Method of forming a sintered powder comprising copper particles

Abstract

A method of forming a sintered powder comprising copper particles, the method comprising: providing a solution comprising copper ions, a base, and a capping agent; contacting the solution with a reducing agent to provide the sintered powder; and recovering the sintered powder, wherein: prior to contacting the solution with the reducing agent, the solution has a pH of 4 to 7; and the capping agent comprises an amino alcohol.

Description

Technical Field

[0001] This invention relates to a method for forming a sintered powder containing copper particles. Background Technology

[0002] Sintered joints offer an alternative to welded joints. A typical method for forming a sintered joint involves placing metal powder (usually in the form of a powder compact) between two workpieces to be joined, and then sintering the metal powder. The resulting atomic diffusion of metal atoms forms a bond between the two workpieces.

[0003] Metal nanoparticles have been used in the electronics industry to form sintered joints and are a useful alternative to lead-free soldering. The different behavior of nanomaterials compared to their bulk counterparts is thought to be due to the higher surface area to volume ratio of nanomaterials. When compared to conventional solder paste, using metal nanoparticles to form conductive joints between two materials offers many advantages in terms of mechanical, electrical, and thermal reliability.

[0004] Sintered powders containing silver nanoparticles are known. Sintered joints formed by atomic diffusion of silver nanoparticles can be processed at temperatures significantly lower than the melting temperature of the bulk and can also be used in high-temperature applications. However, the sintering temperature of such sintered powders is still too high for effective use in most electronic applications.

[0005] The sintering temperature can be reduced by applying external pressure during sintering. Pressure-assisted low-temperature sintering with silver paste has been proven to be a viable alternative to solder reflow in die-attachment methods. Applying high pressure has been shown to significantly reduce the sintering temperature and achieve the desired die-attachment characteristics at a relatively faster rate, resulting in sintered joints formed within minutes. However, higher external pressure makes automation of this process difficult. Furthermore, applying higher external pressure can lead to workpiece damage.

[0006] Silver has long been used in the electronics industry for die attachment applications due to its excellent electrical and thermal conductivity. However, its high cost limits its widespread use in many fields. Furthermore, silver faces ion migration issues at relatively high temperatures and humidity levels, which is another major concern.

[0007] Copper is a much cheaper material than silver and also has extremely high electrical conductivity (only 6% lower than Ag). In addition to its lower cost, copper does not exhibit ion migration problems, giving it an advantage over silver. However, the inherent tendency of copper nanoparticles to oxidize remains a major concern.

[0008] Several reports have presented various methods demonstrating that copper nanoparticles, when properly coated with a protective layer, can resist oxidation under environmental conditions. The utility of these copper nanoparticles in conductive die bonding pastes for die bonding applications remains to be extensively explored. Therefore, there is a significant demand in the electronics market for copper die bonding pastes, which offer almost the same beneficial effects as nano-silver but at a much lower cost.

[0009] WO 2014 / 068299 relates to sintered powders containing particles with an average longest diameter of less than 10 micrometers and specifically to silver nanoparticles with a bimodal particle size distribution. WO 2015 / 155542 relates to low-pressure sintered powders and also specifically to silver nanoparticles with a bimodal particle size distribution. Because both documents utilize silver, ion migration issues may arise.

[0010] WO2020 / 002890 relates to sintered powders containing copper particles. The particle size distribution of the copper particles is controlled in an attempt to reduce the oxidation level. However, increasing the particle size adversely affects the sintering properties. The sintered powder is prepared in a solution with a high pH (see, for example, the description of the manufacturing method in Example 1, which references pH > 7, possibly in the range of 8).

[0011] There is a need for a copper sintered powder that is less prone to oxidation and / or agglomeration compared to conventional copper sintered powders, but exhibits sintering characteristics similar to those of silver sintered powders.

[0012] This invention seeks to solve at least some of the problems associated with the prior art or to provide at least a commercially acceptable alternative to the prior art. Summary of the Invention

[0013] In a first aspect, the present invention provides a method for forming a sintered powder comprising copper particles, the method comprising: Provides an aqueous solution containing copper ions, alkali, and a coating agent; The solution is contacted with a reducing agent to provide the sintered powder; and The sintered powder is recycled. in: Before contacting the solution with the reducing agent, the solution has a pH of 4 to 7; and The coating agent contains amino alcohols.

[0014] Each aspect or embodiment as defined herein may be combined with any other aspect or embodiment unless expressly indicated to the contrary. Specifically, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0015] The inventors have surprisingly discovered that the resulting sintered powder exhibits favorable sintering properties and is less prone to oxidation compared to conventional copper-containing sintered powders.

[0016] The resulting sintered powder copper particles may have a thin outer layer / shell comprising copper oxide and copper hydroxide. Based on powder X-ray diffraction and XPS analysis, this layer appears to differ chemically and / or structurally from the typical copper oxide layer formed on conventional copper particles when exposed to air. Without being bound by theory, it is thought that this thin outer layer may contribute to the favorable sintering properties and oxidation resistance of the sintered powder. Specifically, the thin outer layer may be thick enough and have a suitable chemical composition to inhibit further oxidation of the copper particles in air and suppress agglomeration. However, at typical sintering temperatures, the thin outer layer can be removed to allow sintering to occur. Similarly, without being bound by theory, it is thought that the presence of copper hydroxide in the thin outer layer may facilitate its reduction at typical sintering temperatures, for example, when the sintered powder is in the form of a paste containing conventional activators.

[0017] Unbound by theory, it is believed that the properties of the thin outer layer can, to some extent, fall between those of an oxide layer formed on, for example, silver and an oxide layer formed on aluminum. As will be understood, when a metal is exposed to oxidizing conditions such as air, an oxide layer forms on the surface of the metal. For some metals, such as silver, with continued exposure to air, the metal will completely transform into its oxide. In contrast, for some metals, such as aluminum, the oxide layer acts as a barrier layer and prevents further oxidation of the bulk metal. Simply put, this difference can be attributed to the volume of the oxide formed—when the metal increases in volume as it forms an oxide, it acts as a barrier layer, while when the metal decreases in volume as it forms its oxide, it exposes the underlying metal to further oxidation. The inventors conjecture that the properties of the thin outer layer of the sintered powder of the present invention will allow the thin outer layer to exhibit more "barrier-like" properties compared to the properties of a typical oxide layer formed on particles of conventional copper sintered powder when exposed to air.

[0018] The sintered powder formed using the method of the present invention can exhibit a particle size distribution that contributes to favorable sintering properties. For example, copper particles can have: D90 from 270nm to 470nm (typically 270nm to 350nm or 420nm to 470nm), and / or D50 from 130nm to 160nm, and / or D10 from 90nm to 110nm.

[0019] Unbound by theory, it is assumed that particle size distribution and / or a thin outer layer can be generated by reaction kinetics. It is believed that during the reaction, copper ions can react with the base to form a complex or colloidal substance, and the nitrogen lone pair electrons of the amino alcohol coating agent can be donated to the copper centers to form a chelate. This intermediate is more easily reduced during the subsequent reduction step. The proportion of copper ions forming the intermediate is controlled using a pH of 4 to 7. In other words, the advantageous properties of the sintered powder can be derived from the combined use of the amino alcohol coating agent and a pH of 4 to 7.

[0020] Advantageously, the use of a coating agent helps reduce particle agglomeration. Such agglomeration is detrimental because it increases the sintering temperature of the sintered powder. Therefore, the use of a coating agent enables the formation of sintered joints between workpieces at lower temperatures and pressures, and thus helps reduce damage to the workpieces caused by exposure to high sintering temperatures. Additionally, the use of a coating agent helps prevent copper degradation, such as damage caused by exposure of the metal to air at temperatures below typical sintering temperatures. This allows the sintered powder to retain its favorable sintering properties over time (i.e., after a period of storage).

[0021] Amino alcohols can evaporate and decompose under typical sintering conditions (e.g., 1 MPa to 30 MPa and 200°C to 300°C). This results in very low levels of organic matter in the sintered joint, typically virtually none. This improves the strength and mechanical properties of the sintered joint. Furthermore, amino alcohols can decompose to produce reducing gases such as CO, NO, and NH3. Without being bound by theory, it is believed that the presence of such reducing gases during sintering can aid sintering by reducing the thin protective shell on the copper particles and / or inhibiting the oxidation of the copper particles.

[0022] The amine group of an amino alcohol can interact with copper to form the intermediates discussed above. The hydroxyl group makes the amino alcohol water-soluble.

[0023] Advantageously, copper sintered powder provides the same or similar beneficial effects as nanosilver in terms of sinterability, thermal conductivity, electrical conductivity, and favorable mechanical properties of the final joint, but at a much lower cost. Furthermore, it overcomes the ion migration problems associated with nanosilver.

[0024] The sintered powder is typically air-stable and non-agglomerated.

[0025] The particle size distribution of sintered powder can be unimodal or bimodal.

[0026] Furthermore, this sintered powder enables universal bonding of surfaces, particularly two or more surfaces with different finishes such as: copper to copper; copper to silver, copper to brass, copper to tin, copper to gold, copper to copper-molybdenum, copper to copper-tungsten, and copper to nickel. The sintered powder is particularly suitable for die, component, and package attachments.

[0027] As used herein, the term "sintered powder" can encompass powders capable of forming sintered joints. Sintered joints are formed through atomic diffusion of metal particles placed between two workpieces to be joined. The term "sintered powder" can also encompass microparticles.

