METHOD FOR MANUFACTURING COMPOSITE MATERIAL TO BE PLATED AND METHOD FOR MANUFACTURING ANISOTROPIC ELECTROCONDUCTIVE SHEET

- MITSUI CHEMICALS, INC.

The present invention addresses the problem of providing a method for manufacturing a plated composite material, the method being capable of forming a plating layer having good adhesiveness to each of a plurality of resin parts each including a different resin. The method for manufacturing a plated composite material for solving the aforementioned problem includes: a step for preparing a composite material having a heat-resistant resin part and a silicone resin part; a step for treating, with an alkaline solution, a plating region of the composite material; a step for irradiating plasma on the plating region; a step for bringing the plating region in contact with a cationic catalyst-containing liquid; and a step for performing an electroless plating treatment on the plating region. The plating region includes at least a portion of the heat-resistant resin part and at least a portion of the silicone resin part.

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Description
TECHNICAL FIELD

The present invention relates to a method for producing a plated composite material and a method for producing an anisotropic conductive sheet.

BACKGROUND ART

Plating layers have been formed on insulating base materials made of a resin or the like for the purpose of imparting conductivity of electromagnetic wave or electricity, imparting electrical heating properties, and increasing the design of products. Sputter plating and the like are known as methods for forming a plating layer on the surface of an insulating base material. In this method, a metal layer is formed on the surface of an insulating base material by sputtering, followed by electrolytic plating. Therefore, an expensive sputtering device is required, and there are also problems, for example, in productivity.

On the other hand, electroless plating is also known as a method for forming a plating layer. Electroless plating can efficiently form a metal plating layer on the surface of an insulating base material. However, depending on the type of insulating base material, the adhesion between the insulating base material and the plating layer may be low. Patent Literature (hereinafter abbreviated as “PTL”) 1 proposes treating the surface of an insulating base material with an alkaline solution before forming a plating layer, thereby increasing the adhesion of the plating layer. PTL 2 proposes, after the treatment with an alkaline solution, further performing treatment with an amino acid aqueous solution or the like to increase the adhesion of a plating layer.

CITATION LIST Patent Literature PTL 1

    • Japanese Patent Application Laid-Open No. 2021-5624

PTL 2

    • Japanese Patent Application Laid-Open No. 2007-56343

SUMMARY OF INVENTION Technical Problem

The methods of PTLs 1 and 2 can increase the adhesion between a plating layer and an insulating base material containing a single resin. However, in a composite material made by laminating a plurality of resin layers containing different resins, or a composite material made by combining a plurality of parts containing different resins, the adhesion strength with the plating layer differs depending on the resin. The conventional methods have problems such that the plating layer cannot not adhere to a certain region (resin), or even when the plating layer can be formed, the plating layer may peel off when stress is applied to the composite material. In particular, when the composite material contains a silicone resin, it is difficult to increase the adhesion between the region containing the silicone resin and the plating layer.

An object of the present invention is to provide a method for producing a plated composite material, in which a plating layer can be formed with satisfactory adhesion on a plurality of resin parts respectively containing different resins, and a method for producing an anisotropic conductive sheet.

Solution to Problem

The present invention provides the following: a method for producing a plated composite material, the method including:

    • preparing a composite material that includes a heat-resistant resin part and a silicone resin part, the heat-resistant resin part containing a heat-resistant resin, the silicone resin part containing a silicone resin; treating a plating target region of the composite material with an alkaline solution; irradiating the plating target region with plasma, the plating target region having been treated with the alkaline solution; bringing a cationic catalyst-containing liquid into contact with the plating target region having been irradiated with the plasma; and performing electroless plating on the plating target region having been brought into contact with the catalyst-containing liquid,
    • in which, the plating target region contains at least a portion of the heat-resistant resin part and at least a portion of the silicone resin part.

The present invention also provides the following: a method for producing an anisotropic conductive sheet, the method including:

    • preparing an insulating sheet in which a heat-resistant resin layer containing a heat-resistant resin and a silicone resin layer containing a silicone resin are laminated in a thickness direction of the insulating sheet, the insulating sheet including a through hole extending between a first surface located on one side in the thickness direction and a second surface located on another side in the thickness direction; treating an outer wall of the through hole of the insulating sheet with an alkaline solution; irradiating the outer wall with plasma, the outer wall having been treated with the alkaline solution; bringing a cationic catalyst-containing liquid into contact with the outer wall having been irradiated with the plasma; and performing electroless plating on the outer wall having been brought into contact with the catalyst-containing liquid.

Advantageous Effects of Invention

According to a method of the present invention for producing a plated composite material, a plating layer can be formed with satisfactory adhesion on a plurality of resin parts respectively containing different resins.

BRIEF DESCRIPTION OF DRAWING

FIG. 1A is a photograph, taken with a scanning electron microscope, of the surface of an untreated silicone resin part, FIG. 1B is a photograph, taken with the scanning electron microscope, of the surface of the silicone resin part after being treated with an alkaline solution, and FIG. 1C is a photograph, taken with the scanning electron microscope, of the surface of the silicone resin part after being subjected to a plasma irradiation step;

FIG. 2A is a plan view illustrating an exemplary structure of an anisotropic conductive sheet produced by the method of the present invention for producing an anisotropic conductive sheet, and FIG. 2B is a partially enlarged cross-sectional view taken along line 1B-1B of FIG. 2A;

FIG. 3 is a graph illustrating the amount of COOH groups on the surfaces of heat-resistant resin parts before the surfaces contact with a catalyst-containing liquid in Examples and Comparative Examples; and

FIG. 4 is a graph illustrating the amount of Si—OH bonds on the surfaces of silicone resin parts.

 DESCRIPTION OF EMBODIMENTS

Hereinafter, methods of the present invention for producing a plated composite material and for producing an anisotropic conductive sheet will be described with specific embodiments as examples. However, the method of the present invention for producing a plated composite material is not limited to the method described below.

