Copper foil and preparation method and application thereof

Abstract

The invention relates to a copper foil and a preparation method and application thereof, the copper foil comprises an electrolytic copper foil layer and secondary long copper layers located on the surfaces of the two sides of the electrolytic copper foil layer, the maximum Feret diameter average value of crystal grains of the secondary long copper layers is 2.5-3 microns, and the maximum Feret diameter average value of crystal grains of the electrolytic copper foil layer is 1-2 microns. The maximum Feret diameter average value of grains of the secondary growing copper layer on the surface of the copper foil is 2.3-3 microns, the maximum Feret diameter average value of grains of the internal electrolytic copper foil layer is 1-2 microns, a structure with the grain size of the surface layer being large and the grain size of the inner layer being small is formed, and when the copper foil is used for transmitting a high-speed high-frequency electric signal, due to the skin effect of current, the high-speed high-frequency electric signal can be transmitted. More electric signals are transmitted along the surface layer of the copper foil, the grain size of the surface layer is large, the grain boundary is correspondingly reduced, and the obstruction to current is reduced, so that the loss of the electric signals is reduced, and the transmission integrity of the electric signals is improved.

Description

Technical Field

[0001] The present application relates to the technical field of high-frequency signal transmission, and in particular to a copper foil and a preparation method and application thereof. Background Art

[0002] When high-speed, high-frequency AC signals are transmitted along the lines of a printed circuit board (PCB), the current distribution within the copper foil of the PCB is uneven, concentrating in a thin layer on the outer surface of the conductor. This phenomenon is known as the skin effect. Research has shown that the higher the frequency of the transmitted signal, the more pronounced the skin effect. Due to the skin effect, high-frequency signals are concentrated on the outer surface of the copper foil, reducing the effective cross-sectional area for transmission. This increases the resistance of the copper foil surface and increases signal transmission loss. To reduce signal transmission loss, traditional techniques roughen the copper foil surface in an attempt to increase the effective signal transmission area by changing the surface roughness, thereby reducing signal attenuation caused by the skin effect. However, the greater the roughness of the copper foil, the longer the signal transmission path and the higher the conductor loss, resulting in greater signal transmission loss. With the advancement of communication technology, the frequency and speed of transmitted circuit signals will continue to increase. However, reducing the signal transmission loss caused by the skin effect is a technical challenge that needs to be urgently addressed in the development of high-frequency signal transmission technology. Summary of the Invention

[0003] Based on this, it is necessary to provide a copper foil capable of reducing electrical signal transmission loss, and a preparation method and application thereof.

[0004] In one aspect of the present application, a copper foil is provided.

[0005] The invention comprises an electrolytic copper foil layer and secondary copper layers located on both sides of the electrolytic copper foil layer. The average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm, and the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1 μm to 2 μm.

[0006] The average maximum Feret diameter of the grains in the secondary copper layer on both sides of the copper foil is 2.3μm to 3μm, while the average maximum Feret diameter of the grains in the internal electrolytic copper foil layer is 1μm to 2μm, forming a structure with large surface grains and small internal grains. When the copper foil is used to transmit high-speed and high-frequency electrical signals, due to the skin effect of the current, the electrical signals will be transmitted more along the secondary copper layer on the surface of the copper foil. The large grain size of the secondary copper layer will correspondingly reduce the number of grains and grain boundaries, and the obstruction to the current will become smaller, thereby reducing the electrical signal transmission loss and improving the integrity of the electrical signal transmission. The small grain size of the electrolytic copper foil layer is conducive to improving the surface flatness and smoothness of the electrolytic copper foil layer, thereby improving the uniformity of the grains in the secondary copper layer and further reducing the electrical signal transmission loss.

[0007] In some embodiments, the thickness of the secondary copper layer is 3 μm to 4 μm; and / or,

[0008] The grains of the secondary copper layer include equiaxed crystals and columnar crystals. Among the grains of the secondary copper layer, the equiaxed crystals account for 70% to 80%, and the columnar crystals account for 20% to 30%.

[0009] In some embodiments, the thickness of the electrolytic copper foil layer is 9 μm to 18 μm; and / or,

[0010] The grains of the electrolytic copper foil layer include equiaxed crystals and columnar crystals. Among the grains of the electrolytic copper foil layer, the equiaxed crystals account for 75% to 90%, and the columnar crystals account for 10% to 25%.

[0011] In some embodiments, the copper foil further includes a copper roughening layer, the copper roughening layer is located on the surface of the secondary long copper layer on at least one side, the SDR value of the copper roughening layer is 1% to 6%; and / or the thickness of the copper roughening layer is 0.5 μm to 2 μm.

[0012] A second aspect of the present application provides a method for preparing a copper foil, comprising the following steps:

[0013] An electrolytic copper foil layer is prepared by using electrolytic green foil, wherein the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1 μm to 2 μm;

[0014] The copper foil is prepared by electroplating a secondary copper layer on both sides of the electrolytic copper foil layer, and the average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm.

