Metal-clad laminate and metal with resin

Abstract

Provided is a metal-clad laminate in which the peel strength between a metal layer and an insulating layer can be improved. This metal-clad laminate comprises: a metal layer; and an insulating layer that is provided on at least one surface of the metal layer and has a thickness of more than 2.0 μm. A ratio Ha / Hb of a hardness Ha (MPa) measured with a nanoindenter at a depth of 0.1 μm in the insulating layer to a hardness Hb (MPa) measured with the nanoindenter at a depth of 2.0 μm in the insulating layer is 0.60 or less. The depth of 0.1 μm in the insulating layer is a depth position at which an indenter of the nanoindenter is pressed 0.1 μm into the insulating layer from a surface of the insulating layer on the metal layer side, and the depth of 2.0 μm in the insulating layer is a depth position at which the indenter of the nanoindenter is pressed 2.0 μm into the insulating layer from the surface of the insulating layer on the metal layer side.

Description

Metal-clad laminates and metal with resin

[0001] The present disclosure relates to metal-clad laminates and metal with resin.

[0002] Printed wiring boards are widely used in electronic devices and the like. In particular, along with the higher functionality of electronic devices and the like in recent years, the frequency of signals has been increasing, and high-speed, large-capacity communication has become possible. Examples of such applications include communication servers, autonomous driving of automobiles, and 5G-compatible mobile phones, etc. There has been a growing demand for printed wiring boards suitable for such high-frequency applications. This high-frequency printed wiring board is desired to have low transmission loss so that high-frequency signals can be transmitted without degrading signal quality. A printed wiring board includes a metal layer (for example, a copper layer) processed into a wiring pattern and an insulating resin base material (for example, a prepreg). Transmission loss mainly consists of conductor loss caused by the metal layer and dielectric loss caused by the insulating resin base material.

[0003] Therefore, for metal-clad laminates applied to high-frequency applications, the insulating resin base material is required to have excellent dielectric properties, particularly a small dielectric loss tangent, in order to suppress dielectric loss caused by the insulating resin base material. However, insulating resin base materials with a small dielectric loss tangent generally have the problem of low adhesiveness to metal layers. Additionally, in order to suppress conductor loss caused by the metal layer, a reduction in the roughness of the metal layer is required. However, the smoother the metal layer is, the lower the adhesiveness to the insulating resin base material becomes. In the case of an unroughened metal layer, the adhesiveness is further reduced.

[0004] To solve these problems, it has been proposed to ensure adhesion between the metal layer and the insulating resin substrate by interposing a primer layer (adhesive layer) between them. For example, Patent Document 1 (Japanese Patent Application Publication No. 2007-305963) discloses a semiconductor device mounting substrate with a stress relaxation layer having an elastic modulus of 3 GPa or less, an elongation of 5% or more, and a thickness of 0.5 to 40 μm between the metal foil and the prepreg. Patent Document 1 discloses that the stress relaxation layer consists of a resin composition comprising (A) epoxy resin, (B) polymer component, (C) epoxy resin curing agent, and (D) curing accelerator, and that this makes it possible to provide a semiconductor device mounting package substrate with good connection reliability. Furthermore, Patent Document 2 (WO2024 / 034463A1) discloses a resin composition comprising a predetermined arylene ether compound and / or styrene copolymer and an organic filler composed of a liquid crystal polymer, and that such a resin composition exhibits excellent dielectric properties and high adhesion to surfaces such as low-roughness copper foil.

[0005] Japanese Patent Publication No. 2007-305963 WO2024 / 034463A1

[0006] Incidentally, when the metal layer and the insulating resin substrate (e.g., prepreg) are peeled apart in a metal-clad laminate, tensile stress is applied particularly to the portion of the insulating resin substrate near the metal layer. In this regard, since the resin used in insulating resin substrates is generally hard (i.e., brittle), there is a risk that the substrate may crack due to the above-mentioned tensile stress. As a result, the peel strength between the metal layer and the insulating resin substrate may decrease.

[0007] The present inventors have now discovered that in a metal-clad laminate comprising a metal layer and an insulating layer, the peel strength between the metal layer and the insulating layer can be improved by controlling the ratio of the hardness or elastic modulus of the insulating layer at a depth of 0.1 μm to the hardness or elastic modulus of the insulating layer at a depth of 2.0 μm to be below a predetermined value.

[0008] Therefore, an object of the present invention is to provide a metal-clad laminate capable of improving the peel strength between the metal layer and the insulating layer.

