Copper nanofluids, plating methods and seed layers

Abstract

This invention relates to a copper nanofluid, a plating method, and a seed layer. The problem this invention aims to solve is to form a well-adhesive coating in ceramics, engineering plastics, etc., without using a precious metal catalyst. The copper nanofluid of this invention comprises copper nanoparticles dispersed in a solvent and aminosilane triol dissolved in the solvent. The solvent contains propylene glycol monomethyl ether. The plating method of this invention forms a coating (4) by electroless copper plating on a seed layer (3) formed by heating and curing the copper nanofluid (2). The seed layer (3) of this invention is composed of a substance formed by heating and curing the copper nanofluid (2), formed on the surface of the adherend, containing copper nanoparticles, forming siloxane bonds formed by the dehydration condensation of aminosilane triol, and without residual aminosilane triol.

Description

Technical Field

[0001] This invention relates to a copper nanofluid, a plating method using the copper nanofluid, and a seed layer formed using the copper nanofluid. Background Technology

[0002] As catalysts for non-electrolytic plating processes, precious metal catalysts such as palladium and silver are commonly used. Palladium (Pd) is the most frequently used precious metal catalyst (see, for example, Patent Document 1). However, palladium prices fluctuate greatly, and future prices remain opaque, leading to concerns about a low-cost and stable supply. Furthermore, the high catalytic activity of palladium catalysts, coupled with the need for a removal process, contributes to a decrease in the insulation reliability of circuits formed by plating.

[0003] On the other hand, a method for electroless copper plating of a substrate using a copper microparticle layer as a seed layer is known (see Patent Document 2). In this method, the substrate (adherent) is a transparent insulating material such as polyethylene terephthalate. However, this method is difficult to implement in ceramics and engineering plastics.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 63-4075.

[0007] Patent document 2: Japanese Patent Application Publication No. 2020-43234. Summary of the Invention

[0008] The present invention aims to solve the above-mentioned problems, and its purpose is to form a well-adhesive coating in ceramics, engineering plastics and the like without using precious metal catalysts.

[0009] The copper nanofluid of the present invention is characterized by having a solvent, copper nanoparticles dispersed in the solvent, and aminosilane triol dissolved in the solvent, wherein the solvent contains propylene glycol monomethyl ether.

[0010] In this copper nanofluid, the aminosilane triol is preferably selected from the group consisting of 3-aminopropylsilane triol, 1-(pyridin-2-yl)-3-(3-(trihydroxysilyl)propyl)urea, 1-butyl-3-(3-(trihydroxysilyl)propyl)thiourea, N-2-(aminoethyl)-3-aminopropylsilane triol, and N-2-(aminoethyl)-8-aminooctylsilane triol.

[0011] The plating method of the present invention is a plating method for forming a coating using the copper nanofluid, characterized in that non-electrolytic copper plating is performed on a seed layer formed by solidifying the copper nanofluid by heating to form a coating.

[0012] The plating method preferably includes: a step of roughening the surface of a substrate made of ceramic; a step of treating the roughened surface of the substrate to be exposed to active oxygen species; a step of coating the surface of the treated substrate with the copper nanofluid; a step of curing the coated copper nanofluid by heating to form a seed layer; and a step of performing electroless copper plating on the seed layer to form a coating film.

[0013] The plating method may also include: a step of coating a substrate with a primer containing a thermoplastic resin to form a resin layer; a step of performing a treatment to expose the surface of the resin layer to active oxygen species; a step of coating the surface of the treated resin layer with the copper nanofluid; a step of curing the coated copper nanofluid by heating to form a seed layer; and a step of performing electroless copper plating on the seed layer to form a coating film.

[0014] In this coating method, the treatment of exposure to active oxygen species is preferably a surface treatment selected from the group consisting of corona treatment, plasma treatment, vacuum ultraviolet treatment and ozone treatment.

[0015] The seed layer of the present invention is characterized in that the seed layer is composed of a substance formed by solidifying the copper nanofluid by heating, the seed layer is formed on the surface of the adhered object, the seed layer contains the copper nanoparticles, the seed layer forms siloxane bonds formed by the dehydration condensation of aminosilanetriol, and there is no aminosilanetriol residue.

[0016] In this seed layer, the adherend is preferably made of ceramic with a roughened surface.

[0017] In this seed layer, the adherend may also have a resin layer containing thermoplastic resin on its surface.

[0018] According to the copper nanofluid of the present invention, propylene glycol monomethyl ether prevents the hydroxyl groups of aminosilanetriol from undergoing dehydration condensation at room temperature. Due to the weak interaction between the amine and copper, aminosilanetriol is unlikely to cause copper nanoparticles to aggregate. Therefore, this copper nanofluid can be stably stored and can be used without a pre-process that converts methoxy groups to hydroxyl groups. Since copper nanoparticles act as a catalyst for electroless copper plating, the copper nanofluid can be used to form a seed layer for electroless copper plating. The adhesion of the seed layer is improved through the siloxane bonds formed by the dehydration condensation of aminosilanetriol. Thus, a coating with good adhesion can be formed. Attached Figure Description

[0019] Figure 1 (a) to (e) are cross-sectional structural diagrams showing the plating method of the first embodiment of the present invention in chronological order.

