Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
  • C25D3/32—Electroplating: Baths therefor from solutions of tin characterised by the organic bath constituents used

Definitions

• aqueous bath for electroplating tin upon various conductive substrates contains stannous ion, sulfate radical, an imidazoline derivative, a carbinamine compound, and a cyclic aldehyde or ketone brightener.
• the bath is highly acid and is operable to produce dense, smooth, bright, adherent deposits, particularly at relatively high current densi ties. These deposits exhibit excellent solderability as plated and after prolonged aging.
• the bath avoids step plating when holes are present in the workpiece, and it minimizes the tendency for pitting to occur in the deposit.
• Another object is to provide a bath capable of producing a deposit that exhibits high corrosion protection and excellent solderability, both as plated and after prolonged aging, which also does not tarnish and is highly resistant to staining.
• Still another object is to provide such a bath for electrodepositing tin at suitable operating rates and which does not require a high level of control of the concentration of the components thereof within critical limits.
• a further specific object is to provide a convenient and relatively rapid method for electroplating tin upon metallic workpieces utilizing an improved sulfate plating bath to obtain highly desirable tin deposits at relatively low cost.
• an aqueous bath comprising about 35.0 to 85.0 grams per liter of stannous ion, about 70.0 to 250.0 grams per liter of sulfate radical; about 0.25 to 25.0 grams per liter of a surface active imidazoline derivative, 0.0 to about 5.0 grams per liter of a condensate of an alkylphenol having an alkyl chain of six to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof, about 0.15 to 15.0 grams per liter of a ten-carbinamine polyoxyalkylene compound, about 0.005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic ketones, cyclic aldehydes and mixtures thereof, and about 0.9 to 4.5 grams per liter of hydrogen ion.
• the carbinamine compound has the wherein R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of -H and the group 'When X is -H, a represents an integer from 15 to 45, b
• bza represents a value from 15 to 67.5 and the ratio bza has a value of 1.01.5:l.0.
• a+c represents an integer from 15 to 45
• b+d represents a number from 15 to 67.5
• the ratio (b+d):(a+c) has a value of 1.0-1.51.0.
• the preferred bath comprises about 55.0 to 75.0 grams per liter of stannous ion, about 125.0 to 200.0 grams per liter of sulfate radical, about 1.0 to 15.0 grams per liter of the imidazoline derivative, about 0.1 to 1.0 gram per liter of the alkylphenol condensate, about 0.5 to 10.0 grams per liter of the carbinamine compound, about 0.05 to 0.5 gram per liter of the brightener and about 1.5 to 3.0 grams per liter of hydrogen ion.
• the imidazoline derivative and the carbinamine compound are present in concentrations of about 5.0 to 10.0 and about 2.0 to 5.0 grams per liter, respectively.
• an aqueous acid bath having the composition previously defined is first prepared and maintained at a temperature of about 45 to 135.
• a workpiece having a metallic surface and a tin anode are immersed in the bath, and a voltage is applied thereacross to deposit tin on the metallic surface, the voltage providing a current density of about 10.0 to 200.0 amperes per square foot at the workpiece.
• the bath is maintained at a temperature of about 60 to Fahrenheit and the voltage provides a current density of about 50.0 to 100.0 amperes per square foot at the workpiece.
• the ratio of the area of the anode to that of the workpiece is about 1.5 to 3.0:1.0, and the current density at the anode is less than about 40.0 amperes per square foot.
• the acid baths of the present invention require the stannous ion, the sulfate radical, an imidazoline derivative, a carbinamine polyoxyalkylene compound, and a cyclic aldehyde or ketone brightener.
• the stannous ion and the sulfate radical may be furnished to the bath by any combination of compounds suitable for use in tin plating solutions, but, to avoid the presence of unnecessary and possibly interfering ions, these components are desirably introduced percent the form of stannous sulfate and sulfuric acid.
• the former compound will provide both the stannous ion and the sulfate radical, whereas the latter compound provides additional sulfate radical which is present in the bath.
• sulfuric acid is also desirable from the standpoint of control of the hydrogen ion concentration, although other acids providing noninterfering radicals may also be used for that purpose.
• tin compounds other than stannous sulfate e.g., stannous fluoborate, may be employed; when used, they are preferably present in concentrations of not more than about 50.0 percent by weight of the sulfate compound, and more preferably they provide less than 20.0 percent by weight thereof.
