Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D1/00—Electroforming
  • C25D1/04—Wires; Strips; Foils
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/38—Improvement of the adhesion between the insulating substrate and the metal
  • H05K3/382—Improvement of the adhesion between the insulating substrate and the metal by special treatment of the metal
  • H05K3/384—Improvement of the adhesion between the insulating substrate and the metal by special treatment of the metal by plating
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/03—Conductive materials
  • H05K2201/0332—Structure of the conductor
  • H05K2201/0335—Layered conductors or foils
  • H05K2201/0355—Metal foils
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/03—Metal processing
  • H05K2203/0307—Providing micro- or nanometer scale roughness on a metal surface, e.g. by plating of nodules or dendrites
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/07—Treatments involving liquids, e.g. plating, rinsing
  • H05K2203/0703—Plating
  • H05K2203/0723—Electroplating, e.g. finish plating
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing of the conductive pattern
  • H05K3/241—Reinforcing of the conductive pattern characterised by the electroplating method; means therefor, e.g. baths or apparatus

Definitions

• This present invention relates to the art of electroplating and more particularly to a method for producing electrodeposits of copper particularly useful for manufacturing printed circuits.
• This invention is applicable to the formation of both conventional electrodeposited copper foil, as well. as so called “ultra-thin” electrodeposited foils of copper on an aluminum carrier. While the present invention will be primarily described in the context of conventional unsupported foils, it is not intended in any way to be limited to such foils, but rather to also include foils of copper on an aluminum or other carrier. These unsupported foils' may have a thickness on the order of from about 12 to about 35 microns or more, while so called supported foils are usually on the order of from about 5 to 12.0 microns and are typically deposited on an aluminum sheet of 50 to 75 microns.
• the term support is intended to include any suitable substrate, while the term aluminum is intended to embrace the commercially pure metal as well as alloys of the metal which are predominantly aluminum.
• the well known basic techniques for manufacturing printed circuit boards involves depositing copper on a revolving drum or on a temporary carrier such as a sheet of aluminum; optionally applying a treatment coating to the exposed surface of the copper foil (such as taught for example in U.S. Patent No. 3,585,010); applying the exposed or treated surface of the copper to a printed circuit board, such as an epoxy resin impregnated fiberglass mat or substrate; bonding the copper surface to the epoxy resin through the use of heat and pressure, and then removing the temporary carrier if any.
• a treatment coating such as taught for example in U.S. Patent No. 3,585,010
• a printed circuit board such as an epoxy resin impregnated fiberglass mat or substrate
• bonding the copper surface to the epoxy resin through the use of heat and pressure, and then removing the temporary carrier if any.
• the foil In order for this laminate of copper foil on the resinous substrate to yield a quality printed circuit board, among other properties the foil must be highly pore-free and securely bondable to the substrate, this is particularly critical with thin foils.
• One way to improve the bond between the copper foil and the substrate is to produce a nodularized exposed surface on the copper foil, such as by producing a dentritic outer surface.
• peel strength is a conventionally used term to refer to the strength of the bond between the foil and the resinous substrate. Peel strength in excess of about 7 lbs./in., according to the standardized measuring method ASTM D/1867 is generally deemed necessary to satisfy printed circuit requirements.
• the multi-step process although capable of producing pore-free foil with a nodularized outer surface does have the drawback of requiring close control and regulation between the steps. Not only does each step need careful monitoring but also process variables of each step such as bath composition, current density in the bath, temperature, etc. must be carefully coordinated with those of each other step. For example, if a two-step process is used in which the bath composition is changed in the second step, close coordination is needed between bath composition and other variables in the first step with the new bath composition of the second step. These control and coordination requirements do not yield a simple process. Even with careful control of this multi-step process, its complexity often gives rise to reliability problems. Additionally, the multiplicity of steps would give rise to the need for more space and equipment and corresponding expense associated with them.
• Another object of the present invention is to provide a one-step copper electroplating process which yields a uniform, virtually pore-free copper foil with a nodularized surface for strong adherence to an epoxy resin impregnated fiberglass circuit board.
• Yet another object of the present invention is to provide a process which increases initial copper nucleation and provides a nodularized outer surface.
• Figure 1 is a schematic illustration, in partial cross-section, of one apparatus suitable for the practice of the present invention.
• Figure 2 is a schematic illustration, in partial cross-section, of another apparatus suitable for the practice of the present invention.
