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, the functional layer contains columnar crystals growing along the thickness direction, the thickness of the functional layer is observed and sliced, in every 50 square micrometers, the length of the long axis of at least 40% of the columnar crystals is larger than 3 / 4 of the thickness of the functional layer, and the length of the long axis of the columnar crystals is larger than 3 / 4 of the thickness of the functional layer. And the number of the columnar crystals surrounding the columnar crystals with the long axis length of more than 1 [mu] m is not more than 6. The lateral etching speed can be effectively reduced in the etching process by forming enough columnar crystals growing in the thickness direction in the functional layer, in addition, the number of crystal boundaries in a vertical section can be effectively reduced by optimizing the long axis length of the columnar crystals and the number of the columnar crystals surrounding the periphery of any columnar crystal with the long axis length larger than 1 micrometer, and therefore the etching efficiency is improved. According to the etching solution, the etching speed in the horizontal direction is low during circuit etching, the bottom etching phenomenon is avoided, meanwhile, the etching speed of the etching solution in the thickness direction is relatively high, and the etching burr phenomenon can be avoided.

Description

Technical Field

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

[0002] Ultra-thin copper foil is the development direction of electrolytic copper foil and a hot spot in the market demand. As a key material in high-frequency and high-speed printed circuit boards for 5G communication, the current market has higher and higher requirements for ultra-thin copper foil. The thickness of electrolytic copper foil is gradually developing towards the ultra-thin direction of less than 5 μm. However, for ultra-thin copper foil, its mechanical strength is relatively low. It is very difficult to achieve complete peeling from the cathode roller during preparation, and it is prone to phenomena such as curling, wrinkling or tearing during transportation, thus affecting subsequent applications. Therefore, some manufacturers have proposed the preparation technology of ultra-thin carrier copper foil. With the support of the carrier, the problems of transportation and storage can be solved.

[0003] The peelable copper foil with a carrier is usually laminated with a circuit board substrate by hot pressing, and then the carrier layer is peeled off, and the thin copper layer is used as a copper-clad laminate. However, when etching the circuit using the thin copper layer at present, it is easy to have the phenomenon that the etching speed of the copper foil is too fast, resulting in undercutting of the circuit. When the undercutting of the circuit is too large, the bonding area between the circuit and the substrate layer decreases, resulting in a decrease in the bonding force between the circuit and the substrate layer, and the reliability of the circuit board is reduced. Summary of the Invention

[0004] The present invention provides a metal foil and a metal-clad laminate, which can avoid the occurrence of undercutting phenomenon when the metal foil is etched to form a circuit on a circuit board substrate, thereby effectively improving the reliability of the metal-clad laminate.

[0005] In order to solve the above technical problems, in the first aspect of the embodiments of the present invention, a metal foil is provided, which includes a functional layer. The functional layer contains columnar crystals growing along the thickness direction. When observing the thickness slice of the functional layer, in every 50 square micrometers, at least 40% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is no more than 6.

[0006] As a preferred solution, when observing the thickness slice of the functional layer, in every 50 square micrometers, at least 70% of the columnar crystals have a major axis length that is 3 to 10 times their minor axis length.

[0007] As a preferred solution, when observing the thickness slice of the functional layer, in the observation area of every 50 square micrometers, the area ratio between the total area of the columnar crystals with a major axis length that is 3 to 5 times their minor axis length and the observation area is less than or equal to 30%, and the area ratio between the total area of the columnar crystals with a major axis length that is 5 to 10 times their minor axis length and the observation area is greater than or equal to 40%.

[0008] As a preferred embodiment, observe the thickness slice of the functional layer. In every 50 square micrometers, at least 50% of the area in the crystal structure of the functional layer is composed of the columnar crystals.

[0009] As a preferred embodiment, the short axis length of the columnar crystals is 0.1 μm to 2 μm.

[0010] As a preferred embodiment, the range between the maximum horizontal cross-sectional width and the minimum horizontal cross-sectional width of the columnar crystals is less than or equal to 0.3 μm.

[0011] As a preferred embodiment, it further includes a carrier layer, and the functional layer is disposed on one side surface of the carrier layer.

[0012] As a preferred embodiment, it further includes a release layer, and the release layer is disposed between the carrier layer and the functional layer.

[0013] As a preferred embodiment, it further includes a heat-resistant layer, and the heat-resistant layer is disposed on one side surface of the carrier layer away from the release layer.

[0014] The second aspect of the embodiments of the present invention provides a metal-coated laminate, and the metal-coated laminate includes the metal foil as described in any one of the first aspect.