[0028] The sintered powder contains copper particles. These particles may include regularly shaped particles (such as, for example, spheres) and / or irregularly shaped particles (such as, for example, whiskers, facets, plates, rods, or flakes). Preferably, at least some of the particles include faceted particles. Preferably, the particles include both regularly shaped and irregularly shaped particles.

[0029] Copper particles may be in the form of, for example, copper metal or copper alloy, preferably copper metal.

[0030] The sintered powder may contain particles other than copper particles. However, the majority of the particles in the sintered powder are copper particles, and typically, virtually all of them are copper particles.

[0031] The method involves providing an aqueous solution comprising copper ions, an alkali, and a coating agent. This solution is aqueous (e.g., the solvent is deionized water) because water is non-toxic, low-cost, and widely available. Copper ions are typically provided in the form of a salt. Therefore, in addition to copper ions, the alkali, and the coating agent, the solution typically contains a counterion of the salt. The copper ions may be the only metal ions present in the solution. Alternatively, other metal ions may be present in the solution. These other metal ions may be counterions of the salt. Preferably, the copper ions are the only metal ions present in the solution. This avoids unwanted impurities in the sintered powder that could impair sintering properties. The copper ions may include copper(I) ions and / or copper(II) ions, preferably copper(II) ions.

[0032] As used herein, the term "coating agent" can encompass substances that, when present on the surface of metal particles, reduce the agglomeration of metal particles, enable particle size control during powder production, and reduce surface oxidation or other contamination of particles.

[0033] This method involves contacting a solution with a reducing agent to provide a sintered powder. Without being bound by theory, it is assumed that the reducing agent reduces copper ions, thereby causing the precipitation of copper metal particles. These copper metal particles are "coated" by a coating agent, thus hindering further agglomeration. These particles are typically nanoparticles. Contacting the solution with a reducing agent may, for example, involve adding the reducing agent to the solution. Alternatively, contacting the solution with a reducing agent may, for example, involve adding the solution to a solution of the reducing agent.

[0034] This method includes recovering sintered powder. In other words, the method may include recovering sintered powder from a solution. The sintered powder may be stored, for example, under a vacuum or in an inert atmosphere. This can further inhibit the oxidation and / or agglomeration of the sintered powder particles.

[0035] Before (i.e., immediately before) contact with the reducing agent, the solution has a pH of 4 to 7. In other words, the step of providing an aqueous solution containing copper ions, a base, and a coating agent may include providing an aqueous solution containing copper ions, a base, and a coating agent with a pH of 4 to 7. As will be understood, once the solution is contacted with the reducing agent, the pH of the solution may change and may fall outside this range.

[0036] The coating agent comprises an amino alcohol. As used herein, the term "amino alcohol" may encompass organic compounds containing both hydroxyl (-OH) and amino (-NH2, -NHR, and -NR2) functional groups on an alkane backbone. Amino alcohols may contain a single hydroxyl group or multiple hydroxyl groups. The hydroxyl group may be present at C2 and C3. n C at any position between positions n The position refers to the terminal position. The alkane backbone can be straight, branched, or cyclic. The carbon chain is usually aliphatic, but can be aromatic. The boiling point of amino alcohols is usually above 50°C. The amine group can be present at the primary or secondary position. Amino alcohols are sometimes referred to in the art as amino-substituted alcohols or alkanolamines. The coating agent can consist of an amino alcohol. Alternatively, the solution may contain a coating agent other than an amino alcohol. The coating agent may contain a single type of amino alcohol or multiple types of amino alcohols.

[0037] Before contacting the solution with the reducing agent, the solution preferably has a pH of 4.1 to less than 7, more preferably 4.2 to 6.5, even more preferably 4.5 to 6, and even more preferably 4.8 to 5.5. This can help provide a favorable particle size distribution, particle shape, and / or thin outer layer.

[0038] The amino alcohol preferably contains two or more hydroxyl groups, more preferably two hydroxyl groups (i.e., only two hydroxyl groups). This increases the intermolecular hydrogen bonds between coating agent molecules, thereby increasing oxidative protection.

[0039] The hydroxyl groups of the amino alcohol are preferably located on a single aliphatic chain (usually an alkyl chain), that is, all hydroxyl groups of the amino alcohol are preferably located on a single aliphatic chain. The amino alcohol preferably contains two hydroxyl groups in a single aliphatic chain, i.e., only two hydroxyl groups, and these groups are both present on the same aliphatic chain. The inventors have surprisingly discovered that the presence of hydroxyl groups on multiple alkyl chains (e.g., in triethanolamine according to WO2020 / 002890) can create steric hindrance and / or orientation hindrance, and thus can lead to weaker chelate complexes and fewer intramolecular hydrogen bonds. Furthermore, the presence of hydroxyl groups on multiple alkyl chains (e.g., in triethanolamine) can also lead to poor reaction kinetic control, resulting in larger particles. On the other hand, the presence of two hydroxyl groups on the same aliphatic chain can create less steric hindrance, and thus create stronger chelate complexes, thereby providing better reaction kinetic control to produce smaller particles. Furthermore, the presence of two hydroxyl groups in a single aliphatic chain can create intramolecular hydrogen bonds, which further contributes to the oxidation protection and agglomeration control of copper particles.

[0040] Amino alcohols preferably include alkylamino alcohols, more preferably dialkylamino alcohols. The alkyl group is preferably methyl or ethyl, more preferably methyl. Amino alcohols more preferably include methylamino alcohols, and even more preferably dimethylamino alcohols. Substituting the nitrogen atom of the amino group with a smaller-chain alkyl group (e.g., methyl or ethyl, preferably methyl) can produce less steric hindrance than with a larger-chain alkyl group (e.g., propyl, butyl, etc.). The presence of alkyl groups, preferably two alkyl groups, can also produce sufficient (+) inductive effect (+I effect) to provide a lone pair of electrons on nitrogen, and thus produce a chelating complex that is sufficiently strong compared to unsubstituted amines (-NH2). In contrast, amino alcohols without alkyl groups (such as amino alcohols containing three alcohol groups, e.g., triethanolamine) can have lower electron-donating capabilities. For example, in the case of triethanolamine, the presence of three terminal -OH groups can reduce the +I effect.

[0041] The amino alcohol preferably does not include triethanolamine. The coating agent is preferably different from the base. The amino alcohol preferably contains at least two hydroxyl groups on adjacent carbon atoms. Preferably, at least two of the substituents on the nitrogen of the amino alcohol are different. The amino alcohol preferably has a pKa greater than 9, more preferably greater than 10, even more preferably greater than 11, even more preferably greater than 12, even more preferably greater than 13.

[0042] Amino alcohols preferably contain 3 to 12 carbon atoms. Such amino alcohols can be used as particularly effective coating agents.

[0043] Amino alcohols may include dihydroamino alcohols, meaning they may contain a -NH2 group.

[0044] Amino alcohols preferably include 3-(dimethylamino)-1,2-propanediol (DMPA), 3-(amino)-1,2-propanediol (AP), and / or 3-(methylamino)-1,2-propanediol (MAP), with 3-(dimethylamino)-1,2-propanediol being the most preferred. Such amino alcohols can be used as particularly effective coating agents.

[0045] 3-(dimethylamino)-1,2-propanediol has the following chemical structure:

[0046] 3-(amino)-1,2-propanediol has the following chemical structure:

[0047] 3-(methylamino)-1,2-propanediol has the following chemical structure:

[0048] Providing a solution containing copper ions, an alkali, and a coating agent preferably involves providing a solution containing copper ions and an alkali, and then contacting the solution containing copper ions and an alkali with a coating agent.

[0049] The copper ions in the solution are preferably provided in the form of a copper salt, more preferably selected from one or more of copper(II) nitrate, copper(II) sulfate, copper(II) acetate, copper(II) formate, and copper(II) hydroxide, even more preferably selected from one or both of copper(II) nitrate and copper(II) acetate, and even more preferably copper(II) nitrate. Such substances are particularly suitable sources of copper ions. The use of copper nitrate relative to copper acetate allows for the use of a lower pH. This is likely due to the fact that the ligand strength of nitrates can be lower than that of acetates, i.e., copper nitrate is almost ionic, while copper acetate is almost covalent.

[0050] The base preferably comprises an amine, such as, for example, triethanolamine, diethanolamine, or triethylamine, preferably triethanolamine. In addition to amines, the base may also comprise hydroxides. The presence of these substances can facilitate the formation of the intermediate substances discussed above and is particularly suitable for providing solutions with the desired pH. The hydroxide is preferably selected from one or more of sodium hydroxide, potassium hydroxide, and ammonium hydroxide. Such hydroxides are particularly suitable bases. More preferably, the hydroxide is ammonium hydroxide. Compared to metallic hydroxides (such as sodium hydroxide and potassium hydroxide), the use of ammonium hydroxide results in a lower level of impurity metals in the sintered powder, which can hinder sintering characteristics and / or impair the characteristics of sintered joints formed using the sintered powder.

[0051] The reducing agent preferably includes one or more of hydrazine (e.g., hydrazine hydrate), sodium borohydride, and lithium borohydride, more preferably hydrazine. Such substances are particularly suitable reducing agents and can help provide the favorable reaction kinetics discussed above. Hydrazine is a particularly suitable reducing agent and can produce particles within the desired particle size range particularly effectively.

[0052] Once the solution has come into contact with the reducing agent, the molar ratio of copper ions:base:coating agent:reducing agent in the solution is preferably 0.2 to 1:0.05 to 2:0.2 to 1.5:1 to 10. Such a ratio can help provide the favorable reaction kinetics discussed above.

