Method for manufacturing solid electrolytic capacitor

Abstract

This method for manufacturing a solid electrolytic capacitor comprises: a step for forming a solid electrolyte layer 39 on a positive electrode foil 31 with a dielectric layer 33 interposed therebetween; a step for forming a thermoplastic-resin-containing silver layer 43 on the solid electrolyte layer 39 to form a solid electrolytic capacitor element 30; a step for stacking a plurality of solid electrolytic capacitor elements 30 to form a stack 110; and a step for thermocompression-bonding the stack 110 to remelt the thermoplastic resin and integrate the plurality of silver layers 43 of the plurality of solid electrolytic capacitor elements 30 so that no interface of the silver layers 43 is formed in the entirety of a region between the adjacent solid electrolytic capacitor elements 30.

Description

Manufacturing method for solid electrolytic capacitors

[0001] The present invention relates to a method for manufacturing a solid electrolytic capacitor.

[0002] Patent Document 1 describes a solid electrolytic capacitor having a structure in which a plurality of capacitor elements are stacked, at least one of the capacitor elements being provided in contact with a cathode lead electrode, and having a sealing resin that seals the plurality of capacitor elements, wherein each of the capacitor elements includes a valve action metal substrate having a porous layer on its surface, a dielectric layer disposed on the porous layer, a solid electrolyte layer formed on the dielectric layer, and a cathode layer formed on the solid electrolyte layer, wherein the cathode layers of the stacked capacitor elements are directly bonded to each other at at least a portion of a surface of the cathode layer, and at least a portion of a surface of the cathode layer of the capacitor element provided in contact with the cathode lead electrode is directly bonded to the cathode lead electrode, and a cathode external electrode containing a conductive resin is formed on the surface of the sealing resin, and the cathode external electrode is connected to the cathode layer via the cathode lead electrode.

[0003] Patent Document 2 describes a method for manufacturing a solid electrolytic capacitor, which includes a preparation step of preparing an element precursor including a valve metal base, a dielectric layer formed on the valve metal base, a solid electrolyte layer formed on the dielectric layer, and a conductive paste layer formed on the solid electrolyte layer, the conductive paste layer being made of a conductive paste; and a lamination step of laminating a plurality of the element precursors so that the conductive paste layers of adjacent element precursors are in contact with each other before the conductive paste constituting the conductive paste layers dries, to obtain a laminate.

[0004] Japanese Patent No. 6776731 Japanese Patent Application Laid-Open No. 2007-194430

[0005] Patent Document 1 describes that the cathode layers of stacked capacitor elements are directly bonded to each other at least in part of the surfaces of the cathode layers.

[0006] Patent Document 2 describes that multiple element precursors are stacked before the conductive paste that constitutes these conductive paste layers dries, and therefore the conductive paste layers of adjacent element precursors are integrated by stacking.

[0007] However, in Patent Document 1, the solid electrolyte layer and the carbon and silver layers serving as the cathode layers are both formed by immersion in a liquid material such as a polymer liquid or paste, which results in the outer surfaces of the formed cathode layers being slightly bulged outward, and therefore, in some cases, the cathode layers of stacked capacitor elements cannot be directly bonded to each other over the entire surface of the cathode layers.

[0008] Furthermore, in Patent Document 2, the solid electrolyte layer and the carbon layer and silver layer serving as the conductive paste layer are formed by immersion in a liquid material, as in Patent Document 1, and so there are also cases where the conductive paste layers cannot be integrated together over the entire surface of the conductive paste layers.

[0009] Therefore, conventional solid electrolytic capacitors have room for improvement in terms of more reliably integrating the cathode layers of multiple solid electrolytic capacitor elements over a wide area and more reliably reducing the ESR (equivalent series resistance) in the stack of solid electrolytic capacitor elements.

[0010] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor that can more reliably reduce the ESR.

[0011] The method for manufacturing a solid electrolytic capacitor of the present invention includes the steps of forming a solid electrolyte layer on an anode foil via a dielectric layer, forming a silver layer containing a thermoplastic resin on the solid electrolyte layer to form a solid electrolytic capacitor element, stacking a plurality of solid electrolytic capacitor elements to form a laminate, and thermocompression bonding the laminate to remelt the thermoplastic resin and integrate the multiple silver layers of the multiple solid electrolytic capacitor elements so that no silver layer interface is formed across the entire area between adjacent solid electrolytic capacitor elements.

[0012] According to the present invention, it is possible to provide a method for manufacturing a solid electrolytic capacitor that can more reliably reduce the ESR.

