Electronic circuit and method for manufacturing the same

Abstract

To provide an electronic circuit in which the occurrence of a silver erosion phenomenon is suppressed without the formation of a new layer or the use of a special material, and in which members are connected by direct soldering to a silver-containing conductive layer, and a method for manufacturing the same. [Solution] An electronic circuit comprising a component connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow, the component being one or more types selected from the group consisting of electronic components, connectors, and wiring boards.

Description

[Technical Field]

[0001] The present invention relates to an electronic circuit having components connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow. The present invention also relates to a method for manufacturing an electronic circuit, in which components are connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow. [Background technology]

[0002] A printed electronics method is used in which a circuit pattern is drawn by printing a metal paste composition on an insulating substrate to form a conductive printed wiring. As the metal paste composition used in the printed electronics method, a silver paste containing silver particles and a resin is generally used because of its low volume resistivity. The silver erosion phenomenon also occurs when silver-coated copper particles are used instead of silver particles, and when copper particles are used instead of silver particles, a copper erosion phenomenon similar to the silver erosion phenomenon occurs.

[0003] Various studies have been conducted to date to find a method for improving the silver erosion phenomenon in printed wiring formed from silver paste. Patent Document 1 discloses an example in which a wiring pattern is formed using silver paste, which is then dried and cured, and a nickel (Ni) layer is then formed as a diffusion prevention layer by electroless plating on the wiring pattern. Patent Document 2 discloses an electronic component mounting body having an adhesive reinforcing portion provided on one surface of an insulating resin substrate at least at the position of a land portion where an electronic component is mounted, a wiring pattern having a land portion made of a conductive resin provided on the adhesive reinforcing portion, and an electronic component mounted via a connection electrode portion formed on the land portion. Patent Document 3 discloses the use of cream solder, which is characterized by its alloy metal composition being composed of two or more types of alloys, each of which has the property of melting at a temperature higher than the reflow temperature, and which melts at a temperature close to the eutectic point solder. Patent Document 4 discloses the use of a solderable thermosetting conductive paint characterized by having as essential components an epoxy resin, a polyhydroxypolyether resin, a reactive diluent, a curing agent, conductive particles, and a dilution solvent. However, the methods of Patent Documents 1 and 2 require a step of forming a new layer, which is unsatisfactory in terms of cost and productivity. Also, the methods of Patent Documents 3 and 4 require a step of preparing a special material, which is unsatisfactory in terms of cost and productivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-3490 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-300038 [Patent Document 3] Japanese Patent Application Publication No. 2-117794 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-212492 Summary of the Invention [Problem to be solved by the invention]

[0005] When soldering is performed by solder reflow to connect components such as electronic parts, connectors, and wiring boards to printed wiring formed with such silver paste, the silver in the printed wiring formed with silver paste dissolves in the molten solder, a phenomenon known as silver erosion. When this phenomenon occurs, holes form in the printed wiring, resulting in poor soldering and the strength of the joint with the component cannot be maintained, resulting in low connection reliability. An object of the present invention is to provide an electronic circuit in which the occurrence of the silver erosion phenomenon is suppressed without the formation of a new layer or the use of a special material, and in which components are connected by direct soldering to a silver-containing conductive layer, and a method for manufacturing the same. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by (i) an electronic circuit including components connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow, and (ii) a method for manufacturing an electronic circuit in which components are connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow, and have thus completed the present invention. That is, the present invention is as follows. Item 1: An electronic circuit comprising a component connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow, the component being one or more types selected from the group consisting of electronic components, connectors, and wiring boards. Item 2: The electronic circuit according to Item 1, wherein the silver-containing conductive layer is formed on the substrate by printing. Item 3: The electronic circuit according to Item 1 or 2, wherein the substrate is made of a material having a melting point of 160° C. or less. Item 4: The electronic circuit according to any one of items 1 to 3, wherein the solder is lead-free solder. Item 5: The electronic circuit according to any one of Items 1 to 4, wherein the melting point of the solder is 140° C. or lower. Item 6: The electronic circuit according to any one of Items 1 to 5, wherein the silver-containing conductive layer contains one or more particles selected from the group consisting of silver particles, silver alloy particles, and silver-coated particles. Item 7: A method for manufacturing an electronic circuit, comprising connecting one or more members selected from the group consisting of electronic components, connectors, and wiring boards to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow. [Effects of the Invention]

