Electroless gold plating method and coated substrate

Abstract

The invention relates to the technical field of printed circuit boards, in particular to a chemical gold plating method and a coated substrate. The chemical gold plating method comprises the following steps: preparing a pretreatment solution containing nano noble metal colloid; the nanometer precious metal colloid is adsorbed on a metal substrate through dipping treatment, and a colloid layer is formed; a gold plating layer is deposited on the colloid layer through chemical gold plating bath treatment; wherein the nanometer precious metal colloid comprises one or more of a nanometer gold colloid, a nanometer silver colloid and a nanometer palladium colloid. By adopting the chemical gold plating method provided by the invention, a metal substrate-gold plating layer interface without corrosion holes and with good binding force can be formed, and a gold plating layer with higher thickness and better uniformity can be obtained within the same gold plating bath time.

Description

Technical Field

[0001] The present application relates to the technical field of printed circuit boards, and in particular to a chemical gold plating method and a film-plated substrate. Background Art

[0002] The surface treatment of printed circuit boards (PCBs) is crucial to improving the performance and reliability of PCBs. Common PCB surface treatments include hot air solder leveling (HASL), organic solderability preservatives (OSP), immersion tin (Imsn), immersion silver (ImsAg), electroless nickel / immersion gold (ENIG), electroless nickel / electroless palladium / immersion gold (ENEPIG) and other processes.

[0003] As the use of wireless networks, IoT devices and handheld devices continues to grow, large amounts of data are transmitted in the form of high-frequency radio frequency signals. The coated substrates produced by the traditional ENIG and ENEPIG processes have a chemical nickel plating layer, and its own ferromagnetic effect will cause signal loss when transmitting high-frequency radio frequency signals. The Direct Immersion Gold (DIG) process developed from this process does not have a chemical nickel plating layer in the produced coated substrate, which can greatly reduce the transmission loss of the conductor and is suitable for high-frequency and high-speed signal transmission, meeting the requirements of the sixth generation mobile communication technology (6G).

[0004] When electroless gold plating is directly implemented on copper circuits, there are mainly two reactions, one is the replacement reaction between gold ions and copper element, and the other is that gold ions are reduced by a reducing agent to gold element and deposited on the copper substrate. Accordingly, chemical gold plating baths are mainly divided into two types: replacement gold plating baths and reduction gold plating baths. Due to the high redox potential of gold ions and low ionization tendency, the replacement reaction between gold ions and copper element is inevitable. The reduction chemical gold plating bath is actually a replacement-reduction mixed gold plating bath. Therefore, traditional chemical gold plating baths will cause uneven dissolution of the copper substrate, resulting in corrosion cavities between the interface of the copper substrate and the gold coating, thereby causing the loss of the transmission signal, and even worse, affecting the adhesion of the gold coating, causing the gold coating to fall off. Summary of the invention

[0005] Based on this, it is necessary to provide a chemical gold plating method and a plated substrate to solve the problem of uneven dissolution of the copper substrate and formation of corrosion cavities caused by the traditional chemical gold plating bath.

[0006] The above-mentioned purpose of the present application is achieved through the following technical solutions:

[0007] In a first aspect of the present application, a chemical gold plating method is provided, comprising the following steps:

[0008] preparing a pretreatment solution containing nano-precious metal colloid;

[0009] Adsorbing the nano noble metal colloid onto the metal substrate through an impregnation process to form a colloid layer;

[0010] Depositing a gold plated layer on the colloid layer by treating it in a chemical gold plating bath;

[0011] Wherein, the nano noble metal colloid includes one or more of nano gold colloid, nano silver colloid and nano palladium colloid.

[0012] In one embodiment, the method for preparing the pretreatment solution comprises the following steps:

[0013] mixing a noble metal source, a coating agent and a polar solvent to obtain a mixed solution;

[0014] The mixed solution is subjected to a reduction reaction to obtain the pretreatment solution.

[0015] In one embodiment, the precious metal source includes one or more of a gold source, a silver source and a palladium source;

[0016] The gold source includes one or more of chloroauric acid, chloroaurate, gold cyanide, gold thiocyanate, gold cyanide, gold sulfite and gold thiosulfate;

[0017] The silver source includes one or more of silver chlorate, silver nitrate and silver citrate;

[0018] The palladium source includes one or more of palladium chloride, palladium sulfate, palladium nitrate, palladium acetate, palladium trifluoroacetate, tetraaminepalladium tetrachloride, sodium tetrachloropalladate, dichlorotetraaminepalladium and dinitrodiamminepalladium.

[0019] In one embodiment, the encapsulating agent includes one or more of a small molecule encapsulating agent, a polymer encapsulating agent, and a biomolecule encapsulating agent;

[0020] The small molecule encapsulating agent includes one or more of organic carboxylic acid, organic carboxylate, amino compound, thiol compound, thiazole compound and quaternary ammonium salt;

[0021] The polymer coating agent includes one or more of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene imine, polyacrylamide and its derivatives, polyacrylic acid and its derivatives, and polyether;

[0022] The biomolecule encapsulating agent includes one or more of polypeptides, proteins, nucleic acids and plant extracts.

