Patent Application
20150125624
The present invention is directed to articles having conductive ink and processes of fabricating such articles. More particularly, the present invention is directed to articles having spray-applied conductive ink and processes of spray-applying such conductive inks.
Electronic devices are continuously becoming smaller, more compact, and more complex. Such changes can result in issues with electrical connectivity, deposition, manufacturing, and adhesion to certain materials. Producing antennas and conductive traces capable of operation on or with such electronic devices is, thus, becoming more difficult and/or more costly.
One process of producing antennas is laser direct structuring. Laser direct structuring uses a composite loaded with a laser-activated precursor that acts as a seed layer for selective plating. Laser direct structuring is limited to types of polymers that incorporate a precursor material and limits adhesion to substrates.
Processes of selective plating include application of latex or other adhered masks by hand. Masking for selective plating is costly due to the multi-step batch processing involved, and the manual aspects can lead to substantial scrap and/or quality control issues. In addition, plating can present an environmental health and safety hazard due to caustic hazardous waste.
Other processes for producing antennas include screen printing, flexographic techniques, gravure-printing, spin-coating, and dip-coating, each of which results in distinct physical features. Such processes suffer from drawbacks that such approaches are limited to specific and/or simple geometries (for example, planar geometries), can be very time consuming to achieve desired thicknesses, and can be costly, due to the time-consuming production aspects.
Certain conductive inks have previously been considered to be unsuitable for use as antennas. For example, resistance, and by extension, direct current resistance, of such inks can be significantly higher than a bulk metal (between 40 and 500 times higher). Antenna efficiency has been described as being inversely related to the square root resistivity of a conductive trace. In view of this, dipole antenna efficiency of certain antennas using conductive inks should fall by at least 10% below that of an aluminum control.
An article with spray-applied conductive ink as well as a process of fabricating such an article that do not suffer from one or more of the above drawbacks would be desirable.
In an embodiment, a selectively metalized article includes a substrate and conductive ink spray-applied to a non-planar region of the substrate. The conductive ink on the non-planar region is at least a portion of a power trace, an antenna, a resistive heater, a conductive lead, a sensor, a functional electrical device, or a combination thereof.
In another embodiment, an antenna includes a spray-applied ink that extends over a non-planar region of a substrate.
In another embodiment, an article includes a substrate and an antenna comprising conductive ink spray-applied onto a non-planar region of the substrate.
In another embodiment, a process includes providing a substrate, spray-applying conductive ink onto a non-planar region of the substrate, and ablating the conductive ink or photo-sintering the conductive ink.
In another embodiment, a process of fabricating an antenna includes providing a substrate and spray-applying conductive ink onto a non-planar region of the substrate to form at least a portion of the antenna.
In another embodiment, a process includes providing a substrate and spray-applying conductive ink onto a non-planar region. The conductive ink has an elemental composition, by weight, of 23% polymer matrix and 67% Ag.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
Provided is an exemplary article having a spray-applied conductive ink and a process of spray-applying conductive ink. Embodiments of the present disclosure, for example, in comparison to similar concepts that fail to include one or more of the disclosed features, include conductive inks that do not have RF insertion loss that is too low in comparison to bulk metal or control samples, are smaller, are more compact, are more complex, have a finer structure, are devoid or substantially devoid of one or more undesirable features of the above-described techniques and components, maintain electrical connectivity, are produced by less complex and/or less costly processes, do not rely upon laser-direct structuring, do not rely upon laser-activated precursors, do not rely upon a seed layer for selective plating, are not limited to specific types of polymers or substrates, do not incorporate a precursor material, permit use of conductive inks having between 30 and 100 times higher direct current resistance than bulk metals, have improved adhesion, decrease hazardous conditions, decrease waste, reduce use of precious metals, permit application on non-planar geometries as well as planar geometries, permit other suitable advantages and distinctions, or combinations thereof.
Referring to
The substrate 102 is polymeric, a composite, metallic, metal, ceramic, thermoset, thermoplastic, glass, any other suitable rigid or flexible material, or a combination thereof. In one embodiment, the substrate 102 is selected from the group consisting of polyetherimide, p-polyphenylene sulfide (for example, with carbon fiber), polyether ether ketone, a blend of polyphenylene oxide and polystyrene, acrylonitrile butadiene styrene, a blend of polycarbonate and acrylonitrile butadiene styrene, and combinations thereof.
The conductive pattern 104 includes conductive ink 106. *****The conductive ink 106 extends over a non-planar region 108 of the substrate 102. The non-planar region 108 is any suitable geometry where all points do not reside in the same two dimensions (e.g. not flat). Suitable geometries include, but are not limited to, a 90-degree non-planar region (see
In one embodiment, the conductive pattern 104 and/or the conductive ink 106 include at least a portion arranged as one or more traces, one or more ground paths, one or more bonding pads, any other suitable and accessible region, or a combination thereof. For example, in one embodiment, the conductive ink 106 is within the accessible region, the accessible region being capable of receiving the conductive ink 106 through line-of-sight spray techniques.