[0013] FIG. 1 is a plan view schematically showing an example of an assembly of solid electrolytic capacitor elements (strip structure type) used in a method for manufacturing a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing an example of a process for performing a masking treatment for chemical conversion on element portions of an assembly of solid electrolytic capacitor elements. FIG. 3 is a plan view schematically showing an example of a process for performing a masking treatment for polarization (polarization treatment) on element portions of an assembly of solid electrolytic capacitor elements. FIG. 4 is a plan view schematically showing an example of a process for forming a solid electrolyte layer on element portions of an assembly of solid electrolytic capacitor elements. FIG. 5 is a cross-sectional view taken along line X-X of the element portion shown in FIG. 4. FIG. 6 is an enlarged cross-sectional view of the polarized portion of the element portion shown in FIG. 5. FIG. 7 is a plan view schematically showing another example of an assembly of solid electrolytic capacitor elements (double-door structure type) used in a method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 8 is a plan view schematically showing yet another example of an assembly of solid electrolytic capacitor elements (strip structure type) used in a method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 9 is a plan view schematically showing yet another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 10 is a plan view schematically showing an example of a process for forming a carbon layer on the element portion of the assembly of solid electrolytic capacitor elements. FIG. 11 is a plan view schematically showing an example of a process for forming a silver layer on the element portion of the assembly of solid electrolytic capacitor elements. FIG. 12 is a schematic diagram of an example of a roller transfer device used for roller transfer of cathode paste. FIG. 13 is a schematic diagram of another example of a roller transfer device used for roller transfer of cathode paste. FIG. 14 is a perspective view schematically showing the appearance of one side of the element portion of the assembly of solid electrolytic capacitor elements to which the cathode paste has been roller-transferred. FIG. 15 is a perspective view schematically showing the appearance of the other side of the element portion of the assembly of solid electrolytic capacitor elements to which the cathode paste has been roller-transferred. FIG. 16 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor element produced by the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present invention, and corresponds to the cross-sectional view shown in FIG. 5. FIG. 17 is a cross-sectional view schematically showing an example of a process for forming a laminate by stacking a plurality of solid electrolytic capacitor elements.Fig. 18 is a cross-sectional view schematically showing an example of a laminate in which a plurality of silver layers are integrated. Fig. 19 is a side view schematically showing an example of a laminate in which a plurality of silver layers are integrated. Fig. 20 is an end view schematically showing one example of a laminate in which a plurality of silver layers are integrated. Fig. 21 is an end view schematically showing the other example of a laminate in which a plurality of silver layers are integrated. Fig. 22 is a main surface view schematically showing an example of a laminate in which a plurality of silver layers are integrated. Fig. 23 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor.

[0014] The following describes a method for manufacturing a solid electrolytic capacitor. However, the present invention is not limited to the following configurations, and can be modified as appropriate within the scope of the present invention. Note that a combination of two or more of the individual desirable configurations described below also falls within the scope of the present invention.

[0015] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0016] In this specification, terms indicating the relationship between elements (e.g., "parallel," "perpendicular," "orthogonal," etc.) and terms indicating the shapes of elements not only mean the literal strict form, but also mean a range that is substantially equivalent, for example, a range that includes a difference of about a few percent.

[0017] A method for manufacturing a solid electrolytic capacitor according to an embodiment of the present invention includes the steps of forming a solid electrolyte layer on an anode foil via a dielectric layer, forming a silver layer containing a thermoplastic resin on the solid electrolyte layer to form a solid electrolytic capacitor element, stacking a plurality of solid electrolytic capacitor elements to form a laminate, and thermocompression-bonding the laminate to remelt the thermoplastic resin and integrate the silver layers of the plurality of solid electrolytic capacitor elements so that no silver layer interface is formed across the entire area between adjacent solid electrolytic capacitor elements.

[0018] In this way, by forming a silver layer containing a thermoplastic resin on a solid electrolyte layer, stacking multiple solid electrolytic capacitor elements each having such a silver layer to form a laminate, and then thermocompression bonding the laminate to remelt the thermoplastic resin, it is possible to more reliably integrate the multiple silver layers so that no silver layer interface is formed across the entire area between adjacent solid electrolytic capacitor elements. This makes it possible to more reliably achieve a low ESR as a laminate of solid electrolytic capacitor elements. In addition, the moisture resistance reliability of the laminate can be improved.

[0019] Hereinafter, the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present invention will be described in more detail with reference to the drawings.

[0020] FIG. 1 is a plan view schematically showing an example of an assembly of solid electrolytic capacitor elements (strip structure type) used in a manufacturing method for a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing an example of a process of performing a masking treatment for chemical conversion on element portions of an assembly of solid electrolytic capacitor elements. FIG. 3 is a plan view schematically showing an example of a process of performing a masking treatment for polarization (polarization treatment) on element portions of an assembly of solid electrolytic capacitor elements. FIG. 4 is a plan view schematically showing an example of a process of forming a solid electrolyte layer on element portions of an assembly of solid electrolytic capacitor elements. FIG. 5 is a cross-sectional view taken along line X-X of the element portion shown in FIG. 4. FIG. 6 is an enlarged cross-sectional view of the polarization portion of the element portion shown in FIG. 5.

[0021] 1 to 4, a solid electrolyte layer 39 is formed on the anode foil 31 via the dielectric layer 33, as shown in FIGS.

[0022] In this embodiment, an example of manufacturing a solid electrolytic capacitor using an assembly 10 of solid electrolytic capacitor elements having a plurality of element portions 11 as shown in FIG. 4 will be described, but the solid electrolytic capacitor of the present invention may also be manufactured using a single solid electrolytic capacitor element.

[0023] Each element portion 11 has a pair of main surfaces 11a and 11b, a pair of side surfaces 11c and 11d, and one end surface 11e.

[0024] 5 and 6 , each element unit 11 has a rectangular flat plate shape in a plan view, and includes an anode foil 31 having a porous surface made of a valve action metal substrate, a dielectric layer 33 (see FIG. 6 , not shown in FIG. 5 ) provided on the surface of the anode foil 31, two insulating mask materials 35 and 37 that are annular (extending in a strip-like shape) insulating members provided around the anode foil 31 with the dielectric layer 33 interposed therebetween, and a solid electrolyte layer 39 provided on the anode foil 31 with the dielectric layer 33 interposed therebetween, on the end face 11 e side of the insulating mask material 37. In each element unit 11, the solid electrolyte layer 39 faces the anode foil 31 with the dielectric layer 33 interposed therebetween.

[0025] As shown in FIG. 4, the solid electrolytic capacitor element assembly 10 includes a belt-shaped holding portion 13 in which a plurality of element portions 11 are connected at regular intervals.

[0026] Each step shown in FIGS. 1 to 4 will be described below.

[0027] First, as shown in FIG. 1 , an anode foil 31 is cut into the shape of a solid electrolytic capacitor element (preferably rectangular) by laser processing, punching, or the like, and then welded to a conveying substrate 15 serving as a holding portion 13, for example, to produce an assembly 10 of solid electrolytic capacitor elements.

