Patent Application
20210129181
The present invention is directed to a process in which particulates in ink are ultrasonically consolidated at ambient temperature in less than 5 seconds resulting in a completely densified, well adhered coating which can be used for various applications, such as electrical components.
Consolidation processes rely upon the application of chemical, mechanical or thermal energy to consolidate and achieve bonding between two materials. Conventional consolidation methods include sintering, extrusion, rolling and hot isotactic pressing. All these conventional methods require a high temperature to achieve consolidation as well as high pressure to produce a consolidated material. Exposure of substrates to high temperatures for long periods of time affects the dimensional stability and/or material microstructure of the substrates and many times precludes the use of the process with materials such as plastics and metals, such as for example copper, which can be affected by high temperatures. In addition, many of these conventional processes need to be carried out in a protective atmosphere or vacuum. Sometimes hot air flow is needed during conventional consolidation methods. Additionally, some conventional processes may necessitate the use of flux to remove oxides, to provide good adhesion or to form an alloy of one material to another. Because of these requirements, these methods are often capital cost intensive and time consuming.
Ultrasonic welding is another used industrial technique that facilitates joining of dissimilar materials. Conventional ultrasonic welding is generally used to weld plastic and/or metal sheets to plastic and/or metal sheets or metal wires/cables to metal sheets or metals wires/cables to other wires/cables.
U.S. Patent Application Publication No. US 2010/0003158 describes a vibratory powder consolidation process that uses powders. The publication describes a process in which a powder is consolidated by application of high frequency vibrations while the powder is maintained under static compressive loading in a mold to form sheet like material. The loadings are in the range of about 15,000 to about 30,000 psi. The powder is heated prior to the consolidation to a temperature between one-third and two-thirds of a melting point in degrees Kelvins of the powder material. The powders are consolidated under a uniaxial pressure by the application of ultrasonic vibration which causes high strain rate deformation in the powder particles resulting in consolidation to form a foil. These processes are time intensive. High temperature and pressures are necessary to obtain useful stand-alone structure/foils and therefore limit the applicability of this process. Compacts which are not subject to high temperatures and pressures using this ultrasonic welding of powders method do not keep their integrity and shred into powders.
It would, therefore, be beneficial to provide a process in which particulates can be positioned and/or aligned on a substrate surface in the form of an ink and are ultrasonically consolidated at ambient temperatures and low pressures, rapidly resulting in completely densified, well adhered coatings, preferably having a sub-millimeter thickness. It would also be beneficial to provide a product made by a process in which particulates in ink are ultrasonically consolidated at ambient temperatures and low pressures, rapidly resulting in a product with a completely densified, well adhered coating.
An embodiment is directed to a process in which particulates in ink are ultrasonically consolidated at ambient temperatures in a short period of time, for example, less than 5 seconds, resulting in a completely densified, well adhered coating.
Another embodiment is directed to a product formed by a process in which particulates in ink are ultrasonically consolidated at ambient temperature in less than 5 seconds resulting in a product having a completely densified well adhered coating.
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.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
Moreover, the features and benefits of the invention are illustrated by reference to the preferred embodiments. Accordingly, the invention expressly should not be limited to such embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features, the scope of the invention being defined by the claims appended hereto.
A process is provided which ultrasonically consolidates particulates positioned and/or aligned on a substrate at ambient temperatures providing for dense well adhered functional coatings on a substrate. The particulates can be in the form of an ink. The functional coatings can be used for electrical components. For example, the functional coatings can be used as contact finishes for connectors. Similarly, the coatings can be used as full density traces on ceramics/printed circuit boards for sensor applications or antenna applications. In addition, the functional coatings can be used as wear resistant coatings for electronic devices.
The process of the instant invention provides for improved conductivity of a coating at a lower temperature. In addition, due to the complete densification of the coating, improved bulk electrical and thermal conductivity can be achieved as compared to conventional consolidation methods. Finally, the process of the instant invention provides for improved adhesion between the coating and substrate when processed quickly and under ambient conditions.