[0020] Figure 2 (a) to (e) are cross-sectional structural diagrams showing the plating method of the second embodiment of the present invention in chronological order.

[0021] The annotations in the attached figures are explained below.

[0022] 1: Substrate.

[0023] 11: The surface of the substrate.

[0024] 2: Copper nanofluid.

[0025] 3: Seed layer.

[0026] 4: Coating formed by non-electrolytic copper plating.

[0027] 5: Copper plating is formed by electroplating.

[0028] 6: Resin layer. Detailed Implementation

[0029] An embodiment of the copper nanofluid of the present invention will be described. This copper nanofluid can be used to form a seed layer for electroless copper plating. The copper nanofluid comprises a solvent, copper nanoparticles, and aminosilanetriol. The copper nanoparticles are dispersed in the solvent. The aminosilanetriol is dissolved in the solvent. The solvent contains propylene glycol monomethyl ether.

[0030] Nanofluids are fluids containing nanoparticles. Copper nanofluids are nanofluids containing copper nanoparticles and are in the form of a paste or liquid.

[0031] Copper nanoparticles serve as a catalyst in electroless copper plating. Copper nanoparticles are nanoparticles of copper, specifically those with a median particle size (D). 50 The copper nanoparticles are copper particles larger than 1 nm and smaller than 1 μm, preferably copper particles with a median particle size of 1 nm or larger and less than 100 nm. The copper nanoparticles can be copper particles with a single median particle size or a mixture of copper particles with different median particle sizes. The particle size of the copper nanoparticles is extracted from images obtained by scanning electron microscopy (SEM images), and the median particle size can be calculated based on its particle size distribution. It is necessary for the copper nanoparticles to be dispersed in a solvent; if the median particle size is greater than 100 nm, the dispersion stability is poor due to the increased particle weight. A dispersant can also be added to the copper nanofluid to disperse the copper nanoparticles in the solvent.

[0032] For copper nanoparticles, the solvent functions as a dispersion medium and is a liquid that dissolves aminosilanetriol. The solvent can be a mixture of propylene glycol monomethyl ether and other solvents, or it can be propylene glycol monomethyl ether alone.

[0033] Aminosilanetriol is a silane coupling agent that improves the adhesion of the seed layer and the adhesion of the coating formed on the seed layer by electroless copper plating.

[0034] Aminosilanetriols are organosilicon compounds having one amino group and three hydroxyl groups (silanol groups) covalently bonded to a silicon atom. For example, 3-aminopropylsilanetriol is an example of an aminosilanetriol. Aminosilanetriols can also be 1-(pyridin-2-yl)-3-(3-(trihydroxysilyl)propyl)urea, 1-butyl-3-(3-(trihydroxysilyl)propyl)thiourea, N-2-(aminoethyl)-3-aminopropylsilanetriol, or N-2-(aminoethyl)-8-aminooctylsilanetriol.

[0035] Typical silane coupling agents contain methoxy groups and require a pre-treatment step of hydrolysis to convert the methoxy group to a hydroxyl group before use. For example, 3-aminopropylsilanetriol is derived from 3-aminopropyltrimethoxysilane. 1-(pyridin-2-yl)-3-(3-(trihydroxysilyl)propyl)urea is derived from 1-(pyridin-2-yl)-3-(3-(trimethoxysilyl)propyl)urea. 1-Butyl-3-(3-(trihydroxysilyl)propyl)thiourea is derived from 1-butyl-3-(3-(trimethoxysilyl)propyl)thiourea. N-2-(aminoethyl)-3-aminopropylsilanetriol is derived from N-2-(aminoethyl)-3-aminopropyltrimethoxysilane. N-2-(aminoethyl)-8-aminooctylsilanetriol is derived from N-2-(aminoethyl)-8-aminooctyltrimethoxysilane. The converted silane coupling agent, because its hydroxyl groups are in an active state, was previously difficult to preserve. Furthermore, solvents containing the converted silane coupling agent previously struggled to stably disperse copper nanoparticles.

[0036] In the copper nanofluid of this embodiment, propylene glycol monomethyl ether stabilizes aminosilane triol.

[0037] Because the copper nanofluid contains aminosilanetriol, a pre-process to convert methoxy groups to hydroxyl groups is unnecessary during use. Propylene glycol monomethyl ether prevents the hydroxyl groups of aminosilanetriol from undergoing dehydration condensation at room temperature. It should be noted that adjusting the pH of the copper nanofluid further prevents the dehydration condensation of the hydroxyl groups of aminosilanetriol. This is because the rate of the dehydration condensation reaction varies with pH. Furthermore, due to the weak interaction between the amine and copper, aminosilanetriol is unlikely to cause copper nanoparticle aggregation. Therefore, this copper nanofluid can be stored stably and can be used without the need for a pre-process to convert methoxy groups to hydroxyl groups. Since copper nanoparticles act as a catalyst for electroless copper plating, the copper nanofluid can be used for the formation of seed layers for electroless copper plating without the need for additional catalysts. The adhesion of the seed layer is improved through the siloxane bonds formed by the dehydration condensation of aminosilanetriol.

