Metal laminates and their manufacturing methods, and printed wiring boards

Abstract

The purpose of this invention is to provide a metal laminate that combines high-frequency characteristics with good adhesion at the lamination interface. This invention relates to a metal laminate, a method for manufacturing the same, and a printed circuit board. The metal laminate is formed by laminating a metal layer comprising at least one layer of metal foil onto at least one side of a low-dielectric thin film. A plurality of protrusions of the metal foil are formed on the surface of the metal foil on the side of the low-dielectric thin film. When the width of each protrusion is 'a' and the height of each protrusion is 'b', the average value of b / a + 3σ (where σ is the standard deviation of b / a) is 2.5 or less, and the peel strength between the low-dielectric thin film and the metal layer is 3 N / cm or more.

Description

Technical Field

[0001] This invention relates to metal laminates and their manufacturing methods, as well as printed wiring boards. Prior Technology

[0002] In the past, metal laminates, such as copper foil laminates with low dielectric properties, were known as substrates for printed circuit board manufacturing. In recent years, with the commencement of 5G mobile communication system services in various countries, there is a demand for metal laminates with excellent high-frequency characteristics in the 5G frequency band.

[0003] As a metal laminate, based on the viewpoint of adhesion to low-dielectric thin films, it is known to use a thermal lamination method that involves heating and pressing together a metal foil with a roughened surface. In a typical thermal lamination method, a metal foil with a roughened surface is used, and the low-dielectric thin film is heated to near its melting point to soften it. The roughened particles on the surface of the metal foil are deeply embedded inside the low-dielectric thin film, thus ensuring adhesion through the so-called anchoring effect.

[0004] Patent Document 1 discloses a surface-treated copper foil with a roughened surface, a copper-laminated laminate of the copper foil laminated onto an insulating substrate, and a printed wiring board using the copper-laminated laminate. It also discloses that the copper-laminated laminate can be manufactured by a thermal deposition method.

[0005] In high-frequency applications, it is known that the smoother the surface of the metal foil in a metal laminate, the better its transmission characteristics. In past metal laminates manufactured by thermal deposition, the surface of the metal foil was roughened. Although the anchoring effect could ensure adhesion, the roughened laminate interface would cause a degradation in transmission characteristics in the high-frequency band due to the skin effect, making it not very useful for high-frequency applications. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-90906 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] As mentioned above, in conventional metal laminates manufactured using the thermal deposition method, roughening the surface of the metal foil ensures good adhesion at the lamination interface, but results in insufficient high-frequency characteristics. Therefore, the object of this invention is to provide a metal laminate that combines high-frequency characteristics with good adhesion at the lamination interface. [Methods used to solve problems]

[0009] As a result of active investigation in order to solve the aforementioned problems, the inventors discovered that by using a surface activation bonding method to fabricate metal laminates, metal foils can be laminated to low-dielectric films while maintaining their surface smoothness, thus achieving both high-frequency characteristics and good adhesion at the lamination interface, thereby completing the present invention. In other words, the essence of the present invention is as follows. (1) A metal laminate, wherein a metal laminate comprising at least one layer of metal foil is laminated on at least one side of a low dielectric film, wherein a plurality of protrusions of the metal foil are formed on the surface of the metal foil on the side of the low dielectric film, wherein when the width of the protrusion is a and the height of the protrusion is b, the average value of b / a + 3σ (where σ is the standard deviation of b / a) is 2.5 or less, and the peel strength between the low dielectric film and the metal layer is 3 N / cm or more. (2) The metal composite as described in (1) above, wherein the metal layer between the low dielectric film and the metal foil does not have a sputtered layer made of copper, nickel, chromium or their alloys. (3) The metal laminate as described in (1) or (2) above, wherein the aforementioned metal foil is rolled copper foil, carrier copper foil or electrolytic copper foil. (4) A method for manufacturing a metal laminate, wherein the metal laminate is formed by laminating a metal layer comprising at least one layer of metal foil onto at least one side of a low-dielectric thin film. A plurality of protrusions are formed on the surface of the aforementioned metal foil on the side of the aforementioned low-dielectric film. When the width of each protrusion is denoted as 'a' and the height of each protrusion is denoted as 'b', the average value of b / a + 3σ (where σ is the standard deviation of b / a) is 2.5 or less, and the peel strength between the aforementioned low-dielectric film and the aforementioned metal layer is 3 N / cm or more. The method includes the following steps: Steps for preparing low-dielectric thin films and metal foils, The step of activating at least one surface of the aforementioned low-dielectric thin film by sputter etching. The step of activating the surface of the aforementioned metal foil by sputtering etching, and The step of rolling and bonding the activated surfaces of the aforementioned low dielectric film and the aforementioned metal foil together with a rolling reduction rate of 0 to 30%. (5) A method for manufacturing a metal laminate, wherein the aforementioned metal laminate is formed by laminating a metal layer comprising at least one layer of metal foil onto at least one side of a low-dielectric thin film. The aforementioned metal layer has an intermediate layer containing metal between the aforementioned low-dielectric thin film and the aforementioned metal foil. A plurality of protrusions are formed on the surface of the aforementioned metal foil on the side of the aforementioned low-dielectric film. When the width of each protrusion is denoted as 'a' and the height of each protrusion is denoted as 'b', the average value of b / a + 3σ (where σ is the standard deviation of b / a) is 2.5 or less, and the peel strength between the aforementioned low-dielectric film and the aforementioned metal layer is 3 N / cm or more. The method includes the following steps: Steps for preparing low-dielectric thin films and metal foils, The step of activating at least one surface of the aforementioned low-dielectric thin film by sputter etching. The step of forming a metal-containing intermediate layer on the activated surface of the aforementioned low-dielectric thin film, The step of activating the surface of the aforementioned intermediate layer by sputter etching. The step of activating the surface of the aforementioned metal foil by sputtering etching, and The step of rolling and bonding the aforementioned intermediate layer and the activated surfaces of the aforementioned metal foil together with a rolling reduction rate of 0 to 30%. (6) The manufacturing method of the metal composite as described in (4) above, wherein the metal layer between the aforementioned low dielectric film and the aforementioned metal foil does not have a sputtered layer made of copper, nickel, chromium or their alloys. (7) The manufacturing method of the metal laminate as described in any of (4) to (6) above, wherein the metal foil is rolled copper foil, carrier copper foil or electrolytic copper foil. (8) A method for manufacturing a metal laminate as described in any of (4) to (6) above, wherein at least one surface of the aforementioned low dielectric thin film is activated by sputter etching with oxygen. (9) The method for manufacturing a metal laminate as described in any of (4) to (6) above, wherein the temperature of the aforementioned rolling bonding step is above 15°C and below 100°C. (10) The method for manufacturing a metal laminate as described in any of (4) to (6) above, wherein after rolling bonding, the low dielectric film is at its melting point. Heat treatment shall be performed at a temperature above -150°C and below the aforementioned melting point by 10°C. (11) A printed wiring board, wherein a circuit is formed on a metal laminate as described in any one of (1) to (3) above. This specification contains the disclosure of Japanese Patent Application No. 2021-174667, which forms the basis of the priority claim of this application. [Invention Effects]

[0010] According to the present invention, a metal laminate that combines high frequency characteristics and adhesion of the lamination interface can be provided. Simple Explanation of the Diagram

[0011] [Figure 1] shows a schematic cross-sectional view of a metal laminate of one embodiment of the present invention. [Figure 2] shows a schematic cross-sectional view of a metal laminate of another form according to the first embodiment of the present invention. [Figure 3] shows a cross-sectional view of a metal laminate of one embodiment of the present invention. [Figure 4] shows a schematic cross-sectional view of a metal laminate of another form according to the second embodiment of the present invention. [Figure 5A] shows an enlarged cross-sectional view of the metal laminate 1A. [Figure 5B] is an enlarged cross-sectional view of the protrusion of the metal foil. [Figure 6] shows a cross-sectional photograph of the metal laminate of Example 1. [Figure 7] shows a cross-sectional photograph of the metal laminate of Example 2. [Figure 8] shows a cross-sectional photograph of the metal laminate of Example 3. [Figure 9] shows a cross-sectional photograph of the metal laminate of Example 4. [Figure 10] shows a cross-sectional photograph of the metal laminate of Example 6. [Figure 11] shows a cross-sectional photograph of the metal laminate of Example 7. [Figure 12] shows a cross-sectional photograph of the metal laminate of Example 8. [Figure 13] shows a cross-sectional photograph of the metal laminate of Example 14. [Figure 14] shows a cross-sectional photograph of the metal laminate of Comparative Example 1. [Figure 15] shows a cross-sectional photograph of the metal laminate of Comparative Example 2. Implementation

[0012] The present invention will now be described in detail. The present invention relates to a metal laminate in which at least one metal layer comprising at least one layer of metal foil is laminated on at least one side of a low-dielectric thin film. The metal laminate of the present invention includes those in which a metal layer is laminated on one side of a low-dielectric thin film, and those in which metal layers are laminated on both sides of a low-dielectric thin film. Because the surface of the metal foil on the low-dielectric thin film side is smooth, the metal laminate of the present invention exhibits excellent high-frequency characteristics, and the low-dielectric thin film and the metal layer have sufficient adhesion.

