Resistance-embedded copper foil and preparation method and application thereof

Abstract

The invention belongs to the technical field of printed circuit boards, and relates to a buried resistor copper foil and a preparation method and application thereof. In the preparation of the buried resistance copper foil, the film with the window is selected to be attached to the upper surface and the lower surface of the copper foil, the copper foil with the resistance window is obtained through etching, then the resistance layer is directly and electrically deposited in the resistance window of the copper foil, and then the film is removed to obtain the buried resistance copper foil. The method can effectively reduce the resistance value difference of the unit area of each square resistance layer on the copper foil so as to improve the resistance value precision of the embedded resistance copper foil, and the preparation process is simple and easy to operate.

Description

Technical Field

[0001] The invention belongs to the technical field of printed circuit boards and relates to a buried barrier copper foil and a preparation method and application thereof. Background Art

[0002] The surface of traditional PCB boards is often covered with resistor components, which not only takes up a lot of board space, but also affects the decoupling effect of signal transmission impedance due to the presence of vias and wires, which may cause problems with the integrity of transmission line signals. In order to solve this problem, embedded resistor technology came into being and became the key to the integration of resistor devices. It plays an important role in resistor power amplification, voltage conversion, signal input / output, temperature compensation and power supply filtering.

[0003] Embedded resistor technology significantly shortens the line length between components, effectively improves electrical characteristics, and increases the utilization rate of PCB packaging area by embedding a large number of embedded passive component resistors directly into the PCB board in the high-frequency and high-speed fields. This technology also reduces the number of solder joints on the PCB board surface, thereby improving the reliability of the package and reducing production costs.

[0004] Buried resistor copper foil is one of the key materials for embedded resistor technology. Currently, the more conventional buried resistor copper foil is prepared by forming a coating with specific resistance properties on the surface of the copper foil through electroplating, chemical plating, metal etching or magnetron sputtering. The resistor material is deposited on the surface of the copper foil to form a buried resistor copper foil, and then buried in the printed circuit through lamination technology. This not only places high demands on the production process cost, buried resistor material development and reliability, but also puts forward new requirements for the buried resistor manufacturing process. Among them, the production process is used to produce the buried resistor resistance value, and reducing the resistance value error generated in the manufacturing process is the current focus of industry research.

[0005] When the buried copper foil is used in the downstream PCB board, it usually needs to go through the following steps: film pasting - exposure - development - etching to remove the copper layer of non-circuit graphics → etching to remove the resistor layer of non-circuit graphics → film stripping - film pasting - exposure - development - etching to remove the copper layer in the circuit graphics to expose the buried resistor graphics - film stripping. Only after the above steps are completed can a circuit with resistor function be obtained, and the process is relatively complicated. This buried copper foil prepared by forming a resistor layer on the surface of the copper foil often has a thin resistor layer thickness of only 0.1-1μm. The buried resistor function circuit formed by multiple etchings needs to undergo multiple pressing and etching in the production of PCB boards, which can easily cause changes in the thickness of the resistor layer, and even deformation and fracture of the resistor layer, affecting the size and accuracy of the resistance value; and after the buried copper foil is etched to expose the buried resistor graphics, there is still a resistor layer under the copper foil, which will also affect the design of the size and accuracy of the resistance value of the buried resistor graphics.

[0006] Chinese invention patent application CN117500173A discloses a method for manufacturing a buried resistor PCB, which first opens a resistor window of the required size on the copper foil on the surface of the copper clad board, then fills the resistor slurry into the resistor window by screen printing, and then obtains the buried resistor copper foil through drying, curing, and grinding. Subsequently, according to the resistor position and circuit design, the required buried resistor PCB board can be obtained through etching. This method reduces the multiple etching of the buried resistor copper foil, which is beneficial to the control of the resistance value, but requires grinding to remove the excess cured resistor slurry outside the resistor window, and the process is still relatively complicated.

