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
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/42—Pretreatment of metallic surfaces to be electroplated of light metals
  • C25D5/44—Aluminium

Definitions

• ABSTRACT Copper is electroplated on aluminum by immersing an aluminum workpiece into an aqueous alkaline plating bath containing a divalent copper salt and a complexing agent consisting of a mixture of an amine and ammonia in predetermined proportions, and passing an electric current through the bath between the aluminum workpiece as cathode and an anode which is generally but not exclusively of copper.
• This process produces uniform and adherent deposits of copper on aluminum with a current efficiency in the neighborhood of 100 percent. It can be used with advantage for a continuous plating of wires, strips, sheets and other sufficiently malleable aluminum objects and for batch plating of any aluminum workpiece.
• the present invention relates to electroplating of copper on aluminum.
• the plating ofcopper on aluminum using an aqueous alkaline electroplating bath which contains a copper salt and a complexing agent consisting of an amine, is not new.
• Suchprocess has several disadvantages.
• the adherence of copper on aluminum, for example, is not entirely satisfactory and the current efficiency isclearly insufficient.
• Tests have also been made to plate copper on aluminum using an aqueous alkaline bath based on a complex of copper and ammonia. However, these tests have not produced desired results because copper deposits obtained thereby were found to be very hard and brittle at high current densities, while forming a black smut with very little adherence at low current densities.
• an aqueous alkaline electroplating bath comprising divalent copper salt and a complexing agent consisting of a mixture of ammonia and of a primary, secondary, or tertiary amine, in predetermined proportions, leads to a substantially improved plating of copper on aluminum.
• an aqueous alkaline electroplating bath consisting of a mixture of (Cu(amine)) and (Cu(Nl-l,,) complexes, in which the (Cu(NH complex is in a proportion of -30 percent and preferably between .14 percent and percent, leads to a plating of copper on aluminum with a very goodadherence and a current efficiency in the neighborhood of 100 percent.
• the electroplating operation is carried out in conventional manner, namely by immersion of an aluminum workpiece to be planted into the plating bath mentioned above and passing an electric current through this bath between the workpiece as' cathode and an anode.
• the workpiece to be plated in accordance with the present invention can be of pure aluminum metal or of a commercial aluminum containing the usual impurities inherent to its manufacture or still of an aluminum alloy of any desired composition.
• the plating bath of the present invention has normally a pH of approximately 8 to 13 and preferably in the range of 9 to 12.
• divalent copper salt present in the bath of this invention is of little importance, however, the salt must be such that cupric ions are produced when the salt is dissolved in water. Suitable salts are, for instance, copper nitrate, copper sulfate, copper acetate, copper chloride, etc.
• the amount of divalent copper salt may vary within wide limits depending on the salt employed as well as on the other substances contained in the bath and on the plating conditions, such as current density, desired thickness of copper deposit, and the like. Generally, the amounts vary so as to obtain cupric ion concentrations between '13 and 105 grams per litre of the bath and preferably between 26 and 78 grams per litre of the bath.
• acyclic lower alkyl amines e.g., ethylamine, diethylamine, and triethylamine
• substituted derivatives such as alkanolamines, e.g., triethanolamine
• polyamines
• the employed amine has preferably at least two nitrogen atoms and should be capable of forming a complex with cupric ions in solution.
• Ammonia which plays a key role in the electroplating bath of this invention is present in said aqueous bath in the form of ammonium hydroxide.
• it can be added to the bath in the form of commercial ammonium hydroxide, namely-an aqueous solution of about 30 percent by weight ammonia, or in the form of any desired concentration.
• pure ammonia can also be added into the bath in which it will be transformed in situ into ammonium hydroxide.
• the mixture of amine and ammonia constitutes the complexing agent for the cupric ions and the amount of this agent must be at least sufficient to complex the cupric ions provided during dissolution of the copper salt. It is, however, preferable to have a small excess of ammonium hydroxide, whereby it can also be used to maintain thepl-l at a desired level.
• the amount of each ingredient forming the-complexing agent must however be such that the copper-ammonia complex which is formed in the bath is in a proportion of between 10 and 30 percent and preferably between 14 and 25 percent with respect to the total quantity of the complex ions existing in the bath.
• tetraethylenepentamine per litre of the bath, perferably between 100 and 300 grams per litre, and also between 7 and 160 ml of ammonium hydroxide of 30 percent by weight ammonia, per litre of the bath, the preferred amounts of ammonium hydroxide being between 15 and 100 ml per litre.
• the amounts of the amine must be generally be sufficient to complex to 90 percent and preferably to 86 percent of the divalent cupric ions present in the solution.
• F fluoride ions
• a source of fluoride ions (F) for instance, in the form of sodium, potassium or ammonium salt, preferably in the form of NIH F, in a concentration of 2 to 7 percent of the amount of the copper salt in the bath, leads to an additional improvement of adherence.
