Compositions and methods for forming and treating conductive structures to improve their surface properties

Abstract

Improved conductive ink compositions and methods of making and using the conductive ink compositions are provided. The improved conductive ink compositions include a silver complex comprising a silver(I) ion and at least one complexing agent, a formate salt, and a fluoride salt. The conductive ink compositions can be used to improve the surface properties of conductive structures formed from conductive ink compositions that contain adhesion promoters or other modifying agents, in particular silicon-containing agents. Such conductive structures have been found to be difficult to wet, for example with traditional soldering pastes, and they discolor over time. Methods of forming conductive structures with improved surface properties, including improved wettability and reduced discoloration over time, are also provided, as are solderable conductive structures prepared according to these methods.

Description

COMPOSITIONS AND METHODS FOR FORMING AND TREATING CONDUCTIVE STRUCTURES TO IMPROVE THEIR SURFACE PROPERTIESCross-reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 588,455, filed on October 6, 2023, the disclosure of which is incorporated by reference herein in its entirety.Field of the Invention

[0002] The present disclosure relates generally to conductive ink compositions that can be used to form conductive structures with improved surface properties. The disclosure also relates to methods of treating conductive structures, in particular silver films, to improve their surface properties.Background of the Invention

[0003] The electronics, display, and energy industries rely on the production and use of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Printed electronics offer an attractive alternative to conventional technologies by enabling the creation of large-area, flexible devices at low cost. There is a great need for high-conductivity materials with fine-scale features in modem electronics such as solar cell electrodes, flexible displays, radio frequency identification tags, antennas, and many more. In efforts to make these high-technology devices increasingly affordable, the substrates used typically have relatively little temperature resilience and require low processing temperatures to maintain integrity.

[0004] The vast majority of commercially produced conductive inks are specifically designed for inkjet printing, screen printing, or roll-to-roll processing methods in order to process large areas with fine-scale features in short time periods. These inks havedisparate viscosities and synthesis parameters. Particle-based inks are based on conductive metal particles, which are typically synthesized separately and then incorporated into an ink formulation. The resulting ink is then tuned for specific particle process. Precursor-based inks (also known as metal organic decomposition (MOD) or particle-free inks) are based on thermally unstable precursor complexes that undergo reduction to a conductive metal upon heating.

[0005] Prior particle- and precursor-based methods generally rely on high temperatures to form conductive coatings and thus may not be compatible with substrates that require low processing temperatures to maintain integrity. For example, silver compounds with carbamate or other relatively low molecular weight ligands (compared to polymer stabilizers) have been synthesized that decompose at temperatures near 150 °C, yielding electrical conductivities approaching that of bulk silver. Unfortunately, even these temperatures can render the ink incompatible with many plastic and paper substrates commonly used in flexible electronic and biomedical devices.

[0006] U.S. Patent No. 9,469,773B2 and PCT International Publication No. WO2013 / 096664A1 provide water-based precursor inks comprising a silver salt and a complexing agent to which a short-chain carboxylic acid or a salt of the short chain carboxylic acid have been added. Upon concentration, the disclosed formulations form conductive silver structures at low temperatures. Modification of these ink compositions with additives to improve their properties for some purposes, for example to increase their adhesion to specific substrates, can in some cases decrease the performance of conductive structures formed from the inks in unexpected ways.

[0007] Despite these and other advances in the field, there continues to be a need for MOD ink compositions with improved properties. There also continues to be a need for conductive structures formed from these compositions with improved properties. Therefore, it is an object of the present invention to provide improved, stable, MOD ink compositions and methods for their preparation and use, in particular compositions and methods that result in conductive structures with surfaces that are solder wettable.Summary of the Invention

[0008] In some aspects, the techniques described herein relate to a method of forming a conductive structure including the steps of: treating a substrate with a first conductive inkcomposition to form a first conductive structure; optionally curing the first conductive structure; and treating the first conductive structure with a plasma.

[0009] In some aspects, the techniques described herein relate to a method, wherein the plasma is a CF4 plasma or an O2 + CF4 plasma.

[0010] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition is a precursor-based conductive ink composition.

[0011] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition includes silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof.

[0012] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition includes silver, copper, nickel, gold, platinum, or a combination thereof.

[0013] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition includes silver.

[0014] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition includes an adhesion promoter.

[0015] In some aspects, the techniques described herein relate to a method, wherein the adhesion promoter includes silicon.

[0016] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition further includes a silver complex and a formate salt, wherein the silver complex includes a silver(I) ion and at least one complexing agent.

[0017] In some aspects, the techniques described herein relate to a method, wherein the formate salt is an ammonium or alkylammonium formate salt.

[0018] In some aspects, the techniques described herein relate to a method, wherein the formate salt is ammonium formate.

[0019] In some aspects, the techniques described herein relate to a method, wherein the at least one complexing agent is a first alkylamine.

[0020] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a primary alkylamine.

[0021] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0022] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is an octylamine or a cyclopentylamine.

[0023] In some aspects, the techniques described herein relate to a method, wherein the silver complex further includes a second alkylamine.

[0024] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0025] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is an octylamine or a cyclopentylamine.

[0026] In some aspects, the techniques described herein relate to a method, further including the step of applying a soldering paste to the first conductive structure.

[0027] In some aspects, the techniques described herein relate to a solderable conductive structure including: a metallic layer disposed on a nonconductive substrate, wherein the metallic layer includes a silicon-containing material; and a solder flux disposed on a surface of the metallic layer, wherein the solder flux includes an aqueous solvent or a mixed aqueous solvent, a fatty acid, and an organic amine.

[0028] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the solder flux is a printable solder flux.

[0029] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the metallic layer is prepared from a conductive ink composition.

[0030] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the metallic layer is prepared from a precursor-based conductive ink composition.

[0031] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the conductive ink composition includes silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof.

[0032] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the conductive ink composition includes silver, copper, nickel, gold, platinum, or a combination thereof.

[0033] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the conductive ink composition includes silver.

[0034] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the conductive ink composition includes an adhesion promoter.

[0035] In some aspects, the techniques described herein relate to a solderable conductive structure, wherein the adhesion promoter includes silicon.

[0036] In some aspects, the techniques described herein relate to a conductive ink composition including: a silver complex; a formate salt; and a fluoride salt; wherein the silver complex includes a silver(I) ion and at least one complexing agent.

[0037] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the fluoride salt is an ammonium or alkylammonium fluoride salt.

[0038] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the fluoride salt is ammonium fluoride.

[0039] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the formate salt is an ammonium or alkylammonium formate salt.

[0040] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the formate salt is ammonium formate.

[0041] In some aspects, the techniques described herein relate to a conductive ink composition, further including an adhesion promoter.

[0042] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the adhesion promoter includes silicon.

[0043] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the at least one complexing agent is a first alkylamine.

[0044] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the first alkylamine is a primary alkylamine.

[0045] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0046] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the first alkylamine is an octylamine or a cyclopentylamine.

[0047] In some aspects, the techniques described herein relate to a conductive ink composition, further including a second alkylamine.

[0048] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0049] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the second alkylamine is an octylamine or a cyclopentylamine .

[0050] In some aspects, the techniques described herein relate to a method of forming a conductive structure including the steps of: treating a substrate with a first conductive ink composition, wherein the first conductive ink composition includes an adhesion promoter; optionally curing the first conductive ink composition to form a first conductive structure; treating the first conductive structure with a second conductive ink composition of the disclosure; and optionally curing the second conductive ink composition to form a second conductive structure.