1. Method for Producing Plated Composite Material

A method of the present invention for producing a plated composite material includes the following steps: preparing a composite material that includes 1) a heat-resistant resin part containing a heat-resistant resin and 2) a silicone resin part containing a silicone resin (hereinafter also referred to as “composite material preparation step”); treating a region to be plated (herein also referred to as “plating target region”) of the composite material with an alkaline solution (hereinafter also referred to as “alkaline solution treatment step”); irradiating the plating target region, which has been treated with the alkaline solution, with plasma (hereinafter also referred to as “plasma irradiation step”); bringing a cationic catalyst-containing liquid into contact with the plating target region having been irradiated with the plasma (hereinafter referred to as “catalyst contacting step”); and performing electroless plating on the plating target region having been brought into contact with the catalyst-containing liquid (hereinafter also referred to as “electroless plating step”). The method may include at least one step in addition to these steps above within a range that does not impair the effects and objects of the present invention.

As described above, when a plating layer is formed on the surface of a composite material including a plurality of resin parts respectively containing different resins, the adhesion strength with the plating layer differs for each resin part. Therefore, there are problems such as the plating layer not adhering to a certain resin part or easily peeling off from an area where the adhesion strength with the plating layer was weak. In the method of the present invention for producing a plated composite material, after performing the alkaline solution treatment step and the plasma irradiation step in this order on the plating target region of the composite material, the catalyst contacting step and the electroless plating step are performed, in view of such problems. By performing the alkaline solution treatment step and the plasma irradiation step in this order, the adhesion between the each region containing a corresponding resin (each of heat-resistant resin part and silicone resin part in the present invention) and the plating layer is significantly increased, and a composite material to be plated having high adhesion to the plating layer in any region can be obtained.

The reason for such an advantage can be considered as follows. FIG. TA illustrates a photograph (hereinafter also referred to as “SEM photograph”), taken with a scanning electron microscope, of the surface of an untreated silicone resin part, FIG. 1B illustrates a SEM photograph of the silicone resin part after the alkaline solution treatment, and FIG. 1C illustrates a SEM photograph of the silicone resin part after being subjected to the plasma irradiation step. As illustrated in FIG. TA, there are a large number of aggregates on the surface of the untreated silicone resin part. When there are such aggregates on the surface, it is considered that it is difficult for a plating layer to adhere to the surface of the silicone resin part during the forming of when a plating layer, and thus the plating layer is more likely to peel off.

When the silicone resin part is treated with an alkaline solution, the aggregates are removed and the surface is smoothed, as illustrated in FIG. 1B. When the silicone resin part is then treated with plasma, Si—OH groups are introduced into the surface of the silicone resin part. As a result, it is considered that the plating layer is more likely to physically and chemically adhere to the silicone resin part, and the adhesion with the plating layer increases. In the heat-resistant resin part, for example, foreign substances are removed by the alkaline solution treatment step, and COOH groups are introduced into the surface of the heat-resistant resin part by the plasma irradiation step in a similar manner. Therefore, it is considered that the adhesion with the plating layer also increases in the heat-resistant resin part.

As a result of extensive studies conducted by the present inventors, it has been found that the plating layer does not adhere satisfactorily when merely the amount of Si—OH groups on the surface of the silicone resin part or the amount of COOH groups on the surface of the heat-resistant resin part increases. As will be described in detail in Examples, when, for example, only the plasma irradiation step is performed without performing the alkaline solution treatment step, the amounts of Si—OH groups and COOH groups in respective regions increase. However, when a plating layer is formed in such regions, the plating layer peels off. In other words, it is considered to be very important for the adhesion of the plating layer to introduce Si—OH groups and COOH groups after the surface of each region is satisfactorily smoothed or normalized by the alkaline solution treatment step, as described above. Each step in the method of the present invention for producing a plated composite material will be described below.

(1) Composite Material Preparation Step

In the composite material preparation step, a composite material including a heat-resistant resin part and a silicone resin part is prepared. The composite material may have any shape, which may be, for example, flat or three-dimensional shape. The shape of the composite material is appropriately selected depending on the use of the plated composite material.

In addition, each of the heat-resistant resin part and the silicone resin part may have any shape as long as the parts are disposed in such a way that a portion of the heat-resistant resin part and a portion of the silicone resin part are exposed on the surface of the composite material. The composite material may have a structure in which a heat-resistant resin part and a silicone resin part are laminated, as in an insulating sheet of an anisotropic conductive sheet described below. Alternatively, the composite material may have a structure in which a member composed of a heat-resistant resin part and a member composed of a silicone resin part are connected or bonded to each other. The composite material may include at least one region in addition to the heat-resistant resin part and the silicone resin part, for example, a region composed of a resin that is not the heat-resistant resin or silicone resin, and/or a region composed of metal or ceramic, within a range that does not impair the effects and the objects of the present invention.

The heat-resistant resin contained in the heat-resistant resin part is preferably a resin with high heat resistance, that is, a resin with a high glass transition temperature. The glass transition temperature of the heat-resistant resin is appropriately selected depending on the use of the plated composite material. When the plated composite material is used as an anisotropic conductive sheet described below, the glass transition temperature of the heat-resistant resin is preferably 150° C. or more, more preferably 150 to 500° C. The glass transition temperature of the heat-resistant resin is measured in accordance with JIS K 7095:2012.

In addition, the heat-resistant resin is preferably a resin that does not corrode easily by chemicals used in the below-described alkaline solution treatment step and electroless plating step. Examples of such a heat-resistant resin include engineering plastics, such as polyamide, polycarbonate, polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, and polyetherimide, acrylic resins, urethane resins, epoxy resins, and olefin resins. The heat-resistant resin part may contain only one of these heat-resistant resins, or may contain two or more of these heat-resistant resins. The heat-resistant resin part may further contain at least one additional component such as fillers, as necessary.

