Preparation of buried copper foil and resistance testing method thereof

Abstract

The present invention discloses a method for preparing a buried copper foil and testing its resistance, and belongs to the technical field of printed circuit boards. It is to solve the problem that the production investment of the vacuum sputtering method and the chemical induced deposition method is large, and the process control of the electroplating method is difficult. The preparation method of the buried copper foil includes deoxidation pretreatment of the base copper foil, electroplating the resistance layer, washing and drying; the resistance testing method of the above buried copper foil includes: bonding and curing the resistance layer and the supporting layer, etching, washing and baking, and testing the resistance; the present invention uses an electroplating process to deposit a layer of resistance alloy material on the copper foil, and ordinary electroplating equipment can meet the requirements. Its biggest advantage is the fast deposition rate. With the process of the present invention, the electroplating process can be controlled and can be adapted to large-scale continuous production in the copper foil industry.

Description

Technical Field

[0001] The invention belongs to the technical field of printed circuit boards, and in particular relates to a preparation method of a buried resistor copper foil and a resistance testing method thereof. Background Art

[0002] PCB buried resistor technology is a method to replace surface resistor patches, which can save the increasingly tight surface space of PCB. Using nickel-phosphorus alloy buried resistor copper foil is one of the ways to achieve buried resistor board. The structure of nickel-phosphorus alloy buried resistor copper foil is generally as follows Figure 1 As shown in FIG. 1 , it refers to a special copper foil material made by sputtering or electroplating a layer of nickel-phosphorus alloy 2 on a copper foil 1. Its structure is as follows Figure 1 The thickness of the nickel-phosphorus alloy resistance layer is mostly controlled between 0.1 and 1 μm.

[0003] At present, the processes for producing buried resistive copper foil can be divided into three categories: the first is to deposit a layer of resistive alloy material on the copper foil by vacuum sputtering; the second is to deposit a layer of resistive alloy material on the copper foil by chemical induced deposition; the third is to electroplate a layer of resistive alloy material on the copper foil by electrochemical method.

[0004] Among them, the sputtering method requires the use of vacuum sputtering equipment, and its deposition rate is relatively limited, and the investment cost of the equipment is very high. The chemical induced deposition method is similar to the method disclosed in Chinese patent CN102324294A-"A method for preparing embedded resistor materials". Before chemically plating the nickel-phosphorus alloy layer material with a porous structure, palladium chloride activation is required, and then thermal tempering treatment is required. The whole method requires the use of precious metals to activate palladium, which is costly, and the subsequent thermal tempering treatment will affect the rate, and it is impossible to meet the needs of industrial production. Finally, the electroplating process has inherent advantages in itself, and the requirements for equipment are not high. Ordinary electroplating equipment can meet the requirements, but the disadvantage of the electroplating process is that compared with chemical plating and sputtering, the process control is more difficult. This disadvantage limits its application in the field of buried resistor copper foil. Therefore, the technical difficulty in this research and development direction lies in breaking through the shortcomings of the electroplating process and obtaining a stable electroplating system.

[0005] The test method of the buried copper foil resistor produced by the above method generally requires setting up a test area during layout, such as Chinese patent CN104619114A-"A PCB board with buried resistor and a test method for buried resistor", which is relatively cumbersome.

[0006] Based on the problems in the above background technology, researchers have proposed a method for preparing buried copper foil and testing its resistance. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a buried copper foil and testing its resistance, so as to solve the problems of large production investment in vacuum sputtering and chemical induced deposition and great difficulty in process control in electroplating.

[0008] Another object of the present invention is to provide a resistance testing method for the buried copper foil to solve the problem of complicated steps in testing the resistance of the buried copper foil.

[0009] In order to solve the above problems, the technical solution of the present invention is:

[0010] A method for preparing a buried copper foil, the method comprising the following steps:

[0011] S1. Pre-treatment of base copper foil for deoxidation:

[0012] Take the copper foil and pickle it;

[0013] S2, electroplating resistance layer:

[0014] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution;

[0015] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0016] Again, adjust the pH of the plating solution;

[0017] Finally, electroplating is performed;

[0018] After electroplating, the thickness of the ultra-thin nickel-phosphorus alloy resistance layer is 0.1-1μm;

[0019] S3, washing and drying:

[0020] The buried copper foil after electroplating was taken out, washed with pure water and then dried to prepare the buried copper foil, the roughness Rz of which was 0.48-9.96 μm.

[0021] Furthermore, the base thickness of the copper foil in S1 is 18-35 μm;

[0022] At a pickling temperature of 20-40°C, the pickling time is 3-20s;

[0023] The pickling solution is a 10-20 wt % sulfuric acid aqueous solution.