[0051] In some aspects, the techniques described herein relate to a method, wherein the adhesion promoter is a silicon-containing adhesion promoter.

[0052] In some aspects, the techniques described herein relate to a method of forming a conductive structure including the steps of: treating a substrate with a first conductive ink composition, wherein the first conductive ink composition includes an adhesion promoter; optionally curing the first conductive ink composition to form a first conductive structure; and treating the first conductive structure with a solution including a fluoride salt.

[0053] In some aspects, the techniques described herein relate to a method, wherein the fluoride salt is an ammonium salt or an alkylammonium salt.

[0054] In some aspects, the techniques described herein relate to a method, wherein the fluoride salt is ammonium fluoride.

[0055] In some aspects, the techniques described herein relate to a method, wherein the adhesion promoter includes silicon.

[0056] In some aspects, the techniques described herein relate to a method, wherein the first conductive ink composition includes a silver complex and a formate salt, wherein the silver complex includes a silver(I) ion and at least one complexing agent.

[0057] In some aspects, the techniques described herein relate to a method, wherein the formate salt is an ammonium or alkylammonium formate salt.

[0058] In some aspects, the techniques described herein relate to a method, wherein the formate salt is ammonium formate.

[0059] In some aspects, the techniques described herein relate to a method, wherein the at least one complexing agent is a first alkylamine.

[0060] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a primary alkylamine.

[0061] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0062] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is an octylamine or a cyclopentylamine.

[0063] In some aspects, the techniques described herein relate to a method, further including a second alkylamine.

[0064] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0065] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is an octylamine or a cyclopentylamine.

[0066] In some aspects, the techniques described herein relate to a method of preparing a conductive ink composition including the steps of: combining an aqueous solution of silver fluoride with a molar excess of at least one complexing agent to form a silver complex; and treating the silver complex with an aqueous solution of ammonium formate.

[0067] In some aspects, the techniques described herein relate to a method, wherein the at least one complexing agent is a first alkylamine.

[0068] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a primary alkylamine.

[0069] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0070] In some aspects, the techniques described herein relate to a method, wherein the first alkylamine is an octylamine or a cyclopentylamine.

[0071] In some aspects, the techniques described herein relate to a method, further including a second alkylamine.

[0072] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

[0073] In some aspects, the techniques described herein relate to a method, wherein the second alkylamine is an octylamine or a cyclopentylamine.Brief Description of the Drawings

[0074] FIG. 1 illustrates the de-wetting of soldering paste that was coated on a silver film prepared from a prior-art ink composition comprising a silicon-containing adhesion promoter.

[0075] FIGs. 2A-2D illustrate color changes of silver films prepared from prior-art ink compositions comprising a silicon-containing adhesion promoter.

[0076] FIGs. 3A and 3B illustrate solder wetting on surfaces coated with conductive ink compositions of the instant disclosure.

[0077] FIGs. 4A-4D show the improved wettability of silver films treated with an aqueous fluoride salt overcoat prior to application of solder paste.

[0078] FIGs. 5A-5D show the decreased color change of silver fdms treated with an aqueous fluoride salt overcoat.

[0079] FIGs. 6A-6C show the solder paste wettability of a conductive film treated with plasma.

[0080] FIG. 7 shows an exemplary process flow for the plasma treatment of a conductive film formed from a conductive ink comprising a silicon-containing adhesion promoter.

[0081] FIGs. 8A and 8B compare the physical properties of plasma-treated conductive films with untreated conductive films.

[0082] FIG. 9 shows the improved solderability of a silver film comprising a silicon- containing adhesion promoter after treatment with a novel printable flux.

[0083] FIGs. 10A-10D shows the properties of silver films soldered using a novel printable flux.Detailed Description of the Invention

[0084] Water-based conductive ink compositions derived from silver metal precursors have been described previously. See, e.g., U.S. Patent No. 9,469,773B2 and PCT International Publication No. WO2013 / 096664A1, which are each incorporated herein by reference in their entireties. These prior ink compositions typically include a silver complex that is preferably formed by dissolving a silver salt in a complexing agent and adding a short-chain carboxylic acid to form the ink composition. The short-chain carboxylic acid can function as a reducing agent for the silver salt to generate a conductive metallic structure. The complexing agent is preferably an amine compound, for examplean alkylamine compound. Alternatively, or in addition, a salt (e.g., an ammonium salt) of the short chain carboxylic acid can be added to form the ink formulation, and the salt of the short chain carboxylic acid can function as the reducing agent for the silver salt. The complexing agent, which is a weak base, is understood to act as a stabilizer and solvent for the silver salt. The short-chain carboxylic acid, or salt of the short-chain carboxylic acid, preferably reduces the silver salt at a temperature of about 120 °C or less.

[0085] Without intending to be bound by theory, it is understood that addition of the short-chain carboxylic acid in the presence of the complexing agent generates an acid-base complex between the short chain carboxylic acid and the complexing agent, thereby preventing the short chain carboxylic acid from reducing the silver salt immediately. As the ink formulation is concentrated, and as the complexing agent is removed by suitable conditions including evaporation, the short chain carboxylic acid becomes liberated, and reduction of the silver salt to elemental silver by the short chain carboxylic acid can occur. Preferably, metallic particle formation can only occur after patterning, as evaporation ensues. A highly conductive silver structure remains after the reduction, even at low processing temperatures, because the low boiling points of non-silver constituents allow for a controlled and complete, or nearly complete, removal of the non-silver constituents.

[0086] Although the just-described ink compositions are advantageously free of metallic particles and can form conductive structures at low temperatures, the conductive structures formed from these inks can, in some cases, display properties that limit their usefulness in printed electronic devices. For example, the inclusion of additives such as adhesion promoters or other agents used to modulate the physical, chemical, and / or electronic properties of the conductive inks, or of the conductive structures prepared from those inks, can result in conductive structures having less than ideal properties. In some cases, the presence of such additives in the conductive ink can result in conductive films with surfaces that display poor wettability with respect to commonly used soldering pastes (e.g. SAC305). This poor wettability can accordingly limit the utility of these inks for metallization in the semiconductor and packaging industries.

[0087] These problems are illustrated in FIG. 1, where a particle-free silver ink that includes a silicon-containing adhesion promoter was used to prepare a metallic silver conductive structure on a test substrate. As shown in this image, treatment of the metallized surface with a commonly used soldering paste (SAC3O5) results in the “de-wetting” of the soldering paste on surface of the conductive film. Although the use of adhesion promoters in conductive ink compositions can be advantageous, because inks containing such promoters can be applied using a spray coater, or the like, rather than a physical vapor deposition (PVD) tool, any undesirable surface properties of conductive structures formed from these conductive inks can limit the utility of the inks.

[0088] In addition to poor wettability, silver films formed from known MOD silver inks can change color after reliability testing at elevated temperatures. For example, FIG. 2A shows a silver film prepared from a particle-free silver ink comprising a silicon-containing adhesion promoter. As shown in FIGs. 2B-2D, the silver film changes color after reliability testing using a high-temperature storage (HTS) test. Color changes in a silver film can be undesirable in some applications, for example where bar codes or other identifying features have been included on a film surface, and where discoloration of the surface may make a later reading of the feature difficult and / or inaccurate.

