Method of manufacturing multi-layer ceramic electronic component, multi-layer ceramic electronic component, and circuit board

Abstract

To provide a method of manufacturing a laminated ceramic electronic component which is hardly adversely affected by hydrogen, is excellent in adhesion of a plating film of an external electrode, and can sufficiently secure bondability of solder in mounting.SOLUTION: A method for manufacturing a multilayer ceramic electronic component according to a preferred embodiment of the present invention includes a step of forming a base film made of a conductive material on a surface of a ceramic body including internal electrodes that are stacked and extend to the surface, the base film being connected to the internal electrodes. A first nickel film is formed on the base film by an electrolytic plating method. After the formation of the first nickel film, heat treatment is performed in a weak reducing atmosphere at a temperature equal to or higher than a temperature at which the first nickel film is recrystallized. A second nickel film is formed on the heat-treated first nickel film by an electrolytic plating method. In the heat treatment, a recrystallized structure having fewer dislocations and lattice defects than the crystal structure of the second nickel film is formed in the first nickel film.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a multilayer ceramic electronic component having external electrodes, a multilayer ceramic electronic component, and a circuit board using the same. [Background technology]

[0002] Generally, the manufacturing process of a multilayer ceramic capacitor includes a plating process to form external electrodes. Hydrogen generated during this plating process tends to remain absorbed in the external electrodes. In multilayer ceramic capacitors, hydrogen in the external electrodes diffuses into the ceramic body, causing problems such as a decrease in insulation resistance.

[0003] In contrast, Patent Document 1 describes a method for manufacturing a multilayer ceramic capacitor, which comprises oxidizing an external electrode body containing Cu to form a protective layer containing CuO, forming a Ni plating layer on the protective layer, performing a heat treatment at a temperature of 150°C or higher after the Ni plating layer is formed, and then forming a Sn plating layer after the heat treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-66783 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when forming a Ni plating layer after oxidizing the external electrode body, there is a possibility that the adhesion between the protective oxide film and the Ni plating layer may decrease. Furthermore, the surface of the Ni plating layer may become unstable due to oxidation after heat treatment. Therefore, forming a Sn plating layer directly on the surface may decrease the adhesion of the Sn plating layer and reduce the wettability of the solder used for board mounting.

[0006] In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a multilayer ceramic electronic component that is less susceptible to the adverse effects of hydrogen, has excellent adhesion of plating films on external electrodes, and is capable of ensuring sufficient solder bondability during mounting; a multilayer ceramic electronic component; and a circuit board using the same. [Means for solving the problem]

[0007] In order to achieve the above object, a method for manufacturing a multilayer ceramic electronic component according to one embodiment of the present invention includes a step of forming a base film made of a conductive material on a surface of a laminated ceramic body having internal electrodes extended to the surface, so as to be connected to the internal electrodes. A first nickel film is formed on the undercoat film by electrolytic plating. After the first nickel film is formed, the first nickel film is heat-treated in a weak reducing atmosphere at a temperature equal to or higher than the temperature at which the first nickel film is recrystallized. A second nickel film is formed on the heat-treated first nickel film by electrolytic plating. In the heat treatment, a recrystallized structure having fewer dislocations and lattice defects than the crystal structure of the second nickel film is formed in the first nickel film. Furthermore, in the heat treatment, crystal grains larger than those of the second nickel film may be formed in the first nickel film.

[0008] After the first nickel film is formed, it is heat-treated at a temperature at which the film recrystallizes, thereby releasing the hydrogen trapped in the first nickel film and other components. Furthermore, the heat-treated first nickel film recrystallizes and is configured to suppress the diffusion of hydrogen, preventing hydrogen from penetrating into the ceramic body after the heat treatment. This makes it possible to suppress problems such as a decrease in insulation resistance due to the diffusion of hydrogen into the ceramic body. Furthermore, by forming the second nickel film on the heat-treated first nickel film, it is possible to arrange the second nickel film on the surface side with a stable surface state with little oxidation. Therefore, when mounting the multilayer ceramic electronic component on a substrate, it is possible to suppress a decrease in solder wettability and ensure sufficient solder bondability. Furthermore, by forming a second nickel film made of the same material on the heat-treated first nickel film, it is possible to ensure sufficient adhesion between them.

[0009] Specifically, the temperature for the heat treatment may be 450°C or higher and 800°C or lower. This allows the first nickel film to be recrystallized, and it is possible to obtain a first nickel film that can sufficiently release hydrogen absorbed in the first nickel film and the like, and that can sufficiently suppress the diffusion of hydrogen.

[0010] For example, the thickness of the first nickel film may be 1.0 μm or more and 10.0 μm or less. This makes it possible to obtain a first nickel film that can sufficiently suppress the diffusion of hydrogen after heat treatment, and also to ease the conditions for the heat treatment for releasing hydrogen.

[0011] For example, the thickness of the second nickel film may be 1.5 μm or more and 6.0 μm or less. This ensures sufficient solder wettability during mounting, and also allows the multilayer ceramic electronic component to be miniaturized.

[0012] For example, the thickness of the undercoat film may be 2 μm or more and 50 μm or less. This allows the surface of the ceramic body to be reliably covered with the base film, while also enabling the multilayer ceramic electronic component to be miniaturized.

[0013] For example, the undercoat film may contain copper or an alloy thereof as a main component.

