WO1993024934A1 - Electrically conductive pastes - Google Patents

Electrically conductive pastes Download PDF

Info

Publication number
WO1993024934A1
WO1993024934A1 PCT/GB1993/001161 GB9301161W WO9324934A1 WO 1993024934 A1 WO1993024934 A1 WO 1993024934A1 GB 9301161 W GB9301161 W GB 9301161W WO 9324934 A1 WO9324934 A1 WO 9324934A1
Authority
WO
WIPO (PCT)
Prior art keywords
paste
metal
powder pigment
metal powder
screen
Prior art date
Application number
PCT/GB1993/001161
Other languages
French (fr)
Inventor
Michael Arthur Slifkin
Michael John Hampshire
Original Assignee
First Class Securities Limited
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 First Class Securities Limited filed Critical First Class Securities Limited
Priority to EP93913267A priority Critical patent/EP0705479A1/en
Publication of WO1993024934A1 publication Critical patent/WO1993024934A1/en

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
    • 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
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys

Definitions

  • the present invention relates to pastes for use in the production of a highly electrically conductive thick film cured by uv radiation with the primary application of screen printing interconnective patterns suitable for electronic circuits.
  • the field is currently served by thermally cured pastes or inks which have a high content of silver flake. Whilst the conductivity is good being as low as 0.05m cm, the films suffer from two disadvantages. Firstly, containing such a high level of silver flake they are expensive and secondly, being thermally cured, the process is long, typically 6 to 10 minutes. This curing time makes for slow processing with the associated costs and the energy costs are also high.
  • the current invention sets out to reduce the costs of the metal pigment or * filler and to produce a uv - cured matrix which has a curing time typically of seconds rather than minutes.
  • a paste comprising at least one chemical which contracts on polymerisation together with metal powder pigment substantially of a spherical geometry with an outer surface of a metal which either does not oxidise or produces a very thin stable oxide.
  • the metal of the pigment is ferromagnetic, preferably nickel powder.
  • the size of the spheres advantageously matches the thickness and definition requirements of the screen printing process. For 25 ⁇ m thick films a particle size distribution from 4 ⁇ m to 15 ⁇ m has been found to be successful.
  • Copper spheres are attractive on a resistivity and cost basis although adhesion of other metal coatings may in some cases be difficult.
  • adhesion of silver (Ag) to nickel (Ni) is good and this has been shown to be a successful combination, namely that of silver (Ag) coated nickel (Ni) spheres.
  • Ni nickel
  • the use of nickel (Ni) spheres in conductive thick film sheets has a further major advantage, in that the ferromagnetic nature of Ni reduces the wavelength of any electromagnetic waves propagating through the film.
  • the film therefore, has a smaller skin depth and hence attenuates an electromagnetic wave more effectively.
  • a (w ⁇ /p)
  • the pigment spheres are advantageously blended with a binding polymer and a photointiator to promote the uv curing of the polymer. Further, a diluent is preferably added to generate the appropriate rheology suitable to screen printing. A viscosity in the range of 5 to 150 poise is appropriate. Finally, the formulation benefits from the addition of small amounts of three further chemicals to improve adhesion, abrasion resistance and to minimise bubble formation.
  • the requirements of the basic polymer is important in that for good results the material must contract on curing, such that the pigment sphere are compressed together in the final film so promoting good electrical contact from one sphere to the next.
  • a satisfactory polymer has been found to be urethane aerylate.
  • the embodiment comprises the following formulation (as a percentage-by weight)
  • Acrylic monomer viscosity modifier 3.35g
  • the major uv emission from the medium power lamp is at a wavelength of 365nm.
  • Typical chemicals in the formulation could be:-
  • Photomer 6140 Aliphatic Polyester Urethane Acrylate dissolved in Tripropylene glycol diacrylate.
  • Viscosity modifier 4237 Tripropylene glycol diacrylate both from Harcros Chemicals UK Ltd.
  • Antibubble - blend of surface active agents in solution including Lecithin and polyvinyl alcohol, Lanco flow - Acrylic copolymer and Lanco-Wax TS1778 - modified micronised PTFE wax are available from Capricorn Chemicals Ltd.
  • a post cure treatment is found to significantly reduce the resistivity. It is known that uv radiation promotes polymerisation to about 95%. Further polymerisation can be achieved by a number of methods such as:-
  • metal spheres overcomes the problem of uv radiation penetration experienced with the prior art flakes by enabling the radiation reflected from their surfaces to penetrate the matrix and promote efficient polymerisation.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Paints Or Removers (AREA)

