Composite metal foil, circuit board, multilayer circuit board and preparation method

Abstract

The invention discloses a composite metal foil, a circuit board, a multi-layer circuit board and a preparation method. The composite metal foil comprises a functional layer used for manufacturing a circuit and a conductive anti-corrosion layer arranged on one side face of the functional layer. Wherein N points are randomly taken on the anti-corrosion layer for square resistance measurement, the average value of the square resistance of the N measurement points is A, the difference between the maximum value and the minimum value of the square resistance is B, and B / A is smaller than or equal to 10%; n is a positive integer greater than or equal to 10. The conductive anti-corrosion layer is arranged on one side face of the functional layer to replace a traditional stripping layer, when a circuit is manufactured, the anti-corrosion layer can be directly removed through etching liquid and does not need to be stripped, the ultra-thin functional layer can be manufactured, the flash corrosion amount can be effectively reduced when the ultra-thin circuit is manufactured through the functional layer, and the manufacturing cost of the ultra-thin circuit is reduced. And the circuit precision and the reliability of the circuit board are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic information materials, and in particular to a composite metal foil, a circuit board, a multilayer circuit board and a preparation method thereof. Background Art

[0002] Under the current environment of rapid development of the 5G industry, the PCB industry has flourished under its influence, and circuit boards tend to develop in a refined manner. When using the Msap process to make ultra-fine circuits, the thinner the copper foil, the less flash corrosion, and the higher the precision of the circuit that can be made. However, the conventional Msap process currently on the market uses a peeling copper foil with a carrier, which is generally more than 1.5μm thick. When making copper foil with a lower thickness, the operability of the peeling copper foil processing is more difficult, and because the peeling layer is formed by sputtering, there will be some voids and it will not be dense. Therefore, the thin copper layer generated by electroplating on the peeling layer is prone to increase pinholes on the thin copper layer due to uneven electroplating. When making the circuit, it is easy to cause the circuit to open, affecting the reliability of the circuit board. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a composite metal foil, a circuit board, a multilayer circuit board and a preparation method. By arranging a conductive anti-corrosion layer on one side of the functional layer instead of the traditional peeling layer, when making the circuit, the anti-corrosion layer can be directly removed by an etching solution without peeling, and an ultra-thin functional layer can be made. When making ultra-fine circuits through the functional layer, the amount of flash corrosion can be effectively reduced, thereby improving the circuit accuracy and the reliability of the circuit board.

[0004] In order to achieve the above-mentioned object, an embodiment of the present invention provides a composite metal foil, comprising a functional layer for making a circuit, and a conductive anti-corrosion layer arranged on one side of the functional layer;

[0005] Wherein, N points are randomly selected on the anti-corrosion layer to measure the square resistance, the average square resistance of the N measurement points is A, the difference between the maximum and minimum square resistance is B, and B / A≤10%;

[0006] N is a positive integer greater than or equal to 10.

[0007] As an improvement of the above solution, the peel strength between the anti-corrosion layer and the functional layer is greater than or equal to 0.5 N / cm.

[0008] As an improvement of the above solution, the thickness of the functional layer is 0.1 to 6 μm.

[0009] As an improvement of the above solution, the roughness Rz of the side of the anti-corrosion layer close to the functional layer is less than or equal to 1 μm.

[0010] As an improvement of the above solution, a side of the anti-corrosion layer close to the functional layer is a rough surface, and the roughness Rz of the rough surface is less than or equal to 1 μm.

[0011] As an improvement of the above solution, a plurality of protrusions are provided on the rough surface, and the straight-line distance between any two adjacent protrusions is less than or equal to 1 μm;

[0012] and / or, the maximum width of the protrusion is 0.3 μm to 1 μm;

[0013] The maximum width is: in the sliced ​​state, the straight-line distance between two points of the protrusion profile that are farthest apart in the horizontal direction.

[0014] As an improvement of the above solution, the anti-corrosion layer can be removed by etching with at least one first etching solution, and the functional layer is resistant to corrosion by the first etching solution.

[0015] As an improvement of the above solution, the composite metal foil further comprises:

[0016] Carrier layer;

[0017] The carrier layer is arranged on a side of the anti-corrosion layer away from the functional layer.

[0018] As an improvement of the above scheme, a first etching rate of the carrier layer in at least one second etching solution is greater than a second etching rate of the anti-corrosion layer in the second etching solution, and the first etching rate = n × second etching rate; wherein n is a real number greater than or equal to 3.

