Multilayer ceramic capacitor and its manufacturing method

Abstract

The present invention provides a multilayer ceramic capacitor and a method for manufacturing the same, which includes a capacitor body and two external electrodes facing each other with a space therebetween. The capacitor body includes a plurality of first and second internal electrodes and a dielectric layer separating the first and second internal electrodes. The external electrode includes a seed layer and an electrode layer in order from the inside to the outside. The seed layer covers the outer surface of the portion where the external electrode is provided on the capacitor body. The electrode layer includes at least an electrode metal layer formed by plating and a welding metal layer formed by plating. By the seed layer of the present invention, the plating formation of the electrode metal layer can be facilitated. The electrode metal layer formed by plating has a uniform and thin thickness, and the stress is uniformly dispersed, preventing cracks from occurring in the external electrode. Further, since the electrode metal layer is formed by plating, the formation by sintering is avoided, the density is high, the penetration of nickel solution or the like is prevented, and the occurrence of cracks in the capacitor body is prevented.

Description

[Technical Field]

[0001] The present invention relates to the technical field of capacitors, and more particularly to a multilayer ceramic capacitor and a method for manufacturing the same. [Background technology]

[0002] For example, Chinese invention patent application CN114078634A discloses a multilayer ceramic capacitor having a capacitor body formed by alternately laminating and sintering dielectric layers and internal electrodes, with external electrodes provided at both ends of the capacitor body. The external electrodes of conventional capacitors generally include, from inside to outside, copper, nickel, and tin layers. The forming process typically involves first immersing the capacitor in copper paste and sintering the resulting copper layer, then electroplating to form a nickel layer, and finally electroplating to form a tin layer. The innermost copper layer is the sintered copper layer, which is thick and uneven. If the sintered copper layer is too thin, the bonding strength between the copper layer and both ends of the capacitor body will be poor. Therefore, to ensure the bonding strength between the copper layer and the capacitor body, the copper layer must be 10-15 μm thick. However, this may result in an increase in electrode size and an increase in the size of the capacitor.

[0003] 1, when manufacturing the copper layers of the external electrodes, the capacitor body 10 is placed vertically, and the end of the capacitor body 10 where the copper paste 200 is to be attached is immersed in the copper paste 200 with the end point facing downward. After lifting the capacitor body 10, the copper paste 200 is attached to the lower end of the capacitor body 10. By sintering the capacitor body 10 with the copper paste 200 attached, the copper layers of the external electrodes can be formed on the ends of the capacitor body 10. However, in the multilayer ceramic capacitor obtained by this manufacturing method, because the copper paste 200 has fluidity, when the capacitor body 10 is lifted, the copper paste 200 adhering to the capacitor body 10 flows downward due to its own gravity, reducing the amount of copper paste 200 adhering to the outer surface of the capacitor body 10, but increasing the amount of copper paste 200 on the end surfaces. This results in an uneven distribution of the copper layer, and stress in the copper layer concentrates near the edges of the copper layer, making it easy for cracks to occur in the external electrodes. Furthermore, because the external electrodes on the outer surface of the capacitor body 10 are thin, the bonding strength between the external electrodes and the capacitor body 10 is weak, making them prone to falling off from the capacitor body 10 due to external impact. Furthermore, the distance extending along the vertical direction of the capacitor body 10 between the external electrodes at both ends of the capacitor body 10 is small, making it easy for short-circuiting of the external electrodes to occur.

[0004] Furthermore, when external electrodes are not formed on a multilayer ceramic capacitor, internal cracking is unlikely to occur in the capacitor body 10. However, during the copper layer sintering process, the bonding stress between the copper layer and the capacitor body 10 releases residual stress, which often causes cracks in the sintered copper layer. Meanwhile, when sintering the copper paste 200 in a multilayer ceramic capacitor, the resin in the copper paste 200 volatilizes, forming cavities in the copper layer. During the nickel electroplating process, a small amount of nickel liquid seeps into the cavities. During the subsequent application of the multilayer ceramic capacitor product, the multilayer ceramic capacitor undergoes a reflow soldering process (SMT - surface mount technology process). The heating temperature of the multilayer ceramic capacitor varies from 260°C to 320°C, and nickel remains inside the copper layer. Because the thermal expansion coefficients (thermal contraction rates) of the copper and nickel metals are different, the resulting internal stress acts on the capacitor body 10, causing cracks. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to solve at least one of the technical problems described in the background art above, and to provide a multilayer ceramic capacitor that can suppress the occurrence of cracks in the capacitor body and external electrodes, and a method for manufacturing the same. [Means for solving the problem]

[0006] The first technical means adopted by the present invention to solve the problems in the prior art is: A multilayer ceramic capacitor including a capacitor body and two external electrodes provided on the capacitor body and facing each other with a gap therebetween, wherein the capacitor body includes a plurality of first internal electrodes, a plurality of second internal electrodes, and a dielectric layer separating the first internal electrodes from the second internal electrodes, and one end of the first internal electrode and one end of the second internal electrode are exposed from an outer surface of the capacitor body and electrically connected to correspond to the two external electrodes, The external electrode includes, from the inside to the outside, a seed layer and an electrode layer, the seed layer covering the outer surface of the capacitor body where the external electrode is provided, the outer surface of the capacitor body where the seed layer is provided is roughened to form a roughened surface layer having an uneven surface, and the electrode layer includes at least an electrode metal layer formed on the surface of the seed layer by plating and a weld metal layer formed by plating and located outside the electrode metal layer, making it a multilayer ceramic capacitor.

[0007] Furthermore, the first internal electrode and the second internal electrode are exposed from the seed layer and directly connected to the electrode metal layer.

