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 a horizontal slice for observing the functional layer, and the number of crystal grains per 50 square microns in the functional layer is greater than or equal to 500; and observing the thickness slice of the functional layer, wherein the number of crystal grains per 50 square microns in the functional layer is less than or equal to 300. According to the metal foil and the metal-clad laminated plate provided by the invention, the number of crystal grains per 50 square microns in the functional layer is relatively large under the condition that the horizontal slice of the functional layer is limited and observed, and the number of crystal grains per 50 square microns in the functional layer is relatively small under the condition that the thickness slice of the functional layer is observed, so that the number of crystal boundaries in the horizontal section of the functional layer is relatively large; the number of crystal boundaries in the vertical cross section is small, so that the etching speed in the thickness direction of the functional layer can be effectively increased, and the phenomenon of etching burrs is effectively avoided.

Description

Technical Field

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

[0002] Electrolytic copper foil is a key material in high-frequency and high-speed printed circuit boards for 5G communications. It plays a very important role, and ultra-thin copper foil is the current development direction and market demand hotspot of electrolytic copper foil. The current market has higher and higher requirements for ultra-thin copper foil, and the thickness of electrolytic copper foil is gradually developing towards the ultra-thin direction of less than 5μm. However, ultra-thin copper foil has low mechanical strength, and it is difficult to completely peel it off from the cathode roller during preparation. It is also prone to curling, wrinkling or tearing during transportation, which affects subsequent applications. Therefore, some manufacturers have proposed the preparation technology of ultra-thin carrier copper foil, which can solve the problems of transportation and storage due to the support of the carrier.

[0003] Strippable copper foil with carrier is widely used to laminate with substrate through hot pressing, and then the carrier layer is peeled off, and the thin copper layer is used as copper clad laminate. However, when etching circuits with thin copper layers, it is easy to have burrs on the circuits due to the slow etching speed of copper foil. When burrs are etched on the circuits, the circuit spacing may be insufficient, thereby increasing the risk of short circuits. Summary of the invention

[0004] The present invention provides a metal foil and a metal-clad laminated plate. When the metal foil is etched on a circuit board substrate to form a circuit, the etching burr phenomenon can be avoided, thereby effectively improving the reliability of the metal-clad laminated plate.

[0005] In order to solve the above technical problems, a first aspect of an embodiment of the present invention provides a metal foil, including a functional layer. When observing a horizontal slice of the functional layer, the number of grains per 50 square microns in the functional layer is greater than or equal to 500; when observing a thickness slice of the functional layer, the number of grains per 50 square microns in the functional layer is less than or equal to 300.

[0006] As a preferred solution, when observing the horizontal slice of the functional layer, the grain size is less than or equal to 0.5 μm; when observing the thickness slice of the functional layer, the grain size is greater than or equal to 0.8 μm.

[0007] As a preferred embodiment, the thickness slice of the functional layer is observed, with each 50 square microns as an observation area. In the observation area, at least 70% of the area is columnar crystals, and in the observation area, the angle between the long axis direction of the columnar crystals and the thickness direction of the functional layer is 0 to 20 degrees.

[0008] As a preferred embodiment, among all the columnar crystals in the observation area, at least 90% of the columnar crystals have major axes greater than or equal to 2 / 3 of the thickness of the functional layer.

[0009] As a preferred solution, when observing the thickness slice of the functional layer, the horizontal width of the columnar crystals gradually decreases from one side to the other side of the functional layer.

[0010] As a preferred embodiment, among all the columnar crystals in the observation area, at least 60% of the columnar crystals have a major axis direction that forms an angle of 0 degree with the thickness direction of the functional layer.

[0011] As a preferred solution, it further comprises a carrier layer, and the functional layer is arranged on one side surface of the carrier layer.

[0012] As a preferred solution, it further comprises a peeling layer, wherein the peeling layer is arranged between the carrier layer and the functional layer.

[0013] As a preferred solution, it further comprises a heat-resistant layer, wherein the heat-resistant layer is arranged on a surface of the carrier layer on a side away from the peeling layer.

[0014] A second aspect of an embodiment of the present invention provides a metal-clad laminate, wherein the metal-clad laminate comprises the metal foil as described in any one of the first aspects.

