Metal foil and metal-clad laminated plate

Abstract

The invention discloses a metal foil and a metal-clad laminated plate, the metal foil comprises a functional layer, and the functional layer comprises a coarsening bonding surface and a brownification surface which are oppositely arranged; wherein the first roughness Rz1 of the brownification surface before the brownification treatment and the second roughness Rz2 of the brownification surface after the brownification treatment meet the following condition: Rz2 / Rz1 is more than or equal to 1 and less than or equal to 1.1; and the first interface expansion area ratio SDR1 of the browned surface before the browning treatment and the second interface expansion area ratio SDR2 of the browned surface after the browning treatment meet the condition that SDR2 / SDR1 is greater than or equal to 1.2, so that the browned surface after the browning can keep a low-profile and rough and compact morphology, the browned surface can be flatter while the laser absorption efficiency is not influenced, and the quality of the laser is improved. The leveling difficulty in the subsequent electroplating thickening process is reduced, and the surface of the electroplated and thickened circuit layer can be effectively kept at low roughness Rz, so that the skin effect of the circuit is reduced, a high-frequency and high-speed fine circuit is convenient to manufacture, and the reliability of the circuit is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of electronic information materials, and in particular to a metal foil and a metal-clad laminate. Background Art

[0002] Metal foil is a key material in high-frequency, high-speed printed circuit boards (PCBs) for 5G communications. When using the MSAP process to produce ultra-fine circuits, the foil is laminated to the substrate at high temperatures, and then laser-drilled into the substrate. The finer the circuit, the smaller the hole size required. After lamination, the copper foil typically has a high gloss, making it difficult for the light to be absorbed by the laser during drilling. This results in low drilling efficiency and poor hole shape.

[0003] Therefore, some manufacturers currently perform browning on the metal foil before laser drilling of copper foil, so as to etch and roughen the surface of the metal foil to form a browning layer. The browning layer is darker in color and lower in glossiness, which can better absorb laser energy and improve drilling efficiency and hole yield.

[0004] Although the browned surface can improve drilling efficiency and yield, when making ultra-fine circuits, it needs to be electroplated again to form a circuit layer after browning. During the electroplating thickening process, a leveling agent needs to be added for leveling. If the roughness Rz of the copper foil surface after browning is too high and the distance between the high and low points of the contour is too large, leveling will be difficult, which may cause the surface contour of the circuit layer after electroplating to remain uneven, thereby enhancing the skin effect on the circuit surface, which is not conducive to the production of high-frequency, high-speed, fine circuits and affects the reliability of the circuit transmission signal. Summary of the Invention

[0005] The present invention provides a metal foil and a metal-clad laminate, which can enable the browned surface after browning to maintain a low profile but rough and dense morphology. While not affecting the laser absorption efficiency, the browned surface can be made flatter, reducing the difficulty of leveling in the subsequent electroplating thickening process. The surface roughness Rz of the circuit layer after electroplating thickening can be effectively maintained to reduce the skin effect of the circuit, facilitate the production of high-frequency, high-speed, fine circuits, and improve the reliability of the circuit.

[0006] In a first aspect, an embodiment of the present invention provides a metal foil including a functional layer, wherein the functional layer includes a roughened bonding surface and a browned surface disposed opposite to each other;

[0007] Wherein, the first roughness Rz1 of the browning surface before the browning treatment and the second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.1;

[0008] Furthermore, a first interface expansion area ratio SDR1 of the browned surface before the browning treatment and a second interface expansion area ratio SDR2 of the browned surface after the browning treatment satisfy the following: 1.2≤SDR2 / SDR1.

[0009] Optionally, the first roughness Rz1 of the browned surface before the browning treatment is ≤1.8 μm and the first interface extension area ratio SDR1 is ≤1.5;

[0010] The second roughness Rz2 of the browned surface after the browning treatment is ≤1.9 μm and the second interface expansion area ratio SDR2 is ≥2.

[0011] Optionally, a first roughness Rz1 of the browned surface before the browning treatment and a second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.05;

[0012] A first interface expansion area ratio SDR1 of the browned surface before the browning treatment and a second interface expansion area ratio SDR2 of the browned surface after the browning treatment satisfy the following: 1.5≤SDR2 / SDR1≤20.

