Conductive film and its manufacturing method

Abstract

This invention provides a conductive film and its manufacturing method. [Objective] The purpose of this invention is to provide a conductive film that exhibits excellent lightweight properties and does not crack during molding and processing, making it suitable for use as an electromagnetic wave shielding material. [Solution] This invention provides a conductive film characterized in that a copper layer and a tin layer are sequentially stacked on at least one side of a resin film, wherein the amount of copper per unit area (g / m²) is... 2 ) and the amount of tin imparted per unit area (g / m²) 2 The ratio of Cu to Sn is 0.15 or less, and the average grain size of the tin crystals constituting the tin layer is 5.0 μm or more.

Description

Technical Field

[0001] This invention relates to conductive films. More specifically, this invention relates to a lightweight conductive film that does not crack during molding and processing, and can be used as an electromagnetic wave shielding material. Background Technology

[0002] In recent years, with the rapid development of IT and OA equipment, the impact of electromagnetic waves generated by electronic devices, cables, motors, inverters, etc., on other electronic or information equipment has become a problem.

[0003] Electromagnetic waves can cause malfunctions in precision equipment, and their effects on human health are also a cause for concern. Therefore, various technologies have been developed to mitigate the effects of electromagnetic waves using electromagnetic shielding materials. One example is a laminate consisting of a resin film layered with metal layers such as copper foil that have electromagnetic shielding properties.

[0004] However, laminates formed by stacking metal layers on a resin film are prone to cracking during molding and processing. Therefore, it is necessary to suppress cracking to improve processability. On the other hand, to suppress cracking, methods such as thickening the metal layer or increasing the number of metal layers can be considered, but these methods increase weight and make it difficult to achieve lightweighting. Simultaneously satisfying both lightweighting and processability is not easy.

[0005] Various proposals have been made regarding electromagnetic wave shielding materials that laminate metal layers onto a resin film. For example, Patent Document 1 discloses an electromagnetic wave shielding material in which resin layers are tightly laminated on both sides of a metal foil to suppress breakage during molding. This material employs a design that improves the ductility of the metal foil, but because the metal foil is sandwiched within the resin layers, it has the disadvantage of not being able to be brazed.

[0006] Patent document 2 discloses that by laminating a resin layer on a copper foil and defining the orientation of the copper foil surface and the relationship between the copper foil thickness and the resin layer thickness, an electromagnetic wave shielding material with excellent three-dimensional formability and lightweight can be obtained. However, this method requires manufacturing a copper foil with a specific orientation and thickness, and then laminating the copper foil and resin layer in multiple layers, which has the disadvantage of complex process.

[0007] Patent document 3 discloses an electromagnetic wave shielding material that uses alternating layers of metal and insulating layers to suppress cracks in the metal layers caused by molding processes. However, this material tends to have an increasing thickness, and the manufacturing process also becomes more complex.

[0008] In addition, Patent Document 4 discloses a conductive film obtained by sequentially stacking copper and tin on a thin film substrate, but this material improves solder wettability by setting a barrier layer composed of organic compounds between the copper layer and the tin layer.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2018-152466

[0012] Patent Document 2: Japanese Patent Application Publication No. 2021-163789

[0013] Patent Document 3: Japanese Patent Application Publication No. 2022-091579

[0014] Patent Document 4: International Publication 2022 / 085374 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] The objective of this invention is to provide a conductive film that is lightweight and does not crack during molding and processing, and can be used as an electromagnetic wave shielding material.

[0017] Methods for solving problems

[0018] To solve the above-mentioned problems, the inventors discovered that in a laminate in which copper and tin layers are sequentially stacked on a resin film, when the ratio of the amount of copper to the amount of tin and the average grain size of the tin crystals constituting the tin layer satisfy certain conditions, the above-mentioned problems can be solved, thus completing the present invention.

[0019] That is, the present invention relates to the following conductive film.

[0020] (1) A conductive film, characterized in that a metal layer having a copper layer and a tin layer sequentially stacked on at least one side of the resin film, wherein the amount of copper per unit area (g / m²) is... 2 ) and the amount of tin imparted per unit area (g / m²) 2 The ratio of Cu to Sn is 0.15 or less, and the average grain size of the tin crystals constituting the tin layer is 5.0 μm or more.

[0021] (2) The conductive film according to (1), characterized in that the amount of copper imparted per unit area of ​​the copper layer is 10 g / m². 2 the following.

[0022] (3) The conductive film according to (1) is characterized in that the arithmetic mean roughness Ra of the surface of the tin layer is 0.25 μm or more.

