination with certain substituted olefins results in an improvement in the brightness of the deposit. Other ingredients which have been suggested as being useful additives in tin and/or lead plating baths include various combinations of aldehydes, ketones, nonionic surfactants, and amines. The plating bath described in US-A-3,785,939 for producing bright deposits of tin-lead alloys comprises a combination of a nonionic polyoxyalkylated surfactant, a lower aliphatic aldehyde, an aromatic aldehyde, and an amine. More recently, plating bath formulations have been suggested which provide for the deposition of tin and/or lead coatings wherein the baths contain no fluoborates. For example, US-A-4,459,185 describes a plating bath which is prepared by adding one or more specified cationic, amphoteric and/or nonionic surfactants and one or more leveling agents to a principal plating bath which contains an alkane sulphonic or alkanol sulphonic acid and either a divalent tin salt or a divalent lead salt of the sulphonic acids or a mixture of these. The patentees suggest that the performance of such plating baths is comparable or even superior to plating baths containing borofluoride. The plating baths contain certain specified surfactants which may be cationic, amphoteric, or nonionic surfactants. The smoothness of the coating is improved by the synergistic effect obtained by the combination of the specified surfactants and certain leveling agents. A variety of leveling agents including benzaldehyde derivatives is described in the patent. Tin-lead alloy plating baths including hydroxyalkyl sulphonic acids are described in US-A-4,132,610. The baths do not contain fluoborates or phenol sulphonates, but do contain the reaction product of o -toluidine with acetaldehyde as a brightener. US-A-3,905,878 describes tin-lead plating baths containing at least one sulphonate salt of tin and lead as well as free phenolsulphonic acid and/or free cresolsulphonic acid. Additionally, the plating baths contain a brightening agent which is prepared by reacting an aliphatic aldehyde with an aromatic primary amine under alkaline conditions. The plating baths also contain acetaldehyde and, optionally, surface active agents. The use of olefinic compounds as brighteners in tin and tin-lead alloy plating baths, salts of fluoboric acid or sulphuric acid, is described in US-A-3,875,029. The olefinic compounds useful as brighteners are characterized by the general formula: formula from page 2 where R₁ is a carboxy, carboxamide, alkali carboxylate, ammonium carboxylate, amine carboxylate, or alkyl carboxylate group, and R₂, R₃ and R₄ are each hydrogen, methyl, or lower alkyl. Such olefins are utilized in combination with a naphthalene monocarboxyldehyde. US-A-774,049 describes a process for electrolytically depositing lead peroxide on lead plates. The baths include a sulphonic acid or oxysulphonic acid derivative of methane and its hydroxy-substituted derivatives such as methyl sulphonic acid, methylene disulphonic acid, oxymethylene disulphonic acid, etc. Tin or tin and lead plating baths containing aromatic sulphones and mono- and poly-sulphonic acids of benzene, phenol and cresol are described in US-A-2,313,371 and GB-A-555,929. The aromatic sulphonic acids form soluble salts of tin and lead, and the disulphonic acids are particularly preferred because they provide extremely soluble salts. US-A-No.3,984,291 describes a plating bath which does not contain any fluoride or fluoborate. These plating baths are based on pyrophosphate and Rochelle salts. The bath is prepared, for example, by dissolving stannous pyrophosphate, potassium pyrophosphate and Rochelle salts (NaK tartrate) together with a lead salt such as lead tartrate or lead pyrophosphate in water. Generally, these types of electrolytic baths are operated at a pH of from 8.0 to 10. Electroplating baths containing an alkane sulphonate ion wherein the alkyl group contains between 1 and 5 carbon atoms are described in US-A-2,525,942. The sulphonate ions are the principal or sole anions in the plating bath. The metallic ions contained in the electrochemical baths may be lead, nickel, chromium, copper, zinc, iron, cobalt, cadmium and silver. The baths are described as being especially suitable for the electroplating of lead and nickel. It has now been found that a smooth, level and bright deposit of tin, lead or tin-alloy can be deposited on a substrate from an