Abstract

Pastes for use in the production of a highly electrically conductive thick film cured by ultraviolet radiation with the primary application of screen printing interconnective patterns suitable for electronic circuits comprise a chemical which contracts on polymerisation and a metal powder pigment in the form of spherical particles. The particles advantageously comprise nickel coated with gold or silver. Metal spheres enable radiation reflected from their surfaces to penetrate the matrix to promote efficient polymerisation. The sphere size is advantageously linked to the thickness of the screen. For example, the sphere size is 4 to 15 νm for a screen thickness of 25 νm.

Description

ELECTRICALLY CONDUCTIVE PASTES
The present invention relates to pastes for use in the production of a highly electrically conductive thick film cured by uv radiation with the primary application of screen printing interconnective patterns suitable for electronic circuits. The field is currently served by thermally cured pastes or inks which have a high content of silver flake. Whilst the conductivity is good being as low as 0.05m cm, the films suffer from two disadvantages. Firstly, containing such a high level of silver flake they are expensive and secondly, being thermally cured, the process is long, typically 6 to 10 minutes. This curing time makes for slow processing with the associated costs and the energy costs are also high. The current invention sets out to reduce the costs of the metal pigment or* filler and to produce a uv - cured matrix which has a curing time typically of seconds rather than minutes.
Attempts to produce a uv-cured ink with flake shaped pigments have not met with success. It is believed that the geometrical stacking of plates prevents the penetration of uv radiation between the flakes and hence satisfactory polymerisation is not achieved.
According to the present invention there is provided a paste comprising at least one chemical which contracts on polymerisation together with metal powder pigment substantially of a spherical geometry with an outer surface of a metal which either does not oxidise or produces a very thin stable oxide.
Advantageously, the metal of the pigment is ferromagnetic, preferably nickel powder.
The size of the spheres advantageously matches the thickness and definition requirements of the screen printing process. For 25μm thick films a particle size distribution from 4μm to 15μm has been found to be successful.
The provision of a metal surface which, when oxidised, produces a very thin stable oxide enables electrons to tunnel through the dielectric layer between the metal spheres. Coatings which do not oxidise, the noble metals such as gold (Au) for example, are, of course, very suitable. Silver (Ag) produces a thin stable oxide and .is most suitable. Copper (Cu) on the other hand does not have a suitable oxide.
Copper spheres are attractive on a resistivity and cost basis although adhesion of other metal coatings may in some cases be difficult. On the other hand adhesion of silver (Ag) to nickel (Ni) is good and this has been shown to be a successful combination, namely that of silver (Ag) coated nickel (Ni) spheres.
The use of nickel (Ni) spheres in conductive thick film sheets has a further major advantage, in that the ferromagnetic nature of Ni reduces the wavelength of any electromagnetic waves propagating through the film. The film, therefore, has a smaller skin depth and hence attenuates an electromagnetic wave more effectively. The attenuation coefficient, a, of an electromagnetic wave of angular frequency, w, through a film of resistivity, p, and permeability, μ, is given by a = (wμ/p) As the relative permeability of pure Ni is about 250, then a film largely composed of Ni spheres will be expected to attenuate up to about 15 times more effectively than a non-ferromagnetic film of the same resistivity.
The pigment spheres are advantageously blended with a binding polymer and a photointiator to promote the uv curing of the polymer. Further, a diluent is preferably added to generate the appropriate rheology suitable to screen printing. A viscosity in the range of 5 to 150 poise is appropriate. Finally, the formulation benefits from the addition of small amounts of three further chemicals to improve adhesion, abrasion resistance and to minimise bubble formation.
The requirements of the basic polymer is important in that for good results the material must contract on curing, such that the pigment sphere are compressed together in the final film so promoting good electrical contact from one sphere to the next. In this respect a satisfactory polymer has been found to be urethane aerylate.
In order that the invention may be more clearly understood, one embodiment will now be described by way of example.
The embodiment comprises the following formulation (as a percentage-by weight)
Silver coated nickel spheres 4 to 15μm 44.15g
Urethane Acrylate 1.25g
Acrylic monomer viscosity modifier 3.35g
Photoinitiator 0.8g
Additives 0.5g
This produces a film with a resistivity of 0.3m Lcm, after curing for a few seconds in uv radiation from a medium pressure Hg lamp with a power of 125W at a distance of about 20cms from the sample. The major uv emission from the medium power lamp is at a wavelength of 365nm.
Typical chemicals in the formulation could be:-
Photomer 6140 - Aliphatic Polyester Urethane Acrylate dissolved in Tripropylene glycol diacrylate.
* Viscosity modifier 4237 - Tripropylene glycol diacrylate both from Harcros Chemicals UK Ltd.
* Photoinitiator 4265 combination of Acrylic Keytone with Lucirin TPO, available from Ciba Geigy, Basle, Switzerland.
* The additives. Antibubble - blend of surface active agents in solution including Lecithin and polyvinyl alcohol, Lanco flow - Acrylic copolymer and Lanco-Wax TS1778 - modified micronised PTFE wax are available from Capricorn Chemicals Ltd.
These are used respectively to prevent bubble formation, to increase adhesion and to improve the abrasion resistance. A post cure treatment is found to significantly reduce the resistivity. It is known that uv radiation promotes polymerisation to about 95%. Further polymerisation can be achieved by a number of methods such as:-
* Heat treatment
* Infra Red heating
* RF heating
* Electron beam irradiation
* Higher energy uv radiation from a low pressure Hg lamp with a major emission at 254nm.
Baking the films in an oven for 6 hours at 100°C reduces the resistivity from 0.3m-&cm to 0.05ΠLΩ.CΠI.
The use of metal spheres overcomes the problem of uv radiation penetration experienced with the prior art flakes by enabling the radiation reflected from their surfaces to penetrate the matrix and promote efficient polymerisation.
It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.