[0013] A. Metal laminate First, the metal laminate of the first embodiment of the present invention will be described below.

[0014] Figure 1 shows a schematic cross-sectional view of a metal laminate according to a first embodiment of the present invention. As shown in Figure 1, the metal laminate 1A of the first embodiment is a metal layer 10 made of metal foil laminated on the surface of a low dielectric thin film 20.

[0015] Figure 2 shows a schematic cross-sectional view of another embodiment of the metal laminate of the first embodiment of the present invention. In this embodiment, a carrier layer metal foil having an extremely thin metal layer, a release layer, and a carrier layer is used as the metal foil. As shown in Figure 2, the metal laminate 1B of the present invention is a metal layer 10 formed by the carrier metal foil laminated on one surface of a low-dielectric film 20. The metal layer 10 is laminated in the following order from the low-dielectric film 20 side: an extremely thin metal layer 14, a release layer 13, and a carrier layer 12.

[0016] The following is a detailed description of each component of the metal laminate according to the first embodiment of the present invention.

[0017] 1. Low dielectric thin film As a material for low-dielectric thin films, low-dielectric polymer materials suitable for use as flexible substrates are applicable. For example, materials with a relative permittivity εr of 3.3 or less and a dielectric loss tangent tanδ of 0.006 or less are suitable, but are not limited to these. Specifically, materials suitable for use include liquid crystal polymers, polyvinyl fluoride (fluorinated resins such as polytetrafluoroethylene), polyamides, isocyanate compounds, polyamide-imides, polyamides, low-dielectric polyamides, polyethylene terephthalate, polyether-imides, and cycloalkene polymers. Liquid crystal polymers, polyvinyl fluoride, polyamides, or low-dielectric polyamides are preferred, and liquid crystal polymers are even more preferred. The low-dielectric thin film can be a single-layer film or a laminate composed of multiple layers. In the case of multiple layers, it is preferable that one or more of the multiple layers are made of the aforementioned low-dielectric polymer material. Layers other than those made of the low-dielectric polymer material can be composed of various materials known in the past, such as epoxy resin. Furthermore, the term "liquid crystal polymer" refers to an aromatic polyester resin with p-hydroxybenzoic acid or similar materials as its basic structure, which exhibits liquid crystal properties in a molten state.

[0018] The thickness of the low-dielectric film can be appropriately set according to the application of the metal laminate. For example, when used as a flexible printed circuit board, the thickness is typically 10 μm to 150 μm, preferably 10 μm to 100 μm, more preferably 10 μm to 75 μm, and especially preferably 10 μm to 50 μm. The thickness of the low-dielectric film refers to the average value obtained by measuring the thickness of the low-dielectric film at any 10 points in an optical microscope photograph of a cross-section of the metal laminate. Furthermore, the thickness of the low-dielectric film before bonding can be measured using a micrometer, etc., referring to the average value of the thickness measured at 10 randomly selected points on the surface of the low-dielectric film to be bonded. Also, the deviation of the low-dielectric film used from the average value of the 10 measured values ​​is preferably within 20% of all measured values, more preferably within 10%.

[0019] 2. Metal layer The metal layer is not particularly limited to those comprising a metal foil; it may be made of the metal foil or may have other layers in addition to the metal foil. When the metal layer has other layers, it is preferable that the other layers are located between the low-dielectric film and the metal foil.

[0020] The type of metal constituting the metal layer varies depending on the intended use of the metal layer composite and is not particularly limited. Examples include copper, iron, nickel, zinc, tin, chromium, gold, silver, platinum, cobalt, titanium, and their alloys. Copper foil or copper alloy foil is preferred as the metal foil. This is because by rolling and bonding these metals with a low-dielectric thin film, a flexible substrate for, for example, forming fine wiring can be obtained.

[0021] The thickness of the metal foil varies depending on the application of the metal laminate and is not particularly limited. However, for example, if it is used for flexible printed wiring boards, it is preferably 3 μm to 100 μm, and more preferably 10 μm to 50 μm. Here, the thickness of the metal foil refers to the average value obtained by taking an optical microscope photograph of the cross-section of the metal laminate and measuring the thickness of the metal foil at any 10 points in the optical microscope photograph.

[0022] The metal foil is preferably rolled metal foil, carrier metal foil, or electrolytic metal foil, and more preferably rolled copper foil, carrier copper foil, or electrolytic copper foil. Furthermore, the metal foil can be a single-layer foil or a laminated foil of the like.

[0023] When using rolled copper foil as a metal foil, there are no particular limitations on the type of rolled copper foil, but examples include JX Metals (Co., Ltd.)'s HA-V2 and Mitsui Sumitomo Metal Mining Shin-Dake (Co., Ltd.)'s C1020R-H. Similarly, when using electrolytic copper foil as a metal foil, there are no particular limitations on the type of electrolytic copper foil, but examples include Fukuda Metal Foil Powder Industry (Co., Ltd.)'s CF-T9DA-SV, CF-V9S-SV, and CF-PLFA.

[0024] In the fabrication of flexible substrates for forming fine wiring, a carrier metal foil having an extremely thin metal layer, a release layer, and a carrier layer is preferred as the metal foil. When using a carrier metal foil, as shown in Figure 2, the carrier metal foil is laminated sequentially from the low-dielectric film side, in the order of the extremely thin metal layer, the release layer, and the carrier layer. When using a carrier metal foil, the "metal foil" in the resulting metal laminate refers to the portion composed of the extremely thin metal layer, the release layer, and the carrier layer. Furthermore, the metal foil prepared in the manufacturing method of the metal laminate can have a roughening particle layer and a rust-preventing layer on the surface of the extremely thin metal layer of the carrier metal foil.

[0025] The carrier layer of the carrier metal foil is a thin sheet, serving as a support material or protective layer to prevent wrinkling and bending of the metal laminate and damage to the extremely thin metal layer. Examples of carrier layers include foils or plates made of copper, aluminum, nickel, and their alloys (stainless steel, brass, etc.), or resins with a metal coating on the surface. Copper foil is preferred as the carrier layer. The thickness of the carrier layer is not particularly limited, but is, for example, between 10 μm and 100 μm.

[0026] The release layer of the carrier metal foil also reduces the peel strength of the carrier layer, thereby suppressing interdiffusion between the carrier layer and the extremely thin metal layer that may occur due to heat treatment. The release layer can be either an organic or inorganic release layer. Examples of components used in organic release layers include nitrogen-containing organic compounds, sulfur-containing organic compounds, and carboxylic acids. Examples of nitrogen-containing organic compounds include triazole compounds and imidazole compounds. Examples of triazole compounds include 1,2,3-benzotriazole, carboxybenzotriazole, N',N'-bis(benzotriazolylmethyl)urea, 1H-1,2,4-triazole, and 3-amino-1H-1,2,4-triazole. Examples of sulfur-containing organic compounds include mercaptobenzothiazole, trithiocyanate, and 2-benzimidazole thiol. Examples of carboxylic acids include monocarboxylic acids and dicarboxylic acids. Furthermore, examples of components used in inorganic release layers include Ni, Mo, Co, Cr, Fe, Ti, W, P, Zn, and chromate-treated films. The thickness of the release layer is typically 1 nm to 1 μm, preferably 5 nm to 500 nm.

