Aqueous Acid Plating Bath and Additives for Producing Bright Electrodeposits of Tin

The present invention relates to an aqueous acid electroplating bath for producing extremely bright electrodeposits of tin. Additionally, the present invention relates to a brightening agent and an acid plating bath containing the brightening agent which produces brighter deposits at higher current densities and with less pitting than with previously known tin plating baths over a very broad current-density range.

In the field of tin brightening compositions for acid tin baths, various aromatic aldehydes and ketones compounds have been utilized. Generally, although many of these such compounds produce an acceptable plating, often it was difficult to avoid pitting as well as to obtain an extremely bright electrodeposit at high current densities.

Plating baths and plating additives heretofore utilized include those set forth in U.S. Pat. No. 3,808,277 to Alvarez; U.S. Pat. No. 3,755,096 to Passal; U.S. Pat. No. 3,875,029 to Rosenberg et al; and, U.S. Pat. No. 3,977,949 to Rosenberg. However, none of these plating baths or tin brighteners are pertinent to the present invention.

Accordingly, it is an object of the present invention to provide brightening agents which produce extremely bright electrodeposits of tin.

It is another object of the present invention to provide certain dialkoxy benzaldehydes as a brightening agent.

It is a further object of the present invention to provide a tin plating bath having a certain dialkoxy benzaldehyde brightening agent which acts synergistically with alpha beta unsaturated carboxylic acids, amides and esters to give extremely bright electrodeposits of tin over a broad current density range and produce low amounts of pitting.

It is yet a further object of the present invention to provide a tin plating bath, as above, wherein emulsifiers are utilized to disperse the brightening agent.

These and other objects of the present invention, together with the advantages thereof over existing prior art compounds and methods, are herein described and claimed.

In general, a primary tin plating brightener additive comprises, a dialkoxy benzaldehyde of the following general formula: ##STR1## where R.sub.1 and R.sub.2 are methyl, ethyl, propyl and isopropyl, and wherein one alkoxy group is ortho and the other alkoxy group is meta to the carbonyl group or where both alkoxy groups are meta to said carbonyl group, and

INCLUDING FROM ABOUT 1 PERCENT TO ABOUT 97 PERCENT BY WEIGHT OF AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALPHA, BETA UNSATURATED CARBOXYLIC ACIDS, AMIDES, AND ESTERS FOR PRODUCING BRIGHT ELECTRODEPOSITS OF TIN FROM AN AQUEOUS ACID PLATING BATH.

Additionally, the aqueous acid electroplating bath for producing electrodeposits of tin containing stannous ions and sulfuric acid comprises from about 0.005 to about 0.2 grams/liter dissolved therein of a dialkoxy benzaldehyde having the following general formula: ##STR2## where R.sub.1 and R.sub.2 is methyl, ethyl, propyl and isopropyl, and where one alkoxy group is ortho to the carbonyl group and the other alkoxy group is meta to the carbonyl group, or where both alkoxy groups are meta to said carbonyl group.

According to the concepts of the present invention, it has been found that very bright electrodeposits with little pitting can be obtained from an aqueous acid tin plating bath when certain dialkoxy benzaldehydes are used as primary brighteners. It has also been found that these dialkoxy benzaldehydes act synergistically with alpha, beta unsaturated carboxylic acids, amides and esters to produce extremely bright electrodeposits. The effect is truly synergistic in that the results obtained with this combination far exceeded those of using the two types of compounds separately.

The dialkoxy benzaldehydes of the present invention have the following general formula: ##STR3## where R.sub.1 and R.sub.2 are methyl, ethyl, propyl, and isopropyl, and where one alkoxy group is ortho and the other alkoxy group is meta to the carbonyl group or both alkoxy groups are meta to the carbonyl group. R.sub.1 and R.sub.2, as methyl groups, are preferred. The dialkoxy benzaldehydes are generally used at a concentration of about 0.005 to 0.2 grams/liter of plating bath and the preferred concentration is about 0.01 to about 0.05 grams/liter. They may be added to the bath in concentrated form or as dilute solutions in various suitable solvents such as methanol and ethanol. Preferred dialkoxy benzaldehydes include 3,5-dimethoxy benzaldehyde, 2,5-dimethoxy benzaldehyde, and 2,3-dimethoxy benzaldehyde. The benzaldehyde compounds containing one alkoxy group at the para position are not part of the present invention since, for some reason, they produce very poor results.