[0023] In one embodiment, the polar solvent includes one or more of water, alcohol solvents, polyalcohol solvents, ether solvents, polyether solvents, ketone solvents and amide solvents.

[0024] In one embodiment, the mass ratio of the precious metal element in the precious metal source to the coating agent is 1:(10~1000).

[0025] In one embodiment, the concentration of the nano-precious metal colloid in the pretreatment solution is 0.01 g / L to 10 g / L.

[0026] In one embodiment, subjecting the mixed solution to a reduction reaction comprises the following steps:

[0027] In the presence of a reducing agent, the mixed solution is subjected to reduction reaction at 0°C to 200°C for 1 min to 6 h.

[0028] In one embodiment, the reducing agent includes one or more of sodium borohydride, hydroxylamine, ascorbic acid, formaldehyde, hydrazine hydrate, dimethylamine borane, trimethylamine borane, citric acid, citrate, ethylene glycol and diethylene glycol.

[0029] In one embodiment, the immersion treatment is carried out at a temperature of 20°C to 80°C and for a time of 1 min to 30 min.

[0030] In one embodiment, the temperature of the chemical gold plating bath treatment is 20° C. to 100° C., and the time is 1 min to 30 min.

[0031] In a second aspect of the present application, a film-plated substrate is provided, which is produced by the chemical gold plating method as described above.

[0032] This application has at least the following beneficial effects:

[0033] The present application utilizes a pre-treatment liquid containing nano-precious metal colloid to immerse the metal substrate, so that the nano-precious metal colloid is adsorbed on the metal substrate to form a colloidal layer. In the chemical gold plating bath process, the colloidal layer can not only reduce the proportion of substitution reaction between gold ions and the metal substrate, reduce the corrosion of the chemical gold plating bath on the metal substrate, thereby forming a metal substrate-gold plating interface without corrosion cavities and good bonding force, but also can be used as a nano-precious metal colloid catalyst to increase the rate of reduction reaction in the chemical gold plating bath, thereby obtaining a gold plating layer with higher thickness and better uniformity within the same gold plating bath time. The pre-treatment liquid of the present application contains nano-gold colloid, nano-silver colloid or nano-palladium colloid, which has the advantages of good dispersion stability, not easy to agglomerate, and good catalytic ability for chemical gold plating compared with nano-precious metal colloids such as nano-platinum colloids, and the gold plating layer obtained by the final catalysis is more uniform and has good bonding force with the metal substrate. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present application, the present application is further described in detail below in conjunction with specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0036] In the present application, the meaning of "and / or" includes any and all combinations of one or more related listed items. "At least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of the present application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0037] When a numerical range is disclosed in this application, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges included therein.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] In this application, "above" or "below" includes the number itself. For example, "1 below" includes 1.

[0040] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0041] In the present application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature intervals: 23°C ± 2°C, 25°C ± 5°C or 20°C ± 5°C.

[0042] Direct immersion gold (DIG) is a process of direct chemical gold plating on copper circuits. During the chemical gold plating process, the substitution reaction between gold ions and copper is inevitable, which can easily cause uneven dissolution of the copper substrate, resulting in corrosion holes at the interface between the copper substrate and the gold plating, thus causing loss of transmission signals. What's worse, it can affect the adhesion of the gold plating and cause it to fall off.

[0043] Based on this, in the first aspect of the present application, a chemical gold plating method is provided to solve the problem of uneven dissolution of the copper substrate and formation of corrosion cavities caused by the traditional chemical gold plating bath.

[0044] In some embodiments, the chemical gold plating method comprises the following steps:

[0045] S100: preparing a pretreatment solution containing nano-precious metal colloid;

[0046] S200: Adsorbing the nano noble metal colloid onto the metal substrate through an impregnation treatment to form a colloid layer;

[0047] S300: depositing a gold plating layer on the colloid layer through a chemical gold plating bath treatment;

[0048] The nano noble metal colloid includes one or more of nano gold colloid, nano silver colloid and nano palladium colloid.

[0049] The present application utilizes a pre-treatment liquid containing nano-precious metal colloid to immerse the metal substrate, so that the nano-precious metal colloid is adsorbed on the metal substrate to form a colloidal layer. In the chemical gold plating bath process, the colloidal layer can not only reduce the proportion of substitution reaction between gold ions and the metal substrate, reduce the corrosion of the chemical gold plating bath on the metal substrate, thereby forming a metal substrate-gold plating interface without corrosion cavities and good bonding force, but also can be used as a nano-precious metal colloid catalyst to increase the rate of reduction reaction in the chemical gold plating bath, thereby obtaining a gold plating layer with higher thickness and better uniformity within the same gold plating bath time. The pre-treatment liquid of the present application contains nano-gold colloid, nano-silver colloid or nano-palladium colloid, which has the advantages of good dispersion stability, not easy to agglomerate, and good catalytic ability for chemical gold plating compared with nano-precious metal colloids such as nano-platinum colloids, and the gold plating layer obtained by the final catalysis is more uniform and has good bonding force with the metal substrate.