[0024] Furthermore, in the electroplating solution prepared in S2, the concentration of nickel sulfate hexahydrate is 90-300 g / L, the concentration of sodium citrate is 30-400 g / L, the concentration of sodium hypophosphite is 3-30 g / L, the concentration of boric acid is 10-50 g / L, the concentration of phosphoric acid is 6-50 g / L, and the concentration of sodium tungstate is 0-200 g / L.

[0025] Furthermore, in S2:

[0026] Among the additives:

[0027] The wetting agent is: saccharin or polyethylene glycol, and the content in the solution is: 0.1-1g / L;

[0028] The inhibitor is: one of dodecylamine ethoxy sulfate and polyethylene imine, and the content in the solution is: 0.05-0.3g / L;

[0029] The stabilizer is: acetate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, etc., and the content in the solution is: 0.5-10g / L;

[0030] Use sulfuric acid or sodium hydroxide to adjust the pH of the plating solution to 1-5;

[0031] The electroplating temperature is controlled at 40-80°C; the electroplating current density is 1-15A / dm 2 .

[0032] Further, S3 is rinsed with pure water for 2-5 seconds, the water washing pressure is 0.5-2MPa, and baked at 80°C for 5-20 minutes.

[0033] The above method prepares a resistance test method for buried copper foil, which is divided into the following steps:

[0034] S4, the resistance layer and the supporting layer are bonded and cured;

[0035] The ultra-thin resistor layer of the buried copper foil is bonded to the plastic film and heated for curing at 40°C for 12 hours.

[0036] S5, etching;

[0037] The copper layer is completely etched using an etching solution;

[0038] S6, washing and baking;

[0039] Take out the plastic film, wash it with water, and dry it at 40-100℃ for 1-5min. At this time, the plastic film is bonded with a nickel-phosphorus alloy resistance layer;

[0040] S7, test resistance;

[0041] The square resistance of the nickel-phosphorus alloy resistor layer can be obtained by testing the resistance of the nickel-phosphorus alloy layer using a four-probe square resistance tester.

[0042] Further, in S5: the etching solution is a mixed solution of hydrogen peroxide, sulfuric acid, citric acid and pure water, and the mass ratios thereof are 1%-5%: 3%-10%: 1%-10%: 75%-95% respectively;

[0043] The etching temperature is 30-60°C, and the etching time is 1min-30min.

[0044] Further, in S5: the etching solution may also be a mixed solution of copper chloride, ammonium chloride, ammonia water and pure water, with the mass ratios of 5%-15%: 3%-15%: 20%-50%: 20%-72% respectively;

[0045] The etching temperature is 40-60°C, and the etching time is 1min-30min.

[0046] Furthermore, in S4: the plastic film is one of PET, PI, PP, and PVC materials;

[0047] The adhesive includes one or more of epoxy adhesive, modified phenolic adhesive, polyurethane adhesive, acrylic adhesive, polyimide adhesive, and UV adhesive.

[0048] The beneficial effects of the present invention are as follows:

[0049] (1) The method of the present invention breaks through the technical difficulties of the traditional electroplating process. The present invention uses sodium hypophosphite as the phosphorus source. The positive monovalent phosphorus is not only easy to co-deposit, but also has a large reduction potential, which can promote the deposition of nickel. Boric acid is used as a buffer and a surface passivator for metallic nickel. The passivation of nickel increases the content of metal oxides in the alloy resistor layer, further increasing the resistivity. By rationally using complexing agents, wetting agents, stabilizers and inhibitors, the electroplating solution has no impurity precipitation and can be recycled for multiple times. The deposited alloy resistor layer has low internal stress, is uniform and dense, has no surface cracks, and has stable resistivity.

[0050] This preparation principle of depositing a layer of resistance alloy material on copper foil using electroplating process not only has low requirements on equipment, ordinary electroplating equipment can meet the requirements, and its biggest advantage is the fast deposition rate, which can be adapted to large-scale continuous production in the copper foil industry.

[0051] (2) The present invention uses copper foils of different thicknesses and roughnesses, and electroplates a layer of resistive alloy material thereon. The prepared buried resistive copper foil can meet different bonding strength and downstream application requirements; standard profile copper foil (Rz is about 5-10 μm) is used on general FR-4, polyimide and other laminates; low profile copper foil (Rz is about 2-7 μm) is mainly used in high frequency, high density interconnect HDI, narrow line width and line spacing and other circuit board fields; ultra-low profile copper foil (Rz is about 0.5-2 μm) is used in high frequency, high speed, narrow tolerance, low loss, packaging and other circuit board fields.