[0014] A surface layer film containing tin or an alloy thereof as a main component may be formed on the second nickel film by electrolytic plating. By forming a surface film that reacts easily with solder, it is possible to more reliably ensure solder bonding during mounting.

[0015] A multilayer ceramic electronic component according to another embodiment of the present invention includes a ceramic body and external electrodes. The ceramic body has internal electrodes that are laminated and drawn out to the surface. The external electrodes include an undercoat film, a first nickel film, and a second nickel film. The underlayer is disposed on the surface of the ceramic body, is connected to the internal electrodes, and is made of a conductive material. The first nickel film is disposed on the underlayer film. The second nickel film has a higher hydrogen concentration than the first nickel film and is disposed on the first nickel film. The first nickel film has a recrystallized structure with fewer dislocations and lattice defects than the crystal structure of the second nickel film. Furthermore, the first nickel film may include crystal grains that are larger than the crystal grains of the second nickel film.

[0016] For example, the first nickel film may include a recrystallized structure. As a result, the recrystallized structure of the first nickel film suppresses the diffusion of hydrogen, and prevents hydrogen from entering the ceramic body.

[0017] For example, the thickness of the first nickel film may be 1.0 μm or more and 10.0 μm or less.

[0018] For example, the thickness of the second nickel film may be 1.5 μm or more and 6.0 μm or less.

[0019] For example, the thickness of the undercoat film may be 2 μm or more and 50 μm or less.

[0020] For example, the undercoat film may contain copper or an alloy thereof as a main component.

[0021] The external electrode may further have a surface layer film disposed on the second nickel film and containing tin or an alloy thereof as a main component.

[0022] A circuit board according to yet another embodiment of the present invention includes a mounting substrate, a multilayer ceramic electronic component, and solder. The ceramic electronic component includes a ceramic body having laminated internal electrodes extending to the surface, and external electrodes disposed on the surface of the ceramic body and connected to the internal electrodes. The solder connects the external electrodes to the mounting board. The external electrodes are a base film formed of a conductive material and disposed on the surface of the ceramic body; a first nickel film disposed on the underlayer; a second nickel film having a higher hydrogen concentration than the first nickel film and disposed on the first nickel film. The first nickel film has a recrystallized structure with fewer dislocations and lattice defects than the crystal structure of the second nickel film. [Effects of the Invention]

[0023] As described above, the present invention can provide a method for manufacturing a multilayer ceramic electronic component that is less susceptible to the adverse effects of hydrogen, has excellent adhesion of plating films on external electrodes, and is capable of ensuring sufficient solder bondability during mounting, as well as a multilayer ceramic electronic component and a circuit board using the same. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a perspective view schematically showing a multilayer ceramic electronic component according to one embodiment of the present invention. [Figure 2] 2 is a cross-sectional view taken along line AA' of the multilayer ceramic electronic component. FIG. [Figure 3]FIG. 2 is a cross-sectional view taken along line BB' of the multilayer ceramic electronic component. [Figure 4] FIG. 2 is a schematic cross-sectional view showing a circuit board on which the multilayer ceramic electronic component is mounted. [Figure 5] 4 is a flowchart showing a method for manufacturing the multilayer ceramic electronic component. [Figure 6] 3A to 3C are perspective views illustrating a manufacturing process of the multilayer ceramic electronic component. [Figure 7] 1 is a graph showing the results of thermal desorption spectroscopy (TDS) performed on test chips in which external electrodes of different configurations are formed on the ceramic body of the multilayer ceramic electronic component, in which the horizontal axis indicates the test chip number and the vertical axis indicates the total amount of hydrogen desorbed from 50 mg of the test chip. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, X-axis, Y-axis, and Z-axis, which are mutually orthogonal, are shown as appropriate, and are common to all the drawings.

[0026] [Configuration of multilayer ceramic capacitor 10] 1 to 3 are diagrams showing a multilayer ceramic capacitor 10 according to one embodiment of the present invention. Fig. 1 is a perspective view of the multilayer ceramic capacitor 10. Fig. 2 is a cross-sectional view of the multilayer ceramic capacitor 10 taken along line A-A' in Fig. 1. Fig. 3 is a cross-sectional view of the multilayer ceramic capacitor 10 taken along line B-B' in Fig. 1.

[0027] The multilayer ceramic capacitor 10 includes a ceramic body 11, a first external electrode 14, and a second external electrode 15. The ceramic body 11 typically has a first end face 11a and a second end face 11b facing the X-axis direction, a first side face 11c and a second side face 11d facing the Y-axis direction, and a first main face 11e and a second main face 11f facing the Z-axis direction. More specifically, the first end face 11a faces in a direction parallel to the X-axis direction, and the second end face 11b faces in a direction parallel to the X-axis direction but opposite the first direction. The first side face 11c faces in a direction parallel to the Y-axis direction, and the second side face 11d faces in a direction parallel to the Y-axis direction but opposite the first direction. The first main face 11e faces in a direction parallel to the Z-axis direction, and the second main face 11f faces in a direction parallel to the Z-axis direction but opposite the first direction. The first end face 11a and the second end face 11b extend along the Y-axis direction and the Z-axis direction. The first side face 11c and the second side face 11d extend along the Z-axis direction and the X-axis direction. The first main face 11e and the second main face 11f extend along the X-axis direction and the Y-axis direction.