• ammonium salt such as NH NO Nl-LCll, (Ni-1.0 etc., in addition to ammonia itself, may improve the color and brightness of the copper deposit, however, at the expense of the adherence. If these salts are used instead of ammonia or of the amine, thre is obtained a substantial reduction of the adherence and of the current efficiency. The same happens when ammonia is replaced by another base such as sodium hydroxide. It is therefore obvious that in order to obtain the beneficial results of the present invention, it is essential that ammonia and the amine be present in the above indicated proportions.
• the plating bath according to the present invention may also contain other conventional compounds and additives such as wetting agents, brightening agents and the like.
• the temperature of the bath will generally be in the range of 25 to 90 and preferably between 25 and 30C.
• the operating voltage between the workpiece used as cathode and an anode is in the range of 5 to 25 volts depending on the current density used, the latter being generally in the range of to 400 amperes per square foot. It is also advantageous to agitate the bath vigorously particularly if one wishes to achieve the upper limits of the current density. Mechanical agitation is used because an agitation with compressed air would produce rapid loss of NH in the bath which, of course, is undersirable.
• the process according to the present invention can be applied with particular advantage to a continuous plating of wires, strips, sheets and other flexible aluminum objects forming the cathode and continuously passing at a predetermined speed in the bath between anodes, for instance, of copper.
• the aluminum wires, strips or the like are unwound from a bobbin at one end or the bath and after passing in the bath where copper is directly plated thereon, they are removed from the bath at the opposite end and are wound on another bobbin or roller in the form of a final product ready to be placed on the market.
• the aluminum workpiece to be plated in accordance with the present invention is preferably subjected to an initial cleaning or degreasing treatment to improve the adherence of the copper deposit.
• an initial cleaning or degreasing treatment to improve the adherence of the copper deposit.
• the alkaline baths mentioned above may consist, for instance, of an aqueous solution of NaOH and the acid bath may be a solution of HCl.
• the plating bath according to the present invention is generally stable and easy to control, producing entirely reproducible results.
• the pH of the bath can easily be checked from time to time and when it decreases due to evaporation of ammonia, it suffices to add a little ammonia to bring it back to the desired level.
• This ammonia addition into the plating bath, to maintain the pH at a predetermined level, is usually carried out at predetermined intervals and presents no difficulty whatsoever.
• the preferred composition of the plating bath in accordance with the present invention comprises copper nitrate Cu(NO as the divalent copper salt, tetraethylenepentamine as the amine and ammonium hydroxide NH OH at about 30 percent by weight Nl-l as the ammonia portion of the bath. Further addition of a small quantity of ammonium fluoride NH E is also preferred.
• Such plated workpiece, particularly in the form of wire, strip, or sheet, has therefore considerable advantages over the same articles made solely of aluminum.
• the aluminum workpiece plated with'copper in accordance with the present invention may be subjected to additional plating operations whereby zinc, tin, nickel or other metals may be plated on the copper layer. Plating of such various metals on copper is easily accomplished, although it is very difficult to plate them on aluminum.
• a method of electroplating copper directly on aluminum which comprises immersing an aluminum workpiece in an aqueous alkaline plating bath containing a divalent copper salt and a complexing agent consisting of a mixture of an amine and ammonia, capable of forming (Cu(amine)) and (Cu(NH complexes, the amounts of the amine and ammonia being such that together they are at least sufficient to complex all cupric ions provided by the divalent copper salt and the amount of the (Cu(NH complex being from to 30 percent of the total complex ions present in the bath, the bath having a pH in the range of 8 to 13, and passing an electric current through the bath between the almunium workpiece as cathode and an anode, said electric current being of sufficient density to effect desired deposit of copper on aluminum.
• the divalent copper salt is selected from the group consisting of copper nitrate, copper sulfate, copper acetate and copper chloride.
• aqueous alkaline bath contains an amount of divalent copper salt which is sufficient to form in solution cupric ions in a concentration of 13 to 105 grams per litre.
• the divalent copper salt is selected from the group consisting of copper nitrate, copper sulfate, copper acetate, and copper chloride and the amount thereof is such as to form in solution cupric ions in a concentration between 26 and 78 grams per litre.
• amine is a primary, secondary, or tertiary amine having more than two nitrogen atoms and capable of forming a complex with the cupric ions in solution.
• amine is selected from the group consisting of ethylamine, diethyamine, triethylarnine, triethanolamine, ethylenediamine, diethylene-triamine, tetraethylenepentamine, hexamethylenetetramine, triethylenetetramine and pyridine.
• ammonia is in the form of commercial ammonium hydroxide containing about 30 percent by weight of ammonia.
