Silver ink comprising adhesion promoter

Abstract

This invention relates to a composition for generating a conductive structure on a substrate. The composition comprises a solution containing at least the following components: a) an organic solvent selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, acetates of such aliphatic hydrocarbons, and mixtures thereof; b) at least one silver carboxylic acid; and c) at least one titanium carboxylic acid.

Description

Technical Field

[0001] This invention relates to a composition for generating a conductive structure and a method for generating a conductive structure by inkjet printing on a substrate, wherein the composition is used. Prior Technology

[0002] The goal is to manufacture electronic products more easily and cheaply. Simultaneously, the demand for producing complex conductive structures is increasing. Chemical and physical vapor deposition (CVD and PVD) methods are commonly used for this purpose. Alternatively, printing methods such as screen printing are also employed. Recently, electronic component manufacturers have increasingly relied on inkjet printing inks, mostly containing metals, which transform into conductive structures after printing. One advantage of using inkjet printing to produce conductive structures is the ability to directly print complex structures, such as conductor traces, without the need for masking and demasking of uncoated areas. Metal nanoparticle inks are commonly used in inkjet printing. Nanoparticles are currently relatively easy to produce and have limited properties. One disadvantage of nanoparticle-based inks is that the particles can precipitate from the dispersion. This is particularly undesirable for inkjet printing, as precipitated particles can clog the nozzles of the printhead.

[0003] An alternative to nanoparticle-based inks for inkjet printing conductive structures is ink based on so-called MOD (metal-organic-decomposition) compounds. These MOD compounds are also known as metal-containing precursor compounds. MOD compounds typically contain organometallic salts, such as silver or copper carboxylate, or metal complexes. One advantage of MOD compound-based inks is that these MOD compounds are dissolved. This prevents the inkjet printer nozzles from becoming clogged (so-called blockage). Furthermore, conductive structures made from MOD compounds can have higher density or higher conductivity than structures made from particulate matter. Various MOD compound-containing inks, specifically copper and silver inks, are known in the prior art, such as those known from EP3597707B1. Using these MOD inks, conductive structures can be applied to various substrates. For this purpose, the ink is first applied to the substrate, specifically printed onto the substrate, more precisely on the surface of the substrate, and then cured. Through curing, the solvent of the ink is removed, and the metal-containing precursor compound is transformed into a conductive metallic structure.

[0004] However, there are still unsatisfactory challenges in dealing with such MOD inks.

[0005] Most MOD inks do not have sufficient storage stability for widespread use in industrial environments because the metals they contain precipitate out of the solution after only a very short time, forming metal-containing particles or particle agglomerates.

[0006] Furthermore, conductive structures made from MOD inks typically exhibit only moderate adhesion to printed-on substrates. To remedy this and achieve satisfactory adhesion, curing temperatures must be very high, for example, exceeding 220°C. However, this is particularly disadvantageous when applying MOD inks to heat-sensitive substrates such as electronic components. Summary of the Invention

[0007] One objective of this invention is to overcome at least one drawback of the prior art.

[0008] One preferred object of the present invention is to provide a composition by which a conductive structure that can be effectively adhered to a substrate is created. Specifically, one object is to achieve particularly good adhesion to polymer surfaces or polymer-containing surfaces (such as epoxy mold compound (EMC)). EMC is an insulating potting compound that can encapsulate electronic components therein. For example, this is the case with system-in-package (SIP).

[0009] A further preferred objective is to provide a composition that can be processed into a conductive structure at the lowest possible temperature. Particularly desirable is that it exhibits good adhesion to various substrates even at curing temperatures not exceeding 200°C, and specifically not exceeding 180°C.

[0010] A further preferred objective is to provide compositions that have the longest possible storage stability as a solution. Specifically, the objective is to provide compositions that are stable for at least two weeks, or even more preferably at least four weeks, at room temperature. Particularly, these compositions are stable even when stored at temperatures of 40°C or 50°C for a specified period. Inks that remain usable for inkjet printing after storage are considered stable during storage and, specifically, do not clog the nozzles of the printhead.

[0011] A further objective is to provide a method for generating conductive structures with high conductivity and good adhesion.

[0012] The object of the independent item helps to at least partially achieve at least one of the foregoing objectives. The subsidiary item provides a preferred embodiment that facilitates at least partially achieving at least one of these objectives.

[0013] Specifically, a composition is provided that simultaneously exhibits high storage stability and enables the formation of a strongly adhesive conductive structure at low temperatures. Preferably, such conductive structures maintain good adhesion even after thermal stress or exposure to environmental influences (such as moisture). Simple Explanation of the Diagram

[0014] none Implementation

[0015] The first aspect of this invention relates to a composition for generating a conductive structure on a substrate, wherein the composition comprises a solution and the solution contains at least the following components: - At least one organic solvent selected from the group consisting of: aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, acetates of such aliphatic hydrocarbons, and mixtures thereof. - at least one silver carboxylate, and - At least one titanium carboxylate.