[0007] The present invention provides an electronic circuit in which the occurrence of the silver erosion phenomenon is suppressed without the formation of a new layer or the use of a special material, and in which components are connected by direct soldering to a silver-containing conductive layer, and a method for manufacturing the same. The electronic circuit and manufacturing method thereof of the present invention do not require the formation of a new layer or the use of a special material to prevent the silver erosion phenomenon, and therefore the process is not complicated, which is advantageous in terms of productivity and cost. The electronic circuit and its manufacturing method of the present invention can suppress the occurrence of the silver erosion phenomenon, thereby suppressing soldering defects, maintaining the strength of the joint with members such as electronic components, and increasing the reliability of the solder joint between the silver-containing conductive layer and members such as electronic components. The electronic circuit and its manufacturing method of the present invention make it possible to use solders such as lead-free solders and solders with a high tin content for soldering printed circuits on which a silver-containing conductive layer is formed using silver paste or the like, thereby reducing the risks to workers and users and the environmental burden. The electronic circuit and manufacturing method of the present invention enable solder joints to be formed by heating for a short period of time, significantly improving work efficiency and also enabling the use of substrates with low heat resistance. The electronic circuit and its manufacturing method of the present invention enable soldering by simple means in the field of printed electronics, and are extremely useful as they can bring the technology much closer to practical implementation in society. The method for manufacturing an electronic circuit of the present invention is extremely useful for mass production of various electronic devices such as display devices, vehicle-related parts, IoT devices, and mobile communication systems, particularly when combined with printed electronics technology. [Brief explanation of the drawings]

[0008] [Figure 1] Photographs of the results of electromagnetic induction heating solder reflow in Example 1. [Figure 2] Photograph of the results of heating in an oven at 160°C in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] The electronic circuit and the method for manufacturing the electronic circuit of the present invention will now be described in detail. The present invention is not limited to the following disclosure, but may include various modifications, changes, and improvements to each disclosed element (including elements described in the claims, specification, and drawings) within the scope of the present invention and based on the technical idea of ​​the present invention. Furthermore, various combinations, substitutions, and selections of each disclosed element are possible within the scope of the technical idea of ​​the present invention.

[0010] [Electronic circuit] The electronic circuit of the present invention comprises a component connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow, the component being one or more members selected from the group consisting of electronic components, connectors, and wiring boards.

[0011] <Substrate> The substrate is not particularly limited as long as it is an insulator, and may be made of any of organic materials, inorganic materials, and organic-inorganic composite materials. Examples include resin films, paper, cloth, glass, and ceramics. A resin film is preferred because it is easy to impart the desired physical properties. Examples of resins that can be used to form the resin film include, without particular limitation, polyester resins, polyamideimide resins, polyimide resins, polyamide resins, polyether ether ketone resins, polysulfone resins, polyphenylene sulfide resins, polyether sulfone resins, fluororesins, ABS resins, polyphenylene oxide resins, acrylic resins, polycarbonate resins, polybutadiene resins, polyurethane resins, polyolefin resins, polyvinyl chloride resins, and polystyrene resins. The film may also be a mixture of these resins, and may contain, as necessary, functional materials such as colorants, ultraviolet absorbers, infrared reflective materials, light-scattering particles, etc. Furthermore, the film may be a laminate formed by arbitrarily combining these resin films, paper, cloth, glass, ceramics, etc.