[0015] In some embodiments, the mass concentration of copper ions in the electrolyte used to prepare the electrolytic copper foil layer is 10 g / L to 20 g / L higher than the mass concentration of copper ions in the electrolyte used to prepare the secondary long copper layer; and / or,

[0016] The electrolyte used to prepare the electrolytic copper foil layer contains a leveling agent, a brightener and an inhibitor with a total mass concentration of 30 mg / L to 50 mg / L, and the electrolyte used to prepare the secondary copper layer contains a total mass concentration of the leveling agent, the brightener and the inhibitor of 0 to 10 mg / L.

[0017] In some embodiments, the leveler comprises at least one of benzotriazole, 2-mercaptobenzimidazole and 2-thiazolidinethione; and / or,

[0018] The brightener comprises at least one of sodium polydipropylene glycol disulfide, polyethyl cellulose and sodium dodecyl sulfate; and / or,

[0019] Such inhibitors include polyethylene glycol.

[0020] In some embodiments, the electrolytic copper foil layer is prepared to meet at least one of the following conditions:

[0021] (1) The mass concentration of copper ions in the electrolytic solution is 90 g / L to 110 g / L, and the mass concentration of sulfuric acid is 100 g / L to 130 g / L;

[0022] (2) The current density of the electrolysis is 70 A / dm 2 ~80 A / dm 2 ;

[0023] (3) The electrolysis temperature is 50°C to 55°C;

[0024] (4) The mass concentration of chloride ions in the electrolytic solution is 10 mg / L to 20 mg / L;

[0025] And / or, the preparation of the secondary copper layer satisfies at least one of the following conditions:

[0026] (1) The mass concentration of copper ions in the electroplating solution is 80 g / L to 90 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L;

[0027] (2) The electroplating temperature is 47°C to 53°C;

[0028] (3) The flow rate of the electroplating solution is 8m 3 / h ~10m 3 / h;

[0029] (4) The electroplating time is 10s~20s;

[0030] (5) The current density of the electroplating is 70A / dm 2 ~80A / dm 2 .

[0031] In some embodiments, after the electroplating of the secondary copper layer, the step of preparing a copper roughening layer is further included:

[0032] performing electrolytic roughening treatment and electrolytic solidification treatment on the surface of the secondary copper layer in sequence;

[0033] Optionally, the copper ion mass concentration in the electrolyte of the electrolytic roughening treatment is 8 g / L to 10 g / L, and the sulfuric acid mass concentration is 100 g / L to 110 g / L;

[0034] Optionally, the mass concentration of copper ions in the electrolyte for the electrolytic solidification treatment is 55 g / L to 60 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L;

[0035] Optionally, after preparing the copper roughening layer, the method further includes the following steps:

[0036] Performing nickel plating on the surface of the copper roughened layer, wherein the mass concentration of nickel ions in the electroplating solution for the nickel plating is 19 g / L to 21 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L; and / or,

[0037] Performing a zinc plating treatment on the surface of the copper roughened layer, wherein the mass concentration of zinc ions in the zinc plating treatment electroplating solution is 4.5 g / L to 5.5 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L; and / or,

[0038] A chromium plating treatment is performed on the surface of the copper roughened layer, wherein the mass concentration of chromium ions in the electroplating solution of the chromium plating treatment is 0.8 g / L to 1.2 g / L.

[0039] The third aspect of the present application provides a printed circuit board, comprising the copper foil described in the first aspect, or the copper foil prepared by the preparation method described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the copper foil structure according to one embodiment.

[0041] Figure 2 Graph showing the relationship between transmission loss and signal frequency for Example 1 and Comparative Example 1 within the measurement frequency range of 0 to 16 GHz.

[0042] Description of reference numerals:

[0043] 1. Electrolytic copper foil layer; 2. Secondary copper layer; 3. Copper roughening layer. DETAILED DESCRIPTION

[0044] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] With the advancement of communication technology, the transmission speed and integrity of circuit signals are becoming increasingly important. This places higher demands on copper foil used in high-speed and high-frequency signal transmission circuit boards, requiring the loss of electrical signal transmission to be minimized as much as possible. When high-speed and high-frequency signals are transmitted on the lines of a printed circuit board, the current tends to be transmitted on the surface of the copper foil due to the skin effect, resulting in a smaller effective cross-sectional area for electrical signal transmission, an increase in the resistance of the copper foil surface, and an increase in electrical signal transmission loss. In order to solve the problem of how to reduce the electrical signal loss caused by the skin effect, traditional technologies usually roughen the surface of the copper foil to form a roughening layer of non-conductive material on the surface of the copper foil, so that high-speed and high-frequency signals are transmitted directly from the inside of the copper foil without passing through the roughening layer, thereby reducing the skin effect; or the surface of the copper foil is micro-roughened and multiple copper nodule-free areas and copper nodule areas are provided in the micro-roughening layer. By increasing the number of copper nodule-free areas or reducing the average width of the copper nodule areas, the obstruction of electrons traveling on the micro-roughened surface during signal transmission is reduced, thereby reducing the loss of electrical signal transmission. However, in the copper foil preparation process of the aforementioned traditional technology, as the thickness of the electrolytic copper foil layer and the growth and coarsening time of the copper grains increase, the copper grains gradually grow from fine equiaxed crystals to dendritic crystals. The dendritic crystals have many grain boundaries in the cross-sectional direction of the copper foil, which causes large losses in electrical signal transmission.

