Copper clad laminate and method for manufacturing the same

Abstract

To provide a copper clad laminate and a method for manufacturing the same that enables high adhesion between low-dielectric resin film and copper plating layer and good volume resistivity while suppressing transmission loss when applied to flexible circuit boards.SOLUTION: A copper clad laminate according to the present invention includes: a low dielectric resin film with 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, the weighted average size of crystallites in the electroless copper plating layer is 25 to 300 nm, and the adhesion strength between the resin film and the electroless copper plating layer is 4.2 N / cm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a copper clad laminate for a flexible circuit board mounted on a communication device or the like, a method for producing the same, and a flexible circuit board made from the copper clad laminate. [Background technology]

[0002] In recent years, electronic devices have become significantly smaller and more powerful, largely due to the development of communication devices that use radio waves, such as mobile phones and wireless LANs. In particular, with the recent increase in the volume of information, exemplified by big data generated by IoT, communication signals between electronic devices are becoming increasingly high-frequency, and the circuit boards used in such communication devices require materials with low transmission loss (dielectric loss) in the high-frequency range.

[0003] It is known that the dielectric loss that occurs in this circuit board is proportional to the product of three elements: the signal frequency, the square root of the dielectric constant of the board material, and the dielectric loss tangent. Therefore, to obtain the excellent dielectric properties described above, a material with as low a dielectric constant and dielectric loss tangent as possible is required.

[0004] In such circuit boards, the circuits are generally formed of metal such as copper. The copper layer in the circuit board is formed by, for example, the lamination method disclosed in Patent Document 1, the casting method disclosed in Patent Document 2, or the plating method disclosed in Patent Document 3. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6202905 [Patent Document 2] Patent No. 5186266 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-256443 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, reducing transmission loss in high-frequency communications has become an important development factor in recent years, and resin films with low transmission loss (hereinafter also referred to as "low dielectric films" or "low dielectric resin films") are beginning to be used as base materials for flexible circuit boards. Such flexible circuit boards (hereinafter also referred to as "FPCs") are manufactured by forming a conductive film such as copper on a low-dielectric film using methods such as sputtering or plating. When manufacturing FPCs using the sputtering method, the manufacturing process becomes complicated, leaving many issues unresolved in terms of productivity and cost.

[0007] In contrast, the plating method disclosed in Patent Document 3 ensures relatively good adhesion between the copper layer and a resin film with a high dielectric constant. On the other hand, when copper plating is applied as a conductive coating as in Patent Document 3, electroless copper plating is used before electrolytic copper plating to form a plating seed layer for subsequent electroplating. As mentioned above, excellent conductive properties are required for modern FPCs, but there are no examples that focus on the relationship between these electrolytic copper plating layers and electroless copper plating layers, so it can be said that there is significant room for improvement. Furthermore, semi-additive methods (SAP, MSAP) are attracting attention as an alternative to subtractive methods for manufacturing FPCs, but current plating methods have issues with the resist removal process, and there is a demand for a method for forming conductive coatings that can actually be applied to such new manufacturing methods.

[0008] The present invention aims to solve the above-mentioned problems by way of example, and aims to provide a copper clad laminate and a method for producing the same that can achieve high adhesion between a low dielectric resin film and a copper plating layer while suppressing transmission loss when applied to a flexible circuit board. Another aim is to provide a high-density flexible circuit board, etc., in order to respond to the trend toward higher density flexible circuit boards. [Means for solving the problem]

[0009] Furthermore, in order to solve the above-mentioned problems, a method for producing a copper clad laminate according to one embodiment of the present invention comprises the steps of: 1 ) A method for producing a copper clad laminate by forming an electroless copper plating layer on a low dielectric resin film having a relative dielectric constant of 3.5 or less and a dielectric loss tangent of 0.008 or less at a frequency of 10 GHz, the method comprising: an electroless copper plating step of forming an electroless copper plating layer on the surface of the low dielectric resin film; and a heating step of heating the copper clad laminate on which the electroless copper plating layer has been formed so that the weighted average size of the crystallites in the electroless copper plating layer is 25 to 300 nm.

[0010] In addition, as mentioned above ( 1 In the method for producing a copper clad laminate described in ( 2 ) In the heating step, it is preferable that the copper clad laminate is heated under one of the following heating conditions: (i) in the atmosphere at 150 to 200°C for 10 to 180 minutes, and (ii) in an inert gas at 150 to 350°C for 5 to 180 minutes.

[0011] Also, as mentioned above ( 1 ) or ( 2 In the method for producing a copper clad laminate described in ( 3 ) The method preferably further comprises an electrolytic copper plating step of forming an electrolytic copper plating layer on the electroless copper plating layer, and the heating step is carried out before a resist patterning step on the electroless copper plating layer.

[0012] Also, as mentioned above ( 1 )~( 3 In the method for producing a copper clad laminate according to any one of ( 4) It is preferable that the method further includes, before the electroless copper plating step, a first surface modification step of imparting carboxyl groups and / or hydroxyl groups to the surface of the low dielectric resin film, a second surface modification step of imparting an electric charge to the surface to which the carboxyl groups and / or hydroxyl groups have been imparted by a wet method, and a catalyst adsorption step of adsorbing a catalyst onto the surface to which the electric charge has been imparted, and the electroless copper plating layer is formed on the surface to which the catalyst has been adsorbed.

[0013] In order to solve the above-mentioned problems, a method for producing a flexible circuit board using a low dielectric resin film according to one embodiment of the present invention comprises the steps of: 5 a resist patterning step of applying a resist to the electroless copper plating layer and patterning the resist; and an electrolytic copper plating step of forming an electroless copper plating layer between the patterned resists. Contains low dielectric resin film and a heating step of heating the copper clad laminate. [Effects of the Invention]

[0014] According to the present invention, it is possible to suppress transmission loss while ensuring high adhesion without excessively roughening the interface between the low dielectric film and the electroless copper plating layer, making it possible to use the low dielectric film in circuit formation, such as forming a resist on the electroless copper plating layer.Furthermore, according to the present invention, it is possible to achieve good volume resistivity. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view showing a copper clad laminate 10 of the present embodiment. [Figure 2] 1 is a schematic diagram showing the state of the interface between a resin film 1 and an electroless copper plating layer in a copper clad laminate 10 of the present embodiment. [Figure 3] 2 is a schematic diagram showing a through-hole H in the copper clad laminate 10 of the present embodiment. FIG. [Figure 4] 1 is a schematic cross-sectional view showing a copper clad laminate 20 of the present embodiment. [Figure 5] 1 is a flowchart showing a method for manufacturing a copper clad laminate 10, a copper clad laminate 20, and a flexible circuit board according to the present embodiment. [Figure 6] 1A and 1B are schematic diagrams showing a flexible circuit board 100 having metal wiring formed on a resin film 1 by a copper clad laminate 10, and a laminated flexible circuit board 200. FIG. [Figure 7] 1 is an image showing a part (an example of metal wiring) of a flexible circuit board obtained in an example, as an example. [Figure 8] As an example, this is an image showing a part (an example of metal wiring) of a flexible circuit board obtained in a comparative example. [Figure 9] 1 is an image showing, as an example, a part (an example of metal wiring) of a four-layer flexible circuit board obtained in an example. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a copper clad laminate 10 of this embodiment will be described with reference to FIG. <Copper clad laminate> 1, the copper clad laminate 10 according to this embodiment has at least a resin film 1 serving as a substrate and an electroless copper plating layer 2 laminated on at least one surface of the resin film 1. As will be described later with reference to FIG. 4, the copper clad laminate of the present invention may have an electrolytic copper plating layer 3 formed on the electroless copper plating layer 2.

[0017] In this embodiment, it is preferable to use a so-called low dielectric resin film, which has excellent electrical properties in the high frequency range, as the resin film 1 serving as the substrate. Specifically, preferred low-dielectric resin films include films of known liquid crystal polymers, fluorine-based resins, polyimide resins, modified polyimide resins, epoxy resins, polytetrafluoroethylene resins, polyphenylene ether resins, and the like, which have lower dielectric loss. These resins may be monopolymers or copolymers. Furthermore, the resins may be used alone or as a composite in which multiple resins are blended.

[0018] Specifically, the electrical properties of the resin film 1 serving as the base material are preferably such that the relative dielectric constant 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 limitations on the thickness of the resin film 1, but in practice it is preferably 5 μm to 100 μm.

[0019] Next, the electroless copper plating layer 2 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. Note that 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, a full-additive method, or the like.

[0020] In this embodiment, the electroless copper plating layer 2 may be a plating of Cu alone, or a copper alloy plating containing a predetermined amount or more of copper. Examples of copper alloys include Cu-Ni alloys, Cu-Zn alloys, and Cu-Sn alloys. In this embodiment, such copper alloy plating is also included in the "copper plating."

[0021] When the electroless copper plating layer 2 is formed of a Cu-Ni alloy, the Ni content is 3 wt% or less, 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 a higher plating deposition rate than Cu, because this also suppresses internal stress in the plating layer, thereby suppressing blistering.