[0012] In the present invention, the substrate is preferably made of a material having a melting point of 160° C. or less. Furthermore, the substrate is preferably made of a flexible material. This allows a general-purpose resin film such as a polyester resin, e.g., polyethylene terephthalate resin, to be used as the substrate, which is advantageous in terms of cost, etc. The thickness of the substrate is not particularly limited and can be, for example, 1 μm or more and 10 mm or less. When the substrate has both strength and flexibility, the thickness is, for example, 10 μm or more, preferably 20 μm or more, and, for example, 3 mm or less, preferably 1 mm or less. The optical properties of the substrate are not particularly limited, and may be any of colorless and transparent, colored and transparent, semi-transparent, and opaque. The shape of the substrate is not particularly limited and may be polygonal or circular. In addition, the substrate may have a three-dimensional structure by combining the same or different shapes.

[0013] The substrate of the present invention may have a conductive pad on a surface other than the surface on which the silver-containing conductive layer is provided, the conductive pad overlapping at least a portion of the silver-containing conductive layer. The conductive pad preferably has a size that covers the solder joint of a member to be solder-joined to the silver-containing conductive layer. The conductive pads are formed from metal materials including gold, silver, copper, aluminum, nickel, chromium, etc. The method for forming the conductive pads is not particularly limited, and they can be formed by coating or printing a metal paste, attaching a thin film of a metal material, etc. The thickness of the conductive pads is not particularly limited, and can be, for example, the same thickness as the silver-containing conductive layer.

[0014] <Silver-containing conductive layer> The silver-containing conductive layer is not particularly limited as long as it contains silver or a silver alloy, and can be formed by various means, such as (a) printing, applying, or drawing a conductive composition such as a conductive paste, conductive ink, or conductive paint containing silver or a silver alloy on a substrate, (b) providing a silver layer on a substrate using a silver foil or the like, followed by etching, (c) plating silver or a silver alloy, or (d) vapor-depositing silver or a silver alloy. Among these, it is preferable that the silver-containing conductive layer is formed on the substrate by printing. The printing method is not particularly limited, but screen printing, inkjet printing, flexographic printing, gravure printing, and gravure offset printing are preferred. Forming the silver-containing conductive layer by printing enables inexpensive and easy mass production. In the present invention, the silver-containing conductive layer on the substrate may be formed by forming a plating resist by printing or the like and then plating the resist, or by printing a plating seed layer and then plating the resist. These methods also allow for inexpensive and easy mass production.

[0015] When forming a silver-containing conductive layer by printing, it is preferable to use a conductive composition containing silver-based metal particles. The silver-based metal particles are not particularly limited as long as they contain metallic silver. Examples include metallic silver particles, silver alloy particles, and silver-coated particles. The silver-based metal particles can be used alone or in combination of two or more types. As the metallic silver particles, for example, those obtained by granulating metallic silver, or silver nanoparticles such as silver nanocolloid obtained by chemical reaction can be used. Examples of silver alloy particles include Ag-Cu alloys, Ag-Pd alloys, and Ag-Pt alloys, each having a silver content of 5.0% by mass or more and less than 99% by mass. The silver-coated particles are particles in which at least a portion of the particle surface is coated with metallic silver. Examples include particles in which silver is coated by plating, vapor deposition, or the like on one or more particles selected from the group consisting of metal particles (e.g., Cu particles, Pd particles, Al particles, alloy particles, etc.), organic polymer particles, inorganic particles such as glass and ceramic particles, and mineral particles. The thickness of the metallic silver coating is not particularly limited, and is, for example, 10 nm to 10 μm. The amount of the metallic silver coating is not particularly limited, and is, for example, 0.3 mass % to 30.0 mass % of the total amount of the silver-coated particles.

[0016] The silver-based metal particles may further contain other atoms that are inevitably mixed in. Examples of such other atoms include one or more selected from the group consisting of Mn, Sb, Si, K, Na, Li, Ba, Sr, Ca, Mg, Be, Zn, Pb, Cd, Tl, V, Al, Zr, W, Mo, Ti, Co, Sn, Cu, Ni, and Au. The content of such other atoms in the silver-containing particles is, for example, 3.0% by mass or less, preferably 1.0% by mass or less. The volume average particle size of the silver-based metal particles is not particularly limited. D50 is, for example, 1 nm or more and 50 μm or less. When D50 is 1 nm or more, oxidation resistance is improved and dispersibility and handling properties are improved. When D50 is 50 μm or less, the volume resistivity can be reduced and dispersibility and handling properties are improved.