[0007] Due to the obvious advantages of embedded resistor PCB, it is widely used in cutting-edge electronic product fields such as military, aviation, aerospace, as well as civilian electronic products such as mobile phones, laptops and network equipment. As a new generation of high-end resistor products, the buried resistor copper foil obtained by the current research and development process has a limited scope of use, and there is still a lot of room for improvement in all aspects of performance. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a buried copper foil and a preparation method and application thereof. The method can effectively reduce the resistance value difference per unit area of ​​each block resistance layer on the copper foil to improve the resistance value accuracy of the buried copper foil, and the preparation process is simple and easy to operate.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] One of the purposes of the present invention is:

[0011] A method for preparing a buried copper foil is provided, comprising the following steps:

[0012] (1) electrolytic preparation of copper foil, washing and drying;

[0013] (2) Covering and laminating the upper and lower surfaces of the copper foil with a film having a resistance window;

[0014] (3) immersing the copper foil after laminating the film into an etching solution, etching the exposed copper foil to form a resistance window, washing and drying;

[0015] (4) A resistor layer is prepared at the resistor window by electroplating, and the film is peeled off after washing to obtain the buried copper foil.

[0016] Furthermore, in step (1), the electrolyte used for electrolysis comprises: copper sulfate solution, chloride ions and additives.

[0017] Preferably, in the electrolyte, the copper ion content is 70-110 g / L, the sulfuric acid content is 90-130 g / L, the chloride ion content is 10-30 mg / L, and the total amount of additives is 25-45 mg / L.

[0018] Furthermore, the additives include brighteners, moving agents and leveling agents.

[0019] Preferably, the brightener is 5-10 mg / L sodium polydisulfide dipropane sulfonate; the moving agent is 10-20 mg / L polyethylene glycol with a molecular weight of 4000-6000 Da; and the leveling agent is 10-20 mg / L hydrolyzed collagen with a molecular weight of 2000-3000 Da.

[0020] Furthermore, the electrolysis conditions are: the current density is 25-50A / m 2 , the flow rate of electrolyte is 10-35m 3 / h.

[0021] In some specific embodiments of the present invention, the specific operation of preparing copper foil by electrolysis is: preparing copper foil by electrolysis using a cathode roller in the electrolyte of an anode tank.

[0022] In some specific embodiments of the present invention, the specific operation of film lamination is: the upper and lower films with resistance windows are tightly laminated on the upper and lower surfaces of the copper foil respectively through upper and lower pressing rollers.

[0023] In the present invention, the position of the resistance window of the copper foil can be designed according to the position of the required buried copper foil; and the size of the resistance window can be calculated according to the resistance value of the required buried copper foil, and the calculation formula is as follows:

[0024] Resistance window length = resistance value × resistance window width × copper foil thickness / resistivity of designed resistance layer

[0025] Then, the position and size of the film window are produced according to the position and size of the resistance window of the ultra-thin copper foil.

[0026] Preferably, the film unwinding and winding speeds are the same, and are the same as the cathode roller rotation speed and the buried copper foil winding speed, both of which are 0.5-5m / min; if the speeds are inconsistent or too fast or too slow, it will affect whether the window positions of the upper and lower films are aligned, affect the size of the etchable part of the copper foil, and then cause the position and size of the resistor window to shift, and ultimately cause the resistor layer to deviate from the design size and vary in size, affecting the precision and accuracy.

[0027] Furthermore, in step (3), the etching solution is an acidic cupric chloride etching solution; wherein the acidic cupric chloride etching solution contains 90-110 g / L of cupric chloride, 3.65-18.25 g / L of hydrochloric acid, and 12-24 mg / L of corrosion inhibitor per 1 L of ultrapure water.

[0028] Furthermore, the corrosion inhibitor includes one or more of benzotriazole, benzimidazole and 2-mercaptobenzothiazole.

[0029] The temperature of the acidic cupric chloride etching solution is 45-55°C.

[0030] The etching solution of the present invention can obtain a faster etching rate and improve production efficiency. The corrosion inhibitor used in the present invention can be effectively adsorbed on the copper surface to form a protective film, improve the flatness of the etching surface of the copper foil, reduce the side etching amount, increase the etching factor, improve the etching accuracy, and reduce the corrosion and loss of the etching equipment.

[0031] Furthermore, in step (4), the electroplating solution used comprises: nickel salt, chromium salt, sodium hypophosphite and boric acid.

[0032] Preferably, the nickel ion concentration in the electroplating solution is 20-32 g / L, the chromium ion concentration is 4-8 g / L, the sodium hypophosphite concentration is 20-32 g / L, and the boric acid concentration is 10-16 g / L.