aqueous plating bath which contains no fluoride or fluoborates. The aqueous plating baths of the invention comprise (a) at least one bath-soluble metal salt which is a stannous salt, a lead salt, or a mixture of stannous and lead salts, (b) at least one alkane sulphonic acid or alkanolsulphonic acid, (c) at least one nonionic, cationic or amphoteric surfactant, (d) an effective amount of at least one primary brightening agent which is an aromatic aldehyde, an acetophenone or a carbonyl compound of the general formula: Ar-C(H)=C(H)-C(O)-CH₃ (III) wherein Ar is a phenyl, naphthyl, pyridyl, thiophenyl or furyl group, and (e) an effective amount of a secondary brightening agent which is a lower aliphatic aldehyde or a substituted olefin of the formula: wherein R₁ is a carboxy, carboxamide, alkali metal carboxylate, ammonium carboxylate, amine carboxylate or allyl carboxylate group, and R₂, R₃ and R₄ are each independently hydrogen or lower alkyl groups. The plating baths of the present invention comprise a mixture of tin ions, lead ions, or a mixture of tin and lead ions; at least one alkane sulphonic acid or alkanol sulphonic acid; at least one surfactant; at least one primary brightening agent, and at least one secondary brightening agent. Generally, the plating baths of the present invention will comprise a mixture of the free sulphonic acid with the tin, lead, or a mixture of tin and lead salts of sulphonic acids, which salts are soluble in the plating baths. Alkane sulphonic acids which may be utilized in the present invention have the following formula: RSO₃H (I) wherein R is an alkyl group suitably containing from 1 to 12 carbon atoms and more preferably, from 1 to 6 carbon atoms. Examples of such alkane sulphonic acids include, for example, methane sulphonic acid, ethane sulphonic acid, propane sulphonic acid, 2-propane sulphonic acid, butane sulphonic acid, 2-butane sulphonic acid, pentane sulphonic acid, hexane sulphonic acid, decane sulphonic acid and dodecane sulphonic acid. The individual alkane sulphonic acids or mixtures of any of the above alkane sulphonic acids can be utilized in the plating baths of the invention. Alkanol sulphonic acids which are useful in the present invention have the formula: wherein n is 0 or an integer from 1 to 10, m is an integer from 1 to 11 and the sum of m + n is up to 12. As can be seen from formula II, the hydroxy group may be a terminal or internal hydroxy group. Examples of useful alkanol sulphonic acids include 2-hydroxy ethyl-1-sulphonic acid, 1-hydroxy propyl-2-sulphonic acid, 2-hydroxy propyl-1-sulphonic acid, 3-hydroxy propyl-1-sulphonic acid, 2-hydroxy butyl-1-sulphonic acid, 4-hydroxy butyl-1-sulphonic acid, 2-hydroxy-pentyl-1-sulphonic acid, 4-hydroxy-pentyl-1-sulphonic acid, 2-hydroxy-hexyl-1-sulphonic acid, 2-hydroxy decyl-1-sulphonic acid, and 2-hydroxydodecyl-1-sulphonic acid. The alkane sulphonic acids and alkanol sulphonic acids are available commercially and can also be prepared by a variety of methods known in the art. One method comprises the catalytic oxidation of mercaptans or aliphatic sulphides having the formula R¹S n R² wherein R¹ or R² are alkyl groups and n is a positive integer between 1 and 6. Air or oxygen may be used as the oxidizing agent, and various nitrogen oxides can be employed as catalysts. The oxidation generally is effected at temperatures below about 150°C. Such oxidation processes are described and claimed in US-A-2,433,396 and US-A-2,433,395. Alternatively, chlorine can be used as the oxidizing agent. When the plating bath is to be a tin plating bath, the bath will contain at least one alkane or alkanol sulphonic acid as described above and a tin salt thereof. Likewise, a lead plating bath contains at least one alkane or alkanol sulphonic acid and a lead salt thereof. Mixtures of said acids and salts are useful. The tin-lead alloy plating baths will contain at least one alkane or alkanol sulphonic acid and the tin and lead salts thereof. The divalent tin and divalent lead salts of alkane sulphonic acids and alkanol sulphonic acids can be readily prepared by the reaction of a divalent tin or divalent lead salt with the desired sulphonic acid. Examples of tin and lead salts which can be reacted with the sulphonic acid to form the desired metal sulphonate include the oxides of tin and lead. The total concentration of metal ion or ions in the bath may vary over a wide range depending upon the desired