The silicone resin contained in the silicone resin part may be any resin having a siloxane structure. Examples of such a resin include polydimethylsiloxane, polyphenylmethylsiloxane, polyalkylalkenylsiloxane, and polyalkylhydrosiloxane. The silicone resin may also be the following: an addition cross-linked product of a silicone elastomer composition containing organopolysiloxane having a hydrosilyl group (SiH group), organopolysiloxane having a vinyl group, and an addition reaction catalyst; or an addition cross-linked product of a silicone rubber composition containing organopolysiloxane having a vinyl group and an addition reaction catalyst. The silicone resin may further be a cross-linked product of a silicone elastomer composition containing organopolysiloxane having a SiCH3 group and an organic peroxide curing agent.

Examples of the addition reaction catalyst include metals, metal compounds, and metal complexes each having catalytic activity for hydrosilylation reactions, and specific examples thereof include platinum, platinum compounds, and complexes thereof. Examples of the organic peroxide curing agent include benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide. The silicone resin part may further contain at least one additional component other than the silicone resin, such as a tackifier, a silane coupling agent, and a filler, as necessary.

(2) Alkaline Solution Treatment Step

In the alkaline solution treatment step, the plating target region in the composite material is treated with an alkaline solution. Herein, a plating target region in a composite material refers to a region where a plating layer is formed by the below-described electroless plating step. For example, the entire surface of the composite material may serve as a plating target region, or only a portion of the surface may serve as a plating target region. Moreover, only one location of the composite material may serve as a plating target region, or a plurality of regions may serve as a plating target region or plating target regions. It is sufficient that at least one area of the plating target region contains at least a portion of the heat-resistant resin part and at least a portion of the silicone resin part. For example, the plating target region may be a combination of a region composed only of a heat-resistant resin part and a region composed only of a silicone resin part. However, it is more preferred that one plating target region includes both the heat-resistant resin part and the silicone resin part. In a conventional method, when a plating layer is formed on a region including both a heat-resistant resin part and a silicone resin part, peeling of the plating layer is particularly likely to occur. In contrast, the method of the present invention is capable of forming a plating layer with satisfactory adhesion even on such a region.

Any method may be used for treating the plating target region with an alkaline solution. Only the plating target region may be brought into contact with the alkaline solution; however, it is preferable to immerse the composite material in the alkaline solution to bring the entire composite material into contact with the alkaline solution, from the viewpoint of, for example, production efficiency.

The type of alkaline solution is not limited as long as the solution can adjust the surface condition of the plating target region or remove foreign substances adhering to the surface of the plating target region. Examples of the alkaline solution include aqueous solutions of sodium hydroxide, potassium hydroxide, and lithium hydroxide. In particular, a sodium hydroxide aqueous solution is preferred.

In addition, the pH of the alkaline solution is preferably 12 or higher. When, for example, sodium hydroxide or potassium hydroxide is used in the alkaline solution, the concentration of the hydroxide is preferably about 1 to 100 g/L, more preferably 5 to 50 g/L. When the concentration in the alkaline solution is within the above range, the plating target region can be treated to bring its surface in a desired state without deteriorating the composite material.

The temperature of the alkaline solution at the time of contact with a composite material is preferably 20° C. to 90° C., more preferably 40° C. to 70° C. When the temperature of the alkaline solution is within the above range, the surface of the plating target region can be efficiently treated.

Further, the period during which the composite material contacts with the alkaline solution is preferably about 10 minutes to 50 minutes, more preferably about 15 minutes to 40 minutes. Within this range, the plating target region can be satisfactorily treated while deterioration of the composite material is less likely occur, thereby efficiently producing the plated composite material.

Furthermore, at the time of bringing the plating target region of the composite material into contact with the alkaline solution, ultrasonic treatment may be performed simultaneously. When ultrasonic treatment is performed simultaneously, foreign substances and the like attached to the surface of the plating target region can be efficiently removed. In addition, when the plating target region is a through hole or a recess provided in a composite material, the alkaline solution can be introduced into the plating target region. The conditions for the ultrasonic treatment are not limited, and can be set to a frequency of 20 to 60 kHz, for example.

After the treatment with an alkaline solution, the alkaline solution adhering to the composite material may be neutralized with an acid solution. Any method may be used for neutralization, and examples thereof include methods such as applying an acid solution to a desired region or immersing the entire composite material in an acid solution. Specific examples of the acid solution used for neutralization include inorganic acids, such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids, such as acetic acid, methanesulfonic acid, and sulfamic acid. In particular, sulfuric acid or hydrochloric acid is preferred from the viewpoints of, for example, handling, availability, and cost. The pH and type of acid solution are appropriately selected depending on the pH and type of alkaline solution.

The temperature of the acid solution at the time of contact with a composite material is preferably 10° C. to 70° C., more preferably 20° C. to 60° C. When the temperature of the acid solution is within the above range, the surface of the plating target region can be efficiently treated.

Further, the period during which the composite material contacts with the acid solution is preferably about 10 seconds to 10 minutes, more preferably about 30 seconds to 5 minutes. Within this range, the plating target region can be satisfactorily treated while deterioration of the composite material is less likely occur, thereby efficiently producing the plated composite material.

Ultrasonic treatment may also be performed at the time of bringing a composite material into contact with the acid solution. When ultrasonic treatment is performed simultaneously, a satisfactory amount of acid solution can be introduced into a plating target region, when the plating target region is a through hole or a recess provided in a composite material. The conditions for the ultrasonic treatment are not limited, and may be the same as those for treatment with an alkaline solution.

(3) Plasma Irradiation Step

In the plasma irradiation step, the plating target region after being subjected to the alkaline solution treatment step is irradiated with plasma. Plasma irradiation may be performed on the composite material from only one direction or from a plurality of directions. For example, a composite material in a sheet form may be irradiated with plasma from both the front and back sides of the composite material. In addition, only the plating target region may be irradiated with plasma, or the entire composite material may be irradiated with plasma.

