TW202506405A - Metal laminate and manufacturing method thereof, and printed wiring board - Google Patents

Abstract

The present invention provides a metal laminate having both high-frequency characteristics and adhesion of the laminated interface. The present invention relates to a metal laminate and a method for manufacturing the same, as well as a printed wiring board. The metal laminate is a metal laminate having a metal layer composed of at least one layer of metal foil laminated on at least one surface of a low-dielectric film. In the interface between the low-dielectric film and the metal layer, the metal contained in the range of 1.3 μm or less from the low-dielectric film side surface toward the metal layer side of the metal layer is composed of a non-magnetic metal, and the peel strength between the low-dielectric film and the metal layer is 1.0 N/cm or more.

Description

Metal laminate and manufacturing method thereof, and printed wiring board

The present invention relates to a metal laminate and a manufacturing method thereof, and a printed wiring board.

In the past, metal laminates made by laminating metal foils such as copper foil to low dielectric films have been known as substrates for printed wiring boards. In recent years, the fifth generation mobile communication system (5G) services have been launched in various countries, and metal laminates with excellent high-frequency characteristics within the 5G frequency band are required.

As metal laminates, generally from the viewpoint of adhesion to low dielectric thin films, it is known that a heat lamination method is used to heat-press a metal foil with a roughened pressing surface. As such metal laminates, for example, Patent Document 1 discloses a treated copper foil for copper-clad laminates having a roughening treatment layer on at least one side of an untreated copper foil and an anti-oxidation treatment layer on the roughening treatment layer, and the anti-oxidation treatment layer contains molybdenum and cobalt, and discloses a copper-clad laminate in which the copper foil is bonded to an insulating resin substrate.

In addition, in the thermal lamination method, in order to ensure the adhesion between the low dielectric film and the metal layer, a layer containing metals such as nickel (Ni) and cobalt (Co) is formed on the surface of the low dielectric film and bonded to the metal foil during the thermal pressing step. However, if ferromagnetic metals such as Ni and Co (also known as high magnetic permeability metals) exist at the lamination interface between the low dielectric film and the metal layer, the transmission characteristics of the metal laminate in the high frequency band will deteriorate. [Prior technical literature] [Patent literature]

Patent document 1: Japanese Patent Application Publication No. 2016-149438

[Problems to be solved by the invention]

As mentioned above, in the previous metal laminates made by the thermal lamination method, the high-frequency characteristics are insufficient because of the presence of ferromagnetic metals such as Ni and Co at the lamination interface between the low-dielectric film and the metal layer. Therefore, the purpose of the present invention is to provide a metal laminate that has both high-frequency characteristics and adhesion of the lamination interface. [Means for solving the problem]

As a result of the active research conducted by the inventors to solve the above-mentioned problems, they found that by using materials without ferromagnetic metal on the surface and manufacturing metal laminates by surface activated bonding method, they can have both high-frequency characteristics and adhesion of the laminate interface, thus completing the present invention. That is, the main points of the present invention are as follows. (1) A metal laminate, wherein a metal layer composed of at least one layer of metal foil is laminated on at least one surface of a low dielectric film, wherein at the interface between the low dielectric film and the metal layer, the metal contained in the range of 1.3 μm or less from the surface of the low dielectric film side toward the metal layer side of the metal layer is composed of a non-magnetic metal, and the peel strength between the low dielectric film and the metal layer is 1.0 N/cm or more. (2) A metal laminate as described in (1), wherein the surface arithmetic mean height Sa of the metal layer side of the low dielectric film is 60 nm or less. (3) A metal laminate as described in (1) or (2) above, wherein the metal foil is a rolled copper foil, a carrier copper foil or an electrolytic copper foil. (4) A metal laminate as described in any one of (1) to (3) above, wherein the metal layer has a chromate treatment layer between the low dielectric film and the metal foil. (5) A metal laminate as described in any one of (1) to (4) above, wherein the metal layer has no organic layer on the low dielectric film side surface. (6) A method for manufacturing a metal laminate, wherein a metal layer composed of at least one layer of metal foil is laminated on at least one surface of a low dielectric film, wherein at the interface between the low dielectric film and the metal layer, the metal contained in the range of 1.3 μm or less from the low dielectric film side surface toward the metal layer side is composed of a non-magnetic metal, and the peeling strength between the low dielectric film and the metal layer is greater than 1.0 N/cm, the method comprises the following steps: a step of preparing a low dielectric film and a metal foil, a step of activating at least one surface of the low dielectric film by sputter etching, A step of activating the surface of the metal foil by sputter etching, and a step of rolling the activated surface of the low dielectric film and the metal foil together at a rolling reduction rate of 0 to 30%. (7) A method for manufacturing a metal laminate as described in (6), wherein the surface arithmetic mean height Sa of the metal layer side of the low dielectric film in the metal laminate is less than 60 nm. (8) A method for manufacturing a metal laminate as described in (6) or (7), wherein the metal foil is a rolled copper foil, a carrier copper foil or an electrolytic copper foil. (9) A method for manufacturing a metal laminate as described in any one of (6) to (8), wherein the metal foil is a metal foil having a chromate treatment layer on the surface. (10) A method for producing a metal laminate as described in any one of (6) to (9), wherein at least one surface of the low dielectric film is activated by sputter etching using oxygen. (11) A method for producing a metal laminate as described in any one of (6) to (10), wherein the step of activating the surface of the metal foil by sputter etching includes the step of removing an organic layer from the surface of the metal foil. (12) A printed wiring board, which is formed by forming a circuit on the metal laminate as described in any one of (1) to (5). This specification includes the disclosure of Japanese Patent Application No. 2023-068300, which is the basis of the priority of this application. [Effect of the Invention]

According to the present invention, a metal laminate having both high-frequency characteristics and laminate interface adhesion can be provided.

The present invention is described in detail below. The present invention relates to a metal laminate material in which a metal layer composed of at least one layer of metal foil is laminated on at least one side of a low dielectric film. The metal laminate material of the present invention includes an alloy layer on one side of the low dielectric film and alloy layers on both sides of the low dielectric film. The metal laminate material of the present invention has excellent high-frequency characteristics because the metal contained in the interface between the low dielectric film and the metal layer is composed of non-magnetic metal and there is no ferromagnetic metal on the interface. In addition, the low dielectric film and the metal layer have sufficient adhesion.