[0013] Optionally, after the browning treatment, in a sliced ​​state, the height difference between the highest point and the lowest point of the outline within any length of 100 μm is ≤1.5 μm.

[0014] Optionally, after the browning treatment, the browned surface forms a plurality of protrusions. In the sliced ​​state, within any length of 100 μm, the distance between two adjacent protrusions is less than or equal to 3 μm, wherein the distance between the protrusions is the shortest straight-line distance between the contours of the two protrusions.

[0015] Optionally, after the browning treatment, the browned surface is formed with a plurality of protrusions, and in a sliced ​​state, within any length of 100 μm, the number of the protrusions is greater than or equal to 30.

[0016] Optionally, after the browning treatment, the browned surface forms a plurality of protrusions. In the sliced ​​state, within any length of 100 μm, the roughness Sku of at least 70% of the protrusions is less than or equal to 3, wherein the roughness Sku of the protrusion is a parameter used to judge the sharpness of the roughness shape.

[0017] Optionally, the metal foil includes:

[0018] carrier layer;

[0019] The carrier layer is arranged on the browned surface of the functional layer.

[0020] Optionally, the metal foil further comprises:

[0021] peeling layer;

[0022] The peeling layer is arranged between the carrier layer and the functional layer.

[0023] In a second aspect, an embodiment of the present invention provides a metal-clad laminate, comprising the metal foil according to any embodiment of the present invention.

[0024] The technical solution provided by the embodiment of the present invention satisfies the following conditions: 1≤Rz2 / Rz1≤1.1 by limiting the first roughness Rz1 of the browned surface before the browning treatment and the second roughness Rz2 after the browning treatment; and the first interface expansion area ratio SDR1 of the browned surface before the browning treatment and the second interface expansion area ratio SDR2 after the browning treatment satisfy: 1.2≤SDR2 / SDR1. This allows the browned surface after browning to maintain a low profile but rough and dense morphology, while not affecting the laser absorption efficiency, making the browned surface smoother, reducing the difficulty of leveling in the subsequent electroplating thickening process, and effectively maintaining a low roughness Rz on the surface of the circuit layer after electroplating thickening, thereby reducing the skin effect of the circuit, facilitating the production of high-frequency and high-speed fine circuits, and improving the reliability of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic structural diagram of a metal foil is provided for an embodiment of the present invention;

[0026] Figure 2 A schematic structural diagram of another metal foil is provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Figure 1 A schematic diagram of the structure of a metal foil is provided in an embodiment of the present invention. Figure 1The metal foil includes a functional layer 110, and the functional layer 110 includes a relatively roughened bonding surface 111 and a browned surface 112; wherein the functional layer 110 can have electrical properties, and the functional layer 110 can use a low resistivity material as a signal transmission line. For example, the functional layer 110 can use any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. The roughened bonding surface 111 is a surface that has been roughened. The rough surface of the roughened bonding surface 111 can increase the surface area, significantly improve the adhesion of materials such as coatings or substrates, and improve the stability and durability of the product. The browned surface 112 after the browning treatment can form a brown browned film. This film has a rough microstructure. When the browned layer is darker in color and has lower glossiness, it can better absorb laser energy and improve drilling efficiency and hole yield.

[0029] In the embodiment of the present invention, in order to avoid the problem of high difficulty in leveling caused by the influence of the browned surface 112 after browning when making ultra-fine circuits, the surface contour of the circuit layer after electroplating is uneven, which leads to an enhanced skin effect on the circuit surface and reduced reliability of circuit signal transmission. After a large number of experimental analyses, the inventors found that the reason for this problem is that the roughness Rz of the browned surface 112 after browning treatment increases. Among them, the roughness Rz in the embodiment of the present invention represents the vertical distance between the highest peak top line and the lowest valley bottom line within the sampling length. When the roughness Rz of the browned surface 112 increases, it means that the vertical distance between the highest peak top line and the lowest valley bottom line increases. When the circuit layer is formed by electroplating, the distance between the high and low points of the contour on the browned surface 112 is too large, resulting in an uneven surface contour of the circuit layer after electroplating, thereby leading to an enhanced skin effect on the circuit surface. In addition, during the process of etching the circuit layer, the uneven surface will also affect the etching uniformity, thereby affecting the preparation accuracy of the circuit. However, when considering reducing the roughness Rz of the browned surface 112 after the browning treatment to reduce the difficulty of leveling the browned surface 112, the lower roughness Rz of the browned surface 112 will affect the absorption efficiency of the laser energy, thereby affecting the drilling efficiency and hole yield. It should be noted that, in the embodiment of the present invention, the roughness Rz can be obtained by selecting the vertical distance between multiple highest peak top lines and lowest valley bottom lines, and calculating the average height difference. The roughness Rz only focuses on extreme peaks and valleys, reflects the local maximum fluctuations, and is sensitive to extreme values. It should be noted that, in the embodiment of the present invention, the roughness Rz can be tested according to the ISO 4287 standard.

