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
  • C25D3/38—Electroplating: Baths therefor from solutions of copper

Definitions

• the invention relates to electrolytic copper plating solutions and a method for their application.
• the invention relates especially to the electrodeposition of copper for decorative use and more particularly to the electrodeposition of copper on substrates having sharp corners such as formed by the holes drilled into copper clads for the production of printed circuit boards.
• Circuit boards are generally prepared by laminating copper clad to both sides of a plastic sheet such as an epoxy-glass. Holes are then drilled through the copper clad and the plastic, exposing the plastic. The exposed plastic must then be plated to effect conductivity from one side of.the board to the other. This is generally accomplished by treating the plastic' with an activator by well known processes, subjecting the entire circuit board to electroless deposition of copper to render the areas receptive to electrolytic copper depositions, and then plating the board and the internal surfaces of the holes by electrodeposition of copper. The sharp corners formed by the perimeter of the holes adjacent the top and bottom of the board must also be plated. This can be accomplished by many different copper electroplating solutions presently on the market, but the copper plate at the corners has a tendency to develop cracks when the boards are subjected to thermal shock necessitated by further processing of the boards.
• This invention relates to novel acid copper electroplating solutions containing the reaction product of a compound containing the structure or a compound of the formula wherein R 1 , R 2 , R 3 and R 4 are as defined below, an alkylene disulfide having terminal acid groups and acrylamide.
• R 1 and R 2 are lower alkyl radicals with 1 to 6 carbon atoms, a hydrogen atom or mixtures thereof, and R 4 is an alkali metal, hydrogen, magnesium, or the groups SX or SSX.
• X is an alkali metal, hydrogen or magensium, or wherein P 3 is an aromatic, heterocyclic or alicyclic radical containing 3 to 12 carbon atoms, and R 4 represents an alkali metal, hydrogen, magnesium, or the groups SX or SSX where X is an alkali metal, hydrogen or magnesium.
• the compounds found to be the most advantageous to date are the sodium salts of tetraalkylthiuram disulfide, wherein R 1 and R 2 are methyl or ethyl or mixtures thereof, 2,2'-dithio-bisbenzothiazole, and 2-mecaptobenzothiazole
• the sodium salts of the compounds (3), (4) and (5) can readily be prepared by known means by heating the compounds dissolved in a solvent such as methanol (preferably under reflux) with sodium hydroxide.
• a solvent such as methanol (preferably under reflux) with sodium hydroxide.
• the compound of formulas (3), (4) and (5) are available commercially and marketed under the marks TUADS, ALTAX and CAPTAX, respectively, by R. T. Vanderbilt Company, Inc.
• the second reactant is an alkylene disulfide compound having terminal acid groups.
• R 1 and R 2 are the same or different and are alkylene radicals containing 1 to 6 carbon atoms, X is hydrogen or -SO 3 H and n equals 2 to 5. Examples of a number of specific compounds coming within the scope of the above formula are set forth in column 2 of U.S. Patent 3,328,273 issued to Creutz et al. on June 27, 1967. It is preferable to use the alkali metal salts of the above compounds.
• alkylene disulfide known to .date is di(sodium 3-sulfonate-1-propyly)sulfide:
• the third reactant is acrylamide.
• reaction product(s) The exact chemical nature of the reaction product is not known.
• the products resulting from these . reactions are hereinafter referred to as the reaction product(s).
• the invention includes the use of oxyalkylene polymers as brightening and leveling agents in combination with the reaction products.
• the oxyalkylene polymers have been found to materially increase the brightness and leveling of the deposits.
• the polyalkylene glycols such as polyethylene glycols, methoxy polyethylene glycols and the polypropylene glycols, have been found to be particularly advantageous.
• the oxyethylene or oxypropylene polymers can be surfactants, anionic, nonionic or cationic. Anionic and nonionic are preferred. These types of surfactants are well known and lists of specific polymers can be obtained by consulting any standard text on the subject such as the various volumes of Kirk-Othmer Encyclopedia of Chemical Technology or the industrial literature. It is the presence of the ethylene oxide or propylene oxide groups that is most important. The compounds should have at least about 8 mols of ethylene and/or propylene oxide and be soluble in the bath solution. Combinations of polyethylene and polypropylene glycols and/or surfactants can also be used.