[0033] Furthermore, the temperature of the electroplating solution is 48-52°C, and the current density used for electroplating is 150-400A / dm 2 .

[0034] In the above steps, ultrapure water is used for washing at a temperature of 25-35°C and a flow rate of 10-30 mL / s; and the drying temperature is 130-140°C.

[0035] In some preferred embodiments of the present invention, the preparation method further comprises: performing a silanization treatment on the buried copper foil obtained in step (4).

[0036] Preferably, the silanization treatment uses a silane coupling agent selected from one or more of γ-aminopropyltriethoxysilane (KH550), γ-glycidyloxypropyltrimethoxysilane (KH560) and γ-methacryloxypropyltrimethoxysilane (KH570).

[0037] More preferably, the concentration of the silane coupling agent solution is 1.0-1.5 g / L, and the pH value is 9-12.

[0038] More preferably, the silanization treatment temperature is 25-35°C.

[0039] The second object of the present invention is:

[0040] Provided is a buried barrier copper foil prepared by any of the above-mentioned preparation methods.

[0041] Furthermore, the roughness of the smooth surface and the matte surface of the buried copper foil are both: Ra≤0.3μm, Rz≤2.5μm, and the resistance error is ≤10%.

[0042] The third object of the present invention is:

[0043] Provided is a buried barrier copper foil prepared by any of the above-mentioned preparation methods or the use of the buried barrier copper foil in preparing a printed circuit board.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. In the preparation of the buried copper foil of the present invention, a film with a window is selected and laminated on the upper and lower surfaces of the copper foil, and then the copper foil with a resistance window is obtained by etching. Then, a resistance layer is directly deposited in the resistance window of the copper foil, and then the film is removed to obtain the buried copper foil. The overall process is simple and easy to operate. The thickness of the resistance layer is consistent with that of the copper foil, which is controllable, and the resistance change caused by the change of the thickness of the resistance layer can be avoided, which effectively improves the resistance accuracy. The buried copper foil can also clearly distinguish the copper foil and the resistance area, effectively reduce the resistance value difference per unit area of ​​the resistance layer of each block on the copper foil, and further improve the resistance accuracy. When in use, there is no resistance layer under the copper foil, the current path is clear, and the resistance value is not easily disturbed by the resistance layer under the copper foil, which makes the design and realization of the size of the resistance layer of the downstream product more accurate.

[0046] 2. In addition, the etching process uses an easily controlled acidic etching solution and introduces a corrosion inhibitor, which can provide a precisely sized resistance window compared to other etching solutions. In the electroplating process, the composition ratio and grain size of each element in the nickel-phosphorus-chromium alloy layer can be changed by controlling the concentration of the electroplating solution and adjusting the current density, thereby adjusting the resistance value. The composition of the resistance layer electroplating solution is stable, and the concentration and parameters are easy to control, which also provides a basis for the precision control of the resistance value.

[0047] 3. The buried copper foil can be further silanized to effectively improve its bonding strength with the substrate, and its comprehensive performance is better;

[0048] 4. After the subsequent pressing, the buried resistor copper foil prepared by this method can only etch the copper foil layer as needed, without etching the resistor layer, which is more convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The buried copper foil in the prior art (a) and its use schematic diagram (b);

[0050] Figure 2 Schematic diagram of the products of each step in preparing the buried copper foil of the present invention: copper foil layer (a), film pasted on both sides of the copper foil layer (b), etching copper foil (c), resistor layer deposition (d), buried copper foil (e), and the effect of using the buried copper foil after downstream etching (f). DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in combination with the drawings in the embodiments of the present invention and the prior art. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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. It is worth noting that the raw materials used in the present invention are all common commercial products, and their sources are not specifically limited.

