Metal wiring

Abstract

To provide a metal wiring with high insulation reliability, capable of suppressing an electro chemical migration by suppressing a cycle from the generation of a silver to an analysis of silver in a wiring using silver with a high conductivity.SOLUTION: In a metal wiring using silver, by suppressing the generation of a silver ion (an elution of silver) from a wiring, an excellent metal wiring with high insulation reliability can be formed. Also, a replacement wiring in which a metal composition ratio of a front surface of the wiring is reproduced or an electrochemical measurement of a sample substrate is executed, and a migration resistance of the metal wiring can be estimated by measuring an elution amount of silver.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to metal wiring that can be used for electrical conduction, such as power lines and signal lines. [Background technology]

[0002] Modern life is supported by a variety of home appliances and electronic devices, and it can be said that we live surrounded by electrically conducting metal wiring. Market demands for smaller appliances and electronic devices are driving performance improvements, and metal wiring is increasingly being placed in extremely close proximity, increasing the demand for reliable insulation. Furthermore, demands for energy savings and high-speed signal transmission necessitate minimizing electrical transmission loss within metal wiring as much as possible.

[0003] Various metals, such as copper, silver, gold, lead, tin, nickel, cobalt, and chromium, are used for the metal wiring installed inside home appliances and electronic devices. However, from the viewpoints of workability, cost, and electrical conductivity, copper has been primarily used as the metal for electrical conduction wiring. On the other hand, in order to suppress electrical conduction loss, it is preferable to use silver, which has lower electrical resistance, as wiring. However, silver is known to be the metal most susceptible to electrochemical migration, and there have been concerns about the insulation reliability when using silver as a wiring material (Non-Patent Document 1).

[0004] Electrochemical migration is an electrochemical phenomenon caused by the generation, diffusion, and deposition of metal ions due to the elution of wiring metal, which ultimately leads to a short circuit between the wiring and electrodes, resulting in failure. In other words, the problem with silver wiring is that it is prone to a cycle that involves the generation of metal ions and the deposition of the eluted metal. [Prior art documents] [Non-patent literature]

[0005] http: / / www1.coralnet.or.jp / fjk / migre / mg100.htm, "Overview of the Migration Phenomenon (coralnet.or.jp)" Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide metal wiring that uses highly conductive silver, and that suppresses the occurrence of electrochemical migration by suppressing the cycle from the generation of silver ions to the deposition of silver, thereby achieving highly reliable insulation. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above-mentioned problems, the inventors have found that, in a silver-based metal wiring, it is possible to form a metal wiring with good insulation reliability by suppressing the generation of silver ions (silver elution) from the wiring. Furthermore, they have found that the migration resistance of a metal wiring can be estimated by performing electrochemical measurements on a substitute wiring or a test substrate that reproduces the metal composition ratio of the wiring surface and measuring the amount of eluted silver, thereby completing the present invention.

[0008] That is, the present invention is 1. A metal wiring using silver, characterized in that the surface of the metal composition has a silver elution rate of 400 ppb or less when measured by the electrochemical measurement method described below. (Electrochemical measurement method) The electrochemical measurement method uses a three-electrode method consisting of a working electrode, a counter electrode, and a reference electrode, and uses a metal wire as the working electrode exposed to the following electrolyte: The counter electrode is an insoluble platinum wire or plate, the reference electrode is a saturated silver-silver chloride electrode, and the reference electrode solution is a saturated KCl solution. An aqueous sodium sulfate solution (concentration: 100 ppm) is used as the electrolyte, and the working electrode and the counter electrode are immersed in the electrolyte and arranged facing each other. The electrolyte and the solution of the reference electrode are connected by a salt bridge made of saturated KCl solution solidified with agar, and the tip of the salt bridge on the electrolyte side is connected to a Luggin capillary filled with the electrolyte. A potentiostat (HA-501, manufactured by Hokuto Denko Corporation) was used as a control device for controlling the current and voltage, and a voltage was applied for 10 minutes to achieve a current density of 1 mA / cm2 as the conditions for electrolysis measurement. Immediately after voltage application, the working electrode was removed from the electrolyte, and the concentration of silver dissolved in the electrolyte was measured. An ICP-MS analyzer (Agilent 8900, manufactured by Agilent) is used to measure the concentration of silver dissolved in the electrolyte. 2. The metal wiring according to 1, characterized in that the surface area of ​​the silver is covered with copper in an amount of 0.07% to 99.9%. 3. The metal wiring according to 1 or 2, wherein the electric field strength of the adjacent metal wiring is in the range of 0.001 V / μm to 400 V / μm. 4. The metal wiring according to any one of 1 to 3, wherein the distance (gap) between adjacent metal wirings is in the range of 0.1 μm to 20 mm. 5. A laminate comprising the metal wiring according to any one of 1 to 4. 6. A printed wiring board characterized by using the laminate described in 5. This provides: [Effects of the Invention]