[0023] (4) The conductive film according to (1) is characterized in that the thickness of the resin film is 100 to 200 μm.

[0024] (5) A method for manufacturing a conductive film according to any one of (1) to (4), characterized in that it includes a step of forming a copper layer on a resin film and a step of forming a tin layer on the copper layer formed by the above steps by electroplating tin.

[0025] (6) The method for manufacturing a conductive film according to (5) is characterized in that, in the tin plating method, a non-glossy tin plating solution is used as the plating solution.

[0026] Invention Effects

[0027] According to the present invention, a conductive film with excellent lightweight properties and no cracking of the metal layer during molding and processing can be obtained, which can be used as an electromagnetic wave shielding material. Attached Figure Description

[0029] [ Figure 1 [Illustration 1] is a schematic cross-sectional view showing an example of the conductive film of the present invention.

[0030] [ Figure 2 [Illustration] is a schematic plan view showing the fixture and sample used in the formability evaluation method of the embodiment.

[0031] [ Figure 3 [Illustration] is a schematic cross-sectional view and a schematic diagram showing the sample holder used in the formability evaluation method of the embodiment.

[0032] [ Figure 4 The method for evaluating the formability of the embodiments is a cross-sectional view schematically representing the molding process.

[0033] [ Figure 5 [Illustration] is a schematic diagram showing the molded conductive film (evaluation sample molded article) of the embodiment.

[0034] [ Figure 6 [Image] is a digital microscope image showing the presence or absence of metal cracks during the evaluation of the formability of the conductive film prepared in Example 1.

[0035] [ Figure 7 [Image] is a digital microscope image of the conductive film prepared in Example 1, used to determine the crystal grain size of the tin layer.

[0036] [ Figure 8 [Image] is a digital microscope image of the conductive film fabricated in Comparative Example 5, showing the presence or absence of metal cracks during the evaluation of its formability.

[0037] [ Figure 9 [Image] is a digital microscope image showing the presence or absence of light leakage during the evaluation of the formability of the conductive film fabricated in Comparative Example 5. Detailed Implementation

[0038] The conductive film of the present invention is composed of at least a resin film and a metal layer formed on the resin film.

[0039] 1. Resin film

[0040] As the resin film, a film formed from a synthetic resin is preferred. There are no particular limitations on the synthetic resin, but examples include films formed from polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyimide, polyetherimide, polyphenylene sulfide, etc.

[0041] As a more ideal resin film, a resin film with an elastic modulus of 3.0 GPa or higher is preferred. Furthermore, a resin film with a tensile strength of 70 MPa or higher is preferred, more preferably 75 MPa or higher, and particularly preferably 100 MPa or higher is preferred. Additionally, a resin film with a glass transition temperature of 90°C or higher is preferred, more preferably 150°C or higher is preferred. Furthermore, a resin film with a melting point of 270°C or higher is preferred, more preferably 300°C or higher is preferred.

[0042] If a resin film that meets these conditions is used, it has advantages such as high film strength and is not easy to break, excellent heat resistance, and tolerance to thermal strain generated by the reflow soldering process after molding. Therefore, it can be used as a material that is easy to mold and has strength, and is preferably used in this invention.

[0043] Specifically, polyetherimide (PEI) and polyphenylene sulfide (PPS) are particularly preferred.

[0044] The thickness of the resin film is not particularly limited, but is preferably 100–200 μm. Within this thickness range, the moldability is improved. When the thickness is above 100 μm, the film is less prone to breakage, does not reduce operability, and can adequately maintain post-molding strength. Furthermore, when the thickness is below 200 μm, the film does not have difficulty following the mold during molding.

[0045] 2. Metal layer

[0046] The metal layer formed on the resin film includes at least a copper layer and a tin layer. The metal layer may be formed on only one side of the resin film or on both sides.

[0047] (1) Copper layer

[0048] The copper layer is formed by contacting the resin film on at least one side of the resin film. In this invention, the copper layer refers not only to a layer formed solely of metallic copper, but also to a layer formed of a copper alloy. That is, the metal forming the copper layer can be either copper or a copper alloy. Examples of copper alloys include alloys of copper with metals such as nickel, zinc, and tin. The proportion of copper in the copper alloy is not particularly limited. Preferably, it consists solely of copper.

[0049] Copper content per unit area of ​​the copper layer (g / m²) 2 There are no specific limitations, but 10.0 g / m³ is preferred. 2 The following applies. When the amount of copper supplied is within this range, there is a tendency for metal cracking to occur during molding. There is no particular limitation on the lower limit of the amount of copper supplied, but 3.0 g / m³ is preferred. 2 above.