[0050] The following is a detailed description of the chemical gold plating method in a step-by-step manner.

[0051] S100: preparing a pretreatment solution containing nano-precious metal colloid.

[0052] Optionally, the method for preparing the pretreatment solution comprises the following steps:

[0053] S110: mixing a noble metal source, a coating agent and a solvent to obtain a mixed solution;

[0054] S120: subjecting the mixed solution to a reduction reaction to obtain a pretreatment solution.

[0055] Optionally, the noble metal source includes one or more of a gold source, a silver source and a palladium source.

[0056] Optionally, the gold source includes one or more of chloroauric acid (III), chloroauric acid (III) salt, gold cyanide (III) salt, gold thiocyanate (III) salt, gold cyanide (I) salt, gold sulfite (I) salt and gold thiosulfate (I) salt, and can further be selected from one or more of gold cyanide (I) salt, gold sulfite (I) salt and gold thiosulfate (I) salt, and can further be selected from gold sulfite (I) salt.

[0057] In the present application, the cation of the salt compound in the gold source can be an alkali metal ion such as sodium or potassium, such as sodium chloroaurate, potassium chloroaurate, sodium gold cyanide, potassium gold cyanide, sodium gold thiocyanate, potassium gold thiocyanate, sodium aurous cyanide, potassium aurous cyanide, sodium gold sulfite, potassium gold sulfite, sodium gold thiosulfate or potassium gold thiosulfate. Compared with the trivalent gold source, the monovalent gold source has the advantages of lower cost and wider industrial sources, which is conducive to reducing the cost of the chemical gold plating process.

[0058] Optionally, the silver source includes one or more of silver chlorate, silver nitrate and silver citrate, and may further be silver nitrate.

[0059] Optionally, the palladium source includes one or more of palladium chloride, palladium sulfate, palladium nitrate, palladium acetate, palladium trifluoroacetate, tetraaminepalladium tetrachloride, sodium tetrachloropalladate, dichlorotetraaminepalladium and dinitrodiamminepalladium, and can further be palladium chloride.

[0060] Optionally, the capping agent includes one or more of a small molecule capping agent, a polymer capping agent and a biomolecule capping agent.

[0061] In the present application, the coating agent is used to coat the surface of the nano-precious metal to form a stable nano-precious metal colloid, thereby preventing the agglomeration and precipitation of the nano-precipitous metal. Therefore, the coating agent should be selected from small molecules, polymers or biomolecules with good interactions with the nano-precipitous metal particles, especially small molecules, polymers or biomolecules containing heteroatoms such as nitrogen, oxygen, and sulfur.

[0062] Optionally, the small molecule encapsulating agent includes one or more of organic carboxylic acid, organic carboxylate, amino compound, thiol compound, thiazole compound and quaternary ammonium amino acid, mercaptoethanol, hydroxybenzothiazole, aminobenzothiazole and hexadecyltrimethylammonium bromide.

[0063] In the present application, in the small molecule coating agent, organic carboxylic acid includes but is not limited to: citric acid, malic acid, succinic acid, thioglycolic acid, mercaptopropionic acid, acetic acid, benzoic acid, oxalic acid, lactic acid, tartaric acid or amino acid. Organic carboxylates are alkali metal salts of organic carboxylic acids, such as sodium citrate, potassium citrate, sodium malate, potassium malate, sodium succinate or potassium succinate. Amino compounds include but are not limited to: amino acids or aminobenzothiazoles. Amino acids contain carboxyl and amino groups, including but not limited to: cysteine, lysine, histidine, arginine, glycine, serine or aspartic acid. Thiol compounds include but are not limited to: mercaptoethanol, thioglycolic acid or mercaptopropionic acid. Thiazole compounds include but are not limited to: hydroxybenzothiazole or aminobenzothiazole. Quaternary ammonium salts include but are not limited to: hexadecyltrimethylammonium bromide. In some specific examples, the small molecule coating agent can further be selected as citric acid or citrate.

[0064] Optionally, the polymer coating agent includes one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyethyleneimine (PEI), polyacrylamide (PAM) and its derivatives, polyacrylic acid (PAA) and its derivatives, and polyether (PEO or PPO), and can further be one or more of PVA, PVP and PEI.

[0065] Optionally, the biomolecule encapsulating agent includes one or more of polypeptides, proteins, nucleic acids and plant extracts.

[0066] Optionally, the polar solvent includes one or more of water, alcohol solvents, polyol solvents, ether solvents, polyether solvents, ketone solvents and amide solvents. Among them, alcohol solvents include but are not limited to: methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol and tetraethylene glycol; polyol solvents can be low molecular weight polyols; ether solvents include but are not limited to: dimethyl ether, methyl ethyl ether, ethyl butyl ether and diethylene glycol dimethyl ether; polyether solvents can be low molecular weight polyethers; amide solvents include N,N'-dimethylformamide. Further optionally, the polar solvent is one or more of water, ethylene glycol and diethylene glycol.

[0067] Optionally, the mass ratio of the precious metal element in the precious metal source to the coating agent is 1:(10~1000), including but not limited to: 1:10, 1:20, 1:40, 1:60, 1:80, 1:100, 1:120, 1:150, 1:180, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900 or 1:1000, and can further be 1:(20~200).