[0019] The embodiment of the present invention further provides a method for preparing a composite metal foil, which is suitable for preparing any of the composite metal foils described above. The method for preparing the composite metal foil comprises:

[0020] The anti-corrosion material is made into a single-layer thin film-shaped conductive anti-corrosion layer, and then one side surface of the anti-corrosion layer is electroplated to form a functional layer;

[0021] Alternatively, a conductive anti-corrosion layer is formed by coating on the carrier layer, and then one side surface of the anti-corrosion layer is electroplated to form the functional layer.

[0022] An embodiment of the present invention further provides a circuit board, wherein the circuit board is made of any of the above-mentioned composite metal foils as one of the materials.

[0023] An embodiment of the present invention further provides a method for preparing a circuit board, using any of the composite metal foils described above to prepare a circuit board, the method for preparing the circuit board comprising:

[0024] Pressing a side of the functional layer away from the anti-corrosion layer onto the substrate, removing the anti-corrosion layer using a first etching solution, and performing circuit fabrication on the functional layer using an MSAP process to obtain an electrical circuit;

[0025] Alternatively, the side of the functional layer away from the anti-corrosion layer is pressed against the substrate, the carrier layer is removed using the second etching solution, the anti-corrosion layer is removed using the first etching solution, and finally the functional layer is subjected to circuit fabrication using the Msap process to obtain an electrical circuit.

[0026] An embodiment of the present invention further provides a multi-layer circuit board, which includes the circuit board described above and / or the circuit board prepared by the method for preparing the circuit board described above.

[0027] Compared with the prior art, the composite metal foil, circuit board, multilayer circuit board and preparation method provided by the embodiment of the present invention have the following beneficial effects: a conductive anti-corrosion layer is arranged on one side of the functional layer used to make the circuit; wherein, N points are randomly selected on the anti-corrosion layer for square resistance measurement, the square resistance average value of the N measurement points is A, the difference between the maximum and minimum square resistance values ​​is B, B / A≤10%; N is a positive integer greater than or equal to 10. In the embodiment of the present invention, a conductive anti-corrosion layer is arranged on one side of the functional layer to replace the traditional stripping layer. When making the circuit, the anti-corrosion layer can be directly removed by etching liquid without stripping, which reduces the difficulty of processing, can be made into an ultra-thin functional layer, and can effectively reduce the amount of flash corrosion when making ultra-fine circuits through the functional layer, and improve the circuit accuracy; at the same time, the present invention further limits the uniformity of the square resistance of the anti-corrosion layer, ensures that its square resistance uniformity is good, and can make the functional layer formed by electroplating thereon uniform and more dense, effectively reducing the formation of voids and improving the reliability of the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of a preferred embodiment of a composite metal foil provided by the present invention;

[0029] Figure 2 It is a schematic structural diagram of an anti-corrosion layer in a composite metal foil provided by the present invention;

[0030] Figure 3 It is a schematic diagram of the cross-sectional structure of the contact surface of the anti-corrosion layer in a composite metal foil provided by the present invention;

[0031] Figure 4 It is a structural schematic diagram of another preferred embodiment of a composite metal foil provided by the present invention;

[0032] The reference numerals are as follows:

[0033] 1. Functional layer; 2. Anti-corrosion layer; 21. Protrusion; 3. Carrier layer. DETAILED DESCRIPTION

[0034] 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. 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.

[0035] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, 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 should not be understood as a limitation on the present application.

[0036] 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.

[0037] 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.

[0038] See also Figure 1 , Figure 1 Schematic diagram of a preferred embodiment of a composite metal foil provided by the present invention. The embodiment of the present invention provides a composite metal foil, comprising a functional layer 1 for making a circuit, and a conductive anti-corrosion layer 2 arranged on one side of the functional layer 1;

[0039] Wherein, N points are randomly selected on the anti-corrosion layer 2 to measure the square resistance, the average square resistance of the N measurement points is A, the difference between the maximum and minimum square resistance is B, and B / A≤10%;

[0040] N is a positive integer greater than or equal to 10.