[0015] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows: By forming a sufficient number of columnar crystals growing along the thickness direction in the crystal structure of the functional layer, the side etching rate can be effectively slowed down during the etching process. In addition, observing the thickness slice of the functional layer, by defining that in every 50 square micrometers, the long axis length of at least 40% of the columnar crystals is greater than 3 / 4 of the thickness of the functional layer, and the number of columnar crystals surrounding any columnar crystal with a long axis length exceeding 1 μm is no more than 6, the number of grain boundaries in the vertical cross-section can be effectively reduced. When etching to form a circuit, the etching rate in the horizontal direction perpendicular to the thickness direction of the functional layer is slower, avoiding the occurrence of undercutting. At the same time, the etching liquid relatively has a faster etching rate in the thickness direction of the functional layer, and the phenomenon of etching burrs can be avoided at the same time. The embodiments of the present invention effectively improve the reliability of the metal-coated laminate. Description of the Drawings

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

[0017] Figure 2 is a physical slice diagram of the occurrence of undercutting in the embodiments of the present invention;

[0018] Figure 3 is a physical slice diagram of the occurrence of etching burrs in the embodiments of the present invention;

[0019] Figure 4 It is a physical slice diagram after the metal foil is etched provided by an embodiment of the present invention;

[0020] Figure 5 It is a schematic diagram of the major axis length and minor axis length of columnar crystals in an embodiment of the present invention;

[0021] Figure 6 It is a schematic diagram of the horizontal cross-section of the functional layer in an embodiment of the present invention;

[0022] Figure 7 It is a schematic diagram of the thickness slice (vertical cross-section) of the functional layer in an embodiment of the present invention;

[0023] Figure 8 It is a schematic diagram of the structure of the second metal foil in an embodiment of the present invention;

[0024] Figure 9 It is a schematic diagram of the structure of the third metal foil in an embodiment of the present invention;

[0025] Figure 10 It is a schematic diagram of the peeling of the carrier layer in an embodiment of the present invention;

[0026] Figure 11 It is a schematic diagram of the structure of the fourth metal foil in an embodiment of the present invention;

[0027] Among them, 1. Functional layer; 2. Columnar crystal; 3. Carrier layer; 4. Peeling layer; 5. Heat-resistant layer. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The purpose of providing these embodiments is to make the disclosure content of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0029] In the description of the present application, the terms "first", "second", "third", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0030] In the description of this application, it should be noted that unless otherwise clearly defined 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. The terms "vertical", "horizontal", "left", "right", "up", "down" and similar expressions used herein are only for the purpose of illustration, rather than indicating or implying that the device or component 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 of the 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.

[0031] In the description of this application, it should be noted that unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the specification of this invention are only for the purpose of describing specific embodiments and are not intended to limit this invention. 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.

[0032] Please refer to Figure 1 , the first aspect of the embodiment of the present invention provides a metal foil, including a functional layer 1, and the functional layer 1 contains columnar crystals 2 growing along the thickness direction. Observe the thickness slice of the functional layer 1. In every 50 square micrometers, at least 40% of the long axis lengths of the columnar crystals 2 are greater than 3 / 4 of the thickness of the functional layer 1, and the number of columnar crystals 2 surrounding any columnar crystal 2 with a long axis length exceeding 1 μm is no more than 6.

[0033] Specifically, the prior art usually adopts the mSAP (Modified Semi-Additive Process) process to quickly etch the functional layer (such as a thin copper layer) of the peelable metal foil, which can be applied to the manufacture of ultra-fine circuits. During the process of etching the circuit, the faster the etching speed of the functional layer, the easier it is for the etched circuit to have the phenomenon of undercutting. The slower the etching speed, the easier it is for the etched circuit to have the phenomenon of etching burrs. Exemplarily, the physical slice diagram of the undercutting phenomenon is as Figure 2 shown, and the physical slice diagram of the etching burr phenomenon is as Figure 3As shown. Therefore, in this embodiment, columnar crystals 2 growing along the thickness direction are first formed in the crystal structure of the functional layer 1. It can be understood that since the columnar crystals 2 are generated along the thickness direction of the functional layer 1, the included angle between the long axes of these columnar crystals 2 and the thickness direction of the functional layer 1 is small, and the structural strength of the columnar crystals 2 is good. Therefore, during the circuit etching process, the lateral etching rate of the etching solution in the functional layer 1 can be effectively reduced, and the phenomenon of bottom etching can be avoided. Preferably, in order to better reduce the included angle between the long axis of the columnar crystal 2 and the thickness direction of the functional layer 1, the columnar crystal 2 in this embodiment grows vertically along the thickness direction of the functional layer 1.