Any method may be used for plasma irradiation, and may be any known plasma irradiation method, such as atmospheric pressure plasma irradiation or plasma irradiation in a vacuum (herein referred to as “vacuum plasma irradiation”) (low-temperature plasma irradiation).

In the atmospheric pressure plasma irradiation, discharge is performed in a gas atmosphere containing one of or a mixture of two or more of, for example, air, water vapor, argon, nitrogen, helium, carbon dioxide, carbon monoxide, alcohols such as isopropyl alcohol, and carboxylic acids such as acrylic acid.

In the vacuum plasma irradiation (low-temperature plasma irradiation), the above-described composite material is placed in an internal electrode type discharge treatment device including, for example, a drum-shaped electrode and a counter electrode consisting of a plurality of rod-shaped electrodes. The pressure in the device is then adjusted to preferably about 1 to 20 Pa, more preferably 10 Pa or less, and a high DC or AC voltage is applied between the electrodes in a treating gas atmosphere to cause discharge. As a result, the plasma of the treating gas is generated, and the composite material is treated by the plasma.

As the above-described treating gas, one of or a mixture of two or more of, for example, argon, nitrogen, helium, carbon dioxide, carbon monoxide, air, water vapor, alcohols such as isopropyl alcohol, carboxylic acids such as acrylic acid can be used.

Among the above plasma irradiations, vacuum plasma irradiation is preferred, and oxygen plasma irradiation using a gas containing oxygen as the treating gas is particularly preferred. Irradiation with oxygen plasma can efficiently introduce COOH groups into the surface of a region containing the heat-resistant resin layer and, furthermore, can efficiently introduce Si—OH groups into the surface of the silicone resin part.

The oxygen supply rate is preferably 5 to 40 ml/min, more preferably 10 to 30 ml/min.

The high frequency output during plasma irradiation is not limited, but when the treatment time is about 1 minute, for example, the high frequency output is preferably 75 to 150 W, more preferably 90 to 125 W. When the output during the plasma irradiation is 75 W or more, plasma can be satisfactorily generated and treatment can be performed efficiently. On the other hand, when the output is 150 W or less, the composite material can be treated without deteriorating.

The plasma irradiation time is preferably 0.1 to 5 minutes, more preferably 0.5 to 2 minutes. When plasma irradiation is performed for 0.5 minutes or more, COOH groups can be introduced into the surface of the region containing the heat-resistant resin layer, and Si—OH groups can be introduced into the surface of the silicone resin part. On the other hand, when the plasma irradiation is performed for 2 minutes or less, the treatment can be performed without damaging the composite material.

(4) Catalyst Contacting Step

The catalyst contacting step is a step of bringing a cationic catalyst-containing liquid into contact with the plating target region after being subjected to the plasma irradiation step.

As a method for bringing the cationic catalyst-containing liquid into contact with the plating target region, for example, immersing of the composite material in a solution containing a cationic catalyst can be used, but the method is not limited thereto. When only a certain region of the composite material is to be plated, masking may be performed by applying a resist or the like so that the catalyst does not adhere to regions other than the plating target region.

The cationic catalyst-containing liquid may be any solution containing ions (cations) of metal serving as a catalyst in the electroless plating step described below. Examples of the metal serving as a catalyst include Ag, Cu, Al, Ni, Co, Fe, and Pd. In particular, from the viewpoint of catalytic ability, Ag or Pd is preferred, and Pd is particularly preferred.

In addition, the metal is contained in the catalyst-containing liquid as a metal salt or a complex. The type of counter ion of the metal in the metal salt and the type of ligand in the complex are appropriately selected depending on the type of metal.

Examples of palladium salts include palladium acetate, palladium chloride, palladium nitrate, palladium bromide, palladium carbonate, palladium sulfate, bis(benzonitrile)dichloropalladium(II), bis(acetonitrile)dichloropalladium(II), and bis(ethylenediamine)palladium(II) chloride. Among these, palladium chloride, palladium nitrate, palladium acetate, and palladium sulfate are preferred in views of ease of handling and solubility.

Examples of the complexing agent for forming the palladium complex include basic amino acids having a cationic group (for example, an amino group or a guanidyl group), such as lysine, arginine, and ornithine, tetrakistriphenylphosphine and trisbenzylideneacetone.

A catalyst-containing liquid usually contains a solvent for dispersing or dissolving the metal salt or complex. Any solvent may be used as long as the solvent does not corrode the composite material. Examples of the solvent include water and organic solvents such as acetone, methyl acetoacetate, ethyl acetoacetate, ethylene glycol diacetate, cyclohexanone, acetylacetone, acetophenone, 2-(1-cyclohexenyl), propylene glycol diacetate, triacetin, diethylene glycol diacetate, dioxane, N-methylpyrrolidone, dimethyl carbonate, and dimethyl cellosolve.

Further, the catalyst-containing liquid may contain a pH buffer, such as boric acid or sodium borate within a range that does not impair the effects of the present invention.

The temperature of the catalyst-containing liquid when the composite material and the cationic catalyst-containing liquid are brought into contact with each other is preferably 20 to 60° C., more preferably 30 to 50° C. When the temperature of the catalyst-containing liquid is 20° C. or higher, the metal ions can efficiently react with COOH groups and Si—OH groups in the plating target region. When the temperature of the catalyst-containing liquid is 60° C. or lower, the composite material is less likely to be affected.

The contact time between the composite material and the cationic catalyst-containing liquid is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. When the contact time between the composite material and the cationic catalyst-containing liquid is 0.5 minutes or more, the metal ions can efficiently react with COOH groups and Si—OH groups in the plating target region. When the contact time is 10 minutes or less, the composite material is less likely to be affected.