[0009] The following embodiments are provided according to this disclosure: [Embodiment 1] A metal-clad laminate comprising: a metal layer; and an insulating layer having a thickness of more than 2.0 μm provided on at least one surface of the metal layer, wherein the ratio Ha / Hb of the hardness Ha (MPa) of the insulating layer measured by a nanoindenter at a depth of 0.1 μm to the hardness Hb (MPa) of the insulating layer measured by a nanoindenter at a depth of 2.0 μm is 0.60 or less, the depth of the insulating layer of 0.1 μm is the depth position obtained by pressing the indenter of the nanoindenter 0.1 μm into the insulating layer from the surface of the insulating layer on the metal layer side, and the depth of the insulating layer of 2.0 μm is the depth position obtained by pressing the indenter of the nanoindenter 2.0 μm into the insulating layer from the surface of the insulating layer on the metal layer side. [Embodiment 2] The metal-clad laminate according to Embodiment 1, wherein the hardness Ha is 300 MPa or less. [Aspect 3] A metal-clad laminate comprising: a metal layer; and an insulating layer having a thickness of more than 2.0 μm provided on at least one surface of the metal layer, wherein the ratio Ea / Eb of the elastic modulus Ea (MPa) of the insulating layer at a depth of 0.1 μm to the elastic modulus Eb (MPa) of the insulating layer at a depth of 2.0 μm is 0.50 or less, the depth of the insulating layer of 0.1 μm is the depth position obtained by pressing the indenter of the nanoindenter 0.1 μm into the insulating layer from the surface of the insulating layer on the metal layer side, and the depth of the insulating layer of 2.0 μm is the depth position obtained by pressing the indenter of the nanoindenter 2.0 μm into the insulating layer from the surface of the insulating layer on the metal layer side. [Aspect 4] The metal-clad laminate according to aspect 3, wherein the elastic modulus Ea is 5000 MPa or less. [Aspect 5] A metal-clad laminate according to any one of aspects 1 to 4, wherein the insulating layer includes a primer layer in contact with the metal layer and a cured prepreg provided on the side of the primer layer opposite to the metal layer. [Aspect 6] A metal-clad laminate according to aspect 5, wherein the primer layer has a thickness of 0.5 μm or more and 2.0 μm or less. [Aspect 7] A metal-clad laminate according to aspect 5 or 6, wherein the dielectric loss tangent of the primer layer at a frequency of 10 GHz is 0.0030 or less.[Aspect 8] A metal-clad laminate according to any one of aspects 5 to 7, wherein the primer layer contains a styrene-based elastomer. [Aspect 9] A metal-clad laminate according to any one of aspects 1 to 8, wherein the developed area ratio Sdr of the interface on the insulating layer side surface of the metal layer, measured in accordance with JIS B0681-2:2018, is 0.1% or more and 5.0% or less. [Aspect 10] A resin-coated metal for manufacturing a metal-clad laminate according to any one of aspects 1 to 8, comprising a metal layer and a primer precursor layer provided on at least one surface of the metal layer.

[0010] This is a schematic cross-sectional view showing an example of a metal-clad laminate in this disclosure.

[0011] Figure 1 schematically shows an example of a metal-clad laminate according to the present disclosure. The metal-clad laminate 10 shown in Figure 1 comprises a metal layer 12 and an insulating layer 14. The insulating layer 14 is provided on at least one surface of the metal layer 12 and has a thickness of more than 2.0 μm. In the first embodiment of the present disclosure, the metal-clad laminate 10 has a ratio Ha / Hb of hardness Ha (MPa) measured by a nanoindenter at a depth of 0.1 μm of the insulating layer 14 to hardness Hb (MPa) measured by a nanoindenter at a depth of 2.0 μm of the insulating layer 14, which is 0.60 or less. In the second embodiment of the present disclosure, the ratio Ea / Eb of elastic modulus Ea (MPa) measured by a nanoindenter at a depth of 0.1 μm of the insulating layer 14 to elastic modulus Eb (MPa) measured by a nanoindenter at a depth of 2.0 μm of the insulating layer 14, which is 0.50 or less. Here, "depth of 0.1 μm" of the insulating layer 14 refers to the depth position where the indenter of the nanoindenter is pressed 0.1 μm into the insulating layer 14 from the surface of the insulating layer 14 on the metal layer 12 side. Also, "depth of 2.0 μm" of the insulating layer 14 refers to the depth position where the indenter of the nanoindenter is pressed 2.0 μm into the insulating layer 14 from the surface of the insulating layer 14 on the metal layer 12 side. In this way, in a metal-clad laminate 10 equipped with a metal layer 12 and an insulating layer 14, the peel strength between the metal layer 12 and the insulating layer 14 can be improved by controlling the ratio of the hardness Ha or elastic modulus Ea at a depth of 0.1 μm of the insulating layer 14 to the hardness Hb or elastic modulus Eb at a depth of 2.0 μm of the insulating layer 14 (i.e., ratio Ha / Hb or ratio Ea / Eb) to a predetermined value or less.

[0012] One example of a mechanism by which the peel strength between the metal layer 12 and the insulating layer 14 is improved by controlling the ratio Ha / Hb or ratio Ea / Eb within the above range is as follows. As mentioned above, when the metal layer and the insulating resin substrate (e.g., prepreg) are peeled apart in a metal-clad laminate, tensile stress is applied particularly to the portion of the insulating resin substrate near the metal layer. In this respect, since the resin used in the insulating resin substrate is generally hard (i.e., brittle), there is a risk that the resin may crack due to the above tensile stress. In contrast, in the metal-clad laminate 10 of this disclosure, the hardness Ha or elastic modulus Ea of the insulating layer 14 at a depth of 0.1 μm is much lower than the hardness Hb or elastic modulus Eb at a depth of 2.0 μm. That is, because the portion of the insulating layer 14 near the metal layer 12 is soft, the above tensile stress can be mitigated. As a result, it is considered that cracking of the insulating layer 14 can be effectively suppressed and the peel strength between the metal layer 12 and the insulating layer 14 can be improved.

[0013] Therefore, according to the first embodiment of the metal-clad laminate 10, the ratio Ha / Hb of the hardness Ha at a depth of 0.1 μm of the insulating layer 14 to the hardness Hb at a depth of 2.0 μm of the insulating layer 14 is 0.60 or less, preferably 0.01 to 0.50, more preferably 0.01 to 0.30, and even more preferably 0.01 to 0.20. The hardness Ha at a depth of 0.1 μm of the insulating layer 14 is preferably 300 MPa or less, more preferably 10 MPa to 200 MPa, even more preferably 10 MPa to 150 MPa, and particularly preferably 10 MPa to 100 MPa. By doing so, tensile stress can be more effectively relieved, and the peel strength between the metal layer 12 and the insulating layer 14 can be further improved. The hardness Hb of the insulating layer 14 at a depth of 2.0 μm is not particularly limited as long as the above ratio Ha / Hb is satisfied, but is typically 60 MPa to 900 MPa, more typically 300 MPa to 800 MPa, even more typically 300 MPa to 700 MPa, and particularly typically 300 MPa to 600 MPa.

