Plating bath for electrodeposition of bright tin and tin-lead alloy
United States Patent Rosenberg et al.  
 [ Apr. 1, 1975 PLATING BATH FOR ELECTRODEPOSITION OF BRIGHT TIN AND TIN-LEAD ALLOY [75] Inventors: William E. Rosenberg, Strongsville;  
 William E. Eckles, Cleveland Heights, both of Ohio [73] Assignee: R. 0. Hull &amp; Company, Inc.,  
 Cleveland, Ohio [22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,406  
 [52] U.S. Cl 204/43 S, 204/53, 204/54 R [51] Int. Cl. C23b 5/14, C23b 5/38, C23b 5/46 [58] Field of Search 204/43 S, 54 R, 53  
 [56] References Cited UNITED STATES PATENTS 3,361,652 1/1968 Korpiun et a1 204/54 R 3,471,379 10/1969 Schoot et a1. 204/54 R 3,769,182 10/1973 Beckwith et al 204/43 S 3,785,939 1/1974 Hsu 204/43 S Primary Examiner-G. L. Kaplan Attorney, Agent, or Firm-Watts, l-loffmann, Fisher &amp; Heinke Co.  
 [5 7] ABSTRACT The invention disclosed herein relates to the electrolytic deposition-of bright tin and tin-lead alloy. This invention is embodied in a new plating bath and a plating bath additive. The new plating bath includes tin or tin and lead ions, sulfuric acid or fluoboric acid, and the new additive. The new additive includes an emulsified naphthalene monocarboxaldehyde with or without a substituted olefin, having the general formula:  
 in which R is carboxy, carboxamido, alkali carboxylate, ammonium carboxylate, ,amine carboxylate, or  
 alkyl carboxylate, and R R and R are hydrogen, methyl, or lower alkyl.  
 15 Claims, No Drawings PLATING BATH FOR ELECTRODEPOSITION OF BRIGHT TIN AND TIN-LEAD ALLOY BACKGROUND OF THE INVENTION The invention pertains to aqueous acid plating baths and additives for producing semi-bright or bright electrodeposits of tin and tin-lead alloy. I  
  Prior to this invention recently introduced commercially usable acid tin baths have been composed of multi-component brightening agents to produce acceptably bright electrodeposits. The essential ingredients of these baths are various combinations of certain aldehydes and ketones, imidazoline surfactants, nonionic surfactants, and amines. While these baths produce significantly bright deposits, many of them lack sufficient broad bright current density ranges. This means careful control of current and time consuming racking procedures are required to avoid dull or-coarse deposits On parts that due to their irregular shapes promote uneven current distribution.  
  The one thing common to all of these combinations is that the ingredients depend on one another to produce bright deposits. Being essential ingredients the lack or absence of any one of them nullifies the effect of the others.  
  What makes our invention unique is that the naphthalene monocarboxaldehyde produces a brightness without dependence on distinct types of emulsifiers and amines. The only essential requirement is that the naphthalene monocarboxaldehyde be made soluble in the plating bath. This can be achieved by use of coupling solvents as well as emulsifiers in .general. Prior brightener systems requirespecific surfactants to be used since their brightening ability is essential in the performance of the system as awhole.  
  While it is true that the addition of compounds of the general formula:  
 are required also for extreme luster, semi-bright to bright, uniform deposits can be obtained without them. Also with the use of this invention a very broad, bright current density range is achieved providing a means for electroplating extremely irregular shapes without stringent controls on current or racking of parts. In addition, higher current-densities can be achieved without obtaining coarse deposits, allowing an electroplater to obtain more plate thickness in a shorter time.  
 SUMMARY OF THE INVENTION This invention is embodied in an aqueous acid electroplating bath containing a dissolved tin salt, together with a lead salt, if an alloy is desired, an acid selected from the group consisting of sulfuric acid and fluoboric acid and a solubilized or dissolved naphthalene monocarboxaldehyde.  
 When compounds of the general formula:  
 where R, is carboxy, carboxamido, alkali carboxylate, ammonium carboxylate, amine carboxylate, or alkyl carboxylate, and R R and R are hydrogen, methyl, or lower alkyl are also added to the plating bath, they act synergistically with the naphthalene monocarboxaldehyde to give significantly brighter deposits than obtained with the dissolved naphthalene monocarboxaldehyde alone.  
 This invention is also a brightening agent for the aqueous acid electroplating baths described above comprised of about l to 99 percent naphthalene monocarboxaldehyde, about 0 to 99 percent emulsifier, 0 to 99 percent of a compound of the general formula:  
 where R, R R and R, are defined as above, and the remaining percentage being a suitable solvent.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The aqueous acid electroplating baths of the present invention generally contain stannous ion, sulfate or flouborate ions and dissolved naphthalene monocarboxaldehyde for proper operation. The stannous ion is introduced usually as stannous sulfate and the lead salt, when an alloy is&#39;desired, is introduced as lead flouborate.  