[0027] The metal constituting the extremely thin metal layer of the carrier metal foil varies depending on the intended use of the metal layer composite and is not particularly limited, but examples include copper, iron, nickel, zinc, tin, chromium, gold, silver, platinum, cobalt, titanium, and their alloys. The extremely thin metal layer is preferably a copper or copper alloy layer. The thickness of the extremely thin metal layer is typically 0.5 μm to 10 μm, preferably 1 μm to 7 μm.

[0028] As a carrier metal foil, it is preferable that the carrier layer and the ultrathin metal layer are made of copper or copper alloy, and more preferably such carrier copper foil. The carrier copper foil is not particularly limited, and examples include MT18FL, MT18GN, MT18EX and MT18SD-H manufactured by Mitsui Metals Mining Co., Ltd.

[0029] Although not shown in Figures 1-2, the metal layer may further comprise at least one of the following layers on the surface of the low-dielectric thin film side of the metal foil: a roughening particle layer, a rust-preventive layer, a heat-resistant layer, and a treatment layer utilizing a silane coupling agent (hereinafter sometimes referred to as a "treatment layer"). The treatment layer may be a single layer or a plurality of layers. The roughening particle layer may comprise, for example, any metal or alloy thereof selected from the group consisting of Cu, Co, and Ni, but is not limited thereto. Specifically, examples include cobalt-nickel alloy plating layers, copper-cobalt-nickel alloy plating layers, etc. Furthermore, the rust-preventive layer may comprise, for example, any metal or alloy thereof selected from the group consisting of Cr, Ni, and Zn, but is not limited thereto. Specifically, examples include chromium oxide film treatment, a mixture film treatment of chromium oxide and zinc / zinc oxide, Ni plating layers, etc. The heat-resistant layer may contain any metal or alloy thereof selected from the group consisting of Co, Ni, and No, but is not limited thereto. Furthermore, examples of silane coupling agents include olefinic silanes, epoxy silanes, acrylic silanes, amino silanes, and mercapto silanes, but are not limited to these. The silane coupling agent can be applied using methods such as spraying, coating with a coater, or impregnation. Also, the roughening particle layer, rust-preventive layer, and heat-resistant layer differ from the intermediate layer described for the metal laminate in the second embodiment below.

[0030] The metal laminate of the first embodiment preferably does not have the intermediate layer described in the second embodiment below. By eliminating the intermediate layer, the manufacturability of the metal laminate can be improved, and manufacturing costs can be reduced. In a preferred embodiment, the metal laminate of the present invention does not have an intermediate layer containing metal between the low-dielectric film and the metal foil, preferably it does not have a sputtered layer made of copper, nickel, chromium or their alloys. In one embodiment of the metal laminate without an intermediate layer, the low-dielectric film and the metal foil (preferably rolled metal foil) are directly laminated. Furthermore, in another embodiment of the metal laminate without an intermediate layer, the aforementioned roughening particle layer and / or the aforementioned anti-rust layer are laminated to the low-dielectric film, and a metal foil (preferably a carrier metal foil) is laminated on top of it. Specifically, in this type of metal laminate, a coarsened particle layer comprising any one of the metals or alloys selected from the group consisting of Cu, Co and Ni, and / or a rust-preventive layer comprising any one of the metals or alloys selected from the group consisting of Cr, Ni and Zn, is laminated with a carrier metal foil.

[0031] Next, the metal laminate of the second embodiment of the present invention will be described below. FIG3 is a schematic cross-sectional view showing a metal laminate of the second embodiment of the present invention. As shown in FIG3, the metal laminate 1C of the present invention has a metal layer 10 laminated on the surface of a low-dielectric thin film 20. The metal laminate 1C has an intermediate layer 15 containing the metal layer between the low-dielectric thin film 20 and the metal foil 11. Therefore, the metal layer 10 has an intermediate layer 15 containing metal laminated on the surface of a low-dielectric thin film 20 and a metal foil 11 laminated on the surface of the intermediate layer 15 opposite to the low-dielectric thin film 20.

[0032] Figure 4 is a schematic cross-sectional view showing another aspect of the metal laminate according to the second embodiment of the present invention. In this aspect, a carrier metal foil having an extremely thin metal layer, a release layer, and a carrier layer is used as the metal foil. As shown in Figure 4, the metal laminate 1D of the present invention has a metal layer 10 laminated on the surface of a low-dielectric film 20. The metal laminate 1D has an intermediate layer 15 containing metal between the low-dielectric film 20 and the metal foil 11 having an extremely thin metal layer 14, a release layer 13, and a carrier layer 12. Thereby, the metal layer 10 is laminated from the low-dielectric film 20 side in the order of intermediate layer 15, extremely thin metal layer 14, release layer 13, and carrier layer 12.

[0033] In the second embodiment of the metal laminate, by providing an intermediate layer, the surface of the metal foil or the low-dielectric film can be protected, and the adhesion between the metal foil and the low-dielectric film can be improved. The intermediate layer is not particularly limited to a metal-containing layer; it can be a layer containing one metal layer, or a layer containing two or more metal layers. Examples of intermediate layers include those formed by sputtering, vapor deposition, or electroless plating on the low-dielectric film, but preferably a layer formed by sputtering (sputtered layer). The presence or absence of an intermediate layer can be determined by analyzing the interface between the metal foil and the low-dielectric film of the metal laminate using a scanning electron microscope or a through-electron microscope (magnification of 20,000x or higher).

[0034] The intermediate layer is not particularly limited in that it contains a metal, but it is preferably composed of any one of the following metals or alloys selected from the group consisting of copper, iron, nickel, zinc, chromium, cobalt, titanium, tin, platinum, silver, gold, aluminum, palladium, and zirconium. More preferably, it contains copper, nickel, chromium, or alloys thereof. It is especially preferred that it contains copper, an alloy of copper and nickel, nickel, or an alloy of nickel and chromium. Furthermore, the intermediate layer may also be a composite of multiple layers containing metals.

[0035] The intermediate layer is preferably a sputtered layer made of copper, nickel, chromium or their alloys, formed by sputtering between a low dielectric thin film and a metal foil.

[0036] The thickness of the intermediate layer is not particularly limited, as long as it can perform functions such as improving adhesion. However, it is preferred to be between 5nm and 200nm, with 10nm and 100nm being more preferred.

[0037] In the second embodiment of the metal laminate, the other components are as described above for the metal laminate of the first embodiment.

[0038] The metal laminate of this invention exhibits superior high-frequency characteristics compared to conventional metal laminates manufactured using thermal deposition methods due to the smooth surface of the low-dielectric thin film side at the lamination interface of the metal foil. The surface of a metal foil typically forms uneven shapes due to roughness and undulations. In this invention, the smoothness of the metal foil surface is evaluated using the ratio of the width to the height of the convex portion of the metal foil (hereinafter sometimes referred to as aspect ratio) calculated from a cross-section of the metal laminate. Surface roughness is widely used as an indicator of surface smoothness. Surface roughness is generally calculated as the degree of deviation in the vertical direction when comparing the surface shape of an object to an ideal surface. Here, in conventional metal laminates manufactured using thermal deposition methods, the roughened particles on the surface of the metal foil are deeply embedded within the low-dielectric thin film, forming complex concave shapes within the low-dielectric thin film. Surface roughness measurement cannot accurately capture these complex concave shapes. In this invention, the longitudinal-to-longitudinal ratio of the protrusions, calculated from cross-section observation of the metal laminate, is used as an indicator of smoothness, allowing for a suitable comparison with conventional metal laminates. Furthermore, the protrusions on the surface of the metal foil originate from the metal foil itself as a material, and are not formed by adding other elements to the metal foil.

