Classifications

• • 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
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
  • H05K3/1283—After-treatment of the printed patterns, e.g. sintering or curing methods
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0386—Paper sheets
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0393—Flexible materials
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
  • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/01—Dielectrics
  • H05K2201/0104—Properties and characteristics in general
  • H05K2201/0116—Porous, e.g. foam
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/01—Tools for processing; Objects used during processing
  • H05K2203/0104—Tools for processing; Objects used during processing for patterning or coating
  • H05K2203/0143—Using a roller; Specific shape thereof; Providing locally adhesive portions thereon
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/02—Details related to mechanical or acoustic processing, e.g. drilling, punching, cutting, using ultrasound
  • H05K2203/0278—Flat pressure, e.g. for connecting terminals with anisotropic conductive adhesive
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/15—Position of the PCB during processing
  • H05K2203/1545—Continuous processing, i.e. involving rolls moving a band-like or solid carrier along a continuous production path
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/102—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern by bonding of conductive powder, i.e. metallic powder
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/14—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using spraying techniques to apply the conductive material, e.g. vapour evaporation

Definitions

• the present invention relates to thin films in general, and, in particular, to a method of forming thin film conductors on a substrate.
• Photonic curing is the high-temperature thermal processing of a thin film using light pulses from a flashlamp. Photonic curing allows thin films on low-temperature substrates to be processed in much shorter time periods (about 1 millisecond) than with an oven (which takes seconds to minutes).
• a thin film precursor material is initially deposited onto a porous substrate.
• the thin film precursor material is then irradiated with a light pulse in order to transform the thin film precursor material to a thin film such that the thin film is more electrically conductive than the thin film precursor material.
• compressive stress is applied to the thin film and the porous substrate to further increase the thin film's electrical conductivity.
• Figure 1 is a high-level process flow diagram of a method for forming thin film conductors on a substrate, in accordance with a preferred embodiment of the present invention
• FIG. 2 is a diagram of a photonic curing apparatus, in accordance with a preferred embodiment of the present invention.
• Figure 3 is a graph showing the height profile of a copper film on a paper substrate before and after being compressed using the method depicted in Figure 1.
• the relatively short processing time enabled by photonic curing can cause problems.
• One of the artifacts of photonic curing is that the rapid heating of a thin film can generate gas within the thin film. If the gas generation is violent enough, the thin film will undergo a complete cohesive failure, i.e., it may explode. More commonly, the thin film develops a slight porosity. Often, the porosity is inconsequential, but it can, under certain conditions, cause the thin film to be more mechanically fragile than its denser counterparts. Furthermore, if the thin film has any electronic functionality, such as electrical conductivity, its sheet resistance will be higher as a result of the porosity. The increased porosity in the thin film can also exhibit increased surface roughness as well.
• a thin film precursor material is initially deposited onto a substrate, as shown in block 110.
• the material is then thermally processed with a photonic curing apparatus such that the thin film precursor material becomes a thin film material, as depicted in block 120.
• the electrical conductivity of the thin film material is higher than that of the thin film precursor material.
• compressive stress is applied to the thin film material located on the substrate to cause the thin film material to density such that its electrical conductivity of the thin film material can be further increased, as shown in block 130.
• the thin film precursor material can be in a particulate form.
• the thin film precursor material can also be dispersed in a liquid.
• the thin film precursor material can be deposited onto a substrate by one or combinations of printing methods such as screen printing, inkjet, aerosol jet, flexographic, gravure, laser, pad, dip pen, syringe, or coating methods such as airbrush, painting, roll coating, slot die coating, etc.
• the thin film precursor material can be deposited without a liquid including vacuum deposition techniques such as chemical vapor deposition (CVD), PECVD, evaporation, sputtering, etc.
• vacuum deposition techniques such as chemical vapor deposition (CVD), PECVD, evaporation, sputtering, etc.
• CVD chemical vapor deposition
• PECVD PECVD
• evaporation evaporation
• sputtering evaporation
• Other dry coating techniques in which the thin film precursor material can be deposited include electrostatic deposition, xerography, etc.
• the thin film precursor material is preferably contains a metal and/or a metal compound such as an oxide, salt, or organometallic.
• the thin film precursor material can be copper, nickel, cobalt, silver, carbon, aluminum, silicon, gold, tin, iron, zinc, titanium, etc.
• oxides include Cu 2 0, CuO, Co 3 0 4 , Co 2 0 3 , NiO, etc.