[0038] The plating method of the present invention is a method for forming a coating film using the aforementioned copper nanofluid. This method involves performing electroless copper plating on a seed layer to form the coating film. The seed layer is formed by solidifying the copper nanofluid through heating.

[0039] Reference Figure 1 Sections (a) to (e) describe the plating method according to the first embodiment of the present invention. The substrate 1 is made of ceramic. The ceramic is, for example, alumina (Al2O3), aluminum nitride (AlN), silicon nitride (Si3N4), or MgTiO3-CaTiO3-based dielectric ceramic.

[0040] like Figure 1 As shown in (a), the surface 11 of the substrate 1 is roughened. The surface 11 of the substrate 1 is roughened by an alkaline treatment or an acid treatment. Alkaline treatment, for example, is performed on aluminum nitride. In alkaline treatment, a strong alkali such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is used. The surface 11 of the substrate 1 after alkaline treatment is washed with water. In acid treatment, a strong acid such as hydrofluoric acid or a chromic acid-sulfuric acid mixture is used. The surface 11 of the substrate after acid treatment is neutralized and washed with water. Then, a treatment is performed to expose the roughened surface 11 of the substrate 1 to active oxygen species. In this embodiment, this treatment is a corona treatment. Corona treatment is a surface treatment that changes the properties of the substrate surface within the space where active oxygen species generated by corona discharge exist. The treatment of exposing the surface 11 of the substrate 1 to active oxygen species is not limited to corona treatment; it can also be a surface treatment such as plasma treatment, vacuum ultraviolet treatment, or ozone treatment.

[0041] In the following processes, such as Figure 1As shown in (b), copper nanofluid 2 is coated on the surface 11 of the substrate 1 that has undergone the above treatment. For example, a spraying method is used to coat the copper nanofluid 2. Spraying can coat a three-dimensional object. Spin coating and dip coating methods can also be used to coat the copper nanofluid 2.

[0042] In the next process (curing process), such as Figure 1 As shown in (c), a seed layer 3 is formed by curing the coated copper nanofluid 2 by heating. This process is carried out under atmospheric conditions. The specific heating temperature and heating time necessary for the curing of the copper nanofluid 2 are design considerations. For example, the heating temperature is 130°C and the heating time is 5 minutes. Since copper nanoparticles are contained in the copper nanofluid 2, they are also contained in the seed layer 3 of the cured copper nanofluid 2.

[0043] On the surface 11 of substrate 1, moisture from the air exists as adsorbed water. Through corona treatment or the like, reactive oxygen species such as ozone and oxygen free radicals generated by corona discharge break the bonds on the surface of substrate 11, and react with the adsorbed water on the substrate surface, increasing the number of hydroxyl groups. The aminosilanetriol contained in the copper nanofluid 2 has silicon atoms and hydroxyl groups (silanol groups). In this process (curing process), siloxane bonds formed by the dehydration condensation of aminosilanetriol are formed between silicon atoms and the surface 11 of substrate 1 and between silicon atoms and copper nanoparticles. Seed layer 3 is formed through these siloxane bonds, and seed layer 3 is tightly bonded to substrate 1. The remaining hydroxyl groups of aminosilanetriol are in an active state, and thus form siloxane bonds through dehydration condensation between the hydroxyl groups. Therefore, no aminosilanetriol remains in seed layer 3.

[0044] In the following processes, such as Figure 1 As shown in (d), electroless copper plating is performed on the seed layer 3 to form the coating 4. In this process, the seed layer 3 is first activated by immersion in a 10% sulfuric acid aqueous solution. Then, it is immersed in a plating solution, and the coating 4 is formed on the seed layer 3 by electroless copper plating. The copper nanoparticles in the seed layer 3 act as a catalyst in the electroless copper plating.

[0045] Then, as Figure 1 As shown in (e), the coating 4 formed by non-electrolytic copper plating can also be used as the cathode, and the coating 5 can be formed by electroplating copper. The coating is thickened by electroplating copper. Electroplating copper can also be omitted. Then, coatings 4 and 5 are subjected to annealing. Annealing is a heat treatment that improves the properties of the material by heating the material, holding it at a constant temperature, and then slowly cooling it to remove internal stress.

[0046] According to the plating method of this embodiment, since the copper nanofluid 2 contains aminosilane triol, and in the seed layer 3, the siloxane bond formed by the dehydration condensation of aminosilane triol is formed between the substrate 1 and the copper nanoparticles, the seed layer 3 is tightly bonded to the substrate 1 and can form a coating 4 with good adhesion.

[0047] Reference Figure 1 Sections (b) to (d) will describe the seed layer of the first embodiment of the present invention. The seed layer 3 of this embodiment is a layer used for electroless copper plating onto a substrate. The substrate is the object to be plated. The seed layer 3 of this embodiment is formed using the aforementioned copper nanofluid and the plating method of the first embodiment.