[0089] The poor wettability of conductive surfaces prepared from known conductive ink formulations and the potential for discoloration of these surfaces over time and at elevated temperature has been addressed in the current disclosure. Specifically, novel conductive ink compositions and treatment methods have been developed that can overcome these problems with conductive films prepared from MOD inks comprising an additive such as an adhesion promoter, and in particular, an adhesion promoter comprising silicon.Without intending to be bound by theory, it is believed that silver films formed from inks comprising silicon-containing additives may have silicate layers on their surfaces that can impair wettability and that can result in discoloration over time and during testing at elevated temperatures. It is also believed that the inclusion of fluoride salts in the inks, or the treatment of silver films prepared from silicon-containing additives with aqueous fluoride salts following their formation, can disrupt the silicates and can thereby result in cleaner silver surfaces that are wettable by standard soldering pastes and that may not be prone to discoloration.

[0090] The advantages of the ink compositions disclosed herein have been demonstrated as shown in FIGs. 3 A and 3B, where the ink formulation described in the Examples section has been coated on an initial conductive film that was prepared from an ink comprising a silicon-containing adhesion promoter. After curing the second conductive layer, the resulting conductive surface was treated with a soldering paste, which fullywetted the conductive structure. Good adhesion was observed of the newly developed overcoat on top of a conductive film made from the known conductive ink, and an increase in the measured conductivity of the overcoated structure was even observed. The process used in these methods differs from PVD-based methods, which use a pure silver source and therefore do not result in the formation of a silicate layer on the surface of the initial film. Traditional PVD-based methods are significantly more expensive than the coating methods described herein, however, with a lower throughput and a larger footprint than these approaches.

[0091] Similar to conductive inks known in the art, the conductive ink compositions disclosed herein can possess low viscosity so that they are compatible with a broad range of patterning techniques, including slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen-printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, and electrohydrodynamic printing. In particular, the inks are compatible with inkjet printing, dip coating, and spray coating. The patterned features may be highly conductive at room temperature and achieve bulk conductivity upon decomposing at mild temperatures (e.g., in some cases at less than about 100 °C). Finally, the ink compositions may remain stable for months without particle precipitation. In some cases, the ink compositions remain stable at room temperature. In other cases, the ink compositions remain stable at 4 °C or colder temperatures.Conductive Ink Compositions

[0092] Accordingly, conductive ink compositions (also referred to as “conductive inks” or “inks”) have been created for printing highly conductive features at low temperatures. Such inks may be stable, particle-free, and suitable for a wide range of patterning techniques.

[0093] Particle-free MOD ink compositions suitable for use in the techniques described herein include MOD ink compositions that are capable of forming conductive structures on the surface of a target substrate rapidly, at low temperature, and under ambient atmospheric conditions. Such compositions include MOD inks that are known in the art but that have not previously been used for these purposes.

[0094] For example, ink compositions prepared from silver metal precursors have been described in PCT International Publication No. WO2013 / 096664A1. Further MOD inkcompositions comprising silver metal precursors are described, for example, in PCT International Publication Nos. WO2015 / 160938A1 and WO2023 / 168452A2, in PCT International Application No. PCT / US2023 / 086353, filed December 29, 2023, and in U.S. Application No. 63 / 622,489, filed January 18, 2024. MOD ink compositions comprising copper are described, for example, in PCT International Publication No.WO2018 / 118460A1, MOD ink compositions comprising palladium are described, for example, in PCT International Publication No. WO2019 / 028435A1, MOD ink compositions comprising gold are described, for example, in PCT International Publication Nos. WO2019 / 028436A1, WO2023 / 215849A2, and W02024 / 006882A2, and MOD ink compositions comprising platinum are described, for example, in PCT International Application No. PCT / US2023 / 073121, filed August 30, 2023. Each of the above disclosures is incorporated by reference herein in its entirety for all purposes.

[0095] Accordingly, in some embodiments, the MOD ink compositions of the instant disclosure comprise silver, copper, palladium, gold, platinum, indium, nickel, or a combination of these metals. In preferred embodiments, the MOD ink compositions comprise silver, copper, nickel, gold, platinum, or a combination of these metals. Even more preferably, the MOD ink compositions comprise silver, or a combination of silver and another metal.

[0096] In some embodiments, a MOD ink is one that does not include any particles at a diameter of greater than about 10 nm. In some embodiments, a MOD ink is one that has less than about 1% particles, preferably less than about 0.1% particles.

[0097] In some embodiments, the conductive ink compositions have a concentration of about 0. 1-50 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 0.1-40 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 1-30 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 1 -20 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 1-10 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 5-15 weight percent metal salt of the ink composition. In some embodiments, the ink compositions have a concentration of about 0.1 weight percent, about 0.2 weight percent, about 0.3 weight percent, about 0.4 weightpercent, about 0.5 weight percent, about 0.6 weight percent, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent, about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent, about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent, about 17 weight percent, about 18 weight percent, about 19 weight percent, or even about 20 weight percent metal of the ink composition.

[0098] In some embodiments, the instant ink compositions have a concentration of at least about 0.1 weight percent, about 0.2 weight percent, about 0.3 weight percent, about 0.4 weight percent, about 0.5 weight percent, about 0.6 weight percent, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent, 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent, about 12 weight percent, about13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent, about 17 weight percent, about 18 weight percent, about 19 weight percent, or about 20 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of at most about 40 weight percent, about 39 weight percent, about 38 weight percent, about 37 weight percent, about 36 weight percent, about 35 weight percent, about 34 weight percent, about 33 weight percent, about 32 weight percent, 31 weight percent, about 30 weight percent, about 29 weight percent, about 28 weight percent, about 27 weight percent, about 26 weight percent, about 25 weight percent, about 24 weight percent, about 23 weight percent, about 22 weight percent, about 21 weight percent, about 20 weight percent, about 19 weight percent, about 18 weight percent, about 17 weight percent, about 16 weight percent, about 15 weight percent, about14 weight percent, about 13 weight percent, or about 12 weight percent metal salt of the ink composition.

[0099] In some embodiments, the instant ink compositions have a concentration of about 0. 1-50 weight percent metal complex of the ink composition. In some embodiments, the ink compositions have a concentration of about 0. 1 -40 weight percent metal complex of the ink composition. In some embodiments, the ink compositions have a concentration ofabout 1 -30 weight percent metal complex of the ink composition. In some embodiments, the ink compositions have a concentration of about 1-20 weight percent metal complex of the ink composition. In some embodiments, the ink compositions have a concentration of about 1-10 weight percent metal complex of the ink composition. In some embodiments, the ink compositions have a concentration of about 5-15 weight percent metal complex of the ink composition.

[0100] In some embodiments, the instant conductive ink compositions have a desired viscosity. In some embodiments, the desired viscosity is obtained using a micro VISC viscometer. In some embodiments, the conductive ink compositions have a viscosity from about 50 centipoise to about 1000 centipoise. In some embodiments, the conductive ink compositions have a viscosity from about 5 centipoise to about 50 centipoise. In some embodiments, the conductive ink compositions have a viscosity from about 10 centipoise to about 40 centipoise. In some embodiments, the conductive ink compositions have a viscosity from about 20 centipoise to about 30 centipoise. In some embodiments, the conductive ink compositions have a viscosity from about 18 centipoise to about 20 centipoise. In some embodiments, the conductive ink compositions have a viscosity of about 18, about 19, or about 20 centipoise. In some embodiments, the conductive ink compositions have a viscosity of at least about 5 centipoise, about 10 centipoise, about 20 centipoise, about 30 centipoise, about 40 centipoise, about 50 centipoise, about 60 centipoise, about 70 centipoise, about 80 centipoise, about 90 centipoise, about 100 centipoise, about 200 centipoise, about 300 centipoise, about 400 centipoise, about 500 centipoise, about 600 centipoise, about 700 centipoise, about 800 centipoise, or about 900 centipoise. In some embodiments, the conductive ink compositions have a viscosity of at most about 1000 centipoise, about 900 centipoise, about 800 centipoise, about 700 centipoise, about 600 centipoise, about 500 centipoise, about 400 centipoise, about 300 centipoise, about 200 centipoise, about 100 centipoise, about 90 centipoise, about 80 centipoise, about 70 centipoise, about 60 centipoise, about 50 centipoise, about 40 centipoise, about 30 centipoise, about 20 centipoise, or about 10 centipoise.

