Plating bath and method for electroplating tin and/or lead

An aqueous acidic plating bath for electrodeposition of tin, lead or tin-lead alloys on a substrate is described. The plating baths are free of fluoride and fluoborate ions and comprise (A) at least one bath-soluble metal salt selected from the group consisting of a stannous salt, a lead salt, or a mixture of stannous and lead salts, (B) at least one alkane sulfonic acid or alkanolsulfonic acid, (C) at least one surfactant, (D) an effective amount of at least one primary brightening agent selected from the group consisting of halogen substituted and dialkoxy and trialkoxy substituted benzaldehydes, (E) an effective amount of a secondary brightening agent which is at least one lower aliphatic aldehyde, and (F) an effective amount of an auxiliary brightening agent which is at least one of the group consisting of aniline and the amino-, carboxy-, halo-, alkyl- or alkoxy-substituted anilines. Methods for the electrodeposition of tin, lead, or tin-lead alloys from such baths also are described.

BACKGROUND OF THE INVENTION 
This invention relates to the electrodeposition of tin, lead, and tin-lead 
alloys, and particularly to a plating bath which is free of fluoride and 
fluoborates 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 have been known in the art, and most of these baths contain, in 
addition to the water-soluble tin and/or lead salts, fluoborates, 
fluosilicates, sulfates, sulfamates, 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 generally are 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, the prior art has 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 U.S. Pat. No. 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 U.S. Pat. No. 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, U.S. Pat. No. 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 sulfonic or alkanol 
sulfonic acid and either a divalent tin salt or a divalent lead salt of 
the sulfonic 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 surfactants, amphoteric 
surfactants, 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 are described in the patent. 
Tin-lead alloy plating baths including hydroxyalkyl sulfonic acids are 
described in U.S. Pat. No. 4,132,610. The baths do not contain fluoborates 
or phenol sulfonates, but do contain the reaction product of o-toluidine 
with acetaldehyde as a brightener. 
U.S. Pat. No. 3,905,878 describes tin-lead plating baths containing at 
least one sulfonate salt of tin and lead as well as free phenolsulfonic 
acid and/or free cresolsulfonic 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 sulfuric acid, is described in 
U.S. Pat. No. 3,875,029. The olefinic compounds useful as brighteners are 
characterized by the general formula 
##STR1## 
where R.sub.1 is carboxy, carboxamide, alkali carboxylate, ammonium 
carboxylate, amine carboxylate, or alkyl carboxylate, and R.sub.2, R.sub.3 
and R.sub.4 are hydrogen, methyl, or lower alkyl. Such olefins are 
utilized in combination with a naphthalene monocarboxaldehyde. 
U.S. Pat. No. 774,049 describes a process for electrolytically depositing 
lead peroxide on lead plates. The baths include a sulfonic acid or 
oxysulfonic acid derivative of methane and its hydroxy-substituted 
derivatives such as methyl sulfonic acid, methylene disulfonic acid, 
oxymethylene disulfonic acid, etc. 
U.S. Pat. No. 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 sulfate, and sulfuric acid is 
included in the baths. 
Tin or tin and lead plating baths containing aromatic sulfones and mono- 
and poly-sulfonic acids of benzene, phenol and cresol are described in 
U.S. Pat. No. 2,313,371 and British Pat. No. 555,929. The aromatic 
sulfonic acids form soluble salts of tin and lead, and the disulfonic 
acids are particularly preferred because they provide extremely soluble 
salts. 
U.S. Pat. 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 sulfonate ion wherein the alkyl 
group contains between 1 and 5 carbon atoms are described in U.S. Pat. No. 
2,525,942. The sulfonate 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. 
SUMMARY OF THE INVENTION 
It now have been found that a smooth, level and bright deposit of tin, lead 
or 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 sulfuric acid. The 
aqueous plating baths of the invention comprise (A) at least one 
bath-soluble metal salt selected from the group consisting of a stannous 
salt, a lead salt, or a mixture of stannous and lead salts, (B) at least 
one alkane sulfonic acid or alkanolsulfonic acid, (C) at least one 
surfactant, (D) an effective amount of at least one primary brightening 
agent selected from the group consisting of halo-, dialkoxy- and 
trialkoxy-substituted benzaldehydes wherein each alkoxy group 
independently contains from one to about four carbon atoms, (E) an 
effective amount of a secondary brightening agent which is at least one 
lower aliphatic aldehyde, and optionally (F) an effective amount of an 
auxiliary brightening agent which is at least one of the group consisting 
of aniline and the halo-, alkyl-, alkoxy-, amino, or carboxy-substituted 
anilines. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The plating baths of the present invention comprise tin ion, lead ions, or 
a mixture of tin and lead ions, at least one alkane sulfonic acid or 
alkanol sulfonic acid, at least one surfactant, at least one primary 
brightening agent which is halo-, dialkoxy- or trialkoxy-substituted 
benzaldehyde and at least one secondary brightening agent. Generally, the 
plating baths of the present invention will comprise a mixture of the free 
sulfonic acid with the tin, lead, or a mixture of tin and lead salts of 
the sulfonic acids, which salts are soluble in the plating baths. 