[0048] Seed layer 3 is composed of a substance formed by solidifying copper nanofluid 2 through heating (see reference). Figure 1 (b) to (c)). Seed layer 3 is formed on the surface of the adhered material.

[0049] In this embodiment, the adherend is a substrate 1 whose surface 11 is roughened, and the substrate 1 is made of ceramic. That is, the adherend is a ceramic with a roughened surface. The ceramic is, for example, alumina (Al2O3), aluminum nitride (AlN), silicon nitride (Si3N4), and MgTiO3-CaTiO3 dielectric ceramics.

[0050] Seed layer 3 contains copper nanoparticles. Since the copper nanoparticles are contained in copper nanofluid 2, they are also contained in the seed layer 3, which is solidified with copper nanofluid 2. Therefore, seed layer 3 can be configured as a single layer, without the need for separate layers of silane coupling agent and copper nanoparticles.

[0051] If the surface of the solidified seed layer 3 is observed using a scanning electron microscope (SEM) at 5,000x and 50,000x magnification, copper nanoparticles are exposed on the surface of the seed layer 3.

[0052] Seed layer 3 has siloxane bonds formed by the dehydration condensation of aminosilanetriol, and no aminosilanetriol remains.

[0053] The presence of siloxane bonds can be confirmed, for example, by infrared spectroscopy. In infrared spectroscopy, the seed layer 3 is irradiated with infrared light, and the reflected light is dispersed to obtain a spectrum. In the presence of siloxane bonds, a peak representing a Si-O bond is observed in the spectrum.

[0054] The formation of siloxane bonds between the seed layer 3, copper nanoparticles, and adherent material can be confirmed by the ability to form a coating through non-electrolytic plating of the seed layer 3 and by the adhesion of the coating.

[0055] Aminosilanetriol is active when heated and does not remain in the seed layer 3.

[0056] If a scanning electron microscope is used to observe the surface of seed layer 3 before and after curing at 5,000x and 50,000x, aminosilanetriol, although it appears as a dotted distribution before curing, cannot be observed after curing.

[0057] According to the seed layer 3 of this embodiment, since it contains copper nanoparticles, the copper nanoparticles can act as a catalyst to perform electroless copper plating on the seed layer 3 (see reference). Figure 1 (d)). Seed layer 3 is tightly bonded to the adherend (a roughened ceramic surface) via siloxane bonds.

[0058] Reference Figure 2 Sections (a) to (e) describe the plating method according to the second embodiment of the present invention. In the second embodiment, the same reference numerals are used in the same places as in the first embodiment. Detailed descriptions of the places equivalent to those in the first embodiment will be omitted in the following description. In the second embodiment, since surface roughening of the substrate 1 is not required, it is suitable for applications where the smoothness of the substrate 1 is desired. The substrate 1 is, for example, made of an engineering plastic. This engineering plastic is, for example, polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), and polyetheretherketone (PEEK). These engineering plastics are difficult to plating materials, and it has been difficult to form a coating with good adhesion in the past.

[0059] like Figure 2 As shown in (a), a primer containing a thermoplastic resin is applied to the substrate 1 to form a resin layer 6. In this embodiment, the primer contains a thermoplastic polyimide and a multifunctional epoxy resin. The thermoplastic polyimide is a thermoplastic resin. The multifunctional epoxy resin is in a semi-cured state at room temperature and bonds the resin layer 6 to the substrate. The primer may also contain bismaleimide and dicumyl peroxide. Bismaleimide is a thermoplastic resin. Dicumyl peroxide is a crosslinking agent upon heating. The applied primer is cured to form the resin layer 6. The resin layer 6 adheres tightly to the substrate 1. Then, a treatment is performed to expose the surface of the resin layer 6 to active oxygen species. In this embodiment, this treatment is a corona treatment. The treatment to expose the surface of the resin layer 6 to active oxygen species is not limited to corona treatment, but may also be a surface treatment such as plasma treatment, vacuum ultraviolet treatment, or ozone treatment.

[0060] In the following processes, such as Figure 2 As shown in (b), copper nanofluid 2 is coated onto the surface of the resin layer 6 after the above treatment. For example, a spray coating method is used to coat the copper nanofluid 2. Spin coating and dip coating methods can also be used to coat the copper nanofluid 2.

[0061] In the next process (curing process), such as Figure 2As shown in (c), a seed layer 3 is formed by curing the coated copper nanofluid 2 by heating. This process is carried out under atmospheric conditions. For example, the heating temperature is 130°C and the heating time is 5 minutes. Since copper nanoparticles are contained in the copper nanofluid 2, they are also contained in the seed layer 3 after the copper nanofluid 2 has been cured.