[0041] It should be noted that currently on the market, the Msap process is used to make ultra-fine circuits using peelable copper foil with a carrier. However, since the carrier needs to be peeled off when making the circuit, its functional layer (thin copper layer) has a certain thickness, generally not less than 1.5μm. If an ultra-thin copper foil below 1.5μm is to be made, the copper layer and the carrier cannot be effectively peeled off because the copper layer is too thin. And because of the existence of the peeling layer, the peeling layer is generally formed by sputtering. When a thin copper layer is electroplated on the peeling layer after sputtering to form a thin copper layer, it is easy to increase pinholes on the thin copper due to uneven electroplating, which may cause the circuit to open when making the circuit, thereby affecting the reliability of the circuit board.

[0042] Based on this, in order to solve the problem that it is difficult to make ultra-thin copper foil by stripping copper foil and pinholes are easily generated, the embodiment of the present invention removes the stripping layer and adds a new anti-corrosion layer 2 to carry the functional layer 1. When making the circuit, the anti-corrosion layer 2 is directly removed by etching liquid without stripping, and the etching liquid for removing the anti-corrosion layer 2 will not affect the functional layer 1. And because the anti-corrosion layer 2 is conductive, the surface of the anti-corrosion layer 2 can be directly electroplated to form the functional layer 1, thereby making an ultra-thin functional layer 1, which significantly reduces the difficulty of producing functional layers below 1.5μm, is conducive to improving the accuracy of ultra-fine circuits, and reduces the amount of flash corrosion during the circuit making process.

[0043] In addition, the embodiment of the present invention further defines the square resistance uniformity of the anti-corrosion layer 2. N points are randomly selected on the anti-corrosion layer 2 to measure the square resistance, the average square resistance of the N measurement points is A, the difference between the maximum square resistance and the minimum square resistance is B, B / A≤10%; wherein N is a positive integer greater than or equal to 10. The embodiment of the present invention defines the square resistance uniformity of the anti-corrosion layer in this way, which can ensure that the square resistance uniformity of the anti-corrosion layer is good, and the functional layer formed by electroplating on the anti-corrosion layer is uniform and more dense, which effectively reduces the formation of voids and improves the reliability of the circuit board.

[0044] It should be noted that, when selecting N measurement points for the anti-corrosion layer, the embodiment of the present invention can adopt a uniform distribution method, a regional division method, a nine-point sampling method, a random distribution method, a grid distribution method, etc. Among them, the uniform distribution method is to select N measurement points on the anti-corrosion layer at the same interval so that the N measurement points can be evenly distributed on the entire surface of the anti-corrosion layer. This method can ensure that each area is measured, thereby obtaining a relatively uniform average value of the overall square resistance. The regional division method is to divide the anti-corrosion layer into multiple small areas, each small area contains a certain number of measurement points (such as 3-5 points in each small area), and the measurement points in each small area can be randomly selected or uniformly selected. In this way, multiple areas can be sampled to understand the square resistance of different areas, and the changes in local square resistance can be captured to improve the accuracy of measurement. The nine-point sampling method is to select nine representative points on the anti-corrosion layer for measurement (such as four corners, the midpoints of four sides and the center point), which can better reflect the overall and local square resistance. On the basis of the basic nine points, the number of measurement points can also be appropriately increased according to the complexity and size of the anti-corrosion layer. Several small points are set around each additional measurement point for auxiliary measurement to improve accuracy. The random distribution method is to randomly select N measurement points on the anti-corrosion layer for measurement. This method can ensure that the distribution of the measurement points has a certain degree of randomness, thereby avoiding deviations caused by human factors and can better reflect the randomness of the overall square resistance. The grid distribution method is to divide the anti-corrosion layer into a grid, and each grid intersection is used as a measurement point. This method can ensure that the measurement points are evenly distributed on the entire anti-corrosion layer and can better reflect the overall situation.

[0045] The composite metal foil provided in the embodiment of the present invention has the advantage of less difficulty in production technology compared to stripped copper foil, and the functional layer (thin copper layer) is directly supported by the anti-corrosion layer. When making circuits, the composite metal foil can directly remove the anti-corrosion layer through etching liquid without stripping, so that the circuit can be directly engraved on the functional layer, which can effectively improve the accuracy of ultra-fine circuits and reduce the amount of flash corrosion.

[0046] In addition, the current carrier peeling force for peeling off the copper foil is generally about 0.3N / cm. In order to prevent the anti-corrosion layer 2 from separating from the functional layer 1, the peeling strength between the anti-corrosion layer and the functional layer is set to be greater than or equal to 0.5N / cm in the embodiment of the present invention. This can effectively ensure the bonding strength between the anti-corrosion layer and the functional layer, and ensure that the anti-corrosion layer 2 and the functional layer 1 will not be delaminated during the application of the composite metal foil.