[0028] The first end face 11a and the second end face 11b, the first side face 11c and the second side face 11d, and the first main face 11e and the second main face 11f of the ceramic body 11 are all flat surfaces. The flat surface according to this embodiment does not have to be a strictly flat surface as long as it is recognized as flat when viewed overall, and includes, for example, a surface having minute irregularities or a gently curved shape.

[0029] The ceramic body 11 has ridges that interconnect the first end face 11 a, the second end face 11 b, the first side face 11 c, the second side face 11 d, and the first main face 11 e, the second main face 11 f. The ridges are, for example, chamfered to be rounded, but may not be chamfered.

[0030] The ceramic body 11 is made of dielectric ceramic. The ceramic body 11 has first internal electrodes 12 and second internal electrodes 13 covered with dielectric ceramic and stacked in the Z-axis direction. The multiple internal electrodes 12, 13 are each in the form of a sheet extending along the XY plane and are arranged alternately along the Z-axis direction.

[0031] That is, the ceramic body 11 has a facing region where the internal electrodes 12, 13 face each other in the Z-axis direction with the ceramic layer 16 sandwiched therebetween. The first internal electrode 12 is drawn from the facing region to the first end face 11a and connected to the first external electrode 14. The second internal electrode 13 is drawn from the facing region to the second end face 11b and connected to the second external electrode 15.

[0032] With this configuration, when a voltage is applied between the first external electrode 14 and the second external electrode 15 in the multilayer ceramic capacitor 10, the voltage is applied to the plurality of ceramic layers 16 in the opposing regions of the internal electrodes 12, 13. As a result, a charge corresponding to the voltage between the first external electrode 14 and the second external electrode 15 is stored in the multilayer ceramic capacitor 10.

[0033] The ceramic body 11 uses a dielectric ceramic with a high dielectric constant to increase the capacitance of each ceramic layer 16 between the internal electrodes 12 and 13. Examples of the dielectric ceramic with a high dielectric constant include materials with a perovskite structure containing barium (Ba) and titanium (Ti), such as barium titanate (BaTiO).

[0034] The dielectric ceramic may also be a composition system such as strontium titanate (SrTiO3), calcium titanate (CaTiO3), magnesium titanate (MgTiO3), calcium zirconate (CaZrO3), calcium titanate zirconate (Ca(Zr,Ti)O3), barium zirconate (BaZrO3), or titanium oxide (TiO2).

[0035] The first external electrode 14 is disposed on the surface of the ceramic body 11, covering, for example, the first end face 11a. The second external electrode 15 is disposed on the surface of the ceramic body 11, covering, for example, the second end face 11b. The external electrodes 14 and 15 face each other in the X-axis direction with the ceramic body 11 in between, and function as terminals of the multilayer ceramic capacitor 10.

[0036] The external electrodes 14 and 15 extend inward in the X-axis direction from the end faces 11a and 11b of the ceramic body 11 along the main faces 11e and 11f and the side faces 11c and 11d, respectively, and are spaced apart from each other on the main faces 11e and 11f and the side faces 11c and 11d.

[0037] The shapes of the external electrodes 14, 15 are not limited to those shown in Figures 1 and 2. For example, the external electrodes 14, 15 may extend from the end faces 11a, 11b of the ceramic body 11 to only one of the main surfaces, and may have an L-shaped cross section parallel to the XZ plane. Furthermore, the external electrodes 14, 15 do not have to extend to any of the main surfaces or side surfaces.

[0038] The first external electrode 14 has a four-layer structure, and includes an underlayer film 140, a first nickel film 141, a second nickel film 142, and a surface film 143. In the first external electrode 14, the underlayer film 140, the first nickel film 141, the second nickel film 142, and the surface film 143 are stacked in this order from the inside of the ceramic body 11 toward the outside.

[0039] The second external electrode 15 has a four-layer structure, and includes an underlayer film 150, a first nickel film 151, a second nickel film 152, and a surface film 153. In the second external electrode 15, the underlayer film 150, the first nickel film 151, the second nickel film 152, and the surface film 153 are laminated in this order from the inside of the ceramic body 11 side to the outside.

[0040] The base films 140 and 150 are formed of a conductive material. For example, the base films 140 and 150 may contain, as a main component, Cu (copper), Ni (nickel), Ag (silver), Au (gold), Pt (platinum), Pd (palladium), Ti (titanium), Ta (tantalum), W (tungsten), or an alloy thereof. As an example, the base films 140 and 150 may contain, as a main component, Cu or an alloy thereof. Note that the main component refers to the component with the highest molar content.

[0041] The base films 140, 150 can be configured, for example, as at least one sputtered film formed by sputtering, or at least one baked film formed by baking a conductive metal paste, etc. Alternatively, the base films 140, 150 may be configured by combining a sputtered film and a baked film.

[0042] The first nickel films 141, 151 are films formed by electroplating and disposed on the base films 140, 150. The first nickel films 141, 151 contain Ni or an alloy thereof as a main component. The first nickel films 141, 151 are films that have been subjected to heat treatment at a temperature equal to or higher than the recrystallization temperature, and contain recrystallized grains of a metal or alloy containing Ni as a main component, as will be described in detail below.