[0034] In addition, observing the thickness slice of the functional layer 1, this embodiment also stipulates that in every 50 square micrometers, at least 40% of the long axis lengths of the columnar crystals 2 are greater than 3 / 4 of the thickness of the functional layer 1. For example, the proportion of the columnar crystals 2 with long axis lengths greater than 3 / 4 of the thickness of the functional layer 1 in all the columnar crystals 2 in any 50-square-micrometer observation area can be 40%, 42%, 45%, 47%, 49%, 51%, 53%, 55%, 57%, 59%, 61%, 63%, 65%, 67%, 69%, 70%, 72%, 75%, 77%, 79%, 81%, 83%, 86%, 88%, 90%, 92%, 94%, 95%, 97%, 99%, 100%, etc. This embodiment does not make specific limitations here. At the same time, in these columnar crystals 2, this embodiment also does not make specific limitations on the long axis length of each columnar crystal 2. For example, assuming the thickness of the functional layer 1 is 2 μm, it is only necessary to ensure that the long axis length of each columnar crystal 2 is greater than 1.5 μm. For example, the long axis length of some columnar crystals 2 is 1.6 μm, the long axis length of some columnar crystals 2 is 1.67 μm, the long axis length of some columnar crystals 2 is 1.75 μm, etc. This embodiment will not elaborate too much here. In this way, it can be ensured that there are enough columnar crystals 2 with a certain length in the functional layer 1, so as to effectively reduce the number of grain boundaries in the vertical cross-section of the functional layer 1. Since the etching rate of the grain boundaries is faster than that of the grains, by reducing the number of grain boundaries in the vertical cross-section of the functional layer 1, the number of grain boundaries in the horizontal cross-section is more than that in the vertical cross-section. Considering that during the circuit etching process, the etching solution starts etching from one side surface of the functional layer 1, this embodiment can ensure that during circuit etching, the etching rate of the etching solution downward from one side surface of the functional layer 1 is faster, while the etching rate in the horizontal direction perpendicular to the thickness direction is slower. Furthermore, while effectively avoiding the occurrence of bottom etching, the phenomenon of etching burrs is also avoided, improving the reliability of the metal-clad laminate.

[0035] Furthermore, in this embodiment, it is also specified that the number of columnar crystals 2 surrounding any columnar crystal 2 with a major axis length exceeding 1 μm is no more than 6. As a result, the number of grain boundaries around any columnar crystal 2 with a major axis length exceeding 1 μm is relatively small, which can further reduce the number of grain boundaries in the functional layer 1 in the vertical cross-section, making the number of grain boundaries in the horizontal cross-section much larger than that in the vertical cross-section. Thus, the lateral etching rate of the etching solution in the functional layer 1 is further slowed down, better avoiding the occurrence of undercutting. Moreover, the etching solution relatively has a faster etching rate in the thickness direction of the functional layer 1, thereby being able to avoid the occurrence of etching burrs at the same time, further improving the reliability of the metal-clad laminate. The columnar crystals surrounding here refer to the number of columnar crystals closest to the target columnar crystal in one circle. As Figure 4 shown, it is a physical slice diagram of the metal foil after etching in this embodiment, significantly improving the undercutting phenomenon and the etching burr phenomenon.

[0036] It should be noted that in this embodiment, the major axis length of the columnar crystal 2 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, while the minor axis length refers to the straight-line distance between two points where a perpendicular line is made at the 1 / 2 position of the major axis and intersects the two side contours of the columnar crystal 2 in the sliced state. As Figure 5 shown.

[0037] In this embodiment, the cross-section of the functional layer 1 refers to the plane cut along the horizontal direction or the vertical direction (thickness direction) in the sliced state, and the number of grain boundaries in the cross-section can be obtained through electron microscope observation and statistics. Based on the statistical results, the number of grain boundaries in different cross-sections can be compared.

[0038] In this embodiment, the horizontal cross-section refers to the cross-section perpendicular to the thickness direction of the functional layer 1. As Figure 6 shown, it is a schematic diagram of the horizontal cross-section of the functional layer 1; the thickness slice refers to the cross-section parallel to the thickness direction of the functional layer 1. As Figure 7 shown, it is a schematic diagram of the thickness slice (vertical cross-section) of the functional layer 1.

[0039] It should be noted that in this embodiment, the formation methods of the columnar crystals 2 in the functional layer 1 mainly include the following several types:

[0040] (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, thereby forming a columnar crystal 2 structure. Specific methods include the Bridgman method, the zone melting method, etc.

[0041] (2) Seed crystal method: Adding a seed crystal with a specific orientation during the solidification process to induce the crystal to grow along the direction of the seed crystal, forming a columnar crystal 2.

[0042] (3) Heat flow control method: By controlling the direction and distribution of heat flow during solidification, heat is mainly dissipated from one end, thereby promoting the growth of crystals in this direction to form columnar crystals 2.

[0043] (4) Magnetic field control method: Apply a magnetic field during solidification, and utilize the influence of the magnetic field on the migration and distribution of solutes in metals or alloys to control the crystal growth direction and form columnar crystals 2.

