Reversed copper foil and preparation method thereof, copper-clad plate and printed circuit board

Abstract

The invention relates to a reverse copper foil and a preparation method thereof, a copper-clad plate and a printed circuit board. The preparation method of the reverse copper foil comprises the following steps: sequentially carrying out roughening treatment and curing treatment on one surface of an electrolytic copper foil; carrying out silanization treatment on at least one surface of the cured electrolytic copper foil to prepare a reversed copper foil; a roughening solution for roughening treatment comprises the following components in mass concentration: 10 to 15 g / L of copper ions, 100 to 110 g / L of sulfuric acid, 10 to 30 mg / L of dimethyl sulfoxide, 20 to 40 mg / L of gelatin and 50 to 80 mg / L of potassium ions; the current density of the roughening treatment is 30A / dm < 2 >-50A / dm < 2 >; a curing liquid for curing treatment comprises the following components in mass concentration: 70g / L-80g / L of copper ions, 90g / L-100g / L of sulfuric acid and 40mg / L-60mg / L of gelatin; the current density of the curing treatment is 15A / dm < 2 >-30A / dm < 2 >. The preparation method can be used for preparing the inverted copper foil with relatively low roughness and relatively high peel strength.

Description

Technical Field

[0001] This application relates to the field of electronic circuit materials, and in particular to inverted copper foil and its preparation method, copper-clad laminates and printed circuit boards. Background Technology

[0002] With the rapid development of electronic technology, the demand for high-frequency and high-speed products continues to grow, and the market's requirements for low-signal-loss circuits are becoming increasingly stringent. This places stricter standards on the performance indicators of copper foil on the board surface. Especially in the 5G era, the increasing frequency of signal transmission is driving the continuous reduction of the dielectric layer thickness on mobile terminal PCBs. This change makes the impact of copper foil surface roughness on signal transmission increasingly prominent. During high-frequency signal transmission, the signal is only transmitted within the order of magnitude of the copper foil surface roughness. Fluctuations in surface roughness can cause signal "standing waves" and "reflections," thereby interfering with signal transmission and increasing signal loss. The higher the surface roughness of the copper foil, the longer the actual transmission path of the high-frequency signal, and the greater the signal loss.

[0003] Currently, reverse electrolytic copper foil (RTF copper foil), as an improved copper foil material, enhances the peel strength between the copper foil and the resin substrate through special surface treatment. However, when traditional RTF copper foil is applied to high-frequency, high-speed printed circuit boards, there is still a challenge in balancing peel strength and signal transmission performance. If surface roughness is reduced to ensure signal transmission, the peel strength between the copper foil and the resin substrate will be lower, making the copper foil prone to detachment during subsequent processing or application.

[0004] Therefore, it is necessary to improve traditional technologies. Summary of the Invention

[0005] Based on this, this application provides a reverse copper foil that can achieve both low roughness and high peel strength, a method for preparing the same, a copper-clad laminate, and a printed circuit board.

[0006] The technical solution to the above-mentioned technical problems in this application is as follows.

[0007] The first aspect of this application provides a method for preparing reverse copper foil, comprising the following steps:

[0008] One surface of the electrolytic copper foil is subjected to roughening and curing treatments in sequence;

[0009] At least one surface of the cured electrolytic copper foil is subjected to silanization treatment to obtain a reverse copper foil;

[0010] The roughening solution, by mass concentration, comprises: copper ions 10 g / L~15 g / L, sulfuric acid 100 g / L~110 g / L, dimethyl sulfoxide 10 mg / L~30 mg / L, gelatin 20 mg / L~40 mg / L, and potassium ions 50 mg / L~80 mg / L; the current density of the roughening treatment is 30 A / dm³. 2 ~50 A / dm 2 ;

[0011] The curing solution for the curing treatment, based on mass concentration, comprises: 70 g / L to 80 g / L copper ions, 90 g / L to 100 g / L sulfuric acid, and 40 mg / L to 60 mg / L gelatin; the current density for the curing treatment is 15 A / dm³. 2 ~30 A / dm 2 .

[0012] In some embodiments, the method for preparing the inverted copper foil satisfies at least one of the following characteristics:

[0013] (1) The current density of the roughening treatment is 35 A / dm. 2 ~45 A / dm 2 ;

[0014] (2) In the roughening solution, the mass concentration of potassium ions is 50 mg / L to 70 mg / L;

[0015] (3) The current density of the curing process is 20 A / dm. 2 ~25 A / dm 2 .

[0016] In some embodiments, the preparation method of the inverted copper foil includes the following steps:

[0017] At a temperature of 45℃~50℃ and a current density of 60 A / dm 2 ~80 A / dm 2 Under certain conditions, electrolysis is carried out in an electrolyte to generate electrolytic copper foil;

[0018] The electrolyte, by mass concentration, comprises: copper ions 80 g / L to 90 g / L, sulfuric acid 90 g / L to 110 g / L, dimethyl sulfoxide 30 mg / L to 50 mg / L, gelatin 10 mg / L to 20 mg / L, and chloride ions 8 mg / L to 15 mg / L.