A. Metal laminate FIG1 is a schematic cross-sectional view showing a metal laminate of one embodiment of the present invention. As shown in FIG1 , the metal laminate 1A is a metal layer 10 formed by laminating a metal foil on a surface of a low dielectric film 20.

FIG2 is a schematic cross-sectional view of another embodiment of the metal laminate of the present invention. In this embodiment, a carrier metal foil having an extremely thin metal layer, a peeling layer and a carrier layer is used as the metal foil. As shown in FIG2, the metal laminate 1B of the present invention is a metal layer 10 formed by a carrier metal foil laminated on one surface of a low dielectric film 20. The metal layer 10 is laminated in the order of an extremely thin metal layer 14, a peeling layer 13 and a carrier layer 12 from the side of the low interfacial film 20.

The following is a detailed description of the various components of the metal laminate of the present invention.

1. Low dielectric film As the material of the low dielectric film, any low dielectric polymer material that can be used as a flexible substrate can be used, for example, a material with a relative dielectric constant _εr of less than 3.3 and a dielectric loss factor tanδ of less than 0.006, but it is not limited to this. Specifically, it can be appropriately selected from liquid crystal polymer, polyvinyl fluoride (fluorine resin such as polytetrafluoroethylene), polyamide, isocyanate compound, polyamide imide, polyimide, low dielectric constant polyimide, polyethylene terephthalate, polyether imide, cycloolefin polymer, etc. It is preferably a liquid crystal polymer, polyvinyl fluoride, polyamide or low dielectric constant polyimide, and more preferably a liquid crystal polymer. The low dielectric film is a single-layer film or a laminate composed of multiple layers. When it is a multiple layer, any one or more of the multiple layers can be a layer composed of the above-mentioned low dielectric polymer material. The layers other than the layer composed of the low dielectric polymer material can be composed of conventionally known materials such as epoxy resins. Liquid crystal polymer refers to an aromatic polyester resin with p-hydroxybenzoic acid as a basic structure that exhibits liquid crystal properties in a molten state.

The thickness of the low dielectric film can be appropriately set according to the purpose of the metal laminate, etc. For example, when used as a flexible printed circuit board, the thickness is usually more than 10μm and less than 150μm, preferably more than 25μm and less than 150μm, more preferably more than 25μm and less than 120μm, and particularly preferably more than 25μm and less than 100μm. The thickness of the low dielectric film refers to the average value of the values 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. The thickness of the low dielectric film before bonding can be measured using a micrometer, etc., and refers to the average value of the thickness measured at 10 points randomly selected on the surface of the low dielectric film to be the object. Furthermore, for the low dielectric film used, the deviation of all measured values from the average value of the measured values at 10 points is preferably within 20%, and more preferably within 10%.

2. Metal layer The metal layer is not particularly limited as long as it includes a metal foil, and may be composed of the metal foil or may have other layers in addition to the metal foil. When the metal layer has other layers in addition to the metal foil, it is preferred that the other layers are between the low dielectric film and the metal foil.

The metal foil is preferably a rolled metal foil, a carrier metal foil or an electrolytic metal foil, and more preferably a rolled copper foil, a carrier copper foil or an electrolytic copper foil. Furthermore, the metal foil may be a single-layer foil or a laminated foil thereof.

When a rolled metal foil or an electrolytic metal foil is used as the metal foil, the type of metal constituting the metal foil is not particularly limited depending on the purpose of the metal laminate, but examples thereof include copper, iron, nickel, zinc, tin, chromium, gold, silver, platinum, cobalt, titanium and their alloys. As the metal foil, a metal foil made of non-magnetic metals such as copper, zinc, tin, chromium, gold, silver, platinum and titanium is preferred, and copper foil or copper alloy foil is preferred. The copper alloy foil referred to here refers to a foil made of copper and a non-magnetic metal. The reason is that by rolling and bonding these with a low dielectric film, a flexible substrate for forming fine wiring can be obtained, for example. Furthermore, when the metal constituting the metal foil contains ferromagnetic metals such as iron, nickel, cobalt, and alloys thereof, it is desirable to use a laminated foil having a layer composed of a non-magnetic metal laminated on the surface of the low dielectric film side of the metal foil. When such a laminated foil is laminated with the low dielectric film, no ferromagnetic metal will exist at the lamination interface of the metal laminate. Examples of non-magnetic metals include copper, zinc, tin, chromium, gold, silver, platinum, and titanium.

When a rolled metal foil or an electrolytic metal foil is used as the metal foil, the thickness of the metal foil is not particularly limited according to the purpose of the metal laminate, but for example, if it is used for a flexible printed wiring board, it is preferably 3 μm to 100 μm, more preferably 10 μm to 50 μm, and particularly preferably 10 μm to 35 μm. In addition, in the case of a laminated foil having a layer composed of a non-magnetic metal on the surface of the low dielectric film side of the metal foil, the thickness of the non-magnetic metal layer formed as the upper layer on the surface of the low dielectric film side of the metal foil is preferably 1.3 μm to 50 μm, more preferably 1.3 μm to 15 μm, and particularly preferably 1.5 μm to 10 μm. Here, the thickness of the metal foil or non-magnetic metal layer is obtained by taking an optical microscope photograph of a cross section of the metal laminate and measuring the thickness of the metal foil or non-magnetic metal layer at any 10 points in the optical microscope photograph. The average value of the values obtained.

When a rolled copper foil is used as the metal foil, the rolled copper foil is not particularly limited, but examples thereof include HA-V2 manufactured by JX Metal (Co., Ltd.) or C1020R-H manufactured by Sumitomo Mitsui Metal Mining & Co., Ltd. When an electrolytic copper foil is used as the metal foil, the electrolytic copper foil is not particularly limited, but examples thereof include CF-PLFA manufactured by Fukuda Metal Foil & Powder Co., Ltd.

When manufacturing a flexible substrate for forming fine wiring, a metal foil with a carrier having an extremely thin metal layer, a peeling layer, and a carrier layer is preferably used as a metal foil. When a metal foil with a carrier is used, the metal foil with a carrier is laminated in the order of an extremely thin metal layer, a peeling layer, and a carrier layer from the low dielectric film side as shown in FIG2. When a metal foil with a carrier is used, the "metal foil" in the obtained metal laminate refers to the portion consisting of the extremely thin metal layer, the peeling layer, and the carrier layer.