The alkane sulfonic acids (B) that can be utilized in the present invention 
have the following formula 
EQU RSO.sub.3 H (I) 
wherein R is an alkyl group containing from about 1 to about 12 carbon 
atoms and more preferably, from about 1 to 6 carbon atoms. Examples of 
such alkane sulfonic acids include, for example, methane sulfonic acid, 
ethane sulfonic acid, propane sulfonic acid, 2-propane sulfonic acid, 
butane sulfonic acid, 2-butane sulfonic acid, pentane sulfonic acid, 
hexane sulfonic acid, decane sulfonic acid and dodecane sulfonic acid. The 
individual alkane sulfonic acids or mixtures of any of the above alkane 
sulfonic acids can be utilized in the plating baths of the invention. 
The alkanol sulfonic acids (B) which are useful in the present invention 
are characterized by the following formula 
##STR2## 
wherein n is from 0 to about 10, m is from 1 to about 11 and the sum of 
m+n is up to about 12. As can be seen from the above formula II, the 
hydroxy group may be a terminal or internal hydroxy group. Examples of 
useful alkanol sulfonic acids include 2-hydroxy ethyl-1-sulfonic acid, 
1-hydroxy propyl-2-sulfonic acid, 2-hydroxy propyl-1-sulfonic acid, 
3-hydroxy propyl-1-sulfonic acid, 2-hydroxy butyl-1-sulfonic acid, 
4-hydroxy butyl-1-sulfonic acid, 2-hydroxy-pentyl-1-sulfonic acid, 
4-hydroxy-pentyl-1-sulfonic acid, 2-hydroxy-hexyl-1-sulfonic acid, 
2-hydroxy decyl-1-sulfonic acid, 2-hydroxy dodecyl-1-sulfonic acid. 
The alkane sulfonic acids and alkanol sulfonic 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 sulfides having the formula R.sub.1 S.sub.n R.sub.2 wherein 
R.sub.1 or R.sub.2 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.degree. C. Such oxidation 
processes are described and claimed in U.S. Pat. No. 2,433,395 and 
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 sulfonic acid as described above and a tin 
salt thereof. Likewise, a lead plating bath contains at least one alkane 
or alkanol sulfonic 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 sulfonic acid and the tin and lead salts 
thereof. The divalent tin and divalent lead salts of alkane sulfonic acids 
and alkanol sulfonic acids can be readily prepared by the reaction of a 
divalent tin or divalent lead salt with the desired sulfonic acid. 
Examples of tin and lead salts which can be reacted with the sulfonic acid 
to form the desired metal sulfonate 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 liter 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 
liter 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 sulfonic acid (b) in the 
plating baths of the invention is in a range of from about 10 to about 500 
grams per liter of bath, and more preferably from about 50 to about 200 
grams per liter of bath. 
In addition to the above components, it is necessary that the plating baths 
of the invention contain (C) at least one surfactant including nonionic, 
cationic, anionic or amphoteric surfactants. A variety 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, 
polyalkylene 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 
EQU R--O--[(CH.sub.2).sub.n O].sub.x H (A) 
wherein R 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 
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 about 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 U.S. Pat. 
No. 3,855,085. Such polyoxyethylene compounds are available commercially 
under the general trade designations "Surfynol" by Air Products and 
Chemicals, Inc. of Wayne, Pa, and under the designation "Pluronic" or 
"Tetronic" by BASF Wyandotte Corp. of Wyandotte, Mich. 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 polypropylene glycol obtained by the 
condensation of 16 moles of propylene oxide. 