[0047] Based on this, one embodiment of the present application provides a copper foil, see Figure 1 , including an electrolytic copper foil layer 1 and a secondary long copper layer 2 located on both side surfaces of the electrolytic copper foil layer 1, the average maximum Feret diameter of the grains of the secondary long copper layer 2 is 2.3μm~3μm, and the average maximum Feret diameter of the grains of the electrolytic copper foil layer 1 is 1μm~2μm.

[0048] The average maximum Feret diameter of the grains in the secondary copper layer on both sides of the copper foil is 2.3μm to 3μm, while the average maximum Feret diameter of the grains in the internal electrolytic copper foil layer is 1μm to 2μm, forming a structure with large surface grains and small internal grains. When the copper foil is used to transmit high-speed and high-frequency electrical signals, due to the skin effect of the current, the electrical signals will be transmitted more along the secondary copper layer on the surface of the copper foil. The large grain size of the secondary copper layer will correspondingly reduce the number of grains and grain boundaries, and the obstruction to the current will become smaller, thereby reducing the electrical signal transmission loss and improving the integrity of the electrical signal transmission. The small grain size of the electrolytic copper foil layer is conducive to improving the surface flatness and smoothness of the electrolytic copper foil layer, thereby improving the uniformity of the grains in the secondary copper layer and further reducing the electrical signal transmission loss.

[0049] The copper foil has low signal transmission loss at 0-16 GHz and high peel strength, especially at 16 GHz, where the signal transmission loss can be reduced to below -0.66 dB / in.

[0050] Feret's diameter: Also known as particle length, Feret's diameter is a parameter used to describe particle size. It is defined as the distance between two parallel lines in a specific direction, when the particle is sandwiched between these two lines. Feret's diameters are typically measured in multiple directions to fully characterize the size and shape of a particle or object.

[0051] Maximum Feret's diameter: The maximum Feret's diameter of a particle measured in all possible directions; Minimum Feret's diameter: The minimum Feret's diameter of a particle measured in all possible directions. Refer to ISO 13322 and ISO 9276.

[0052] Average Maximum Feret's Diameter: The average of the maximum Feret's diameters of all particles.

[0053] The average value of the maximum Feret diameter of the grains can be tested by the following method: first prepare a copper foil sample to be polished, then place the copper foil sample in an argon ion polisher for cross-section polishing, and finally affix the polished copper foil sample to a 70° inclined sample stage. The copper foil is characterized using a ZEISS FE-SEM Sigma 300 field emission scanning electron microscope (EBSD) system to calculate the average value of the maximum Feret diameter of the grains of the copper foil sample.

[0054] As an example, the average maximum Feret diameter of the grains of the secondary copper layer can be 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, and 3.0 μm, or can be within a range consisting of any two of the above values. The average maximum Feret diameter of the grains of the secondary copper layer is preferably 2.5 μm to 3.0 μm.

[0055] As an example, the average maximum Feret diameter of the grains of the electrolytic copper foil layer can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, and 2.0 μm, or can be within a range consisting of any two of the aforementioned values. The average maximum Feret diameter of the grains of the electrolytic copper foil layer is preferably 1.7 μm to 2.0 μm.

[0056] In some embodiments, the thickness of the electrolytic copper foil layer is 9 μm to 18 μm. When the thickness of the electrolytic copper foil layer produced by electrolytic green foil is 9 μm to 18 μm, it can not only reduce the formation of dendrites and obtain smaller copper grains, but also make the surface of the electrolytic copper foil layer smooth and low in roughness, providing excellent conditions for the subsequent growth of the secondary copper layer and improving the uniformity of the grains of the secondary copper layer.

[0057] As an example, the thickness of the electrolytic copper foil layer can be 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, or 18.0 μm, or can be within a range consisting of any two of the above values as end values. The thickness of the electrolytic copper foil layer is preferably 9 μm to 12 μm. When the thickness is 9μm ~ 12μm, most of the copper grains are mainly small equiaxed crystals. This thickness can shorten the time for copper grain growth and coarsening, prevent the grains from gradually growing into dendritic crystals, thereby obtaining small-sized grains and further reducing the surface roughness of the electrolytic copper foil layer. At the same time, the electrolytic copper foil layer of 9μm ~ 12μm has good mechanical properties. When undergoing secondary copper growth treatment and / or micro-roughening treatment, the copper foil roll made of electrolytic raw foil can be placed on the winding part of the surface treatment equipment for production without foil breakage, ensuring the feasibility of mass production and improving production efficiency.

[0058] In some embodiments, the grains of the electrolytic copper foil layer include equiaxed grains and columnar grains.