[0068] Optionally, the concentration of the precious metal element in the precious metal source in the mixed solution is 0.01g / L~10g / L, including but not limited to: 0.01g / L, 0.05g / L, 0.1g / L, 0.2g / L, 0.5g / L, 0.8g / L, 1g / L, 1.2g / L, 1.5g / L, 1.8g / L, 2g / L, 3g / L, 4g / L, 5g / L, 6g / L, 7g / L, 8g / L, 9g / L or 10g / L, and can be further optionally 0.05g / L~2g / L.

[0069] Optionally, the concentration of the coating agent in the mixed solution is 0.01g / L~200g / L, including but not limited to: 0.01g / L, 0.05g / L, 0.1g / L, 0.5g / L, 1g / L, 2g / L, 5g / L, 8g / L, 10g / L, 12g / L, 15g / L, 18g / L, 20g / L, 40g / L, 60g / L, 80g / L, 100g / L, 120g / L, 140g / L, 160g / L, 180g / L or 200g / L, and can be further selected from 0.1g / L~30g / L.

[0070] Optionally, the mixed solution also contains auxiliary agents such as pH buffer, preservative and anti-settling agent. Among them, pH buffer includes but is not limited to: acetic acid-sodium acetate buffer system, potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer system, ammonia-ammonium chloride buffer system or amino acid buffer system; preservative includes but is not limited to: sodium benzoate, potassium sorbate, sodium dehydroacetate, isothiazolinone preservative and quaternary ammonium salt preservative; anti-settling agent includes but is not limited to: organic bentonite, fumed silica, polyvinyl alcohol and polyamide wax.

[0071] Optionally, subjecting the mixed solution to a reduction reaction comprises the following steps: subjecting the mixed solution to a reaction at 0°C to 200°C for 1 min to 6 h in the presence of a reducing agent. The reaction temperature of the reduction reaction includes, but is not limited to, 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C; the reaction time of the reduction reaction includes, but is not limited to, 1 min, 10 min, 20 min, 30 min, 40 min, 50 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h.

[0072] Optionally, the reducing agent includes one or more of sodium borohydride, hydroxylamine, ascorbic acid, formaldehyde, hydrazine hydrate, dimethylamine borane, trimethylamine borane, citric acid, citrate, ethylene glycol and diethylene glycol, and further can be selected from one or more of sodium borohydride, ascorbic acid, citric acid, citrate, ethylene glycol and diethylene glycol.

[0073] Optionally, the mass ratio of the precious metal element and the reducing agent in the precious metal source is 1:(0.01~10), including but not limited to: 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, and can be further optionally 1:(0.1~2.5).

[0074] In this application, according to whether the mixed solution contains reducing components or according to the reaction temperature of the reduction reaction, it is mainly divided into the following three situations:

[0075] First, if the mixed solution does not contain a reducing component, a reducing agent is added to the mixed solution, and the mixture is reacted at 0°C to 80°C for 1 min to 6 h, wherein the reducing agent includes one or more of sodium borohydride, hydroxylamine, ascorbic acid, formaldehyde, hydrazine hydrate, dimethylamine borane, and trimethylamine borane;

[0076] Second, if the mixed solution contains a reducing coating agent such as citric acid or citrate, no additional reducing agent is needed, and the mixed solution is reacted at 80°C to 120°C for 0.1h to 6h;

[0077] Third, if the mixed solution contains a reducing solvent such as ethylene glycol or diethylene glycol, there is no need to add an additional reducing agent, and the mixed solution is allowed to react at 120° C. to 200° C. for 0.1 h to 6 h.

[0078] It is understandable that the method of subjecting the mixed solution to reduction reaction is not limited to the above three situations. In some specific examples, even if the mixed solution contains reducing components such as citric acid, additional reducing agents such as sodium borohydride and ascorbic acid can be added to accelerate the reaction rate and shorten the reaction time.

[0079] Optionally, the concentration of nano noble metal colloid in the pretreatment liquid is 0.01g / L~10g / L, including but not limited to 0.01g / L, 0.05g / L, 0.1g / L, 0.5g / L, 1g / L, 2g / L, 3g / L, 4g / L, 5g / L, 6g / L, 7g / L, 8g / L, 9g / L or 10g / L, and can be further optionally 0.05g / L~2g / L.

[0080] Optionally, the average particle size of the nano noble metal colloid is 1nm~100nm, including but not limited to: 1nm, 2nm, 5nm, 8nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, further optionally 5nm~80nm, further optionally 10nm~50nm.

[0081] S200: Adsorbing the nano-precious metal colloid onto the metal substrate through an immersion treatment to form a colloid layer.

[0082] Optionally, the metal substrate includes one or more of a copper substrate, an aluminum substrate, an iron substrate, a nickel substrate and a titanium substrate, and may further be a copper substrate.