[0039] As mentioned above, in this invention, the surface smoothness index is the ratio of the width to the height of the protrusion calculated from cross-sectional observation. Specifically, in the metal laminate of this invention, when the width of the protrusion of the metal foil is set as 'a' and the height of the protrusion is set as 'b', the average value of b / a + 3σ (where σ is the standard deviation of b / a) is 2.5 or less, preferably 2.0 or less, more preferably 1.5 or less, and especially preferably 1.0 or less. The smaller the value of the average value of b / a + 3σ, the smoother the surface. By setting this value to 2.5 or less, the surface of the low-dielectric thin film side of the metal foil can be smoothed, resulting in excellent high-frequency characteristics of the metal laminate. When using rolled copper foil without surface roughening treatment, the average value of b / a + 3σ can be very small, typically 0.5 or less, preferably 0.3 or less, and more preferably 0.2 or less. Furthermore, in this invention, the minimum value of b / a is 0. In this invention, when the protrusion is very small and its width or height cannot be measured, b / a is set to 0, and the average value of b / a +3σ in this case is also 0. Therefore, in the metal laminate of this invention, the average value of b / a +3σ is 0 to 2.5. Furthermore, in this invention, when no protrusion is observed on the surface of the metal foil through cross-section, b / a is also set to 0.

[0040] The aspect ratio b / a of the protrusions of the metal foil is measured on the surface (bonding surface) of the low-dielectric thin film side of the metal foil. For example, even if the metal laminate has an intermediate layer between the low-dielectric thin film and the metal foil, the measurement is still performed on the surface of the low-dielectric thin film side of the metal foil.

[0041] The width 'a' and height 'b' of the protrusions of the metal foil can be measured as follows. First, a cross-sectional photograph of the metal laminate is obtained using a scanning electron microscope. In this cross-sectional photograph, the width 'a' and height 'b' of the protrusions are measured on the surface of the low-dielectric thin film side of the metal foil. Figure 5A shows an enlarged cross-sectional view of the metal laminate 1A shown in Figure 1. The metal laminate 1A is a metal layer 10 formed of metal foil laminated on one surface of a low-dielectric thin film 20. Figure 5B shows an enlarged cross-sectional view of the protrusions of the metal foil. As shown in Figure 5B, the protrusions of the metal foil are formed by particles of the metal constituting the metal foil. Each metal particle can be a single particle, or, as shown in Figure 5B, it can be a collection of metal particles, such as secondary particles formed from primary particles, and further, tertiary particles. As shown in Figures 5A and 5B, the width *a* of the convexity is defined as the length of the straight line connecting the two points where the convexity begins (the length of the bottom slice of the primary particle), and the height *b* of the convexity is defined as the length from this straight line to the apex of the convexity (the apex of the final particle). In this invention, the average value of *b* / *a* is used as an indicator of smoothness, and the deviation of the value is considered, using the average value of *b* / *a* + 3σ (where σ is the standard deviation of *b* / *a*). Preferably, at least 10 convexities are measured.

[0042] The metal laminate of this invention exhibits a peel strength of 3 N / cm or higher, preferably 5 N / cm or higher, between the low-dielectric thin film and the metal layer. A peel strength of 3 N / cm or higher improves the reliability of fine wiring in printed circuit boards.

[0043] When determining the aforementioned peel strength value, a test piece is first prepared from the metal layer composite material, and a 1 cm wide incision is made in the metal layer using a blade or similar tool. Next, a portion of the metal layer is peeled off from the low-dielectric film, the low-dielectric film is fixed to a support, and the metal layer is stretched at a speed of 50 mm / min in a 90° direction relative to the low-dielectric film. The peel strength (unit: N / cm) is based on the force required for peeling at this point. Furthermore, if the metal layer is thin and brittle, there is a risk of breakage during peel strength testing. In such cases, electroplating can be performed on the surface of the metal layer (e.g., copper plating if the metal layer is copper) to increase the thickness of the metal layer to approximately 5 μm to approximately 50 μm before measuring the peel strength. The method for determining the peel strength value is the method specified in JIS C6471.

[0044] When this specification refers to "peel strength between the low-dielectric film and the metal layer," it refers not only to the peel strength at the interface between the low-dielectric film and the metal layer, but also to the peel strength due to internal damage to the metal layer, and the peel strength due to internal damage to the low-dielectric film. Furthermore, when a roughening particle layer, rust-preventive layer, heat-resistant layer, or treatment layer using a silane coupling agent is laminated to the surface of the low-dielectric film side of the metal foil, as mentioned above, it refers to the peel strength at the interface between the metal foil and the treatment layer, and the peel strength due to internal damage to the treatment layer. Also, when the aforementioned metal laminate has an intermediate layer, it also refers to the peel strength at the interface between the metal foil and the intermediate layer, and the peel strength due to internal damage to the intermediate layer.

[0045] B. Manufacturing method of metal laminate This invention also relates to a method for manufacturing the aforementioned metal laminate. The metal laminate of this invention can be manufactured by a surface activation bonding method. By using a surface activation bonding method, the metal foil can be laminated onto a low-dielectric film while maintaining its surface smoothness, thus the metal laminate has excellent high-frequency characteristics. Furthermore, because a strong bond is formed at the bonding interface through surface activation treatment, it does not rely on the physical anchoring effect of coarsened particles as is the case with metal laminates manufactured by thermal deposition, thus ensuring the adhesion of the lamination interface.

[0046] The metal laminate of the first embodiment of the present invention preferably does not have an intermediate layer containing metal. The manufacturing method of the metal laminate of the first embodiment includes: a step of preparing a low-dielectric thin film and a metal foil (step 1); a step of activating at least one surface of the low-dielectric thin film by sputter etching (step 2-1); a step of activating the surface of the metal foil by sputter etching (step 2-2); and a step of rolling and bonding the activated surfaces of the low-dielectric thin film and the metal foil together at a rolling reduction rate of 0-30% (step 3-1). Steps 1, 2 (steps 2-1 and 2-2), and 3-1 are performed sequentially, but steps 2-1 and 2-2 can be performed simultaneously or sequentially.

[0047] The metal laminate of the second embodiment of the present invention has an intermediate layer containing metal between a low-dielectric thin film and a metal foil. The manufacturing method of the metal laminate of the second embodiment, after step 2-1 of the manufacturing method of the metal laminate of the first embodiment, includes a step of forming an intermediate layer containing metal on the activated surface of the low-dielectric thin film (step 2-3), and a step of activating the surface of the intermediate layer by sputter etching (step 2-4). Furthermore, instead of step 3-1, it includes a step of rolling and bonding the activated surfaces of the intermediate layer and the metal foil together at a rolling reduction rate of 0-30% (step 3-2). In this case, steps 2-2 and 2-4 can be performed simultaneously or sequentially.

[0048] That is, the manufacturing method of the metal laminate in the second embodiment includes: a step of preparing a low-dielectric thin film and a metal foil (step 1); a step of activating at least one side of the low-dielectric thin film by sputter etching (step 2-1); a step of forming an intermediate layer containing metal on the activated surface of the low-dielectric thin film (step 2-3); a step of activating the surface of the intermediate layer by sputter etching (step 2-4); a step of activating the surface of the metal foil by sputter etching (step 2-2); and a step of rolling and bonding the activated surfaces of the intermediate layer and the metal foil together with a rolling reduction rate of 0 to 30% (step 3-2).

[0049] In the manufacturing method of the metal laminate of the present invention, the steps of activating at least one surface of a low-dielectric thin film by sputter etching (step 2-1), activating the surface of a metal foil by sputter etching (step 2-2), forming an intermediate layer containing metal on the activated surface of the low-dielectric thin film as needed (step 2-3), activating the surface of the intermediate layer by sputter etching (step 2-4), rolling and bonding the activated surfaces of the low-dielectric thin film and the metal foil together with a rolling reduction rate of 0 to 30% (step 3-1), and rolling and bonding the activated surfaces of the intermediate layer and the metal foil together with a rolling reduction rate of 0 to 30% (step 3-2) can be performed at a temperature of 15°C to 100°C, preferably at a temperature of 15°C to 60°C, and even more preferably at room temperature (15°C to 25°C). By performing these steps at room temperature, the smoothness of the metal foil surface can be maintained during lamination onto a low-dielectric film.