[0030] Therefore, the embodiment of the present invention proposes to limit the roughness Rz of the browned surface 112 after the browning treatment while also limiting the interface expansion area ratio of the browned surface 112 after the browning treatment, so that the browned surface 112 after the browning treatment has a low-profile peak-to-valley difference, and ensures the density of the undulating wrinkles of the browned surface 112, so as to achieve the reduction of the peak-to-valley difference on the side of the browned surface 112 without affecting the laser absorption efficiency, and reduce the difficulty of leveling the browned surface 112, which is beneficial to improve the flatness of the circuit layer after electroplating thickening and the accuracy of preparing high-frequency and high-speed circuits, thereby improving the reliability of the circuit. It should be noted that the low profile here can be understood as the height difference between the peak features and the valley features in the microstructure of the browned surface 112 meeting the preset height difference range.

[0031] Continue to see Figure 1 The metal foil in the embodiment of the present invention includes a functional layer 110, and the functional layer 110 includes a roughened bonding surface 111 and a browned surface 112 that are oppositely disposed;

[0032] The first roughness Rz1 of the browned surface 112 before the browning treatment and the second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.1;

[0033] Furthermore, a first interface expansion area ratio SDR1 of the browned surface 112 before the browning treatment and a second interface expansion area ratio SDR2 of the browned surface 112 after the browning treatment satisfy: 1.2≤SDR2 / SDR1.

[0034] Specifically, according to the relationship between the second roughness Rz2 of the browned surface 112 after the browning treatment and the first roughness Rz1 of the browned surface 112 before the browning treatment, the increase range of the second roughness Rz2 compared with the first roughness Rz1 is limited to within 10%, that is, the vertical distance between the highest peak top line and the lowest valley bottom line of the browned surface 112 after the browning treatment within the sampling length is within 10%, which indicates that the vertical distance between the highest peak top line and the lowest valley bottom line on the browned surface 112 after the browning treatment has a smaller increase, so that the peaks and valleys of the surface after the browning can appear as a lower contour. Therefore, the browned surface 112 after the browning can still maintain better undulation uniformity than the browned surface 112 before the browning, thereby reducing the difficulty of leveling in the subsequent thickening electroplating process, so as to avoid causing the surface contour of the electroplated circuit layer to fluctuate too much, thereby affecting the reliability of the subsequent etching of ultra-fine circuits.

[0035] At the same time, to reduce the impact on laser energy absorption efficiency, the surface development ratio (SDR) before and after browning is also limited, ensuring that the second surface development ratio (SDR2) after browning is at least 1.2 times the first surface development ratio (SDR1) before browning. It should be noted that in this embodiment of the present invention, the surface development ratio is the ratio of the actual surface area of ​​the browned surface 112 to its projected area. The SDR can be calculated by measuring surface data using a three-dimensional topography instrument (such as a white light interferometer). For example, the projected area of ​​the browned surface 112 is set to D. Because before browning, the browned surface 112 has a certain degree of roughness due to micro-etching, its actual surface area is recorded as S1, that is, the interface expansion area ratio SDR1 of the browned surface 112 before browning is S1 / D. Similarly, after browning, the browned surface 112 is further etched and its surface morphology changes. At this time, its actual surface area is recorded as S2, but its projected area remains unchanged, that is, the interface expansion area ratio SDR2 of the browned surface 112 after browning is S2 / D.