[0043] The second nickel films 142, 152 are films formed by electrolytic plating and are disposed on the first nickel films 141, 151. The second nickel films 142, 152 also contain Ni or an alloy thereof as a main component. The second nickel films 142, 152 are formed after the above-mentioned heat treatment, and therefore are not subjected to the above-mentioned heat treatment.

[0044] The surface films 143, 153 are films formed by electrolytic plating and disposed on the second nickel films 142, 152. The surface films 143, 153 contain, for example, Sn (tin) or an alloy thereof as a main component, which increases the reactivity of the external electrodes 14, 15 with the solder during soldering to mount the multilayer ceramic capacitor 10 on a mounting board, thereby enabling them to be sufficiently bonded.

[0045] [Configuration of circuit board 100] FIG. 4 is a cross-sectional view showing the circuit board 100 of this embodiment, and is a view showing a cross section corresponding to FIG.

[0046] As shown in FIG. 4, the circuit board 100 includes a mounting substrate 110 and a multilayer ceramic capacitor. 10, a first solder H1 and a second solder H2.

[0047] The mounting substrate 110 is a substrate on which the multilayer ceramic capacitor 10 is mounted, and may have a circuit (not shown) formed thereon. The mounting substrate 110 has a mounting surface 110a facing the multilayer ceramic capacitor 10, and a first land L1 and a second land L2 formed on the mounting surface 110a for connection to the circuit board 100.

[0048] The first solder H1 connects the first land L1 of the mounting board 110 to the first external electrode 14. The second solder H2 connects the second land L2 of the mounting board 110 to the second external electrode 15. These solders H1 and H2 are formed, for example, by solder paste applied to the lands L1 and L2 melting and wetting onto the external electrodes 14 and 15.

[0049] In the multilayer ceramic capacitor 10, the surface films 143, 153 react well with the solder, thereby promoting the wetting up of the solder and enabling the first solder H1 and second solder H2 to be joined to the external electrodes 14, 15 sufficiently.

[0050] Furthermore, the wetting of the solder is affected not only by the surface films 143, 153 but also by the surface condition of the layer below them. In this embodiment, by providing the second nickel films 142, 152, which have not been subjected to heat treatment, below the surface films 143, 153, it is possible to maintain good solder wettability.

[0051] The detailed effects of the first nickel films 141, 151 and the second nickel films 142, 152 will be described later.

[0052] [Method of manufacturing the multilayer ceramic capacitor 10] Fig. 5 is a flowchart showing a method for manufacturing the multilayer ceramic capacitor 10. Fig. 6 is a diagram showing the manufacturing process of the multilayer ceramic capacitor 10. The method for manufacturing the multilayer ceramic capacitor 10 will be described below along Fig. 5, with reference to Fig. 6 as needed.

[0053] (Step S01: Fabricating ceramic body 11) In step S01, the first ceramic sheet S1, the second ceramic sheet S2, and the third ceramic sheet S3 are stacked as shown in FIG.

[0054] The ceramic sheets S1, S2, and S3 are formed as unsintered dielectric green sheets mainly composed of dielectric ceramics. An unsintered first internal electrode 12u corresponding to the first internal electrode 12 is formed on the first ceramic sheet S1, and an unsintered second internal electrode 13u corresponding to the second internal electrode 13 is formed on the second ceramic sheet S2. No internal electrode is formed on the third ceramic sheet S3.

[0055] In the green ceramic body 11u shown in Fig. 6, ceramic sheets S1 and S2 are alternately stacked, and a third ceramic sheet S3 is stacked on the top and bottom surfaces in the Z-axis direction. The green ceramic body 11u is integrated by pressure-bonding the ceramic sheets S1, S2, and S3. The number of ceramic sheets S1, S2, and S3 is not limited to the example shown in Fig. 6.

[0056] Although the above has described an unfired ceramic body 11u corresponding to one ceramic body 11, in reality, a laminated sheet is formed as a large, undivided sheet, and then the laminated sheet is divided into individual ceramic bodies 11u.

[0057] The ceramic body 11 shown in FIGS. 1 to 3 is produced by sintering the unsintered ceramic body 11u. The firing temperature can be determined based on the sintering temperature of the ceramic body 11u. For example, when a barium titanate-based material is used as the dielectric ceramic, the firing temperature can be set to approximately 1000 to 1300°C. Furthermore, firing can be performed, for example, in a reducing atmosphere or a low-oxygen partial pressure atmosphere.

[0058] (Step S02: Formation of base films 140 and 150) In step S02, base films 140, 150 made of a conductive material are formed on the surface of the ceramic body 11 so as to be connected to the internal electrodes 12, 13. In this embodiment, the base films 140, 150 are formed so as to cover the first end face 11a and the second end face 11b.

[0059] The base films 140, 150 are formed by applying a conductive paste to the end faces 11a, 11b of the ceramic body 11 by, for example, a dipping method, a printing method, or the like, and then baking the paste. In this case, the conductive material constituting the base films 140, 150 may contain, for example, Cu, Ni, Ag, Au, Pt, Pd, or an alloy thereof as a main component.

[0060] Alternatively, the base films 140 and 150 may be formed by sputtering. In this case, the conductive material forming the base films 140 and 150 may contain, for example, Ti, Ni, Ag, Au, Pt, Pd, Ta, W, or an alloy thereof as a main component.