[0016] The composition according to the invention is preferably stable during storage at room temperature for at least 14 days or at least 28 days. Particularly, the composition is stable during this period even when stored at 40°C, and specifically even at 50°C.

[0017] The composition is a mixture, specifically a homogeneous mixture of chemical substances. The composition according to the invention comprises or is composed of a solution. This means that at least one silver carboxylate and at least one titanium carboxylate are preferably at least partially or completely dissolved in the at least one organic solvent.

[0018] This composition is suitable for producing conductive structures. Conductive structures should be understood to mean all conductive structures known to those skilled in the art and suitable for this application, specifically conductor traces, circuit diagrams, EMI shielding, and the like. Within the scope of this invention, a structure (e.g., a conductor trace) is preferably conductive if its volume conductivity σ at 25°C is 1.10⁶ S / m or higher. This conductivity can be determined using an ohmmeter (e.g., an HM 8118 LCR meter from Rhode & Schwarz). The composition itself is preferably non-conductive, and conductivity only appears after the conversion of silver carboxylate or titanium carboxylate onto the substrate.

[0019] Preferably, the conductive structure of the present invention produced by the composition has a conductivity of at least 15% based on the conductivity of pure silver under standard conditions, and specifically at least 30%.

[0020] The composition contains at least one silver carboxylate and at least one titanium carboxylate. Both silver carboxylate and titanium carboxylate can be described as metal precursor compounds. These metal precursor compounds can be converted into elemental metals, that is, metals with an oxidation state of 0. The presence of elemental metals imparts electrical conductivity to the structure. The conversion of metal precursors into metals can be partial or complete.

[0021] To create a conductive structure, the composition is applied to a substrate. The composition can then be transformed into a metallic structure. This transformation can preferably be carried out by removing the organic components of the composition and reducing the metal ions contained therein to elemental metals.

[0022] The composition comprises or consists of a solution. In other words, the composition is typically a solution. Preferably, the composition does not contain undissolved components, and specifically, does not contain solid components. Within the scope of this invention, the term "no undissolved components" should be understood to mean that the solution contains no more than 1 wt.%, and specifically no more than 0.5 wt.%, or no more than 0.2 wt.%, of solids by weight of the total composition. These solids may contain metal particles. Such metal particles may, for example, contain silver or titanium particles.

[0023] The composition according to the invention contains at least one organic solvent. This organic solvent is typically a liquid under standard conditions. The at least one organic solvent is selected from the group consisting of: aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, acetates of such aliphatic hydrocarbons, and mixtures of the aforementioned solvents.

[0024] The viscosity of the organic solvent is preferably less than 10 mPas at 20°C. The flash point of the solvent is preferably above 45°C, and specifically above 60°C. This allows the composition to be used in large-scale electronic manufacturing plants. The surface tension of the solvent is preferably greater than 25 mN / m under standard conditions.

[0025] Aliphatic hydrocarbons can preferably be linear or cyclic, but are specifically linear. Furthermore, they can be saturated or unsaturated.

[0026] Examples of aliphatic hydrocarbons are selected from the group consisting of: decahydronaphthalene, cyclohexane, dodecane, heptane, tetradecane, decane, decene, terpenes (such as terpinene, limonene (specifically DL-limonene), and pinene), and combinations thereof.

[0027] Aliphatic hydrocarbon alcohols may be selected, for example, from the group consisting of: α-, β- or γ-terpineol, pinanol, borneol, geraniol, dihydrocaryophyllein, nerol, geraniol, phytol, and linalool, and mixtures thereof.

[0028] Acetates of aliphatic hydrocarbons can be selected, for example, from the group consisting of amyl acetate and heptyl acetate.

[0029] Aromatic solvents may be selected from the group consisting of: toluene, xylene, derivatives of toluene, derivatives of xylene, and mixtures thereof.

[0030] Furthermore, the composition contains one or more silver carboxylates. The silver carboxylates comprise silver ions, typically in the oxidized (+I) state, and carboxylate anions. The carboxylate anions generally carry a single negative charge. Preferably, the silver carboxylates contain one or more saturated aliphatic carboxylate ligands. The silver carboxylates of the present invention preferably have a decomposition temperature in the range of up to 250°C, more preferably up to 210°C, and particularly preferably up to 180°C. This decomposition temperature can be considered as the temperature at which the metal is completely converted into a metallic state. Within the scope of the present invention, the decomposition temperature can be determined, for example, by thermogravimetry (TGA) at a temperature ramp of 1°C / min (typically a final temperature of 300°C), and achieved at a temperature at which the mass of the sample no longer changes.

