CN116209787A - Conductive film with excellent solder wettability - Google Patents

Abstract

The purpose of the present invention is to manufacture a conductive film with low cost, which suppresses the reduction of solder wettability caused by long-term storage or the like, through a simple process. The surface of a copper layer and/or a copper alloy layer formed on a film substrate is provided with a barrier layer containing an organic compound bonded to copper, and a conductive film formed by stacking a tin plating layer on the barrier layer. The organic compound is preferably selected from heterocyclic compounds, thiourea compounds and thiol compounds.

Description

Conductive film with excellent solder wettability

technical field

The present invention relates to a conductive film. Specifically, it relates to a conductive film having excellent solder wettability and little decrease in solder wettability over time.

Background technique

Tin-plated copper and/or copper alloy materials are used in various electronic components such as terminals and connectors for electrical connection. The purpose of performing tin plating is to reduce the contact resistance value. In addition, in order to improve the corrosion resistance of the surface of the copper and/or copper alloy material, it is also possible to impart good solder wettability.

Conventionally, in the case of long-term storage after tin plating, it is known that the solder wettability decreases. When the storage condition is high temperature, the problem of lowering of solder wettability becomes more remarkable. The reason for this is considered to be that copper atoms and other metal atoms diffuse from the copper and/or copper alloy material at the grain boundary inside the tin-plated layer to reach the surface of the tin-plated layer.

In order to solve this problem, it has been proposed to form a diffusion barrier layer composed of nickel plating between the copper base material (copper-based solder) and tin plating (Patent Document 1), or to provide an intermediate layer containing an intermetallic compound of nickel and tin ( Patent Document 2). The diffusion coefficient of nickel to tin plating is much lower than that of copper. Furthermore, it has been proposed to sequentially form a surface plating layer composed of a nickel layer and a copper-tin alloy layer on the surface of a base material composed of copper and/or a copper alloy, and to have a conductive material for a connecting member having a tin layer on the surface plating layer (patent document 3).

prior art literature

patent documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. H10-302864

Patent Document 2: Japanese Patent Application Laid-Open No. 04-329891

Patent Document 3: Japanese Patent Laid-Open No. 2004-068026

Contents of the invention

The problem to be solved by the invention

As proposed in the above-mentioned Patent Documents 1-3, the method of providing a metal layer such as nickel between the copper and/or copper alloy material and the tin-plated layer can achieve a certain effect in suppressing the decrease in solder wettability during long-term storage. Effect. However, since it is necessary to sequentially form a plurality of metal layers, the process becomes complicated and the cost becomes high.

In addition, in recent years, in electronic devices that have become increasingly smaller and lighter, flexible circuit boards in which circuits are formed on a flexible film and electronic components are mounted are becoming mainstream. In addition, in electronic devices that are worn on the body and used called so-called wearable devices, flexible circuit boards bend at a relatively high frequency. In the contact portion of the flexible circuit board, etc., the multilayer structure of the metal not only hinders its flexibility, but also has the problem of easy occurrence of peeling between the metal layers due to repeated bending.

means to solve the problem

In order to solve the above-mentioned problems, the present inventors studied a new method for suppressing the diffusion of copper atoms from the copper layer and/or copper alloy layer formed on the film substrate to the tin-plated layer laminated on the surface. As a result, it has been found that the diffusion of copper atoms into the tin-plated layer can be suppressed by forming a barrier layer in which copper is bonded to a specific organic compound on the surface of the copper layer and/or copper alloy layer, and laminating a tin-plated layer on the barrier layer. The present invention has thus been accomplished.

That is, the present invention is a conductive film in which a barrier layer containing an organic compound bonded to copper is provided on the surface of a copper layer and/or a copper alloy layer formed on a film substrate, and the barrier layer is laminated on the barrier layer. With tin plating. Accordingly, the diffusion of copper atoms from the copper layer and/or copper alloy layer to the tin-plated layer can be effectively suppressed, so that a conductive film having a small temporal change in solder wettability can be obtained.