• Figure 3 is a schematic illustration, in partial cross-section, of yet another apparatus suitable for the practice of the present invention.
• the present invention concerns the providing of a process for electroplating copper in one single step which provides a highly pore-free ultra-thin foil with a nodularized outer surface.
• the present invention involves a process particularly suitable for providing highly pore-free, foil with a nodularized surface for strong adhesion to a printed circuit board by electroplating copper, in a single step in an acidic copper bath in which at least two different current densities are employed.
• This process is typically performed employing a drum, or a carrier material such as aluminum as the cathode surface, and at least two anodes, at least one primary anode, and at least one treatment anode.
• the present invention concerns a process for electroplating copper foil which increases initial copper nucleation for pore-free foil and provides a nodularized outer surface.
• the present invention involves a process for producing surface treated metal foil, said process comprising: providing an electrolytic cell having an electrolyte and a cathodic surface immersed in said electrolyte, said electrolyte containing a concentration of metal ions; applying a first current density in a first zone for plating a relatively smooth metal foil deposit on said cathodic surface; and superimposing a second current density having a magnitude greater than the limiting current density over said first current density in a second zone, said second current density forming a plurality of dendrites on said metal deposit and said first current density plating an additional metal deposit on said metal foil for firmly bonding said dendrites to said metal foil in said second zone.
• the copper foil is electrodeposited on the surface of a rotating drum cathode in an acid copper bath, employing at least one primary anode, and in addition, at least one treatment or high current density anode which provides a high current density to produce a nodularized surface on the copper foil.
• the treatment effected by the high current density anode is preferably effected at or near the exit of the copper foil from the bath.
• the carrier serves as the cathodic surface.
• an aluminum carrier is cleaned, etched in a caustic solution, rinsed and then pretreated with an alkaline, aqueous alkali metal zincate solution containing one or more water soluble salts selected from the group consisting of iron, cobalt and nickel salts.
• This coating is then substantially entirely removed by treating it with acid yielding a uniform thin oxide parting layer on the aluminum.
• This parting layer which is more fully explained in U.S. Patent No. 3,969,199, assigned to the assignee of the present application, and incorporated herein by reference, provides an aluminum surface suitable for uniform high density copper nucleation during copper electrodeposition.
• the apparatus illustrated in Figure 1 comprises an electrolytic cell having a tank 10 formed from a suitable inert material such as lead or stainless steel.
• the tank 10 may be formed from an appropriate non-conducting material such as concrete and lined with a metal, such as lead or stainless steel, or a nonmetallic material such as polyvinvlchloride or rubber.
• a drum cathode 12 is mounted for rotation by suitable conventional mounting rae ⁇ ans not shown.
• the drum cathode may be formed from any suitable electrically conductive metal or metal alloy including lead, stainless steel, columbium, tantalum, titanium and alloys thereof.
• the drum cathode comprises a stainless steel drum having a polished plating surface formed from titanium, chromium, columbium, tantalum or an alloy thereof.
• the drum cathode 12 may be rotated by any suitable motor drive arrangement (not shown) known in the art.
• the drum cathode 12 is mounted in the tank 10 so that it is at least partially immersed in an electrolyte solution 14. In a preferred arrangement, about half of the drum cathode extends beneath the surface of the electrolyte 14.
• the electrolyte 14 generally comprises an acidic solution containing a concentration of ions of a metal to be electrodeposited.
• the electrolyte 14 contains a concentration of copper ions.
• the electrolyte 14 comprises a copper sulfate-sulfuric acid solution.
• the solution while mixed at room temperature, is preferably maintained at a slightly elevated temperature.
• the solution has a concentration of copper, preferably in the form of copper sulfate of about 10 grams/liter, hereinafter g/1, to about 60 g/1, preferably from about 15 g/1 to about 40 g/1.
• the sulfuric acid can be present in the electrolyte 14 in a concentration up to that which causes copper to precipitate out as copper sulfate.
• the concentration of sulfuric acid for an electrolyte substantially at room temperature is from about 10 g/1 to aout 100 g/1.
• the aforementioned copper sulfate and sulfuric acid concentrations are dependent upon the electrolyte temperature.
• the tank 10 is provided with means not shown for maintaining the electrolyte temperature at a desired level.
• the temperature maintaining means may comprise any suitable means known in the art such as a heating and/or cooling loop.
• the copper sulfate concentration range may be increased beyond the aforementioned concentration range because its solubility limit increases with temperature.
• a proteinaceous material such as gelatin and/or a suitable surfactant may be added as is known in the art to the copper sulfate-sulfuric acid electrolyte to further facilitate the surface treatment process.