[0009] The present invention can provide metal wiring with high insulating reliability for conducting electricity, such as power lines and signal lines, and can be suitably used for various electrical wiring, printed wiring boards, MIDs (molded circuit boards), etc. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a water drop test. [Figure 2] FIG. 1 is a schematic diagram showing one embodiment of the present invention used in a water drop test. [Figure 3]Schematic diagram of electrochemical measurement method [Figure 4] FIG. 1 is a schematic diagram showing one embodiment of the present invention used in electrochemical measurement. [Explanation of symbols]

[0011] 1. Schematic diagram of the water drop test 2 glass slides 3 Metal Wire 4 water drops 5. Potentiostat 6 Schematic diagram showing one embodiment of the present invention used in a water drop test 7 Lacquer 8 Metal Wire 9 Coated Metal 10 Schematic diagram of electrochemical measurement method 11 Potentiostat 12 metal plate 13 Electrolyte 14 Opposite 15 Luggin's tubule 16 Salt Bridge 17 Reference pole 18 Saturated KCl solution 19 Schematic diagram showing one embodiment of the present invention used in electrochemical measurement 20 metal plate 21 Lacquer 22 Surface of metal plate or coated metal exposed to electrolyte DETAILED DESCRIPTION OF THE INVENTION

[0012] The metal wiring of the present invention is a metal wiring using silver, characterized in that the elution rate of eluted silver is 400 ppb or less, as determined by the electrochemical measurement method described below.

[0013] Silver is oxidation-resistant, has the highest electrical conductivity (low electrical resistance), and is also the metal with the highest thermal conductivity. Furthermore, it is highly malleable and easy to process, making it a metal that has long been used in the electronics field. However, there have been concerns that in environments where electric fields and humidity coexist, electrochemical migration occurs, making it prone to failure due to short circuits.

[0014] In the metal wiring of the present invention, as a means for solving the problem of electrochemical migration while utilizing the electrical conductivity and oxidation resistance of silver, a portion of the silver surface is coated with a metal having a higher ionization tendency than silver, thereby forming a local galvanic battery and suppressing the elution of silver, thereby making it possible to improve resistance to electrochemical migration. As the metal used to coat the silver, various metals can be suitably used as long as they have a higher ionization tendency than silver and maintain adhesion to the silver. However, from the viewpoints of copper, which has the second highest electrical conductivity as a metal wiring after silver, and is excellent in cost and processability, it is preferable to use copper as the metal used for coating.

[0015] Although ion migration is known to occur in copper wiring, copper wiring has been widely used for a long time, and as long as the elution of silver from a metal wiring in which silver is coated with copper is suppressed and the amount of copper eluted is kept at the same level as the amount of copper eluted alone, the ion migration resistance in normal use is at a level where it does not pose a problem. From this viewpoint, it is particularly preferable that the metal species that coats silver is copper.

[0016] In the metal wiring of the present invention, the surface area of ​​the metal coating with silver relative to the silver surface may be set so that the amount of silver elution measured using the electrochemical measurement method described below is 400 ppb or less, and may be appropriately selected from the viewpoints of conductivity and cost, but when copper is used as the coating metal, it is preferable that the silver surface be coated with copper at a surface area of ​​0.07% to 99.9%. From the viewpoint of suppressing the amount of silver elution, the copper coating amount should be 1% or more of the surface area, but from the viewpoint of wiring formation cost, it is more preferable that it be 50% to 99.9%.

[0017] The electrochemical measurement method used in the present invention uses a three-electrode method consisting of a working electrode, a counter electrode, and a reference electrode. There are no particular limitations on the devices and containers used for the three-electrode electrochemical measurement, and any known or commonly used devices may be used. For example, devices with the following specifications, size, and capacity can be suitably used.