• the amount of stannous ion present in the baths may vary between about 35.0 and 85.0 grams per liter, it is preferably about 55.0 to 75.0 grams per liter.
• the concentration of sulfate ion may normally be between about 70.0 and 250.0, it is preferably about 125.0 to 200.0 grams per liter.
• a broad range of about 0.9 to 4.5 grams per liter is suitable for the hydrogen ion concentration, however, it is most desirably maintained at about 1.5 to 3.0 grams per liter. If the concentration of stannous ion in the bath is too low, the efficiency of plating and the quality of the deposit produced will be unsatisfactory at low current densities, and burning willbe apparent at the high end of the current density range.
• the acid baths of the present invention require effective amounts of an imidazoline derivative and of a carbinamine compound, and preferably but optionally they may contain a condensate of an alkyl phenol with an alkylene oxide.
• the imidazoline derivative corresponds to the formula:
• R represents an alkyl radical having five to 24 carbon atoms; 6 is the -OH ion, an acid salt radical, an anionic surface-active sulfate salt radical such as preferably -OSO -OR, or an anionic surface-active sulfonate salt radical; and Z is -COOM, -CH COOM, or -CHOH-CH SO:,M radical.
• the substituent designated M in the foregoing formula is a hydrogen atom, an alkali metal or an organic base, and that designated Y is either an -OR or -N(R) A group.
• Each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH ),,COOM; A
• G represents the radical -OSO -OR, particularly in which R is a C to C alkyl group, and Z is a -COOM radical in which M is preferably an alkali metal cation.
• Exemplary of the compounds corresponding to the foregoing formula which are satisfactory for use in the baths described herein are 2-alkyl-l-(ethyl-beta-oxypropanoic acid) imidazolines wherein the alkyl group is capryl, undecyl or a mixture of C -C chains, and the disodium salt of lauroylcycloimidinium-l-ethoxyethanoic acid-2-ethanoic acid. Moreover, it may be found that the best results are obtained by using combinations of the imidazoline derivatives.
• a second beneficial system may be a mixture of an imidazoline corresponding to the aforementioned general formula wherein Z is COONa, -G is OH, and Y is OCH COONa; and a second imidazoline wherein the groups G and -CH Z are omitted and Y is -N(CH CH COOH) (CH COOH)CI.
• the first-mentioned imidazoline derivative is provided in a weight ratio of about 1 to 8:1 relative to the second-mentioned imidazoline derivative and preferably in a ratio of about 4.5 to 6.5.
• the carbinamine compound employed is that which has hereinbefore been presented and defined. Preferably, however, it has the general formula wherein e is an integer from 12 to 15; most desirably, X is -H and a and b each represent numbers from 15 to 20.
• the carbinamine compounds are described in Boettner et al. U.S. Pat. No. 3,117,999, granted on Jan. 4, 1964.
• the carbinamine compound (or mixture thereof) should be used in a concentration of about 0.15 to 15.0 grams per liter.
• the amount thereof is about 0.5 to 10.0 grams per liter, and most desirably it is about 2.0 to 5.0 grams per liter.
• the carbinamine compound and the imidazoline derivative are generally adequate, as the only surface-active agents, to attain the objects of the present invention, most often the best deposits will be produced by use of the combination along with the alkylphenol/alkylene oxide condensate.
• the alkylene oxide will be present in a molar ratio relative to the alkyl phenol of about 8.0 to 25.0:l.O, and is selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof.
• the alkyl substituent of the phenol has a carbon chain of six to 12 carbon atoms and preferably eight to 10.
• alkyl phenol condensates are octyl phenoxy polyethoxy ethanols and nonyl phenoxy polyethoxy ethanols, with the preferred agents being nonyl phenoxy polyethoxy ethanols having an oxidezphenol molar ratio of about 19.0 to 20.0: 1 .0.
• the remaining essential component of the bath is a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones and mixtures thereof. Any suitable compounds of these types may be employed, and the carbonyl group may be attached directly to the ring or connected through one or more atoms.
• cyclic aldehydes that are suitable as brighteners are 2-pentyl-3-phenyl-propenal, o-anisaldehyde, p-anisic aldehyde bisulfite, furfural, glutaraldehyde, cinnamaldehyde, veratraldehyde, benzaldehyde, o-chlorobenzaldehyde and p-chlorobenzaldehyde.
