Silver inks comprising adhesion promoters

Abstract

The invention relates to a silver ink comprising an adhesion promoter. In particular, the present invention relates to a composition for producing an electrically 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 and alcohols and acetates of these aliphatic hydrocarbons and mixtures thereof, b) at least one silver carboxylate, and c) at least one titanium carboxylate.

Description

[0001] The present invention relates to a composition for producing conductive structures and to a method for producing conductive structures on a substrate by inkjet printing in which the composition is used.

[0002] The goal is to manufacture electronic products more easily and cheaply. Simultaneously, the demand for producing complex conductive structures is increasing. For this purpose, chemical and physical vapor deposition (CVD and PVD) methods are commonly used. Alternatively, printing methods such as screen printing are also used. Recently, manufacturers of electronic components have increasingly relied on inkjet printing inks, primarily metal-containing inks, which transform into conductive structures after printing. One advantage of using inkjet printing to produce conductive structures is that complex structures, such as conductor tracks, can be printed directly without masking and exposing areas to be left uncoated. Metal nanoparticle inks are commonly used in inkjet printing. Nanoparticles are now relatively easy to manufacture and possess defined properties. A disadvantage of nanoparticle-based inks is that particles may precipitate from the dispersion. This is particularly undesirable for inkjet printing, as precipitated particles can clog the nozzles of the printhead.

[0003] Alternatives to nanoparticle-based inks used for inkjet printing conductive structures are based on so-called MOD (Metal-Oxide-Dipole Ink). Metal - organic - break down Inks based on MOD compounds. These MOD compounds are also known as metal-containing precursor compounds. MOD compounds typically include organometallic salts, such as silver or copper carboxylate, or metal complexes. An advantage of MOD compound-based inks is that these MOD compounds are dissolved. This prevents 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 compositions. Various MOD compound-containing inks (particularly copper and silver inks) are known in the prior art, such as those described in EP3597707B1. Using these MOD inks, conductive structures can be applied to various substrates. To do this, the ink is first applied, particularly printed, onto the substrate, more precisely, onto 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 aggregates.

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

[0007] The purpose of this invention is to overcome at least one of the disadvantages of the prior art.

[0008] A preferred object of the present invention is to provide a composition that can create a conductive structure that adheres effectively to a substrate. In particular, one object is to achieve particularly good adhesion to polymer surfaces or polymer-containing surfaces, such as epoxy molding compounds (EMC). EMC is an insulating potting compound in which electronic components are encapsulated. This is the case, for example, in system-in-package (SIP).

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

[0010] Another preferred objective is to provide a composition that, as a solution, exhibits the longest possible storage stability. In particular, the objective is to provide a composition that is stable during storage at room temperature for at least two weeks, or preferably at least four weeks. Particularly preferably, the composition is stable even at temperatures of 40°C or 50°C during the specified storage period. In particular, inks that remain usable for inkjet printing after storage are considered stable during storage, especially without clogging the nozzles of the printhead.

[0011] Another objective is to provide a method for producing conductive structures with high conductivity and good adhesion.

[0012] The subject matter of the independent claim contributes to at least partially satisfying at least one of the foregoing objectives. The dependent claims provide preferred embodiments that help to at least partially fulfill at least one of the objectives.

[0013] In particular, a composition is provided that exhibits high storage stability and enables the production of strongly adhesive conductive structures at low temperatures. Particularly preferably, these conductive structures exhibit good adhesion even after thermal stress or exposure to environmental influences such as moisture.

[0014] A first aspect of the present invention relates to a composition for producing a conductive structure on a substrate, wherein the composition comprises a solution, and the solution contains at least the following components:

[0015] - At least one organic solvent, selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, alcohols and acetates of these aliphatic hydrocarbons, and mixtures thereof.

[0016] - at least one silver carboxylic acid, and

[0017] - At least one titanium carboxylate.

[0018] The compositions according to the invention are preferably stable for at least 14 days or at least 28 days during storage at room temperature. Particularly preferably, the compositions are stable even at 40°C, and especially even at 50°C, during this storage period.

[0019] The composition is a mixture, particularly a homogeneous mixture of chemical substances. The composition according to the invention comprises or consists 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 at least one organic solvent.