properties of the plating to be deposited in the substrate. Generally, from 0.5 to 350 grams per litre or more of the metal ion or ions is included in the bath, and more generally, the bath will contain from 10 to 100 grams per litre of metal ion or ions. Obviously, when a tin deposit is desired, the lead ion should be omitted from the bath, and, conversely, when a lead deposit is desired, the tin ion is omitted from the bath. The concentration of the free alkane or alkanol sulphonic acid (b) in the plating baths of the invention is suitably from 10 to 500 grams per litre, and more preferably from 50 to 200 grams per litre of bath. In addition to the above components, it is necessary that the plating baths of the invention contain at least one nonionic, cationic or amphoteric surfactant. A group of nonionic surfactants which can be utilized in the present invention are the condensation products of ethylene oxide and/or propylene oxide with compounds containing a hydroxy, mercapto or amino group containing at least one N-H. Examples of materials containing hydroxyl groups include alkyl phenols, styrenated phenols, fatty alcohols, fatty acids, polyalkalene glycols, etc. Examples of materials containing amino groups include alkylamines and polyamines, fatty acid amides, etc. Examples of nonionic surfactants useful in the plating baths of the invention include ether containing surfactants having the formula: R―O―[(CH₂) n O] x H (A) wherein R is an aryl or alkyl group containing from 6 to 20 carbon atoms, n is 2 or 3 and x is an integer of from 1 to 100. Such surfactants are produced generally by treating fatty alcohols or alkyl or alkoxy substituted phenols or naphthols with excess ethylene oxide or propylene oxide. The alkyl carbon chain may contain from 14 to 24 carbon atoms and may be derived from a long chain fatty alcohol such as oleyl alcohol or stearyl alcohol. Nonionic polyoxyethylene compounds of this type are described in US-A-3,855,085. Such polyoxyethylene compounds are available commercially under the general trade designations "Surfynol" by Air Products and Chemicals, Inc. of Wayne, Pennsylvania, and under the designation "Pluronic" or "Tetronic" by BASF Wyandotte Corp. of Wyandotte, Michigan. Examples of specific polyoxyethylene condensation products useful in the invention include "Surfynol 465" which is a product obtained by reacting about 30 moles of ethylene oxide with tetramethyldecynediol. "Pluronic L 35" is a product obtained by reacting about 22 moles of ethylene oxide with polypropylene glycol obtained by the condensation of about 16 moles of propylene oxide. Alkoxylated amine, long chain fatty amine, long chain fatty chain, alkanol amines, diamines, amides, alkanol amides and polyglycol-type surfactants known in the art ate also useful. One type of amine surfactant found particularly useful in a tin or lead plating bath is the group obtained by the addition of a mixture of propylene oxide and ethylene oxide to diamines. More specifically, compounds formed by the addition of propylene oxide to ethylene diamine followed by the addition of ethylene oxide are useful and are available commercially from BASF Wyandotte Ind. Chemical Group under the general trade designation "Tetronic". Carbowax-type surfactants which are polyethylene glycols having different molecular weights also are useful. For example Carbowax No. 1000 has a molecular weight range of from about 950 to 1,050 and contains from 20 to 24 ethoxy units per molecule. Carbowax No.4000 has a molecular weight range of from 3000 to 3700 and contains from 68 to 85 ethoxy units per molecule. Other known nonionic glycol derivatives such as polyalkylene glycol ethers and methoxy polyethylene glycols which are available commercially can be utilized as surfactants in the compositions of the invention. Ethylene oxide condensation products with fatty acids are also useful nonionic surfactants. Many of these are available commercially such as under the general tradename "Ethofat" from Armak Ind. Examples include condensate of coco acids, oleic acid, etc. Ethylene oxide condensates of fatty acid amides, e.g. oleamide, also are available from Armak Ind. In some of the baths, improved results are obtained when polyoxyalkylated glycols, phenols and/or naphthols are included. For example ethylene oxide and propylene oxide condensates with aliphatic alcohols, sorbitan alkyl esters, alkyl, alkoxy and styrenated phenols and