• aqueous alkaline bath contains a quantity of amine sufficient to complex to percent of the divalent cupric ions in solution and contains from 7 to 160 ml of ammonia per litre of bath, in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains a quantity of amine sufficient to complex 75 to 86 percent of divalent cupric ions in solution and contains between 15 and ml of ammonia per litre of bath, in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains 50 to 500 grams of tetraethylene-pentamine per litre and 7 to ml of ammonia per litre, the latter being in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains between 100 and 300 grams of tetraethylenepentamine per litre and between 15 and lOO ml of ammonia per litre, the latter being in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• Method according to claim 1 in which the pH of the aqueous alkaline bath is maintained at a predetermined level during the entire plating operation by intermittent addition of ammonium hydroxide.
• Method according to claim 1 in which the aluminum workpiece is subjected to a degreasing and clean- 7 ing pretreatment prior to its immersion into the plating bath.
• Method as claimed in claim 1 in which a small quantity of a source of fluoride ions in the form of sodium, potassium, or ammonium salt, is also introduced into the plating bath.
• Method according to claim 21 in which a source of fluoride ions in the form of Nl-LF and in the amount of 2 to 7 percent of the amount of divalent copper salt, is also introduced into the plating bath.
• a continuous method of electroplating copper directly on wires, strips, sheets and other flexible workpieces of aluminum which comprises continuously forwarding the workpiece at a predetermined speed through an aqueous alkaline plating bath containing a divalent copper salt and a complexing agent consisting of a mixture of an amine and ammonia, capable of forming (Cu(amine)) and (Cu(NH complexes, the amounts of the amine and ammonia being such that together they are at least sufficient to complex all cupric ions provided by the divalent copper salt and the amount of the (Cu(Nl-l complex being from to 30 percent of the total complex ions present in the bath, the bath having a pH in the range of 8 to 13, and passing an electric current through the bath between the aluminum workpiece continuously travelling through the bath as cathode and an anode, said electric current being of sufficient density to effect desired deposit of copper on the aluminum workpiece while the latter travels through the bath.
• the divalent copper salt is selected from the group consisting of copper nitrate, copper sulfate, copper acetate and copper chloride.
• the divalent copper salt is selected from the group consisting of copper nitrate, copper sulfate, copper acetate, and copper chloride and the amount thereof is such as to form in solution cupric ions in a concentration between 26 and 78 grams per litre.
• Method according to claim 24 in which the amine is a primary, secondary, or tertiary amine having more than two nitrogen atoms and capable of forming a complex with the cupric ions in solution.
• amine is selected from the group consisting of ethylamine, diethyamine, triethylamine, triethanolamine, cthylenediarnine, diethylenetriamine, tetraethylenepentamine. hexamethylenetetramine, triethylenetetramine and pyridine.
• aqueous alkaline bath contains a quantity of amine sufficient to complex to percent of divalent cupric ions in solution and contains from 7 to 160 ml of ammonia per litre of bath, in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains a quantity of amine sufficient to complex 75 to 86 percent of divalent cupric ions in solution and contains between 15 and ml of ammonia per litre of bath, in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains 50 to 500 grams of tetraethylene-pentamine per litre and 7 to ml of ammonia per litre, the latter being in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• aqueous alkaline bath contains between 100 and 300 grams of tetraethylenepentamine per litre and between 15 and 100 ml of ammonia per litre, the latter being in the form of ammonium hydroxide of about 30 percent by weight ammonia.
• Method according to claim 24 in which the current density is in the range between 10 and 400 amplfoot 41.
• Method according to claim 24 in which a source of fluoride ions in the form of NH F and in the amount of 2 to 7 percent of the amount of divalent copper salt, is also introduced into the plating bath.
• the divalent copper salt is copper nitrate Cu(NO the amine plex all cupric ions provided by the divalent copper salt and the amount of the (Cu(NH H complex being from 10 to 30 percent of the total complex ions present in the bath, the bath having a pH in the range of 8 to 13.
• An aqueous alkaline electroplating bath according to claim 48 in which the amount of the (Cu(NH complex is from 14 to 25 percent of the total complex ions present in the bath.
• line 2 change "Nanbhai” to Nanabhai.
• Column 1 line 20, after “comprising” insert -a--'; line 37, change "planted” to --plated-; line 43, after “of” delete “a”; line 63, after “plating” insert -bath-.
• aqueous alkaline bath containsan amount of divalen copper salt which is sufficient to form in' solution cupric ions in a concentration of 13 to 1 05 grams per litre.; line 47, change "26" to ,--27; line 53, change "27” to --28 line 57, change "28” to 29--; line 63, change "29” to' -,-30-; line 66, change "30" to 3l--.

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

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• 1972
  • 1972-02-15 CA CA134,787A patent/CA1001581A/en not_active Expired
  • 1972-03-09 US US00233361A patent/US3775264A/en not_active Expired - Lifetime
  • 1972-04-11 GB GB1657372A patent/GB1347936A/en not_active Expired
  • 1972-04-25 FR FR7214666A patent/FR2159239B1/fr not_active Expired
  • 1972-10-06 DE DE2249037A patent/DE2249037A1/de active Pending

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