[0018] The metal wiring of the present invention was used as the working electrode, and the area was 0.5 cm 2 The electrode is then exposed to an aqueous solution of sodium sulfate (concentration: 100 ppm) as an electrolyte. An insoluble metal is preferably used as the counter electrode, and platinum is particularly preferred. The area of ​​the counter electrode is 0.5 cm. 2 A saturated silver-silver chloride electrode is used as the reference electrode, and a saturated KCl solution is used as the reference electrode solution.

[0019] The working electrode and the counter electrode are immersed in the electrolyte and arranged facing each other. The electrolyte and the reference electrode solution are connected by a salt bridge made of saturated KCl solution solidified with agar. The tip of the salt bridge on the electrolyte side is connected to a Luggin capillary filled with the electrolyte, and the tip of the Luggin capillary is positioned approximately several mm from the working electrode.

[0020] A potentiostat is used as a control device for controlling the current and voltage, such as the HA-501 potentiostat manufactured by Hokuto Denko Corporation.

[0021] The conditions for electrolytic measurement were 1 mA / cm 2 A voltage is applied for 10 minutes so as to achieve a current density of 1000 kJ / cm2. After the voltage application, the working electrode is quickly removed from the electrolyte.

[0022] The concentration of silver dissolved in the electrolyte is measured using an ICP-MS analyzer, such as Agilent 8900 manufactured by Agilent.

[0023] In the case of wiring that is actually used, if the size of the wiring is not suitable for the electrochemical measurement, the electrochemical measurement can be performed using an alternative test substrate that reproduces the metal composition ratio of the wiring surface.

[0024] For example, in the case of wiring formed on a substrate, measurements can be performed using an alternative test substrate in which a metal film corresponding to the metal composition ratio of the target wiring surface is formed on the surface of a substrate of a size suitable for the electrochemical measurement.If the metal wiring is a wire or the like, electrochemical measurements can be performed using multiple wires so that the area is suitable for the electrochemical measurement.

[0025] The metal wiring of the present invention may contain a different metal in addition to silver and the metal coating the silver surface, as long as the amount of silver eluted by electrochemical measurement does not exceed 400 ppb. If the amount of silver eluted exceeds 400 ppb, migration resistance will be significantly reduced, which is undesirable. Here, "containing a different metal" means that the different metal is contained in the wiring or that the different metal is present on a portion of the surface of the metal wiring. "Presence of a different metal on a portion of the surface of the metal wiring" means, for example, when connecting the metal wiring of the present invention to a component, a solder metal coats the metal wiring, or when nickel / gold plating or tin plating is partially formed.

[0026] The metal wiring of the present invention, despite using silver, exhibits excellent resistance to ion migration. Ion migration is a phenomenon in which metal components of wiring or electrodes migrate across or within a non-metallic medium under the influence of an electric field, and occurs in metal wiring placed in an electric field. The metal wiring of the present invention can be used when the electric field strength between adjacent metal wirings is in the range of 0.001 V / μm to 400 V / μm, but in small home appliances and the like, a range of 0.001 V / μm to 20 V / μm is sufficient without any particular problems. Here, the electric field strength is the value obtained by dividing the electric field applied between the target metal wirings by the distance between the wirings.

[0027] When ion migration occurs, there are at least two metal wirings between which a potential difference exists. In the present invention, these two metal wirings are defined as adjacent metal wirings. The adjacent metal wirings may be straight metal wirings arranged parallel to each other, or a bent wiring may be arranged adjacent to a straight wiring at a corner thereof. Any configuration may be selected depending on the purpose of using the metal wirings.

[0028] Typically, the electric field strength is greatest at the shortest distance between two metal wirings where the potential difference exists, and therefore ion migration is most likely to occur at the shortest distance between the metal wirings. Therefore, the distance between two adjacent metal wirings can be considered as the shortest distance between the wirings and can be appropriately selected depending on the specifications and purpose of the device or product that uses the metal wirings. When used in small home appliances, etc., the distance between adjacent metal wirings is particularly preferably in the range of 0.1 μm to 20 mm.