[0083] The chemical gold plating method of the present application is not only applicable to copper substrates, but also to other metal substrates, such as aluminum substrates, iron substrates, nickel substrates and titanium substrates, and can reduce the corrosion of gold ions on the metal substrates, so as to form a gold-copper (or aluminum, iron, nickel, titanium) interface with no corrosion voids and good bonding strength.

[0084] Optionally, before the immersion treatment, the following steps are further included: micro-etching the metal substrate using a micro-etching solution. The micro-etching solution includes, but is not limited to, a sodium persulfate system, an ammonium persulfate system, a hydrogen peroxide system, a sulfuric acid-chromic acid system, and an organic acid system; the temperature of the micro-etching treatment can be 20°C to 40°C, and the time can be 1 min to 10 min.

[0085] Through micro-etching treatment, impurities such as oxides on the surface of the metal substrate can be removed, the surface roughness of the metal substrate can be improved, and the adsorption effect of nano-precious metal colloids on the surface of the metal substrate can be promoted.

[0086] Optionally, the temperature of the immersion treatment is 20°C to 80°C, including but not limited to: 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C; the time of the immersion treatment is 1min to 30min, including but not limited to: 1min, 2min, 4min, 6min, 8min, 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min or 30min.

[0087] S300: depositing a gold plating layer on the colloid layer through a chemical gold plating bath treatment.

[0088] Optionally, the chemical gold plating bath in the chemical gold plating bath treatment includes one or more of a replacement type, a reduction type, and a mixed type.

[0089] Optionally, the temperature of the chemical gold plating bath treatment is 20°C~100°C, including but not limited to: 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C; the time of the chemical gold plating bath treatment is 1min~30min, including but not limited to: 1min, 2min, 4min, 6min, 8min, 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min or 30min.

[0090] Optionally, after the chemical gold plating bath treatment, the concentration of metal ions displaced from the metal substrate into the chemical gold plating bath is ≤ 4 ppm.

[0091] It can be understood that the metal ions in the chemical gold plating bath are derived from the replacement reaction between gold ions and the metal substrate, the metal substrate is selected from a copper substrate, an aluminum substrate, an iron substrate, a nickel substrate or a titanium substrate, and the metal ions in the chemical gold plating bath are selected from copper ions, aluminum ions, iron ions, nickel ions or titanium ions.

[0092] Optionally, the thickness of the gold plating layer is ≥20nm, including but not limited to: 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm or 200nm, and can be further optionally 25nm~60nm.

[0093] In a second aspect of the present application, a film-plated substrate is provided, which is produced by the chemical gold plating method as described above.

[0094] Optionally, the film-plated substrate includes a metal base, a colloid layer and a gold-plated layer stacked in sequence.

[0095] The following is further described in conjunction with specific embodiments and comparative examples. The raw materials involved in the following specific embodiments and comparative examples, unless otherwise specified, can all be commercially available, the instruments used, unless otherwise specified, can all be commercially available, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0096] Example 1

[0097] Please refer to Table 1 and Table 2. The chemical gold plating method of this embodiment is as follows:

[0098] (1) Polyvinyl pyrrolidone (PVP) and sodium gold (I) sulfite are dissolved in pure water to obtain a mixed solution; in the mixed solution, the concentration of PVP is 10 g / L, and the concentration of gold element in the sodium gold (I) sulfite is 0.5 g / L.

[0099] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of gold element in sodium gold (I) sulfite to sodium borohydride being 1:0.2. The reduction reaction was carried out at room temperature (25°C) for 0.5 h to obtain a nano-gold colloidal solution with a gold element concentration of 0.5 g / L.

[0100] (3) A printed circuit board with copper lines was used as a copper substrate. It was placed in a sodium persulfate system micro-etching solution at room temperature for 2 minutes and washed twice with pure water. It was then placed in a nano-gold colloidal solution and immersed at 40°C for 5 minutes to form a colloidal layer, and then washed twice with pure water.

[0101] (4) The copper substrate obtained in step (3) was placed in a newly prepared mixed chemical gold plating bath (Guangdong Dongshuo Technology Co., Ltd., trade name AEG, gold concentration 0.3 g / L) at 82°C for 10 min to form a gold plating layer on the colloidal layer. Steps (1) to (4) were repeated for 20 metal substrates to be chemically gold plated. During the experiment, there was no case of the chemical gold plating bath getting out of control.

[0102] Example 2

[0103] The chemical gold plating method of the present embodiment is as follows:

[0104] (1) The same as step (1) of Example 1.

[0105] (2) The same as step (2) of Example 1, the gold element concentration of the nano-gold colloidal solution is then diluted to 0.15 g / L using pure water.

[0106] (3) A printed circuit board with copper lines was used as a copper substrate. It was placed in a sodium persulfate system micro-etching solution at room temperature for 2 minutes and washed twice with pure water. It was then placed in a nano-gold colloidal solution and immersed at 60°C for 5 minutes to form a colloidal layer, and then washed twice with pure water.

[0107] (4) Same as step (4) of Example 1.

[0108] Example 3

[0109] The chemical gold plating method of the present embodiment is as follows:

[0110] (1) Polyvinyl pyrrolidone (PVP) and potassium aurous (I) cyanide are dissolved in pure water to obtain a mixed solution; in the mixed solution, the concentration of PVP is 20 g / L, and the concentration of gold element in potassium aurous (I) cyanide is 0.1 g / L.