[0015] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that when observing the horizontal slice of the functional layer, the number of grains per 50 square microns in the functional layer is limited to be large, and when observing the thickness slice of the functional layer, the number of grains per 50 square microns in the functional layer is limited to be small, so that the number of grain boundaries in the horizontal cross-section of the functional layer is large, and the number of grain boundaries in the vertical cross-section is small, thereby effectively accelerating the etching speed in the thickness direction of the functional layer and effectively avoiding the occurrence of etching burrs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of a first metal foil in an embodiment of the present invention;

[0017] Figure 2 This is an electron microscope image of an observation area of ​​50 square micrometers in a horizontal slice (horizontal cross section) of the functional layer in an embodiment of the present invention;

[0018] Figure 3 This is an electron microscope image of an observation area of ​​50 square micrometers in a thickness slice (vertical cross section) of the functional layer in an embodiment of the present invention;

[0019] Figure 4 It is a physical slice diagram of the bottom erosion phenomenon in the embodiment of the present invention;

[0020] Figure 5is a physical slice diagram of an etching burr phenomenon occurring in an embodiment of the present invention;

[0021] Figure 6 This is a physical slice diagram of the metal foil after etching provided by an embodiment of the present invention;

[0022] Figure 7 is a schematic structural diagram of a second metal foil in an embodiment of the present invention;

[0023] Figure 8 is a schematic structural diagram of a third metal foil in an embodiment of the present invention;

[0024] Fig. 9 is a schematic diagram of peeling off the carrier layer in an embodiment of the present invention;

[0025] Fig.10 is a schematic structural diagram of a fourth metal foil in an embodiment of the present invention;

[0026] Among them, 1. functional layer; 2. columnar crystals; 3. first surface; 4. second surface; 5. carrier layer; 6. peeling layer; 7. heat-resistant layer. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0029] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0030] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0031] See also Figure 1 According to a first aspect of an embodiment of the present invention, a metal foil is provided, comprising a functional layer 1. When observing a horizontal slice of the functional layer 1, the number of grains per 50 square microns in the functional layer 1 is greater than or equal to 500; when observing a thickness slice of the functional layer 1, the number of grains per 50 square microns in the functional layer 1 is less than or equal to 300.

[0032] Specifically, considering that the slow etching speed in the thickness direction of the functional layer 1 is likely to cause etching burrs, in order to effectively speed up the etching speed in the thickness direction of the functional layer 1, this embodiment limits the number of grains per 50 square microns to be greater than or equal to 500 when observing the horizontal slice of the functional layer 1. For example, the number of grains per 50 square microns in the horizontal slice is 500, 527, 554, 572, 604, 651, 687, 710, 724, 768, 800, etc. This embodiment is not specifically limited here. Figure 2As shown, it is an electron microscope image of an observation area of ​​50 square microns in a horizontal slice (horizontal cross section); further, when observing the thickness slice of the functional layer 1, the number of grains per 50 square microns is limited to less than or equal to 300. For example, the number of grains per 50 square microns in the thickness slice is 45, 96, 123, 156, 178, 196, 208, 216, 234, 257, 269, 284, 300, etc. This embodiment is not specifically limited here. Figure 3 As shown, it is an electron microscope image of one of the 50 square micrometer observation areas in the thickness slice (vertical section). It can be understood that the grain boundary is the contact interface between grains with the same structure but different orientations, and the number of grain boundaries will affect the etching speed of the etching solution, because the etching speed of the grain boundary is faster than the etching speed of the grain. Therefore, by limiting the observation of the horizontal slice of the functional layer 1, the number of grains per 50 square micrometers in the functional layer 1 is large, and the number of grains per 50 square micrometers in the functional layer 1 is small when observing the thickness slice of the functional layer 1, so that the number of grain boundaries in the horizontal section of the functional layer 1 is large, and the number of grain boundaries in the vertical section is small, so that the etching speed in the thickness direction of the functional layer 1 can be effectively accelerated, and the phenomenon of etching burrs can be effectively avoided.

[0033] It is worth noting that the cross section of the functional layer 1 refers to a plane cut along a horizontal direction or a vertical direction in a sliced ​​state, and the number of grains and grain boundaries in the cross section can be obtained by observation and statistics using an electron microscope.