[0044] (5) Mechanical vibration method: Apply mechanical vibration to metals or alloys during solidification to promote crystal nucleation and growth, and at the same time control the crystal growth direction to form columnar crystals 2.

[0045] The columnar crystals 2 in the embodiments of the present invention can be formed by the above-mentioned methods, but are not limited to the above-mentioned methods, and can also be other methods, etc., which are not listed here.

[0046] As a preferred solution, observe the thickness section of the functional layer 1. In every 50 square micrometers, the long axis length of at least 70% of the columnar crystals 2 is 3 to 10 times its short axis length.

[0047] Specifically, in this embodiment, the ratio of the major axis length to the minor axis length of the columnar crystal 2 is further limited. For example, the major axis length of the columnar crystal 2 can be 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, etc. of its minor axis length. This embodiment does not make specific limitations here. In addition, among all the columnar crystals 2 in any observation area of 50 square micrometers, the columnar crystals 2 whose major axis length satisfies the above ratio relationship account for at least 70%, such as 70%, 72%, 75%, 77%, 79%, 81%, 83%, 86%, 88%, 90%, 92%, 94%, 95%, 97%, 99%, 100%, etc. This embodiment does not make specific limitations here. It can be understood that if the ratio between the major axis length and the minor axis length of the columnar crystal 2 is too low, that is, less than 3 times, most of the columnar crystals 2 in the thickness direction of the functional layer 1 are thick and short, which means that the number of grain boundaries in the horizontal cross-section is not much different from the number of grain boundaries in the vertical cross-section, resulting in too slow etching speed in the thickness direction, so that the residual etching burrs cannot be effectively reduced; if the ratio between the major axis length and the minor axis length of the columnar crystal 2 is too high, that is, greater than 10 times, although most of the columnar crystals 2 in the thickness direction of the functional layer 1 are slender, this also means that there are too many grain boundaries in the horizontal cross-section. At this time, due to the disordered atomic arrangement at the grain boundaries, the scattering of electrons and phonons increases, and too many grain boundaries will lead to a decrease in the electrical conductivity and thermal conductivity of the functional layer 1, thus affecting the reliability of the circuit etched from the functional layer 1. At the same time, too many grain boundaries in the horizontal cross-section will cause the etching speed of the etching solution from one side surface of the functional layer 1 downward to be too fast, and it is easy to occur the situation of over-etching. Therefore, in this embodiment, by limiting that when observing the thickness slice of the functional layer 1, in each 50 square micrometers, at least 70% of the columnar crystals 2 have a major axis length that is 3 to 10 times of its minor axis length, it is ensured that there are enough columnar crystals 2 with sufficient height in the thickness direction of the functional layer 1, which can effectively slow down the side etching speed of the etching solution in the functional layer 1, and at the same time avoid the etching speed of the etching solution from one side surface of the functional layer 1 downward being too slow, avoiding the phenomena of bottom etching and etching burrs, thereby effectively improving the reliability of the metal-clad laminate.

[0048] As a preferred solution, when observing the thickness slice of the functional layer 1, in each observation area of 50 square micrometers, the area ratio between the total area of the columnar crystals 2 whose major axis length is 3 to 5 times of the minor axis length and the observation area is less than or equal to 30%, and the area ratio between the total area of the columnar crystals 2 whose major axis length is 5 to 10 times of the minor axis length and the observation area is greater than or equal to 40%.

[0049] Specifically, in this embodiment, when observing the thickness slice of the functional layer 1, the total area of the columnar crystals 2 with different ratios of the major axis length to the minor axis length in each observation area of 50 square micrometers is further defined. Exemplarily, in any observation area of 50 square micrometers, the area ratio between the total area of the columnar crystals 2 with the major axis length being 3 to 5 times the minor axis length and the observation area can be 0%, 2%, 4%, 6%, 8%, 10%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, 25%, 27%, 29%, 30%, etc., and the area ratio between the total area of the columnar crystals 2 with the major axis length being 5 to 10 times the minor axis length and the observation area can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 57%, 59%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 81%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 97%, 99%, 100%, etc. This embodiment does not make specific limitations here. Through the above limitations, it can be further ensured that there are enough slender columnar crystals formed in the functional layer 1, which is beneficial to reducing the number of grain boundaries in the vertical section. Furthermore, during the circuit etching, the etching rate of the functional layer 1 in the thickness direction can be neither too slow nor too fast, and the structural strength of the functional layer 1 in the horizontal direction perpendicular to the thickness direction can be enhanced, avoiding too fast side etching rate, and further improving the improvement effect of the bottom etching phenomenon and the etching burr phenomenon.