• At least one arcuate insoluble primary anode is mounted in the tank 10 in close proximity to the rotating drum cathode 12.
• the purpose of the primary anode or anodes is to plate onto the drum surface 30 a relatively smooth deposit of metal from the electrolyte 14. While any number of primary anodes may be used, it is preferred as shown in Fig. 1 to use two arcuate anodes 16 and 17. It is also preferred to arrange the primary anodes 16 and 17 substantially concentric with the rotating drum cathode 12 and to space each anode from the drum surface 30 by a distance of about 4 mm. to about 25 mm. Most preferably, each anode is spaced from the drum surface 30 by a distance in the range of about 5 mm. to about 15 mm.
• the primary anodes 16 and 17 may be mounted in the tank 10 by any suitable conventional mounting device or devices not shown.
• the primary anodes 16 and 17 are preferably arranged with respect to each other so as to form an electrolyte passageway 18.
• the electrolyte is caused to flow through the passageway 18 and into the gaps 20 between the primary anodes 16 and 17 and the drum surface 30 by a pump not shown. Any suitable pump known in the art may be used to create this electrolyte flow.
• a manifold not shown may be mounted in the tank 10 adjacent the lower portion of the passageway 18 to assist in distributing electrolyte to the passageway 18.
• the primary anodes 16 and 17 may be formed from any suitable electrically conductive material known in the art. For example, they can be formed from a variety of metals particularly lead or alloys thereof well known in the art. Anodes 16 and 17 may also be called “diraensionally stable anodes" or "DSA" such as those disclosed and claimed in U.S. Patent Nos. 3,265,526, 3,632,498 and/or 3,711,385. Both anodes 16 and 17 are electrically connected to a common power supply 22. Any suitable electrical connection can be made between the power supply 22 and anodes 16 and 17. The operation of the primary anodes 16 and 17 during the foil fabrication process is discussed below.
• a zone high current density for applying a dendritic layer to the electrodeposited foil is created by one or more treatment anodes 24 in the end portion of the anode 17.
• Each treatment anode 24 may be electrically insulated from the anode 17 by an air gap or suitable dielectric material (not shown) which completely separates it from the anode 17. Where a dielectric material is used, any suitable dielectric material known in the art may be utilized.
• each treatment anode 24 is joined to anode 17 in such a manner that a substantially smooth anode face 32, all portions of which are substantially equidistant from the drum surface 30, is formed.
• the spacing between each treatment anode is preferably from about 1- to about 3 times the gap beween the anode surface and the drum surface. Most preferably, the spacing between treatment anodes is from about 1.0 to about 2.5 times the gap between the anode and the cathode surfaces 32 and 30, respectively.
• Each treatment anode 24 is electrically connected to a power supply which is separate and distinct from the primary power supply.
• a power supply which is separate and distinct from the primary power supply.
• each power supply could be a rectifier for applying a DC current or a variable power supply having means for generating a current having a regularly recurring pulse wave such as a sine wave, a square wave, a triangular wave or any other desired waveform.
• the electrolyte 14 is pumped into the passageway 18 and the gaps 20 between the primary anodes 16 and 17 and the rotating drum cathode 12 at a desired flow rate.
• a first current sufficient to generate a desired base current density is applied to the primary anodes 16 and 17 by the primary power supply.
• the base current density should be below the limiting current density.
• metal from the electrolyte 14 is deposited onto the drum surface 30 in the primary plating zone. Since the base current density is preferably less than the limiting current density, a relatively smooth metal deposit having a substantially uniform thickness, e.g. a metal foil, forms on the drum surface 30.
• a second current is applied to the treatment anode or anodes 24.
• the second current should be sufficient to generate in the treatment zone a second current density greater than the limiting current density.
• the second current may be a pulsed current having a first portion during which the second current density is greater than the limiting current density and a second portion during which the second current density is less than the limiting current density. While the second current is being applied to the anode or anodes 24, the first current is being applied to the anode or anodes 24, the first current is preferably still being applied to the anode 17.
• the electrolyte 14 should flow through the passageway 18 and the gaps 20 at a flow rate in the range of about 0.1 m/sec to about 4 m/sec, preferably from about 1 m/sec to about 2.5 m/sec.
• the base current density should be from about 0.2 A/cm 2 to about 2 A/cm7, preferably from about 0.75 A/cm2 to about 1.5 A/cm .
• the second current density superimposed over the base current density should be an average current density from about 1.1 A/cm 2 to about 6 A/cm 2 , preferably from about 2 A/cm 2 to about 3 A/cm 2 .
• the treated metal foil 28 may be removed from the drum cathode 12 in any suitable manner known in the art.
• a knife blade not shown may be used to strip the treated foil from the drum cathode.
• the foil may be rinsed, dried, slit to size, rolled onto a take-up reel 13 and/or passed onto one or more treatment zones for one or more additional treatments, such as for example taught by U.S. Patent 3,585,010 noted hereinbefore.
