JP5582498B2 - Electrical conductor and method for forming the same - Google Patents

Description

  The present invention relates to an electric conductor used in an electronic device and an electric conductor used for bonding while conducting the electric component and a method for forming the electric conductor.

  With the development of the electronics industry, various electronic devices such as personal computers, personal digital assistants, and televisions are produced, and these electronic devices have built-in electronic circuits.

  The electronic circuit is formed by adhering electronic components such as electronic elements with an electric conductor, and is an electronic circuit board such as a printed wiring board or a module board.

  As the electrical conductor, an electrical component or an electronic component can be firmly bonded, and Pb—Sn solder is widely used because it has excellent conductivity. However, when an electronic device containing an electronic circuit board or the like is left outdoors or disposed of, there is a problem in that lead is eluted from the soldering material of the electronic component due to acid rain and contaminates groundwater. Yes.

  For this reason, lead-free solders such as SnAgCu-based, SnZnBi-based, and SnCn-based which do not contain lead are currently being developed, and switching from lead-containing solder to lead-free solder is progressing. Although lead-free solder can prevent environmental pollution due to lead, it has a higher melting point than lead-containing soldering, and thus has problems such as element destruction and deterioration. Furthermore, as an electrical conductor, in addition to solder, a conductive adhesive in which a resin to be fixed and conductive metal particles are mixed is used (see Patent Document 1).

  In addition, transparent electrodes are used for solar cells and the like. As a transparent electrode for such a transparent electrode, for example, in Patent Document 2, a coating film containing a metal nanowire, a granular metal compound, and a reducing agent is heated, and at least a part of the metal nanowire is passed through metal fine particles generated from the metal compound. A transparent electrode is disclosed in which an electrical conductor formed by bonding is formed.

JP 2009-7453 A JP 2009-129882 A

  Although the conductive adhesive proposed in Patent Document 1 described above generally has a bonding temperature lower than that of soldering, it has an advantage that it is possible to suppress the influence of heat on an electrical component or electronic component. There are also problems such as weak bonding force and low conductivity. In addition, in the method for producing a transparent electrode proposed in Patent Document 2, it is difficult to reliably place the granular metal compound between the metal nanowires, and a solid electric conductor is reliably formed in the coating film. It is difficult to do. Furthermore, the reducing agent may remain in the coating film and affect the characteristics of the obtained transparent electrode.

  Accordingly, an object of the present invention is to provide an electric conductor that has less heat influence on an electric component or electronic component with low heat resistance, has excellent conductivity, and has a firm bonding force, and a method for forming the electric conductor. .

The electrical conductor according to claim 1, which has been made to achieve the above object, is an electrical conductor formed by joining metal nanowires, and the metal nanowires are The metal salt in the organic layer made of an organic compound having a carboxyl group covering at least a part of the surface thereof or the metal complex of the organic compound and the metal salt is reduced by the heat treatment for eliminating the organic layer. The part is metal-bonded by molten metal.

  The electrical conductor according to claim 2 is the electrical conductor according to claim 1, wherein the metal salt is a metal salt selected from chloroauric acid, silver nitrate, copper chloride, and chloroplatinic acid. And

  The electrical conductor according to claim 3 is the electrical conductor according to claim 1, wherein the organic compound having a carboxyl group has at least 5 carbon atoms having a polymer carboxylic acid, a hydrophilic group or a hydrophobic group. It is characterized by being a low molecular weight carboxylic acid.

The method for forming an electric conductor according to claim 4, wherein the metal nanowire is mixed with a solution in which a carboxylic acid compound having an organic layer forming ability to form an organic layer on the surface of the metal nanowire and a metal salt are dissolved. after blended by dispersing the metal complex and the metal salt or the metal salt and the carboxylic acid compound in an organic layer comprising an organic compound having a carboxyl group that covers at least a portion of the metal nanowires on the surface, the solution heat treatment is performed to separate the metal nanowires from, with a loss of the organic layer, in metallic thawed said metal salt or reduced and a portion of said metal complex, to metal bonding the metal nanowires to each other It is characterized by.

  The method for forming an electric conductor according to claim 5 is the method according to claim 4, wherein the metal salt is a metal salt selected from chloroauric acid, silver nitrate, copper chloride, and chloroplatinic acid. It is characterized by that.