[0050] As a preferred solution, when observing the thickness slice of the functional layer 1, in each 50 square micrometers, at least 50% of the area in the crystal structure of the functional layer 1 is the columnar crystal 2.

[0051] Specifically, in this embodiment, by defining that when observing the thickness slice of the functional layer 1, at least 50% of the area in the crystal structure of each 50 square micrometers is the columnar crystal 2. For example, in any observation area of 50 square micrometers, the area ratio between the total area occupied by the columnar crystal 2 and the observation area can be 50%, 51%, 53%, 55%, 57%, 59%, 61%, 63%, 65%, 67%, 69%, 70%, 72%, 74%, 76%, 78%, 81%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 98%, 100%, etc. This embodiment does not make specific limitations here, so as to further ensure that enough columnar crystals 2 are formed in the crystal structure of the functional layer 1 along the thickness direction. The columnar crystals 2 are closely arranged and have good structural strength, and can effectively slow down the side etching rate during the circuit etching.

[0052] As a preferred solution, the minor axis length of the columnar crystal 2 is 0.1 μm to 2 μm.

[0053] Specifically, in this embodiment, the minor axis length of the columnar crystal 2 is further limited to 0.1 μm to 2 μm. For example, the minor axis length of the columnar crystal 2 can be 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.4 μm, 1.6 μm, 1.8 μm, 1.9 μm, 2 μm, etc. This embodiment does not make specific limitations here. It can ensure that the minor axis of the columnar crystal 2 is neither too long nor too short, so that while the number of grain boundaries in the horizontal cross-section is not excessive, the number of grain boundaries in the vertical cross-section is effectively reduced, ensuring the reliability of the circuit etched in the functional layer 1, and at the same time avoiding the occurrence of undercutting and etching burr phenomena. In addition, when the major axis length of the columnar crystal 2 is 3 to 10 times its minor axis length, by limiting the minor axis length to 0.1 μm to 2 μm, it can ensure that the major axis length of the columnar crystal 2 is appropriate, avoiding the situation where the number of grain boundaries in the horizontal cross-section is not much different from that in the vertical cross-section due to its being too short, resulting in an overly slow etching speed in the vertical direction; at the same time, avoiding its being too long and causing an excessive number of grain boundaries in the horizontal cross-section, which affects the reliability of the etched circuit.

[0054] As a preferred solution, the range between the maximum horizontal cross-section width and the minimum horizontal cross-section width of the columnar crystal 2 is less than or equal to 0.3 μm.

[0055] It should be noted that the horizontal cross-section width refers to the width of the cross-section obtained by horizontally cutting the columnar crystal 2 in the horizontal direction perpendicular to the thickness direction of the functional layer 1. In this embodiment, by limiting the range between the maximum horizontal cross-section width and the minimum horizontal cross-section width of the columnar crystal 2 to be less than or equal to 0.3 μm, for example, the range between the maximum horizontal cross-section width and the minimum horizontal cross-section width is 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.12 μm, 0.15 μm, 0.17 μm, 0.19 μm, 0.21 μm, 0.23 μm, 0.25 μm, 0.27 μm, 0.29 μm, 0.3 μm, etc. This embodiment does not make specific limitations here, so as to ensure the width uniformity of the columnar crystal 2 as a whole, making it closer to a cylindrical crystal, effectively enhancing the structural strength of the columnar crystal 2, ensuring that the side surface of the columnar crystal 2 is more resistant to etching during the circuit etching process, slowing down the side etching speed of the etching solution, and effectively avoiding the occurrence of undercutting.

[0056] Please refer to Figure 8 , as a preferred solution, it further includes a carrier layer 3, and the functional layer 1 is provided on one side surface of the carrier layer 3.

[0057] Specifically, during actual application, the carrier layer 3 is stacked with other material layers such as the functional layer 1 in the metal foil, and is used to carry and protect the functional layer 1, so that the functional layer 1 is not damaged by external contact or collision, etc. After the functional layer 1 is hot-pressed onto the circuit board substrate, the carrier layer 3 needs to be peeled off.

[0058] As one of the optional embodiments, in this embodiment, the material of the carrier layer 3 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 3 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.

[0059] Please refer to Figure 9 , as a preferred solution, a release layer 4 is further included, and the release layer 4 is disposed between the carrier layer 3 and the functional layer 1.

[0060] Specifically, the function of the release layer 4 is to achieve the separation of the carrier layer 3 and the functional layer 1 through peeling; at the same time, due to the existence of the release layer 4, it can block the metal migration between the functional layer 1 and the carrier layer 3, and moreover, the release layer 4 can cover or fill the uneven surface of the carrier layer 3, making the functional layer 1 formed on the other surface of the release layer 4 smoother, more uniform and denser, which is beneficial to reducing the occurrence of pinholes during the subsequent processing of the functional layer 1, ensuring the use quality of the functional layer 1, and thus being beneficial to the subsequent circuit manufacturing. In the specific implementation process, when the carrier layer 3 is removed by peeling, the peeling method can be, for example: manually peeled off directly, or peeled off by means of mechanical equipment.