[0020] This composition is suitable for producing conductive structures. Conductive structures are understood to mean all conductive structures known to those skilled in the art and that appear suitable in the present context, particularly conductor tracks, circuit diagrams, EMI shielding, etc. If the volume conductivity σ at 25°C is 1.10... 6 If the conductivity is S / m or greater, then within the scope of this invention, the structure (e.g., conductor track) is preferably conductive. This conductivity can be determined using an ohmmeter HM 8118 LCR from Rhode & Schwarz. The composition is preferably non-conductive itself, but conductivity only appears after the conversion of silver carboxylate or titanium carboxylate onto the substrate.

[0021] Preferably, the conductivity is based on that of pure silver under standard conditions. The conductive structure of the present invention, which can be produced from this composition, has a conductivity of at least 15%, and particularly at least 30%.

[0022] This 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. Metal precursor compounds can be converted into elemental metals, i.e., metals with an oxidation state of 0. The presence of elemental metals imparts electrical conductivity to the structures. The conversion of metal precursors to metals can be partial or complete.

[0023] To produce a conductive structure, the composition is applied to a substrate. The composition can then be converted into a metallic structure. This conversion can preferably be carried out by removing the organic components of the composition and reducing the metal ions contained therein to elemental metals.

[0024] The composition comprises or consists of a solution. In other words, the composition is typically a solution. Particularly preferably, the composition does not contain undissolved components, particularly solid components. Within the scope of this invention, the term "undissolved components" should be understood to mean that, based on the total weight of the composition, the solution contains no more than 1% by weight, particularly no more than 0.5% by weight, or no more than 0.2% by weight of solids. The solids may comprise metal particles. The metal particles may, for example, comprise silver particles or titanium particles.

[0025] The compositions according to the invention contain at least one organic solvent. The 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 and acetates of these aliphatic hydrocarbons, and mixtures of the aforementioned solvents.

[0026] 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 particularly above 60°C. This allows the composition to be used in large-scale electronics manufacturing plants. The surface tension of the solvent is preferably greater than 25 mN / m under standard conditions.

[0027] Aliphatic hydrocarbons are preferably linear or cyclic, especially linear. Furthermore, aliphatic hydrocarbons can be saturated or unsaturated.

[0028] Examples of aliphatic hydrocarbons are selected from the group consisting of decahydronaphthalene, cyclohexane, dodecane, heptane, tetradecane, decane, decene, terpenes such as terpinene, limonene, especially DL-limonene and pinene, and combinations thereof.

[0029] The alcohols of aliphatic hydrocarbons may be selected, for example, from the group consisting of α-terpineol, β-terpineol or γ-terpineol, pinol, borneol, myrceneol, dihydrocarboxylol, nerol, geraniol, phytol and linalool, and mixtures thereof.

[0030] Acetates of aliphatic hydrocarbons can be selected, for example, from the group consisting of amyl acetate and heptyl acetate.

[0031] The aromatic solvent is optionally selected from the group consisting of toluene, xylene, toluene derivatives, xylene derivatives, and mixtures thereof.

[0032] Furthermore, the composition contains one or more silver carboxylates. The silver carboxylates comprise silver ions, typically in the oxidized state (+I), and carboxylate anions. The carboxylate anions typically carry a single negative charge. Preferably, the silver carboxylates comprise 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, preferably up to 210°C, and particularly preferably up to 180°C. The decomposition temperature can be considered as the temperature at which the transformation to a metallic state is completed. Within the scope of the present invention, the decomposition temperature can be determined, for example, by thermogravimetric analysis (TGA) at a temperature ramp of 1°C / min (typically a final temperature of 300°C), and reached at a temperature at which the mass of the sample no longer changes.

[0033] Linear saturated silver carboxylate is preferred. Particularly preferred are elements selected 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 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 neopentanoate, neohexanoate, neoheptanoate, neooctanoate, neononanoate, neodecanoate, and neododecanate. Neodecanoate is particularly preferred as a silver carboxylate. Silver carboxylate also includes substituted silver carboxylates, such as silver trifluoroacetate.

[0034] 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 produced from the composition to the substrate without adversely affecting the storage stability of the composition.

[0035] Titanium in titanium carboxylate is typically in the (+II) or (+IV) oxidation state, particularly the (+IV) oxidation state. Titanium carboxylate contains at least one carboxylate ligand. The carboxylate ligand (also simply referred to as the carboxylate ion) is the anion of an organic carboxylic acid.