[0014] According to a second embodiment of the metal-clad laminate 10, the ratio Ea / Eb of the elastic modulus Ea at a depth of 0.1 μm of the insulating layer 14 to the elastic modulus Eb at a depth of 2.0 μm of the insulating layer 14 is 0.50 or less, preferably 0.01 to 0.40, more preferably 0.01 to 0.35, and even more preferably 0.01 to 0.30. The elastic modulus Ea at a depth of 0.1 μm of the insulating layer 14 is preferably 5000 MPa or less, more preferably 100 MPa to 4000 MPa, even more preferably 100 MPa to 3000 MPa, and particularly preferably 100 MPa to 2000 MPa. By doing so, tensile stress can be more effectively relieved, and the peel strength between the metal layer 12 and the insulating layer 14 can be further improved. The elastic modulus Eb of the insulating layer 14 at a depth of 2.0 μm is not particularly limited as long as the above ratio Ea / Eb is satisfied, but is typically 2000 MPa to 18000 MPa, more typically 5000 MPa to 15000 MPa, even more typically 5000 MPa to 12000 MPa, and particularly typically 5000 MPa to 10000 MPa.

[0015] It goes without saying that the metal-clad laminate 10 in the first embodiment may satisfy the various parameters (elastic modulus Ea, elastic modulus Eb, and ratio Ea / Eb) of the second embodiment, and the metal-clad laminate 10 in the second embodiment may satisfy the various parameters (hardness Ha, hardness Hb, and ratio Ha / Hb) of the first embodiment.

[0016] The hardness and modulus of elasticity of the insulating layer 14 at the above-mentioned specific depth can be measured using a commercially available nanoindenter. The specific method for measuring hardness and modulus of elasticity using a nanoindenter will be shown in the examples described later. In this specification, hardness means the indentation hardness by the nanoindenter, that is, the value obtained by dividing the test force applied to the sample by the area of ​​the indenter that was in contact with the sample when the test force was applied (contact projected area). In this specification, modulus of elasticity means reduced modulus.

[0017] The thickness of the insulating layer 14 can be appropriately determined according to the circuit design of the printed circuit board and is not particularly limited, but is greater than 2.0 μm, typically 3.0 μm to 5 mm, more typically 10 μm to 4 mm, and even more typically 30 μm to 1 mm.

[0018] The insulating layer 14 typically contains a resin (insulating resin). In this specification, the term "resin" includes not only polymer materials (resins in the narrow sense) such as thermoplastic resins, thermosetting resins, and elastomers having rubber-like properties, but also low molecular weight materials (resins in the broad sense) such as oligomers and prepolymers. In this regard, a metal-clad laminate 10 satisfying the above ratio Ha / Hb or ratio Ea / Eb can preferably be manufactured by forming the insulating layer 14 with two or more resins having different hardness or elastic moduli. In other words, by forming the portion of the insulating layer 14 near the metal layer 12 (including a depth of 0.1 μm) with a resin with low hardness or elastic modulus (for example, a styrene-based elastomer described later), and forming the portion of the insulating layer 14 away from the metal layer 12 (including a depth of 2.0 μm) with a resin with high hardness or elastic modulus (for example, epoxy resin, cyanate ester resin, polyimide resin, bismaleimide triazine resin (BT resin), phenolic resin, polyphenylene ether resin, hydrocarbon resin, acrylic resin, and resin compositions containing one or more of these resins), a metal-clad laminate 10 with a small Ha / Hb ratio or Ea / Eb ratio can be preferably produced. In this regard, the Ha / Hb ratio or Ea / Eb ratio can also be controlled to a desired range by appropriately changing the resin blending ratio. The portion of the insulating layer 14 away from the metal layer 12 (including a depth of 2.0 μm) may contain glass fibers and / or inorganic fillers such as silica. Because the insulating layer 14 contains glass fibers, its hardness and elastic modulus can be increased compared to the resin alone, making it easier to manufacture a metal-clad laminate 10 that satisfies the above ratios of Ha / Hb or Ea / Eb.

[0019] In a preferred embodiment of the present disclosure, as shown in Figure 1, the insulating layer 14 includes a primer layer 14a in contact with the metal layer 12 and a cured prepreg 14b (hereinafter simply referred to as "prepreg 14b") provided on the side of the primer layer 14a opposite to the metal layer 12.

[0020] The primer layer 14a is an adhesive layer that improves the adhesion between the metal layer 12 and the prepreg 14b. Therefore, the primer layer 14a typically has a lower hardness or modulus of elasticity than the prepreg 14b. In this way, the tensile stress applied to the insulating layer 14 when the metal layer 12 and the insulating layer 14 are peeled apart can be effectively relieved by the primer layer 14a. From this viewpoint, in the metal-clad laminate 10 of this embodiment, the position of the insulating layer 14 at a depth of 0.1 μm is typically located within the primer layer 14a, and the position of the insulating layer 14 at a depth of 2.0 μm is typically located within the prepreg 14b.

[0021] The thickness of the primer layer 14a is preferably 0.5 μm or more and 2.0 μm or less, more preferably 0.5 μm or more and less than 2.0 μm, even more preferably 0.5 μm or more and 1.5 μm or less, particularly preferably 0.8 μm or more and 1.5 μm or less, and most preferably 0.9 μm or more and 1.4 μm or less. As mentioned above, since the primer layer 14a has the function of easing the tensile stress applied to the insulating layer 14, making the primer layer 14a thicker is advantageous from the viewpoint of improving the peel strength between the metal layer 12 and the insulating layer 14. However, if a thick primer layer 14a is provided, it will deviate significantly from the expected thickness of the insulating resin substrate (i.e., the thickness of the prepreg 14b), which will impose constraints on the circuit design and the resulting thickness of the printed circuit board. In this regard, according to the metal-clad laminate 10 of this embodiment, by controlling the ratio Ha / Hb or ratio Ea / Eb within the above predetermined range, the adhesion between the metal layer 12 and the insulating layer 14 can be improved even when the thickness of the primer layer 14a is made thin so that it falls within the above range.