After the metal ions are introduced into the surface of the composite material, the metal ions may be reduced. The reduction may be performed during the electroless plating step described below or may be performed before performing the electroless plating step by treating the surface with a reducing agent (catalyst activation liquid). For example, the composite material may be immersed in a solution containing a reducing agent.

Examples of the reducing agent include boron-based reducing agents, such as sodium borohydride, dimethylamine borane, and boric acid, formaldehyde, and hypophosphorous acid.

The temperature of the reducing agent during the treatment with the reducing agent and the contact time between the composite material and the reducing agent are appropriately selected depending on the type of reducing agent.

(5) Electroless Plating Step

In the electroless plating step, a plating target region, to which a metal serving as a catalyst is attached, is subjected to electroless plating. In the electroless plating step, an electroless plating bath containing metal ions to be precipitated as plating is brought into contact with the plating target region, thereby precipitating metal on the surface of the plating target region by a chemical reaction. Any method may be used for bringing the electroless plating bath into contact with the plating target region. For example, only the plating target region may be brought into contact with the electroless plating bath, or the entire composite material may be immersed in the electroless plating bath. When only a certain region of the composite material is to be plated, masking may be performed by applying a resist or the like so that the electroless plating bath does not adhere to regions other than the plating target region.

An electroless plating bath usually contains a salt, which is a raw material for a desired plating layer, a reducing agent, a solvent, a stabilizer, and the like. Examples of the metal for forming the plating layer include copper, tin, lead, nickel, gold, palladium, and rhodium, which can be used alone or in combination. In particular, for producing a conductive layer of an anisotropic conductive sheet described below, for example, copper or gold is preferred from the viewpoint of conductivity.

In addition, the reducing agent, solvent, and stabilizer are appropriately selected depending on the type of metal to be used. For example, for forming a plating layer made of copper, the electroless plating bath may contain, for example, CuSO4, a reducing agent such as HCOH, glyoxylic acid, or the salt thereof, a chelating agent such as EDTA or Rochelle salt, and a stabilizer such as trialkanolamine, a solvent such as water, a ketone (e.g., acetone), or an alcohol (e.g., methanol, ethanol, or isopropanol), and an organic compound such as 2,2′-dipyridyl disulfide, 6,6′-dithiodinicotinic acid, 2,2′-dithiodibenzoic acid, or bis(6-hydroxy-2-naphthyl)disulfide.

The temperature of the electroless plating bath when the composite material and the electroless plating bath are brought into contact with each other is preferably 25 to 70° C., more preferably 30 to 50° C. When the temperature of the electroless plating bath is 25° C. or higher, a plating layer can be formed efficiently. When the temperature of the electroless plating bath is 70° C. or lower, the composite material is less likely to be affected.

The contact time between the composite material and the electroless plating bath is preferably 3 to 45 minutes, more preferably 10 to 30 minutes. When the contact time between the composite material and the electroless plating bath is 3 minutes or more, a plating layer can be formed efficiently. When the contact time is 45 minutes or less, the composite material is less likely to be affected. As a result, a plated composite material is obtained in which a desired plating layer is formed in the plating target region. After contact with the electroless plating bath, annealing or the like may be performed as necessary. The annealing is preferably performed by heating at about 100° C. to 150° C., and the treatment time is preferably 5 minutes to 30 minutes.

2. Method for Producing Anisotropic Conductive Sheet

It is also possible to produce an anisotropic conductive sheet according to the method for producing a plated composite material as described above. An anisotropic conductive sheet herein is a sheet having conductivity in the thickness direction thereof and insulating properties in the surface direction thereof. The anisotropic conductive sheet can be used as a probe (contact) in electrical testing. An anisotropic conductive sheet produced in the method of the present invention includes an insulating sheet and a conductive layer (plating layer). In the insulating sheet, a heat-resistant resin layer containing a heat-resistant resin and a silicone resin layer containing a silicone resin are laminated in the thickness direction of the sheet. The insulating sheet includes at least one through hole extending between a first surface located on one side in the thickness direction and a second surface located on the other side in the thickness direction. The conductive layer is formed inside the through hole.

For the purpose of reliably performing the electrical contact between an electrode of the board of the electrical testing apparatus and a terminal of an object to be tested (herein also referred to as “test object”), an anisotropic conductive sheet is disposed between the board of the electrical testing apparatus and the test object. During electrical testing, an indentation load is applied in order to reliably perform electrical connection between the board of the electrical testing apparatus and the test object. Therefore, the anisotropic conductive sheet is required to be readily and elastically deformed in the thickness direction thereof. Therefore, studies has been conducted for using a sheet, in which a heat-resistant resin layer with a relatively high elastic modulus and a silicone resin layer with a low elastic modulus are laminated, as the insulating sheet. However, with the conventional art, it has been difficult to form a plating layer with high adhesion to both the heat-resistant resin layer and the silicone resin layer. Therefore, when a conductive layer is formed by plating as in the conventional art, the conductive layer is more likely to peel off when an indentation load was applied.

In contrast, when an anisotropic conductive sheet is produced according to the method for producing a plated composite material as described above, a plating layer (conductive layer) with satisfactory adhesion to both the heat-resistant resin layer and the silicone resin layer can be formed, and the anisotropic conductive sheet that is highly reliable can be obtained. Hereinafter, the configuration of the anisotropic conductive sheet will be described first, and then the method for producing the anisotropic conductive sheet will be described.

(1) Configuration of Anisotropic Conductive Sheet

FIGS. 2A and 2B illustrate an exemplary structure of an anisotropic conductive sheet produced by the method of the present invention for producing an anisotropic conductive sheet. However, the structure of the anisotropic conductive sheet is not limited to the structure. FIG. 2A is a plan view illustrating anisotropic conductive sheet 10, and FIG. 2B is a partially enlarged cross-sectional view of anisotropic conductive sheet 10 taken along line 1B-1B of FIG. 2A.