[0031] Linear, saturated silver carboxylate is preferred. Particularly preferred systems are those composed of elements from the group consisting of: silver acetate, silver propionate, silver butyrate, silver valerate, silver hexanoate, silver heptanoate, silver octanoate, silver nonanoate, silver decanoate, silver undecanoate, silver dodecanoate, silver tetradecanoate, silver hexadecanoate, silver octadecanoate, and silver isocarboxylate and neocarboxylate of the above elements, or combinations of two or more thereof. Particularly preferred are neocarboxylates having five or more carbon atoms, such as neosilver valerate, neosilver hexanoate, neosilver heptanoate, neosilver octanoate, neosilver nonanoate, neosilver decanoate, and neosilver dodecanoate. Neodecanoate is particularly preferred as this silver carboxylate. Silver carboxylate also includes substituted silver carboxylates, such as silver trifluoroacetate.

[0032] Furthermore, the composition contains at least one titanium carboxylate. Titanium carboxylate typically contains a central titanium cation. The titanium carboxylate in the composition can improve the adhesion of the conductive structure that can be generated from the composition to the substrate without adversely affecting the storage stability of the composition.

[0033] Titanium in titanium carboxylate is typically in an oxidation state of (+II) or (+IV), specifically in the (+IV) oxidation state. This titanium carboxylate contains at least one carboxylate ligand. The carboxylate ligand (also simply referred to as the carboxylate ion) is an anion of an organic carboxylic acid.

[0034] Preferably, the titanium carboxylate contains one or more carboxylate ligands and satisfies at least one or more of the following characteristics: - The titanium carboxylate contains at least one aliphatic carboxylate ligand, preferably only aliphatic carboxylate ligands. - The titanium carboxylate contains at least one branched carboxylate ligand, preferably only branched carboxylate ligands. - The titanium carboxylate contains at least one saturated carboxylate ligand, preferably only saturated carboxylate ligands. - The titanium carboxylate contains at least one carboxylate ligand, wherein the carboxylate ligand is a monocarboxylate ligand, and - The titanium carboxylate contains at least one carboxylate ligand having 5 to 15 C atoms, preferably 7 to 12 C atoms.

[0035] In a preferred embodiment, one or all of the carboxylate ligands of the titanium carboxylate satisfy two, some, or all of the above conditions. It is particularly preferred if all of the above conditions are satisfied.

[0036] The carboxylate ligands of this titanium carboxylate may be the same or different. Preferably, all carboxylate ligands of the titanium carboxylate are the same, because such titanium carboxylate is easier to produce than, for example, mixed variants. The titanium carboxylate is preferably titanium 2-ethylhexanoate (IV), titanium neodecanoate (IV), or titanium neoalkylene-neodecanate (IV). These titanium carboxylates can be used to produce compositions that are stable during storage.

[0037] The titanium carboxylate of the present invention preferably has a decomposition temperature in the region of up to 230°C, and more specifically up to 200°C. This decomposition temperature can be considered as the temperature at which the metal undergoes transformation into a metallic state. The decomposition temperature within the scope of the present invention can be determined by thermogravimetric analysis (TGA) with a temperature ramp of 1°C / min up to a final temperature of 300°C.

[0038] In a preferred embodiment, the at least one titanium carboxylate is present in the composition in an amount of at least 0.1 wt.%, preferably at least 0.3 wt.%, and specifically at least 0.5 wt.%, based on the total weight of the composition.

[0039] Furthermore, the titanium carboxylate is preferably present in the composition in an amount of up to 5 wt.%, particularly up to 2 wt.%, and specifically up to 1 wt.%, based on the total weight of the composition.

[0040] If the composition contains titanium carboxylate within a specified range, the composition has high storage stability and the conductive structure generated therefrom has good adhesion.

[0041] For example, the composition may contain at least 20 wt.% silver carboxylate based on the total weight of the composition. Furthermore, the composition may, for example, contain up to 60 wt.% silver carboxylate based on the total weight of the composition.

[0042] In the composition according to the invention, the metal content, preferably the precious metal content, and specifically the silver content, is preferably in the range of 1 wt.% to 30 wt.% and specifically 10 to 25 wt.% based on the total weight of the composition. In one possible embodiment, the composition, in addition to silver, also contains at least one other metal or precious metal, which may be selected from the group consisting of gold, platinum, nickel, cobalt, and copper, and combinations thereof.

[0043] Preferably, the composition comprises 35 to 75 wt.%, more preferably 40 to 65 wt.%, of solvent based on the total weight of the composition.

