Copper-clad laminate and method for manufacturing the same

Abstract

To provide a copper-clad laminate capable of ensuring high adhesion between a resin film and a copper plating layer while suppressing transmission loss when applied to a flexible circuit board.SOLUTION: A copper-clad laminate includes a resin film 1 having a relative permittivity of 3.5 or lower and a dielectric loss tangent of 0.008 or lower at a frequency of 10 GHz and an electroless copper plating layer 2 laminated on at least one surface of the resin film 1, the average surface roughness Ra of the resin film 1 being 1-150 nm at the plating layer side interface in contact with the electroless copper plating layer 2, and the adhesive strength of the resin film 1 and the electroless copper plating layer 2 being 4.2 N / cm or higher.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a copper-clad laminate for a flexible printed circuit board mounted on a communication device or the like, and a method for manufacturing the same.

Background Art

[0002] In recent years, the miniaturization and high performance of electronic devices have been remarkable. For example, the development of communication devices using radio waves such as mobile phones and wireless LANs has greatly contributed to this. Especially recently, with the increase in the amount of information represented by big data by IoT, the high-frequencyization of communication signals between electronic devices has progressed. For such circuit boards mounted on communication devices, materials with low transmission loss (dielectric loss) in the high-frequency region are required.

[0003] Here, it is known that the dielectric loss generated in this circuit board is proportional to the product of three elements composed of "signal frequency", "square root of the dielectric constant of the substrate material", and "dielectric tangent". Therefore, in order to obtain the excellent dielectric characteristics described above, materials with as low dielectric constant and dielectric tangent as possible are necessarily required.

[0004] In such a circuit board, a circuit is generally formed of a metal such as copper. The copper layer in this circuit board is formed by, for example, the lamination method shown in Patent Document 1, the casting method shown in Patent Document 2, or the plating method shown in Patent Document 3.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] As mentioned above, in recent years, suppressing transmission loss in high-frequency communications has become an important development element, and resin films with low transmission loss (hereinafter also referred to as "low-dielectric films" or "low-dielectric resin films") are increasingly being used as substrates for flexible circuit boards. However, conventional technologies, including the aforementioned patent documents, have not been able to ensure sufficient adhesion between the low-dielectric film and the metal layer (e.g., copper layer) for forming the circuit. For example, in the lamination method exemplified in Patent Document 1 and the casting method exemplified in Patent Document 2, the interface between the copper layer and the low-dielectric film must be roughened, which degrades the smoothness of the interface and causes transmission loss.

[0007] On the other hand, according to the plating method described in Patent Document 3, relatively good adhesion can be ensured between a high dielectric constant resin film and a copper layer. However, low dielectric films have a relatively rigid molecular structure and little surface polarization, so ensuring adhesion when a copper layer is formed by plating has been a challenge. In other words, when a low dielectric film is used as a substrate, a common conventional method for ensuring adhesion has been to roughen the interface, but this has a trade-off relationship with transmission loss, so a way to achieve both was desired. While other manufacturing methods, such as sputtering, could also be cited, their more complex manufacturing processes result in numerous challenges in terms of productivity and cost compared to the methods described above.

[0008] The present invention aims to solve the above-mentioned problems as an example, and specifically aims to provide a copper-clad laminate and a method for manufacturing the same that can ensure high adhesion while ensuring smoothness at the interface between a low-dielectric film that serves as a base material and a metal layer for circuit formation in order to suppress transmission loss. [Means for solving the problem]

[0009] To solve the above-mentioned problems, a copper-clad laminate in one embodiment of the present invention comprises (1) a low-dielectric resin film having a relative permittivity of 3.5 or less and a dielectric loss tangent of 0.008 or less at a frequency of 10 GHz, and an electroless copper plating layer laminated on at least one surface of the low-dielectric resin film, wherein the electroless copper plating layer is an electroless Cu-Ni alloy plating layer, and the average surface roughness Ra at the plating layer side interface of the low-dielectric resin film that is in contact with the electroless Cu-Ni alloy plating layer is 1~ 50 The value is nm, and the 90° peel strength between the resin film and the electroless Cu-Ni alloy plating layer is 4.2 N / cm or more. The interface on the plating layer side is provided with a functional group specified by the following structural formula 1, The TOF-SIMS spectrum of the interface on the plating layer side is characterized in that the peak intensity of mass number 121 is 1000 or more.

[0011] Furthermore, in the copper-clad laminate described in (1) above, 2 The resin film is preferably one of polyimide, modified polyimide, liquid crystal polymer, fluororesin, or a mixture thereof.

[0013] Furthermore, in the copper-clad laminate described in (1) above, (3) the electroless Cu-Ni alloy The thickness of the plating layer is preferably in the range of 0.1 to 1.0 μm.

[0014] Furthermore, in the copper-clad laminate described in (1) above, 4 ) The aforementioned resin film, without electricity Dissolved at the interface on the Cu-Ni alloy plating layer side, a metal composed of one of Cu, Ni, Pd, or Ag. It is preferable that it is present.

[0015] Furthermore, in the copper-clad laminate described in (1) above, 5 ) The electroless Cu-Ni alloy Preferably, the plated layer further includes a protective layer formed on the plated layer.

[0016] Furthermore, in the copper-clad laminate described in (1) above, 6The electroless Cu-Ni alloy The plating layer is formed on both sides of the resin film, and the resin film has through holes, and at least a part of the electroless Cu-Ni alloy plating layer is preferably formed on the inner wall of the through holes.

[0022] Furthermore, in order to solve the above problems, a flexible circuit board according to an embodiment of the present invention is characterized in that a circuit formed by the copper-clad laminate according to any one of (1) to ( 6 ) described above is formed.

Advantages of the Invention

[0023] According to the present invention, it is possible to ensure high adhesion without roughening the interface between the low-dielectric film and the electroless copper plating layer.

Brief Description of the Drawings

[0024] [Figure 1] It is a schematic cross-sectional view showing the copper-clad laminate 10 of the present embodiment. [Figure 2] In the copper-clad laminate 10 of the present embodiment, it is a schematic diagram showing the state of the interface between the resin film 1 and the electroless copper plating layer. [Figure 3] In the copper-clad laminate 10 of the present embodiment, it is a schematic diagram showing the through hole H. [Figure 4] It is a diagram showing the flow of the manufacturing method of the copper-clad laminate 10 of the present embodiment. [Figure 5] It is a schematic cross-sectional view showing the copper-clad laminate 20 of the present embodiment.