[0101] In some embodiments, the viscosity of the conductive ink compositions are adjusted based upon an amount of a dissolving agent or solvent used in the composition. In some embodiments, the viscosity of the compositions are adjusted based upon the type of dissolving agent or solvent used.

[0102] The conductive ink compositions of the instant disclosure preferably possess viscosities that are compatible with a broad range of application techniques, including slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen-printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, and electrohydrodynamic printing. In particular, the inks may be compatible with inkjet printing, dip coating, and spray coating. The conductive structures formed from the ink compositions using the disclosed methods are preferably highly conductive at room temperature and preferably achieve bulk conductivity upon decomposition at mild temperatures (c.g., in some cases at less than about 100 °C). Finally, the ink compositions preferably remain stable at 4 °C for months without particle precipitation. They are also preferably stable to the process by which they are applied to the surface of the target structure, so they do not form significant amounts of a conductive metallic structure until they are in full contact with the target substrate.

[0103] As just described, the conductive ink composition of the instant disclosure preferably have a desired viscosity. In some embodiments, the desired viscosity is obtained using a Brookfield viscometer. Unless otherwise indicated, all viscosity values are for samples at room temperature.

[0104] In some embodiments, the ink compositions of the instant methods comprise an adhesion promoter, as will be further described below. Conductive ink compositions comprising exemplary adhesion promoters are also described in PCT International Publication No. WO2023 / 168452A2 and in PCT International Application No. PCT / US2023 / 086353, filed December 29, 2023, the disclosures of which are incorporated by reference herein for all purposes.

[0105] In one aspect, the conductive ink composition includes a silver complex formed by mixing a silver salt with at least one complexing agent. In some embodiments, the silver salt is soluble in the complexing agent. Solubility, as known to one of ordinary skill, is the property of a substance, such as a silver salt, to dissolve in a solvent, such as a complexing agent. In some embodiments, the silver salt is dissolved in water prior to reaction with the complexing agent.

[0106] In some embodiments, the silver salt is a silver fluoride salt. It should be understood that fluoride ions released from the silver fluoride salt, either as the silver fluoride salt is dissolved in water or as the silver reacts with the complexing agent, canreact with residual agents on the surface of an existing conductive film, for example silicate layers that may result from the presence of a silicon-containing additive in the precursor ink. Such reactions can reduce the likelihood that the surface of the existing conductive film, or the surface of a conductive film formed from the ink itself, will be unwettable or will become discolored over time after the film is formed.

[0107] The complexing agent of the instant disclosure is preferably an alkylamine or a plurality of alkylamines. An alkylamine is an amino group substituted by at least one Ci-io alkyl group, where an alkyl group refers to a hydrocarbon group which may be linear, cyclic, or branched or a combination thereof having the number of carbon atoms designated (i.e., Ci-io means one to ten carbon atoms). Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, pentyl, isopentyl, cyclohexyl, cyclopentyl, hexyl, heptyl, octyl, nonyl, decyl, and the like. An alkylamine may be a primary, secondary, or tertiary amine, preferably a primary amine. The alkylamine, which is a weak base, can act as a stabilizer and solvent for the silver salt. The alkylamine is not intended to act as a reducing agent for the silver salt i.e., it is not intended to appreciably reduce the silver salt). Any suitable alkylamine, or combination of alkylamines, that stabilizes the silver salt may be employed. Preferably, the alkylamine has a boiling point of about 200° C. or less. Examples of alkylamines having a boiling point of about 200° C. or less include but are not limited to isomers of CsH N, isomers of C7H17N, isomers of CgHuN, isomers of C5H13N, isomers of C4H11N, isomers of C3H9N, isomers of C2H7N, and isomers of CH5N. For convenience in handling, it may be desirable for the alkylamine to have a boiling point of about 40° C. or greater. Examples of alkylamines having boiling points between about 40° C. and 120° C. include, but are not limited to propylamine, n-butylamine, amylamine, s-butylamine, diethylamine, triethylamine, iso-butylamine, isopentylamine, 1 -methylbutylamine, 1 -amino-2- methylbutane, and N-methyldiethylamine. Preferably the alkylamine is octylamine, cyclopentylamine, or a combination thereof.

[0108] In some embodiments, the conductive ink composition of the instant disclosure comprises a silver complex, a formate salt, and a fluoride salt, wherein the silver complex comprises a silver(I) ion and at least one complexing agent. The silver complex in these compositions can be formed by reaction of a silver salt, for example silver fluoride, withthe complexing agent or agents. Without intending to be bound by theory, the fluoride ion can thereby become available to react with surfaces treated with the ink composition.Adhesion Promoter

[0109] In another aspect are provided conductive ink compositions that further comprise an adhesion promoter to increase adhesion of the ink to the substrate on which it is printed. It is envisioned that any agent that both improves the adhesive properties of the ink and that does not significantly degrade either the fluidic or other physical properties of the ink composition, including stability of the ink composition, or the electrical or other physical properties of conductive structures that are generated using the ink, can be utilized as an adhesion promoter in the instant ink compositions.

[0110] The adhesion promoter is preferably chosen in coordination with the choice of substrate on which the ink will be printed.

[0111] In some embodiments, the adhesion promoter comprises a reactive silane. Reactive silanes are known in the chemical and material science arts to enhance the performance of coatings. For example, they can improve adhesion to inorganic substrates, provide crosslinking, improve the dispersion of components of a composition, improve hydrophobicity, and scavenge moisture. In specific embodiments, the reactive silane comprises an alkoxysilane group, for example a trialkoxysilyl group. In some embodiments the alkoxysilyl group can be oligomerized or polymerized into a number of different chain length configurations. In some embodiments, the adhesion promoter comprises an alkyl group, and more specifically an alkyl group that comprises a second reactive moiety. For example, the adhesion promoter can comprise a polyalkene, for example a poly-l,2-butadiene. Suitable adhesion promoters are commercially available, for example from Gelest, Inc., Morrisville, PA, USA.

[0112] In some embodiments, the adhesion promoter comprises an epoxy group. More specifically, the adhesion promoter can comprise an epoxy group coupled to a silane, for example any of the just-described reactive silanes. In some embodiments, the adhesion promoter can comprise an epoxy group coupled to an alkoxysilane group, such as a trialkoxysilyl group. In specific embodiments, the adhesion promoter can comprise an epoxy group coupled to a trialkoxysilyl group, such as a trimethoxysilyl group or a triethoxysilyl group.

[0113] The adhesion promoter preferably comprises a linker group that couples a reactive silane group to second reactive group, for example an alkyl group comprising a reactive constituent such as a polyalkene or an epoxy group. The linker group can be any suitable chemical linker. In some embodiments, the linker group is an alkyl linker group, for example a Ci-Cio-alkyl linker group. In some embodiments, the linker group is a substituted alkyl linker group, where the alkyl linker group is substituted with any suitable substituent. For example, the alkyl linker group can be substituted with one or more alkyl, alkenyl, alkynyl, alkoxy, alkanoyl, alkylamino, hydroxy, thio, amino, alkanoylamino, alkylcarboxy, carbonate, halo, nitro, cyano groups, or the like. In some embodiments, one or more of the carbon atoms in the linker can be substituted with a suitable heteroatom. In specific embodiments, the heteroatom can be oxygen, sulfur, or nitrogen, in any combination. More specifically, the heteroatom can be oxygen.