[0029] There are no particular restrictions on the length of the metal wiring of the present invention, but in the case of metal wiring formed on large control boards such as those used in data centers, a length of 100 cm or less may be considered, and in the case of metal wiring formed on boards used in general home appliances, etc., a length of 20 cm or less may be considered.

[0030] In the metal wiring of the present invention, the amount of silver eluted as determined by the electrochemical measurement is preferably uniform over the entire length of the metal wiring, but there may be some distribution as long as the amount of silver eluted is lower than 400 ppb.

[0031] As mentioned above, ion migration is most likely to occur between metal wirings where the electric field strength is strongest, i.e., in the area where the distance between the metal wirings is shortest. A composition in which the amount of silver elution determined by the electrochemical measurement mentioned above does not exceed 400 ppb should be realized at least in the area where the distance between two adjacent metal wirings is shortest. The area where the distance between two adjacent metal wirings is shortest can be considered to be the area along the metal wirings that is 1,000 times the thickness of the metal wiring from the center point of the shortest distance between the metal wirings.

[0032] In the present invention, the thickness of a metal wiring refers to the distance from the surface of the substrate to the vertex of the wiring in the thickness direction when the metal wiring is formed on a substrate. When the metal wiring is a wire, if the cross section of the wire is circular or elliptical, the diameter and major axis of the wire can be considered to be the thickness of the wire, and if the cross section of the wire is rectangular, the length of the diagonal can be considered to be the thickness. When the cross section of the metal wiring is irregular, the longest length of the cross section can be considered to be the thickness of the wiring.

[0033] The production of the metal wiring of the present invention is achieved by coating a commercially available silver wire or the like with a metal having a higher ionization tendency than silver, such as copper. The coating method is not particularly limited, and a known, commonly used method may be selected depending on the purpose. For example, when coating a silver wire with copper, electroless copper plating may be performed on the silver wire, or electrolytic copper plating may be performed using the silver wire as the cathode. Alternatively, silver may be coated on a metal wire made of a metal having a higher ionization tendency than silver. When coating a copper wire with silver, electroless silver plating or electrolytic copper plating may be performed on the copper wire.

[0034] The cross-sectional shape of the metal wiring of the present invention is not particularly limited as long as the required purpose of electrical conduction is achieved, and any shape may be selected depending on the purpose, for example, a circle, a semicircle, an ellipse, a semi-ellipse, a rectangle, etc. Furthermore, in the present invention, the metal wiring includes not only linear ones but also electrode portions at the ends of the wiring.

[0035] The surface of the metal wiring of the present invention may be coated with an insulating material. The method for coating the surface of the metal wiring may be, for example, to coat each linear wiring individually, or to coat a plurality of adjacent metal wirings together. Furthermore, the entire surface area of ​​the metal wiring may be coated with the insulating material, or a portion of the surface area may be insulated by the insulating material.

[0036] When the surface of the metal wiring is coated with an insulating material, the insulating material for coating the surface may be a single material or a combination of multiple materials. For example, when coating each individual linear metal wiring, insulating materials such as polyvinyl chloride, fluororesin, cross-linked polyethylene, natural rubber, synthetic rubber, etc. can be suitably used. For example, a method can be used in which the metal wiring is immersed in the insulating material that has been heated and melted, and then cooled and solidified to coat the surface. Alternatively, the surface of the metal wiring may be coated by applying a solution, melt, or dispersion of various insulating materials described below as materials for the insulating substrate to the metal wire and drying it.

[0037] When the surface of the metal wiring is coated with an insulating material, a plurality of metal wirings formed on an insulating substrate may be coated with different insulating substrates. When the metal wiring is formed on an insulating substrate, examples of the insulating substrate include polyimide resin, polyamideimide resin, polyamide resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, polycarbonate resin, acrylonitrile-butadiene-styrene (ABS) resin, polyarylate resin, polyacetal resin, acrylic resin such as poly(methyl meth)acrylate, polyvinylidene fluoride resin, polytetrafluoroethylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, vinyl chloride resin graft copolymerized with acrylic resin, polyvinyl alcohol resin, polyethylene resin, polypropylene resin, urethane resin, cycloolefin resin, polystyrene, liquid crystal polymer (LCP), polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS), polyphenylene sulfone (PPSU), cellulose nanofiber, silicon, silicon carbide, gallium nitride, sapphire, ceramics, glass, diamond-like carbon (DLC), and alumina.