naphthols are useful additives. About 6 to about 40 moles of the oxide may be condensed with the above identified compounds. Many of these condensates are available commercially under such trade names as "Tween" from ICI America, "Triton" from Rohm & Haas Co., "Tergitol" from Union Carbide, and "Igepal" from General Aniline and Film Corp. The surfactants utilized in the plating baths of the present invention may be amphoteric surfactants. The preferred amphoteric surfactants include betaines and sulphobetaines, and sulphated or sulphonated adducts of the condensation products of ethylene oxide and/or propylene oxide with an alkyl amine or diamine. The betaines may be represented by the general formula: wherein R¹ is an alkyl group containing from about 8 to 20 carbon atoms, and R² and R³ are alkyl groups containing from 1 to about 4 carbon atoms. Typical betaines include lauryldimethylammonium betaine and stearyl dimethylammonium beatine. Sulphated and sulphonated adducts include Triton QS-15 (Rohm & Haas Co.), a sulphated adduct of an ethoxylated alkylamine, Miranol HS, a sodium salt of a sulphonated lauric derivative, Miranol OS, a sodium salt of a sulphonated oleic acid, etc. Cationic surfactants also are useful in the plating baths of the present invention and such surfactants may be higher alkyl amine salts, quaternary ammonium salts, alkyl pyridinium salts or alkylimidazolium salts. Cationic surfactants obtained by condensation of various amounts of ethylene oxide or propylene oxide with primary fatty amines are useful and may be represented by formula in which R is a fatty acid alkyl group containing from about 8 to about 22 carbon atoms, R¹ is an alkylene radical contianing up to about 5 carbon atoms, R² and R³ are each independently an ethylene or propylene group, a is o or 1, and x, y and z are each independently integers from 1 to about 30, and the sum of x, y, and z is an integer of from about 2 to about 50. More particularly, the alkoxylated amines utilized in the baths of the invention may be epresented by the formulae wherein R⁴ is a fatty acid alkyl group containing from 12 to 18 carbon atoms, and x, y and z are as defined about for formula C. The above described cationic surfactants are known in the art and are available from a variety of commercial sources. The surfactants of the type represented by formula D can be prepared by condensing various amounts of ethylene oxide with primary fatty amines which may be a single amine or a mixture of amines such as are obtained by the hydrolysis of tallow oils, sperm oils, coconut oils, etc. Specific examples of fatty acid amines containing from 8 to 22 carbon atoms include saturated as well as unsaturated aliphatic amines such as octyl amine, decyl amine, lauryl amine, stearyl amine, oleyl amine, myristyl amine, palmityl amine, dodecyl amine, and octadecyl amine. The alkoxylated amines which are useful in the plating baths of the invention can be prepared as mentioned above, by condensing alkylene oxides with the above-described primary amines by techniques known to those in the art. A number of such alkoxylated amines is commercially avaiable from a variety of sources. The above described amines can be prepared, as mentioned above, by condensing alkylene oxides with the above-described primary amines by techniques known to those in the art. A number of such alkoxylated amines is commercially available from a variety of sources. The alkoxylated amines of the type represented by formula B are available from the Armak Chemical Division of Akzona, Inc., Chicago, Illinois, under the general trade designation "Ethomeen". Specific examples of such products include "Ethomeen C/15" which is an ethylene oxide condensate of a coconut fatty amine containing about 5 moles of ethylene oxide; "Ethomeen C/20" and "C/25" which also are ethylene oxide condensation products from coconut fatty amine containing about 10 and 15 moles of ethylene oxide respectively; "Ethomeen S/15" and "S/20" which are ethylene oxide condensation products with stearyl amine containing about 5 and 10 moles of ethylene oxide per mole of amine repectively; and "Ethomeen T/15" and T/25" which are ethylene oxide condensation products of tallow amine containing about 5 and 15 moles of ethyleme oxide per mole of amine respectively. Commercially available examples of the alkoxylated amines of the type represented by formula C include "Ethoduomeen T/13" and "T/20" which