[0022] If the Ni content in the Cu-Ni alloy exceeds 3 wt%, magnetism may occur in the Cu circuit, increasing transmission loss and complicating etching when forming copper wiring, so the Ni content in the Cu-Ni alloy is preferably 3 wt% or less. If the Ni content in the Cu-Ni alloy falls below 0.01 wt%, plating deposition properties will deteriorate. The Ni content in the electroless copper plating layer 2 can be measured by known methods such as an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) analyzer.

[0023] In this embodiment, any known method may be used as the electroless copper plating method for forming the electroless copper plated layer 2, as long as it is possible to form an electroless copper plated 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.

[0024] If the thickness of the electroless copper plating layer 2 is less than 0.1 μm, it may not function as a seed layer when manufacturing a flexible circuit board by a semi-additive process, 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 a fine circuit pattern when manufacturing a flexible circuit board, which is undesirable.

[0025] The thickness of the electroless copper plating layer 2 is more preferably 0.1 μm to 0.8 μm, because, particularly in circuit formation by the SAP method, a shorter etching time (thinner thickness) enables the formation of a finer pattern with less impedance variation in the cross-sectional direction of the circuit.

[0026] The copper clad laminate 10 of this embodiment is characterized in that the resin film 1 has an average surface roughness Ra of 1 to 150 nm, preferably 20 to 150 nm, at the interface on the plating layer side that contacts the electroless copper plating layer 2. In particular, when the resin film 1 is a liquid crystal polymer, the average surface roughness Ra of the interface on the plating layer side that contacts the electroless copper plating layer 2 is desirably 20 to 150 nm. Furthermore, in particular, when the resin film 1 is a modified polyimide (MPI), the average surface roughness Ra of the interface on the plating layer side that contacts the electroless copper plating layer 2 is desirably 1 to 150 nm, more preferably 1 to 50 nm. The reasons for this are as follows:

[0027] That is, in the copper clad laminate of this embodiment, in order to be suitably applicable to high frequency circuit boards as described above, it is desired that the transmission characteristics at high frequencies of GHz or higher be high. It is generally known that, due to the skin effect, transmission signals tend to propagate along the conductor surface at higher frequencies, and that the rougher the conductor surface, the greater the transmission loss. Therefore, in this embodiment, in order to reduce the influence of the skin effect on transmission loss, it is preferable to reduce the average surface roughness Ra of the electroless copper plating layer 2 that forms the wiring conductor at the interface with the resin film 1.

[0028] On the other hand, it has been widely practiced to obtain an anchor effect by roughening the interface between the electroless copper plating layer 2 and the resin film 1 in order to ensure adhesion between the metal and the resin. Thus, in the copper clad laminate of this embodiment, there is a trade-off between the roughness (adhesion) and the transmission loss between the electroless copper plating layer 2 and the resin film 1. The present inventors have conducted extensive research to achieve both of the above-mentioned properties at a higher level, and as a result, have found that in this embodiment, it is preferable that the average surface roughness Ra of the resin film 1 at the plating layer side interface in contact with the electroless copper plating layer 2 be 1 nm to 150 nm.

[0029] As a result of continued investigations, the inventors have concluded that when the average surface roughness Ra is less than 1 nm, it is not possible to obtain favorable adhesion 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 a wiring conductor is formed on a circuit board using the electroless copper plating layer 2, favorable transmission characteristics at high frequencies may not be obtained due to transmission loss caused by the skin effect. Under these circumstances, in the present invention, roughening to about 300 nm is considered to be excessive roughening treatment.

[0030] In this embodiment, the object is to achieve both reduced roughness (reduced transmission loss) and good adhesion between the electroless copper plating layer 2 and the resin film 1 as described above. The specific adhesive strength between the electroless copper plating layer 2 and the resin film 1 is preferably 4.2 N / cm or more in practical use. Furthermore, the adhesive strength is more preferably 5.0 N / cm or more, and even more preferably 6.4 N / cm or more.

[0031] 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 characteristics be further provided. 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. That is, it is preferable that hydroxyl groups and / or carboxyl groups are provided at the interface on the side of the electroless copper plating layer 2 of the resin film 1. This is for the following reason.

[0032] 1, in the copper clad laminate 10 of this embodiment, when an electroless copper plating layer 2 is formed by electroless plating on at least one surface of a resin film 1, 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 may be produced using a palladium catalyst.

[0033] In this embodiment, by providing at least one of a hydroxyl group and a carboxyl group on the surface of the resin film 1, it becomes possible to strengthen the adsorption of metallic palladium onto the surface of the resin film 1. As a result, it becomes possible to improve the adhesion between the resin film 1 and the electroless copper plating layer 2.

[0034] The presence of hydroxyl groups and / or carboxyl groups at the interface between the resin film 1 and the electroless copper plating layer 2 can be confirmed by known surface analysis methods, such as Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (ESCA), and time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0035] In particular, in this embodiment, it is preferable that, at the interface between the resin film 1 and the electroless copper plating layer 2, the peak intensity at mass 121 on the side of the electroless copper plating layer 2 is 800 (0.12 amu bin) or more as a result of analysis by time-of-flight mass spectrometry (TOF-SIMS). That is, in this embodiment, it is preferable that, as a result of TOF-SIMS analysis, a functional group having a mass of 121 and containing a hydroxyl group and / or a carboxyl group is present at the interface between the resin film 1 and the electroless copper plating layer 2. The functional group having a mass of 121 is preferably represented by either structural formula 1 or structural formula 2 below, with structural formula 1 being particularly preferable.

[0036] <Structural formula 1> TIFF2025183255000002.tif64166

[0037] <Structural formula 2> TIFF2025183255000003.tif64166

[0038] The "hydroxyl and / or carboxyl-containing functional groups" provided at the interface between the resin film 1 and the electroless copper plating layer 2 are not limited to those described above. Furthermore, if a "hydroxyl-containing functional group" is provided, a "carboxyl-containing functional group" does not necessarily have to be provided. The reverse is also possible. Furthermore, both a "hydroxyl-containing functional group" and a "carboxyl-containing functional group" may be provided.

[0039] In particular, in this embodiment, it is preferable that more "hydroxyl-containing functional groups" than "carboxyl-containing functional groups" are provided at the interface between the resin film 1 and the electroless copper plating layer 2. Alternatively, it is preferable that "hydroxyl-containing functional groups" are provided but "carboxyl-containing functional groups" are not provided.

[0040] The copper clad laminate of this embodiment may have an electrolytic copper plating layer 3 further formed on the above-described electroless copper plating layer 2, as shown in Fig. 4 as copper clad laminate 20. That is, when a flexible circuit board is produced by a semi-additive method, it is possible to form an electrolytic copper plating layer 3 after forming a resist pattern using the electroless copper plating layer 2 as a seed layer. 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, and other known methods such as the full-additive method and the subtractive method can also be applied.

[0041] 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 therein as shown in Fig. 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 so 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 the copper clad laminate of this embodiment is used for flexible circuit board applications. The position, size, etc. of the through-holes H can be determined appropriately depending on the flexible circuit board to be manufactured, so detailed explanations will be omitted.

[0042] The copper clad laminate in this embodiment comprises the resin film 1 and the electroless copper plating layer 2 as described above, but if there is a time lag before the formation of the electroless copper plating layer 3, a known protective layer (not shown) for preventing oxidation of the electroless copper plating layer 2 may be further formed on the surface of the electroless copper plating layer 2 (the side opposite to the resin film 1). The protective layer for the electroless copper plating layer 2 is formed, for example, by performing an anti-rust treatment by a known method, with the aim of suppressing oxidation.

[0043] [Crystallite size in electroless copper plating layer 2] The electroless copper-plated layer 2 in the copper clad laminate of this embodiment is characterized in that the weighted average size of the crystallites (hereinafter also referred to as "first crystallites") is 25 to 300 nm. Note that "crystallite" refers to the largest group of crystal grains that can be regarded as a single crystal. In this case, it is preferable that the volume resistivity of the electroless copper-plated layer 2 is 7.0 μΩ cm or less. One method for controlling the weighted average crystallite size in the electroless copper plating layer 2 within the above range is to subject the electroless copper plating layer 2 formed on the resin film 1 to a heating (annealing) treatment under predetermined conditions. The heating (annealing) treatment of the electroless copper plating layer 2 is also characterized in that it is performed after the electroless copper plating layer 2 is formed and before the resist patterning described below is formed. Specific methods for the heating (annealing) treatment will be described later.

[0044] The reason why the weighted average size of the crystallites in the electroless copper plating layer 2 is set to 25 to 300 nm in this embodiment will be described in detail below. That is, when manufacturing FPCs using the SAP method described above, the target circuit is formed through resist patterning (resist formation (coating or laminating), exposure, and patterning), electrolytic copper plating, removal of the patterned resist, and etching of the electroless copper plating layer. Here, it is expected that the L / S (line and space) that make up the circuit pattern will have a narrower pitch to improve performance, and it is important to determine how precisely this circuit pattern can be formed.