[0036] Particularly preferably, the titanium carboxylate contains one or more carboxylate ligands and satisfies at least one or more of the following characteristics:

[0037] - Titanium carboxylate contains at least one aliphatic carboxylate ligand, preferably only aliphatic carboxylate ligands.

[0038] - Titanium carboxylate contains at least one branched carboxylate ligand, preferably only branched carboxylate ligands.

[0039] - Titanium carboxylate contains at least one carboxylate ligand, preferably only saturated with carboxylate ligands.

[0040] - Titanium carboxylate contains at least one carboxylate ligand, wherein the carboxylate ligand is a monocarboxylate ligand, and

[0041] - Titanium carboxylate contains at least one carboxylate ligand having 5 to 15 C atoms, preferably 7 to 12 C atoms.

[0042] In a preferred embodiment, one or all of the carboxylate ligands of titanium carboxylate satisfy two, some, or all of the conditions. Particularly preferred is that all of the above conditions are satisfied.

[0043] The carboxylate ligands of titanium carboxylate can be the same or different. Preferably, all carboxylate ligands of titanium carboxylate are the same, because such titanium carboxylate is easier to produce, for example, than mixed variants. Titanium carboxylate may be particularly preferably titanium 2-ethylhexanoate (IV), titanium neodecanoate (IV), or neoalkanolate trinedecanoate (IV). These titanium carboxylates can be used to produce compositions that are stable during storage.

[0044] The titanium carboxylate of the present invention preferably has a decomposition temperature in the range of up to 230°C, particularly up to 200°C. The decomposition temperature can be considered as the temperature at which the transformation into a metallic form occurs. The decomposition temperature within the range of the present invention can be determined by thermogravimetric analysis (TGA) at a temperature ramp of 1°C / min, up to a final temperature of 300°C.

[0045] In a preferred embodiment, at least one titanium carboxylate is present in the composition in an amount of at least 0.1% by weight, particularly preferably at least 0.3% by weight, and especially at least 0.5% by weight, based on the total weight of the composition.

[0046] Furthermore, titanium carboxylate is preferably present in the composition in an amount of up to 5% by weight, particularly preferably up to 2% by weight, and especially at most 1% by weight, based on the total weight of the composition.

[0047] If the composition contains titanium carboxylate within a specified range, the composition has high storage stability and the conductive structure produced therefrom has good adhesion.

[0048] For example, based on the total weight of the composition, the composition may contain at least 20% by weight of silver carboxylate. Furthermore, based on the total weight of the composition, the composition may, for example, contain up to 60% by weight of silver carboxylate.

[0049] In the composition according to the invention, the metal content, preferably the precious metal content, and particularly the silver content, is preferably in the range of 1% to 30% by weight, particularly 10% to 25% by weight, based on the total weight of the composition. In one possible embodiment, in addition to silver, the composition 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.

[0050] Preferably, based on the total weight of the composition, the composition contains 35% to 75% by weight, preferably 40% to 65% by weight, of a solvent.

[0051] The viscosity of the composition is preferably in the range of 2 mPas to 150 mPas, particularly 2 mPas to 50 mPas, and especially preferably 2 mPas to 20 mPas or even 2 mPas 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. Optionally, if the composition is used for screen printing, it can also have a viscosity up to 1000 mPas.

[0052] In an optional embodiment, the composition may contain additional components that positively affect one or more properties, such as storage stability, printability, flash point, decomposition temperature, appearance of the silver layer, or conductivity of the silver layer.

[0053] 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 solids, in particular no metals or metal compounds, precipitate from the composition, especially no silver or titanium or compounds containing at least one of these metals.

[0054] Free carboxylic acids can be selected, for example, from octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, etc., as well as branched carboxylic acids such as saturated isomethyl branched acids, new carboxylic acids (with a terminal tert-butyl group or with two isomethyl groups), saturated / unsaturated medium-chain methyl branched acids, and isoprene-like carboxylic acids.

[0055] Free carboxylic acids, especially tertiary carboxylic acids having at least five carbon atoms, and most preferably novel carboxylic acids.

[0056] For example, free carboxylic acids can be selected from the group consisting of neodecanoic acid and rosin acid.

[0057] In an optional embodiment, the composition may contain one or more amines. This improves the storage stability of the composition. Optionally, the composition may contain additional components, such as esters of terpene alcohols, particularly acetates of terpene alcohols. This improves the flash point of the composition.