Claims

1. A paste comprising at least one chemical which contracts on polymerisation together with metal powder pigment substantially of a spherical geometry with an outer surface of a metal which either does not oxidise or produces a very thin stable oxide.
2. A paste as claimed in claim 1, in which the metal powder pigment is fluromagnetic.
3. A paste as claimed in claim 1 or 2, in which the metal powder pigment is nickel.
4. A paste as claimed in any of claims 1 to 3, in which the particle size of the metal powder pigment is linked to the thickness.of the screen printing process in which the paste is to be used.
5. A paste as claimed in claim 4, in which the particle size lies in the range 4μm to 15um for a screen thickness of 25μm.
6. A paste as claimed in any preceding claim, in which the surface of the metal is a coating of a noble metal.
7. A paste as claimed in claim 6, in which the noble metal is gold.
8. A paste as claimed in claim 6, in which the noble metal is silver.
9. A paste as claimed in any preceding claim in which the metal powder pigment is blended with a binding polymer and a photoinitiator to promote the curing of the polymer.
10. A paste as claimed in any preceding claim, in which a diluent is added having a viscosity in the range of 5 to 150 poise.
11. A paste as claimed in any preceding claim including chemicals to improve adhesion, abrasion resistance and to minimise bubble formation.
12. A paste formulated in accordance with the example described in the specification.
PCT/GB1993/001161 1992-05-30 1993-06-01 Electrically conductive pastes WO1993024934A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP93913267A EP0705479A1 (en) 1992-05-30 1993-06-01 Electrically conductive pastes

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB929211500A GB9211500D0 (en) 1992-05-30 1992-05-30 Pastes
GB9211500.5 1992-05-30

Publications (1)

Publication Number Publication Date
WO1993024934A1 true WO1993024934A1 (en) 1993-12-09

Family

ID=10716287

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1993/001161 WO1993024934A1 (en) 1992-05-30 1993-06-01 Electrically conductive pastes

Country Status (4)