[0036] The second interface expansion area ratio SDR2 after browning treatment is at least 1.2 times the first interface expansion area ratio SDR1 before browning treatment, indicating that the surface area of ​​the browned surface 112 after browning is increased compared with before browning. Since the actual surface area increase brought about by the increase in the second roughness Rz2 is limited, in order to meet the requirements of the second interface expansion area ratio SDR2, it is reflected on the browned surface 112 after browning as an increase in peaks and valleys, that is, the number of undulating wrinkles increases, and the wrinkle density increases, but the overall contour undulation is low, so that it can ensure that the browned surface 112 can have enough coarsened and dense areas, but the flatness after browning is better, so that it can better absorb laser energy without increasing the roughness Rz, so as to ensure drilling efficiency and hole yield.

[0037] In an embodiment of the present invention, the first roughness Rz1 of the browned surface 112 before the browning treatment and the second roughness Rz2 after the browning treatment satisfy the following conditions: 1≤Rz2 / Rz1≤1.1; and the first interface expansion area ratio SDR1 of the browned surface 112 before the browning treatment and the second interface expansion area ratio SDR2 after the browning treatment satisfy the following conditions: 1.2≤SDR2 / SDR1. This allows the browned surface 112 after the browning treatment to maintain a low profile but rough and dense morphology, and while not affecting the laser absorption efficiency, allows the browned surface 112 to appear smoother, reducing the difficulty of leveling in the subsequent thickening electroplating process, so as to avoid causing the surface profile of the electroplated circuit layer to fluctuate excessively, thereby affecting the reliability of the subsequent etching of ultra-fine circuits.

[0038] Optionally, the embodiment of the present invention further limits the first roughness Rz1≤1.8μm and the first interface expansion area ratio SDR1≤1.5 of the browned surface 112 before the browning treatment; the second roughness Rz2≤1.9μm and the second interface expansion area ratio SDR2≥2 of the browned surface 112 after the browning treatment. By limiting the first roughness Rz1 and the first interface expansion area ratio SDR1 of the browned surface 112 before the browning treatment, it is avoided that the browned surface 112 before the browning treatment does not meet the application requirements, thereby further aggravating the product defect rate after the browning. And further, by limiting the second roughness Rz2 and the second interface expansion area ratio SDR2 of the browned surface 112 after the browning treatment, the browned surface 112 after the browning treatment can meet the requirements of a good low profile and a rough and dense morphology.

[0039] Based on the above embodiment, optionally, the first roughness Rz1 of the browned surface 112 before the browning treatment and the second roughness Rz2 after the browning treatment satisfy the following conditions: 1 ≤ Rz2 / Rz1 ≤ 1.05; and the first interface extension area ratio SDR1 of the browned surface 112 before the browning treatment and the second interface extension area ratio SDR2 after the browning treatment satisfy the following conditions: 1.5 ≤ SDR2 / SDR1 ≤ 20. In other words, the increase in the second roughness Rz2 relative to the first roughness Rz1 is within 5%, maintaining a low profile after the browning treatment, and the second interface extension area ratio SDR2 is within a range of 1.5-20 times the first interface extension area ratio SDR1. This ensures that the browned surface 112 has a sufficiently rough and dense surface, while avoiding the problem of excessive density that would result in a long signal transmission path on the circuit surface, leading to signal loss and high resistance. For example, Rz2 / Rz1 can be 1, 1.01, 1.02, 1.03, 1.04, or 1.05. SDR2 / SDR1 can be 1.5, 2, 2.5, 3, 3.5, ..., 18.5, 19, 19.5, or 20. The ratio of the second roughness Rz2 to the first roughness Rz1, as well as the ratio of the first interface extension area ratio SDR1 to the second interface extension area ratio SDR2, can be set according to actual product requirements and will not be further described here.

[0040] Furthermore, optionally, after the browning treatment is performed on the browning surface 112, in the sliced ​​state, the height difference between the highest point and the lowest point of the profile is ≤1.5μm within any 100μm length. The height difference between the highest point and the lowest point of the profile may refer to the vertical distance between the highest peak line and the lowest valley line in the browning surface 112. The height difference between the highest point and the lowest point of the profile is ≤1.5μm, indicating that within the sliced ​​area, the height of all peak morphological positions is less than or equal to 1.5μm, which also ensures that the surface after the browning treatment can have a relatively high flatness in morphology. This flatness helps to reduce the difficulty of leveling in the subsequent electroplating thickening process, so that the surface of the circuit layer formed by electroplating also maintains a low profile, reduces the skin effect of the circuit surface to a certain extent, and improves the integrity of the circuit transmission signal.