[0058] The composition comprises a solution containing no more than 1% by weight, particularly no more than 0.5% by weight, and very particularly preferably no more than 0.1% by weight, of solids based on the total weight of the composition. The solids may, for example, comprise particles. These particles may include metallic silver or titanium particles or compounds, particularly oxides of silver or titanium, or mixtures of both elements.

[0059] 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 flat layer or a structured layer, such as for conductor tracks.

[0060] The thickness of the wet layer printed on the substrate surface is preferably at least 0.5 µm, particularly at least 1 µm, and especially preferably at least 2 µm. Furthermore, the thickness of the composition layer on the substrate is preferably at most 10 µm, particularly 20 µm, and especially preferably at most 40 µm.

[0061] In one possible embodiment, the substrate comprises or is composed of an electrically insulating material. In particular, the surface of the substrate comprises or is composed of an electrically insulating material. Very particularly preferred is the portion of the substrate on which the composition layer is disposed comprises an electrically insulating material. Particularly preferred substrates contain 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. Glass may be, for example, selected from silicate glass. Ceramic may be, for example, selected from oxide ceramics, nitride ceramics, carbide ceramics, phosphide ceramics, arsenide ceramics, or mixtures of these ceramics. Plastic may be, for example, selected from polyethylene terephthalate (PET), polyimide (PI), polyamide, polyethylene naphthalate (PEN), polycarbonate (PC), and resins, such as epoxy resins. The electrically insulating material may be, for example, 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, such as chips.

[0062] Alternatively, the substrate may comprise or be composed of metal. In particular, the surface of the substrate may comprise or be composed of metal. For example, the metal may be copper or steel.

[0063] In one conceivable embodiment, the layer is in contact with at least one electrical conductor. The electrical conductor may be part of the substrate or separate from the substrate.

[0064] The substrate may include or be composed of electronic components. Examples of electronic components are so-called SIPs (System-in-Package) or printed circuit boards (PCBs). Electronic components may be encapsulated with electrically insulating potting compounds. Electronic components may include electronic parts such as semiconductor chips or transistors. Electronic components may be embedded in electrically insulating potting compounds.

[0065] A second aspect of the invention relates to an ink, particularly an ink for inkjet printing, wherein the ink contains the composition described herein. Within the scope of the invention, the ink can be understood as any composition suitable for printing. The printing process may include methods selected from the group consisting of inkjet printing, offset printing, screen printing, and spraying. In possible embodiments, the ink may also be used in methods selected from the group consisting of spin coating, dip coating, and dispensing.

[0066] In one embodiment, the ink comprises a composition. Alternatively, the ink may contain additional components in addition to the composition. These additional components may be specifically used to improve the application of inks for printing, particularly for inkjet printing.

[0067] In some cases, the inks according to the invention contain viscosity modifiers. Based on the total weight of the inks according to the invention, the inks may contain a viscosity modifier in a weight percentage of up to 10% by weight, more preferably in the range of up to 5% by weight. Rosin resin or its derivatives are preferably selected as viscosity modifiers. Typical commercial products are balsam resins.

[0068] Optionally, the ink according to the invention may contain additional additives, particularly in the range of 0.05% to 3% by weight, more preferably 0.05% to 1% by weight, based on the total weight of the ink according to the invention in each case. Optionally, additional additives may include any chemical substances and mixtures known to those skilled in the art and deemed suitable for the intended purpose. As additional additives, silicone-containing additives are particularly preferred, such as one or more additives containing polyether-modified polydimethylsiloxanes.

[0069] The above composition may optionally contain a rheology modifier.

[0070] A third aspect of the present invention relates to a method for producing a conductive structure on a substrate, the method comprising the steps of:

[0071] A) Provide a substrate and a composition according to the first aspect of the invention;

[0072] B) Applying the composition to a substrate by inkjet printing to obtain a layer of the composition;

[0073] C) Process the layer by selecting a group consisting of the following items:

[0074] a. Hot sintering at temperatures ranging from 140°C to 210°C

[0075] b. Photonic sintering, or

[0076] The combination of ca) and b),

[0077] To obtain a conductive structure.

[0078] 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 combinations of two or more of these materials. Optionally, the provided substrate may also comprise a metal, particularly a metallic surface. Preferably, the substrate comprises or is composed of electrical or electronic components.