[0052] (3) In the preparation method of the present invention, the functions of the various substances in the electroplating solution components are as follows:

[0053] The main function of nickel sulfate hexahydrate is to provide nickel ions. Another function is that nickel chloride is used in the traditional nickel electroplating industry. In this case, nickel sulfate is used to replace nickel chloride. Because chloride ions can corrode the anode and cathode, nickel sulfate reduces the corrosion of the anode and cathode.

[0054] Sodium citrate is the main complexing agent, which controls the concentration of free electrolyte in the plating solution, improves cathode polarization, and prolongs the life of the plating solution.

[0055] Sodium hypophosphite is used as the phosphorus source of the present invention. The phosphorus valence is monovalent and is very easy to be reduced. It can not only increase the co-deposition rate of phosphorus and increase the phosphorus content in the coating; but also the reduction potential of sodium hypophosphite itself is very large under acidic conditions (its reduction potential is <-0.7V), which makes it have strong reducing properties, can promote the deposition of nickel, and increase the cathode electrodeposition rate.

[0056] Phosphoric acid and boric acid are two weak acids used as buffers in the present invention. In addition to adjusting the pH of the plating solution, phosphoric acid can inhibit the oxidation of hypophosphite at the anode, inhibit the precipitation of nickel phosphite, provide hydrogen ions at the cathode interface, and promote the deposition of phosphorus. In addition, boric acid has a passivating effect on metallic nickel. Boric acid first contacts the cathode, so that the metallic nickel on the surface of the alloy resistance layer of the cathode generates active sites. The active sites can adsorb oxygen dissolved in the plating solution. Oxygen is further reduced under the action of electrons and combines with nickel to generate oxidized nickel. Oxidized nickel is an insulator, and the oxidized nickel in the coating effectively improves the resistivity of the coating.

[0057] The alloy resistor layer of the present invention contains not only nickel and phosphorus, but also tungsten. Sodium tungstate in the present invention provides tungsten element. The square resistance of the resistor layer is negatively correlated with the thickness. To obtain high square resistance, the thickness of the coating must be reduced. During the manufacturing process of the circuit board, the copper layer is chemically etched to form a circuit. Tungsten has extremely strong corrosion resistance and can protect the resistor layer from corrosion by etching solution, thereby keeping the square resistance of the resistor layer stable.

[0058] In addition, complexing agents, wetting agents, stabilizers and inhibitors are added to the electroplating solution of the present invention. This is because the thickness of the alloy resistor layer is very thin and cracks are easily generated on the surface. Complexing agents and wetting agents must be used to improve the uniformity of nickel-phosphorus co-deposition or nickel-phosphorus-tungsten co-deposition, reduce the internal stress of the coating, and prevent the generation of surface cracks; stabilizers can make the cathode current density distribution more uniform, promote the uniform flow of electrolytes under the action of a uniform electric field, and improve the compactness and uniformity of cathode deposition; the addition of inhibitors, attached to the cathode surface, inhibits the abnormal increase of micro-area current density, and on the one hand reduces the precipitation of impurity metal ions in the plating solution. The additives cooperate with each other within a certain concentration range (0.005-10g / L), and the compounding of all the above components and their contents forms a stable electroplating system, which can make the square resistance value of the final buried copper foil resistor layer more stable, and its square resistance tolerance is less than 5%.

[0059] (4) The resistance testing method provided by the present invention does not require first pressing the buried copper foil laminate into a board, then exposing, developing, and etching into a specific pattern, and then performing resistance testing. The resistance testing method first uses a low-temperature curing method to bond the alloy resistance layer of the buried copper foil to the support layer, then uses an etching solution to completely etch away the copper layer, exposing the side where the alloy resistance layer is bonded to the copper foil, then washes and dries the alloy resistance layer, and finally uses a four-probe probe to measure the square resistance of the alloy resistance layer. Compared with the traditional process, the method is simpler and more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic diagram of the structure of the buried copper foil of the present invention;

[0061] Figure 2 The actual photograph and electron microscope image of the buried copper foil product 3 prepared in Example 3 of the present invention;

[0062] Figure 3 is a flow chart of the present invention;

[0063] The reference numerals are as follows: 1-copper foil, 2-nickel-phosphorus alloy. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed but is merely representative of selected embodiments of the present invention.