[0028] As described above, the assembly 10 of solid electrolytic capacitor elements includes a conveying substrate 15 made of a metal or resin material that is provided parallel to the conveying direction in which the assembly 10 is conveyed in the cathode paste transfer process described below, and the element portion 11 is provided on only one side of the conveying substrate 15. The side surfaces 11c and 11d of the element portion 11 extend in a direction perpendicular to the conveying direction (holding portion 13), and the end surface 11e of the element portion 11 extends parallel to the conveying direction (holding portion 13).

[0029] A valve metal substrate having a porous portion on its surface is used as the anode foil 31 constituting the element portion 11. As shown in Fig. 6, the anode foil 31 is a thin film (foil) having a rectangular shape in a plan view, and including a metal substrate portion 31a and a porous portion 31b on the metal substrate portion 31a. A dielectric layer 33 is provided on the surface of the porous portion 31b.

[0030] In this specification, the term "plan view" means a view from the normal direction of the main surface of the anode foil.

[0031] The valve metal substrate is made of a valve metal such as an elemental metal such as aluminum, tantalum, niobium, titanium, or zirconium, or an alloy containing these metals.

[0032] The valve metal substrate may be formed of a core and a porous portion provided on at least one of the main surfaces of the core, and may be formed from a metal foil having an etched surface, a metal foil having a porous sintered powder body formed on the surface, or the like.

[0033] FIG. 7 is a plan view schematically showing another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention.

[0034] The solid electrolytic capacitor element assembly 10 is not particularly limited to the strip structure type shown in Fig. 1, but may also have a double-open structure (fishbone structure) type as shown in Fig. 7. In this case, the element portions 11 are provided on both sides of the conveying substrate 15.

[0035] Examples of the metal material for the transport substrate 15 include aluminum and stainless steel. Examples of the resin material for the transport substrate 15 include fluororesin, phenolic resin, and glass-epoxy resin composites.

[0036] In any case, unlike the anode foil 31, the transport base material 15 is a highly rigid member, and can prevent the solid electrolytic capacitor element assembly 10 from flapping even in the cathode paste transfer step described below.

[0037] Fig. 8 is a plan view schematically showing yet another example (strip structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. Fig. 9 is a plan view schematically showing yet another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention.

[0038] The solid electrolytic capacitor element assembly 10 does not necessarily have to include the conveying substrate 15 shown in FIGS. 1 and 7 , but may instead include, as shown in FIGS. 8 and 9 , bones 17 as holding portions 13, which are arranged parallel to the conveying direction in which the assembly 10 is conveyed in the cathode paste transfer step described below. In this case, the element portions 11 contain the same material as the bone portions 17. Specifically, both are made of the same valve metal substrate and are formed by cutting the same anode foil. The element portions 11 may be provided on only one side of the bone portion 17 (strip structure type) as shown in FIG. 8 , or may be provided on both sides of the bone portion 17 (double-open structure (fishbone structure) type) as shown in FIG. 9 .

[0039] Next, as shown in FIG. 2, an insulating mask material 35 is applied to the element portion 11, and a masking process for chemical conversion is carried out.

[0040] The insulating mask material 35 is formed by applying a mask material such as a composition containing an insulating resin by screen printing, roller transfer, dispenser, inkjet printing, etc. Examples of insulating resins include polyphenylsulfone (PPS), polyethersulfone (PES), cyanate ester resin, fluororesin (tetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylether copolymer, etc.), a composition consisting of soluble polyimidesiloxane and epoxy resin, polyimide resin, polyamideimide resin, and derivatives or precursors thereof.

[0041] When the bone portion 17 is used instead of the transport substrate 15, the entire bone portion 17 is subjected to chemical conversion treatment, and the polarization of the anode and cathode is carried out separately, so that the masking treatment for chemical conversion is not required.

[0042] Next, the solid electrolytic capacitor element assembly 10 is subjected to a chemical conversion treatment (anodic oxidation treatment). This forms an oxide film that serves as a dielectric layer on the surface of the valve metal substrate. For example, the dielectric layer is made of aluminum oxide. At this time, an oxide film is also formed on the pair of side faces 11c and 11d and one end face 11e of the element portion 11 that has been cut by laser processing, punching, or the like.

[0043] Alternatively, a chemically-formed foil on which aluminum oxide has already been formed may be used as the valve metal substrate. In this case, too, a chemical conversion treatment is performed on the valve metal substrate after cutting, thereby forming an oxide film on the pair of side faces 11c and 11d and one end face 11e of the cut element portion 11.

[0044] Next, as shown in FIG. 3, an insulating mask material 37 is applied to the element portion 11, and a masking process (polarization process) for polarization of the anode portion and the cathode portion is performed.

[0045] The insulating mask material 37 is formed by applying a mask material such as a composition containing an insulating resin by screen printing, roller transfer, dispenser, inkjet printing, etc. Examples of insulating resins include polyphenylsulfone (PPS), polyethersulfone (PES), cyanate ester resin, fluororesin (tetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylether copolymer, etc.), a composition consisting of soluble polyimidesiloxane and epoxy resin, polyimide resin, polyamideimide resin, and derivatives or precursors thereof.

[0046] Next, as shown in FIG. 4 , a solid electrolyte layer 39 is formed on the dielectric layer of the element portion 11. Specifically, the element portion 11 is immersed in a treatment liquid containing a solid electrolyte, thereby impregnating the porous portion of the valve metal substrate with the treatment liquid. After immersion for a predetermined time, the element portion 11 is removed from the treatment liquid and dried at a predetermined temperature for a predetermined time. The solid electrolyte layer 39 is formed by repeating the immersion in the treatment liquid, removal, and drying process a predetermined number of times. The solid electrolyte layer 39 may also be formed by repeating a predetermined number of times of immersion in a treatment liquid containing a solid electrolyte precursor (a monomer that becomes a solid electrolyte by oxidative polymerization) and further immersion in a treatment liquid containing an oxidizing agent that oxidatively polymerizes the solid electrolyte precursor.