[0050] The thickness of the copper layer is not particularly limited, but is preferably 1.0 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more. When the thickness of the copper layer is within this range, a conductive film that maintains sufficient conductivity while possessing flexibility and excellent formability can be obtained.

[0051] The copper layer can be a single layer or two or more layers. The preferred number of copper layers is one to two. When multiple copper layers are stacked, their properties and formation methods can be the same or different. However, when the composition of the materials constituting the layers is the same, they are considered as one layer. When multiple copper layers are stacked, the preferred range of the metal content and thickness of the copper layers is the total metal content and thickness of the stacked copper layers.

[0052] There are no limitations on the method for forming the copper layer, and known methods can be used. Examples include: methods using adhesives to bond copper foil; dry film-forming methods such as vacuum evaporation or sputtering; and wet film-forming methods such as electroless plating or electroplating. Furthermore, these methods can be combined to form the copper layer. Preferred methods are dry film-forming methods or wet film-forming methods. Additionally, resin films (including commercially available products) with pre-formed copper layers can also be used.

[0053] When the copper layer is a single layer, the amount of copper per unit area of ​​the copper layer (g / m²) 2 There are no specific limitations, but 10.0 g / m³ is preferred. 2 The following is more preferably 5.0 g / m 2 The following applies. There is no particular limitation on the lower limit of the amount administered, but it is preferably 3.0 g / m³. 2 above.

[0054] The thickness of the copper layer is not particularly limited, but is preferably 0.5 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 0.1 μm or more, and more preferably 0.3 μm or more. When the thickness of the copper layer is within this range, a conductive film that maintains sufficient conductivity while possessing flexibility and excellent formability can be obtained.

[0055] (2) Tin layer

[0056] In this invention, the tin layer is stacked on the side of the copper layer opposite to the resin film side, in contact with the copper layer.

[0057] Tin content per unit area of ​​the tin layer (g / m²) 2 There are no specific limitations, but 20g / m³ is preferred. 2 The above, preferably 30g / m 2 The above. A higher tin content tends to result in better formability. There is no specific upper limit to the tin content, but 110 g / m² is preferred. 2 The following is more preferably 80g / m 2 The following applies. When the amount of tin imparted within this range, a conductive film with excellent formability can be obtained.

[0058] The thickness of the tin layer is not particularly limited, but is preferably 5 μm or more, more preferably 7.5 μm or more. The upper limit of the tin layer thickness is not particularly limited, but is preferably 20 μm or less, more preferably 15 μm or less. When the tin layer thickness is within this range, there is a tendency for metal cracks to occur during molding, and a conductive film with excellent formability can be obtained.

[0059] A tin layer can be a single layer or two or more layers. When two or more tin layers are stacked, their properties and formation methods can be the same or different. When the materials constituting the layers are of the same composition, they are considered as one layer.

[0060] The preferred number of tin layers is one. When multiple tin layers are stacked, the preferred range of the metal content and thickness of the tin layers is the total metal content and thickness of the stacked tin layers.

[0061] There are no particular limitations on the method for forming the tin layer. Examples include wet film formation methods such as electroless plating or electroplating. It can be formed by either electroless plating or electroplating, but electroplating is preferred for reasons such as control of film thickness and ease of continuous processing.

[0062] In electroplating, when a single electroplating process cannot form a sufficient tin film thickness, one method to form the tin layer to the desired thickness is to perform multiple electroplating processes using a tin plating bath with the same composition. That is, the tin can be passed through multiple tin plating baths with the same composition.

[0063] For example, after the first tin plating treatment, a water rinse can be performed. Then, a second tin plating treatment using a tin plating solution with the same composition as the first treatment can be performed, followed by a water rinse. A third tin plating treatment using the same composition can then be performed, followed by a water rinse, thereby forming a tin layer with the desired thickness. There is no particular limit to the number of tin plating treatments using the same composition; the number of treatments can be adjusted appropriately to achieve the desired thickness. It should be noted that a tin layer of the desired thickness formed in this way can be considered as a single layer because the composition of the plating bath is the same.

[0064] In the tin layer, the average grain size of the tin crystals constituting the tin layer is 5.0 μm or more. There is no particular upper limit to the average grain size, but it is preferably 10 μm or less. When the crystal grain size is 5 μm or more, it is advantageous that metal cracks are less likely to occur during molding.

[0065] One method for adjusting the crystal grain size of the tin layer is to appropriately adjust the plating time during electroplating. When the plating time is short, crystal growth is often insufficient, and the grain size tends to be smaller. On the other hand, when the plating time is extended, crystal growth is sufficient, and the grain size tends to be larger.