[0059] In some embodiments, the mass proportion of equiaxed crystals in the electrolytic copper foil layer is 75% to 90%, and the mass proportion of columnar crystals is 10% to 25%. The grains of the electrolytic copper foil layer are mostly equiaxed crystals, and the equiaxed crystals are approximately spherical or polyhedral in shape, with relatively small and uniform sizes in all directions. This not only reduces the surface roughness of the electrolytic copper foil layer, but also ensures that the electrolytic copper foil layer has uniform mechanical properties, good processing performance, and uniform electrical and thermal conductivity.

[0060] As an example, in the grains of the electrolytic copper foil layer, the mass proportion of equiaxed crystals can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89% and 90%, or it can be within the range formed by any two of the above point values as end values.

[0061] As an example, the mass proportion of columnar crystals in the grains of the electrolytic copper foil layer can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% and 25%, or it can be within the range formed by any two of the above point values as end values.

[0062] In some embodiments, the thickness of the secondary copper layer is 3 μm to 4 μm. A thickness of 3 μm to 4 μm can further shorten the electrical signal transmission path and reduce electrical signal loss while also balancing the mechanical strength of the copper foil, making it less likely to break.

[0063] As an example, the thickness of the secondary copper layer can be 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, and 4.0 μm, or can be within a range consisting of any two of the above values. The thickness of the secondary copper layer is preferably 3.5 μm to 4.0 μm.

[0064] In some embodiments, the grains of the secondary copper layer include equiaxed grains and columnar grains.

[0065] In some embodiments, among the grains of the secondary copper layer, the mass proportion of equiaxed crystals is 70% to 80%, and the mass proportion of columnar crystals is 20% to 30%.

[0066] In some embodiments, the average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm, and the thickness of the secondary copper layer is 3 μm to 4 μm; the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1 μm to 2 μm, and the thickness of the electrolytic copper foil layer is 9 μm to 18 μm.

[0067] In some implementations, see Figure 1 The copper foil also includes a copper roughening layer 3 located on at least one side of the secondary copper layer 2. The copper roughening layer 3 has an SDR value of 1% to 10%. This SDR value of the copper roughening layer not only improves the peel strength between the copper foil and the resin substrate, but also reduces the signal transmission path due to its lower surface roughness, further reducing signal transmission losses.

[0068] The SDR value of the copper roughened layer is preferably 1% to 3.2%. The SDR value of the copper roughened layer within this range can further improve the peel strength between the copper foil and the resin substrate and reduce electrical signal transmission loss.

[0069] The SDR value is the interface expansion area ratio, which is the increase in the expanded surface area of a defined region relative to the original surface area of the defined region. It can be measured and analyzed using an Olympus OLS5100 laser confocal microscope.

[0070] As an example, the SDR value of the copper roughened layer=(surface area of the copper roughened layer−surface area of one side of the secondary copper layer) / surface area of one side of the secondary copper layer.

[0071] A second aspect of the present application provides a method for preparing a copper foil, comprising the following steps S1 to S2:

[0072] S1: Electrolytic copper foil is prepared by electrolytic green foil, and the average maximum Feret diameter of the grains of the electrolytic copper foil is 1μm~2μm;

[0073] S2: A copper foil is produced by electroplating a secondary copper layer on both sides of the electrolytic copper foil layer. The average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm.

[0074] The above method forms a copper grain layer with an average maximum Feret diameter of 2.3μm~3μm on the surface of the copper foil through secondary copper growth, while the average maximum Feret diameter of the internal grains is 1μm~2μm. When used to transmit high-speed and high-frequency electrical signals, due to the skin effect of current, the electrical signals will be transmitted more along the surface of the copper foil, and the surface grains are large, with fewer grain boundaries, less obstruction to the current and less loss, thereby improving the integrity of electrical signal transmission.

[0075] Understandably, secondary copper growth is double-sided copper growth, which can be evenly electroplated on both sides of the electrolytic copper foil to form a flat and large-sized secondary copper layer with a thickness of 2.3μm to 3μm. Compared with the copper foil after primary electrolysis, the cross-sectional grains of the copper foil after secondary copper growth are mainly equiaxed grains, which is more conducive to controlling the flatness of the copper foil surface and subsequent micro-roughening treatment. In addition, the use of secondary copper growth can reduce the growth and coarsening time of the electrolytic copper foil, thereby avoiding the formation of dendrites, reducing grain boundaries and current obstruction, and improving the integrity of electrical signal transmission.

[0076] In some embodiments, the mass concentration of copper ions in the electrolyte used to prepare the electrolytic copper foil layer is 10 g / L to 20 g / L higher than the mass concentration of copper ions in the electrolyte used to prepare the secondary long copper layer.

[0077] As an example, the mass concentration of copper ions in the electrolyte used to prepare the electrolytic copper foil layer can be 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L and 20 g / L higher than the mass concentration of copper ions in the electrolyte used to prepare the secondary long copper layer, or it can be within the range consisting of any two of the above point values as end values.