[0047] The solid electrolyte layer 39 is formed over the entire device portion 11 on the end face 11e side of the insulating mask material 37. The solid electrolyte layer 39 may be in contact with the insulating mask material 37, as shown in FIGS.

[0048] The solid electrolyte layer 39 is provided on the dielectric layer 33. As shown in Fig. 6 , the solid electrolyte layer 39 is preferably provided so as to fill a plurality of pores (recesses) in the porous portion 31b of the anode foil 31. However, it is sufficient that the solid electrolyte layer 39 covers part of the outer surface of the dielectric layer 33, and there may be pores (recesses) in the porous portion 31b of the anode foil 31 that are not filled with the solid electrolyte layer 39.

[0049] As a treatment liquid containing a solid electrolyte, for example, a dispersion of a conductive polymer such as polypyrroles, polythiophenes, or polyanilines is used. Among these, polythiophenes are preferred, and poly(3,4-ethylenedioxythiophene), also known as PEDOT, is particularly preferred. Furthermore, the conductive polymer may contain a dopant such as polystyrene sulfonic acid (PSS). A conductive polymer film can be formed by applying a dispersion of a conductive polymer to the outer surface of the dielectric layer and drying it. Alternatively, a liquid containing a polymerizable monomer, such as 3,4-ethylenedioxythiophene, may be used as a treatment liquid containing a solid electrolyte precursor. The polymerizable monomer may contain a dopant, such as polystyrene sulfonic acid. Furthermore, the treatment liquid containing a solid electrolyte precursor may contain an oxidizing agent. This treatment liquid can be applied to the outer surface of the dielectric layer to form a conductive polymer film by oxidative polymerization (chemical polymerization). This conductive polymer film becomes the solid electrolyte layer 39.

[0050] FIG. 10 is a plan view schematically showing an example of a process for forming a carbon layer on the element portion of an assembly of solid electrolytic capacitor elements.

[0051] Next, a carbon paste is transferred as a cathode paste to each element portion 11 of the solid electrolytic capacitor element assembly 10 by roller transfer, forming a carbon layer 41 on each element portion 11 as shown in FIG.

[0052] The carbon layer 41 is formed over the entire element portion 11 on the end face 11e side of the insulating mask material 37. The carbon layer 41 may completely cover the solid electrolyte layer 39, or may be in contact with the insulating mask material 37, as shown in FIG.

[0053] The method for forming the carbon layer 41 (the method for applying the carbon paste) is not particularly limited to roller transfer and may be, for example, immersion, but roller transfer or screen printing is preferred. This makes it possible to more easily and reliably form the silver layer 43 having a flat outer surface on the carbon layer 41. Furthermore, the application of the carbon paste itself may be omitted.

[0054] FIG. 11 is a plan view schematically showing an example of a process for forming a silver layer on the element portion of an assembly of solid electrolytic capacitor elements.

[0055] Next, a silver layer 43 containing a thermoplastic resin is formed on the solid electrolyte layer 39, and a solid electrolytic capacitor element 30 is formed in each element portion 11. More specifically, a silver paste is transferred as a cathode paste to each element portion 11 of the solid electrolytic capacitor element assembly 10 by roller transfer, and a silver layer 43 is formed in each element portion 11, as shown in Fig. 11. The silver layer 43 may have a flat outer surface, which makes it possible to more reliably integrate the multiple silver layers so that no silver layer interface is formed over the entire area between adjacent solid electrolytic capacitor elements.

[0056] In this specification, the term "silver layer having a flat outer surface" means that the entire area of ​​a pair of main surfaces of the silver layer, which face each other in the stacking direction of the solid electrolytic capacitor element, are both flat and parallel to each other. More specifically, the outer surface of the silver layer may be determined to be flat when the thickness of the cathode portion of the solid electrolytic capacitor element is measured at multiple locations and the standard deviation is 30 μm or less, preferably 20 μm or less. Here, the "multiple locations" may be five locations, namely, the top, middle, bottom, left, and right of the cathode portion of the solid electrolytic capacitor element.

[0057] In the present invention, the "silver layer having a flat outer surface" refers to a silver layer having at least a dry outer surface. That is, a silver layer having a flat outer surface is typically in a state after a silver paste supplied onto a solid electrolyte layer has been dried or pre-dried. Therefore, in this embodiment, the solid electrolytic capacitor element assembly 10 and the solid electrolytic capacitor element 30 are easily handled in the subsequent steps.

[0058] The silver layer 43 is formed over the entire element portion 11 on the side of the end face 11 e closer to the insulating mask material 37 .

[0059] Furthermore, the silver layer 43 is preferably formed so that the solid electrolyte layer 39 and the carbon layer 41 are not exposed on the outer surface of the solid electrolytic capacitor element 30. That is, the silver layer 43 preferably completely covers the carbon layer 41, as shown in FIG. 11 . If the carbon layer 41 is not formed, the silver layer 43 preferably completely covers the solid electrolyte layer 39. This can further improve the moisture resistance reliability of the laminate of the solid electrolytic capacitor element 30. Furthermore, the silver layer 43 is preferably in contact with the insulating mask material 37.

[0060] The method for forming the silver layer 43 (the method for applying the silver paste) is not particularly limited to roller transfer, but roller transfer or screen printing is preferred. These methods are suitable for forming a silver layer 43 with a flat outer surface.