Embodiments for Carrying Out the Invention

[0025] Hereinafter, the copper-clad laminate 10 of the present embodiment will be described with reference to FIG. 1. <Copper-Clad Laminate> ​The copper-clad laminate 10 according to this embodiment has a resin film 1 that serves as a base material and an electroless copper plating layer 2 laminated on at least one surface of the resin film 1. In this embodiment, it is preferable to use a so-called low-dielectric resin film that has excellent electrical properties in the high-frequency range as the resin film 1 that serves as the base material. Specifically, films of known liquid crystal polymers, fluororesins, polyimide resins, modified polyimide resins, epoxy resins, polytetrafluoroethylene resins, and polyphenylene ether resins, which have lower dielectric loss, are preferably used. These resins may be monopolymers or copolymers. Furthermore, the resins may be used individually or as a hybrid by blending multiple resins.

[0026] Specifically, the electrical properties of the resin film 1 used as the base material are preferably such that the relative permittivity at a frequency of 10 GHz is 3.5 or less, and the dielectric loss tangent is 0.008 or less. There are no particular restrictions on the thickness of the resin film 1, but in practical terms, it is preferably 5 μm to 100 μm.

[0027] Next, the electroless copper plating layer 2, which is laminated on at least one surface of the resin film 1, will be described. In this embodiment, the electroless copper plating layer 2 is preferably formed by electroless copper plating. That is, since the resin film 1 has insulating properties, the copper plating layer is formed by electroless plating. This electroless copper plating layer 2 may also serve as a seed layer when manufacturing a flexible circuit board by a semi-additive method (SAP method or MSAP method), a subtractive method, or a fully additive method.

[0028] In this embodiment, the electroless copper plating layer 2 may be a plating of pure Cu, or a copper alloy plating containing a predetermined amount or more of copper. Examples of copper alloys include Cu-Ni alloy, Cu-Zn alloy, Cu-Sn alloy, etc.

[0029] Furthermore, when the electroless copper plating layer 2 is formed of a Cu-Ni alloy, the Ni content is preferably 3 wt% or less, more preferably 0.01 to 3 wt%, more preferably 0.01 to 1.5 wt%, and even more preferably 0.01 to 0.3 wt%. When the electroless copper plating layer 2 is made of a Cu-Ni alloy, it is preferable to include Ni, which has higher plating deposition properties than Cu, because this suppresses internal stress in the plating layer and thus suppresses blistering. On the other hand, if the amount of Ni in the Cu-Ni alloy exceeds 3 wt%, magnetism may be generated in the Cu circuit, potentially increasing transmission loss, and the etching process during copper wiring formation may become complicated. Therefore, it is preferable that the amount of Ni in the Cu-Ni alloy be 3 wt% or less. Furthermore, if the amount of Ni in the Cu-Ni alloy falls below 0.01 wt%, the plating deposition properties deteriorate. Furthermore, known methods such as X-ray fluorescence (XRF) or plasma emission spectroscopy (ICP) can be used to measure the Ni content in the electroless plating layer 2.

[0030] In this embodiment, as a method for electroless copper plating to form the electroless copper plating layer 2, any known method may be used, as long as it can form an electroless copper plating layer 2 having a predetermined thickness. The electroless copper plating method will be described in detail in the manufacturing method section below. In this embodiment, the thickness of the electroless copper plating layer 2 is preferably in the range of 0.1 μm to 1.0 μm from the viewpoint of manufacturing efficiency and cost.

[0031] If the thickness of the electroless copper plating layer 2 is less than 0.1 μm, it may not be able to function as a seed layer when manufacturing flexible circuit boards by the semi-additive method, which is undesirable. On the other hand, if the thickness of the electroless copper plating layer 2 exceeds 1.0 μm, it may become difficult to form fine circuit patterns when manufacturing flexible circuit boards, which is also undesirable.

[0032] Furthermore, it is even more preferable that the thickness of the electroless copper plating layer 2 is 0.1 μm to 0.8 μm. In particular, in circuit formation using the SAP method, a shorter etching time (thinner thickness) allows for the formation of finer patterns with less variation in impedance in the cross-sectional direction of the circuit.

[0033] In the copper-clad laminate 10 of this embodiment, the average surface roughness Ra at the plating layer-side interface of the resin film 1 in contact with the electroless copper plating layer 2 is 1 to 150 nm, preferably 20 to 150 nm. In particular, when the resin film 1 is a liquid crystal polymer, it is desirable that the average surface roughness Ra at the plating layer-side interface in contact with the electroless copper plating layer 2 be 20 to 150 nm. Furthermore, in particular when the resin film 1 is a modified polyimide (MPI), it is desirable that the average surface roughness Ra at the plating layer-side interface in contact with the electroless copper plating layer 2 be 1 to 150 nm, more preferably 1 to 50 nm. The reasons for this are as follows:

[0034] In other words, in the copper-clad laminate of this embodiment, it is desirable that it has high transmission characteristics at high frequencies of GHz or higher, in order to be suitably applicable to high-frequency circuit boards as described above.

[0035] Generally, it is known that transmission signals propagate along the conductor surface as the frequency increases due to the skin effect, and transmission loss increases as the roughness of the conductor surface increases. Therefore, in this embodiment, in order to reduce the effect of transmission loss due to the skin effect, it is preferable to reduce the average surface roughness Ra at the interface between the electroless copper plating layer 2 that forms the wiring conductor and the resin film 1.

[0036] On the other hand, obtaining an anchoring effect by roughening the interface between the electroless copper plating layer 2 and the resin film 1 is a commonly practiced method to ensure adhesion between the metal and the resin. Thus, in the copper-clad laminate of this embodiment, there is a trade-off relationship between roughness (adhesion) and transmission loss between the electroless copper plating layer 2 and the resin film 1. The inventors diligently studied how to achieve a higher level of compatibility between the two characteristics mentioned above. As a result, they found that in this embodiment, it is preferable to set the average surface roughness Ra at the electroless copper plating layer side interface of the resin film 1 in contact with the electroless copper plating layer 2 to 1 nm to 150 nm.

[0037] As a result of the inventors' continued investigations, it was concluded that when the average surface roughness Ra is less than 1 nm, desirable adhesion cannot be obtained between the electroless copper plating layer 2 and the resin film 1. On the other hand, when the average surface roughness Ra exceeds 150 nm, as described above, when wiring conductors are formed on the circuit board by the electroless copper plating layer 2, it is possible that desirable transmission characteristics at high frequencies cannot be obtained due to transmission loss caused by the skin effect.