As illustrated in FIGS. 2A and 2B, anisotropic conductive sheet 10 includes the following: insulating sheet 11 including a plurality of through holes 12; and a plurality of conductive layers 13 disposed so as to respectively correspond to the plurality of through holes 12 (for example, two conductive layers 13 surrounded by broken lines in FIG. 2B).

This insulating sheet 11 is a sheet in which silicone resin layer 11A and two heat-resistant resin layers 11B and 11C are laminated. The silicone resin contained in silicone resin layer 11A is the same as the silicone resin contained in the silicone resin part of the plated composite material described above. In addition, the heat-resistant resins contained in heat-resistant resin layers 11B and 11C are the same as the heat-resistant resin contained in the heat-resistant resin part of the plated composite material describe above. The two heat-resistant resin layers 11B and 11C may contain the same resin or may contain different resins. In addition, insulating sheet 11 may include an adhesive layer (not illustrated) or the like between silicone resin layer 11A and heat-resistant resin layer 11B and/or between silicone resin layer 11A and heat-resistant resin layer 11C, as necessary.

Through hole 12 may have any shape, which may be of a pillar, for example. Through hole 12 may have a cylindrical shape, a prismatic shape, or another shape. The shape of the cross section of through hole 12 orthogonal to the axial direction of the through hole is, for example, circular, oval, quadrangular, or another polygon.

Through hole 12 may be a hole formed by any method, for example, a hole formed mechanically (for example, by pressing or punching), or a hole formed by laser processing.

The thickness of insulating sheet 11 is such that the board of an electrical testing apparatus and a test object can be insulated, and usually is preferably 40 to 500 μm, more preferably 100 to 300 μm.

Conductive layer 13 is a layer formed on outer wall 12c of through hole 12 by electroless plating. A unit of conductive layer 13 surrounded by a broken line functions as one conductive path (see FIG. 2B). The volume resistivity of the material for forming conductive layer 13 is not limited as long as satisfactory conduction can be obtained. The volume resistivity is preferably, for example, 1.0×10×10−4 Ω·cm or less, more preferably 1.0×10×10−6 to 1.0×10−9 Ω·cm. The volume resistivity of the material for forming conductive layer 13 can be measured by the method described in ASTM D 991.

The thickness of conductive layer 13 may be within a range such that satisfactory conduction can be obtained. In general, the thickness of conductive layer 13 is preferably 0.1 to 5 μm. When the thickness of conductive layer 13 is a predetermined value or more, satisfactory conduction is more likely to be obtained, and when the thickness is less than the predetermined value, through hole 12 is less likely to be blocked and the terminal of a test object is less likely to be damaged due to contact with conductive layer 13. The thickness of conductive layer 13 is the thickness in the direction orthogonal to the thickness direction of insulating sheet 11.

Although FIG. 2B illustrates a mode in which conductive layer 13 is formed only on outer wall 12c of through hole 12, conductive layer 13 may also be formed on the first surface and/or the second surface of insulating sheet 11.

(2) Method for Producing Anisotropic Conductive Sheet

An anisotropic conductive sheet can be produced a method that includes the following steps: preparing an insulating sheet in which a heat-resistant resin layer containing a heat-resistant resin and a silicone resin layer containing a silicone resin are laminated in the thickness direction of the sheet, and which includes at least one through hole extending between a first surface located on one side in the thickness direction and a second surface located on the other side in the thickness direction (hereinafter also referred to as “insulation sheet preparation step”); treating an outer wall of the through hole of the insulating sheet with an alkaline solution (hereinafter also referred to as “alkaline solution treatment step”); irradiating the outer wall, which has been treated with an alkaline solution, with plasma (hereinafter also referred to as “plasma irradiation step”); bringing a cationic catalyst-containing liquid into contact with the outer wall having been treated with the plasma (hereinafter also referred to as “catalyst contacting step”); and performing electroless plating on the outer wall having been brought into contact with the catalyst-containing liquid (hereinafter also referred to as “electroless plating step”). The method may include at least one step in addition to these steps above within a range that does not impair the effects and objects of the present invention.

In the insulating sheet preparation step, an insulating sheet is prepared. In the insulating sheet, the heat-resistant resin layer (containing the heat-resistant resin) and the silicone resin layer (containing the silicone resin) as described above are laminated in the thickness direction of the insulating sheet. The insulating sheet includes at least one through hole extending between a first surface located on one side in the thickness direction and a second surface located on the other side in the thickness direction. For example, the heat-resistant resin layer and the silicone resin layer may be laminated, or the through hole may be formed in the insulating sheet preparation step.

In the alkaline solution treatment step, the outer wall of the through hole of the insulating sheet is treated with an alkaline solution. The alkaline solution treatment step may be performed in the same manner as in the alkaline solution treatment step of the method for producing a plated composite material as described above.

In the plasma irradiation step, plasma treatment is performed on the outer wall of the through hole in the insulating sheet. The plasma irradiation step may be performed in the same manner as in the plasma irradiation step of the method for producing a plated composite material as described above. For example, by performing oxygen plasma treatment on both sides of the insulating sheet, COOH groups and Si—OH groups can be introduced into the outer wall of the through hole.

In the catalyst contacting step, a cationic catalyst-containing liquid is brought into contact with the outer wall of the through hole having been subjected to the plasma treatment. The catalyst contacting step may be performed in the same manner as in the catalyst contacting step of the method for producing a plated composite material as described above, but masking may be performed by applying a resist or the like so that the catalyst does not adhere, for example, to regions other than the outer wall of the through hole.