[0111] (2) Ascorbic acid was added to the mixed solution. The mass ratio of gold element in potassium cyanide gold (I) to ascorbic acid was 1:2.5. The reduction reaction was carried out at room temperature (25°C) for 1 hour to obtain a nano-gold colloidal solution with a gold element concentration of 0.1 g / L.

[0112] (3) Same as step (3) of Example 1.

[0113] (4) Same as step (4) of Example 1.

[0114] Example 4

[0115] The chemical gold plating method of the present embodiment is as follows:

[0116] (1) Dissolve trisodium citrate and potassium aurous (I) cyanide in pure water to obtain a mixed solution; in the mixed solution, the concentration of trisodium citrate is 5 g / L, and the concentration of gold element in potassium aurous (I) cyanide is 0.05 g / L.

[0117] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of gold element in potassium cyanide gold(I) to sodium borohydride being 1:0.5. The reduction reaction was carried out at room temperature (25°C) for 0.5 h to obtain a nano-gold colloidal solution with a gold element concentration of 0.05 g / L.

[0118] (3) Same as step (3) of Example 1.

[0119] (4) Same as step (4) of Example 1.

[0120] Example 5

[0121] The chemical gold plating method of the present embodiment is as follows:

[0122] (1) Polyvinyl pyrrolidone (PVP) and silver nitrate are dissolved in pure water to obtain a mixed solution; in the mixed solution, the concentration of PVP is 20 g / L, and the concentration of silver element in the silver nitrate is 0.5 g / L.

[0123] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of silver element in silver nitrate to sodium borohydride being 1:0.1. The reduction reaction was carried out at room temperature (25°C) for 0.5 h to obtain a nanosilver colloidal solution with a silver element concentration of 0.5 g / L.

[0124] (3) Same as step (3) of Example 1.

[0125] (4) Same as step (4) of Example 1.

[0126] Example 6

[0127] The chemical gold plating method of the present embodiment is as follows:

[0128] (1) Polyvinyl pyrrolidone (PVP) is dissolved in ethylene glycol, heated to 160°C, and silver nitrate is added to obtain a mixed solution; in the mixed solution, the concentration of PVP is 30 g / L, and the concentration of silver element in the silver nitrate is 2 g / L.

[0129] (2) The mixed solution was subjected to a reduction reaction at 160° C. for 3 h, and diluted with pure water to obtain a nanosilver colloidal solution with a silver element concentration of 0.5 g / L.

[0130] (3) Same as step (3) of Example 1.

[0131] (4) Same as step (4) of Example 1.

[0132] Example 7

[0133] The chemical gold plating method of the present embodiment is as follows:

[0134] (1) Dissolve trisodium citrate and silver nitrate in pure water to obtain a mixed solution; in the mixed solution, the concentration of trisodium citrate is 20 g / L, and the concentration of silver element in the silver nitrate is 0.5 g / L.

[0135] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of silver element in silver nitrate to sodium borohydride being 1:0.1. The reduction reaction was carried out at room temperature (25°C) for 0.5 h to obtain a nanosilver colloidal solution with a silver element concentration of 0.5 g / L.

[0136] (3) Same as step (3) of Example 1.

[0137] (4) Same as step (4) of Example 1.

[0138] Example 8

[0139] The chemical gold plating method of the present embodiment is as follows:

[0140] (1) Polyvinyl pyrrolidone (PVP) is dissolved in ethylene glycol, heated to 160°C, and palladium chloride is added to obtain a mixed solution; in the mixed solution, the concentration of PVP is 30 g / L, and the concentration of palladium element in palladium chloride is 2 g / L.

[0141] (2) The mixed solution was subjected to a reduction reaction at 160° C. for 3 h, and diluted with pure water to obtain a nano-palladium colloidal solution with a palladium element concentration of 0.5 g / L.

[0142] (3) Same as step (3) of Example 1.

[0143] (4) Same as step (4) of Example 1.

[0144] Example 9

[0145] The chemical gold plating method of the present embodiment is as follows:

[0146] (1) Polyvinyl pyrrolidone (PVP) is dissolved in ethylene glycol, heated to 160°C, and palladium chloride is added to obtain a mixed solution; in the mixed solution, the concentration of PVP is 30 g / L, and the concentration of palladium element in palladium chloride is 2 g / L.

[0147] (2) The mixed solution was subjected to a reduction reaction at 160° C. for 3 h, and diluted with pure water to obtain a nano-palladium colloidal solution with a palladium element concentration of 0.5 g / L.

[0148] (3) A printed circuit board with copper lines was used as a copper substrate. It was placed in a hydrogen peroxide system micro-etching solution at room temperature for 2 minutes and then rinsed twice with pure water. It was then placed in a nano-palladium colloidal solution and immersed at 40°C for 5 minutes to form a colloidal layer, and then rinsed twice with pure water.

[0149] (4) Same as step (4) of Example 1.