[0053] The solution containing copper ions, alkali, and a coating agent is preferably contacted with the reducing agent for 1 to 20 hours, preferably 2 to 10 hours, and more preferably 3 to 5 hours, i.e., prior to the step of recovering the sintered powder. This helps to demonstrate the favorable particle size distribution, particle shape, and / or outer layer discussed above. Shorter times may lead to reduced yield and / or the formation of unfavorable small particles. Longer times may lead to the formation of unfavorable large particles or may cause unfavorable oxidation.

[0054] The recovery of sintered powder preferably includes one or more of the following: a solution obtained from sintered powder decantation, washing of sintered powder, and drying of sintered powder.

[0055] Drying is preferably carried out in a non-inert atmosphere or in an inert atmosphere, more preferably air or nitrogen.

[0056] The sintered powder formed by this method can be the sintered powder described below.

[0057] In another aspect, the present invention provides a method for forming a sintered powder comprising copper particles, the method comprising: An aqueous solution comprising copper ions, an alkali, and a coating agent is provided, the aqueous solution having a pH of 4 to 7; The solution is contacted with a reducing agent to provide the sintered powder; and The sintered powder is recycled. The coating agent contains an amino alcohol.

[0058] The advantages and preferred features of the first aspect also apply to this aspect.

[0059] In another aspect, the present invention provides a sintered powder formed using the methods described herein.

[0060] The advantages and preferred features of the first aspect also apply to this aspect.

[0061] Specifically, this sintered powder can exhibit the particle size distribution discussed above, and the particles of the sintered powder can have the particle shape and / or outer layer discussed above. As discussed above, this outer layer is chemically different from the outer layer formed when conventional copper sintered powder is left in air.

[0062] In another aspect, the present invention provides a sintered powder comprising copper particles, wherein at least some of the copper particles are coated with a coating agent comprising an amino-substituted alcohol.

[0063] The advantages and preferred features of the first aspect also apply to this aspect.

[0064] At least some of the copper particles are coated with a coating agent containing an amino-substituted alcohol. Typically, the majority (>50% by weight) of the copper particles are coated with a coating agent containing an amino-substituted alcohol, and more typically, virtually all of the copper particles are coated with a coating agent containing an amino-substituted alcohol.

[0065] Preferably, at least some of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide. In this case, a coating agent is applied to the layer. Typically, most (>50% by weight) of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide, and more typically, substantially all of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide.

[0066] The layer (comprising copper oxide and copper hydroxide) preferably has a thickness of 20 nm to 60 nm, more preferably 25 nm to 55 nm. The thickness can be an average thickness and can be measured using the methods described in the examples. This thickness can help provide the advantageous combination of sintering properties and oxidation resistance discussed above.

[0067] Amino alcohols preferably contain two or more hydroxyl groups, more preferably two hydroxyl groups. Amino alcohols preferably contain 3 to 12 carbon atoms. Preferably, the hydroxyl groups of the amino alcohol are located on a single aliphatic chain. Preferably, the amino alcohol contains two hydroxyl groups, both located on the same aliphatic chain. Amino alcohols preferably include alkylamino alcohols, more preferably dialkylamino alcohols. Amino alcohols preferably include methylamino alcohols, more preferably dimethylamino alcohols. Amino alcohols preferably include dihydroamino alcohols.

[0068] The amino alcohol preferably includes 3-(dimethylamino)-1,2-propanediol, 3-(amino)-1,2-propanediol and / or 3-(methylamino)-1,2-propanediol, preferably 3-(dimethylamino)-1,2-propanediol.

[0069] The sintered powder preferably contains 0.1% to 12% by weight, more preferably up to 3% by weight, and even more preferably up to 1% by weight of a coating agent based on the total weight of the sintered powder. Lower levels of coating agent may not be sufficient to provide the advantageous combination of sintering properties and oxidation resistance discussed above. Higher levels may result in unfavorable levels of organic matter remaining in the sintered joint and / or may increase the cost of the manufacturing process.

[0070] Copper particles preferably have: D90 from 200nm to 500nm, and / or D50 from 120nm to 195nm, and / or D10 from 55nm to 115nm.

[0071] The copper particles more preferably have: D90 of 270nm to 470nm (preferably 270nm to 350nm or 420nm to 470nm), and / or D50 from 130nm to 160nm, and / or D10 from 90nm to 110nm.

[0072] This type of particle size distribution can improve the sintering properties of sintered powders. Furthermore, sintered joints formed using such powders exhibit favorable mechanical properties. Without being bound by theory, it is believed that this particle size distribution (including a large number of smaller particles) can produce particularly favorable packing densities. D90 refers to the size at 90% of the cumulative particle size distribution, meaning that 90% of the particles have a size smaller than this value. D50 refers to the size at 50% of the cumulative particle size distribution (i.e., the mode), and D10 refers to the size at 10% of the cumulative particle size distribution. Particle size refers to particle diameter. As is customary in the art, this diameter corresponds to the equivalent sphere diameter, and this distribution corresponds to the volume distribution. D90, D50, and D10 can be measured using suitable techniques known in the art, such as, for example, laser diffraction, dynamic light scattering, and SEM image analysis.

[0073] Copper particles preferably have: D90 from 270nm to 470nm D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

[0074] In a particularly preferred embodiment, the copper particles have: The D90 ranges from 420nm to 470nm. D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

[0075] In another particularly preferred embodiment, the copper particles have: The D90 ranges from 270nm to 350nm. D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

[0076] The copper particles preferably comprise faceted particles. Compared to spherical particles, such particles can produce improved packing density. Preferably, at least 50% by volume of the particles are faceted, more preferably at least 75% by volume, even more preferably at least 90% by volume, and even more preferably 30% by volume to 90% by volume.

[0077] In another aspect, the present invention provides a sintered powder comprising copper particles, wherein at least some of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide, the layer having a thickness of 20 nm to 60 nm, preferably 25 nm to 55 nm.

[0078] The advantages and preferred features of the first aspect also apply to this aspect. Thickness can be measured using the methods described in the examples.

[0079] In another aspect, the present invention provides a sintering paste comprising the sintering powder described herein.

[0080] The advantages and preferred features of the first aspect also apply to this aspect.

[0081] The paste may also contain one or more of the following: solvents, activators, binders, defoamers, reducing agents, and rheology modifiers.

[0082] In another aspect, the present invention provides a sintered film comprising the sintered powder described herein.

[0083] The advantages and preferred features of the first aspect also apply to this aspect.

[0084] The sintered membrane may also contain, for example, an adhesive. The membrane may be a self-supporting membrane. The membrane may include a release layer. The membrane may be on a polymer substrate.

[0085] In another aspect, the present invention provides a method for forming a joint between two or more workpieces, the method comprising: Provide two or more workpieces to be joined. The sintering powder and / or sintering paste and / or sintering film described herein are provided near the two or more workpieces. The sintering powder and / or the sintering paste and / or the sintering film are heated to at least partially sinter the copper particles.

[0086] The advantages and preferred features of the first aspect also apply to this aspect.

[0087] Two or more workpieces preferably comprise a die and a substrate. Heating is preferably performed at a temperature of 150°C to 400°C, more preferably 200°C to 300°C, and even more preferably 230°C to 280°C. Heating can be performed without applied pressure. Alternatively, pressure can be applied during heating, preferably 1 MPa to 35 MPa, more preferably 5 MPa to 32 MPa, and even more preferably 8 MPa to 30 MPa. Higher temperatures and pressures can produce improved sintering and more favorable properties of the sintered joint. Lower temperatures and pressures are more energy-efficient and reduce the likelihood of damage to the workpieces being joined.

[0088] In another aspect, the present invention provides the use of the sintering powder and / or the sintering paste and / or the film described herein in a selection of methods including: die attachment; wafer-to-wafer bonding; hermetically and near-hermetically sealed; sintering a film comprising sintering powder and an adhesive formed in a film on a backing layer; dispensing and generating interconnects.

[0089] The advantages and preferred features of the first aspect also apply to this aspect.

[0090] In another aspect, the present invention provides the use of the sintered powders and / or sintered pastes and / or films described herein in the manufacture of additive printed structures, human-machine interface (HMI) electronics, capacitive switches, wire harnesses, solderable electronic circuits and devices, IME structures, structured / embedded electronic devices, large-area electronic devices, lighting / luminaires, large-area lighting, flexible and formable displays, embedded sensors, printed battery assemblies, printed heaters, flexible circuits and cables, Cu-coated dielectric materials, die attachment applications, or package attachment and component attachment applications.

[0091] The advantages and preferred features of the first aspect also apply to this aspect.

[0092] In another aspect, the present invention provides sintered joints formed using the sintering powders and / or sintering pastes and / or films and / or methods described herein.

[0093] The advantages and preferred features of the first aspect also apply to this aspect.

[0094] In another aspect, the present invention provides the use of an amino alcohol containing two hydroxyl groups as a coating agent for copper particles.

[0095] The advantages and preferred features of the first aspect also apply to this aspect.

[0096] The invention will now be further described with reference to the following numbered clauses: 1. A sintered powder comprising copper particles, wherein at least some of the copper particles are coated with a coating agent comprising an amino-substituted alcohol.

[0097] 2. The sintered powder according to Clause 1, wherein the amino-substituted alcohol comprises two or more hydroxyl groups.

[0098] 3. The sintered powder according to Clause 1 or Clause 2, wherein the amino-substituted alcohol comprises 3 to 12 carbon atoms.

[0099] 4. The sintered powder according to any of the preceding clauses, wherein the amino-substituted alcohol comprises 3-(dimethylamino)-1,2-propanediol.

