EP1142456A1 - Process for depositing conducting layer on substrate - Google Patents

Process for depositing conducting layer on substrate

Info

Publication number
EP1142456A1
EP1142456A1 EP99958371A EP99958371A EP1142456A1 EP 1142456 A1 EP1142456 A1 EP 1142456A1 EP 99958371 A EP99958371 A EP 99958371A EP 99958371 A EP99958371 A EP 99958371A EP 1142456 A1 EP1142456 A1 EP 1142456A1
Authority
EP
European Patent Office
Prior art keywords
substrate
layer
conducting layer
ink
electrically conducting
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Withdrawn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
EP99958371A
Other languages
German (de)
French (fr)
Inventor
Darren Brunel University LOCHUN
David Brunel University HARRISON
Blue John Brunel University RAMSEY
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.)
Brunel University
Original Assignee
RT Microwave Ltd
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
Priority claimed from GBGB9826446.8A external-priority patent/GB9826446D0/en
Priority claimed from GBGB9826447.6A external-priority patent/GB9826447D0/en
Application filed by RT Microwave Ltd filed Critical RT Microwave Ltd
Publication of EP1142456A1 publication Critical patent/EP1142456A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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 the conductive pattern
    • H05K3/245—Reinforcing conductive patterns made by printing techniques or by other techniques for applying conductive pastes, inks or powders; Reinforcing other conductive patterns by such techniques
    • H05K3/246—Reinforcing conductive paste, ink or powder patterns by other methods, e.g. 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
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
    • H05K3/1275—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by other printing techniques, e.g. letterpress printing, intaglio printing, lithographic printing, offset printing
    • 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
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
    • H05K1/095—Dispersed materials, e.g. conductive pastes or inks for polymer thick films, i.e. having a permanent organic polymeric binder
    • 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
    • H05K2203/11—Treatments characterised by their effect, e.g. heating, cooling, roughening
    • H05K2203/1173—Differences in wettability, e.g. hydrophilic or hydrophobic areas
    • 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
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/18—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using precipitation techniques to apply the conductive material
    • H05K3/181—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using precipitation techniques to apply the conductive material by electroless plating
    • H05K3/182—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using precipitation techniques to apply the conductive material by electroless plating characterised by the patterning method
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a process for forming an electrically conductive layer on a substrate, and in particular to a process for forming such a layer on a substrate which can be used as a circuit board in an electrical assembly.
  • a printed circuit board generally consists of etched copper on glass fiber laminate, tin plated and possibly carrying further layers of lacquer for protection and labeling. Many operations of cropping, drilling, etching and plating are involved in its preparation. It is not cheap, and the production processes can have significant environmental impact.
  • waste effluent which is acidic and contains heavy metals (especially copper), and the use of hydrocarbons in photoresist developer and stripper.
  • Stricter pollution limits imposed by water authorities are one driving force to reduce copper in effluent.
  • waste effluent could be eliminated by a totally additive process for copper deposition, which would also offer considerable cost savings, but a satisfactory process has not yet been developed.
  • Resistors are formed on a ceramic substrate by depositing tracks of a suitable film, sometimes trimmed to precise values by laser etching. A film of higher conductivity is generally used for interconnection.
  • WO 97/48257 which has common applicants with the present application, the disclosure of which is incorporated herein, discloses an alternative method of forming an electrical circuit board, whereby a conducting ink is lithographically printed onto a substrate in order to form an electrical circuit.
  • the ink comprises electrically conductive particles (such as metallic silver) suspended in an organic resin such as an alkyd resin.
  • electrical components such as resistors, capacitors and antennae is also described.
  • circuit printing technique disclosed in WO 97/48257 is a significant improvement on previous techniques, it has a number of disadvantages.
  • particulate conductive material with a particulate surface treatment (e.g. a coating of a long chain fatty acid) to enable the particles to be dispersed in the resin in such a manner as to render the dried ink electrically conductive.
  • a particulate surface treatment e.g. a coating of a long chain fatty acid
  • this surface treatment precludes further treatment of the dried ink, for example it prevents deposition of a further conductive layer by electroless deposition.