The process can be either a batch type process or a roll to roll process. Whether the process is implemented as a batch type process or a roll to roll process, there are two main steps needed to ultrasonically consolidate the particulates in ink to achieve a dense, well adhered functional coating. In the first step, the ink is formulated and applied selectively to a desired substrate and then dried on the substrate. If desired, the ink may be applied to the substrate in a patterned form. In the second step, ultrasonic plating occurs. A flow diagram illustrating the two-step process to ultrasonically consolidate particulates in ink can be found in
The first step of the process 1, the ink is formulated and applied selectively to a desired substrate and then dried on the substrate. Inks which can be used in the process include any ink with particulates, preferably metal particulates. The particulates can be in any shape such as flakes, spherical or dendritic powders or nano-powders. The particulates can be in any suitable size, for example, nanoparticles, micron particles or mixtures thereof. The particulates are preferably tin, tin-zinc, silver, silver palladium, gold, aluminum, titanium, copper, silver-platinum, palladium, their alloys and the like. These particulates are dispersed in a binder and/or solvent. Any suitable materials can be used as the binder. Examples of binders can be polymers, oligomers, glass and the like. Examples of polymer binders can be polyester, polyamide, polyimide, epoxy polymer, phenoxy polymer, polyether, cellulose, polycarbonate, acrylate polymer, polyurethane, polyolefin, styrene polymers and the like. Any suitable solvents can be used for the ink formulation. Examples of solvents include alcohol, acetate, ketone, ether, water, aliphatic or aromatic hydrocarbon, and the like. Other additives such as dispersants, surfactants, leveling agents, deforming agents, rheology modifiers and the like can be added to the ink as well. The particulates can be more than 20%, or more than 30%, or more than 50%, or more than 70% by weight of the ink. The particulates can be less than 95%, or less than 90%, or less than 85% by weight of the ink. The binder can be more than 0.1%, or more than 0.5%, or more than 1%, or more than 5% by weight of the ink. The binders can be less than 20%, or less than 10%, or less than 5%, or less than 3% by weight of the ink. The particulate to the binder ratio can be greater than 60:40, more than 70:30, more than 80:20, or more than 90:10, including more than 95:5. It is believed that the binder helps in adhering the particulates to the substrate during the processing.
The ink can also contain lubricants such as polytetrafluoroethylene (PTFE), silver monosulfide (AgS), copper sulfide (CuS), molybdenum disulfide (MoS2), graphite particles or nanoparticles. Preferably, the lubricant can be mixed into the ink. The lubricant can be more than 0.1%, or more than 0.5%, or more than 1%, or more than 5% by weight of the ink. The lubricant can be less than 20%, or less than 10%, or less than 5%, or less than 3% by weight of the ink. The amount of lubricant added to the ink is well within the scope of one of ordinary skill in the art in order to obtain the desired lubricating properties of the resultant coating. Similarly, to increase the hardness and wear resistance of the coating, hard particles or nanoparticles can also be added to the ink. Examples of suitable particles include aluminum oxide (Al2O3), diamonds, and tungsten carbide (WC). The hard particles or nanoparticles can be more than 0.1%, or more than 0.5%, or more than 1%, or more than 5% by weight of the ink. The hard particles or nanoparticles can be less than 20%, or less than 10%, or less than 5%, or less than 3% by weight of the ink. Nano carbon materials such as graphene and carbon nanotubes can also be added to the ink to customize the electrical conductivity or thermal performance of the coating.
The inks can be selectively applied by either analog printing methods or digital printing methods to a desired substrate. Analog printing methods require a mask, screen or patterned roll. Contact needs to be established between the ink and substrate to transfer the ink to the substrate.
Alternatively, the ink can be selectively applied to the substrate using digital printing. Digital printing methods are mask less and the ink is generally dispensed onto the substrate with the use of a printing tool directly controlled by a computer. Examples of digital printing methods include dispense jet, aerosol jet and ink jet methods.
Depending upon the method used to apply the ink, the thickness of the ink varies. If inkjet printing or aerosol jet printing are used to apply the ink, the thickness of the ink is generally in the range of about tens of nanometers to about several microns. If flexographic printing, gravure printing, pad printing, stencil printing, screen printing or dispense jet printing methods are used to apply the ink, the thickness of the ink is in the range of sub-microns to tens of microns to sub-millimeters. The amount of printed ink can be increased to the desired thickness by using the printing process repeatedly to achieve the desired thickness. The desired thickness of the ink is dependent upon the desired end application and can be easily determined by one of ordinary skill in the art.