Country Link
EP (1) EP0705479A1 (en)
AU (1) AU4339493A (en)
GB (1) GB9211500D0 (en)
WO (1) WO1993024934A1 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2001269313C1 (en) * 2000-07-10 2002-01-21 De La Rue International Limited Method of providing an image on a substrate, and an ink for use therein
WO2005038823A1 (en) * 2003-10-17 2005-04-28 Sun Chemical Corporation Energy-curable coating compositions
EP1575099A1 (en) * 2004-03-09 2005-09-14 RWE SCHOTT Solar GmbH Method of forming a structure
DE102009043916A1 (en) 2009-05-19 2010-12-16 Schott Solar Ag Method for producing electrical contacts on a semiconductor component
WO2013097846A1 (en) * 2011-12-29 2013-07-04 Gp Solar Gmbh Process and apparatus for producing a coating on a semiconductor component

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0081323A1 (en) * 1981-12-08 1983-06-15 Johnson Matthey Public Limited Company Curable ink or paint containing electrically conductive metal particles
EP0174776A2 (en) * 1984-09-04 1986-03-19 Minnesota Mining And Manufacturing Company Flexible tape having stripes of electrically conductive particles for making multiple connections
EP0234347A1 (en) * 1986-02-24 1987-09-02 International Business Machines Corporation Electrically conductive composition and use thereof
US4732702A (en) * 1986-02-13 1988-03-22 Hitachi Chemical Company, Ltd. Electroconductive resin paste
EP0291064A2 (en) * 1987-05-15 1988-11-17 E.I. Du Pont De Nemours And Company Conductive paste composition
EP0343836A1 (en) * 1988-05-26 1989-11-29 Potters Industries, Inc. Particulate material useful in an electroconductive body and method of making such particles

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0081323A1 (en) * 1981-12-08 1983-06-15 Johnson Matthey Public Limited Company Curable ink or paint containing electrically conductive metal particles
EP0174776A2 (en) * 1984-09-04 1986-03-19 Minnesota Mining And Manufacturing Company Flexible tape having stripes of electrically conductive particles for making multiple connections
US4732702A (en) * 1986-02-13 1988-03-22 Hitachi Chemical Company, Ltd. Electroconductive resin paste
EP0234347A1 (en) * 1986-02-24 1987-09-02 International Business Machines Corporation Electrically conductive composition and use thereof
EP0291064A2 (en) * 1987-05-15 1988-11-17 E.I. Du Pont De Nemours And Company Conductive paste composition
EP0343836A1 (en) * 1988-05-26 1989-11-29 Potters Industries, Inc. Particulate material useful in an electroconductive body and method of making such particles

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Derwent's abstract, No 87-275 700/39, week 8739, ABSTRACT OF SU 10 980 441, (KHIMCHENKO YU I), 1987-03-07 *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2001269313C1 (en) * 2000-07-10 2002-01-21 De La Rue International Limited Method of providing an image on a substrate, and an ink for use therein
AU2001269313B2 (en) * 2000-07-10 2005-02-24 De La Rue International Limited Method of providing an image on a substrate, and an ink for use therein
EP1299250B2 (en) † 2000-07-10 2013-09-25 De La Rue International Limited Method of providing an image on a substrate, and an ink for use therein
WO2005038823A1 (en) * 2003-10-17 2005-04-28 Sun Chemical Corporation Energy-curable coating compositions
EP1575099A1 (en) * 2004-03-09 2005-09-14 RWE SCHOTT Solar GmbH Method of forming a structure
WO2005088730A3 (en) * 2004-03-09 2005-10-27 Rwe Schott Solar Gmbh Method for forming a structure
US7790508B2 (en) 2004-03-09 2010-09-07 Schott Solar Ag Method for forming a structure
DE102009043916A1 (en) 2009-05-19 2010-12-16 Schott Solar Ag Method for producing electrical contacts on a semiconductor component
EP2280425A2 (en) 2009-05-19 2011-02-02 SCHOTT Solar AG Method for producing electric contacts on a semiconductor element
US8273596B2 (en) 2009-05-19 2012-09-25 Schott Solar Ag Method for producing electric contacts on a semiconductor component
WO2013097846A1 (en) * 2011-12-29 2013-07-04 Gp Solar Gmbh Process and apparatus for producing a coating on a semiconductor component

Also Published As

Publication number Publication date
GB9211500D0 (en) 1992-07-15
AU4339493A (en) 1993-12-30
EP0705479A1 (en) 1996-04-10

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