[0078] In some embodiments, the electrolyte used to prepare the electrolytic copper foil layer contains a leveler, brightener and inhibitor with a total mass concentration of 30 mg / L to 50 mg / L, and the total mass concentration of the leveler, brightener and inhibitor in the electrolyte used to prepare the secondary copper layer is 0 to 10 mg / L.

[0079] Furthermore, no leveling agent, brightener or inhibitor needs to be added to the electrolyte used to prepare the secondary copper layer.

[0080] It is understood that the grain size of the secondary copper layer and the electrolytic copper foil layer can be controlled by adjusting the copper ion and additive concentrations. The thickness of the electrolytic copper foil layer, the secondary copper layer, and the copper roughening layer can be controlled by adjusting the copper ion concentration and the treatment time.

[0081] In some embodiments, in S1, the mass concentration of copper ions in the electrolyzed electrolyte is 90 g / L to 110 g / L, and the mass concentration of sulfuric acid is 100 g / L to 130 g / L.

[0082] In some embodiments, in S1, the current density of the electrolysis is 70A / dm 2 ~80A / dm 2 .

[0083] In some embodiments, in S1, the electrolysis temperature is 50°C to 55°C.

[0084] In some embodiments, in S1, the mass concentration of chloride ions in the electrolyzed electrolyte is 10 mg / L to 20 mg / L.

[0085] In some embodiments, in S1, the electrolytic solution contains a leveling agent, brightener, and inhibitor at a total mass concentration of 30 mg / L to 50 mg / L. Adding the leveling agent, brightener, and inhibitor to the electrolyte can refine the grain size and further improve the surface flatness and glossiness of the electrolytic copper foil. It also prevents excessive electrolysis reaction from causing uneven growth or other defects in the electrolytic copper foil.

[0086] Furthermore, the mass ratio of the leveler, brightener and inhibitor in the electrolyte for preparing the electrolytic copper foil layer is 3:2:1.

[0087] Furthermore, the leveler includes at least one of benzotriazole, 2-mercaptobenzimidazole and 2-thiazolidinethione.

[0088] Furthermore, the brightener includes at least one of sodium polydipropylene sulfonate, polyethyl cellulose and sodium dodecyl sulfonate.

[0089] Furthermore, the inhibitor comprises polyethylene glycol.

[0090] In some embodiments, the prepared electrolytic copper foil layer is pickled before the secondary copper growth, specifically: the prepared electrolytic copper foil roll is moved to the surface line, and the oxide layer on the surface of the electrolytic copper foil is first pickled to remove the oxide layer, wherein the mass concentration of copper ions in the pickling solution is ≤5g / L, the mass concentration of sulfuric acid is 80g / L~90g / L, the temperature is 33℃~37℃, and the flow rate is 8m 3 / h~10m 3 / h; pickling and then water washing.

[0091] In some embodiments, in S2, the mass concentration of copper ions in the electroplating solution is 80 g / L-90 g / L, and the mass concentration of sulfuric acid is 100 g / L-110 g / L.

[0092] In some embodiments, in S2, the electroplating temperature is 47°C to 53°C.

[0093] In some embodiments, in S2, the flow rate of the plating solution is 8m 3 / h ~10m 3 / h.

[0094] In some embodiments, in S2, the electroplating time is 10s to 20s.

[0095] In some embodiments, the electroplating current density is 70 A / dm 2 ~80A / dm 2 ;

[0096] In some embodiments, after electroplating the secondary copper layer, the following step of preparing a copper roughening layer is further included:

[0097] Electrolytic roughening treatment and electrolytic solidification treatment are sequentially performed on the surface of the secondary copper layer.

[0098] In some embodiments, the mass concentration of copper ions in the electrolyte of the electrolytic roughening treatment is 8 g / L to 10 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L.

[0099] In some embodiments, the mass concentration of copper ions in the electrolyte of the electrolytic solidification treatment is 55 g / L to 60 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L.

[0100] In some embodiments, the following nickel plating step is further included after preparing the copper roughening layer:

[0101] Nickel plating is performed on the surface of the copper roughened layer. The mass concentration of nickel ions in the nickel plating solution is 19 g / L to 21 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L.

[0102] In some embodiments, the following zinc plating step is further included after preparing the copper roughening layer:

[0103] The surface of the copper roughened layer is zinc-plated. The mass concentration of zinc ions in the zinc-plating electroplating solution is 4.5 g / L to 5.5 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L.

[0104] In some embodiments, the following chromium plating step is further included after preparing the copper roughening layer:

[0105] The surface of the copper roughened layer is chromium-plated, and the mass concentration of chromium ions in the electroplating solution of the chromium-plating is 0.8 g / L to 1.2 g / L.

[0106] In some embodiments, nickel plating, zinc plating, and chromium plating are performed sequentially after forming the copper roughening layer. The nickel plating, zinc plating, and chromium plating performed sequentially after forming the copper roughening layer significantly improve the corrosion resistance, welding performance, wear resistance, and oxidation resistance of the copper foil.