[0045] In the current SAP method, an electroless copper plating layer 2 is formed as a seed plating layer, and then the circuit pattern is defined by a resist on the electroless copper plating layer 2, and then an electrolytic copper plating layer is formed. At this time, if the electrolytic copper plating layer is subjected to a heating (annealing) treatment for the purpose of releasing the internal stress of the electroless copper plating layer, the resist hardens due to this heat treatment, making it difficult to remove the resist later. On the other hand, since heat treatment cannot be performed after the electrolytic copper plating layer is formed as described above, there is a concern that the adhesion strength of the electrolytic copper plating is low and the copper plating pattern may peel off when the resist is removed.

[0046] In addition to the above issues, as high-frequency devices evolve, FPCs will also be required to have good high-frequency characteristics, and it is expected that a reduction in the volume resistivity of copper plating as a conductive coating will become essential. As a result of extensive research, the inventors have concluded that by performing the above-mentioned heating (annealing) treatment before the above-mentioned resist patterning process, the size of the crystallites in the electroless copper plating layer 2 can be controlled, thereby improving the volume resistivity of the electroless copper plating layer 2 while ensuring good adhesion between the entire conductive coating (electroless copper plating layer 2 and electrolytic copper plating layer 3) and the low dielectric resin film.

[0047] More specifically, after electroless copper plating layer 2 is formed on resin film 1, a heating (annealing) treatment is performed under any of the heating conditions described below, thereby growing the Cu crystals that were fine after electroless copper plating, and setting the weighted average crystallite size to 25 to 300 nm. Note that the weighted average crystallite size in electroless copper plating layer 2 in this embodiment is preferably 25 to 100 nm, and more preferably 25 to 65 nm. This reduces the difference in weighted average crystallite size between electroless copper plating layer 2 and electrolytic copper plating layer 3, improving the elongation properties in the planar direction of electroless copper plating layer 2 and enabling high peel strength to be maintained.

[0048] According to this embodiment, it is preferable that an electrolytic copper plating layer 3, as shown in Fig. 4, etc., is further formed on the above-described electroless copper plating layer 2. The electrolytic copper plating layer 3 is preferably formed by electrolytic plating.

[0049] The electrolytic copper plated layer 3 laminated on the electroless copper plated layer 2 preferably has a weighted average size of Cu crystallites (also referred to as "second crystallites") in the electrolytic copper plated layer of 40 to 300 nm. Furthermore, in the copper clad laminate of this embodiment, the ratio of the first crystallites to the second crystallites (second crystallites / first crystallites) is preferably 2.0 or less, more preferably 1.8 or less, which reduces the difference in size between the second crystallites and the first crystallites, thereby reducing lattice misfit and ensuring good adhesion strength. In this case, the volume resistivity of the electrolytic copper plating layer 3 is preferably 5.0 μΩ·cm or less.

[0050] The weighted average size of the crystallites in the electrolytic copper plating layer 3 is more preferably 40 to 100 nm, and even more preferably 40 to 80 nm. Furthermore, as long as the weighted average size of the crystallites of the electrolytic copper plating layer 3 is within this range, even when the ratio of the first crystallites to the second crystallites (second crystallites / first crystallites) is kept at 2.0 or less, transmission loss can be suppressed while ensuring high adhesion to the low dielectric film and achieving good volume resistivity.

[0051] <Calculation method for weighted average crystallite size> The size of the Cu crystallites (first and second crystallites) in this embodiment is determined from the peak half-width by X-ray diffraction using the following formula. X-ray diffraction measurement is performed, for example, using a known X-ray diffraction device. The crystallite size can be calculated by weighting the copper peaks appearing at 2θ = 43 to 46 degrees with respect to the planes defined by Miller indices ((111) plane, (200) plane, (220) plane, and (311) plane). Specific 2θ angles were set to 43.3 degrees for the (111) plane, 50.5 degrees for the (200) plane, 74.1 degrees for the (220) plane, and 90.0 degrees for the (311) plane.

[0052] D=K×λ / (β×cosθ) D: Crystallite diameter K: Scherrer constant (K = 0.94 is used) λ: wavelength of X-rays used β: Half-width of diffracted X-rays from crystallites θ: Bragg angle

[0053] After calculating the copper crystallite size in each orientation plane defined by the Miller indices as described above, the crystallite size (weighted average size) in the copper plating layer was calculated using a weighted average as follows: That is, to determine the weighted average size of the crystallites in this embodiment, the peak intensity of each orientation plane was first integrated, and the integrated value was divided by the number of orientation planes (four in this example) to obtain the orientation ratio. Next, the crystallite size in each orientation plane obtained by X-ray diffraction measurement was multiplied by the corresponding orientation rate calculated above, and the average value of the four crystallite sizes taking into account the obtained orientation rate was calculated as the "weighted average crystallite size."

[0054] <Method of manufacturing copper clad laminate> Next, a method for manufacturing the copper clad laminate 10 of this embodiment will be described with reference to FIG. The method for manufacturing the copper clad laminate 10 in this embodiment includes a first surface modification process (step 1) of adding carboxyl groups and / or hydroxyl groups to at least one surface of the resin film 1, a second surface modification process (step 2) of wet-type charge application to the surface to which the carboxyl groups and / or hydroxyl groups have been added, a catalyst adsorption process (step 3) of adsorbing a catalyst onto the charged surface, an electroless copper plating process (step 4) of forming an electroless copper plating layer 2 on the catalyst-adsorbed surface, and a heating (annealing) process (step 5) of heating the copper clad laminate on which the electroless copper plating layer has been formed. As will be described later, the second surface modification step in step 2 above is not essential and may be omitted as appropriate depending on the material of the resin film 1, the molar ratio in the first surface modification step, and the like.

[0055] Furthermore, the method for manufacturing the copper clad laminate 20 in this embodiment may include a step of forming an electrolytic copper plating layer, and may also include a resist patterning step (step 6) of forming a resist on the electroless copper plating layer after a heating (annealing) step (step 5) of heating the copper clad laminate on which the electroless copper plating layer has been formed, an electrolytic copper plating step (step 7) of forming an electrolytic copper plating layer 3 between the patterned resist, a resist removal step (step 8) of removing the patterned resist, and a flash etching step (step 9) of etching the electroless copper plating layer after resist removal.

[0056] In the method for producing a copper clad laminate in this embodiment, steps 2 and 6 to 9 may be omitted as appropriate. In this case, depending on the required specifications of copper clad laminate 10 or copper clad laminate 20, for example, only the second surface modification step of step 2 may be omitted, or step 2 may be omitted while steps 6 to 9 are retained, or steps 2 and 6 to 9 may be omitted. As an example, when the resin film 1 constituting the copper clad laminate is LCP, it is desirable to have the second surface modification step described above, but when the resin film 1 is MPI (modified polyimide) or PI, the second surface modification step may be omitted. In other words, the method for manufacturing the copper clad laminate 10 in the present invention includes at least an electroless copper plating process for forming an electroless copper plating layer 2 on at least one surface of the resin film 1, and a heating (annealing) process for heating the copper clad laminate on which the electroless copper plating layer has been formed prior to the resist patterning process. Each step will be described in detail below, with reference to FIG. 5 as needed.

[0057] First, regarding the first surface modification step (Step 1), as described above, the resin film 1 used is preferably a so-called low-dielectric resin film. Specific electrical properties of the resin film 1 are preferably a relative dielectric constant of 3.5 or less at a frequency of 10 GHz and a dielectric loss tangent of 0.008 or less.

[0058] In the first surface modification step of this embodiment, carboxyl groups and / or hydroxyl groups are imparted to at least one surface of the resin film 1. Examples of a method for imparting these carboxyl groups and / or hydroxyl groups include a method in which a mixed solution of an alkaline aqueous solution and an amino alcohol is brought into contact with at least one surface of the resin film 1.

[0059] The alkaline aqueous solution used in the first surface modification step may be either an inorganic alkali or an organic alkali. Examples of inorganic alkali include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or carbonates thereof. Examples of organic alkali include tetraalkylammonium hydroxide. The above alkalis may be used alone or in combination.

[0060] On the other hand, the amino alcohol used in the first surface modification step may specifically be an aliphatic amino alcohol or an aromatic amino alcohol, or may be a derivative thereof. Specific examples of amino alcohols that can be used include ethanolamine, heptaminol, isoethanolamine, butanolamine, propanolamine, sphingosine, methanolamine, dimethylethanolamine, and N-methylethanolamine. Of these, aminoethanol is particularly preferred.

[0061] The mixing ratio of the alkaline aqueous solution and amino alcohol in the mixed solution in the first surface modification step is preferably adjusted so that the molar ratio of -OH groups to -NH2 groups (-NH2 groups / -OH groups) is 2.00 to 3.00. By setting the molar ratio within the above range, it is possible to achieve the objective of the present invention of achieving both reduced roughness (further reduction in transmission loss) and good adhesion between the electroless copper plating layer 2 and the resin film 1. The reason for this is not clear at present, but as a result of investigations by the inventors, it is presumed to be due to the following reasons.