[0047] The embodiment of the present invention also limits the thickness of the functional layer 1, which is 0.1 to 6 μm. The embodiment of the present invention provides a conductive anti-corrosion layer 2 on one side of the functional layer 1 to replace the traditional peeling layer for carrying the functional layer 1. Since the anti-corrosion layer 2 is conductive, when making a circuit, the functional layer 1 can be directly electroplated on the surface of the anti-corrosion layer 2, so that an ultra-thin functional layer 1 can be made, which significantly reduces the difficulty of producing functional layers below 1.5 μm, is conducive to improving the accuracy of ultra-fine circuits, and reduces the amount of flash corrosion during the circuit making process.

[0048] In another preferred embodiment, a surface of the anti-corrosion layer 2 close to the functional layer 1 is a rough surface, and the roughness Rz of the rough surface is less than or equal to 1 μm.

[0049] Specifically, see Figure 2 , Figure 2 It is a schematic diagram of the structure of the anti-corrosion layer in a composite metal foil provided by the present invention. In the embodiment of the present invention, the side of the anti-corrosion layer 2 close to the functional layer 1 is a rough surface, and the roughness Rz of the rough surface is less than or equal to 1μm, so that the contact surface between the anti-corrosion layer 2 and the functional layer 1 can maintain a low profile, and then during electroplating, the contact surface with a sufficiently low profile can effectively enhance the density of the functional layer and reduce the formation of pinholes.

[0050] In another preferred embodiment, a plurality of protrusions 21 are provided on the rough surface, and the straight-line distance between any two adjacent protrusions 21 is less than or equal to 1 μm.

[0051] Specifically, see Figure 3 , Figure 3 It is a schematic diagram of the cross-sectional structure of the contact surface of the anti-corrosion layer in a composite metal foil provided by the present invention. In the embodiment of the present invention, a plurality of protrusions 21 are provided on the rough surface of the anti-corrosion layer 2, and the distribution density of the protrusions 21 is further limited, and the straight-line distance d between any two adjacent protrusions 21 on the rough surface of the anti-corrosion layer 2 is set to be less than or equal to 1 μm. It should be noted that the straight-line distance d between the two protrusions 21 refers to: a vertical line is drawn to the highest points of the two protrusions 21, and the straight-line distance d between the two vertical lines.

[0052] In the embodiment of the present invention, the protrusions 21 are evenly distributed to ensure that the anti-corrosion layer 2 is in close contact with the functional layer 1 , thereby ensuring the peeling strength between the anti-corrosion layer 2 and the functional layer 1 .

[0053] In another preferred embodiment, the maximum width of the protrusion 21 is 0.3 μm to 1 μm;

[0054] The maximum width is: in the sliced ​​state, the straight-line distance between two points of the contour of the protrusion 21 that are farthest apart in the horizontal direction.

[0055] Specifically, the embodiment of the present invention can further limit the size of the protrusion 21 on the contact surface of the anti-corrosion layer 2, and set the maximum width L of the protrusion 21 on the rough surface of the anti-corrosion layer 2 to 0.3μm to 1μm. Exemplarily, the maximum width L is 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1μm and / or an interval consisting of any two values. It should be noted that since the cross-sectional shape of the rough surface of the anti-corrosion layer 2 is a corrugated shape with convex and concave shapes, it is generally observed by slicing under an electron microscope with a magnification of tens of thousands of times, and the maximum width L is: in the sliced ​​state, the straight-line distance between the two points of the contour of the protrusion 21 that are farthest apart in the horizontal direction. The embodiment of the present invention makes the protrusions evenly distributed to ensure close contact between the pitting layer and the functional layer, while making the size of the protrusions not too large to avoid a decrease in the bonding force, and also making the size of the protrusions not too small to avoid being too dense and resulting in an excessively large contact area. The embodiment of the present invention limits the size of the protrusions on the basis of ensuring the peeling strength between the anti-corrosion layer and the functional layer, so that the two can be effectively combined while avoiding an excessively large contact area that increases the path for signal transmission. The embodiment of the present invention makes the contact surface of the functional layer formed by electroplating on the surface of the anti-corrosion layer more dense, and can keep a low profile when forming a circuit on the functional layer, which is convenient for high-frequency and high-speed signal transmission.