[0044] The viscosity of the composition is preferably in the range of 2 to 150 mPas, specifically 2 to 50 mPas, and particularly preferably 2 to 20 mPas or even 2 to 15 mPas. The preferred viscosity of the composition at 40°C is in the range of 1 to 30 mPas. This makes it particularly suitable for inkjet printing. Alternatively, if the composition is intended for screen printing, it may also have a viscosity up to 1000 mPas.

[0045] In an alternative embodiment, the composition may contain additional components that have a positive effect on one or more properties, such as storage stability, printability, flash point, decomposition temperature, appearance of the silver layer, or conductivity of the silver layer.

[0046] In a preferred embodiment, the composition may contain a free carboxylic acid. This free carboxylic acid may, for example, help stabilize the composition so that no solid, specifically no metal or metal compound precipitates from the composition, specifically no silver or titanium or a compound containing at least one of such metals.

[0047] The free carboxylic acid may be selected, for example, from the group consisting of: octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptanoic acid, octadecanoic acid, nonadecanoic acid, icosanoic acid, and the like, and branched carboxylic acids, such as saturated isomethyl branched acids, new carboxylic acids (with a terminal tertiary butyl group or with two isomethyl groups), saturated / unsaturated medium-chain methyl branched acids, and isoprenoid carboxylic acids.

[0048] The free carboxylic acid is specifically a tertiary carboxylic acid having at least five carbon atoms, and preferably a new carboxylic acid.

[0049] For example, the free carboxylic acid can be selected from the group consisting of neodecanoic acid and pinoresinic acid.

[0050] In an alternative embodiment, the composition may contain one or more amines. This can improve the storage stability of the composition. Alternatively, the composition may contain additional components, such as esters of terpene alcohols, and specifically acetates of terpene alcohols. This can improve the flash point of the composition.

[0051] The composition comprises a solution containing no more than 1 wt.%, specifically no more than 0.5 wt.%, and preferably no more than 0.1 wt.%, of solids by weight of the total composition. The solids may, for example, contain particles. These particles may comprise metallic silver or titanium particles, or compounds, specifically oxides, of silver, titanium, or mixtures of these two elements.

[0052] In one possible embodiment, the composition may be in the form of a layer on a substrate. The geometry of the layer is not subject to any further limitations. The layer may be, for example, a continuous planar layer or a structured layer, such as for conductor traces.

[0053] The thickness of the wet layer printed on the surface of the substrate is preferably at least 0.5 µm, specifically at least 1 µm, and particularly preferably at least 2 µm. Furthermore, the thickness of the composition on the substrate is preferably at most 10 µm, specifically 20 µm, and particularly preferably at most 40 µm.

[0054] In one possible embodiment, the substrate comprises or is composed of an electrically insulating material. Specifically, the surface of the substrate comprises or is composed of an electrically insulating material. Preferably, the portion of the substrate on which the composition is disposed comprises an electrically insulating material. A particularly preferred substrate contains a material selected from the group consisting of semiconductors (e.g., silicon, glass, ceramics, and plastics, or combinations of two or more of these materials). The glass may, for example, be selected from silicate glass. The ceramics may, for example, be selected from the group consisting of oxide ceramics, nitride ceramics, carbide ceramics, phosphide ceramics, arsenide ceramics, or mixtures of these ceramics. The plastics may, for example, be selected from polyethylene terephthalate (PET), polyimide (PI), polyamide, polyethylene naphthalate (PEN), polycarbonate (PC), and resins, such as epoxy resins. The electrically insulating material may, for example, be an epoxy molding compound (EMC). Epoxy molding compounds are known to those skilled in the art and contain epoxy resin and inorganic fillers, such as glass powder or ceramic powder. EMC is commonly used as a potting compound for electronic components (e.g., chips).

[0055] Alternatively, the substrate may comprise or be composed of a metal. Specifically, the surface of the substrate comprises or is composed of a metal. The metal may be, for example, copper or steel.

[0056] In one conceivable embodiment, the layer is in contact with at least one electrical conductor. This electrical conductor may be part of the substrate or separate from it.

[0057] The substrate may contain or consist of electronic components. Examples of electronic components are so-called SIPs (System-in-Package) or printed circuit boards (PCBs). These electronic components may contain electrically insulating potting compounds. Electronic components may include electronic components such as semiconductor wafers or transistors. These electronic components may be embedded in electrically insulating potting compounds.

[0058] A second aspect of the invention relates to an ink, specifically an ink for inkjet printing, wherein the ink contains the components described herein. Within the scope of the invention, ink can be understood as any component suitable for printing. The printing process may include a method selected from the group consisting of inkjet printing, offset printing, screen printing, and spraying. In a possible embodiment, the ink may also be used in a method selected from the group consisting of spin coating, dip coating, and application.