[0061] Before the metal foil product is manufactured and applied, the carrier layer 3, the release layer 4, and the functional layer 1 are stacked. As the product is applied, the functional layer 1 of the metal foil is hot-pressed onto the application carrier such as the circuit board substrate. After the hot-pressing process is completed, the entire metal foil is adhered to the application carrier through the adhesion between the roughened surface of the functional layer 1 and the application carrier. Before the metal foil is further processed and etched for the circuit, the carrier layer 3 is peeled off through the release layer 4, as Figure 10 shown, is a schematic diagram of the peeling of the carrier layer 3. Subsequently, circuits are formed on the circuit board substrate by means of copper plating, masking, etching, etc.

[0062] The processing method of the peelable metal foil is as follows: First, the carrier layer 3 is formed by means of electrochemically deposition, vacuum sputtering + electroplating, vacuum sputtering, etc.; then a release layer 4 is formed on one side surface of the carrier layer 3, and the forming method can also be electroplating, vacuum sputtering, etc.; then a functional layer 1 is processed on the release layer 4, and the forming method can be vacuum sputtering, electroplating, etc.

[0063] In this embodiment, the release layer 4 is processed on the carrier layer 3 by physical vapor deposition, such as by magnetron sputtering. The material of the release layer 4 can be an organic release layer, such as a nitrogen-containing compound, a sulfur-containing compound, and a carboxylic acid, or an inorganic release layer, including a metal base layer or an alloy layer. It can also be an inorganic layer and an organic layer stacked as the release layer 4, such as using a mixture of a metal oxide and an organic substance. This embodiment does not make specific limitations here.

[0064] Please refer to Figure 11 , as a preferred solution, it further includes a heat-resistant layer 5, and the heat-resistant layer 5 is provided on the surface of the carrier layer 3 away from the release layer 4.

[0065] Specifically, during the high-temperature lamination process of the functional layer 1 and the circuit board substrate, the carrier layer 3 may come into contact with the high-temperature pressing plate of the press, resulting in melting or deformation, making it difficult to peel the carrier layer 3 from the functional layer 1 and affecting the peeling stability between the two. In addition, during the high-temperature lamination process, the release layer 4 will also be affected by high temperature and cause melting or deformation, making the carrier layer 3 prone to mutual diffusion and bonding with the functional layer 1 at high temperature, thus making it difficult to peel the carrier layer 3 from the functional layer 1 and affecting the peeling stability between the two. Therefore, in this embodiment, by providing the heat-resistant layer 5 on the surface of the carrier layer 3 away from the release layer 4, it can play a heat-insulating role during the high-temperature lamination process, reduce the heating temperature of the carrier layer 3 and the release layer 4, ensure the thermal stability of the carrier layer 3 and the release layer 4, and ensure that after the functional layer 1 is laminated on the circuit board substrate, the carrier layer 3 can be smoothly peeled from the functional layer 1.

[0066] As an optional embodiment, the material of the heat-resistant layer 5 in this embodiment can be a tetrafluoroethylene film, a polyimide film, a heat-resistant adhesive, etc. The above materials all have certain heat-resistant properties and can effectively protect the metal foil from thermal damage during the lamination process.

[0067] In the second aspect of the embodiments of the present invention, a metal-clad laminate is provided, and the metal-clad laminate includes the metal foil as described in any one of the embodiments of the first aspect.

[0068] The beneficial effects of the metal foil and the metal-clad laminate provided by the embodiments of the present invention are at least one of the following:

[0069] (1) By forming a sufficient number of columnar crystals 2 growing along the thickness direction in the crystal structure of the functional layer 1, the side etching rate can be effectively slowed down during the etching process. In addition, by observing the thickness section of the functional layer 1, it is defined that in every 50 square micrometers, at least 40% of the long-axis lengths of the columnar crystals 2 are greater than 3 / 4 of the thickness of the functional layer 1, and the number of columnar crystals 2 surrounding any columnar crystal 2 with a long-axis length exceeding 1 μm is no more than 6. Thus, the number of grain boundaries in the vertical cross-section can be effectively reduced, making the etching rate in the horizontal direction perpendicular to the thickness direction of the functional layer slower when forming a circuit, avoiding the occurrence of undercutting. At the same time, the etching liquid relatively has a faster etching rate in the thickness direction of the functional layer, and the phenomenon of etching burrs can be avoided simultaneously. The embodiment of the present invention effectively improves the reliability of the metal-clad laminate.