[0066] Furthermore, by using a non-glossy tin plating solution, the crystal size of tin can be increased. When using a glossy tin plating solution to create a tin layer, the resulting tin layer often has a smaller, microparticle-like grain size in order to achieve a smooth and glossy surface.

[0067] Non-glossy tin plating solutions specifically refer to tin plating solutions that do not contain gloss enhancers. Examples of gloss enhancers include acrylic acid, methyl acrylate, methyl methacrylate, benzyl acetone, benzaldehyde, and acetophenone. The desired tin plating solution is one that does not contain these gloss enhancers.

[0068] The arithmetic surface roughness Ra of the tin layer is preferably 0.25 μm or more. Here, the surface of the tin layer refers to the surface of the tin layer opposite to the surface where the copper layer is formed, which is the outermost surface of the metal layer side in the conductive film of the present invention. There is no particular upper limit to the arithmetic surface roughness Ra, but it is preferably 0.7 μm or less.

[0069] When the arithmetic surface roughness Ra of the tin layer is too small, crack initiation is easy, and sometimes large cracks are easily generated. If the arithmetic surface roughness Ra of the tin layer is within the above range, the tin coating is less prone to cracking. The arithmetic surface roughness Ra of the tin layer refers to the surface roughness of the outermost layer of the conductive film after stacking, and can be measured after stacking according to the method conforming to JIS B 0601:2001.

[0070] To ensure that the arithmetic surface roughness Ra of the tin layer is within the aforementioned range, it is preferable to form the tin layer by electroplating. As the electroplating solution, a non-glossy tin plating solution is preferred. This increases the arithmetic surface roughness Ra of the tin layer surface.

[0071] 3. Layered structure

[0072] The conductive film of the present invention comprises at least a copper layer and a tin layer sequentially stacked on a resin film. In this invention, "sequentially" means stacked in the order of copper and tin layers, starting from the side closest to the resin film. The copper and tin layers may be stacked on only one side of the resin film or on both sides.

[0073] Examples of the layer structure of the conductive film of the present invention include: resin film / copper layer / tin layer, resin film / copper layer (one) / copper layer (two) / tin layer, tin layer / copper layer / resin film / copper layer / tin layer, etc. It should be noted that examples including copper layer (one) and copper layer (two) refer to cases where multiple copper layers of the same or different properties or formation methods are stacked. More preferably, a layer structure of "resin film / copper layer (evaporated copper) / copper layer (electroplated copper) / tin layer" can be cited.

[0074] Figure 1 A cross-section of an example of the conductive film of the present invention is shown in schematic diagram. Figure 1 (A) indicates resin film / copper layer / tin layer. Figure 1 (B) represents the structure of resin film / copper layer (one) / copper layer (two) / tin layer. In Figure 1 In (A), a is the resin film, b is the copper layer, and c is the tin layer. Additionally, in Figure 1 In (B), a is the resin film, b is the copper layer (one of the layers), b' is the copper layer (the second layer), and c is the tin layer.

[0075] In the conductive film of the present invention, in addition to the necessary layers such as the resin film, copper layer, and tin layer, various arbitrary layers can be provided as needed. For example, an adhesive layer can be provided between the layers. Specifically, an adhesive layer can be provided between the resin film and the copper layer to improve adhesion, etc. In addition, the tin layer becomes the outermost layer of the conductive film, and its surface can be treated with an anti-discoloration agent to improve resistance to discoloration, etc.

[0076] In the copper and tin layers of the conductive film of the present invention, the amount of copper imparted per unit area (g / m²) 2 ) and the amount of tin imparted per unit area (g / m²) 2 The ratio of Cu to Sn is 0.15 or less. When Cu / Sn is in this range, metal cracking is less likely to occur during molding. There is no particular limitation on the lower limit of Cu / Sn, but it is preferably 0.05 or more.

[0077] 4. Manufacturing method

[0078] The conductive film of the present invention is manufactured by a method comprising the following steps: a step of forming a copper layer on a resin film, and a step of forming a tin layer on the copper layer formed in the aforementioned step by means of electroplating tin.

[0079] (1) Process of forming copper layer

[0080] There are no particular limitations on the method for forming a copper layer on a film substrate; any known method can be used. Examples include copper vapor deposition, copper electroplating, and electroless copper plating. Copper vapor deposition is preferred. Using vapor deposition to form the copper layer results in a copper layer with high surface smoothness.

