EP4263120A1 - Sintering paste and use thereof for connecting components - Google Patents

Sintering paste and use thereof for connecting components

Info

Publication number
EP4263120A1
EP4263120A1 EP21749560.5A EP21749560A EP4263120A1 EP 4263120 A1 EP4263120 A1 EP 4263120A1 EP 21749560 A EP21749560 A EP 21749560A EP 4263120 A1 EP4263120 A1 EP 4263120A1
Authority
EP
European Patent Office
Prior art keywords
silver
components
weight
sintering
acid
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.)
Pending
Application number
EP21749560.5A
Other languages
German (de)
French (fr)
Inventor
Ly May CHEW
Wolfgang Schmitt
Michael Schäfer
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.)
Heraeus Electronics & Co Kg GmbH
Original Assignee
Heraeus Deutschland GmbH and Co KG
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 Heraeus Deutschland GmbH and Co KG filed Critical Heraeus Deutschland GmbH and Co KG
Publication of EP4263120A1 publication Critical patent/EP4263120A1/en
Pending legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
    • B23K35/3006—Ag as the principal constituent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0545—Dispersions or suspensions of nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0551—Flake form nanoparticles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/107—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing organic material comprising solvents, e.g. for slip casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
    • B22F1/147—Making a dispersion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
    • B22F7/062—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools involving the connection or repairing of preformed parts
    • B22F7/064—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools involving the connection or repairing of preformed parts using an intermediate powder layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
    • B22F7/08—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools with one or more parts not made from powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • B23K35/025—Pastes, creams, slurries
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
    • B23K35/3601—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with inorganic compounds as principal constituents
    • B23K35/3602—Carbonates, basic oxides or hydroxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
    • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
    • B23K35/3613—Polymers, e.g. resins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/016—Layered products comprising a layer of metal all layers being exclusively metallic all layers being formed of aluminium or aluminium alloys
    • 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
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
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    • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L24/28—Structure, shape, material or disposition of the layer connectors prior to the connecting process
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/36—Electric or electronic devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/08—Non-ferrous metals or alloys
    • B23K2103/10—Aluminium or alloys thereof
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    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/832—Applying energy for connecting
    • H01L2224/83201—Compression bonding
    • H01L2224/83203—Thermocompression bonding, e.g. diffusion bonding, pressure joining, thermocompression welding or solid-state welding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/8338—Bonding interfaces outside the semiconductor or solid-state body
    • H01L2224/83399—Material
    • H01L2224/834—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
    • H01L2224/83417—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof the principal constituent melting at a temperature of greater than or equal to 400°C and less than 950°C
    • H01L2224/83424—Aluminium [Al] as principal constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/8338—Bonding interfaces outside the semiconductor or solid-state body
    • H01L2224/83399—Material
    • H01L2224/834—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
    • H01L2224/83438—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
    • H01L2224/83447—Copper [Cu] as principal constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/838—Bonding techniques
    • H01L2224/8384—Sintering

Definitions

  • the present invention relates to a sintering paste and a method for connecting components using this sintering paste.
  • sinter pastes are products that should not be confused with conductive adhesives.
  • Conductive adhesives can also be used to connect components, with mechanically strong and electrically conductive connections being produced; however, due to their comparatively low metal content, the connections are naturally not as thermally conductive as connections made from sinter pastes.
  • component used herein refers in particular to components used in electronics, in short electronic components. Examples include diodes, LEDs (light emitting diodes), dies, IGBTs (insulated-gate bipolar transistors), MOSFETs (metal-oxide-semiconductor field effect transistors), ICs (integrated circuits). circuits), sensors, heat sinks, resistors, capacitors, coils, connectors (e.g. clips), base plates, antennas, lead frames, PCBs (printed circuit boards), flexible electronics, ceramic substrates, metal-ceramic substrates such as DCB substrates ( direct copper bonded substrates), IMS (insulated metal substrate), and the like.
  • diodes LEDs (light emitting diodes), dies, IGBTs (insulated-gate bipolar transistors), MOSFETs (metal-oxide-semiconductor field effect transistors), ICs (integrated circuits). circuits), sensors, heat sinks, resistors, capacitors, coils, connectors (e.g.
  • Metal sintering paste is often used as the connecting material, the main components of which are dispersed, sinterable metal particles.
  • Prominent examples of such sinter pastes include silver sinter pastes known to those skilled in the art.
  • the sintered connection technique represents a very simple method for the stable connection of components, the components to be connected being transferred with their contact surfaces to be connected facing one another into a sandwich arrangement with sintered connection material applied in between, for example sintered paste.
  • the sandwich arrangement created using sintering paste is then subjected to a drying and sintering step, during which the mechanically strong, electrically and thermally conductive connection between the components is formed.
  • the mechanically fixed connection of two components is therefore a fastening of one component to or on the second component via their respective contact surfaces.
  • the object of the invention was to provide a sintered paste which is improved in particular with regard to its drying properties.
  • the sintering paste to be found should allow the formation of sintered connections between components which have no or at least acceptable (tolerably minor) defects caused by drying in the layer applied and dried from the sintering paste and connecting the components. Defects caused by drying are in particular so-called drying channels. Such defects can not only weaken the mechanical strength of the final sintered joints, but also cause a reduction in thermal and electrical conductivity.
  • average particle size used herein in connection with the silver flakes (A) means the volume-average primary particle diameter (D50) that can be determined by means of static automated analysis of microscopic images.
  • ECAD Equivalent Circular Area Diameter
  • the so-called Equivalent Circular Area Diameter (ECAD) can expediently be used as a measure for the particle diameter (cf. RENLIANG XU ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), vol. 132, No. 2-3, 24 June 2003 (2003-06-24), pages 145-153).
  • the static, automated analysis of the microscopic images can be carried out, for example, using the Morphologi 4 measuring system from Malvern Instruments using the dry determination method.
  • average particle size as used herein in connection with the silver particles (B) means the volume-average determinable by means of laser diffraction primary particle diameter (D50).
  • ECAD Equivalent Circular Area Diameter
  • Laser diffraction measurements can be carried out using an appropriate particle sizer, for example a Mastersizer 3000 or a Mastersizer 2000 from Malvern Instruments, using the wet determination method. In the case of the wet determination method, 1 g of silver particles (B) can be dispersed in 200 ml of ethanol using ultrasound as part of the sample preparation.
  • the sintering paste according to the invention contains as component (A) 30 to 40% by weight, preferably 32 to 37% by weight, of silver flakes with an average particle size in the range from 1 to 20 ⁇ m, preferably 1 to 10 ⁇ m.
  • the aspect ratio of the silver flakes can be >5:1 to several hundred:1, for example.
  • the aspect ratio of particles describes the quotient of the largest and smallest length extension of the same and thus their shape; just to avoid misunderstandings, in the case of particles in the form of flakes or platelets, the quotient of the greatest and smallest linear expansion is the quotient of the greatest linear expansion and the platelet thickness. It can be determined by scanning electron microscopy and evaluating the electron micrographs by determining the dimensions of a statistically significant number of individual particles.
  • the silver flakes are usually coated (coated).
  • the weight information given here then includes the weight of the coating (coating) on the silver flakes.
  • the silver flakes can include flakes of pure silver (purity of the silver of at least 99.9% by weight) and/or those made of silver alloys with up to 10% by weight of at least one other alloying metal.
  • suitable alloying metals are copper, gold, nickel, palladium, platinum and aluminum. Silver flakes of pure silver are preferred.
  • the aforementioned coating can be an adherent layer on the surface of the silver flakes. It is usually an organic coating.
  • the proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on silver or silver alloy, lying.
  • such an organic coating can comprise 90 to 100% by weight of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters.
  • fatty acids examples include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
  • caprylic acid octanoic acid
  • capric acid decanoic acid
  • lauric acid diodecanoic acid
  • myristic acid tetradecanoic acid
  • palmitic acid hexadecanoic acid
  • margaric acid heptadecanoic acid
  • stearic acid
  • the silver flakes are commercially available. Examples include Metalor's LIA8320, P6908, Ames Goldsmith's SF30L, and Technic's Silflake 40-592 and Silflake 40-50 products.
  • the sintering paste according to the invention contains as component (B) 8 to 20% by weight, preferably 10 to 16% by weight, of silver particles with an average particle size in the range from 20 to 100 nm.
  • the silver particles are usually coated.
  • the weight information given here then includes the weight of the coating on the silver particles.
  • the silver particles are not silver flakes, their aspect ratio is significantly smaller than that of flakes, for example in the range from 1:1 to 5:1.
  • spherical particles have an aspect ratio of 1:1.
  • the aspect ratio of the silver particles is in the range of 1:1: 1 to 5:1 means that the silver particles have, for example, a spherical, an essentially spherical, an elliptical, an egg-shaped or an irregular shape, but in no way the shape of flakes.
  • the silver particles can comprise particles of pure silver (purity of the silver of at least 99.9% by weight) and/or particles made of silver alloys with up to 10% by weight of at least one other alloying metal.
  • suitable alloying metals are copper, gold, nickel, palladium, platinum and aluminum.
  • Silver particles made of pure silver are preferred.
  • the aforementioned coating can be an adherent layer on the surface of the silver particles. It is usually an organic coating.
  • the proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on the silver or silver alloy.
  • such an organic coating can contain 90 to 100% by weight % of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters.
  • fatty acids examples include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
  • caprylic acid octanoic acid
  • capric acid decanoic acid
  • lauric acid diodecanoic acid
  • myristic acid tetradecanoic acid
  • palmitic acid hexadecanoic acid
  • margaric acid heptadecanoic acid
  • stearic acid
  • the silver particles are commercially available. Examples include Arnes Goldsmith's 18060-NM2 and Technic's SIL 41-193, SIL 40-277, SIL 40-147, and SIL40-050-0720-2 products.
  • At least a portion of the silver particles may be attached to at least a portion of the silver flakes.
  • the sintering paste according to the invention contains, as component (C), 30 to 45% by weight, preferably 32 to 40% by weight, of silver(I) oxide particles.
  • the silver(I) oxide particles serve as a silver precursor, from which metallic silver can be formed by thermal decomposition.
  • the silver(I) oxide particles can have an average particle size in the range from 0.4 to 4 ⁇ m, for example.
  • average particle size used herein in connection with the silver(I) oxide particles (C) means the volume-average primary particle diameter (D50) that can be determined by means of laser diffraction.
  • ECAD Equivalent Circular Area Diameter
  • RENLIANG XU ET AL "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), vol. 132, No. 2-3, 24 June 2003 (2003-06-24), pages 145-153).
  • Laser diffraction measurements can be carried out using an appropriate particle sizer, for example a Mastersizer 3000 or a Mastersizer 2000 from Malvern Instruments, using the wet determination method.
  • an appropriate particle sizer for example a Mastersizer 3000 or a Mastersizer 2000 from Malvern Instruments
  • 1 g of silver(I) oxide particles (C) can be dispersed in 200 ml of ethanol using ultrasound as part of the sample preparation.
  • the silver(I) oxide particles can be coated.
  • the silver(I) oxide particles are preferably uncoated.
  • the weight information given here includes the weight of the coating on the silver(I) oxide particles.
  • the coating can be a firmly adhering layer on the surface of the silver(I) oxide particles. It is usually an organic coating.
  • the proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on the silver(I) oxide.
  • such an organic coating can comprise 90 to 100% by weight of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters.