[0041] Furthermore, optionally, after the browning treatment, the copper nodule particles on the browning surface 112 may form a plurality of protrusions. In a sliced ​​state, within any 100 μm length, the spacing between two adjacent protrusions is less than or equal to 3 μm. This allows the distance between the protrusions formed by the copper nodule particles to be relatively compact, thereby limiting the formation of a rough and dense morphology of the browning surface 112 after the browning treatment. The spacing between the protrusions is the shortest straight-line distance between the contours of two adjacent protrusions.

[0042] Furthermore, after the browning treatment, the copper nodules on the browning surface 112 form multiple protrusions. In a sliced ​​state, within any 100 μm length, the number of protrusions is greater than or equal to 30. This ensures that the density of the protrusions on the browning surface 112 after the browning treatment is high, thereby ensuring that the browning surface 112 forms a rough and dense morphology.

[0043] Furthermore, after the browning treatment, the multiple protrusions formed by the copper nodules on the browning surface 112 have a roughness Sku of less than or equal to 3 for at least 70% of the protrusions within any 100 μm length in a sliced ​​state. Roughness Sku is a dimensionless factor and a parameter used to determine the sharpness of the roughness shape. A roughness Sku of less than or equal to 3 indicates that the height distribution of the protrusions is relatively flat or normally distributed. This ensures that after the browning treatment, the protrusions formed by the copper nodules on the browning surface 112 have a high density and low fluctuation, ensuring that the entire browned surface has a low-profile, rough, and dense morphology, which can effectively improve the reliability of the circuits formed by subsequent electroplating.

[0044] Optionally, the roughness Rz of the roughened bonding surface 111 of the functional layer 110 is less than or equal to 2.5 μm, which ensures sufficient bonding force while presenting a lower profile, avoiding a large skin effect on the bonding side, and further improving the high-frequency and high-speed performance of the circuit.

[0045] Figure 2 A schematic diagram of the structure of another metal foil is provided for the embodiment of the present invention, see Figure 2 The metal foil further includes a carrier layer 120 ; the carrier layer 120 is arranged on the browned surface 112 of the functional layer 110 .

[0046] Specifically, the carrier layer 120 can play a supporting role, and the material of the carrier layer 120 can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0047] Optionally, the metal foil further includes: a peeling layer 130 ; the peeling layer 130 is disposed between the carrier layer 120 and the functional layer 110 .

[0048] Specifically, the release layer 130 is used to separate the functional layer 110 from the carrier layer 120 by peeling, facilitating subsequent circuit fabrication. The release layer 130 can be made of an organic release layer 130, such as a nitrogen-containing compound, a sulfur-containing compound, or a carboxylic acid, or an inorganic release layer 130, such as a metal base layer or an alloy layer. Alternatively, the release layer 130 can be made of both an inorganic layer and an organic layer, such as a mixture of a metal oxide and an organic material.

[0049] For example, an embodiment of the present invention is directed to a comparative verification of the metal foil design in the above-mentioned embodiment, wherein the browned surface 112 of the metal foil can be browned by a chemical oxidation reaction, so that the first roughness Rz1 of the browned surface 112 before the browning treatment and the second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.1; and the first interface expansion area ratio SDR1 of the browned surface 112 before the browning treatment and the second interface expansion area ratio SDR2 after the browning treatment satisfy: 1.2≤SDR2 / SDR1.

[0050] The interface extension area ratio is the ratio of the actual surface area of ​​the browned surface 112 to its projected area. The surface roughness Rz can be calculated by measuring surface data using a three-dimensional topography instrument (such as a white light interferometer). The roughness Rz can be obtained by calculating the average height difference between the vertical distances between the five highest peaks and the lowest valleys. In embodiments of the present invention, the roughness Rz can be tested according to ISO 4287.