[0066] Example 1

[0067] like Figure 3 The process shown:

[0068] A method for preparing a buried copper foil, the method comprising the following steps:

[0069] S1. Pre-treatment of base copper foil for deoxidation:

[0070] Take a copper foil with a base thickness of 18 μm and a surface roughness Rz of 3.5 μm, and pickle it at a temperature of 25°C for 20 seconds;

[0071] The pickling liquid is a 10wt% sulfuric acid aqueous solution;

[0072] S2, electroplating resistance layer:

[0073] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0074] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 200 g / L, the concentration of sodium citrate is 230 g / L, the concentration of sodium hypophosphite is 16 g / L, the concentration of boric acid is 35 g / L, the concentration of phosphoric acid is 30 g / L, and the concentration of sodium tungstate is 110 g / L.

[0075] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0076] The wetting agent is saccharin, and its content in the solution is 0.5 g / L;

[0077] The inhibitor is: dodecylamine ethoxy sulfate, and its content in the solution is: 0.15 g / L;

[0078] The stabilizer is sodium acetate, and its content in the solution is 3 g / L.

[0079] Again, adjust the pH of the plating solution to 2 with sulfuric acid or sodium hydroxide.

[0080] Finally, the electroplating temperature was controlled at 65°C and the electroplating current density was 10A / dm 2 .

[0081] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.3 μm.

[0082] S3, washing and drying:

[0083] The buried copper foil after electroplating was taken out, rinsed with pure water for 3 seconds at a water washing pressure of 0.5 MPa, and baked at 80° C. for 20 minutes to prepare a buried copper foil product 1.

[0084] At this time, the copper foil roughness of product 1 was tested, and its roughness Rz was 3.51 μm.

[0085] The resistance test method of the buried copper foil is divided into the following steps:

[0086] S4, the resistance layer and the supporting layer are bonded and cured;

[0087] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0088] The plastic film is PET; the adhesive is epoxy adhesive.

[0089] S5, etching;

[0090] Use etching solution to completely etch away the copper layer.

[0091] The etching solution is a mixed solution of copper chloride, ammonium chloride, ammonia water and pure water, and the mass ratios thereof are 10%:10%:35%:45% respectively;

[0092] The etching temperature is 40°C and the etching time is 30 min.

[0093] S6, washing and baking;

[0094] The PET film was taken out, washed with water, and baked at 40°C for 5 minutes. At this time, the PET film was bonded with a nickel-phosphorus alloy resistance layer;

[0095] S7, test resistance;

[0096] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 32.3Ω / □, and the resistance fluctuation was 3.5%.

[0097] Example 2

[0098] A method for preparing a buried copper foil, the method comprising the following steps:

[0099] S1. Pre-treatment of base copper foil for deoxidation:

[0100] A copper foil with a substrate thickness of 18 μm and a surface roughness Rz of 3.5 μm was pickled at a temperature of 20°C for 3 s;

[0101] The pickling liquid is a 15wt% sulfuric acid aqueous solution;

[0102] S2, electroplating resistance layer:

[0103] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0104] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 150 g / L, the concentration of sodium citrate is 30 g / L, the concentration of sodium hypophosphite is 30 g / L, the concentration of boric acid is 10 g / L, the concentration of phosphoric acid is 50 g / L, and the concentration of sodium tungstate is 0 g / L.

[0105] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0106] The wetting agent is saccharin, and its content in the solution is 0.1 g / L;

[0107] The inhibitor is: dodecylamine ethoxy sulfate, and its content in the solution is: 0.05g / L;

[0108] The stabilizer is potassium dihydrogen phosphate, and its content in the solution is 0.5 g / L.

[0109] Again, adjust the pH of the plating solution to 3 with sulfuric acid or sodium hydroxide.

[0110] Finally, the electroplating temperature was controlled at 40°C and the electroplating current density was 1A / dm 2 .

[0111] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.1 μm.

[0112] S3, washing and drying:

[0113] The buried copper foil after electroplating was taken out, rinsed with pure water for 2 seconds at a water washing pressure of 1.8 MPa, and baked at 80°C for 6 minutes to prepare buried copper foil product 2.

[0114] At this time, the copper foil roughness of product 2 was tested, and its roughness Rz was 3.48 μm.

[0115] The resistance test method of the buried copper foil is divided into the following steps:

[0116] S4, the resistance layer and the supporting layer are bonded and cured;

[0117] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0118] The plastic film is PP; the adhesive is modified phenolic adhesive.

[0119] S5, etching;

[0120] Use etching solution to completely etch away the copper layer.

[0121] The etching solution may also be a mixed solution of cupric chloride, ammonium chloride, ammonia water and pure water, with the mass ratios of 5%:3%:20%:72% respectively;

[0122] The etching temperature is 50°C and the etching time is 5 min.

[0123] S6, washing and baking;

[0124] Take out the PP film, wash it with water, and bake it at 100℃ for 1min. At this time, the PP film is bonded with the nickel-phosphorus alloy resistance layer;

[0125] S7, test resistance;

[0126] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 96.2Ω / □, and the resistance fluctuation was 4.5%.

