PLATING BATH AND METHOD FOR ELECTROPLATING TIN AND/OR LEAD

Abstract: An aqueous tin, lead or tin-lead alloy electroplating bath comprises (A) a bath-soluble stannous salt and or a bath-soluble lead salt; (B) an alkane sulphonic acid and/or an alkanol sulphonic acid; (C) a surfactant; (D) a primary binding agent which is a halo-substituted benzaldehyde or a dialkoxy- or tri-substituted benzaldehyde containing from 1 to 4 carbon atoms in the alkoxy groups; and (E) a secondary brightening agent which is a lower alipha­ tic aldehyde.

Description: This invention relates to the electrodeposition of tin, lead or tin-lead alloys, and particularly to a plating bath which is free of fluoride and fluoborates and which depposits smooth, level and bright tin and/or lead coatings. Aqueous acidic plating baths for depositing tin and/or lead coating 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 containing 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, it has been proposed to improve 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 described in the patent, 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 anonionic 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 and which 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 levelling 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. It it is supgested that the performance of such plating baths is comparable or even superior to that of 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 levelling 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 containing at least one sulphonate salt of tin and lead as well as free phenolsuphonic 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 agent. 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 has the formula where R₁ is a carboxy, carboxyamide, alkali carboxylate, ammonium carboxylate, amine carboxylate, or alkyl carboxylate group, and R₂ , R₃ and R₄ are hydrogen, methyl, or lower alkyl. Such olefins are utilized in combination with a naphthalene monocarboxaldehyde. US-A-774,049 describes a process for electrolytically depositing lead peroxide on lead plates. The baths included 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. US-A-4,072,582 describes tin plating baths containing dialkoxy benzaldehydes emulsifying agents and alpha, beta unsaturated carboxylic acids, amides and esters for producing bright tin deposits. The tin is introduced into the bath as stannous sulphate, and sulphuric acid is included in the baths. Tin or and 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 from soluble salts of tin and lead, and the disulphonic acids are paricularly preferred because they provide extremely soluble salts. U.S.-A-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 U.S.-A-2,525,942. The sulphonate ions are the principal or sole anions in the platin bath. The metallic ions contained in the electrochemical baths may be lead, nickel, chromium, copper, zinc, iron, colbalt, cadmium and silver. The baths are described as being especially suitable for the electroplating of lead and nickel. It now has been found that a smooth, level and bright deposit of tin, lead or a tin-lead alloy can be deposited on a substrate from an aqueous plating bath which contains no fluoride or fluoborates. Preferably the plating baths also are free of strong inorganic acids such as sulphuric acid. 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 surfactant, (d) an effective amount of 0.02 to 5 g/ℓ of at least one primary brightening agent which is a halosubstituted or a dialkoxy or trialkoxy benzaldehyde wherein each alkoxy group independently contains from one to about four carbon atoms, and (e) an effective amount of a secondary brightening agent which is at least one lower C₁-C₆ aliphatic aldehyde. The plating baths of the present invention comprise a mixture of tin ions, lead 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 which is a dialkoxy or trialkoxy benzaldehyde, and at least one secondary brightening agent. Generally, the plating baths of the invention will comprise a mixture of the free sulphonic acid with the tin and/or lead salts of the sulphonic acids, which salts are soluble in the plating baths. Alkane sulphonic acids that can be utilized in the invention have the formula RSO₃H (I) wherein R is an alkyl group containing from about 1 to about 12 carbon atoms and more preferably, from 1 to 6 atoms. Examples of such alkane sulphonic acids include 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 thereof can be utilized in the plating baths of the invention. Alkanol sulphonic acids which may be use in the invention have the formula C n H 2n+1 -CH-(CH₂) m -SO₃H (II) wherein n is from 0 to about 10, m is from 1 to about 11 and the sum of m and n is up to about 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, 2-hydroxy-hexyl-1- sulphonic acid, 2-hydroxy decyl-1-sulphonic acid and 2-hydroxy dodecyl-1-sulphonic acid. The alkane sulphonic acids and alkanol sulphonic acids are available commercially and can also be prepared by a variety of methods know in the art. One method comprises the catalytic oxidation of mercaptans or aliphatic sulfides 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 agents, and various nitrogen oxides can be employed as catalysts. The oxidation generally is effected at temperature below about 150°C. Such oxidation processes are described and claimed in US-A- 2,433,395 US-A- 2,433,396. 