[0019] In some embodiments, the method for preparing inverted copper foil, after the curing treatment and before the silanization treatment, includes: sequentially subjecting at least one surface of the electrolytic copper foil obtained by the curing treatment to nickel plating, zinc plating, and chromium plating, wherein the preparation method satisfies at least one of the following characteristics:

[0020] (1) The nickel plating solution for nickel plating treatment comprises, by mass concentration: 20 g / L to 25 g / L of nickel ions and 30 g / L to 35 g / L of boric acid;

[0021] (2) The temperature of the nickel plating treatment is 40℃~50℃;

[0022] (3) The current density of the nickel plating treatment is 10 A / dm. 2 ~12 A / dm 2 ;

[0023] (4) The zinc plating solution for the zinc plating treatment comprises, by mass concentration, 5 g / L to 10 g / L of zinc ions;

[0024] (5) The galvanizing temperature is 35℃~45℃;

[0025] (6) The current density of the zinc plating treatment is 15 A / dm. 2 ~20 A / dm 2 ;

[0026] (7) The chromium plating solution for the chromium plating treatment comprises, by mass concentration, 1 g / L to 5 g / L of chromium ions;

[0027] (8) The temperature of the chrome plating treatment is 25℃~35℃;

[0028] (9) The current density of the chromium plating treatment is 18 A / dm. 2 ~25 A / dm 2 .

[0029] The second aspect of this application provides a reverse copper foil, one surface of which is a roughened surface. The roughened surface includes a copper nodule-free area, a copper nodule-laying area, and a copper nodule-stacking area. The copper nodule-laying area has 1 to 2 layers of copper nodules, and the copper nodule-stacking area has at least 3 copper nodules stacked. The area of ​​the copper nodule-laying area accounts for 65% to 80% of the total area of ​​the roughened surface.

[0030] In some embodiments, in the reversed copper foil, the copper nodule is spherical and the diameter of the copper nodule is 0.8 μm to 1.5 μm.

[0031] In some embodiments, in the reversed copper foil, the crystal texture of the copper nodule stacking region and the copper nodule tiling region independently includes (111) crystal planes, (200) crystal planes, and (220) crystal planes, respectively; the reversed copper foil satisfies at least one of the following characteristics:

[0032] (1) In the copper nodule stacked region, the texture factor of the (200) crystal plane accounts for 30% to 50% of the total texture factor of the (111) crystal plane, the (200) crystal plane, and the (220) crystal plane;

[0033] (2) In the copper nodule tiling area, the texture coefficient of the (200) crystal plane accounts for 10% to 30% of the total texture coefficient of the (111) crystal plane, the (200) crystal plane and the (220) crystal plane.

[0034] In some embodiments, in the reversed copper foil, the roughened surface satisfies at least one of the following characteristics:

[0035] (1) The surface roughness Rz of the roughened surface is 1.5 μm to 2.5 μm;

[0036] (2) The surface arithmetic mean waviness Wa of the roughened surface is 0.5 μm to 2 μm;

[0037] (3) The peak count roughness Rpc of the roughened surface is 40 peaks / cm to 80 peaks / cm;

[0038] (4) The surface aspect ratio Str of the roughened surface is 0.4~0.8.

[0039] A third aspect of this application provides a copper-clad laminate, comprising a copper foil and a resin substrate, wherein the copper foil includes a reverse copper foil prepared by the method for preparing reverse copper foil provided in the first aspect or a reverse copper foil provided in the second aspect, and the resin substrate is disposed on the roughened surface of the reverse copper foil.

[0040] The fourth aspect of this application provides a printed circuit board, including a reverse copper foil prepared by the method for preparing reverse copper foil provided in the first aspect, a reverse copper foil provided in the second aspect, or a copper-clad laminate provided in the third aspect.

[0041] The method for preparing the reverse copper foil of this application includes sequentially subjecting the electrolytic copper foil to roughening treatment, curing treatment, and silanization treatment. In the roughening solution, gelatin provides inhibition and leveling effects, preventing the formation of coarse and loose dendrites and establishing the basic "skeleton" of the roughened structure. Dimethyl sulfoxide (DMSO), in the inhibitory environment created by gelatin, undergoes fine microscopic adjustment, effectively compensating for insufficient nucleation caused by gelatin by locally promoting the formation of numerous fine crystal nuclei. Potassium ions can affect the adsorption strength and distribution of negatively charged gelatin and polar DMSO, and can improve the conductivity of the roughening solution, thereby enabling gelatin and DMSO to exert their leveling and refining effects. The interaction of DMSO, gelatin, and potassium ions in the roughening solution under appropriate ratios and current densities, combined with a suitable curing solution and current density, promotes the formation of fine crystal nuclei, increases the number of copper nodules per unit area, and improves the density and uniformity of the roughened structure on the copper foil surface.

[0042] The reverse copper foil prepared by the method of this application has high peel strength when bonded to a resin substrate, and when applied to a circuit printed circuit board, it can effectively suppress or reduce the degree of interference loss under high frequency transmission, thereby improving the high frequency signal transmission performance of the reverse copper foil. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a scanning electron microscope image of the RTF copper foil prepared in Example 1. Detailed Implementation

[0045] The present application will be further described in detail below with reference to the embodiments and examples. It should be understood that these embodiments and examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive.

[0046] It should also be understood that this application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various alterations or modifications without departing from the spirit of this application, and the resulting equivalent forms also fall within the protection scope of this application. For example, features described or illustrated as part of one embodiment can be combined in a suitable manner in another embodiment to produce new embodiments. Furthermore, numerous specific details are set forth in the following description to provide a fuller understanding of this application; it should be understood that this application can be implemented without one or more of these details.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for descriptive purposes only and is not intended to be limiting of the application.

[0048] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0049] In this application, the terms "multiple", "various", "multiple times", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0050] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0051] In this document, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0052] In this document, terms such as "preferred," "better," "more suitable," and "ideal" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0053] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0054] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0055] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0056] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0057] In this application, when numerical intervals (i.e., numerical ranges) are mentioned, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include numerical interval types such as percentage intervals, ratio intervals, and proportion intervals.

[0058] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0059] In this application, the terms "room temperature" or "normal temperature" generally refer to 4℃ to 35℃, for example, 20℃ ± 5℃. In some embodiments of this application, "room temperature" or "normal temperature" refers to 10℃ to 30℃. In some embodiments of this application, "room temperature" or "normal temperature" refers to 20℃ to 30℃.