[0062] On the surface of resin layer 6, reactive oxygen species such as ozone and oxygen free radicals generated by corona discharge, etc., cleave the carbon bonds of the resin and combine with oxygen in the air, thereby undergoing oxidation, and increasing the number of polar functional groups such as hydroxyl, carbonyl, and carboxyl groups. Copper nanoparticles are attached with hydroxyl groups. The aminosilanetriol contained in copper nanofluid 2 has silicon atoms and hydroxyl groups. In this process (curing process), siloxane bonds formed by the dehydration condensation of aminosilanetriol are formed between silicon atoms and the surface of resin layer 6, and between silicon atoms and copper nanoparticles. Through these siloxane bonds, a seed layer 3 is formed, and the seed layer 3 is tightly bonded to resin layer 6. Since the remaining hydroxyl groups of aminosilanetriol are in an active state, siloxane bonds formed by dehydration condensation are formed between the hydroxyl groups. Therefore, no aminosilanetriol remains in the seed layer 3.

[0063] In the following processes, such as Figure 2 As shown in (d), electroless copper plating is performed on the seed layer 3 to form the coating 4. In this process, the seed layer 3 is first activated by immersion in a 10% sulfuric acid aqueous solution. Then, it is immersed in a plating solution, and the coating 4 is formed on the seed layer 3 by electroless copper plating. The copper nanoparticles in the seed layer 3 act as a catalyst in the electroless copper plating.

[0064] Then, as Figure 2 As shown in (e), the coating 4 formed by non-electrolytic copper plating can also be used as the cathode to form the coating 5 formed by electroplated copper. The coating is thickened by copper electroplating. Alternatively, the copper electroplating can be omitted. Then, coatings 4 and 5 are annealed.

[0065] According to the plating method of this embodiment, since the copper nanofluid 2 contains aminosilane triol, and in the seed layer 3, the siloxane bond formed by the dehydration condensation of aminosilane triol is formed between the resin layer 6 and the copper nanoparticles, the seed layer 3 is closely bonded to the resin layer 6, and since the resin layer 6 is closely bonded to the substrate 1 by thermoplastic resin, a coating 4 with good adhesion can be formed.

[0066] Reference Figure 2 Sections (b) to (d) will describe the seed layer of the second embodiment of the present invention. The seed layer 3 of this embodiment is a layer used for electroless copper plating onto a substrate. The substrate is the object to be plated. The seed layer 3 of this embodiment is formed using the aforementioned copper nanofluid and the plating method of the second embodiment.

[0067] Seed layer 3 is composed of a substance formed by solidifying copper nanofluid 2 through heating (see reference). Figure 2 (b) to (c)). Seed layer 3 is formed on the surface of the adhered material.

[0068] In this embodiment, the adherend is a substrate 1 having a resin layer 6 on its surface. The substrate 1 is, for example, made of an engineering plastic. This engineering plastic is, for example, polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), and polyetheretherketone (PEEK). The resin layer 6 contains a thermoplastic resin. That is, the adherend has a resin layer 6 containing a thermoplastic resin on its surface.

[0069] The thermoplastic resin of resin layer 6 has good adhesion to substrate 1, and preferably is a resin that readily forms siloxane bonds.

[0070] Seed layer 3 contains copper nanoparticles. Since the copper nanoparticles are contained in copper nanofluid 2, they are also contained in the seed layer 3, which is solidified with copper nanofluid 2. Therefore, seed layer 3 can be a single layer and does not need to be divided into a silane coupling agent layer and a copper nanoparticle layer.

[0071] Seed layer 3 has siloxane bonds formed by the dehydration condensation of aminosilanetriol, and no aminosilanetriol remains.

[0072] According to the seed layer 3 of this embodiment, since it contains copper nanoparticles, the copper nanoparticles act as a catalyst to enable electroless copper plating to be performed in the seed layer 3 (see reference). Figure 2 (d) The seed layer 3 is bonded to the resin layer 6 via siloxane bonds. The resin layer 6 is bonded to the substrate 1 via thermoplastic resin.

[0073] [Example 1]

[0074] The copper nanofluid of this invention was prepared. The solvent was a mixture of propylene glycol monomethyl ether and hexanediol. 3-Aminopropylsilanetriol (a silane coupling agent) was dissolved in the solvent. Copper nanoparticles with a median particle size of 1 nm to 100 nm were used. A dispersant (manufactured by BYK Company, trade name "DISPERBYK-111") was added to the solvent to disperse the copper nanoparticles. The pH of the copper nanofluid was then adjusted.

[0075] The concentration of copper nanoparticles in the copper nanofluid was set to 8% by weight. The concentration of the dispersant was set to 0.32% by weight. The concentration of the silane coupling agent was set to 1% by weight. The concentration of propylene glycol monomethyl ether was set to 19% by weight. The remainder was hexanediol.

[0076] Using the prepared copper nanofluid and the plating method of the first embodiment, a seed layer was formed on the surface of a substrate made of AlN (aluminum nitride) ceramic. The heating temperature of the copper nanofluid used to form the seed layer was set to 130°C and the heating time was set to 5 minutes. Then, electroless copper plating was attempted on the seed layer. Electroless copper plating precipitated and formed a film.