  The method for forming an electric conductor according to claim 6 is the method according to claim 4, wherein a carboxylic acid compound having an organic layer forming ability is a polymer carboxylic acid or a hydrophilic group or a hydrophobic group. The low-molecular carboxylic acid having at least 5 carbon atoms is used.

A method for forming an electric conductor according to a seventh aspect is the method according to the fourth aspect, wherein the organic layer is a polymer film .

  The method for forming an electric conductor according to claim 8 is the method according to claim 4, wherein the metal nanowire includes a metal salt, a form adjusting agent for adjusting the form of the obtained metal nanowire, and a chloride. It is characterized by using metal nanowires obtained by dissolving in a solvent and then heating while blowing oxygen gas.

  The electrical conductor according to the present invention reduces metal nanowires to each other between a metal salt in an organic layer composed of an organic compound having a carboxyl group covering at least a part of the surface thereof, or a metal complex of the organic compound and the metal salt. The metal is joined by the metal formed. For this reason, the metal nanowires are firmly connected to each other while being electrically connected to each other, and a strong electrical conductor composed of one continuous body can be easily formed.

  Furthermore, such an electrical conductor comprises adding a metal nanowire and a solution in which a carboxylic acid compound having an organic layer forming ability to form an organic layer on the surface of the metal nanowire and a metal salt are dissolved, and at least the surface of the metal nanowire. A metal salt or a metal complex of a carboxylic acid compound and a metal salt is dispersed and blended in an organic layer composed of an organic compound having a carboxyl group covering a part, and then the metal salt or metal complex is reduced to form a metal. The metal nanowires are formed by metal bonding. For this reason, a metal salt and a carboxylic acid compound having an organic layer forming ability to form an organic layer on the surface of the metal nanowire are dissolved in a solvent, and the solution containing the metal nanowire is added to the metal parts of the electrical component or the electronic component. After dripping at the joint location, the metal locations can be electrically connected by reduction of the metal salt or metal complex. Alternatively, in a solvent, a metal salt and a carboxylic acid compound having an organic layer forming ability to form an organic layer on the surface of the metal nanowire are dissolved in a metal nanowire placed at a joint between metal parts of an electrical component or an electronic component in a solvent. After the dropped solution is dropped, the metal sites can be electrically connected to each other by reduction of the metal salt or metal complex. In addition, the reduction of the metal salt or metal complex can be processed at a relatively low temperature, and even when an electrical component having low heat resistance is used, the thermal influence can be suppressed.

It is a photograph of the scanning electron microscope of the silver nanowire employ | adopted by this invention. It is a photograph of the scanning electron microscope of the silver nanowire obtained by the conventional manufacturing method. It is a transmission microscope picture of the solution which stirs and melt | dissolves silver nitrate, polyacrylic acid, and ethylene glycol. It is the photograph of the scanning electron microscope of the silver nanowire obtained by heating up the solution which stirred and melt | dissolved silver nitrate, polyacrylic acid, and ethylene glycol to predetermined temperature, and then adding silver nanowire and reacting for predetermined time. It is a photograph of the transmission microscope of the silver nanowire shown in FIG. It is a photograph of the scanning electron microscope of the silver nanowire obtained by adding the ethanol solution of silver nitrate and lauric acid to the silver nanowire.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, the scope of the present invention is not limited to these forms.

  The electrical conductor according to the present invention is an electrical conductor formed by joining metal nanowires, and the metal nanowires are organic layers made of an organic compound having a carboxyl group covering at least a part of the surface thereof. The metal salt is metal-bonded by a metal formed by reducing a metal complex of the inner metal salt or the organic compound and the metal salt.

  Gold nanowires, silver nanowires, platinum nanowires, and copper nanowires can be suitably used as the metal nanowires used here. The diameter of the metal nanowire is preferably 200 nm or less, particularly preferably 100 nm or less. As a method for producing a metal nanowire, a conventionally known production method can be adopted, but after dissolving a metal salt, a form modifier for adjusting the form of the obtained metal nanowire and a chloride in a solvent, oxygen gas is blown into the solution. The manufacturing method of the metal nanowire to heat can be employ | adopted suitably. Here, the metal salt is preferably a chloride of the same metal as the metal nanowire to be formed, and an inorganic salt such as nitrate or sulfate or an organic salt such as acetate is used depending on the solvent. it can. Further, sodium chloride (NaCl) or potassium chloride (KCl) is used as the chloride, and polyvinyl pyrrolidone or polyvinyl alcohol can be used as the form adjusting agent for adjusting the form of the obtained metal nanowire. As the solvent, high boiling alcohols such as ethylene glycol and triethylene glycol can be suitably used. Furthermore, as the heating temperature, a temperature near the boiling point of the solvent can be employed. Thus, uniform metal nanowires can be obtained by blowing oxygen while heating near the boiling point of the solvent. In particular, uniform silver nanowires can be obtained by applying this production method to the production of silver nanowires.