In the electroless plating step, electroless plating is performed on the outer wall having been brought into contact with the catalyst-containing liquid. The electroless plating step may be performed in the same manner as in the electroless plating step of the method for producing a plated composite material as described above, but masking may be performed by applying a resist or the like so that the plating layer does not formed, for example, to regions other than the outer wall of the through hole. Alternatively, after the plating layer is formed also on the regions (for example, on the first surface and second surface of the insulating sheet) other than the outer wall of the through hole, the plating layer on the regions where the plating is unnecessary may be removed.

In the method for producing the anisotropic conductive sheet, annealing or the like may also be performed as necessary, as in the same manner as in the method for producing a plated composite material as described above.

EXAMPLES

Hereinafter, the invention will be described with reference to Examples. The scope of the present invention is not interpreted to be limited by the Examples.

Example 1 (1) Preparation of Composite Material

Two heat-resistant resin films (EXPEEK manufactured by Kurabo Industries, Ltd.) containing polyetheretherketone (PEEK) and having a thickness of 9 μm were prepared. Subsequently, a silicone resin film (manufactured by Fusogomu Co., Ltd.) containing polydimethylsiloxane (PDMS) and having a thickness of 300 μm was prepared. The heat-resistant resin films were then placed on both sides of the silicone resin film, and these films were adhered to each other. Subsequently, through holes were generated so that each through hole connects the surface (first surface) of one of the heat-resistant resin films of the obtained laminate to the surface (second surface) of the other one of the heat-resistant resin films of the obtained laminate. The through holes were generated by using a laser. In addition, the shape of the through hole was made into a columnar shape with a diameter of 70 μm.

(2) Treatment with Alkaline Solution and Neutralization Treatment

The composite material was immersed in a 50° C. sodium hydroxide solution (concentration: 20 g/L, pH: 13.4) for 30 minutes. Ultrasonic treatment (frequency: 40 kHz) was also performed simultaneously with the immersion. The composite material was then taken out and immersed in sulfuric acid (concentrated sulfuric acid: 100 ml/L solution) for 1 minute. At this time, ultrasonic treatment (frequency: 40 kHz) was also performed.

(3) Vacuum Plasma Treatment

Subsequently, vacuum plasma treatment was performed on the composite material for 1 minute from the first surface side and for 1 minute from second surface side. The plasma treatment conditions are as follows.

(Plasma Treatment Conditions)

    • Plasma irradiation device: PDC210 manufactured by Yamato Scientific Co., Ltd.
    • Output: 100 W
    • Pressure of the atmosphere: 5 Pa
    • Oxygen supply rate: 20 ml/min
    • Oscillation frequency: 13.56 MHz
    • High frequency output: 125 W
    • Treatment time: 1 minute
      (4) Treatment with Catalyst-Containing Liquid

The composite material after being subjected to the plasma treatment was immersed for 2 minutes in a complex solution of palladium ions (Top SAPINA Catalyst, palladium concentration: 100 ppm, manufactured by OKUNO Chemical Industries Co., Ltd.) heated to 40° C., thereby adhering palladium ions to the surface of the composite material. Thereafter, the composite material was immersed in a reducing agent (Top SAPINA Accelerator, manufactured by OKUNO Chemical Industries Co., Ltd.) for 1.5 minutes to reduce the palladium ions.

(5) Electroless Plating

The composite material was immersed in a 35° C. solution containing ATS ADDCOPPER IW-A (50 mL), ATS ADDCOPPER IW-M (80 mL), ATS ADDCOPPER C (15 mL), and ATS ADDCOPPER R-N (3 mL) (all manufactured by OKUNO Chemical Industries Co., Ltd.) for 15 minutes.

(6) Annealing

The composite material after being subjected to the electroless plating was annealed at 110° C. for 20 minutes to obtain a plated composite material (anisotropic conductive sheet).

Example 2

A plated composite material was obtained in the same manner as in Example 1, except that the plasma output during plasma treatment was changed to 150 W.

Example 3

A plated composite material was obtained in the same manner as in Example 1, except that the type of heat-resistant resin film was changed to polyimide (PI) (Kapton 30EN, manufactured by DuPont-Toray Co., Ltd.) with a thickness of 7.5 μm.

Comparative Example 1

A plated composite material was obtained in the same manner as in Example 1, except that the treatment with an alkaline solution, the neutralization treatment, and the vacuum plasma treatment were not performed.

Comparative Example 2

A plated composite material was obtained in the same manner as in Example 1, except that the neutralization treatment and the vacuum plasma treatment were not performed.

Comparative Example 3

A plated composite material was obtained in the same manner as in Example 1, except that the vacuum plasma treatment was not performed.

Comparative Example 4

A plated composite material was obtained in the same manner as in Example 1, except that in place of the plasma treatment, corona treatment was performed under the following conditions.

(Corona Treatment Conditions)

    • Corona treatment device: TEC-4AX manufactured by KASUGA DENKI, INC.
    • Output: 90 W 0.4 m/min
    • Discharge gap: 1 mm
    • Atmosphere: Atmospheric pressure
    • Working temperature: 25° C.

Comparative Example 5

A plated composite material was obtained in the same manner as in Example 1, except that the treatment with an alkaline solution and the neutralization treatment were not performed.

Comparative Example 6

A plated composite material was obtained in the same manner as in Example 1, except that after preparing the composite material, the vacuum plasma treatment was performed, and then the treatment with an alkaline solution and the neutralization treatment were performed.

(Evaluation)

A cross-cut tape peeling test of the plating layer was performed on the plated composite materials obtained in Examples and Comparative Examples in accordance with the cross-cut test (JIS Z 1522). The results were evaluated based on the following criteria.