[0061] Here, the roller transfer device used for roller transfer of the cathode paste and the roller transfer step of the cathode paste will be further described with reference to FIG. 12 .

[0062] FIG. 12 is a schematic diagram of an example of a roller transfer device used for roller transfer of cathode paste.

[0063] 12 includes an unwinding section 210, a vertical conveying type roller transfer section 220A, a preliminary drying section 230, a drying section 240, and a winding section 250, and the assembly 10 of solid electrolytic capacitor elements unwound from the unwinding section 210 is transported through the roller transfer section 220A, the preliminary drying section 230, and the drying section 240 in this order, and then wound up by the winding section 250. The assembly 10 is transported through each section at a predetermined transport speed.

[0064] Unwinding unit 210 unwinds assembly 10 of solid electrolytic capacitor elements wound in a roll around a winding reel. Roller transfer unit 220A transfers cathode paste to element portions 11 of assembly 10 while transporting assembly 10 supplied from unwinding unit 210. Pre-drying unit 230 pre-dries the transferred cathode paste by transporting assembly 10 to which element portions 11 have been transferred. Drying unit 240 heats and dries the pre-dried cathode paste while transporting assembly 10. Winding unit 250 winds assembly 10, on which the cathode paste has been dried, into a roll around a winding reel.

[0065] The roller transfer unit 220A has a plurality of transport rollers 221 that transport the assembly 10 of solid electrolytic capacitor elements on a transport path formed by the assembly 10, a pair of rollers (transfer rollers) 222 between which the element parts 11 of the assembly 10 are transported, and a dispenser 223 and a squeegee 224 provided on each roller 222.

[0066] The pair of rollers 222 are provided on both sides of the assembly 10 of solid electrolytic capacitor elements transported by the transport roller 221. Each roller 222 has a circumferential surface made of metal or rubber, and a groove is formed in the circumferential surface to supply the cathode paste. The depth of the groove can be set appropriately taking into account the desired coating thickness of the cathode paste. Note that the circumferential surface of each roller 222 does not need to have a groove, and may have a smooth circumferential surface. The circumferential surfaces of the pair of rollers 222 are configured to press against both main surfaces 11a and 11b of the element portion 11 of the assembly 10. This pressing contact transfers the cathode paste on the circumferential surfaces of the pair of rollers 222 onto both main surfaces 11a and 11b of the element portion 11 of the assembly 10.

[0067] Each dispenser 223 supplies an appropriate amount of cathode paste to the corresponding roller 222, and the cathode paste does not drip from the circumferential surface of the roller 222. This makes it possible to minimize the amount of cathode paste consumed.

[0068] Each squeegee 224 is disposed a predetermined distance from the circumferential surface of the corresponding roller 222, and adjusts the amount of cathode paste to an appropriate amount by scraping off the cathode paste adhering to the circumferential surface of the corresponding roller 222. Note that if the cathode paste has a low viscosity, for example, scraping by squeegee 224 may not be necessary.

[0069] Using the roller transfer device 200 shown in FIG. 12, first, carbon paste is transferred to the solid electrolyte layer 39 of the element portion 11 of the assembly 10 shown in FIG. 4, and then the carbon paste is dried to form a carbon layer 41 (see FIG. 10).

[0070] Similarly, using the roller transfer device 200 shown in Figure 12, silver paste is transferred to the carbon layer 41 of the element portion 11 of the assembly 10 shown in Figure 10, and then the silver paste is dried to form a silver layer 43 (see Figure 11).

[0071] In this way, the step of forming the silver layer 43 preferably includes a step of drying the silver paste. Here, "drying the silver paste" means, as described above, drying the silver paste so that at least the outer surface of the silver layer 43 is in a dry state, and includes the case of provisionally drying the silver paste.

[0072] The drying temperature t of the silver paste can be set as appropriate, but is preferably 130° C. or higher and 180° C. or lower, and more preferably 140° C. or higher and 160° C. or lower. The drying time of the silver paste can also be set as appropriate, but is preferably 20 minutes or higher and 90 minutes or lower, and more preferably 30 minutes or higher and 60 minutes or lower.

[0073] More specifically, first, cathode paste is supplied onto a pair of rollers 222 of roller transfer device 200. At this time, while each roller 222 is rotated along the transport direction of assembly 10 of solid electrolytic capacitor elements, cathode paste is supplied onto each roller 222 from each dispenser 223, and the amount of cathode paste is adjusted by each squeegee 224.

[0074] The carbon paste is a conductive paste containing carbon particles as a conductive component and a resin component such as an epoxy resin or a phenolic resin.

[0075] The viscosity and thixotropy of the carbon paste are set taking into consideration the shear rate of roller transfer, etc. Furthermore, since it is used in roller transfer, it is preferable to use a high-boiling point solvent as the organic solvent. By using a high-boiling point solvent, it is possible to impart slow drying properties and prevent drying on the circumferential surface of the roller.

[0076] The silver paste is a conductive paste containing silver particles as a conductive component and a resin component.

[0077] The silver paste also contains at least a thermoplastic resin as a resin component, thereby forming a silver layer containing a thermoplastic resin.

[0078] A saturated copolymer polyester resin is suitable as this thermoplastic resin. Furthermore, it is preferable that this thermoplastic resin has a glass transition temperature of 0°C or lower and exhibits a weight loss rate of 0.1% or lower when heated from 25°C to 200°C, as measured by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). Such a thermoplastic resin is suitable for integrating multiple silver layers of multiple solid electrolytic capacitor elements.

[0079] The glass transition temperature of the thermoplastic resin is preferably 25°C or lower, and more preferably 0°C or lower.

[0080] The thermoplastic resin may be amorphous and have no glass transition point.

