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
• • 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
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing the conductive pattern
  • H05K3/244—Finish plating of conductors, especially of copper conductors, e.g. for pads or lands

Definitions

• the present invention relates to a tin plating solution and tin electroplating method.
• the present invention relates to a virtually lead-free tin electroplating solution that is used for joining electronic parts and the like, and a method for forming a tin film.
• Tin-lead alloy plating has excellent bonding properties, low cost, electric properties, and solderability, and is therefore widely used in chips, crystal oscillators, lead frames, printed circuit boards, and other electronic parts that require electrical contact; and as an etching resist in steps used for the manufacture of semiconductor devices and printed substrates.
• Tin-silver alloy plating, tin-copper alloy plating, and tin-bismuth alloy plating have been proposed as substitute materials. Nevertheless, difficulties are presented when handling tin-silver plating solutions due to electronic substitution of the metallic silver, as well as other problems. Tin-copper alloy plating has the drawback that the melting point thereof tends to increase and solder wettability decreases, and tin-bismuth alloy plating has the drawback in that the resulting film is brittle.
• Tin plating solutions have also been investigated, but the resulting precipitate is rough, and problems are presented with regard to solder wettability.
• Gloss plating has been used in the past; however, the organic matter precipitate derived from the brightener in the glossy plating film clearly causes a reduction in solder joint strength and cracking.
• the use of an aldehyde compound or other organic brightener, or an ammonium salt or other amine-based brightener results in the formation of a fine tin precipitate and improved solderability, but solder wettability deteriorates over time due to an increase in the amount of organic precipitate in the film.
• a glossy plating film is generally brittle and not appropriate for use in lead frames and other applications where the plating film is required to be bent. Consequently, a demand has existed for semi-glossy plating in applications where gloss is not required.
• Naphtholsulfonic acids have been used for years as an additive for tin electroplating solutions.
• naphtholsulfonic acids or salts thereof e.g., 2-naphthol-6-sulfonic acid, 2-naphthol-7-sulfonic acid, and 1-naphthol-4-sulfonic acid
• fluorinated tin chloride baths consisting of tin chloride and an alkali fluoride and having a pH of 1 to 5.
• This patent does not disclose a combination of an organic acid bath and naphtholsulfonic acid.
• JP Korean 49-16176
• a complex salt of an aromatic sulfonic acid consisting of ⁇ -naphtholsulfonic acid and a metal compound is used as a base.
• This patent does not disclose the addition of ⁇ -naphtholsulfonic acid to an organic acid bath as an additive.
• JP (Kokai) 2002-17478 a tin-lead alloy plating bath is disclosed, consisting of a soluble stannous salt, a soluble lead salt, and one or more specific naphtholsulfonic acids.
• This patent does not disclose the use of 2-naphthol-7-sulfonic acid in a tin plating bath.
• the plating solution of the present invention is capable of forming a tin film of good appearance, and of providing a good semi-glossy film with which the good solder wettability of the deposited tin film does not deteriorate, particularly after pressure cooker treatment.
• the present invention provides a tin electroplating solution consisting of one, two, or more components selected from the group consisting of stannous ions, organic acids, and 2-naphthol-7-sulfonic acid or salts thereof, and comprising virtually no lead ions.
• the present invention provides the above-mentioned tin electroplating solution, wherein the organic acid is one, two, or more acids selected from the group consisting of alkane sulfonic acids and alkanol sulfonic acids.
• the present invention provides a plating solution comprising a tin salt of an organic acid as tin ions; one, two, or more acids selected from alkane sulfonic acids; one, two, or more compounds selected from the group consisting of 2-naphthol-7-sulfonic acid and salts thereof; one, two, or more antioxidants selected from the group consisting of substituted or unsubstituted dihydroxybenzene compounds; and one, two, or more nonionic surfactants; and consisting of virtually no lead ions.
• the present invention provides a tin electroplating solution consisting of a tin salt of an organic acid; one, two, or more alkane sulfonic acids; one, two, or more compounds selected from a group comprising 2-naphthol-7-sulfonic acid and an alkali salt thereof; one, two, or more antioxidants selected from substituted or unsubstituted dihydroxybenzene compounds; one, two, or more nonionic surfactants; and water.
• the present invention provides a method for electrodepositing a tin film on a substrate using any of the tin electroplating solutions described above.
• the present invention provides a method for manufacturing electronic components having a tin film on a substrate, including the step of electroplating a substrate using an acidic tin electroplating solution consisting of a tin salt of an organic acid; one, two, or more alkane sulfonic acids; one, two, or more compounds selected from a group consisting of 2-naphthol-7-sulfonic acid and an alkali salt thereof; one, two, or more antioxidants selected from a group consisting of substituted and unsubstituted dihydroxybenzene compounds; one, two, or more nonionic surfactants; and water.