• the cell of Fig. 1 has been shown as having two primary anodes 16 and 17 forming a central fluid passageway 18, a single insoluble arcuate anode not shown may be used in lieu of the anodes 16 and 17.
• one or more openings should be provided in the central portion of the anode to permit electrolyte flow into the gap betwen the rotating drum surface and the anode surface.
• the treatment anode or anodes would be located as before forming the treatment zone.
• the treated metal foil may also be produced in a batchwise fashion if it is so desired.
• a pulsed current applied to a portion of at least one primary anode could be used in lieu of the treatment anode or anodes 24 to apply the dendritic treatment to the foil.
• the pulsed current has a first portion during which a first current density in excess of the limiting current density is produced and a second portion during which a second current density less than the limiting current density is provided.
• a metal foil Prior to the application of the pulsed current, a metal foil is electrodeposited in a conventional manner on a moving cathodic surface immersed in an electrolyte.
• the pulsed current is then applied for a relatively short time period as compared to the time period needed to produce the metal foil to apply the dentritic treatment to the metal foil.
• the pulsed current must be of sufficient density and duty cycle (on time) to deposit dendrites of copper.
• the density of the pulsed current is in the range of from about 2,000 to about 10,000 amps per square foot with a duty cycle of from about 10 to 90t, preferably from abut 40 to 60 .
• two high current density zones are employed, one at the exit end of the bath using anode 24, as in the embodiment of Fig. 1, and a second high current density zone at the entrance end of the bath using anode 25, which is constructed and insulated in a manner similar to that previously set forth hereinbefore with respect to anode 24.
• the high current density zone at the entrance end provided using anode 25, provides the highly desirable nucleation centers noted hereinbefore which facilitate formation of pore-free foil.
• Anode 25 may operate at the same current density as anode 24, or using a third power supply means, at a higher or lower current density than anode 24.
• anode 25 may be connected to a switch means, not shown, whereby it can be optionally connected to the second or third power supply means to operate at a high current density, or to the primary power supply means in which case it operates at the lower current density and becomes, in effect, an extension of primary anode 16.
• Fig. 3 illustrates yet another embodiment of the present invention in which a plurality of bar elements, designated a through h, are employed as anode 16 and anode 17.
• a plurality of bar elements designated a through h
• One or more of the bar elements a, b, and/or c of anode 17 can be insulated from the remaining bar elements forming anode 17, and suitably connected to the second power supply means, can serve instead as high current density anode 24.
• one or more of the bar elements a, b, and/or c of anode 16 can be insulated from the remaining bar elements forming anode 16, and suitably connected to the second or third power supply means, can serve instead as high current density anode 25.
• dendrites are caused to grow from the deposit already on the cathodic surface and they will be well adhered to the base foil. If the current density exceeds the optimum, the deposit will be more powdery than dendrites, and an additional deposit of smooth copper may be required to insure adhesion of the "powdery" dendrites.
• the treated metal foil produced by the present invention may be laminated to an appropriate substrate.
• the particular substrate used in the laminate will vary depending upon the use of which the laminate is intended and the service conditions under which the laminate will be used.
• Particularly approprate substrates include polytetrafluorethylene- impreganted fiberglass, polyimides, fiberglass impregnated by certain fluorocarbon products including polymers of trifluorochloroethylene and certain copolymers, and the like.
• an adhesive may be used to bond the treated foil to the substrate. Any suitable conventional technique known in the art may be used to bond the treated foil to the substrate.
• the technique of the present invention is equally applicable to the electrodeposition of other metals including but not limited to lead, tin, zin, iron, nickel, gold and silver.
• other metals including but not limited to lead, tin, zin, iron, nickel, gold and silver.
• the type of electrolyte, the metal and acid concentrations in the electrolyte, the flow rate, and the current densities used will have to be altered in accordance with the metal being plated.
• cathode for the plating apparatus has been described as being a rotating drum cathode, it is as earlier noted possible to perform the process of the present invention using an endless belt-type cathode, i.e., a carrier support.
• treatment anodes have been illustrated as having a bar shape, they may also as noted be round shaped or they may have square, oval, elongated or any other suitable shape.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electroplating Methods And Accessories (AREA)
• Electrolytic Production Of Metals (AREA)
• Physical Vapour Deposition (AREA)
• Polymers With Sulfur, Phosphorus Or Metals In The Main Chain (AREA)
• Laminated Bodies (AREA)
• Coupling Device And Connection With Printed Circuit (AREA)
• Control Of El Displays (AREA)
• Spinning Or Twisting Of Yarns (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25211440