Alkoxylated amine, long chain fatty amine, long chain fatty acid, alkanol 
amines, diamines, 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 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 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 
commercially 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 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 compound. 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 (C) utilized in the plating baths of the present invention 
may be amphoteric surfactants. The preferred amphoteric surfactants 
include betaines and sulfobetaines, and sulfated or sulfonated 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 
##STR3## 
wherein R.sup.1 is an alkyl group containing from about 8 to 20 carbon 
atoms, and R.sup.2 and R.sup.3 are alkyl groups containing from 1 to about 
4 carbon atoms. 
Typical betaines include lauryldimethylammonium betaine and stearyl 
dimethylammonium betaine. Sulfated and sulfonated adducts include Triton 
QS-15 (Rohn & Haas Co.), a sulfated adduct of an ethoxylated alkylamine, 
Miranol HS, a sodium salt of a sulfonated lauric derivative, Miranol OS, a 
sodium salt of a sulfonated oleic acid, etc. 
Cationic surfactants also are useful in the plating baths of the present 
invention and such surfactants may be selected from the group consisting 
of higher alkyl amine salts, quaternary ammonium salts, alkyl pyridinium 
salts and 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 
##STR4## 
wherein R is a fatty acid alkyl group containing from about 8 to about 22 
carbon atoms, 
R.sup.1 is an alkylene radical containing up to about 5 carbon atoms, 
R.sup.2 and R.sup.3 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 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 are represented by the formulas D and E 
##STR5## 
wherein R.sup.4 is a fatty acid alkyl group containing from 12 to 18 
carbon atoms, and x, y and z are as defined in 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 
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 D are available from the Armak 
Chemical Division of Akzona, Inc., Chicago, Ill., 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 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 E include "Ethoduomeen I/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. 
Another type of useful cationic surfactant is represented by the formula 
##STR6## 
where R is an alkyl group containing from about 8 to about 12 carbon 
atoms, Y is a methyl or a hydroxyl group, m and n are integers, the sum of 
which is from about 2 to about 20. 
The amine ethoxylate surfactants of the type represented by formula C-1 
exhibit the characteristics of both cationic and nonionic surfactants with 
the nonionic properties increasing at the higher levels of ethoxylation. 
That is, as the sum of x and y increases, the ethoxylated amine behaves 
more like a nonionic surfactant. 
The surfactants represented by formula C-1 wherein Y is a methyl group are 
available commercially such as from Texaco Chemical Company under the 
trade designation "M-300 Series". The M-300 Series compounds currently 
available from Texaco and which have been found to be useful in the 
aqueous acid plating baths of the invention include those designated as 
M-302, M-305, M-310, M-315 and M-320 which contain a total to two five, 
ten, fifteen and twenty moles of ethylene oxide respectively. In all of 
these compounds, R is a mixture of 10 and 12 carbon alkyl groups. 
The cationic surfactant also may be: 
(a) a quaternary ammonium salt of the formula 
##STR7## 
wherein X represents a halogen, a hydroxyl group, or the residue of a 
C.sub.1-5 alkanesulfonic acid; R.sub.1 represents alkyl groupl R' and R" 
represent a C.sub.1-4 alkyl group; and R'" represents a C.sub.1-10 alkyl 
group or a benzyl group; 
(b) pyridinium salts represented by the general formula (G) 
##STR8## 
wherein X represents a halogen, a hydroxyl group, or the residue of a 
C.sub.1-5 alkanesulfonic acid; R.sub.1 represents a C.sub.8-20 alkyl 
group; and R.sub.a represents hydrogen or a C.sub.1-4 alkyl group; 
(c) imidazolinium salts represented by the general formula H 
##STR9## 
wherein X represents a halogen, a hydroxyl group, or the residue of a 
C.sub.1-10 alkanesulfonic acid; R.sub.1 represents a C.sub.8-20 alkyl 
group; R.sub.d represents a hydroxy-containing C.sub.1-5 alkyl group; and 
R'" represents a C.sub.1-10 alkyl group or a benzyl group; and 
(d) higher alkyl amine salts represented by the general formula (I) 
EQU [R.sub.1 --NH.sub.3 ].sup..sym. CH.sub.3 --(CH.sub.2).sub.n 
--COO.sup..crclbar. (I) 
wherein R.sub.1 represents a C.sub.8-20 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, 
octadecyldimethylethylammonium salt, dimethylbenzyllaurylammonium salt, 
cetyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, 
trimethylbenzylammonium salt, triethylbenzylammonium 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 sulfated alkyl alcohols, sulfated 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 
present invention in a concentration of from about 0.01 to about 50 grams 
per liter of bath and more preferably from about 0.05 to about 20 grams 
per liter of bath. 