[0061] The thickness of the base films 140, 150 can be set to 2 μm or more and 50 μm or less. This allows the end faces 11 a, 11 b to be reliably covered by the base films 140, 150 while miniaturizing the multilayer ceramic capacitor 10. The thickness of the base films 140, 150 can be, for example, the thickness of the region on the end faces 11 a, 11 b, and can be the dimension along the X-axis direction of the center in the Z-axis direction and the Y-axis direction.

[0062] (Step S03: Forming first nickel films 141 and 151) In step S03, first nickel films 141, 151 are formed on the base films 140, 150. The first nickel films 141, 151 contain Ni or an alloy thereof as a main component and are formed by electrolytic plating.

[0063] (Step S04: Heat treatment) In step S04, after the first nickel films 141, 151 are formed, they are heat-treated in a weakly reducing atmosphere. In this embodiment, a weakly reducing atmosphere means an atmosphere with an oxygen concentration of 30 ppm or less. This prevents excessive oxidation of the first nickel films 141, 151. The heat-treatment temperature is equal to or higher than the temperature at which the first nickel films 141, 151 recrystallize, and specifically, can be set to 450°C or higher and 800°C or lower. The heat-treatment time can be, for example, 5 minutes or higher and 30 minutes or lower.

[0064] (Step S05: Forming second nickel films 142 and 152) In step S05, second nickel films 142, 152 are formed on the heat-treated first nickel films 141, 151. The second nickel films 142, 152 contain Ni or an alloy thereof as a main component and are formed by electrolytic plating.

[0065] (Step S06: Formation of surface films 143, 153) In step S06, surface films 143, 153 are formed on the second nickel films 142, 152. The surface films 143, 153 contain, for example, Sn or an alloy thereof as a main component, and are formed by electrolytic plating.

[0066] The thickness of the surface films 143, 153 can be set to 3 μm or more and 10 μm or less, thereby ensuring sufficient reactivity with solder while miniaturizing the multilayer ceramic capacitor 10. The thickness of the surface films 143, 153 can be, for example, the thickness of the regions on the end faces 11 a, 11 b, and can be the dimension along the X-axis direction of the center portion in the Z-axis direction and the Y-axis direction.

[0067] In this manner, the multilayer ceramic capacitor 10 is manufactured.

[0068] [Detailed description of external electrodes 14 and 15] The plating process using electrolytic plating to form the first nickel films 141, 151, the second nickel films 142, 152, and the surface films 143, 153 generates hydrogen, which has a strong effect of deteriorating the ceramic body 11. The hydrogen generated during the plating process is likely to be occluded in the base films 140, 150, the first nickel films 141, 151, the second nickel films 142, 152, and the surface films 143, 153 of the external electrodes 14, 15.

[0069] When the hydrogen absorbed in the external electrodes 14, 15 diffuses into the ceramic body 11 and reaches the opposing regions of the internal electrodes 12, 13, the insulation resistance of the ceramic layer 16 between the internal electrodes 12, 13 decreases, which makes the multilayer ceramic capacitor 10 more susceptible to insulation failure.

[0070] The hydrogen absorbed in the external electrodes 14, 15 is not limited to hydrogen generated in the plating process, but may be, for example, hydrogen contained in moisture such as water vapor in the atmosphere, etc. Furthermore, the hydrogen absorbed in the external electrodes 14, 15 may be in any state that hydrogen can be in, such as hydrogen atoms, hydrogen ions, or hydrogen isotopes.

[0071] In this embodiment, a heat treatment is performed in step S04 after the formation of the first nickel films 141, 151 in step S03, whereby hydrogen absorbed in the first nickel films 141, 151, etc. is released and removed to the outside.

[0072] Furthermore, this heat treatment promotes recrystallization of the first nickel films 141, 151, resulting in a configuration in which the first nickel films 141, 151 suppress the diffusion of hydrogen. In other words, the first nickel films 141, 151 include a recrystallized structure. As a result, even if hydrogen is generated during the formation of the second nickel films 142, 152 and the surface films 143, 153, the first nickel films 141, 151 suppress the diffusion of the hydrogen and prevent the hydrogen from penetrating into the ceramic body 11. The heat treatment also prevents hydrogen from penetrating from outside the multilayer ceramic capacitor 10. As a result, the diffusion of hydrogen into the ceramic body 11 is suppressed in the multilayer ceramic capacitor 10.

[0073] The recrystallized structure of the first nickel films 141, 151 can be confirmed as a crystalline structure with fewer dislocations and lattice defects compared to the second nickel films 142, 152. The recrystallized structure of the first nickel films 141, 151 also has larger crystal grains compared to the second nickel films 142, 152. To confirm these crystalline structures, for example, the target surface can be chemically polished and then observed at 500 to 5000 times magnification using an optical microscope or a scanning electron microscope (SEM).

[0074] For example, a method for verifying the recrystallized structure of the first nickel films 141, 151 is to first check the structures of the first nickel films 141, 151 and the second nickel films 142, 152, then subject the second nickel films 142, 152 to a heat treatment (referred to as a verification heat treatment) similar to that in step S04, and compare the structure of the second nickel films 142, 152 after the verification heat treatment with the structure of the first nickel films 141, 151 before the verification heat treatment. If the structure of the second nickel films 142, 152 after the verification heat treatment has changed to a structure similar to the structure of the first nickel films 141, 151 before the verification heat treatment, it can be confirmed that the first nickel films 141, 151 have become recrystallized structures by the heat treatment in step S04.