[0077] The adhesion of the coating was evaluated using a tape peel test. To conduct the tape peel test, the coating was thickened to 0.5–1.0 μm using electroless copper plating. The tape peel test was performed according to ASTM standard D2259. In this standard, 6 longitudinal × 6 transverse slits were cut into the coating to create 25 squares of 2 mm × 2 mm size. The tape peel test was then conducted, and the adhesion was evaluated based on the proportion of peeled area.

[0078] In the tape peel test, the coating exhibited good adhesion.

[0079] [Example 2]

[0080] Experiments were conducted by varying the concentration of the silane coupling agent. The concentration of the silane coupling agent in the copper nanofluid was set to 2% by weight (higher than in Example 1). All other experimental conditions were the same as in Example 1. Electroless copper plating was attempted using the prepared copper nanofluid. Electroless copper plating precipitated and formed a film. The film exhibited good adhesion in the tape peel test.

[0081] [Example 3]

[0082] The concentration of the silane coupling agent in the copper nanofluid was set to 3% by weight (higher than in Examples 1 and 2). All other test conditions were the same as in Examples 1 and 2. Electroless copper plating was attempted using the prepared copper nanofluid. Electroless copper plating precipitated and formed a film. The film exhibited good adhesion in the tape peel test.

[0083] (Comparative Example 1)

[0084] The concentration of the silane coupling agent in the copper nanofluid was set to 0.3% by weight (far lower than in Example 1). All other test conditions were the same as in Example 1. Electroless copper plating was attempted using the prepared copper nanofluid. Electroless copper plating was deposited, forming a film. However, the film peeled off in a tape peel test.

[0085] The concentration of silane coupling agent in copper nanofluid is too low to achieve the effect of improved adhesion through silane coupling agent. Although a coating is formed, the adhesion of the coating is poor.

[0086] (Comparative Example 2)

[0087] The concentration of the silane coupling agent in the copper nanofluid was set to 5% by weight (higher than in Examples 1-3). All other test conditions were the same as in Examples 1-3. Electroless copper plating was attempted using the prepared copper nanofluid. Electroless copper plating was achieved. The plating was successfully peeled off in a tape peel test.

[0088] With the addition of silane coupling agent, the dispersibility of copper nanoparticles is destroyed. Although non-electrolytic copper plating is produced, the coating lacks adhesion.

[0089] (Comparative Example 3)

[0090] The concentration of the silane coupling agent in the copper nanofluid was set to 10% by weight (higher than Comparative Example 2). All other test conditions were the same as in Comparative Example 2. Electroless copper plating was attempted using the prepared copper nanofluid. Slight electroless copper plating occurred. The coating peeled off in a tape peel test.

[0091] By further increasing the concentration of the silane coupling agent in the copper nanofluid, electroless copper plating failed to form a uniform in-plane coating. The coating adhesion was also poor.

[0092] (Comparative Example 4)

[0093] The concentration of the silane coupling agent in the copper nanofluid was set to 20% by weight (higher than Comparative Example 3). All other experimental conditions were the same as in Comparative Example 3. Electroless copper plating was attempted using the prepared copper nanofluid. No electroless copper plating was achieved.

[0094] (Comparative Example 5)

[0095] The concentration of the silane coupling agent in the copper nanofluid was set to 50% by weight (higher than Comparative Example 4). All other experimental conditions were the same as in Comparative Example 4. Electroless copper plating was attempted using the prepared copper nanofluid. No electroless copper plating was observed.

[0096] By comparing Examples 4 and 5, it can be seen that if the concentration of silane coupling agent in the copper nanofluid is too high, non-electrolytic copper plating will not be deposited.

[0097] Examples 1-3 and Comparative Examples 1-5 demonstrate that a suitable concentration range exists for the silane coupling agent in copper nanofluids. This suitable concentration range for the silane coupling agent can be discovered through experimentation.

[0098] Then, tests were conducted to evaluate the adhesion of the formed film by varying the silane coupling agent in the copper nanofluid. Adhesion was evaluated using a 90° peel test (JIS K6854-1:1999). For the 90° peel test, the film thickness was increased to 30 μm by electroplating copper after non-electrolytic copper plating.

[0099] The 90° peel test (JIS K6854-1:1999) is described below. A 10×50 mm piece of specimen dried at 120°C was cut as a peel test piece. Approximately 5 mm was peeled off from one end of the peel test piece, and the substrate side was adhered to the substrate using double-sided tape. The coated side was then fixed to the measuring fixture of a peel strength testing machine. The peel speed was set to 50 mm / min, and the peel distance was set to 20 mm or more. The peel strength was then measured. Since peel strength represents the strength of adhesion, this refers to the adhesion strength of the coating.

[0100] In Example 1 above, the silane coupling agent in the copper nanofluid was 3-aminopropylsilanetriol. The adhesion strength of the coating was 6.2 N / cm in a 90° peel test.

[0101] [Example 4]

[0102] The silane coupling agent in the copper nanofluid was set as 1-(pyridin-2-yl)-3-(3-(trihydroxysilyl)propyl)urea. All other test conditions were the same as in Example 1. Although the silane coupling agent differed from that in Example 1, the concentration of the silane coupling agent and other parameters were the same as in Example 1.