The carrier layer of the metal foil attached to the carrier is in the shape of a thin sheet and functions as a supporting material or a protective layer to prevent the metal laminate from wrinkling or bending and to prevent the extremely thin metal layer from being scratched. Examples of the carrier layer are foils or plates made of copper, aluminum, nickel and their alloys (stainless steel, brass, etc.) with a metal resin on the surface. The carrier layer is preferably copper foil. The thickness of the carrier layer is not particularly limited, but for example, it is 10 μm or more and 100 μm or less.

The peeling layer of the metal foil attached to the carrier also has the function of reducing the peeling strength of the carrier layer, and further suppressing the mutual diffusion between the carrier layer and the ultra-thin metal layer that may be caused by heat treatment. The peeling layer can be any of an organic peeling layer and an inorganic peeling layer. Examples of components used in the organic peeling layer include nitrogen-containing organic compounds, sulfur-containing organic compounds, carboxylic acids, etc. Examples of nitrogen-containing organic compounds include triazole compounds, imidazole compounds, etc. 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 hydroxybenzothiazole, thiocyanuric acid, and 2-benzimidazolethiol. Examples of carboxylic acids include monocarboxylic acids and dicarboxylic acids. 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 usually 1 nm or more and 1 μm or less, and preferably 5 nm or more and 500 nm or less.

The metal of the ultra-thin metal layer constituting the metal foil of the carrier varies depending on the purpose of the metal layer material and is not particularly limited, but examples thereof include copper, zinc, tin, chromium, gold, silver, platinum, titanium, and alloys thereof. The ultra-thin metal layer is preferably a layer of copper or a copper alloy. The thickness of the ultra-thin metal layer is usually 1.5 μm to 10 μm, preferably 1.5 μm to 7 μm.

The metal foil, carrier layer and ultra-thin metal layer as a carrier are preferably copper or copper alloy, and more preferably the copper foil of the carrier is copper.

The metal layer may also have a chromate treatment layer between the low dielectric film and the metal foil. When the metal foil is an electrolytic metal foil or a metal foil of a carrier, the metal layer preferably has a chromate treatment layer between the low dielectric film and the metal foil. The chromate treatment layer can function as a rust-proof layer. The chromate treatment layer is preferably formed on the surface of the metal foil. In particular, when the surface of the metal foil having the chromate treatment layer is laminated with the low dielectric film as the metal layer, it is preferred that the metal layer and the low dielectric film have a higher adhesion.

The chromate treatment layer is preferably in contact with the surfaces of both the low dielectric film and the metal foil. The thickness of the chromate treatment layer is usually more than 0 nm and less than 20 nm, preferably more than 1 nm and less than 10 nm. Here, the method for measuring the thickness of the chromate treatment layer is exemplified by thickness measurement using X-ray photoelectron spectroscopy (XPS) or Aujet electron spectroscopy (AES), but is not limited thereto.

In the present invention, the chromate-treated layer refers to a layer formed using a solution containing chromic anhydride, chromic acid, dichromic acid, chromate or dichromate (also referred to as a chromate-treated solution). The chromate-treated layer is preferably formed of chromate.

FIG3 is a schematic cross-sectional view of a metal laminate having a chromate treatment layer in an embodiment of the present invention. As shown in FIG3 , the metal laminate 1C of the present invention has a metal layer 10 laminated on a surface of a low dielectric film 20. The metal laminate 1C has a chromate treatment layer 15 between the low dielectric film 20 and the metal foil 11. In the metal laminate 1C, the chromate treatment layer 15 is in contact with the surfaces of both the low dielectric film 20 and the metal foil 11. The metal laminate 1C is formed by laminating the low dielectric film 20, the chromate treatment layer 15, and the metal foil 11 in this order.

FIG4 is a schematic cross-sectional view of a metal laminate having a chromate treatment layer in another embodiment of the present invention. In this embodiment, a metal foil with a carrier having an extremely thin metal layer, a peeling layer, and a carrier layer is used as the metal foil. As shown in FIG4, the metal laminate 1D of the present invention is formed by laminating a metal layer 10 on one surface of a low dielectric film 20. The metal laminate 1D has a chromate treatment layer 15 between the low dielectric film 20 and the metal foil 11 having an extremely thin metal layer 14, a peeling layer 13, and a carrier layer 12. In the metal laminate 1D, the chromate treated layer 15 is in contact with the surfaces of both the low dielectric thin film 20 and the metal foil 11. The metal laminate 1D is formed by stacking the low dielectric thin film 20, the chromate treated layer 15, the ultra-thin metal layer 14, the peeling layer 13 and the carrier layer 12 in this order.

The metal laminate material may have an organic layer such as a treatment layer obtained by a silane coupling agent on the surface of the low dielectric film side of the metal layer. Examples of silane coupling agents include olefinic silanes, epoxy silanes, acrylic silanes, amino silanes, and alkyl silanes, but are not limited thereto. The silane coupling agent may be applied by blowing with a sprayer, applying with a coater, or dipping. Furthermore, the metal laminate material may also have a treatment layer obtained by a benzotriazole (BTA) compound on the surface of the low dielectric film side of the metal layer.

The metal laminate material preferably does not have an organic layer such as a treatment layer obtained by a silane coupling agent or a benzotriazole compound on the surface of the metal layer on the low dielectric film side. When the metal laminate material does not have a treatment layer obtained by a silane coupling agent, the silicon (Si) content on the surface of the metal layer on the low dielectric film side (for example, within a range of 100 nm or less from the outermost surface in the thickness direction) is preferably 0.03 μg/cm ² or less, and more preferably 0.025 μg/cm ² or less. The Si content can be measured, for example, by fluorescent X-ray analysis.

The metal laminate is preferably a metal foil without a roughened particle layer and a heat-resistant layer on its surface. Since such layers usually contain ferromagnetic metals such as Ni and Co, the presence of ferromagnetic metals at the lamination interface of the metal laminate will reduce the high-frequency characteristics of the metal laminate. The roughened particle layer is, for example, any metal selected from the group consisting of Cu, Co and Ni or its alloy, specifically a Cobalt-Nickel alloy plating layer, a Copper-Cobalt-Nickel alloy plating layer, etc. Furthermore, the heat-resistant layer contains, for example, any metal selected from the group consisting of Co, Ni and Mo or its alloy, specifically a Ni plating layer, etc.