Plating baths of the present invention also contain (D) an effective amount 
of at least one primary brightening agent which is at least one 
halogen-substituted benzaldehyde or a dialkoxy- or trialkoxy-benzaldehyde 
such as represented by the following general formula 
##STR10## 
wherein R.sub.1 and R.sub.2 are each independently alkyl groups containing 
from one to about four carbon atoms, and R.sub.3 is hydrogen or an alkoxy 
group containing from one to about four carbon atoms. Examples of the 
R.sub.1 and R.sub.2 groups include methyl, ethyl, propyl and isopropyl, 
and examples of the alkoxy group R.sub.3 include methoxy, ethoxy, propoxy, 
isopropoxy, etc. Preferably the primary brightener is a dialkoxy 
benzaldehyde, such as the various dimethoxy benzaldehydes. Specific 
examples of useful substituted benzaldehydes of the type represented by 
formula III include: 
2,3-dimethoxybenzaldehyde 
3,4-dimethoxybenzaldehyde 
2,4-dimethoxybenzaldehyde 
2,5-dimethoxybenzaldehyde 
2,6-dimethoxybenzaldehyde 
3,5-dimethoxybenzaldehyde 
2,3,4-trimethoxybenzaldehyde 
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. 
Examples of halogen-substituted benzaldehydes useful as primary brighteners 
(D) include: 
o-chlorobenzaldehyde 
p-chlorobenzaldehyde 
o-bromobenzaldehyde 
p-bromobenzaldehyde 
2,4-dichlorobenzaldehyde 
2,4-dibromobenzaldehyde 
2,6-dichlorobenzaldehyde 
2,6-dibromobenzaldehyde 
The preferred compounds are the mono- and dichlorobenzaldehydes, and most 
preferably, 2,4-dichlorobenzaldehyde. 
The primary brightening agents useful in the plating baths and concentrates 
of the invention may be water soluble adducts of the primary brightening 
agents described above. For example the bisulfite adducts of the various 
benzaldehydes are available and/or are easily obtained by procedures known 
in the art. The use of the water-soluble adduct of the primary brightening 
agent permits the use of water-based concentrates and eliminates the need 
for toxic solutions such as alcohol solutions. When added to the acidic 
plating baths, the adducts decompose to the benzaldehyde. Thus, the 
plating results are not adversely affected by the use of the adducts. 
The amount of the above described primary brightening agents utilized in 
the plating baths of the present invention can range from about 0.02 to 
about 5 grams per liter of bath and more generally is within the range of 
from about 0.05 to about 1 gram per liter 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 
preferably are 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 present invention may range from about 0.1 to about 20 grams per 
liter of bath and more generally range from about 0.5 to about 10 grams 
per liter of the plating bath. 
Plating baths of the present invention may also contain (F) an effective 
amount of at least one auxiliary brightening agent. The compounds used as 
the auxiliary brightening agents can be generally described as aniline and 
its ring-substituted derivatives. Suitable substituents on the aniline 
ring are halogen, amino, carboxy, alkyl and alkoxy groups. The auxiliary 
brighteners as a class of compounds are represented in formula VI as 
follows: 
##STR11## 
wherein X may be hydrogen, halogen, amino, carboxy, alkyl or an alkoxy 
group or mixtures thereof, and wherein a is an integer from 0 to 3 
inclusive. 
Mixtures of aniline and/or substituted anilines may also be used as the 
auxiliary brightening agent. 
Examples of useful substituted anilines include: 
o-aminoaniline 
p-aminoaniline 
o-chloroaniline 
p-chloroaniline 
o-aminobenzoic acid 
p-aminobenzoic acid 
2-amino-3-methylbenzoic acid 
2-amino-5-methylbenzoic acid 
4-amino-3-methylbenzoic acid 
3-amino-4-methylbenzoic acid 
2-chloro-5-methylaniline 
3-chloro-4-methylaniline 
3,4-diaminobenzoic acid 
3,5-diaminobenzoic acid 
2,3-dimethylaniline 
2,4-dimethylaniline 
2,5-dimethylaniline 
3,5-dimethylaniline 
2,6-diethylaniline 
2-methoxy-5-methylaniline 
3-methoxy-4-methylaniline 
o-toluidine 
m-toluidine 
p-toluidine 
6-ethyl-o-toluidine 
The preferred auxiliary brighteners are the methyl- and ethyl-substituted 
anilines, particularly the dimethyl- and diethyl-anilines. The most 
preferred of these have been found to be 2,4-dimethylaniline (xylidine) 
and 2,5-dimethylaniline. The preferred to the halogen substituted anilines 
are the chloroanilines, particularly monochloroaniline and most 
particularly o-chloroaniline. 