The organic compound is preferably a mixture of one or more selected from heterocyclic compounds, thiourea compounds, and thiol compounds. The heterocyclic compound is preferably selected from triazole compounds, pyrrole compounds, pyrazole compounds, thiazole compounds, and imidazole compounds.

The arithmetic average roughness Ra of the surface of the tin-plated layer is preferably 0.02-0.3 μm, more preferably 0.08-0.2 μm. Thereby, it is possible to further suppress the decrease in solder wettability over time.

Invention effect

According to the present invention, it is possible to manufacture a conductive film that suppresses a decrease in solder wettability over time by a simple process at low cost.

Detailed ways

The conductive film of the present invention is composed of a flexible film and a copper layer and/or copper alloy layer formed on the film. As the flexible film, a film made of synthetic resin is preferably used. The synthetic resin is not particularly limited, and examples thereof include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, and polyimide. wait. Among them, polyimide films are preferred. The thickness of the film is preferably 4 to 100 μm, more preferably 10 to 50 μm.

As a method of forming a copper layer and/or a copper alloy layer on the film, known methods can be employed without limitation. For example, a method of affixing copper foil and/or copper alloy foil with an adhesive, dry film formation methods such as vacuum deposition and sputtering, and wet film formation methods such as electroless plating and electroplating. In addition, these methods may be combined to form a copper layer and/or a copper alloy layer. A preferred method is a dry film-forming method. Nickel, zinc, tin, etc. are mentioned as another metal which can be used for a copper alloy.

The thickness of the copper layer and/or copper alloy layer is not particularly limited, but is preferably 0.5 to 5 μm. When the thickness of the copper layer and/or copper alloy layer is within this range, a conductive film having both excellent conductivity and flexibility can be obtained. A more preferable thickness is in the range of 1 to 3 μm. The copper layer and/or copper alloy layer may be only one layer, or two or more layers having different properties may be laminated.

In the conductive film of the present invention, a barrier layer containing an organic compound bonded to copper is formed on the surface of the copper layer and/or copper alloy layer. The organic compound is preferably an organic compound selected from heterocyclic compounds, thiourea compounds, and thiol compounds. In these organic compounds, nitrogen atoms or sulfur atoms contained in their molecular structures are chemically bonded to copper atoms, and a thin film at the molecular level can be formed on the surface of the copper layer and/or copper alloy layer.

Examples of heterocyclic compounds include those selected from triazole compounds, pyrrole compounds, pyrazole compounds, thiazole compounds, imidazole compounds, thiadiazole compounds, oxazole compounds, and thiazoline compounds. compound.

Among them, benzotriazole, tolyltriazole, mercaptobenzothiazole, mercaptothiadiazole, benzimidazole, benzimidazolethiol, benzoxazolethiol, methylbenzothiazole, and mercaptothiazoline are particularly preferred. wait.

Examples of thiourea compounds include thiourea, diethylthiourea, dibutylthiourea, 1,3-diethyl-2-thiourea, trimethylthiourea, 1,3-dimethyl Thiourea, 1-acetylthiourea, N-allylthiourea, ethylenethiourea, N-methylthiourea, etc.

Examples of the thiol compound include methaneedithiol, 1,2-ethaneedithiol, 1,1-propaneedithiol, triazinethiol, and the like.

The organic compound is preferably a heterocyclic compound, more preferably a triazole compound, particularly preferably a benzotriazole or a derivative thereof.

The tin plating layer is formed to be laminated on the barrier layer. The thickness of the tin plating layer is preferably 0.5 to 3.0 μm. When the thickness of the tin plating layer is within this range, excellent solder wettability can be maintained for a long period of time. The tin-plated layer may be formed by any of electroless plating and electroplating, but is preferably formed by electroplating because of film thickness control and ease of continuous processing.