  • fatty acids examples include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
  • caprylic acid octanoic acid
  • capric acid decanoic acid
  • lauric acid diodecanoic acid
  • myristic acid tetradecanoic acid
  • palmitic acid hexadecanoic acid
  • margaric acid heptadecanoic acid
  • stearic acid
  • the sintering paste according to the invention contains, as component (D), 12 to 20% by weight, preferably 14 to 16% by weight, of at least one organic solvent.
  • suitable organic solvents include terpineols, N-methyl-2-pyrrolidone, ethylene glycol, dimethylacetamide, 1-tridecanol, 2-tridecanol, 3-tridecanol, 4-tridecanol, 5-tridecanol, 6-tridecanol, isotridecanol, dibasic esters (preferably dimethyl ester of glutaric, adipic or succinic acid or mixtures thereof), glycerol, diethylene glycol, triethylene glycol and aliphatic, in particular saturated aliphatic hydrocarbons having 5 to 32 carbon atoms, more preferably 10 to 25 carbon atoms and even more preferably 16 to 20 carbon atoms -Atoms.
  • Such aliphatic hydrocarbons are sold, for example, by Exxon Mobil under the ExxsolTM D140 brand or under the Isopar MTM brand. Combinations of at least one terpineol with at least one dibasic ester are particularly preferred as component (D).
  • the sintering paste according to the invention can contain, as component (E), 0 to 1% by weight, preferably 0.1 to 0.7% by weight, of at least one polymeric binder.
  • the at least one polymeric binder comprises neither self-crosslinkable polymers nor covalently crosslinkable binder/hardener combinations.
  • suitable polymeric binders include, in particular, cellulose derivatives, for example methyl cellulose, ethyl cellulose, ethyl methyl cellulose, carboxy cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose.
  • the sintering paste according to the invention can contain, as component (F), 0 to 0.5% by weight, preferably 0 to 0.3% by weight, of at least one additive different from components (A) to (E).
  • additives include surfactants, defoamers, wetting agents, and anti-corrosion additives.
  • Constituent (F) preferably does not include any glass particles (glass frit).
  • the sinter paste according to the invention is a silver sinter paste.
  • the sintering paste according to the invention can be produced by mixing the components (A) to (D) and optionally (E) and optionally (F).
  • Conventional devices known to those skilled in the art can be used here, for example agitators, three-roll mills, jet mixers and/or dispersers. It can be expedient to first premix the silver flakes and the silver particles with one another, for example by means of a paddle stirrer, a ball mill, a tumble mixer or a gas jet mixer.
  • the adhesion of the silver particles to the silver flakes can be understood by determining the particle size distribution after premixing.
  • the previously mentioned laser diffraction measurement can be used as a method of determination.
  • a bimodal particle size distribution is initially evident, which shifts more and more in the direction of a monomodal particle size distribution as premixing progresses.
  • an essentially or completely monomodal particle size distribution appears as the final state.
  • substantially monomodal means that at least one of several peaks of a particle size distribution curve covers at least 90% of the area under the
  • Particle size distribution curve accounts for.
  • the adhesion of the silver particles to the silver flakes can prevent or prevent agglomeration in the sinter paste according to the invention; it can thus promote or bring about a homogeneous distribution of both the silver particles and the silver flakes in the sinter paste according to the invention.
  • the sintering paste according to the invention can be used in a sintering process, for example in a sintering process as explained above.
  • Sintering means connecting of two or more components by heating while avoiding that the silver flakes and the silver particles reach the liquid phase.
  • the solid mechanical connection formed in this way is both electrically and thermally conductive; it consists of >95% by weight, for example 95 to 100% by weight, of silver and is therefore not comparable to a connection between such components produced from a conventional silver conductive adhesive.
  • a connection produced from a customary silver conductive adhesive usually includes a silver content of ⁇ 90% by weight, for example in the range from 40 to 90% by weight, with the portion missing from 100% by weight usually including a polymer portion and optionally a filler portion can.
  • the invention also relates to a method for connecting components, in which (1) a sandwich arrangement is provided which has at least two components and a sintering paste according to the invention located between the components, (2) optionally, but preferably, the sintering paste is dried and (3) the sandwich assembly sinters. Drying is understood as meaning the removal of organic solvent from the applied sinter paste according to the invention.
  • Steps (1), (2) and (3) form a sequence of steps of type (1)-(2)-(3) with step (2) as an optional step.
  • step (1) can already include drying and step (2) can therefore be omitted.
  • step (1) does not comprise the drying or only partly and the optional step (2) can be omitted or take place preferentially; if step (2) is omitted here, it can take place in the course of step (3) or overlap with it.
  • the components can comprise at least one metal contact surface, for example in the form of a metallization layer, via which the already mentioned sandwich arrangement takes place within the scope of the method according to the invention.
  • Even components made of aluminum, aluminum alloys (aluminum content >90% by weight) or with an aluminum contact surface or aluminum-based contact surface, each with the strong thermal expansion behavior for aluminum, can be used successfully in the context of the method according to the invention; in other words, they can be successfully sinter-bonded with the sinter paste of the present invention.
  • step (1) the two or more components are first brought into contact with one another.
  • the contacting takes place via the sintering paste according to the invention.
  • a sandwich arrangement is provided in which sintering paste according to the invention is located between two of the at least two components.
  • Under sandwich arrangement is to be understood as an arrangement in which two components are located one above the other and the components are arranged substantially parallel to each other.
  • the sandwich arrangement can be produced using a method known from the prior art.
  • the relevant metal contact surface of one of the components is provided with the sintering paste according to the invention.
  • the metal contact surface of the other component is then placed on the sintering paste that has been applied to the metal contact surface of one component and, if appropriate, has already been dried.
  • the sintering paste according to the invention can be applied to the relevant metal contact surface of one component using conventional methods, for example using printing methods such as screen printing or stencil printing.
  • the sintering paste according to the invention can also be applied by means of the dispensing technique, jetting, by means of pin transfer or by dipping.
  • the sinter paste according to the invention is particularly suitable for application by means of an application technique in which repeated shear stress acts on the sinter paste.
  • an application technique in which repeated shear stress acts on the sinter paste For example, when applying by means of a dispensing technique, such a repeated shearing stress can occur due to repeated pressure changes in the sintering paste storage container.
  • the sintering paste according to the invention exhibits thixotropic behavior and, when the shearing stress decreases or without shearing stress (at rest), in each case returns remarkably quickly to almost or entirely to the initial viscosity.
  • the viscosity behavior can be examined, for example, by means of rotational viscometry, for example at 20°C using the plate-cone measuring principle with a cone diameter of 25 mm and a cone angle of 2° with a measuring gap of 0.05 mm and, for example, within 15 minutes steadily increasing shear rate over the range of 0.05 to 30 s- 1 .
  • the so-called recovery rate after shear stress can be determined, for example, as in example 2.2. explained below.
  • the wet layer thickness of the sintering paste is preferably in the range from 20 to 400 ⁇ m.
  • the preferred wet layer thickness depends, for example, on the selected application method for the sinter paste. If the sintering paste is applied, for example, by means of a screen printing process, then a wet layer thickness of, for example, 20 to 60 ⁇ m may be preferred. If the sintering paste is applied, for example, by means of stencil printing, then the preferred wet layer thickness can be, for example, in the range from 20 to 400 ⁇ m.
  • the preferred wet layer thickness can be in the range from 20 to 400 ⁇ m, depending on the application tool used, for example during use a hollow needle in the range from 20 to 100 ⁇ m or, for example, when using a slot die that also functions as a doctor blade in the range from 50 to 400 ⁇ m.
  • the metal contact surface of this component which may already have been partially or completely dried, is brought into contact with the corresponding metal contact surface of the component to be connected via the sintering paste.
  • a layer of partially or completely dried sintering paste according to the invention in terms of the formation of the sandwich arrangement.
  • the proportion of organic solvent in the sinter paste after drying is, for example, 0 to 5% by weight, based on the original proportion of organic solvent in the sinter paste according to the invention.
  • the proportion of organic solvent in the sinter paste after drying is, for example, 0 to 5% by weight, based on the original proportion of organic solvent in the sinter paste according to the invention.
  • for example 95 to 100% by weight of the organic solvent(s) originally present in the sinter paste according to the invention are removed.
  • the drying temperature in an ongoing step (2) is preferably in the range of 100 to 150°C. Typical drying times are, for example, in the range from 5 to 45 minutes. A vacuum can be used to shorten the drying time, for example a pressure in the range from 100 to 300 mbar.
  • the sintering paste according to the invention is characterized in that the formation of so-called drying channels within the layer of sintering paste located between the components can be largely or even completely avoided. This is surprising insofar as it would have been expected that the comparatively small silver particles (B) would fill the cavities between the larger silver flakes (A) within the layer of sinter paste. With such an expected dense arrangement of silver flakes (A) and silver particles (B), however, it should be more difficult for the organic solvent to escape, so that an increased formation of drying-related defects and drying channels would have been expected.
  • drying channels can be checked experimentally by a person skilled in the art by carrying out steps (1) and (2) above and doing so instead of the second Component used a glass plate or a ceramic plate.
  • a ceramic substrate for example, can be used as the first component.
  • he can observe or visually assess the extent to which drying-related defects or drying channels form in the sinter paste layer, while volatile organic solvent leaves the sinter paste layer of the sandwich arrangement at the edge.
  • the sinter paste according to the invention is characterized by favorable drying behavior with little or no tendency to form drying channels. The drying behavior can be evaluated, for example, as in example 2.1. explained below.
  • step (3) of the method according to the invention can be carried out under pressure or without pressure.
  • Pressureless implementation means that a sufficiently strong connection between the components can be achieved despite dispensing with the application of mechanical pressure.
  • the actual sintering takes place at a temperature of, for example, 200 to 280 °C and, as mentioned, either as a pressureless process or as pressure sintering.
  • the process pressure is preferably below 30 MPa and more preferably below 15 MPa.
  • the process pressure is in the range of 1 to 30 MPa, and more preferably in the range of 5 to 15 MPa.
  • the sintering time is for example in the range from 2 to 90 minutes, in the case of pressure sintering for example in the range from 2 to 5 minutes, in the case of pressureless sintering for example in the range from 30 to 75 minutes.
  • the sintering process can be carried out in an atmosphere which is not particularly restricted. On the one hand, sintering can be carried out in an atmosphere containing oxygen. On the other hand, it is also possible to carry out the sintering in an oxygen-free atmosphere or in a vacuum.
  • an oxygen-free atmosphere means an atmosphere in which the oxygen content is no more than 300 ppm by weight (ppm by weight), preferably no more than 100 ppm by weight, and even more preferably no more than 50 ppm by weight amounts to.
  • the sintering is carried out in a conventional device suitable for sintering, in which the process parameters described above can be set.
  • compositions of the sintering pastes 1, 2 and 3 according to the invention and of the comparison pastes C1, C2 and C3 in % by weight are listed in Table 1.
  • sinter paste 1 In the case of sinter paste 1, the silver flakes and the silver particles were premixed in a tumble mixer for 120 minutes and then added to the other paste components listed in Table 1. In contrast, in the case of sinter pastes 2 and 3 and in the comparison pastes C1, C2 and C3, the silver flakes and the silver particles were not premixed, but instead were added directly one after the other to the other paste components.
  • Table 1 Composition of inventive sintering pastes 1, 2 and 3 and the
  • Silver flakes D50: 3 ⁇ m, coated with 0.7% by weight of a 1:1 mixture of stearic and lauric acid
  • the sintering pastes 1, 2 and 3 according to the invention and the comparison pastes C1, C2 and C3 were examined with regard to their drying behavior, their ability to recover after shear stress and their ability to sinter on aluminum and copper surfaces.