[0060] In this application, if the unit of a data range is only followed by the right endpoint, it indicates that the units of the left and right endpoints are the same. For example, 3~5 h means that the units of the left endpoint "3" and the right endpoint "5" are both h (hours).

[0061] All references to documents mentioned in this application are incorporated herein by reference as if each document were individually incorporated by reference. Unless they conflict with the inventive purpose and / or technical solution of this application, all cited documents are incorporated herein by reference in their entirety and for all purposes. When citing documents in this application, the definitions of relevant technical features, terms, nouns, phrases, etc., are also incorporated herein by reference. When citing documents in this application, examples and preferred embodiments of the cited technical features may also be incorporated herein by reference, but only to the extent that they enable the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, this application shall prevail or modifications shall be made adaptably to the description in this application.

[0062] The mass or weight of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship of mass or weight between the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass or weight mentioned in the embodiments of this application can be units known in the chemical industry, such as μg, mg, g, and kg.

[0063] Conventional electrolytic copper foil: During the electrolysis process, copper ions are reduced and deposited on the surface of the cathode roller. The side in contact with the roller surface forms a smooth surface (S surface) due to the high smoothness of the roller surface, while the other side forms a rough surface (M surface) due to the adsorption of additives in the electrolyte and uneven grain growth. In conventional applications, the rough surface is bonded to the resin substrate.

[0064] Reverse copper foil (RTF): The smooth surface is roughened to give it high adhesion to the substrate, allowing for direct attachment of the substrate to this roughened surface without the need for further pretreatment. Because the roughened surface has lower surface roughness, reverse copper foil is easier to etch cleanly when fabricating fine lines, effectively reducing lateral etching and thus improving the fabrication of fine lines and yield.

[0065] Developing a copper foil material that simultaneously achieves low roughness and high peel strength requires not only achieving a low-profile, or even near-profile-less, surface morphology on the copper foil, but also ensuring good adhesion between the copper foil and the substrate. Simultaneously, it's necessary to consider how to improve the peel strength of the copper foil without altering its roughness to meet the demands of high-frequency, high-speed circuit boards. Solving these problems is crucial for enhancing the signal transmission performance and reliability of electronic products under high-frequency transmission conditions.

[0066] One embodiment of this application provides a method for preparing reverse copper foil, comprising the following steps:

[0067] Step S100: Roughen one surface of the electrolytic copper foil to obtain the first copper foil intermediate.

[0068] It is understandable that in step S100, the surface (smooth surface) in contact with the cathode roller of the electrolytic copper foil is roughened.

[0069] In some of these examples, in step S100, the roughening solution used in the roughening process includes copper ions, sulfuric acid, dimethyl sulfoxide, gelatin, and potassium ions.

[0070] In some examples, in step S100, the roughening solution, by mass concentration, comprises: copper ions 10 g / L~15 g / L, sulfuric acid 100 g / L~110 g / L, dimethyl sulfoxide 10 mg / L~30 mg / L, gelatin 20 mg / L~40 mg / L, and potassium ions 50 mg / L~80 mg / L; the current density for the roughening treatment is 30 A / dm³. 2 ~50 A / dm 2 .

[0071] In the roughening solution, the morphology of the roughened structure of electrolytic copper foil can be controlled by combining dimethyl sulfoxide (DMSO), gelatin, and potassium ions at appropriate concentrations. First, gelatin provides a macroscopic and strong inhibitory and leveling effect, preventing the formation of large, loose dendrites and laying the basic "skeleton" of the roughened structure. Dimethyl sulfoxide, within the inhibitory environment created by gelatin, performs "microscopic fine-tuning," effectively compensating for insufficient nucleation caused by gelatin by promoting the formation of numerous fine crystal nuclei locally. Gelatin ensures the solidity and uniformity of the roughened structure, while DMSO effectively improves its density and fineness. The synergistic effect of gelatin and DMSO yields surface morphologies including copper nodule stacking zones, copper nodule flattening zones, and copper nodule-free zones, with the copper nodule flattening zone accounting for 65%–80% of the surface area. Meanwhile, the presence of potassium ions alters the charge state of the cathode surface, affecting the adsorption strength and distribution of negatively charged gelatin and polar dimethyl sulfoxide, which is beneficial for the uniform deposition of copper nodules. Furthermore, potassium ions can enhance the conductivity of the roughening solution and improve the uniformity of current distribution on the cathode surface, providing a more ideal "stage" for gelatin and dimethyl sulfoxide to exert their leveling and refining effects. The synergistic effect of gelatin, dimethyl sulfoxide, and potassium ions effectively increases the peak count of the reverse copper foil, reduces its roughness, and effectively improves the adhesion between the reverse copper foil and the substrate.

[0072] High peak count: The combined action of dimethyl sulfoxide and gelatin forms a large number of fine crystal nuclei, resulting in a high number of copper nodules per unit area; Low roughness: The inhibitory and leveling effects of gelatin prevent the nodules from growing indefinitely, while potassium ions ensure overall uniformity and avoid excessive local roughness; Good adhesion: The dense, uniform, and robust coarsened structure provides a large specific surface area and strong mechanical anchoring points, improving the peel strength between the copper foil and the resin substrate.