Family Applications (1)

Country Status (13)

Cited By (4)

Families Citing this family (46)

Citations (2)

Family Cites Families (2)

• 1986
  • 1986-12-23 HU HU87913D patent/HU208556B/hu not_active IP Right Cessation
  • 1986-12-23 WO PCT/US1986/002797 patent/WO1987003915A1/en not_active Ceased
  • 1986-12-23 AU AU68981/87A patent/AU602673B2/en not_active Ceased
  • 1986-12-23 FI FI873643A patent/FI873643L/fi not_active Application Discontinuation
  • 1986-12-23 DE DE87900763T patent/DE3688840T2/de not_active Expired - Fee Related
  • 1986-12-23 AT AT87900763T patent/ATE92544T1/de not_active IP Right Cessation
  • 1986-12-23 EP EP87900763A patent/EP0252139B1/en not_active Expired - Lifetime
  • 1986-12-23 BR BR8607061A patent/BR8607061A/pt not_active Application Discontinuation
• 1987
  • 1987-01-27 IN IN78/CAL/87A patent/IN166842B/en unknown
  • 1987-08-21 NO NO873533A patent/NO873533L/no unknown
  • 1987-08-24 DK DK439887A patent/DK439887A/da not_active Application Discontinuation
  • 1987-12-23 JP JP62326681A patent/JPS63241193A/ja active Granted
• 1988
  • 1988-12-22 US US07/288,472 patent/US4898647A/en not_active Expired - Lifetime

Patent Citations (2)

Also Published As

Similar Documents

Legal Events