[0038] In this embodiment, as described above, the objective is to achieve both roughness reduction (reduction of transmission loss) and adhesion between the electroless copper plating layer 2 and the resin film 1. In practical terms, the specific adhesion strength between the electroless copper plating layer 2 and the resin film 1 is preferably 4.2 N / cm or higher. Furthermore, the adhesion strength described above is more preferably 5.0 N / cm or higher, and even more preferably 6.4 N / cm or higher.

[0039] In this embodiment, in order to ensure the above-mentioned adhesion between the electroless copper plating layer 2 and the resin film 1, it is preferable that the following features are further present. Figure 2 schematically shows the state of the interface between the resin film 1 and the electroless copper plating layer in the copper-clad laminate 10 of this embodiment. Specifically, at the interface of the resin film 1 on the electroless copper plating layer 2 side, hydroxyl groups and / or It is preferable that a carboxyl group be added. This is for the following reasons:

[0040] As shown in Figure 1, in the copper-clad laminate 10 of this embodiment, when forming an electroless copper plating layer 2 on at least one side of the resin film 1 by electroless plating, it is generally known that metallic palladium, which serves as a nucleus for plating formation, is applied to the surface of the resin film 1. This metallic palladium can be produced using a palladium catalyst.

[0041] In this embodiment, by imparting at least one of hydroxyl groups and carboxyl groups to the surface of the resin film 1, it is possible to strengthen the adsorption of metallic palladium onto the surface of the resin film 1. Therefore, it is possible to improve the adhesion between the resin film 1 and the electroless copper plating layer 2.

[0042] Furthermore, hydroxyl groups at the interface between the resin film 1 and the electroless copper plating layer 2 and / or The presence of carboxyl groups can be confirmed by known surface analysis methods. For example, known analytical methods such as Fourier transform infrared spectrophotometer (FT-IR), X-ray photoelectron spectroscopy (ESCA), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) can be used.

[0043] In particular, in this embodiment, at the interface between the resin film 1 and the electroless copper plating layer 2, it is preferable that the peak intensity at mass 121 is 800 (0.12 amu bin) or higher, as a result of time-of-flight mass spectrometry (TOF-SIMS) analysis on the electroless copper plating layer 2 side. In other words, in this embodiment, the results of analysis by TOF-SIMS showed that the mass was 121 and the hydroxyl group and / or It is preferable that a functional group containing a carboxyl group is present at the interface between the resin film 1 and the electroless copper plating layer 2. The functional group with a mass of 121 is preferably either structural formula 1 or structural formula 2 below, but structural formula 1 is particularly preferred.

[0044] <Structural formula 1> JPEG0007849440000001.jpg6182

[0045] <Structural formula 2> JPEG0007849440000002.jpg4582

[0046] Furthermore, the "functional groups containing hydroxyl groups and / or carboxyl groups" applied to the interface between the resin film 1 and the electroless copper plating layer 2 are not limited to those described above. Also, if a "functional group containing a hydroxyl group" is applied, a "functional group containing a carboxyl group" is not required. The reverse is also true. Moreover, both a "functional group containing a hydroxyl group" and a "functional group containing a carboxyl group" may be applied.

[0047] In particular, in this embodiment, it is preferable that the interface between the resin film 1 and the electroless copper plating layer 2 has more "functional groups containing hydroxyl groups" than "functional groups containing carboxyl groups." Alternatively, it is preferable that "functional groups containing hydroxyl groups" are present and "functional groups containing carboxyl groups" are not.

[0048] Furthermore, as shown in Figure 5, the copper-clad laminate of this embodiment may have an electrolytic copper plating layer 4 formed on top of the electroless copper plating layer 2 described above. In other words, when manufacturing a flexible circuit board by the semi-additive method, it is possible to use the electroless copper plating layer 2 as a seed layer and further form an electrolytic plating layer on top of the electroless copper plating layer 2.

[0049] Furthermore, the method for forming a flexible circuit board using the copper-clad laminate of this embodiment is not limited to the semi-additive method described above, but other known methods can also be applied.

[0050] Furthermore, in the copper-clad laminate of this embodiment, it is preferable that electroless copper plating layers are formed on both sides of the resin film, and that through-holes H are formed as shown in Figure 3. That is, it is preferable that the resin film 1 has through-holes in its cross-section, and that the through-holes H are formed such that at least a portion of the electroless copper plating layer 2 covers the inner surface of the through-holes. Forming such through-holes H is preferable when using the copper-clad laminate of this embodiment as a flexible circuit board. The position and size of the through-holes H can be determined as appropriate for the flexible circuit board being manufactured, so a detailed explanation will be omitted.

[0051] The copper-clad laminate in this embodiment comprises a resin film 1 and an electroless copper plating layer 2 as described above. Furthermore, a known protective layer for preventing oxidation of the electroless copper plating layer 2 may be formed on the surface of the electroless copper plating layer 2 (the side opposite to the resin film 1). The protection of the electroless copper plating layer 2 is intended to suppress oxidation and is formed by rust prevention treatment using a known method.

[0052] <Method for manufacturing copper-clad laminates> Next, the manufacturing method of the copper-clad laminate 10 of this embodiment will be explained with reference to Figure 4. The method for manufacturing the copper-clad laminate 10 in this embodiment involves placing carboxyl groups on at least one surface of the resin film 1. and / or A first surface modification step (step 1) to impart hydroxyl groups, and the carboxyl groups and / or The process includes a second surface modification step (step 2) in which an electric charge is applied to the surface to which hydroxyl groups have been applied by a wet method; a catalyst adsorption step (step 3) in which a catalyst is adsorbed onto the surface to which the electric charge has been applied; an electroless copper plating step (step 4) in which an electroless copper plating layer 2 is formed on the surface to which the catalyst has been adsorbed; and a heating step (step 5) in which the copper-clad laminate on which the electroless copper plating layer has been formed is heated.

[0053] First, regarding the first surface modification step (step 1), the resin film 1 used is preferably a so-called low-dielectric resin film, as described above. Specifically, the electrical properties of the resin film 1 are preferably such that the relative permittivity at a frequency of 10 GHz is 3.5 or less, and the dielectric loss tangent is 0.008 or less.

[0054] In the first surface modification step of this embodiment, carboxyl groups are added to at least one surface of the resin film 1. and / or A hydroxyl group is added. This carboxyl group and / or One method for imparting hydroxyl groups is to bring a mixture of an alkaline aqueous solution and an amino alcohol into contact with at least one surface of the resin film 1.