[0073] It is understood that the mass concentration of copper ions in the roughening solution includes, but is not limited to, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, and 15 g / L; the mass concentration of sulfuric acid includes, but is not limited to, 107 g / L, 108 g / L, 109 g / L, and 110 g / L; the mass concentration of dimethyl sulfoxide includes, but is not limited to, 10 mg / L, 12 mg / L, 15 mg / L, 18 mg / L, 20 mg / L, 22 mg / L, 25 mg / L, 28 mg / L, and 30 mg / L; the mass concentration of gelatin includes, but is not limited to, 20 mg / L, 22 mg / L, 25 mg / L, 28 mg / L, 30 mg / L, 32 mg / L, 35 mg / L, 38 mg / L, and 40 mg / L; and the mass concentration of potassium ions includes, but is not limited to, 50 mg / L, 52 mg / L, 55 mg / L, 58 mg / L, 60 mg / L, 62 mg / L, and 65 mg / L. mg / L, 68 mg / L, 70 mg / L, 72 mg / L, 75 mg / L, 78 mg / L, 80 mg / L. In some examples, any two of these point values ​​can be used as the endpoints within a range, and the same applies below.

[0074] In some examples, in step S100, the roughening solution, by mass concentration, comprises: 10 g / L copper ions, 100 g / L sulfuric acid, 10 mg / L~30 mg / L dimethyl sulfoxide, 20 mg / L~40 mg / L gelatin, and 50 mg / L~80 mg / L potassium ions; the current density for the roughening treatment is 30 A / dm³. 2 ~50 A / dm 2 .

[0075] In some of these examples, in step S100, the mass concentration of potassium ions in the roughening solution is 50 mg / L to 70 mg / L.

[0076] In some of these examples, the current density for the roughening process in step S100 is 35 A / dm. 2 ~45 A / dm 2 It is understood that the current density for roughening treatment includes, but is not limited to, 35 A / dm². 2 36 A / dm 2 37 A / dm 2 38 A / dm 2 39 A / dm 2 40 A / dm 2 41 A / dm 2 42 A / dm 2 43 A / dm 244 A / dm 2 45 A / dm 2 .

[0077] By adjusting the composition, concentration, and current density of the roughening solution, the surface morphology of the electrolytic copper foil is controlled, reducing the surface roughness of the electrolytic copper foil and effectively mitigating the "standing wave" and "reflection" phenomena that occur during high-frequency signal transmission, thereby effectively reducing signal transmission loss.

[0078] It can be understood that the electrolytic copper foil roughened in step S100 is the raw foil.

[0079] In some of these examples, step S100, the preparation of the electrolytic copper foil includes the following steps:

[0080] Step S110: Electrolysis is carried out in the electrolyte to generate electrolytic copper foil.

[0081] In some examples, the electrolysis temperature in step S110 is 45°C to 50°C. It is understood that the electrolysis temperature includes, but is not limited to, 45°C, 46°C, 47°C, 48°C, 49°C, and 50°C.

[0082] It is understood that an electric current is applied to the cathode roller and the insoluble anode. In some examples, in step S110, the current density for electrolysis is 60 A / dm³. 2 ~80 A / dm 2 It is understood that the current density during electrolysis includes, but is not limited to, 60 A / dm³. 2 62 A / dm 2 65 A / dm 2 68 A / dm 2 70 A / dm 2 72 A / dm 2 75 A / dm 2 78 A / dm 2 80 A / dm 2 .

[0083] In some of these examples, in step S110, the electrolyte comprises, by mass concentration: 80 g / L to 90 g / L copper ions, 90 g / L to 110 g / L sulfuric acid, 30 mg / L to 50 mg / L dimethyl sulfoxide, 10 mg / L to 20 mg / L gelatin, and 8 mg / L to 15 mg / L chloride ions.

[0084] The method for preparing reverse copper foil provided in this application uses raw materials from the electrolyte used in preparing electrolytic copper foil, except for potassium ions, for the roughening solution used in the roughening treatment. This reduces the problem of mixing and redundant material accumulation caused by a wide variety of raw materials, and facilitates management.

[0085] In some examples, in step S110, the thickness of the electrolytic copper foil is 6 μm to 35 μm. It is understood that the thickness of the electrolytic copper foil includes, but is not limited to, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, and 35 μm.

[0086] In some of these examples, step S100, prior to the coarsening process, includes:

[0087] Step S120: The electrolytic copper foil is sequentially acid-washed and water-washed.

[0088] It is understood that this application does not limit the pickling and washing methods; conventional methods in the field are sufficient.

[0089] Step S200: The surface of the first copper foil intermediate after roughening is cured to obtain the second copper foil intermediate.

[0090] In some examples, in step S200, the curing solution for the curing treatment, by mass concentration, comprises: 70 g / L to 80 g / L copper ions, 90 g / L to 100 g / L sulfuric acid, and 40 mg / L to 60 mg / L gelatin; the current density for the curing treatment is 15 A / dm³. 2 ~30 A / dm 2 .

[0091] It is understood that the mass concentration of copper ions in the curing solution includes, but is not limited to, 70 g / L, 71 g / L, 72 g / L, 73 g / L, 74 g / L, 75 g / L, 76 g / L, 77 g / L, 78 g / L, 79 g / L, and 80 g / L; the mass concentration of sulfuric acid includes, but is not limited to, 90 g / L, 91 g / L, 92 g / L, 93 g / L, 94 g / L, 95 g / L, 96 g / L, 97 g / L, 98 g / L, 99 g / L, and 100 g / L; and the mass concentration of gelatin includes, but is not limited to, 40 mg / L, 42 mg / L, 45 mg / L, 48 mg / L, 50 mg / L, 52 mg / L, 55 mg / L, 58 mg / L, and 60 mg / L.

[0092] In some of these examples, the current density for the curing process in step S200 is 20 A / dm². 2 ~25 A / dm 2 It is understood that the current density during the curing process includes, but is not limited to, 20 A / dm². 2 21 A / dm 222 A / dm 2 23 A / dm 2 24 A / dm 2 25 A / dm 2 .

