EP0025220A1 - Dépôt d'or dur sans additif par voie électrolytique et produit obtenu - Google Patents

Dépôt d'or dur sans additif par voie électrolytique et produit obtenu Download PDF

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Publication number
EP0025220A1
EP0025220A1 EP80105298A EP80105298A EP0025220A1 EP 0025220 A1 EP0025220 A1 EP 0025220A1 EP 80105298 A EP80105298 A EP 80105298A EP 80105298 A EP80105298 A EP 80105298A EP 0025220 A1 EP0025220 A1 EP 0025220A1
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EP
European Patent Office
Prior art keywords
gold
fluid
plating
percent
process according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP80105298A
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German (de)
English (en)
Inventor
Daniel Robert Blessington
Reginald Russ Buckley
Frederick Bayard Koch
Yutaka Okinaka
Richard Sard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Western Electric Co Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Western Electric Co Inc filed Critical Western Electric Co Inc
Publication of EP0025220A1 publication Critical patent/EP0025220A1/fr
Withdrawn legal-status Critical Current

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    • 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
    • C25D5/02—Electroplating of selected surface areas
    • 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
    • C25D3/48—Electroplating: Baths therefor from solutions of gold
    • 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
    • C25D5/08—Electroplating with moving electrolyte e.g. jet electroplating
    • 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
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
    • C25D5/611—Smooth layers