[0107] In some embodiments, copper foil for high-speed and high-frequency signal transmission circuit boards is obtained by coating a silane coupling agent on both sides of the copper foil, drying the foil, and then rolling the foil up. The silane coupling agent used has a mass concentration of 0.1% to 1.5%.

[0108] Furthermore, the silane coupling agent is obtained by compounding one or two of epoxy silane coupling agent, amino silane coupling agent, acrylic silane coupling agent, vinyl silane coupling agent and mercapto silane coupling agent.

[0109] The third aspect of the present application provides a printed circuit board, comprising the copper foil of the first aspect, or the copper foil prepared by the preparation method of the second aspect.

[0110] In some embodiments, a printed wiring board includes a PPO resin substrate (polyphenylene oxide resin) and a copper foil located on at least one side of the PPO resin substrate.

[0111] Furthermore, the copper foil is laminated with the PPO resin substrate by thermal compression.

[0112] The following are specific examples.

[0113] Example 1

[0114] A method for preparing copper foil comprises the following steps:

[0115] (a) Preparation of electrolytic copper foil: The electrolytic copper foil was prepared by electrolysis in an electrolytic cell. Pure copper was added to sulfuric acid to adjust the copper ion concentration in the electrolyte to 95 g / L and the sulfuric acid concentration to 110 g / L. Hydrochloric acid was added to fine-tune the electrolyte salt to adjust the chloride ion concentration to 13 mg / L. The electrolyte was supplemented with benzotriazole, sodium polydisulfide dipropylene glycol, and polyethylene glycol, with the contents of the three in the electrolyte being 21 mg / L, 14 mg / L, and 7 mg / L, respectively. The electrolysis temperature was 55°C and the current density was 70 A / dm 2 After preparation, the copper foil is peeled and rolled to obtain an electrolytic copper foil layer with an average maximum Feret diameter of 1.53 μm in cross-sectional grains. The thickness of the electrolytic copper foil layer is 12 μm. Among the grains in the electrolytic copper foil layer, equiaxed crystals account for 80% by mass, and columnar crystals account for 20% by mass.

[0116] (b) Pickling: The prepared electrolytic copper foil layer is moved to the surface line, and the oxide layer on the surface of the electrolytic copper foil is firstly pickled to remove it, and then washed with water; wherein, the mass concentration of copper ions in the pickling solution is ≤5g / L, the mass concentration of sulfuric acid in the pickling solution is 80g / L, the pickling temperature is maintained at 35±2℃, and the pickling solution flow rate is 10m 3 / h.

[0117] (c) Secondary copper growth: In the surface treatment equipment, the anode is an anode plate, and the electrolytic copper foil is used as the cathode. The secondary copper layer is electroplated on both sides of the electrolytic copper foil layer. The average maximum Feret diameter of the secondary copper layer is a copper grain layer of 2.3~3μm. The secondary copper is double-sided copper. After the double-sided copper treatment, the total thickness of the copper foil is 18μm (that is, the thickness of the single-sided secondary copper layer is 3μm); wherein, the mass concentration of copper ions in the electroplating solution is 90 g / L (pure copper material is added), the mass concentration of sulfuric acid is 110g / L, the electroplating temperature is 50±3℃, and the electroplating solution flow rate is 10m 3 / h, the electroplating time was 15s, and a secondary long copper layer with an average maximum Feret diameter of the cross-sectional grains of 2.32μm was obtained.

[0118] (d) Micro-roughening: A fine roughness structure with an SDR of 1% to 10% is formed on the treated surface of the copper foil after secondary copper growth. This process involves two steps: a roughening treatment in the roughening tank containing electrolyte parameters of 10 g / L copper ions and 110 g / L sulfuric acid; and a curing treatment in the curing tank containing electrolyte parameters of 55 g / L copper ions and 100 g / L sulfuric acid, resulting in a copper roughening layer with an SDR of 3.2%.

[0119] (e) Blackening nickel plating, graying zinc plating, and passivation chromium plating: After washing the copper foil, blackening nickel plating, graying zinc plating, and passivation chromium plating are performed. The electroplating conditions for the blackening nickel plating are as follows: the mass concentration of nickel ions in the electroplating solution is 20 g / L, and the mass concentration of boric acid is 30 g / L; the electroplating conditions for the graying zinc plating are as follows: the mass concentration of zinc ions in the electroplating solution is 5 g / L, and the mass concentration of boric acid is 30 g / L; and the electroplating conditions for the passivation chromium plating are as follows: the mass concentration of chromium ions in the electroplating solution is 1 g / L. The blackening nickel plating, graying zinc plating, and passivation chromium plating can all be performed in surface treatment equipment.

[0120] (f) Coating a coupling agent: Coating a silane coupling agent on both sides of the copper foil, drying it, and then rolling it up to obtain a copper foil for high-speed and high-frequency signal transmission circuit boards. The silane coupling agent used is an epoxy silane coupling agent with a mass concentration of 1%.

[0121] Example 2

[0122] The preparation method of Example 2 is substantially the same as that of Example 1, except that the copper ion concentration in the electrolyte is reduced in the secondary copper growth step so that the average maximum Feret diameter of the grains of the secondary copper growth layer is 3 μm.