[0100] 5. The sintered powder according to any of the preceding clauses, wherein the sintered powder comprises 0.1% to 12% by weight, preferably up to 3% by weight, and more preferably up to 1% by weight of a coating agent based on the total weight of the sintered powder.

[0101] 6. The sintered powder according to any of the preceding clauses, wherein the copper particles have: D90 from 450nm to 800nm, and / or D50 from 100nm to 150nm, and / or D10 from 60nm to 90nm.

[0102] This particle size distribution provides favorable sintering properties.

[0103] 7. The sintered powder according to any of the preceding clauses, wherein the copper particles have: The D90, ranging from 450nm to 800nm, and D50 from 100nm to 150nm, and D10 from 60nm to 90nm.

[0104] This particle size distribution provides favorable sintering properties.

[0105] 8. The sintered powder according to any of the preceding clauses, wherein the copper particles include faceted particles.

[0106] 9. A sintered powder comprising copper particles, wherein at least some of the copper particles are coated with a coating agent, and wherein the copper particles have: The D90, ranging from 450nm to 800nm, and D50 from 100nm to 150nm, and D10 from 60nm to 90nm.

[0107] This particle size distribution provides favorable sintering properties.

[0108] 10. A sintered powder comprising copper particles, wherein at least some of the copper particles are coated with a coating agent comprising a polymer, said polymer comprising a lactam, preferably a γ-lactam.

[0109] This coating agent is particularly effective at inhibiting the oxidation and / or aggregation of copper particles. However, its wetting and / or activity may be lower compared to amino alcohol coating agents.

[0110] 11. The sintered powder according to Clause 10, wherein the lactam comprises 2-pyrrolidone.

[0111] 12. The sintered powder according to Clause 10 or Clause 11, wherein the polymer comprising a lactam comprises polyvinylpyrrolidone.

[0112] 13. The sintered powder according to any one of clauses 10 to 12, wherein the polymer has a molecular weight of 2 kDa to 400 kDa, preferably 5 kDa to 50 kDa, and more preferably 7 kDa to 35 kDa.

[0113] 14. The sintered powder according to any one of clauses 10 to 13, wherein the copper particles have: D90 from 450nm to 800nm, and / or D50 from 100nm to 150nm, and / or D10 from 60nm to 90nm.

[0114] This particle size distribution provides favorable sintering properties.

[0115] 15. The sintered powder according to any one of clauses 10 to 13, wherein the copper particles have: The D90, ranging from 450nm to 800nm, and D50 from 100nm to 150nm, and D10 from 60nm to 90nm.

[0116] This particle size distribution provides favorable sintering properties.

[0117] 16. A sintered powder comprising copper particles, wherein the copper particles are substantially free of coating agents, and wherein the copper particles have: The D90, ranging from 1000nm to 1800nm, and D50 from 200nm to 500nm, and D10 from 120nm to 160nm.

[0118] This particle size distribution provides favorable sintering properties.

[0119] 17. The sintered powder according to Clause 16, wherein the sintering agent comprises less than 1% by weight, preferably less than 0.7% by weight, and more preferably less than 0.5% by weight, of a coating agent based on the total weight of the sintered powder.

[0120] 18. The sintered powder according to any of the preceding clauses, wherein at least some of the copper particles have a longest dimension of 100 nm to 1000 nm.

[0121] 19. The sintered powder according to any of the preceding clauses, wherein at least some of the copper particles are at least partially coated with a layer comprising copper oxide and / or copper hydroxide, the layer having a thickness of 20 nm to 60 nm, preferably 25 nm to 55 nm.

[0122] 20. A sintered powder comprising copper particles, wherein at least some of the copper particles are at least partially coated with a layer comprising copper oxide and / or a layer comprising copper hydroxide, said layer having a thickness of 20 nm to 60 nm, preferably 25 nm to 55 nm.

[0123] 21. A method for forming sintered powder, the method comprising: A solution comprising copper ions, a base, and an optional coating agent is provided, the solution having a pH of 4 to 7.5; The solution is contacted with a reducing agent to provide the sintered powder; and The sintered powder is recovered.

[0124] 22. The method according to Clause 21, wherein providing the solution comprising copper ions, a base, and an optional coating agent comprises providing a solution comprising copper ions and a base, and then contacting the solution comprising copper ions and a base with a coating agent.

[0125] 23. The method according to Clause 21 or Clause 22, wherein the copper ions in the solution are provided in the form of a copper salt, wherein the copper salt is preferably selected from one or more of copper(II) nitrate, copper(II) sulfate, copper(II) acetate, copper(II) formate, and copper(II) hydroxide, more preferably selected from one or both of copper(II) nitrate and copper(II) acetate.

[0126] 24. The method according to any one of clauses 21 to 23, wherein the base comprises triethanolamine and a hydroxide, wherein the hydroxide is preferably selected from one or more of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

[0127] 25. The method according to any one of clauses 21 to 24, wherein the solution comprising copper ions, a base and an optional coating agent has a pH of 4 to 7, preferably 4.2 to less than 7.

[0128] 26. The method according to any one of clauses 21 to 25, wherein the reducing agent comprises one or more of hydrazine, sodium borohydride and lithium borohydride, preferably hydrazine.

[0129] 27. The method according to any one of clauses 21 to 26, wherein the molar ratio of copper ions: base: coating agent: reducing agent is 0.2 to 1: 0.05 to 2: 0.2 to 1.5: 1 to 10.

[0130] 28. The method according to any one of clauses 21 to 27, wherein a solution containing copper ions, an alkali and an optional coating agent is contacted with the reducing agent for 1 hour to 20 hours, preferably 2 hours to 10 hours, more preferably 3 hours to 5 hours.

[0131] 29. The method according to any one of clauses 21 to 28, wherein recovery comprises one or more of the following: decantation of the solution obtained from the sintered powder, washing the sintered powder, and drying the sintered powder.

[0132] 30. The method according to any one of clauses 21 to 29, wherein the method is carried out in a non-inert atmosphere or in an inert atmosphere, preferably air or nitrogen.

[0133] 31. The method according to any one of Clauses 21 to 30, wherein the sintered powder is according to any one of Clauses 1 to 17.

[0134] 32. A sintering paste comprising sintering powder according to any one of clauses 1 to 20.

[0135] 33. A sintered membrane comprising sintered powder according to any one of clauses 1 to 20.

[0136] 34. A method for forming a joint between two or more workpieces, the method comprising: Provide two or more workpieces to be joined. Sintering powder according to any one of clauses 1 to 20 and / or sintering paste according to clause 32 and / or sintering film according to clause 33 are provided near the two or more workpieces. The sintering powder and / or the sintering paste and / or the sintering film are heated to at least partially sinter the copper particles.

[0137] 35. The method according to Clause 34, wherein the two or more workpieces comprise a die and a substrate.

[0138] 36. Use of the sintered powder according to any one of Clauses 1 to 20 and / or the sintered paste according to Clause 29 and / or the film according to Clause 30 in a manner selected from: die attachment; wafer-to-wafer bonding; hermetically and near-hermetically sealed; sintering a film comprising sintered powder and a binder formed in a film on a backing layer; dispensing and generating interconnects.

[0139] 37. Use of the sintered powder according to any one of Clauses 1 to 20 and / or the sintered paste according to Clause 32 and / or the film according to Clause 33 in the manufacture of additive printed structures, human-machine interface (HMI) electronics, capacitive switches, wire harnesses, solderable electronic circuits and devices, IME structures, structured / embedded electronic devices, large-area electronic devices, lighting / luminaires, large-area lighting, flexible and formable displays, embedded sensors, printed battery assemblies, printed heaters, flexible circuits and cables, Cu-coated dielectric materials, die attachment applications or encapsulation attachment and component attachment applications.

[0140] 38. A sintered joint formed using sintering powder according to any one of clauses 1 to 20 and / or sintering paste according to clause 32 and / or sintering film according to clause 33 and / or methods according to clauses 34 or 35.

[0141] 39. Use of amino-substituted alcohols as coating agents for copper particles. Attached Figure Description

[0142] The invention will be described in conjunction with the following non-limiting drawings, in which: Figure 1 The following FESEM images are shown: (a) Sample 1, (b) Sample 2, (c) Sample 3, (d) Sample 4, (e) Sample 5, (f) Sample 8, (g) Sample 9, (h) Sample 10 and (i) Sample 12.

[0143] Figure 2 The following FESEM images are shown: (a) Sample 14, (b) Sample 15, (c) Sample 16, (d) Sample 17, (e) Sample 18, (f) Sample 19, (g) Sample 20, (h) Sample 21 and (i) Sample 22.

[0144] Figure 3 The following photographs are shown: (a) Sample 4, (b) Sample 5, (c) Sample 14, (d) Sample 9, (e) Sample 10 and (f) Sample 16.

[0145] Figure 4The following TEM micrographs are shown: (a) Sample 4, (b) Sample 5, (c) Sample 9 and (d) Sample 9.

[0146] Figure 5 Powder X-ray diffraction patterns of samples 4, 5, 9 and 14, as well as PDF data of Cu, Cu2O and CuO, are shown.

[0147] Figure 6 The following XPS full spectrum scans are shown: (a) Sample 14, (b) Sample 4, (c) Sample 5 and (d) Sample 9.

[0148] Figure 7 The following high-resolution and deconvolutioned Cu2p XPS spectra are shown: (a) Sample 14, (b) Sample 4, (c) Sample 5 and (d) Sample 9.

[0149] Figure 8 The following depth profiles (etch depth versus atomic percentage of carbon, oxygen, and copper) are shown: (a) Sample 14, (b) Sample 4, (c) Sample 5, and (d) Sample 9.