Many of the various dialkoxy benzaldehyde compounds of the present invention are readily available in commerce. Moreover, they can be readily prepared by one skilled in the art such as through alkylation of the corresponding dihydroxy toluene followed by oxidation to the aldehyde.

Since the dialkoxy benzaldehydes exhibit limited solubility in the plating bath, emulsifying agents generally must be used to disperse them. A brightener additive mixture may therefore contain the dialkoxy benzaldehyde and from about 1 percent to about 96 percent by weight of the emulsifying agent based upon the total weight of only these two components. The types of emulsifiers or wetting agents that have been found to work quite well are listed in Table I. Depending upon the emulsifying ability of the particular emulsifying agent used, an amount in the range of about 2 to 40 grams/liter of plating bath is generally sufficient.

The preferred emulsifying agents have been found to be the nonionics made by condensing ethylene oxide with lipophilic groups such as long chain fatty alcohols, long chain fatty amines, long chain fatty acids, and long chain alkylphenols, the long chain containing from 6 to 30 and preferably from 6 to about 20 carbon atoms. The optimum amount of ethylene oxide is about 10 to 30 moles per mole of lipophile. While these are the highly preferred nonionics, it is not meant to limit the invention to these types only. For example, ethylene oxide derivatives of naphthols and polysaccharides also perform satisfactorily. In addition, propylene oxide condensates and ethylene oxide-propylene oxide block copolymers are considered part of the invention.

Generally, any alpha-beta unsaturated carboxylic acids, amides, and esters may be utilized with the brightener to form the synergistic increase in the production of extremely bright electrodeposits of tin which have very little pitting.

Preferred alpha, beta unsaturated carboxylic acids, amides and esters are listed in Table II.

Acrylic acid

Acrylamide

Methyl acrylate

Methacrylic Acid

Methacrylamide

Methylmethacrylate

Crotonic Acid

The alpha, beta unsaturated compounds are generally added as aqueous or alcoholic (e.g. methyl, ethyl, propyl, isopropyl alcohol) solutions to insure good dispersion in the plating bath. The alpha, beta unsaturated compounds are used in a concentration of about 0.02 to about 5 grams/liter of bath and the preferred concentration is about 0.2 to about 2 grams/liter. These compounds may also be a part of a brightener agent mixture containing the dialkoxy benzaldehyde and from about 1 to about 97 percent by weight of the alpha, beta unsaturated carboxylic acids, amides, and esters of the two component mixture (i.e. brightener and unsaturated compound). Of course, an emulsifying agent may also be added to this mixture wherein the amount of emulsifying agent ranges from about 1 to 96 percent by weight based upon the total weight of the three component mixture (i.e. brightener the unsaturated compound, and the emulsifying agent exclusive of any solvent). A preferred mixture of the present invention contains all of the three noted components.

Conventional addition agents konwn to the art such as aromatic and aliphatic ketones and aldehydes may be used in conjunction with this invention, if desired. However, such compounds generally do not affect the brightness of the electrodeposit.

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. In general, a source of stannous ions such as stannous sulfate, is present. A suitable amount is from about 10 to about 100 grams/liter. Also present is sulfuric acid. A suitable amount is from about 75 to about 260 grams/liter.

All testing was done in a conventional 267 ml. Hull Cell, using steel cathode panels and tin anodes. A current of 2 amperes was used for five minutes at temperatures ranging from 70.degree. C to 85.degree. F. The results of tests using Examples I through IV, along with several variations, are discussed in Table III.

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 in accordance with the patent statutes, the subject matter which is regarded as being my invention is particularly pointed out and distinctly claimed in the appended claims.