[0050] Next, the steps of the manufacturing method of the metal laminate of the present invention will be described in detail.

[0051] 1. Preparation steps Step 1 involves preparing a low-dielectric thin film and a metal foil. The aforementioned description of the metal laminate can be used as the low-dielectric thin film and metal foil.

[0052] 2. Surface activation step and intermediate layer formation step 2-A. Surface activation steps for low-dielectric thin films In step 2-1, at least one surface of the low-dielectric thin film is activated by sputter etching. The sputter etching process can be performed, for example, by preparing the low-dielectric thin film as a long roll with a width of 100 mm to 600 mm, setting the bonding surface of the low-dielectric thin film as a grounded electrode, applying an alternating current of 1 MHz to 50 MHz between the low-dielectric thin film and other electrodes that are insulated and supported to induce a glow discharge, and ensuring that the area of ​​the electrode exposed to the plasma generated by the glow discharge is less than 1 / 3 of the area of ​​the other electrodes. In the sputter etching process, the grounded electrode is shaped like a cooling roller to prevent the temperature of the conveyed material from rising.

[0053] The sputtering etching process in the surface activation step involves completely removing adsorbates from the bonding surface of the low-dielectric thin film under vacuum by sputtering with an active or inert gas. Oxygen or a mixture containing oxygen can be used as the active gas. Argon, neon, xenon, krypton, nitrogen, or a mixture containing at least one of these can be used as the inert gas. Oxygen is preferred as the gas for sputtering etching of the low-dielectric thin film. When oxygen is used, the peel strength between the low-dielectric thin film and the metal layer is higher compared to using inert gases such as argon or nitrogen, especially when the metal layer composite does not have an interlayer.

[0054] The sputtering etching process conditions can be appropriately set, for example, it can be performed under vacuum with a plasma output of 100W~10kW and a linear velocity of 0.5m / min~30m / min. When using oxygen, the sputtering etching conditions are also, for example, under vacuum with a plasma output of 100W~10kW and a linear velocity of 0.5m / min~30m / min. A higher vacuum level is better to prevent re-adsorption of substances onto the surface, but it can be, for example, 1×10⁻⁵ Pa~10 Pa.

[0055] 2-B. Intermediate Layer Formation Steps As needed, an intermediate layer containing a metal is formed on the surface of the low-dielectric thin film activated in step 2-3 and step 2-1. The method for forming the intermediate layer is not particularly limited, but preferably includes, for example, sputtering an intermediate layer containing a metal onto the activated surface of the low-dielectric thin film, or forming a sputtered layer. The conditions for sputtering the film using this method can be appropriately set according to the type of metal constituting the intermediate layer and the thickness of the intermediate layer. The type of metal constituting the intermediate layer and the thickness of the intermediate layer are as described above for metal laminates.

[0056] 2-C. Surface activation steps for metal foil and intermediate layer In step 2-2, the surface of the metal foil is activated by sputter etching. Also, if necessary, the surface of the intermediate layer can be activated by sputter etching in step 2-4.

[0057] For example, in sputtering etching with surface activation steps, a low-dielectric film containing a bonded metal foil or interlayer can be prepared as a long roll with a width of 100 mm to 600 mm. The bonding surface of the metal foil or interlayer is used as one of the grounded electrodes. A glow discharge is generated by applying an alternating current of 1 MHz to 50 MHz between the electrode and the other electrodes that are supported by insulation. The area of ​​the electrode exposed to the plasma generated by the glow discharge is less than 1 / 3 of the area of ​​the other electrodes. In sputtering etching, the grounded electrode is shaped like a cooling roller to prevent the temperature of the conveying material from rising.

[0058] The sputtering etching process in the surface activation step involves sputtering a low-dielectric film bonded to a metal foil or interlayer under vacuum using an inert gas to completely remove surface adsorbates and partially or completely remove the oxide layer. Complete removal of the oxide layer is preferred. Argon, neon, xenon, krypton, or mixtures containing at least one of these inert gases can be used. While the specific inert gas depends on the type of metal, adsorbates on the surface of the metal foil and interlayer can be completely removed with an etching depth of approximately 1 nm, especially for copper oxide layers, which can typically be removed at a depth of approximately 5 nm to 12 nm (converted from SiO₂).

[0059] The processing conditions for sputter etching can be appropriately set according to the type of metal foil and intermediate layer. For example, it can be carried out under vacuum with a plasma output of 100W to 10kW and a linear velocity of 0.5m / min to 30m / min. The vacuum level should be as high as possible to prevent re-adsorption of substances on the surface, but it can be, for example, 1×10⁻⁵Pa to 10Pa.

[0060] Furthermore, when a roughening particle layer and a rust-preventive layer are provided on the surface of the metal foil, the surface of the roughening particle layer and the rust-preventive layer is activated by sputter etching. At this time, the roughening particle layer and the rust-preventive layer can be completely removed by sputter etching, or they can remain without removal.

[0061] Furthermore, on the surface of the metal foil activated by sputtering etching or on the surface of the intermediate layer, Ni plating, chromate treatment, silane coupling agent treatment, etc., may be performed as needed to improve oxidation resistance and adhesion. Also, the surface of the metal foil may be roughened as needed to improve adhesion to low-dielectric thin films or to the intermediate layer.

[0062] 3. Calendering and joining steps The bonding (calendering) of the surfaces activated by sputtering etching in steps 3-1 and 3-2 can be performed by roll bonding. The rolling line load for roll bonding is not particularly limited, but can be set to, for example, a range of 0.1 tf / cm to 10 tf / cm. However, in cases where the metal foil or low-dielectric film has a large thickness before bonding, it may be necessary to increase the rolling line load to ensure the pressure during bonding, and there is no limitation to this numerical range. On the other hand, if the rolling line load is too high, not only are the surfaces of the low-dielectric film, metal foil, or intermediate layer prone to deformation, but the bonding interface is also prone to deformation, which may reduce the thickness accuracy of each layer in the metal laminate. Furthermore, a high rolling line load may increase the processing strain applied during bonding.

[0063] The shrinkage rate during rolling bonding is 0-30%, preferably 0-15%. By employing the surface activation bonding method described above, the shrinkage rate can be reduced, thus preventing wrinkles and cracks, and allowing the formation of a metal layer with excellent thickness accuracy. Furthermore, because the undulations at the interface between the metal foil and the low-dielectric thin film or the intermediate layer can be reduced, precise wiring can be obtained when sputtering and etching a metal layer containing the metal foil and the intermediate layer to form wiring, due to its excellent thickness accuracy. Also, the temperature during rolling bonding is, for example, 15°C to 100°C, preferably 15°C to 60°C, and more preferably room temperature.

[0064] To prevent the adhesion of the laminated interface from decreasing due to the re-adsorption of oxygen on the metal foil, the bonding by roll pressing is preferably carried out in a non-oxygen environment, such as a vacuum environment or an inert gas environment such as Ar.

[0065] The metal laminate obtained by lamination can be further heat-treated as needed, preferably. Heat treatment can eliminate strain in the metal layers and improve interlayer adhesion. The heat treatment temperature can be above -150°C and below +10°C of the melting point of the low-dielectric film. For example, in the case of liquid crystal polymer films, it is between 160°C and 350°C, preferably between 160°C and 320°C, and even more preferably between 260°C and 320°C.

[0066] The environment for heat treatment is not particularly limited, but a vacuum environment or an inert gas environment such as N2 or Ar is preferred. This is because heat treatment can prevent oxidation of the metal layer, which would reduce the adhesion between the metal layer and the low-dielectric thin film.

[0067] The heat treatment time is not particularly limited if it sufficiently improves the adhesion between the metal layer and the low-dielectric film. For example, the soaking time is preferably 0 seconds to 25,200 seconds, more preferably 0 seconds to 18,000 seconds, and particularly preferably 180 seconds to 15,000 seconds. By setting it above the lower limit of these ranges, sufficient adhesion between the metal layer and the low-dielectric film can be ensured, and by setting it below the upper limit of these ranges, high production efficiency and low cost of the metal layer composite can be achieved. Furthermore, even if the soaking time is 0 seconds (i.e., after reaching the target temperature, there is no soaking time and the material is directly cooled), the adhesion between the metal layer and the low-dielectric film can still be sufficiently improved.