[0038] Furthermore, a resin substrate containing a thermosetting resin and an inorganic filler can also be suitably used as the insulating substrate. Examples of the thermosetting resin include epoxy resin, phenolic resin, unsaturated imide resin, cyanate resin, isocyanate resin, benzoxazine resin, oxetane resin, amino resin, unsaturated polyester resin, allyl resin, dicyclopentadiene resin, silicone resin, triazine resin, and melamine resin. Examples of the inorganic filler include silica, alumina, talc, mica, aluminum hydroxide, magnesium hydroxide, calcium carbonate, aluminum borate, and borosilicate glass. These thermosetting resins and inorganic fillers can be used alone or in combination of two or more.

[0039] The insulating substrate may be in the form of a flexible material, a rigid material, or a rigid-flexible material. More specifically, the insulating substrate may be a commercially available material formed into a film, sheet, or plate, or may be formed from a solution, melt, or dispersion of the above-mentioned resin.

[0040] When the metal wiring of the present invention is formed on an insulating substrate, an insulating material that improves adhesion between the insulating substrate and the metal wiring may be inserted between the insulating substrate and the metal wiring.

[0041] As a method for producing metal wiring on the insulating substrate, for example, a silver foil may be laminated on the insulating substrate, and then a silver wire of the desired width may be formed by etching. The metal wiring of the present invention can be formed by coating the silver surface with a metal having a higher ionization tendency than silver by electroless plating, electrolytic plating, or a combination of electroless and electrolytic plating. Alternatively, a foil of a metal having a higher ionization tendency than silver may be laminated on the insulating substrate, and then a metal wire of the desired width may be formed by etching, and then the metal wiring of the present invention can be formed by electroless silver plating, electrolytic silver plating, or a combination of electroless silver and electrolytic silver plating.

[0042] In this way, the metal wiring formed on the insulating substrate can be further coated with an insulating material. In this case, the insulating material coating the top of the metal wiring may be the same material as the insulating substrate on which the metal wiring is formed, or a different insulating material. The insulating material coating the top of the metal wiring formed on the insulating substrate can be any of the various materials described above as the insulating substrate. Furthermore, depending on the application and use of the metal wiring, the metal wiring may be coated with a commercially available coverlay, bonding sheet, solder resist, etc.

[0043] When metal wiring is coated with an insulating material in this way, when the cross section is observed, the metal wiring layer and the insulating material are stacked, and this is called a laminate in the present invention. The laminate of the present invention may have a single or multiple combinations of metal wiring and insulating material. For example, it may be formed in a form in which multiple layers of a structure in which a metal wiring layer formed on a planar substrate is coated with an insulating material are stacked. In this way, a laminate formed by combining multiple layers of structures in which a metal wiring layer is coated with an insulating material can be considered a "multilayered" laminate, but in the laminate of the present invention, the metal wiring of different layers may be connected at one point or multiple points.

[0044] Such a multilayer laminate may be manufactured by laminating one layer of metal wiring and one layer of insulating material, or by preparing multiple structures in which metal wiring is covered with an insulating base material and laminating them together.

[0045] The laminate of the present invention can be suitably used as a printed wiring board, which is formed by forming the metal wiring having a shape suited to the purpose on an insulating substrate or inside an insulating material, thereby forming an electric circuit.

[0046] The printed wiring board of the present invention may not have any components mounted thereon, but may have the metal wiring formed on an insulating substrate or inside an insulating material in a shape suited to the purpose, forming an electric circuit, or may have various electronic components mounted thereon.

[0047] The metal wiring of the present invention can provide metal wiring with high insulating reliability for conducting electricity, such as power lines and signal lines, and can be suitably used for various electrical wiring, printed wiring boards, MIDs (molded circuit boards), etc. [Example]

[0048] The present invention will be described in more detail below using examples and comparative examples. In the following examples and comparative examples, "parts" and "%" are all based on mass.