[0093] It is understandable that in some of these examples, the roughening and curing processes in the preparation of the reversed copper foil can be repeated once or multiple times, for example, by sequentially performing roughening-curing-roughening-curing-roughening-curing, etc.

[0094] Step S300: Silanize at least one surface of the second copper foil intermediate to obtain a reverse copper foil.

[0095] In some of these examples, in step S300, both sides of the second copper foil intermediate are silanized.

[0096] In some of these examples, the silane coupling agent used in step S300 includes an acrylic-based silane coupling agent.

[0097] In some of these examples, step S300, the silanization process includes the following steps:

[0098] An aqueous solution of silane coupling agent is coated onto at least one surface of the second copper foil intermediate and then dried.

[0099] In some of these examples, in step S300, the mass concentration of the silane coupling agent aqueous solution is 0.8 wt% to 1.2 wt%.

[0100] In some of these examples, the drying temperature in step S300 is 100°C to 120°C.

[0101] In some examples, the method for preparing inverted copper foil, after step S200 curing treatment and before step S300 silanization treatment, includes:

[0102] Step S400: At least one surface of the electrolytic copper foil obtained by the curing treatment is sequentially subjected to nickel plating, zinc plating and chromium plating.

[0103] In some of these examples, in step S400, the nickel plating solution for the nickel plating treatment comprises, by mass concentration: 20 g / L to 25 g / L of nickel ions and 30 g / L to 35 g / L of boric acid.

[0104] It is understood that the mass concentration of nickel ions in the nickel plating solution includes, but is not limited to, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, and 25 g / L; and the mass concentration of boric acid includes, but is not limited to, 30 g / L, 31 g / L, 32 g / L, 33 g / L, 34 g / L, and 35 g / L.

[0105] In some examples, the nickel plating temperature in step S400 is 40°C to 50°C. It is understood that the nickel plating temperature includes, but is not limited to, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, and 50°C.

[0106] In some of these examples, in step S400, the current density for the nickel plating process is 10 A / dm. 2 ~12 A / dm 2 It is understood that the current density for nickel plating includes, but is not limited to, 10 A / dm². 2 11 A / dm 2 12 A / dm 2 .

[0107] In some examples, in step S400, the zinc plating solution for the zinc plating treatment comprises, by mass concentration, 5 g / L to 10 g / L of zinc ions. It is understood that the mass concentration of zinc ions in the zinc plating solution includes, but is not limited to, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, and 10 g / L.

[0108] In some examples, the galvanizing temperature in step S400 is 35°C to 45°C. It is understood that the galvanizing temperature includes, but is not limited to, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, and 45°C.

[0109] In some of these examples, the current density for the zinc plating process in step S400 is 15 A / dm. 2 ~20 A / dm 2 It is understood that the current density for galvanizing is, but is not limited to, 15 A / dm². 2 16 A / dm 2 17 A / dm 2 18 A / dm 2 19 A / dm 2 20 A / dm 2 .

[0110] In some examples, in step S400, the chromium plating solution for the chromium plating treatment comprises, by mass concentration, 1 g / L to 5 g / L of chromium ions. It is understood that the mass concentration of chromium ions in the chromium plating solution includes, but is not limited to, 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L.

[0111] In some examples, the temperature of the chrome plating process in step S400 is 25°C to 35°C. It is understood that the temperature of the chrome plating process includes, but is not limited to, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, and 35°C.

[0112] In some of these examples, in step S400, the current density for the chromium plating process is 18 A / dm. 2 ~25 A / dm 2 It is understood that the current density for chrome plating includes, but is not limited to, 18 A / dm². 2 19 A / dm 2 20 A / dm 2 21 A / dm 2 22 A / dm 2 23 A / dm 2 24 A / dm 2 25 A / dm 2 .

[0113] One embodiment of this application provides a reverse copper foil, which is prepared using the above-described method for preparing reverse copper foil.

[0114] Another embodiment of this application provides a reverse copper foil, one surface of which is a roughened surface. The roughened surface includes a copper nodule-free area, a copper nodule-flat area, and a copper nodule-stacked area. The copper nodule-flat area has 1 to 2 layers of copper nodules, and the copper nodule-stacked area has at least 3 copper nodules stacked. The area of ​​the copper nodule-flat area accounts for 65% to 80% of the total area of ​​the roughened surface.

[0115] By employing a special surface morphology design with copper nodule stacking area, copper nodule flat area, and no copper nodule area, the surface morphology of the copper foil is controlled, resulting in higher peel strength when it is bonded to the resin substrate. This effectively solves the problem of traditional reverse copper foil easily falling off under high-frequency transmission and improves product yield.

[0116] It is understood that the percentage of the area of ​​the copper nodule tiling area to the total area of ​​the roughened surface includes, but is not limited to, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, and 80%.

[0117] In some examples, in the reversed copper foil, the area of ​​the copper nodule stack region accounts for 15% to 25% of the total roughened surface area. It can be understood that the percentage of the copper nodule stack region to the total roughened surface area includes, but is not limited to, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0118] It is understandable that the copper nodule-free area refers to the area on the roughened surface where no copper nodules grow.

[0119] In some examples, the area of ​​the copper-free region in the reversed copper foil accounts for 1% to 10% of the total roughened surface area. It can be understood that the percentage of the copper-free region to the total roughened surface area includes, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%.

[0120] In some of these examples, the copper nodules in the reversed copper foil are spherical, with a diameter of 0.8 μm to 1.5 μm. It is understood that the diameter of the copper nodules includes, but is not limited to, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, and 1.5 μm.

[0121] In some of these examples, in the reversed copper foil, the stacking shape of the copper nodule stacking area includes at least one of columnar and tree-like shapes.