Definitions

  • the invention is concerned with gold electroplating procedure and resulting product. More specifically, the invention is concerned with gold electroplate of hardness and wear characteristics generally associated with so-called "hard gold”. Such gold is of significance in electrical switch contacts, and in a variety of other devices, as well as in ornamentation.
  • the noble metal elements particularly gold, have found extensive use because of their resistance to corrosion.
  • Gold generally as electroplated, is of extreme device interest as contact surface in electrical switches of a variety of designs. Aside from silicon and its related compounds, gold is the one element common to large-scale integrated circuits. Due, again, to corrosion resistance and, consequently, retention of initial appearance, gold has been used for ornamentation since ancient times. This field, to a large extent, too, is preempted by electroplating.
  • Elemental gold is a physically soft material with generally poor wear qualities. Twenty-four karat (pure) gold is impractical for most uses. A variety of alloying elements improve these qualities without significantly affecting corrosion resistance, and resultant alloys are in extensive use.
  • hard gold generally takes the form of gold of reasonable purity containing tenths of a percent of an alloying ingredient. Alloying ingredients in prevalent use, particularly in electroplated hard gold, are cobalt and nickel. Decades of use have yielded a sophisticated technology with baths of well- controlled composition and long shelf life, and with processes characterized by reliability and high throughput.
  • Bath compositions generally contain gold and other metallic ingredients in complexed or ionic form with the gold introduced often as a potassium or sodium cyanide salt.
  • hard gold bath compositions are buffered to acid or near neutral pH values, for example, in citrate or phosphate systems. Initially introduced to avoid substrate attack, for example, on phenol formaldehyde impregnated circuit boards, such buffered baths have other advantages and are in general use.
  • contact resistance is a function of and is strongly dependent upon closely controlled alloy metal concentration. Further, it has been observed that contact resistance, at an acceptable level on a freshly plated structure, deteriorates with age. Other studies are directed at economic implications in processing, so that there is a constant emphasis on improving throughput and, generally, on reducing cost.
  • AFHG electroplate produced in accordance with this invention from buffered cyanide bath under specified plating conditions satisfies demanding requirements, for example, for electrical switch use.
  • AFHG electroplate of the invention is characterized by a high degree of surface smoothness as well as values both of physical hardness and initial contact resistance comparable to cobalt hardened gold electroplate. Aging, either shelf or in use, results in little change in contact resistance relative to that experienced with cobalt hardened gold--an advantage likely attributable to the aging mechanism for cobalt hardened gold electroplate (which invokes the surface oxidation of initially present or migrating cobalt to form the resistive compound CoO). As expected, some cost reduction results from simplification of the bath chemistry.
  • plating efficiency is high. Typical values are at least twice that of plating from usual additive hardened gold bath solutions. Under many circumstances, increased limiting current conditions are permitted so that actual plating rate and, therefore, throughput may be increased.
  • contemplated flow conditions of the bath fluid in the vicinity of the workpiece is at about 50 cm/sec or preferably 100 cm/sec or higher.
  • Nonimmersion apparatus may permit equivalent agitation at lower bulk liquid flow.
  • nonconventional means of agitation i.e., nonimmersion apparatus, fins, or other provision for "spoiling" streamline flow
  • bulk flow may be lower.
  • Other preferred processing parameters are set to satisfy high throughput. These include gold concentration of at least 5 g/1 expressed as elemental gold, plating current density greater than 5 mA/cm 2 and a temperature range of from about 0-50 degrees C..
  • FIG. 1 depicts a "rug" electroplating apparatus 1 consisting of recepticle 2 containing electroplating bath 3.
  • Workpiece to be plated is depicted as 4 which may be a front elevational view of the first of a series of separable connectors to be plated on both of faces 5 and 6.
  • Bath is partly carried and partly projected at surfaces 5 and 6 by means of rotating electrodes 7 and 8, each provided with looped pile fabric surfaces 9 and 10, respectively.
  • Stop 11 serves as a support for workpiece 4 and may also assure an appropriate path for bath carried by electrodes 7 and 8.
  • Jaws 12 and 13 adjustable as schematically depicted by the double-headed arrows are tipped by titanium members 14 and 15. Jaws 12 and 13 are biased cathodic relative to rotating electrodes 7 and 8 by means not shown and thereby serve both as guides and electrical contacts for workpiece 4.
  • FIG. 2 is a schematic representation of a typical strip plating line 20. As depicted, pieceparts on a continuous strip 21 are fed through the line by capstans 22 and 23. Processing positions 24-28 are defined by partitions within common member 29. Each reservoir is provided with means for circulating fluid contents--such means including schematically depicted outlet path 30 and inlet path 31 with such paths connecting processing positions 24-28 with reservoirs 32-36.