[0150] Example 10

[0151] The chemical gold plating method of the present embodiment is as follows:

[0152] (1) Dissolve trisodium citrate and palladium chloride in pure water to obtain a mixed solution; in the mixed solution, the concentration of trisodium citrate is 20 g / L, and the concentration of palladium element in palladium chloride is 0.5 g / L.

[0153] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of palladium element in palladium chloride to sodium borohydride being 1:0.3. The reduction reaction was carried out at room temperature (25°C) for 0.5 h to obtain a nano-palladium colloidal solution with a palladium element concentration of 0.5 g / L.

[0154] (3) Same as step (3) of Example 1.

[0155] (4) Same as step (4) of Example 1.

[0156] Comparative Example 1

[0157] The chemical gold plating method of this comparative example is as follows:

[0158] A printed circuit board with copper circuits was used as a copper substrate. It was placed in a sodium persulfate system micro-etching solution at room temperature for 2 minutes and washed twice with pure water. It was then placed in a newly prepared mixed chemical gold plating bath (Guangdong Dongshuo Technology Co., Ltd., trade name AEG, gold concentration 0.3g / L) at 82°C for 10 minutes to form a gold plating layer on the copper substrate. The chemical gold plating was repeated for 20 metal substrates, and no loss of control of the chemical gold plating bath occurred during the experiment.

[0159] Comparative Example 2

[0160] The pretreatment solution of this comparative example contains nano-platinum colloid, and the chemical gold plating method is as follows:

[0161] (1) Polyvinyl pyrrolidone (PVP) and sodium chloroplatinate are dissolved in pure water to obtain a mixed solution; in the mixed solution, the concentration of PVP is 10 g / L, and the concentration of platinum element in chloroplatinic acid is 0.5 g / L.

[0162] (2) Sodium borohydride was added to the mixed solution, with the mass ratio of platinum element in chloroplatinic acid to sodium borohydride being 1:0.4. The reduction reaction was carried out at room temperature (25°C) for 1 hour to obtain a nano-platinum colloidal solution with a platinum element concentration of 0.5 g / L.

[0163] (3) A printed circuit board with copper lines was used as a copper substrate. It was placed in a sodium persulfate system micro-etching solution at room temperature for 2 minutes and washed twice with pure water. It was then placed in a nano-platinum colloidal solution and immersed at 40°C for 5 minutes to form a colloidal layer, and then washed twice with pure water.

[0164] (4) The copper substrate obtained in step (3) was placed in a newly prepared mixed chemical gold plating bath (Guangdong Dongshuo Technology Co., Ltd., trade name AEG, gold concentration 0.3 g / L) at 82°C for 10 min to form a gold plating layer on the colloidal layer. Steps (1) to (4) were repeated for 20 metal substrates to be chemically gold plated. During the experiment, there was no case of the chemical gold plating bath getting out of control.

[0165] Test Case

[0166] The following tests were performed on the coated substrates prepared in each embodiment and each comparative example:

[0167] (1) Average thickness of gold plating: The thickness of the gold plating was tested using an X-ray fluorescence spectrometer. Nine points were taken for quantitative testing on each coated substrate and the average value was calculated. The results are shown in Table 3.

[0168] (2) Bonding strength of gold plating: Place 3M 600# tape on the coated substrate with a length of about 2 inches, wipe the tape surface three times with your hand to ensure that it is flat, and then quickly pull up the tape perpendicular to the board surface; if no gold is observed on the tape, it is recorded as OK; if gold is observed on the tape, it is recorded as NG (not good). The results are shown in Table 3.

[0169] (3) Copper ion concentration in the chemical gold plating bath: The copper ion concentration in the chemical gold plating bath was tested by atomic absorption spectroscopy. Combined with the gold film thickness of the test piece, the proportion of the replacement reaction was calculated. The results are shown in Table 3.

[0170] The ratio of the replacement reaction is calculated as follows:

[0171] The molar amount of copper element participating in the replacement reaction (mol) = the copper ion concentration in the chemical gold plating bath (ppm or g / L) × the volume of the chemical gold plating bath (L) ÷ the molar mass of the copper element (g / mol);

[0172] The molar amount of gold plating formed by chemical gold plating (mol) = the total area of ​​20 metal substrates (cm2 )×average thickness of gold plating (nm)×density of gold element (g / cm 3 )÷ molar mass of gold element (g / mol);

[0173] The proportion of the replacement reaction (%) = 2 × the molar amount of the copper element participating in the replacement reaction (mol) ÷ the molar amount of the gold plating layer formed by chemical gold plating (mol) × 100%.

[0174] As shown in Table 3, the average thickness of the gold coating obtained in Examples 1 to 10 can reach more than 30 nm; the bonding force between the gold coating and the copper substrate is high and not easy to fall off; after the chemical gold plating bath is finished, the copper ions in the chemical gold plating bath are less than 4.1ppm, and the replacement reaction ratio of gold ions and copper ions is less than 36.6%, which effectively avoids the corrosion of copper ions by gold ions. It can be seen that the use of a pretreatment solution containing nano-gold / silver / palladium colloid to immerse the micro-etched copper substrate to form a colloidal layer can reduce the occurrence ratio of the replacement reaction between the gold ions and the copper substrate, avoid the corrosion of the copper substrate by gold ions, thereby forming a copper-gold / silver / palladium interface without corrosion cavities and good bonding force, and on the other hand, the colloidal layer catalyzes the reduction gold plating reaction of the chemical gold plating bath, so that a thicker gold coating is obtained within the same gold plating bath time.