• the aldehyde has a five-membered heterocyclic ring, and most desirably the aldehyde group is attached to one of the carbons in the ring, which generally will be that in the two-position.
• aldehydes may be used, the particularly preferred compounds are those which contain a simple aldehyde group (-CHO), and the aldehydes may be ring or chain substituted. Particularly good results are attained by the use of aldehydes based upon thiophene, furan and pyrrole, and specific heterocyclic carboxaldehydes which have proven highly effective are furfural (Z-furaldehyde), Z-thiophene carboxaldehyde and 2-pyrrole carboxaldehyde.
• furfural Z-furaldehyde
• Z-thiophene carboxaldehyde Z-thiophene carboxaldehyde
• 2-pyrrole carboxaldehyde 2-pyrrole carboxaldehyde
• the brightener in amounts of as little as 0.0005 gram per liter, it is preferably included in amounts of at least about 0.05 gram per liter.
• the concentration of brightener is increased above about 0.5 gram per liter, it becomes increasingly difficult to control operation of the bath, and above about 1.0 gram per liter pitting and burning become quite evident and the level of brightness at low current densities is diminished significantly.
• the baths preferably employ the aldehyde or ketone compounds in amounts of about 0.05 to 0.5 gram per liter.
• the suitable brighteners demonstrate relatively low solubility in the acid bath, it may be necessary to em ploy a solvent solution thereof to facilitate formulation of the bath.
• solvents which may be employed, depending upon the particular brightener involved, are the low molecular weight alkanols (methanol, ethanol and propanol) and the low molecular weight glycol ethers (ethylene glycol monoethyl ether, etc.).
• the brightener is added to the solvent in amounts of about 1.0 to 50.0, and preferably in about 5.0 to 25.0 grams per liter thereof, so as to obtain a stable solvent solution which may be readily dispersed in the acid bath.
• auxiliary brighteners are the polyvinyl alcohols which should usually be added in amounts of less than 1.0 gram per liter and preferably less than 0.2 gram per liter.
• a chelating agent such as citric acid, malic acid and the aminopolyacetic acids, e.g., ethylene-diamine tetraacetic acid, diethylene-triamine pentaacetic acid, and nitrilotriacetic acid.
• chelating agents when employed, are generally included in an amount of5.0 to 20.0 grams per liter.
• the baths of the present invention are operable over a fairly wide range of cathode current density, depending upon other factors such as temperature, agitation, etc. More specifically, the operable range is about 10.0 to 200.0 amperes per square foot (ASF) and preferably about 25.0 to 150.0 ASF, with a narrower range of 50.0 to 100.0 ASF being most desirable.
• the plating efficiency is generally quite high and will range up to about 95 percent under optimum conditions, based upon the theoretical rate of deposition, and bright deposits of excellent quality can normally be produced at a bath efficiency in excess of 70 percent.
• the anodezcathode ratio should be about 1.5 to 3.0:l.0, and preferably about :10 Moreover, the anode current density should not exceed about 40 ASF since there is an apparent tendency for inefficient operation, excessive sludging and rough deposits to be formed at higher anode current densities.
• the applied voltage should be about 0.2 to 5.0 volts and preferably 0.5 to 4.0 volts.
• the baths should be operated at temperatures between about 45 and 135 Fahrenheit, and preferably about 60 to 90 Fahrenheit. Operation below about 45 Fahrenheit tends to be inefficient and to produce undesirable deposits, whereas temperatures higher than about 135 Fahrenheit tend to produce dull, rough and generally unacceptable deposits, and the bath is consumed at an excessive rate.
• Any metallic substrate or metal-surfaced article which can be plated with tin using prior art baths may be coated in accordance with the present invention.
• good deposits of tin may be produced upon articles of copper, nickel, iron, steel, etc. The best results are obtainable with these baths if relatively pure tin anodes are employed, but alloy anodes may also be feasible.
• Agitation is highly desirable to obtain high quality, uniform deposits and to avoid development of sludge or film, and plating at high current densities and temperatures is improved by more intense agitation.
• excessively high rates of agitation are undesirable because they can cause excessive consumption of the bath and impose limitations upon the current densities at which brightness is achieved.