[0075] That is, in this embodiment, the release of hydrogen absorbed in ceramic body 11, base films 140, 150, and first nickel films 141, 151 and the formation of the diffusion-preventing layer that suppresses the diffusion of hydrogen are performed in the same heat treatment process. Therefore, a configuration that is resistant to the adverse effects of hydrogen can be obtained while minimizing the thermal load on ceramic body 11 and the like that accompanies the release of hydrogen and the formation of the diffusion-preventing layer.

[0076] The thickness of the first nickel films 141, 151 can be, for example, 1.0 μm to 10.0 μm, more preferably 1.0 μm to 4.5 μm. The thickness of the first nickel films 141, 151 can be, for example, the thickness of the region on the end faces 11 a, 11 b, and can be the dimension along the X-axis direction of the center in the Z-axis direction and the Y-axis direction.

[0077] By setting the thickness of the first nickel films 141, 151 to 1.0 μm or more, the first nickel films 141, 151 sufficiently cover the base films 140, 150, effectively suppressing hydrogen diffusion. Furthermore, components of the base films 140, 150 are less likely to diffuse to the surfaces of the first nickel films 141, 151, improving adhesion between the surfaces and the second nickel films 142, 152. Setting the thickness of the first nickel films 141, 151 to 10.0 μm or less suppresses the amount of hydrogen generated by the formation of the first nickel films 141, 151, and eases the conditions for the heat treatment to release hydrogen. Furthermore, by setting the thickness of the first nickel films 141, 151 to 4.5 μm or less, the thickness of the external electrodes 14, 15 is suppressed, enabling the multilayer ceramic capacitor 10 to be miniaturized.

[0078] Here, an oxide film is easily formed on the heat-treated surface of the first nickel film 141, 151, and the surface is in an unstable state. If the surface layer film 143, 153 is formed directly on such first nickel film 141, 151, the wettability of the solder may be reduced in the solder mounting process, and good solder bonding may not be achieved.

[0079] Furthermore, if the surface films 143, 153 are formed on the unstable surfaces of the first nickel films 141, 151, the adhesion of the surface films 143, 153 may decrease, possibly causing problems such as peeling of the surface films 143, 153.

[0080] Therefore, in this embodiment, second nickel films 142, 152 are formed on the heat-treated first nickel films 141, 151. By arranging the second nickel films 142, 152, which are less susceptible to oxidation, on the surface layer side, it is possible to suppress a decrease in the wettability of the solder.

[0081] Furthermore, because the second nickel films 142, 152 use the same type of metal or alloy as the first nickel films 141, 151, sufficient adhesion can be ensured between the first nickel films 141, 151 and the second nickel films 142, 152. Furthermore, because the surface films 143, 153 are formed on the second nickel films 142, 152, which are less affected by oxide films and the like, sufficient adhesion can be ensured between the second nickel films 142, 152 and the surface films 143, 153. This improves the adhesion of the plating films of the external electrodes 14, 15, and prevents peeling of the plating films.

[0082] Furthermore, the heat treatment reduces the hydrogen concentration in the first nickel films 141, 151. Meanwhile, the second nickel films 142, 152 absorb hydrogen generated in the plating process after the heat treatment. Therefore, the hydrogen concentration in the second nickel films 142, 152 is higher than the hydrogen concentration in the first nickel films 141, 151. The hydrogen concentration can be expressed as the concentration (mol %) of hydrogen when nickel or its alloy, which is the main component of the nickel film, is taken as 100 mol %.

[0083] The hydrogen concentration is measured by, for example, secondary ion mass spectrometry (SIMS). As a sample for measuring the hydrogen concentration, for example, a multilayer ceramic capacitor 10 cut parallel to the XZ plane can be used. The cross section of the sample is mirror-polished using, for example, diamond paste or the like, to obtain a surface smooth enough for measurement.

[0084] The thickness of the second nickel films 142, 152 can be, for example, 1.5 μm or more and 6.0 μm or less. The thickness of the second nickel films 142, 152 can be, for example, the thickness of the region on the end faces 11 a, 11 b, and can be the dimension along the X-axis direction of the center in the Z-axis direction and the Y-axis direction.

[0085] By setting the thickness of the second nickel films 142, 152 to 1.5 μm or more, the second nickel films 142, 152 are configured to sufficiently cover the heat-treated first nickel films 141, 151. This ensures sufficient solder wettability during mounting and improves adhesion between the surface films 143, 153. By setting the thickness of the second nickel films 142, 152 to 6.0 μm or less, the thickness of the external electrodes 14, 15 can be reduced, allowing the multilayer ceramic capacitor 10 to be miniaturized.

[0086] Next, test results will be shown to further explain the effects of this embodiment.

[0087] [Test example] Thermal desorption spectroscopy (TDS) was performed on test chips in which external electrodes of different configurations were formed on the ceramic body 11. In TDS, the amount of hydrogen desorbed from 50 mg of the test chip (approximately eight electronic components) was measured while the temperature was raised from 100°C to 1000°C.