[0062] That is, when a resin film 1 using the above-mentioned resin with low dielectric loss (such as a liquid crystal polymer or a modified polyimide resin) is subjected to the first surface modification step using a liquid mixture with a molar ratio (-NH group / -OH group) within the above range, it is believed that the surface condition of the resin film 1 can be adjusted to have an average surface roughness Ra of 1 nm to 150 nm on the surface on the electroless copper plating layer 2 side. Therefore, when a wiring conductor is formed on a circuit board using an electroless copper plating layer, transmission loss due to the skin effect is suppressed, and favorable transmission characteristics can be exhibited.

[0063] 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, the adhesion between the resin film 1 and the electroless copper plating layer 2 can also be ensured. Therefore, the present inventors have come up with the idea of ​​achieving the object of the present invention by undergoing the first surface modification step as described above.

[0064] In the first surface modification step, by setting the molar ratio of (-NH2 group / -OH group) in the mixed solution within the above range, it is possible to provide more hydroxyl groups than carboxyl groups on the surface of the resin film 1.

[0065] In the first surface modification step, a known method can be appropriately applied as a method for bringing the mixed solution of the alkaline aqueous solution and the amino alcohol into contact with the surface of the resin film 1, such as a method of immersing the resin film 1 in the mixed solution or a method of spraying the mixed solution onto the resin film 1 with a spray or the like. The method is not limited to these, and any method other than the above-mentioned methods may be applied as long as it can impart carboxyl groups and / or hydroxyl groups to the surface of the resin film 1.

[0066] In the first surface modification step, the deposition and adhesion of plating can be improved by adjusting the contact angle on the film surface. In particular, when the resin film 1 is a liquid crystal polymer, the contact angle at the interface on the plating layer side that contacts the electroless copper plating layer 2 is preferably 30° or less. Furthermore, in particular, when the resin film 1 is a modified polyimide (MPI), the contact angle at the interface on the plating layer side that contacts the electroless copper plating layer 2 is preferably 45° or less.

[0067] Next, the second surface modification step (Step 2) of this embodiment will be described. The second surface modification step in this embodiment is preferably a step performed after the first surface modification step described above. In other words, it is not necessarily necessary to perform the second surface modification step after the first surface modification step, and as described above, the second surface modification step as Step 2 can be omitted as appropriate. Such a second surface modification step is a step of further imparting an electric charge after imparting carboxyl groups and / or hydroxyl groups to the surface of the resin film 1 in the first surface modification step, which is preferable because imparting an electric charge can improve the adhesion between the resin film 1 and the electroless copper plating layer 2.

[0068] That is, as described above, in order to form 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. In order 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.

[0069] 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. These steps enable a negative charge to be reliably attached to the surface of the resin film 1, which is preferable from the viewpoints of the adhesion of the metal palladium and the adhesion of the electroless copper plating layer 2.

[0070] In the above-mentioned process of imparting a positive charge to the surface of the resin film 1, specific methods that can be applied include immersing the resin film 1 after imparting carboxyl groups and / or hydroxyl groups to the surface in a known cationic surfactant, or spraying a known cationic surfactant into contact with the resin film 1.

[0071] Similarly, in the step of adsorbing negative charges onto the surface of the resin film 1, a method of immersing the film in a known anionic surfactant or a method of spraying the film can be used. The second surface modification step of this embodiment is preferably performed by a wet method as described above. Performing the process by a wet method is advantageous in that it is suitable for mass production by reel-to-reel or the like and also enables cost reduction.

[0072] Next, the catalyst adsorption step (step 3) in the manufacturing method of this embodiment will be described. The catalyst adsorption step of this embodiment is a step of further adsorbing a catalyst onto the surface of the resin film 1, to which at least a negative charge has been imparted by the second surface modification step described above.

[0073] In the catalyst adsorption step, a catalyst can be further adsorbed onto the surface of the resin film 1 by, for example, contacting a known catalyst liquid with the surface of the resin film 1 by a known method. Examples of catalysts that can be used include Cu, Ni, Pd, and Ag. Examples of known catalyst liquids that can be used include, but are not limited to, tin-palladium-based or palladium colloid-based catalyst liquids.

[0074] In the catalyst adsorption step, the amount of catalyst applied to the resin film 1 is 15 μg / dm in terms of metallic palladium. 2The lower limit of the catalyst content is preferably 1 μg / dm or less, taking into consideration the etching process during circuit formation. However, it is necessary to add the catalyst to such an extent that the electroless copper plating layer is well formed. 2 It is preferable that there is more than this.

[0075] If the amount of metallic palladium applied to the resin film 1 exceeds the above-mentioned value, it is not preferable because the reliability of insulation between circuits may be reduced when the film is made into a flexible circuit board. The amount of metallic palladium can be measured by a known method, for example, by peeling 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 the residue by ICP.

[0076] Next, the electroless copper plating step (step 4) in the manufacturing method of this embodiment will be described. The electroless copper plating step is preferably carried out after the catalyst adsorption step. Here, as the electroless copper plating bath in this embodiment, a known bath such as an EDTA bath, a Rochelle bath, or a triethanolamine bath can be used. Through the above steps, the copper clad laminate 10 of this embodiment is manufactured.

[0077] The immersion time of the resin film 1 in the plating bath may be appropriately determined so that the thickness of the electroless copper plating layer 2 becomes 0.1 to 1.0 μm. Furthermore, the plating layer formed in this electroless copper plating step is not limited to plating of simple Cu, but may also be plating of a copper alloy, such as a Cu-Ni alloy, a Cu-Zn alloy, or a Cu-Sn alloy. In this case, a known plating bath can be appropriately used as the plating bath.

[0078] For the reasons mentioned above, the manufacturing method of this embodiment includes a heating (annealing) step (step 5) after forming the electroless copper plating layer 2 on the resin film 1 and before the resist patterning step, in which the copper clad laminate is heated so that the weighted average crystallite size in the electroless copper plating layer 2 becomes 25 to 300 nm. Note that the heating (annealing) step of step 5 may be performed not only for the purpose of causing the structural transformation as described above, but also for the purpose of releasing internal stress in the electroless copper plating layer (for the purpose of aging).

[0079] The heating conditions in such a heating (annealing) step are preferably, for example, as follows, so that the weighted average crystallite size in the electroless copper plating layer 2 is 25 to 300 nm. <Example of heating conditions> Heating temperature: 150~350℃ Heating (soaking) time: 5 to 180 minutes Atmosphere: In air or inert gas (nitrogen, etc.)

[0080] The atmosphere may be air, an inert gas, or a vacuum, and the inert gas may be nitrogen gas, a mixed gas of hydrogen and nitrogen, argon gas, or helium gas. From the viewpoint of equipment cost, air or an inert gas is preferable. Furthermore, the heating atmosphere is more preferably an inert gas atmosphere or a vacuum in order to suppress the formation of an oxide film.

[0081] When performing a heating (annealing) treatment in the air, the heating time and temperature are preferably in the range of 180 to 200°C and 10 to 60 minutes to suppress the formation of an oxide film. On the other hand, when performing a heating (annealing) treatment in an inert gas atmosphere, the heating time and temperature are preferably in the range of 220 to 350°C and 10 to 180 minutes.

[0082] By carrying out this heating (annealing) step, the Cu crystallites, which were fine after electroless copper plating, can be grown and coarsened. Note that this heating (annealing) step preferably results in the weighted average size of the Cu crystallites (first crystallites) in the electroless copper-plated layer 2 and the weighted average size of the Cu crystallites (second crystallites) in the electrolytic copper-plated layer 3 by the subsequent electrolytic copper plating step being in the above-mentioned ratio.

[0083] This improves the elongation characteristics of the electroless copper plating layer 2, making it possible to maintain high peel strength.

[0084] Furthermore, by carrying out the heating (annealing) step, peeling of the electroless copper plating layer 2 from the resin film 1 can be suppressed, and the adhesion between the electroless copper plating layer 2 and the resin film 1 can also be ensured.

[0085] After the heating (annealing) step in step 5 described above, the resist is patterned (formed (coated or attached) and patterned according to the desired circuit) by a known method (step 6), and an electrolytic copper plating layer 3 is formed between the resist on the electroless copper plating layer 2 under the electrolytic copper plating conditions described above (step 7). The thickness of this electrolytic copper plating layer 3 is preferably, for example, 10 to 30 μm.

[0086] In this case, it is preferable that at least one of the following be satisfied: the weighted average crystallite size in the electrolytic copper plated layer 3 is 40 to 300 nm; and the volume resistivity in the electrolytic copper plated layer 3 is 5.0 μΩ·cm or less.

[0087] A known copper sulfate bath or copper pyrophosphate bath can be used as the electrolytic copper plating step for forming this electrolytic copper plating layer 3. 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. Through the above steps, the copper clad laminate 20 of this embodiment is manufactured.