[0122] In some of these examples, the crystal texture of the copper nodule stacking region and the copper nodule tiling region in the reversed copper foil independently includes (111) crystal plane, (200) crystal plane and (220) crystal plane, respectively.

[0123] In some examples, in the inverted copper foil, in the copper nodule stack region, the texture factor of the (200) crystal plane accounts for 30% to 50% of the total texture factor of the (111), (200), and (220) crystal planes. It can be understood that the percentage of the texture factor of the (200) crystal plane to the total texture factor of the (111), (200), and (220) crystal planes refers to the ratio of the texture factor of the (200) crystal plane in the copper nodule stack region to the sum of the texture factors of the (111), (200), and (220) crystal planes; furthermore, the percentage of the texture factor of the (200) crystal plane to the total texture factor of the (111), (200), and (220) crystal planes includes, but is not limited to, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, and 50%.

[0124] By employing a special surface morphology design with copper nodule stacking area, copper nodule flat area and no copper nodule area, and further designing the crystal texture, the peel strength when it is bonded to the resin substrate is further improved.

[0125] In some examples, in the inverted copper foil, the texture factor of the (200) crystal plane in the copper nodule area accounts for 10% to 30% of the total texture factor of the (111), (200), and (220) crystal planes. It can be understood that the percentage of the texture factor of the (200) crystal plane to the total texture factor of the (111), (200), and (220) crystal planes includes, but is not limited to, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and 30%.

[0126] In some of these examples, the surface roughness Rz of the roughened surface in the reversed copper foil is 1.5 μm to 2.5 μm. It can be understood that the surface roughness Rz of the roughened surface includes, but is not limited to, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, and 2.5 μm.

[0127] In some of these examples, the surface arithmetic mean waviness Wa of the roughened surface in the inverted copper foil is 0.5 μm to 2 μm. It can be understood that the surface arithmetic mean waviness Wa of the roughened surface includes, but is not limited to, 0.5 μm, 1.0 μm, 1.5 μm, and 2.0 μm.

[0128] In some examples, in the reverse copper foil, the peak count roughness Rpc of the roughened surface is 40 peaks / cm to 80 peaks / cm. It can be understood that the peak count roughness Rpc of the roughened surface includes, but is not limited to, 40 peaks / cm, 42 peaks / cm, 45 peaks / cm, 48 peaks / cm, 50 peaks / cm, 52 peaks / cm, 55 peaks / cm, 58 peaks / cm, 60 peaks / cm, 62 peaks / cm, 65 peaks / cm, 68 peaks / cm, 70 peaks / cm, 72 peaks / cm, 75 peaks / cm, 78 peaks / cm, and 80 peaks / cm.

[0129] In some of these examples, the aspect ratio Str of the roughened surface in the reversed copper foil is 0.4 to 0.8. It can be understood that the aspect ratio Str of the roughened surface includes, but is not limited to, 0.4, 0.5, 0.6, 0.7, and 0.8.

[0130] One embodiment of this application provides a copper-clad laminate, including a reverse copper foil prepared by the above-described method for preparing reverse copper foil or the above-described reverse copper foil.

[0131] In some of these examples, the copper-clad laminate also includes a resin substrate disposed on the roughened surface of the reverse copper foil.

[0132] It can be understood that in the reverse copper foil prepared by the above method, the surface that has undergone roughening and curing treatment is the roughened surface of the reverse copper foil.

[0133] The copper-clad laminate of this application includes the reverse copper foil prepared by the above-described method or the above-described reverse copper foil, and therefore has at least the same advantages as the reverse copper foil prepared by the above-described method or the above-described reverse copper foil.

[0134] One embodiment of this application provides a printed circuit board, including a reverse copper foil prepared by the above-described method, the above-described reverse copper foil, or the above-described copper-clad laminate.

[0135] The printed circuit board of this application includes the reverse copper foil prepared by the above-described method, the above-described reverse copper foil, or the above-described copper clad laminate, and therefore has at least the same advantages as the reverse copper foil prepared by the above-described method, the above-described reverse copper foil, or the above-described copper clad laminate.

[0136] The present application will be described in further detail below with reference to specific embodiments, but the embodiments of the present application are not limited thereto.

[0137] Example 1

[0138] A method for preparing low-roughness RTF copper foil includes the following steps:

[0139] S1. Electrolysis of green foil. Electrolyte preparation: dimethyl sulfoxide concentration 30 mg / L, gelatin concentration 10 mg / L, chloride ion concentration 10 mg / L, copper ion concentration 90 g / L, sulfuric acid concentration 110 g / L; At 50℃, a current density of 70 A / dm² is applied to the cathode roller and the insoluble anode. 2 The current is used to continuously wind the green foil on the guide roller to obtain a thickness of 18 μm.

[0140] S2. Roughening and Curing Treatment. The electrolytic green foil obtained in S1 is drawn to the surface treatment line, first subjected to acid washing and water washing, and then the surface of the green foil in contact with the cathode roller is roughened and cured. The process sequence is roughening treatment-curing treatment-roughening treatment-curing treatment-roughening treatment-curing treatment, combining three-step roughening treatment with three-step curing treatment. The roughening solution composition is: copper ion concentration 10 g / L, sulfuric acid concentration 100 g / L, dimethyl sulfoxide concentration 20 mg / L, gelatin concentration 30 mg / L, potassium ion concentration 60 mg / L; the current density for roughening treatment is 40 A / dm³. 2 Curing solution composition: copper ion concentration 70 g / L, sulfuric acid concentration 90 g / L, gelatin 50 mg / L, current density: 20 A / dm³ 2 .