    • o: No peeling
    • Δ: Peeling less than 5%
    • x: Peeling over 5%

TABLE 1 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Heat-resistant PEEK PEEK PI PEEK PEEK PEEK PEEK PEEK PEEK resin layer Silicone resin PDMS PDMS PDMS PDMS PDMS PDMS PDMS PDMS PDMS layer Alkaline NaOH NaOH NaOH — NaOH NaOH NaOH — NaOH solution treatment Neutralization H2SO4 H2SO4 H2SO4 — — H2SO4 H2SO4 — H2SO4 treatment Vacuum Output Output Output — — — *1 — Output *2 Output plasma 100 W 150 W 100 W 100 W 100 W treatment Catalyst- Pd2+ Pd2+ Pd2+ Pd2+ Pd2+ Pd2+ Pd2+ Pd2+ Pd2+ containing complex complex complex complex complex complex complex complex complex liquid Electroless Cu Cu Cu Cu Cu Cu Cu Cu Cu plating Annealing 110° C. 20 minutes Evaluation ◯ Δ ◯ X: X: X: X: X: X: Not Not adhered PEEK is not Not adhered Peeled Peeled precipitated adhered during during PDMS is not plating plating precipitated *1 Corona treatment, *2 Corona treatment before alkaline solution treatment

As Table 1 shows, performing treatment with an alkaline solution, plasma irradiation, treatment with a catalyst-containing liquid, and electroless plating on a composite material could have formed a plating layer with satisfactory adhesion to both the heat-resistant resin layer and the silicone resin layer (Examples 1 to 3). On the other hand, it was confirmed that the plating did not precipitate, that peeling occurred during plating, or that a plating layer with satisfactory adhesion could not be obtained, for example, in the following cases: when the plasma irradiation was not performed (Comparative Examples 1 to 4), when the treatment with an alkaline solution was not performed (Comparative Examples 1 and 5), and when the order of the plasma irradiation and the treatment with an alkaline solution was reversed (Comparative example 6).

In addition, for each of Examples and Comparative Examples, FIG. 3 shows the amount of COOH groups on the surface of the heat-resistant resin part before the surface contacts with the catalyst-containing liquid, and FIG. 4 shows the amount of Si—OH groups on the surface of the silicone resin part before the surface contacts with the catalyst-containing liquid. The amount of COOH groups and the amount of Si—OH groups are analyzed by X-ray photoelectron spectroscopy, and the atomic ratio is calculated from the bond energies of COOH from the peak value around 289 eV of C1s and Si—OH from the peak value around 104 eV of Si2p. As FIGS. 3 and 4 show, performing the treatment with an alkaline solution and the plasma irradiation in this order could have increased both the amount of COOH groups and the amount of Si—OH groups (Example 1). When only the plasma irradiation was performed, as is clear from the results of Comparative Example 5, the amount of COOH groups and the amount of Si—OH groups increased, but the adhesion strength of the plating layer did not increase. In other words, it is considered that not only plasma treatment but also alkaline solution treatment is significantly important for the adhesion strength of a plating layer in the electroless plating.

This application is entitled to and claims the benefit of Japanese Patent Application No. 2021-161758 filed on Sep. 30, 2021, the disclosure of which including the specification and drawings is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

According to the method of the present invention for producing a plated composite material, the plated composite material can be produced with high adhesion between the composite material and the plating layer. Therefore, the present invention is particularly advantageous for producing anisotropic conductive sheets and various products.

REFERENCE SIGNS LIST

    • 10 Anisotropic conductive sheet
    • 11 Insulating sheet
    • 11A Silicone resin layer
    • 11B, 11C Heat-resistant resin layer
    • 12 Through hole
    • 12c Outer wall
    • 13 Conductive layer

Claims

1. A method for producing a plated composite material, the method comprising:

preparing a composite material that includes a heat-resistant resin part and a silicone resin part, the heat-resistant resin part containing a heat-resistant resin, the silicone resin part containing a silicone resin;
treating a plating target region of the composite material with an alkaline solution;
irradiating the plating target region with plasma, the plating target region having been treated with the alkaline solution;
bringing a cationic catalyst-containing liquid into contact with the plating target region having been irradiated with the plasma; and
performing electroless plating on the plating target region having been brought into contact with the catalyst-containing liquid,
wherein
the plating target region contains at least a portion of the heat-resistant resin part and at least a portion of the silicone resin part.

2. The method for producing a plated composite material according to claim 1, wherein

the plasma is oxygen plasma.

3. The method for producing a plated composite material according to claim 1, wherein

high frequency output of the plasma is 75 W to 150 W.

4. The method for producing a plated composite material according to claim 1, wherein:

in the composite material, the heat-resistant resin part and the silicone resin part are laminated in a thickness direction of the composite material;
the composite material further includes a through hole extending between a first surface located on one side in the thickness direction and a second surface located on another side in the thickness direction; and
the plating target region is an outer wall of the through hole.

5. A method for producing an anisotropic conductive sheet, the method comprising:

preparing an insulating sheet in which a heat-resistant resin layer containing a heat-resistant resin and a silicone resin layer containing a silicone resin are laminated in a thickness direction of the insulating sheet, the insulating sheet including a through hole extending between a first surface located on one side in the thickness direction and a second surface located on another side in the thickness direction;
treating an outer wall of the through hole of the insulating sheet with an alkaline solution;
irradiating the outer wall with plasma, the outer wall having been treated with the alkaline solution;
bringing a cationic catalyst-containing liquid into contact with the outer wall having been irradiated with the plasma; and
performing electroless plating on the outer wall having been brought into contact with the catalyst-containing liquid.
Patent History
Publication number: 20240360562
Type: Application
Filed: Jun 30, 2022
Publication Date: Oct 31, 2024
Applicant: MITSUI CHEMICALS, INC. (Chuo-ku, Tokyo)
Inventors: Masao HORI (Chiba-shi, Chiba), Katsunori NISHIURA (Chiba-shi, Chiba), Yuichi ITOU (Ichihara-shi, Chiba), Daisuke YAMADA (Hidaka-shi, Saitama)
Application Number: 18/687,930
Classifications
International Classification: C23C 18/20 (20060101); C23C 18/16 (20060101); C23C 18/31 (20060101);