  • the pastes were each first applied to the surface of an aluminum sheet by means of stencil printing squares (5 cm ⁇ 5 cm) in a wet layer thickness of 300 ⁇ m. Subsequently, the surfaces of the wet, non-dried pastes were each covered completely with a 1 mm thick glass plate covered so that only the outer edges of the pastes were exposed. These test structures were then placed on a hot plate and the paste layers covered with the glass plates were dried at 130° C. for 15 minutes. The development of any drying channels or voids was examined using an optical microscope and rated as indicated in Table 2.
  • the recovery rate after shear stress was determined for the different sinter pastes by means of rotational viscometry using the plate-cone measuring principle with a cone diameter of 25 mm and a cone angle of 2° with a measuring gap of 0.05 mm at changing shear rates. For this purpose, a measurement run was selected in which, starting with a low shear rate of 30 s -1 lasting 30 seconds, there was a sudden change to a high shear rate of 100 s -1 lasting 30 seconds. This measurement run was repeated a total of twelve times in direct succession. The recovery rate was determined as the percent change in final viscosity compared to initial viscosity [(final viscosity divided by initial viscosity) x 100%]. The initial viscosity is defined as the last measurement point at a low shear rate in the first measurement run and the final viscosity as the last measurement point at a low shear rate in the twelfth measurement run.
  • the shear strengths of the respective sintered connection material were determined on aluminum or copper.
  • the sintering pastes according to the invention and the comparison pastes were applied by means of stencil printing to an aluminum sheet 5 mm thick or to the 300 ⁇ m thick copper surface of a DCB substrate in a wet layer thickness of 50 ⁇ m.
  • the applied sintering pastes were then pre-dried at 140° C. for 10 minutes and then brought into full-area contact with a silicon chip with a silver contact area (4 mm ⁇ 4 mm).
  • the subsequent pressure sintering took place under a nitrogen atmosphere ( ⁇ 100 ppm oxygen) in a hot press at 230° C. and 12 MPa for 5 minutes.

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Abstract

The invention relates to a sintering paste consisting of: (A) 30 to 40 wt.% of silver flakes with an average particle size ranging from 1 to 20 µm, (B) 8 to 20 wt.% of silver particles with an average particle size ranging from 20 to 100 nm, (C) 30 to 45 wt.% of silver(I) oxide particles, (D) 12 to 20 wt.% of at least one organic solvent, (E) 0 to 1 wt.% of at least one polymer binder, and (F) 0 to 0.5 wt.% of at least one additive differing from the components (A) to (E).

Description

SINTERPASTE UND DEREN VERWENDUNG ZUM VERBINDEN VON BAUELEMENTEN SINTERING PASTE AND ITS USE FOR CONNECTING COMPONENTS
Die vorliegende Erfindung betrifft eine Sinterpaste und ein Verfahren zum Verbinden von Bauelementen, bei dem diese Sinterpaste eingesetzt wird. The present invention relates to a sintering paste and a method for connecting components using this sintering paste.
Wie später noch erläutert wird, handelt es sich bei Sinterpasten um nicht mit Leitklebern zu verwechselnde Produkte. Leitkleber können zwar auch zum Verbinden von Bauelementen verwendet werden, wobei mechanisch feste und elektrisch leitfähige Verbindungen erzeugt werden; jedoch sind die Verbindungen aufgrund ihres vergleichsweise geringen Metallanteils naturgemäß nicht so wärmeleitfähig wie aus Sinterpasten hergestellte Verbindungen. As will be explained later, sinter pastes are products that should not be confused with conductive adhesives. Conductive adhesives can also be used to connect components, with mechanically strong and electrically conductive connections being produced; however, due to their comparatively low metal content, the connections are naturally not as thermally conductive as connections made from sinter pastes.
Der hierin verwendete Begriff „Bauelement“ bezeichnet insbesondere Bauteile, die in der Elektronik verwendet werden, kurz gesagt, elektronische Bauelemente. Beispiele dafür umfassen Dioden, LEDs (light emitting diodes, lichtemittierende Dioden), Dies, IGBTs (insulated-gate bipolar transistors, Bipolartransistoren mit isolierter Gate-Elektrode), MOSFETs (Metall-Oxid-Halbleiter-Feldeffekttransistoren), ICs (integrated circuits, integrierte Schaltungen), Sensoren, Kühlkörper, Widerstände, Kondensatoren, Spulen, Verbindungselemente (z. B. Clips), Bodenplatten, Antennen, Leadframes, PCBs (printed circuit boards, gedruckte Leiterplatten), flexible Elektronik, Keramiksubstrate, Metallkeramiksubstrate wie beispielsweise DCB-Substrate (direct copper bonded-Substrate), IMS (isoliertes Metallsubstrat) und dergleichen. The term "component" used herein refers in particular to components used in electronics, in short electronic components. Examples include diodes, LEDs (light emitting diodes), dies, IGBTs (insulated-gate bipolar transistors), MOSFETs (metal-oxide-semiconductor field effect transistors), ICs (integrated circuits). circuits), sensors, heat sinks, resistors, capacitors, coils, connectors (e.g. clips), base plates, antennas, lead frames, PCBs (printed circuit boards), flexible electronics, ceramic substrates, metal-ceramic substrates such as DCB substrates ( direct copper bonded substrates), IMS (insulated metal substrate), and the like.
Im Bereich der Leistungs- und Konsumerelektronik stellt das Sinterverbinden elektronischer Bauelemente ein gängiges Verfahren dar. Als Verbindungsmaterial wird dabei häufig Metallsinterpaste verwendet, deren Hauptbestandteile dispergierte sinterfähige Metallpartikel sind. Prominente Beispiele für solche Sinterpasten umfassen dem Fachmann bekannte Silbersinterpasten. Die Sinterverbindungstechnik stellt ein sehr einfaches Verfahren zum stabilen Verbinden von Bauelementen dar, wobei die zu verbindenden Bauelemente mit ihren zu verbindenden Kontaktflächen zueinander gewandt in eine Sandwichanordnung überführt werden mit dazwischen appliziertem Sinterverbindungsmaterial, beispielsweise Sinterpaste. Die unter Verwendung von Sinterpaste geschaffene Sandwichanordnung wird anschließend einem Trocknungs- und Sinterschritt unterworfen, in dessen Verlauf die mechanisch feste, elektrisch und wärmeleitfähige Verbindung zwischen den Bauelementen ausgebildet wird. Das mechanisch feste Verbinden zweier Bauelemente ist also ein Befestigen des einen Bauelements an bzw. auf dem zweiten Bauelement über deren jeweilige Kontaktflächen. Aufgabe der Erfindung war die Bereitstellung einer insbesondere in Hinblick auf ihre Trocknungseigenschaften verbesserten Sinterpaste. Insbesondere sollte die zu findende Sinterpaste die Ausbildung von Sinterverbindungen zwischen Bauelementen erlauben, die keine oder zumindest akzeptable (tolerierbar geringfügige) trocknungsbedingte Fehlstellen in der aus der Sinterpaste applizierten und getrockneten, die Bauelemente verbindenden Schicht aufweisen. Trocknungsbedingte Fehlstellen sind insbesondere sogenannte Trocknungskanäle. Derartige Fehlstellen können nicht nur die mechanische Festigkeit der finalen Sinterverbindungen schwächen, sondern auch eine Verminderung der Wärme- und der elektrischen Leitfähigkeit bedingen. In the field of power and consumer electronics, the sintering of electronic components is a common process. Metal sintering paste is often used as the connecting material, the main components of which are dispersed, sinterable metal particles. Prominent examples of such sinter pastes include silver sinter pastes known to those skilled in the art. The sintered connection technique represents a very simple method for the stable connection of components, the components to be connected being transferred with their contact surfaces to be connected facing one another into a sandwich arrangement with sintered connection material applied in between, for example sintered paste. The sandwich arrangement created using sintering paste is then subjected to a drying and sintering step, during which the mechanically strong, electrically and thermally conductive connection between the components is formed. The mechanically fixed connection of two components is therefore a fastening of one component to or on the second component via their respective contact surfaces. The object of the invention was to provide a sintered paste which is improved in particular with regard to its drying properties. In particular, the sintering paste to be found should allow the formation of sintered connections between components which have no or at least acceptable (tolerably minor) defects caused by drying in the layer applied and dried from the sintering paste and connecting the components. Defects caused by drying are in particular so-called drying channels. Such defects can not only weaken the mechanical strength of the final sintered joints, but also cause a reduction in thermal and electrical conductivity.
Überraschenderweise kann die Aufgabe gelöst werden durch Bereitstellung einer Sinterpaste bestehend aus: Surprisingly, the task can be solved by providing a sintering paste consisting of:
(A) 30 bis 40 Gew.-% (Gewichts-%) Silberflakes (Silberplättchen) mit einer durchschnittlichen Teilchengröße im Bereich von 1 bis 20 pm, (A) 30 to 40% by weight (weight %) silver flakes (silver platelets) with an average particle size in the range from 1 to 20 μm,
(B) 8 bis 20 Gew.-% Silberpartikel mit einer durchschnittlichen Teilchengröße im Bereich von 20 bis 100 nm, (B) 8 to 20% by weight of silver particles with an average particle size in the range from 20 to 100 nm,
(C) 30 bis 45 Gew.-% Silber(l)oxidpartikel, (C) 30 to 45% by weight silver(I) oxide particles,
(D) 12 bis 20 Gew.-% mindestens eines organischen Lösemittels, (D) 12 to 20% by weight of at least one organic solvent,
(E) 0 bis 1 Gew.-% mindestens eines polymeren Bindemittels, und (E) 0 to 1% by weight of at least one polymeric binder, and
(F) 0 bis 0,5 Gew.-% mindestens eines von den Bestandteilen (A) bis (E) verschiedenen Additivs. (F) 0 to 0.5% by weight of at least one additive different from components (A) to (E).
Der hierin im Zusammenhang mit den Silberflakes (A) verwendete Begriff „durchschnittliche Teilchengröße“ bedeutet den mittels statischer automatisierter Analyse mikroskopischer Bilder bestimmbaren volumenmittleren Primärteilchendurchmesser (D50). Als Maß für den Teilchendurchmesser kann dabei zweckmäßig der sogenannte Equivalent Circular Area Diameter (ECAD) verwendet werden (vgl. RENLIANG XU ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), Bd. 132, Nr. 2-3, 24. Juni 2003 (2003-06-24), Seiten 145-153). Die statische automatisierte Analyse der mikroskopischen Bilder kann beispielsweise mit dem Messsystem Morphologi 4 von Malvern Instruments nach der Trockenbestimmungsmethode durchgeführt werden. The term “average particle size” used herein in connection with the silver flakes (A) means the volume-average primary particle diameter (D50) that can be determined by means of static automated analysis of microscopic images. The so-called Equivalent Circular Area Diameter (ECAD) can expediently be used as a measure for the particle diameter (cf. RENLIANG XU ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), vol. 132, No. 2-3, 24 June 2003 (2003-06-24), pages 145-153). The static, automated analysis of the microscopic images can be carried out, for example, using the Morphologi 4 measuring system from Malvern Instruments using the dry determination method.