  In such metal nanowires, at least a part of the surface thereof is covered with a shape adjusting agent such as polyvinyl pyrrolidone or polyvinyl alcohol described above. At least a part of the surface of such a metal nanowire is covered with an organic layer made of an organic compound having a carboxyl group. Such an organic layer may be a polymer film or may be formed of an aggregate of surfactants such as fatty acids. In this organic layer, it is presumed that the carboxyl group acts on the surface of the metal nanowire or the shape adjusting agent to coat the surface of the metal nanowire. As the organic layer composed of an organic compound having a carboxyl group, for example, when a polymer carboxylic acid such as polyacrylic acid is used, an organic layer composed of a polymer film can be formed, and a fatty acid such as lauric acid is used. In some cases, an organic layer composed of an aggregate of surfactants is formed.

  Further, the metal nanowires are made of a metal formed by reducing a metal complex of a metal salt or an organic compound having a carboxyl group and a metal salt present in an organic layer covering at least a part of the surface of the metal nanowire. Metal bonded. For this reason, metal nanowires are also electrically connected. As this metal salt, chloroauric acid, silver nitrate, copper chloride, and chloroplatinic acid can be used. As described above, in the electric conductor according to the present invention, the metal nanowires are metal-bonded, so that a firm electric conductor can be formed.

  Such an electrical conductor is obtained by adding a metal nanowire and a solution in which a carboxylic acid compound and a metal salt having an organic layer forming ability to form an organic layer on the surface of the metal nanowire are dissolved, and at least a part of the surface of the metal nanowire is formed. By dispersing and compounding a metal complex of a metal salt or a carboxylic acid compound and a metal salt in an organic layer comprising an organic compound having a carboxyl group to cover, the metal salt or metal complex is reduced and metallized Can be formed. Here, as the carboxylic acid compound having an organic layer forming ability, a high molecular carboxylic acid or a low molecular carboxylic acid having at least 5 carbon atoms having a hydrophilic group or a hydrophobic group can be suitably used. Examples of the polymer carboxylic acid include polyacrylic acid, polymethacrylic acid, polyglutamic acid, and polyaspartic acid. In particular, polyacrylic acid can be suitably used as the polymer carboxylic acid, and the average molecular weight is preferably 5,000 to 100,000. As the low molecular carboxylic acid having at least 5 carbon atoms and having a hydrophilic group or a hydrophobic group, a fatty acid having at least 5 carbon atoms, particularly lauric acid, can be preferably used.

  Furthermore, as the solvent, ethanol can be used in addition to high boiling alcohols such as ethylene glycol and triethylene glycol. However, when the reaction temperature is high, a high boiling alcohol is preferable. In particular, ethylene glycol is preferable. A metal salt and a carboxylic acid compound having an organic layer forming ability to form an organic layer on the surface of the metal nanowire (hereinafter sometimes referred to as a carboxylic acid compound having an organic layer forming ability) are added to such a solvent and stirred. Dissolve. At this time, a part of the carboxylic acid compound having the ability to form an organic layer reacts with the metal salt, and a small amount of metal particles covered with the organic layer are precipitated. The precipitation of the metal particles is considered to be caused by the carboxyl group of the carboxylic acid compound acting on the metal salt. Next, if necessary, the temperature of the solution in which the metal salt and the carboxylic acid compound are dissolved is increased to a predetermined temperature. Further, the metal nanowire is added to this solution and the reaction is continued for a predetermined time while stirring. It is easy to add the metal nanowire by adding an aqueous solution in which the metal nanowire is dispersed. This reaction time is about 0.5 to 30 minutes. After completion of the reaction, if necessary, the solution is cooled to room temperature and then the metal nanowires are separated. The separated metal nanowire has at least a part of its surface covered with an organic layer, a metal salt or a metal complex is dispersed in the organic layer, and a small amount of metal particles may be observed. In addition, at least a part of the surface of the metal nanowire can be converted into a metal salt by adding a solution in which a metal salt and a carboxylic acid compound having an organic layer forming ability are dissolved in a dry state or in a metal nanowire dispersed in the solution. Alternatively, it can be covered with an organic layer containing a metal complex.