[0034] In this embodiment, a horizontal slice (horizontal cross section) refers to a cross section perpendicular to the thickness direction of the functional layer 1 , and a thickness slice (vertical cross section) refers to a cross section parallel to the thickness direction of the functional layer 1 .

[0035] As a preferred solution, when observing the horizontal slice of the functional layer 1 , the grain size is less than or equal to 0.5 μm; when observing the thickness slice of the functional layer 1 , the grain size is greater than or equal to 0.8 μm.

[0036] It is worth noting that in order to avoid the occurrence of etching burrs and bottom corrosion at the same time, the present embodiment further limits the particle size of the grains under different slicing states. Specifically, when observing the horizontal slice of the functional layer 1, the particle size of the grain is less than or equal to 0.5μm. For example, in the horizontal slice, the particle size of the grain may be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, etc., which is not specifically limited in the present embodiment; and when observing the thickness slice of the functional layer 1, the particle size of the grain is greater than or equal to 0.8μm. For example, in the thickness slice, the particle size of the grain may be 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, etc., which is not specifically limited in the present embodiment. By limiting the grain size of the grains under the horizontal slice to be smaller, the number of grain boundaries in the horizontal cross section can be increased to a certain extent, thereby further accelerating the etching speed in the thickness direction of the functional layer 1, and effectively avoiding the occurrence of etching burrs. At the same time, by limiting the grain size of the grains under the thickness slice to be larger, the grains in the vertical cross section tend to be long strips, which can effectively slow down the side etching rate during the etching process, avoid side etching, and reduce the number of grain boundaries in the vertical cross section to a certain extent, thereby slowing down the etching speed in the horizontal direction perpendicular to the thickness direction, and effectively avoiding the occurrence of bottom etching.

[0037] It is worth noting that the grain size refers to the straight-line distance between the two farthest points on the grain outline when observing a horizontal slice or a thickness slice.

[0038] As a preferred embodiment, the thickness slice of the functional layer 1 is observed, with each 50 square microns as an observation area. In the observation area, at least 70% of the area is columnar crystals 2, and in the observation area, the angle between the long axis direction of the columnar crystals 2 and the thickness direction of the functional layer 1 is 0 to 20 degrees.

[0039] Specifically, the prior art generally adopts mSAP (Modified Semi-Additive Process) technology to quickly etch the functional layer 1 (such as a thin copper layer) of the strippable metal foil, which can be applied to the manufacture of ultra-fine circuits. In the process of etching the circuit, the faster the etching speed of the functional layer 1, the easier it is for the circuit formed by etching to have an undercut phenomenon, and the slower the etching speed, the easier it is for the circuit formed by etching to have an etching burr phenomenon. For example, a physical slice diagram of the undercut phenomenon is shown in FIG. Figure 4 As shown in the figure, the actual slice diagram of the etching burr phenomenon is as follows Figure 5 Therefore, in this embodiment, when observing the thickness slice of the functional layer 1, every 50 square micrometers is an observation area, and in the observation area, at least 70% of the area is columnar crystals 2, as shown in FIG. Figure 3 As shown, among all the grains in the observation area of ​​every 50 square microns in the functional layer 1, the area ratio between the total area of ​​the columnar crystals 2 and the observation area can be 70%, 72%, 74%, 76%, 78%, 81%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 98%, 100%, etc., which is not specifically limited in this embodiment. In addition, in the observation area, the angle between the long axis direction of the columnar crystal 2 and the thickness direction of the functional layer 1 is 0 to 20 degrees, for example , the angle can be 0 degrees, 2 degrees, 4 degrees, 7 degrees, 9 degrees, 11 degrees, 13 degrees, 14 degrees, 16 degrees, 18 degrees, 19 degrees, 20 degrees, etc., and this embodiment does not specifically limit it, so that the functional layer 1 contains enough columnar crystals 2 that are basically vertically arranged, and the columnar crystals 2 are closely arranged and have good structural strength. While optimizing the deburring effect, the structural strength in the horizontal direction of the functional layer 1 is effectively strengthened, and the side etching rate can be effectively slowed down during circuit etching, thereby preventing the occurrence of bottom etching. Figure 6 As shown, it is a physical slice diagram of the metal foil after etching of this embodiment, which significantly improves the bottom etching phenomenon and etching burr phenomenon.