[0081] Regarding the formation of the copper layer, a copper layer can first be formed by vapor deposition, and then a copper layer can be further formed on top using electroplating. This allows for a more efficient formation of a thicker copper layer. In this case, a second copper layer formed by electroplating is stacked on the surface of the copper layer formed by vapor deposition. It should be noted that, in this invention, a commercially available resin film with a pre-formed copper layer can also be used.

[0082] When forming a copper layer by electroplating, if a single electroplating process cannot produce a sufficient copper film thickness, one method to achieve the desired copper layer thickness is to perform multiple electroplating processes using a copper plating solution of the same composition. That is, the copper layer can be passed through multiple copper plating solution baths with the same composition.

[0083] For example, after the first copper plating treatment, the sample can be rinsed with water. Then, a second copper plating treatment with the same composition as the first treatment can be performed, followed by rinsing with water. A third copper plating treatment with the same composition can then be performed, followed by rinsing with water, thereby forming a copper layer of the desired thickness. There is no particular limit to the number of copper plating treatments using the same composition; the number of treatments can be adjusted appropriately to achieve the desired thickness. It should be noted that a copper layer of the desired thickness formed in this way, since the composition of the plating bath is the same, can be considered as a single layer.

[0084] (2) The process of forming the tin layer

[0085] As a process for forming a tin layer on the copper layer, an electroplating tin method is used, and the tin layer can be formed by a general electroplating tin method. Regarding the plating solution used in the electroplating tin method, as the tin supply source, an aqueous solution such as stannous sulfate can be used, or a commercially available electroplating tin solution can be used.

[0086] Furthermore, a non-glossy tin plating solution is preferred as the tin plating bath. This allows for an increase in the average grain size of the tin crystals or an increase in the arithmetic surface roughness Ra of the tin layer surface.

[0087] It is particularly preferred to restrict the addition of organic compounds (glossing agents) such as aldehydes, amines, and carboxylic acids (esters) that can be used in tin plating solutions for gloss.

[0088] Examples of gloss agents that should be restricted include: acrylic acid, methyl acrylate, methyl methacrylate, benzyl acetone, benzaldehyde, acetophenone, etc. It is desirable to use tin plating solutions that do not contain these gloss agents.

[0089] There are no particular limitations on the conditions for tin electroplating, as long as they are set within the range that allows for the formation of a tin plating layer of the desired thickness. However, it is desirable to select conditions that result in an average tin crystal size of 5.0 μm or larger in the tin layer. Preferred conditions include a plating bath temperature of 20–50°C and a current density of 0.5–5.0 A / dm³. 2 The processing time can be 200 to 600 seconds, but is not limited to this.

[0090] Example

[0091] The present invention is illustrated below by way of examples, but the present invention is not limited to these examples in any way. Furthermore, the evaluation in the examples is performed according to the following methods.

[0092] [Evaluation of moldability]

[0093] Samples (20mm × 30mm) were cut from the conductive films prepared in each embodiment and comparative example and used as evaluation samples. Figures 2-5 The methods shown are evaluated as follows. Please explain. Figure 2 It is a schematic plan view showing the fixtures and samples used in the formability evaluation method. Figure 3 This is a schematic cross-sectional view and diagram showing the sample holder used in the formability evaluation method. Figure 4 It is a schematic cross-sectional view representing the molding process. Figure 5 This is a schematic diagram showing the molded conductive film (evaluation sample). The diagram illustrates a conductive film with a layer structure of resin film / copper layer / tin layer as an example, but it is not limited to this as long as the layer structure is within the scope of this invention. Furthermore, the dimensions in the diagram are not necessarily precise proportions for the purpose of simplicity and clarity.

[0094] (1) The above sample ( Figure 2 In (A), 1) a commercially available clamp (stainless steel bending plate grommet clamp; length 98mm × width 20mm × thickness 0.84mm) is provided with 4 holes p with a diameter of 5mm and 4 holes q with a diameter of 3.5mm (total number of holes 8); Figure 2 In (A) and (2), the center of the sample overlaps with the 3.5mm diameter hole. At this time, the 20mm wide side of the sample is positioned along the length of the clamp, and the 30mm wide side is positioned along the width of the clamp. The portion of the 30mm wide side of the sample extending from both sides of the clamp is bent towards the back of the clamp, while polyimide tape is wrapped along the width direction. Figure 2 (B) 3), to fix the sample.

[0095] At this point, sample 1 is fixed with the resin film a side on the surface and the metal layer (tin layer c) side in contact with fixture 2 (refer to...). Figure 3(A)). Furthermore, in fixture 2, when the inner edge of the hole has both a smooth and a non-smooth surface, it is fixed with the smooth surface facing upwards (the side in contact with the metal layer c of the sample). By making the smooth surface of the inner edge face upwards, it is possible to avoid the sample breaking at a location different from the observed metal crack due to stress on the inner edge of the hole when placing the copper needle subsequently, thereby avoiding the possibility of light leakage at a location different from the observed object, which could affect the evaluation.