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 on the substrate. Generally, from about 0.5 to about 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 about 6 to about 100 grams per litre of metal ion or ions. Obviously, when a tin deposit is desired, the lead ion is 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 about 10 to about 500 grams per litre of bath, and more preferably from about 50 to about 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 surfactant while may be a nonionic, cationic, anionic or amphoteric surfactant. One class of nonionic surfactants which can be utilized in the invention comprises the condensation products of ethylene oxide and/or propylene oxide with compounds containing a hydroxy or mercapto group and or amino group containing at least one N-H. Examples of materials containing hydroxyl groups include alkyl phenols, styrenated phenols, fatty alchols, fatty acids, polyalkalene glycols, etc. Examples of materials containing amino groups include alkylamines and poyamines, fatty acid amides, etc. Examples of nonionic surfactants useful in the plating baths of the invention include ether containing surfactants of the formula R² - O - [(CH₂) n O] x H (A) wherein R² is an aryl or alkyl group containing from about 6 to 20 carbon atoms, n is two or three, and x is an integer between 2 and 100. Such surfactant are gererally produced by treating fatty alchols or alkyl or alkoxy subtituted phenols or naphthols with excess ethylene oxide or propylene oxide. The alkyl carbon chain may contain from about 14 to 24 carbon atoms and may be derived from a long chain fatty alcohol such as oleyl or stearyl alchol. 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"® from air Products and Chemicals, Inc. of Wayne Pennsylvania, and under the designation "Pluronic"® or Tetronic"® from 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 10 moles of ethylene oxide with 1 mole of tetramethyldecynediol. ""Surfynol 485" is the product obtained by reacting 30 moles of ethylene oxide with tetramethyldecynediol. "Pluronic L 35"® is a product obtained by reacting 22 moles of ethylene oxide with a polypropylene glycol obtained by the condensation of 16 moles of propylene oxide. Alkoxylated amine, long chain fatty amine, long chain fatty acid, alkanol amines, daimines, amides, alkanol amides and polyglycol-type surfactants known in the art are also useful. One type of amine surfactant found particularly useful in a tin or lead plating bath is that 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 are also 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 about 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 commerciallly can be utilized as surfactants in the compositions of the invention. Ethylene oxide condensation products with fatty acids also are useful non-ionic 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 alchols, sorbitan alkyl esters, alkyl, alkoxy and styrenated phenols and naphthols are useful additives. About 6 to about 40 moles of the oxides 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 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 betaine. Sulphated and sulphonated adducts include Triton® QS-15 (Rohn & 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 invention and such surfactants may be higher alkyl amine salts, quaternary ammonium salts, alkyl pyridinium salts alkyl imidazolium 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 the following formula wherein R is a fatty acid alkyl group containing from about 8 to about 22 carbon atoms, R¹ is an alkylene radical containing up to about 5 carbon atoms, R² and R³ are each independently an ethylene or propylene group, a is 0 or 1, and x, y and z are each independently integers from 1 to about 30, and the sum of z,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 are represented by the formulae D and E wherein R⁴ is a fatty acid alkyl group containing from 12 to 18 carbon atoms, and x, y and z are as defined 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 containg 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 available 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, lllinois, 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 moles of amine respectively; and "Ethomeen T/15"® and "T/25" which are ethylene oxide condensation products of tallow amine containing about 5 and 15 moles of ethylene oxide per mole of amine respectively. Commercially available examples of the alkoxylated amines of the type represented by formula C include "Ethoduomeen 1/13"® and "T/20" which are ethylene 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) a quaternary ammonium salt of the formula wherein X represents a halogen atom 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; (b) pyridinium salts of the formula wherein X represents a halogen atom hydroxyl group, or the residue of a C₁₋₅ alkanesulphonic acid; R₁ represents a C₈₋₂₀ alkyl group; and R a represents hydrogen or a C₁₋₄ alkyl group; (c) imidazolinium salts of the formula wherein X represents a halogen atom 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 C₁₋₁₀ alkyl group or a benzyl group; and (d) higher alkyl amine salts of the formula [R₁-NH₃] ⊕ CH₃-(CH₂) n -COO ⊖ (I) wherein R₁ represents a C₈₋₂₀ alkyl group; and n is from about 0 to about 4. Examples of the above described cationic surfactants, in the form of salts, are lauryltrimethylammonium salt, cetyltrimethylammonium salt, stearyltrimethylammonium salt, lauryldimethylethylammonium salt, octodecyldimethylethlammonium salt, dimethylbenzyllaurylammonium salt, cetyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, trimethylbenzylammonium salt, trethylbenzylammonium salt, hexadecylpyridinium salt, laurylpyridinium salt, dodecylpicolinium salt, 1-hydroxyethyl -1-benzyl-2-laurylimidazolinium salt, 1-hydroxyethyl-1-benzyl-2-oleylimidazolinium