[0022] The primer layer 14a is particularly preferably composed of a styrene-based elastomer from the viewpoint of controlling hardness or elastic modulus to a low level. In this specification, a styrene-based elastomer means a copolymer containing styrene-derived parts, and is typically a block copolymer composed of styrene-derived hard blocks (hard segments) and soft blocks (soft segments). The styrene content (hard block content) in the styrene-based elastomer is preferably 10% to 60% by weight, more preferably 20% to 50% by weight, and even more preferably 20% to 40% by weight, from the viewpoint of balancing dielectric properties, flexibility, and peel strength. The primer layer 14a may contain resins other than styrene-based elastomers, but it is preferable that it does not contain epoxy resin from the viewpoint of controlling hardness or elastic modulus to a low level and ensuring excellent dielectric properties. The content of styrene-based elastomer in the primer layer 14a is preferably 50 parts by weight or more and 100 parts by weight or less, more preferably 60 parts by weight or more and 90 parts by weight or less, and even more preferably 60 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the total amount of resin components (solids). Here, the total amount of resin components (solids) of 100 parts by weight includes not only the resin but also the weight of additives (crosslinking agents, reaction initiators, etc.) that constitute part of the resin, and fillers are not included.

[0023] Styrene elastomers may or may not be hydrogenated. Preferred examples of styrene elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and styrene-4-methylstyrene-isoprene-butadiene block copolymer. These styrene elastomers may be chemically modified to introduce various functional groups into the molecule. Examples of such chemical modification include amine modification, pyridine modification, and carboxy modification (e.g., maleic anhydride modification). The functional group introduction site may be a soft block (i.e., main chain modification type) or a hard block (i.e., end modification type).

[0024] Styrene-based elastomers are preferably those that have reactive unsaturated bonds in their molecules that exhibit reactivity in response to heat or ultraviolet light. Preferred examples of reactive unsaturated bonds include cyanate groups, maleimide groups, vinyl groups, (meth)acryloyl groups, allyl groups, ethynyl groups, styryl groups, and combinations thereof. Styryl groups are particularly preferred because they are highly reactive and allow for reaction control (reactions are less likely to occur over time, allowing for resin storage and ensuring a long product life).

[0025] The dielectric loss tangent of the primer layer 14a at a frequency of 10 GHz is preferably 0.0030 or less, more preferably 0.0010 or less, and even more preferably 0.0007 or less. A lower dielectric loss tangent is preferable, and the lower limit is not particularly limited, but is typically 0.0001 or higher. This dielectric loss tangent shall be measured by the perturbation cavity resonator method in accordance with JIS R 1641-2007.

[0026] The primer layer 14a may contain additives commonly added to resins. Examples of additives include crosslinking agents, reaction initiators, reaction accelerators, flame retardants, silane coupling agents, dispersants, and antioxidants.

[0027] The primer layer 14a may contain a crosslinking agent. The crosslinking agent is not particularly limited as long as it forms a three-dimensional network within the primer layer, but from the viewpoint of controlling the dielectric loss tangent to a low level, it is preferable to have a reactive unsaturated bond in the molecule that exhibits reactivity in response to heat or ultraviolet light. Preferred examples of reactive unsaturated bonds include cyanate groups, maleimide groups, terminal vinyl groups, (meth)acryloyl groups, allyl groups, ethynyl groups, styryl groups, and combinations thereof. Styryl groups are particularly preferred because they are highly reactive and allow for reaction control (reactions are less likely to occur over time, allowing for resin storage and ensuring a long product life). Furthermore, from the viewpoint of controlling hardness or elastic modulus to a low level, the content of the crosslinking agent in the primer layer 14a is preferably less than 50 parts by weight, more preferably less than 40 parts by weight, and even more preferably less than 35 parts by weight, per 100 parts by weight of the total amount of resin components. Such crosslinking agents provide desirable properties for electronic materials, such as improved dielectric properties (i.e., reduction of dielectric loss tangent Df) and a reduction in the coefficient of thermal expansion (CTE).

[0028] The primer layer 14a may or may not contain a filler. Examples of fillers that can be included in the primer layer 14a include inorganic fillers such as silica, talc, alumina, and boron nitride (BN), and organic fillers composed of liquid crystal polymer (LCP). The filler is preferably in particulate form. The average particle size D50 (by volume) of the filler is preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.03 μm or more and 0.7 μm or less. An average particle size D50 within this range is less than the thickness of the primer layer, making it suitable for inclusion in the primer layer, and also brings about desirable properties as an electronic material, such as improved dielectric properties (i.e., reduction of dielectric loss tangent Df) and reduction of linear thermal expansion coefficient (CTE). The filler content can be any amount and is not particularly limited, but from the viewpoint of ease of filler dispersion and fluidity of the resin composition, it is preferable that the volume ratio of the filler to the total volume of the resin components and filler is 5 vol% to 60 vol%, more preferably 10 vol% to 50 vol%, even more preferably 10 vol% to 40 vol%, and particularly preferably 15 vol% to 35 vol%.

[0029] The prepreg 14b typically comprises glass fibers and a resin (preferably an insulating resin) impregnated into the glass fibers. Preferred examples of resins included in the prepreg 14b include epoxy resins, cyanate ester resins, polyimide resins, bismaleimide triazine resins (BT resins), phenolic resins, polyphenylene ether resins, hydrocarbon resins, acrylic resins, and resin compositions containing one or more of these resins. From the viewpoint of ensuring that the insulating layer 14 has sufficient rigidity when used in a printed circuit board, the prepreg 14b typically contains a thermosetting resin. In the metal-clad laminate 10, the thermosetting resin included in the prepreg 14b is in a cured state (C-stage).