[0096] On the sample fixing fixture obtained in this way, another identical fixture is superimposed. Figure 3 (B) , 2'), so that the size and position of the hole are consistent (refer to Figure 3 (B) The whole assembly is then fixed with polyimide tape as a sample fixing fixture for evaluation. Figure 3 (C)).

[0097] (2) The obtained evaluation sample fixture was placed in a multi-functional oven (trade name "MOV-300SB"; AS ONE) set at 230°C and left to stand for 2 minutes.

[0098] Two minutes later, inside the aforementioned multi-functional oven, the total weight, adjusted to 7.5 kg after adding counterweights, was... 3.0mm copper needles (copper pins) (mold; place counterweights in the base with the mold until the total weight is 7.5kg; Figure 4 In (A), 4) is placed in the sample clamping position. In a 3.5mm hole, let it stand for 1 minute to form (refer to...). Figure 4 (B) Next, the evaluation sample holder was removed from the multi-functional oven, and the sample was then removed from the holder to obtain... Figure 5 The sample molded part shown is used for evaluation and has a cylindrical protrusion shape.

[0099] (3) In the evaluation sample molded part with a cylindrical protrusion shape formed by a counterweight copper needle, the presence of metal cracks is observed in the area formed by the bottom surface of the copper needle (the circumference of the cylindrical protrusion) using a digital microscope (trade name "VHX-8000", manufactured by Keyence Co., Ltd.). At this time, only the area formed by the bottom surface of the copper needle is used as the evaluation object for metal cracks. Figure 4 (B) 5), without considering whether there are metal cracks in other locations.

[0100] (4) Under the condition of irradiation from the rear of the sample molded object (the side opposite to the protruding side of the protrusion forming part), observe using the above-mentioned digital microscope (trade name "VHX-8000", manufactured by Keyence Co., Ltd.) to confirm whether there is light leakage.

[0101] (5) Based on the presence or absence of metal cracks and light leakage, the formability is evaluated according to the following criteria.

[0102] Formability ○: No cracks in the metal layer, no light leakage.

[0103] Formability △: No cracks in the metal layer, but light leakage is present.

[0104] Formability △: Cracks in the metal layer "exist," light leakage "absent."

[0105] Formability ×: Cracks in the metal layer are present; light leakage is present.

[0106] [Determination of the amount and thickness of the metal layer (copper and tin layers)]

[0107] The sample was cut into 3cm × 3cm pieces and immersed in 10ml of aqua regia diluted 1 / 2 to completely dissolve the metal layer, obtaining a solution with the metal layer dissolved. Then, the amount of copper (Cu) and tin (Sn) in the solution was determined (unit: mg / L) using atomic absorption spectrometry. The obtained metal amounts (mg / L) were converted to weight per unit area (g / m²). 2 The amount of metal imparted is then determined. Additionally, the thickness of the metal layer (μm) is calculated by converting the specific gravity of each metal into its equivalent thickness.

[0108] Average grain size of tin crystals

[0109] The average grain size of tin crystals in the tin layer was determined using the automatic area measurement: crystal grain size function of a digital microscope (trade name "VHX-8000"; manufactured by Keyence Corporation), and the average cross-sectional length obtained was taken as the average crystal grain size.

[0110] [Determination of Arithmetic Surface Roughness Ra]

[0111] Arithmetic surface roughness Ra was determined according to the method conforming to "JIS B 0601:2001".

[0112] <Examples 1-4, 6>

[0113] A resin film (manufactured by Toray KP Film Co., Ltd.; hereinafter referred to as "copper vapor-deposited resin film") was prepared, in which copper was deposited on one side by conventionally known methods. The materials of the resin film in Table 1 are shown below.

[0114] [PEI]: Polyetherimide film (elastic modulus: 3.2 GPa, tensile strength: 110 MPa, glass transition temperature: 215℃, melting point: 340℃)

[0115] [PPS]: Polyphenylene sulfide film (elastic modulus: 3.5 GPa, tensile strength: 80 MPa, glass transition temperature: 90℃, melting point: 280℃)

[0116] Next, the copper-plated resin film was acid-washed with a 50 mL / L sulfuric acid solution (sulfuric acid concentration: 5% v / v), and then immersed in tin plating solution A with the following composition, using a soluble tin anode, at 40°C and a current density of 2.0 A / dm³. 2 Under the conditions shown in Table 1, electrolytic tin plating is performed to form a tin layer on the surface of the copper vapor-deposited layer of the copper vapor-deposited resin film.