are ethyleme oxide condensation products of N-tallow trimethylene diamine containing about 3 and 10 moles of ethylene oxide per mole of diamine respectively. The cationic surfactant also may be a quaternary ammonium salt of the formula wherein X represents a halogen, a hydroxyl group, or the residue of a C₁₋₅ alkanesulphonic acid; R₁ represents a C₈₋₂₀ alkyl group, R, and R'' each represent a C₁₋₄ alkyl group and R''' represents a C₁₋₁₀ alkyl group or a benzyl group; a pyridinium salt of the formula wherein X represents a halogen, a hydroxyl group, the residue of a C₁₋₅ alkanesulphonic acid, R₁ represent a C₈₋₂₀ alkyl group, and R a represents hydrogen or a C₁₋₄ alkyl group; an imidazolinium salt of the formula wherein X represents a halogen, a hydroxyl group, or the residue of a C₁₋₁₀ alkanesulphonic acid; R₁ represents a C₈₋₂₀ alkyl group; R d represents a hydroxy-containing C₁₋₅ alkyl group; and R''' represents a C₁₋₅ alkyl group or a benzyl group; or A higher alkyl amine salt of the formula (1) wherein R₁ represents a C₈₋₂₀ alkyl group; and n is 0 or from 1 to about 4 Examples of the above described cationic surfactants, in the form of salts, are lauryltrimethylammonium salt, cetyltrimethylammonium salt, octadecyldimethylethylammonium salt, dimethylbenzyllaurylammonium salt, cetyldimethylbezylammonium salt, octadecyldimethylbezylammonium salt, trimethylbenzylammonium salt triethylbezylammonium salt, hexadecylpyridinium salt, laurylpyridinium salt, dodecylpicolinium salt, 1-hydroxyethyl-1-benzyl-2-lauryl-imidazolinium salt, 1-hydroxyethyl-1-benzyl-2-oleylimidazolinium salt, stearylamine acetate, laurylamine acetate, and octadecylamine acetate. The surfactants descrbed above may be used in the plating baths of the present invention in a concentration of from 0.01 to 50 grams per litre and more preferably from 0.05 to 20 grams per litre. Plating baths of the present invention also contain an effective amount of at least one primary brightening agent which generally are aromatic aldehydes or ketones. The primary brightening agents are selected from aromatic aldehydes, acetophenones, and carbonyl compounds having the general formula Ar-C(H)=C(H)-C(O)-CH₃ III wherein Ar is a phenyl, napthyl, thiophenyl or furyl group. The aromatic aldehydes may be the benzaldehydes. naphthaldehydes, pyridinecarboxaldehyes, thiophenecarboxaldehydes and furaldehydes. Suitable benzaldehydes include derivatives of the formula wherein X is hydrogen or a nitro, halo, amino, alkoxy or lower alkyl group. Specific examples of benzaldehydes include benzaldehyde, o -chloro-benzaldehyde, tolualdehyde, cinnamaldehyde and anisaldehyde. Suitable naphthaldehydes are substituted or unsubstituted 1-naphthaldehydes or 2-naphthaldehydes of the following formula wherein X₁ and X₂ are independently hydrogen, hydroxy, alkoxy, chloro or bromo, and the alkyl group of the alkoxy group contains from about 1 to 5 carbon atoms. Specific examples of such naphthaldehydes include 1-naphthaldehyds 2-napthaldehyde, 2-methoxy-1-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, 2-ethoxy-1-naphthaldehyde, 4-methoxy-1-naphthaldehyde, 4-ethoxy-1-naphthaldehyde, 4-hydroxy-1-naphthaldehyde, 2-chloro-1-naphthaldehyde, 4-chloro-1-naphthaldehyde, etc. Suitable pyridinecarboxaldehydes which can be utilized as the primary brightening agents may have the formula wherein X is hydrogen, hydroxy, alkoxy, chloro, or bromo, and the alkyl group of the alkoxy group contains from 1 to 5 carbon atoms. Specific examples of such aldehydes include pyridine-2-carboxaldehyde, pyridine-3-carboxaldehyde, pyridine-4-carboxaldehyde, and 6-methoxy-pyridine-2-carbox-aldehyde. Suitable thiophenecarboxaldehydes may be represented by the formula wherein X is as defined above for formula L. Specific examples of such carboxaldehydes include 2-thiophenecarboxaldehyde, 3-thiophebecarboxaldehyde, etc. Suitable furaldehydes include those represented by the following general formula wherein X is as defined above for formlula L. Specific examples of such furaldehydes include 2-furaldehyde and 3-furaldehyde. The primary brightenning agent utilized in the plating baths of the present invention also may be an acetophenone of the formula wherein X₁ and X₂ are each independently hydrogen and chlorine. Examples of such compounds are acetophenone and 3',4'-dichloroacetophenone. In another preferred embodiment, the primary brightening agent is a carbonyl compound having the