  • a process for forming a conductive layer on the substrate comprising the steps of depositing ink on the substrate by means of lithographic printing to form a seeding layer, and depositing a first electrically conducting layer on the seeding layer by electroless deposition.
  • Electroless deposition is a well-known technique which involves coating an object (or part of an object) by means of a chemical reduction process, which, once initiated, is also-catalytic. The process is similar to electroplating except that no external current is required.
  • a seeding layer of suitable geometry and electrical and chemical characteristics must be formed on the object in order to provide nucleation sites for the metal to be deposited. It is thought that the seeding layer acts as a catalyst, in that it reduces the activation energy for the deposition step.
  • lithographic printing referred to herein is a printing process which utilizes differences in surface chemistry of the printing plate, including hydrophilic and hydrophobic properties. It does not refer to the commonly used process involving photoresist and etching occurring during the production of etched circuit boards and/or silicon semiconductor micro electronics.
  • the term “ink” is intended to mean any material suitable for printing.
  • the ink which is employed in the present invention preferably comprises a particulate material suspended in a mixture of a resin and an organic solvent.
  • the particulate material is particulate metal or carbon.
  • Particularly suitable materials include silver, gold, copper, zinc or nickel.
  • the particle size may be from 0J to 10 micrometers, and preferably from 0.25 to 1 micrometers, more preferably greater than 0.1 micrometers and less than (but not equal to) 1 micrometer, and most preferably from 0.25 to 0.75 micrometers.
  • the amount of the particulate material in the ink is preferably from 50 to 90% w/w, and most preferably about 75% w/w.
  • the resin for use in the ink may be a polymer blended with various oils.
  • the resin comprises a polymer having amide groups, for example a nylon-based polymer.
  • Nypol 3 comprises a modified polyamide and tung oil and vegetable oil blends.
  • resins which have exhibited acceptable performance include phenolic modified resin and alkyd resins, which are blended with modified mineral oils and vegetable oils.
  • the resin is mixed with a solvent and a suspension of the particulate material is formed.
  • the solvent or diluent
  • the solvent can be any suitable organic solvent with a boiling point of about 250°C.
  • the substrate onto which the conductive layer is printed is preferably formed from a polymer, and preferably comprises a flexible sheet.
  • Suitable polymers include polyethylene, polypropylene, a polyester, a polyamide, a polyimide or a polysulphone.
  • the substrate may be treated to improve adhesion of the ink to the substrate surface.
  • the substrate may be coated with a copolymer adhesive layer, or the surface may be chemically treated or subjected to corona treatment.
  • the substrate is formed from a polyester, polyethylene, polypropylene or a polyamide, with or without a copolymer adhesive layer.
  • the substrate is a copolymer coated polyester, such as that available commercially from GBC (UK) Ltd of Rutherford Road, Basingstoke, Hampshire, RG24 8PD.
  • GBC GBC
  • modified polyamide resins work acceptably well with substrates formed from polyethylene, polypropylene, polyamide and polysulphone.
  • Modified phenolic resins work acceptably well with polyester, polyimide or polysulphone substrates. Alkyd resins adhere reasonable well to polyester substrates.
  • the ink is deposited onto a substrate by means of a lithographic printing process in order to form a seeding layer for electroless deposition.
  • the thickness of the seeding layer in the present invention is preferably from 3 to 5 micrometers.
  • Electroless deposition of a first electrically conductive layer is carried out by conventional means.
  • the conducting layer may be formed from any suitable electrically conductive material which can be deposited by electroless deposition, for example copper, silver, nickel or gold.
  • the thickness of the first conducting layer may be up to 4 micrometers and is preferably about 1 micrometer (although the thickness will be determined by the required electrical specifications).
  • the process of the present invention may comprise the step of electroplating a second electrically conducting layer onto the first conducting layer.
  • Electroplating is a well-known method whereby an object or part of an object is coated by means of electrolytic deposition.
  • the object In order to be electroplated, the object has to have an electrode which exhibits a suitable geometry and electrical and chemical characteristics.
  • the first conducting layer which is deposited on the seed layer acts as an electrode in the electroplating process, thereby enabling the second conducting layer to be electrolytically deposited onto the first conducting layer.
  • the addition of a second conducting layer improves the conductivity of the circuit tracks and improves the soldering of electrical components directly onto the substrate in order to form electrical assemblies (components may be soldered directly onto the first conducting layer).
  • the first layer does not need to be as much as 1 micrometer thick; a thickness which render the substrate conductive is required, for example from 0.25 to 0.5 ⁇ m.
  • the second layer may comprise any suitable electrically conducting material which can be electroplated.