The metal laminate of the present invention does not have a strong magnetic metal (also called a high magnetic permeability metal) at the interface between the low dielectric film and the metal layer. That is, since the metal contained in the interface between the low dielectric film and the metal layer is made of non-magnetic metal, the high-frequency characteristics are excellent.

In the present invention, the analysis of the components contained in the interface between the low dielectric film and the metal layer can be performed by, for example, glow discharge luminescence surface analysis (GDS). Specifically, the components contained in the range of 1.3 μm or less from the surface of the low dielectric film side of the metal layer toward the metal layer side can be measured by, for example, GDS. Therefore, in the metal laminate material of the present invention, the metal contained in the range of 1.3 μm or less from the surface of the low dielectric film side of the metal layer toward the metal layer side (thickness direction) at the interface between the low dielectric film and the metal layer is composed of non-magnetic metal.

GDS is an analysis method that performs elemental analysis in the depth direction of a sample, and is a destructive analysis using sputtering. In addition, analysis of components contained in interfaces can be performed using X-ray photoelectron spectroscopy (XPS).

In the present invention, non-magnetic metal refers to metals other than ferromagnetic metals (such as iron, nickel, cobalt, etc.). In the present invention, ferromagnetic metals are also referred to as high magnetic permeability metals, for example, metals having a relative magnetic permeability of 10.0 or more. In addition, the relative magnetic permeability of non-magnetic metals is, for example, less than 1.5. Examples of non-magnetic metals include copper, zinc, tin, chromium, gold, silver, platinum, and titanium, among which copper or chromium is preferred. In particular, when the components contained in the interface between the low dielectric film and the metal layer include chromium, it is preferred because the adhesion between the low dielectric film and the metal layer can be further improved. In one embodiment, the non-magnetic metals present at the lamination interface of the metal laminate are copper and chromium. In one embodiment, no iron, nickel or cobalt exists at the lamination interface of the metal laminate.

In the present invention, the non-magnetic metal contained in the range of 1.3 μm or less from the surface of the low dielectric film side of the metal layer toward the metal layer side is preferably composed of a single layer (1 layer). That is, the metal layer composed of non-magnetic metal is preferably composed of a single layer of metal foil (excluding the chromate-treated layer). By setting it as a single layer structure, it is believed that the high-frequency characteristics can be made better and the gap at the bonding interface between the metal layer and the low dielectric film can be suppressed. On the other hand, when there are two or more layers made of non-magnetic metal (for example, a metal layer/metal foil structure made of non-magnetic metal, etc.) in the range of less than 1.3μm from the surface of the low dielectric film side of the metal layer toward the metal layer side, it is considered that gaps are generated at the lamination interface between the metal layers during bonding, and there is a possibility of bulging due to the solder reflow step when used as a printed wiring board.

The metal laminate of the present invention has a peel strength of 1.0 N/cm or more between the low dielectric film and the metal layer, preferably 3.0 N/cm or more, and more preferably 5.0 N/cm or more. When the peel strength is 1.0 N/cm or more, the reliability of fine wiring of a printed wiring board can be improved.

When measuring the above-mentioned peel strength, first make a test piece from the metal laminate, and use a knife or the like to cut a 1 cm wide incision in the metal layer. Then, after partially peeling off the metal layer and the low dielectric film, fix the low dielectric film on a support, and pull the metal layer at a speed of 50 mm/min at a 90° direction relative to the low dielectric film. The force required for peeling at this time is set as the peel strength (unit: N/cm). In addition, when the metal layer is thin and fragile, there is a risk of breaking when measuring the peel strength. In this case, the metal layer surface may be electrolytically plated (for example, copper plating when the metal layer is copper) to increase the thickness of the metal layer to about 5 μm to about 50 μm, and then the above-mentioned peeling strength may be measured. The above-mentioned peeling strength value is measured in accordance with the measurement method specified in JIS C6471.

In this specification, the so-called "peeling strength of a low dielectric film and a metal layer" refers to the peeling strength at the interface between the low dielectric film and the metal layer, and also means the peeling strength when the metal layer is damaged and the peeling strength when the low dielectric film is damaged. In addition, as mentioned above, when a chromate treatment layer or a treatment layer obtained by a silane coupling agent or a benzotriazole compound is laminated between a low dielectric film and a metal foil, in addition to referring to the peeling strength at the interface between the low dielectric film and the treatment layer, it also refers to the peeling strength at the interface between the metal foil and the treatment layer and the peeling strength when the treatment layer is peeled off due to damage inside the treatment layer.

The metal laminate of the present invention has a smooth lamination interface, and therefore has superior high-frequency characteristics compared to conventional metal laminates produced by thermal lamination. In the present invention, the smoothness of the lamination interface of the metal laminate can be confirmed by measuring the surface roughness of the metal layer side surface of the low dielectric film. For example, after removing the metal layer from the metal laminate by etching, the surface (joining surface) of the low dielectric film can be measured by an atomic force microscope (AFM) according to ISO25178.

The surface arithmetic average height Sa of the metal layer side of the low dielectric thin film of the metal laminate of the present invention measured according to ISO25178 is preferably 60nm or less, more preferably 50nm or less, and particularly preferably 20nm or less.

The maximum surface height Sz of the metal layer side of the low dielectric film of the metal laminate of the present invention measured according to ISO25178 is preferably 700nm or less, more preferably 600nm or less, even more preferably 450nm or less, and particularly preferably 300nm or less.

The metal laminate of the present invention has a surface development area Sdr of the metal layer side of the low dielectric film measured according to ISO25178 of preferably 35% or less, more preferably 10% or less, even more preferably 5% or less, and particularly preferably 1.5% or less.

B. Method for manufacturing metal laminates The present invention also relates to a method for manufacturing the aforementioned metal laminates. The metal laminates of the present invention can be manufactured by a surface activated bonding method. Since a strong bond is formed at the bonding interface by surface activation treatment, the adhesion of the interface can be ensured even if there is no ferromagnetic metal such as Ni and Co at the interface. Moreover, the adhesion of the laminated interface can be ensured without relying on the physical anchoring effect obtained by roughening particles as in metal laminates manufactured by thermal lamination. In addition, by manufacturing by a surface activated bonding method, the surface of the metal foil can be laminated to a low dielectric film while maintaining its smoothness. Based on these, the metal laminate has excellent high-frequency characteristics and adhesion of the laminated interface.