[0127] Example 3

[0128] A method for preparing a buried copper foil, the method comprising the following steps:

[0129] S1. Pre-treatment of base copper foil for deoxidation:

[0130] Take a copper foil with a base thickness of 18 μm and a surface roughness Rz of 3.5 μm, and pickle it at a temperature of 30°C for 20 seconds;

[0131] The pickling liquid is a 20wt% sulfuric acid aqueous solution;

[0132] S2, electroplating resistance layer:

[0133] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0134] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 300 g / L, the concentration of sodium citrate is 360 g / L, the concentration of sodium hypophosphite is 4 g / L, the concentration of boric acid is 50 g / L, the concentration of phosphoric acid is 12 g / L, and the concentration of sodium tungstate is 180 g / L.

[0135] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0136] The wetting agent is saccharin, and its content in the solution is 0.9 g / L;

[0137] The inhibitor is: dodecylamine ethoxy sulfate, and its content in the solution is: 0.3 g / L;

[0138] The stabilizer is ammonium acetate, and its content in the solution is 10 g / L.

[0139] Again, adjust the pH of the plating solution to 1 with sulfuric acid or sodium hydroxide.

[0140] Finally, the electroplating temperature was controlled at 60°C and the electroplating current density was 15A / dm 2 .

[0141] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.4 μm.

[0142] S3, washing and drying:

[0143] The buried copper foil after electroplating was taken out, rinsed with pure water for 3 seconds at a water washing pressure of 0.8 MPa, and baked at 80°C for 15 minutes to prepare buried copper foil product 3.

[0144] The photo of the buried barrier copper foil product 3 is shown in Figure 2 As shown in (a), its surface color is uniform; under the electron microscope, Figure 2 As shown in (b), it presents a pointed ball cluster morphology, and the ball cluster particles are evenly distributed, which is consistent with the morphology of the copper foil treatment surface, indicating that the electroplating process will not have a negative impact on the original morphology of the copper foil, and can ensure good bonding with the semi-cured sheet during the pressing process.

[0145] At this time, the copper foil roughness of product 3 was tested, and its roughness Rz was 3.52 μm.

[0146] The resistance test method of the buried copper foil is divided into the following steps:

[0147] S4, the resistance layer and the supporting layer are bonded and cured;

[0148] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0149] The plastic film is PET; the adhesive is polyurethane adhesive.

[0150] S5, etching;

[0151] Use etching solution to completely etch away the copper layer.

[0152] The etching solution may also be a mixed solution of cupric chloride, ammonium chloride, ammonia water and pure water, with the mass ratios being 15%:15%:50%:20% respectively;

[0153] The etching temperature is 60°C and the etching time is 1 min.

[0154] S6, washing and baking;

[0155] The PET film was taken out, washed with water, and baked at 70°C for 3 minutes. At this time, the PET film was bonded with a nickel-phosphorus alloy resistance layer;

[0156] S7, test resistance;

[0157] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 24.8Ω / □, and the resistance fluctuation was 3.0%.

[0158] Example 4

[0159] A method for preparing a buried copper foil, the method comprising the following steps:

[0160] S1. Pre-treatment of base copper foil for deoxidation:

[0161] Take a copper foil with a base thickness of 35 μm and a surface roughness Rz of 5.5 μm, and pickle it at a temperature of 35°C for 10 seconds;

[0162] The pickling liquid is a 10wt% sulfuric acid aqueous solution;

[0163] S2, electroplating resistance layer:

[0164] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0165] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 250 g / L, the concentration of sodium citrate is 260 g / L, the concentration of sodium hypophosphite is 16 g / L, the concentration of boric acid is 40 g / L, the concentration of phosphoric acid is 30 g / L, and the concentration of sodium tungstate is 150 g / L.

[0166] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0167] The wetting agent is polyethylene glycol, and its content in the solution is 0.4 g / L;

[0168] The inhibitor is polyethyleneimine, and its content in the solution is 0.15 g / L;

[0169] The stabilizer is ammonium acetate, and its content in the solution is 3 g / L.

[0170] Again, adjust the pH of the plating solution to 3 with sulfuric acid or sodium hydroxide.

[0171] Finally, the electroplating temperature was controlled at 70°C and the electroplating current density was 12A / dm 2 .

[0172] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.2 μm.

[0173] S3, washing and drying:

[0174] The buried copper foil after electroplating was taken out, rinsed with pure water for 4 seconds at a water washing pressure of 1.5 MPa, and baked at 80°C for 10 minutes to prepare buried copper foil product 4.