The arithmetic mean roughness Ra of the surface of the tin-plated layer is preferably 0.02-0.3 μm, more preferably 0.08-0.2 μm. When the arithmetic mean roughness Ra of the tin-plated layer surface is small, there exists a tendency for solder wettability to fall easily. If the arithmetic mean roughness Ra of the surface of the tin plating layer is within the above range, a conductive film in which the temporal decrease in solder wettability is further suppressed can be obtained. The arithmetic average roughness Ra of the surface of the tin-plated layer refers to the surface roughness of the outermost layer of the conductive film after lamination, and can be measured according to the method of JIS B 0601:2001 after lamination.

The aforementioned relationship between the arithmetic mean roughness Ra of the surface of the tin-plated layer and the decrease in solder wettability over time is considered to be attributable to organic substances contained in the tin-plated layer. In particular, among the brighteners added to the plating solution described later, some brighteners remarkably lower the solder wettability due to oxidation. Therefore, it is preferable to perform a tin plating treatment without using such a brightener excessively, and as a result, it is preferable to set the arithmetic mean roughness Ra of the surface of the tin plating layer to be in the range of 0.02 to 0.3 μm. The arithmetic mean roughness Ra of the surface of the tin-plated layer varies depending on the type of brightener, current density, plating thickness, and the like. In addition, it may also be affected by the surface roughness of the copper layer and/or copper alloy layer of the substrate.

The manufacturing method of the conductive film of the present invention includes: a first step of making the treatment liquid in which the organic compound is dissolved contact the copper layer and/or copper alloy layer formed on the film base material to form the organic film containing the organic compound bonded to copper. a compound barrier layer; and a second step of laminating a tin plating layer on the barrier layer by electroplating.

The method for forming the copper layer on the film substrate is not particularly limited, and known methods can be employed. Specifically, a copper vapor deposition method, a copper electroplating method, an electroless copper plating method, etc. are mentioned. Among them, the copper vapor deposition method is preferably used. When the vapor deposition method is used for forming the copper layer, a copper layer with high surface smoothness can be formed.

Regarding formation of the copper layer, a copper layer may be formed by a vapor deposition method first, and then a copper layer may be further formed thereon by a copper electroplating method. In this way, a thick copper layer thickness can be formed more efficiently. In this case, the 2nd copper layer by the copper electroplating method is laminated|stacked on the surface of the copper layer formed by the vapor deposition method.

In the step of forming a barrier layer as the first step, the film substrate on which the copper layer and/or copper alloy layer is formed is brought into contact with a treatment solution in which the organic compound is dissolved. Here, examples of solvents that can be used for the treatment liquid include water, alcohols, and the like. A surfactant or the like for dispersing the organic compound may also be added.

The concentration of the organic compound in the treatment liquid is preferably 0.1 to 10 g/L. In addition, the temperature of the treatment liquid is preferably 20 to 40° C., and the contact time is 5 to 60 seconds. Accordingly, the barrier layer can be formed on the surface of the copper layer and/or copper alloy layer with a thickness within the above range.

The second step is a step of forming a tin-plated layer by a general electrolytic tin plating method. As the plating solution used in the tin electroplating method, for example, an aqueous solution such as stannous sulfate can be used as a tin supply source, and a commercially available tin plating solution can also be used. The content of organic substances in the tin-plated layer formed in the second step is affected by the composition of the plating solution. Therefore, in order to control the content of organic substances in the tin-plated layer within a predetermined range, it is necessary to properly manage the compounding amount of organic substances in the plating solution.

Examples of organic substances added to the plating solution include various surfactants, brighteners, antioxidants, and the like. It is important to appropriately design the compounding amount of these organic substances in the plating solution, and appropriately control the content of the organic substances in the tin-plated layer formed in the second step.

Among the organic substances, especially eutectoid organic substances derived from brighteners represented by aldehyde compounds and amine compounds tend to form an oxide film on the surface of the tin plating layer, which significantly reduces solder wettability, so it is preferable to limit its added. However, only carboxylic acids and carboxylic acid esters such as acrylic acid, methyl acrylate, and methyl methacrylate can be added in the range of 0.01 to 1 g/L for the purpose of adjusting the appearance quality.