salt, stearylamine acetate, laurylamine acetate, and octadecylamine acetate. The surfactants also may be anionic surfactants. Examples of useful anionic surfactants include sulphated alkyl alcohols, sulphated lower ethoxylated alkyl alcohols, and their salts such as alkali metal salts. The surfactants described above may be used in the plating baths of the invention in a concentration of from about 0.01 to about 50 grams per litre of bath, more preferably from about 0.05 to about 20 grams per litre of bath. The plating baths of the invention also contain an effective amount of at least one primary brightening agent which is at least one dialkoxy or trialkoxy benzaldehyde such as represented by the following formula wherein R₁ and R₂ are each independently alkyl group containing from one to about four carbon atoms, and R₃ is a hydrogen a form or an alkoxy group containing from one to about four carbon atoms. Examples of the R₁ and R₂ group include methyl, ethyl, propyl and isopropyl, and examples of the alkoxy group R₃ include methoxy, ethoxy, propoxy, idopropoxy, etc. Preferably the primary brightener is a dialkoxy benzaldenyde, such as the various dimethoxy benzaldehydes. Specific examples of useful substituted benzaldehydes of the type represented by formula III include: 2,3-dimethoxybezaldehyde 3,4-dimethoxybenzaldehyde 2,4-dimethoxybenzaldehyde 2,5-dimethoxybenzaldehyde 2,6-dimethoxybenzaldehyde 3,5-dimethoxybenzaldehyde 2,3,4-trimetthoxybenzaldehyde 2,4,5-trimethoxybenzaldehyde 2,4,6-trimethoxybenzaldehyde 3,4,5-trimethoxybenzaldehyde One or more of the methoxy groups can be replaced by other alkoxy groups such as ethoxy, propoxy and isopropoxy. The amount of the above described primary brightening agents utilized in the plating baths of invention can suitably be from about 0.02 to about 5 grams per litre of bath and more generally is from about 0.05 to about 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 at least one lower aliphatic aldehyde. The aliphatic aldehydes which are useful as a secondary brightening agent are preferably lower aliphatic aldehydes containing up to about 6 carbon atoms, and the aliphatic group may be either saturated or unsaturated. Examples of such aldehydes include formaldehyde, acetaldehyde, paraldehyde, butyraldehyde, propionaldehyde, acrolein, crotonaldehyde and 3-hydroxy-butanal. The amount of secondary brightening agent (E) utilized in the plating baths of the invention is suitably from about 0.1 to about 20 grams per litre of bath and more preferably is from about 0.5 to about 10 grams per litre of the plating bath. Antioxidants mormally used in tin, lead and tin/lead baths may be included in the baths of this invention. For example, catechol (1,2-dihydroxybenzene) is useful as an antioxidant stabilizer in the baths and prevents air oxidantion of stannous to stannic tin. Generally amounts of from about 0.05 to about 2 grams of antioxidant per litre of bath are sufficient. The tin, lead, and tin-lead plating baths of the invention which contain no fluoride or fluoborate ions, and preferably no sulphuric acid, 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 (except for the control examples) illustrate the plating baths of the invention. Unless otherwise indicated in the following examples and elsewhere in the specification and all parts and percentages are by weight, and temperatures are in °C. Example 1 An aqueous plating bath has prepared by mixing with water, sufficient quantitees of stannous methane sulphonate to provide 20 g/l of stannous ion, 80 g/l of free methane sulphonic acid, 8 g/l of a nonionic surfactant which is nonylphenol condensed with 10 moles of ethylene oxide. 1 g/l of acetaldehyde, and 0.3 g/l of 2,5-dimethoxybenzaldehyde. Control 1A A plating bath was prepared as in Example 1 except that the 2,5-dimethoxybenzaldehyde and acetaldehyde was omitted. Control 1B A plating bath was prepared as in Example 1except that the acetaldehyde was omitted. Control 1C A bath was prepared as in Example 1 except that the 2,5-dimethoxybenzaldehyde was omitted. The following additional plating baths were prepared following the general procedure of Example 1. Example 2 Example 3 Example 4 Example 5 Example 6 Control 6A A bath was prepared as in Example 6 except that the dimethoxybenzalde was replaced by 2-methoxybenzaldehyde Control 6B A bath was prepared as in Example 6 except that the dimethoxybenzaldehyde was replaced by 3-methoxybenzaldehyde. Example 7 Example 8 Example 9 Example 10 Example 11 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 was plated at a current of 2 amps for a period of five minutes. Mild mechanical bath agitation was employed, and the bath temperature was maintained at about 20 to about 25°C. The results of the plating tests are summarized in the following Table. The plated deposit approximated the metal composition of the bath but may vary ±5% depending on the current density. 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 to time, components of the bath have to be replenished. The various components may be added alone as required or may be added in combination. 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 undesiiable 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 so 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 wich results in less anode polarization and a reduced amount of stannate tin in the bath. The coatings 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 protetive layers to prevent corrosion or in a patterning procedure during the fabrication of printed circuits. The coatings also provide chemically stable surfaces for soldering on printed wire boards, etc.