[0141] S3. Non-copper metal electroplating: Nickel plating, zinc plating, and chromium plating are performed. For nickel plating, a nickel ion concentration of 20 g / L and a boric acid concentration of 30 g / L are used as raw materials, with the temperature controlled at 45 ± 2℃ and the current density at 10 A / dm³. 2 Zinc plating: using a zinc ion concentration of 5 g / L as raw material, the temperature is controlled at 40±5℃, and the current density is 15 A / dm³. 2 Chromium plating: using chromium ion concentration of 1 g / L as raw material, temperature controlled at 30±5℃, and current density of 18 A / dm³. 2 .

[0142] S4. Silanization Treatment: Acrylic-based silane coupling agent was selected and diluted with water to prepare an aqueous solution with a concentration of 1 ± 0.2 wt%. This solution was then applied to both sides of the coating. After coating, the solution was dried in an oven at 120°C and then wound up to obtain RTF copper foil. The scanning electron microscope image is shown below. Figure 1 As shown.

[0143] See Figure 1 The mark in Figure 1 Regions 11 and 12 are copper nodules-free areas; regions 21 and 22 are copper nodule stacking areas, where copper nodules in region 21 are stacked into spherical copper nodules with a diameter of 3.52 μm, and copper nodules in region 22 are stacked into arc-shaped copper nodules with a length of 5 μm; regions 31 and 32 are copper nodule flat-laying areas, where copper nodules do not stack and grow, and spherical copper nodules are flat-laying on the copper foil surface with a diameter of 1.1 μm; the area of ​​copper nodule flat-laying areas accounts for 70%, the area of ​​copper nodule stacking areas accounts for 25%, and the area of ​​copper nodules-free areas accounts for 5%.

[0144] Example 2

[0145] It is basically the same as Example 1, except that the concentration of dimethyl sulfoxide in the S2 roughening solution is 30 mg / L.

[0146] Example 3

[0147] It is basically the same as Example 1, except that the concentration of gelatin in the S2 roughening solution is 40 mg / L.

[0148] Example 4

[0149] It is basically the same as Example 1, except that the concentration of potassium ions in the S2 roughening solution is 80 mg / L.

[0150] Example 5

[0151] The process is basically the same as in Example 1, except that the current density for the S2 roughening treatment is 30 A / dm. 2 .

[0152] Example 6

[0153] The process is basically the same as in Example 1, except that the current density for the S2 roughening treatment is 50 A / dm. 2 .

[0154] Example 7

[0155] It is basically the same as Example 1, except that the concentration of gelatin in the S2 curing solution is 60 mg / L.

[0156] Example 8

[0157] The process is basically the same as in Example 1, except that the current density for the S2 curing treatment is 30 A / dm³. 2 .

[0158] Comparative Example 1

[0159] It is basically the same as Example 1, except that the concentration of dimethyl sulfoxide in the S2 roughening solution is 5 mg / L.

[0160] Comparative Example 2

[0161] It is basically the same as Example 1, except that the concentration of gelatin in the S2 roughening solution is 10 mg / L.

[0162] Comparative Example 3

[0163] It is basically the same as Example 1, except that the concentration of potassium ions in the S2 roughening solution is 30 mg / L.

[0164] Comparative Example 4

[0165] The process is basically the same as in Example 1, except that the current density for the S2 roughening treatment is 20 A / dm. 2 .

[0166] Comparative Example 5

[0167] It is basically the same as Example 1, except that the concentration of gelatin in the S2 curing solution is 30 mg / L.

[0168] Comparative Example 6

[0169] The process is basically the same as in Example 1, except that the current density for the S2 curing treatment is 10 A / dm³. 2 .

[0170] The main parameters of each embodiment and comparative example are shown in Table 1:

[0171] Table 1

[0172]

[0173] Surface morphology and crystal texture coefficient observation

[0174] A scanning electron microscope (TESCAN VEGA3) was used with a tilt angle of 40° and a magnification of 8000x to observe the surface morphology of each sample. The built-in software was used to identify the copper nodule stacking area, the copper nodule flat area, and the area without copper nodule, and the proportion of the projected area was calculated.

[0175] The texture coefficient of the sample was analyzed using an XRD diffractometer, and the texture coefficient of the crystal plane was obtained using the Harris formula.

[0176] Performance testing

[0177] (1) Surface roughness Rz, surface arithmetic mean waviness Wa, peak count roughness Rpc, and surface aspect ratio Str were tested using an Olympus OLS5100 laser confocal microscope at an objective magnification of 50x.

[0178] (2) Peel resistance test: The RTF copper foils prepared in each example and comparative example were stacked in the order of copper foil-prepreg-copper foil to form a sandwich structure. The copper-clad laminate was formed by hot pressing under vacuum press. The copper-clad laminate was cut into strips with a width of 3.0 mm using a cutter. The copper foil on one side of the copper-clad laminate was peeled off by 1 cm to 2 cm using a utility knife. The peeled copper foil was fixed to one end of a weight. Finally, the copper foil was tested on the peel strength tester by moving the weight.

[0179] (3) Electrical performance loss test: The RTF copper foils prepared in each embodiment and comparative example were stacked in the order of copper foil-prepreg-copper foil to form a sandwich structure, and then hot-pressed under a vacuum press to form a copper-clad laminate; multilayer printed circuit boards were fabricated in the order of dry film application-exposure-etching-dry film removal-bonding sheet stacking-hot pressing. The parameters in the multilayer printed circuit board processing process are as follows: pressing temperature 220℃; pressing time 120 min; surface pressure 25 kg / cm 2 The copper-clad laminate obtained by lamination is used for PCB printing and SI signal transmission performance testing. The SI performance test parameters are as follows: characteristic impedance of 50 Ω, impedance tolerance of ±10%, and microstrip wiring.

[0180] The results are shown in Table 2.