  • the thickness of the second conducting layer may be anything up to 35 micrometers, depending on the required specification of the circuit board.
  • a conducting layer can be electroplated onto an electrical circuit prepared according to the process disclosed in WO 97/48257, the resulting circuit board is structurally unstable due to the poor adhesion of the conducting ink onto the substrate.
  • an electrical component can be soldered directly onto an electrical circuit prepared by the present method, particularly if a second conducting layer is deposited by means of the electroplating step, since by this step sufficient conducting layer can be deposited to which a good solder link can be formed.
  • One example application of the present invention is in the manufacture of electronic circuit boards.
  • the lithographically deposited seeding layer is printed in the graphical configuration of an electrical or electronic circuit.
  • the seeding layer can then be electrolessly plated with copper and a further layer of tin or other protective layer.
  • Ink layers deposited by the preferred lithographic printing process are about 5 micrometers (5 x 10 "6 m) thick. This may be compared to about 25 micrometers for conductive layers deposited by screen printing, and 20-75 micrometers of copper typically laminated onto a conventional printed circuit board.
  • the adopted approach has been to formulate an ink from particles suspended in an organic resin. Manipulation of the resin formulation permits a degree of control over certain mechanical characteristics of the ink (e.g. viscosity).
  • the particulate material should be such as to enable the electroless deposition step.
  • Suitable materials include silver, copper, carbon and palladium.
  • Hydrocarbon solvents and other suitable additives are used to adjust the printing, wear resistance and drying properties of the printed layer.
  • An antioxidant (such as eugenol) is preferably incorporated to react with free radicals and thereby prevent auto- oxidation of the resin. In other words, the antioxidant prevents the resin from drying too quickly.
  • a drying agent such as a cobalt salt can be included to dry the resin once the antioxidant is used up.
  • An example of a preferred formulation of an ink is:
  • the resulting ink formulation exhibits Newtonian properties, exhibiting a viscosity of about 5 4 to 10 mPaS @ 25 degrees C. Suitable viscosities of ink formulations are considered to lie in the range 10 3 mPaS @ 25 degrees C to 10 5 mPaS @ 25 °C.
  • the copolymer-coated polyester from GBC (UK) Ltd was used.
  • the required artwork (that is, the pattern which is to become the electrical circuit) is applied to an anodised aluminium plate using the standard photoresist method used in the lithographic printing process.
  • the aluminium plate is used as a template in a lithographic process to apply the ink to the substrate in the required artwork pattern.
  • the electroless process involves placing the inked substrate in an electroless bath (such as the bath supplied by Shipley Ronal Limited) which contains a commercially available electroless plating solution.
  • an electroless bath such as the bath supplied by Shipley Ronal Limited
  • This comprises a solution of a copper salt (such as copper sulphate); a chelating agent e.g. EDTA; stabilisers such as sulphur compounds or heavy metals; an aqueous alkaline solution, for example aqueous sodium hydroxide; a reducing agent for example formaldehyde; and, optionally, a surfactant.
  • a copper salt such as copper sulphate
  • a chelating agent e.g. EDTA
  • stabilisers such as sulphur compounds or heavy metals
  • an aqueous alkaline solution for example aqueous sodium hydroxide
  • a reducing agent for example formaldehyde
  • a surfactant is known under the trade mark "CP78 process”.
  • Typical deposition rates achievable by use of this commercial process are approximately 4 micrometers of metal per hour. Typically therefore for a 1 micrometer layer, the substrate is placed in the electroless bath for ten to fifteen minutes.
  • the substrate is subsequently to be electroplated, then it is not necessary to electroless deposit a 1 micrometer layer.
  • a sufficiently thick layer to act as an electrode in the electroplating process will result from placing the substrate in the electroless bath for about three to seven minutes.
  • Electroplating processes are well known in the art. For example, copper sulphate solution is used as the electrolyte. The rate of copper deposition is dependent upon the surface area of the cathode and the current density. A typical current density is 25 Amps per square decametre.
  • the anode is copper and the cathode is the item to be plated (i.e. the conductive tracks).
  • electrical components can be soldered directly onto the conductive layers on substrate formed by the above processes.
  • a conductive polymer adhesive can be used such as an epoxy adhesive.
  • the present process can be employed to form a variety of devices comprising electrical circuitry.
  • electrical assemblies which can be created using the above processes include battery interconnect circuitry, microwave integrated circuits, antennae, such as microwave antennae, planar antennae or contoured antennae structures.
  • a method of depositing an electrically conducting layer onto a conducting layer of a substrate prepared by the method disclosed in WO 97/48257 by means of electroplating, electroless deposition, or a combination thereof.