[0040] It is worth noting that the long axis of the columnar crystal 2 in this embodiment refers to the straight-line distance between the lowest point and the highest point along the growth direction of the columnar crystal 2 in the sliced ​​state. Figure 3 shown.

[0041] It is worth noting that, in this embodiment, the methods for forming the columnar crystals 2 in the functional layer 1 are mainly the following:

[0042] (1) Directional solidification technology: By controlling the temperature gradient and solidification rate during the solidification process, the metal or alloy grows in a specific direction to form a columnar crystal structure. Specific methods include the Bridgman method, zone melting method, etc.

[0043] (2) Seed crystal method: adding seed crystals with specific orientation during the solidification process to induce the crystal to grow along the direction of the seed crystal to form columnar crystals2.

[0044] (3) Heat flow control method: By controlling the direction and distribution of heat flow during solidification, the heat is mainly dissipated from one end, thereby promoting the growth of crystals in that direction and forming columnar crystals 2.

[0045] (4) Magnetic field control method: A magnetic field is applied during the solidification process, and the influence of the magnetic field on the migration and distribution of solutes in the metal or alloy is used to control the growth direction of the crystal and form columnar crystals2.

[0046] (5) Mechanical vibration method: Mechanical vibration is applied to the metal or alloy during the solidification process to promote the nucleation and growth of crystals, while controlling the growth direction of the crystals to form columnar crystals2.

[0047] As a preferred solution, among all the columnar crystals 2 in the observation area, at least 90% of the columnar crystals 2 have major axes greater than or equal to 2 / 3 of the thickness of the functional layer 1 .

[0048] Specifically, since the grain boundary is the contact interface between grains with the same structure but different orientations, and the number of grain boundaries will affect the etching speed of the etching solution, the present embodiment limits the major axis of at least 90% of the columnar crystals 2 in every 50 square micrometers of the observation area to be greater than or equal to 2 / 3 of the thickness of the functional layer 1. For example, assuming that the thickness of the functional layer 1 is 3 μm, the proportion of the columnar crystals 2 in the functional layer 1 with a major axis greater than or equal to 2 μm in all the columnar crystals 2 in every 50 square micrometers of the observation area can be 90%, 92%, 94%, 95%, 97%, 99%, 100%, etc., which is not discussed in this embodiment. Specifically defined, in addition, in these columnar crystals 2, the major axis can be 2μm, or greater than 2μm, such as 2.1μm, 2.3μm, 2.5μm, 2.6μm, 2.8μm, 2.9μm, 3μm, etc., and this embodiment will not be described in detail here, so as to ensure that the number of columnar crystals 2 with a certain height in the functional layer 1 is sufficient, which is beneficial to enhance the regularity of the overall functional layer 1 in the thickness direction, reduce the number of grain boundaries in the vertical cross section, and then when etching the circuit, it can enhance the structural strength in the horizontal direction perpendicular to the thickness direction, and further improve the improvement effect of the bottom etching phenomenon and the etching burr phenomenon.

[0049] As a preferred solution, when observing the thickness slice of the functional layer 1 , the horizontal width of the columnar crystals 2 gradually decreases from one side of the functional layer 1 to the other side.

[0050] Specifically, this embodiment limits the horizontal width of the columnar crystal 2 to gradually decrease from one side of the functional layer 1 to the other side when observing the thickness slice of the functional layer 1. It can be understood that the definition of the horizontal width is: in the sliced ​​state, a horizontal line is drawn in the thickness direction perpendicular to the functional layer 1, and the horizontal line passes through two intersections of the outline of the grain. The distance between the two intersections is the horizontal width, so that the shape of the columnar crystal 2 can be limited to a larger width near the side of the functional layer 1 and a smaller width near the other side of the functional layer 1. Since the width of the columnar crystal 2 is larger and larger as it approaches one side surface of the functional layer, the etching liquid etches toward the side surface, and the etching difficulty is greater, so when the side surface is used as the surface pressed with the circuit board substrate, the anti-bottoming effect can be effectively enhanced.