[0059] In one embodiment, the ink comprises the composition. Alternatively, the ink may contain additional components in addition to the composition. These additional components may specifically improve the application of the ink for printing, and more specifically for inkjet printing.

[0060] In some cases, the ink according to the invention contains a viscosity enhancer. The ink may contain a viscosity enhancer in a weight percentage of up to 10 wt.%, more preferably in the range of up to 5 wt.%, based on the total weight of the ink according to the invention. Rosin resin or a derivative thereof is preferably selected as the viscosity enhancer. Typical commercial products are rosin resins.

[0061] Optionally, the ink according to the invention may contain additional additives, specifically in the range of 0.05 to 3 wt.%, more preferably in the range of 0.05 to 1 wt.%, all in all cases based on the total weight of the ink according to the invention. Optionally, the additional additives may include any chemical substances and mixtures known to those skilled in the art and considered suitable for the intended purpose. Particularly preferred additional additives are polysiloxane-containing additives, such as one or more additives containing polyether-modified polydimethylsiloxane.

[0062] The above-mentioned components may optionally contain rheology modifiers.

[0063] The third aspect of this invention relates to a method for generating a conductive structure on a substrate, comprising the following steps: A) Provide a substrate and the composition of the first state sample according to the present invention; B) Applying the composition to the substrate by inkjet printing to obtain a layer of the composition; C) Process this layer by selecting from the following groups: a. Hot sintering at temperatures ranging from 140℃ to 210℃. b. Photonic sintering, or c. A combination of a) and b). To obtain a conductive structure.

[0064] The substrate provided by the present invention preferably comprises a surface made of a material selected from the group consisting of semiconductors, glass, ceramics, and plastics, or a combination of two or more of these materials. Optionally, the provided substrate may also contain metal, specifically a metallic surface. Preferably, the substrate contains or is composed of electrical or electronic components.

[0065] In step B), the composition is applied to the substrate by inkjet printing to obtain a layer of the composition.

[0066] Inkjet printing is performed digitally using an inkjet printer. The printhead of this inkjet printer is, for example, a bulk piezoelectric printhead, a thermal printhead, an electrohydrodynamic (EHD) printhead, or a thin-film MEMS printhead. The droplet size in inkjet printing is preferably in the range of 1 pL to 30 pL. The nozzle diameter of the printhead is preferably in the range of 10 to 50 µm, specifically 10 to 20 µm or 15 to 25 µm. Specifically, when using EHD printheads and MEMS printheads, nozzle diameters of 2-10 µm can also be used. One advantage of the composition according to the invention is that it can be used with printheads having smaller nozzle diameters. This can be explained specifically by the fact that the composition of the invention contains or is composed of a solution. In contrast, with small nozzle diameters, prior art nanoparticle-based compositions can lead to clogging.

[0067] The layer obtained in step B) preferably has an average thickness of at least 0.5 µm, specifically at least 1 µm, and most preferably 2 µm. Furthermore, the layer obtained in step B) preferably has an average thickness of up to 40 µm, specifically up to 20 µm, and most preferably up to 10 µm. These specified layer thicknesses preferably refer to the layer thickness immediately following inkjet printing, and specifically before the drying step. If the layer thickness is within the specified range, the processing in step C) can be performed particularly effectively to create a conductive structure. Simultaneously, fine structures can be printed particularly effectively.

[0068] Optionally, a drying step is performed after step B) and before step C), wherein the solvent of the composition is at least partially removed. Preferably, the drying step does not involve any transformation of the composition into a conductive structure, or at least not a complete transformation. The drying step may be performed, for example, to temporarily fix the resulting layer. Specifically, the dried layer is less affected when another layer, especially a wet layer, is applied.

[0069] Following step B) is the processing step, step C). The processing of this layer in step C) is preferably carried out in an oxygen-containing atmosphere (e.g., in air). Hot sintering preferably occurs at a temperature of 140°C to 210°C, specifically 160°C to 180°C, for example, in a furnace. This furnace may be a continuous furnace. For example, hot sintering may be carried out for at least 2 minutes.

[0070] Photonic sintering can be UV sintering, IR sintering, or a combination thereof. UV sintering is preferably carried out with light having a wavelength in the range of 100 nm to 450 nm, more preferably in the range of 365 nm to 420 nm. The UV radiation intensity is preferably in the range of 1.0 W / cm² to 12.0 W / cm², more preferably in the range of 2.0 W / cm² to 9.0 W / cm².