Abstract

A process for forming a conductive layer on a substrate, comprising the steps of depositing ink on the substrate by means of lithographic printing to form a seeding layer, and depositing a first electrically conducting layer on the seeding layer by electroless deposition.

Description

PROCESS FOR DEPOSITING CONDUCTING LAYER ON SUBSTRATE
The present invention relates to a process for forming an electrically conductive layer on a substrate, and in particular to a process for forming such a layer on a substrate which can be used as a circuit board in an electrical assembly.
Conventionally, silicon devices are mounted on printed circuit boards (PCB). A printed circuit board generally consists of etched copper on glass fiber laminate, tin plated and possibly carrying further layers of lacquer for protection and labeling. Many operations of cropping, drilling, etching and plating are involved in its preparation. It is not cheap, and the production processes can have significant environmental impact.
The two major environment hazards posed by PCB manufacture are the waste effluent which is acidic and contains heavy metals (especially copper), and the use of hydrocarbons in photoresist developer and stripper. Stricter pollution limits imposed by water authorities are one driving force to reduce copper in effluent. In theory, waste effluent could be eliminated by a totally additive process for copper deposition, which would also offer considerable cost savings, but a satisfactory process has not yet been developed.
Attempts to avoid the use of a circuit board as such include the use of both thick and thin film techniques, normally associated with higher cost, not lower. Resistors are formed on a ceramic substrate by depositing tracks of a suitable film, sometimes trimmed to precise values by laser etching. A film of higher conductivity is generally used for interconnection.
WO 97/48257, which has common applicants with the present application, the disclosure of which is incorporated herein, discloses an alternative method of forming an electrical circuit board, whereby a conducting ink is lithographically printed onto a substrate in order to form an electrical circuit. The ink comprises electrically conductive particles (such as metallic silver) suspended in an organic resin such as an alkyd resin. The manufacture of electrical components such as resistors, capacitors and antennae is also described.
Although the circuit printing technique disclosed in WO 97/48257 is a significant improvement on previous techniques, it has a number of disadvantages.
First, it is advantageous to electroplate a second conducting layer onto the conductive ink disclosed in WO 97/48257 in order that electrical components can then be soldered on to the substrate and/or to reduce the resistivity of the circuit. The problem is that the ink does not adhere sufficiently well to the substrate to enable electroplating.
Second, in order to prepare a conductive ink, it is necessary to employ particulate conductive material with a particulate surface treatment (e.g. a coating of a long chain fatty acid) to enable the particles to be dispersed in the resin in such a manner as to render the dried ink electrically conductive. However, this surface treatment precludes further treatment of the dried ink, for example it prevents deposition of a further conductive layer by electroless deposition.
Third, it is difficult to solder electrical components onto an electrical circuit formed from conductive ink layers, because the layers do not contain sufficiently a high metal loading to create a suitable solder join. This means that components must be affixed using conductive polymer adhesive or a mechanical joint. However, it is thought that these joining methods do not age as well as solder, and exhibit higher electrical resistance. Moreover, any increase in the content of conductive particles in the ink is to the detriment of the ink's rheological properties.
According to a first aspect of the present invention, there is provided a process for forming a conductive layer on the substrate, comprising the steps of depositing ink on the substrate by means of lithographic printing to form a seeding layer, and depositing a first electrically conducting layer on the seeding layer by electroless deposition.
Electroless deposition (or plating) is a well-known technique which involves coating an object (or part of an object) by means of a chemical reduction process, which, once initiated, is also-catalytic. The process is similar to electroplating except that no external current is required. In order to electroless plate an object, a seeding layer of suitable geometry and electrical and chemical characteristics must be formed on the object in order to provide nucleation sites for the metal to be deposited. It is thought that the seeding layer acts as a catalyst, in that it reduces the activation energy for the deposition step.
The term "lithographic printing" referred to herein is a printing process which utilizes differences in surface chemistry of the printing plate, including hydrophilic and hydrophobic properties. It does not refer to the commonly used process involving photoresist and etching occurring during the production of etched circuit boards and/or silicon semiconductor micro electronics. The term "ink" is intended to mean any material suitable for printing.