[0114] In some embodiments, the adhesion promoter is a structure of formula I:wherein each R’ is independently a Ci-Ce alkyl group, and L’ is an alkyl linker group. In more specific embodiments of structural formula I, each R’ is independently a methyl or an ethyl group. In other more specific embodiments of structural formula I, L’ can be a C2-Cw-alkyl linker group, including a substituted Cz-Cw-alkyl linker group. In some embodiments of structural formula I, one or more of the carbon atoms in L’ can be substituted with a suitable heteroatom, for example an oxygen, a sulfur, or a nitrogen, in any combination. More specifically, the heteroatom can be oxygen.

[0115] In some more specific embodiments, the adhesion promoter is a structure of formula II:

[0116] wherein each R’ is independently a methyl or an ethyl group, X is a heteroatom, and each n is independently 1-6. In some embodiments of structural formula II, each R’ is a methyl group, X is oxygen, and each n is independently 1-3.

[0117] In some specific embodiments, the adhesion promoter of the instant conductive ink compositions is:(3-glycidyloxypropyl)trimethoxysilaneThis compound is readily soluble in typical ink formulations. Specifically, ink formulations including this adhesion promoter can be prepared at 0.1 -0.5% without reducing the conductivity of structures produced from the inks on different substrates. Furthermore, inks comprising this adhesion promoter are stable at 40 °C over 14-30 days with no visible precipitation or plating. These formulations likewise display viscosities suitable for use with typical industrial inkjet printhead technologies. Addition of water in the ink formulations up to 3% does not decrease stability of these inks at 40 °C.

[0118] In some specific embodiments, the adhesion promoter of the instant conductive ink compositions is:(3-glycidyloxypropyl)triethoxysilaneMethods of Forming Conductive Structures

[0119] In another aspect are provided methods of forming conductive structures, wherein the conductive structures formed by the methods display desirable surface properties, for example good wettability and lack of discoloration over time. In some embodiments, the methods include the steps of treating a substrate with a first conductive ink composition, wherein the first conductive ink composition comprises an adhesion promoter, optionally curing the first conductive ink composition to form a first conductive structure, treating the first conductive structure with a second conductive ink composition, wherein the second conductive ink composition is any of the above-described conductive ink compositions, and optionally curing the second conductive ink composition to form a second conductive structure. In some embodiments, the adhesion promoter is a silicon- containing adhesion promoter.

[0120] Tn yet another aspect, the disclosure provides methods of forming conductive structures with desirable surface properties. These methods include the steps of treating a substrate with a first conductive ink composition, wherein the first conductive ink composition comprises an adhesion promoter, optionally curing the first conductive ink composition to form a first conductive structure, and treating the first conductive structure with a solution comprising a fluoride salt. The conductive structures formed from these methods display good wettability and do not become discolored over time, even when subjected to HTS testing.

[0121] In some embodiments, the fluoride salt is an ammonium salt or an alkylammonium salt. More specifically, the fluoride salt can be ammonium fluoride. Tn preferred embodiments, the fluoride salt is dissolved in water. For example, the fluoride salt can be an ammonium fluoride salt dissolved in water at 5-25 weight percent.

[0122] In some embodiments, the adhesion promoter comprises silicon.

[0123] In some embodiments, the first conductive ink composition further comprises a silver complex and a formate salt, wherein the silver complex comprises a silver(I) ion and at least one complexing agent. More specifically, the formate salt in these methods can be an ammonium or alkylammonium formate salt, for example ammonium formate.

[0124] In some embodiments, the at least one complexing agent is a first alkylamine. In more specific embodiments, the first alkylamine is a primary alkylamine. In other more specific embodiments, the first alkylamine is a C3-C10 alkylamine. Even more specifically, the first alkylamine is an octylamine.

[0125] In some embodiments, the composition further comprises a second alkylamine. More specifically, the second alkylamine can be a C3-C10 cycloalkylamine, and even more specifically, the second alkylamine can be a cyclopentylamine.

[0126] In some embodiments, the ink compositions are cured by heating them on a substrate at a decomposition temperature of about 250 °C or less to form the conductive structure. In some embodiments, the ink compositions are cured by heating them on a substrate at a decomposition temperature of about 100 °C or less to form the conductive structure. In some embodiments, the ink compositions are cured by heating them on a substrate at a decomposition temperature of about 210 °C or less, of about 200 °C or less, of about 190 °C, of about 180 °C or less, of about 170 °C or less, of about 160 °C, of about 150 °C or less, of about 140 °C or less, of about 130 °C or less, of about 120 °C or less, ofabout 1 10 °C or less, of about 90 °C or less, of about 80 °C or less, of about 70 °C or less, of about 60 °C or less, or of about 50 °C or less to form the conductive structure. In some embodiments, the conductive ink composition is heated with a heat source. Examples of heat sources include an IR lamp, oven, or a heated substrate.

[0127] In some embodiments, the electrical conductivity of the conductive structures is measured. In some embodiments, the electrical conductivity of the conductive structures is about IxlO’6Ohm-cm or greater. In some embodiments, the electrical conductivity of the conductive structures is from about IxlO-6Ohm-cm to about 8xl0-4Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is from about 3x10‘6Ohm-cm to about 6x1 O'6Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is at least about IxlO-6Ohm-cm, about 2xl0-6Ohm-cm, about 3x1 O’6Ohm-cm, about 4x1 O’6Ohm- cm, about 5xl0-6Ohm-cm, about 6x1 O’6Ohm-cm, about 7x106Ohm-cm, about 8x106Ohm-cm, about 9x106Ohm-cm, about 1x105Ohm- cm, about 2xl0‘5Ohm-cm, about 3x10sOhm-cm, about 4x10sOhm-cm, about 5x10sOhm-cm, about 6x10sOhm-cm, about 7x10'5Ohm-cm, about 8x10'5Ohm-cm, about 9xl0-5Ohm-cm, about IxlO-4Ohm-cm, about 2xl0-4Ohm-cm, about 3xl04Ohm-cm, about 4xl0-4Ohm-cm, about 5xl0-4Ohm-cm, about 6xl0-4Ohm-cm, or about 7xl0-4Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is at most about 8xl0-4Ohm-cm, 7xl0-4Ohm -cm, about 6xl0 Ohm-cm, about 5xl0-4Ohm- cm, about dxlO-4Ohm-cm, about 3xl0-4Ohm-cm, about 2xl0-4Ohm-cm, or about IxlO-4Ohm-cm, about 9x10sOhm-cm, about 8x10sOhm-cm, about 7x10sOhm-cm, about 6x10sOhm-cm, about 5x10sOhm-cm, about 4x10sOhm-cm, about 3x10sOhm-cm, about 2x10sOhm-cm, about 1x10sOhm-cm, about 9xl0‘6Ohm-cm, about 8xl0-6Ohm-cm, about 7xl0-6Ohm-cm, about 6xl0-6Ohm-cm, about 5xl0-6Ohm-cm, about 4xl0-6Ohm - cm, about 3xl0-6Ohm-cm, or about 2xl0-6Ohm-cm.