[0079] In step B), the composition is applied to a substrate by inkjet printing to obtain a layer of the composition.

[0080] Inkjet printing is a digital printing process using an inkjet printer. The printhead of an 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 can preferably be in the range of 1 pL to 30 pL. The nozzle diameter of the printhead can preferably be in the range of 10 µm to 50 µm, particularly 10 µm to 20 µm or 15 µm to 25 µm. Especially when using EHD printheads and MEMS printheads, nozzle diameters of 2 µm to 10 µm can also be used. One advantage of the compositions according to the invention is that they can be used with printheads having smaller nozzle diameters. This can be explained in particular by the fact that the compositions of the invention contain or are composed of solutions. In contrast, prior art nanoparticle-based compositions may lead to clogging with small nozzle diameters.

[0081] The layer obtained in step B) preferably has an average thickness of at least 0.5 µm, particularly at least 1 µm, and very particularly preferably 2 µm. Furthermore, the layer obtained in step B) preferably has an average thickness of at most 40 µm, particularly at most 20 µm, and very preferably at most 10 µm. These specified layer thicknesses preferably refer to the layer thickness immediately following inkjet printing, particularly before the drying step. If the layer thickness is within the specified range, the processing in step C) can be performed particularly effectively to produce a conductive structure. Simultaneously, fine structures can be printed particularly effectively.

[0082] 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 conversion of the composition to a conductive structure, or at least does not involve a complete conversion of the composition to a conductive structure. For example, the drying step may be performed to temporarily fix the resulting layer. In particular, the dried layer is less affected when another layer (especially a wet layer) is applied.

[0083] Following step B), the next step is a processing step, step C). The layer processing in step C) is preferably carried out in an oxygen-containing atmosphere, such as air. Hot sintering is preferably carried out at a temperature of 140°C to 210°C, particularly 160°C to 180°C, for example, in a furnace. The furnace can be a continuous furnace. For example, hot sintering can be carried out for at least 2 minutes.

[0084] Photonic sintering can be UV sintering, IR sintering, or a combination thereof. UV sintering is preferably performed using light with wavelengths 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 1.0 W / cm². 2 Up to 12.0 W / cm 2 Preferably 2.0W / cm 2 Up to 9.0 W / cm 2 Within the range.

[0085] The UV radiation intensity is preferably 1.0 W / cm². 2 Up to 12.0 W / cm 2 Preferably 2.0W / cm 2 Up to 9.0 W / cm 2 The irradiation time can vary depending on the ink used and can range from, for example, 10 s to 1000 s. When printing multiple molecular metal precursor ink layers, the UV radiation intensity of subsequent layers can be the same or different.

[0086] IR sintering is preferably performed using light with wavelengths in the range of 780 nm to 10 µm, particularly in the range of 800 nm to 3000 nm. Longer wavelengths of light in the range of about 2000 nm to 3000 nm penetrate deeper into the layer to be treated, which may be advantageous for thicker layers of the sintered composition.

[0087] The processing steps, particularly the duration of photonic sintering, are generally not subject to any further restrictions. Preferably, the processing steps are carried out until the layer of the composition transforms into a conductive structure. Preferably, photonic sintering is performed for as short a time as possible. This is advantageous for both process economy and energy saving. The duration and intensity of sintering can be adjusted by experts. If the conductivity of the resulting layer is sufficient for the intended application, the sintering process can be stopped. In particular, the sintering process can be stopped when the conductivity of the resulting conductive structure no longer continues to increase, i.e., a plateau has been reached. Typically, the processing in step C) is carried out for at least 1, 2, 3, 4, or 5 minutes. Optionally, the processing can also be in the range of 10 to 1000 seconds. This is particularly suitable for photonic sintering, such as UV sintering or IR sintering.

[0088] When multiple layers are applied, the radiation intensity of subsequent layers can be the same or different.

[0089] The conductive structure obtained in step C) preferably has an average thickness of at least 100 nm, particularly at least 150 nm, and very particularly preferably 200 nm. Furthermore, the layer obtained in step B) preferably has an average thickness of at most 1000 nm, particularly at most 500 nm, and very preferably at most 250 nm. This specified layer thickness refers to the thickness of a single printed and sintered layer.