The ink which is employed in the present invention preferably comprises a particulate material suspended in a mixture of a resin and an organic solvent. Most preferably, the particulate material is particulate metal or carbon. Particularly suitable materials include silver, gold, copper, zinc or nickel. The particle size may be from 0J to 10 micrometers, and preferably from 0.25 to 1 micrometers, more preferably greater than 0.1 micrometers and less than (but not equal to) 1 micrometer, and most preferably from 0.25 to 0.75 micrometers.
The amount of the particulate material in the ink is preferably from 50 to 90% w/w, and most preferably about 75% w/w. The resin for use in the ink may be a polymer blended with various oils. Preferably, the resin comprises a polymer having amide groups, for example a nylon-based polymer.
One resin which has been found to be particularly suitable is available commercially Lawter International (of Ketenislaan lc-Haven 1520, B-9130 Kallow, Belgium) under the trade name "Nypol 3". Nypol 3 comprises a modified polyamide and tung oil and vegetable oil blends.
Other resins which have exhibited acceptable performance include phenolic modified resin and alkyd resins, which are blended with modified mineral oils and vegetable oils.
In order to form the ink, the resin is mixed with a solvent and a suspension of the particulate material is formed. The solvent (or diluent) can be any suitable organic solvent with a boiling point of about 250°C.
The substrate onto which the conductive layer is printed is preferably formed from a polymer, and preferably comprises a flexible sheet. Suitable polymers include polyethylene, polypropylene, a polyester, a polyamide, a polyimide or a polysulphone. The substrate may be treated to improve adhesion of the ink to the substrate surface. For example, the substrate may be coated with a copolymer adhesive layer, or the surface may be chemically treated or subjected to corona treatment.
Preferably, the substrate is formed from a polyester, polyethylene, polypropylene or a polyamide, with or without a copolymer adhesive layer. In a particularly preferred embodiment, the substrate is a copolymer coated polyester, such as that available commercially from GBC (UK) Ltd of Rutherford Road, Basingstoke, Hampshire, RG24 8PD. It has been discovered that modified polyamide resins work acceptably well with substrates formed from polyethylene, polypropylene, polyamide and polysulphone. Modified phenolic resins work acceptably well with polyester, polyimide or polysulphone substrates. Alkyd resins adhere reasonable well to polyester substrates.
As described above, the ink is deposited onto a substrate by means of a lithographic printing process in order to form a seeding layer for electroless deposition. The thickness of the seeding layer in the present invention is preferably from 3 to 5 micrometers.
Electroless deposition of a first electrically conductive layer is carried out by conventional means. The conducting layer may be formed from any suitable electrically conductive material which can be deposited by electroless deposition, for example copper, silver, nickel or gold.
The thickness of the first conducting layer may be up to 4 micrometers and is preferably about 1 micrometer (although the thickness will be determined by the required electrical specifications).
The process of the present invention may comprise the step of electroplating a second electrically conducting layer onto the first conducting layer.
Electroplating is a well-known method whereby an object or part of an object is coated by means of electrolytic deposition. In order to be electroplated, the object has to have an electrode which exhibits a suitable geometry and electrical and chemical characteristics. In the case of the present invention, the first conducting layer which is deposited on the seed layer acts as an electrode in the electroplating process, thereby enabling the second conducting layer to be electrolytically deposited onto the first conducting layer. The addition of a second conducting layer improves the conductivity of the circuit tracks and improves the soldering of electrical components directly onto the substrate in order to form electrical assemblies (components may be soldered directly onto the first conducting layer).
If a second layer is going to be electroplated onto the first, then the first layer does not need to be as much as 1 micrometer thick; a thickness which render the substrate conductive is required, for example from 0.25 to 0.5 μm.
As with the first conducting layer, the second layer may comprise any suitable electrically conducting material which can be electroplated. The thickness of the second conducting layer may be anything up to 35 micrometers, depending on the required specification of the circuit board.
Although a conducting layer can be electroplated onto an electrical circuit prepared according to the process disclosed in WO 97/48257, the resulting circuit board is structurally unstable due to the poor adhesion of the conducting ink onto the substrate.
By contrast, an electrical component can be soldered directly onto an electrical circuit prepared by the present method, particularly if a second conducting layer is deposited by means of the electroplating step, since by this step sufficient conducting layer can be deposited to which a good solder link can be formed.