formula wherein Ar is a phenyl, naphthyl, pyridyl, thiophenyl or furyl group. When Ar is a phenyl group, the carbonyl compound can be represented by the formula wherein X₁ and X₂ may be hydrogen, hydroxyl, alkoxy, chlorine or bromine, and the alkyl group of the alkoxy group may contain from about 1 to about 5 carbon atoms. Examples of such compounds include benzylidine acetone and 3'-chlorobenzylidine acetone. Carbonyl compound of formula III wherein Ar is a naphthyl group can be represented by the formula wherein X₁ and X₂ are as defined above for formula P. A specific example of such a brightener is 4(1-naphthyl)-3-butene-2-one. The pyridyl, thiophenyl and furyl containing carbonyl compounds may be represented by the formulae wherein X₁ is as defined above for formula P. Specific examples of such carbonyl compounds include 4-(2-furyl)-3-butene-2-one, 4-(pyridyl-2-)-3-butene-2-one, and 4-(thiophenyl-2-)-3-butene-2-one. The amount of the above described primary brightening agents utilized in the plating baths of the present invention can suitable range from 0.05 to 5 grams per litre and more generally is from 0.2 to 1 gram per litre of plating bath. In addition to the primary brightening agent, the plating baths of the present invention also contain (E) an effective amount of a secondary brightening agent which is a low aliphatic aldehydes or substituted olefin of the formula. wherein R₁ is a carboxy, carboxamide, alkali metal carboxylate, ammonium carboxylate amine carboxylate or allyl carboxylate group and R₂ R₃ and R₄ are each independently hydrogen or lower alkyl groups. The aliphatic aldehydes which are useful as secondary brightening agent as preferably lower aliphatic aldehydes containing up to about 6 atoms, and the aliphatic group may be either saturated or unsaturated. Example of such aldehydes include formaldehyde, acetaldehyde, paraldehyde, butyraldehyde, propionaldehyde, acrolein, crotonaldehyde and 3-hydroxy-butanal. In a preferred embodiment, the olefinic compounds of formula IV are alpha unsaturated carboxylic acids, amides or esters. Examples of such materials include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethacrylic acid, ethyl acrylate, acrylamide, methacrylamide, crotonic acid, cinnamic acid, butyl methacrylate, etc. These alpha unsaturated compounds are generally added to the plating bath as aqueous or alcoholic (e.g., methyl, ethyl, propyl and isopropyl alcohol) solutions to ensure good dispersion in the plating bath. The amount of secondary brightening agents (E) utilized in the plating baths of the present invention may suitably be from 0.1 to 20 grams per litre of and more preferably from 0.5 to 10 grams per litre. The tin, lead, and tin-lead plating baths of the present invention which contain no fluoride or fluoborate ions deposit a bright level coating of the metal or alloy on substrates at any conventional temperature used or normally used with tin and/or lead plating baths, and over a wide current density range. The following examples illustrate the plating baths of the invention. Unless otherwise indicated in the following examples and elsewhere in the specification and claims, all parts and percentages are by weight, and temperatures are in °C. EXAMPLE 1 An aqueous plating bath was prepared by mixing with water, sufficient quantities of stannous methane sulphonate to provide 20 g/l of stannous ion, 100 g/l of free methane sulphonic acid, 5 g/l of a nonionic surfactant which is nonylphenol condensed with 10 moles of ethylene oxide, 1 g/l of methyl methacrylate, and 0.2 g/l of benzylidine acetone. Additional plating baths were prepared in accordance with the present invention following the general procedure of Example 1. EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 EXAMPLE 7 EXAMPLE 8 EXAMPLE 9 EXAMPLE 10 EXAMPLE 11 EXAMPLE 12 The utility of the plating baths of the present invention in depositing tin and tin-lead coatings was demonstrated by conducting plating tests in standard 267 ml Hull cells using as the anode, a tin or tin-lead alloy (60/40, tin/lead). Steel panels were plated at a current of 2 amps for a period of five minutes. Mechanical bath agitation has employed, and the bath temperature was maintained at about 20 to 25°C. The results of the plating tests are summarized in the following Table. In practice, the improved tin, lead, and tin-lead, alloy plating baths containing the brightener compositions of the invention