Der hierin im Zusammenhang mit den Silberpartikeln (B) verwendete Begriff „durchschnittliche Teilchengröße“ bedeutet den mittels Laserbeugung bestimmbaren volumenmittleren Primärteilchendurchmesser (D50). Als Maß für den Teilchendurchmesser kann dabei zweckmäßig der sogenannte Equivalent Circular Area Diameter (ECAD) verwendet werden (vgl. RENLIANG XII ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), Bd. 132, Nr. 2-3, 24. Juni 2003 (2003-06- 24), Seiten 145-153). Laserbeugungsmessungen können mit einem entsprechenden Teilchengrößenmessgerät, beispielsweise einem Mastersizer 3000 oder einem Mastersizer 2000 von Malvern Instruments nach der Nassbestimmungsmethode durchgeführt werden. Bei der Nassbestimmungsmethode können im Rahmen der Probenvorbereitung beispielsweise 1 g Silberpartikel (B) in 200 ml Ethanol mittels Ultraschall dispergiert werden. The term "average particle size" as used herein in connection with the silver particles (B) means the volume-average determinable by means of laser diffraction primary particle diameter (D50). The so-called Equivalent Circular Area Diameter (ECAD) can expediently be used as a measure for the particle diameter (cf. RENLIANG XII ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), Vol. 132, No. 2-3, 24 June 2003 (2003-06-24), pages 145-153). Laser diffraction measurements can be carried out using an appropriate particle sizer, for example a Mastersizer 3000 or a Mastersizer 2000 from Malvern Instruments, using the wet determination method. In the case of the wet determination method, 1 g of silver particles (B) can be dispersed in 200 ml of ethanol using ultrasound as part of the sample preparation.
Die erfindungsgemäße Sinterpaste enthält als Bestandteil (A) 30 bis 40 Gew.-% bevorzugt 32 bis 37 Gew.-% Silberflakes mit einer durchschnittlichen Teilchengröße im Bereich von 1 bis 20 pm, bevorzugt 1 bis 10 pm. Das Aspektverhältnis der Silberflakes kann beispielsweise bei > 5 : 1 bis mehrere Hundert : 1 liegen. The sintering paste according to the invention contains as component (A) 30 to 40% by weight, preferably 32 to 37% by weight, of silver flakes with an average particle size in the range from 1 to 20 μm, preferably 1 to 10 μm. The aspect ratio of the silver flakes can be >5:1 to several hundred:1, for example.
Das Aspektverhältnis von Teilchen beschreibt den Quotienten aus größter und kleinster Längenausdehnung derselben und damit deren Form; nur um Missverständnissen vorzubeugen, im Falle von Teilchen in Form von Flakes oder Plättchen ist der Quotient aus größter und kleinster Längenausdehnung der Quotient aus größter Längenausdehnung und der Plättchendicke. Es kann durch Rasterelektronenmikroskopie und Auswertung der elektronenmikroskopischen Bilder durch Bestimmung der Abmessungen einer statistisch bedeutsamen Anzahl von einzelnen Teilchen bestimmt werden. The aspect ratio of particles describes the quotient of the largest and smallest length extension of the same and thus their shape; just to avoid misunderstandings, in the case of particles in the form of flakes or platelets, the quotient of the greatest and smallest linear expansion is the quotient of the greatest linear expansion and the platelet thickness. It can be determined by scanning electron microscopy and evaluating the electron micrographs by determining the dimensions of a statistically significant number of individual particles.
Die Silberflakes sind üblicherweise gecoatet (beschichtet). Die hier gemachten Gewichtsangaben schließen dann das Gewicht des Coatings (Beschichtung) auf den Silberflakes mit ein. The silver flakes are usually coated (coated). The weight information given here then includes the weight of the coating (coating) on the silver flakes.
Die Silberflakes können Flakes aus reinem Silber (Reinheit des Silbers von wenigstens 99,9 Gew.-%) und/oder solche aus Silberlegierungen mit bis zu 10 Gew.-% wenigstens eines anderen Legierungsmetalls umfassen. Beispiele für geeignete Legierungsmetalle sind Kupfer, Gold, Nickel, Palladium, Platin und Aluminium. Bevorzugt sind Silberflakes aus reinem Silber. The silver flakes can include flakes of pure silver (purity of the silver of at least 99.9% by weight) and/or those made of silver alloys with up to 10% by weight of at least one other alloying metal. Examples of suitable alloying metals are copper, gold, nickel, palladium, platinum and aluminum. Silver flakes of pure silver are preferred.
Das vorerwähnte Coating kann eine festhaftende Schicht auf der Oberfläche der Silberflakes sein. Üblicherweise handelt es sich um ein organisches Coating. Der Anteil des organischen Coatings kann beispielsweise im Bereich von 0,5 bis 1 ,5 Gew.-%, bezogen auf Silber respektive Silberlegierung, liegen. Im Allgemeinen kann ein solches organisches Coating 90 bis 100 Gew.- % einer oder mehrerer Fettsäuren und/oder Fettsäurederivate umfassen. Beispiele für Fettsäurederivate umfassen insbesondere Fettsäuresalze und Fettsäureester. Beispiele für Fettsäuren umfassen Caprylsäure (Octansäure), Caprinsäure (Decansäure), Laurinsäure (Dodecansäure), Myristinsäure (Tetradecansäure), Palmitinsäure (Hexadecansäure), Margarinsäure (Heptadecansäure), Stearinsäure (Octadecansäure), Ölsäure (9-Octadecensäure), Arachinsäure (Eicosansäure/Icosansäure), Behensäure (Docosansäure), Lignocerinsäure (T etracosansäure). The aforementioned coating can be an adherent layer on the surface of the silver flakes. It is usually an organic coating. The proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on silver or silver alloy, lying. In general, such an organic coating can comprise 90 to 100% by weight of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters. Examples of fatty acids include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
Die Silberflakes sind kommerziell erhältlich. Beispiele umfassen LIA8320, P6908 von Metalor, SF30L von Ames Goldsmith sowie die Produkte Silflake 40-592 und Silflake 40-50 von Technic. The silver flakes are commercially available. Examples include Metalor's LIA8320, P6908, Ames Goldsmith's SF30L, and Technic's Silflake 40-592 and Silflake 40-50 products.
Die erfindungsgemäße Sinterpaste enthält als Bestandteil (B) 8 bis 20 Gew.-%, bevorzugt 10 bis 16 Gew.-% Silberpartikel mit einer durchschnittlichen Teilchengröße im Bereich von 20 bis 100 nm. The sintering paste according to the invention contains as component (B) 8 to 20% by weight, preferably 10 to 16% by weight, of silver particles with an average particle size in the range from 20 to 100 nm.
Die Silberpartikel sind üblicherweise gecoatet. Die hier gemachten Gewichtsangaben schließen dann das Gewicht des Coatings auf den Silberpartikeln mit ein. The silver particles are usually coated. The weight information given here then includes the weight of the coating on the silver particles.
Die Silberpartikel sind keine Silberflakes, ihr Aspektverhältnis ist deutlich kleiner als das von Flakes, es liegt beispielsweise im Bereich von 1 : 1 bis 5 : 1. Ideal kugelförmige Partikel haben ein Aspektverhältnis von 1 : 1. Das Aspektverhältnis der Silberpartikel im Bereich von 1 : 1 bis 5 : 1 bedeutet, dass die Silberpartikel beispielsweise eine sphärische, eine im Wesentlichen sphärische, eine elliptische, eine eiförmige oder eine unregelmäßige Form aufweisen, keinesfalls jedoch die Form von Flakes. The silver particles are not silver flakes, their aspect ratio is significantly smaller than that of flakes, for example in the range from 1:1 to 5:1. Ideally spherical particles have an aspect ratio of 1:1. The aspect ratio of the silver particles is in the range of 1:1: 1 to 5:1 means that the silver particles have, for example, a spherical, an essentially spherical, an elliptical, an egg-shaped or an irregular shape, but in no way the shape of flakes.
Die Silberpartikel können Partikel aus reinem Silber (Reinheit des Silbers von wenigstens 99,9 Gew.-%) und/oder solche aus Silberlegierungen mit bis zu 10 Gew.-% wenigstens eines anderen Legierungsmetalls umfassen. Beispiele für geeignete Legierungsmetalle sind Kupfer, Gold, Nickel, Palladium, Platin und Aluminium. Bevorzugt sind Silberpartikel aus reinem Silber. The silver particles can comprise particles of pure silver (purity of the silver of at least 99.9% by weight) and/or particles made of silver alloys with up to 10% by weight of at least one other alloying metal. Examples of suitable alloying metals are copper, gold, nickel, palladium, platinum and aluminum. Silver particles made of pure silver are preferred.
Das vorerwähnte Coating kann eine festhaftende Schicht auf der Oberfläche der Silberpartikel sein. Üblicherweise handelt es sich um ein organisches Coating. Der Anteil des organischen Coatings kann beispielsweise im Bereich von 0,5 bis 1 ,5 Gew.-%, bezogen auf Silber respektive Silberlegierung, liegen. Im Allgemeinen kann ein solches organisches Coating 90 bis 100 Gew.- % einer oder mehrerer Fettsäuren und/oder Fettsäurederivate umfassen. Beispiele für Fettsäurederivate umfassen insbesondere Fettsäuresalze und Fettsäureester. Beispiele für Fettsäuren umfassen Caprylsäure (Octansäure), Caprinsäure (Decansäure), Laurinsäure (Dodecansäure), Myristinsäure (Tetradecansäure), Palmitinsäure (Hexadecansäure), Margarinsäure (Heptadecansäure), Stearinsäure (Octadecansäure), Ölsäure (9-Octadecensäure), Arachinsäure (Eicosansäure/Icosansäure), Behensäure (Docosansäure), Lignocerinsäure (Tetracosansäure). The aforementioned coating can be an adherent layer on the surface of the silver particles. It is usually an organic coating. The proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on the silver or silver alloy. In general, such an organic coating can contain 90 to 100% by weight % of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters. Examples of fatty acids include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
Die Silberpartikel sind kommerziell erhältlich. Beispiele umfassen 18060-NM2 von Arnes Goldsmith sowie die Produkte SIL 41-193, SIL 40-277, SIL 40-147 und SIL40-050-0720-2 von Technic. The silver particles are commercially available. Examples include Arnes Goldsmith's 18060-NM2 and Technic's SIL 41-193, SIL 40-277, SIL 40-147, and SIL40-050-0720-2 products.
Zumindest ein Teil der Silberpartikel kann an zumindest einen Teil der Silberflakes angehaftet sein. At least a portion of the silver particles may be attached to at least a portion of the silver flakes.
Die erfindungsgemäße Sinterpaste enthält als Bestandteil (C) 30 bis 45 Gew.-%, bevorzugt 32 bis 40 Gew.-% Silber(l)oxidpartikel. Die Silber(l)oxidpartikel dienen als Silberprecursor, woraus im Wege einer thermischen Zersetzung metallisches Silber gebildet werden kann. The sintering paste according to the invention contains, as component (C), 30 to 45% by weight, preferably 32 to 40% by weight, of silver(I) oxide particles. The silver(I) oxide particles serve as a silver precursor, from which metallic silver can be formed by thermal decomposition.
Die Silber(l)oxidpartikel können eine durchschnittliche Teilchengröße beispielsweise im Bereich von 0,4 bis 4 pm aufweisen. The silver(I) oxide particles can have an average particle size in the range from 0.4 to 4 μm, for example.