One example application of the present invention is in the manufacture of electronic circuit boards. The lithographically deposited seeding layer is printed in the graphical configuration of an electrical or electronic circuit. The seeding layer can then be electrolessly plated with copper and a further layer of tin or other protective layer.
These layers improve the conductivity of the circuit tracks and allow them to be soldered directly onto via existing solder technologies. The lithographic process of production of seeding layers offers advantages of speed of production and very fine track and gap width resolution.
An embodiment of the present invention is below, by way of illustration only. For ease of understanding, the embodiment is described by way of its component parts.
The ink
Ink layers deposited by the preferred lithographic printing process are about 5 micrometers (5 x 10"6m) thick. This may be compared to about 25 micrometers for conductive layers deposited by screen printing, and 20-75 micrometers of copper typically laminated onto a conventional printed circuit board.
The adopted approach has been to formulate an ink from particles suspended in an organic resin. Manipulation of the resin formulation permits a degree of control over certain mechanical characteristics of the ink (e.g. viscosity).
As described above, the particulate material should be such as to enable the electroless deposition step. Suitable materials include silver, copper, carbon and palladium.
Hydrocarbon solvents and other suitable additives are used to adjust the printing, wear resistance and drying properties of the printed layer. An antioxidant (such as eugenol) is preferably incorporated to react with free radicals and thereby prevent auto- oxidation of the resin. In other words, the antioxidant prevents the resin from drying too quickly.
A drying agent such as a cobalt salt can be included to dry the resin once the antioxidant is used up.
An example of a preferred formulation of an ink is:
The resulting ink formulation exhibits Newtonian properties, exhibiting a viscosity of about 54 to 10 mPaS @ 25 degrees C. Suitable viscosities of ink formulations are considered to lie in the range 103mPaS @ 25 degrees C to 105mPaS @ 25 °C.
The substrate
The copolymer-coated polyester from GBC (UK) Ltd was used.
Printing process
First, the required artwork (that is, the pattern which is to become the electrical circuit) is applied to an anodised aluminium plate using the standard photoresist method used in the lithographic printing process. Second, the aluminium plate is used as a template in a lithographic process to apply the ink to the substrate in the required artwork pattern.
Electroless plating
The electroless process involves placing the inked substrate in an electroless bath (such as the bath supplied by Shipley Ronal Limited) which contains a commercially available electroless plating solution. This comprises a solution of a copper salt (such as copper sulphate); a chelating agent e.g. EDTA; stabilisers such as sulphur compounds or heavy metals; an aqueous alkaline solution, for example aqueous sodium hydroxide; a reducing agent for example formaldehyde; and, optionally, a surfactant. This is known under the trade mark "CP78 process".
Typical deposition rates achievable by use of this commercial process are approximately 4 micrometers of metal per hour. Typically therefore for a 1 micrometer layer, the substrate is placed in the electroless bath for ten to fifteen minutes.
As mentioned above, if the substrate is subsequently to be electroplated, then it is not necessary to electroless deposit a 1 micrometer layer. A sufficiently thick layer to act as an electrode in the electroplating process will result from placing the substrate in the electroless bath for about three to seven minutes.
Electroplating process
Electroplating processes are well known in the art. For example, copper sulphate solution is used as the electrolyte. The rate of copper deposition is dependent upon the surface area of the cathode and the current density. A typical current density is 25 Amps per square decametre. The anode is copper and the cathode is the item to be plated (i.e. the conductive tracks).
Manufacture of electrical circuit board
As described above, electrical components can be soldered directly onto the conductive layers on substrate formed by the above processes. Alternatively, a conductive polymer adhesive can be used such as an epoxy adhesive.
The present process can be employed to form a variety of devices comprising electrical circuitry. Examples of electrical assemblies which can be created using the above processes include battery interconnect circuitry, microwave integrated circuits, antennae, such as microwave antennae, planar antennae or contoured antennae structures.
In a further aspect of the present invention, there is provided a method of depositing an electrically conducting layer onto a conducting layer of a substrate prepared by the method disclosed in WO 97/48257 by means of electroplating, electroless deposition, or a combination thereof.
The disclosures in UK patent application numbers GB 9826446.8 and GB9826447.6, from which this application claims priority, and in the abstract accompanying this application, are incorporated herein by reference.