[0088] 7 is a graph showing the results of TDS, with the horizontal axis representing the test chip number and the vertical axis representing the total amount of hydrogen desorbed from 50 mg of test chips. Specifically, the vertical axis represents the relative amount of hydrogen molecules desorbed from each 50 mg test chip, based on the number of hydrogen molecules desorbed from 50 mg of test chip 1.

[0089] The test chip was made by forming a 40 μm thick Cu-based underlayer on a ceramic body, and then forming a predetermined plating film on the underlayer. The dimensions of the ceramic body were approximately 1.5 mm in the X-axis direction, 0.7 mm in the Y-axis direction, and 0.7 mm in the Z-axis direction.

[0090] Test chips 1 to 3 all have a first nickel film with a thickness of 3 μm. Test chip 1 has an external electrode made of an undercoat film and the first nickel film, and has not been subjected to heat treatment. Test chip 2 has external electrodes made of an undercoat film and a first nickel film, and after the first nickel film was formed, it was heat-treated in a weakly reducing atmosphere at 450 to 550°C for 20 minutes. Test chip 3 has external electrodes made of an undercoat film, a first nickel film, and a second nickel film, and after the first nickel film was formed, it was heat-treated under the same conditions as test chip 2. The thickness of the second nickel film of test chip 3 is 6 μm.

[0091] Test chips 4 to 6 all have a first nickel film with a thickness of 6 μm. Test chip 4 has external electrodes made of an undercoat film and the first nickel film and has not been heat treated. Test chip 5 has external electrodes made of an undercoat film and the first nickel film and has been heat treated under the same conditions as test chip 2 after the formation of the first nickel film. Test chip 6 has external electrodes made of an undercoat film, the first nickel film, and a second nickel film and has been heat treated under the same conditions as test chip 2 after the formation of the first nickel film. The thickness of the second nickel film on test chip 6 is 6 μm.

[0092] Test chips 7 to 9 all have a first nickel film with a thickness of 10 μm. Test chip 7 has external electrodes made of an undercoat film and the first nickel film and has not been heat-treated. Test chip 8 has external electrodes made of an undercoat film and the first nickel film and has been heat-treated under the same conditions as test chip 2 after the first nickel film has been formed. Test chip 9 has external electrodes made of an undercoat film, the first nickel film, and a second nickel film and has been heat-treated under the same conditions as test chip 2 after the first nickel film has been formed. The thickness of the second nickel film on test chip 9 is 6 μm.

[0093] Referring to Figure 7, comparing the results of test chip 1, which was not heat-treated, and test chip 2, which was heat-treated, it was found that the amount of hydrogen desorption from test chip 2 was significantly reduced. The results were similar for test chips 4 and 5, and test chips 7 and 8. A low amount of hydrogen desorption in TDS means that the test chip contained a small amount of hydrogen. In other words, these results showed that hydrogen absorbed in the first nickel film and other layers was released to the outside by heat treatment.

[0094] Test chips 4 and 7, which had first nickel films of 6 μm and 10 μm, had significantly greater amounts of hydrogen desorption than test chip 1, which had a first nickel film of 3 μm. This indicates that forming a thicker first nickel film increases the amount of hydrogen absorbed in the first nickel film, etc.

[0095] On the other hand, test chips 5 and 8, which had first nickel films of 6 μm and 10 μm and were heat-treated, showed a significantly reduced amount of hydrogen desorption compared to test chips 4 and 7, which were not heat-treated. This shows that even when the first nickel film is formed to a thickness of 6 μm or 10 μm, the absorbed hydrogen can be sufficiently released by heat treatment.

[0096] Test chip 3, which had the second nickel film, had a larger amount of hydrogen desorption than test chip 2, which did not have the second nickel film. Similar results were obtained for test chips 6 and 5, and test chips 9 and 8. This shows that forming a second nickel film after heat treatment causes hydrogen to be absorbed in the external electrodes.

[0097] Next, to confirm whether the adverse effects of hydrogen were suppressed by heat treatment, a Highly Accelerated Limit Test (HALT) was conducted on each test chip. In the HALT, ten chips of each type (1 to 9) were prepared, and a voltage of 200 V was applied at 150°C for 400 hours, and the number of chips with insulation failure was counted.

[0098] As a result, all ten test chips 1, 4, and 7, which were not subjected to heat treatment after the formation of the first nickel film, showed insulation defects. On the other hand, none of test chips 2, 3, 5, 6, 8, and 9, which were subjected to heat treatment after the formation of the first nickel film, showed insulation defects.

[0099] From these results, it can be seen that if heat treatment is not performed, the hydrogen absorbed in the external electrodes will diffuse to the opposing area of ​​the ceramic body due to high temperature and high voltage application, and the insulation resistance will likely decrease. On the other hand, when heat treatment was performed as in the case of test chips 2, 3, 5, 6, 8 and 9, it was found that the decrease in insulation resistance due to hydrogen was suppressed even under severe conditions.

[0100] In particular, after heat treatment, insulation failure was also suppressed for test chips 3, 6, and 9, which had a second nickel film formed on them. This shows that even if the external electrodes absorb hydrogen due to the formation of the second nickel film, the heat-treated first nickel film is configured to suppress the diffusion of hydrogen, thereby suppressing the adverse effects of hydrogen on the ceramic body.