  • processing positions may include electrocleaning at 24 (workpieces reverse biased with the processing fluid typically consisting of a strong alkali solution), electropolishing at 25, (again, with the workpiece anodic, and with the fluid typically consisting of a highly viscous acid (such as phosphoric acid), nickel plating at 26, gold strike plating at 27, possibly by AFHG plating, but here using a highly dilute solution and high current density to cause high hydrogen evolution and to "scrub" the surface to be plated and, finally, the inventive AFHG plating at 28.
  • electrocleaning at 24 workpieces reverse biased with the processing fluid typically consisting of a strong alkali solution
  • electropolishing at 25 (again, with the workpiece anodic, and with the fluid typically consisting of a highly viscous acid (such as phosphoric acid), nickel plating at 26, gold strike plating at 27, possibly by AFHG plating, but here using a highly dilute solution and high current density to cause high hydrogen evolution and to "scrub" the surface to be plated
  • FIG. 3 depicts an in-line plating cell 40 suitable for incorporation at 28 in FIG. 2.
  • the cell consists of recepticle 41, containing a plenum 42, which carries a moving stream of plating solution 43. Fluid 43 is maintained under pressure to result in jet 44 emanating from slit 45.
  • Control means for positioning of jet 44 include movable plate 46 provided with vertical adjusting means 47, as well as plenum 48 which carries pressurized gas 49 to result in stream 50, which emanates through slit 51.
  • the workpiece 52 depicted may, again, be regarded as a separable contact which is maintained in position, while moving by walls 53 and 54, as well as roller support 55. As shown, workpiece 52 is to be plated only on lower portion of surface 56. Overplating on surface 57 is prevented by means of gas stream 50. In operation, workpiece 52 is biased cathodically relative to plenum 42 which is biased anodically both by means not shown. Recirculating means also not shown includes reservoir 58.
  • FIG. 4 on coordinates of Knoop hardness under 25 grams load on the ordinate, and plating temperature in degrees Celsius on the abscissa, is a typical curve form showing the relationship between those two parameters.
  • the high temperature limit of 70 degrees C shown is outside the inventive scope and is barely sufficient to result in a hardness of value of 90.
  • the low temperature limit of zero degrees C is not limiting in these terms.
  • All processing in accordance with the invention presupposes conditions yielding a hard plate--i.e., a plate of at least 90 and preferably at least 100 on the Knoop hardness scale.
  • This desideratum requires only operation at or below 50 degrees C or preferably at or below 45 degrees C.
  • Other variables are considered in terms of surface smoothness--i.e., a surface topology in which elevation variations are no greater than about 0.5 pm total peak-to-valley as measured over a sample area 5 pm square. In these terms, such processing variables and convenient units are:
  • Mass transport limiting current density (the total current beyond which gold deposition rate does not increase, i 1 (mA/cm 2 )
  • Certain practical limits may be set on operating parameters. These are based on a plating rate of at least 0.01 pm/sec and include:
  • This section is largely in terms of a permissible throughput corresponding with a plating rate of at least 0.01 pm/sec.
  • Agitation For most commercial processing, at least on a regular basis, it is expected that processing will take the form of throughput values which approach permissible limits for particular equipment. Equipment limitations are most significant in terms of agitation. Preferred embodiments are described in terms of agitation resulting in flow rates of at least 25 cm/sec or at least about 50 or 100 cm/sec in order of increasing preference.
  • the general purpose of agitation is to increase the transport limited current so as in turn to decrease the fraction represented by the actual current density divided by the transport limited current density. As discussed, requisite surface smoothness results from a lessening value of this fraction. Where no unusual provision is made for disturbing streamline flow, desired smoothness is realized only with for flow rates of at least 50 cm/sec or preferably at least 100 cm/sec. Such rates are used in apparatus such as that depicted in FIG. 3. Provision of baffles, fins, ultrasonic vibration, etc. permits attainment of desired surface smoothness for somewhat lower bulk flow rates and for this purpose a minimum of about 25 cm/sec is generally prescribed. Use of nonimmersion equipment, such as that depicted in FI G . 1, may permit such low bulk flow rate or even lower values. Here the general mechanism by which bath fluid is transported to the workpiece gives rise to the requisite degree of agitation.
  • agitation defines that condition which obtains at some distance from the surface being plated. This distance corresponds with the thickness of the "hydrodynamic boundary layer.”
  • Use of "flow rate” or “bulk flow rate” refers to flow rates as measured outside of this boundary layer. Measurement at a distance of a millimeter is appropriate.
  • the maximum permissible temperature remains at about 50 degrees C. Higher temperatures result in coatings of lowered hardness values. A low temperature limit of about 0 degrees C is considered a practical limit due to lowered efficiency, as well as reduced throughput. The maximum temperature is somewhat arbitrary, since further decrease results in increased hardness. A preferred maximum temperature is 45 degrees C.