Der hierin im Zusammenhang mit den Silber(l)oxidpartikeln (C) verwendete Begriff „durchschnittliche Teilchengröße“ bedeutet den mittels Laserbeugung bestimmbaren volumenmittleren Primärteilchendurchmesser (D50). Als Maß für den Teilchendurchmesser kann dabei zweckmäßig der sogenannte Equivalent Circular Area Diameter (ECAD) verwendet werden (vgl. RENLIANG XU ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), Bd. 132, Nr. 2-3, 24. Juni 2003 (2003-06-24), Seiten 145-153). Laserbeugungsmessungen können mit einem entsprechenden Teilchengrößenmessgerät, beispielsweise einem Mastersizer 3000 oder einem Mastersizer 2000 von Malvern Instruments nach der Nassbestimmungsmethode durchgeführt werden. Bei der Nassbestimmungsmethode können im Rahmen der Probenvorbereitung beispielsweise 1 g Silber(l)oxidpartikel (C) in 200 ml Ethanol mittels Ultraschall dispergiert werden. Die Silber(l)oxidpartikel können gecoatet sein. Bevorzugt sind die Silber(l)oxidpartikel ungecoatet. The term “average particle size” used herein in connection with the silver(I) oxide particles (C) means the volume-average primary particle diameter (D50) that can be determined by means of laser diffraction. The so-called Equivalent Circular Area Diameter (ECAD) can expediently be used as a measure for the particle diameter (cf. RENLIANG XU ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), vol. 132, No. 2-3, 24 June 2003 (2003-06-24), pages 145-153). Laser diffraction measurements can be carried out using an appropriate particle sizer, for example a Mastersizer 3000 or a Mastersizer 2000 from Malvern Instruments, using the wet determination method. In the case of the wet determination method, 1 g of silver(I) oxide particles (C) can be dispersed in 200 ml of ethanol using ultrasound as part of the sample preparation. The silver(I) oxide particles can be coated. The silver(I) oxide particles are preferably uncoated.
Im Falle gecoateter Silber(l)oxidpartikel schließen die hier gemachten Gewichtsangaben das Gewicht des Coatings auf den Silber(l)oxidpartikeln mit ein. Das Coating kann eine festhaftende Schicht auf der Oberfläche der Silber(l)oxidpartikel sein. Üblicherweise handelt es sich um ein organisches Coating. Der Anteil des organischen Coatings kann beispielsweise im Bereich von 0,5 bis 1 ,5 Gew.-%, bezogen auf das Silber(l)oxid, liegen. Im Allgemeinen kann ein solches organisches Coating 90 bis 100 Gew.-% einer oder mehrerer Fettsäuren und/oder Fettsäurederivate umfassen. Beispiele für Fettsäurederivate umfassen insbesondere Fettsäuresalze und Fettsäureester. Beispiele für Fettsäuren umfassen Caprylsäure (Octansäure), Caprinsäure (Decansäure), Laurinsäure (Dodecansäure), Myristinsäure (Tetradecansäure), Palmitinsäure (Hexadecansäure), Margarinsäure (Heptadecansäure), Stearinsäure (Octadecansäure), Ölsäure (9-Octadecensäure), Arachinsäure (Eicosansäure/Icosansäure), Behensäure (Docosansäure), Lignocerinsäure (Tetracosansäure). In the case of coated silver(I) oxide particles, the weight information given here includes the weight of the coating on the silver(I) oxide particles. The coating can be a firmly adhering layer on the surface of the silver(I) oxide particles. It is usually an organic coating. The proportion of the organic coating can be, for example, in the range from 0.5 to 1.5% by weight, based on the silver(I) oxide. In general, such an organic coating can comprise 90 to 100% by weight of one or more fatty acids and/or fatty acid derivatives. Examples of fatty acid derivatives specifically include fatty acid salts and fatty acid esters. Examples of fatty acids include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid/ icosanoic acid), behenic acid (docosanic acid), lignoceric acid (tetracosanoic acid).
Die erfindungsgemäße Sinterpaste enthält als Bestandteil (D) 12 bis 20 Gew.-%, bevorzugt 14 bis 16 Gew.-% mindestens eines organischen Lösemittels. Beispiele für geeignete organische Lösemittel umfassen Terpineole, N-Methyl-2-pyrrolidon, Ethylenglykol, Dimethylacetamid, 1- Tridecanol, 2-Tridecanol, 3-Tridecanol, 4-Tridecanol, 5-Tridecanol, 6-Tridecanol, Isotridecanol, dibasische Ester (vorzugsweise Dimethylester der Glutar-, Adipin- oder Bernsteinsäure oder Mischungen davon), Glycerin, Diethylenglykol, Triethylenglykol und aliphatische, insbesondere gesättigte aliphatische Kohlenwasserstoffe mit 5 bis 32 C-Atomen, mehr bevorzugt 10 bis 25 C- Atomen und noch mehr bevorzugt 16 bis 20 C-Atomen. Solche aliphatischen Kohlenwasserstoffe werden beispielsweise von Exxon Mobil unter der Marke Exxsol™ D140 oder unter der Marke Isopar M™ vertrieben. Besonders bevorzugt als Bestandteil (D) sind Kombinationen mindestens eines Terpineols mit mindestens einem dibasischen Ester. The sintering paste according to the invention contains, as component (D), 12 to 20% by weight, preferably 14 to 16% by weight, of at least one organic solvent. Examples of suitable organic solvents include terpineols, N-methyl-2-pyrrolidone, ethylene glycol, dimethylacetamide, 1-tridecanol, 2-tridecanol, 3-tridecanol, 4-tridecanol, 5-tridecanol, 6-tridecanol, isotridecanol, dibasic esters (preferably dimethyl ester of glutaric, adipic or succinic acid or mixtures thereof), glycerol, diethylene glycol, triethylene glycol and aliphatic, in particular saturated aliphatic hydrocarbons having 5 to 32 carbon atoms, more preferably 10 to 25 carbon atoms and even more preferably 16 to 20 carbon atoms -Atoms. Such aliphatic hydrocarbons are sold, for example, by Exxon Mobil under the Exxsol™ D140 brand or under the Isopar M™ brand. Combinations of at least one terpineol with at least one dibasic ester are particularly preferred as component (D).
Die erfindungsgemäße Sinterpaste kann als Bestandteil (E) 0 bis 1 Gew.-%, bevorzugt 0,1 bis 0,7 Gew.-% mindestens eines polymeren Bindemittels enthalten. Das mindestens eine polymere Bindemittel umfasst dabei weder selbstvernetzbare Polymere noch kovalent vernetzbare Bindemittel/Härter-Kombinationen. Beispiele für geeignete polymere Bindemittel umfassen insbesondere Cellulosederivate, beispielsweise Methylcellulose, Ethylcellulose, Ethylmethylcellulose, Carboxycellulose, Hydroxypropylcellulose, Hydroxyethylcellulose, Hydroxymethyl cellulose. Die erfindungsgemäße Sinterpaste kann als Bestandteil (F) 0 bis 0,5 Gew.-%, bevorzugt 0 bis 0,3 Gew.-% mindestens eines von den Bestandteilen (A) bis (E) verschiedenen Additivs enthalten. Beispiele umfassen Tenside, Entschäumer, Benetzungsmittel und Antikorrosionsadditive. Bestandteil (F) umfasst bevorzugt keine Glaspartikel (Glasfritte). The sintering paste according to the invention can contain, as component (E), 0 to 1% by weight, preferably 0.1 to 0.7% by weight, of at least one polymeric binder. The at least one polymeric binder comprises neither self-crosslinkable polymers nor covalently crosslinkable binder/hardener combinations. Examples of suitable polymeric binders include, in particular, cellulose derivatives, for example methyl cellulose, ethyl cellulose, ethyl methyl cellulose, carboxy cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose. The sintering paste according to the invention can contain, as component (F), 0 to 0.5% by weight, preferably 0 to 0.3% by weight, of at least one additive different from components (A) to (E). Examples include surfactants, defoamers, wetting agents, and anti-corrosion additives. Constituent (F) preferably does not include any glass particles (glass frit).
Bei der erfindungsgemäßen Sinterpaste handelt es sich um eine Silbersinterpaste. The sinter paste according to the invention is a silver sinter paste.
Die Summe der Gew.-% der Bestandteile (A) bis (F) beträgt 100 Gew.-%, bezogen auf die erfindungsgemäße Sinterpaste, d.h. vor ihrer Applikation. Dementsprechend kann die Herstellung der erfindungsgemäßen Sinterpaste durch Vermischen der Bestandteile (A) bis (D) sowie gegebenenfalls (E) und gegebenenfalls (F) erfolgen. Dabei können übliche dem Fachmann bekannte Vorrichtungen verwendet werden, beispielsweise Rührwerke, Dreiwalzwerke, Leitstrahlmischer und/oder Dispermixer. Es kann zweckmäßig sein, die Silberflakes und die Silberpartikel zunächst miteinander vorzuvermischen, beispielsweise mittels eines Flügelrührers, einer Kugelmühle, eines Taumelmischers oder Gasstrahlmischers. Durch ein solches Vorvermischen der Silberflakes und der Silberpartikel kann zumindest ein Teil der Silberpartikel an zumindest einen Teil der Silberflakes angehaftet werden. Die Anhaftung der Silberpartikel an die Silberflakes kann durch Bestimmung der Teilchengrößenverteilung im Anschluss an das Vorvermischen nachvollzogen werden. Als Bestimmungsmethode kann die schon vorerwähnte Laserbeugungsmessung angewendet werden. Vor dem Vorvermischen zeigt sich zunächst eine bimodale Teilchengrößenverteilung, welche sich mit fortschreitendem Vorvermischen mehr und mehr in Richtung einer monomodalen Teilchengrößenverteilung verschiebt. Nach praktisch vollständigem Vorvermischen zeigt sich eine im Wesentlichen oder vollständig monomodale Teilchengrößenverteilung als Endzustand. In dem Zusammenhang bedeutet „im Wesentlichen monomodal“, dass mindestens einer von mehreren Peaks einer Teilchengrößenverteilungskurve mindestens 90 % der Fläche unter derThe sum of the % by weight of the components (A) to (F) is 100% by weight, based on the sinter paste according to the invention, i.e. before its application. Accordingly, the sintering paste according to the invention can be produced by mixing the components (A) to (D) and optionally (E) and optionally (F). Conventional devices known to those skilled in the art can be used here, for example agitators, three-roll mills, jet mixers and/or dispersers. It can be expedient to first premix the silver flakes and the silver particles with one another, for example by means of a paddle stirrer, a ball mill, a tumble mixer or a gas jet mixer. By pre-mixing the silver flakes and the silver particles in this way, at least a part of the silver particles can be attached to at least a part of the silver flakes. The adhesion of the silver particles to the silver flakes can be understood by determining the particle size distribution after premixing. The previously mentioned laser diffraction measurement can be used as a method of determination. Before premixing, a bimodal particle size distribution is initially evident, which shifts more and more in the direction of a monomodal particle size distribution as premixing progresses. After practically complete pre-mixing, an essentially or completely monomodal particle size distribution appears as the final state. In this context, "substantially monomodal" means that at least one of several peaks of a particle size distribution curve covers at least 90% of the area under the
Teilchengrößenverteilungskurve ausmacht. Die Anhaftung der Silberpartikel an die Silberflakes kann einer Agglomeration in der erfindungsgemäßen Sinterpaste vorbeugen oder eine solche verhindern; sie kann somit eine homogene Verteilung sowohl der Silberpartikel als auch der Silberflakes in der erfindungsgemäßen Sinterpaste fördern oder bewirken. Particle size distribution curve accounts for. The adhesion of the silver particles to the silver flakes can prevent or prevent agglomeration in the sinter paste according to the invention; it can thus promote or bring about a homogeneous distribution of both the silver particles and the silver flakes in the sinter paste according to the invention.