Alternatively, using the printing processes to apply the particulates in the ink to the substrate, the particulates can be applied by any known method so that the particulates are positioned on the substrate. The particulates can then be aligned using any method to align particulates including electrostatic aligning methods.
Suitable substrates to which the ink with particulates is applied to include copper alloys, steel, stainless steel, nickel, nickel alloys, nickel plates copper, nickel plates steel, zinc, zinc alloys, aluminum and aluminum alloys, magnesium and magnesium alloys and titanium. Additionally, ceramic materials, such as alumina, zirconia, aluminum nitride and the like or plastics or metals coated with a plastic, or ceramic with a plastic may be used as a substrate in the process.
The second step 2 of novel process of the invention as shown in
The ultrasonic plating of the process occurs very quickly at ambient temperature. The process takes less than 5 seconds, preferably less than 2 seconds. The process occurs at ambient temperature. Ambient temperature is considered room temperature. There is no external heating applied during the process to achieve the ultrasonically plated coating. Although no external heat is necessary to achieve the desired results, localized heat may be generated within the particulates in the ink. It is believed that the localized heat generated falls in tin is in the range of slightly above room temperature to about 0.8-0.9 times the melting point of the particulates in the ink. The localized heating softens the materials above their cold work temperature and enhances deformation between particulates, thereby improving the diffusion between the particulates and promotion of densification/fusion of the particulates as well as adhesion of the particulates to the substrate. The process therefore occurs at a temperature much lower than the temperature required for conventional sintering, pressing or reflow processes or conventional powder ultrasonic welding processes. In addition, the resultant coating has much better adhesion to the substrate than a coating formed by conventional processes. Although not necessary, if desired the process can use external heating as an option to increase the efficacy of the ultrasonic welding.
Ultrasonic consolidation is based upon the particulates in the ink joining under high strain rate surface and cyclic deformation. Vibratory energy is transmitted to the surface of the ink through an ultrasonic welding system having a sonotrode or other high frequency transducer. With ultrasonic consolidation, full density consolidation is achieved at ambient temperatures within a very short period of time. Consolidation results from the inter-particle rubbing action caused by imposing high frequency vibrations. As a result of the vibrations, oxide-free particle surfaces are produced, particles deform and join. Consolidation initiates at the surface of the ink facing the sonotrode tool tip through which the vibratory energy is transmitted to the ink. Full densification occurs while deformation enhanced diffusion facilitates interparticle joining at ambient temperatures. During the process, the native oxide layers and surface films on the substrate are broken down and a perfect metallurgical bond is formed between the particulates in the ink and the substrate surface. The high strain rate deformation gives rise to a high vacancy concentration which promotes consolidation through enhanced rates of mass transport and phase transformation.
The process of the instant invention completely densifies the particulates in the ink onto the substrate at near theoretical density above 90 vol %, preferably above 95 vol %, most preferably above 99 vol %, including above 99.9 vol % to form a coating layer to the desired thickness as described above. In another words, the conductive layer formed by the process for consolidating particulates in an ink has a porosity less than 10 vol %, less than 5 vol %, preferably less than 1 vol %, including less than 0.1 vol %. The ultrasonically consolidated coating has a thickness of greater than 0.1 micron, or greater than 0.5 micron or greater than 1 micron. The ultrasonically consolidated coating has a thickness of less than 100 microns or less than 50 microns, or less than about 25 microns. The thickness of the coating is dependent upon the ink, the particulates in the ink, and, the substrate as well as the desired end application.
Moreover, the process of the invention results in a coating having improved conductivity of at least 50% compared to conventional processes. Furthermore, using the novel process of the instant invention, it is believed that the conductivity of the coating can be improved almost 100% compared to coatings formed according to conventional processes.
Ultrasonic plating can also break down other detrimental species on substrate surfaces. Examples of such detrimental species include dust, dirt, native oxides, tarnish layers, nickel silicides on copper nickel silicon substrates and corrosion protection coatings such as benzotriazole.