[0117] Subsequently, the film was immersed in a 50 mL / L anti-discoloration treatment solution (trade name "501SN"; manufactured by Ishihara Chemical Co., Ltd.) at 40°C for 60 seconds to obtain a conductive film with a layer structure of resin film / copper layer / tin layer. Its formability was evaluated, and the results are shown in Table 1. Furthermore, Figure 6 Digital microscopic images of the conductive film obtained in Example 1, showing the presence or absence of metal cracks, are shown. According to... Figure 6 It can be seen that no metal cracks were generated in the formed part of the conductive film obtained in Example 1. It should be noted that images observing the presence or absence of light leakage are not shown because all examples are completely black due to the absence of light leakage.

[0118] The average grain size of tin crystals in the obtained conductive film was measured, and the results are shown in Table 1. Additionally, Figure 7 The image shows a digital microscope image of the crystal grain size measurement observed in the tin layer of the conductive film obtained in Example 1. According to... Figure 7 It can be seen that the average cross-sectional length is 9.17 μm, which is taken as the average crystal grain size of the tin layer in Example 1.

[0119] It should be noted that the measured metal content and crystal size in this embodiment and comparative example may have very subtle fluctuations, even under the same manufacturing and measurement conditions, resulting in slight differences in the measured values.

[0120] [Composition of Tin Plating Solution A]

[0121] Tin (main component is tin mesylate) (trade name "UTB PF-SN15", manufactured by Ishihara Chemical Co., Ltd.); 400g / L

[0122] Conductive salt (main component is methanesulfonic acid) (trade name "UTB PF-A", manufactured by Ishihara Chemical Co., Ltd.); 80g / L

[0123] Coating additive (methanesulfonic acid-based additive without brightener) (trade name "UTB PF-095SA", manufactured by Ishihara Chemical Co., Ltd.); 25 mL / L

[0124] <Example 5>

[0125] A copper layer and a tin layer are formed on the copper vapor-deposited resin film shown in Table 1 to create a conductive film.

[0126] First, the copper vapor-deposited resin film was acid-washed with an acid treatment solution in the same manner as in Example 1, and then immersed in copper plating solution a with the following composition. An insoluble anode was used, and the plating was carried out at 40°C and a current density of 2.5 A / dm³. 2 Under the specified conditions, copper plating was performed according to the processing time (seconds) shown in Table 1. Afterwards, the copper layer was immersed in a rust-preventive solution (trade name "PAL C"; manufactured by Takuji Electric Co., Ltd.) at 10 mL / L at 21°C for 10 seconds to obtain a copper layer laminate with a resin film / copper layer / copper layer layer structure.

[0127] Next, the obtained copper layer laminate was immersed in tin plating solution A under the plating conditions shown in Table 1, using the same method as in Example 1, to perform tin plating treatment, thereby obtaining a conductive film with a layer structure of resin film / copper layer / copper layer / tin layer. Its formability was evaluated, and the results are shown in Table 1. It should be noted that the copper layer thickness in Table 1 is the total thickness of the formed copper layers.

[0128] Copper plating solution a:

[0129] Copper sulfate pentahydrate; 200 g / L

[0130] Sulfuric acid (concentration; 5.5% v / v); 55 mL / L

[0131] NaCl; 85 mg / L

[0132] Soft copper film forming agent (additive name "CU-SOFT", manufactured by JCU Corporation); 25 mL / L

[0133] <Comparative Examples 1 and 3>

[0134] Using the copper vapor-deposited resin film shown in Table 2, except that the conditions are set as shown in Table 2, a tin layer is formed on the copper vapor-deposited layer of the copper vapor-deposited resin film using the same method as in Example 1, to create a conductive film with a layer structure of resin film / copper layer / tin layer. The results are shown in Table 2.

[0135] <Comparative Example 2>

[0136] Using the copper vapor-deposited resin film shown in Table 2, and using tin plating solution B (for bright tin plating) as the tin plating solution, with a soluble tin anode, at 21°C and a current density of 2.0 A / dm³. 2Under the conditions specified in Table 2, plating was performed for the processing times (seconds) listed in the table. Afterwards, the film was immersed in a 50 mL / L anti-discoloration treatment solution (501SN, manufactured by Ishihara Chemical Co., Ltd.) at 40°C for 60 seconds. Except for the tin plating treatment under the conditions shown in Table 2, a tin layer was formed on the copper vapor-deposited layer using the same method as in Example 1, creating a conductive film with a layer structure of resin film / copper layer / tin layer. Its formability was evaluated, and the results are shown in Table 2. Due to the use of a tin plating solution for bright tin plating, the crystal grain size of the tin layer was relatively small.