Die erfindungsgemäße Sinterpaste kann in einem Sinterverfahren, beispielsweise in einem Sinterverfahren wie vorstehend erläutert, eingesetzt werden. Unter Sintern wird das Verbinden von zwei oder mehr Bauelementen durch Erhitzen unter Vermeidung dessen, dass die Silberflakes und die Silberpartikel die flüssige Phase erreichen, verstanden. Die dabei gebildete feste mechanische Verbindung ist zugleich elektrisch und thermisch leitfähig; sie besteht zu > 95 Gew.-%, beispielsweise zu 95 bis 100 Gew.-%, aus Silber und ist daher nicht mit einer aus einem üblichen Silberleitkleber erzeugten Verbindung zwischen solcherlei Bauelementen vergleichbar. Eine aus einem üblichen Silberleitkleber erzeugte Verbindung umfasst üblicherweise einen Silberanteil von < 90 Gew.-%, beispielsweise im Bereich von 40 bis 90 Gew.-%, wobei der zu 100 Gew.-% fehlende Anteil üblicherweise einen Polymeranteil umfasst und gegebenenfalls einen Füllstoffanteil umfassen kann. Die Erfindung betrifft insofern auch ein Verfahren zum Verbinden von Bauelementen, bei dem man (1) eine Sandwichanordnung bereitstellt, die wenigstens zwei Bauelemente und eine zwischen den Bauelementen befindliche erfindungsgemäße Sinterpaste aufweist, (2) optional, jedoch bevorzugt die Sinterpaste trocknet und (3) die Sandwichanordnung sintert. Unter Trocknen wird das Entfernen von organischem Lösemittel aus der applizierten erfindungsgemäßen Sinterpaste verstanden. Die Schritte (1), (2) und (3) bilden eine Schrittfolge vom Typ (1)-(2)-(3) mit Schritt (2) als optionalem Schritt. In einer Ausführungsform des Verfahrens kann Schritt (1) schon ein Trocknen umfassen und Schritt (2) kann somit entfallen. In einer anderen Ausführungsform umfasst Schritt (1) das Trocknen nicht oder nur teilweise und der optionale Schritt (2) kann entfallen oder bevorzugt stattfinden; falls Schritt (2) hier entfällt, kann er im Zuge von Schritt (3) stattfinden bzw. damit überlappen. The sintering paste according to the invention can be used in a sintering process, for example in a sintering process as explained above. Sintering means connecting of two or more components by heating while avoiding that the silver flakes and the silver particles reach the liquid phase. The solid mechanical connection formed in this way is both electrically and thermally conductive; it consists of >95% by weight, for example 95 to 100% by weight, of silver and is therefore not comparable to a connection between such components produced from a conventional silver conductive adhesive. A connection produced from a customary silver conductive adhesive usually includes a silver content of <90% by weight, for example in the range from 40 to 90% by weight, with the portion missing from 100% by weight usually including a polymer portion and optionally a filler portion can. In this respect, the invention also relates to a method for connecting components, in which (1) a sandwich arrangement is provided which has at least two components and a sintering paste according to the invention located between the components, (2) optionally, but preferably, the sintering paste is dried and (3) the sandwich assembly sinters. Drying is understood as meaning the removal of organic solvent from the applied sinter paste according to the invention. Steps (1), (2) and (3) form a sequence of steps of type (1)-(2)-(3) with step (2) as an optional step. In one embodiment of the method, step (1) can already include drying and step (2) can therefore be omitted. In another embodiment, step (1) does not comprise the drying or only partly and the optional step (2) can be omitted or take place preferentially; if step (2) is omitted here, it can take place in the course of step (3) or overlap with it.
Die Bauelemente können - soweit sie nicht ohnehin aus Metall bestehen - wenigstens eine Metallkontaktfläche, beispielsweise in Form einer Metallisierungsschicht, umfassen, worüber die schon erwähnte Sandwichanordnung im Rahmen des erfindungsgemäßen Verfahrens erfolgt. Selbst Bauelemente aus Aluminium, Aluminiumlegierungen (Aluminiumanteil >90 Gew.%) oder mit Aluminiumkontaktfläche oder Aluminium-basierter Kontaktfläche jeweils mit dem für Aluminium starken Wärmeausdehnungsverhalten können im Rahmen des erfindungsgemäßen Verfahrens mit Erfolg verwendet werden; mit anderen Worten, sie lassen sich mit der erfindungsgemäßen Sinterpaste erfolgreich Sinterverbinden. Unless they are made of metal anyway, the components can comprise at least one metal contact surface, for example in the form of a metallization layer, via which the already mentioned sandwich arrangement takes place within the scope of the method according to the invention. Even components made of aluminum, aluminum alloys (aluminum content >90% by weight) or with an aluminum contact surface or aluminum-based contact surface, each with the strong thermal expansion behavior for aluminum, can be used successfully in the context of the method according to the invention; in other words, they can be successfully sinter-bonded with the sinter paste of the present invention.
In Schritt (1) werden zunächst die zwei oder mehr Bauelemente miteinander in Kontakt gebracht. Das Kontaktieren erfolgt dabei über die erfindungsgemäße Sinterpaste. Zu diesem Zweck wird eine Sandwichanordnung bereitgestellt, bei der sich zwischen jeweils zwei der wenigstens zwei Bauelemente erfindungsgemäße Sinterpaste befindet. Unter Sandwichanordnung ist eine Anordnung zu verstehen, bei der sich zwei Bauelemente übereinander befinden und die Bauelemente im Wesentlichen parallel zueinander angeordnet sind. In step (1), the two or more components are first brought into contact with one another. The contacting takes place via the sintering paste according to the invention. For this purpose, a sandwich arrangement is provided in which sintering paste according to the invention is located between two of the at least two components. Under sandwich arrangement is to be understood as an arrangement in which two components are located one above the other and the components are arranged substantially parallel to each other.
Die Sandwichanordnung kann nach einem aus dem Stand der Technik bekannten Verfahren hergestellt werden. Dabei wird die betreffende Metallkontaktfläche eines der Bauelemente mit der erfindungsgemäßen Sinterpaste versehen. Anschließend wird das andere Bauelement mit seiner Metallkontaktfläche auf die Sinterpaste, die auf die Metallkontaktfläche des einen Bauelements aufgetragen und gegebenenfalls auch schon getrocknet worden ist, aufgesetzt. The sandwich arrangement can be produced using a method known from the prior art. The relevant metal contact surface of one of the components is provided with the sintering paste according to the invention. The metal contact surface of the other component is then placed on the sintering paste that has been applied to the metal contact surface of one component and, if appropriate, has already been dried.
Die Auftragung der erfindungsgemäßen Sinterpaste auf die betreffende Metallkontaktfläche des einen Bauelements kann mittels herkömmlicher Verfahren erfolgen, beispielsweise mittels Druckverfahren wie Siebdruck oder Schablonendruck. Andererseits kann die Auftragung der erfindungsgemäßen Sinterpaste auch mittels Dispenstechnik, Jetten, mittels Pintransfer oder durch Dippen erfolgen. Die erfindungsgemäße Sinterpaste eignet sich besonders für die Applikation mittels einer Auftragungstechnik, bei welcher eine wiederholte Scherbelastung auf die Sinterpaste einwirkt. Beispielsweise bei der Applikation mittels Dispenstechnik kann es zu einer solchen wiederholten Scherbelastung aufgrund wiederholter Druckwechsel im Sinterpasten-Vorratsbehälter kommen. Die erfindungsgemäße Sinterpaste zeigt thixotropes Verhalten und kehrt bei nachlassender Scherbelastung oder ohne Scherbelastung (in Ruhe) jeweils bemerkenswert schnell wieder nahe zur oder gänzlich zur Ausgangsviskosität zurück.The sintering paste according to the invention can be applied to the relevant metal contact surface of one component using conventional methods, for example using printing methods such as screen printing or stencil printing. On the other hand, the sintering paste according to the invention can also be applied by means of the dispensing technique, jetting, by means of pin transfer or by dipping. The sinter paste according to the invention is particularly suitable for application by means of an application technique in which repeated shear stress acts on the sinter paste. For example, when applying by means of a dispensing technique, such a repeated shearing stress can occur due to repeated pressure changes in the sintering paste storage container. The sintering paste according to the invention exhibits thixotropic behavior and, when the shearing stress decreases or without shearing stress (at rest), in each case returns remarkably quickly to almost or entirely to the initial viscosity.
Das Viskositätsverhalten kann beispielsweise mittels Rotationsviskosimetrie untersucht werden, beispielsweise bei 20°C unter Verwendung des Platte-Kegel-Messprinzips bei einem Kegeldurchmesser von 25 mm und einem Kegelwinkel von 2° mit einem Messspalt von 0,05 mm und beispielsweise mit einer innerhalb von 15 Minuten gleichmäßig über den Bereich von 0,05 bis 30 s'1 ansteigenden Scherrate. Die sogenannte Erholungsrate nach Scherbelastung kann beispielsweise so bestimmt werden wie in Beispiel 2.2. nachstehend erläutert. The viscosity behavior can be examined, for example, by means of rotational viscometry, for example at 20°C using the plate-cone measuring principle with a cone diameter of 25 mm and a cone angle of 2° with a measuring gap of 0.05 mm and, for example, within 15 minutes steadily increasing shear rate over the range of 0.05 to 30 s- 1 . The so-called recovery rate after shear stress can be determined, for example, as in example 2.2. explained below.
Die Nassschichtdicke der Sinterpaste liegt vorzugsweise im Bereich von 20 bis 400 pm. Die bevorzugte Nassschichtdicke ist beispielsweise abhängig vom gewählten Auftragungsverfahren für die Sinterpaste. Wird die Sinterpaste beispielsweise mittels Siebdruckverfahren aufgetragen, dann kann eine Nassschichtdicke von beispielsweise 20 bis 60 pm bevorzugt sein. Erfolgt die Auftragung der Sinterpaste beispielsweise mittels Schablonendruck, dann kann die bevorzugte Nassschichtdicke beispielsweise im Bereich von 20 bis 400 pm liegen. Beispielsweise bei der Dispenstechnik kann die bevorzugte Nassschichtdicke beispielsweise im Bereich von 20 bis 400 pm liegen je nach verwendetem Auftragungswerkzeug, beispielsweise bei Verwendung einer Hohlnadel im Bereich von 20 bis 100 pm oder beispielsweise bei Verwendung einer zugleich als Rakel fungierenden Breitschlitzdüse im Bereich von 50 bis 400 pm. The wet layer thickness of the sintering paste is preferably in the range from 20 to 400 μm. The preferred wet layer thickness depends, for example, on the selected application method for the sinter paste. If the sintering paste is applied, for example, by means of a screen printing process, then a wet layer thickness of, for example, 20 to 60 μm may be preferred. If the sintering paste is applied, for example, by means of stencil printing, then the preferred wet layer thickness can be, for example, in the range from 20 to 400 μm. For example, in the case of the dispensing technique, the preferred wet layer thickness can be in the range from 20 to 400 μm, depending on the application tool used, for example during use a hollow needle in the range from 20 to 100 μm or, for example, when using a slot die that also functions as a doctor blade in the range from 50 to 400 μm.