[0052] Example 1

[0053] Prepare buried resistor PCB (resistance 25Ω, resistivity 3×10 -5 Ω·m, buried resistance line with line width of 1.0mm and thickness of 3μm), the specific preparation process steps are as follows:

[0054] (1) Electrolysis was performed using a cathode roller in an anode tank containing an electrolyte (wherein the electrolyte contained 100 g / L copper ions, 125 g / L sulfuric acid, 10 mg / L chloride ions, 10 mg / L SPS, 15 mg / L PEG, and 15 mg / L HC) (the current density was set to 50 A / m 2 , the flow rate of electrolyte is 30m 3 / h, temperature 50°C) to prepare copper foil, and then washed with ultrapure water (temperature 30°C, water washing flow rate 20mL / s) and dried (drying temperature 130°C) to obtain a copper foil layer. Figure 2 (a)

[0055] (2) Calculate the resistance window length according to the design requirements. Resistance window length = resistance value × resistance window width × copper foil thickness / resistivity of designed resistance layer = 25Ω × 1.0mm × 3μm / (3 × 10 -5 Ω·m)=2.5mm; that is, the size of the resistance window is 2.5mm long and 1.0mm wide; the upper and lower films with the resistance window of this size are tightly attached to the upper and lower surfaces of the copper foil layer prepared in step (1) through upper and lower pressing rollers (wherein the film unwinding speed is 2m / min), and the structure is as follows Figure 2 As shown in (b);

[0056] (3) immersing the copper foil obtained in step (2) into an acidic copper chloride etching solution (wherein the acidic copper chloride etching solution contains 100 g / L copper chloride, 11 g / L hydrochloric acid, and 18 mg / L benzotriazole as a corrosion inhibitor), heating the solution to 50° C., etching the exposed copper foil to form a resistance window, and washing the copper foil with ultrapure water (temperature 30° C., water washing flow rate 20 mL / s) to obtain the following: Figure 2 The structure shown in (c);

[0057] (4) The copper foil obtained in step (3) was immersed in an electroplating tank containing an electroplating solution (wherein the nickel ion concentration in the electroplating solution was 26 g / L, the chromium ion concentration was 6 g / L, the sodium hypophosphite concentration was 26 g / L, and the boric acid concentration was 13 g / L), and the temperature was raised to 50° C., and the copper foil was used as a cathode for electroplating (the current density was 200 A / dm 2 ), and washed with ultrapure water (temperature 30°C, washing flow rate 20mL / s), to obtain Figure 2 The structure shown in (d);

[0058] (5) After the upper and lower films are peeled off from the buried copper foil by a peeling roller, they are rolled up (wherein the film rolling speed is 2 m / min) to obtain a buried copper foil having a structure as shown in FIG. Figure 2 As shown in (e);

[0059] The buried copper foil structure in the prior art is as follows Figure 1 As shown, there is a resistance layer under the copper foil layer, and the present invention can clearly distinguish the copper foil and the resistance area. There is no resistance layer under the copper foil when in use, the current path is clear, and the current changes with the frequency and rate. There will be different running depths when running on different conductors, that is, the skin effect. The present invention has no redundant resistance layer, and the resistance value is not easily affected by the resistance layer under the copper foil, so the size design of the resistance layer of downstream products can be more accurate.

[0060] (6) The surface of the buried copper foil obtained in step (5) that needs to be bonded to the substrate is sprayed with KH550 (concentration of 1.0 g / L, pH of 10, temperature of 30° C.), and then attached to the substrate (epoxy resin, surface roughness Rz = 0.11 μm), and dried at 130° C. to obtain a buried PCB board with a structure as shown in FIG. Figure 2 As shown in (f) in .

[0061] Example 2

[0062] Compared with Example 1, the only difference is that the resistance of the buried copper foil is designed to be 50Ω and the resistivity is 3×10 -5 Ω·m, corresponding to the film window size of 5 mm in length and 1.0 mm in width; other steps are the same as those in Example 1.

[0063] Example 3

[0064] Compared with Example 1, the only difference is that the resistance of the buried copper foil is designed to be 100Ω and the resistivity is 3×10 -5 Ω·m, corresponding to the film window size of 10 mm in length and 1.0 mm in width; other steps are the same as those in Example 1.

[0065] Example 4

[0066] Compared with Example 1, the only difference is that the copper chloride content in the etching solution is 90 g / L, the hydrochloric acid content is 3.65 g / L, and the corrosion inhibitor benzotriazole is 12 mg / L; the nickel ion concentration in the plating solution is 20 g / L, the chromium ion concentration is 4 g / L, the sodium hypophosphite concentration is 20 g / L, and the boric acid concentration is 10 g / L), wherein the resistivity of the resistor layer is 3.11×10- 5 Ω·m, according to the calculation, the film window size is 2.4mm long.