• salts include copper (II) nitrate, copper (II) chloride, copper (II) acetate, copper (II) sulphate, as well as nitrates, chorides, acetates, and sulphates of cobalt, nickel, silver, etc. If the thin film precursor material contains a metal compound, a reducing agent generally accompanies it as well.
• the substrate which may be porous, preferably has a maximum working temperature of less than 450°C.
• examples include polymers and cellulose.
• porous substrates include fiber based films that are calendered such as cellulose (e.g. , paper) or polyethylene (e.g., Tyvek ® manufactured by DuPont ® ).
• the porosity may be induced in the substrate by foaming the substrate material.
• thermal processing of the thin film precursor material evaporates the solvent. If the thin film precursor material is the particulate form of the final thin film, the photonic curing additionally sinters the thin film precursor material. If the thin film precursor material is composed of multiple species designed to chemically react with each other (such as a metal compound and a reducing agent), then the thermal processing additionally reacts the precursor thin film material to form the final thin film which is generally a metal.
• a photonic curing apparatus 200 includes a conveyor system 210, a strobe head 220, a relay rack 230, and a reel-to-reel feeding system 240.
• Photonic curing apparatus 200 is capable of irradiating a thin film precursor material 202 deposited on a substrate 203 situated on a web being conveyed past strobe head 220 at a relatively high speed.
• Strobe head 220 includes a high-intensity xenon flashlamp 221 for curing thin film precursor material 202 located on substrate 203.
• Xenon flashlamp 221 can provide pulses of different intensity, pulse length, and pulse repetition frequency.
• xenon flashlamp 221 can provide 10 /- s to 10 ms pulses with a 3" by 6" wide footprint at a pulse repetition rate of up to 1 kHz.
• the spectral content of the emissions from xenon flashlamp 221 ranges from 200 nm to 2,500 nm. The spectrum can be adjusted by replacing the quartz lamp with a ceria doped quartz lamp to remove most of the emission below 350 nm.
• the quartz lamp can also be replaced with a sapphire lamp to extend the emission from approximately 140 nm to approximately 4,500 nm.
• Xenon flashlamp 221 can also be a water wall flash lamp that is sometimes referred to as a Directed Plasma Arc (DP A) lamp.
• DP A Directed Plasma Arc
• Relay rack 230 includes an adjustable power supply, a conveyance control module, and a strobe control module.
• the adjustable power supply can produce pulses with energy of up to 4 kJ per pulse.
• Adjustable power supply is connected to xenon flashlamp 221, and the intensity of the emission from xenon flashlamp 221 can be varied by controlling the amount of current passing through xenon flashlamp 221.
• the adjustable power supply controls the emission intensity of xenon flashlamp 221.
• the power, pulse duration, and pulse repetition frequency of the emission from xenon flashlamp 221 are electronically adjusted in real time and synchronized to the web speed to allow optimum curing of thin film precursor material 202 without damaging substrate 203, depending on the optical, thermal, and geometric properties of thin film precursor material 202 and substrate 203.
• the time duration of irradiation of each light pulse is less than the time to thermal equilibration time of the stack comprising thin film precursor material 202 on substrate 203.
• Conveyor system 210 moves thin film precursor material 202 under strobe head 220 where thin film precursor material 202 is cured by rapid light pulses from xenon flashlamp 221.
• the power, duration, and repetition rate of the emissions from xenon flashlamp 221 are controlled by the strobe control module, and the speed at which substrate 203 is being moved past strobe head 220 is determined by the conveyor control module.
• thin film precursor material 202 When xenon flashlamp 221 is emitting light pulses, thin film precursor material 202 is momentarily heated to provide the energy for curing thin film precursor material 202.
• a rapid pulse train is synchronized to moving substrate 203, a uniform cure can be attained over an arbitrarily large area as each section of thin film precursor material 202 may be exposed to multiple light pulses, which approximates a continuous curing system such as an oven.
• thin film precursor material 202 located on substrate 203 has been photonically cured with flashlamp 221 to form a thin film material 202'
• compressive stress is applied to thin film material 202' and substrate 203 in order to densify thin film material 202 and substrate 203.
• Thin film material 202' on substrate 203 can be compressed by one or combinations of existing technologies such as stamping, forging, rolling, calendering, pressing, embossing, laminating, etc.
• Rolling is preferably used in a reel-to-reel manufacturing setting by a set of pinch rollers 260.