[0150] Figure 9 The TGA characterization results of “copper sintered powder” are shown: weight loss due to decomposition of organic coatings and absorbed volatile substances as a function of temperature in (a) Examples 4, 5, 9 and 10 and (b) Examples 16 and 17.

[0151] Figure 10 Optical images are shown of self-supporting sintered copper foils prepared using a laboratory press at different pressures (a) 10 MPa, (b) 20 MPa and (c) 30 MPa for 2 minutes at 260 °C.

[0152] Figure 11 The resistivity (surface and volume resistivity) of various self-supported sintered copper foils prepared at different pressures of 1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa and 30 MPa (260 °C for 2 minutes) and the resistivity of bulk copper are shown.

[0153] Figure 12 FE-SEM images of the microstructure of self-supported sintered copper foils sintered at various cross-sections at (a) 30 MPa, (b) 20 MPa, (c) 10 MPa, (d) 5 MPa and (e) 1 MPa are shown. Detailed Implementation

[0154] The invention will now be described in conjunction with the following non-limiting examples.

[0155] Preparation of sintered powder

[0156] sample 1 : 100 g of copper(II) nitrate trihydrate and 30 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution with a pH of 3.9–4.1. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40 °C. The dried copper sintered powder is packaged in a vacuum-sealed container for further storage, characterization, processing, and use.

[0157] sample 2 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of ammonium hydroxide (50 g) under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. Next, hydrazine hydrate (200 g) was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., a Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0158] sample 3 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in deionized water (1200 ml). The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of ammonium hydroxide (35 g) under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 5–5.2. Next, hydrazine hydrate (250 g) was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0159] sample 4 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of ammonium hydroxide (10 g) under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.3–4.5. Next, hydrazine hydrate (200 g) was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0160] sample 5 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in deionized water (1200 ml). The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of ammonium hydroxide (24 g) under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.6–4.9. Next, hydrazine hydrate (110 g) was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0161] sample 6 : 100 g of copper(II) acetate monohydrate and 30 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 90 g of ammonium hydroxide under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 8–8.1. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., a Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0162] sample 7 : 100 g of copper(II) acetate monohydrate and 30 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 15 g of ammonium hydroxide under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.3–4.5. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., a Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0163] sample 8 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 24 g of 3-(dimethylamino)-1,2-propanediol (DMPA) with vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.1–4.3. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture with vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0164] sample 9 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 48 g of 3-(dimethylamino)-1,2-propanediol (DMPA) with vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.6–4.9. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture with vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0165] sample 10 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 96 g of 3-(dimethylamino)-1,2-propanediol (DMPA) with vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 4.8–5. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture with vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) at approximately 1300 rpm for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0166] sample 11 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 48 g of 3-(dimethylamino)-1,2-propanediol (DMPA) under vigorous stirring. The reaction mixture was stirred for another 15 minutes, followed by the dropwise addition of 10.5 g of ammonium hydroxide under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 5.1–5.3. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0167] sample 12 : 100 g of copper(II) acetate monohydrate and 30 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 mL of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 48 g of 3-(dimethylamino)-1,2-propanediol (DMPA) with vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 5–5.2. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture with vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) at approximately 1300 rpm for 4 hours, followed by the addition of 1200 mL of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0168] sample 13 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (30 g) were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of ammonium hydroxide (90 g) under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 8–8.1. Next, hydrazine hydrate (250 g) was added dropwise to the reaction mixture via a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone. The collected wet copper sintered powder, after filtration and washing, was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was then packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0169] sample 14 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. Next, 200 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The collected wet copper sintered powder after filtration and washing was air-dried in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0170] sample 15 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 28 g of polyvinylpyrrolidone (PVP 10 kDa; 28 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0171] sample 16 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 56 g of polyvinylpyrrolidone (PVP 10 kDa; 56 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0172] sample 17 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 84 g of polyvinylpyrrolidone (PVP 10 kDa; 84 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0173] sample 18 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 56 g of polyvinylpyrrolidone (PVP 30 kDa; 56 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0174] sample 19 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 28 g of polyvinylpyrrolidone (PVP 30 kDa; 28 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0175] sample 20 : Copper(II) nitrate trihydrate (100 g) and triethanolamine (20 g) were added to a 5 L beaker and dissolved in deionized water (1200 ml). The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of sodium hydroxide (20 g) dissolved in deionized water (200 ml) with vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of polyvinylpyrrolidone (PVP 30 kDa; 56 g) dissolved in water with stirring. The reaction mixture was stirred for another 15 minutes. Next, hydrazine hydrate (250 g) was added dropwise to the reaction mixture with vigorous stirring (approximately 1500–1600 rpm) via a dropping funnel. The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0176] sample 21 : 100 g of copper(II) nitrate trihydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 56 g of polyvinylpyrrolidone (PVP 10 kDa; 56 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0177] sample 22 : 100 g of copper(II) acetate monohydrate and 20 g of triethanolamine were added to a 5 L beaker and dissolved in 1200 ml of deionized water. The reaction mixture was then stirred for 15 minutes to prepare a homogeneous solution, followed by the dropwise addition of 20 g of sodium hydroxide dissolved in 200 ml of deionized water under vigorous stirring. The reaction mixture was stirred for another 15 minutes until the pH of the solution mixture was 7.2–7.5. The reaction mixture was then stirred for another 15 minutes to prepare a homogeneous solution, followed by the slow addition of 56 g of polyvinylpyrrolidone (PVP 360 kDa; 56 g) dissolved in water under stirring. The reaction mixture was stirred for another 15 minutes. Next, 250 g of hydrazine hydrate was added dropwise to the reaction mixture through a dropping funnel under vigorous stirring (approximately 1500–1600 rpm). The resulting reaction mixture was then stirred at room temperature (22 °C) (approximately 1300 rpm) for 4 hours, followed by the addition of 1200 ml of deionized water and stirring for another 15 minutes. The reaction mixture was then allowed to stand for 15 minutes to allow the precipitate to settle. The synthesized copper sintered powder was separated from the reaction mixture using standard laboratory filtration equipment and processes (e.g., Buchner funnel), followed by repeated washing with water, a water-acetone mixture, and acetone in sequence. The wet copper sintered powder collected after filtration and washing was dried in air in a standard box oven at a temperature range of 40°C. The dried copper sintered powder was packaged in vacuum-sealed containers for further storage, characterization, processing, and use.

[0178] Sample characterization

[0179] Detailed information on various characterization techniques and a summary of the detailed characterization results for samples 1-22 are as follows: (i) Instrument Details : a. JEOL JSM-7800F prime field emission scanning electron microscope (FE-SEM) is used for morphology studies and particle size measurement.

[0180] b. The surface microstructure was studied by transmission electron microscopy (TEM, T2O ST) operated at 200 kV.

[0181] c. By using Cu K at 40kV and 30mA Powder X-ray diffraction (p-XRD) patterns of the samples were collected using a RigakuSmartLab X-ray diffractometer operated by radiation (λ=0.15406nm).

[0182] d. Through dynamic light scattering technology (Microtrac, model name: Nanotrac ULTRA) ™ )Measure particle size distribution (PSD).

[0183] e. X-ray photoelectron spectroscopy (XPS) measurements were performed using a Thermo Fisher, K-α instrument, with monochromatic Al Kα X-rays.

[0184] f. Thermogravimetric analysis (TGA) The PerkinElmer TGA 8000 instrument is used to quantify organic coatings and adsorbed volatile substances in samples. Because copper is highly susceptible to oxidation, TGA measurements are performed in an inert atmosphere (N2 atmosphere).

[0185] (ii) Sample preparation method : a. FE-SEM samples are prepared by sprinkling copper sintered powder onto a carbon ribbon or by drop casting copper sintered powder dispersed in ethanol onto a Si wafer, followed by drying at 45°C.

[0186] b. By sintering copper powder (5×10) dispersed in ethanol -5 TEM samples were prepared by drop casting (mg / l) onto a carbon-coated copper TEM grid, followed by drying in an oven at 45°C and then drying in a vacuum overnight at room temperature.

[0187] c. DLS analysis was performed using copper sintered powder that was highly diluted in ethanol and well dispersed, prepared by ultrasonic treatment with a probe.

[0188] d. XPS analysis was performed on samples prepared by drop casting copper sintered powder (5 × 10⁻⁵ mg / L) dispersed in ethanol onto ethanol on a Si wafer, followed by drying at 45 °C.

[0189] (iii) Morphological characterization and particle size distribution measurement using FE-SEM, TEM and DLS : Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used for morphological characterization of various copper sintered powders. For example, Figure 1 A summary of uncovered ( Figure 1 (ae), representing samples 1-5 respectively, and amino alcohol (DMPA) coated with ( Figure 1 (fi) are FE-SEM micrographs of copper sintered powder samples 8-10 and 12, respectively. Furthermore, Figure 2 (a) shows an uncoated FE-SEM micrograph of (sample 14), and Figure 2 (bi) shows FE-SEM micrographs of PVP-coated copper sintered powders (samples 15-22, respectively). Figure 3 The following physical appearances are shown: (a) Sample 4, (b) Sample 5, (c) Sample 14, (d) Sample 9, (e) Sample 10 and (f) Sample 16. Table 1 below summarizes the physical appearance and average particle size (FE-SEM analysis) of samples 1-22.

[0190]

[0191] Table 1

[0192] Figure 4 (a) and (b) show TEM micrographs of uncoated copper sintered powder (samples 4 and 5, respectively), while Figure 4 (c and d) show the DMPA-coated copper sintered powder (sample 9). Furthermore, Table 2 summarizes the average particle size (TEM analysis) of samples 4, 5, and 9.