[0030] From the viewpoint of ensuring adhesion with the primer layer 14a, it is preferable that the prepreg 14b contains a resin having reactive unsaturated bonds in its molecule. By having both the primer layer 14a and the prepreg 14b contain resins having reactive unsaturated bonds in their molecules, the adhesion between them can be further improved. Furthermore, from the viewpoint of compatibility and reactivity with the primer layer 14a, it is preferable that the prepreg 14b contains a vinylbenzene-based resin. The vinylbenzene-based resin can be any resin having a styryl group in its molecule, such as divinylbenzene or its prepolymer, and is not particularly limited. Examples of commercially available vinylbenzene-based resins include the DVB series from Nippon Steel Chemical & Material Co., Ltd. and the OPE series from Mitsubishi Gas Chemical Company, Inc.

[0031] The thickness of the prepreg 14b can be appropriately determined according to the circuit design of the printed circuit board and is not particularly limited, but the thickness of the prepreg per layer to be laminated is typically 30 μm or more and 0.2 mm or less, and more typically 50 μm or more and 0.15 mm or less. In the metal-clad laminate 10, the number of layers to which the prepreg 14b is laminated is one or more, and typically seven or less.

[0032] The metal layer 12 is a layer composed of a metal (preferably copper), and is typically a metal foil such as copper foil. The metal layer 12 may be a metal foil in the as-is state after electrolytic foil manufacturing or rolling (so-called raw foil), or it may be a surface-treated foil in which a surface treatment has been applied to at least one of its surfaces. The surface treatment can be any type of surface treatment performed to improve or impart certain properties (e.g., rust prevention, moisture resistance, chemical resistance, acid resistance, heat resistance, and adhesion to the substrate) to the surface of the metal foil. The surface treatment may be performed on one side of the metal foil or on both sides of the metal foil. Examples of surface treatments performed on the metal layer 12 include rust prevention treatment, silane treatment, roughening treatment, barrier formation treatment, etc.

[0033] The interface area ratio Sdr on the surface of the metal layer 12 on the insulating layer 14 side is preferably 0.1% to 5.0%, more preferably 0.1% to 2.0%, even more preferably 0.1% to 1.0%, and particularly preferably 0.1% to 0.5%. In this specification, "interface area ratio Sdr" or "Sdr" is a parameter measured in accordance with JIS B0681-2:2018 that represents how much the developed area (surface area) of the defined region has increased relative to the area of ​​the defined region. In this specification, the interface area ratio Sdr is expressed as the increase in surface area (%). A smaller value indicates a surface shape that is closer to flat, and the Sdr of a perfectly flat surface is 0%. On the other hand, a larger value indicates a surface shape with many irregularities. For example, if the Sdr of a surface is 1.0%, it indicates that the surface area of ​​this surface has increased by 1.0% compared to a perfectly flat surface. When Sdr is within the above range, transmission loss in high-frequency applications can be desirablely reduced. In other words, it is possible to reduce conductor loss caused by the metal layer 12, which can increase due to the skin effect of the metal layer, which becomes more pronounced at higher frequencies, thereby achieving a further reduction in transmission loss. Sdr can be calculated by measuring the surface profile of a predetermined measurement area on the surface of the metal layer 12 using a commercially available laser microscope. Preferred measurement and analysis conditions for Sdr using a laser microscope are shown in the examples described later.

[0034] The thickness of the metal layer 12 is not particularly limited, but is typically between 0.1 μm and 100 μm. However, if the thickness of the metal layer is, for example, 10 μm or less, the metal-clad laminate 10 of this disclosure may be a metal foil with a carrier equipped with a release layer and a carrier, with an insulating layer formed on the surface of the metal foil to improve handling.

[0035] The metal-clad laminate 10 may have a metal layer 12 provided on one side of the insulating layer 14, or it may have metal layers 12 provided on both sides of the insulating layer 14. Furthermore, the metal-clad laminate 10 may have an additional insulating layer provided on the side of the metal layer 12 opposite to the insulating layer 14. In the metal-clad laminate 10, the peel strength between the metal layer 12 and the insulating layer 14 (i.e., normal peel strength), measured in accordance with JIS C 6481-1996, is preferably 0.5 kgf / cm or more, more preferably 0.6 kgf / cm or more, and even more preferably 0.7 kgf / cm or more, for example, when the thickness of the metal layer is 18 μm. A higher peel strength is desirable, and its upper limit is not particularly limited, but it is typically 1.5 kgf / cm or less. The method for measuring the peel strength will be as shown in the examples described later.

[0036] The metal-clad laminate 10 of the present disclosure is preferably manufactured using a resin-coated metal. Accordingly, according to a preferred embodiment of the present disclosure, a resin-coated metal (for example, a resin-coated metal foil such as resin-coated copper foil) for manufacturing the metal-clad laminate 10 is provided. This resin-coated metal comprises a metal layer 12 and a primer precursor layer provided on at least one surface of the metal layer 12. The metal layer 12 is as described above with respect to the metal-clad laminate 10. The primer precursor layer is a layer that becomes the aforementioned primer layer 14a by undergoing various reactions such as crosslinking reactions and curing reactions during lamination with the prepreg 14b.

[0037] The method for forming the primer precursor layer is not particularly limited, but it is preferably carried out by dissolving the raw material components of the primer layer 14a in a solvent such as toluene or methyl ethyl ketone to prepare a resin varnish, and then coating the resin varnish onto the surface of the metal layer 12 to a predetermined thickness and drying it. The coating method is arbitrary, but in addition to the gravure coating method, the die coating method, knife coating method, etc. can be used. It is also possible to coat using a doctor blade or bar coater.

[0038] A preferred method for manufacturing a metal-clad laminate 10 using resin-coated metal foil is as follows: A semi-cured (B-stage) prepreg is laminated onto the surface of the primer precursor layer of the resin-coated metal foil, and vacuum hot press molding is performed. This transforms the primer precursor layer into a primer layer 14a and brings the prepreg to a cured state (C-stage). In this way, a metal-clad laminate 10 can be obtained in which the primer layer 14a and the prepreg 14b are laminated in this order on the surface of the metal layer 12.