[0175] At this time, the copper foil roughness of product 4 was tested, and its roughness Rz was 5.46.

[0176] The resistance test method of the buried copper foil is divided into the following steps:

[0177] S4, the resistance layer and the supporting layer are bonded and cured;

[0178] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0179] The plastic film is PI; the adhesive is acrylic adhesive.

[0180] S5, etching;

[0181] Use etching solution to completely etch away the copper layer.

[0182] The etching solution is a mixed solution of hydrogen peroxide, sulfuric acid, citric acid and pure water, with the mass ratios of 3%:7%:5%:85% respectively;

[0183] The etching temperature is 60°C and the etching time is 10 min.

[0184] S6, washing and baking;

[0185] The PI film was taken out, washed with water, and baked at 50°C for 4 minutes. At this time, the PI film was bonded with the nickel-phosphorus alloy resistance layer;

[0186] S7, test resistance;

[0187] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 49.5Ω / □, and the resistance fluctuation was 3.5%.

[0188] Example 5

[0189] A method for preparing a buried copper foil, the method comprising the following steps:

[0190] S1. Pre-treatment of base copper foil for deoxidation:

[0191] Take a copper foil with a base thickness of 35 μm and a surface roughness Rz of 0.5 μm, and pickle it at a temperature of 40°C for 3 seconds;

[0192] The pickling liquid is a 15wt% sulfuric acid aqueous solution;

[0193] S2, electroplating resistance layer:

[0194] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0195] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 90 g / L, the concentration of sodium citrate is 50 g / L, the concentration of sodium hypophosphite is 30 g / L, the concentration of boric acid is 10 g / L, the concentration of phosphoric acid is 50 g / L, and the concentration of sodium tungstate is 0 g / L.

[0196] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0197] The wetting agent is polyethylene glycol, and its content in the solution is 0.2 g / L;

[0198] The inhibitor is polyethyleneimine, and its content in the solution is 0.05 g / L;

[0199] The stabilizer is sodium dihydrogen phosphate, and its content in the solution is 0.5 g / L.

[0200] Again, adjust the pH of the plating solution to 3 with sulfuric acid or sodium hydroxide.

[0201] Finally, the electroplating temperature was controlled at 75°C and the electroplating current density was 2A / dm 2 .

[0202] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.1 μm.

[0203] S3, washing and drying:

[0204] The buried copper foil after electroplating was taken out, rinsed with pure water for 5 seconds, the water washing pressure was 2MPa, and baked at 80°C for 5 minutes to prepare the buried copper foil product 5.

[0205] At this time, the copper foil roughness of product 5 was tested, and its roughness Rz was 0.48 μm.

[0206] The resistance test method of the buried copper foil is divided into the following steps:

[0207] S4, the resistance layer and the supporting layer are bonded and cured;

[0208] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0209] The plastic film is PVC; the adhesive is a polyimide adhesive.

[0210] S5, etching;

[0211] Use etching solution to completely etch away the copper layer.

[0212] The etching solution is a mixed solution of hydrogen peroxide, sulfuric acid, citric acid and pure water, with the mass ratios of 1%:3%:1%:95% respectively;

[0213] The etching temperature is 40°C and the etching time is 30 min.

[0214] S6, washing and baking;

[0215] Take out the PVC film, wash it with water, and bake it at 80℃ for 2 minutes. At this time, the PVC film is bonded with a nickel-phosphorus alloy resistance layer;

[0216] S7, test resistance;

[0217] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 97Ω / □, and the resistance fluctuation was 4.8%.

[0218] Example 6

[0219] A method for preparing a buried copper foil, the method comprising the following steps:

[0220] S1. Pre-treatment of base copper foil for deoxidation:

[0221] Take a copper foil with a base thickness of 35 μm and a surface roughness Rz of 10 μm, and pickle it at a temperature of 25°C for 20 seconds;

[0222] The pickling liquid is a 20wt% sulfuric acid aqueous solution;

[0223] S2, electroplating resistance layer:

[0224] First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution.

[0225] In the prepared electroplating solution, the concentration of nickel sulfate hexahydrate is 300 g / L, the concentration of sodium citrate is 400 g / L, the concentration of sodium hypophosphite is 3 g / L, the concentration of boric acid is 50 g / L, the concentration of phosphoric acid is 6 g / L, and the concentration of sodium tungstate is 200 g / L.

[0226] Secondly, adding additives, which include one or more of wetting agents, inhibitors, and stabilizers;

[0227] The wetting agent is polyethylene glycol, and its content in the solution is 1 g / L;

[0228] The inhibitor is polyethyleneimine, and its content in the solution is 0.3 g / L;

[0229] The stabilizer is sodium acetate, and its content in the solution is 6 g / L.