  The naphthalene monocarboxaldehydes are readily available in commerce and their uniqueness as brightening agents compared to other aldehydes and ketones can be partially explained by a close study of their chemical structure.  
  Three resinance bond structures for naphthalene are possible, the symmetrical structure I and the two unsymmetrical, equivalent structures II and Ila; In formulations of the unsymmetrical structure s,one of the two rings is indicated as quinoid (q) because the arrangement of double bonds corresponds to that of obenzoquinone.  
  b I b I Various chemical reactions of naphthalene show that the bond structure of the naphthalene nucleus is not so mobile as that of benzene and that there is a relative fixation of bonds in at least part of the molecule at which substitution occurs. This is generally described as an enhanced l,2-double bond character.  
  A much more detailed explanation of monosubstituted naphthalenes unique chemical behavior is given in Advanced Organic Chemistry by Fieser and Fieser, page 880. As can be concluded from the above discussion, monosubstituted binuclear aromatic aldehydes will show distinctly different chemical properties such as electron donating ability and reactivity when compared to aldehydes and ketones derived from benzene, heterocyclic aromatic single ring compounds, and certainly those of cyclic and straight chained aliphatic compounds.  
  The naphthalene monocarboxaldehyde is used at a concentration of about 0.05 to 0.5 gms/liter and the preferred concentration is 0.2 gms/liter.  
  Due to its low solubility, coupling agents or emulsifying agents must be used to dissolve the naphthalene monocarboxaldehyde in the plating bath. Some of the suitable coupling agents are diethylene glycol monomethyl ether, diethylene glycol monobutylether, ethylene glycol monomethyl ether, and diethylene glycol monoethylether. 5  
  The emulsifying agents that have been found to work best are cationics such as the alkyl tertiery heterocyclic amines and alkyl imadazolinium salts, amphoterics such as the alkyl imidazoline carboxylates, and nonionics such as the aliphatic alcohol ethylene oxide condensates, sorbitan alkyl ester ethylene oxide condensates, and alkyl phenol ethylene oxide condensates. The nonionics are generally condensed with to moles of ethylene oxide per mole of lipophilic group. Listed in Table l are the commercial names and manufacturers of these emulsifiers. This invention is not limited to the use of these emulsifiers only, it being pointed out that this is merely a list of preferred types.  
 TABLE I 20 Trade name Type Manufacturer 1. Miranol HM Miranol HS Amine C Amine S Tween 40 t Triton N-lOl Tergitol TMN Amphoteric Amphoteric Cationic Cationic Nonionic Nonionic Nonionic Miranol Chemical Co.  
  o. Ciba-Geigy do. lCl America Rohm &amp; Haas Co. Union Carbide where R is carboxy, carboxamido, alkali carboxylate, ammonium carboxylate, amine carboxylate, or alkyl carboxylate, and R R R are hydrogen, methyl, or lower alkyl. The olefinic compound as set forth above may be added to a plating bath using the naphthalene 0.5 gms/liter. The required amount of the naphthalene monocarboxaldehyde in this synergistic combination is the same as when it is used alone.  
  Other known addition agents may be used in combination with the addition agents of this invention such as other aromatic and aliphatic aldehydes and ketones, but it has been generally found that they are not neces sary. Antioxidants such as pyrocatechol and cresol sulfonic acids may be used with this invention as well as chelating agents to prevent metal sludge build-up on anodes.  
  The brightening agents of this invention are generally added as aqueous, or methyl alcohol solutions, but other suitable solvents can be used as long as they dont cause detrimental results during electrodeposition. In some cases the addition agents may be added in their concentrated form, provided the plating bath is thoroughly stirred.  
  While the brightening agents of this invention are effective in many aqueous, acid tin plating bath formulations, it is preferred to use any-of the basic baths described in the following examples. It will be understood that the following examples are just illustrations and are not meant to limit the use of the invention to these bath formulations only.  
 EXAMPLE 1 Bath Composition Concentration in gms/liter Stannous Sulfate 30 Sulfuric Acid 200 l-naphthalene carboxaldehyde 0.2 diethyleneglycol monomethyl ether 40 EXAMPLE ll Bath Composition Concentration in gms/liter EXAMPLE lV Bath Composition monocarboxylate to obtain a much brighter deposit gta pnousAs ljfate 238 u unc c1 than can be obtained with the naphthalene monocar .zmphthalene carboxadehyde O2 boxaldehyde alone. The olefimc compound has no Methacrylic acid 0.5 brightening ability when used by itself, and acts as a NW1 8 brightener only when used in the above mentioned ExAMpLEv combination.  