The conditions of the tin electroplating method in the second step are not particularly limited, and may be set within a range in which a tin plating layer of a desired thickness can be formed. If general conditions are enumerated, the temperature of the plating bath can be set at 20-40° C., the current density can be set at 0.5-5.0 A/dm ² , and the treatment time can be set at 20-200 seconds.

The first step and the second step may be implemented continuously. In addition, before the first step, a step of forming the copper layer and/or copper alloy layer on the film base material may be provided, and these steps may be performed continuously. As an example of the step of forming the copper layer and/or copper alloy layer on the film substrate, the following step can be cited: For the film substrate on which a thin copper film has been formed in advance by vacuum evaporation, , form a copper layer to a desired thickness by electroless copper plating or electroplating copper. In addition, between each of these steps, a water washing step and a drying step may be appropriately performed.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited by these examples. In addition, the evaluation in an Example was performed by the following method.

[Solder wettability evaluation]

Solder paste (manufactured by Senju Metal Industry Co., Ltd., trade name "ECO SOLDER PASTE L20-BLT5-T7F") was printed and applied to the surface of the sample with a radius of 6 mm and a thickness of 70 μm, and a constant temperature dryer (manufactured by ADVANTEC Toyo Co., Ltd. , trade name "DRA630DA") was heat-treated at 250° C. for 3 minutes, and the major axis (N=3) of the wetted and spread “solder” was measured, and the average value was calculated.

[Evaluation of changes in solder wettability over time]

The above-mentioned solder wettability evaluation was performed on samples before and after treatment in an atmosphere at 155°C for 5 hours (assuming storage at 80°C for one month), and the ratio of the major diameter of the solder after the treatment to the length of the solder before the treatment was calculated. The diameter ratio R (%) was evaluated. 100% means that there is no decrease in solder wettability over time, and a higher numerical value (%) means less decrease in solder wettability over time.

[Measurement of arithmetic mean roughness Ra]

The arithmetic mean roughness Ra is measured by a method in accordance with "JIS B 0601:2001".

<Example 1>

A copper vapor-deposited polyimide film manufactured by Toray KP Film Co., Ltd. (polyimide film thickness 25 μm and copper layer thickness 1.5 μm) was immersed in 1, 2, 3 - 1 g/L aqueous solution of benzotriazole for 60 seconds to form a barrier layer (first process). Then, tin electroplating was performed using the following tin electroplating solution A to form a tin plating layer on the barrier layer (second step). The temperature of the electroplating tin solution is 40°C, and the treatment is performed for 140 seconds at a current density of 1.5A/dm ² . Then, it was washed with water, and a discoloration preventing treatment was performed using a known discoloration preventing agent.

[Electrotin plating solution A]

・Solution containing tin alkyl sulfonate (trade name "UTB PF-SN15", manufactured by Ishihara Chemical Co., Ltd.): 400 g/L

・Alkylsulfonic acid-based pH adjuster (trade name "UTB PF-A", manufactured by Ishihara Chemical Co., Ltd.): 80 g/L

・Additive for alkylsulfonic acid-based plating (trade name "UTB PF-095SA", manufactured by Ishihara Chemical Co., Ltd., does not contain brightener): 25mL/L

Then, an annealing treatment was performed at 150° C. for 1 hour using a constant temperature dryer (manufactured by Advantec Toyo Co., Ltd., trade name “DRA630DA”) to obtain a conductive film. The thickness of the tin plating layer in the obtained conductive film was 1.7 μm, and the arithmetic average roughness Ra of the surface was 0.14 μm. When the change in solder wettability over time was evaluated, the solder wettability before treatment was 11.0 mm, the solder wettability after treatment was 10.7 mm, and the ratio R was 97.3%, which was good.