[0230] Again, adjust the pH of the plating solution to 1.5 with sulfuric acid or sodium hydroxide.

[0231] Finally, the electroplating temperature was controlled at 80°C and the electroplating current density was 8A / dm 2 .

[0232] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 0.5 μm.

[0233] S3, washing and drying:

[0234] The buried copper foil after electroplating was taken out, rinsed with pure water for 3 seconds at a water washing pressure of 1 MPa, and baked at 80°C for 18 minutes to prepare buried copper foil product 6.

[0235] At this time, the copper foil roughness of product 6 was tested, and its roughness Rz was 9.96 μm.

[0236] The resistance test method of the buried copper foil is divided into the following steps:

[0237] S4, the resistance layer and the supporting layer are bonded and cured;

[0238] Use adhesive to tightly bond the resistor layer to the plastic film, with a curing temperature of 40°C and a curing time of 12 hours;

[0239] The plastic film is PI; the adhesive is UV glue.

[0240] S5, etching;

[0241] Use etching solution to completely etch away the copper layer.

[0242] The etching solution is a mixed solution of hydrogen peroxide, sulfuric acid, citric acid and pure water, with the mass ratios of 5%:10%:10%:75% respectively;

[0243] The etching temperature is 30°C and the etching time is 10 min.

[0244] S6, washing and baking;

[0245] The PI film was taken out, washed with water, and baked at 60°C for 4 min. At this time, the PI film was bonded with a nickel-phosphorus alloy resistor layer;

[0246] S7, test resistance;

[0247] The resistance of the nickel-phosphorus alloy layer was tested using a four-probe square resistance tester. The square resistance of the nickel-phosphorus alloy resistance layer was 20Ω / □, and the resistance fluctuation was 3.3%.

[0248] Comparative Example 1

[0249] The difference from Example 1 is that:

[0250] S2, electroplating resistance layer:

[0251] When adding additives, saccharin and dodecylamine ethoxysulfate were removed and only sodium acetate was added. The content of sodium acetate in the solution was also 3 g / L.

[0252] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 1 μm.

[0253] S3, washing and drying:

[0254] After washing and drying, the comparison buried copper foil product 1 was obtained.

[0255] At this time, the copper foil roughness of the buried copper foil product 1 was tested and compared, and its roughness Rz was 3.53 μm.

[0256] Finally, the buried copper foil was tested for resistance. The square resistance of the nickel-phosphorus alloy resistance layer was 8.6Ω / □, and the resistance fluctuation was 5.3%.

[0257] Compared with Example 1, the square resistance of this comparative example is significantly reduced, and the resistance fluctuation is increased.

[0258] Comparative Example 2

[0259] The difference from Example 4 is that:

[0260] S2, electroplating resistance layer:

[0261] In the prepared electroplating solution, the boric acid concentration is 0 g / L.

[0262] Among the additives added, polyethyleneimine is removed, leaving only polyethylene glycol and sodium acetate.

[0263] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 1 μm.

[0264] S3, washing and drying:

[0265] After washing and drying, the comparison buried copper foil product 2 was obtained.

[0266] At this time, the copper foil roughness of the buried copper foil product 2 was tested and compared, and its roughness Rz was 5.48 μm.

[0267] Finally, the buried copper foil was tested for resistance. The square resistance of the nickel-phosphorus alloy resistance layer was 8.7Ω / □, and the resistance fluctuation was 5.1%.

[0268] Compared with Example 4, the square resistance of this comparative example is significantly reduced, and the resistance fluctuation is increased.

[0269] Comparative Example 3

[0270] The difference from Example 1 is that:

[0271] S2, electroplating resistance layer:

[0272] In the prepared electroplating solution, the concentration of sodium citrate is 0 g / L.

[0273] Among the additives added, dodecylamine ethoxysulfate was removed, and only saccharin and sodium acetate were retained.

[0274] After electroplating, the thickness of the nickel-phosphorus alloy ultra-thin resistor layer is 1 μm.

[0275] S3, washing and drying:

[0276] After washing and drying, the comparison buried copper foil product 3 was obtained.

[0277] At this time, the copper foil roughness of the buried copper foil product 3 was tested and compared, and its roughness Rz was 5.49 μm.

[0278] Finally, the buried copper foil was tested for resistance. The square resistance of the nickel-phosphorus alloy resistance layer was 8.3Ω / □, and the resistance fluctuation was 5.5%.

[0279] Compared with Example 1, the square resistance of this comparative example is significantly reduced, and the resistance fluctuation is increased.