Im Anschluss an die Auftragung der erfindungsgemäßen Sinterpaste auf die Metallkontaktfläche des einen Bauelements wird die mit der gegebenenfalls schon teilweise oder vollständig getrockneten Sinterpaste versehene Metallkontaktfläche dieses Bauelements mit der entsprechenden Metallkontaktfläche des damit zu verbindenden Bauelements über die Sinterpaste in Kontakt gebracht. Somit befindet sich zwischen den zu verbindenden Bauelementen eine Schicht nicht, teilweise oder vollständig getrocknete erfindungsgemäße Sinterpaste im Sinne der Bildung der Sandwichanordnung. After the sintering paste according to the invention has been applied to the metal contact surface of one component, the metal contact surface of this component, which may already have been partially or completely dried, is brought into contact with the corresponding metal contact surface of the component to be connected via the sintering paste. Thus, between the components to be connected there is a layer of partially or completely dried sintering paste according to the invention in terms of the formation of the sandwich arrangement.
Gemäß einer bevorzugten Ausführungsform liegt der Anteil an organischem Lösemittel in der Sinterpaste nach der Trocknung beispielsweise bei 0 bis 5 Gew.-%, bezogen auf den ursprünglichen Anteil an organischem Lösemittel in der erfindungsgemäßen Sinterpaste. Mit anderen Worten, bei der Trocknung gemäß dieser bevorzugten Ausführungsform werden beispielsweise 95 bis 100 Gew.-% des oder der ursprünglich in der erfindungsgemäßen Sinterpaste enthaltenen organischen Lösemittel entfernt. According to a preferred embodiment, the proportion of organic solvent in the sinter paste after drying is, for example, 0 to 5% by weight, based on the original proportion of organic solvent in the sinter paste according to the invention. In other words, during the drying according to this preferred embodiment, for example 95 to 100% by weight of the organic solvent(s) originally present in the sinter paste according to the invention are removed.
Die Trocknungstemperatur in einem stattfindenden Schritt (2) liegt vorzugsweise im Bereich von 100 bis 150 °C. Übliche Trocknungszeiten liegen beispielsweise im Bereich von 5 bis 45 Minuten. Zur Verkürzung der Trocknungszeit kann unterstützend ein Vakuum verwendet werden, beispielsweise ein Druck im Bereich von 100 bis 300 mbar. The drying temperature in an ongoing step (2) is preferably in the range of 100 to 150°C. Typical drying times are, for example, in the range from 5 to 45 minutes. A vacuum can be used to shorten the drying time, for example a pressure in the range from 100 to 300 mbar.
Die erfindungsgemäße Sinterpaste zeichnet sich dadurch aus, dass die Bildung sogenannter Trocknungskanäle innerhalb der zwischen den Bauelementen befindlichen Schicht aus Sinterpaste weitgehend oder sogar vollständig vermieden werden kann. Dies ist insofern überraschend, als zu erwarten gewesen wäre, dass die vergleichsweise kleinen Silberpartikel (B) die Hohlräume zwischen den größeren Silberflakes (A) innerhalb der Schicht aus Sinterpaste ausfüllen. Bei einer so erwarteten dichteren Anordnung von Silberflakes (A) und Silberpartikeln (B) sollte jedoch ein Entweichen des organischen Lösemittels erschwert sein, so dass eine vermehrte Bildung trocknungsbedingter Fehlstellen und Trocknungskanäle zu erwarten gewesen wäre. The sintering paste according to the invention is characterized in that the formation of so-called drying channels within the layer of sintering paste located between the components can be largely or even completely avoided. This is surprising insofar as it would have been expected that the comparatively small silver particles (B) would fill the cavities between the larger silver flakes (A) within the layer of sinter paste. With such an expected dense arrangement of silver flakes (A) and silver particles (B), however, it should be more difficult for the organic solvent to escape, so that an increased formation of drying-related defects and drying channels would have been expected.
Die Neigung zur Bildung von Trocknungskanälen kann der Fachmann experimentell prüfen, indem er die vorerwähnten Schritte (1) und (2) durchführt und dabei anstelle des zweiten Bauelements eine Glasplatte oder eine Keramikplatte verwendet. Als erstes Bauelement kann dabei beispielsweise ein Keramiksubstrat verwendet werden. Während bzw. nach Beendigung der Trocknung entsprechend Schritt (2) kann er so beobachten oder visuell bewerten, inwieweit sich trocknungsbedingte Fehlstellen oder Trocknungskanäle in der Sinterpastenschicht ausbilden, während flüchtiges organisches Lösemittel randseitig die Sinterpastenschicht der Sandwichanordnung verlässt. Die erfindungsgemäße Sinterpaste zeichnet sich durch ein günstiges Trocknungsverhalten aus mit geringer oder ohne Neigung zur Bildung von Trocknungskanälen. Das Trocknungsverhalten kann beispielsweise so evaluiert werden wie in Beispiel 2.1. nachstehend erläutert. The propensity for the formation of drying channels can be checked experimentally by a person skilled in the art by carrying out steps (1) and (2) above and doing so instead of the second Component used a glass plate or a ceramic plate. A ceramic substrate, for example, can be used as the first component. During or after the end of drying according to step (2), he can observe or visually assess the extent to which drying-related defects or drying channels form in the sinter paste layer, while volatile organic solvent leaves the sinter paste layer of the sandwich arrangement at the edge. The sinter paste according to the invention is characterized by favorable drying behavior with little or no tendency to form drying channels. The drying behavior can be evaluated, for example, as in example 2.1. explained below.
Nach Beendigung von Schritt (1) respektive Schritt (2) wird die Sandwichanordnung schließlich einem Sinterprozess unterworfen. Dieser Sinterschritt (3) des erfindungsgemäßen Verfahrens kann unter Druckanwendung oder drucklos durchgeführt werden. Drucklose Durchführung bedeutet, dass trotz Verzichts auf die Anwendung von mechanischem Druck eine hinreichend feste Verbindung zwischen den Bauelementen erzielt werden kann. After completion of step (1) or step (2), the sandwich arrangement is finally subjected to a sintering process. This sintering step (3) of the method according to the invention can be carried out under pressure or without pressure. Pressureless implementation means that a sufficiently strong connection between the components can be achieved despite dispensing with the application of mechanical pressure.
Das eigentliche Sintern erfolgt bei einer Temperatur von beispielsweise 200 bis 280 °C und dabei wie gesagt entweder als druckloser Prozess oder als Drucksintern. The actual sintering takes place at a temperature of, for example, 200 to 280 °C and, as mentioned, either as a pressureless process or as pressure sintering.
Beim Drucksintern liegt der Prozessdruck vorzugsweise unter 30 MPa und mehr bevorzugt unter 15 MPa. Beispielsweise liegt der Prozessdruck im Bereich von 1 bis 30 MPa und mehr bevorzugt im Bereich von 5 bis 15 MPa. In the case of pressure sintering, the process pressure is preferably below 30 MPa and more preferably below 15 MPa. For example, the process pressure is in the range of 1 to 30 MPa, and more preferably in the range of 5 to 15 MPa.
Die Sinterzeit liegt beispielsweise im Bereich von 2 bis 90 Minuten, beim Drucksintern beispielsweise im Bereich von 2 bis 5 Minuten, beim Drucklossintern beispielsweise im Bereich von 30 bis 75 Minuten. The sintering time is for example in the range from 2 to 90 minutes, in the case of pressure sintering for example in the range from 2 to 5 minutes, in the case of pressureless sintering for example in the range from 30 to 75 minutes.
Der Sinterprozess kann in einer Atmosphäre erfolgen, die keinen besonderen Beschränkungen unterliegt. So kann das Sintern einerseits in einer Atmosphäre durchgeführt werden, die Sauerstoff enthält. Andererseits ist es auch möglich, das Sintern in sauerstofffreier Atmosphäre oder im Vakuum durchzuführen. Unter sauerstofffreier Atmosphäre ist im Rahmen der Erfindung eine Atmosphäre zu verstehen, deren Sauerstoffgehalt nicht mehr als 300 Gew.-ppm (Gewichts-ppm), vorzugsweise nicht mehr als 100 Gew.-ppm und noch mehr bevorzugt nicht mehr als 50 Gew.-ppm beträgt. Das Sintern wird in einer herkömmlichen, zum Sintern geeigneten Vorrichtung durchgeführt, in der sich die vorstehend beschriebenen Prozessparameter einstellen lassen. The sintering process can be carried out in an atmosphere which is not particularly restricted. On the one hand, sintering can be carried out in an atmosphere containing oxygen. On the other hand, it is also possible to carry out the sintering in an oxygen-free atmosphere or in a vacuum. In the context of the invention, an oxygen-free atmosphere means an atmosphere in which the oxygen content is no more than 300 ppm by weight (ppm by weight), preferably no more than 100 ppm by weight, and even more preferably no more than 50 ppm by weight amounts to. The sintering is carried out in a conventional device suitable for sintering, in which the process parameters described above can be set.
Beispiele examples
1. Herstellung von Sinterpasten: 1. Production of sinter pastes:
Die Zusammensetzungen der erfindungsgemäßen Sinterpasten 1 , 2 und 3 sowie der Vergleichspasten V1 , V2 und V3 in Gew.-% sind in Tabelle 1 aufgeführt. The compositions of the sintering pastes 1, 2 and 3 according to the invention and of the comparison pastes C1, C2 and C3 in % by weight are listed in Table 1.
Bei Sinterpaste 1 wurden die Silberflakes und die Silberpartikel in einem Taumelmischer für 120 min vorgemischt und anschließend zu den in der Tabelle 1 aufgeführten weiteren Pastenbestandteilen gegeben. Bei den Sinterpasten 2 und 3 sowie bei den Vergleichspasten V1, V2 und V3 wurden die Silberflakes und die Silberpartikel hingegen nicht vorgemischt, sondern nacheinander direkt zu den weiteren Pastenbestandteilen gegeben. In the case of sinter paste 1, the silver flakes and the silver particles were premixed in a tumble mixer for 120 minutes and then added to the other paste components listed in Table 1. In contrast, in the case of sinter pastes 2 and 3 and in the comparison pastes C1, C2 and C3, the silver flakes and the silver particles were not premixed, but instead were added directly one after the other to the other paste components.
Tabelle 1 : Zusammensetzung erfindungsgemäßer Sinterpasten 1 , 2 und 3 sowie derTable 1: Composition of inventive sintering pastes 1, 2 and 3 and the
Vergleichspasten V1, V2 und V3 Comparative pastes V1, V2 and V3
Silberflakes: D50: 3 pm, gecoatet mit 0,7 Gew.-% eines 1 :1 -Gemischs aus Stearin- und LaurinsäureSilver flakes: D50: 3 μm, coated with 0.7% by weight of a 1:1 mixture of stearic and lauric acid
** Silberpartikel: D50: 50 nm, gecoatet mit 1 ,5 Gew.-% Ölsäure ** Silver particles: D50: 50 nm, coated with 1.5% by weight oleic acid
***Silber(l)oxid: D50: 1.7 pm, ungecoatet ***Silver(I)oxide: D50: 1.7 pm, uncoated
2. Evaluierung der Sinterpasten: 2. Evaluation of the sinter pastes:
Die erfindungsgemäßen Sinterpasten 1 , 2 und 3 sowie die Vergleichspasten V1 , V2 und V3 wurden hinsichtlich ihres Trocknungsverhaltens, ihres Erholungsvermögens nach Scherbelastung sowie ihres Sintervermögens auf Aluminium- und Kupferoberflächen untersucht. The sintering pastes 1, 2 and 3 according to the invention and the comparison pastes C1, C2 and C3 were examined with regard to their drying behavior, their ability to recover after shear stress and their ability to sinter on aluminum and copper surfaces.