[0017] The content of the silver-based metal particles in the conductive composition containing silver-based metal particles is not particularly limited and can be determined appropriately from the viewpoint of the conductivity of the conductive composition, etc. For example, the content is 5.0 mass % or more and 97.0 mass % or less of the total solid content in the conductive composition. The conductive composition containing silver-based metal particles may contain, in addition to the silver-based metal particles, one or more additive components selected from the group consisting of resins, solvents, metal particles other than silver-based metal particles, organic acid compounds, pigments, fillers, antioxidants, corrosion inhibitors, surfactants, antifoaming agents, dispersants, viscosity modifiers (thixotropy modifiers), adhesion promoters, coupling agents, anti-settling agents, pH adjusters (amine compounds), leveling agents, ultraviolet absorbers, antioxidants, flame retardants, etc., as needed. The conductive composition containing silver-based metal particles can be obtained by placing the above-mentioned components in a mixing container, mixing them using one or more types of mixers selected from the group consisting of a ball mill, a roll mill, a bead mill, a planetary mixer, a tumbler, a stirrer, an agitator, a mechanical homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, and the like, to form a varnish or paste.

[0018] The thickness of the silver-containing conductive layer can be set to an appropriate thickness depending on various applications, for example, 1 μm or more, preferably 2 μm or more, and for example, 300 μm or less. When the silver-containing conductive layer forms wiring, particularly a circuit, its width is 10 μm to 3 mm, preferably 30 μm to 2 mm. If the width is less than 10 μm, it may be difficult to form the wiring, and when the electronic circuit is deformed, the silver-containing conductive layer may not be able to withstand the generated stress and may break. If the width exceeds 3 mm, the amount of silver-containing conductive layer-forming material used increases, which is disadvantageous in terms of cost. The silver-containing conductive layer may have a terminal at any position, if necessary.

[0019] <Electromagnetic induction heating solder reflow> The electronic circuit of the present invention includes components connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow. Electromagnetic induction heating solder reflow (IH reflow) is a technology that places solder between a silver-containing conductive layer and a component, melting the solder with electromagnetic induction heating to join them. Electromagnetic induction heating utilizes the phenomenon of Joule heat being generated by passing eddy current through a conductive material, and by causing the conductive material to self-heat, it is possible to melt solder at any location in a short time. For example, IH reflow can be performed using an apparatus that includes, in a plan view, a coil having a space inside, a plurality of ferrites arranged in the space of the coil along the transport direction of the substrate, an adjustment mechanism that independently adjusts the distance between each ferrite and the silver-containing conductive layer formed on the substrate, and a power source that applies an AC voltage to the coil to inductively heat the silver-containing conductive layer formed on the substrate.

[0020] IH reflow can melt solder and form solder joints in a short time, so it is possible to use a substrate made of a material that does not have a very high heat resistance. Furthermore, by using a substrate having a conductive pad on a side other than the side on which the silver-containing conductive layer is provided, the silver-containing conductive layer and the member can be more reliably soldered by IH reflow. In electronic circuits, conductive pads provided on a side of a substrate other than the side on which the silver-containing conductive layer is provided are larger in volume than the silver-containing conductive layer, solder, etc., and therefore generate a large amount of heat due to electromagnetic induction heating. Heat generated in the conductive pads by electromagnetic induction heating is transferred to the solder through the substrate and the silver-containing conductive layer, efficiently heating and melting the solder and soldering components together. In this process, the heat generated in the conductive pads by electromagnetic induction heating is quickly transferred to the solder, which has high thermal conductivity, suppressing the temperature rise of the substrate, making it possible to construct the substrate from a material with low heat resistance.