[0055] The alkaline aqueous solution used in the first surface modification step may be either an inorganic alkali or an organic alkali. Examples of inorganic alkalis include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or their carbonates. Examples of organic alkalis include tetraalkylammonium hydroxide. The alkalis mentioned above may be used individually or in combination.

[0056] On the other hand, the amino alcohol used in the first surface modification step may be an aliphatic amino alcohol or an aromatic amino alcohol. It may also be a derivative thereof.

[0057] Specifically, amino alcohols such as ethanolamine, heptaminol, isoethanolamine, butanolamine, propanolamine, sphingosine, methanolamine, dimethylethanolamine, and N-methylethanolamine can be used. Of these, aminoethanol is particularly preferred.

[0058] In the first surface modification step, the mixing ratio of the alkaline aqueous solution and the amino alcohol mixture is preferably adjusted so that the molar ratio of -OH groups to -NH2 groups is (-NH2 groups / -OH groups) = 2.00 to 3.00. By keeping the molar ratio within the above range, it is possible to achieve both the reduction of roughness (reduction of transmission loss) and adhesion between the electroless copper plating layer 2 and the resin film 1, which is the objective of the present invention. The reason for this is not clear at present, but based on the inventors' investigations, it is presumed to be due to the following reasons.

[0059] In other words, when a first surface modification step is applied to a resin film 1 using the low dielectric loss resin (liquid crystal polymer, modified polyimide resin, etc.) described above, with a mixed solution in which the molar ratio of (-NH2 groups / -OH groups) is within the above range, it is considered that the average surface roughness Ra of the surface on the electroless copper plating layer 2 side of the resin film 1 can be set to 1 nm to 150 nm. Therefore, when wiring conductors are formed on a circuit board by the electroless copper plating layer, transmission loss due to the skin effect is suppressed, and desirable transmission characteristics can be achieved. In addition, if the average surface roughness Ra of the surface on the electroless copper plating layer 2 side is within the range of 1 nm to 150 nm, adhesion between the resin film 1 and the electroless copper plating layer 2 can also be ensured. Therefore, the inventors have conceived of achieving the objective of the present invention by going through the first surface modification step described above.

[0060] Furthermore, by setting the molar ratio of (-NH2 groups / -OH groups) in the mixed solution within the above range during the first surface modification step, it is possible to impart more hydroxyl groups than carboxyl groups to the surface of the resin film 1.

[0061] In the first surface modification step, known methods can be appropriately applied to bring the mixture of alkaline aqueous solution and amino alcohol into contact with the surface of the resin film 1. For example, methods such as immersing the resin film 1 in the mixture or spraying the mixture onto the resin film 1 with a sprayer are available. The method is not limited to these, but also applies to bringing carboxyl groups onto the surface of the resin film 1. and / or Any method that can impart a hydroxyl group is acceptable, other than the method described above.

[0062] Furthermore, in the first surface modification step, the deposition properties and adhesion of the plating can be improved by adjusting the contact angle of the film surface. In particular, when the resin film 1 is a liquid crystal polymer, the contact angle at the plating layer side interface in contact with the electroless copper plating layer 2 is preferably 30° or less. In particular, when the resin film 1 is a modified polyimide (MPI), the contact angle at the plating layer side interface in contact with the electroless copper plating layer 2 is preferably 45° or less.

[0063] Next, the second surface modification step (step 2) of this embodiment will be described. In this embodiment, the second surface modification step is preferably performed after the first surface modification step described above. The second surface modification step involves adding carboxyl groups to the surface of the resin film 1 in the first surface modification step. and / or This step involves imparting an electric charge after imparting hydroxyl groups. This is preferable because the imparting of the electric charge can improve the adhesion between the resin film 1 and the electroless copper plating layer 2.

[0064] In other words, as described above, for the formation of the electroless copper plating layer 2, it is preferable that metallic palladium, which serves as a nucleus for plating growth, is present on the resin film 1. Furthermore, for this metallic palladium to adhere firmly to the resin film 1, it is preferable that the surface of the resin film 1 has at least a negative charge.

[0065] Preferably, the second surface modification step of this embodiment further includes a step of applying a positive charge to the surface of the resin film 1 and a step of applying a negative charge to the positively charged surface. By going through these steps, it is possible to reliably attach a negative charge to the surface of the resin film 1, which is preferable from the viewpoint of the attachment of the metallic palladium and the adhesion of the electroless copper plating layer 2.

[0066] Next, the second surface modification step (step 2) of this embodiment will be described. In this embodiment, the second surface modification step is preferably performed after the first surface modification step described above. The second surface modification step involves adding carboxyl groups to the surface of the resin film 1 in the first surface modification step. and / or This step involves imparting an electric charge after imparting hydroxyl groups. This is preferable because the imparting of the electric charge can improve the adhesion between the resin film 1 and the electroless copper plating layer 2.

[0067] Similarly, in the process of adsorbing negative charges onto the surface of the resin film 1, methods such as immersion in a known anionic surfactant or spray application can also be applied. Furthermore, the second surface modification step in this embodiment is preferably carried out by a wet method, as described above. Performing the process wet is suitable for mass production using reel-to-reel methods, and also offers the advantage of lower costs.

[0068] Next, the catalyst adsorption step (step 3) in the manufacturing method of this embodiment will be described. The catalyst adsorption step in this embodiment is a step in which a catalyst is further adsorbed onto the surface of the resin film 1, which has been given at least a negative charge on its surface by the second surface modification step described above.

[0069] In the catalyst adsorption process, further adsorption of the catalyst onto the surface of the resin film 1 can be carried out, for example, by contacting a known catalyst solution with the surface of the resin film 1 using a known method. The catalyst can be Cu, Ni, Pd, Ag, etc. Known catalyst solutions include, but are not limited to, tin-palladium or palladium colloidal catalyst solutions.

[0070] In the catalyst adsorption process, the amount of catalyst to be applied to the resin film 1 is 15 μg / dm³ of metallic palladium. 2The following is preferable. Regarding the lower limit of the catalyst, the lower the value, the better, considering etching during circuit formation, but it needs to be applied to the extent that the electroless copper plating layer is formed well, which is 1 μg / dm 2 It is preferable that there be more than the above. If the amount of metallic palladium applied to the resin film 1 exceeds the above value, it is undesirable because it may reduce the insulation reliability between circuits when used as a flexible circuit board. The amount of metallic palladium can be obtained by known measurement methods. For example, it can be obtained by peeling off only the copper from the resin film 1, dissolving the palladium residue on the resin film 1 with nitric acid, and measuring the amount of residue by ICP.