[0051] In an optional embodiment, the functional layer 1 has a first surface 3 and a second surface 4 arranged back to the first surface 3, wherein the first surface 3 is used for pressing with the circuit board substrate, and the second surface 4 is used for forming a circuit after etching. In order to further enhance the effect of preventing bottom corrosion, this embodiment stipulates that when observing the thickness slice of the functional layer 1, along the thickness direction of the functional layer 1, the horizontal width of the columnar crystal 2 gradually decreases from one side of the first surface 3 to one side of the second surface 4. Since the closer to the first surface 3, the larger the width of the columnar crystal 2, the more the etching liquid etches toward the first surface 3, the greater the etching difficulty, thereby effectively enhancing the effect of preventing bottom corrosion.

[0052] As a preferred embodiment, among all the columnar crystals 2 in the observation area, at least 60% of the columnar crystals 2 have a major axis direction that forms an angle of 0 degree with the thickness direction of the functional layer 1 .

[0053] Specifically, in order to further enhance the effect of preventing bottom erosion while solving the problem of etching burrs, the present embodiment further defines that among all columnar crystals 2 in the observation area of ​​every 50 square microns, at least 60% of the columnar crystals 2 have an angle of 0 degrees between the long axis direction and the thickness direction of the functional layer 1. For example, among all columnar crystals 2, the columnar crystals 2 with an angle of 0 degrees between the long axis direction and the thickness direction of the functional layer 1 account for 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 81%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 97%, 99%, 100%, etc., and the present embodiment does not make specific limitations here. Through this definition, it can be ensured that most of the columnar crystals 2 are vertical, while optimizing the deburring effect, the structural strength in the horizontal direction of the functional layer 1 can be further enhanced, and the side erosion rate can be further slowed down during line etching, thereby preventing the occurrence of bottom erosion.

[0054] See also Figure 7 As a preferred solution, it also includes a carrier layer 5, and the functional layer 1 is arranged on one side surface of the carrier layer 5.

[0055] Specifically, in actual application, the carrier layer 5 is stacked with other material layers in the metal foil such as the functional layer 1 to support and protect the functional layer 1 so that the functional layer 1 is not damaged by external contact or collision. After the functional layer 1 is pressed onto the circuit board substrate at high temperature, the carrier layer 5 needs to be peeled off.

[0056] As one optional embodiment, the material of the carrier layer 5 in this embodiment can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. For example, in the peelable copper foil, the material of the carrier layer 5 is copper. The material of the functional layer 1 can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. For example, in the peelable copper foil, the material of the functional layer 1 is copper.

[0057] See also Figure 8 As a preferred solution, it also includes a peeling layer 6, which is arranged between the carrier layer 5 and the functional layer 1.

[0058] Specifically, the role of the peeling layer 6 is to separate the carrier layer 5 from the functional layer 1 by peeling; at the same time, due to the existence of the peeling layer 6, the metal migration between the functional layer 1 and the carrier layer 5 can be blocked, and the peeling layer 6 can cover or fill the uneven surface of the carrier layer 5, so that the functional layer 1 formed on the other surface of the peeling layer 6 is more flat, uniform and dense, which is conducive to reducing the occurrence of pinholes in the subsequent processing of the functional layer 1, ensuring the use quality of the functional layer 1, and further facilitating the subsequent production of circuits. In the specific implementation process, when the carrier layer 5 is removed by peeling, the peeling method is, for example: manually peeling it off and removing it directly, or peeling it off with the help of mechanical equipment.

[0059] Before the metal foil product is manufactured and applied, the carrier layer 5, the peeling layer 6, and the functional layer 1 are stacked. As the product is applied, the functional layer 1 of the metal foil is pressed onto the application carrier such as the circuit board substrate. After the pressing process is completed, the metal foil as a whole is bonded to the application carrier through the bonding force between the roughened surface of the functional layer 1 and the application carrier. Before the metal foil is further processed and the circuit is etched, the carrier layer 5 is peeled off through the peeling layer 6. Fig. 9 As shown, it is a schematic diagram of the peeling of the carrier layer 5, and subsequently a circuit is formed on the circuit board substrate by copper plating, masking, etching and other means.

[0060] The processing method of the strippable metal foil is: first, a carrier layer 5 is formed by electrochemical deposition, vacuum sputtering + electroplating, vacuum sputtering, etc.; then a stripping layer 6 is formed on one side surface of the carrier layer 5, and the formation method can also be electroplating, vacuum sputtering, etc.; then a functional layer 1 is processed on the stripping layer 6, and the formation method can be vacuum sputtering, electroplating, etc.