[0128] In still yet another aspect, the disclosure provides methods of forming conductive structures with desirable surface properties. These methods include the steps of treating a substrate with a first conductive ink composition, optionally curing the first conductive ink composition to form a first conductive structure, and treating the first conductive structure with a plasma.

[0129] In some embodiments, the plasma is a CF4 plasma or an O2 + CF4 plasma.

[0130] Tn some embodiments, the first conductive ink composition comprises an adhesion promoter, in particular an adhesion promoter comprising silicon. For example, the adhesion promoter can be any of the adhesion promoters described above.

[0131] In some embodiments, the first conductive ink composition is a precursor-based conductive ink composition, for example any of the MOD ink compositions described above.

[0132] In some embodiments, the first conductive ink composition comprises silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof. More specifically, the first conductive ink composition comprises silver, copper, nickel, gold, platinum, or a combination thereof. Even more specifically, the first conductive ink composition comprises silver.

[0133] In some specific embodiments, the first conductive ink composition comprises a silver complex and a formate salt, wherein the silver complex comprises a silver(I) ion and at least one complexing agent. More specifically, the formate salt is an ammonium or alkylammonium formate salt, for example ammonium formate

[0134] In other more specific embodiments, the at least one complexing agent is a first alkylamine, for example the first alkylamine is a primary alkylamine, or a C3-C10 alkylamine or a C3-C10 cycloalkylamine, such as an octylamine or a cyclopentylamine.

[0135] In still other more specific embodiments, the silver complex further comprises a second alkylamine, such as a C3-C10 alkylamine or a C3-C10 cycloalkylamine or even wherein the second alkylamine is an octylamine or a cyclopentylamine.

[0136] In some embodiments, the methods further comprise the step of applying a soldering paste to the first conductive structure.Solderable Conductive Structures

[0137] In another aspect are provided solderable conductive structures comprising a metallic layer disposed on a nonconductive substrate, wherein the metallic layer comprises a silicon-containing material; and a solder flux disposed on a surface of the metallic layer, wherein the solder flux comprises an aqueous solvent or a mixed aqueous solvent, a fatty acid, and an organic amine. The metallic layer is preferably formed from any of the above-described conductive ink compositions, wherein the conductive ink composition further comprises any of the above-described adhesion promoters.

[0138] Tn some embodiments, the conductive ink composition comprises silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof. More specifically, the conductive ink composition comprises silver, copper, nickel, gold, platinum, or a combination thereof. Even more specifically, the conductive ink composition comprises silver.

[0139] The solder flux used in the solderable conductive structures is preferably a printable solder flux. For example, the solder flux can be any of the solder fluxes disclosed in U.S. Patent No. 11 ,597,042. In these fluxes, the fatty acid and / or a fatty acid derivative can be saturated or unsaturated. Suitable saturated fatty acids include propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, archidic acid, heneicosylic acid, behenic acid, tricosylic acid, lignoceric acid, pentacosylic acid, cerotic acid, heptacosylic acid, montanic acid, henatriacontylic acid, lacceroic acid, psyillic acid, geddic acid, ceroplastic acid, hexatriacontylic acid heptatriacontanoic acid, and octatriacontanoic acid. Suitable unsaturated fatty acids include alpha linoleic acid, stearidonic acid, eicospentaenoic acid, docosahexaenoic acid, linoleic acid, linolelaidic acid, gamma linolenic acid, dihomo-gamma-linolenic acid, arachidonic acid, docosatetraenoic acid, palmitoleic acid, vaccenic acid, paulinic acid, oleic acid, elaidic acid, gondoic acid, erucic acid, nervonic acid, and mead acid. Such fatty acids can be in the form of free acids or in the form of salts (for example, an ammonium, sodium, or potassium salt). In some embodiments the fatty acid is palmitic acid or palmitate.

[0140] The organic amine used in the instant solder flux can be any suitable organic amine. Such organic amines can include a carbon chain of from 2 to 12 carbons in length, and include at least one amine group. In some embodiments the organic amine can include additional substituents, such as a hydroxyl group, a carboxyl group, and / or a halogen. In some embodiments the organic amine can be present as a free base. In other embodiments the organic amine can be present as a salt (such as a tetrafluoroborate salt) or as a complex with a mineral acid (such as HC1 or HF). Suitable organic amines include ethanolamine and dodecylamine.Methods for Preparing Conductive Ink Compositions

[0141] According to another aspect, the disclosure provides methods of preparing a conductive ink composition, in particular any of the conductive ink compositions described above. These methods comprise the steps of combining a silver(I) salt with a molar excess of at least one complexing agent to form a silver complex and treating the silver complex with an aqueous solution of ammonium formate. The silver(I) salt is preferably silver fluoride.

[0142] In some embodiments, the at least one complexing agent of the above method is an alkylamine. More specifically, the alkylamine can be a C3-C10 cycloalkylamine or a C3-C10 alkylamine. Even more specifically, the alkylamine can be a cyclopentylamine or an octylamine. In some specific embodiments, the alkylamine can be a C3-C10 cycloalkylamine and a C3-C10 alkylamine, and more specifically, the alkylamine can be a cyclopentylamine and an octylamine.

[0143] In another aspect are provided conductive ink compositions that have been prepared using any of the above-described methods.Applications of the Conductive Ink Compositions

[0144] The conductive ink compositions of the instant disclosure can be used in various printing applications, including slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, dispenser, and electrohydrodynamic printing. In particular, the inks can be used in inkjet printing, dip coating, and spray coating.

[0145] Furthermore, patterns can be created using photolithography to create a mask to etch silver from certain areas, thereby creating high-fidelity features. Both positive and negative patterning processes may be used to create the patterns.

[0146] It will be readily apparent to one of ordinary skill in the relevant arts that other suitable modifications and adaptations to the compositions and methods described herein may be made without departing from the scope of the invention or any embodiment thereof. Having now described the present invention in detail, the same will be more clearly understood by reference to the following Examples, which are included herewith for purposes of illustration only and are not intended to be limiting of the invention.EXAMPLESPreparation of an improved conductive ink composition

[0147] As noted above, the conductive ink compositions of the instant disclosure can be used to coat surfaces that are poorly wettable. In particular, the ink compositions can be used to coat conductive structures formed using conductive ink compositions that comprise adhesion promoters, specifically silicon-containing adhesion promoters.

[0148] In one exemplary preparation, the conductive ink composition was prepared as follows:Added a stir bar to a 25ml bottle (Bottle A) and placed on a stir plate.Measured out ~4.593g cyclopentylamine into Bottle A.Added ~6.957g octylamine to Bottle A, swirled to mix.Placed Bottle A into a freezer.Set up an ice bath on a stir plate.In a separate vial (Bottle B), added a stir bar and ~3.78g D.I. H2O.Measured out -3. 18g AgF.Transferred Bottle B into the ice bath and slowly added the AgF while stirring. Transferred Bottle A into the ice bath and turned on the stirring.Dropwise, added the contents of Bottle B mixture into Bottle A.Let stir, in a separate vial (Bottle C) mixed -1.117g ammonium formate and -1.117g D.I. H2O until dissolved.Once solids in Bottle A were completely dissolved, added contents of Bottle C to Bottle A. Let stir.After ~30min., filtered with 0.22 um h.p. ptfe filter. The new solution is 16% ammonium fluoride dissolved in water.