• an acidic tin electroplating solution consisting of a tin salt of an organic acid; one, two, or more alkane sulfonic acids; one, two, or more compounds selected from a group consisting of 2-naphthol-7-sulfonic acid and an alkali salt thereof; one, two, or more antioxidants selected from a group consisting of
• the tin electroplating solution of the present invention is composed of stannous ions, an organic acid, and 2-naphthol-7-sulfonic acid or a salt thereof.
• alkane and “alkanol” refer to a linear or branched alkane or alkanol.
• organic acid examples include acids selected from alkane sulfonic acids and alkanol sulfonic acids or salts thereof.
• Preferred alkane sulfonic acids or alkanol sulfonic acids include substituted or unsubstituted alkane sulfonic acids and alkanol sulfonic acids. Examples include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, and 1-hydroxypropane-2-sulfonic acid. Methanesulfonic acid is particularly preferred. One or a mixture of two or more of these acids can be used.
• the organic acid content of the plating solution is at least the stoichiometric equivalent of the bivalent tin ions present in the plating bath.
• the free acid content in the plating bath is 30 g/L to 500 g/L, particularly 50 g/L to 300 g/L, and ideally 70 g/L to 250 g/L.
• Stannous ions are bivalent ions.
• a variety of compounds can be used as long as they are capable of supplying such ions to the plating bath. Examples include stannous salts of sulfuric acid, hydrochloric acid, methanesulfonic acid, citric acid, malic acid, or other organic acids.
• An example of a preferred source of stannous ions is a tin salt selected from the above-mentioned organic acids. Particularly preferred examples are compounds selected from an alkane sulfonic acid stannous salt or an alkanol sulfonic acid stannous salt. It is generally preferred that a tin salt of an organic acid be used in the plating solution. One or a mixture of two or more of these stannous salts can be used.
• the stannous ion content of the plating bath in terms of stannous ions is for instance, 10 g/L to 150 g/L, preferably 30 g/L to 120 g/L, and particularly 50 g/L to 100 g/L.
• 2-naphthol-7-sulfonic acid can be used as a free acid or in the form of a salt.
• ideal salts are soluble salts of potassium, sodium, ammonium, tin, or the like. Potassium and sodium salts are preferred, with sodium 2-naphthol-7-sulfonate being particularly preferred.
• One or a mixture of two or more of these salts can be used.
• the amount of 2-naphthol-7-sulfonic acid or salt thereof contained in the plating bath is, e.g., 0.01 g/L to 20 g/L, preferably 0.2 g/L to 10 g/L, and particularly 0.3 g/L to 5 g/L.
• a surfactant can be used as needed in the plating solution of the present invention.
• a variety of surfactants can be used, but nonionic surfactants are more suitable.
• preferred nonionic surfactants include polyoxyethylene lauryl ether, polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene nonylphenyl ether, polyoxyethylene polyoxypropylene alkylamine, and polyoxyalkylene adducts of ethylene diamine, with tetrakis-(polyoxyalkylene)ethylene diamine or polyoxyethylene polyoxypropylene (C 8 -C 18 ) alkyl amines being particularly preferred.
• Such surfactants can be obtained commercially from Lion Akzo Co., Ltd. under such brand names as Ethopropomeen C18/18, or from Asahi Denka Co., Ltd. under the brand name Adekanol TR-704.
• the appropriate surfactant concentration of the plating bath is, e.g., 0.01 g/L to 50 g/L, preferably 0.1 g/L to 20 g/L, and particularly 1 g/L to 15 g/L.
• An example of an especially preferred composition for the tin electroplating solution of the present invention is an acidic tin electroplating solution consisting of a tin salt of an organic acid; one, two, or more alkane sulfonic acids; one, two, or more compounds selected from a group consisting of 2-naphthol-7-sulfonic acid and alkali salts thereof; one, two, or more anti-oxidants selected from substituted or unsubstituted dihydroxybenzene compounds; one, two, or more nonionic surfactants; and water.
• composition of the present invention consists of virtually no lead. “Consists of virtually no lead” indicates that no lead is added to the plating bath as an additional component, but does not rule out the possibility of a lead component being present in the compound components. Moreover, the composition of the present invention preferably contains no metallic stabilizers, such as bismuth.
• the method for electroplating using the plating solution of the present invention can be a conventional method.
• the concentration of each component of the plating solution is selected as needed according to the plating method; e.g., barrel plating, through-hole plating, rack plating, or high-speed continuous plating.
• Electroplating using the electroplating solution of the present invention can be performed at a plating bath temperature of, e.g., 10° to 65° C., and preferably room temperature to 50° C.
• the cathode current density can be selected from within a range of, e.g., 0.01 to 100 A/dm 2 , and preferably 0.05 to 70 A/dm 2 .
• the plating solution of the present invention can be used for a variety of plated articles as a substitute for conventional tin plating and tin-lead alloy plating for soldering or etching resists.
• the article to be plated should have a conductive component capable of being electroplated, and includes composites made from conductive materials such as copper or nickel and insulating materials such as ceramics, glass, plastics, ferrite, and the like. Before being electroplated, the articles can be pretreated by a conventional method depending on the material used.