[0123] Example 3

[0124] The preparation method of Example 3 is substantially the same as that of Example 1, except that in the step of preparing the electrolytic copper foil layer, the amount of additives is reduced so that the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 2 μm.

[0125] Example 4

[0126] The preparation method of Example 4 is substantially the same as that of Example 1, except that the rotation speed of the cathode roller in the electrolytic copper foil process is slowed down so that the thickness of the electrolytic copper foil layer is 18 μm.

[0127] Example 5

[0128] The preparation method of Example 5 is substantially the same as that of Example 1, except that in the secondary copper growth step, the electroplating time is shortened so that the thickness of the secondary copper layer is 4 μm.

[0129] Example 6

[0130] The preparation method of Example 6 is basically the same as that of Example 1, except that in the micro-roughening step, the copper ion concentration in the electrolyte is increased during the roughening process, so that the SDR value of the copper roughened layer is 4.8%.

[0131] Comparative Example 1

[0132] Comparative Example 1 is substantially the same as Example 1, except that the secondary copper layer is omitted and the thickness of the electrolytic copper foil layer is 18 μm.

[0133] Comparative Example 2

[0134] Comparative Example 2 is substantially the same as Example 1, except that the average maximum Feret diameter of the grains of the secondary copper layer is 1 μm.

[0135] Comparative Example 3

[0136] Comparative Example 3 is substantially the same as Example 1, except that the average maximum Feret diameter of the electrolytic copper foil layer is 5 μm.

[0137] The copper foils prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were tested for electrical performance loss and peel strength at 16 GHz. The test results are shown in Table 1 below.

[0138] Among them, the test methods and conditions for various performance parameters are as follows:

[0139] Surface roughness Sdr value test: tested using Olympus OLS5100 laser confocal microscope.

[0140] Statistics on the average maximum Feret diameter of cross-sectional grains: The prepared copper foil samples were placed in an argon ion polisher for cross-sectional polishing. The polished copper foil samples were then attached to a 70° inclined sample stage and characterized using a ZEISS FE-SEM Sigma300 field emission scanning electron microscope (EBSD) system. The average maximum Feret diameters of the grains in the secondary copper layer on the surface of the copper foil samples and the grains in the internal electrolytic copper foil layer were calculated.

[0141] Peel strength test: The prepared copper foil and prepreg were stacked, and four PPO resin prepregs with a glass transition temperature of 200°C were placed between the two copper foils. Then, they were hot pressed at a temperature of 220°C to 250°C and a surface pressure of 20kg / m 2 ~25kg / m2 , the hot pressing time is 90min~150min; use a cutter to cut the hot pressed copper clad laminate into strips with a width of 3.0mm; then use a utility knife to peel off 1cm~2cm of the copper foil on one side of the copper clad laminate, and fix the peeled copper foil on one end of the weight; finally, the peel strength test is carried out on the peel strength tester by moving the copper foil through the weight.

[0142] Electrical Loss Test: Samples for electrical loss measurement were prepared using the aforementioned heat-pressed copper-clad laminates, and transmission loss was measured within a high-frequency bandwidth. The electrical loss evaluation used the stripline resonator method with a 0-16 GHz bandwidth. The microstrip structure employed a dielectric thickness of 50 μm, a conductor length of 1.0 mm, a conductor thickness of 18 μm, a conductor circuit width of 120 μm, and a characteristic impedance of 50 Ω.

[0143] Table 1

[0144]

[0145] As shown in Table 1 above, the PCBs produced by laminating the copper foil and PPO resin substrates prepared in Examples 1-6 exhibit electrical performance losses ranging from -0.5 dB / in to -0.8 dB / in at 16 GHz, and peel strengths of no less than 2.3 lb / in. Comparative Examples 1-3 exhibit high electrical signal transmission losses, and the peel strength between the copper foil and the resin substrate is also inferior to that of Examples 1-6.

[0146] from Figure 2 It can be seen that at the test frequency of 0~16GHz, the electrical signal transmission loss of Example 1 is smaller than that of Comparative Example 1 (the larger the absolute value of the negative value, the greater the transmission electrical signal loss). The difference is largest at 16GHz. The electrical signal transmission loss of Example 1 is -0.74dB / in, and the electrical signal transmission loss of Comparative Example 1 is -0.87dB / in.

[0147] Moreover, when the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1.7μm ~ 2.0μm, the thickness of the electrolytic copper foil layer is 9μm ~ 12μm, and the average maximum Feret diameter of the grains of the long copper layer is 2.5μm ~ 3.0μm, or the thickness of the long copper layer is 3.5μm ~ 4μm, the electrical signal transmission loss is smaller when the copper foil is used to transmit high-speed and high-frequency electrical signals.

[0148] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0149] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A copper foil, characterized in that The invention comprises an electrolytic copper foil layer and secondary copper layers located on both sides of the electrolytic copper foil layer. The average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm, and the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1 μm to 2 μm.