[0088] <Flexible circuit board> Next, the flexible circuit board of this embodiment will be described. The flexible circuit board in this embodiment 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, the copper clad laminate 10 of this embodiment 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.

[0089] Furthermore, since it is possible to improve the adhesion between the resin film 1 and the electroless copper plating layer 2, it is preferable because it enables the formation of a fine circuit pattern even when a semi-additive process is employed. More specifically, when using the SAP process or MSAP process, for example, the method for producing a flexible circuit board in this embodiment includes, after the above-mentioned steps 1 to 5 (see also FIG. 4), a known resist patterning step in which a resist is formed (applied or attached) and patterned on the electroless copper plating layer 2, and then the above-mentioned electrolytic copper plating step is carried out, thereby forming the electrolytic copper plating layer 3 between the patterned resist.

[0090] 6(a) schematically shows a flexible circuit board 100 made of a copper clad laminate 20 according to this embodiment (i.e., a copper clad laminate in which an electrolytic copper plating layer 3 is further formed on an electroless copper plating layer 2). In this flexible circuit board 100, metal wiring MW having a specific conductor shape obtained according to this embodiment forms at least a part of the circuit. Note that the flexible circuit board 100 according to this embodiment only needs to use the copper clad laminate 20 for at least a part of the conductors (metal wiring) that form the circuit, and metal wiring may be formed by conventional methods in other circuit parts.

[0091] In this case, as shown in the figure, it is preferable that the metal wiring MW in the flexible circuit board 100 satisfies the following formula (1), where Hw is the wiring height from the resin film 1, Lb is the width of the base that contacts the resin film 1, Lt is the width of the top surface of the metal wiring MW, and S is the distance between the wiring and other adjacent metal wiring MW on the resin film 1. A≧2.5 (1)

[0092] In this embodiment, A in formula (1) represents the rectangularity of the conductor shape in the cross section of the metal wiring MW in the width direction perpendicular to the current flow direction. Thus, the rectangularity A in this embodiment is defined as the value obtained by dividing the wiring height Hw by the difference between the base width Lb and the top width Lt. Rectangularity of conductor shape A=Hw / (Lb-Lt)

[0093] Furthermore, it is preferable that the metal wiring MW in the flexible circuit board 100 satisfies the following formula (2) in addition to the above formula (1). Distance between wires S≦60μm (2)

[0094] Furthermore, when the conductor wiring density WD is the value (S / A) obtained by dividing the distance S between the wirings by the rectangularity A of the conductor shape, it is preferable that the metal wiring MW in the flexible circuit board 100 satisfy the following formula (3): Conductor wiring density WD≦10.0 (3)

[0095] Here, in order to increase the conductor wiring density WD in the flexible circuit board, it is necessary to make the rectangularity A of the conductor shape as close to a rectangle as possible and to make the distance S between the wirings as small as possible. Based on the above findings, the inventors conducted extensive research and concluded that it is preferable that the rectangularity A of the conductor shape be 2.5 or more, the above-mentioned inter-wire distance S be 60 μm or less, and the conductor wiring density WD be 10.0 or less. By simultaneously satisfying these values, the rectangularity A of the conductor shape can be said to be rectangular (A≧2.5), and the cross section (conductor shape) in the width direction of the metal wiring MW becomes substantially rectangular, reducing the wiring resistance while making the acute angle on the bottom side relatively obtuse compared to a non-rectangular shape (for example, a trapezoid with a relatively large base), making it possible to suppress a decrease in transmission loss of high-frequency current, etc.

[0096] 6(b) is a schematic diagram showing a flexible circuit board 200 in which conductor layers are laminated using the copper clad laminate 20 of this embodiment. Specifically, the flexible circuit board 200 of this embodiment is configured to include a pair of conductor layers CL1 on the outermost layers, a conductor layer CL2 in which the metal wiring MW of this embodiment is formed between the pair of conductor layers CL1, and a dielectric layer such as a known adhesive layer BL that bonds these conductor layers. In this case, the conductor layers CL1 and CL2 represent electrical conductor layers arranged on the same plane, and do not include upper and lower conductive layers in which via holes, through holes, etc. are formed in the copper clad laminate 20.

[0097] In this embodiment, the number of stacked conductor layers CL is defined as the number of layers. In this case, the flexible circuit board 200 has at least four stacked conductor layers CL, each including the metal wiring MW. In this case, the flexible circuit board 200 preferably has an average thickness of 50 μm or less, calculated by dividing the overall thickness TA of the conductor layers CL (the distance between the outermost conductor layers) by the number of conductor layers CL (four in FIG. 6(b)).

[0098] As a result, according to the flexible circuit board 200 of this embodiment, it is possible to make the wiring in the flexible circuit board finer and thinner, and it is also possible to reduce the thickness of the dielectric layer in the multilayer wiring board, thereby simultaneously increasing the density and fine wiring properties.

[0099] <Method of manufacturing flexible circuit board> Next, a method for manufacturing the flexible circuit board 100 according to this embodiment will be described in detail. As an example, the following describes a case where the flexible circuit board 100 is manufactured by a known SAP (Semi-Additive Process) method using the above-described copper clad laminate 20.

[0100] That is, in the manufacturing method of the flexible circuit board 100, first, a copper clad laminate 10 is formed by going through the processes up to the above-mentioned step 5. This provides a copper clad laminate 10 on which the above-mentioned electroless copper plating layer 2 (e.g., an electroless Cu-Ni layer) is formed. At this time, as a preliminary process carried out before the above-mentioned step 1, the above-mentioned through holes H, for example, with a diameter of about 70 to 100 μm, may be appropriately formed in the resin film 1, and the position and size of these through holes H can be appropriately determined depending on the specifications of the flexible board. Furthermore, two methods can be exemplified for forming the through holes H: drilling and laser processing.

[0101] For drilling, for example, several layers of substrate (film) may be stacked and through-holes may be drilled at predetermined positions using a known mechanical drill at high speed. For laser processing, two types of lasers, known as CO2 lasers and UV-YAG lasers, may be used. Laser processing is suitable for forming small-diameter through-holes H, and UV-YAG lasers are particularly preferred. After the through-holes H are formed by the above-described method, a known desmearing process may be performed.

[0102] Next, a resist is formed (laminated or coated) by a known method on the electroless copper plating layer 2 of the copper clad laminate 10, and patterned (step 6 above). As an example, in this embodiment, a DFR (dry film resist) may be laminated to the electroless copper plating layer 2 using a known roll laminator, and then a resist pattern may be formed on the electroless copper plating layer 2 by performing known exposure and development processes using a mask on which a wiring pattern has been formed.

[0103] Examples of such DFRs that can be used include Sunfort (registered trademark) manufactured by Asahi Kasei E-materials Corporation, Photec (registered trademark) manufactured by Showa Denko Materials Co., Ltd., and Riston (registered trademark) manufactured by DuPont. After the resist pattern is formed, it is preferable to perform a known plasma ashing process (for example, a plasma process in a mixed gas atmosphere of CF4 and O2) to remove resist residues.

[0104] After the resist pattern is formed on the electroless copper plating layer 2 of the copper clad laminate 10, a known electrolytic copper plating bath (one example of which is a plating bath having the bath composition shown below) is used to form an electrolytic copper plating layer 3 on the electroless copper plating layer 2 (step 7 above). The thickness of this electrolytic copper plating layer 3 is preferably, for example, 10 to 30 μm. The electrolytic copper plating layer 3 was not subjected to any further heat treatment.

[0105] <Electrolytic copper plating conditions (example)> Bath composition: Copper sulfate hexahydrate 200g / L Sulfuric acid 50g / L Chloride ions 50 ppm Brightener 5ml / L (Okuno Pharmaceutical Additive Top Lucina (registered trademark)) Bath temperature: 20~25℃ Current density: 2.0~3.0A / dm 2

[0106] After forming the electrolytic copper plating layer 3 to the above thickness on the electroless copper plating layer 2 by the above method, the resist is removed by a known method (above step 8). That is, in this example, the above DFR is used as the resist material, and therefore, for example, any of the known NaOH aqueous solution, amine-based stripping liquid, and inorganic-based stripping liquid can be used to strip this DFR.

[0107] After the resist removal step, known flash etching is performed to finish each wiring pattern (step 9 above). In such flash etching, a sulfuric acid / hydrogen peroxide solution can be used as a soft etching agent, and known processing solutions such as "Ebachem (registered trademark) Fine Etch FE-830 (II)" and "Ebachem (registered trademark) Fine Etch SAC" manufactured by JCU Corporation can be used.

[0108] By going through the above steps, a flexible circuit board 100 having a desired pattern of metal wiring can be manufactured. Furthermore, the flexible circuit board 200 (multilayer flexible circuit board) of the present embodiment described above can be manufactured by stacking multiple flexible circuit boards 100 using a known adhesive layer BL for multilayer FPCs (for example, a known bonding sheet having a thickness of 15 μm to 25 μm, such as AU manufactured by Arisawa Manufacturing Co., Ltd., SAFY manufactured by Nikkan Industries Co., Ltd., Vecstar (registered trademark) CTF manufactured by Kuraray Co., Ltd., or R-BM17 manufactured by Panasonic Corporation).