In one embodiment, the conductive ink 106 includes metal or metallic particulates in a polymer matrix. The metal or metallic particulates include or are silver, copper, nickel, silver-coated copper, other suitable conductive metals, or a combination thereof. The metal or metallic particulates include or are flakes, particles, rods, dendritic particles, particles having multiple form factors and/or aspect ratios, other suitable particles permitting conductivity within the conductive ink 106, or a combination thereof.
The conductive ink 106 includes any suitable concentration of conductive and non-conductive components. Suitable concentrations of polymer include being, by weight, between at or about 20% and at or about 40%, between at or about 30% and at or about 40%, between at or about 30% and at or about 35%, between at or about 25% and at or about 35%, at or about 33%, or any suitable combination, sub-combination, range, or sub-range therein. Suitable elemental concentrations of silver include being, by weight, between at or about 50% and at or about 80%, between at or about 60% and at or about 80%, between at or about 50% and at or about 70%, between at or about 65% and at or about 75%, between at or about 60% and at or about 70%, at or about 67%, or any suitable combination, sub-combination, range, or sub-range therein.
The metal or metallic particulates are of any suitable dimensions capable of being within the polymer matrix. Suitable dimensions include, but are not limited to, a maximum dimension (for example, of a dendritic particle) being between at or about 1 and at or about 10 micrometers, a maximum dimension being between at or about 5 and at or about 10 micrometers, a maximum dimension being between at or about 8 and at or about 10 micrometers, a longest axis (for example, of a flake) being between at or about 20 and at or about 50 micrometers, a longest axis being at between at or about 30 and at or about 50 micrometers, a longest axis being between at or about 40 and at or about 50 micrometers, a longest axis being at between at or about 20 and at or about 30 micrometers, or any suitable combination, sub-combination, range, or sub-range therein. In one embodiment, two or more of the metal or metallic particulates with varied dimensions and/or geometries are within the polymer matrix.
The polymer matrix includes epoxy, acrylic, thermoplastic, polyurethane, other suitable materials capable of suspending the metal particulates, other suitable polymers capable of being dissolved in solvent, or a combination thereof.
As a whole, the conductive ink 106 is any suitable material(s) capable of conducting within predetermined parameters through the non-planar region 108.
The conductive ink 106 generally conducts via percolation, for example, where electrons transfer by tunneling or other mechanisms between the metal or metallic particulates, which are conductive, within the polymer matrix, which includes resistive properties.
In one embodiment, the distance between the metal or metallic particulates corresponds to a suitable conductivity loss at the frequency of operation. Suitable frequencies include, but are not limited to, being between at or about 100 kHz and at or about 1 THz, between at or about 100 kHz and at or about 10 GHz, between at or about 100 kHz and at or about 100 MHz, between at or about 100 kHz and at or about 10 MHz, between at or about 100 kHz and at or about 1 MHz, between at or about 1 MHz and at or about 10 GHz, between at or about 10 MHz and at or about 10 GHz, between at or about 100 MHz and at or about 10 GHz, between at or about 10 GHz and at or about 1 THz, or any suitable combination, sub-combination, range, or sub range therein.
Suitable direct current (DC) resistivity values for the conductive ink 106 include, but are not limited to, being between at or about 4×10−7 and at or about 25×10−7 Ω·m, between at or about 12×10−7 and at or about 25×10−7 Ω·m, between at or about 0.2×10−7 and at or about 25×10−7 Ω·m, at or about 4×10−7 Ω·m, at or about 12×10−7 Ω·m, at or about 25×10−7 Ω·m, or any suitable combination, sub-combination, range, or sub-range therein.
In one embodiment, the conductive ink 106 includes dipole efficiency matching an aluminum foil reference at 2 GHz and below, varying by an average of less than 0.1 dB. Additionally or alternatively, the conductive ink 106, at above 2 GHz, has a variance of dipole efficiency averaging less than 0.25 dB. In another embodiment, the dipole efficiency of the conductive ink 106 differs from the dipole efficiency of an aluminum foil reference by an average of 0.3 dB above and below 2 GHz. In further embodiments, the conductive ink 106 includes dipole efficiency, as shown in
In one embodiment, the conductive ink 106 has insertion loss differing from an aluminum foil reference at 2 GHz by about 0.2 dB. In another embodiment, the conductive ink 106 has insertion loss being at a difference of about 0.75 dB at 2 GHz, in comparison to the aluminum foil reference. In further embodiments, the conductive ink 106 includes insertion loss, as shown in
The conductive ink 106 is spray-applied by any suitable spray device, such as, an automotive paint sprayer, an atomizing sprayer, an aerosol sprayer, an ultrasonic sprayer, or a combination thereof. The conductive ink 106 is spray-applied in a single-pass application or with multiple-pass application.