The manufacturing method of the metal laminate of the present invention includes: preparing a low dielectric film and a metal foil (step 1); activating at least one surface of the low dielectric film by sputter etching (step 2-1); activating the surface of the metal foil by sputter etching (step 2-2); and bonding the low dielectric film and the activated surface of the metal foil by rolling at a reduction rate of 0-30% (step 3). Although step 1, step 2 (steps 2-1 and 2-2), and step 3 are performed in sequence, steps 2-1 and 2-2 can be performed simultaneously or in sequence.

Next, each step of the manufacturing method of the metal laminate of the present invention is described in detail.

1. Preparation step In step 1, a low dielectric film and a metal foil are prepared. As the low dielectric film and the metal foil, those described above for the metal laminate can be used. In the present invention, by using a metal foil without a ferromagnetic metal on the surface, preferably a metal foil without a roughening layer on the surface, when the metal foil and the low dielectric film are laminated, a metal laminate without a ferromagnetic metal at the lamination interface is obtained.

2. Surface activation step 2-1. Surface activation step of low dielectric film In step 2-1, at least one surface of the low dielectric film is activated by sputter etching. The sputter etching process can be performed by, for example, preparing the low dielectric film as a long strip roll with a width of 100 mm to 600 mm, setting the joint surface of the low dielectric film as a grounded electrode, applying 1 MHz to 50 MHz alternating current between the electrode and other electrodes supported by insulation to generate glow discharge, and setting the area of the electrode exposed to the plasma generated by the glow discharge to less than 1/3 of the area of the other electrodes. During the sputter etching process, the grounded electrode is used as a cooling roller to prevent the temperature of the transported material from rising.

In the sputter etching process of the surface activation step, the surface to be bonded of the low dielectric film is sputtered with an active gas or an inert gas under vacuum to completely remove the adsorbents on the surface. As an active gas, oxygen or a mixed gas containing oxygen can be used. As an inert gas, argon, neon, xenon, krypton, nitrogen, etc., or a mixed gas containing at least one of these can be used. As the gas used for the sputter etching process of the low dielectric film, oxygen is preferably used. When oxygen is used, for example, functional groups such as carboxyl or hydroxyl groups can be given to the surface of the low dielectric film, which can improve the adhesion between the low dielectric film and the metal layer compared to the case of using inert gases such as argon or nitrogen.

The processing conditions of sputter etching can be appropriately set, for example, under vacuum, with a plasma output of 100W~10kW and a line speed of 0.5m/min~30m/min. When using oxygen, the processing conditions of sputter etching are also, for example, under vacuum, with a plasma output of 100W~10kW and a line speed of 0.5m/min~30m/min. In order to prevent re-adsorption of substances on the surface, a higher vacuum is better, but for example, 1×10 ^-5 Pa~10Pa is sufficient.

2-2. Surface activation step of metal foil In step 2-2, the surface of the metal foil is activated by sputter etching.

The sputter etching process of the surface activation step can be performed by, for example, preparing the metal foil to be joined into a long roll with a width of 100 mm to 600 mm, setting the joining surface of the metal foil as a grounded electrode, applying 1 MHz to 50 MHz alternating current between the other electrodes supported by insulation to generate glow discharge, and setting the area of the electrode exposed to the plasma generated by the glow discharge to less than 1/3 of the area of the other electrodes. During the sputter etching process, the grounded electrode is made into a cooling roll to prevent the temperature of the transported material from rising.

In the sputter etching process of the surface activation step, the surface of the metal foil to be bonded is sputtered with an inert gas under vacuum to completely remove the adsorbents on the surface and remove part or all of the oxide layer on the surface. It is better to completely remove the oxide layer. As an inert gas, argon, neon, xenon, krypton, etc., or a mixed gas containing at least one of these can be used, but argon is preferred. Although it depends on the type of metal, the adsorbents on the surface of the metal foil can be completely removed with an etching amount of about 1nm, especially the oxide layer of copper can usually be removed by about 5nm~12nm ( _SiO2 conversion).

The processing conditions of sputter etching can be appropriately set according to the type of metal foil, for example, under vacuum, with a plasma output of 100W~10kW and a linear speed of 0.5m/min~30m/min. In order to prevent re-adsorption of substances on the surface, the vacuum degree at this time is better, but for example, 1×10 ^-5 Pa~10Pa is sufficient.

The surface of the metal foil before activation by sputter etching can be treated with chromate, silane coupling agent, benzotriazole compound, etc. as needed. That is, a metal foil having a chromate treatment layer, a silane coupling agent treatment layer, or a benzotriazole compound treatment layer on the surface can be used. When these treatment layers are provided on the surface of the metal foil, the surface of the treatment layer is activated by sputter etching. At this time, the treatment layer can be completely removed by sputter etching, or it can remain without removal. It is preferred to remove the organic layer such as the silane coupling agent treatment layer or the benzotriazole compound treatment layer from the surface of the metal foil by sputter etching. In this case, the etching amount is usually 1nm~100nm. On the other hand, when a chromate treatment layer is provided on the surface of the metal foil before sputter etching activation, it is preferable to activate the surface by sputter etching in such a way that the treatment layer remains, because the adhesion when joining with the above-mentioned low dielectric film can be improved. In particular, when the surface of the low dielectric film to which functional groups such as carboxyl or hydroxyl are given is joined with the surface of the metal foil having the chromate treatment layer, the low dielectric film and the metal foil can be firmly bonded, and the adhesion is significantly improved, so it is preferable.

3. Rolling bonding step In step 3, the surfaces activated by sputter etching are pressed together (rolling bonding) by roller pressing. The rolling line load of roller pressing is not particularly limited, and can be set in the range of 0.1tf/cm~10tf/cm, for example. However, in the case where the thickness of the metal foil or low-dielectric film before bonding is large, in order to ensure the pressure during bonding, it is necessary to increase the rolling line load, and it is not limited to this numerical range. On the other hand, if the rolling line load is too high, not only the surface of the low-dielectric film or metal foil is easily deformed, but also the bonding interface is easily deformed, so there is a risk that the thickness accuracy of each layer in the metal laminate will be reduced. Furthermore, if the rolling line load is high, the processing strain applied during joining may increase.