[0181] Table 2

[0182]

[0183] As can be seen from Table 2, compared with the comparative example, the reverse copper foil prepared in the example has both lower roughness and higher peel strength.

[0184] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0185] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a reverse copper foil, characterized in that, Includes the following steps: One surface of the electrolytic copper foil is subjected to roughening and curing treatments in sequence; At least one surface of the cured electrolytic copper foil is subjected to silanization treatment to obtain a reverse copper foil; The roughening solution, by mass concentration, comprises: copper ions 10 g / L~15 g / L, sulfuric acid 100 g / L~110 g / L, dimethyl sulfoxide 10 mg / L~30 mg / L, gelatin 20 mg / L~40 mg / L, and potassium ions 50 mg / L~80 mg / L; the current density of the roughening treatment is 30 A / dm³. 2 ~50 A / dm 2 ; The curing solution for the curing treatment, based on mass concentration, comprises: 70 g / L to 80 g / L copper ions, 90 g / L to 100 g / L sulfuric acid, and 40 mg / L to 60 mg / L gelatin; the current density for the curing treatment is 15 A / dm³. 2 ~30 A / dm 2 .

2. The method for preparing the reverse copper foil as described in claim 1, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The current density of the roughening treatment is 35 A / dm. 2 ~45 A / dm 2 ; (2) In the roughening solution, the mass concentration of potassium ions is 50 mg / L to 70 mg / L; (3) The current density of the curing process is 20 A / dm. 2 ~25 A / dm 2 .

3. The method for preparing the reverse copper foil according to any one of claims 1 to 2, characterized in that, The preparation of the electrolytic copper foil includes the following steps: At a temperature of 45℃~50℃ and a current density of 60 A / dm 2 ~80 A / dm 2 Under certain conditions, electrolysis is carried out in an electrolyte to generate electrolytic copper foil; The electrolyte, by mass concentration, comprises: copper ions 80 g / L to 90 g / L, sulfuric acid 90 g / L to 110 g / L, dimethyl sulfoxide 30 mg / L to 50 mg / L, gelatin 10 mg / L to 20 mg / L, and chloride ions 8 mg / L to 15 mg / L.

4. The method for preparing the reverse copper foil according to any one of claims 1 to 2, characterized in that, After the curing treatment and before the silanization treatment, the method includes: sequentially subjecting at least one surface of the electrolytic copper foil obtained by the curing treatment to nickel plating, zinc plating, and chromium plating, wherein the preparation method satisfies at least one of the following characteristics: (1) The nickel plating solution for nickel plating treatment comprises, by mass concentration: 20 g / L to 25 g / L of nickel ions and 30 g / L to 35 g / L of boric acid; (2) The temperature of the nickel plating treatment is 40℃~50℃; (3) The current density of the nickel plating treatment is 10 A / dm. 2 ~12 A / dm 2 ; (4) The zinc plating solution for the zinc plating treatment comprises, by mass concentration, 5 g / L to 10 g / L of zinc ions; (5) The galvanizing temperature is 35℃~45℃; (6) The current density of the zinc plating treatment is 15 A / dm. 2 ~20 A / dm 2 ; (7) The chromium plating solution for the chromium plating treatment comprises, by mass concentration, 1 g / L to 5 g / L of chromium ions; (8) The temperature of the chrome plating treatment is 25℃~35℃; (9) The current density of the chromium plating treatment is 18 A / dm. 2 ~25 A / dm 2 .

5. A reverse copper foil, characterized in that, One surface of the reverse copper foil is a roughened surface, which includes a copper nodule-free area, a copper nodule-laying area, and a copper nodule-stacked area. The copper nodule-laying area has 1 to 2 layers of copper nodules, and the copper nodule-stacked area has at least 3 copper nodules stacked. The area of ​​the copper nodule-laying area accounts for 65% to 80% of the total area of ​​the roughened surface.

6. The reverse copper foil as described in claim 5, characterized in that, The copper nodule is spherical, and its diameter is 0.8 μm to 1.5 μm.

7. The reverse copper foil as described in claim 5, characterized in that, The crystal textures of the copper nodule stacking region and the copper nodule tiling region independently include (111) crystal planes, (200) crystal planes, and (220) crystal planes, respectively; the inverted copper foil satisfies at least one of the following characteristics: (1) In the copper nodule stacked region, the texture factor of the (200) crystal plane accounts for 30% to 50% of the total texture factor of the (111) crystal plane, the (200) crystal plane, and the (220) crystal plane; (2) In the copper nodule tiling area, the texture coefficient of the (200) crystal plane accounts for 10% to 30% of the total texture coefficient of the (111) crystal plane, the (200) crystal plane and the (220) crystal plane.

8. The reverse copper foil as described in any one of claims 5 to 7, characterized in that, The roughened surface satisfies at least one of the following characteristics: (1) The surface roughness Rz of the roughened surface is 1.5 μm to 2.5 μm; (2) The surface arithmetic mean waviness Wa of the roughened surface is 0.5 μm to 2 μm; (3) The peak count roughness Rpc of the roughened surface is 40 peaks / cm to 80 peaks / cm; (4) The surface aspect ratio Str of the roughened surface is 0.4~0.

8.

9. A copper-clad laminate, characterized in that, The invention includes a copper foil and a resin substrate, wherein the copper foil includes a reverse copper foil prepared by the method for preparing reverse copper foil as described in any one of claims 1 to 4 or a reverse copper foil as described in any one of claims 5 to 8, and the resin substrate is disposed on the roughened surface of the reverse copper foil.

10. A printed circuit board, characterized in that, This includes the reverse copper foil prepared by the method for preparing reverse copper foil as described in any one of claims 1 to 4, the reverse copper foil as described in any one of claims 5 to 8, or the copper clad laminate as described in claim 9.

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