  Furthermore, a reduction treatment of the metal salt is performed in order to reduce the metal salt or metal complex present in the organic layer covering at least a part of the surface of the metal nanowire to precipitate the metal particles. By such reduction treatment, metal particles are deposited and melted together at a location where the metal nanowires are bonded to each other, so that the metal nanowires can be bonded to each other. As such reduction treatment, heat treatment is the simplest and most effective. By adopting a heat treatment temperature at which a part of the deposited metal particles is melted as the heat treatment temperature at this time, the metal nanowires can be bonded more firmly. Even when the organic layer disappears during the heat treatment, the metal nanowires are bonded to each other, so that the bonded state can be maintained. Moreover, you may use a reducing agent for this reduction process. As such a reducing agent, sodium borohydride, citric acid, hydrazine and the like can be used, but those having a high reducing power are preferable.

  As described above, the electrical conductor according to the present invention is a strong electrical conductor in which the metal nanowires are firmly connected to each other while being electrically connected to each other. Therefore, it can be used for a conductive film or the like. In addition, after dissolving a metal salt and a carboxylic acid compound having an organic layer forming ability in a solvent, and dropping a solution containing metal nanowires at a joint portion between metal portions of an electrical component or an electronic component, the metal salt or Metal parts can be electrically connected to each other by reduction of the metal complex. Alternatively, after a solution in which a metal salt and a carboxylic acid compound having an organic layer-forming ability are dissolved in a solvent is dropped onto a metal nanowire placed at a joint between metal parts of an electrical component or an electronic component, the metal salt or Metal parts can be electrically connected to each other by reduction of the metal complex. Furthermore, it is possible to assemble a metal structure as a bottom-up method. In the present invention, metal nanowires are used, but metal nanoparticles may be mixed, and metal nanoparticles may be used instead of metal nanowires.

Example 1
(1) Production of silver nanowires 0.15 g of silver nitrate, 0.58 g of polyvinylpyrrolidone having an average molecular weight of 40,000 as a form modifier, 0.004 g of sodium chloride (NaCl) and ethylene glycol (18 ml) After adding to the attached flask and dissolving with stirring, the temperature was raised to 198 ° C., which is near the boiling point of ethylene glycol, and reacted for 20 minutes while blowing oxygen. After completion of the reaction, it was allowed to cool at room temperature. Next, after diluting the contents diluted with distilled water in the flask, washing was performed to remove the supernatant. After performing such washing several times, the obtained silver nanowires were dispersed in distilled water. FIG. 1 shows a photograph (SEM photograph) of the obtained silver nanowire with a scanning electron microscope (manufactured by Hitachi, Ltd., trade name S-5000). As is apparent from FIG. 1, silver nanowires having a smooth surface and a uniform diameter were obtained. The obtained silver nanowire had a diameter of 60 to 80 nm and a length of several tens of μm.

  As a reference example, silver nanowires were produced in the same manner as in Example 1 except that no salt was used in the method for producing silver nanowires and the reaction temperature was 160 ° C. The SEM photograph of the obtained silver nanowire is shown in FIG. As apparent from FIG. 2, the obtained silver nanowire had a variation of 150 to 250 nm in diameter, and a large number of triangular or polygonal particles having a diameter of 400 nm or more.

(2) Formation of electric conductor 0.034 g of silver nitrate and 0.014 g of polyacrylic acid having an average molecular weight of 25,000 were dissolved by stirring in ethylene glycol (10 ml). A photograph (TEM photograph) of a transmission electron microscope (trade name JEM-2010, manufactured by JEOL Ltd.) of this solution is shown in FIG. As is apparent from FIG. 3, there are a large number of fine particles having a diameter of about 20 nm coated with a polymer film. Such fine particles are considered to be produced by the action of carboxyl groups of polyacrylic acid on the surface of silver particles.