The reduction rate during the rolling bonding is 0-30%. Preferably, it is 0-15%. Since the surface activation bonding method can reduce the reduction rate, a metal layer with excellent thickness accuracy can be formed without wrinkles, cracks, etc. In addition, since the fluctuation of the interface between the metal foil and the low dielectric film can be reduced, when the metal foil is pattern-etched to form wiring, precise wiring can be obtained due to excellent thickness accuracy. In addition, the temperature during the rolling bonding is, for example, above 15°C and below 100°C, preferably above 15°C and below 60°C, and more preferably room temperature.

In order to prevent the adhesion of the laminated interface from being reduced due to the re-adsorption of oxygen into the metal layer, the bonding using roller compression is preferably performed in a non-oxidizing environment, such as a vacuum environment or an inert gas environment such as Ar.

The metal laminate obtained by pressing can be further heat treated as needed, preferably. Heat treatment can eliminate the strain of the metal layer and improve the adhesion between the layers. The heat treatment temperature can be set to a temperature range of -150°C above the melting point of the low dielectric film and +10°C below the melting point of the low dielectric film. For example, in the case of a liquid crystal polymer film, it is 150°C to 350°C, preferably 160°C to 340°C, and more preferably 260°C to 340°C.

The environment for performing the heat treatment is not particularly limited, but preferably a vacuum environment or an inert gas environment such as N ₂ , Ar, etc. This is because oxidation of the metal layer due to the heat treatment can be avoided, thereby preventing the metal layer from being oxidized and thus reducing the adhesion between the metal layer and the low dielectric film.

The time for heat treatment is not particularly limited as long as the adhesion between the metal layer and the low dielectric film can be sufficiently improved, but 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. This is because by setting it above the lower limit of the range, the sufficient adhesion between the metal layer and the low dielectric film can be ensured, and by setting it below the upper limit of the range, high production efficiency and low cost of the metal laminate can be achieved. Even if the soaking time is 0 seconds (i.e., cooling immediately after reaching the target temperature without soaking time), the adhesion between the metal layer and the low dielectric film can be fully improved.

Examples of methods for performing heat treatment include maintaining the 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 , Ar, etc.) using a batch heat treatment furnace. In addition, heat treatment may be performed in a roll-to-roll manner using a continuous heat treatment furnace, depending on the heat treatment temperature and environment. In this case, at least the heating part or the cooling part in the continuous heat treatment furnace is set to a desired environment (e.g., a vacuum environment or an inert gas environment such as _N2 , Ar, etc.), maintained at a desired temperature, and then the metal laminate is passed through the heating part or the cooling part at a desired speed to maintain the metal laminate at the desired heat treatment temperature for a desired time.

C. Use of metal laminates The metal laminates of the present invention can be used as metal laminates for making flexible printed circuit boards.

By using the metal laminate material of the present invention, a printed wiring board with fine wiring can be obtained. Therefore, the present invention also relates to a printed wiring board with a circuit formed on a metal laminate material. In the step of forming the wiring, an additional metal layer can also be formed only on the wiring portion. Specifically, a printed wiring board can be obtained by appropriately using a previously known method such as a modified semi-additive method (MSAP method), a semi-additive method (SAP method) or a subtractive method. For example, when using the modified semi-additive method (MSAP method), the non-wiring portion on the metal layer in the metal laminate material is masked, and copper plating is performed on the unmasked portion to form an additional metal layer, the mask is removed, and the metal layer hidden by the mask is removed by etching, so that a printed wiring board can be manufactured. The "printed wiring board" of the present invention includes not only a laminated body with wiring formed, but also a laminated body with electronic components such as IC mounted thereon after the wiring is formed.

In FIG. 1 to FIG. 4, the case where the metal layer is laminated on one surface of the low dielectric film in the metal laminate is described, but the metal laminate is not limited to this. That is, the metal layer can be provided on both surfaces of the low dielectric film as needed. By using the metal laminate in which the metal layer is provided on both surfaces of the low dielectric film, a flexible printed circuit board with wiring formed on both surfaces of the low dielectric film can be obtained. [Example]

Hereinafter, the present invention will be described in more detail based on embodiments and comparative examples, but the present invention is not limited to these embodiments.

(Example 1) A 50 μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was prepared, and as a metal foil, a 12 μm thick electrolytic copper foil made of copper with a chromate-treated layer on the surface (CF-PLFA manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) was prepared. Next, one surface of the liquid crystal polymer film was activated by sputter etching using _O2 gas (etching amount 300 nm), and the surface of the electrolytic copper foil was activated by sputter etching using Ar gas (etching amount 2 nm), and the activated surfaces of the liquid crystal polymer film and the electrolytic copper foil were bonded to each other by rolling at a line load of 1.5 tf/cm to produce a metal laminate. The reduction ratio was 2.0%. Next, the metal laminate was subjected to a heat treatment at 310°C to obtain the metal laminate of Example 1 (layer structure: electrolytic copper foil/liquid crystal polymer film).

(Example 2) A 50 μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was prepared, and as a metal foil, a 12 μm thick rolled copper foil made of copper having a benzotriazole treatment layer (organic layer) on the surface was prepared (HA-V2 manufactured by JX Metal Co., Ltd.). Next, one surface of the liquid crystal polymer film was activated by sputter etching using _O2 gas (etching amount 300 nm), and the treated layer on the rolled copper foil surface was completely removed by sputter etching using Ar gas (etching amount 2 nm) to activate the surface, and the activated surfaces of the liquid crystal polymer film and the rolled copper foil were bonded to each other by rolling at a line load of 1.5 tf/cm to produce a metal laminate. The reduction ratio was 2.0%. Next, the metal laminate was subjected to a heat treatment at 310°C to obtain the metal laminate of Example 2 (laminate structure: rolled copper foil/liquid crystal polymer film).

(Example 3) A 25 μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was prepared, and a 18 μm thick rolled copper foil made of copper (C1020R-H manufactured by Sumitomo Mitsui Metal Mining & Manufacturing Co., Ltd.) was prepared. One surface of the liquid crystal polymer film was activated by sputter etching using Ar gas (etching amount 10 nm). In addition, the metal laminate of Example 3 (layer structure: rolled copper foil/liquid crystal polymer film) was obtained in the same manner as in Example 2.