[0109] Examples of methods for laminating flexible circuit board 100 include a method in which a predetermined number of flexible boards are stacked on top of each other and vacuum-pressed together while heating them to a temperature at which the film layer softens, and a method in which the above-mentioned bonding sheet is attached to one or both sides of flexible circuit board 100 and bonded by heat pressing. [Example]

[0110] Next, the present invention will be described more specifically with reference to examples.

[0111] Example 1 First, a liquid crystal polymer film (Vexstar CTQLCP, manufactured by Kuraray Co., Ltd., thickness: 50 μm) was prepared as resin film 1. As for electrical properties, the relative permittivity at 10 GHz was 3.3, and the dielectric loss tangent at 10 GHz was 0.002.

[0112] Next, as the first surface modification step, both sides of the prepared resin film 1 were immersed in a mixed solution of potassium hydroxide aqueous solution and monoethanolamine for 5 minutes to introduce carboxyl groups and / or hydroxyl groups to both surfaces, followed by immersion and water rinsing. The temperature of the mixed solution used was 40°C, and the molar ratio of -OH groups to -NH groups (-NH groups / -OH groups) was 2.29. The peak intensity of mass 121 in TOF-SIMS was 1000.

[0113] 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 a cationic surfactant for 2 minutes to adsorb positive charges. After immersion and rinsing with water, the film was immersed in an aqueous solution of 3 g / L of anionic surfactant for 1 minute. In this way, positive charges were adsorbed, and then negative charges were adsorbed. Furthermore, as the catalyst adsorption process and electroless copper plating process, the substrate was immersed in an aqueous solution of palladium chloride (PdCl2) (2 g / L, pH 12, 40°C) as a plating catalyst for 5 minutes, followed by immersion and rinsing with water.Furthermore, the substrate was immersed in an aqueous solution (25°C) containing 1 g / L of dimethylamine borane (DMAB) and 6 g / L of boric acid as a catalyst activator (reducing agent) for 5 minutes, followed by immersion and rinsing with water.

[0114] Thereafter, an electroless Cu-Ni plating layer was formed to a thickness of 0.2 μm in an electroless plating bath under the following electroless plating conditions.

[0115] [Electroless plating conditions] Bath composition: Copper sulfate 7.5g / L Nickel sulfate 0.7g / L Rochelle salt 20g / L Sodium hydroxide 5g / L pH:9 Bath temperature: 32℃

[0116] [Heat (annealing) treatment] In this example, after the electroless copper plating layer 2 was formed, a heat treatment was carried out using a vacuum drying device (DQ-46P-LP manufactured by Sato Vacuum Co., Ltd.) under the following conditions. <Heating conditions> Heating temperature: 290℃ Heating (soaking) time: 10 minutes Heating atmosphere: inert gas (N2 gas)

[0117] The Ni content in the resulting electroless Cu-Ni plating layer was determined to be 1.18 wt% by a method using an inductively coupled plasma (ICP) emission spectrometer (described later). The weighted average crystallite size in the resulting electroless Cu-Ni plating layer 2 was 33.4 nm.

[0118] Thereafter, the electrolytic copper-plated layer 3 of the copper-clad laminate 10 was formed on the electroless copper-plated layer 2 using the following electrolytic plating bath to obtain a copper-clad laminate 20. The electrolytic copper-plated layer 3 was not further subjected to a heat treatment. The electrolytic copper plating conditions were as follows: Bath composition: Copper sulfate hexahydrate 200g / L Sulfuric acid 50g / L Chloride ions 50 ppm Brightener 5ml / L (Okuno Pharmaceutical Additive Top Lucina (registered trademark)) Bath temperature: 20~25℃ Current density: 2~3A / dm 2 (In this example, 2.5A / dm 2 ) pH: less than 1

[0119] The thickness of the obtained electrolytic copper plated layer was 18 μm. The weighted average size of the crystallites in the obtained electrolytic copper plated layer 3 was 53.0 nm. In this case, assuming that the weighted average size of the crystallites in the electroless copper plated layer is the first crystallite and the weighted average size of the crystallites in the electrolytic copper plated layer is the second crystallite, the ratio of the first crystallites to the second crystallites (second crystallites / first crystallites) was 1.59.

[0120] [Evaluation] [Measurement of crystallite size and calculation of weighted average size] After forming the electroless copper plating layer, heat treatment was performed under the conditions shown in Table 1, and the obtained copper-clad laminate 10 was measured using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation). After this measurement, the weighted average size was calculated by the <method for calculating the weighted average size in crystallites> described above. [Measurement of Ni content rate of electroless copper plating layer 2] After forming the electroless copper plating layer under the conditions shown in Table 1, a 2 cm × 2 cm portion was immersed in 30% nitric acid (room temperature) to dissolve the electroless copper plating layer, and the obtained solution was used to measure the weights of Cu (copper) and Ni (nickel) using an inductively coupled plasma optical emission spectrometer (ICP) (ICPE-9820 manufactured by Shimadzu Corporation), and the Ni content rate of the electroless copper plating layer 2 was calculated by calculating Ni weight / (Cu weight + Ni weight).

[0121] [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, with respect to the obtained copper-clad laminate 10, without performing 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 out to a size of 20 mm × 20 mm to obtain a measurement sample. This measurement sample was measured using an X-ray photoelectron spectrometer (JPS-9200 manufactured by JEOL Ltd., 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. According to the measurement results in 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.

[0122] The surface of the measurement sample was analyzed using a TOF-SIMS TRIFT-II (manufactured by ULVAC-PHI, Inc.). An untreated resin film sample was used as a control. The measurement conditions were as follows: Primary ions: 69 Ga Accelerating voltage: 15 kV Measurement range: 100 μm x 100 μm Mass range: 0.5 to 300 (m / z)

[0123] The obtained results were analyzed using the analysis software Win Cadence (Physical Electronics). It was confirmed that a peak characteristic of mass 121 was observed in the TOF-SIMS spectrum only on the surface of the sample from which the electroless copper plating had been removed. No peak characteristic of mass 121 was observed on the surface of the untreated sample. According to the results of ESCA, the presence of carboxyl groups could not be confirmed, and therefore it was determined that C8H9O (-CH-CH3-C6H4-OH) groups had been introduced after the first and second surface modification processes.

[0124] <Ra after plating layer peeling> The electroless copper plating layer 2 was peeled off from the obtained copper clad laminate 10 (thickness of the electroless copper plating layer: thickness shown in Table 1) using an FeCl3 solution to expose 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.

[0125] <Contact angle> The electroless copper plating layer 2 of the obtained copper clad laminate 10 was peeled off using an FeCl3 solution in the same manner as described above, exposing the resin film. The exposed resin film surface was cut into a 20 mm x 20 mm measurement sample. 2.0 μL of pure water was dropped onto the sample surface, and the contact angle was measured using a contact angle measuring device (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 14 was 58°.

[0126] <Tape peel strength> A tape peeling test was performed on a copper clad laminate 10 having an electroless copper plating layer 2 (thickness of the electroless copper plating layer: thickness shown in Table 1) 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 confirmed visually, the evaluation result was rated as good. The results are shown in Table 2.

[0127] <90° peel strength> A 40 mm × 40 mm specimen was cut out of the copper clad laminate 20 on which the electrolytic copper plating layer 3 was formed, and the specimen was attached to an aluminum plate with polyimide tape. The 90° peel strength, which represents the adhesive strength between the resin film and the electroless copper plating layer, was measured as follows. Specifically, strips were cut into the copper-plated surface of each test piece at 5 mm intervals with a cutter, and the edges of the strips were then forcibly peeled off to create a peeling trigger, creating a peeled resin film and copper-plated area. The peeled resin film and copper-plated layer were then clamped between Tensilon chucks, and the 90° peel strength was measured using an autograph. The 90° peel strength was converted to N / cm (width). The results are shown in Table 2.

[0128] <Platability (visual inspection)> The appearance of the electroless copper plating layer of the obtained copper clad laminate 10 was visually inspected, and those without peeling or blistering were marked with a circle and shown in Table 2.

[0129] <Volume resistivity> The volume resistivity (μΩ·cm) of the obtained copper clad laminate 10 was measured by the four-probe method using Loresta GP (MCP-T600 manufactured by Mitsubishi Chemical Corporation). The measurement results of the volume resistivity are shown in Table 2.

[0130] <Overall rating> The above evaluation items were comprehensively judged, and the results are shown in Table 2, with ◯ indicating that there is no problem in practical use and × indicating that it is not practical.

[0131] <Example 2> The same procedure as in Example 1 was carried out except that the heating temperature in the heating (annealing) step was set to 280° C. The results are shown in Tables 1 and 2.