[0175] Comparative Example 1 is not treated by the immersion of the pre-treatment solution, resulting in a significant increase in the copper ion concentration in the chemical gold plating bath, and the ratio of the replacement reaction reaches 53.5%, which has very serious corrosion on the copper substrate, and there are corrosion holes at the copper-gold interface, which may even affect the binding force of the gold coating. Comparative Example 2 uses a pre-treatment solution containing nano-platinum colloid to immerse the copper substrate after micro-etching to form a colloidal layer, but the thickness of the gold coating obtained by its catalysis is thinner and has poor uniformity, and no gold coating is formed at some positions, exposing the copper substrate, and the copper ion concentration in the chemical gold plating bath is significantly increased, and the ratio of the replacement reaction reaches 49.1%, which is difficult to suppress the corrosion of the copper substrate in the chemical gold plating process, and the binding force of the gold coating is reduced. This may be because compared with nano-gold colloid, nano-silver colloid and nano-palladium colloid, the dispersion stability of nano-platinum colloid is poor, and it is relatively easy to reunite, and the catalytic ability is insufficient.

[0176] Table 1. Process parameters for preparing pretreatment solution

[0177]

[0178] Table 2. Process parameters of chemical gold plating method

[0179]

[0180] Table 3. Effects of chemical gold plating methods

[0181]

[0182] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0183] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of protection of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A chemical gold plating method, characterized in that: The following steps are involved: preparing a pretreatment solution containing nano-precious metal colloid; Adsorbing the nano noble metal colloid onto the metal substrate through an impregnation process to form a colloid layer; Depositing a gold plated layer on the colloid layer by chemical gold plating bath treatment; Wherein, the nano noble metal colloid includes one or more of nano gold colloid, nano silver colloid and nano palladium colloid.

2. The chemical gold plating method according to claim 1, wherein The preparation method of the pretreatment solution comprises the following steps: mixing a noble metal source, a coating agent and a polar solvent to obtain a mixed solution; The mixed solution is subjected to a reduction reaction to obtain the pretreatment solution.

3. The chemical gold plating method as claimed in claim 2, characterized in that The noble metal source includes one or more of a gold source, a silver source and a palladium source; The gold source includes one or more of chloroauric acid, chloroaurate, gold cyanide, gold thiocyanate, gold cyanide, gold sulfite and gold thiosulfate; The silver source includes one or more of silver chlorate, silver nitrate and silver citrate; The palladium source includes one or more of palladium chloride, palladium sulfate, palladium nitrate, palladium acetate, palladium trifluoroacetate, tetraaminepalladium tetrachloride, sodium tetrachloropalladate, dichlorotetraaminepalladium and dinitrodiamminepalladium.

4. The chemical gold plating method according to claim 2, wherein: The coating agent includes one or more of a small molecule coating agent, a polymer coating agent and a biomolecule coating agent; The small molecule encapsulating agent includes one or more of organic carboxylic acid, organic carboxylate, amino compound, thiol compound, thiazole compound and quaternary ammonium salt; The polymer coating agent includes one or more of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene imine, polyacrylamide and its derivatives, polyacrylic acid and its derivatives, and polyether; The biomolecule encapsulating agent includes one or more of polypeptides, proteins, nucleic acids and plant extracts.

5. The chemical gold plating method according to claim 2, wherein: One or more of the following conditions are met: (1) The polar solvent includes one or more of water, alcohol solvents, polyalcohol solvents, ether solvents, polyether solvents, ketone solvents and amide solvents; (2) The mass ratio of the precious metal element in the precious metal source to the coating agent is 1:(10-1000); (3) The concentration of the nano-precious metal colloid in the pretreatment solution is 0.01 g / L to 10 g / L.

6. The chemical gold plating method according to any one of claims 2 to 5, wherein: The mixed solution is subjected to a reduction reaction, comprising the following steps: In the presence of a reducing agent, the mixed solution is subjected to reduction reaction at 0°C to 200°C for 1 min to 6 h.

7. The chemical gold plating method according to claim 6, wherein: The reducing agent includes one or more of sodium borohydride, hydroxylamine, ascorbic acid, formaldehyde, hydrazine hydrate, dimethylamine borane, trimethylamine borane, citric acid, citrate, ethylene glycol and diethylene glycol.

8. The chemical gold plating method according to claim 1, wherein: The immersion treatment is performed at a temperature of 20° C. to 80° C. and for a time of 1 min to 30 min.

9. The chemical gold plating method according to claim 1, wherein: The temperature of the chemical gold plating bath treatment is 20° C. to 100° C., and the time is 1 min to 30 min.

10. A film-coated substrate, characterized in that: The method is prepared by the chemical gold plating method as described in any one of claims 1 to 9.

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