[0149] This conductive ink composition can be spray-coated or spin-coated on a conductive surface that was prepared from a conductive ink composition comprising a silicon-containing adhesion promoter and that displays poor wettability with solder paste. Rather than coat an entirely pure silver film onto the substrate, a film is instead created with an MOD ink that contains an adhesion promoter. This allows for application of the film with a spray coater or spin coater, rather than a PVD tool or similar alternative. After coating the initial film layer on the substrate, the film is overcoated with the modified ink formulation, which provides the solder paste wettability seen on pure silver.

[0150] This approach differs from PVD-based methods, which use a pure silver source and which do not, therefore, result in the formation of a silicate layer.Use of a fluoride salt overcoat to improve the surface properties of a silver film prepared from a silicon-containing conductive ink composition

[0151] As an alternative to using the above-described ink compositions for preparing conductive films with improved surface properties, or as an overcoat for improving the surface properties of silver films formed from silicon-containing conductive ink compositions, it was discovered that a fluoride salt overcoat solution can also be used to improve the surface properties of silver films formed from silicon-containing conductive ink compositions. As shown in FIGs. 4A-4D, silver films were prepared from a particle- free silver ink that included a silicon-containing adhesion promoter. As had also been shown in FIG. 1, an untreated control silver film (FIG. 4A) was poorly wetted by solder paste applied to the surface. In contrast, silver films prepared from an ink composition comprising a silicon-containing adhesion promoter displayed improved wettability after treatment with 2 passes (FIG. 4B), 4 passes (FIG. 4C), or 8 passes (FIG. 4D) of an ammonium fluoride solution (16% in water) overcoat.

[0152] The overcoating with an ammonium fluoride solution also inhibits discoloration of the silver film surface over time. An untreated control silver film surface (FIG. 5D) shows significant color change upon aging, whereas silver films treated with 2 passes (FIG. 5C), 4 passes (FIG. 5B), or 8 passes (FIG. 5A) of an ammonium fluoride solution show significantly less color change over time than the control.Use of a plasma treatment to improve the surface properties of a silver film prepared from a silicon-containing conductive ink composition

[0153] As another alternative to using the above-described ink compositions for preparing conductive films with improved surface properties, or using the above-described ink compositions or a fluoride salt solution as an overcoat to improve the surface properties of silver films formed from silicon-containing conductive ink compositions, it was found that the surface properties of such films could also be greatly improved using a brief plasma treatment. As was shown in FIGs. 1 and 4A, an untreated control silver film formed from a conductive ink comprising a silicon-containing adhesion promoter was poorly wetted by solder paste applied to the surface (FIG. 6A). In contrast, the same silver film displayed significantly improved wettability after brief treatment with a CF4 plasma(FIG. 6B) or an O2 + CF4 plasma (FIG. 6C). An exemplary process flow for the plasma treatment methods is illustrated in FIG. 7.

[0154] FIGs. 8A and 8B demonstrate the improved surface properties of a plasma- treated silver film (FIG. 8B) compared to a control silver film (FIG. 8A), where the silver film was formed from a silver ink composition comprising 19.80 wt% silver acetate, 30.66 wt% octylamine, 20.21 wt% cyclopentylamine, 17.95 wt% H2O, 5.26 wt% ammonium formate (50% in H2O), and 1.0 wt% jV-(2-ami noethyl )-3-ami nopropyltri methoxysilane (Gelest SIA 591.1) as an adhesion promoter. The film properties tested in each case included a standard tape test for rating adhesion (ASTM D3359), a contact angle measurement with water, and a hot-plate soldering test (SRA SSLTNC Type 3). Some of the control samples were subjected to a post-treatment isopropanol wipe (FIG. 8A; “IPA Wipe”) prior to testing. As shown in FIG. 8B, the plasma treatments were with a CF4 plasma for 1 minute, 3 minutes, 5 minutes, or 10 minutes.

[0155] As can be seen in the results of FIG. 8B, all of the plasma treatments resulted in a silver film surface with greatly improved wettability compared to untreated silver films. In particular, these treatments result in silver films that display the solder paste wettability seen on pure silver. The use of a plasma treatment is simpler than the above-described overcoating methods and does not otherwise damage the surface of the conductive structure or cause loss of adhesion. In addition, plasma treatments are commonly used in the electronics industry and can readily be incorporated into standard process flows.Use of a novel printable flux to improve the surface properties of a silver film prepared from a silicon-containing conductive ink composition

[0156] As described above, surface treatments of a silver film prepared from a conductive ink composition comprising a silicon-containing adhesion promoter displayed improved solder wettability compared to untreated films. For example, surface treatments with a fluoride salt and / or a plasma can help to improve solder wettability on the surface of such films.

[0157] The instant inventors have also discovered that a printable flux composition can be used, together with solder preforms, to achieve good solder wettability, improved shear force tests, and minimum void formation (<10%) in soldered joints formed on the surface of metallic films prepared with conductive inks comprising a silicon-containing adhesion promoter.

[0158] Tn some controls, a solder preform was coated with a conventional LV2K flux (both preform and flux are available from Indium Corporation (www.indium.com)). These tests demonstrated that the LV2K flux was not able to clean the surface of the above-described silver film enough to let the solder preform wet properly. Specifically, as shown with the top two examples in the left panel of FIG. 9, treatment of the silver film with LV2K flux and heating at 176 °C did not clean the surface sufficiently to allow wetting of the silver film. Instead, the solder preform balls up on top of the silver film. As shown with the bottom two examples in the left panel of FIG. 9, when the LV2K flux is removed from the preform with isopropyl alcohol, the preform stays in place without balling up. These results demonstrate that LV2K flux is not compatible with conductive films formed from a conductive ink comprising a silicon-containing adhesion promoter.

[0159] In contrast to the above results, if the above-described silver film is treated with a printable solder flux, in particular a solder flux comprising an aqueous solvent or a mixed aqueous solvent, a fatty acid, and an organic amine, a solder preform placed on the surface of the treated silver surface is properly wetted. For example, as shown in the center panel of FIG. 9, a solder preform (97% In / 3% Ag, Indium Corp.) placed on the surface of a 7 pm silver film prepared from a silver ink composition comprising a silver-containing adhesion promoter that is treated with Mina™ flux paste (Taiyo America, Inc.) and heated on a hot plate is wetted properly.

[0160] Soldered sandwich structures have also been formed using the above-described approaches. For example, a sandwich stack was formed using a silicon substrate coated with the above-described silver ink composition comprising a silicon-containing adhesion promoter. The silver film was then treated with Mina™ flux paste, a solder preform layer, an additional layer of Mina™ flux paste, and another silicon substrate coated with the silver ink composition comprising a silicon-containing adhesion promoter. An air gun set to 186 °C was used to heat the Mina™ flux paste layer until it changes from a translucent clear to white. The sandwich structure was placed on a hot plate at -170-180 °C to form the structure shown in the right panel of FIG. 9. As described below and in FIGs. 10A- 10D, this sandwich structure was then tested for void formation (X-ray), shear testing, and SEM EDS analysis to study the physical and structural properties of the intermetallic layer.

[0161] FIG. 10A graphically illustrates the soldered sandwich structure formed using a printable solder flux. FIG. 10B shows an EDS analysis of the sandwich structure. FIG.10C shows a cross-sectional SEM image of the sandwich structure and inter metallic (IMC) layer, and FIG. 10D shows an X-ray analysis of the sandwich structure. The X-ray analysis indicates <5% void in the sandwich structure, and a shear force test of the structure is -6.3 MPa.

[0162] All patents, patent publications, and other published references mentioned herein are hereby incorporated by reference in their entireties as if each had been individually and specifically incorporated by reference herein.