[0071] Next, the electroless copper plating process (step 4) in the manufacturing method of this embodiment will be described. The electroless copper plating process is preferably carried out after the catalyst adsorption process described above. Hereinafter, an example of the conditions for electroless plating in this embodiment is given below. [Example of electroless copper plating conditions] Bath composition: Copper sulfate 5~10g / L Nickel sulfate 0.5~1.0 g / L Rochelle salt 10-30g / L Sodium hydroxide 3-8 g / L pH: 7-13 Bath temperature: 29~35℃

[0072] The immersion time of the resin film 1 in the plating bath can be appropriately determined so that the thickness of the electroless copper plating layer 2 is 0.1 to 1.0 μm.

[0073] Furthermore, the plating layer formed in this electroless copper plating process is not limited to plating of pure Cu, but may also be a copper alloy plating. For example, it may form a Cu-Ni alloy, Cu-Zn alloy, Cu-Sn alloy, etc. In this case, any known plating bath can be appropriately applied.

[0074] In the manufacturing method of this embodiment, it is preferable to have a heating step (step 5) in which, after forming the electroless copper plating layer 2 on the resin film 1, the entire copper-clad laminate on which the electroless copper plating layer is formed is heated for purposes such as releasing internal stress in the electroless copper plating layer or causing a transformation of the structure. The heating temperature for stress relaxation is preferably 100 to 200°C, and more preferably 120 to 150°C. The heating time for stress relaxation is preferably 5 to 60 minutes, and more preferably 10 to 30 minutes. Furthermore, the heating temperature for tissue transformation is preferably 150 to 350°C, and more preferably 150 to 300°C. The heating time for tissue transformation is preferably 5 to 180 minutes, and more preferably 10 to 30 minutes. Furthermore, the heating atmosphere may be, for example, air, or an inert gas atmosphere such as nitrogen. By performing this heating process, it is possible to suppress the peeling of the electroless copper plating layer 2 from the resin film 1 and to ensure adhesion between the electroless copper plating layer 2 and the resin film 1. Furthermore, as the crystallites of the electroless copper plating layer 2 grow, the adhesion between the copper plating layer (electroless copper plating layer 2 and electrolytic copper plating layer 4) after the electrolytic copper plating layer 4 described later is laminated and the resin film 1 can be improved.

[0075] In addition, the method for manufacturing the copper-clad laminate of this embodiment may include an electrolytic copper plating step in which an electrolytic copper plating layer 4 is formed by an electrolytic plating step after the formation of the electroless copper plating layer 2 by an electroless copper plating step. As the electrolytic copper plating step, known copper sulfate baths or copper pyrophosphate baths can be applied, and the electrolytic plating conditions (pH, temperature, current density, immersion time, etc.) can be appropriately selected based on the thickness of the electrolytic plating layer, etc. The copper-clad laminate 20 in this embodiment is manufactured through the above process.

[0076] In the manufacturing method of this embodiment, step 5 described above may be performed by heating (annealing) the entire copper-clad laminate after the electrolytic copper plating layer 4 has been formed on the resin film 1 (i.e., after the electroless copper plating layer and the electrolytic copper plating bath have been formed). In other words, in this embodiment, the heating step described above may be performed after the electrolytic copper plating layer 4 has been formed on the resin film 1, or the heating step may be performed after the electroless copper plating layer 2 has been formed on the resin film 1 and before the electrolytic copper plating layer 4 has been formed, in which case the entire copper-clad laminate may be heated. When step 5 described above is performed before the formation of the electrolytic copper plating layer 4, it is more preferable to perform it before the resist patterning step described later.

[0077] <Flexible Circuit Board> Next, the flexible circuit board of this embodiment will be described. In this embodiment, the flexible circuit board is preferably a flexible circuit board in which a circuit is formed by the electroless copper plating layer 2 of the copper-clad laminate 10 described above. As described above, in this embodiment, the copper-clad laminate 10 has a surface roughness Ra between the resin film 1 and the electroless copper plating layer 2 that is below a predetermined value, making it possible to suppress transmission loss as a flexible circuit board. Furthermore, since it is possible to improve the adhesion between the resin film 1 and the electroless copper plating layer 2, it is preferable that a semi-additive method is used, as it enables the formation of fine circuit patterns.

[0078] More specifically, in the case of the SAP method or MSAP method, the manufacturing method of the flexible circuit board in this embodiment involves, after going through steps 1 to 5 described above (see also Figure 4), a known resist patterning step of applying and patterning a resist on the electroless plating layer 2 is performed, and then the electrolytic copper plating step described above is performed to form an electrolytic plating layer 4 between the patterned resists. Furthermore, the method for forming the flexible circuit board in this embodiment is not limited to the semi-additive method described above, but other known methods such as the fully additive method and the subtractive method can also be applied. [Examples]

[0079] Next, the present invention will be described in more detail with reference to examples.

[0080] <Example 1> First, a liquid crystal polymer film (Vecter CTQLCP, manufactured by Kuraray Co., Ltd., thickness: 50 μm) was prepared as resin film 1. In terms of electrical properties, the relative permittivity at 10 GHz was 3.3 and the dielectric loss tangent at 10 GHz was 0.002.

[0081] Next, as a first surface modification step, both sides of the prepared resin film 1 were immersed for 5 minutes in a mixture of potassium hydroxide aqueous solution and monoethanolamine to introduce carboxyl groups and / or hydroxyl groups to both surfaces, followed by immersion rinsing with water. The temperature of the mixture used was 30°C, and the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) was 2.29. The peak intensity of mass 121 in TOF-SIMS was 1000.

[0082] Next, as a second surface modification step, both sides of the resin film 1 were immersed in an aqueous solution of 10 g / L of cationic surfactant for 2 minutes to adsorb positive charges. After rinsing with water, it was immersed in an aqueous solution of 3 g / L of anionic surfactant for 1 minute. In this way, positive charges were adsorbed, followed by negative charges. Furthermore, as part of the catalytic adsorption and electroless copper plating processes, the material was immersed for 5 minutes in an aqueous solution of palladium chloride (PdCl2) (2 g / l, pH 12, 40°C) as a plating catalyst, followed by immersion rinsing with water. In addition, it was immersed for 5 minutes in an aqueous solution (25°C) to which 1 g / L of dimethylamine borane (DMAB) and 6 g / L of boric acid were added as catalytic activators (reducing agents), followed by immersion rinsing with water. Subsequently, an electroless Cu-Ni plating layer of 0.3 μm thickness was formed using an electroless plating bath. The electroless plating conditions were as follows. The Ni content of the obtained electroless Cu-Ni plating layer was determined to be 1.18 wt% using the plasma emission spectrometer (ICP) described above.