[0090] In a preferred embodiment, the process of applying the composition according to step B) and the processing according to step C) can be repeated to obtain a thicker conductive structure. In this case, the conductive structure comprises a stack of individually applied conductive substructures.

[0091] For example, step B) can be performed several times. A drying step can optionally be performed after each inkjet print.

[0092] Optionally, after repeated inkjet printing according to step B), the processing according to step C) can be performed. The layers of the composition may or may not optionally undergo a drying step beforehand.

[0093] The layer thickness of conductive structures obtained by repeatedly applying the composition via inkjet printing is generally unlimited. The layer thickness of the conductive structure then depends largely on the number of individual layers applied.

[0094] Optionally, after sintering, additional materials can be disposed on the substrate or conductive structure, particularly by inkjet printing. For example, a protective layer can be disposed on the conductive structure. The protective layer can protect the conductive structure from changes caused by environmental influences. The protective layer can, for example, contain polymers such as polyimide.

[0095] In another optional embodiment, the substrate is pretreated, for example, to remove impurities. This improves adhesion to the substrate. Pretreatment may include methods selected from the group consisting of plasma cleaning, corona pretreatment, chemical cleaning, CVD treatment, UV ozone treatment, and rinsing. Plasma cleaning may be performed, for example, using argon-oxygen plasma, air plasma, argon plasma, or low-pressure plasma. Pretreatment may generate oxygen-containing groups on the surface of the substrate to be coated. Oxygen-containing groups (e.g., aldehydes, alcohols, or carboxyl groups) may further improve the adhesion of the conductive structure to the substrate.

[0096] Another aspect of the 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 layers of the composition according to the described invention are arranged on the surface. Preferably, the substrate is obtained in step B) by the method described herein. Preferably, the substrate comprises or is composed of electrical or electronic components. The substrate may include, for example, a system-in-package (SIP) or a printed circuit board (PCB).

[0097] Another aspect of the invention relates to a conductive structure on a substrate, particularly a conductive structure 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 an adhesion rating of at least 3B as measured by the cross-cut test according to ASTM D3359-23. Preferably, the conductive structure has an adhesion rating of at least 5B.

[0098] In a particularly preferred embodiment, the substrate of the present invention comprises plastic or a plastic-containing material. Very particularly preferred, the plastic-containing material is an electronic potting compound, such as an epoxy molding compound. EMV is generally understood to be an epoxy resin mixed with inorganic fillers. Particularly good adhesion can be achieved on these plastic-containing materials.

[0099] The volume conductivity σ of the conductive structure is preferably at least 1.10 at 25°C. 6 S / m. Preferably, titanium is uniformly distributed in the conductive structure. For example, titanium can form an alloy with silver. Alternatively, the titanium in the conductive structure can have a gradient, for example, an increasing concentration towards the substrate surface.

[0100] The conductive structure is preferably made from the composition according to the invention. In this context, the conductive structure may contain components of the composition according to the invention, particularly as impurities or as incompletely removed residues in the organic components of the composition. 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 the method according to the invention. Additionally, the conductive structure is preferably obtained from a substrate according to the invention.

[0101] In one possible implementation, the conductive structure comprises at most 0.2% by weight, particularly at most 0.5% by weight, of titanium based on the total weight of the conductive structure.

[0102] More preferably, the conductive structure comprises up to 0.05% by weight of carbon based on the total weight of the composition, as determined by XPS measurements. Such XPS measurements are known to those skilled in the art.

[0103] Optionally, the conductive structure may contain 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.

[0104] In another possible implementation, the conductive structure does not contain any 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, particularly not more than 100 ppm of metals.

[0105] After production, the adhesion between the conductive structure and the substrate preferably has a rating of at least 5B as determined by the cross-cut test according to ASTM D3359-23. Particularly preferably, this good adhesion, as specified in the test, is maintained even after UHAST.

[0106] In one embodiment, the conductive structure does not include any areas produced by subtractive methods, such as cut edges, milled edges, or etched sides. Alternatively, no more than 10% of the edge length of the conductive structure contains areas produced by subtractive methods.

[0107] 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.

[0108] Within the scope of this invention, features disclosed with respect to one aspect of the invention may also be applied to other aspects of the invention. For example, material features described in the context of a method may also be applied to compositions according to the invention, or method features disclosed in the context of a composition may also be applied to methods according to the invention.