[0056] It should be noted that, in practical applications, the protrusions 21 on the rough surface of the anti-etching layer 2 can be arranged according to actual needs to simultaneously meet the following conditions: the straight-line distance between any two adjacent protrusions 21 is less than or equal to 1 μm, and the maximum width of the protrusions 21 is 0.3 μm to 1 μm. The protrusions 21 on the rough surface of the anti-etching layer 2 can also be arranged to meet only one of the two conditions, that is, the straight-line distance between any two adjacent protrusions 21 is less than or equal to 1 μm, or the maximum width of the protrusions 21 is 0.3 μm to 1 μm.

[0057] In yet another preferred embodiment, the anti-corrosion layer 2 can be removed by etching with at least one first etching solution, and the functional layer 1 is resistant to the first etching solution.

[0058] Specifically, when the circuit is being drawn, the first etching solution can be used to etch away the anti-etching layer 2, and due to the corrosion resistance of the functional layer 1 to the first etching solution, the functional layer 1 is not affected. Therefore, under the first etching solution, the anti-etching layer can be effectively removed without excessively affecting the functional layer, and the flatness of the surface of the functional layer for subsequent circuit drawing is better guaranteed.

[0059] It should be noted that the functional layer 1 is resistant to corrosion by the first etching solution, which means that the functional layer 1 will not or is difficult to be corroded by the first etching solution, or the etching speed is slow. A suitable first etching solution can be selected to ensure that when the anti-corrosion layer is removed by the first etching solution, the first etching solution will not affect the surface of the functional layer. The specific type of the first etching solution in the embodiment of the present invention is not particularly limited, and those skilled in the art can select it according to actual needs, as long as the above functions can be achieved.

[0060] In addition, the thickness of the anti-corrosion layer 2 is greater than the thickness of the functional layer 1. By setting the thickness of the anti-corrosion layer to be thicker than the functional layer, the anti-corrosion effect of the functional layer can be effectively enhanced.

[0061] Preferably, the composite metal foil further comprises:

[0062] Carrier layer 3;

[0063] The carrier layer 3 is disposed on a side of the anti-corrosion layer 2 away from the functional layer 1 .

[0064] Specifically, see Figure 4 , Figure 4 It is a structural schematic diagram of another preferred embodiment of a composite metal foil provided by the present invention. In order to better protect the composite metal foil during transportation or before application, the embodiment of the present invention adds a carrier layer 3 to carry the anti-corrosion layer 2 and the extremely thin functional layer 1 thereon, thereby reducing the risk of damage during processing and transportation. Before the composite metal foil product is manufactured and used, the carrier layer 3, the anti-corrosion layer 2, and the functional layer 1 are stacked. Among them, the material of the carrier layer 3 can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. The material of the anti-corrosion layer 2 can be any one of nickel, chromium, zirconium and / or any one of their alloys. The material of the functional layer 1 can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0065] Preferably, the first etching rate of the carrier layer 3 in at least one second etching solution is greater than the second etching rate of the anti-corrosion layer 2 in the second etching solution, and the first etching rate = n × second etching rate; wherein n is a real number greater than or equal to 3.

[0066] Specifically, when the composite metal foil in the embodiment of the present invention is used to depict ultrafine circuits, the carrier layer 3 needs to be etched away first. During the etching of the carrier layer 3, the etching speed of the second etching solution on the carrier layer 3 is much faster than that of the anti-corrosion layer 2, so that the anti-corrosion layer 2 can protect the functional layer 1 well. In this way, the second etching solution can be used to effectively remove the carrier layer 3 before application without affecting the functional layer 1.

[0067] The embodiment of the present invention further provides a method for preparing a composite metal foil, which is suitable for preparing the composite metal foil described in any of the above embodiments. The method for preparing the composite metal foil comprises:

[0068] The anti-corrosion material is made into a single-layer thin film-shaped conductive anti-corrosion layer 2, and then one side surface of the anti-corrosion layer 2 is electroplated to form a functional layer 1;

[0069] Alternatively, a conductive anti-corrosion layer 2 is formed by coating on the carrier layer 3 , and then one side surface of the anti-corrosion layer 2 is electroplated to form the functional layer 1 .

[0070] An embodiment of the present invention further provides a circuit board, wherein the circuit board is made of the composite metal foil described in any of the above embodiments as one of the materials.