[0081] The weight loss rate of the thermoplastic resin when heated from 25° C. to 200° C. by TG-DTA is preferably 0.1% or less, more preferably 0.05% or less.

[0082] The content of the thermoplastic resin in the total amount of the silver paste can be, for example, 5% by mass or more and 25% by mass or less.

[0083] The viscosity and thixotropy of the silver paste are set taking into consideration the shear rate of roller transfer, etc. A silver paste that has a low viscosity at high shear rates (20 to 250 (1 / s)) and a high viscosity at low shear rates (0.01 to 0.5 (1 / s)) is preferred. Furthermore, as with the carbon paste, since it is used in roller transfer, it is preferred to use a high-boiling-point solvent as the organic solvent. By using a high-boiling-point solvent, it is possible to impart slow drying properties and prevent drying on the circumferential surface of the roller.

[0084] Next, the assembly 10 of solid electrolytic capacitor elements including the element portions 11 on which the solid electrolyte layer 39 is formed is conveyed between a pair of rollers 222 to which the cathode paste is supplied. At this time, the assembly 10 is conveyed in the extension direction of the holding portion 13 so that only the element portions 11 are sandwiched between the pair of rollers 222, thereby printing the cathode paste continuously on the plurality of element portions 11. Only the region of the element portion 11 on the side of the end face 11e from the insulating mask material 37, on which the carbon layer 41 (or the solid electrolyte layer 39 if no carbon layer 41 is formed) is conveyed between the pair of rollers 222.

[0085] The conveying speed of the assembly 10 is, for example, 20 to 150 mm / s. The rotation speed (rpm) of each roller 222 is calculated from the conveying speed and the roller diameter. The gap (mm) between the pair of rollers 222 is set in consideration of the thickness of the element portion 11 (thickness after the solid electrolyte layer is formed), but is set to be at least larger than the thickness of the anode foil.

[0086] The thickness of the anode foil may be 100 μm or more and 150 μm or less, but is preferably 110 μm or more and 130 μm or less.

[0087] The thickness of the element portion 11 (thickness after the solid electrolyte layer is formed) may be 110 μm or more and 180 μm or less, but is preferably 120 μm or more and 160 μm or less.

[0088] As shown in FIG. 12, the solid electrolytic capacitor element assembly 10 may be transported between a pair of rollers 222 while being transported in a direction perpendicular to the horizontal direction.

[0089] FIG. 13 is a schematic diagram of another example of a roller transfer device used for roller transfer of cathode paste.

[0090] 13, the roller transfer device 200 may include a horizontally conveying roller transfer unit 220B instead of the vertically conveying roller transfer unit 220A. Similar to the vertically conveying roller transfer unit 220A, the horizontally conveying roller transfer unit 220B includes, on a conveyance path formed by the aggregate 10 of solid electrolytic capacitor elements, a plurality of conveyance rollers 221 for conveying the aggregate 10, a pair of rollers (transfer rollers) 222 between which the element portions 11 of the aggregate 10 are conveyed, and a dispenser 223 and a squeegee 224 provided on each roller 222.

[0091] However, in the horizontal conveyance type roller transfer section 220B, the solid electrolytic capacitor element assembly 10 is conveyed between a pair of rollers 222 while being conveyed in the horizontal direction.

[0092] 14 and 15 are perspective views schematically illustrating the appearance of one side of an element portion of an assembly of solid electrolytic capacitor elements to which a cathode paste has been roller-transferred, respectively.

[0093] The cathode paste on the pair of rollers 222 is then transferred to the pair of main surfaces 11a and 11b of the element portion 11, and the cathode paste transferred to the pair of main surfaces 11a and 11b is connected to the pair of side surfaces 11c and 11d and to one end surface 11e. More specifically, the cathode paste that spills out between each roller 222 and each main surface 11a and 11b wraps around and contacts the side surfaces 11c and 11d and end surface 11e from both main surfaces 11a and 11b, thereby connecting the cathode paste to the side surfaces 11c and 11d and end surface 11e. Therefore, as shown in FIGS. 14 and 15 , the cathode paste layers 50 on both main surfaces 11a and 11b, both side surfaces 11c and 11d, and end surface 11e are seamlessly connected without generating interfaces at their boundaries.

[0094] FIG. 16 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor element produced by a method for producing a solid electrolytic capacitor according to an embodiment of the present invention, and corresponds to the cross-sectional view shown in FIG.

[0095] As a result of the above, a solid electrolytic capacitor element 30 is formed on each element portion 11, as shown in Fig. 16. Furthermore, the silver layers 43 on each surface of the solid electrolytic capacitor element 30 are connected seamlessly (without interruption) without creating an interface at the boundary between them.

[0096] In each element portion 11, the solid electrolyte layer 39, the carbon layer 41, and the silver layer 43 (or the solid electrolyte layer 39 and the silver layer 43 if the carbon layer 41 is not formed) located closer to the end face 11e than the insulating mask material 37 function as a cathode, and the anode foil 31 on the opposite side functions as an anode. Therefore, a two-terminal solid electrolytic capacitor can be fabricated using each element portion 11.

[0097] FIG. 17 is a cross-sectional view schematically showing an example of a process for forming a laminate by stacking a plurality of solid electrolytic capacitor elements.

[0098] Thereafter, a plurality of assemblies 10 are stacked to form a laminate 110 by stacking a plurality of solid electrolytic capacitor elements 30 (element portions 11) as shown in Fig. 17. At this stage, the plurality of solid electrolytic capacitor elements 30 are simply stacked on top of each other, and interfaces 43a exist between the silver layers 43 of the elements over the entire area. At this time, it is not necessary to provide a conductive adhesive between adjacent solid electrolytic capacitor elements 30.

[0099] FIG. 18 is a cross-sectional view schematically showing an example of a laminate in which a plurality of silver layers are integrated.