[0101] Furthermore, when 10 test chips each of 3, 6, and 9 were coated with a 4 μm tin plating film and soldered to the board by reflow soldering, all chips had good solder wettability and no mounting failures occurred. Furthermore, when the external electrodes of these test chips 3, 6, and 9 were inspected visually and with a stereomicroscope, no peeling of the plating film was confirmed on any of the chips.

[0102] Therefore, according to this embodiment, a multilayer ceramic capacitor can be obtained that is less susceptible to the adverse effects of hydrogen, has good adhesion of the plating film, and can ensure sufficient bondability with solder.

[0103] As can be seen from the TDS results in Figure 7, reducing the number of plating film layers is considered to reduce the amount of hydrogen generated. On the other hand, in this embodiment, the second nickel film is intentionally provided after the first nickel film is heat-treated at a temperature that recrystallizes it. As a result, according to this embodiment, the first nickel film functions as a diffusion suppression layer that suppresses the diffusion of hydrogen, thereby suppressing the adverse effects of hydrogen and solving problems with adhesion to the surface film and solder wettability.

[0104] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the gist of the present invention.

[0105] The configuration of the external electrode according to the present invention is not limited to the four-layer structure of the above embodiment, but may have at least three layers: an undercoat film, a first nickel film, and a second nickel film. For example, the external electrode according to the present invention may have a five-layer or more structure.

[0106] Furthermore, the present invention is applicable not only to multilayer ceramic capacitors but also to general multilayer ceramic electronic components having external electrodes, such as chip varistors, chip thermistors, and multilayer inductors, in addition to multilayer ceramic capacitors. [Explanation of symbols]

[0107] 10...Multilayer ceramic capacitors (multilayer ceramic electronic components) 11...Ceramic body 12,13…Internal electrode 14,15...External electrode 140,150...Base film 141,151...First nickel film 142, 152...Second nickel film 143,153…Surface membrane

Claims

1. A ceramic body; a plurality of internal electrodes provided within the ceramic body; An external electrode; Equipped with one end of one or more first internal electrodes among the plurality of internal electrodes is exposed on a surface of the ceramic body, The external electrode is a conductive base film provided on the surface of the ceramic body and connected to the one or more first internal electrodes; a first nickel film provided on the underlayer; a second nickel film provided on the first nickel film; a first oxidation portion provided between the first nickel film and the second nickel film and containing nickel oxide; A multilayer ceramic electronic component comprising:

2. the second nickel film has a higher hydrogen concentration than the first nickel film; The multilayer ceramic electronic component according to claim 1 .

3. the first nickel film has a recrystallized structure; The multilayer ceramic electronic component according to claim 1 .

4. the second nickel film has more lattice defects than the first nickel film; The multilayer ceramic electronic component according to claim 1 .

5. The thickness of the first nickel film is 1.0 μm or more and 10.0 μm or less. The multilayer ceramic electronic component according to claim 1 .

6. The thickness of the second nickel film is 1.5 μm or more and 6.0 μm or less. The multilayer ceramic electronic component according to claim 1 .

7. The thickness of the undercoat film is 2 μm or more and 50 μm or less. The multilayer ceramic electronic component according to claim 1 .

8. the undercoat film contains copper or an alloy thereof as a main component; The multilayer ceramic electronic component according to claim 1 .

9. The external electrode further has a surface layer film disposed on the second nickel film and containing tin or an alloy thereof as a main component. The multilayer ceramic electronic component according to claim 1 .

10. the second nickel film has a first surface facing the first nickel film and a second surface located on the opposite side to the first surface, the external electrode further includes a second oxidized portion provided on a second surface of the second nickel film, the second oxidized portion contains a smaller amount of nickel oxide than the first oxidized portion; The multilayer ceramic electronic component according to claim 1 .

11. the first oxidation portion is an oxide film; The multilayer ceramic electronic component according to claim 1 .

12. The first nickel film is a plating film. The multilayer ceramic electronic component according to claim 1 .

13. The second nickel film is a plating film. The multilayer ceramic electronic component according to claim 1 .

14. The first nickel film is configured to prevent hydrogen from permeating the ceramic body. The multilayer ceramic electronic component according to claim 1 .

15. The first nickel film includes crystal grains that are larger than the crystal grains of the second nickel film. The multilayer ceramic electronic component according to claim 1 .

16. the second nickel film is in direct contact with the first nickel film; The multilayer ceramic electronic component according to claim 1 .

17. the surface film is in direct contact with the second nickel film; The multilayer ceramic electronic component according to claim 9 .

18. a mounting board; a multilayer ceramic electronic component having a ceramic body, a plurality of internal electrodes provided in the ceramic body, and external electrodes; solder connecting the external electrodes and the mounting substrate; Equipped with one end of one or more first internal electrodes among the plurality of internal electrodes is exposed on a surface of the ceramic body, The external electrode is a first internal electrode provided on the surface of the ceramic body and connected to the one or more first internal electrodes, a conductive base film provided on the surface of the ceramic body; a first nickel film provided on the underlayer; a second nickel film provided on the first nickel film; a first oxidation portion provided between the first nickel film and the second nickel film and containing nickel oxide; Equipped with Circuit board.

19. the second nickel film has more lattice defects than the first nickel film; 20. The circuit board of claim 18.

20. the second nickel film has a higher hydrogen concentration than the first nickel film; 20. The circuit board of claim 18.

Images