Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/16—Polishing
  • C25F3/22—Polishing of heavy metals

Definitions

• This invention relates to a phosphoric acid contaming electrolyte for anodically polishing copper.
• the invention further pertains to methodsof electropolishing copper in such an electrolyte.
• a bath heretofore preferred for the anodic polishlng of copper consists of 75% to 85% m phosphoric acid, saturated with chromic acid.
• composition oi. this bath will range from 69% orthophosphoric acid and 7% chromic acid to 81% orthophosphoric,.-acid and chromic acid.
• Orthophosphoric acid can be used alone for electro-polishing copper, but only at the impractically low temperature 01! 70 F.
• the addition oi hexavalent chromium in the form of chromic acid thus serves to make possible electropolish: ing oi. copper in phosphoric acid at practically But the progressive rise in current density andtank voltage characteristic of chromic acid containing phosphoric acid baths is thought to be due to this chromic acid addition, being caused, inore particularly, by continuous reduction of hexavalent chromium to trivalent chromium and by continuous accumulation in the bath of anodically dissolved copper.
• Another-important object of this invention is to provide methods for anodically polishing copper in phosphoric acid at low current densities and tank voltages operative at commercially desirable temperatures.
• a further important object or the invention is to provide methods for continuously electropolishing copper in an electrolyte from which anodically dissolved copper is plated out cathodically in easily recoverable form.
• baths of the present invention contain preferably about 75 to 84% (by weight) 0! 100% orthophosphoric acid, about from 0.25 to 2.0% or, preferably, 0.3 to 1.5% trivalent aluminum, from 0 to 2% trivalent chromium, and,
• Such baths produce, with little or no agitation, a brilliant, mirror-like finish on copper at temperatures of from to or F. at current densities of from 50 to 200 or, preierably,
• the baths can be used continuously, with very simple chemical control and maintenance. The only replacements required .are those compensating for loss of decomposed water and for a limited amount of loss due to dragging out of the not very viscous electrolyte.
• the new baths are further less cor- Bath No. 1 Bath No 2 Per cent by Per cent by o: I o.s as
• Balance Bath No. 1 may be prepared by adding a trivalent chromium salt to 75% orthophosphoric acid, the required amount of aluminum metal having been dissolved in the phosphoric acid by heating.
• chromic chloride may be dissolved in the phosphoric acid, the resulting solution being heated until all the hydrochloric 4 acid has been driven 01!, as evidenced by the 'acid, 1% chromic acid and 0.5% metallic aluminum dissolved in the phosphoric acid, this bath being electrolyzed and water being added to the bath until all the hexavalent chromium has been reduced to trivalent chromium.
• Bath No. 2 may be prepared similarly to bath No. 1.
• Copper is electropolished in bath No. 1, with very little or no agitation, to a brilliant, mirrorlike finish at 100 to 2 amperes per square foot at a temperature'o't' from 110 to 125 F.
• Bath No. 2 electropolishes copper well at a current density of 150 amperes per-square foot at a temperature of 120 F. The operative temperature ranges at various current densities for bath No. 2
• Temperatures lower than the indicated minima may be employed but then provisions must be made for cooling the baths. At current densities of at least 200 amperes per square foot, temperatures of 170 F. or higher may be employed with ood results.
• bath No. 2 requires a slightly longer time than bath No. l, which has greater anode efllciency.
• Table II assume of divalent copper, trivalent chromium and trivalent aluminum) of less than 2.5%. Theinfluence of dilution on cell voltage and current emciency when electropolishing at1120 F. and a current density of 150 amperes per square toot is indicated in the following table:
• Table V further indicates the critical importance of the aluminum content of the baths according tothe present invention. This table. further shows that the presence and concentration of chromium are not critical. This table is in- Current den- If the water concentration is over 23 to 25% in the type of bath exemplified by baths Nos. 1 and 2, good electropolishing is not secured at a current density below amperes per square foot, at temperatures above 110 F., or at a metal 7 concentration (including the total concentration The eilect at 120 F. and a current density r 150 amperes per square foot of aging on baths according to the present invention and on baths T6016 7 Tabla VIII Q mmaluminum Noaluminnm mp Jrr flw ammo. am Or.0.4%Al 0.2%.01
• Tables I to 1x include data showing that the inclusion oi. trivalent aluminum with phosphoric acid makes possible continuous electropolishing of copper in the resulting bath, dissolved copper being recovered as electropolishing is continued.
• chromium is not harmful, but does not add to the efliciencyot the bath.
• a larger cathode area lowers cell voltage and raises current eihciency for plating out copper during electropolishing.
• the bath having an original composition in-- cluding 84% HaPO4, 1% CrOa and 0.5% A1 is similar to bath No. 2 discussed on page-4.
• An electrolyte ioruse in the anodic polishing of'copper containing from to 84% by weight ortho phosphoric acid and from 0.25 to 2% trivalent aluminum, the balance comprising essentially water.
• An electrolyte for use in the anodic polishing of copper containing from '15 to 84% by weight ortho phosphoric acid, from 0.25 to 2% trivalent aluminum, and from 0.3 to 1% divalent copper, the balance comprisir'rg essentially water.
• the method of electrolytically polishing copper which comprises making the copper the anode in an electrolyte comprising from 75 to 84% by weight ortho phosphoric acid and from 0.25 to 2% trivalent aluminum, the balance comprising essentially water, and at a temperature of at least 100 F. passing current therethrough of sufllcient density and for a sufflcient period of time to effect a polish on said copper.
• the method of electrolytically polishing copper which comprises making the copper the anode in an electrolyte containing from '75 to 84% by weight .ortho phosphoric acid, from 0.25 to 2% trivalent aluminum, and from 0.3 to 1% divalent copper, the balance comprising essentially water, and at a temperature of at least 100 F. passing current through said electrolyte at a sufflcient current density and for a suiiicient period of time to effect a polish on said copper.
• the method of electrolytically polishing copper which comprises making the copper the anode by weight orthophosphoric acid, from 0.25% to 2% trivalent aluminum, and from 0.3 to 1% divalent copper, the balance comprising essentially water, and passing a current through said elec trolyte at a temperature of from 100 to 170 F. at a current density of from to 250 amperes per square foot, the exact current density depending upon the temperature as indicated by the follow ng table:

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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)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electrolytic Production Of Metals (AREA)

Priority Applications (10)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23748371

Family Applications (1)

Country Status (8)

Cited By (4)

• 0
  • BE BE478066D patent/BE478066A/xx unknown
  • NL NL68813D patent/NL68813C/xx active
  • LU LU28771D patent/LU28771A1/xx unknown
• 1942
  • 1942-04-24 US US440337A patent/US2366714A/en not_active Expired - Lifetime
• 1943
  • 1943-01-13 GB GB648/43A patent/GB558726A/en not_active Expired
  • 1943-01-13 GB GB649/43A patent/GB558727A/en not_active Expired
• 1946
  • 1946-02-28 FR FR922994D patent/FR922994A/fr not_active Expired
• 1947
  • 1947-08-08 CH CH270547D patent/CH270547A/fr unknown
• 1950
  • 1950-09-26 DE DES19568A patent/DE833287C/de not_active Expired

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