(Example 4) A metal laminate of Example 4 (laminate structure: rolled copper foil/liquid crystal polymer film) was obtained in the same manner as in Example 3 except that one surface of the liquid crystal polymer film was activated by sputter etching using _N2 gas (etching amount: 140 nm).

(Comparative Example 1) As the electrolytic copper foil, an electrolytic copper foil with a thickness of 12 μm and a rust-proof layer containing Co etc. on the surface (CF-T9DA-SV manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) was used. In the same manner as in Example 1, a metal laminate material of Comparative Example 1 (layer structure: electrolytic copper foil/liquid crystal polymer film) was obtained.

(Comparative Example 2) A 25 μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was prepared, and a 18 μm thick rolled copper foil (HA-V2 manufactured by JX Metal Co., Ltd.) was prepared as a metal foil. Next, after one surface of the liquid crystal polymer film was activated by sputter etching (etching amount 300 nm) using _O2 gas, a 5 nm NiCr alloy sputtering layer was sputtered on the activated surface as a base layer, and a 10 nm Cu sputtering layer was sputtered as an upper layer to form a metal layer. Next, the metal layer surface and the rolled copper foil surface were activated by sputter etching using Ar gas (etching amount: metal layer 2nm, rolled copper foil 2nm), and the activated surfaces of the metal layer and rolled copper foil were bonded to each other by rolling at a line load of 1.5tf/cm to produce a metal laminate. The reduction ratio was 2.3%. Next, the metal laminate was subjected to a heat treatment at 300°C to obtain the metal laminate of Comparative Example 2 (layer structure: rolled copper foil/metal layer/liquid crystal polymer film).

(Comparative Example 3) A 25 μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was prepared, and a 18 μm thick rolled copper foil (HA-V2 manufactured by JX Metal Co., Ltd.) was prepared as a metal foil. Next, one surface of the liquid crystal polymer film was activated by sputter etching (etching amount 300 nm) using _O2 gas, and then a 28 nm NiCr alloy sputtering layer was sputtered on the activated surface to form a metal layer. Next, the metal layer surface and the rolled copper foil surface were activated by sputter etching using Ar gas (etching amount: metal layer 2nm, rolled copper foil 2nm), and the activated surfaces of the metal layer and rolled copper foil were bonded to each other by rolling at a line load of 1.5tf/cm to produce a metal laminate. The reduction ratio was 2.3%. Next, the metal laminate was subjected to a heat treatment at 300°C to obtain the metal laminate of Comparative Example 3 (layer structure: rolled copper foil/metal layer/liquid crystal polymer film).

(Comparative Example 4) By hot lamination, a 50μm thick liquid crystal polymer film (Bextor CTQ manufactured by Kuraray Co., Ltd.) was hot-pressed at a temperature of 310°C or above onto an 18μm thick electrolytic copper foil having a treatment layer composed of a roughened particle layer on one side, to produce a metal laminate of Comparative Example 4 (layer composition: electrolytic copper foil (with roughening treatment)/liquid crystal polymer film/electrolytic copper foil (with roughening treatment)).

The following properties were evaluated for the metal laminates of Examples 1 to 4 and Comparative Examples 1 to 4.

[Metal components at the interface] In order to analyze the metal components contained in the interface between the liquid crystal polymer film and the metal layer of the metal laminate, the GDS measurement was performed on the range of 1.3μm or less from the surface of the liquid crystal polymer film side of the metal layer toward the metal layer side (thickness direction). The GDS measurement was carried out under the following conditions. ・GDS measurement device: High-frequency GDS spectrophotometer (manufactured by Horiba, Ltd., GD-Profiler2) ・Excitation mode: Normal ・Light source pressure: 600Pa ・Light source output: 30W ・Anode diameter: 4mm

[Interface Surface Morphology] In order to evaluate the surface morphology of the laminated interface of the metal laminate, the surface roughness of the interface was measured. Specifically, after the copper foil was removed from the metal laminate (comparison example 2 is the copper foil and the metal layer), the surface roughness of the liquid crystal polymer film after the copper foil was removed was measured by atomic force microscopy (AFM) according to ISO25178.

[Transmission loss (S21)] In order to evaluate the high-frequency transmission characteristics of the metal laminate, the transmission loss (S21) of the metal laminate of Examples 1~2 and Comparative Examples 1~2 and 4 was measured. Since Examples 1~2 and Comparative Examples 1~2 are single-sided materials, a copper layer was provided on the surface of the exposed liquid crystal polymer film on the opposite side of the copper foil laminate by electroless copper plating, and after making through holes, electrolytic copper plating was performed to obtain a measurement sample with a copper layer (25μm) on both sides. After making through holes in the metal laminate of Comparative Example 4, electrolytic copper plating was performed to obtain a sample for measurement with a copper layer (25μm) on both sides.

The transmission path is 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. The measurement is performed using a network analyzer N5227B (manufactured by Keysight Technology Co., Ltd.) at a frequency of 40 GHz. In addition, Examples 1-2 and Comparative Examples 1-2 are measured by making a microstrip line on the laminated copper foil side.

[Peeling strength] A test piece is made from a metal laminate, and a 1 cm wide incision is cut on the metal layer using a knife or the like. Then, after partially peeling off the metal layer and the liquid crystal polymer film, the liquid crystal polymer film is fixed to a support, and the metal layer is pulled apart at a speed of 50 mm/min in a direction of 90° relative to the liquid crystal polymer film. The force required for peeling at this time is taken as the peeling strength (unit: N/cm).

[Presence of voids at the interface] In order to evaluate whether there are voids at the lamination interface of the metal laminate, the cross-sections of the laminates of Examples 1 to 4 and Comparative Examples 1 to 4 were observed at 20,000 times using a scanning electron microscope (SEM).

The composition and evaluation results of the metal laminates of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1. In Table 1, LCP means liquid crystal polymer film.

As for the high-frequency transmission characteristics of the metal laminate, as shown in Table 1, the metal laminate of Examples 1-2, where no ferromagnetic metal exists at the lamination interface of the metal laminate, has a smaller high-frequency transmission loss (S21) and excellent high-frequency characteristics compared with the metal laminate of Comparative Examples 1-2 and 4, where ferromagnetic metal (Ni, Co) exists at the lamination interface of the metal laminate. In particular, when compared with Comparative Example 4 having a coarsened particle layer, the interface of the metal laminate of Examples 1-2 is smoother, and since no ferromagnetic metal exists at the lamination interface, it is confirmed that the high-frequency transmission loss (S21) is smaller and the high-frequency transmission characteristics are more excellent. In the metal laminates of Examples 3-4, since there is no ferromagnetic metal at the laminate interface and the laminate interface is smooth, it is inferred that the metal laminates of Examples 3-4 also have excellent high-frequency transmission characteristics like the metal laminates of Examples 1-2.