Claims

1. A process for forming a conductive layer on a substrate, comprising the steps of depositing ink on the substrate by means of lithographic printing to form a seeding layer, and depositing a first electrically conducting layer on the seeding layer by electroless deposition.
2. A process as claimed in claim 1, comprising the step of electroplating a second electrically conducting layer onto the first electrically conducting layer.
3. A process as claimed in any preceding claim, wherein the substrate is formed from a polymer into a flexible sheet.
4. A process as claimed in any preceding claim, wherein the substrate is coated with a copolymer adhesive.
5. A process as claimed in any preceding claim, wherein the ink comprises a particulate material suspended in a mixture of a resin and an organic solvent.
6. A process as claimed in claim 5, wherein said material is a metal or carbon.
7. A process as claimed in claim 5 or 6, wherein the resin is a polymer having amide groups.
8. A process as claimed in any preceding claim, wherein the thickness of the seeding layer is from 3 to 5μm.
9. A process as claimed in any preceding claim, wherein the thickness of the first electrically conducting layer is up to 4μm.
10. A process as claimed in any preceding claim, wherein the thickness of the first electrically conducting layer is about 0.25μm.
11. A process as claimed in any preceding claim, wherein the first electrically conducting layer is formed from copper, palladium, silver, gold, platinum, nickel.
12. A process as claimed in any preceding claim, including the step of soldering an electrical component on the substrate.
13. A process as claimed in any of claims 1 to 11, including the step of attaching an electrical component to the first or second conducting layer by means of a conductive polymer adhesive.
14. A electrical assembly comprising a substrate having at least one electrically conducting layer, which layer has been formed by a process as claimed in any of claims 1 to 13.
15. A lithographic ink for use in a lithographic printing process onto a polymer substrate, the ink comprising a particulate material suspended in a mixture of a resin and an organic solvent, wherein the resin comprises a polyamide.
16. An ink as claimed in claim 15, wherein said material is a metal or carbon.
17. An interconnect for a battery which is formed by a process as claimed in any of claims 1 to 13.
18. A battery including an interconnect as claimed in claim 17.
EP99958371A 1998-12-03 1999-12-03 Process for depositing conducting layer on substrate Withdrawn EP1142456A1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
GBGB9826446.8A GB9826446D0 (en) 1998-12-03 1998-12-03 Electrical battery interconnect device
GBGB9826447.6A GB9826447D0 (en) 1998-12-03 1998-12-03 Fabrication of a seeding layer to enable electroplating and electroless platingvia a lithographic printing process
GB9826446 1998-12-03
GB9826447 1998-12-03
PCT/GB1999/004064 WO2000033625A1 (en) 1998-12-03 1999-12-03 Process for depositing conducting layer on substrate