The conductive ink 106 is spray-applied at any thickness capable of permitting the conductive ink 106 to conduct through the non-planar region 108. For example, in one embodiment, the conductive ink 106 is spray-applied at a thickness at, averaging, or between at or about 15 micrometers and at or about 25 micrometers, between at or about 15 micrometers and at or about 20 micrometers, between at or about 20 micrometers and at or about 25 micrometers, between at or about 20 micrometers and at or about 22 micrometers, between at or about 18 micrometers and at or about 22 micrometers, between at or about 18 micrometers and at or about 20 micrometers, between at or about 19 micrometers and at or about 21 micrometers, at or about 19 micrometers, at or about 20 micrometers, at or about 21 micrometers, or any suitable combination, sub-combination, range, or sub-range therein.
In one embodiment, the spray-applying of the conductive ink 106 establishes conductive traces and/or an antenna pattern by broad-area spray coating. A conformal shadow mask or adhesive mask is used to define the conductive traces through the non-planar region 108. The conformal shadow mask is a flexible or rigid material and is reusable or single-use, which is removed to define the conductive traces and/or antenna pattern. The conductive ink 106 is cured and the conformal mask is removed, revealing the conductive traces. Alternatively, the conformal mask can be removed from the conductive traces prior to curing of the conductive ink.
In one embodiment, the spray-applying of the conductive ink 106 includes using a computer-numerical control (CNC) laser system and a laser-markable tape to develop the conductive traces and/or antenna pattern. The laser-markable tape is sensitive to a laser and is spray-applied to the non-planar region 108 of the substrate 102. In one embodiment, the laser-markable tape is a polyester tape of less than 50 micrometers in thickness. The CNC laser system ablates the laser-markable tape to form a template for the conductive traces and/or antenna pattern. In one embodiment, portions of the laser-markable tape are then removed and/or additional portions are covered with tape or foil to prevent coating. The conductive ink 106 is then spray-applied and cured within the template to form the conductive traces and/or antenna pattern. Any remaining portions of the laser-markable tape are then removed.
In one embodiment, the spray-applying of the conductive ink 106 includes using the CNC laser system to directly form the conductive traces and/or the antenna pattern by laser ablation. In this embodiment, the conductive ink 106 is sensitive to a laser and is ablated by the laser, thereby forming non-conductive portions. In addition to or alternative to the laser ablation, other suitable ablation techniques are used. Suitable techniques include, but are not limited to, focused ion beam (FIB) milling, electron beam ablation, proton beam ablation, ultrasonic ablation, abrasive ablation (bead blasting), other suitable ablation processes providing suitable resolution, or a combination thereof.
In one embodiment, the spray-applying of the conductive ink 106 includes directly forming the conductive traces and/or the antenna pattern by ablation, using a pattern or program to define the non conductive regions. In this embodiment, the ablation pattern is communicated to the CNC laser system or other ablative tool by means of a computer program or drawing.
The non-conductive portions define the geometry of the conductive ink 106 on the non-planar region 108. In one embodiment, the laser ablation of the conductive ink 106 is performed after initial or partial curing of the conductive ink 106, for example, upon the conductive ink 106 being devoid or substantially devoid of solvent through solvent evaporating. In one embodiment, the conductive pattern 104 includes laser-ablated regions in a dielectric region 110 or substantially dielectric region defining at least a portion of a pattern of the conductive ink 106.
The laser ablation is within any suitable operational parameters and may be achieved in a single exposure to the laser, two exposures to the laser, three exposures to the laser, or more.
In one embodiment, the laser ablation of the conductive ink 106 results in 15.7 MΩ resistance and/or a depth of 4.5 micrometers after a first laser pass, 349 MΩ resistance and/or a depth of 11.1 micrometers after a second laser pass, 513 MΩ resistance and/or a depth of 24.7 micrometers after a third laser pass, 345 MΩ resistance and/or a depth of 66.6 micrometers after a fourth laser pass, 333 MΩ resistance and/or a depth of 83.9 micrometers after a fifth laser pass, or a combination thereof. In one embodiment, the laser ablation of the conductive ink 106 results in a resistance increase to the MΩ range (106Ω) and/or a depth of 4.5 micrometers after a first laser pass, an increase to the 100 MΩ range (108Ω) and/or a depth of 11.1 micrometers after a second laser pass, and further resistance increases for additional passes, as well as a depth of 24.7 micrometers after a third laser pass, 1 a depth of 66.6 micrometers after a fourth laser pass, and a depth of 83.9 micrometers after a fifth laser pass, or a combination thereof. Additionally or alternatively, the first laser pass, the second laser pass, and/or additional laser passes of the laser ablation of the conductive ink 106 result in increases in resistance of between at or about 100 MΩ and at or about 200 MΩ, between at or about 100 MΩ and at or about 300 MΩ, between at or about 200 MΩ and at or about 300 MΩ, at least 100 MΩ, at least 200 MΩ, at least 300 MΩ, or any suitable combination, sub-combination, range, or sub-range therein.