  In this way, the temperature of the solution in which a large number of fine particles are generated is raised to 130 ° C., and the silver nanowires dispersed in the distilled water obtained in (1) are dropped together with the distilled water and reacted for 20 minutes. Continued. After completion of the reaction, it was allowed to cool at room temperature. Next, after diluting the contents diluted with distilled water in the flask, washing was performed to remove the supernatant. FIG. 4 shows an SEM photograph of the silver nanowire obtained by performing such washing a plurality of times. As is clear from FIG. 4, the surface of the silver nanowire is covered with a polymer film, and the silver nanowires are joined together by the polymer film. Furthermore, when the obtained silver nanowires were observed including the joints, silver particles were found in the polymer film covering the surface of the silver nanowires, as is apparent from the TEM photographs shown in FIGS. It is recognized that silver particles are present [FIG. 5 (a)] and silver particles are also present in the polymer film at the junction of the silver nanowires [FIG. 5 (b)].

  Thereafter, the silver nanowires shown in FIG. 4 and FIG. 5 were subjected to a heat treatment of heating to 270 ° C. in an atmosphere of air or nitrogen for 5 minutes to reduce the silver nitrate in the polymer film. The molecular film disappeared, a large number of silver particles were deposited on the surface of the silver nanowires, and silver bonding was performed at the joint between the silver nanowires.

(Example 2)
An ethanol solution obtained by adding ethanol to a 1: 1 mixture of silver nitrate and lauric acid, which is a kind of fatty acid, was added dropwise to the silver nanowires dispersed in distilled water obtained in Example 1 (1). Then, after centrifuging, washing was performed to remove the supernatant. FIG. 6 shows an SEM photograph of the silver nanowire obtained by performing such washing multiple times. As is clear from FIG. 6, silver particles are deposited in an uneven shape in the organic layer covering the surface of the silver nanowire.

  Next, the silver nanowire shown in FIG. 6 was subjected to a heat treatment in air at 270 ° C. for 5 minutes to reduce the silver nitrate in the organic layer, whereby an organic layer covering the surface of the silver nanowire. Disappeared, and silver bonding was performed at the bonding portion between the silver nanowires.

  The electrical conductor of the present invention is used as an adhesive, an electrical wiring material, or a conductive film for joining electrical components in the electronics field.

Claims (8)

An electrical conductor formed by joining metal nanowires, wherein the metal nanowires are a metal salt in an organic layer made of an organic compound having a carboxyl group covering at least a part of the surface thereof, or the organic compound An electric conductor , wherein the metal complex with the metal salt is metal-bonded by a metal reduced and partially melted by heat treatment for eliminating the organic layer .   The electrical conductor according to claim 1, wherein the metal salt is a metal salt selected from chloroauric acid, silver nitrate, copper chloride, and chloroplatinic acid.   2. The electrical conductor according to claim 1, wherein the organic compound having a carboxyl group is a high molecular carboxylic acid or a low molecular carboxylic acid having at least 5 carbon atoms having a hydrophilic group or a hydrophobic group. A carboxyl group that mixes at least a part of the surface of the metal nanowire by mixing a metal nanowire and a solution in which a carboxylic acid compound having an organic layer forming ability and a metal salt are dissolved to form an organic layer on the surface of the metal nanowire. after blended by dispersing a metal complex of an organic compound wherein the metal salt or the carboxylic acid compound in an organic layer composed of said metal salt with, subjected to heat treatment to the metal nanowires separated from the solution, the with a loss of organic layer, reducing the metal salt or the metal complex and a portion in metallic thawed the method of forming the electrical conductor, characterized in that the metal bonding the metal nanowires to each other.   The method for forming an electric conductor according to claim 4, wherein a metal salt selected from chloroauric acid, silver nitrate, copper chloride, and chloroplatinic acid is used as the metal salt.   5. The electric conduction according to claim 4, wherein the carboxylic acid compound having the organic layer forming ability is a high-molecular carboxylic acid or a low-molecular carboxylic acid having at least 5 carbon atoms having a hydrophilic group or a hydrophobic group. Body formation method. The method for forming an electric conductor according to claim 4, wherein the organic layer is a polymer film .   The metal nanowire is a metal nanowire obtained by dissolving a metal salt, a form modifier for adjusting the form of the metal nanowire to be obtained, and a chloride in a solvent and then heating while blowing oxygen gas. The method for forming an electric conductor according to claim 4.

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