[0071] An embodiment of the present invention further provides a method for preparing a circuit board, using the composite metal foil described in any of the above embodiments to prepare a circuit board, and the method for preparing the circuit board comprises:

[0072] Pressing a side of the functional layer 1 away from the anti-corrosion layer 2 onto the substrate, removing the anti-corrosion layer 2 using a first etching solution, and performing circuit fabrication on the functional layer 1 using an MSAP process to obtain an electrical circuit;

[0073] Alternatively, the side of the functional layer 1 away from the anti-etching layer 2 is pressed against the substrate, the carrier layer 3 is removed using the second etching solution, and then the anti-etching layer 2 is removed using the first etching solution. Finally, the functional layer 1 is subjected to circuit fabrication using the Msap process to obtain an electrical circuit.

[0074] Specifically, the specific process of applying the composite metal foil product is to press one side of the functional layer 1 of the composite metal foil onto a carrier such as a circuit board substrate. After the pressing process is completed, the composite metal foil as a whole is bonded to the circuit board substrate through the bonding force between the roughened surface of the functional layer 1 and the circuit board substrate. Before the composite metal foil is further processed and the circuit is etched, the carrier layer 3 and the anti-etching layer 2 are removed, and then an electrical circuit is formed on the other side of the functional layer 1 through conventional MSAP process, using copper plating, masking, etching and other processes.

[0075] An embodiment of the present invention further provides a multilayer circuit board, which includes the circuit board described in the above embodiment and / or the circuit board prepared by the method for preparing the circuit board described in the above embodiment.

[0076] In order to demonstrate the beneficial effects of the composite metal foil, circuit board, multilayer circuit board and preparation method provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0077] Example 1

[0078] In this embodiment, a composite metal foil is provided, which includes a functional layer 1 and a conductive anti-corrosion layer 2 disposed on one side of the functional layer 1. The thickness of the anti-corrosion layer 2 is 1 μm, the peel strength between the anti-corrosion layer 2 and the functional layer 1 is 0.7 N / cm, and the roughness Rz of the side of the anti-corrosion layer 2 close to the functional layer 1 is 0.8 μm. In addition, before the functional layer 1 is formed by electroplating on the anti-corrosion layer 2, 20 points are randomly selected on the upper surface of the anti-corrosion layer 2 for square resistance measurement, and the square resistance average value of the 20 measurement points is A, A=20 mΩ, and the difference between the maximum and minimum square resistance is B, B=1.6 mΩ, that is, B / A=8%. Finally, the composite metal foil is sliced ​​and placed under an electron microscope for observation at a magnification of 20,000 times. Taking any 50 μm length, it is observed that the number of pinholes on the functional layer 1 is 1.

[0079] Example 2

[0080] In this embodiment, a composite metal foil is provided, which comprises a carrier layer 3, an anti-corrosion layer 2 and a functional layer 1 which are stacked in sequence. The anti-corrosion layer 2 is made of a conductive material, the thickness of the anti-corrosion layer 2 is 1.2 μm, the peel strength between the anti-corrosion layer 2 and the functional layer 1 is 1 N / cm, and the roughness Rz of the side of the anti-corrosion layer 2 close to the functional layer 1 is 0.9 μm. In addition, before the functional layer 1 is formed by electroplating on the anti-corrosion layer 2, 15 points are randomly taken on the upper surface of the anti-corrosion layer 2 for square resistance measurement, and the square resistance average value of the 15 measurement points is A, A=17 mΩ, and the difference between the maximum and minimum square resistance is B, B=1.2 mΩ, that is, B / A=7%. Finally, the composite metal foil is sliced ​​and placed under an electron microscope for observation at a magnification of 20,000 times. Taking any 50 μm length, it is observed that the number of pinholes on the functional layer 1 is 0.