[0100] Next, the laminate 110 is thermocompression-bonded to remelt the thermoplastic resin in each silver layer 43. As a result, as shown in FIG. 18 , the silver layers 43 of the solid electrolytic capacitor elements 30 are more reliably integrated, and the interfaces of the silver layers 43 disappear throughout the entire area between adjacent solid electrolytic capacitor elements 30. This makes it possible to more reliably reduce the ESR of the laminate 110 and improve the moisture resistance reliability of the laminate 110. Furthermore, since there is no need to use a conductive adhesive, costs can be reduced and the thickness (height) of the laminate 110 in the stacking direction can be reduced.

[0101] The temperature T during thermocompression bonding of the laminate 110 can be set as appropriate, but is preferably higher than the drying temperature t of the silver paste described above. Specifically, the difference (T-t) between the temperature T and the drying temperature t is preferably 50°C or higher and 150°C or lower, and more preferably 80°C or higher and 100°C or lower.

[0102] The temperature T during thermocompression bonding of the laminate 110 is preferably 150° C. or higher and 250° C. or lower, and more preferably 180° C. or higher and 230° C. or lower. The time for thermocompression bonding of the laminate 110 can be set as appropriate, but is preferably 10 seconds or higher and 90 seconds or lower, and more preferably 20 seconds or higher and 60 seconds or lower. Furthermore, the pressure for thermocompression bonding of the laminate 110 can also be set as appropriate, but is preferably 5 N or higher and 50 N or lower, and more preferably 10 N or higher and 30 N or lower per laminate.

[0103] Fig. 19 is a side view schematically showing an example of a laminate in which a plurality of silver layers are integrated. Fig. 20 is an end view schematically showing one example of a laminate in which a plurality of silver layers are integrated. Fig. 21 is an end view schematically showing the other example of a laminate in which a plurality of silver layers are integrated. Fig. 22 is a main surface view schematically showing an example of a laminate in which a plurality of silver layers are integrated.

[0104] 19 to 22, the laminate 110 after thermocompression bonding includes a capacitance forming portion 111 having a rectangular parallelepiped outer shape. The capacitance forming portion 111 corresponds to the capacitor portion of the solid electrolytic capacitor excluding the external terminals, the sealing portion, and the electrode lead portion, and has a first main surface 111a and a second main surface 111b that face each other in the stacking direction (height direction) T of the solid electrolytic capacitor element 30, a first side surface 111c and a second side surface 111d that face each other in the width direction W, and a first end surface 111e and a second end surface 111f that face each other in the length direction L.

[0105] 19 to 22, it is preferable that the silver layers 43 on six sides of the capacitance forming portion 111 are integrated together, thereby further improving the moisture resistance reliability of the laminate 110.

[0106] 19 , on the first side surface 111c and the second side surface 111d, the entire cathode of the laminate 110 (capacitance forming portion 111) is covered with the silver layer 43, and the solid electrolyte layer 39 and the carbon layer 41 are not exposed. The silver layer 43 has irregularities that allow each solid electrolytic capacitor element 30 to be identified, but the silver layer portions of adjacent solid electrolytic capacitor elements 30 are connected by a surface. The anode foil 31 is exposed on the anode side of the laminate 110 relative to the insulating mask material 37.

[0107] 20 , even on the first end surface 111e, the entire cathode of the laminate 110 (capacitance forming portion 111) is covered with the silver layer 43, and the solid electrolyte layer 39 and the carbon layer 41 are not exposed. The silver layer 43 has irregularities that allow each solid electrolytic capacitor element 30 to be distinguished, but the silver layer portions of adjacent solid electrolytic capacitor elements 30 are connected by a surface.

[0108] 21 , even on the second end surface 111f, the entire cathode of the laminate 110 (capacitance forming portion 111) is covered with the silver layer 43, and the solid electrolyte layer 39 and the carbon layer 41 are not exposed. The silver layer 43 has irregularities that allow each solid electrolytic capacitor element 30 to be distinguished, but the silver layer portions of adjacent solid electrolytic capacitor elements 30 are connected by a surface. On the other hand, the anode foil 31 and the insulating mask material 37 are not covered with the silver layer 43 and are exposed.

[0109] 22 , the entire cathode of the laminate 110 (capacitance forming portion 111) is covered with the silver layer 43 on both the first main surface 111 a and the second main surface 111 b, and the solid electrolyte layer 39 and the carbon layer 41 are not exposed. The anode foil 31 is exposed on the anode side of the laminate 110 relative to the insulating mask material 37.

[0110] Thereafter, the anode and cathode of the laminate 110 are connected to the lead frames, respectively.

[0111] Then, the laminate 110 is sealed, and the lead frames are formed and cut to form external terminals.

[0112] As a result of the above, a solid electrolytic capacitor is fabricated. This solid electrolytic capacitor is a two-terminal solid electrolytic capacitor.

[0113] FIG. 23 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor.

[0114] The solid electrolytic capacitor 100 shown in FIG. 23 is a two-terminal solid electrolytic capacitor, and has a structure in which a lead frame 101 is located at the bottom and solid electrolytic capacitor elements 30 are stacked in order on the lead frame 101 .

[0115] Note that FIG. 23 shows only the characteristic parts of the configuration of the solid electrolytic capacitor, and omits details such as the joining of the anode to the outside and resin sealing, but these can be configured in the same way as in a normal solid electrolytic capacitor.

[0116] Furthermore, the lead frame 101 does not have to be arranged in the bottom layer, and may be sandwiched between the cathodes of two solid electrolytic capacitor elements 30. Therefore, the cathodes of a plurality of solid electrolytic capacitor elements 30 may be stacked to form a laminate of a plurality of solid electrolytic capacitor elements 30, the lead frame 101 may be placed on the laminate, and the cathode of another solid electrolytic capacitor element 30 may be stacked on the lead frame 101 to form another laminate of a plurality of solid electrolytic capacitor elements 30, and a laminate in which the lead frame 101 is sandwiched between the cathode portions may be produced, and then heated and pressed.