The amount of the auxiliary brightening agent (F) utilized in the plating 
baths of the present invention may range from about 0.02 to about 5 grams 
per liter of the plating bath and more generally range from about 0.05 to 
about 1 gram per liter of the plating bath. 
Acceptable results are obtained using either the halo-substituted or 
alkoxy-substituted primary brighteners unaugmentd by an auxiliary 
brightener. However, results are improved for either primary brightener 
through use of the above-described auxiliary brighteners (F). This is 
especially true of the halo-substituted primary brighteners whose 
performance in a plating bath is much improved by the inclusion of at 
least one auxiliary brightener in the bath. 
Optimal results are obtained using the dialkoxy- and trialkoxybenzaldehydes 
as primary brightening agents with acetaldehyde as the secondary 
brightening agent and dimethyl- and trimethyl-amines as the auxiliary 
brightening agent. 
Antioxidants normally 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 oxidation of stannous to stannic tin. Generally amounts 
of from about 0.05 to about 2 grams of antioxidant per liter of bath is 
sufficient. 
The tin, lead, and tin-lead plating baths of the present invention which 
contain no fluoride and fluoborate ions, and preferably no sulfuric 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 claims, all parts and percentages are 
by weight, and temperatures are in .degree.C.

EXAMPLE 1 
An aqueous plating bath is prepared by mixing the water, sufficient 
quantities of stannous methane sulfonate to provide 20 g/l of stannous 
ion, 80 g/l of free methane sulfonic 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 is prepared as in Example 1 except that the 
2,5-dimethoxybenzaldehyde and acetaldehyde are omitted. 
CONTROL 1B 
The preparation of Example 1 is repeated except that the acetaldehyde is 
omitted. 
CONTROL 1C 
A bath is prepared as in Example 1 except that the 
2,5-dimethoxybenzaldehyde is omitted. 
The following additional plating baths were prepared following the general 
procedure of Example 1. 
EXAMPLE 2 
______________________________________ 
g/l 
______________________________________ 
Stannous ion (added as the stannous 
20 
2-hydroxypropane sulfonate 
Free 2-hydroxypropane sulfonic acid 
90 
An ethylene diamine which has been 
10 
propoxylated followed by condensation 
with ethylene oxide 
Methacrylic Acid 0.5 
2,4,5-trimethoxybenzaldehyde 
0.3 
Water to make 1 liter 
______________________________________ 
EXAMPLE 3 
______________________________________ 
Stannous ion (added as stannous ethane 
18 
sulfonate) 
Plumbous ion (added as plumbous ethane 
3 
sulfonate) 
Free ethane sulfonic acid 
100 
alpha-naphthol condensed with 12 moles 
6 
ethylene oxide 
Paraldehyde 15 
2,4-dimethoxybenzaldehyde 
0.3 
Water to make 1 liter 
______________________________________ 
EXAMPLE 4 
______________________________________ 
g/l 
______________________________________ 
Divalent tin (added as stannous methane 
18 
sulfonate) 
Divalent lead (added as plumbous 
3 
methane sulfonate) 
Free methane sulfonic acid 
100 
Amidox C-5 (ethoxylated fatty acid amide) 
10 
Crotonaldehyde 3 
2,5-dimethoxybenzaldehyde 
0.5 
Water to make 1 liter 
______________________________________ 
EXAMPLE 5 
______________________________________ 
Stannous ion (added as stannous hydroxy 
18 
ethane sulfonate) 
Plumbous ion (added as plumbous 
3 
hydroxy ethane sulfonate) 
Free hydroxy ethane sulfonate 
120 
Surfynol 485 (an ethoxylated 
5 
tetramethyldecyne diol) 
3,4-dimethoxybenzaldehyde 
0.5 
Water to make 1 liter 
______________________________________ 
EXAMPLE 6 
______________________________________ 
Stannous ion (added as stannous methane 
18 
sulfonate) 
Plumbous ion (added as plumbous 
9 
methane sulfonate) 
Free methane sulfonic acid 
80 
Texaco M-315 4 