[0071] The UV radiation intensity is preferably in the range of 1.0 W / cm² to 12.0 W / cm², and more preferably 2.0 W / cm² to 9.0 W / cm². The irradiation time can vary depending on the ink used and can, for example, range from 10 s to 1000 s. When printing multiple molecular metal precursor ink layers, the UV radiation intensity used for subsequent layers can be the same or different.

[0072] IR sintering is preferably carried out with light having wavelengths in the range of 780 nm to 10 µm, and more specifically 800 nm to 3000 nm. Longer wavelengths of light in the range of approximately 2000–3000 nm can penetrate deeper into the layer to be treated, which can be advantageous for sintering thicker constituent layers.

[0073] The duration of this processing step, specifically photonic sintering, is generally not subject to any further limitations. Preferably, the processing step is performed until the layer of the composition transforms into a conductive structure. Preferably, the photonic sintering time is as short as possible. This is advantageous for both procedural economics and energy conservation. The duration and intensity of sintering can be adjusted by a professional. If the conductivity of the resulting layer is sufficient for the intended application, the sintering process can be stopped. Specifically, the sintering process can be stopped when the conductivity of the resulting conductive structure no longer increases, i.e., it has reached a plateau. Generally, the processing step C) is performed for at least 1, 2, 3, 4, or 5 minutes. Alternatively, the processing can also be in the range of 10 to 1000 seconds. This is particularly applicable to photonic sintering, such as UV sintering or IR sintering.

[0074] When multiple layers are applied, the radiation intensity used for subsequent layers may be the same or different.

[0075] The conductive structure obtained in step C) preferably has an average thickness of at least 100 nm, specifically at least 150 nm, and most preferably 200 nm. Furthermore, the layer obtained in step B) preferably has an average thickness of at most 1000 nm, specifically at most 500 nm, and most preferably at most 250 nm. The specified layer thickness refers to the thickness of a single printed and sintered layer.

[0076] In a preferred embodiment, the procedure of applying the composition according to step B) and the processing procedure according to step C) can be repeated to obtain a thicker conductive structure. In this case, the conductive structure contains a stack of individually applied conductive substructures.

[0077] For example, step B) can be performed several times. The drying step may optionally occur after each inkjet print.

[0078] Optionally, after repeated inkjet printing consistent with step B), a processing procedure consistent with step C) may be performed. The layers of the composition may or may not have undergone a drying step in advance.

[0079] The thickness of a conductive structure obtained by repeatedly applying the composition via inkjet printing is generally unlimited. However, the thickness of the conductive structure largely depends on the number of individual layers applied.

[0080] Optionally, after sintering, additional materials can be deposited on the substrate or conductive structure, specifically by inkjet printing. For example, a protective layer can be disposed above the conductive structure. The protective layer protects the conductive structure from changes caused by environmental influences. The protective layer may, for example, comprise a polymer, such as polyimide.

[0081] In a further optional embodiment, the substrate is pretreated, for example, to remove impurities. This can improve adhesion to the substrate. The pretreatment may include a method selected from the group consisting of plasma cleaning, corona pretreatment, chemical cleaning, CVD treatment, UV ozone treatment, and rinsing. Plasma cleaning may be carried out, for example, using argon-oxygen plasma, air plasma, argon plasma, or low-voltage plasma. The pretreatment may generate oxygen-containing groups on the surface of the substrate to be coated. These oxygen-containing groups (e.g., aldehyde, alcohol, or carboxyl groups) can further improve the adhesion of the conductive structure to the substrate.

[0082] A further embodiment of the present invention relates to a substrate comprising a surface made of a material selected from the group consisting of semiconductors, glass, ceramics, and plastics, or combinations of two or more of these materials, characterized in that a layer of the composition of the invention is disposed on the surface. Preferably, the substrate is obtained in step B) by the method described herein. Preferably, the substrate contains or is composed of electrical or electronic components. The substrate may comprise, for example, a system-in-package (SIP) or a printed circuit board (PCB).

[0083] A further embodiment of the present invention relates to a conductive structure on a substrate, specifically obtainable by the method according to the invention, characterized in that the conductive structure comprises silver and titanium and preferably adheres to the substrate with a grade of at least 3B, measured according to the cross-hatch test of ASTM D3359-23. Preferably, the conductive structure has an adhesion of at least 5B.

[0084] In a preferred embodiment, the substrate of the present invention comprises plastic or a plastic-containing material. Preferably, the plastic-containing material is an electronic potting compound, such as an epoxy molding compound. EMC should generally be understood as an epoxy resin mixed with inorganic fillers. Particularly good adhesion can be achieved on such plastic-containing materials.

[0085] The volume conductivity σ of the conductive structure is preferably at least 1.10⁶ S / m at 25°C. Preferably, the titanium is uniformly distributed in the conductive structure. For example, the titanium may be alloyed with the silver. Alternatively, the titanium in the conductive structure may have a gradient, for example, with an increasing concentration towards the surface of the substrate.