  • This paramater is not truly an independent variable but results directly from the current density and plating efficiency. Preferred embodiments are considered to correspond with a plating rate of at least about 0.03 pm/sec. Experimentally, this plating rate was found to correspond with a current density of about 50 mA/cm 2 .
  • a Gold Gold, always measured in terms of equivalent elemental content, is desirable at a level of 25 grams/liter or higher. In common with other plating processes, gold content may become limiting for high throughput; and, accordingly, the solubility limit may be approached. All results obtained have been from cyanide solution and the invention is discussed in terms of alkali metal gold cyanide regardless of the form in which gold is initially introduced.
  • the alkali metal is usually potassium so that gold content is considered to be in the nominal form KAu(CN) 2 .
  • Lithium salts are an order of magnitude more soluble than potassium salts and may be particularly useful for very high throughput processes.
  • cyanide is considered essential for AF H G plating and at least some amount of cyanide must be present in the bath to realize required hardness. For these purposes, it is considered that the amount of cyanide must be such as to satisfy the nominal formula KAu(CN) 2 for at least 50 percent of the gold in the bath.
  • B pH Modifier Useful results in accordance with the inventive teaching have been realized only at bath pH below about 9.0 with a preference for a pH maximum of about 7.5.
  • pH is a relevant quantity for ideal plating morphology. While smooth coatings may result at somewhat higher pH values, practical buffer systems are largely within a range defined by that maximum and by a minimum of about 3.0. A system considered particularly desirable depends upon presence of phosphate ion. Accepted buffer systems are known.
  • K H 2 P0 4 has a natural buffer pH range over 4.3 - 4.5 (for 100 g/1 equivalent KH 2 P0 4 ).
  • the range may be shifted in the alkaline direction so that--e.g., addition of 28 g/1 KOH results in a pH range of 6.8 to 7.2.
  • buffer is not intended to serve as a rigorous, mechanistic description. Ranges set forth whether “buffered” or not are conveniently maintained in bath compositions indicated.
  • Phosphate ion has the desired effect of cleansing the bath of nonnoble metal ingredients. Such contaminants are precipitated out in the form of phosphates. Other acidifying ingredients may otherwise be substituted in whole or in part. Such subsitutions include citrate ion, possibly considered present as potassium citrate. Use of citrate ion, again, as optionally supplemented by a soluble base, such as KOH, results in an easily maintained pH range of from 3.0 to 6.0.
  • C Reducing Agent as in other gold plating, formation of Au(III) is a contributor to diminishing plating efficiency. In the inventive processes, permitted throughput may also suffer. Addition of reducing agent may lessen this source of inefficiency. Reducing agents should be chosen so as to avoid contamination to levels above those indicated in section D below. Hydrazine hydrate has been slowly added as Au(III) forms to maintain initial plating efficiency. Use of excess hydrazine, however, results in reduction of Au(I) and, consequently, in decomposition of the bath.
  • IV APPARATUS Suitable apparatus is exemplified by that depicted in FIGS. 1, 2, and 3. Other apparatus permitting agitation and plating rates set forth may be used. Common to other gold plating processes, gold may be introduced as a soluble bath constitutent or as an anode constituent. It has been noted that loss in efficiency results from oxidation of Au(I) -----> Au(III). Au(III) accumulation is significantly lessened by use of gold anode, with the probable mechanism based on anode gold dissolution preferential to oxidation. Anode dissolution was found to be impractically fast with loss of the anode after 100 hours of continuous plating for apparatus such as that depicted in FIG. 1 under one set of conditions.
  • An alternative designed to lessen Au(III) accumulation depends upon use of a ruthenium oxide/titanium oxide catalyzed anode.
  • the electrode structure is primarily titanium, which is coated with a mixture of the two oxides and is known as "dimensionally stable anode". (See U. S. Patent No. 4,067,783 issued January 10, 1978 (Okinaka et al Case 10-3). In one set of experiments using a dimensionally stable anode, Au(III) never exceeded 5 percent of total gold and current efficiency remained above 87 percent over four bath turnovers.
  • An alternative structure is coated with iridium oxide and tantalum oxide.
  • Hardness stability was measured by one hour anneals at temperatures of 250, 350, and 450 degrees C. There was no measurable softening at 250 degrees C and only at 450 degrees C was softening significant.
  • Coating growth at currents closely approaching i 1 may result in i l controlled deposition.
  • Current reduction to levels of 0.9 i l and lower permit equilibration at the interface so that coating is not i i limited but is controlled by random processes which tend both to prevent nodules and/or minimize nodule contribution to surface topology.
  • growth is both lateral and in the direction of the concentration gradient within the delta layer with any nodules thickening at rates presumed at least equal to that resulting in vertical growth.