[0132] Example 3 The same procedure as in Example 1 was carried out except that the heating temperature in the heating (annealing) step was set to 270° C. The results are shown in Tables 1 and 2.

[0133] Example 4 The same procedures as in Example 1 were carried out except that the heating temperature in the heating (annealing) step was set to 260°C and the plating thickness of the electroless Cu-Ni plating layer 2 was changed to 0.1 μm, 0.2 μm, and 0.3 μm, respectively. The results are shown in Tables 1 and 2.

[0134] <Example 5> The same procedure as in Example 1 was carried out except that the heating temperature in the heating (annealing) step was set to 250° C. The results are shown in Tables 1 and 2.

[0135] Example 6 The same procedure as in Example 5 was carried out except that the heating (soaking) time in the heating (annealing) step was set to 30 minutes. The results are shown in Tables 1 and 2.

[0136] Example 7 The same procedure as in Example 5 was carried out except that the heating (soaking) time in the heating (annealing) step was set to 60 minutes. The results are shown in Tables 1 and 2.

[0137] Example 8 The same procedure as in Example 5 was carried out except that the heating (soaking) time in the heating (annealing) step was set to 120 minutes. The results are shown in Tables 1 and 2.

[0138] Example 9 The same procedure as in Example 5 was carried out except that the heating (soaking) time in the heating (annealing) step was set to 180 minutes. The results are shown in Tables 1 and 2.

[0139] Example 10 The same procedures as in Example 1 were carried out except that the heating temperature in the heating (annealing) step was set to 220°C and the plating thickness of the electroless Cu-Ni plating layer 2 was changed to 0.1 μm, 0.2 μm, and 0.3 μm, respectively. The results are shown in Tables 1 and 2.

[0140] Example 11 The same procedures as in Example 10 were carried out except that the plating thickness of the electroless Cu—Ni plating layer 2 was set to 0.2 μm and the heating (soaking) time in the heating (annealing) step was set to 60 minutes. The results are shown in Tables 1 and 2.

[0141] Example 12 The same procedures as in Example 10 were carried out except that the plating thickness of the electroless Cu-Ni plating layer 2 was set to 0.2 μm and the heating (soaking) time in the heating (annealing) step was set to 180 minutes. The results are shown in Tables 1 and 2.

[0142] Example 13 The same procedures as in Example 1 were carried out except that the heating temperature in the heating (annealing) step was set to 200°C and the heating atmosphere was set to air using a dry oven (DY300 manufactured by Yamato Scientific Co., Ltd.) The results are shown in Tables 1 and 2.

[0143] Example 14 The same procedure as in Example 13 was carried out, except that resin film 1 was a modified polyimide (MPI), the electroless copper plating conditions were a pH of 12.5, the plating thickness of electroless Cu-Ni plating layer 2 was 0.3 μm, the heating temperature in the heating (annealing) step was 150°C, and the heating (soaking) time was 60 minutes. The modified polyimide (MPI) used was FS-L (thickness: 50 μm) manufactured by SKC Kolon PI. The electrical properties of this resin film 1 were a relative dielectric constant of 3.4 at 10 GHz and a dielectric loss tangent of 0.0035 at 10 GHz. The results are shown in Tables 1 and 2.

[0144] Example 15 The same procedures as in Example 13 were carried out, except that the resin film 1 was a modified polyimide (MPI), the first surface modification step was a mixture of 40% by volume of a potassium hydroxide aqueous solution and monoethanolamine with 60% by volume of water to prepare a surface modification mixture, the second surface modification step was omitted, the plating thickness of the electroless Cu-Ni plating layer 2 was 0.3 μm, the heating (annealing) step was a heating temperature of 220°C, a heating (soaking) time of 30 minutes, and an inert gas (N2 gas) atmosphere. The modified polyimide (MPI) used was FS-L (thickness: 50 μm) manufactured by SKC Kolon PI. The electrical properties of this resin film 1 were a relative dielectric constant of 3.4 at 10 GHz and a dielectric loss tangent of 0.0035 at 10 GHz. The results are shown in Tables 1 and 2.

[0145] Example 16 The same procedures as in Example 15 were carried out except that the heating temperature in the heating (annealing) step was set to 300° C. and the heating (soaking) time was set to 60 minutes. The results are shown in Tables 1 and 2.

[0146] Example 17 The copper clad laminate 20 produced in Example 9 above was used as the FCCL (flexible copper clad laminate). A known DFR (dry film resist) was laminated to this copper clad laminate 20 using a known roll laminator. Next, the negative portion of the resist was hardened by exposing it to ultraviolet light using a known exposure device through a mask on which a predetermined resist pattern image was formed.

[0147] Next, the unexposed areas of the resist were dissolved using a known alkaline developer such as a 1% by mass aqueous solution of sodium carbonate, forming a resist pattern on the electroless copper plating layer. After the resist pattern was formed, a known plasma treatment was performed in a mixed gas atmosphere of CF4 and O2 to remove the resist residue.

[0148] Next, the FCCL of this example having the resist pattern formed thereon obtained as described above was acid-washed by immersing it in a 5 wt % sulfuric acid solution at 30°C for 30 seconds before electroplating, to remove the oxide film on the electroless copper plating layer. Next, electrolytic copper plating was formed on the electroless copper plating layer on which the resist pattern had been formed, under the plating conditions shown below, to a predetermined wiring height Hw shown in Table 3.

[0149] <Plating conditions for electrolytic copper plating in Example 17> Bath composition: Copper sulfate hexahydrate 70g / L 98% sulfuric acid 200g / L 35% hydrochloric acid 0.15ml / L Additive: Okuno Pharmaceutical Top Lucina (registered trademark) SF Base WR 2.5ml / L Top Lucina® SF-B 1.0 ml / L, and Top Lucina (registered trademark) SF Leveler 5.0ml / L Bath temperature: 25℃ Current density (cathode): 3.0A / dm 2

[0150] Next, the resist pattern of the FCCL of this example on which electrolytic copper plating had been formed was removed by spraying a known amine-based stripping solution onto the resist pattern for 180 seconds.Furthermore, as the flash etching treatment described above, an etching bath having the following composition was prepared and sprayed at 25°C for 30 seconds.

[0151] <Flash Etching Bath Composition in Example 17> Bath composition: 35% hydrogen peroxide 4.5% by volume 98% sulfuric acid 5% by volume, Copper sulfate pentahydrate 30g / L

[0152] In this way, a flexible circuit board (FPC) of this example was obtained. To examine the specifications of the metal wiring in the obtained FPC, a cross section was cut in the width direction (direction perpendicular to the current direction) of a specific metal wiring, and the wiring height Hw, base width Lb, top width Lt, conductor shape rectangularity A, distance between wirings S, and conductor wiring density WD were measured using a known electron microscope using the following methods. That is, first, tangent lines are drawn to the bottom, top, and both side surfaces of the metal wiring on the cross-sectional photograph obtained with the electron microscope. Then, using these tangent lines as a reference, the distance between the intersections of the tangent lines on both sides is measured for the width Lb of the bottom surface and the width Lt of the top surface, based on the scale displayed in the electron microscope image. Furthermore, for the wiring height Hw, a vertical line is drawn from the midpoint (half point) of the width Lb of the bottom surface to intersect with the top surface, and the distance between the intersection with the top surface and the midpoint of the bottom surface is measured based on the scale displayed in the electron microscope image. The results are shown in Table 3. A portion of the obtained flexible circuit board (an example of metal wiring) is shown in Figure 7(a).

[0153] Example 18 The same procedure as in Example 17 was carried out, except that the exposure photomask was changed to one designed to have the base width Lb and the inter-wiring distance S shown in Table 3. The results obtained are shown in Table 3. A portion of the obtained flexible circuit board (an example of metal wiring) is shown in Figure 7(b).

[0154] Example 19 The same procedure as in Example 17 was carried out, except that the copper clad laminate 20 produced in Example 6 above was used as the FCCL (flexible copper clad laminate) and that the exposure photomask was changed to one designed to have the base width Lb and the inter-wiring distance S shown in Table 3. The results obtained are shown in Table 3.

[0155] Example 20 The same procedures as in Example 19 were carried out except that the exposure photomask was changed to one designed to have the base width Lb and the wiring distance S shown in Table 3. The results obtained are shown in Table 3.

[0156] <Example 21> The same procedures as in Example 19 were carried out except that the exposure photomask was changed to one designed to have the base width Lb and the wiring distance S shown in Table 3. The results obtained are shown in Table 3.

[0157] <Example 22> The same procedure as in Example 6 was carried out except that after the electroless plating bath was prepared, polyethylene glycol (PEG) having a weight-average molecular weight of 1,000 was added to the electroless plating bath to a concentration of 0.8 g / L and the plating thickness of the electroless Cu-Ni plating layer 2 was set to 0.3 μm. The results are shown in Tables 1 and 2.

[0158] Example 23 The same procedure as in Example 22 was repeated, except that after preparing the electroless plating bath, polyethylene glycol (PEG) having a weight-average molecular weight of 1,000 was added to the electroless plating bath to a concentration of 1.0 g / L. The results are shown in Tables 1 and 2.