• Pinch rollers 260 are loaded, in compression, such that the peak pressure applied to thin film material 202' and substrate 203 exceeds 25% of the ultimate tensile strength (UTS) of the bulk thin film material after photonic curing at standard conditions.
• UTS ultimate tensile strength
• the preferred compression pressure range is between 7,500 and 30,000 psi (i.e., 25% to 100% of its ultimate tensile strength at standard conditions).
• substrate 203 is porous, it is compressible and responds to compression by reducing in thickness while keeping the same width, such as a fiber based substrate like paper. This single dimensional change ensures that thin film material 202' is not damaged by lateral deformation of substrate 203.
• the peak pressure capable of being applied by pinch rollers 260 to polymer substrates that are non-porous, such as PET, may be limited because PET is a low-temperature polymer that tends to be relatively soft. PET will deform laterally at a lower pressure threshold than other substrates, which can cause damage to thin film material 202' and substrate 203.
• Heating pinch rollers 260 to a temperature between standard temperature and the maximum working temperature of substrate 203 can decrease the required pressure to achieve a similar result with standard temperature pinch rollers 260 due to the softening of thin film material 202' during compression.
• Compressive stress applied to thin film material 202' deposited on substrate 203 can increase the density of thin film material 202'.
• a particle or solution-based deposited material has a density lower than the bulk precursor material due to a residual pore structure within the deposited layer. Additionally, the photonic curing process may introduce additional porosity in thin film material 202'.
• the volume of pore space relative to layer volume (volume fraction) will vary depending on material, process, and particle size. Reducing the pore space volume fraction densities the material improving its performance in terms of increased electrical conductivity if it is conductive, improved mechanical stability and hardness, alters the surface properties like reducing surface roughness and improving solder-ability, and improved chemical resistance if the material is prone to corrosion by reducing the surface area to volume ratio. Compressing thin film material 202' increases it density, which brings deposited thin film material 202' closer to the properties of the bulk thin film material.
• Example 1 Compressive stress applied to thin films of mesoporous copper on paper substrates
• a screen printable version of a copper oxide reduction ink (part no. ICI-021 available from NovaCentrix in Austin, Texas) was printed on Wausau 110 lb exact index paper with a 230 mesh flat screen. The print was then dried in a 140°C oven for 5 minutes to remove excess solvents. Initially, the ink had a sheet resistance that was ⁇ 1 ⁇ /D . That is, the resistance as measured by an ordinary multimeter was an open circuit. The ink was converted to a conductive mesoporous copper thin film using a photonic curing apparatus (such as PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas).
• a photonic curing apparatus such as PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas.
• the settings on the machine used for curing were 430 V, 1,600 ms, overlap factor of 5, and at a web speed of 16 feet per minute.
• the sheet resistance after photonic curing was 17.2 mQ/ ⁇ .
• the mesoporous copper thin film underwent densification via the following process: A pair of steel rollers (1.7" diameter x 3.0" length) applied a compressive force of 2,875 lbf to the foamed copper thin film on paper as it was drawn through the rollers.
• the cross sectional area of compression was 0.074 in 2 , yielding an average 38,850 psi applied to the printed conductors.
• Densification, via compression, of the mesoporous copper reduced the sheet resistance to 9.3 ⁇ /D .
• Both the total height and the surface roughness are reduced indicating increased density and reduced surface roughness of the copper film.
• the surface roughness was reduced from 25 micron to 5 microns.
• the entire thin film stack was reduced in thickness by about 50 microns.
• As-converted mesoporous copper measured about 30 ⁇ /D in sheet resistance.
• Mesoporous copper film compressed at 8,300 psi (27%o UTS of pure copper) measured 22 mQ/D in sheet resistance. At a pressure of 12,000 psi (40%o UTS of pure copper) the sheet resistance reached a minimum value of 20 ⁇ /D (saturation point).
• the converted mesoporous copper After photonic curing, the converted mesoporous copper has a high surface area to volume ratio contributing to its poor native corrosion resistance. Compressing the mesoporous copper greatly reduces the surface area to volume ratio of the copper and improves the material's corrosion resistance.