As shown in Table 1, the metal laminates of Examples 1 to 4 have sufficient peeling strength even though there is no ferromagnetic metal at the interface that contributes to the adhesion of the laminate interface and the interface is smooth. This is believed to be because in the metal laminates of Examples 1 to 4, a strong bond is formed at the interface between the liquid crystal polymer film and the copper foil through surface activation treatment, so the adhesion of the laminate interface can be ensured without relying on the physical anchoring effect of the roughened particles. In particular, the metal laminates of Examples 1-2 in which the surface of the liquid crystal polymer film was activated by sputter etching using _O2 gas were compared with the metal laminates of Examples 3-4 in which the surface of the liquid crystal polymer film was activated by sputter etching using Ar gas or _N2 gas, confirming that the interface between the liquid crystal polymer film and the copper foil was more strongly bonded and had excellent peeling strength. Moreover, Example 1 in which the metal foil surface (liquid crystal polymer film side) of the metal laminate had a chromate treatment layer was compared with Example 2 in which the metal foil surface of the metal laminate did not have a chromate treatment layer, confirming that the interface between the liquid crystal polymer film and the copper foil was even more strongly bonded and had better peeling strength.

Regarding the presence or absence of voids at the bonding interface of the metal laminate, the evaluation results of the metal laminates of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1, and the cross-sectional view of the presence or absence of voids at the bonding interface of the metal laminate of Example 1 and Comparative Examples 2 to 3 is shown in FIG5. As shown in Table 1 and FIG5, the metal laminate of Examples 1 to 4, in which the metal contained in the range of 1.3 μm or less from the low dielectric film side surface of the metal layer toward the metal layer side is composed of a single layer (1 layer), has no voids at the bonding interface, and therefore it is confirmed that it can be preferably used in the solder reflow step when used as a printed wiring board. On the other hand, the metal contained in the range of 1.3μm or less from the low dielectric film side surface of the metal layer toward the metal layer side is composed of two or more layers (metal layer/copper foil) in Comparative Examples 2-3. Since the bonding interface has voids, it is confirmed that there is a risk of bulging caused by the voids in the solder reflow step when used as a printed wiring board. In particular, in Comparative Example 3, since the thickness of the sputtering layer (metal layer) is greater than that of Comparative Example 2, it is confirmed that more voids are generated at the bonding interface.

All publications, patents, and patent applications cited in this specification are incorporated into this specification by direct citation.

1A: Metal laminate 1B: Metal laminate 1C: Metal laminate 1D: Metal laminate 10: Metal layer 11: Metal foil 12: Carrier layer 13: Stripping layer 14: Ultra-thin metal layer 15: Chromium salt treatment layer 20: Low dielectric film

[Figure 1] is a schematic cross-sectional view showing a metal laminate of one embodiment of the present invention. [Figure 2] is a schematic cross-sectional view showing a metal laminate of another embodiment of the present invention. [Figure 3] is a schematic cross-sectional view showing a metal laminate having a chromate treatment layer of one embodiment of the present invention. [Figure 4] is a schematic cross-sectional view showing a metal laminate having a chromate treatment layer of another embodiment of the present invention. [Figure 5] is a cross-sectional view showing the presence or absence of voids at the bonding interface of the metal laminates of Example 1 and Comparative Examples 2-3.

1A: Metal laminates

10: Metal layer

20: Low dielectric film

Claims (12)

A metal laminate is a metal laminate having a metal layer composed of at least one layer of metal foil laminated on at least one surface of a low dielectric film, wherein at the interface between the low dielectric film and the metal layer, the metal contained in the range of 1.3 μm or less from the surface of the low dielectric film side toward the metal layer side is composed of a non-magnetic metal, and the peel strength between the low dielectric film and the metal layer is greater than 1.0 N/cm. The metal laminate of claim 1, wherein the surface arithmetic average height Sa of the metal layer side of the low dielectric film is less than 60 nm. The metal laminate of claim 1 or 2, wherein the metal foil is a rolled copper foil, a carrier copper foil or an electrolytic copper foil. The metal laminate of claim 1 or 2, wherein the metal layer has a chromate treatment layer between the low dielectric film and the metal foil. The metal laminate material of claim 1 or 2, wherein there is no organic layer on the low dielectric film side surface of the metal layer. A method for manufacturing a metal laminate, wherein a metal layer composed of at least one layer of metal foil is laminated on at least one surface of a low dielectric film, In the interface between the low dielectric film and the metal layer, the metal contained in the range of 1.3 μm or less from the low dielectric film side surface toward the metal layer side of the metal layer is composed of non-magnetic metal, and the peeling strength of the low dielectric film and the metal layer is greater than 1.0 N/cm, The method comprises the following steps: A step of preparing a low dielectric film and a metal foil, A step of activating at least one surface of the low dielectric film by sputter etching, A step of activating the surface of the metal foil by sputter etching, and a step of bonding the low dielectric film and the activated surface of the metal foil by rolling at a reduction rate of 0-30%. A method for manufacturing a metal laminate as claimed in claim 6, wherein in the metal laminate, the surface arithmetic mean height Sa of the metal layer side of the low dielectric film is less than 60 nm. A method for manufacturing a metal laminate as claimed in claim 6 or 7, wherein the metal foil is a rolled copper foil, a carrier copper foil or an electrolytic copper foil. A method for manufacturing a metal laminate as claimed in claim 6 or 7, wherein the metal foil is a metal foil having a chromate treatment layer on the surface. A method for manufacturing a metal laminate as claimed in claim 6 or 7, wherein at least one surface of the low dielectric film is activated by sputter etching using oxygen. A method for manufacturing a metal laminate as claimed in claim 6 or 7, wherein the step of activating the surface of the metal foil by sputter etching includes the step of removing an organic layer from the surface of the metal foil. A printed wiring board is formed by forming a circuit on the metal laminate material as claimed in claim 1.