[0021] In the present invention, even when a substrate is used that does not have a conductive pad on one side of the substrate other than the side on which the silver-containing conductive layer is provided, it is possible to efficiently solder-bond the silver-containing conductive layer and the component by IH reflow by extending the current-flow time (extending the heating time), increasing the current, reducing the resistance, etc.

[0022] <Solder> The type of solder used in the present invention is not particularly limited. In the present invention, it is preferable to use lead-free solder, which does not contain lead, in consideration of the effects on workers, users, environmental load, etc. There are no particular limitations on lead-free solder, so long as it does not contain more than the unavoidable amount of lead. For example, lead-free solder is specified in JIS Z 3282 (Solder - Chemical Composition and Shape). The lead content in lead-free solder is 0.10% by mass or less, preferably 0.05% by mass or less. The lead-free solder may be, for example, a lead-free solder based on tin (Sn) and containing at least one selected from the group consisting of silver (Ag), antimony (Sb), bismuth (Bi), copper (Cu), indium (In), zinc (Zn), nickel (Ni), germanium (Ge), phosphorus (P), gallium (Ga), and aluminum (Al) (for example, Sn-Bi based, Sn-Cu based, Sn-Sb based, Sn-Z based, etc.). Examples of suitable lead-free solder include Sn-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Zn-Bi-based, Sn-Ag-In-Bi-based, Sn-Zn-Al-based, Sn-Ag-Bi-based, Sn-Ag-Cu-Bi-based, Sn-Ag-Cu-Bi-In-Sb-based, etc.), Bi-based lead-free solder (Bi-In-based, etc.), and In-based lead-free solder (In-Ag-based, In-Bi-based, etc.).

[0023] The melting point of lead-free solder is, for example, 300°C or lower, preferably 220°C or lower, more preferably 140°C or lower, and preferably 50°C or higher. If the melting point of lead-free solder exceeds 300°C, components such as circuit boards and electronic components may be thermally damaged or deteriorated. If the melting point of lead-free solder is lower than 50°C, the mechanical strength may be weakened, and the reliability of the conductive connection may be reduced. If the melting point of the solder is set to 140° C. or less, even a resin material with low heat resistance can be used for the substrate. Examples of such low-melting-point solder include Sn—Bi solder and Sn—In solder.

[0024] <Components> In the electronic circuit of the present invention, the member connected to the silver-containing conductive layer on the substrate via solder by electromagnetic induction heating solder reflow is one or more members selected from the group consisting of electronic components, connectors, and wiring boards. The electronic components are not particularly limited and can be selected appropriately depending on the application of the electronic circuit, and two or more different types can also be mounted. Examples of electronic components include (i) semiconductor elements such as insulated gate bipolar transistor (IGBT) elements, intelligent power module (IPM) elements, metal oxide field effect transistor (MOSFET) elements, LED elements, EL elements, freewheeling diode (FWD) elements, giant transistor (GTR) elements, and Schottky barrier diodes (SBD); (ii) sensors for temperature, pressure, electric field, magnetism, light, etc.; and (iii) solar cell elements. The connector is not particularly limited as long as it is a member for connecting the flow of power or electrical signals between the silver-containing conductive layer on the substrate and a member such as an electronic component, etc. It may be a connection terminal or a lead wire. Examples of wiring boards include wiring boards (electronic circuits) formed separately for each function, or connection terminals of wiring boards.

[0025] <Applications of electronic circuits> The electronic circuit of the present invention can be used in a wide range of applications without any particular limitations, including, for example, as an electronic circuit in a printed electronics material, and can be used in various electronic devices such as display devices, vehicle-related parts, IoT devices, and mobile communication systems. In particular, when combined with printed electronics technology, it can be used in a variety of products for electronic circuits, electrodes, wiring, antennas, etc. For example, it can be used as electronic circuits, electrodes, antennas, wiring, etc. in displays, FPC jumper circuits, membrane switches combined with PET film, medical biosensors, wearable devices, in-vehicle sensors, RFID (electronic tags), in-vehicle communication devices, mobile devices (smartphones, etc.), and planar heating elements.