[0039] The metal-clad laminate 10 or resin-coated metal of this disclosure is preferably used in the manufacture of printed circuit boards. That is, according to a preferred embodiment of this disclosure, a printed circuit board comprising a metal-clad laminate 10, or a printed circuit board manufactured using a metal-clad laminate 10, is provided. The printed circuit board according to this embodiment includes a layer configuration in which an insulating layer and a metal layer are laminated in that order. Known layer configurations can be used for the printed circuit board. Specific examples of printed circuit boards include single-sided or double-sided printed circuit boards in which circuits are formed on the metal layer 12 of the metal-clad laminate 10, and multilayer printed circuit boards made by layering these. Other specific examples include flexible printed circuit boards in which the resin-coated metal of this disclosure is formed on a resin film to form circuits, COF, TAB tape, build-up multilayer printed circuit boards, and direct build-up on wafers in which the lamination of resin-coated metal and circuit formation are alternately repeated on a semiconductor integrated circuit. In particular, the metal-clad laminate 10 of this disclosure is preferably applicable as an insulating layer and a conductor layer for printed circuit boards for high-frequency digital communication in network equipment. Examples of such network equipment include (i) servers and routers within base stations, (ii) corporate networks, and (iii) core systems for high-speed mobile communications.

[0040] The present invention will be further described in detail by the following examples. However, the present invention is not limited to the following examples.

[0041] Examples 1 to 9 (1) Preparation of resin varnish First, the styrenic elastomer or polyvinyl acetal resin shown below was prepared as a raw material component for the resin varnish. Further, for Examples 7 to 9, the crosslinking agent and reaction initiator shown below were prepared. <Styrenic elastomer> -Examples 1 and 9: V9461 (manufactured by Kuraray Co., Ltd., Septon (registered trademark), hydrogenated styrene·4-methylstyrene·isoprene·butadiene block copolymer having a styryl group, hard block (styrene and 4-methylstyrene) content: 30% by weight) -Examples 2 and 8: TR2250 (manufactured by ENEOS Materials Corporation, styrene·butadiene·styrene block copolymer, styrene / butadiene ratio (ST / BD ratio) = 52 / 48) -Example 3: TR2827 (manufactured by ENEOS Materials Corporation, styrene·butadiene·styrene block copolymer, styrene / butadiene ratio (ST / BD ratio) = 24 / 76) -Examples 4 and 7: MP10 (manufactured by Asahi Kasei Corporation, Tuftec (registered trademark), amine-modified hydrogenated styrene·ethylene·butylene·styrene block copolymer, styrene / ethylene·butylene ratio (S / EB ratio) = 32 / 68) -Example 5: M1913 (manufactured by Asahi Kasei Corporation, Tuftec (registered trademark), maleic anhydride-modified hydrogenated styrene·ethylene·butylene·styrene block copolymer, styrene / ethylene·butylene ratio (S / EB ratio) = 29 / 71) <Polyvinyl acetal resin> -Example 6: KS-1 (manufactured by Sekisui Chemical Co., Ltd., high heat resistance grade) <Crosslinking agent> -Example 7: Taiku prepolymer (manufactured by Nippon Kasei Chemical Co., Ltd., triallyl isocyanurate prepolymer, functional group type: allyl group, number average molecular weight Mn: 7400) -Example 8: B-1000: manufactured by Nippon Soda Co., Ltd., NISSO-PB B series, polybutadiene oligomer, functional group type: 1,2-vinyl group, number average molecular weight Mn: 1200) -Example 9: OPE-2st-1200 (manufactured by Mitsubishi Gas Chemical Company, Inc., polyphenylene ether oligomer, functional group type: styryl group, number average molecular weight Mn: 1150) <Reaction initiator> -Examples 7 to 9: Perbutyl P (manufactured by NOF CORPORATION, peroxide)

[0042] For Examples 1 to 6, the above raw material components were weighed into a round flask, and a solvent was added so that the raw material component concentrations shown in Table 1 were obtained. A mantle heater, a stirring blade, and a flask lid equipped with a reflux condenser were attached to the round flask containing the raw material components and the solvent, and the temperature was raised to 60°C while stirring. Stirring was continued at 60°C for 2 hours to dissolve the raw material components, and then the obtained resin varnish was allowed to cool. Thus, a resin varnish having the raw material component concentrations shown in Table 1 was obtained.

[0043]

[0044] For Examples 7 to 9, the above styrenic elastomer as the main raw material component was weighed into a round flask, and a crosslinking agent was added to the main raw material component so as to obtain the ratio shown in Table 2. Here, the crosslinking agent ratio shown in Table 2 means the ratio (% by weight) of the crosslinking agent when the total amount of the main raw material component and the crosslinking agent is 100% by weight. Thereafter, 0.5 parts by weight of Perbutyl P as a reaction initiator was added based on 100 parts by weight of the total of the main raw material component and the crosslinking agent, and a solvent was added so that the raw material component concentration shown in Table 2 was obtained. A mantle heater, a stirring blade, and a flask lid equipped with a reflux condenser were attached to the round flask containing these raw material components and the solvent, and the temperature was raised to 60°C while stirring. Stirring was continued at 60°C for 2 hours to dissolve the raw material components, and then the obtained resin varnish was allowed to cool. Thus, a resin varnish having the raw material component concentrations shown in Table 2 was obtained.