[0081] Example 3

[0082] In this embodiment, a composite metal foil is provided, which includes a carrier layer 3, an anti-corrosion layer 2 and a functional layer 1 which are stacked in sequence. The anti-corrosion layer 2 is made of a conductive material, the thickness of the anti-corrosion layer 2 is 0.6 μm, the peel strength between the anti-corrosion layer 2 and the functional layer 1 is 1.5 N / cm, the roughness Rz of the side of the anti-corrosion layer 2 close to the functional layer 1 is 1 μm, and a plurality of protrusions 21 are provided, the straight-line distance between any two adjacent protrusions is less than 0.7 μm, and the maximum width of the protrusion is 0.5 μm. In addition, before the functional layer 1 is formed by electroplating on the anti-corrosion layer 2, 25 points are randomly taken on the upper surface of the anti-corrosion layer 2 for square resistance measurement, and the square resistance average value of the 25 measurement points is A, A=23 mΩ, and the difference between the maximum and minimum square resistance is B, B=1 mΩ, that is, B / A=4%. Finally, the composite metal foil was sliced ​​and observed under an electron microscope at a magnification of 20,000 times. By taking any 50 μm length, it was observed that the number of pinholes on the functional layer 1 was 2.

[0083] Comparative Example 1

[0084] In this embodiment, a composite metal foil is provided, which includes a functional layer 1 and an anti-corrosion layer 2 disposed on one side of the functional layer 1, wherein the thickness of the anti-corrosion layer 2 is 1.2 μm. In addition, before the functional layer 1 is formed by electroplating on the anti-corrosion layer 2, 20 points are randomly selected on the upper surface of the anti-corrosion layer 2 for square resistance measurement, and the square resistance average value of the 20 measurement points is A, A=24 mΩ, and the difference between the maximum and minimum square resistance values ​​is B, B=6 mΩ, that is, B / A=25%. Finally, the composite metal foil is sliced ​​and placed under an electron microscope for observation at a magnification of 20,000 times. Taking any 50 μm length, it is observed that the number of pinholes on the functional layer 1 is 12.

[0085] Comparative Example 2

[0086] In this embodiment, a composite metal foil is provided, which includes a peeling layer and a functional layer 1 stacked in layers, wherein the thickness of the functional layer 1 is 2 μm. After the functional layer 1 is directly peeled off, 20 points are randomly selected on the surface of the functional layer for square resistance measurement, and the average square resistance of the 20 measurement points is A, A=16 mΩ, and the difference between the maximum and minimum square resistance is B, B=5 mΩ, that is, B / A=31%. Finally, the composite metal foil is sliced ​​and placed under an electron microscope for observation at a magnification of 20,000 times. Taking any 50 μm length, it is observed that the number of pinholes on the functional layer 1 is 18.

[0087] In embodiments 1-3 of the present invention, a conductive anti-corrosion layer is provided on one side of the functional layer, and the square resistance of the anti-corrosion layer is measured. The difference between the maximum and minimum square resistance values ​​and the square resistance average value are measured to be less than 10%, which is in line with the preferred range defined by the present invention, and can effectively ensure that the square resistance uniformity of the anti-corrosion layer is good; at the same time, the above embodiments further set a more preferred range for the peeling strength, contact roughness, and distribution and size of the protrusions on the rough surface of the anti-corrosion layer 2 and the functional layer 1, so that the square resistance uniformity of the anti-corrosion layer is further improved; that is, the present invention can make the functional layer formed by electroplating on the anti-corrosion layer uniform, making it more dense, and in the sliced ​​state, the number of pinholes on the functional layer 1 at any 50μm length is less than or equal to 2, which effectively reduces the formation of voids in the functional layer and improves the reliability of the circuit board. In addition, when making the circuit, the anti-corrosion layer can be directly removed by etching liquid, which reduces the difficulty of processing, can be made into an ultra-thin functional layer, and can effectively reduce the amount of flash corrosion when making ultra-fine circuits through the functional layer, and improve the circuit accuracy.

[0088] In Comparative Example 1, an anti-corrosion layer is provided on one side of the functional layer, and the square resistance of the anti-corrosion layer is measured. The quotient of the difference between the maximum and minimum square resistance values ​​and the average square resistance value is measured to be 25%, which is not within the preferred range defined by the present invention. This will result in poor uniformity of the square resistance of the anti-corrosion layer, and further lead to poor uniformity and insufficient density of the functional layer formed by electroplating on the anti-corrosion layer. In the sliced ​​state, at any 50μm length, it is observed that the number of pinholes on the functional layer 1 is 12, which is at least 6 times that of Examples 1-3, forming more voids, which significantly reduces the reliability of the circuit board.