[0137] Tin plating solution B:

[0138] Stannous sulfate (concentration; 5% by weight (w / v)); 50 g / L

[0139] Sulfuric acid (concentration; 11% v / v); 110 mL / L

[0140] Additive for bright tin plating (trade name "ST-10", manufactured by Ishihara Chemical Co., Ltd.); 50 mL / L

[0141] (For clarification, "ST-10" is an additive containing the components required for bright tin plating. In addition to polyoxyethylene nonylphenyl ether, catechol, methanol, etc., it also contains methyl acrylate as a brightening agent.)

[0142] <Comparative Examples 4-9>

[0143] The copper vapor-deposited resin film shown in Table 2 was acid-washed with the same acid treatment solution as in Example 1, and then immersed in the copper plating solution a composed of the above-mentioned components. An insoluble anode was used, and the plating was carried out at 40°C and a current density of 2.5 A / dm³. 2 Under the specified conditions, copper plating was performed according to the processing times (seconds) shown in Table 2. Afterwards, the copper was immersed in a 10 mL / L rust-preventive solution (trade name "PAL C"; manufactured by Takuji Electric Co., Ltd.) at 21°C for 10 seconds to obtain a copper layer laminate with a resin film / copper layer / copper layer layer structure. It should be noted that the copper layer thicknesses in Table 2 are the total thicknesses of the formed copper layers.

[0144] Next, the obtained copper layer laminate was immersed in tin plating solution A under the plating conditions shown in Table 2, using the same method as in Example 1, to obtain a conductive film with a layer structure of resin film / copper layer / copper layer / tin layer. Its formability was evaluated, and the results are shown in Table 2.

[0145] Figure 8 Digital microscopic images of the conductive film obtained in Comparative Example 5, showing the presence or absence of metal cracks, are presented. According to... Figure 8 It can be seen that metal cracks were generated at the circumference of the cylindrical protrusion. Furthermore, Figure 9Digital microscopic images showing the presence or absence of light leakage in the conductive film obtained in Comparative Example 5 are presented. According to... Figure 9 It can be seen that light leakage occurred (the whitish part).

[0146] [Table 1]

[0147]

[0148] [Table 2]

[0149]

[0150] Industrial practicality

[0151] The conductive film of this invention has excellent lightweight properties, and the metal layer does not crack during molding and processing. Therefore, in addition to being used as an electromagnetic wave shielding material, it can also be used as a grounding material for noise removal, etc.

[0152] Explanation of reference numerals in the attached figures

[0153] 1. Conductive film (sample for formability evaluation)

[0154] 2. Fixtures for evaluating formability

[0155] 2'. Fixture for evaluating formability

[0156] 3. Polyimide tape

[0157] 4. Copper needle

[0158] 5. The area to observe for the presence or absence of metal cracks in the forming part (the circumference of the cylindrical protrusion).

[0159] 6. Evaluate the cylindrical protrusions of the molded sample.

[0160] a. Resin film

[0161] b. Copper layer or one of the copper layers

[0162] b'. Copper layer (Part Two)

[0163] c. Tin layer

[0164] p. Hole (diameter) 5mm)

[0165] q. Hole (diameter) 3.5mm)

Claims

1. A conductive film, characterized in that, A metal layer having copper and tin layers sequentially stacked on at least one side of the resin film, wherein the amount of copper per unit area (g / m²) is specified. 2 ) and the amount of tin imparted per unit area (g / m²) 2 The ratio of Cu to Sn is 0.15 or less, and the average grain size of the tin crystals constituting the tin layer is 5.0 μm or more.

2. The conductive film according to claim 1, characterized in that, The copper content per unit area of ​​the copper layer is 10 g / m². 2 the following.

3. The conductive film according to claim 1, characterized in that, The arithmetic mean roughness Ra of the surface of the tin layer is greater than 0.25 μm.

4. The conductive film according to claim 1, characterized in that, The thickness of the resin film is 100–200 μm.

5. A method for manufacturing a conductive film according to any one of claims 1 to 4, comprising a step of forming a copper layer on a resin film, and a step of forming a tin layer on the copper layer formed by the aforementioned step by electroplating tin.

6. The method for manufacturing a conductive film according to claim 5, characterized in that, In the electroplating tin method, a non-glossy tin plating solution is used as the plating solution.

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