[0049] [Production Example 1] A silver wire with a diameter of 2 mm was prepared, and the surface of the silver wire, 1 cm from its tip, was immersed in an electroless copper plating solution (CIRCUPOSIT 6550 manufactured by Rohm and Haas Electronic Materials Co., Ltd.) at 35°C for 14 minutes to form a copper plating layer (film thickness 0.34 μm), producing a metal wiring consisting of a copper-coated silver wire. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99.93:0.07. The sides of the copper-coated silver wire were covered with lacquer (insulating film) to prepare a metal wiring sample so that the metal elution area was limited to the cross section of the copper-coated silver wire.

[0050] [Production Example 2] A silver wire with a diameter of 0.5 mm was prepared, and the surface of the silver wire, 1 cm from its tip, was immersed in an electroless copper plating solution (CIRCUPOSIT 6550, manufactured by Rohm and Haas Electronic Materials Co., Ltd.) at 35°C for 5 minutes to form a copper plating layer (film thickness 0.13 μm), producing a metal wiring consisting of a copper-coated silver wire. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99.9:0.1. The sides of the copper-coated silver wire were covered with lacquer (insulating film) to prepare a metal wiring sample so that the metal elution area was limited to the cross section of the copper-coated silver wire.

[0051] [Preparation Example 3] A metal wiring sample was produced in the same manner as in Preparation Example 2, except that the silver wire with a diameter of 0.5 mm was changed to a silver wire with a diameter of 1 mm, and the immersion time in the electroless plating solution was changed from 5 minutes to 11 minutes to form a copper plating layer (film thickness 0.25 μm). The area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99.9:0.1.

[0052] [Preparation Example 4] A metal wiring sample was prepared in the same manner as in Preparation Example 2, except that the silver wire with a diameter of 0.5 mm was changed to a silver wire with a diameter of 2 mm and the immersion time in the electroless plating solution was changed from 5 minutes to 20 minutes. The area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99.9:0.1.

[0053] [Preparation Example 5] By bundling four metal wirings prepared in Preparation Example 3, a metal wiring having the same silver:copper ratio and cross-sectional area as Preparation Example 4 was prepared.

[0054] [Preparation Example 6] A 1 mm diameter silver wire was prepared, and the surface of the silver wire, 1 cm from its tip, was immersed in an electrolytic copper plating solution (Top Lucina SF, manufactured by Okuno Chemical Industries Co., Ltd.) and electrolytic copper plating was performed for 5 minutes to form a 2.5 μm thick copper plating layer on the silver wire, producing a copper-coated silver wiring. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99:1. The sides of the copper-coated silver wire were covered with lacquer (an insulating film) to ensure that the metal elution area was limited to the cross section of the copper-coated silver wire, producing a metal wiring sample.

[0055] [Preparation Example 7] A 2 mm diameter silver wire was prepared, and the surface of the silver wire 1 cm from its tip was immersed in an electrolytic copper plating solution (Top Lucina SF, manufactured by Okuno Chemical Industries Co., Ltd.) and electrolytic copper plating was performed for 10 minutes to form a 5 μm thick copper plating layer on the silver wire, producing a copper-coated silver wiring. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 99:1. The sides of the copper-coated silver wire were covered with lacquer (an insulating film) to ensure that the metal elution area was limited to the cross section of the copper-coated silver wire, producing a metal wiring sample.

[0056] [Preparation Example 8] By bundling four metal wirings prepared in Preparation Example 6, a metal wiring having the same silver:copper ratio and cross-sectional area as Preparation Example 7 was prepared.

[0057] [Preparation Example 9] A 2-mm diameter silver wire was prepared, and the surface of the silver wire, 1 cm from its tip, was immersed in an electrolytic copper plating solution (Top Lucina SF, manufactured by Okuno Chemical Industries Co., Ltd.) to form a 54-μm-thick copper plating layer on the silver wire, producing copper-coated silver wiring with different silver:copper area ratios. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 90:10. The sides of the copper-coated silver wire were covered with lacquer (an insulating film) to ensure that the metal elution area was limited to the cross section of the copper-coated silver wire, producing a metal wiring sample.

[0058] [Preparation Examples 10 and 11] A 0.5 mm diameter silver wire was prepared, and the surface of the silver wire, 1 cm from its tip, was immersed in an electrolytic copper plating solution (Top Lucina SF, manufactured by Okuno Chemical Industries Co., Ltd.). Electrolytic copper plating was performed for varying periods of time to form a copper plating layer on the silver wire, producing copper-coated silver wiring with different silver:copper area ratios. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was 70:30 or 50:50. The sides of the copper-coated silver wire were covered with lacquer (an insulating film) to ensure that the metal elution was limited to the cross section of the copper-coated silver wire, producing metal wiring samples.