[0068] Methods for performing heat treatment can be exemplified by using a batch heat treatment furnace to maintain a metal laminate at a desired heat treatment temperature for a desired time in a desired environment (e.g., a vacuum environment or an inert gas environment such as N2 or Ar). Alternatively, depending on the heat treatment temperature and environment, a continuous heat treatment furnace can be used to perform heat treatment in a roll-to-roll manner. In this case, an example can be found by setting at least one heating section or cooling section within the continuous heat treatment furnace to a desired environment (e.g., a vacuum environment or an inert gas environment such as N2 or Ar), maintaining the desired temperature, and then passing the metal laminate through the heating or cooling section at a desired speed to maintain the metal laminate at the desired heat treatment temperature for the desired time.

[0069] C. Use of metal laminates The metal laminate of the present invention can be used as a metal laminate for fabricating flexible printed circuit boards.

[0070] Printed wiring boards with fine wiring can be obtained using the metal laminate of the present invention. Therefore, the present invention also relates to printed wiring boards formed on metal laminates. In the wiring formation step, an additional metal layer can also be formed only on the wiring portion. Specifically, it is suitable to use previously known methods such as the modified semi-additive process (MSAP) or the semi-additive process (SAP) and subtractive process to obtain printed wiring boards. For example, in the case of using the modified semi-additive process (MSAP), by masking the non-wiring portion of the metal layer in the metal laminate, copper plating is performed on the unmasked portion to form an additional metal layer, the mask is removed, and the masked metal layer is removed by etching, thus manufacturing a printed wiring board. Furthermore, in the present invention, "printed wiring board" not only refers to a laminate with wiring formed, but also includes electronic components such as ICs mounted after wiring is formed.

[0071] Figures 1-4 illustrate the case where a metal layer is laminated on one surface of a low-dielectric thin film in a metal laminate, but the metal laminate is not limited to this. That is, metal layers can be deposited on both surfaces of the low-dielectric thin film as needed. By using a metal laminate with metal layers deposited on both surfaces of a low-dielectric thin film, a flexible printed circuit board with wiring formed on both surfaces of the low-dielectric thin film can be obtained. [Example]

[0072] The present invention will now be described in detail based on embodiments and comparative examples, but the present invention is not limited to these embodiments.

[0073] (Example 1) First, prepare a 25μm thick liquid crystal polymer film (KURARY). A rolled copper foil (HA-V2, manufactured by JX Metals) with a thickness of 18 μm was prepared as the metal foil (Vecstar-CTQ). Next, one surface of the liquid crystal polymer film was activated by sputtering etching with O2 gas. A 5 nm NiCr alloy sputtered layer was sputtered on the activated surface as the base layer, and a 10 nm Cu sputtered layer was sputtered as the top layer to form an intermediate layer (hereinafter also referred to as the Cu / NiCr alloy intermediate layer). Next, the surface of the intermediate layer and the surface of the rolled copper foil were activated by sputtering etching with Ar gas. The activated surfaces of the intermediate layer and the rolled copper foil were rolled together with a linear load of 1.5 tf / cm to produce a metal laminate. The shrinkage rate was 2.3%. Next, the metal laminate was heat-treated at 300°C to obtain the metal laminate of Example 1 (layer composition: rolled copper foil / intermediate layer / liquid crystal polymer film).

[0074] (Example 2) Except for using a 16μm thick rolled copper foil (Mitsui Sumitomo Metal Mining Shinko Co., Ltd. C1020R-H) as the rolled copper foil, the metal laminate of Example 2 (layer composition: rolled copper foil / intermediate layer / liquid crystal polymer film) was prepared in the same manner as in Example 1.

[0075] (Example 3) First, prepare a 25μm thick liquid crystal polymer film (KURARY). The rolled copper foil (HA-V2, manufactured by JX Metals) was prepared as the metal foil for use in Example 1. Next, one surface of the liquid crystal polymer film was activated by sputtering etching with O2 gas, and the surface of the rolled copper foil was activated by sputtering etching with Ar gas. The activated surfaces of the liquid crystal polymer film and the rolled copper foil were then rolled together with a linear load of 1.5 tf / cm to produce a metal laminate. The shrinkage rate was 2.3%. Next, the metal laminate was heat-treated at 320°C to obtain the metal laminate of Example 3 (layer composition: rolled copper foil / liquid crystal polymer film).

[0076] (Example 4) Except for the rolled copper foil (Mitsui Sumitomo Metal Mining Shinko Co., Ltd. C1020R-H) used in Example 2, the metal laminate of Example 4 (layer composition: rolled copper foil / liquid crystal polymer film) was made in the same way as in Example 3.

[0077] (Example 5) Except for using a 50 μm thick liquid crystal polymer film (KURARY Vecstar-CTQ), the same metal laminate as in Example 4 was fabricated (layer composition: rolled copper foil / liquid crystal polymer film).

[0078] (Example 6) First, prepare a 25μm thick liquid crystal polymer film (KURARY). A 1.5 μm thick copper layer (Mitsui Metal Mining Co., Ltd. MT18FL) was prepared as a carrier copper foil, consisting of a 18 μm thick copper carrier layer, an organic release layer, and a roughening particle layer and an anti-rust layer on its surface. Next, one surface of the liquid crystal polymer film was activated by sputtering etching with O2 gas, and a Cu / NiCr alloy intermediate layer was sputtered onto the activated surface in the same manner as in Example 1. Then, the surfaces of the intermediate layer and the ultrathin copper layer were activated by sputtering etching with Ar gas, and the activated surfaces of the intermediate layer and the ultrathin copper layer were rolled together with a linear load of 1.5 tf / cm to produce a metal laminate. The shrinkage rate was 3.4%. Next, the metal laminate was heat-treated at 300°C to obtain the metal laminate of Example 6 (layer composition: carrier copper foil / intermediate layer / liquid crystal polymer film).

[0079] (Example 7) As a carrier copper foil, except for the carrier copper foil (prototype A) which is used on a carrier layer with a thickness of 18 μm made of copper and an inorganic release layer to separate an extremely thin copper layer with a thickness of 2 μm and an anti-rust layer on its surface, the metal laminate of Example 7 (layer composition: carrier copper foil / intermediate layer / liquid crystal polymer film) is obtained in the same way as in Example 6.

[0080] (Example 8) First, prepare a 25μm thick liquid crystal polymer film (KURARY). The carrier copper foil (MT18FL manufactured by Mitsui Metal Mining Co., Ltd.) was prepared as the metal foil for use in Example 6. Next, one surface of the liquid crystal polymer film was activated by sputter etching using O2 gas, and the surface of the extremely thin copper layer of the carrier copper foil was activated by sputter etching using Ar gas. The activated surfaces of the liquid crystal polymer film and the extremely thin copper layer were rolled together with a linear load of 1.5 tf / cm to produce a metal laminate. The shrinkage rate was 3.4%. Next, the metal laminate was heat-treated at 300°C to obtain the metal laminate of Example 8 (layer composition: carrier copper foil / liquid crystal polymer film).

[0081] (Example 9) Except for the copper foil used as a carrier, which is used on a carrier layer of 18 μm thickness made of copper and has an extremely thin copper layer of 2 μm thickness on it, along with a roughening particle layer and an anti-rust layer on its surface (MT18EX manufactured by Mitsui Metal Mining Co., Ltd.), the metal composite material of Example 9 (layer composition: carrier copper foil / liquid crystal polymer film) was obtained in the same way as in Example 8.

[0082] (Example 10) Except for the copper foil used as a carrier, which is used on a carrier layer of 18 μm thickness made of copper and has an extremely thin copper layer of 5 μm thickness, a roughening particle layer and an anti-rust layer on its surface, the copper foil (MT18SD-H manufactured by Mitsui Metal Mining Co., Ltd.) is used as a carrier copper foil, the metal composite material of Example 10 (layer composition: carrier copper foil / liquid crystal polymer film) is obtained in the same way as in Example 8.