may be operated on a continuous or intermittent basis, and from time time, components of the bath have to be replenished. The various components may be added singularly as required or may be added in combination. The amounts of the various additive compositions to be added to the plating baths may be varied over a wide range depending on the nature and performance of the plating bath to which the composition is added. Such amounts can be determined readily by one skilled in the art. As mentioned above, the major advantage of the plating baths of the present invention is that they contain no fluoride or fluoborate ions which eliminates the need for the recovery and disposal of these undesirable ions. The fluoride and fluoborate ions are undesirable because of the environmental pollution problems created on disposal, and further because of their corrosive nature when present in plating baths. The plating baths of the present invention which do not contain fluoride or fluoborate ions are less corrosive to machinery and glass parts, and also permit the use of titanium and titanium alloy anode baskets. It also has been observed that anode dissolution is improved in the plating baths of the present invention which results in less anode polarization and a reduced amount of stannate tin in the bath. The coating deposited from the plating baths of the invention are useful in electronic circuits, electronic devices and electrical connectors. The surface layers of tin, lead and tin-lead alloys can be used as protective layers to prevent corrosion or in a patterning procedure during the fabrication of printed circuits or integrated circuits. The coatings also provide chemically stable surfaces for soldering on printed wire boards, etc.

Claims: An aqueous tin, lead or tin-lead alloy plating bath free of fluoride or fluoborate ions and comprising: (A) a bath-soluble metal salt which is a stannous salt, a lead salt, or a mixture of stannous and lead salts; (B) an alkane sulphonic acid or alkanol sulphonic acid; (C) a nonionic, cationic or amphoteric surfactant; (D) a primary brightening agent which is an aromatic aldehyde, an acetophenone or a carbonyl compound of the formula: Ar-CH=CH-CO-CH₃ (III) in which Ar is a substituted or unsubstituted phenyl, naphthyl, pyridyl, thiophenyl or furyl group; and (E) a secondary brightening agent which is a lower aliphatic aldehyde or a substituted olefin of the formula: in which R₁ is a carboxy, carboxamide, alkali metal carboxylate, ammonium carboxylate, amine carboxylate or allyl carboxylate group; and R₂, R₃ and R₄ are each independently hydrogen or lower alkyl groups. A bath as claimed in claim 1 characterized in that the bath-soluble metal salts (A) are alkane sulphonic acid and/or alkanol sulphonic acid salts. A bath as claimed in claim 1 or claim 2 characterized in that it contains from 0.5 to 350 grams per litre of bath-soluble metal salts (A). A bath as claimed in any one of the preceding claims characterized in that the alkane sulphonic acid has the formula: RSO₃H (I) (in which R is a C₁-C₂ aliphatic group), and/or the alkanol sulphonic acid has the formula: (in which n is 0 or an integer from 1 to 10; m is an integer from 1 to 11 and the sum of m and n is up to 12). A bath as claimed in any one of the preceding claims characterized in that it contains from 10 to 500 grams per litre of alkane sulphonic acid and/or sulphonic acid. A bath as claimed in any one of the preceding claims characterized in that the primary brightening agent is a naphthaldehyde or a benzylidene acetone. A bath as claimed in any one of the preceding claims characterized in that it contains from 0.05 to 5 grams per litre of primary brightening agent. A bath as claimed in any one of the preceding claims characterized in that the secondary brightening agent is a lower aliphatic aldehyde or a compound of formula (IV) in which R₁ is a carboxy group. A bath as claimed in any one of the preceding claims characterized in that it contains from 0.1 to 20 grams per litre of secondary brightening agent. A method of electrodepositing a bright tin and/or lead deposit on a substrate characterized in that it comprises electroplating the substrate with a plating bath as claimed in any one of the preceding claims.

Inventors: CANARIS, VALERIE M., OPASKAR, VINCENT C, WILLIS, WILLIAM J.
Applicants: MCGEAN-ROHCO, INC.
Application year: 1986
Main classification: C25D3
IPC codes: C25D3, H05K3