[0059] [Preparation Example 12] A copper wire with a diameter of 0.5 mm was prepared, and the surface of the copper wire 1 cm from the tip was immersed in a displacement electroless silver plating solution (Dainsilver EL-3S, manufactured by Daiwa Kasei Co., Ltd.) at 50°C for 5 minutes to form a silver plating layer (film thickness 0.13 μm) that substituted the surface of the conductor, producing metal wiring consisting of silver-coated copper wire. The tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 0.1:99.9. The sides of the copper-coated silver wire were covered with lacquer (insulating film) to prepare a metal wiring sample so that the metal elution area was limited to the cross section of the copper-coated silver wire.

[0060] [Preparation Example 13] (Preparation of Silver Particle Dispersion) A nano-sized silver particle dispersion was prepared by dispersing silver particles with an average particle size of 30 nm in a mixed solvent of 45 parts by mass of ethylene glycol and 55 parts by mass of ion-exchanged water using a compound in which polyoxyethylene is added to polyethyleneimine as a dispersant. (Formation of metal wiring) A copper wire with a diameter of 0.5 mm was prepared, and the surface of the copper wire was immersed in the dispersion of silver particles for 1 cm from the tip, and a silver nanoparticle coating film was formed on the surface of the copper wire by dip coating (copper wire pulling speed: 4 mm / s). The copper wire was then heated and dried at 180°C for 5 minutes to form a silver nanoparticle layer with a thickness of 0.1 μm, producing a silver-coated copper wire. The tip of the silver-coated copper wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper = 0.1:99.9. The side of the copper-coated silver wire was covered with lacquer (insulating film) so that the metal elution area was limited to the cross section of the copper-coated silver wire, and a metal wiring sample was obtained.

[0061] (Comparative Preparation Example 1) A copper plating layer (film thickness 0.13 μm) was formed on the silver wire in the same manner as in Preparation Example 4, except that the immersion time in the electroless copper plating solution was changed from 20 minutes to 11 minutes, thereby forming metal wiring consisting of copper-coated silver wire. In the same manner as in Preparation Example 4, the tip of the copper-coated silver wire was polished with emery paper so that the area ratio of silver to copper in the cross section of the silver-coated copper wire was silver:copper=99.95:0.05. The sides of this copper-coated silver wire were covered with lacquer (insulating film) to prepare a metal wiring sample so that the metal elution area was limited to the cross section of the copper-coated silver wire.

[0062] (Comparative Preparation Example 2) A silver wire with a diameter of 2 mm was prepared, and one tip was polished with emery paper to obtain a silver wire with an area ratio of silver to copper in the cross section of silver:copper=100:0.

[0063] (Examples 1 to 13 and Comparative Examples 1 and 2) Using the metal wiring produced in the above production example, electrochemical migration resistance was evaluated by the water drop test described below. The results are shown in Tables 1 and 2.

[0064] (Method for evaluating electrochemical migration resistance) To evaluate the electrochemical migration resistance of metal wiring, a water drop test was conducted to forcibly induce electrochemical migration. The metal wiring fabricated in the above-mentioned Preparation Example and Comparative Preparation Example was used as the anode and cathode, and was placed on a glass substrate with a gap of approximately 1.1 mm between the electrodes. Pure water was dropped onto the electrodes, and a cover glass was then placed over them. A voltage of 15 V was applied across the gap between the metal wiring using a potentiostat, and the voltage across the gap was monitored. The time until the voltage dropped to 10 V was determined as the short-circuit time. A short-circuit time of 60 seconds or longer was considered to have good migration resistance, and migration resistance was evaluated according to the following criteria.

[0065] (Evaluation criteria for electrochemical migration resistance) A Short circuit for 180 seconds or more B Short circuit for 120 seconds or more but less than 180 seconds C Short circuit for 60 seconds or more but less than 120 seconds D Short circuit for 10 seconds or more but less than 60 seconds E Short circuit for less than 10 seconds

[0066] [Table 1]

[0067] [Table 2]

[0068] (Examples 14 to 17 and Comparative Examples 3 and 4) The metal wirings prepared in the above Preparation Example and Comparative Preparation Example were used to measure the amount of eluted silver by electrochemical measurement described below.