[0045]

[0046] (2) Production of electrolytic copper foil An electrolytic copper foil was produced by the following method. In a copper sulfate solution, a titanium rotating electrode (surface roughness Ra: 0.20 μm) was used as the cathode, and a dimensionally stable anode (DSA) was used as the anode, with a solution temperature of 45°C and a current density of 55 A / dm ２Electrolytic copper foil was prepared as the raw material by electrolysis. The composition of this copper sulfate solution was as follows: copper concentration 80 g / L, free sulfuric acid concentration 140 g / L, bis(3-sulfopropyl) disulfide concentration 30 mg / L, diallyldimethylammonium chloride polymer concentration 50 mg / L, and chlorine concentration 40 mg / L. Particulate protrusions were formed on the surface of the raw material foil facing the electrolyte. The formation of particulate protrusions was carried out in a copper sulfate solution (copper concentration: 13 g / L, free sulfuric acid concentration 55 g / L, 9-phenylacridine concentration 140 mg / L, chlorine concentration: 35 mg / L) at a solution temperature of 30°C and a current density of 50 A / dm². ２ This was carried out by electrolysis under the following conditions.

[0047] On the electrolyte surface of the raw foil obtained in this way, zinc-nickel film formation, chromate layer formation, and silane layer formation were carried out sequentially under the conditions shown below. <Zinc-nickel film formation> ・Potassium pyrophosphate concentration: 80 g / L ・Zinc concentration: 0.2 g / L ・Nickel concentration: 2 g / L ・Liquid temperature: 40°C ・Current density: 0.5 A / dm ２ <Chromate layer formation> ・Chromic acid concentration: 1 g / L, pH 11 ・Solution temperature: 25°C ・Current density: 1 A / dm ２ <Silane layer formation> • Silane coupling agent: 3-aminopropyltrimethoxysilane (3 g / L aqueous solution) • Liquid treatment method: Shower treatment

[0048] The Sdr on the surface-treated surface of this electrolytic copper foil was 0.3%. This Sdr was measured using a laser microscope (OLS5000, manufactured by Olympus Corporation) in accordance with JIS B0681-2:2018. Specifically, the surface profile of a 64 μm × 64 μm area on the surface-treated surface of the electrolytic copper foil was measured at four locations (N=4) using the laser microscope with a 100x lens with an numerical aperture (N.A.) of 0.95. After noise reduction and primary linear surface tilt correction were performed on the surface profile of the treated surface at each measurement location, the above Sdr was calculated by averaging the Sdr of the developed area ratio of the interface obtained by surface property analysis. The total thickness of the electrolytic copper foil, including the surface-treated surface, was 18 μm.

[0049] (3) Preparation of resin film The obtained resin varnish was applied to the surface of a release film (AGC Inc., "Aflex®") using a comma coating machine so that the thickness of the resin after drying was 20 μm, and dried in an oven at 130°C for 2 minutes. The release film was peeled off the dried resin, and two layers of only the dried resin were laminated together and dried at 200°C for 90 minutes at 20 kgf / cm². ２ A resin film with a thickness of 40 μm was obtained by vacuum press molding under these conditions.

[0050] (4) Preparation of copper-clad laminate The obtained resin varnish was applied to the surface-treated surface of the electrolytic copper foil using a gravure coating machine so that the resin thickness after drying was 1.0 μm, and dried in an oven at 130°C for 2 minutes to obtain a resin-coated copper foil with copper foil and a primer precursor layer. Two sheets of 68 μm thick prepreg (Panasonic Corporation, MEGTRON 7 series "R-5680") were stacked to a thickness of 0.136 mm, and the resin-coated copper foil was laminated on top of it so that the resin was in contact with the prepreg, and dried at 200°C for 90 minutes at 30 kgf / cm². ２ Vacuum press molding was performed under these conditions. In this way, a copper-clad laminate with copper foil and an insulating layer (primer layer and prepreg) was obtained.

[0051] (5) Various evaluations The following evaluations were performed on the resin films and copper-clad laminates that were prepared.

[0052] <Evaluation 1: Measurement of Hardness and Elastic Modulus> The hardness and elastic modulus of the insulating layer of the copper-clad laminate were measured as follows using a nanoindenter test apparatus (FT-NMT04, manufactured by Femto Tools).

[0053] (a) Sample preparation The copper foil of the obtained copper-clad laminate was removed by etching to obtain an insulating layer sample. This insulating layer sample was cut to a size of 10 mm square, and with the test surface (i.e., the surface that was in contact with the electrolytic copper foil) facing upwards, it was fixed to an aluminum pin stub using a resin mainly composed of cyanoacrylate, ensuring that there were no air bubbles or voids. The pin stub with the sample fixed to it was fixed to the sample holder of the nanoindentation test apparatus.

[0054] (b) Apparatus Setup The nanoindenter testing apparatus was installed inside an electron microscope (Carl Zeiss, SUPRA55VP). This made it possible to perform the indentation test while observing with an SEM (scanning electron microscope). After setting up the apparatus, the position of the sample was adjusted so that the test surface was accurately positioned at the measurement location of the nanoindenter.

[0055] (c) Indentation Test An indentation test was performed based on the following SEM observation conditions and indentation test conditions. (SEM observation conditions) ・Acceleration voltage: 3kV ・Aperture size: 30μm ・Observation magnification: 1000x ・Observation mode: Secondary electron image (SE2) mode ・Working distance: 15mm (Indentation test conditions) ・Probe material: Diamond indenter ・Probe tip shape: Berkovich (tip angle: 65.3°) ・Measurement mode: Indentation CSM (Continuous Stiffness Measurement) ・Frequency: 200Hz ・Maximum indentation load: 200mN ・Maximum indentation displacement: 10μm ・Elastic modulus calibration value: 70.2 GPa in fused silica

[0056] The indentation test was performed using Femto Tools' control and analysis software, "Femto Tools Software Ver. 2.6.7," as follows. First, the nanoindenter probe was brought into contact with the sample surface to apply a load of 40 μN. Immediately afterward, the probe was moved 1.5 μm perpendicular to the sample, and the measurement position was moved 10 μm in both the X and Y directions. The load was then gradually increased according to the load profile set at the maximum indentation displacement. After reaching the maximum load or the set indentation displacement, the load was gradually decreased. During the indentation test, the progress of the indentation was observed in real time using a SEM. The indentation test was performed in this manner, and load-displacement data recorded during the test was obtained. In addition, SEM images were obtained by photographing the shape of the indentation marks.