[0070] (2) By defining that in every 50 square micrometers when observing the thickness section of the functional layer 1, at least 70% of the long-axis lengths of the columnar crystals 2 are 3 to 10 times their short-axis lengths, the side etching rate of the etching liquid in the functional layer 1 can be effectively slowed down. At the same time, the etching rate of the etching liquid from one side surface of the functional layer 1 downward is also prevented from being too slow, avoiding the occurrence of undercutting and etching burrs, thereby effectively improving the reliability of the metal-clad laminate.

[0071] (3) By defining that in the observation area of every 50 square micrometers when observing the thickness section of the functional layer 1, the area ratio between the total area of the columnar crystals 2 with long-axis lengths 5 to 10 times their short-axis lengths and the area of this observation area is relatively large, it can be further ensured that there are enough slender columnar crystals 2 formed in the functional layer 1, which is beneficial to reducing the number of grain boundaries in the vertical cross-section. Furthermore, during circuit etching, the etching rate of the functional layer 1 in the thickness direction can be neither too slow nor too fast, and the structural strength of the functional layer 1 in the horizontal direction perpendicular to the thickness direction can be enhanced, avoiding too fast a side etching rate, and further improving the improvement effect of undercutting and etching burrs.

[0072] (4) By defining that the range difference between the maximum horizontal cross-section width and the minimum horizontal cross-section width of the columnar crystal 2 is less than or equal to 0.3 μm, the width uniformity of the columnar crystal 2 as a whole can be ensured, making it closer to a cylindrical crystal. The structural strength of the columnar crystal 2 can be effectively enhanced, ensuring that the side surface of the columnar crystal 2 is more resistant to etching during the circuit etching process, slowing down the side etching rate of the etching liquid, and effectively avoiding the occurrence of undercutting and etching burrs.

[0073] In order to reflect the beneficial effects of the metal foil and the metal-clad laminate provided by the embodiments of the present invention, several embodiments and comparative examples will be described below.

[0074] Example 1

[0075] A metal foil includes a carrier layer, a release layer, and a functional layer. When observing the thickness section of the functional layer, in any observation area of 50 square micrometers, at least 52% of the area is composed of columnar crystals growing along the thickness direction. The thickness of the functional layer is 4 μm, the major axis length of the columnar crystals is 2.5 μm to 3.8 μm, and the minor axis length is 0.5 μm to 0.6 μm. Among them, 75% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer. The ratio of the total area of the columnar crystals with a major axis length 3 to 5 times the minor axis length to the area of the observation area is 20%, the ratio of the total area of the columnar crystals with a major axis length 5 to 10 times the minor axis length to the area of the observation area is 60%, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is 3.

[0076] Example 2

[0077] A metal foil includes a carrier layer, a release layer, and a functional layer. When observing the thickness section of the functional layer, in any observation area of 50 square micrometers, at least 75% of the area is composed of columnar crystals growing along the thickness direction. The thickness of the functional layer is 3 μm, the major axis length of the columnar crystals is 2 μm to 2.8 μm, and the minor axis length is 0.4 μm to 0.5 μm. Among them, 78% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer. The ratio of the total area of the columnar crystals with a major axis length 3 to 5 times the minor axis length to the area of the observation area is 15%, the ratio of the total area of the columnar crystals with a major axis length 5 to 10 times the minor axis length to the area of the observation area is 65%, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is 4.

[0078] Example 3

[0079] A metal foil includes a carrier layer, a release layer, and a functional layer. When observing the thickness section of the functional layer, in any observation area of 50 square micrometers, at least 80% of the area is composed of columnar crystals growing vertically along the thickness direction. The thickness of the functional layer is 2 μm, the major axis length of the columnar crystals is 1.2 μm to 1.8 μm, and the minor axis length is 0.2 μm to 0.3 μm. Among them, 70% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer. The ratio of the total area of the columnar crystals with a major axis length 3 to 5 times the minor axis length to the area of the observation area is 10%, the ratio of the total area of the columnar crystals with a major axis length 5 to 10 times the minor axis length to the area of the observation area is 80%. In addition, the range between the maximum horizontal cross-section width and the minimum horizontal cross-section width of the columnar crystals is 0.1 μm, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is 3.

[0080] Example 4

[0081] A metal foil includes a heat-resistant layer, a carrier layer, a release layer, and a functional layer. When observing the thickness slice of the functional layer, in any observation area of 50 square micrometers, at least 65% of the area is columnar crystals growing along the thickness direction. The thickness of the functional layer is 1 μm, the major axis length of the columnar crystals is 0.7 μm to 0.9 μm, and the minor axis length is 0.1 μm to 0.2 μm. Among them, the major axis length of 65% of the columnar crystals is greater than 3 / 4 of the thickness of the functional layer. The area ratio between the total area of the columnar crystals with the major axis length being 3 to 5 times the minor axis length and the area of this observation area is 28%, and the area ratio between the total area of the columnar crystals with the major axis length being 5 to 10 times the minor axis length and the area of this observation area is 63%. In addition, the range between the maximum horizontal cross-sectional width and the minimum horizontal cross-sectional width of the columnar crystals is 0.05 μm, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is 2.