[0086] The conductive structure is preferably made from a composition according to the invention. In this context, the conductive structure may contain components of the composition according to the invention, specifically as impurities or as residues of organic components of the composition that have not been completely removed. This may be the case, for example, after a processing step that converts silver carboxylate or titanium carboxylate into an elemental metal. Furthermore, the conductive structure is preferably produced by a method according to the invention. Additionally, the conductive structure can preferably be obtained from a substrate according to the invention.

[0087] In one possible embodiment, the conductive structure contains up to 0.2 wt.% or, specifically, up to 0.5 wt.% of titanium by weight of the total conductive structure.

[0088] More preferably, the conductive structure contains up to 0.05 wt.% carbon based on the total weight of the composition, as determined by XPS measurement. Such XPS measurements are known to those skilled in the art.

[0089] Optionally, the conductive structure may include at least one additional metal, which may be selected, for example, from the group consisting of Sn, Ni, Bi, Cr, Mn, Fe, Ru, Rh, Ir, and Cu, and combinations thereof.

[0090] In another possible embodiment, the conductive structure contains no metallic components other than silver and titanium, except for unavoidable impurities. Unavoidable impurities may include all substances not intentionally added to the composition or the resulting conductive structure according to the invention. Examples of unavoidable impurities are metals associated with the presence of silver in minerals. Preferably, the total amount of unavoidable impurities does not exceed 200 ppm, and specifically not more than 100 ppm of metal.

[0091] The conductive structure exhibits excellent adhesion to the substrate after fabrication, achieving a grade of at least 5B according to the cross-cut adhesion test of ASTM D3359-23. Ideally, this good adhesion, as determined by the specified test, is maintained after UHAST.

[0092] In one embodiment, the conductive structure does not contain any areas created by a subtractive method, such as cut edges, milled edges, or etched sides. Alternatively, no more than 10% of the edge length of the conductive structure contains areas created by a subtractive method.

[0093] Within the scope of this invention, the conductive structure may be, for example, a conductor track, an electrode, a contact layer, an electromagnetic shield (EMI shield), or an antenna.

[0094] Within the scope of this invention, features disclosed for one embodiment of the invention may also be applied to other embodiments of the invention. For example, material features described in the context of a method may also be applied to the composition according to the invention, or method features disclosed in the context of a composition may also be applied to the method according to the invention. definition

[0095] In the absence of specific measurement conditions, the standard ambient temperature and standard ambient pressure shall be used (as a temperature of 298.15 K (25°C) and an absolute pressure of 101.325 kPa (1 atm). Test methods conductivity

[0096] Conductivity was determined by performing four-point measurements using a four-point probe ohmmeter from Ossila. viscosity

[0097] The viscosity of a paste sample can be determined using a DV3 Brookfield rheometer with shaft number 14, 10 RPM and 25°C, according to standard DIN 53019.

[0098] According to standard DIN 53019, the viscosity of a liquid sample is determined individually using an Ametek DV3T rheometer. Adhesion test

[0099] Within the scope of this invention, adhesiveness was tested using Method B (cross-cut test) of the tape test method according to ASTM D3359-23. Scotch Tape 600 from 3M was used as the adhesive tape. Reliability testing

[0100] The UHAST (Unbiased Highly Accelerated Stress Test) method, according to JESD22-A118, was used for reliability testing of the conductive structure described herein. This method simulates accelerated aging of the structure under test.

[0101] For this purpose, the test substrate was exposed to elevated temperature under limited humidity conditions in a chamber. Conditions: Temperature: 130°C; Humidity: 85% RH; Time: 96 hours; Pressure: 2 bar.

[0102] Then, the conductive structure to be tested can be subjected to an adhesion test as described in this article. Storage stability

[0103] Visually assess storage stability. If no visible particles are visible in the solution, the composition or ink containing that composition is considered stable. Use a laser pointer held in the solution (Level 1) to check for the absence of visible particles. If no visible particle scattering is observed after shaking, the solution is considered stable. Furthermore, no significant color change toward darker colors is observed. Example

[0104] The invention will be illustrated below by way of examples. However, the invention is not limited to these examples. Instance composition

[0105] The compositions listed in Table 1 below were prepared by first preparing a solution of silver neodecanoate in limonene at room temperature, and then mixing the other components with this solution. The amounts are given as wt.% of each component based on the total weight of the composition.

[0106] It is evident that for compositions 1 and 7 (each containing titanium carboxylate as a titanium component), a particularly high degree of storage stability was observed for at least 28 days at room temperature. In the case of titanium 2-ethylhexanoate, increased storage stability was observed even at a storage temperature of 40°C.