Claims: An aqueous tin, lead or tin-lead alloy electroplating bath comprising: (A) a bath-soluble stannous salt and/or a bath-soluble lead salt; (B) an alkane sulphonic acid and/or an alkanol sulphonic acid; (C) a surfactant; (D) a primary brightening agent and (E) and secondary brightening agent, characterised in that the the primary brightening agent is a halosubstituted benzaldehyde or a dialkoxy- or tri-substituted benzaldehyde containing from 1 to 4 carbon atoms in the alkoxy groups, present in an amount of from 0.02 to 5 g/ℓ; the secondary brightening agent is a C₁-C₆ aliphatic aldehyde; and that the electrolyte is free from fluorine and fluoborate ions. A plating bath as claimed in claim 1 characterised in that the stannous and/or lead salts are alkane sulphonate or alkanol sulphonate salts. A plating bath as claimed in claim 1 or claim 2 characterised in that the alkane sulphonic acid has the formula: RSO₃ H (I) in which R is a C₁-C₁₂ alkyl group. A plating bath as claimed in any one of the preceding claims characterised in that the alkanol sulphonic acid has the formula: Cn H 2n+1 - CH(OH) -(- CH₂) m - SO₃H (II) in which n is 0 or from 1 to 10 and m is from 1 to 11, the sum of m and n being up to 12. A plating bath as claimed in any one of the preceding claims characterised in that it contains from 0.5 to 350 g/l of stannous and/or lead salt ions. A plating bath as claimed in any one of the preceding claims characterised in that it contains from 10 to 500 g/l of alkane sulphonic acid or alkanol sulphonic acid. A plating bath as claimed in any one of the preceding claims characterised in that it contains from 0.01 to 50 g/l of surfactant. A plating bath as claimed in any one of the preceding claims characterised in that the substituted benzaldehyde is a mono-chloro- or di-chlorobenzaldehyde. A plating bath as claimed in any one of claims 1 - 7 characterised in that the substituted benzaldehyde is a dialkoxy benzaldehyde. A plating bath as claimed in claim 9 characterised in that the substituted benzaldehyde is a dimethoxybenzaldehyde. A plating bath as claimed in any one of the preceding in which the secondary brightening agent is acetylaldehyde. A plating bath as claimed in any one of the preceding claims characterised in that it contains from 0.1 to 20 g/l of secondary brightening agent. A plating bath as claimed in any one of the preceding claims characterised in that it contains an auxiliary brightening agent of the formula: in which X is a hydrogen or halogen atom or an amino, carboxy, alkyl or alkoxy group and a is 0, 1, 2 or 3, the groups X possibly being different when a is 2 or 3. A plating bath as claimed in claim 13 characterised in that the auxiliary brightening agent is a diethyl, dimethyl, triethyl or trimethyl aniline. A plating bath as claimed in claim 13 in which the auxiliary brightening agent is xylidene. A plating bath as claimed in any one of claims 12-14 characterised in that it contains from 0.02 to 5 g/l of auxiliary brightening agent. A plating as claimed in any one of the preceding claims also containing an antioxidant. A plating bath as claimed in claim 17 in which the antioxidant is catechol. A method of electrodepositing the tin, lead, or tin-lead alloy on a substrate which comprises electroplating the substrate in an aqueous acidic plating bath as claimed in any one of the preceding claims.

Inventors: BOKISA, GEORGE S., OPASKAR, VINCENT C.
Applicants: MCGEAN-ROHCO, INC.
Application year: 1986
Main classification: C25D3
IPC codes: C25D3, H05K3