• Environmental testing was performed on bare as-converted and compressed copper films on paper substrate. Compressed copper demonstrates a significantly improved corrosion resistance when tested in an environment at 85°C/100% relative humidity for 24 hours. Uncoated mesoporous copper on paper does not survive such an environmental test, but compressed copper survives un-coated and without a detectable change in conductivity. Uncoated compressed copper films passed an industry standard (1,000 hours at 85°C/85% relative humidity) with only an increase in resistivity by 20%. Additional cost benefits pertaining to production become apparent as required volumes of materials for encapsulating the compressed copper films are decreased relative to as-converted copper.
• Example 2 Compressive stress applied to porous thin films of nickel on paper substrates
• a screen printable version of a nickel flake ink (part no. 79-89-16 available from NovaCentrix in Austin, Texas) was printed on Wausau 110 lb exact index paper with a 230 mesh flat screen. The prints were dried in a 150°C oven for 5 minutes to remove excess solvents. After oven drying the sheet resistance measured 77 ⁇ /D .
• the dried ink was photonically cured to form a highly conductive porous nickel thin film using a photonic curing apparatus (such as PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas).
• a photonic curing apparatus such as PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas.
• the settings on the photonic curing apparatus used for curing were 540 V, 1,100 ms, overlap factor of 4, at a web speed of 14 feet per minute.
• Photonic curing reduced the sheet resistance of the nickel film on the paper substrate to 550 mQ/D .
• the porous nickel thin film underwent densification via the following process: A pair of steel rollers (1.7" diameter x 3.0" length) applied a compressive force of 2,464 lbf to the porous nickel thin films on paper as they were drawn through the rollers. The cross-sectional area of compression was 0.074 in 2 , yielding an average 33,300 psi applied to the printed conductors. Densification, via compression, of the porous nickel reduced the sheet resistance to 60 mQ/D . Compressing the porous nickel decreased its resistivity by 89%.
• Example 3 Compressive stress applied to thin films of silver on paper substrates
• a screen printable version of a silver flake ink (part no. HPS-030LV available from NovaCentrix in Austin, Texas) was printed on Wausau 110 lb exact index paper with a 230 mesh flat screen. The print was dried in a 170°C oven for 5 minutes to remove excess solvents and cause sintering of the silver flakes. After oven drying the sheet resistance measured 16.9 mQ/D .
• the 5 micron thick silver trace on paper substrate underwent densification via the following process: A pair of steel rollers (1.7" diameter x 3.0" length) applied a compressive force of 1,848 lbf to the silver thin films on paper as they were drawn through the rollers. The cross sectional area of compression was 0.074 in 2 , yielding an average 24,970 psi applied to the printed conductors. Densification, via compression, of the silver reduced the sheet resistance to 14.2 ⁇ /D . Compressing the silver film decreased the resistivity by 16%.
• Example 4 Compressive stress applied to thin films of mesoporous copper on PET substrates
• a screen printable version of a copper oxide reduction ink (part no. ICI-021 available from NovaCentrix in Austin, Texas) was printed on ST505 polyethylene terephthalate (PET) film with a 230 mesh flat screen. The print was then dried in a 140°C oven for 5 minutes to remove excess solvents. Initially, the ink had a sheet resistance that was -lGQ/rj . That is, the resistance as measured by an ordinary multimeter was an open circuit. The ink was converted to a conductive mesoporous copper thin film using a photonic curing apparatus (PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas).
• a photonic curing apparatus PulseForge ® 3300 X2 photonic curing system manufactured by NovaCentrix in Austin, Texas.
• the settings on the machine used for curing were 360 V, 2,500 ms, overlap factor of 1, and at a web speed of 16 feet per minute.
• the sheet resistance after photonic curing was 46 mQ/D .
• the mesoporous copper thin film underwent densification via the following process: A pair of steel rollers (1.7" diameter x 3.0" length) applied a compressive force of 1,027 lbf to the foamed copper thin film on paper as it was drawn through the rollers.
• the cross sectional area of compression was 0.074 in 2 , yielding an average 13,873 psi applied to the printed conductors. Densification, via compression, of the mesoporous copper reduced the average sheet resistance to 34 mQ/D .
• the present invention provides a method for forming thin film conductors on a substrate. While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

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• Dispersion Chemistry (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Manufacturing Of Printed Wiring (AREA)
• Manufacturing Of Electric Cables (AREA)

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• 2012
  • 2012-12-03 EP EP12889427.6A patent/EP2926367A4/de not_active Withdrawn
  • 2012-12-03 JP JP2015545022A patent/JP6202763B2/ja active Active
  • 2012-12-03 CA CA2893584A patent/CA2893584C/en active Active
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