Classifications

• • 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
• • 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 accordingly provides a method of electroplating copper directly onto aluminum which comprises immersing an aluminum workpiece in an aqueous alkaline plating bath which has a'pI-l of from 8.5 to 13 and which comprises from to 450 grams per litre of a salt of divalent copper and from 5 to 450 grams per litre of, as complexing agent, A mixture of a primary, secondary or tertiary amine with ammonium hydroxide, said mixture being capable of forming a complex ion with divalent copper, andpassing an electric current through said bath between said workpiece as cathode and an anode.
• the aluminum workpiece which is electroplated in accordance with the invention may be of pure aluminum metal or may be of commercial aluminum containing its usual manufacturing impurities or may be an aluminum alloy.
• the plating bath which is used in the method of the present invention is alkaline having a pH of from 8.5 to 13.
• Preferred pH values are in the range 9.5 to 10.5 (as measured by a glass electrode pH metre) and the optimum pH varies with the concentrations as well as with the nature of the various ingredients of the plating bath.
• the pH may be adjusted to the most suitable value within the given range for a particular operation by using appropriate amounts of the ammonium hydroxide.
• an alkaline plating bath in accordance with the invention in which the copper ions are complexed by the amine ammonium hydroxide complexing agent means that chemical deposition of the copper is prevented and the passage of electric current through the bath produces a coating of electroplated copper at thickness which may range as high as about 5 mils (about 125 microns). Since, however the degree of adhesion of the deposit of copper tends to fall off with an increase in thickness clearly there is no advantage in providing too thick a deposit, especially as thicknesses of up to about 1 mil, and preferably up to about 0.5 mil, are generally quite adequate for most practical pur- P
• the aqueous plating bath which is used should comprise a divalent copper salt.
• h salt i r atively unimportant but should be such h pr ions are produced when the salt is dissolved in water.
• Suitable salts include copper nitrate, which is preferred, copper sulfate, copper acetate and copper chloride-
• the amount of divalent copper salt can vary between wide limits depending, in part, upon the salt used and upon the other plating conditions. In general suitable amounts are from 5 to 450 grams per litre with amounts of from 50, especially 100, to 200 grams per litre being preferred.
• the other essential ingredient of the aqueous plating bath is the mixture of amine with ammonium hydroxide which acts as a complexing agent for the cupric ions in solution.
• amines A wide variety of amines is known to be capable of complexing copper in solution including aliphatic primary, secondary and tertiary amines, forexample acyclic lower alkyl amines, such as ethylamine, diethylamine, and triethylamine, and substituted derivatives thereof including the alkanolamines, such as triethanolamine, and polyarnines, such as ethylenediamine, diethylenetriamine and tetraethylene pentamine; cycloaliphatic amines such as hexamethylenetetrarnine and triethylenetetramine; and aromatic amines such as pyridine and derivatives thereof.
• the amine contains at least two nitrogen atoms and is capable of forming a chelate with divalent copper. It has been found that such amines, for example ethylene diamine, diethylene triamine and tetraethylene pentamine, together with ammonium hydroxide providethe right complexing behaviour consistent with ease of deposition of the copper on the workpiece.
• the amount of the amine-ammonium hydroxide complexing agent present in the plating bath should be atleast sufficient to complex the cupric ions provided by thecopper salt. Thus the amount will depend upon the-amount of copper salt and ammonium hydroxide and upon the type and amount of amine used.
• Ammonium hydroxide is generally used in the form of a commercial 30 percent solution although other concentrations can be employed. It can also be formed in situ by introducing ammonia into the bath. The amount of ammonium hydroxide with reference to the amine can varyto a great extentbut generally will be such as to produce the desiredcomplexing effect. A good indication of suitable amounts is given in the Table on pages 7 and 8 hereinafter. Suitable amounts of the copper salt, the amine and ammonium hydroxide can readily be determined by routine experiment but,
• the behaviour of the plating bath can be improved, particularly when the workpiece is of an aluminum alloy, by adding thereto a source of fluoride ions, particularly ammonium and potassium fluorides and bifluorides.
• fluoride ions particularly ammonium and potassium fluorides and bifluorides.
• fluorides may be incorporated in the bath in concentrations of, for example, from 0.1 to l0grams per litre, especially from 0.5 to 2 grams per litre.
• the plating bath may also contain other compounds and additivessuch as are commonly used in the art, for example wetting agents and brighteningagents.