Upon completion of the ultrasonic welding process and consolidation of the particulates in the ink, the coating contains less than 1% organic materials. In addition, the adhesion strength of the coating to the substrate is substantially higher than the adhesion strength of a conventional sintered coating. The adhesion is improved by breaking down the surface films on the surface of the substrate by creating a physical bond between the substrate and the coating.
Any conventional ultrasonic welding system can be used in the process of this invention. One embodiment of an ultrasonic welding system suitable for use to ultrasonically consolidate particles in the ink according to the process of the instant invention is shown schematically in
The sonotrode also applies a static pressure on the ink (shown as 107), normal to the ink surface as indicated by arrow. The sonotrode is coupled with an appropriate coupling to a transducer and compression assembly to provide high frequency electric energy for transformation to mechanical energy and to provide uniaxial static compression as known in the art.
During the process of this invention, the sonotrode frequency ranges from about 15 to about 60 kilohertz, preferably 40 kilohertz. The amplitude typically ranges from about 8 to about 100 microns without a load. The amplitude with a load is about 1 micron. Preferably, the amplitude ranges from 20 to 40 microns. The peak power of the unit ranges from 1 to about 10,000 watts. Preferably, the peak power is in the range of 250 to 1500 watts. The duration of the vibration occurs from about 0.1 to about 5 seconds, preferably less than 2 seconds.
A controller may be provided to control the sonotrode system to achieve the desired process parameters, such as frequency, amplitude, pressure, and time. The system can also include appropriate sensors such as thermocouples, pressure transducers and strain gauges to measure compression and shear stress. The sensors are in communication with the controller.
The sonotrode exerts a constant or static uniaxial pressure normal to the direction of vibrations. The sonotrode moves downwardly during vibration to provide constant pressure. The pressure should be in the range of 1 to 80 psi (0.1 to 5.5 bar or 7 to 550 kPa), preferably 2 to 60 psi (14 to 414 kPa), 3 to 50 psi (21 to 345 kPa) preferably, less than 45 psi (3.1 bar or 310 kPa).
The sonotrode can be made of any materials, such as steel, for example. The sonotrode tip should preferably be made of material which does not stick to the ink. Preferably the tip is coated with a non-stick material.
The cavity for the substrate is supported by a rigid supporting fixture that is capable of absorbing the pressure and vibratory forces exerted on the ink. The cavity can be any suitable size and shape depending upon the desired finished part or alternatively, can be adjustable for various different desired finished parts.
The optional cap 105 that can be used in the process of the instant invention depends upon the ink as well as the substrate composition. Examples of suitable cap materials include aluminum, copper, steel, nickel, and their alloys as well as ceramics. Ceramics having higher thermal conductivity are preferable. Examples of such preferred ceramics include aluminum nitride, aluminum oxide, and silicon nitride. The cap is beneficial to control the surface finish of the coating. The smoother the cap, the smoother the finish of the coating. Preferably a material is chosen for the cap so that it prevents the ink from sticking to the sonotrode itself.
The cap can also be used to emboss wave like structures or pits that are advantageous to increase contact resistance and improve friction behavior. Moreover, the cap can also be used to emboss information onto the end product. Examples of possible information include logos, product identification or serial numbers.
In yet another embodiment of the invention, the ultrasonic consolidation process can occur in a roll to roll process as illustrated in
Using the process of this invention in which the ink is formulated and selectively applied to a substrate and dried on the substrate and then subject to vibratory consolidation allows the achievement of a dense layer of functional coating at low pressure and ambient temperatures. The thickness of the coating is preferably about 1 micron to about 50 microns.
In another embodiment of the invention, silver is ultrasonically plated into aluminum nitride ceramic at room temperature in less than 5 seconds. The ceramic substrate did not fracture during the processing. The sheet resistance of the sample was less than 60 micro-ohms. The sample survived both tape and adhesion tests indicating good adhesion.
The process of the instant invention can be used to apply a fully dense, well adhered coating very quickly onto a variety of substrates at ambient temperatures
While the invention has been described with reference to preferred embodiments, 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 spirit and scope of the invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials and components and otherwise used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims, and not limited to the foregoing description or embodiments.