• agitation of the bath itself desirable but agitation of the cathode may be beneficial in obtaining a uniform plate and enabling extension of the range of satisfactory current density.
• the process is adapted to still plating and barrel plating apparatus with equal efficacy, and may be used for strip, wire and connector strip.
• Use of the bath and process is particularly significant with respect to connector strip and the like because of the excellent solderability of the plate produced and the avoidance of step plating (i.e., due to upsetting of polarization) thereby.
• Filtration of the bath is not essential but will normally be beneficial when contamination of the bath is encountered due to airborne impurities and carryover from other finishing operations; preferably, it will be effected on a continuous basis.
• Various filtering media may be utilized including fabric, porous stoneware and other conventional filtering materials.
• the depletion of the various components of the bath is best corrected by analysis for the several components on a periodic basis which can be established for a given facility.
• a surface-active agent To determine the necessity for the addition of a surface-active agent, the best procedure is to evaluate a sample of the bath in a suitable test cell, and a suitable schedule may be established for a given facility and workpiece.
• a suitable schedule may be established for a given facility and workpiece.
• stannous salt a 0.1 N potassium iodate solution and a 1.0 percent solution of starch may be used for titration.
• the free sulfuric acid concentration may be determined by simple titration procedures with a suitable indicator such as thymophtalein.
• the amount of brightener required is best evaluated by testing a sample of the bath in a suitable test cell.
• An aqueous bath is prepared containing 120.0 grams per liter of stannous sulfate, 92.0 grams per liter of sulfuric acid; 4.5 grams per liter of a commercial imidazoline derivative wherein groups -G and -CH,Z are omitted and Y is N(CH CH COOH) (CH COOH)Cl; 0.75 gram per liter of a second commercial imidazoline derivative wherein Z is COONa, -G is -OH, and -Y is OCH COONa; 0.93 gram per liter of an ethylene oxide/octyl phenol condensate having a molar ratio of about 10.0:l.0; 4.1 grams per liter ofa commercial mixture of carbinamine compounds having the formula t- C,H ,,+,NH(C H,O),,(C;,H O),,H, wherein e is an integer from 12 to 15 and a and h each represent numbers 15 to 20; and 0.08 gram per a commercial imidazo
• a punched steel connector strip and a pure tin anode Into the bath is introduced a punched steel connector strip and a pure tin anode. A potential of about 3 volts is impressed across the strip and the anode, providing a current density at the cathode of about ASF and at the anode of less than 40 ASF.
• the strip is agitated and plated for a period of about 2 minutes in the bath. Upon inspection of the strip after removal from the bath, rinsing and drying, a bright, dense, adherent deposit of tin is found to be present, which deposit is smooth and free of pitting and is uniform throughout, even about the holes. Solderability as plated and after prolonged aging is found to be excellent.
• a tin solution is prepared by dissolving in water 132.0 grams per liter of stannous sulfate, 55.0 milliliters per liter of sulfuric acid and about 0.1 gram per liter of thiophene aldehyde.
• a first aqueous stock solution (designated A) is prepared by admixing the octylphenol condensate and the imidazoline derivative first mentioned in example one, in concentrations of 20.0 and 80.0 grams per liter, respectively.
• a second stock solution (designated B) is prepared by dissolving in water 100.0 grams per liter ofthe same mixture of carbinamine compounds as is used in that example.
• the present invention provides a bath and method for producing a smooth, adherent, dense, bright and relatively nonporous deposit of tin; pitting is minimized, step plating about holes in the workpiece is avoided and relatively smooth deposits may be produced upon relatively rough surfaces.
• the bath is capable of producing a deposit that does not tarnish, is highly resistant to staining, and that exhibits high corrosion protection and excellent solderability, both as plated and after prolonged aging.
• An aqueous acid bath for producing an adherent electroplated tin deposit comprising about 35.0 to 85.0 grams per liter of stannous ion; about 70.0 to 250.0 grams per liter of sulfate radical; about 0.25 to 25.0 grams per liter of a surface active imidazoline derivative; 0.0 to about 5.0 grams per liter of a condensate of an alkylphenol having an alkyl chain of six to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof; about 0.15 to 15.0 grams per liter of a tert.-carbinamine polyoxyalkylene compound having the general formula:
• R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of-H and the group a representing an integer from to 45, b representing a number from 15 to 67.5 and the ratio b:a having a value of 1.0-1.51.0 when X is -H, and a+c representing an integer from 15 to 45, b+d representing a number from 15 to 67.5 and the ratio (b+d):(a+c) having a value of l.0-l.5:l.0 when X is said group; about 0.005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones and mixtures thereof; and about 0.9 to 4.5 grams per liter of hydrogen ion.