[0083] [Electroless plating conditions] Bath composition: Copper sulfate 7.5g / L Nickel sulfate 0.7 g / L Rochelle salt 20g / L Sodium hydroxide 5g / L pH:9 Bath temperature: 32℃

[0084] Subsequently, an electrolytic copper plating layer with a thickness of 18 μm was formed on top of the electroless Cu-Ni plating layer in the copper-clad laminate using an electrolytic plating bath. The electrolytic copper plating conditions were as follows. Bath composition: Copper sulfate hexahydrate 200g / L Sulfuric acid 50g / L Chloride ions 50 ppm Polishing agent 5ml / L (Okuno Pharmaceutical Co., Ltd. additive Toplutiner) Bath temperature: 20~25℃ pH: 1 or less Current density: 2~3A / dm 2

[0085] [Heat (annealing) treatment] In this embodiment, after forming an electroless copper plating layer, a first heat treatment was performed under the following heating conditions, and after forming an electrolytic copper plating layer, a second heat treatment was performed under the following heating conditions. <Heating conditions in the first heat treatment> Heating temperature: 150℃ Heating time: 10 minutes Heating atmosphere: In the air <Heating conditions in the second heat treatment> Heating temperature: 230℃ Heating time: 10 minutes Heating atmosphere: In the air By going through the above steps, the copper-clad laminate 10 in Example 1 was obtained.

[0086] [Evaluation] <TOF-SIMS and ESCA> In order to confirm the presence of carboxyl groups and / or hydroxyl groups at the interface between the resin film 1 and the electroless copper plating layer 2, the surface state was confirmed. First, for the obtained copper-clad laminate 10, without heat treatment, the electroless copper plating layer 2 was immersed in a 42 Baumé FeCl3 solution (50 °C), and the electroless copper plating layer 2 was peeled off by taking it out at the timing when it was visually confirmed that the electroless copper plating layer 2 had disappeared, exposing the resin film. The exposed surface of the resin film was cut into a size of 20 mm × 20 mm to obtain a measurement sample. This measurement sample was measured with an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., JPS-9200, X-ray source: Mg, analysis area: φ3 mm) to obtain a C1s spectrum. Then, the intensity of the peak derived from the carboxyl group (COO(H) bond) appearing at a binding energy of 288.8 eV and the intensity of the peak derived from the C-C bond appearing at a binding energy of 284.7 eV were calculated.

[0087] According to the measurement results by the above ESCA, the presence of carboxyl groups could not be confirmed. Next, the surface state of the above measurement sample was confirmed by TOF-SIMS.

[0088] The surface of the above measurement sample was analyzed by TOF-SIMS TRIFT-II (manufactured by ULVAC-PHI, Inc.). Also, an untreated resin film sample was used as a control. The measurement conditions are as follows. Primary ion: 69 Ga Acceleration voltage: 15 kV Measurement range: 100 μm × 100 μm Mass range: 0.5 - 300 (m / z)

[0089] The obtained results were analyzed using the analysis software Win Cadence (Physical Electronics). In the TOF-SIMS spectrum, a peak characteristic of mass 121 was observed only from the surface of the sample from which the electroless copper plating had been removed. No peak characteristic of mass 121 was observed from the untreated sample surface. Based on the measurement results from ESCA, the presence of carboxyl groups could not be confirmed, leading to the conclusion that C8H9O(-CH-CH3-C6H4-OH) groups were introduced after the first and second surface modification processes.

[0090] <Ra after plating layer removal> The electroless copper plating layer 2 was peeled off from the obtained copper-clad laminate 10 (thickness of the electroless copper plating layer: 0.3 μm (for Examples 1-5, Example 11, and Comparative Examples 1-8) or 0.2 μm (for Examples 6-10 and Comparative Example 9)) using the FeCl3 solution in the same manner as described above, exposing the resin film. The surface roughness (Ra) of the exposed resin film was measured using a laser microscope (Olympus OLS3500) in AFM mode, with a field of view of 5 μm × 5 μm. The obtained values ​​are shown in Table 2.

[0091] <Contact angle> The obtained copper-clad laminate 10 was stripped of its electroless copper plating layer 2 using an FeCl3 solution in the same manner as described above, exposing the resin film. The exposed resin film surface was cut into 20 mm x 20 mm sections to serve as a measurement sample. 2.0 μL of pure water was dropped onto the surface of this sample, and the contact angle was measured using a contact angle meter (DropMaster, manufactured by Kyowa Interface Science Co., Ltd.). The contact angle of the untreated resin surface used in Example 1 was 65°, and the contact angle of the untreated resin surface used in Example 5 was 58°.

[0092] <Tape peel strength> A tape peel test was performed on the obtained copper-clad laminate 10 (thickness of the electroless copper plating layer: 0.3 μm (for Examples 1-5, Example 11, and Comparative Examples 1-8) or 0.2 μm (for Examples 6-10, and Comparative Example 9)) by applying adhesive tape (manufactured by Nichiban Co., Ltd.) to the surface of the electroless copper plating layer 2 and then peeling it off. If peeling of the electroless copper plating layer 2 was not observed visually, the evaluation result was marked as ○. The results are shown in Table 2.

[0093] <90° Peel Strength> A copper-clad laminate 20, which had undergone a second heat treatment at 230°C for 10 minutes after electrolytic copper plating was formed, was cut into 40mm x 40mm specimens, and these specimens were attached to an aluminum plate with polyimide tape. The 90° peel strength was measured as the adhesive strength between the resin film and the electroless copper plating layer as follows.

[0094] Specifically, on each test specimen, an electrolytic copper plating layer was formed, and strip-shaped cuts were made in the copper-plated surface at 5 mm intervals using a cutter. Then, the ends of the strips were forcibly peeled off to create a starting point for peeling, resulting in a peeled resin film and a copper-plated portion. Next, the peeled resin film and copper-plated layer were clamped in a Tensilon chuck, and the 90° peel strength was measured using an autograph. The 90° peel strength was converted to N / cm (width). These results are shown in Table 2.