[0103] Electroless copper plating was attempted using the fabricated copper nanofluid. Electroless copper plating was deposited and formed a film. The adhesion strength of the film was 5.8 N / cm.

[0104] [Example 5]

[0105] The silane coupling agent in the copper nanofluid was set as 1-butyl-3-(3-(trihydroxysilyl)propyl)thiourea. All other experimental conditions were the same as in Example 1.

[0106] Electroless copper plating was attempted using the fabricated copper nanofluid. Electroless copper plating was deposited and formed a film. The adhesion strength of the film was 4.9 N / cm.

[0107] [Example 6]

[0108] The silane coupling agent in the copper nanofluid was set as N-2-(aminoethyl)-3-aminopropylsilanetriol. All other experimental conditions were the same as in Example 1.

[0109] Electroless copper plating was attempted using the fabricated copper nanofluid. Electroless copper plating was deposited and formed a film. The adhesion strength of the film was 4.0 N / cm.

[0110] [Example 7]

[0111] The silane coupling agent in the copper nanofluid was set as N-2-(aminoethyl)-8-aminooctylsilanetriol. All other experimental conditions were the same as in Example 1.

[0112] Electroless copper plating was attempted using the fabricated copper nanofluid. Electroless copper plating was deposited and formed a film. The adhesion strength of the film was 3.2 N / cm.

[0113] According to Examples 1 and 4-7, when the silane coupling agent contained in the copper nanofluid is aminosilanetriol, although the adhesion strength of the coating is different depending on the end group of the aminosilanetriol, the adhesion is good.

[0114] (Comparative Example 6)

[0115] The silane coupling agent in the copper nanofluid was set as 3-mercaptopropylsilanetriol. 3-mercaptopropylsilanetriol is not an aminosilanetriol, but a thiol compound with a thiol terminal group. All other experimental conditions were set to be the same as in Examples 4-7.

[0116] Electroless copper plating was attempted using the fabricated copper nanofluid. No electroless copper plating was achieved.

[0117] When the terminal group of the silane coupling agent is not amino but mercapto, it is presumed that the excessive interaction with copper (Cu) will cause it to coat the surface of copper nanoparticles and lose the coating activity of copper nanoparticles.

[0118] (Comparative Example 7)

[0119] No silane coupling agent was added to the copper nanofluid. All other experimental conditions were the same as in Examples 4-7.

[0120] Electroless copper plating was attempted using the fabricated copper nanofluid. During electroless copper plating, copper nanoparticles detached, and no copper plating was deposited.

[0121] Then, in the process of curing the copper nanofluid in the plating method, experiments were conducted with varying heating temperatures and times. Six heating temperatures were set: 80°C, 100°C, 115°C, 130°C, 150°C, and 200°C. Six heating times were set: 1 minute, 3 minutes, 5 minutes, 10 minutes, 20 minutes, and 30 minutes. A total of 36 conditions were created combining heating temperature and time. All test conditions other than heating temperature and time were the same as in Example 1.

[0122] After heating a substrate coated with copper nanofluid, it was immersed in a 10% sulfuric acid aqueous solution and washed with water to attempt electroless copper plating. The deposition state of the electroless copper plating was then evaluated. The deposition state was rated as "Good," "Neutral," and "Bad." In "Good," copper nanoparticles were stably attached during washing, and the electroless copper plating was well deposited. In "Neutral," some copper nanoparticles detached during washing, and the electroless copper plating was uneven (non-uniform). In "Bad," copper nanoparticles detached during washing, and no electroless copper plating was deposited.

[0123] In the test with the heating temperature set at 80℃, the deposition state of non-electrolytic copper plating was "poor" when the heating time was 1 minute to 20 minutes, and "medium" when the heating time was 30 minutes.

[0124] In the test where the heating temperature was set to 100℃, the precipitation status was "poor" when the heating time was 1 minute to 10 minutes, and "moderate" when the heating time was 20 minutes and 30 minutes.

[0125] In the test with the heating temperature set at 115℃, the precipitation status was "poor" when the heating time was 1 minute, "moderate" when the heating time was 3 to 10 minutes, and "good" when the heating time was 20 minutes and 30 minutes.

[0126] In the test where the heating temperature was set to 130°C, the precipitation status was "poor" when the heating time was 1 minute, and "good" when the heating time was 3 to 30 minutes.

[0127] In the test where the heating temperature was set to 150°C, the precipitation status was "poor" when the heating time was 1 minute, and "good" when the heating time was 3 to 30 minutes.

[0128] In the experiment where the heating temperature was set to 200℃ and the heating time was 1 minute to 30 minutes, the precipitation status was "good".

[0129] In summary, when using the copper nanofluid of Example 1, the preferred curing conditions for forming the seed layer by solidifying the copper nanofluid are a heating time of 3 minutes or more at a heating temperature of 130°C. At heating temperatures below 130°C, a longer heating time is required.