[0061] The peeling layer 6 in this embodiment is processed on the carrier layer 5 by physical vapor deposition, for example, by magnetron sputtering. The material of the peeling layer 6 can be an organic peeling layer, such as a nitrogen-containing compound, a sulfur-containing compound, and a carboxylic acid, or an inorganic peeling layer, including a metal base layer or an alloy layer, or an inorganic layer and an organic layer can be stacked as the peeling layer 6, for example, a mixture of a metal oxide and an organic substance, which is not specifically limited in this embodiment.

[0062] See also Fig.10 As a preferred embodiment, it further includes a heat-resistant layer 7 , and the heat-resistant layer 7 is disposed on a surface of the carrier layer 5 away from the peeling layer 6 .

[0063] Specifically, during the high-temperature pressing process of the functional layer 1 and the circuit board substrate, the carrier layer 5 may contact with the high-temperature pressing plate of the press and cause melting or deformation, making it difficult to peel the carrier layer 5 and the functional layer 1, affecting the peeling stability between the two. In addition, during the high-temperature pressing process, the peeling layer 6 will also be affected by the high temperature and cause melting or deformation, making it easy for the carrier layer 5 and the functional layer 1 to diffuse with each other at high temperature to cause adhesion, making it difficult to peel the carrier layer 5 and the functional layer 1, affecting the peeling stability between the two. Therefore, this embodiment provides a heat-resistant layer 7 on the side surface of the carrier layer 5 away from the peeling layer 6, which can play a heat-insulating role during the high-temperature pressing process, reduce the heating temperature of the carrier layer 5 and the peeling layer 6, ensure the thermal stability of the carrier layer 5 and the peeling layer 6, and ensure that after the functional layer 1 is pressed on the circuit board substrate, the carrier layer 5 can be smoothly peeled from the functional layer 1.

[0064] As one of the optional embodiments, the material of the heat-resistant layer 7 in this embodiment can be tetrafluoroethylene film, polyimide film, heat-resistant adhesive, etc. The above materials all have certain heat resistance and can effectively protect the metal foil from heat damage during the lamination process.

[0065] A second aspect of the embodiments of the present invention provides a metal-clad laminate, wherein the metal-clad laminate comprises the metal foil as described in any embodiment of the first aspect.

[0066] The metal foil and metal-clad laminate provided by the embodiments of the present invention have the following beneficial effects:

[0067] (1) When observing the horizontal slice of the functional layer 1, the number of grains per 50 square microns in the functional layer 1 is limited to be large, while when observing the thickness slice of the functional layer 1, the number of grains per 50 square microns in the functional layer 1 is limited to be small. As a result, the number of grain boundaries in the horizontal cross section of the functional layer 1 is large, while the number of grain boundaries in the vertical cross section is small, thereby effectively accelerating the etching speed in the thickness direction of the functional layer 1 and effectively avoiding the occurrence of etching burrs.

[0068] (2) By limiting the grain size of the grains under horizontal slicing to be smaller, the number of grain boundaries in the horizontal cross section can be increased to a certain extent, thereby further accelerating the etching speed in the thickness direction of the functional layer 1, and effectively avoiding the occurrence of etching burrs. At the same time, by limiting the grain size of the grains under thickness slicing to be larger, the grains in the vertical cross section tend to be long strips, which can effectively slow down the side etching rate during the etching process and avoid side etching, and can reduce the number of grain boundaries in the vertical cross section to a certain extent, thereby slowing down the etching speed in the horizontal direction perpendicular to the thickness direction, and effectively avoiding the occurrence of bottom etching.

[0069] (3) By limiting the thickness slice of the functional layer 1 to be observed, with each 50 square microns as an observation area, in the observation area, at least 70% of the area is columnar crystals 2, and in the observation area, the angle between the long axis direction of the columnar crystals 2 and the thickness direction of the functional layer 1 is 0 to 20 degrees, so that the functional layer 1 contains a sufficient number of columnar crystals 2 that are basically vertically arranged, and the columnar crystals 2 are closely arranged and have good structural strength. While optimizing the deburring effect, the structural strength of the functional layer 1 in the horizontal direction is effectively enhanced, and the side etching rate can be effectively slowed down during circuit etching, thereby preventing the occurrence of bottom etching.