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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)
  • Electroplating Methods And Accessories (AREA)
EP80105298A 1979-09-06 1980-09-05 Dépôt d'or dur sans additif par voie électrolytique et produit obtenu Withdrawn EP0025220A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US7306679A 1979-09-06 1979-09-06
US73066 1979-09-06

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EP0025220A1 true EP0025220A1 (fr) 1981-03-18

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JP (1) JPS5644791A (fr)
KR (1) KR830003601A (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0582353A1 (fr) * 1992-08-07 1994-02-09 International Business Machines Corporation Dépôt électrolytique d'or à faibles contraintes pour la fabrication d'un masque à rayons X
ES2166660A1 (es) * 1999-05-06 2002-04-16 Torres Josep Ferre Procedimiento y equipo para la electrodeposicion de oro o aleaciones de oro.
WO2006073960A3 (fr) * 2005-01-03 2006-10-12 Gillette Co Pile primaire a boitier plat
DE102005036133A1 (de) 2005-07-26 2007-02-01 Wieland Dental + Technik Gmbh & Co. Kg Bad für die galvanische Abscheidung von Gold und Goldlegierungen und Zusatzgemisch für ein solches Bad

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH444608A (de) * 1964-04-01 1967-09-30 Engelhard Ind Inc Elektrolytlösung zur Verwendung beim Gold-Elektroplattieren
CH480444A (de) * 1966-01-21 1969-10-31 Engelhard Ind Inc Elektrolytlösung zur elektrolytischen Ablagerung von Goldlegierungen
CH485863A (de) * 1966-02-23 1970-02-15 Engelhard Ind Inc Elektrolytlösung zur Verwendung bei der elektrolytischen Ablagerung von Gold
DE1941822B2 (de) * 1969-08-16 1972-12-28 Deutsch Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt Galvanisches goldlegierungsbad zur abscheidung definiert hoch- und niedriglegierter goldueberzuege
CH552069A (de) * 1969-07-03 1974-07-31 Engelhard Min & Chem Verfahren zum elektrolytischen ablagern von gold allein oder zusammen mit anderen matallen.
DE2523510B1 (de) * 1975-05-27 1976-10-14 Siemens Ag Saures galvanisches goldbad zum abscheiden von gold- oder goldlegierungsueberzuegen

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH444608A (de) * 1964-04-01 1967-09-30 Engelhard Ind Inc Elektrolytlösung zur Verwendung beim Gold-Elektroplattieren
CH480444A (de) * 1966-01-21 1969-10-31 Engelhard Ind Inc Elektrolytlösung zur elektrolytischen Ablagerung von Goldlegierungen
CH485863A (de) * 1966-02-23 1970-02-15 Engelhard Ind Inc Elektrolytlösung zur Verwendung bei der elektrolytischen Ablagerung von Gold
CH552069A (de) * 1969-07-03 1974-07-31 Engelhard Min & Chem Verfahren zum elektrolytischen ablagern von gold allein oder zusammen mit anderen matallen.
DE1941822B2 (de) * 1969-08-16 1972-12-28 Deutsch Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt Galvanisches goldlegierungsbad zur abscheidung definiert hoch- und niedriglegierter goldueberzuege
DE2523510B1 (de) * 1975-05-27 1976-10-14 Siemens Ag Saures galvanisches goldbad zum abscheiden von gold- oder goldlegierungsueberzuegen

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0582353A1 (fr) * 1992-08-07 1994-02-09 International Business Machines Corporation Dépôt électrolytique d'or à faibles contraintes pour la fabrication d'un masque à rayons X
US5459001A (en) * 1992-08-07 1995-10-17 International Business Machines Corporation Low stress electrodeposition of gold for x-ray mask fabrication
ES2166660A1 (es) * 1999-05-06 2002-04-16 Torres Josep Ferre Procedimiento y equipo para la electrodeposicion de oro o aleaciones de oro.
WO2006073960A3 (fr) * 2005-01-03 2006-10-12 Gillette Co Pile primaire a boitier plat
DE102005036133A1 (de) 2005-07-26 2007-02-01 Wieland Dental + Technik Gmbh & Co. Kg Bad für die galvanische Abscheidung von Gold und Goldlegierungen und Zusatzgemisch für ein solches Bad
DE102005036133B4 (de) 2005-07-26 2013-09-12 Wieland Dental + Technik Gmbh & Co. Kg Bad für die galvanische Abscheidung von Gold und Goldlegierungen und Zusatzgemisch für ein solches Bad
DE102005036133C5 (de) * 2005-07-26 2017-07-13 Ivoclar Vivadent Ag Bad für die galvanische Abscheidung von Gold und Goldlegierungen und Zusatzgemisch für ein solches Bad

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Publication number Publication date
JPS5644791A (en) 1981-04-24
KR830003601A (ko) 1983-06-21

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