[0026] [Electronic circuit manufacturing method] The method for manufacturing an electronic circuit of the present invention is a method for manufacturing an electronic circuit in which one or more members selected from the group consisting of electronic components, connectors, and wiring boards are connected to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow. The substrate, silver-containing conductive layer, electromagnetic induction heating solder reflow, and member may be the same as those described in the [Electronic Circuit]. [Example]

[0027] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0028] [Example 1] A silver-containing conductive layer having a thickness of approximately 20 μm was formed on a substrate made of a 100 μm polyethylene terephthalate resin film by printing using a silver particle-containing paste (Dotite manufactured by Fujikura Chemical Co., Ltd.). 0.05g of tin-bismuth low-melting-point solder (manufactured by Harima Chemicals) was placed on the silver-containing conductive layer and heated for 6 seconds using electromagnetic induction solder reflow (IH reflow) with a working distance of 10mm and a gap of 2.9mm. After 6 seconds, the temperature was 170°C, and the solder had melted and become integrated with the silver-containing conductive layer. Furthermore, no solder penetration of the silver-containing conductive layer due to silver erosion was visually observed. The results are shown in Figure 1.

[0029] [Comparative Example 1] In Example 1, the heating by IH reflow was changed to heating in an oven with an internal temperature set to 160°C. When the heating time was 10 seconds, the solder did not melt and was not integrated with the silver-containing conductive layer. When the heating time was 30 seconds, the solder partially melted and solder penetration through the silver-containing conductive layer due to silver erosion was visually observed. When the heating time was 120 seconds, the solder completely melted and solder penetration through the silver-containing conductive layer due to silver erosion was visually observed. The results are shown in Figure 2.

[0030] [Example 2] The silver particle-containing paste was replaced with a silver-coated copper-containing paste, and a copper pad was attached to a side of the substrate other than the side on which the silver-containing conductive layer was provided. Heating was performed by IH reflow in the same manner as in Example 1. The temperature after 6 seconds was 169°C, and the solder had melted and was integrated with the silver-containing conductive layer. Furthermore, no solder penetration of the silver-containing conductive layer due to silver erosion was visually observed.

[0031] Comparative Example 2 Except for replacing the silver particle-containing paste with a silver-coated copper-containing paste, heating was performed in an oven with an internal temperature set to 160°C in the same manner as in Comparative Example 1. When the heating time was 10 seconds, the solder did not melt and was not integrated with the silver-containing conductive layer. When the heating time was 60 seconds, the solder partially melted and thinning of the silver-containing conductive layer due to silver erosion was visually observed. When the heating time was 120 seconds, the solder completely melted and thinning of the silver-containing conductive layer due to silver erosion was visually observed.

[0032] The results of Examples 1 and 2 and Comparative Examples 1 and 2 show that by using IH reflow, it is possible to suppress the occurrence of the silver erosion phenomenon without forming a new layer or using a special material, and it is possible to solder components directly to the silver-containing conductive layer.

Claims

1. a member connected to the silver-containing conductive layer on the substrate via solder by electromagnetic induction heating solder reflow; An electronic circuit, wherein the member is one or more members selected from the group consisting of electronic components, connectors, and wiring boards.

2. 2. The electronic circuit of claim 1, wherein the silver-containing conductive layer is formed on the substrate by printing.

3. 3. The electronic circuit according to claim 1, wherein the substrate is made of a material having a melting point of 160° C. or less.

4. 4. The electronic circuit according to claim 1, wherein the solder is a lead-free solder.

5. 5. The electronic circuit according to claim 1, wherein the melting point of the solder is 140° C. or lower.

6. 6. The electronic circuit according to claim 1, wherein the silver-containing conductive layer contains at least one kind of particles selected from the group consisting of silver particles, silver alloy particles, and silver-coated particles.

7. A method for manufacturing an electronic circuit, comprising connecting one or more members selected from the group consisting of electronic components, connectors, and wiring boards to a silver-containing conductive layer on a substrate via solder by electromagnetic induction heating solder reflow.

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