2. The copper foil according to claim 1, wherein The thickness of the secondary copper layer is 3 μm to 4 μm; and / or, The grains of the secondary copper layer include equiaxed crystals and columnar crystals. Among the grains of the secondary copper layer, the equiaxed crystals account for 70% to 80%, and the columnar crystals account for 20% to 30%.

3. The copper foil according to any one of claims 1 to 2, characterized in that The thickness of the electrolytic copper foil layer is 9 μm to 18 μm; and / or, The grains of the electrolytic copper foil layer include equiaxed crystals and columnar crystals. Among the grains of the electrolytic copper foil layer, the equiaxed crystals account for 75% to 90%, and the columnar crystals account for 10% to 25%.

4. The copper foil according to any one of claims 1 to 2, wherein The invention also includes a copper roughening layer, which is located on at least one side of the surface of the secondary long copper layer, and the SDR value of the copper roughening layer is 1% to 6%; and / or the thickness of the copper roughening layer is 0.5 μm to 2 μm.

5. A method for preparing copper foil, characterized in that: The following steps are involved: An electrolytic copper foil layer is prepared by using electrolytic green foil, wherein the average maximum Feret diameter of the grains of the electrolytic copper foil layer is 1 μm to 2 μm; The copper foil is prepared by electroplating a secondary copper layer on both sides of the electrolytic copper foil layer, and the average maximum Feret diameter of the grains of the secondary copper layer is 2.3 μm to 3 μm.

6. The method for preparing the copper foil according to claim 5, wherein: The mass concentration of copper ions in the electrolyte used to prepare the electrolytic copper foil layer is 10 g / L to 20 g / L higher than the mass concentration of copper ions in the electrolyte used to prepare the secondary long copper layer; and / or, The electrolyte used to prepare the electrolytic copper foil layer contains a leveling agent, a brightener and an inhibitor with a total mass concentration of 30 mg / L to 50 mg / L, and the electrolyte used to prepare the secondary copper layer contains a total mass concentration of the leveling agent, the brightener and the inhibitor of 0 to 10 mg / L.

7. The method for preparing the copper foil according to claim 6, wherein: The leveler comprises at least one of benzotriazole, 2-mercaptobenzimidazole and 2-thiazolidinethione; and / or, The brightener comprises at least one of sodium polydipropylene glycol disulfide, polyethyl cellulose and sodium dodecyl sulfate; and / or, Such inhibitors include polyethylene glycol.

8. The method for preparing the copper foil according to any one of claims 5 to 7, wherein: The preparation of the electrolytic copper foil layer satisfies at least one of the following conditions: (1) The mass concentration of copper ions in the electrolytic solution is 90 g / L to 110 g / L, and the mass concentration of sulfuric acid is 100 g / L to 130 g / L; (2) The current density of the electrolysis is 70 A / dm 2 ~80 A / dm 2 ; (3) The electrolysis temperature is 50°C to 55°C; (4) The mass concentration of chloride ions in the electrolytic solution is 10 mg / L to 20 mg / L; And / or, the preparation of the secondary copper layer satisfies at least one of the following conditions: (1) The mass concentration of copper ions in the electroplating solution is 80 g / L to 90 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L; (2) The electroplating temperature is 47°C to 53°C; (3) The flow rate of the electroplating solution is 8m 3 / h ~10m 3 / h; (4) The electroplating time is 10s~20s; (5) The current density of the electroplating is 70A / dm 2 ~80A / dm 2 .

9. The method for preparing the copper foil according to any one of claims 5 to 7, wherein: After the electroplating of the secondary copper layer, the method further includes the following steps of preparing a copper roughening layer: performing electrolytic roughening treatment and electrolytic solidification treatment on the surface of the secondary copper layer in sequence; Optionally, the copper ion mass concentration in the electrolyte of the electrolytic roughening treatment is 8 g / L to 10 g / L, and the sulfuric acid mass concentration is 100 g / L to 110 g / L; Optionally, the mass concentration of copper ions in the electrolyte for the electrolytic solidification treatment is 55 g / L to 60 g / L, and the mass concentration of sulfuric acid is 100 g / L to 110 g / L; Optionally, after preparing the copper roughening layer, the method further includes the following steps: Performing nickel plating on the surface of the copper roughened layer, wherein the mass concentration of nickel ions in the electroplating solution for the nickel plating is 19 g / L to 21 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L; and / or, Performing a zinc plating treatment on the surface of the copper roughened layer, wherein the mass concentration of zinc ions in the zinc plating treatment electroplating solution is 4.5 g / L to 5.5 g / L, and the mass concentration of boric acid is 28 g / L to 32 g / L; and / or, A chromium plating treatment is performed on the surface of the copper roughened layer, wherein the mass concentration of chromium ions in the electroplating solution of the chromium plating treatment is 0.8 g / L to 1.2 g / L.

10. A printed circuit board, characterized in that: The invention relates to a copper foil comprising the copper foil according to any one of claims 1 to 4, or a copper foil prepared by the preparation method according to any one of claims 5 to 9.

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