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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin

Definitions

• the present invention relates to an acidic electrolyte for depositing tin-bismuth alloys, to a process in which this electrolyte is used, to coatings obtainable by the process, and to the use of the electrolyte for coating electronic components.
• components In the field of production of electrical and electronic assemblies, components are often used which contain a coating with electrolytically deposited tin-lead layers for functional reasons. These coatings ensure a good Weichlötbarkeit of the components even after prolonged storage.
• the whisker formation in tin layers can be prevented by the co-deposition of small amounts of another metal.
• the co-deposition of small amounts of lead (at least 3% by weight) has proven to be effective.
• this co-decision is only allowed for a few applications.
• whisker avoidance has also been the deposition of a tin-bismuth alloy with about 2-4 wt.% Bismuth proven. Higher levels of bismuth are detrimental because it reduces the ductility of the deposited layers and thus creates the risk of cracking of the coating upon mechanical deformation of the terminal legs of electronic components. As a result, properties such as solderability and corrosion resistance of the layers are deteriorated. At a lower co-decision than 2 wt.% Bi, the formation of whiskers can not be completely excluded.
• the bismuth deposited in this charge exchange reaction accumulates in the form of a loose, spongy deposit. This dissolves over time from the anodes and thus enters the electrolyte and thus also on the components to be coated. These bismuth particles can then be incorporated into the electrodeposited layers, thus causing highly dendritic and technically unusable layers. This can also lead to high losses in production.
• the object underlying the present invention is to provide an electrolyte for depositing a tin-bismuth alloy having an alloying content of at least 2-4 wt.% At which there is no deposition of bismuth in the charge exchange on one already coated surface occurs during a power interruption.
• an acidic aqueous electrolyte for the deposition of tin-bismuth alloys comprising one or more alkylsulfonic acids and / or alkanolsulfonic acids, one or more soluble stannous salts, one or more soluble bismuth (III) salts, or several nonionic surfactants and one or more thiazole and / or thiadiazole compounds.
• the solution of the above object by the electrolyte of the present invention is therefore surprising to a person skilled in the art, because none of the compounds contained in the electrolyte shifts the electrode potential of bismuth in the negative direction, which the person skilled in the art as a prerequisite for preventing the deposition of a nobler to a less noble would expect metal. Even in combination, the components contained in the electrolyte cause no shift of the equilibrium potential in the cathodic direction.
• the prevention of the deposition of bismuth on a freshly deposited tin-bismuth surface can therefore not be explained on an electrochemical basis. There may be an inhibition effect, ie the substance combination used blocks the electroless cementation, but not the electrolytic deposition of bismuth.
• thiazole and thiadiazole compounds are not particularly limited.
• thiazole compound is meant “ any "" substituted or unsubstituted, saturated or unsaturated thiazole compounds.”
• the thiazole compound may be mentioned: benzothiazole, 2-aminobenzothiazole, 6-aminobenzothiazole, 2- Hydroxybenzothiazole, S-hydroxybenzothiazole, 2-methylbenzothiazole, 2-mercaptobenzothiazole, ⁇ -methoxy-2-aminobenzothiazole and 2-thiazolethiol-2 Among these, 2-mercaptobenzothiazole is particularly preferred.
• thiadiazole compounds Any examples of the substituted or unsubstituted, saturated or unsaturated thiadiazole compounds may be mentioned as examples of the thiadiazole compound: 2-amino-5-methyl-1,3,3,4-thiadiazole, 2-amino-5-mercapto-1 , 3, 4-thiadiazole, 2-mercapto-5-methyl-1,3,3,4-thiadiazole, 2-amino-1,3,4-thiadiazole and 2,5-dimercapto-1,3,3,4-thiadiazole Thiazole or thiadiazole compound may be alone or in Combination with others can be used.
• the concentration of thiazole and / or thiadiazole compound in the electrolyte is preferably from 5 to 1000 mg / l electrolyte, more preferably 50 to 500 mg / l electrolyte.
• nonionic surfactant any known nonionic surfactants can be used.
• block copolymers and copolymers of ethylene and propylene oxide may be mentioned.
• Particularly preferred is a polyethylene oxide / polypropylene oxide copolymer of the general formula H- (OCH 2 -CH 2 ) m - (OCH (CH 3 ) -CH 2 ) n -OH, wherein m and n are integers between 5 and 60, and has a weight average molecular weight of 2,000 to 10,000.
• the nonionic surfactant has a cloud point of> 30 0 C.
• the concentration of nonionic surfactant in the electrolyte of the present invention is preferably in a range of 1-50 g / L, more preferably 2-20 g / L, and particularly preferably 5-10 g / L.
• the tin (II) may be present in the electrolyte as a salt of mineral, alkylsulfonic or alkanolsulfonic acids.
• salts of mineral acids are sulfates and tetrafluoroborates.