[0159] Example 24 The same procedures as in Example 15 were carried out except that the first surface modification step was carried out by mixing 20% ​​by volume of a mixed solution of potassium hydroxide aqueous solution and monoethanolamine with 80% by volume of water to prepare a mixed solution for the first surface modification, the second surface modification was carried out, the plating thickness of the electroless Cu-Ni plating layer 2 was set to 0.1 μm, and the heating (annealing) step was carried out at a heating temperature of 250°C for a heating (soaking) time of 30 minutes. The results are shown in Tables 1 and 2.

[0160] Example 25 The same procedures as in Example 15 were carried out except that the first surface modification step was carried out by mixing 15% by volume of a mixed solution of potassium hydroxide aqueous solution and monoethanolamine with 85% by volume of water to prepare a mixed solution for the first surface modification, the second surface modification was carried out, the plating thickness of the electroless Cu-Ni plating layer 2 was set to 0.1 μm, and the heating (annealing) step was carried out at a heating temperature of 250° C. for a heating (soaking) time of 30 minutes. The results are shown in Tables 1 and 2.

[0161] <Example 26> The same procedure as in Example 17 was carried out, except that the copper clad laminate 20 prepared in Example 24 above was used as the FCCL (flexible copper clad laminate) and the exposure photomask was changed to one designed to have the base width Lb and the wiring distance S shown in Table 3. The results obtained are shown in Table 3.

[0162] Example 27 A flexible circuit board (FPC) with metal wiring patterns formed on both sides was produced in the same manner as in Example 19, except that the wiring height Hw was 12 μm and L / S=25 / 25 μm (Line & Space, which corresponds to Lb / S in this example). This board was used as the core layer.

[0163] Next, a commercially available single-sided copper-clad laminate was prepared, which had a liquid crystal polymer thickness of 25 μm and a 12 μm-thick copper foil on one side. Using this single-sided copper-clad laminate, a single-sided flexible circuit board with a metal wiring pattern was fabricated using a known subtractive method. This was used as the outer layer. Commercially available bonding sheets (15 μm thick) were then placed on both sides of the core layer, and the single-sided flexible circuit board was then superimposed on both outer layers with the copper foil facing outward. After that, a four-layer flexible circuit board was obtained by adhesively laminating them using a high-temperature press.

[0164] The total thickness TA of the obtained four-layer flexible circuit board was 156 μm, and the thickness of each conductor layer was 39 μm. The four-layer flexible circuit board obtained in this example had high-density, fine wiring consisting of four conductor layers. Furthermore, a multilayer flexible circuit board was obtained that combined high flexibility and transmission characteristics. FIG. 9 shows a cross-sectional image (photographed by an electron microscope) of a portion of the four-layer flexible circuit board obtained in this example.

[0165] Example 28 A flexible circuit board with metal wiring patterns formed on both sides was produced in the same manner as in Example 19, except that the wiring height Hw was 12 μm and the L / S (Line & Space, which corresponds to Lb / S in this example) was 20 μm / 25 μm. This board was used as the core layer.

[0166] Next, a single-sided flexible circuit board was prepared in the same manner as in Example 27, and a four-layer flexible circuit board was obtained in the same manner as in Example 27, except that the flexible circuit board was used as the core layer.

[0167] The four-layer flexible circuit board obtained had an overall thickness TA of 164 μm, and the thickness of each conductor layer was 41 μm. The four-layer flexible circuit board obtained in this example had four conductor layers with high density and fine wiring. Furthermore, a multilayer flexible circuit board was obtained that combined high flexibility and transmission characteristics.

[0168] <Comparative Example 1> The same procedures as in Example 1 were carried out except that the heating (annealing) step was omitted and the pH of the electroless copper plating conditions was set to 12.5. The results are shown in Tables 1 and 2.

[0169] <Comparative Example 2> A commercially available copper clad laminate was prepared as an FCCL (flexible copper clad laminate). The thickness of the liquid crystal polymer film of this FCCL was 50 μm, and the thickness of the electrolytic copper foil was 18 μm. This prepared FCCL was electrolytically copper plated using a known method so that the thickness of the metal wiring (wiring height Hw) was 30 μm.

[0170] Using the copper clad laminate prepared above, a flexible circuit board (FPC) was produced using the following known subtractive method. That is, a known DFR (dry film resist) was laminated to the obtained copper clad laminate using a known roll laminator. Next, the positive portion of the resist was hardened by exposing it to ultraviolet light using a known exposure device through a mask on which a predetermined resist pattern image was formed.

[0171] Next, the unexposed areas of the resist were dissolved using a known alkaline developer such as a 1% by mass aqueous solution of sodium carbonate as the developer, forming a resist pattern on the electrolytic copper plating layer. Then, for the FCCL of this comparative example on which the resist pattern was formed, a known etching process including ferric chloride was used to form conductor wiring. Next, for the FCCL of this example on which the electrolytic copper plating was formed, the resist pattern was removed by spraying a known amine-based stripper on the resist pattern for only 60 seconds. In this way, a flexible circuit board (FPC) of Comparative Example 2 was obtained. The specifications of the metal wiring in the obtained FPC are shown in Table 3. A part of the obtained flexible circuit board (an example of the metal wiring) is shown in Figure 8(a).

[0172] <Comparative Example 3> The same procedure as in Comparative Example 2 was carried out, except that a 50 μm liquid crystal polymer film and an 18 μm rolled copper foil were used as the copper-clad laminate, and the thickness of the metal wiring after electrolytic copper plating (wiring height Hw) was set to 29.2 μm. The results are shown in Table 3. A portion of the obtained flexible circuit board (an example of metal wiring) is shown in FIG. 8(b).

[0173] <Comparative Example 4> A commercially available smartphone was prepared and disassembled to remove the flexible circuit board installed inside. This flexible circuit board used a liquid crystal polymer as the base resin and had a five-layer laminated structure. The specifications of the metal wiring of this flexible printed circuit board were investigated in the same manner as in Example 17. The results are shown in Table 3.

[0174] <Comparative Example 5> The specifications of the flexible printed circuit board obtained in Comparative Example 4 and the metal wiring at other locations were investigated in the same manner as in Example 17. The results are shown in Table 3.

[0175] [Table 1]

[0176] [Table 2]

[0177] [Table 3] [Industrial Applicability]

[0178] The copper clad laminate of the present invention can achieve high adhesion and good volume resistivity while suppressing transmission loss, and therefore it is clear that the copper clad laminate of the present invention is suitable for use in wiring boards and the like that require multilayer fine wiring. [Explanation of symbols]

[0179] 1 Resin film 2. Electroless copper plating layer 3. Electrolytic copper plating layer 10 Copper clad laminate

Claims

1. A method for producing a copper clad laminate by forming an electroless copper plating layer on a low dielectric resin film having a relative dielectric constant of 3.5 or less and a dielectric loss tangent of 0.008 or less at a frequency of 10 GHz, an electroless copper plating step of forming an electroless copper plating layer on the surface of the low dielectric resin film; a heating step of heating the copper clad laminate on which the electroless copper plating layer is formed so that the weighted average size of the crystallites in the electroless copper plating layer is 25 to 300 nm; A method for producing a copper clad laminate, comprising:

2. 2. The method for producing a copper clad laminate according to claim 1, wherein in the heating step, the copper clad laminate is heated under one of the following heating conditions: (i) in the atmosphere at 150 to 200°C for 10 to 180 minutes; and (ii) in an inert gas at 150 to 350°C for 5 to 180 minutes.

3. The method for producing a copper clad laminate according to claim 1 or 2, wherein the heating step is carried out before a resist patterning step on the electroless copper plating layer.

4. Prior to the electroless copper plating step, a first surface modification step of adding carboxyl groups and / or hydroxyl groups to the surface of the low dielectric resin film; a second surface modification step of imparting electric charges to the surface to which the carboxyl groups and / or hydroxyl groups have been imparted by a wet method; a catalyst adsorption step of adsorbing a catalyst onto the surface to which the charge has been applied, The method for producing a copper clad laminate according to any one of claims 1 to 3, wherein the electroless copper plating layer is formed on the surface on which the catalyst is adsorbed.

5. A method for manufacturing a flexible circuit board using a low dielectric resin film, comprising: an electroless copper plating step of forming an electroless copper plating layer on the low dielectric resin film having a relative dielectric constant of 3.5 or less and a dielectric loss tangent of 0.008 or less at a frequency of 10 GHz; a resist patterning step of applying a resist onto the electroless copper plating layer and patterning the resist; an electrolytic copper plating step of forming an electrolytic copper plating layer between the patterned resist; a heating step, prior to the resist patterning step, of heating the copper clad laminate having the low dielectric resin film on which the electroless copper plating layer has been formed so that the weighted average size of the crystallites in the electroless copper plating layer is 25 to 300 nm; 1. A method for manufacturing a flexible circuit board, comprising:

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