[0193]

[0194] Table 2

[0195] In addition, the particle size distribution (PSD) of Examples 1, 3-5, 8-10, 12 and 14-22 was measured using DLS technology, as summarized in Table 3.

[0196]

[0197] Table 3

[0198] Based on FE-SEM, TEM, and DLS characterization, the following properties of the copper sintered powder were revealed when organic coatings (such as PVP and DMPA) were used during synthesis: a. Average particle size (d50): 100nm-150nm, if measured and characterized using DLS technology. b. Shape: The mixture of faceted (“faceted particles”) and regular and irregular shaped nanoparticles was observed and characterized using FE-SEM. c. Size distribution: ○ As measured and characterized using TEM, a large number of particles with a size <50 nm are present. ○ As measured and characterized using DLS, TEM, and FE-SEM, there are particles with sizes up to 450 nm-800 nm. ○ DLS characterization shows the particle size distribution as follows: d10: 90nm-110nm d50: 130nm-160nm d90: 270nm-470nm Furthermore, based on FE-SEM, TEM, and DLS characterization, the following properties of the copper sintered powder were revealed when no organic coating was used during synthesis: a. Average particle size (d50): 200nm-500nm, if measured and characterized using DLS technology. b. Shape: The mixture of faceted (“faceted particles”) and regular and irregular shaped nanoparticles was observed and characterized using FE-SEM. c. Size distribution: ○ As measured and characterized using TEM, a large number of particles with a size of 150nm-250nm were found. ○ As measured and characterized using DLS, TEM, and FE-SEM, there are particles with sizes up to 1000 nm-1800 nm. ○ DLS characterization shows the particle size distribution as follows: d10: 120nm-160nm d50: 200nm-700nm d90: 1000nm-1800nm (iv) X-ray diffraction (p-XRD) characterization : p-XRD analysis was performed to assess the crystallinity of the copper sintered powder. Figure 5 The p-XRD patterns of various copper sintered powders (samples 4, 5, 9, and 14) are shown. The p-XRD diffraction patterns of the copper sintered powders are also compared with standard (PDF data) p-XRD data for Cu(0) (PDF 01-071-4609), Cu2O (PDF 01-073-6237), and CuO (PDF 01-078-0428). Figure 5 As shown in the image. Figure 5 The p-XRD patterns of the copper sintered powders shown can be identified as having a face-centered cubic (fcc) crystal structure, where strong peaks caused by the Cu(111), Cu(200), and Cu(220) crystal planes are clearly visible at (2θ values) 43.3°, 50.4°, and 74.1°, respectively. Cu was also observed in all samples. x The weak peak of O at 36.5°, with no other obvious oxide peaks visible, indicates that a very small amount of copper oxide (Cu₂O or CuO) can exist as a passivation layer for copper sintered powder.

[0199] (v) XPS characterization : XPS characterization of the copper sintered powder was performed to assess its chemical composition. For example, Figure 6 Sample 14 is shown. Figure 6 (a)], sample 4 [ Figure 6 (b)], Sample 5 Figure 6(c)] and sample 9 [ Figure 6 XPS full spectrum scan of sample 14 [d]. The presence of carbon, copper, oxygen, and nitrogen was confirmed in all samples. However, sample 14 [ Figure 6 The N1s peak intensity of (a) is very weak compared to other samples, indicating that nitrogen is present in very little in sample 14 compared to other samples.

[0200] also, Figure 7 Sample 14 is shown. Figure 7 (a)], sample 4 [ Figure 7 (b)], Sample 5 Figure 7 (c)] and sample 9[ Figure 7 (d) High-resolution Cu2p spectra. Since different oxidation states of copper occur at different binding energies (eV), peak fitting of high-resolution Cu2p spectra helps to understand the existence of different oxidation states of copper [Cu(0), Cu(I), and Cu(II)].

[0201] The Cu2p spectrum of sample 14 can be obtained as follows: Figure 7 The two spectra shown in (a) are deconvolved, which can be identified as having Cu(0) and copper oxide (I) oxidation states. The peak intensity of Cu(0) is significantly stronger than that of copper oxide (I), indicating that the presence of Cu(0) is the dominant oxidation state in Example 14. Furthermore, several literature reports confirm that the Cu2p spectrum [ Figure 7 The presence of the companion peak in [a] can be attributed to the oxidation of copper (i.e., copper oxide). Furthermore, the strong companion peak can be attributed to the Cu(II) oxidation state, while the weak companion peak can be attributed to the Cu(I) oxidation state. Therefore, Figure 7 The weak accompanying peak shown in (a) can be attributed to the presence of Cu2O in sample 14. Therefore, it can be concluded that a very thin shell of copper oxide (I) exists on copper (O) in sample 14.

[0202] In stark contrast, the Cu2p spectra of samples 4, 5, and 9 can be seen in... Figure 7 The three spectra shown in (bd) are deconvolved and can be specified as Cu(0), copper oxide (I), and / or copper(II) oxide (Cu). x O) and copper(II) hydroxide [Cu(OH)] 2 ]substance.

[0203] For example, the deconvolutioned Cu2p spectrum of sample 4 [ Figure 7[b] shows the presence of a strong accompanying peak signal, which clearly indicates that Cu(II) oxide is present as the main substance (as previously discussed). However, the peak intensity of Cu(0) is weaker than that of copper(II) oxide and copper(II) hydroxide in sample 4. Therefore, it can be concluded that a very thick or robust shell of copper(0) oxide and copper(II) hydroxide exists on the copper(0) in sample 4.

[0204] Furthermore, the Cu2p spectra of samples 5 and 9 are in Figure 7 As shown in (cd). Interestingly, in both Sample 5 and Sample 9, the peak intensity of Cu(0) is significantly stronger than that of copper oxide (I & II) and copper(II) hydroxide. Therefore, it can be concluded that a thin shell of copper(I & II) oxide and copper(II) hydroxide exists on copper(0) in Sample 5 and Sample 9.

[0205] (vi) Thickness of oxide layer in copper sintered powder (depth profiling technique followed by simultaneous XPS acquisition) : Depth profiling was used, followed by simultaneous XPS data acquisition, to analyze the thickness of the oxide layer in the copper sintered powder. Depth profiling uses an EX-06 ion beam (single atom) operating at 1000V (source energy) to etch the surface layers, revealing subsurface information. In this study, a total etching depth of 157 nm was performed in six steps, with each etching step lasting 55 seconds.

[0206] First, the sample is mounted on a sample holder, and the spectrum of the sample surface is recorded, along with atomic composition analysis. Next, a 2mm × 2mm square region of the sample is etched using an ion beam, and the spectrum of the sample surface is recorded, with atomic composition analysis performed again. This process (i.e., etching a 2mm × 2mm square region of the sample using an ion beam, followed by spectrum recording) is then repeated five times, with atomic composition analysis performed after each step.

[0207] Figure 8 Depth profiling (etch depth versus atomic percentage of carbon, oxygen, and copper) of different copper sintered powders is shown: Sample 14 [ Figure 8 (a)], sample 4 [ Figure 8 (b)], Sample 5 Figure 8 (c)] and sample 9 [ Figure 8 (d)].

[0208] It is clearly visible that as the etching depth increases, the atomic percentage of oxygen decreases while the atomic percentage of copper increases in these samples. For example, for sample 14 [ Figure 8 (a)], sample 4 [ Figure 8 (b)], Sample 5 Figure 8 (c)] and sample 9 [ Figure 8 [d] It was found that the atomic percentage of oxygen decreased from 40 atomic% to approximately 4 atomic%, 16 atomic%, 10 atomic% and 7 atomic% with the etch depth from 0 nm to 158 nm.

[0209] The thickness of the oxidized copper layer (e.g., Cu₂O, CuO, or Cu(OH)₂) surrounding the copper(O) nanoparticles can be estimated by determining the starting point (nm) at which the atomic percentage of oxygen begins to saturate. Figure 8 (Marked in the image for auxiliary observation). Furthermore, the percentage of oxygen atoms from these points did not show any significant change with increasing etching depth (nm). For example, for sample 14 [ Figure 8 (a)], sample 4 [ Figure 8 (b)], Sample 5 Figure 8 (c)] and sample 9 [ Figure 8 [d] The thickness of the oxidized copper layer (e.g., Cu2O, CuO, or Cu(OH)2) surrounding the copper (0) nanoparticles can be calculated to be 26 nm, 52 nm, 52 nm, and 40 nm, respectively. Therefore, we can conclude that the thickness of the oxidized copper varies in the range of approximately 20 nm to 60 nm for the measured copper sintered powder samples.

[0210] (vii) Thermogravimetric analysis (TGA) : Figure 9 The weight loss of various copper sintered powders as a function of temperature is shown, resulting from the decomposition of organic coatings and absorbed volatile substances. For example, Figure 9 (a) shows the weight loss of samples 4, 5, 9 and 10 due to the decomposition of organic coatings and absorbed volatile substances.

[0211] Because copper is highly oxidizable, even trace amounts of oxygen (ppm level) can convert metallic copper into copper oxide at temperatures above approximately >150°C. Therefore, temperatures above 150°C-175°C are suitable. Figure 9 The weight increase in (a) can be attributed to the formation of copper oxide.

[0212] Below approximately <170°C, removal of 3-(dimethylamino)-1,2-propanediol (DMPA) and any other volatile adsorbents (such as solvents or triethanolamine) is expected. Any weight loss in TGA analysis can be attributed to the quantification of organic coatings and adsorbed volatiles in the sample.