[0070] (4) By limiting the observation of the thickness slice of the functional layer 1, the horizontal width of the columnar crystal 2 gradually decreases from one side of the functional layer 1 to the other side. Since the width of the columnar crystal 2 becomes larger as it approaches one side surface of the functional layer, the etching liquid etches toward the side surface, and the etching difficulty becomes greater. Therefore, when the side surface is used as the surface for pressing with the circuit board substrate, the anti-bottom etching effect can be effectively enhanced.

[0071] In order to demonstrate the beneficial effects of the metal foil and metal-clad laminate provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0072] Example 1

[0073] A metal foil comprises a carrier layer, a peeling layer and a functional layer. When observing a horizontal slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area in the functional layer is greater than or equal to 525, and the maximum grain size of the crystal grains is 0.48 μm. When observing a thickness slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area is less than or equal to 231, and the minimum grain size of the crystal grains is 0.88 μm. In addition, in the observation area, 75% of the area is columnar crystals, and the angle between the long axis direction of the columnar crystals and the thickness direction of the functional layer is at most 4 degrees, wherein, among all the columnar crystals in the observation area, the long axis of 90% of the columnar crystals is 2 / 3 of the thickness of the functional layer.

[0074] Example 2

[0075] A metal foil includes a carrier layer, a peeling layer and a functional layer. When observing the horizontal slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area in the functional layer is greater than or equal to 628, and the maximum grain size of the crystal grain is 0.38 μm; when observing the thickness slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area is less than or equal to 189, and the minimum grain size of the crystal grain is 0.94 μm, and in the observation area, 80% of the area is columnar crystals, and the angle between the long axis direction of the columnar crystal and the thickness direction of the functional layer is at most 8 degrees, wherein, among all the columnar crystals in the observation area, the long axis of 92% of the columnar crystals is 2 / 3 of the thickness of the functional layer. In addition, when observing the thickness slice of the functional layer, the horizontal width of the columnar crystal gradually decreases from one side of the first surface to one side of the second surface, wherein the first surface is used for pressing with the circuit board substrate, and the second surface is used for forming a circuit after etching.

[0076] Example 3

[0077] A metal foil comprises a carrier layer, a peeling layer and a functional layer. When observing the horizontal slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area in the functional layer is greater than or equal to 668, and the maximum grain size of the crystal grain is 0.34 μm; when observing the thickness slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area is less than or equal to 124, and the minimum grain size of the crystal grain is 1.08 μm, and in the observation area, 85% of the area is columnar crystals, and the angle between the long axis direction of the columnar crystal and the thickness direction of the functional layer is at most 10 degrees, wherein, among all the columnar crystals in the observation area, the long axis of 94% of the columnar crystals is 2 / 3 of the thickness of the functional layer, and the angle between the long axis direction of 74% of the columnar crystals and the thickness direction of the functional layer is 0 degrees. In addition, when observing the thickness slice of the functional layer, the horizontal width of the columnar crystal gradually decreases from one side of the first surface to one side of the second surface, wherein the first surface is used for pressing with the circuit board substrate, and the second surface is used for forming a circuit after etching.

[0078] Example 4

[0079] A metal foil comprises a heat-resistant layer, a carrier layer, a peeling layer and a functional layer. When observing the horizontal slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area of ​​the functional layer is greater than or equal to 710, and the maximum grain size of the crystal grain is 0.28 μm; when observing the thickness slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area is less than or equal to 88, and the minimum grain size of the crystal grain is 1.58 μm, and in the observation area, 90% of the area is columnar crystals, and the angle between the long axis direction of the columnar crystal and the thickness direction of the functional layer is at most 12 degrees, wherein, among all the columnar crystals in the observation area, the long axis of 95% of the columnar crystals is 2 / 3 of the thickness of the functional layer, and the angle between the long axis direction of 86% of the columnar crystals and the thickness direction of the functional layer is 0 degrees. In addition, when observing the thickness slice of the functional layer, the horizontal width of the columnar crystal gradually decreases from one side of the first surface to one side of the second surface, wherein the first surface is used for pressing with the circuit board substrate, and the second surface is used for forming a circuit after etching.