[0095] <Plating properties (visual inspection)> The obtained copper-clad laminates were visually inspected for the appearance of the electroless copper plating layer, and those without peeling or blistering were marked with a circle (○) and shown in Table 2.

[0096] <Measurement of Ni content in electroless copper plating layer 2> After forming the electroless copper plating layer 2 under the conditions shown in Table 1, a 2cm x 2cm section was immersed in 30% nitric acid (room temperature) to dissolve the electroless copper plating layer 2. The weight of Cu (copper) and Ni (nickel) in the resulting solution was measured using a plasma atomic emission spectrometer (ICP) (Shimadzu Corporation ICPE-9820), and the Ni content of the electroless copper plating layer 2 was calculated by dividing the Ni weight by the Cu weight and Ni weight.

[0097] <Overall Rating> Based on a comprehensive evaluation of the above criteria, items that are practically usable are marked with ○, and those that are impractical are marked with ×, as shown in Table 2.

[0098] <Example 2> The procedure was carried out in the same manner as in Example 1, except that the temperature of the mixed solution in the first surface modification step was changed to the temperature shown in Table 1. The results are shown in Tables 1 and 2.

[0099] <Example 3> The procedure was carried out in the same manner as in Example 1, except that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) in the mixed solution during the first surface modification step was changed to the values ​​shown in Table 1. The results are shown in Tables 1 and 2.

[0100] <Example 4> The procedure was carried out in the same manner as in Example 1, except that the temperature of the mixed solution in the first surface modification step was changed to the temperature shown in Table 1. The results are shown in Tables 1 and 2.

[0101] <Example 5> As resin film 1, a modified polyimide (MPI) resin (SKC Kolon PI FS-L, thickness: 50 μm) was prepared. In terms of electrical properties, the relative permittivity at 10 GHz was 3.4 and the dielectric loss tangent at 10 GHz was 0.0035.

[0102] Next, as a first surface modification step, both sides of the prepared resin film 1 were immersed for 5 minutes in a mixture of aqueous sodium hydroxide solution and monoethanolamine to introduce carboxyl groups and / or hydroxyl groups to both surfaces, followed by immersion washing. The temperature of the mixture used at this time was 40°C, and the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) was 0.19.

[0103] Next, as a second surface modification step, positive charges were adsorbed onto both sides of the resin film 1 using the same method as in Example 1, and then negative charges were adsorbed on both sides. Furthermore, as part of the catalytic adsorption and electroless copper plating processes, the material was immersed for 5 minutes in an aqueous solution of palladium chloride (PdCl2) (2 g / l, pH 12, 40°C) as a plating catalyst, followed by immersion rinsing with water. In addition, it was immersed for 5 minutes in an aqueous solution (25°C) to which 1 g / L of dimethylamine borane (DMAB) and 6 g / L of boric acid were added as catalytic activators (reducing agents), followed by immersion rinsing with water.

[0104] Subsequently, an electroless Cu-Ni plating layer of 0.3 μm thickness was formed using an electroless plating bath. The electroless plating conditions were as follows. At this time, the Ni content in the electroless Cu-Ni plating layer was 1.18 wt%. [Electroless plating conditions] Bath composition: Copper sulfate 7.5g / L Nickel sulfate 0.7 g / L Rochelle salt 20g / L Sodium hydroxide 5g / L pH: 12.5 Temperature: 32℃ Processing time: 10 minutes

[0105] Subsequently, using the same method as in Example 1, an electrolytic copper plating layer with a thickness of 18 μm was further formed on the electroless Cu-Ni plating layer of the copper-clad laminate using an electrolytic plating bath.

[0106] [Heat (annealing) treatment] In Example 5, after forming an electroless copper plating layer, a first heat treatment was performed using a dry oven (DY300, manufactured by Yamato Scientific Co., Ltd.) under the following heating conditions. The second heat treatment after electroplating described above was omitted. <Heating conditions in the first heat treatment> Heating temperature: 150℃ Heating time: 60 minutes Heating atmosphere: In the air By following the above steps, the copper-clad laminate 10 in Example 5 was obtained. In this way, the copper-clad laminate 10 of Example 5 was obtained, and this copper-clad laminate was evaluated in the same manner as in Example 1. The results of Example 5 are shown in Tables 1 and 2.

[0107] <Example 6> A copper-clad laminate was obtained in the same manner as in Example 2, except that the plating thickness of the electroless Cu-Ni plating layer was set to 0.2 μm, and annealing (heat treatment) was performed in an inert (nitrogen) gas at 280°C for 180 minutes using a vacuum drying apparatus (DQ-46P-LP manufactured by Sato Vacuum Co., Ltd.), and this annealing (heat treatment) was performed after electroless copper plating and before electrolytic copper plating. No heat treatment was performed after electrolytic copper plating. Then, similar to Example 1, the copper-clad laminate of Example 6 was evaluated. The results of Example 6 are shown in Tables 1 and 2.

[0108] <Example 7> A copper-clad laminate was obtained in the same manner as in Example 6, except that the nickel sulfate content in the electroless Cu-Ni plating bath was set to 0.32 g / L. The Ni content in the obtained electroless Cu-Ni plating layer was 0.74 wt%. The copper-clad laminate of Example 7 was then evaluated in the same manner as in Example 1. The results of Example 7 are shown in Tables 1 and 2.

[0109] <Example 8> A copper-clad laminate was obtained in the same manner as in Example 6, except that the nickel sulfate content in the electroless Cu-Ni plating bath was set to 0.13 g / L. The Ni content in the obtained electroless Cu-Ni plating layer was 0.41 wt%. The copper-clad laminate of Example 8 was then evaluated in the same manner as in Example 1. The results of Example 8 are shown in Tables 1 and 2.

[0110] <Example 9> A copper-clad laminate was obtained in the same manner as in Example 6, except that the nickel sulfate content in the electroless Cu-Ni plating bath was set to 0.065 g / L. The Ni content in the obtained electroless Cu-Ni plating layer was 0.18 wt%. The copper-clad laminate of Example 9 was then evaluated in the same manner as in Example 1. The results of Example 9 are shown in Tables 1 and 2.

[0111] <Example 10> A copper-clad laminate was obtained in the same manner as in Example 6, except that the nickel sulfate content in the electroless Cu-Ni plating bath was set to 0.013 g / L. The Ni content in the obtained electroless Cu-Ni plating layer was 0.14 wt%. The copper-clad laminate of Example 10 was then evaluated in the same manner as in Example 1. The results of Example 10 are shown in Tables 1 and 2.