[0107] Furthermore, components 1 to 7 were printed onto the epoxy molding compound (EMC) using inkjet printing. The EMC surface was first cleaned with argon-oxygen plasma each time. The printed layers of components 1 to 7 were then converted into a conductive structure by UV sintering at an average wavelength of 395 nm for 2 minutes. The temperature of the component was 180°C, measured using a contact thermometer.

[0108] As described in this article, adhesion tests were performed on each conductive structure. High numbers indicate good adhesion.

[0109] The results are also summarized in Table 1 (data in wt.%). experiment 1 2 3 4 5 6 annotation According to the present invention Compare Compare Compare Compare According to the present invention Neodecanoic acid 1.95% 1.95% 1.95% 1.95% 1.95% 1.95% Silver neodecanoate 50.31% 50.31% 50.31% 50.31% 50.31% 50.31% Limonene 47.19% 47.19% 47.19% 47.19% 47.19% 47.19% Titanium ethylhexanoate IV 0.54% Triethanolamine titanate 0.54% Butanol Titanium IV 0.54% Butanol Titanium IV Polymer 0.54% Titanium Isopropoxide IV 0.54% Neoalkyl alcohol root ginseng neodecanoate titanium IV 0.54% Storage stability ++ - - - - 0 Adhesion t0 5 B 0-2 B 0-2 B 0-2 B 0-2 B 3 B [Table 1]

[0110] Storage stability at room temperature for at least 21 days is classified as adequate (0), storage stability for at least 28 days is classified as good (+), and storage stability at 40°C for at least 28 days is classified as very good (++). Adhesion t0 refers to the tackiness after manufacturing (without aging treatment) as measured according to ASTM D3359-23.

[0111] none

Claims

1. A composition for generating a conductive structure on a substrate, wherein the composition comprises a solution containing at least the following components: - an organic solvent selected from the group consisting of: aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, acetates of such aliphatic hydrocarbons, and mixtures thereof; - at least one silver carboxylate; and - at least one titanium carboxylate.

2. The composition of claim 1, wherein the at least one titanium carboxylate contains one or more carboxylate ligands and satisfies at least one or more of the following characteristics: a. the titanium carboxylate contains one or more aliphatic carboxylate ligands, b. the titanium carboxylate contains one or more branched carboxylate ligands, c. the titanium carboxylate contains one or more saturated carboxylate ligands, d. the titanium carboxylate contains one or more carboxylate ligands, wherein the carboxylate ligands are monocarboxylate ligands, and e. the titanium carboxylate contains one or more carboxylate ligands having 5 to 15 carbon atoms.

3. The composition of claim 1, wherein the titanium carboxylate is present in the composition in an amount of 0.1 to 2 wt.% based on the total weight of the composition.

4. The composition of claim 1, wherein the composition contains 35 to 75 wt.% solvent by weight of the total composition.

5. The composition of claim 1, wherein the composition contains 20 to 60 wt.% silver carboxylate based on the total weight of the composition.

6. A composition as claimed in claim 1, wherein the composition comprises free carboxylic acid.

7. The composition of claim 1, wherein the composition comprises a solution, and wherein the solution comprises silver particles of not more than 0.5 wt.% by weight of the total weight of the composition.

8. The composition of claim 1, wherein the composition is in the form of a layer on a substrate.

9. The composition of claim 8, wherein the composition contacts an electrically insulating material, wherein the electrically insulating material is selected from the group consisting of semiconductors, glass, ceramics, and plastics, or a combination of two or more of these materials.

10. A substrate comprising a surface made of a material selected from the group consisting of semiconductors, glass, ceramics, and plastics, or a combination of two or more of these materials, characterized in that a layer of a composition of any one of claims 1 to 9 is disposed on the surface.

11. The substrate of claim 10, wherein the substrate contains or is composed of electrical or electronic components.

12. A method for forming a conductive structure on a substrate, comprising the steps of: A) providing a substrate and a composition as claimed in any one of claims 1 to 9; B) applying the composition to the substrate by inkjet printing to obtain a layer of the composition; C) processing the layer by a method selected from the group consisting of: a. thermal sintering at a temperature in the range of 140°C to 210°C, b. photonic sintering, or c. a) and b) to obtain a conductive structure.

13. As in request item 12, wherein, After sintering, at least one additional material is applied to the substrate or the conductive structure.

14. The method of claim 13, wherein the at least one additional material is applied by inkjet printing.

15. A conductive structure on a substrate, which can be obtained by any one of claims 12 to 14, characterized in that the conductive structure comprises silver and titanium and is adhered to the substrate with a grade of at least 3B, the grade being measured according to the cross-hatch test of ASTM D3359-23.