• the incorporation ,of sodium chloride in the bath also has been found to enhance the adhesion of the copper deposit to ,the aluminum .workpiece.
• Theternperature forthe bath suitably is within the range of from.,25C. to C. and for the most cases temperature of from 25C. to 30C. can be used.
• the operating voltage in actual practice may be largely dictated by the work load such as the jigging arrangement (the spacing between anodes and the articles to -be plated) but thegoverning parameter is the current den- Dense, adherent and semi-bright deposits of copper are produced in accordance with the invention in a regular and uniform manner with reproduceable results.
• the operating conditions of the method need not be subject to any more stringent control than is usual in conventional electroplating processes.
• One suitable cleaning operation comprises treating the workpiece with an aqueous solution of sodium bicarbonate, sodium hydroxide and trisodium phosphate, rinsing with water, etching with nitric acid and again rinsing with water.
• the aqueous solution may, for
• nitric acid is suitable for use in the etching step and immersion in such acid for a period of up to 3 minutes, for example 10 to seconds, is sufficient.
• the cleaning process can be varied substantially within wide limits depending for example on the nature of the workpiece and on the degree and type of surface soiling. After the cleaning operation, when such is carried out, the workpiece is transferred to the plating bath and plated at a suitable current density and temperature in accordance with the method of the invention.
• Examples 1 to 9 are summarised in the Table below.
• the Table gives details of the plating bath compositions, the conditions under which plating took place and the results and performance of the plating operation.
• the electroplating was carried out on an aluminum workpiece in a Hull Cell (see Metal Finishing, January 1947, pages 59 to 63).
• the workpiece Prior to immersion in the plating bath the workpiece had been cleaned with an aqueous solution containing 23 grams per litre sodium carbonate, 46 grams per litre sodium hydroxide and 23 grams per litre trisodium phosphate, rinsed with water, etched for 10 to 20 seconds with 50% nitric acid, and again rinsed with water.
• pentamine Ammonium hydroxide ml/l (30%). Copper nitrate g/l Tetraethylene 150 g/l 5 pentamine. 10.0 25 4 ll 5 10-200 20 .5 Good.
• Ammonium hydroxide 450 ml/l a The adhesion of the copper deposit on the workpiece was assessed by the 90 bend test. In this test the workpiece is bent through an angle of 90. Poor and inadequate adhesion is indicated by flaking off of the deposit, while cracking of the deposit is indicative of only a fair adhesion. The absence of flaking or cracking indicates a good, strongly adherent, deposit.
• the present invention provides a method of electroplating copper directly onto aluminum and produces strongly adherent deposits.
• Themethod avoids theneed for involved and costly pretreatments of the aluminum workpiece and it is notnecessary to provide a metal strike layer, for example of zinc, on the aluminum before depositing the copper layer.
• the plating bath is alkaline and hence is unlike the acidic plating-baths generally used in the plating of copper or aluminum; Because of this the method also avoids the disadvantages associated with the presence of hydrogen at the copper- /aluminum interface. Not only does hydrogenat the interface deleteriously affect the adhesion of the copper deposit but it is usually also necessary totake steps to remove the hydrogen from the plated workpiece after the plating operation. This can involve either leaving the plated workpiece at room temperature for prolonged periods or heating it at a high temperature to facilitate rapid removal of the hydrogen.
• This method may be applied to the deposition of copper on aluminum workpieces of virtually any shape, and irregularly shaped workpieces have been satisfactorily plated in accordance with the invention.
• a method of electroplating copper directly onto aluminum without the necessity of providing a pretreatment zinc coating which comprises the steps of a. immersing an aluminum workpiece in an aqueous ammonium hydroxide plating bath having a pH of 8.5. to 13 and which comprises from 5 to 450 grams per liter of a salt of divalent copper and from 5 to 450 grams per liter of a complexing agent selected from the group consisting of primary, secondary and tertiary amines, whereby said complexing agent is capable of forming a complex ion with divalent copper; and
• a method of electroplating copper directly onto aluminum without the necessity of providing a pretreatment zinc coating which comprises the steps of a. immersing an aluminum workpiece in an aqueous plating bath having a pH of 8.5 to 13 consisting essentially of from 5 to 450 grams per liter of ammoniumhydroxide from 5 to 450-grams per liter of the nitrate, sulfate, acetate or chloride salt of divalent copper and from 5 to 450 gramsper li er of a complexing agent selected from the group consistin of primary. secondary and tertiary amines, whereby' said complexing agent-ls capable of forming a complea: ion with divalent copper; and
• said electric current being of sufiicientdensity to, achieve the desired plating of a layer ofcoppenon aluminum.