[0112] <Example 11> A copper-clad laminate was obtained in the same manner as in Example 6, except that the nickel sulfate content in the electroless Cu-Ni plating bath was set to 0.0065 g / L and the thickness of the electroless Cu-Ni plating layer was set to 0.3 μm. The Ni content in the obtained electroless Cu-Ni plating layer was 0.09 wt%. The copper-clad laminate of Example 11 was then evaluated in the same manner as in Example 1. The results of Example 11 are shown in Tables 1 and 2.

[0113] <Comparative Example 1> First, a polyimide film (Kapton, manufactured by Toray DuPont, thickness: 50 μm) was prepared as resin film 1. Its electrical properties included a relative permittivity of 3.4 at 1 MHz and a dielectric loss tangent of 0.0024 at 1 MHz. Next, the prepared resin film 1 was immersed in a potassium hydroxide aqueous solution (200 g / L) at 30°C for 10 minutes and then rinsed with water.

[0114] In the catalyst adsorption step and the electroless plating step, the plating catalyst was immersed in an aqueous solution of palladium chloride (PdCl2), then immersed in an aqueous solution of dimethylamine borane (DMAB) as a catalyst activator (reducing agent), and after rinsing with water, a 0.5 μm electroless nickel-phosphorus plating layer was formed using an electroless nickel-phosphorus plating bath. The electroless plating conditions were as follows. The conditions for the catalyst adsorption step were the same as in Example 1. Furthermore, the subsequent electrolytic copper plating and annealing (heat treatment) were the same as in Example 1.

[0115] [Electroless plating conditions] Bath composition: Nickel sulfate 27g / L Sodium hypophosphite 30g / L Malic acid 30g / L Lactic acid 15g / L Stabilizer 0.6 ppm pH: 4.5 Temperature: 89℃ Processing time: 5 minutes

[0116] <Comparative Example 2> The procedure was the same as in Comparative Example 1, except that the liquid crystal polymer film used in Example 1 was used as the resin film. The results are shown in Tables 1 and 2.

[0117] <Comparative Example 3> The procedure was the same as in Comparative Example 2, except that the electroless plating layer was replaced with an electroless copper plating layer. [Electroless plating conditions] Bath composition: Copper sulfate 6g / L Rochelle salt 20g / L Formalin 5g / L pH: 11.5 Temperature: 30℃ Processing time: 10 minutes

[0118] <Comparative Example 4> The procedure was the same as in Comparative Example 3, except that the second surface modification step was performed under the same conditions as in Example 1.

[0119] <Comparative Example 5> The procedure was carried out in the same manner as in Example 1, except that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) of the mixed solution used as the first surface modification step was set to 0.23.

[0120] <Comparative Example 6> The procedure was carried out in the same manner as in Example 1, except that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) of the mixed solution used as the first surface modification step was set to 0.45.

[0121] <Comparative Example 7> The procedure was carried out in the same manner as in Example 1, except that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) of the mixed solution used as the first surface modification step was set to 0.92.

[0122] <Comparative Example 8> The procedure was carried out in the same manner as in Example 1, except that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) of the mixed solution used as the first surface modification step was set to 1.83.

[0123] <Comparative Example 9> The procedure for Comparative Example 9 was the same as in Example 2, except that the electroless plating formed on the resin film was copper plating (Ni content 0), the same plating solution as in Comparative Example 3 was used, and the plating thickness of this electroless Cu plating was set to 0.2 μm, and the same apparatus as in Example 6 was used for annealing (heat treatment) in an inert (nitrogen) gas at 280°C for 180 minutes, and this annealing (heat treatment) was performed after the electroless copper plating and before the electrolytic copper plating. In this Comparative Example 9, since the electroless Cu plating layer was locally unplated, electrolytic Cu plating was performed only on the areas where the electroless Cu plating layer was formed, and evaluations other than the measurement of peel strength were performed.

[0124] [Table 1]

[0125] [Table 2] [Industrial applicability]

[0126] The copper-clad laminate of the present invention has a surface roughness Ra between the resin film and the electroless copper plating layer that is below a predetermined value, which makes it possible to suppress transmission loss as a flexible circuit board and provide high transmission characteristics at high frequencies. Furthermore, since it is possible to improve the adhesion between the resin film and the electroless copper plating layer, it is possible to form fine circuit patterns even when a fully additive method or a semi-additive method is used as the circuit formation method. The copper-clad laminate of the present invention is clearly suitable for use in wiring boards and the like where a multilayer structure of fine wiring is required. [Explanation of Symbols]

[0127] 1. Resin film 2. Electroless copper plating layer 4. Electrolytic plating layer 10 Copper-clad laminate 20 Copper-clad laminate

Claims

1. A low-dielectric resin film having a relative permittivity of 3.5 or less and a dielectric loss tangent of 0.008 or less at a frequency of 10 GHz, The low dielectric resin film comprises an electroless copper plating layer laminated on at least one surface, The electroless copper plating layer is an electroless Cu-Ni alloy plating layer, The average surface roughness Ra at the interface of the low-dielectric resin film that contacts the electroless Cu-Ni alloy plating layer is 1 to 50 nm, and the 90° peel strength between the resin film and the electroless Cu-Ni alloy plating layer is 4.2 N / cm or more. The aforementioned plating layer interface is provided with a functional group specified by the following structural formula 1, A copper-clad laminate characterized in that the peak intensity of mass number 121 in the TOF-SIMS spectrum of the interface on the plating layer side is 1000 or more. 【Chemistry 1】

2. The copper-clad laminate according to claim 1, wherein the resin film is any of polyimide, modified polyimide, liquid crystal polymer, fluororesin, or a mixture thereof.

3. The copper-clad laminate according to claim 1, wherein the thickness of the electroless Cu-Ni alloy plating layer is in the range of 0.1 to 1.0 μm.

4. The copper-clad laminate according to claim 1, wherein a metal consisting of Cu, Ni, Pd, or Ag is present at the interface of the resin film on the electroless Cu-Ni alloy plating layer side.

5. The copper-clad laminate according to claim 1, further comprising a protective layer formed on the electroless Cu-Ni alloy plating layer.

6. The copper-clad laminate according to claim 1, wherein the electroless Cu-Ni alloy plating layer is formed on both sides of the resin film, and the resin film has through holes, and at least a portion of the electroless Cu-Ni alloy plating layer is formed on the inner walls of the through holes.

7. A flexible circuit board having a circuit formed on it using a copper-clad laminate as described in any one of claims 1 to 6.

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