[0082] Comparative Example 1

[0083] A metal foil includes a carrier layer, a release layer, and a functional layer. When observing the thickness slice of the functional layer, in any observation area of 50 square micrometers, at most only 30% of the area is columnar crystals. The thickness of the functional layer is 4 μm, and only 28% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer, and the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is 10.

[0084] The metal foils in the above-mentioned examples and comparative examples are subjected to high-temperature lamination on a circuit board substrate for circuit etching, and whether undercutting or etching burr phenomenon occurs after circuit etching is observed. The detection results are shown in Table 1 below.

[0085] Table 1 Circuit etching conditions

[0086] Circuit etching condition Example 1 No under-etching phenomenon and etching burr phenomenon occur Example 2 No under-etching phenomenon and etching burr phenomenon occur Example 3 No under-etching phenomenon and etching burr phenomenon occur Example 4 No under-etching phenomenon and etching burr phenomenon occur Comparative example 1 Under-etching phenomenon occurs

[0087] As can be seen from Table 1 above, in Examples 1 to 4, the functional layer of the metal foil contains a sufficient number of columnar crystals growing along the thickness direction. When observing the thickness section of the functional layer, the ratio of the total area of the columnar crystals to the area of the observation area in each 50 square micrometer observation area is greater than or equal to 50%. Among them, at least 40% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer, and at least 70% of the columnar crystals satisfy the ratio of the major axis length to the minor axis length limited in the embodiments of the present invention, which is 3 to 10 times. Moreover, in any 50 square micrometer observation area, the ratio of the total area of the columnar crystals with a major axis length 5 to 10 times the minor axis length to the area of the observation area is greater than or equal to 60%. In addition, the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is no more than 4, and the range between the maximum horizontal cross-sectional width and the minimum horizontal cross-sectional width of the columnar crystals also satisfies being less than or equal to 0.3 μm. Therefore, when etching to form a circuit, the side etching rate can be effectively slowed down, so that the etching rate of the etching solution in the thickness direction of the functional layer is relatively fast, while the etching rate in the horizontal direction perpendicular to the thickness direction is relatively slow. While avoiding the occurrence of etching burrs, the occurrence of undercutting is also avoided, and the reliability of the metal-clad laminate is improved.

[0088] In Comparative Example 1, the functional layer of the metal foil contains too few columnar crystals, and the proportion of columnar crystals with a major axis length greater than 3 / 4 of the thickness of the functional layer is too low. At the same time, the number of columnar crystals surrounding any columnar crystal with a major axis length exceeding 1 μm is too large, resulting in too many grain boundaries in the vertical cross-section. Therefore, during the circuit etching process, the side etching rate of the etching solution cannot be effectively slowed down, resulting in undercutting in the finally etched circuit.

[0089] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A metal foil, characterized in that: The present invention comprises a functional layer, wherein the functional layer contains columnar crystals growing in the thickness direction. When observing the thickness slice of the functional layer, in every 50 square microns, at least 40% of the columnar crystals have a major axis length greater than 3 / 4 of the thickness of the functional layer, and any columnar crystal with a major axis length exceeding 1 μm is surrounded by no more than 6 columnar crystals.

2. The metal foil according to claim 1, characterized in that By observing the thickness slice of the functional layer, at least 70% of the columnar crystals in every 50 square microns have a major axis length that is 3 to 10 times the minor axis length thereof.

3. The metal foil according to claim 2, characterized in that Observe the thickness slice of the functional layer. In every 50 square microns observation area, the area ratio between the total area of ​​the columnar crystals whose major axis length is 3 to 5 times the minor axis length and the observation area is less than or equal to 30%, and the area ratio between the total area of ​​the columnar crystals whose major axis length is 5 to 10 times the minor axis length and the observation area is greater than or equal to 40%.

4. The metal foil according to claim 1, characterized in that By observing the thickness slice of the functional layer, at least 50% of the area of ​​the crystal structure of the functional layer in every 50 square microns is the columnar crystals.

5. The metal foil according to claim 2, characterized in that The short axis length of the columnar crystal is 0.1 μm to 2 μm.

6. The metal foil according to claim 1, wherein The maximum horizontal cross-sectional width of the columnar crystal and the minimum horizontal cross-sectional width thereof are less than or equal to 0.3 μm.

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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