[0067] Example 5

[0068] Compared with Example 1, the only difference is that: the cupric chloride content in the etching solution is 110 g / L, the hydrochloric acid content is 18.25 g / L, and the corrosion inhibitor benzotriazole is 24 mg / L; the nickel ion concentration in the plating solution is 32 g / L, the chromium ion concentration is 8 g / L, the sodium hypophosphite concentration is 32 g / L, and the boric acid concentration is 16 g / L), wherein the resistivity of the resistor layer is 2.93×10-5Ω·m, and the film window size is calculated to be 2.6 mm long.

[0069] The relevant performance characterization results of the raw foil and buried resistor PCB prepared in the above embodiments are shown in Table 1 and Table 2.

[0070] Table 1 Surface roughness results of raw foil

[0071] Smooth surface Ra(μm) Smooth surface Rz(μm) Rough surface Ra(μm) Rough surface Rz(μm) Example 1 0.25±0.02 1.65±0.12 0.23±0.01 1.63±0.08 Example 2 0.24±0.03 1.62±0.08 0.22±0.02 1.62±0.08 Example 3 0.24±0.02 1.69±0.11 0.23±0.01 1.65±0.07 Example 4 0.23±0.03 1.63±0.11 0.22±0.01 1.63±0.07 Example 5 0.24±0.03 1.67±0.09 0.22±0.01 1.62±0.09

[0072] Table 2 Characterization results of related performance of buried resistance PCB board

[0073]

[0074] Comparative Example 1

[0075] On the basis of Example 3, a buried resistor PCB board (resistance value 25Ω, line width 1.0mm, thickness 3μm) was prepared according to the method of Example 1 of patent application CN202311453465.8, and the specific steps were as follows:

[0076] (1) Experimental materials: copper foil prepared in step (1) of Example 1; low-temperature curing resistor paste having a resistivity of 1000 Ω·mm 2 / m; the material of the substrate is epoxy resin (surface roughness Rz ≤ 5% of the copper foil thickness);

[0077] (2) According to calculation, the length of the resistance window is:

[0078] Copper foil thickness × resistor window (line) width × design resistor / paste resistivity = 0.03mm × 1.0mm × 25Ω / 1000 (Ω·mm 2 / m)=0.00075m=0.75mm; that is, the size of the resistor window is 0.75mm long and 1.0mm wide;

[0079] (3) According to the requirements of the position, length and width of the resistor, a dry film is produced, and the film is stripped by exposure, development and etching to form a resistor window on the upper copper layer of the copper-clad laminate. The etching solution used is an acidic etching solution (the same acidic copper chloride etching solution as in Example 1);

[0080] (4) Fill the resistor slurry into the resistor window by screen printing; then put it into an oven for drying, and then put it into a 200°C curing furnace for curing for 30 minutes;

[0081] (5) Use a non-woven cloth grinding machine to grind the resistor paste to remove excess solidified resistor paste outside the resistor window, so that the upper end surface of the resistor paste in the resistor window is flush with the surface of the upper copper layer.

[0082] Comparative Example 2

[0083] Compared with Example 1, the only difference is that step (3) adopts step (3) in comparative example 1 for etching; the other steps are the same as Example 1.

[0084] Comparative Example 3

[0085] Compared with Example 1, the only difference is that steps (4)-(5) are used to prepare the resistance layer by using steps (4)-(5) in Comparative Example 1; the other steps are the same as Example 1.

[0086] Comparative Example 4

[0087] Compared with Example 1, the only difference is that the etching solution uses basic copper sulfate; the other steps are the same as Example 1.

[0088] Comparative Example 5

[0089] Compared with Example 1, the only difference is that the film unwinding and winding speed is 0.3 m / min.

[0090] Comparative Example 6

[0091] Compared with Example 1, the only difference is that the nickel ion concentration in the electroplating solution is 34 g / L, the chromium ion concentration is 4.25 g / L, the sodium hypophosphite concentration is 34 g / L, and the boric acid concentration is 26 g / L.

[0092] Comparative Example 7

[0093] Compared with Example 1, the only difference is that the nickel ion concentration in the electroplating solution is 18 g / L, the chromium ion concentration is 4 g / L, the sodium hypophosphite concentration is 18 g / L, and the boric acid concentration is 9 g / L.

[0094] Comparative Example 8

[0095] Compared with Example 1, the only difference is that during the electroplating process, the current density is 500A / dm 2 .