[0280] The comparison between the above embodiments and the comparative examples shows that:

[0281] By adjusting the amount of complexing agent and additives in the electroplating system, the electroplating uniformity of the alloy resistor layer can be adjusted, thereby controlling the fluctuation of square resistance. Appropriate complexing agent and additives are conducive to stabilizing the electroplating system and reducing the fluctuation of square resistance.

[0282] In conclusion, the present invention has indeed established a stable electroplating system, and the square resistance of the produced buried copper foil resistor layer is more stable, and its resistance tolerance is up to 4.8%, which is significantly lower than that of each comparative example.

Claims

1. A method for preparing buried copper foil, It is characterized in that The method consists of the following steps: S1. Pre-treatment of base copper foil for deoxidation: Take the copper foil and pickle it; S2, electroplating resistance layer: First, pure water is used as a solvent, and the following components of the electroplating solution are added thereto to prepare the electroplating solution; In the electroplating solution, the concentration of nickel sulfate hexahydrate is 90-300 g / L, the concentration of sodium citrate is 30-400 g / L, the concentration of sodium hypophosphite is 3-30 g / L, the concentration of boric acid is 10-50 g / L, the concentration of phosphoric acid is 6-50 g / L, and the concentration of sodium tungstate is 0-200 g / L; Secondly, adding additives, the additives include wetting agents, inhibitors, and stabilizers, wherein the wetting agent is: saccharin, polyethylene glycol, one of the two, the content of which in the solution is: 0.1-1g / L; The inhibitor is: one of dodecylamine ethoxy sulfate and polyethylene imine, and the content in the solution is: 0.05-0.3g / L; The stabilizer is one of acetate, potassium dihydrogen phosphate and sodium dihydrogen phosphate, and the content in the solution is 0.5-10g / L; Again, adjust the pH of the plating solution to 1-5 with sulfuric acid or sodium hydroxide; Finally, electroplating is performed; After electroplating, the thickness of the ultra-thin nickel-phosphorus alloy resistance layer is 0.1-1μm; S3, washing and drying: The buried copper foil after electroplating was taken out, washed with pure water and then dried to prepare the buried copper foil, the roughness Rz of which was 0.48-9.96 μm.

2. A method for preparing a buried copper foil as claimed in claim 1, It is characterized in that The base thickness of the copper foil in S1 is 18-35 μm; At a pickling temperature of 20-40°C, the pickling time is 3-20s; The pickling solution is a 10-20 wt % sulfuric acid aqueous solution.

3. A method for preparing a buried copper foil as claimed in claim 1 or 2, It is characterized in that In S2: the electroplating temperature is controlled at 40-80°C; the electroplating current density is 1-15A / dm 2 .

4. A method for preparing a buried copper foil as claimed in claim 3, It is characterized in that Rinse with pure water in S3 for 2-5s, the water washing pressure is 0.5-2MPa, and bake at 80℃ for 5-20min.

5. A method for testing the resistance of a buried copper foil prepared by the method according to any one of claims 1 to 4, It is characterized in that The method consists of the following steps: S4, the resistance layer and the supporting layer are bonded and cured; The ultra-thin resistor layer of the buried copper foil is bonded to the plastic film and heated for curing at 40°C for 12 hours. S5, etching; The copper layer is completely etched using an etching solution; S6, washing and baking; Take out the plastic film, wash it with water, and dry it at 40-100℃ for 1-5min. At this time, the plastic film is bonded with a nickel-phosphorus alloy resistance layer; S7, test resistance; The square resistance of the nickel-phosphorus alloy resistor layer can be obtained by testing the resistance of the nickel-phosphorus alloy layer using a four-probe square resistance tester.

6. A method for testing resistance of buried copper foil as claimed in claim 5, It is characterized in that In S5: the etching solution is a mixed solution of hydrogen peroxide, sulfuric acid, citric acid and pure water, and the mass ratios thereof are 1%-5%: 3%-10%: 1%-10%: 75%-95% respectively; The etching temperature is 30-60°C, and the etching time is 1min-30min.

7. A method for testing resistance of buried copper foil as claimed in claim 5, It is characterized in that In S5: the etching solution is a mixed solution of copper chloride, ammonium chloride, ammonia water and pure water, and the mass ratios thereof are 5%-15%: 3%-15%: 20%-50%: 20%-72% respectively; The etching temperature is 40-60°C, and the etching time is 1min-30min.

8. A method for testing resistance of buried copper foil as claimed in claim 6 or 7, It is characterized in that In S4: the plastic film is one of PET, PI, PP and PVC; The adhesive includes one or more of epoxy adhesive, modified phenolic adhesive, polyurethane adhesive, acrylic adhesive, polyimide adhesive, and UV adhesive.

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