• tin films can be deposited on the surface of conductive materials on substrates or a variety of electronic parts, including chip capacitors, chip resistors, and other chip parts, crystal oscillators, pumps, connector pins, lead frames, printed circuit boards, and the like.
• a tin plating solution was prepared with the following composition.
• Stannous methanesulfonate (as tin ions) 70 g/L Methanesulfonic acid (as a free acid) 175
• Sodium 2-naphthol-7-sulfonate 0.5
• Potassium hydroquinone sulfonate 2 Distilled water Remainder
• a Hull cell test was performed using a plating bath with the above-mentioned composition and a 6.7 cm ⁇ 10 cm copper sheet, with electrolysis performed at 5 A ⁇ 1 minute and a bath temperature of 50° C., and stirring by cathode vibration at a rate of 4 to 6 m/minute.
• Table 1 shows the results obtained by macroscopically evaluating the appearance of the plating film; i.e., precipitation anomalies, uniformity, and gloss.
• precipitation anomalies generally refers to unplated areas that tend to form where the current is low, and precipitation regions known as “burns” or “burnt deposits” that tend to form where current density is too high. “Uniformity” means that the state of a precipitated film surface was observed in the current density region generally used by the electroplating method.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the 0.5 g/L of sodium 2-naphthol-7-sulfonate in Working Example 1 was substituted for 0.5 g/L of sodium 2-naphthol-6-sulfonate.
• the appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the 0.5 g/L of sodium 2-naphthol-7-sulfonate in Working Example 1 was substituted for 0.5 g/L of disodium 2-naphthol-3,6-sulfonate.
• the appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the 0.5 g/L of sodium 2-naphthol-7-sulfonate in Working Example 1 was substituted for 0.5 g/L of disodium 1-naphthol-3,6-sulfonate.
• the appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the amount of sodium 2-naphthol-7-sulfonate in Working Example 1 was changed from 0.5 g/L to 0.2 g/L. The appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the amount of sodium 2-naphthol-7-sulfonate in Working Example 1 was changed from 0.5 g/L to 0.3 g/L. The appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the amount of disodium 2-naphthol-3,6-disulfonate added in Comparative Example 2 was changed from 0.5 g/L to 1.0 g/L. The appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a Hull cell test was conducted under the same conditions as in Working Example 1 using a plating bath wherein the 0.5 g/L of sodium 2-naphthol-7-sulfonate in Working Example 1 was changed to 0.2 g/L of 2-naphthol. The appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• a hull cell test was conducted under the same conditions as in Working Example 1 with a plating bath wherein the 0.5 g/L of sodium 2-naphthol-7-sulfonate in Working Example 1 was changed to 10 mg/L of salicylic aldehyde. The appearance of the plating film was observed macroscopically, with the results shown in Table 1.
• the plating films obtained in the working examples all exhibited some precipitation anomalies but were uniform and had a semi-glossy appearance.
• the film obtained in Comparative Example 4 had some precipitation anomalies and a uniform appearance, but its gloss was diminished compared to those of the working examples. A uniform film could not be obtained in the other comparative examples.
• each of the resulting tin plating films was subjected to a moisture-resistance test at 105° C. and 100% RH for eight hours (PCT treatment (105° C., 100% RH, 8 hours)), and the solder wettability of the plating films after the moisture-resistance test was evaluated by measuring the zero cross time in accordance with the meniscograph method using a solder checker.
• the measurement conditions were as shown below:
• Table 2 shows the results obtained in the above-mentioned tests.
• TABLE 2 Solder wettability Plating current after moisture resistance test density (A/dm 2 )
• Working Example 1 Comparative Example 4 5 1.6 seconds 5 seconds or longer 10 1.4 seconds 5 seconds or longer 15 — 5 seconds or longer 20 1.2 seconds 5 seconds or longer 25 — 5 seconds or longer 30 1.1 seconds 5 seconds or longer 35 — Not measured 40 1.7 seconds Not measured
• the tin plating time was adjusted for each current density so that the plating film thickness would be 10 ⁇ m. A uniform film could not be obtained at a current density of 35 A/dm 2 with the plating solution of Comparative Example 4; therefore, the test was not conducted.
• the tin electroplating solution of the present invention is very safe. Moreover, the plating solution is easily handled because plating is not conducted with an alloy, and a uniform plating film can be obtained. The resulting tin plating film is uniform, semi-glossy, and has excellent solder wettability; and is therefore useful as a joining material.

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• Chemical & Material Sciences (AREA)
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• Electrochemistry (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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• 2005
  • 2005-08-19 JP JP2005238921A patent/JP4812365B2/ja active Active
• 2006
  • 2006-08-18 TW TW095130386A patent/TWI328621B/zh active
  • 2006-08-18 EP EP06254345A patent/EP1754805B1/en active Active
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