[0069] <Method for evaluating the amount of silver elution> The amount of silver eluted from the metal wiring was measured using a 300 ml flask and electrochemical measurement by the three-electrode method (Figure 3). The metal wiring prepared in the above Preparation Example and Comparative Preparation Example was attached to the working electrode, with an area of ​​0.5 cm. 2 The number of electrodes was set so that the measurement was performed. A platinum electrode was used as the counter electrode, and the area of ​​the counter electrode was 0.5 cm. 2 A saturated silver-silver chloride electrode was used as a reference electrode. 200 ml of a sodium sulfate aqueous solution (concentration: 100 ppm) was used as an electrolyte, and the working electrode and the counter electrode were immersed in the electrolyte and arranged facing each other. The electrolyte and the solution of the reference electrode were connected by a salt bridge made of saturated KCL solution solidified with agar. The tip of the salt bridge on the electrolyte side was connected to a Luggin capillary filled with the electrolyte, and the tip of the Luggin capillary was positioned several mm from the working electrode. A potentiostat (HA-501, manufactured by Hokuto Denko Corporation) was used as a control device for constant current electrolysis measurement. The conditions for galvanostatic measurement were 1 mA / cm 2 A voltage was applied for 10 minutes at a current density of 0.5 cm. The area of ​​the working electrode exposed to the electrolyte was 0.5 cm. 2 The silver elution rate in the electrolyte was measured using an ICP-MS analyzer (Agilent 8900, manufactured by Agilent). Table 3 shows the amount of elution from the metal wiring measured by electrochemical measurement and the results of the migration resistance evaluation using the water drop test.

[0070] [Table 3]

[0071] From the results of the above examples and comparative examples, electrochemical measurements have shown that silver wiring with a silver elution amount of 400 ppb or less suppresses short circuits even in a water drop test that forcibly induces electrochemical migration, and has sufficient electrochemical migration resistance. Furthermore, the form of silver wiring with a silver elution amount of 400 ppb or less is preferably such that a portion of its surface is coated with copper, and the copper coated area is 0.07% or more of the surface area.

Claims

1. A metal wiring using silver, characterized in that the metal wiring has a surface composition in which the elution rate of eluted silver is 400 ppb or less, as determined by the following electrochemical measurement method. (Electrochemical measurement method) As the electrochemical measurement method, a three-electrode method consisting of a working electrode, a counter electrode, and a reference electrode is used, and a metal wire is used as the working electrode, which is exposed to the following electrolyte. The counter electrode is an insoluble platinum wire or plate, the reference electrode is a saturated silver-silver chloride electrode, and the reference electrode solution is a saturated KCl solution. An aqueous sodium sulfate solution (concentration: 100 ppm) was used as the electrolyte, and the working electrode and the counter electrode were immersed in the electrolyte and arranged facing each other. The electrolyte and the solution of the reference electrode are connected by a salt bridge made of saturated KCl solution solidified with agar, and the tip of the salt bridge on the electrolyte side is connected to a Luggin capillary filled with the electrolyte. A potentiostat (HA-501, manufactured by Hokuto Denko Corporation) was used as a control device for controlling the current and voltage, and the electrolysis measurement conditions were 1 mA / cm ２ A voltage is applied for 10 minutes so as to obtain a current density of 1000 ppm or less. Immediately after the voltage application, the working electrode is removed from the electrolyte, and the concentration of silver dissolved in the electrolyte is measured. An ICP-MS analyzer (Agilent 8900, manufactured by Agilent) is used to measure the concentration of silver dissolved in the electrolyte.

2. 2. The metal wiring according to claim 1, wherein the surface area of ​​the silver is covered with copper in an amount of 0.07% to 99.9% by surface area.

3. 3. The metal wiring according to claim 1, wherein the electric field strength between adjacent metal wirings is in the range of 0.001 V / μm to 400 V / μm.

4. 4. The metal wiring according to claim 1, wherein the distance (gap) between adjacent metal wirings is in the range of 0.1 μm to 20 mm.

5. A laminate comprising the metal wiring according to any one of claims 1 to 4.

6. A printed wiring board using the laminate according to claim 5.

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