[0109] definition

[0110] In the absence of specific measurement conditions, standard ambient temperature and standard ambient pressure are applicable (e.g., a temperature of 298.15 K (25 °C) and an absolute pressure of 101.325 kPa (1 atm)).

[0111] Test methods

[0112] electrical conductivity

[0113] Conductivity was determined using a four-point probe ohmmeter from Ossila with four-point measurements.

[0114] Viscosity

[0115] The viscosity of the paste sample can be determined according to standard DIN 53019 using a DV3 Brookfield rheometer, spindle No. 14 at 10 RPM and 25°C.

[0116] The viscosity of the liquid samples was determined individually using an Ametek DV3T rheometer according to standard DIN 53019.

[0117] Adhesion test

[0118] Within the scope of this invention, adhesion testing was performed using Method B (cross-cut test) of the tape test method according to ASTM D3359-23. 3M transparent tape 600 was used as the tape.

[0119] Reliability testing

[0120] The UHAST (Unbiased High Accelerated Stress Test) method according to the JESD22-A118 standard is used for reliability testing of the conductive structure described herein. This method simulates accelerated aging of the structure under test.

[0121] Therefore, the test substrate was exposed to elevated temperature in a room under limited humidity. Conditions: Temperature: 130°C; Humidity: 85% RH; Time: 96 hours; Pressure: 2 bar.

[0122] Then, the conductive structure to be tested can be subjected to an adhesion test as described in this article.

[0123] Storage stability

[0124] Storage stability was assessed visually. The composition or ink containing the composition was considered stable if no visible particles were observed in the solution. The absence of visible particles was checked using a laser pointer (level 1) held in the solution. The solution was considered stable if no visible particle scattering was observed after shaking. Furthermore, no significant color change toward darker colors was observed.

[0125] Example

[0126] The present invention will be illustrated below by way of examples. However, the present invention is not limited to these examples.

[0127] Example Composition

[0128] The compositions listed in Table 1 below as examples were prepared by first preparing a solution of silver neodecanoate in limonene at room temperature, and then mixing the other components with the solution. Amounts are given as a percentage by weight of each component based on the total weight of the composition.

[0129] It can be seen that compositions 1 and 7 exhibit exceptionally high storage stability for at least 28 days at room temperature, each containing titanium carboxylate as the titanium component. In the case of titanium 2-ethylhexanoate, increased storage stability was observed even at a storage temperature of 40°C.

[0130] Furthermore, compositions 1-7 were printed onto epoxy molding compound (EMC) using inkjet printing. The EMC surface was first cleaned with argon-oxygen plasma each time. The printed layers of compositions 1-7 were converted into a conductive structure by UV sintering at an average wavelength of 395 nm for 2 minutes. The temperature of the part was 180°C, measured using a contact thermometer.

[0131] As described in this paper, adhesion tests were performed on each conductive structure in the conductive structure. High values ​​indicate good adhesion.

[0132] The results are summarized in Table 1 (data is in weight %).

[0133]

[0134] 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 post-manufacturing adhesion (without aging treatment) as measured according to ASTM D3359-23.

Claims

1. A composition for producing a conductive structure on a substrate, wherein the composition comprises a solution, and the solution contains at least the following components: - An organic solvent, selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, alcohols and acetates of these aliphatic hydrocarbons, and mixtures thereof. - at least one silver carboxylic acid, and - At least one titanium carboxylate.

2. The composition according to 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 ligand is a monocarboxylate ligand, and e. The titanium carboxylate contains one or more carboxylate ligands having 5 to 15 C atoms.

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

4. The composition of claim 1, wherein the composition comprises 35% to 75% by weight of a solvent based on the total weight of the composition.

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

6. The composition according to 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 comprising no more than 0.5% by weight of the total weight of the composition.

8. The composition according to 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 combinations 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 combinations of two or more of these materials, characterized in that... The layer of the composition according to any one of claims 1 to 9 is disposed on the surface.

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

12. A method for producing a conductive structure on a substrate, the method comprising the steps of: A) Provide a substrate and the composition according to 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) The layer is processed by selecting a group of the following: a. Hot sintering at temperatures ranging from 140°C to 210°C b. Photonic sintering, or The combination of ca) and b), To obtain a conductive structure.

13. The method according to claim 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, said conductive structure being obtainable by the method according to 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 as measured by the cross-cut test according to ASTM D3359-23.

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