[0083] (Example 11) Except for the copper foil used as a carrier in Example 7 (prototype A), the metal laminate of Example 11 (layer composition: carrier copper foil / liquid crystal polymer film) was made in the same way as in Example 8.

[0084] (Example 12) Except for the copper foil used as a carrier, which is used on a carrier layer of 18 μm thickness with an interlayer release layer (organic release layer) and an ultra-thin copper layer of 1.5 μm thickness, and a roughening particle layer and an anti-rust layer on its surface, the metal composite material of Example 12 (layer composition: carrier copper foil / liquid crystal polymer film) was obtained in the same way as in Example 8.

[0085] (Example 13) Except for the copper foil used as a carrier, which is used on a carrier layer of copper with a thickness of 18 μm and an inorganic release layer to form an extremely thin copper layer of 2 μm thickness, as well as a roughening particle layer and an anti-rust layer on its surface, the copper foil of Example 13 (layer composition: carrier copper foil / liquid crystal polymer film) is obtained in the same way as in Example 8.

[0086] (Example 14) A 50 μm thick liquid crystal polymer film (KURARY, Vecstar-CTQ) was prepared, and a 12 μm thick electrolytic copper foil (Fukuda Metal Foil Powder Industry, CF-T9DA-SV) was prepared as the metal foil. Next, one surface of the liquid crystal polymer film was activated by sputtering etching with O2 gas, and the surface of the electrolytic copper foil was activated by sputtering etching with Ar gas. The activated surfaces of the liquid crystal polymer film and the electrolytic copper foil were then rolled together with a linear load of 1.5 tf / cm to produce a metal laminate. The shrinkage rate was 2.3%. The metal laminate was then heat-treated at 320°C to obtain the metal laminate of Example 14 (layer composition: electrolytic copper foil / liquid crystal polymer film).

[0087] (Example 15) Except that an electrolytic copper foil with a thickness of 12 μm made of copper (CF-PLFA manufactured by Fukuda Metal Foil Powder Co., Ltd.) was used as the electrolytic copper foil, the same as in Example 14 was used to obtain the metal laminate of Example 15 (layer composition: electrolytic copper foil / liquid crystal polymer film).

[0088] (Example 16) Except for using a 25μm thick liquid crystal polymer film (KURARY Vecstar-CTQ) as the electrolytic copper foil and an 18μm thick electrolytic copper foil (Fukuda Metal Foil Powder Industry Co., Ltd. CF-V9S-SV) as the electrolytic copper foil, the same as in Example 14 was used to obtain the metal laminate of Example 16 (layer composition: electrolytic copper foil / liquid crystal polymer film).

[0089] (Comparative Example 1) Using the thermal deposition method, a 50 μm thick liquid crystal polymer film ( KURARY (stock) manufactures Vecstar-CTQ. On both sides of the two surfaces, a rolled copper foil with a thickness of 18 μm having a treatment layer made of roughened particles on one side is hot-pressed at a temperature of 310°C or higher to produce a metal laminate material of Comparative Example 1 (layer composition: rolled copper foil (with roughening treatment) / liquid crystal polymer film / rolled copper foil (with roughening treatment).

[0090] (Comparative Example 2) In addition to using it as rolled copper foil for electrolytic copper foil with a thickness of 18 μm on one side having a treatment layer made of coarsening particles, the same as Comparative Example 1, the metal laminate of Comparative Example 2 (layer composition: electrolytic copper foil / liquid crystal polymer film / electrolytic copper foil) was made.

[0091] Cross-sectional photographs of the metal laminates of Examples 1-16 and Comparative Examples 1-2 were obtained using a scanning electron microscope (20,000x magnification). Figures 6-13 show cross-sectional photographs of the metal laminates of Examples 1-4, 6-8, and 14, respectively, while Figures 14 and 15 show cross-sectional photographs of the metal laminates of Comparative Examples 1 and 2, respectively. Furthermore, the following characteristics were evaluated for the metal laminates of Examples 1-16 and Comparative Examples 1-2.

[0092] [Aspect ratio of the raised portion of the metal foil] As described in item "A. Metal laminate", in the cross-sectional photograph of the obtained metal laminate, the width a and height b of the protrusion of the copper foil on the surface of the liquid crystal polymer film side of the copper foil are measured.

[0093] As an example of using rolled copper foil, a cross-sectional photograph (Fig. 8) of the metal laminate of Example 3 is used for illustration. As shown in Fig. 8, on the surface of the copper foil (HA-V2 in Fig. 8) on the side of the liquid crystal polymer film (LCP in Fig. 8), the length of the straight line connecting the two points of the protrusion to the copper foil, i.e., the width a of the protrusion, and the length from the straight line to the apex of the protrusion, i.e., the height b of the protrusion, are measured for each protrusion. The average value of b / a is obtained from the measured width a and height b of the protrusion, and then the deviation of the value is taken into account to obtain the average value of b / a + 3σ (where σ is the standard deviation of b / a).

[0094] Furthermore, as an example of using a carrier copper foil, a cross-sectional photograph (Fig. 12) of the metal laminate of Example 8 is used for explanation below. As shown in Fig. 12, on the surface of the liquid crystal polymer film (LCP) side of the ultrathin copper layer of the carrier copper foil (MT18FL in Fig. 12), the straight line length from the two points connecting the protrusion of the copper foil (ultrathin copper layer), i.e., the width a of the protrusion, and the length from the straight line to the apex of the protrusion, i.e., the height b of the protrusion, are measured, and the average value of b / a + 3σ is calculated as described above.

[0095] [Transmission loss (S21)] To evaluate the high-frequency transmission characteristics of the metal laminates of Example 5 and Comparative Example 2, transmission loss was measured (S21). In Example 5, being a single-sided material, an electroless copper plating was performed on the side of the liquid crystal polymer film exposed on the opposite side where rolled copper foil was laminated. After creating a through-hole, electrolytic copper plating was performed to obtain a sample with copper layers (25 μm) on both sides for measurement. In Comparative Example 2, the metal laminate was obtained by electrolytic copper plating after creating a through-hole, resulting in a sample with copper layers (25 μm) on both sides for measurement.

[0096] The transmission path was set as a single-ended wiring of a microstrip transmission path, with a wiring height of 25 μm, a wiring width of 110 μm, and a wiring length of 100 mm. Measurements were performed using a network analyzer E8363B (manufactured by KEYSIGHT Technologies) at a frequency of 40 GHz. Furthermore, in Example 5, the microstrip transmission path was constructed on the side of a laminated rolled copper foil for measurement.

[0097] [Peel strength] Test pieces were prepared from the metal laminate material. A 1cm wide incision was made in the metal layer using a blade or similar tool. Next, a portion of the metal layer was peeled off from the liquid crystal polymer film. The liquid crystal polymer film was then fixed to a support, and the metal layer was stretched at a speed of 50mm / min in a 90° direction relative to the liquid crystal polymer film. The force required to peel off at this point was taken as the peel strength (unit: N / cm). Furthermore, for the metal laminate materials of Examples 6-13, the carrier layer and release layer of the copper foil were removed, exposing an extremely thin copper layer. An 18μm thick electrolytic copper plating was then applied to the surface of the extremely thin copper layer. The peel strength between the metal layer and the liquid crystal polymer film was measured as the thickness of the extremely thin copper layer increased.

[0098] The composition and evaluation results of the metal laminates of Examples 1-16 and Comparative Examples 1-2 are shown in Table 1. In Table 1, LCP refers to liquid crystal polymer film.