• the plating bath comprises from 100 to 200 grams perlitre of the salt of divalent copper and from 100 to ZOOgrams perv litre of the complexing agent, A
• l 6 wl 1ere in the amine is selected from ethylenediamine, diethylenetriamine. and tetraethylenepentamine and; is admixed monium hydroxide of predetermined; concentration to form the complexing agent. 7
• the copper; salt is selected from copper nitrate, copper sulfate, per acetate and copper chloride and the complexing agent is an admixture of ammonium hydroxide with an amine selected from ethylenediamine, diethylenetriamine and tetraethylenepentamine.
• the plating bath also contains a source of fluoride ions.
• V H v 16 Method as claimed in claim 1 wherein the copper salt is selected from copper nitrate copper sulfate, copper acetate and copper chloride and the complexing agent is an admixture of ammonium hydroxide .with an amine selected from ethylenediamine, t .lie,thylen etriamine and tetraethylenepentarnine, .the electroplating beingcarriedout at current densities between 10 and 300 amperesper square footand at voltages between 5 to25 volts to.achievedesiredplating of copper on aluminum, and the aluminum workpiece ubeingldcgreased before it isirnrnersed into-th plating-bath ,and theplating operationbeing carried out in thepresence of a source of fluorideions which consists of ammonium orpotassium fluorides or bifluorides andispresent lathe bath in concen
• the plating bath comprises 150 g/l of copper nitrate, 150 g/l of triethylamine'and 100 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 9.5, and the plating is carried out in a current density range of 80 250 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/1 of copper nitrate, 150 g/l of triethanolamine and 200 m/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 9 and the plating is carried out in a current density range of 115 300 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/l of copper nitrate, 150 g/l of diethylenetriamine and 100 ml/l of ammonium hydroxide of 30% concentration and has a pH of about 10.7, and the plating is carried out in a current density range of 10 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/l of copper nitrate, 150 g/l of tetraethylenepentamine and 100 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 10, and the plating is carried out in a current density range of 85 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/l of copper nitrate, 150 g/ 1 of tetraethylenepentamine, 12 g/l of ammonium nitrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/l of copper nitrate, 150 g/l of tetraethylenepentamine, 50 g/l of ammonium citrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 10 210 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 150 g/l of copper nitrate, 120 g/l of tetraethylenepentamine, 50 g/l of sodium chloride and an amount of ammonium hydroxide of 30% concentration sufiicient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 5 amperes per square foot for a time sufficient to achieve a plating of predetennined thickness.
• the plating bath comprises 250 g/l of copper nitrate, 250 g/l of tetraethylenepentamine and 165 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 10.8, and the plating is carried out in a current density range of 5 100 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
• the plating bath comprises 450 g/l of copper nitrate, 450 g/l of tetraethylenepentamine and 450 m/l of ammonium hydroxide of 30% concentration and has a pH of about 11.6, and the plating is carried out in a current density range of 5 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

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

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• 1970
  • 1970-05-25 CA CA898183A patent/CA898183A/en not_active Expired
  • 1970-09-25 US US00075673A patent/US3775265A/en not_active Expired - Lifetime
• 1971
  • 1971-04-22 ES ES390466A patent/ES390466A1/es not_active Expired
  • 1971-04-22 SE SE7105270A patent/SE375810B/xx unknown
  • 1971-04-23 ZA ZA712647A patent/ZA712647B/xx unknown
  • 1971-04-26 FI FI711152A patent/FI52360C/fi active
  • 1971-04-30 IT IT50041/71A patent/IT942091B/it active
  • 1971-05-01 JP JP46029344A patent/JPS512901B1/ja active Pending
  • 1971-05-07 NO NO1716/71A patent/NO131083C/no unknown
  • 1971-05-11 BR BR2811/71A patent/BR7102811D0/pt unknown
  • 1971-05-14 NL NL717106640A patent/NL148362B/xx unknown
  • 1971-05-18 GB GB1578971*[A patent/GB1309497A/en not_active Expired
  • 1971-05-19 BE BE767398A patent/BE767398A/fr unknown
  • 1971-05-24 FR FR7118585A patent/FR2090261B1/fr not_active Expired

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