In one embodiment, the spray-applying of the conductive ink 106 includes using the CNC laser system to directly form the conductive traces and/or the antenna pattern by selective photo-sintering, for example, of a metallic filler in the conductive ink 106. In this embodiment, the conductive ink 106 is spray-applied to the non-planar region 108 of the substrate 102 and the conductive ink 106 is devoid or substantially devoid of solvent through solvent evaporating. The laser then melts and/or fuses the metallic filler and ablates the polymer matrix to form the conductive traces and/or the antenna pattern. The conductive ink 106 is then washed, for example, with solvent (such as 2-butanone followed by acetone), to remove portions that have not been exposed to the laser, revealing the conductive traces and/or the antenna pattern.
The selective photo-sintering is within any suitable operational parameters and is capable of being achieved in a single exposure to the laser, two exposures to the laser, three exposures to the laser, four exposures to the laser, five exposures to the laser, or more. A suitable power for each exposure is 3 W. A suitable frequency for the laser is 200 kHz. The selective photo-sintering increases the concentration of the conductive metal, for example, silver, in the conductive ink 106. In one embodiment, the increase is, by weight, from 66% to at or about 92%. In a further embodiment, the concentration of the conductive ink 106 includes the elemental concentration or elemental differentials between a first composition, by weight, of at or about 22% C, at or about 11% O, and at or about 67% Ag, and a second composition, by weight, of at or about 5% C, at or about 2.2% O, at or about 0.3% Mg, and at or about 92% Ag. Additionally or alternatively, the selective photo-sintering increases the concentration, by weight, of the silver by between at or about 20% and at or about 40%, between at or about 20% and at or about 30%, between at or about 25% and at or about 30%, at or about 10% or more, at or about 20% or more, at or about 25% or more, or any suitable combination, sub-combination, range, or sub-range therein. Additionally or alternatively, the selective photo-sintering decreases the concentration, by weight, of the carbon by between at or about 10% and at or about 20%, between at or about 10% and at or about 15%, at or about 10% or more, at or about 15% or more, or any suitable combination, sub-combination, range, or sub-range therein.
The laser used for embodiments of the spray-applying of the conductive ink 106 are any suitable laser capable of achieving operational parameters, for example, power and frequency to achieve the increase and/or the decrease in conductivity/resistivity. Suitable lasers include, but are not limited to, an Nd:YAG laser, an Nd:YVO4 laser, an Nd:YLF laser, a Yb:YAG laser, a Yb:KGW laser, a Yb:KYW laser, a Yb:SYS laser, a Yb:BOYS laser, a Yb:CaF2 laser, other suitable lasers having sufficient power, frequency, and/or wavelength, or a combination thereof. In one embodiment, the laser operates at a selected wavelength, such as, between at or about 1,020 nm and at or about 1,070 nm, between at or about 1,020 nm and at or about 1,050 nm, between at or about 1,050 nm and at or about 1,070 nm, at or about 1,020 nm, at or about 1,050 nm, at or about 1,064 nm, or any suitable combination, sub-combination, range, or sub-range therein.
In a first example, dipole antenna and transmission line samples are deposited using a first conductive ink having silver flakes and particulate in an epoxy, a second conductive ink having silver-coated copper flakes and dendritic silver particles in an acrylic, a third conductive ink having silver-coated copper flakes in an epoxy, and a fourth conductive ink having copper particulate in a polyurethane. The first conductive ink has a resistivity of 7×10−7 Ω·m. The second conductive ink has a resistivity of 12×10−7 Ω·m. The third conductive ink has a resistivity of 83×10−7 Ω·m. The fourth conductive ink has a resistivity of 1.7×10−5 Ω·m. A scanning electron micrograph of the first conductive ink is shown in
In a second example, laser ablation of the first conductive ink is analyzed.
As shown in
Laser ablation of the first conductive ink also impacts resistance. Measuring with a Kelvin probe for resistance and using stylus profilometry for depth, after the first pass of the laser to be 15.7 MΩ at a depth of 4.5 micrometers. After the second pass of the laser, the resistance is 349 MΩ at a depth of 11.1 micrometers. After a third pass of the laser, the resistance is 513 MΩ at a depth of 24.7 micrometers. After a fourth pass of the laser, the resistance is 345 MΩ at a depth of 66.6 micrometers. After a fifth pass of the laser, the resistance is 333 MΩ at a depth of 83.9 micrometers.
In a third example, a conductive ink having a metallic filler comprising flake and dendritic particles is photo-sintered.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