[0099]

[0100] As shown in Figures 6-15, it was found that in the metal laminates of Comparative Examples 1 and 2 (Figures 14 and 15 respectively) prepared by the thermal deposition method, the coarsened particles of the copper foil were deeply embedded in the liquid crystal polymer film, resulting in increased unevenness at the bonding interface. In contrast, in the metal laminates of Examples 1-4 and 14 (Figures 6-9 and 13 respectively) prepared by the surface activation bonding method using rolled or electrolytic copper foil with a smooth surface, the interface between the copper foil and the liquid crystal polymer film was very smooth. Furthermore, it was found that even when using a carrier copper foil with a coarsened particle layer or an anti-rust layer on its surface, the metal laminates of Examples 6-8 (Figures 10-12 respectively) prepared by the surface activation bonding method had a smaller embedding depth of the protrusions on the copper foil surface compared to the metal laminates of Comparative Examples 1-2. Therefore, it was found that by using the surface activation bonding method, metal foil can be laminated onto a low-dielectric film while maintaining its surface smoothness.

[0101] This can also be confirmed by the aspect ratio (average of b / a + 3σ) of the raised portion of the copper foil shown in Table 1. Compared with the metal laminates of Comparative Examples 1 and 2, the value is very small for the metal laminates of Examples 1-5 using rolled copper foil with a smooth surface. Furthermore, the value is also significantly smaller for the metal laminates of Examples 6-13 using carrier copper foil and the metal laminates of Examples 14-16 using electrolytic copper foil. Therefore, the metal laminates of Examples 1-16 produced by surface activation bonding show that the surface roughness of the rolled copper foil, carrier copper foil, or electrolytic copper foil is smaller and the surface is smoother.

[0102] Regarding the high-frequency transmission characteristics of the metal laminate, as shown in Table 1, the metal laminate of Example 5, with a smaller average value of b / a +3σ for the protrusions and a smoother copper foil surface, exhibits lower high-frequency transmission loss (S21) and superior high-frequency characteristics compared to the metal laminate of Comparative Example 2. Generally, since a smooth surface of the metal foil in the metal laminate can suppress transmission loss, it can be inferred that the metal laminates of Examples 1-4 and 6-16 also exhibit the same superior high-frequency transmission characteristics as the metal laminate of Example 5.

[0103] Regarding the peel strength between the liquid crystal polymer film and the metal layer of the metal laminate, as shown in Table 1, compared with the metal laminates of Comparative Examples 1 and 2, the copper foil of Examples 1-16 has a smooth surface, but the peel strength is equal or higher. This is believed to be because in the metal laminates of Examples 1-16, a strong bond is formed at the interface between the liquid crystal polymer film and the copper foil through surface activation treatment, thus ensuring the adhesion of the laminate interface without relying on the physical anchoring effect caused by coarsened particles.

[0104] Based on these results, the metal laminates of Examples 1 to 16 prepared by surface activation bonding method and the metal laminates of Comparative Examples 1 and 2 prepared by thermal deposition method exhibit superior high-frequency characteristics because the peel strength between the metal layer and the liquid crystal polymer film is equal or higher and the surface of the metal foil is smoother.

[0105] Influence of the gas used in sputtering etching of liquid crystal polymer thin films The effect of changing the type of gas used to activate the liquid crystal polymer film by sputter etching on the peel strength of the metal laminate was investigated.

[0106] Metal laminate with intermediate layer O2, Ar, and N2 gases were used as the gases for sputtering and etching the liquid crystal polymer film. The sample using O2 gas employed the metal laminate of Example 2.

[0107] (Example 17) Except that Ar gas was used as the gas for sputtering and etching the liquid crystal polymer film, the same as in Example 2, the metal laminate of Example 17 was obtained.

[0108] (Example 18) Except for using N2 gas as the gas for sputtering and etching the liquid crystal polymer film, the metal laminate of Example 18 was obtained in the same manner as in Example 2.

[0109] Metal laminates without an intermediate layer O2, Ar, and N2 gases were used as the gases for sputtering and etching the liquid crystal polymer film. The sample using O2 gas employed the metal laminate of Example 4.

[0110] (Comparative Example 3) Except that Ar gas was used as the gas for sputtering and etching the liquid crystal polymer film, the metal laminate of Comparative Example 3 was obtained in the same manner as in Example 4.

[0111] (Comparative Example 4) Except for using N2 gas as the gas for sputtering and etching the liquid crystal polymer film, the metal laminate of Comparative Example 4 was obtained in the same manner as in Example 4.

[0112] Regarding the fabricated metal laminates, the peel strength between the liquid crystal polymer film and the metal layer was measured as described above. The results showed that for metal laminates with an intermediate layer, the peel strength was 8.2 N / cm in Example 2 (O2 gas), 5.4 N / cm in Example 17 (Ar gas), and 7.9 N / cm in Example 18 (N2 gas). Furthermore, for metal laminates without an intermediate layer, the peel strength was 7.6 N / cm in Example 4 (O2 gas), 1.0 N / cm in Comparative Example 3 (Ar gas), and 2.2 N / cm in Comparative Example 4 (N2 gas). Therefore, when the sputtering etching gas used for the liquid crystal polymer film is O2 gas, compared to when both Ar and N2 gases are used, the peel strength tends to be higher, and the increase in peel strength is greater for metal laminates without an intermediate layer than for those with an intermediate layer.

[0113] 1A: Metal laminate 1B: Metal laminate 1C: Metal laminate 1D: Metallic laminate 10: Metal layer 11:Metal foil 12: Carrier layer 13: Peel-off layer 14: Extremely thin metal layer 15: Intermediate Layer 20: Low dielectric thin film

Claims

1. A metal laminate comprising a metal layer consisting of at least one layer including a metal foil laminated on at least one side of a low-dielectric thin film, wherein the metal laminate does not have an intermediate layer containing metal between the low-dielectric thin film and the metal foil, a plurality of protrusions of the metal foil are formed on the surface of the metal foil on the side of the low-dielectric thin film, wherein the width of the protrusion is denoted as a, the height of the protrusion is denoted as b, and σ is the standard deviation of b / a, wherein the average value of b / a + 3σ is 2.5 or less, and the peel strength between the low-dielectric thin film and the metal layer is 3 N / cm or more, wherein the metal foil is a rolled metal foil or an electrolytic metal foil.

2. The metal laminate of claim 1, wherein the metal laminate does not have a sputtered layer made of copper, nickel, chromium or an alloy thereof between the aforementioned low dielectric film and the aforementioned metal foil.

3. The metal laminate as claimed in claim 1 or 2, wherein the aforementioned metal foil is rolled copper foil or electrolytic copper foil.

4. A method for manufacturing a metal laminate, wherein the metal laminate comprises a metal layer consisting of at least one layer including a metal foil laminated on at least one side of a low-dielectric thin film, wherein the metal laminate does not have an intermediate layer containing metal between the low-dielectric thin film and the metal foil, a plurality of protrusions of the metal foil are formed on the surface of the metal foil on the side of the low-dielectric thin film, wherein the width of the protrusion is denoted as a, the height of the protrusion is denoted as b, and σ is the standard deviation of b / a, wherein the average value of b / a + 3σ is 2.5 or less, and the peel strength between the low-dielectric thin film and the metal layer is 3 N / cm or more, wherein the metal foil is a rolled metal foil or an electrolytic metal foil, the method comprising the following steps: preparing the low-dielectric thin film and the metal foil, and activating at least one surface of the low-dielectric thin film by oxygen sputter etching. The steps of activating the surface of the aforementioned metal foil by sputtering etching and the steps of rolling and bonding the activated surfaces of the aforementioned low dielectric film and the aforementioned metal foil together with a rolling reduction rate of 0 to 30%.

5. The method for manufacturing the metal laminate as claimed in claim 4, wherein the metal laminate does not have a sputtered layer made of copper, nickel, chromium or an alloy thereof between the aforementioned low-dielectric thin film and the aforementioned metal foil.

6. The method for manufacturing the metal laminate as claimed in claim 4 or 5, wherein the aforementioned metal foil is rolled copper foil or electrolytic copper foil.

7. The method for manufacturing the metal laminate as claimed in claim 4 or 5, wherein the temperature of the aforementioned rolling bonding step is above 15°C and below 100°C.

8. A method for manufacturing a metal laminate as claimed in claim 4 or 5, wherein after rolling bonding, heat treatment is performed at a temperature above -150°C and below the melting point of the aforementioned low dielectric film.

9. A printed wiring board having a circuit formed on a metal laminate as claimed in any one of claims 1 to 3.

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