2.1. Evaluierung des Trocknungsverhaltens: 2.1. Evaluation of the drying behavior:
Zur Evaluierung des Trocknungsverhaltens wurden die Pasten jeweils zunächst mittels Schablonendruck quadratisch (5 cm x 5 cm) in einer Nassschichtdicke von 300 pm auf die Oberfläche eines Aluminiumblechs aufgebracht. Anschließend wurden die Oberflächen der nassen nicht getrockneten Pasten jeweils vollständig mit einem 1 mm dicken Glasplättchen abgedeckt, so dass nur die Außenränder der Pasten frei lagen. Anschließend wurden diese Testaufbauten auf eine Wärmeplatte gelegt und die mit den Glasplättchen abgedeckten Pastenschichten bei 130°C für 15 min getrocknet. Die Entstehung etwaiger Trocknungskanäle oder Fehlstellen wurde mit Hilfe eines optischen Mikroskops untersucht und, wie in Tabelle 2 angegeben, bewertet. To evaluate the drying behavior, the pastes were each first applied to the surface of an aluminum sheet by means of stencil printing squares (5 cm×5 cm) in a wet layer thickness of 300 μm. Subsequently, the surfaces of the wet, non-dried pastes were each covered completely with a 1 mm thick glass plate covered so that only the outer edges of the pastes were exposed. These test structures were then placed on a hot plate and the paste layers covered with the glass plates were dried at 130° C. for 15 minutes. The development of any drying channels or voids was examined using an optical microscope and rated as indicated in Table 2.
2.2. Evaluierung der Erholungsrate nach Scherbelastung: 2.2. Evaluation of recovery rate after shear stress:
Die Erholungsrate nach Scherbelastung wurde für die verschiedenen Sinterpasten mittels Rotationsviskosimetrie unter Verwendung des Platte-Kegel-Messprinzips bei einem Kegeldurchmesser von 25 mm und einem Kegelwinkel von 2° mit einem Messspalt von 0,05 mm bei veränderlicher Scherrate bestimmt. Hierzu wurde ein Messdurchlauf gewählt, bei dem angefangen mit einer 30 Sekunden dauernden niedrigen Scherrate von 30 s-1 ein sprunghafter Wechsel zu einer 30 Sekunden dauernden hohen Scherrate von 100 s-1 stattfand. Dieser Messdurchlauf wurde in direkter Folge insgesamt zwölf Mal wiederholt. Die Erholungsrate wurde als prozentuale Veränderung der Endviskosität im Vergleich zur Anfangsviskosität bestimmt [(Quotient aus Endviskosität und Anfangsviskosität) x 100%]. Die Anfangsviskosität ist dabei als letzter Messpunkt bei niedriger Scherrate beim ersten Messdurchlauf und die Endviskosität als letzter Messpunkt bei niedriger Scherrate beim zwölften Messdurchlauf definiert. The recovery rate after shear stress was determined for the different sinter pastes by means of rotational viscometry using the plate-cone measuring principle with a cone diameter of 25 mm and a cone angle of 2° with a measuring gap of 0.05 mm at changing shear rates. For this purpose, a measurement run was selected in which, starting with a low shear rate of 30 s -1 lasting 30 seconds, there was a sudden change to a high shear rate of 100 s -1 lasting 30 seconds. This measurement run was repeated a total of twelve times in direct succession. The recovery rate was determined as the percent change in final viscosity compared to initial viscosity [(final viscosity divided by initial viscosity) x 100%]. The initial viscosity is defined as the last measurement point at a low shear rate in the first measurement run and the final viscosity as the last measurement point at a low shear rate in the twelfth measurement run.
2.3. Bestimmung der Scherfestigkeit: 2.3. Determination of the shear strength:
Zur Bestimmung des Sintervermögens auf Aluminium und Kupfer wurden die Scherfestigkeiten des jeweiligen Sinterverbindungsmaterials auf Aluminium bzw. Kupfer bestimmt. Hierzu wurden die erfindungsgemäßen Sinterpasten sowie die Vergleichspasten mittels Schablonendruck auf ein Aluminiumblech von 5 mm Dicke bzw. auf die 300 pm dicke Kupferoberfläche eines DCB- Substrats in einer Nassschichtdicke von 50 pm appliziert. Anschließend wurden die applizierten Sinterpasten bei 140 °C für 10 min vorgetrocknet und danach mit einem Siliziumchip mit Silberkontaktfläche (4 mm x 4 mm) vollflächig in Kontakt gebracht. Das anschließende Drucksintern erfolgte unter Stickstoffatmosphäre (<100 ppm Sauerstoff) in einer Heißpresse bei 230 °C und 12 MPa für 5 Minuten. Zwecks Bestimmung der Scherfestigkeit wurden die Bauelemente mit einem Schermeißel bei einer Geschwindigkeit von 0,3 mm/s bei 20°C abgeschert. Die Kraft wurde mittels einer Kraftmessdose aufgenommen (Gerät DAGE 2000 der Firma DAGE, Deutschland). Tabelle 2: Evaluierung der erfindungsgemäßen Sinterpasten 1 , 2 und 3 sowie der Vergleichspasten V1, V2 und V3 hinsichtlich Trocknungsverhalten, Erholungsrate direkt nach Scherbelastung sowie der Scherfestigkeit auf Aluminium- und Kupferoberflächen To determine the sintering ability on aluminum and copper, the shear strengths of the respective sintered connection material were determined on aluminum or copper. For this purpose, the sintering pastes according to the invention and the comparison pastes were applied by means of stencil printing to an aluminum sheet 5 mm thick or to the 300 μm thick copper surface of a DCB substrate in a wet layer thickness of 50 μm. The applied sintering pastes were then pre-dried at 140° C. for 10 minutes and then brought into full-area contact with a silicon chip with a silver contact area (4 mm×4 mm). The subsequent pressure sintering took place under a nitrogen atmosphere (<100 ppm oxygen) in a hot press at 230° C. and 12 MPa for 5 minutes. To determine the shear strength, the components were sheared off with a shearing tool at a speed of 0.3 mm/s at 20°C. The force was recorded using a load cell (DAGE 2000 device from DAGE, Germany). Table 2: Evaluation of the sinter pastes 1, 2 and 3 according to the invention and the comparison pastes V1, V2 and V3 with regard to drying behavior, recovery rate directly after shear stress and the shear strength on aluminum and copper surfaces

Claims

Patentansprüche patent claims
1. Sinterpaste bestehend aus: 1. Sintering paste consisting of:
(A) 30 bis 40 Gew.-% Silberflakes mit einer durchschnittlichen Teilchengröße im Bereich von 1 bis 20 pm, (A) 30 to 40% by weight silver flakes with an average particle size in the range from 1 to 20 μm,
(B) 8 bis 20 Gew.-% Silberpartikel mit einer durchschnittlichen Teilchengröße im Bereich von 20 bis 100 nm, (B) 8 to 20% by weight of silver particles with an average particle size in the range of 20 to 100 nm,
(C) 30 bis 45 Gew.-% Silber(l)oxidpartikel, (C) 30 to 45% by weight silver(I) oxide particles,
(D) 12 bis 20 Gew.-% mindestens eines organischen Lösemittels, (D) 12 to 20% by weight of at least one organic solvent,
(E) 0 bis 1 Gew.-% mindestens eines polymeren Bindemittels, und (E) 0 to 1% by weight of at least one polymeric binder, and
(F) 0 bis 0,5 Gew.-% mindestens eines von den Bestandteilen (A) bis (E) verschiedenen Additivs. (F) 0 to 0.5% by weight of at least one additive different from components (A) to (E).
2. Sinterpaste nach Anspruch 1 , wobei die Silberpartikel ein Aspektverhältnis im Bereich von 1 : 1 bis 5 : 1 aufweisen. 2. Sintering paste according to claim 1, wherein the silver particles have an aspect ratio in the range from 1:1 to 5:1.
3. Sinterpaste nach Anspruch 1 oder 2, wobei die Silber(l)oxidpartikel eine durchschnittliche Teilchengröße im Bereich von 0,4 bis 4 pm aufweisen. 3. Sintering paste according to claim 1 or 2, wherein the silver(I) oxide particles have an average particle size in the range from 0.4 to 4 μm.
4. Sinterpaste nach einem der vorhergehenden Ansprüche, wobei das mindestens eine organische Lösemittel eine Kombination aus mindestens einem Terpineol mit mindestens einem dibasischen Ester ist. 4. Sintering paste according to one of the preceding claims, wherein the at least one organic solvent is a combination of at least one terpineol with at least one dibasic ester.
5. Sinterpaste nach einem der vorhergehenden Ansprüche, wobei das mindestens eine polymere Bindemittel aus Cellulosederivaten ausgewählt ist. 5. Sintering paste according to one of the preceding claims, wherein the at least one polymeric binder is selected from cellulose derivatives.
6. Sinterpaste nach einem der vorhergehenden Ansprüche, wobei zumindest ein Teil der Silberpartikel an zumindest einen Teil der Silberflakes angehaftet ist. 6. Sintering paste according to any one of the preceding claims, wherein at least part of the silver particles are adhered to at least part of the silver flakes.
7. Verfahren zur Herstellung einer Sinterpaste nach einem der vorhergehenden Ansprüche, wobei die Bestandteile (A) bis (D) sowie gegebenenfalls (E) und gegebenenfalls (F) miteinander vermischt werden, und wobei die Bestandteile (A) und (B) zunächst miteinander vorvermischt werden. 7. A method for producing a sintering paste according to any one of the preceding claims, wherein the components (A) to (D) and optionally (E) and optionally (F) are mixed together, and wherein the components (A) and (B) are first mixed together be premixed.
8. Verfahren zum Verbinden von Bauelementen, bei dem man (1) eine Sandwichanordnung bereitstellt, die wenigstens zwei Bauelemente und eine zwischen den Bauelementen befindliche Sinterpaste nach einem der Ansprüche 1 bis 6 oder hergestellt nach einem Verfahren gemäß Anspruch 7 aufweist, (2) optional, die Sinterpaste trocknet und (3) die Sandwichanordnung sintert. 8. A method for connecting components, in which (1) a sandwich arrangement is provided which has at least two components and a sintering paste located between the components according to one of claims 1 to 6 or produced by a method according to claim 7, (2) optionally , the sinter paste dries and (3) sinters the sandwich assembly.
9. Verfahren nach Anspruch 8, wobei wenigstens eines der Bauelemente aus Aluminium oder einer Aluminiumlegierung besteht oder eine Aluminiumkontaktfläche oder eine Aluminiumbasierte Kontaktfläche aufweist, über die die Sandwichanordnung erfolgt. 9. The method according to claim 8, wherein at least one of the components consists of aluminum or an aluminum alloy or has an aluminum contact surface or an aluminum-based contact surface over which the sandwich arrangement takes place.
10. Verfahren nach Anspruch 8 oder 9, wobei die Sinterpaste mittels Dispenstechnik appliziert wird. 10. The method according to claim 8 or 9, wherein the sintering paste is applied by means of dispensing technology.
11 . Verfahren nach einem der Ansprüche 8 bis 10, wobei man unter Druckanwendung oder drucklos sintert. 11 . Process according to one of Claims 8 to 10, in which the sintering is carried out under pressure or without pressure.
12. Verfahren nach einem der Ansprüche 8 bis 11 , wobei es sich bei den Bauelementen um in der Elektronik verwendete Bauteile handelt. 12. The method according to any one of claims 8 to 11, wherein the components are components used in electronics.
EP21749560.5A 2020-12-16 2021-07-22 Sintering paste and use thereof for connecting components Pending EP4263120A1 (en)

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