[0051] A represents the metal foil product of the embodiment of the present invention. Four metal foil samples, A1, A2, A3, and A4, are randomly selected for comparison with comparative examples B1, B2, and B3. The parameters of each metal foil sample are as follows:

[0052] Table 1: Parameters of various metal foil samples

[0053]

[0054]

[0055] Metal foil samples A and B were used to prepare multi-layer circuit boards and laser drilled to observe whether the hole shape was qualified and to measure whether the signal transmission was qualified.

[0056] Table 2: Test results of various metal samples

[0057]

[0058] As can be seen from the table above, the embodiment of the present invention proposes limiting the roughness Rz of the browned surface 112 after the browning treatment while also limiting the interface expansion area ratio of the browned surface 112 after the browning treatment. This ensures that the browned surface 112 has a low profile after the browning treatment while maintaining a certain interface expansion area ratio. Therefore, during laser drilling, energy is more easily absorbed, thereby improving the drilling yield. In addition, after the browning treatment, the surface roughness fluctuation height does not change significantly, and the surface of the browned surface 112 is smoother, which reduces the difficulty of leveling during subsequent electroplating thickening. As a result, when producing fine circuits, the circuit surface is smoother, the thickness is more uniform, the circuit yield is high, the skin effect is small, and it is suitable for high-frequency and high-speed fine circuits, effectively improving the reliability of the circuit.

[0059] Based on the above embodiments, the embodiments of the present invention further provide a metal-clad laminate comprising the metal foil of any embodiment of the present invention, and thus having the same beneficial effects as the metal foil of any embodiment of the present invention, which will not be described in detail here.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A metal foil, characterized in that The functional layer includes a roughened bonding surface and a browned surface that are arranged opposite to each other; Wherein, the first roughness Rz1 of the browning surface before the browning treatment and the second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.1; Furthermore, a first interface expansion area ratio SDR1 of the browned surface before the browning treatment and a second interface expansion area ratio SDR2 of the browned surface after the browning treatment satisfy the following: 1.2≤SDR2 / SDR1.

2. The metal foil according to claim 1, wherein The browned surface has a first roughness Rz1≤1.8 μm and a first interface extension area ratio SDR1≤1.5 before the browning treatment; The second roughness Rz2 of the browned surface after the browning treatment is ≤1.9 μm and the second interface expansion area ratio SDR2 is ≥2.

3. The metal foil according to claim 1, wherein The first roughness Rz1 of the browning surface before the browning treatment and the second roughness Rz2 after the browning treatment satisfy: 1≤Rz2 / Rz1≤1.05; A first interface expansion area ratio SDR1 of the browned surface before the browning treatment and a second interface expansion area ratio SDR2 of the browned surface after the browning treatment satisfy the following: 1.5≤SDR2 / SDR1≤20.

4. The metal foil according to claim 1, wherein After the browning treatment, in a sliced ​​state, the height difference between the highest point and the lowest point of the outline within any length of 100 μm is ≤1.5 μm.

5. The metal foil according to claim 1, wherein After the browning treatment, the browned surface forms a plurality of protrusions. In the sliced ​​state, within any length of 100 μm, the distance between two adjacent protrusions is less than or equal to 3 μm, wherein the distance between the protrusions is the shortest straight-line distance between the contours of the two protrusions.

6. The metal foil according to claim 1, wherein After the browning treatment, the browned surface is formed with a plurality of protrusions. In a sliced ​​state, within any length of 100 μm, the number of the protrusions is greater than or equal to 30.

7. The metal foil according to claim 1, wherein After the browning treatment, the browned surface forms a plurality of protrusions. In the sliced ​​state, within any 100 μm length, the roughness Sku of at least 70% of the protrusions is less than or equal to 3, wherein the roughness Sku of the protrusion is a parameter used to judge the sharpness of the roughness shape.

8. The metal foil according to any one of claims 1 to 7, characterized in that include: carrier layer; The carrier layer is arranged on the browned surface of the functional layer.

9. The metal foil according to claim 8, characterized in that include: peeling layer; The peeling layer is arranged between the carrier layer and the functional layer.

10. A metal-clad laminate, characterized in that: The metal-clad laminate includes the metal foil according to any one of claims 1 to 9.

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