[0213] Therefore, when no additional coating agent was added during the synthesis of samples 4 and 5 (uncoated copper sintered powder), the weight loss observed in the TGA was found. Figure 9(a)] Up to about 150°C, the amount is on the order of <0.2%. This weight can be attributed to the removal of volatile adsorbed substances, while the formation of copper oxide at >150°C can be considered a sharp weight increase.

[0214] In contrast, when 3-(dimethylamino)-1,2-propanediol (DMPA) was added as a coating agent during the synthesis of samples 9 and 10 (DMPA-coated copper sintered powder), the weight loss observed in the TGA was not as significant. Figure 9 (a)] Up to about 180°C, the amount is on the order of about <0.6%. This weight can be attributed to the removal of DMPA and volatile adsorbed substances, while the formation of copper oxide at >180°C can be considered a sharp weight increase.

[0215] Since PVP is stable up to 400-450°C, small quantities of samples 16 and 17 were incubated at 150°C for 10 hours in an oven for analysis of PVP-coated copper sintered powder. This low-temperature heat treatment ensured that all metallic copper material was converted to copper oxide. This ensured that no further oxidation occurred during TGA analysis, and any weight loss could be attributed solely to the removal of the PVP coating from the copper sintered powder.

[0216] Interestingly, Figure 9 (b) shows the weight loss characteristics as a function of temperature, which are on the order of about 10%-12% up to about 500°C due to the decomposition of PVP 10 kDa from various PVP-coated copper sintered powders (samples 16 and 17).

[0217] (viii) Discussion : The combination of these reactant mixtures and their molar ratios were found to be highly efficient in controlling the reaction kinetics, which yielded copper sintered powders with the desired advantages. The effects of synthesis conditions (nature of the coating and / or pH) on the morphology and color of the copper sintered powders are summarized below: (a) Uncoated copper sintered powder: The following is an example of uncoated copper sintered powder: Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Sample 6, Sample 7, Sample 13 and Sample 14.

[0218] When the pH of the reaction medium is >5.2: these copper sintered powders form dark brown to black, irregularly shaped, hard, porous, and relatively large (0.7-2) μm particles, except for sample 14.

[0219] When the pH of the reaction medium is <5.2: these copper sintered powders form brown to dark brown, hard, irregularly shaped (spherical, plate-like, rod-like), non-faceted, and relatively large (0.2 μm-1.3 μm). These particles contain higher levels of oxides and higher particle size distribution (PSD) than desired.

[0220] (b) Copper sintered powder coated with 3-(dimethylamino)-1,2-propanediol (DMPA): The following are examples of copper sintered powders coated with 3-(dimethylamino)-1,2-propanediol (DMPA): Sample 8, Sample 9, Sample 10, Sample 11 and Sample 12.

[0221] These copper sintered powders form with a good copper-like color (pink to light brown), good faceting, soft properties, and small size (0.1 μm to 0.8 μm, some less than 0.05 μm).

[0222] These particles contain lower surface oxides and the desired PSD.

[0223] (c) Water-soluble polymer-coated (PVP) copper sintered powder: The following are examples of copper sintered powders coated with water-soluble polymer (PVP): Sample 15, Sample 16, Sample 17, Sample 18, Sample 19, Sample 20, Sample 21 and Sample 22.

[0224] These copper sintered powders form dark brown to black particles, spherical but not faceted, soft in nature, and very small in size, from 0.05 μm to 0.3 μm.

[0225] These particles contain high levels of surface oxides and very low and narrow PSD.

[0226] Sintering applications of copper sintered powder : Self-supported sintered copper foils were prepared using a stencil-printable copper nanoparticle paste, with copper sintered powder serving as a key component to exhibit sintering activity. The resistivity, density, and thermal conductivity of these self-supported sintered copper foils were measured in response to applied sintering pressure. The microstructure of these self-supported sintered copper foils was analyzed using FE-SEM to understand how densification changes with applied sintering pressure.

[0227] (a) Preparation of copper nanoparticle paste : The stencil-printable copper nanoparticle paste was prepared by mixing copper sintered powder (e.g., sample 9) with terpineol, epoxy acrylate resin, organic acid as an activator, and dispersing additives, and homogenizing these components using a laboratory high-speed roller mill. The homogeneous copper nanoparticle paste was then stored in a refrigerator at 4°C–8°C.

[0228] (b) Preparation of self-supporting sintered copper foil : First, copper nanoparticle paste is printed onto FR4 plates using a stencil. Second, the printed copper nanoparticle paste is dried in a laboratory oven at 80°C–120°C. Third, the printed and dried copper nanoparticle paste is further sintered using a laboratory press at different pressures (1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, and 30 MPa) at 260°C for 2 minutes to prepare self-supporting sintered copper foil. For example, Figure 10 Optical images are shown of self-supporting sintered copper foils prepared using a laboratory press at different pressures (a) 10 MPa, (b) 20 MPa and (c) 30 MPa for 2 minutes at 260 °C.

[0229] (c) Resistivity measurement of self-supporting sintered copper foil : The resistivity (surface resistivity and volume resistivity) of various self-supporting sintered copper foils was measured using a four-probe method. Measurements were performed using a Jandel (RM 3000+) four-probe measurement system with a constant probe pressure of 50g for better connectivity. For stand-alone electrical measurements, the sintered copper foil samples were mounted on a flat FR4 PCB board or glass plate for resistivity measurements.

[0230] The thickness of self-supporting sintered copper foil was measured using the HEIDENHAIN film thickness measurement system.

[0231] Using the film's resistance value and size, the volume resistivity (ρ) and surface resistivity (R) are obtained using the formulas given below. s ) and conductivity (C): Volume resistivity , Surface resistance, Rs = R × W / l R = resistance of the foil A = (Foil) Width (W) × Thickness (t) L = Length of the foil W = width of the foil electrical conductivity ( ) = 1 /

[0232] The resistivity (surface resistivity and volume resistivity) of various self-supported sintered copper foils prepared at different pressures of 1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa and 30 MPa (260 °C, for 2 minutes) was measured and compared with that of bulk copper. Figure 11 (and Table 4).

[0233]

[0234] Table 4

[0235] For example, the volume resistivity of self-supporting sintered copper foils prepared using 1 MPa and 5 MPa pressures, 260 °C temperature, and 2 minutes were 17 × 10⁻⁶. -08 Ω.m and 4.1×10 -08 Ω.m. Furthermore, the volume resistivity of self-supported sintered copper foil prepared using pressures ranging from 10 MPa to 30 MPa, temperatures of 260 °C, and a duration of 2 minutes was found to be 3.6 × 10⁻⁶ Ω.m. -08 Ω.m to 3.2×10 -08 Within Ω.m.

[0236] Interestingly, it was found that the volume resistivity of self-supporting sintered copper foil prepared using pressures >10 MPa and at 260 °C was approximately <2 times that of bulk copper. This is likely because as the pressure increases, the agglomeration of the copper sintering powder increases, leading to an increase in densification during the sintering process.

[0237] (d) Thermal conductivity measurement of self-supporting sintered copper foil : The in-plane thermal diffusivity (α) of self-supporting sintered copper foil was measured using a Netzsch laser flash instrument (LFA-447).

[0238] A specific in-plane sample holder is used to guide thermal energy along the sample, thus providing the corresponding in-plane thermal diffusivity value (α). The sample is cut to an appropriate size and placed in a specific stage and sample holder. For in-plane thermal diffusivity measurements, the surfaces need to be rough; they must have low emissivity, therefore a very thin graphite layer is deposited by graphite-spraying self-supporting sintered copper foil.

[0239] Thermal conductivity (K) is obtained by the following formula: K = ραC p Where ρ is the apparent mass density of the self-supporting sintered copper foil, and C p Let be the specific heat capacity of the membrane. The specific heat capacity of copper is known to be 0.385 J / g. -1 .℃ -1 .

[0240] The apparent mass density (ρ) of each self-supporting sintered copper foil is calculated using the formula ρ = m / v, where "ρ" is the apparent mass density, "m" is the mass, and "v" is the volume. This apparent mass density is needed to calculate the thermal conductivity (K) according to the above equation.

[0241] To calculate the apparent mass density (ρ), each self-supporting sintered copper foil was first cut into (l) 1.2 cm × (w) 1.2 cm pieces. Secondly, the average thickness of each self-supporting sintered copper foil was calculated by measuring the thickness (t) at nine different locations. Thirdly, the volume (v) of each self-supporting sintered copper foil was calculated by multiplying the length (l), width (w), and thickness (t). Finally, the weight (m) of each self-supporting sintered copper foil was measured using a standard laboratory balance.

[0242] Table 5 summarizes the typical apparent mass density (ρ), thermal diffusivity (α), and thermal conductivity (K) values ​​of 99.5% pure commercial copper foil, POCO graphite as a standard, and various self-supporting sintered copper foils prepared under different processing conditions (pressures of 30 MPa, 20 MPa, and 10 MPa, respectively, at 260 °C for 2 minutes).

[0243]

[0244] Table 5

[0245] The measured thermal diffusivity (α) and thermal conductivity (K) values ​​of pure commercial copper foil and POCO graphite were found to be in excellent agreement with reported literature. Interestingly, the density, thermal diffusivity, and thermal conductivity of the self-supporting sintered copper foil were found to increase with increasing sintering pressure, indicating that the degree of densification increases with variations in sintering pressure. The thermal conductivity of the self-supporting sintered copper foil disclosed in this invention is >60 W·m. -1 .K -1 .