• the amounts of the oxyalkylene polymers can be about the same as is usually employed in acid copper baths. A sufficient amount should, of course, be used to obtain the brightness and leveling desired which will in turn depend on the ultimate use intended. Generally about 0.1 to 0.5 g/1 or ml/l can be employed.
• the copper deposited according to this invention is useful as decorative use, in the electronic industry generally, and'for the conduction of electricity on substrates that do not have sharp corners or on articles where thermal shock is not a problem.
• the amounts of the reaction products employed in the acid copper plating solutions may therefore differ depending on the result desired, but in any event the amounts should be sufficient to improve the brightness and smoothness of the metallic deposits over that obtainable from the basic plating solutions.
• the amounts should be sufficient to prevent cracks in the deposit at the corners when the plated substrate is subjected to thermal shock. As far as it is known today, the amounts to accomplish both of these results will be substantially the same.
• the acid copper plating solutions to which the reaction products can be added are conventional and well known.
• the two essential constituents are a copper salt, such as copper sulfate., and an acid, such as sulfuric acid.
• the salt furnishes the metal ions and the acid serves to reduce the resistivity or promote conductivity.
• These baths typically contain between about 70-250 g/1 of copper sulfate and 30 to 250 g/1 of sulfuric acid.
• the reaction products can be formed by dissolving compounds of formulas (1) and/or (2), such as tetralakylthiuram disulfide sodium salt in a suitable solvent, adding a bis(3-sulfoalkyl) disulfide salt to the reaction mixture together with acrylamide under reflux. Concentrated sulfuric acid is then added (dropwise in the laboratory) during the reflux and continued until gassing has ceased or no precipitate or turbidity is present.
• the reactants can be the mixtures as described above.
• the exact proportions of the reactants are not very critical but best results to date are obtained by using stoichiometric amounts.
• the reaction can include additional reactants so long as they do not affect the function and advantageous properties of the resulting reaction product.
• 0.6 g of formaldehyde can be added to the methanol solution and reacted with the sodium hydroxide before the addition of the disulfide compound and the resulting reaction product has substantially the same advantageous properties.
• a 2 gallon tank and a Hull cell was used on an acid copper plating solution of the following composition:
• the plating bath was operated at 75°F in a Hull cell with air agitation at a current of 2 amps for 10 minutes.
• the plating bath in the 2 gallon tank was operated at identical parameters, but at a current density of 15 ASF for an hour.
• Printed circuit boards with the holes drilled therein after being activated and electrolessly plated with copper were plated in this tank.
• the copper deposit on the circuit board was smooth and semi-lustrous over current density range of 2 to 20 ASF and showed no signs of corner cracks after thermal shock.
• Example 2 The procedure of Example 2 was followed except that the following material was also incorporated into the plating bath:
• the copper deposit on the plated material was very bright and leveled over a current density range of from 1 to 100 ASF and showed no signs of corner cracks after thermal shock.
• Example 2 The procedure of Example 2' was followed except that the following materials were also incorporated into the plating bath:
• the deposit on the plated material was very bright and leveled in the current density range of from 1 to 100 ASF.
• the deposit on the printed circuit board plated in the 2 gallon tank was very bright and leveled and showed no signs of corner cracks after thermal shock.
• the thermal -shock test to which the plated boards are subjected in the above examples is conventional. After the boards are baked for about an hour at 150°C, they are cooled to room temperature and allowed to float on one side in molten solder at 288°C for 10 seconds, then turned over and allowed to float on the solder on the other side for 10 seconds. The boards are then removed and inspected for cracks.

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

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• 1983
  • 1983-09-28 WO PCT/US1983/001508 patent/WO1984001393A1/en unknown
  • 1983-09-28 JP JP58503351A patent/JPS59501829A/ja active Granted
  • 1983-09-30 AT AT83109814T patent/ATE32611T1/de not_active IP Right Cessation
  • 1983-09-30 EP EP83109814A patent/EP0107109B1/de not_active Expired
  • 1983-09-30 DE DE198383109814T patent/DE107109T1/de active Pending
  • 1983-09-30 DE DE8383109814T patent/DE3375732D1/de not_active Expired

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