[0117] The present specification discloses the following:

[0118] <1> A method for manufacturing a solid electrolytic capacitor, comprising: a step of forming a solid electrolyte layer on an anode foil with a dielectric layer interposed therebetween; a step of forming a solid electrolytic capacitor element by forming a silver layer containing a thermoplastic resin on the solid electrolyte layer; a step of stacking a plurality of solid electrolytic capacitor elements to form a laminate; and a step of thermocompression-bonding the laminate to remelt the thermoplastic resin and integrate the plurality of silver layers of the plurality of solid electrolytic capacitor elements so that no silver layer interface is formed across the entire area between adjacent solid electrolytic capacitor elements.

[0119] <2> The method for manufacturing a solid electrolytic capacitor according to <1>, further comprising a step of forming a carbon layer between the solid electrolyte layer and the silver layer, wherein the silver layer is formed so that the solid electrolyte layer and the carbon layer are not exposed on an outer surface of the solid electrolytic capacitor element.

[0120] <3> The method for manufacturing a solid electrolytic capacitor according to <1> or <2>, wherein the laminate includes a capacitance forming portion having a rectangular parallelepiped outer shape, and the silver layers on six sides of the capacitance forming portion are integrated.

[0121] <4> The method for manufacturing a solid electrolytic capacitor according to any one of <1> to <3>, wherein the thermoplastic resin includes a saturated copolymer polyester resin.

[0122] <5> The method for manufacturing a solid electrolytic capacitor according to any one of <1> to <4>, wherein the thermoplastic resin has a glass transition temperature of 0°C or lower and a weight loss rate of 0.1% or lower when heated from 25°C to 200°C as measured by simultaneous thermogravimetry and differential thermal analysis.

[0123] <6> The method for manufacturing a solid electrolytic capacitor according to any one of <1> to <5>, wherein the step of forming the silver layer includes a step of applying a silver paste containing the thermoplastic resin onto the solid electrolyte layer.

[0124] <7> The method for manufacturing a solid electrolytic capacitor according to <6>, wherein the step of forming the silver layer includes a step of drying the silver paste, and a temperature during thermocompression bonding of the laminate is higher than a drying temperature of the silver paste.

[0125] <8> The method for producing a solid electrolytic capacitor according to <6> or <7>, wherein the silver paste is applied onto the solid electrolyte layer by roller transfer or screen printing.

[0126] DESCRIPTION OF SYMBOLS 10 Assembly of solid electrolytic capacitor elements 11 Element portion 11a, 11b Main surface of element portion 11c, 11d Side surface of element portion 11e End surface of element portion 13 Holding portion 15 Transport substrate 17 Rib portion 30 Solid electrolytic capacitor element 31 Anode foil 31a Metal base portion 31b Porous portion 33 Dielectric layer 35, 37 Insulating mask material 39 Solid electrolyte layer 41 Carbon layer 43 Silver layer 43a Interface of silver layer 50 Cathode paste layer 100 Solid electrolytic capacitor 101 Lead frame 110 Laminate 111 Capacitance forming portion 111a First main surface 111b Second main surface 111c First side surface 111d Second side surface 111e First end surface 111f Second end surface 200 Roller transfer device 210 Unwinding section 220A Vertical conveying type roller transfer section 220B Horizontal conveying type roller transfer section 221 Conveying roller 222 Roller (transfer roller) 223 Dispenser 224 Squeegee 230 Pre-drying section 240 Drying section 250 Winding section

Claims

1. A step of forming a solid electrolyte layer on an anode foil through a dielectric layer; a step of forming a silver layer containing a thermoplastic resin on the solid electrolyte layer to form a solid electrolytic capacitor element; a step of laminating a plurality of solid electrolytic capacitor elements to form a laminate; and a step of thermocompression bonding the laminate to remelt the thermoplastic resin and integrate a plurality of silver layers of the plurality of solid electrolytic capacitor elements so that an interface of the silver layer is not formed in the entire area between adjacent solid electrolytic capacitor elements. A method for manufacturing a solid electrolytic capacitor comprising these steps.

2. The method for manufacturing a solid electrolytic capacitor according to claim 1, further comprising a step of forming a carbon layer between the solid electrolyte layer and the silver layer, and forming the silver layer so that the solid electrolyte layer and the carbon layer are not exposed on the outer surface of the solid electrolytic capacitor element.

3. The method for manufacturing a solid electrolytic capacitor according to claim 1 or 2, wherein the laminate includes a capacitance forming portion having a rectangular parallelepiped outer shape, and the silver layers on six surfaces of the capacitance forming portion are integrated.

4. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein the thermoplastic resin includes a saturated copolymer polyester resin.

5. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 4, wherein the thermoplastic resin has a glass transition temperature of 0 ° C or lower, and a weight loss rate of 0.1% or less when heated from 25 ° C to 200 ° C by thermogravimetry - differential thermal simultaneous measurement.

6. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 5, wherein the step of forming the silver layer includes a step of applying a silver paste containing the thermoplastic resin on the solid electrolyte layer.

7. The method for manufacturing a solid electrolytic capacitor according to claim 6, wherein the step of forming the silver layer includes a step of drying the silver paste, and the temperature during thermocompression bonding of the laminate is higher than the drying temperature of the silver paste.

8. The method for manufacturing a solid electrolytic capacitor according to claim 6 or 7, wherein the silver paste is applied on the solid electrolyte layer by roller transfer or screen printing.

Images