• Preferred salts of the alkylsulfonic acids are e.g. Methanesulfonates, ethanesulfonates, n- and iso-propanesulfonates, methanedisulfonates, ethanedisulfonates, 2,3-propanedisulfonates and 1,3-propanedisulfonates.
• Usable alkanol sulfonates are 2-hydroxyethanesulfonates, 2-hydroxypropanesulfonates and 3-hydroxypropanesulfonates. Particularly preferred is tin (II) methanesulfonate.
• the tin (II) salts are present in the electrolyte preferably in an amount of 5 to 200 g / l of electrolyte, more preferably 10 to 100 g / l of electrolyte, calculated as tin (II).
• the bismuth (III) salts can be added to the electrolyte in any form which provides sufficient solubility in the electrolyte in Bi (III) ions.
• the addition may be in the form of dissolved Bi (III) salts or in the form of solid compounds which are converted in the electrolyte in the presence of the free acid into soluble Bi (III) compounds.
• Bi (III) salts are salts of mineral acids such as chlorides, tetrafluoroborates or nitrates, salts of alkylsulfonic acids such as methanesulfonates, ethanesulfonates, methanedisulfonates, ethanedisulfonates, 2,3-propanedisulfonates and 1,3-propanedisulfonates, salts of alkanolsulfonic acids such as 2-hydroxyethanesulfonates and 3-hydroxypropanesulfonates. Particularly preferred is bismuth (III) methanesulfonate.
• bismuth (III) carbonate or bismuth (III) oxide may preferably be used. Solve these connections in the presence of alkyl and / or alkanol sulfonic acid in the electrolyte to soluble Bi (III) compounds.
• the concentration of bismuth depends on the desired content of Bi in the resulting tin-bismuth alloy and the selected concentration of tin (II) salts.
• the bismuth (III) salts are contained in the electrolyte at a concentration which permits the deposition of a tin-bismuth alloy having an alloy composition of 2-4% Bi.
• the concentration of bi-ions is preferably 3-6%, particularly preferably 5%, based on the selected tin (II) concentration.
• the alkylsulfonic acid and the alkanolsulfonic acid preferably have 1 to 10, particularly preferably 1 to 5, carbon atoms.
• the alkylsulfonic acids e.g. Methanesulfonic acid, ethanesulfonic acid, n-propanesulfonic acid, iso-propanesulfonic acid, methanedisulfonic acid, ethanedisulfonic acid, 2, 3-propanedisulfonic acid or 1,3-propane disulfonic present.
• Useful alkanolsulfonic acids are e.g. 2-hydroxyethanesulfonic acid, 2-hydroxypropanesulfonic acid and 3-hydroxypropanesulfonic acid.
• the alkyl and / or alkanol sulfonic acid is preferably present in the electrolyte in a concentration of 50 to 300 g / l of electrolyte, more preferably 100 to 200 g / l of electrolyte.
• the electrolyte may also contain conventional antioxidants to prevent tin oxidation, for example mono- or polyhydroxyphenyl compounds such as catechol, hydroquinone or phenolsulfonic acid. Preference is given to the use of catechol.
• the concentration of these antioxidants may be 50 to 2000 mg / l electrolyte, preferably 500 to 1000 mg / l.
• the electrolyte may also contain various additives commonly used in acidic electrolytes for the deposition of tin alloys, eg grain refining additives, wetting agents and / or brighteners.
• the grain-refining additive is preferably present in an amount of 0.1 to 50 g / l of electrolyte, preferably 1 to 10 g / l of electrolyte.
• the wetting agent may be present in an amount of 0.1 to 50 g / l of electrolyte, preferably 0.5 to 10 g / l of electrolyte.
• the pH of the acidic electrolyte is preferably 0 to ⁇ 1.
• the present invention further provides a process for the electrolytic coating of substrates with tin-bismuth alloys, in which the coating is applied while passing through direct current using the electrolyte according to the invention, an anode made of metallic tin and a cathode from the substrate to be coated, and coatings available by this method.
• the current density can be 0.1 A / dm 2 (drum or rack technology) up to 100 A / dm 2 (high-speed systems).
• the temperature of the electrolyte is preferably in the range from 0 to 70 ° C., more preferably in the range from 20 to 50 ° C.
• the substrate to be coated there may be any materials commonly used for manufacturing electronic components, eg, copper, copper-containing alloys, nickel-iron alloys (eg, Alloy 42), or nickel-plated materials.
• the electrolyte according to the invention can be used for the coating of electronic components.
• An electrolyte was used, consisting of:
• the thus obtained tin-bismuth coating had a layer thickness of 10 ⁇ m with an alloy content of 2.8% Bi (remainder Sn).

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Mechanical Engineering (AREA)
• Electroplating Methods And Accessories (AREA)

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• 2005
  • 2005-04-12 DE DE200510016819 patent/DE102005016819B4/de not_active Expired - Lifetime
• 2006
  • 2006-03-09 JP JP2008505749A patent/JP5278675B2/ja not_active Expired - Lifetime
  • 2006-03-09 KR KR1020077026116A patent/KR20070120592A/ko not_active Withdrawn
  • 2006-03-09 WO PCT/EP2006/002183 patent/WO2006108476A2/de not_active Ceased
  • 2006-04-12 TW TW095113052A patent/TWI328052B/zh active

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