[0246] (e) Microstructure analysis of self-supporting sintered copper foil : Figure 12(ae) shows FE-SEM images of the microstructure of self-supported sintered copper foils with various cross-sections sintered at 30 MPa, 20 MPa, 10 MPa, 5 MPa, and 1 MPa, respectively. Cross-sectional analysis of the self-supported sintered copper foils reveals very good densification, especially at pressures ≥10 MPa. Densification of the copper sintered powder increases significantly with increasing sintering pressure. For example, the diffusion and densification of samples prepared using 30 MPa are superior to those prepared using 1 MPa or 10 MPa. Furthermore, the highest densification is observed for a sintering pressure of 30 MPa, while the lowest densification is evident for a sintering pressure of 1 MPa. Higher pressures promote neck growth, grain growth, shrinkage, and elimination of porosity to produce a continuous metal layer. Therefore, it is clear that the excellent resistivity and thermal conductivity of the observed self-supported sintered copper foils are due to the densification of the copper sintered powder during sintering.

[0247] The combination of these properties is one of the key aspects of copper sintered powder. These characteristics allow for the achievement of very close-packed and high-density sintered structures using medium to low sintering conditions, such as temperature: <300°C and pressure: <35MPa.

[0248] These features can be used to develop copper sintering inks for several practical applications, such as for the production of high-current and solderable electronic circuits, the joining of two metal sheets, and the attachment of dies or electronic components to various metallized substrates, such as DBC and wafer bonding.

[0249] The detailed description above has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the preferred embodiments of the invention shown herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method for forming a sintered powder containing copper particles, the method comprising: Provides an aqueous solution containing copper ions, alkali, and a coating agent; The solution is brought into contact with a reducing agent to provide the sintered powder; as well as The sintered powder is recycled. in: Before contacting the solution with the reducing agent, the solution has a pH of 4 to 7; and The coating agent contains amino alcohols.

2. The method according to claim 1, wherein the solution has a pH of 4.1 to less than 7, preferably 4.2 to 6.5, more preferably 4.5 to 6, and even more preferably 4.8 to 5.5, before contacting the solution with the reducing agent.

3. The method according to claim 1 or claim 2, wherein the amino alcohol comprises two hydroxyl groups.

4. The method according to any of the preceding claims, wherein the hydroxyl group of the amino alcohol is located on a single aliphatic chain.

5. The method of claim 1, wherein the amino alcohol comprises two hydroxyl groups and both are located on the same aliphatic chain.

6. The method according to any of the preceding claims, wherein the amino alcohol comprises an alkyl amino alcohol, preferably a dialkyl amino alcohol.

7. The method according to any of the preceding claims, wherein the amino alcohol comprises a methyl amino alcohol, preferably a dimethyl amino alcohol.

8. The method according to any one of claims 1 to 3, wherein the amino alcohol comprises a dihydroamino alcohol.

9. The method according to any of the preceding claims, wherein the amino alcohol comprises one or more of 3-(dimethylamino)-1,2-propanediol, 3-(amino)-1,2-propanediol and 3-(methylamino)-1,2-propanediol, preferably 3-(dimethylamino)-1,2-propanediol.

10. The method according to any of the preceding claims, wherein providing the aqueous solution comprising copper ions, an alkali, and a coating agent comprises providing a solution comprising copper ions and an alkali, and then contacting the solution comprising copper ions and an alkali with a coating agent.

11. The method according to any of the preceding claims, wherein the copper ions in the solution are provided in the form of a copper salt, wherein the copper salt is preferably selected from one or more of copper(II) nitrate, copper(II) sulfate, copper(II) acetate, copper(II) formate, and copper(II) hydroxide, more preferably selected from one or both of copper(II) nitrate and copper(II) acetate, and even more preferably copper(II) nitrate.

12. The method according to any of the preceding claims, wherein the base comprises triethanolamine alone or together with a hydroxide, wherein the hydroxide is preferably selected from one or more of sodium hydroxide, potassium hydroxide and ammonium hydroxide, more preferably ammonium hydroxide.

13. The method according to any of the preceding claims, wherein the reducing agent comprises one or more of hydrazine, sodium borohydride and lithium borohydride, preferably hydrazine.

14. The method according to any of the preceding claims, wherein once the solution has been contacted with the reducing agent, the molar ratio of copper ions: base: coating agent: reducing agent in the solution is 0.2 to 1: 0.05 to 2: 0.2 to 1.5: 1 to 10.

15. The method according to any of the preceding claims, wherein the solution comprising copper ions, an alkali and a coating agent is contacted with the reducing agent for 1 hour to 20 hours, preferably 2 hours to 10 hours, more preferably 3 hours to 5 hours.

16. The method according to any preceding claim, wherein recovering the sintered powder comprises one or more of the following: decantation of the sintered powder into a solution, washing the sintered powder, and drying the sintered powder.

17. The method according to any of the preceding claims, wherein the drying is carried out in a non-inert atmosphere or in an inert atmosphere, the atmosphere preferably being air or nitrogen.

18. A sintered powder, said sintered powder being formed using the method according to any of the preceding claims.

19. A sintered powder comprising copper particles, wherein at least some of the copper particles are coated with a coating agent comprising an amino alcohol.

20. The sintered powder of claim 19, wherein at least some of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide.

21. The sintered powder according to claim 19 or claim 20, wherein the layer has a thickness of 20 nm to 60 nm, preferably 25 nm to 55 nm.

22. The sintered powder according to any one of claims 19 to 21, wherein the amino alcohol comprises two or more hydroxyl groups.

23. The sintered powder according to any one of claims 19 to 22, wherein the amino alcohol comprises 3 to 12 carbon atoms.

24. The sintered powder according to any one of claims 19 to 23, wherein the hydroxyl group of the amino alcohol is located on a single aliphatic chain.

25. The sintered powder according to any one of claims 19 to 24, wherein the amino alcohol comprises two hydroxyl groups and both are located on the same aliphatic chain.

26. The sintered powder according to any one of claims 19 to 25, wherein the amino alcohol comprises an alkyl amino alcohol, preferably a dialkyl amino alcohol.

27. The sintered powder according to any one of claims 19 to 26, wherein the amino alcohol comprises methyl amino alcohol, preferably dimethyl amino alcohol.

28. The sintered powder according to any one of claims 19 to 25, wherein the amino alcohol comprises a dihydroamino alcohol.

29. The sintered powder according to any one of claims 15 to 19, wherein the amino alcohol comprises one or more of 3-(dimethylamino)-1,2-propanediol, 3-(amino)-1,2-propanediol and 3-(methylamino)-1,2-propanediol, preferably 3-(dimethylamino)-1,2-propanediol.

30. The sintered powder according to any one of claims 19 to 29, wherein the sintered powder comprises 0.1% to 12% by weight, preferably up to 3% by weight, and more preferably up to 1% by weight of a coating agent based on the total weight of the sintered powder.

31. The sintered powder according to any one of claims 19 to 30, wherein the copper particles have: D90 from 270nm to 470nm, and / or D50 from 130nm to 160nm, and / or D10 from 90nm to 110nm.

32. The sintered powder according to any one of claims 19 to 31, wherein the copper particles have: D90 from 270nm to 470nm D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

33. The sintered powder according to any one of claims 19 to 32, wherein the copper particles have: The D90 ranges from 420nm to 470nm. D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

34. The sintered powder according to any one of claims 19 to 32, wherein the copper particles have: The D90 ranges from 270nm to 350nm. D50 from 130nm to 160nm, and D10 from 90nm to 110nm.

35. The sintered powder according to any one of claims 19 to 34, wherein the copper particles comprise faceted particles.

36. A sintered powder comprising copper particles, wherein at least some of the copper particles are at least partially coated with a layer comprising copper oxide and copper hydroxide, the layer having a thickness of 20 nm to 60 nm, preferably 25 nm to 55 nm.

37. A sintering paste comprising sintering powder according to any one of claims 18 to 36.

38. A sintered membrane comprising sintered powder according to any one of claims 18 to 36.

39. A method for forming a joint between two or more workpieces, the method comprising: Provide two or more workpieces to be joined. Sintering powder according to any one of claims 18 to 36 and / or sintering paste according to claim 37 and / or sintering film according to claim 38 are provided near the two or more workpieces. The sintering powder and / or the sintering paste and / or the sintering film are heated to at least partially sinter the copper particles.

40. The method of claim 39, wherein the two or more workpieces comprise a die and a substrate.

41. Use of the sintered powder according to any one of claims 18 to 36 and / or the sintered paste according to claim 37 and / or the membrane according to claim 38 in a manner selected from: die attachment; component attachment; package attachment; electronic device attachment; wafer-to-wafer bonding; hermetic and near-hermetic sealing; sintering a membrane comprising sintered powder and an adhesive formed in a film on a backing layer; dispensing and generating interconnects.

42. Use of the sintered powder according to any one of claims 18 to 36 and / or the sintered paste according to claim 37 and / or the film according to claim 38 in the manufacture of additive printed structures, human-machine interface (HMI) electronics, capacitive switches, wire harnesses, solderable electronic circuits and devices, IME structures, structured / embedded electronic devices, large-area electronic devices, lighting / luminaires, large-area lighting, flexible and formable displays, embedded sensors, printed battery assemblies, printed heaters, flexible circuits and cables, Cu-coated dielectric materials, die attachment applications, or encapsulation attachment and component attachment applications.

43. A sintered joint, said sintered joint being formed using sintering powder according to any one of claims 18 to 36 and / or sintering paste according to claim 37 and / or sintering film according to claim 38 and / or the method according to claim 39 or 40.

44. Use of amino alcohols containing two hydroxyl groups as coating agents for copper particles.

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