Acetaldehyde 2 
2,4-dimethoxybenzaldehyde 
0.3 
Water to make 1 liter 
______________________________________ 
CONTROL 6A 
A bath is prepared as in Example 6 except that the dimethoxybenzaldehyde is 
replaced with 2-methoxybenzaldehyde 
CONTROL 6B 
A bath is prepared as in Example 6 except that the dimethoxybenzaldehyde is 
replaced with 3-methoxybenzaldehyde 
EXAMPLE 7 
______________________________________ 
g/l 
______________________________________ 
Divalent tin (added as stannous hydroxy 
18 
propylsulfonate) 
Divalent lead (added as plumbous hydroxy 
9 
propylsulfonate) 
Free hydroxy propylene sulfonic acid 
80 
Pluronic L-44 (an ethylene oxide condensate 
4 
with a hydrophobic base of 
polypropylene glycol) 
Igepal CO-610 [nonylphenoxypoly- 
4 
(ethylenoxy)ethanol] 
Formaldehyde (added as 37% aq. sol'n) 
10 
2,5-dimethoxybenzaldehyde 
0.5 
Water to make 1 liter 
______________________________________ 
EXAMPLE 8 
______________________________________ 
Divalent tin (as methane sulfonate salt) 
18 
Divalent lead (as methane sulfonate salt) 
3 
Free methane sulfonic acid 
100 
Miranol J2M-SF (amphoteric surfactant 
2 
from Miranol Chemical Co. identified 
as a dicarboxylic caprylic derivative, 
disodium salt, salt free) 
2,4,5-trimethoxybenzaldehyde 
0.15 
Water to make 1 liter 
______________________________________ 
EXAMPLE 9 
______________________________________ 
Divalent lead (as methane sulfonate salt) 
20 
Free methane sulfonic acid 
40 
Texaco M-315 8 
Acetaldehyde 6 
2,5-dimethoxybenzaldehyde 
0.2 
Water to make 1 liter 
______________________________________ 
EXAMPLE 10 
______________________________________ 
g/l 
______________________________________ 
Divalent tin (as methane sulfonate salt) 
20 
Divalent lead (as methane sulfonate salt) 
2 
Free methane sulfonic acid 
80 
Ethoxylated beta-naphthol 
8 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde 
0.2 
Water to make 1 liter 
______________________________________ 
EXAMPLE 11 
______________________________________ 
Divalent tin (as ethane sulfonate salt) 
20 
Divalent lead (as ethane sulfonate salt) 
10 
Free ethane sulfonic acid 
60 
Igepal CO 630 8 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde 
0.25 
Water to make 1 liter 
______________________________________ 
EXAMPLE 12 
______________________________________ 
Stannous ion (as methane sulfonate) 
20 
Plumbous ion (as methane sulfonate) 
10 
Free methane sulfonic acid 
80 
Igepal CO 630 6 
Acetaldehyde 8 
2,5-dimethoxybenzaldehyde 
0.5 
o-chloroaniline 0.16 
Water to make 1 liter 
______________________________________ 
EXAMPLE 13 
______________________________________ 
g/l 
______________________________________ 
Divalent tin (as methane sulfonate salt) 
20 
Divalent lead (as methane sulfonate salt) 
2 
Free methane sulfonic acid 
80 
Ethoxylated beta-naphthol 
8 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde 
0.2 
2,5-dimethylaniline 0.2 
Water to make 1 liter 
______________________________________ 
EXAMPLE 14 
______________________________________ 
Divalent tin (as ethane sulfonate salt) 
20 
Divalent lead (as ethane sulfonate salt) 
10 
Free ethane sulfonic acid 
60 
Igepal CO 630 8 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde 
0.25 
2.4-dimethylaniline 0.15 
Water to make 1 liter 
______________________________________ 
EXAMPLE 15 
______________________________________ 
Divalent tin (as methane sulfonate salt) 
20 
Divalent lead (as methane sulfonate salt) 
2 
Texaco M 315 8 
Acetaldehyde 8 
2,4-dichlorobenzaldehyde 
0.12 
2,4-dimethylaniline 0.12 
Water to make 1 liter 
______________________________________ 
EXAMPLE 16 
______________________________________ 
g/l 
______________________________________ 
Stannous ion (as methane sulfonate) 
20 
Plumbous ion (as methane sulfonate) 
10 
Free methane sulfonic acid 
80 
Igepal CO 630 6 
Acetaldehyde 8 