[0057] (d) Data Analysis Data analysis was performed using the "Data Analysis" function of "Femto Tools Software Ver. 2.6.7," control analysis software manufactured by Femto Tools. Specifically, the mechanical properties (hardness and modulus of elasticity) of the sample were calculated using the acquired load-displacement data. In particular, contact points were set for the depth at which the hardness and modulus of elasticity of the sample were to be determined from the Displacement-Ampultitude force curve. For hardness and elastic modulus at a depth of 2.0 μm, the tangent to the Displacement-Amplitude force curve was set within the Displacement range of 0.8 μm to 2.0 μm, a Contact Point was set, and the average values ​​of hardness and elastic modulus within the Displacement range of 0.8 μm to 2.0 μm were calculated. On the other hand, for hardness and elastic modulus at a depth of 0.1 μm, the tangent to 0.1 μm was measured starting from the point where the nanoindenter probe contacted the sample, a Contact Point was set, and the average values ​​of hardness and elastic modulus within the Displacement range of 0.07 μm to 0.13 μm were adopted. The above indentation tests were performed and analyzed at five locations per sample. The average values ​​were adopted as the hardness Ha and elastic modulus Ea at a depth of 0.1 μm, and the hardness Hb and elastic modulus Eb at a depth of 2.0 μm for each example. The results are shown in Table 3.

[0058] <Evaluation 2: Peel Strength> Copper wiring with a wiring width of 10 mm and a wiring thickness of 18 μm was formed on a copper-clad laminate using a subtractive method, and the peel strength was measured at room temperature (25°C) in accordance with JIS C 6481-1996. The measurement was performed five times, and the average value was used as the peel strength value. A peel strength of 0.50 kgf / cm or higher was judged as passing, and a peel strength of less than 0.50 kgf / cm was judged as failing. The peel strength measured here reflects four peel modes: interfacial peeling between the prepreg / primer layer, cohesive failure of the primer layer, interfacial peeling within the primer layer, and interfacial peeling between the primer layer and copper foil. A higher value indicates better adhesion to the substrate such as the prepreg, strength of the primer layer, and adhesion of the resin (insulating layer) to the low-roughness foil. The results are shown in Table 3.

[0059] <Evaluation 3: Dielectric Loss Tangent> The dielectric loss tangent at 10 GHz was measured for the resin film using the perturbed cavity resonator method. This measurement was performed in accordance with JIS R 1641-2007, using a measuring device (KEYCOM resonator and KEYSIGHT network analyzer) after cutting the resin film to the sample size of the resonator. A measured dielectric loss tangent at 10 GHz of 0.0030 or less was judged as passing, and a value greater than 0.0030 was judged as failing. The results are shown in Table 3.

[0060]

[0061] 10 Metal-clad laminate 12 Metal layer 14 Insulating layer 14a Primer layer 14b Prepreg

Claims

1. A metal-clad laminate comprising: a metal layer; and an insulating layer having a thickness of more than 2.0 μm provided on at least one surface of the metal layer, wherein the ratio Ha / Hb of the hardness Ha (MPa) of the insulating layer measured by a nanoindenter at a depth of 0.1 μm to the hardness Hb (MPa) of the insulating layer measured by a nanoindenter at a depth of 2.0 μm is 0.60 or less, the depth of the insulating layer of 0.1 μm is the depth position obtained by pressing the indenter of the nanoindenter 0.1 μm into the insulating layer from the surface of the insulating layer on the metal layer side, and the depth of the insulating layer of 2.0 μm is the depth position obtained by pressing the indenter of the nanoindenter 2.0 μm into the insulating layer from the surface of the insulating layer on the metal layer side.

2. The metal-clad laminate according to claim 1, wherein the hardness Ha is 300 MPa or less.

3. A metal-clad laminate comprising: a metal layer; and an insulating layer having a thickness of more than 2.0 μm provided on at least one surface of the metal layer, wherein the ratio Ea / Eb of the elastic modulus Ea (MPa) of the insulating layer at a depth of 0.1 μm to the elastic modulus Eb (MPa) of the insulating layer at a depth of 2.0 μm is 0.50 or less, the depth of the insulating layer of 0.1 μm is the depth position obtained by pressing the indenter of the nanoindenter 0.1 μm into the insulating layer from the surface of the insulating layer on the metal layer side, and the depth of the insulating layer of 2.0 μm is the depth position obtained by pressing the indenter of the nanoindenter 2.0 μm into the insulating layer from the surface of the insulating layer on the metal layer side.

4. The metal-clad laminate according to claim 3, wherein the elastic modulus Ea is 5000 MPa or less.

5. The metal-clad laminate according to any one of claims 1 to 4, wherein the insulating layer includes a primer layer in contact with the metal layer and a cured prepreg provided on the side of the primer layer opposite to the metal layer.

6. The metal-clad laminate according to claim 5, wherein the primer layer has a thickness of 0.5 μm or more and 2.0 μm or less.

7. The metal-clad laminate according to claim 5, wherein the dielectric loss tangent of the primer layer at a frequency of 10 GHz is 0.0030 or less.

8. The metal-clad laminate according to claim 5, wherein the primer layer contains a styrene-based elastomer.

9. The metal-clad laminate according to any one of claims 1 to 4, wherein the developed area ratio Sdr of the interface on the insulating layer side surface of the metal layer, measured in accordance with JIS B0681-2:2018, is 0.1% or more and 5.0% or less.

10. A resin-coated metal for manufacturing a metal-clad laminate according to any one of claims 1 to 4, comprising a metal layer and a primer precursor layer provided on at least one surface of the metal layer.

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