<Example 2>

Instead of copper vapor-deposited polyimide film (polyimide film thickness 25 μm, and copper layer thickness 1.5 μm), use copper vapor-deposited polyimide film (polyimide film thickness 25 μm, and copper layer thickness thickness of 0.3 μm), and performing copper electroplating using the following copper electroplating solution on it, and further laminating a polyimide film of a copper layer of 1.2 μm, a conductive film was obtained in the same manner as in Example 1. The temperature of the copper electroplating solution was 40° C., and the copper electroplating treatment was performed for 109 seconds at a current density of 3.0 A/dm ² .

[Copper plating solution]

Copper sulfate pentahydrate: 200g/L

Sulfuric acid: 55mL/L

Sodium chloride: 85mg/L

Additive for dull copper plating (trade name "CU-SOFT", manufactured by JCU Co., Ltd.): 20mL/L

The thickness of the tin plating layer in the obtained conductive film was 1.8 μm, and the arithmetic average roughness Ra of the surface was 0.16 μm. When the change in solder wettability over time was evaluated, the solder wettability before treatment was 11.5 mm, the solder wettability after treatment was 11.3 mm, and the ratio R was 98.3%, which was good.

<Example 3>

A conductive film was obtained in the same manner as in Example 1, except that the following tin-plating solution B was used instead of the tin-plating solution A at a liquid temperature of 21°C.

[Electrotin plating solution B]

Stannous sulfate: 50g/L

Sulfuric acid: 110mL/L

Methyl acrylate: 0.6g/L

Other additives: appropriate amount (including antioxidants, surfactants)

The thickness of the tin plating layer in the obtained conductive film was 2.0 μm, and the arithmetic average roughness Ra of the surface was 0.03 μm. When the change in solder wettability over time was evaluated, the solder wettability before treatment was 10.3 mm, the solder wettability after treatment was 8.3 mm, and the ratio R was 80.6%, which was good.

＜Comparative example 1＞

A conductive film was obtained in the same manner as in Example 1, except that the first step (barrier layer formation) was not implemented. The thickness of the tin plating layer in the obtained conductive film was 1.7 μm, and the arithmetic mean roughness Ra of the surface was 0.10 μm. When the change in solder wettability over time was evaluated, the solder wettability before the treatment was 11.6 mm, and the solder wettability after the treatment decreased to 7.7 mm. The ratio R was 66.4%, which was bad.

＜Comparative example 2＞

Except not implementing the 1st process (barrier layer formation), it carried out similarly to Example 2, and obtained the electroconductive film. The thickness of the tin plating layer in the obtained conductive film was 1.7 μm, and the arithmetic mean roughness Ra of the surface was 0.16 μm. When the change in solder wettability over time was evaluated, the solder wettability before the treatment was 12.0 mm, and the solder wettability after the treatment decreased to 9.0 mm. The ratio R was 75.0%, which was unfavorable.

Industrial Utilization Possibility

The conductive film of the present invention suppresses the decrease in solder wettability over time, and can be produced in a simpler process than conventional techniques. Therefore, it can be used in wearable devices and parts of various electronic devices that require electrical connections. In addition, it may be configured as a gasket material used for grounding the case of an electronic device by being wound around an elastic material or the like.

Claims (4)

1. And a conductive film having a barrier layer containing an organic compound bonded to copper on the surface of the copper layer and/or copper alloy layer formed on the film substrate, wherein a tin plating layer is laminated on the barrier layer.

2. The conductive film according to claim 1, wherein the organic compound is a mixture of 1 or more selected from the group consisting of heterocyclic compounds, thiourea compounds, thiol compounds.

3. The conductive film according to claim 2, wherein the heterocyclic compound is selected from the group consisting of triazole-based compounds, pyrrole-based compounds, pyrazole-based compounds, thiazole-based compounds, and imidazole-based compounds.

4. The conductive film according to claim 1, wherein the tin-plated layer surface has an arithmetic average roughness Ra of 0.02 to 0.3 μm.