[0163] While specific examples have been provided, the above description is illustrative and not restrictive. Any one or more of the features of the previously described embodiments can be combined in any manner with one or more features of any other embodiments in the present invention. Furthermore, many variations of the invention will become apparent to those skilled in the art upon review of the specification. The scope of the invention should, therefore, be determined by reference to the appended claims, along with their full scope of equivalents.

Claims

What is Claimed is:

1. A method of forming a conductive structure comprising the steps of: treating a substrate with a first conductive ink composition to form a first conductive structure; optionally curing the first conductive structure; and treating the first conductive structure with a plasma.

2. The method of claim 1 , wherein the plasma is a CF4 plasma or an O2 + CF4 plasma.

3. The method of claim 1, wherein the first conductive ink composition is a precursorbased conductive ink composition.

4. The method of claim 1 , wherein the first conductive ink composition comprises silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof.

5. The method of claim 4, wherein the first conductive ink composition comprises silver, copper, nickel, gold, platinum, or a combination thereof.

6. The method of claim 5, wherein the first conductive ink composition comprises silver.

7. The method of claim 1, wherein the first conductive ink composition comprises an adhesion promoter.

8. The method of claim 7, wherein the adhesion promoter comprises silicon.

9. The method of claim 7, wherein the first conductive ink composition further comprises a silver complex and a formate salt, wherein the silver complex comprises a silver(I) ion and at least one complexing agent.

10. The method of claim 9, wherein the formate salt is an ammonium or alkylammonium formate salt.

11. The method of claim 10, wherein the formate salt is ammonium formate.

12. The method of claim 9, wherein the at least one complexing agent is a first alkylamine.

13. The method of claim 12, wherein the first alkylamine is a primary alkylamine.

14. The method of claim 12, wherein the first alkylamine is a C3-C10 alkylamine or a C3- C10 cycloalkylamine.

15. The method of claim 14, wherein the first alkylamine is an octylamine or a cyclopentylamine.

16. The method of claim 12, wherein the silver complex further comprises a second alkylamine.

17. The method of claim 16, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

18. The method of claim 17, wherein the second alkylamine is an octylamine or a cyclopentylamine.

19. The method of claim 1, further comprising the step of applying a soldering paste to the first conductive structure.

20. A solderable conductive structure comprising: a metallic layer disposed on a nonconductive substrate, wherein the metallic layer comprises a silicon-containing material; and a solder flux disposed on a surface of the metallic layer, wherein the solder flux comprises an aqueous solvent or a mixed aqueous solvent, a fatty acid, and an organic amine.

21. The solderable conductive structure of claim 20, wherein the solder flux is a printable solder flux.

22. The solderable conductive structure of claim 20, wherein the metallic layer is prepared from a conductive ink composition.

23. The solderable conductive structure of claim 22, wherein the metallic layer is prepared from a precursor-based conductive ink composition.

24. The solderable conductive structure of claim 22, wherein the conductive ink composition comprises silver, copper, palladium, gold, platinum, indium, nickel, or a combination thereof.

25. The solderable conductive structure of claim 24, wherein the conductive ink composition comprises silver, copper, nickel, gold, platinum, or a combination thereof.

26. The solderable conductive structure of claim 25, wherein the conductive ink composition comprises silver.

27. The solderable conductive structure of claim 22, wherein the conductive ink composition comprises an adhesion promoter.

28. The solderable conductive structure of claim 27, wherein the adhesion promoter comprises silicon.

29. A conductive ink composition comprising: a silver complex; a formate salt; and a fluoride salt; wherein the silver complex comprises a silver(I) ion and at least one complexing agent.

30. The conductive ink composition of claim 29, wherein the fluoride salt is an ammonium or alkylammonium fluoride salt.

31. The conductive ink composition of claim 30, wherein the fluoride salt is ammonium fluoride.

32. The conductive ink composition of claim 29, wherein the formate salt is an ammonium or alkylammonium formate salt.

33. The conductive ink composition of claim 32, wherein the formate salt is ammonium formate.

34. The conductive ink composition of claim 29, further comprising an adhesion promoter.

35. The conductive ink composition of claim 34, wherein the adhesion promoter comprises silicon.

36. The conductive ink composition of claim 29, wherein the at least one complexing agent is a first alkylamine.

37. The conductive ink composition of claim 36, wherein the first alkylamine is a primary alkylamine.

38. The conductive ink composition of claim 36, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

39. The conductive ink composition of claim 38, wherein the first alkylamine is an octylamine or a cyclopentylamine.

40. The conductive ink composition of claim 36, further comprising a second alkylamine.

41. The conductive ink composition of claim 40, wherein the second alkylamine is a C3- C10 alkylamine or a C3-C10 cycloalkylamine.

42. The conductive ink composition of claim 41, wherein the second alkylamine is an octylamine or a cyclopentylamine.

43. A method of forming a conductive structure comprising the steps of: treating a substrate with a first conductive ink composition, wherein the first conductive ink composition comprises an adhesion promoter; optionally curing the first conductive ink composition to form a first conductive structure; treating the first conductive structure with a second conductive ink composition, wherein the second conductive ink composition is the conductive ink composition of any one of claims 29-42; and optionally curing the second conductive ink composition to form a second conductive structure.

44. The method of claim 43, wherein the adhesion promoter is a silicon-containing adhesion promoter.

45. A method of forming a conductive structure comprising the steps of: treating a substrate with a first conductive ink composition, wherein the first conductive ink composition comprises an adhesion promoter; optionally curing the first conductive ink composition to form a first conductive structure; and treating the first conductive structure with a solution comprising a fluoride salt.

46. The method of claim 45, wherein the fluoride salt is an ammonium salt or an alkylammonium salt.

47. The method of claim 46, wherein the fluoride salt is ammonium fluoride.

48. The method of claim 45, wherein the adhesion promoter comprises silicon.

49. The method of claim 45, wherein the first conductive ink composition comprises a silver complex and a formate salt, wherein the silver complex comprises a silver(I) ion and at least one complexing agent.

50. The method of claim 49, wherein the formate salt is an ammonium or alkylammonium formate salt.

51. The method of claim 50, wherein the formate salt is ammonium formate.

52. The method of claim 49, wherein the at least one complexing agent is a first alkylamine.

53. The method of claim 52, wherein the first alkylamine is a primary alkylamine.

54. The method of claim 52, wherein the first alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

55. The method of claim 54, wherein the first alkylamine is an octylamine or a cyclopentylamine.

56. The method of claim 52, further comprising a second alkylamine.

57. The method of claim 56, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

58. The method of claim 57, wherein the second alkylamine is an octylamine or a cyclopentylamine.

59. A method of preparing a conductive ink composition comprising the steps of: combining an aqueous solution of silver fluoride with a molar excess of at least one complexing agent to form a silver complex; and treating the silver complex with an aqueous solution of ammonium formate.

60. The method of claim 59, wherein the at least one complexing agent is a first alkylamine.

61. The method of claim 60, wherein the first alkylamine is a primary alkylamine.

62. The method of claim 60, wherein the first alkylamine is a C3-C10 alkylamine or a C3- C10 cycloalkylamine.

63. The method of claim 62, wherein the first alkylamine is an octylamine or a cyclopentylamine.

64. The method of claim 60, further comprising a second alkylamine.

65. The method of claim 64, wherein the second alkylamine is a C3-C10 alkylamine or a C3-C10 cycloalkylamine.

66. The method of claim 65, wherein the second alkylamine is an octylamine or a cyclopentylamine.

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