Publications (1)

Publication Number Publication Date
EP1142456A1 true EP1142456A1 (en) 2001-10-10

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EP99958371A Withdrawn EP1142456A1 (en) 1998-12-03 1999-12-03 Process for depositing conducting layer on substrate

Country Status (8)

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EP (1) EP1142456A1 (en)
JP (1) JP2002531961A (en)
CN (1) CN1242659C (en)
AU (1) AU762686B2 (en)
CA (1) CA2350506A1 (en)
HK (1) HK1042627A1 (en)
IL (1) IL143440A0 (en)
WO (1) WO2000033625A1 (en)

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FR2825228B1 (en) * 2001-05-25 2003-09-19 Framatome Connectors Int METHOD FOR MANUFACTURING A PRINTED CIRCUIT AND PLANAR ANTENNA MANUFACTURED THEREWITH
GB0117431D0 (en) * 2001-07-17 2001-09-12 Univ Brunel Method for printing conducting layer onto substrate
US6828713B2 (en) * 2002-07-30 2004-12-07 Agilent Technologies, Inc Resonator with seed layer
GB2394725A (en) * 2002-10-04 2004-05-05 Qinetiq Ltd Method of forming a magnetic information tag by electroless deposition
US7255782B2 (en) 2004-04-30 2007-08-14 Kenneth Crouse Selective catalytic activation of non-conductive substrates
US20050241951A1 (en) * 2004-04-30 2005-11-03 Kenneth Crouse Selective catalytic activation of non-conductive substrates
GB0413076D0 (en) 2004-06-11 2004-07-14 Medtronic Inc Deep brain stimulation of the Zona incerta
CN102415222B (en) * 2009-04-24 2015-02-04 住友电气工业株式会社 Substrate for printed wiring board, printed wiring board, and methods for producing same
EP2740818B1 (en) * 2012-12-05 2016-03-30 ATOTECH Deutschland GmbH Method for manufacture of wire bondable and solderable surfaces on noble metal electrodes
US10076032B2 (en) 2014-03-20 2018-09-11 Sumitomo Electric Industries, Ltd. Substrate for printed circuit board, printed circuit board, and method for producing substrate for printed circuit board
CN106134298B (en) 2014-03-27 2019-02-22 住友电气工业株式会社 Printed wiring board substrate, printed wiring board and the method for manufacturing printed wiring board substrate
WO2016117575A1 (en) 2015-01-22 2016-07-28 住友電気工業株式会社 Substrate for printed wiring board, printed wiring board, and method for manufacturing printed wiring board
CN105405490A (en) * 2015-12-23 2016-03-16 东洋油墨Sc控股株式会社 Conductive paste for laser processing, conductive sheet, fabrication method of signal layout line and electronic device
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See also references of WO0033625A1

Also Published As

Publication number Publication date
CN1335045A (en) 2002-02-06
IL143440A0 (en) 2002-04-21
JP2002531961A (en) 2002-09-24
HK1042627A1 (en) 2002-08-16
AU1574600A (en) 2000-06-19
AU762686B2 (en) 2003-07-03
CA2350506A1 (en) 2000-06-08
CN1242659C (en) 2006-02-15
WO2000033625A1 (en) 2000-06-08

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