[0130] Then, tests were conducted using different substrates to evaluate the adhesion of the formed coatings. In Examples 1, 8, and 9 below, since a substrate with a roughened surface was used and the coating method of the first embodiment was employed, no resin layer was present. In Examples 10-16, since a substrate with a micron-level smooth surface was used and the coating method of the second embodiment was employed, a resin layer was formed on the surface of the substrate. The resin layer was formed using a primer containing thermoplastic polyimide and a multifunctional epoxy resin. Except for the conditions of the substrate and the resin layer, everything was set to be the same as in Example 1. The adhesion of the coatings was evaluated by a 90° peel test (JIS K6854-1:1999).

[0131] As mentioned above, in Example 1, the substrate was AlN (aluminum nitride), and the adhesion strength of the coating was 6.2 N / cm.

[0132] [Example 8]

[0133] The substrate was set as MgTiO2Ca (calcium magnesium titanate). The adhesion strength of the coating was 9 N / cm.

[0134] [Example 9]

[0135] The substrate was set as Al2O3 (alumina). The adhesion strength of the coating was 4 N / cm.

[0136] [Example 10]

[0137] The substrate was set as PBT (polybutylene terephthalate). The adhesion strength of the coating was 14 N / cm.

[0138] [Example 11]

[0139] The substrate is set as PPS (polyphenylene sulfide). The adhesion strength of the coating is 10 N / cm.

[0140] [Example 12]

[0141] The substrate is set as LCP (liquid crystal polymer). The adhesion strength of the coating is 8 N / cm.

[0142] [Example 13]

[0143] The substrate is set to PEEK (polyetheretherketone). The adhesion strength of the coating is 7 N / cm.

[0144] [Example 14]

[0145] The substrate is set as amide resin (nylon 6). The adhesion strength of the coating is 6 N / cm.

[0146] [Example 15]

[0147] The substrate was set to SPS (syndiotactic polystyrene). The adhesion strength of the coating was 7 N / cm.

[0148] [Example 16]

[0149] The substrate is glass (alkali-free glass). Although glass is not an engineering plastic, it is a difficult material to coat. The adhesion strength of the coating is 6 N / cm.

[0150] According to Examples 1, 8-16, the copper nanofluid and plating method of the present invention can form a coating with good adhesion on difficult-to-plate materials such as ceramics and engineering plastics.

[0151] It should be noted that the present invention is not limited to the configuration of the above embodiments, but can be modified in various ways without changing the essence of the invention. For example, in the plating method of the present invention, copper nanofluid can also be coated by printing. In addition, the substrate is not limited to ceramics or engineering plastics; for example, it can also be glass.

Claims

1. A copper nanofluid, characterized in that, The copper nanofluid has the following characteristics: Solvent; Copper nanoparticles dispersed in the solvent; and aminosilanetriol dissolved in the solvent, The solvent contains propylene glycol monomethyl ether.

2. The copper nanofluid according to claim 1, characterized in that, The aminosilane triol is selected from the group consisting of 3-aminopropylsilane triol, 1-(pyridin-2-yl)-3-(3-(trihydroxysilyl)propyl)urea, 1-butyl-3-(3-(trihydroxysilyl)propyl)thiourea, N-2-(aminoethyl)-3-aminopropylsilane triol, and N-2-(aminoethyl)-8-aminooctylsilane triol.

3. A plating method, wherein the plating method uses the copper nanofluid of claim 1 to form a coating film, characterized in that, Electroless copper plating is performed on a seed layer formed by solidifying the copper nanofluid through heating to form a coating.

4. The plating method according to claim 3, characterized in that, The plating method has the following characteristics: A process for roughening the surface of a ceramic substrate; The process of exposing the surface of the roughened substrate to reactive oxygen species is carried out. The process of coating the surface of the substrate that has undergone the treatment with the copper nanofluid; The process of forming a seed layer by heating and solidifying the coated copper nanofluid; and The process of forming a coating by performing non-electrolytic copper plating on the seed layer.

5. The plating method according to claim 3, characterized in that, The plating method has the following characteristics: The process of applying a primer containing thermoplastic resin onto a substrate to form a resin layer; The process of exposing the surface of the resin layer to reactive oxygen species is carried out. The process of coating the surface of the resin layer that has undergone the treatment with the copper nanofluid; The process of forming a seed layer by heating and solidifying the coated copper nanofluid; and The process of forming a coating by performing non-electrolytic copper plating on the seed layer.

6. The plating method according to claim 4 or 5, characterized in that, The treatment involving exposure to reactive oxygen species is a surface treatment selected from the group consisting of corona treatment, plasma treatment, vacuum ultraviolet treatment, and ozone treatment.

7. A seed layer, characterized in that, The seed layer is composed of a substance formed by solidifying the copper nanofluid of claim 1 by heating. The seed layer is formed on the surface of the adhered material. The seed layer contains the copper nanoparticles. The seed layer forms siloxane bonds formed by the dehydration condensation of aminosilanetriol, and there is no aminosilanetriol residue.

8. The seed layer according to claim 7, characterized in that, The adherend is made of ceramic with a roughened surface.

9. The seed layer according to claim 7, characterized in that, The adherend has a resin layer containing thermoplastic resin on its surface.

Images