• the bath of claim 1 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion.
• R is an alkyl radical having five to 24 carbon atoms; 2.
• G is a radical selected from the group consisting of -OH,
• anionic surface active sulfate salt radicals anionic surface active sulfonate salt radicals
• Z is a radical selected from the group consisting of COOM, -CH COOM, and -CHOH-CH SO M;
• M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;
• Y is selected from the group consisting of -OR and 6. each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM;
• A is an anionic monovalent radical
• n is an integer from 1 to 4.
• imidazoline derivative has a structure wherein -G is an anionic surface active sulfate salt radical having the formula -OSO -OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms,
• Z is a -CO0M radical in which M is an alkali metal cation.
• said imidazoline derivative is selected from the group consisting of 2-alkyl-l-(ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C -C chains, and the disodium salt of lauroyl-cycloimidinium-l-ethoxy-ethan0ic acid-Z-ethanoic acid.
• said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -Cl-1 Z are both omitted and Y is -N[(CH COOHhCl n being equal to l to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to O(CH ),,COOM and wherein Z is equal to -(CH ),,,COOM, n being equal to 1 to 4 and m equal to 0 to I, and M being an alkali metal.
• imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) ofabout 1.0 to 8.0:1 .0.
• R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of -l-l and the group a representing an integer from 15 to 45, b representing a number from 15 to 67.5 and the ratio bza having a value of l.01.5:1.0 when X is l-l, and n+0 representing an integer from 15 to 45, Irl-d representing a number from 15 to 67.5 and the ratio (lH-d):(a+c) having a value of 1.0-1.51.0 when X is said group; 0005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones, and mixtures thereof; and about 0.9 to 4.5 grams per liter of hydrogen ion; 2.
• the method of claim 16 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion.
• R is an alkyl radical having tive to 24 carbon atoms; 2.
• G is a radical selected from the group consisting of -OH,
• anionic surface active sulfate salt radicals anionic surface active sulfonate salt radicals
• Z is a radical selected from the group consisting of COOM, -CH CO0M, and -CHOH-Cl-l,SO M;
• M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;
• Y is selected from the group consisting of -OR' and 6. eachrR' substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM; 7. A is an anionic monovalent radical;
• n is an integer from 1 to 4.
• imidazoline derivative has a structure wherein -G is an anionic surface-active sulfate salt radical having the formula -OSO -OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms, and wherein Z is a -COOM radical in which M is an alkali metal cation.
• imidazoline derivative is selected from the group consisting of 2-alkyl-l- (ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C chains, and the disodium salt of lauroylcyclo-imidinium-l-ethoxyethanoic acid-Z-ethanoic acid.
• said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -CH Z are both omitted and Y is N[(CH )-COOH] -,C1, n being equal to l to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to -O(CH ),,COOM and wherein Z is equal to -(CH ),,,COOM, n being equal to l to 4 and m equal to 0 to l, and M being an alkali metal.
• Claim 7 line 35 delete the numeral '1" and substitute therefor the numeral --4--.
• Claim 24 line 27 delete the numeral "16" and substitute therefor the numeral --21--.

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• Chemical Kinetics & Catalysis (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electroplating Methods And Accessories (AREA)

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Cited By (16)

Family Cites Families (1)

• 1969
  • 1969-11-19 US US878221A patent/US3616306A/en not_active Expired - Lifetime
• 1970
  • 1970-10-15 GB GB4899070A patent/GB1324014A/en not_active Expired
  • 1970-10-22 JP JP45093143A patent/JPS4921212B1/ja active Pending
  • 1970-11-18 FR FR7041348A patent/FR2067374B1/fr not_active Expired
  • 1970-11-19 DE DE2056954A patent/DE2056954C2/de not_active Expired
• 1975
  • 1975-12-30 MY MY185/75A patent/MY7500185A/xx unknown

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