2,5-dimethoxybenzaldehyde bisulfite 
0.5 
o-chloroaniline 0.16 
Water to make 1 liter 
______________________________________ 
EXAMPLE 17 
______________________________________ 
Stannous ion (added as stannous methane 
18 
sulfonate 
Plumbous ion (added as plumbous methane 
9 
sulfonate) 
Free methane sulfonic acid 
80 
Surfonic N 150 6 
Acetaldehyde 8 
2,4-dichlorobenzaldehyde 
0.12 
2,4-dimethylaniline 0.12 
Water to make 1 liter 
______________________________________ 
EXAMPLE 18 
______________________________________ 
Stannous ion (added as stannous methane 
18 
sulfonate) 
Plumbous ion (added as plumbous methane 
9 
sulfonate) 
Free methane sulfonic acid 
80 
Texaco M-315 4 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde bisulfite adduct 
0.12 
Aniline 0.16 
Water to make 1 liter 
______________________________________ 
EXAMPLE 19 
______________________________________ 
g/l 
______________________________________ 
Divalent tin (as methane sulfonate salt) 
20 
Divalent lead (as methane sulfonate salt) 
2 
Free methane sulfonic acid 
80 
Surfonic N 150 4 
Acetaldehyde 4 
2,5-dimethoxybenzaldehyde bisulfite adduct 
0.12 
p-chloroaniline 0.3 
Water to make 1 liter 
______________________________________ 
The utility of the plating baths of the present invention in depositing tin 
and tin-lead coatings is 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 are plated at a current of 2 amps for a 
period of five minutes. Mild mechanical bath agitation is employed, and 
the bath temperature is maintained at about 20.degree. to about 25.degree. 
C. The results of the plating tests are summarized in the following Table. 
______________________________________ 
TEST RESULTS 
Example # 
Bath Plating Results on Panel 
______________________________________ 
1 100% tin Clear bright 100 ASF to 10 ASF 
Control 1A 
100% tin Matte dull 80 ASF to 2 ASF. Slight 
burn high current density 
Control 1B 
100% tin Burn HCD, hazy bright to 4 ASF 
Control 1C 
100% tin Grey matte 100 ASF to 5 ASF. 
2 100% tin Semibright 80 ASF to 40 ASF 
3 80/20 T/L Hazy bright 60 ASF to 40 ASF 
4 80/20 T/L Bright 80 ASF to 40 ASF and 
hazy bright to 20 ASF 
5 80/20 T/L Hazy bright 80 ASF to 40 ASF 
6 60/40 T/L Clear bright 100 ASF to 16 ASF 
7 60/40 T/L Bright 80 ASF to 50 ASF, and 
hazy bright 50 ASF to 30 ASF 
Control 6A 
60/40 T/L Pitted, bright to 40 ASF, skip plate 
Control 6B 
60/40 T/L Pitted, hazy bright 100 ASF to 
8 ASF, dull to 0 
8 60/40 T/L Hazy bright 90 ASF to 40 ASF, 
Matte to 0 
9 100% lead Hazy bright 50 ASF to 20 ASF 
10 90/10 T/L Clear bright 100 ASF to 4 ASF 
11 60/40 T/L Clear bright 80 ASF to 30 ASF 
12 60/40 T/L Bright and very clear high current 
density - 100 ASF to 60 ASF. 
At 0.32 g/l o-chloroaniline, 
clarity extends to 20 ASF 
13 90/10 T/L Bright and very clear from 
100 ASF to 12 ASF 
14 60/40 T/L Bright and very clear from 
100 ASF to 30 ASF 
15 90/10 T/L Clear bright 100 ASF to 12 ASF 
16 60/40 T/L Very clear bright 100 ASF to 16 ASF 
17 60/40 T/L Clear bright 100 ASF to 20 ASF 
18 60/40 T/L Very clear bright 100 ASF to 12 ASF 
19 90/10 T/L Very clear bright 100 ASF to 8 ASF 
______________________________________ 
The plated deposit approximates 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 
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 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 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. 
Having best described the invention in full, clear, concise, and exact 
terms as to enable any person skilled in the art to which it pertains to 
make and use the invention, and having set forth the best modes 
contemplated of carrying out the invention, it should be understood that 
equivalents or substitutions for parts of the above specifically described 
embodiments of the invention may be made without departing from the scope 
and concept of the invention.