  Examples of some of the preferred olefmic com- Bath g Cmcenmmn&#34; gms/me&#39; pounds are listed in Table II. me 88 l-naphthalene carboxaldehyde 0.2 TABLE II Acrylic acid 0.4 Triton N-lOl l0 Acrylic Acid Acrylamide EXAMPLE vi Methacryl?mld e Bath Composition Concentration in gms/liter Methacfyhc acld Lead Flouborate 4.5 Crotonic acid goriglActid 10 in ou orate l4 Ethyl aFrylate 5 Flouboric Acid 90 The required concentration of the olefinic compound 2-naphthalene carboxaldehyde 0.2 Methacrylic acid 0.5 is about 0.1 to 5 gms/liter, the preferred amount being Tergitol TMN 0 Concentration in gms/liter where R is carboxy, carboxamido, alkali carboxylate,  
 ammonium carboxylate, amine carboxylate, or alkyl carboxylate, and R R and R are hydrogen, methyl, or lower alkyl.  
  4. The bath of claim 3 wherein R, is carboxy, and R R and R are hydrogen.  
 5. The bath of claim 4 wherein the emulsifying agent TABLE III Basic bath as described in examples but no addition group on naphthalene Position of aldehyde Olefinic compound Emulsificr or Results coupling agent agent. emulsifiers. or ring coupling agent 1. Bath of Example I l Triton N-lOl Semi-bright to bright from I to I amps/ft? 2. Bath of Example I l Methacrylic acid Miranol HM Very bright from l to 80 amps/ft. 3. Bath of Example I 2 Amine C Semi-bright from 1 to 80 amps/ft. 4. Bath of Example I l Acrylic Acid Tween 40 Very bright from 5 to 60 amps/ft.-&#39; 5. Bath of Example I 2 Methacrylic Acid Tergitol TMN Very bright from 5 to 80 amps/ft. 6. Bath of Example VI 1 Methacrylamide Triton N-lOl Very bright de osit from to 80 amps ft. of an alloy composed of about 60% tin and 40% lead 7. Bath of Example I Acrylic Acid Very dull at all current densities 8. Bath of Example Vl Methacrylic acid Very dull at all current densities 9. Bath of Example I l diethyleneglycol Bright from 1 to I00 monomcthyl amps/ft. I ether 10. Bath of Example ll 1 Crotonic acid Tergitol TMN Bright from l0 to 100 amps/ft.  
  Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, we state that the subject matter which we regard as being our invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substituitions for, parts of the above specifically described imbodiment of the invention may be made without departing from the scope of the invention as set forth in what is claimed.  
 What we claim is:  
  1. An aqueous acid tin electroplating bath containing stannous ions, at least one acid from the group consisting of sulfuric acid and flouboric acid, and having dissolved therein as a brightening agent about 0.05 to 0.5 gms/liter of a naphthalene monocarboxaldehyde.  
  2. The bath of claim 1 wherein about 1 to 10 gms/liter of an emulsifying agent is added to solubilize the naphthalene monocarboxaldehyde.  
  3. The bath of claim 2 containing about 0.1 to 0.5 gms/liter of a substituted olefin of the general formula:  
 is an alkyl phenol condensed with about l0 to 20 moles of ethylene oxide per mole of alkyl phenol.  
  6. The bath of claim 3 wherein R, is carboxy, R is methyl, and R and R are hydrogen.  
  7. The bath of claim 6 wherein the emulsifying agent is an alkyl phenol condensed with about 10 to 20 moles of ethylene oxide per mole of alkyl phenol.  
  8. The bath of claim 3 wherein there is also present a dissolved lead salt and the acid is flouboric acid.  
 9. The bath of claim 2 wherein the acid is sulfuric acid.  
  10. The bath of claim 2 wherein the acid is flouboric acid.  
  11. The bath&#39; of claim 2 wherein the emulsifying agent is selected from the group consisting of cationic surfactants, nonionic surfactants, and mixtures thereof.  
  12. The bath of claim 2 wherein the emulsifying agent is an alkyl phenol condensed with about 10 to 20 moles of ethylene oxide per mole of alkyl phenol.  
  13. The bath of claim 2 wherein the naphthalene monocarboxaldehyde is 2-naphthalene monocarboxaldehyde.  
  14. The bath of claim 2 wherein the naphthalene monocarboxaldehyde is l-naphthalene carboxaldehyde.  
 15. The bath of claim 2 wherein there is also present a dissolved lead salt and the acid is flouboric acid.