[0080] Comparative Example 1

[0081] A metal foil comprises a carrier layer, a peeling layer and a functional layer. When observing a horizontal slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area of ​​the functional layer is less than or equal to 320; when observing a thickness slice of the functional layer, the number of crystal grains in any 50 square micrometer observation area of ​​the functional layer is greater than or equal to 567.

[0082] The metal foils in the above-mentioned embodiments and comparative examples were pressed at high temperature on a circuit board substrate to perform circuit etching, and whether bottom etching or etching burrs occurred after circuit etching was observed. The test results are shown in Table 1 below.

[0083] Table 1 Circuit etching situation

[0084]

[0085]

[0086] It can be seen from Table 1 that in the functional layer of the metal foil in Examples 1 to 4, when observing the horizontal slice of the functional layer, the number of grains per 50 square microns is large and the grain size of the grains is small, while when observing the thickness slice of the functional layer, the number of grains per 50 square microns is small and the grain size of the grains is large, so that the number of grain boundaries in the horizontal section of the functional layer is large, while the number of grain boundaries in the vertical section is small, and the grains tend to be long strips, thereby effectively accelerating the etching speed in the thickness direction of the functional layer, effectively avoiding the occurrence of etching burrs, and effectively slowing down the side etching rate during the etching process to avoid the occurrence of bottom etching. In addition, in Examples 1 to 4, a sufficient number of columnar crystals are formed in the functional layer of the metal foil, the angle between the long axis direction of the columnar crystals and the thickness direction of the functional layer is small, and the horizontal width of the columnar crystals gradually decreases from one side of the functional layer to the other side, thereby optimizing the deburring effect while effectively enhancing the structural strength in the horizontal direction of the functional layer, effectively slowing down the side etching rate during circuit etching, and making the etching difficulty greater as the etching solution etches toward the side with a larger horizontal width of the columnar crystal, thereby preventing the occurrence of bottom etching.

[0087] In the functional layer of the metal foil in Comparative Example 1, when observing the horizontal slice of the functional layer, the number of grains per 50 square microns is too small, while when observing the thickness slice of the functional layer, the number of grains per 50 square microns is too large, resulting in a small number of grain boundaries in the horizontal section and a large number of grain boundaries in the vertical section, which in turn causes the etching speed in the thickness direction to be too slow during the etching process, and the phenomenon of etching burrs is easily generated.

[0088] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A metal foil, characterized in that: Including a functional layer, when observing a horizontal slice of the functional layer, the number of grains per 50 square microns in the functional layer is greater than or equal to 500; when observing a thickness slice of the functional layer, the number of grains per 50 square microns in the functional layer is less than or equal to 300.

2. The metal foil according to claim 1, characterized in that When observing the horizontal slice of the functional layer, the grain size is less than or equal to 0.5 μm; when observing the thickness slice of the functional layer, the grain size is greater than or equal to 0.8 μm.

3. The metal foil according to claim 1, wherein Observe the thickness slice of the functional layer, with each 50 square microns as an observation area. In the observation area, at least 70% of the area is columnar crystals, and in the observation area, the angle between the long axis direction of the columnar crystals and the thickness direction of the functional layer is 0 to 20 degrees.

4. The metal foil according to claim 3, characterized in that Among all the columnar crystals in the observation area, at least 90% of the columnar crystals have major axes greater than or equal to 2 / 3 of the thickness of the functional layer.

5. The metal foil according to claim 3, characterized in that Observing the thickness slice of the functional layer, the horizontal width of the columnar crystals gradually decreases from one side to the other side of the functional layer.

6. The metal foil according to claim 3, characterized in that Among all the columnar crystals in the observation area, at least 60% of the columnar crystals have a major axis direction that forms an angle of 0 degree with the thickness direction of the functional layer.

7. The metal foil according to any one of claims 1 to 6, characterized in that It also includes a carrier layer, and the functional layer is arranged on one side surface of the carrier layer.

8. The metal foil according to claim 7, characterized in that The invention also comprises a peeling layer, wherein the peeling layer is arranged between the carrier layer and the functional layer.

9. The metal foil according to claim 8, characterized in that It also includes a heat-resistant layer, which is arranged on a surface of the carrier layer on one side away from the peeling 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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