[0089] In Comparative Example 2, a functional layer 1 is formed by electroplating on the peeling layer, and the square resistance of the functional layer 1 is measured. The quotient of the difference between the maximum and minimum square resistance values ​​and the average square resistance value is 31%, which does not fall within the preferred range defined by the present invention. It can be seen that the functional layer formed by electroplating on the traditional peeling layer has poor uniformity and is not dense enough. In the sliced ​​state, at any 50μm length, it is observed that the number of pinholes on the functional layer 1 is 18, which is at least 9 times that of Examples 1-3, forming a large number of voids, which significantly reduces the reliability of the circuit board.

[0090] In summary, the composite metal foil prepared by setting a conductive anti-corrosion layer on one side of the functional layer and limiting the uniformity of the square resistance of the anti-corrosion layer as defined in the present invention can make the functional layer used to prepare the circuit uniform and dense, effectively reducing the formation of its voids, thereby improving the reliability of the circuit board. At the same time, when making the circuit, the anti-corrosion layer of the composite metal foil in the present invention can be directly removed by etching liquid without peeling, which reduces the difficulty of processing operations, can be made into an ultra-thin functional layer, and when making ultra-fine circuits through the functional layer, the amount of flash corrosion can be effectively reduced, and the circuit accuracy can be improved.

[0091] 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 composite metal foil, characterized in that: It comprises a functional layer for making a circuit, and a conductive anti-corrosion layer arranged on one side of the functional layer; Wherein, N points are randomly selected on the anti-corrosion layer to measure the square resistance, the average square resistance of the N measurement points is A, the difference between the maximum and minimum square resistance is B, and B / A≤10%; N is a positive integer greater than or equal to 10.

2. The composite metal foil according to claim 1, characterized in that The peel strength between the anti-corrosion layer and the functional layer is greater than or equal to 0.5 N / cm.

3. The composite metal foil according to claim 1, characterized in that The thickness of the functional layer is 0.1-6 μm.

4. The composite metal foil according to claim 1, characterized in that A surface of the anti-corrosion layer close to the functional layer is a rough surface, and a roughness Rz of the rough surface is less than or equal to 1 μm.

5. The composite metal foil according to claim 4, characterized in that The rough surface is provided with a plurality of protrusions, and the straight-line distance between any two adjacent protrusions is less than or equal to 1 μm; and / or, the maximum width of the protrusion is 0.3 μm to 1 μm; The maximum width is: in the sliced ​​state, the straight-line distance between two points of the protrusion profile that are farthest apart in the horizontal direction.

6. The composite metal foil according to claim 1, characterized in that The anti-corrosion layer can be removed by etching with at least one first etching solution, and the functional layer is resistant to the first etching solution.

7. The composite metal foil according to any one of claims 1 to 6, characterized in that: The composite metal foil further comprises: Carrier layer; The carrier layer is arranged on a side of the anti-corrosion layer away from the functional layer.

8. The composite metal foil according to claim 7, characterized in that The first etching rate of the carrier layer in at least one second etching solution is greater than the second etching rate of the anti-corrosion layer in the second etching solution, and the first etching rate=n×second etching rate; wherein n is a real number greater than or equal to 3.

9. A method for preparing a composite metal foil, characterized in that: Suitable for preparing the composite metal foil as claimed in any one of claims 1 to 8, the preparation method of the composite metal foil comprising: The anti-corrosion material is made into a single-layer thin film-shaped conductive anti-corrosion layer, and then one side surface of the anti-corrosion layer is electroplated to form a functional layer; Alternatively, a conductive anti-corrosion layer is formed by coating on the carrier layer, and then one side surface of the anti-corrosion layer is electroplated to form the functional layer.

10. A circuit board, characterized in that: The circuit board is made of the composite metal foil as described in any one of claims 1 to 8 as one of the materials.

11. A method for preparing a circuit board, characterized in that: A circuit board is prepared using the composite metal foil according to any one of claims 18, wherein the method for preparing the circuit board comprises: Pressing a side of the functional layer away from the anti-corrosion layer onto the substrate, removing the anti-corrosion layer using a first etching solution, and performing circuit fabrication on the functional layer using an MSAP process to obtain an electrical circuit; Alternatively, the side of the functional layer away from the anti-corrosion layer is pressed against the substrate, the carrier layer is removed using the second etching solution, the anti-corrosion layer is removed using the first etching solution, and finally the functional layer is subjected to circuit fabrication using the Msap process to obtain an electrical circuit.

12. A multilayer circuit board, characterized in that: The multilayer circuit board includes the circuit board as claimed in claim 10 and / or the circuit board prepared by the method for preparing the circuit board as claimed in claim 11.

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