[0096] Table 3 Characterization results of buried copper foil related properties

[0097]

[0098] It can be seen from the above table that compared with Example 1, the buried copper foil obtained by the preparation method of the present invention has small roughness and high resistance accuracy through Comparative Examples 1-3. After the etching solution is replaced by basic copper sulfate, the problem of large side corrosion occurs, and the resistance accuracy cannot be guaranteed. Similarly, the film unwinding and winding speed is too slow, the etching time is long, resulting in side corrosion, and the thickness of the resistor layer will also increase. In addition, the ion concentration in the electroplating solution also has a great influence on the resistance. If the concentration is too high, the resistor layer becomes thicker and the resistance value is too small; if the concentration is too low, the resistor layer becomes thinner and the resistance value is too large; in addition, during the electroplating process, if the current density is too large, the surface roughness will increase, and the grain size of the resistor layer will become smaller, resulting in a large resistance value.

[0099] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a buried copper foil, characterized in that: The following steps are involved: (1) preparing copper foil by electrolysis, washing and drying; (2) Covering and laminating the upper and lower surfaces of the copper foil with a film having a resistance window; (3) immersing the copper foil after laminating the film into an etching solution, etching the exposed copper foil to form a resistance window, washing and drying; (4) A resistor layer is prepared at the resistor window by electroplating, and the film is peeled off after washing to obtain the buried copper foil.

2. The preparation method according to claim 1, characterized in that: In step (1), the electrolyte used for electrolysis comprises: copper sulfate solution, chloride ions and additives; wherein the copper ion content in the electrolyte is 70-110 g / L, the sulfuric acid content is 90-130 g / L, the chloride ion content is 10-30 mg / L, and the total amount of additives is 25-45 mg / L; the conditions for electrolysis are: the current density is 25-50 A / m 2 , the flow rate of electrolyte is 10-35m 3 / h.

3. The preparation method according to claim 2, characterized in that: The additives include brightener, displacement agent and leveling agent; wherein the brightener is 5-10 mg / L sodium polydisulfide dipropane sulfonate; the displacement agent is 10-20 mg / L polyethylene glycol with a molecular weight of 4000-6000 Da; and the leveling agent is 10-20 mg / L hydrolyzed collagen with a molecular weight of 2000-3000 Da.

4. The preparation method according to claim 1, characterized in that: The film unwinding and rewinding speeds are the same, and are the same as the cathode roller rotation speed and the buried copper foil rewinding speed, both of which are 0.5-5m / min.

5. The preparation method according to claim 1, characterized in that: In step (3), the etching solution is an acidic cupric chloride etching solution; wherein, in the acidic cupric chloride etching solution, each 1L of ultrapure water contains 90-110g / L of cupric chloride, 3.65-18.25g / L of hydrochloric acid, and 12-24mg / L of corrosion inhibitor; the corrosion inhibitor includes one or more of benzotriazole, benzimidazole and 2-mercaptobenzothiazole; the temperature of the acidic cupric chloride etching solution is 45-55°C.

6. The preparation method according to claim 1, characterized in that: In step (4), the electroplating solution used for electroplating comprises: nickel salt, chromium salt, sodium hypophosphite and boric acid; wherein the nickel ion concentration in the electroplating solution is 20-32 g / L, the chromium ion concentration is 4-8 g / L, the sodium hypophosphite concentration is 20-32 g / L, and the boric acid concentration is 10-16 g / L.

7. The preparation method according to claim 6, characterized in that: The plating solution temperature is 48-52°C, and the electroplating current density is 150-400A / dm 2 .

8. The preparation method according to claim 1, characterized in that: The preparation method further comprises: performing silanization treatment on the buried copper foil obtained in step (4); the silanization treatment uses a silane coupling agent selected from one or more of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane; the concentration of the silane coupling agent solution is 1.0-1.5 g / L, and the pH value is 9-12; the silanization treatment temperature is 25-35°C.

9. The buried copper foil prepared by the preparation method according to any one of claims 1 to 8, characterized in that: Roughness Ra≤0.3μm, Rz≤2.5μm, resistance error≤10%.

10. Use of the buried barrier copper foil prepared by the preparation method according to any one of claims 1 to 8 or the buried barrier copper foil according to claim 9 in the preparation of printed circuit boards.

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