[0008] Additionally, the seed layer includes at least one seed metal selected from the group consisting of gold, silver, and platinum group metals.

[0009] Furthermore, the roughness of the roughened surface layer is greater than the roughness of the outer surface of the portion of the capacitor body where the external electrode is not provided, and the seed metal of the seed layer is distributed at intervals in the roughened surface layer.

[0010] Furthermore, the electrode metal layer is formed on the outer surface of the seed layer by chemical plating.

[0011] Furthermore, the portions of the first internal electrode and the second internal electrode that are exposed from the outer surface of the capacitor body are not roughened, and the first internal electrode and the second internal electrode are exposed from the rough surface layer.

[0012] Additionally, the seed metal is palladium metal.

[0013] Furthermore, the electrode metal layer is a copper metal layer or a nickel metal layer, and the thickness of the electrode metal layer ranges from 0.5 um to 8 um.

[0014] Furthermore, the seed metal of the seed layer is replaced by the electrode metal solution to precipitate the electrode metal layer, the seed metal is replaced and reduced, and the electrode metal layer is plated onto the seed layer and the portions of the first internal electrode and the second internal electrode exposed from the outer surfaces of the surface roughening layer.

[0015] The electrode layer further includes a protective layer made of a metal material formed on the outer surface of the electrode metal layer by chemical plating or electroplating.

[0016] Furthermore, the protective layer is made of nickel metal.

[0017] Furthermore, the capacitor body includes two end faces opposing each other in the longitudinal direction and an outer peripheral surface connecting the two end faces, the two external electrodes each cover the corresponding end face and at least a portion of the outer peripheral surface, one end of the first internal electrode and the second internal electrode are exposed from each of the two end faces, and the edge of the electrode metal layer located on the outer peripheral surface forms a boundary edge that extends linearly in the width direction perpendicular to the longitudinal direction.

[0018] Furthermore, the outer peripheral surface of the capacitor body on which the external electrode is not provided is covered with a layer of protective film, the thickness of the protective film is equal to or greater than the thickness of the electrode metal layer, and the protective film shields at least the boundary edge of the electrode metal layer.

[0019] Furthermore, the protective film is made of an insulating chemical material, which, when heat-treated, penetrates into gaps formed after sintering of the capacitor body.

[0020] Furthermore, the protective film is methyl silicone oil, and the thickness of the protective film is 0.3-5 um.

[0021] The second technical means adopted by the present invention to solve the conventional technical problems is: A method for manufacturing a multilayer ceramic capacitor including a capacitor body and two external electrodes provided on the capacitor body and facing each other with a gap therebetween, wherein the capacitor body includes a plurality of first internal electrodes, a plurality of second internal electrodes, and a dielectric layer separating the first internal electrodes and the second internal electrodes, and one end of the first internal electrodes and one end of the second internal electrodes are exposed from an outer surface of the capacitor body, Step 1: performing a surface roughening treatment on an outer surface of the capacitor body where the external electrodes are to be provided, to form a roughened surface layer having an uneven surface; Step 2: immersing at least the outer surface of the capacitor body on which the roughened surface layer is provided in a solution of an ion catalyst containing at least one seed metal ion selected from gold, silver, and platinum group metal ions, and allowing the seed metal ions in the ion catalyst to be adsorbed onto the outer surface of the roughened surface layer; Step 3: immersing at least the outer surface of the capacitor body having the roughened surface layer in a reducing chemical solution to reduce the adsorbed seed metal ions to seed metal, and the reduced seed metal is fixed to the outer surface of the roughened surface layer to form a seed layer; Step 4: plating the seed layer to form an electrode metal layer; and step 5 of forming a welding metal layer by plating the outside of the electrode metal layer.

[0022] Furthermore, after step 4 and before step 5, the method further includes a step of forming a protective layer of a metal material, such as a nickel metal layer, having a thickness of 2-5 μm on the outer surface of the electrode metal layer by chemical plating or electroplating.

[0023] Furthermore, the weld metal layer is a tin metal layer formed by chemical plating or electroplating, and the thickness of the tin metal layer is 2-5 μm.

[0024] Furthermore, in the plating method of step 4, at least the outer surface of the capacitor body on which the roughened surface layer is provided is immersed in an electrode metal solution, and the electrode metal in the electrode metal solution replaces part of the seed metal, and the electrode metal is precipitated and plated onto the seed layer and the portions of the first internal electrode and the second internal electrode exposed from the outer surface of the capacitor body, thereby forming the electrode metal layer.

[0025] Furthermore, the surface roughening treatment is carried out by sandblasting, laser beam irradiation, or heating. .

[0026] Furthermore, after step 1 and before step 2, The method further includes a step of immersing the roughened surface layer of the capacitor body in an activation chemical solution to perform a surface activation treatment, thereby improving the adsorption ability of the capacitor body to the ion catalyst.

[0027] Furthermore, before step 1, The method further includes a pre-treatment step 2 of immersing the capacitor body in an insulating chemical solution to coat the entire outer surface of the capacitor body with a layer of a protective film formed of an insulating chemical material.

[0028] Furthermore, when the protective film is heat treated, the insulating chemical material in the protective film permeates into gaps formed on the sintered outer surface of the capacitor body.

[0029] Furthermore, the protective film is made of methyl silicone oil.

[0030] Furthermore, after performing the surface roughening treatment, the portions of the protective film corresponding to the locations of the external electrodes of the capacitor body are removed, and the portions of the protective film corresponding to the locations of the capacitor body where the external electrodes are not provided are left.

[0031] Furthermore, before the pre-treatment step 2, The method further includes a pre-treatment step 1 in which the entire capacitor body is subjected to a cleaning treatment.

[0032] Furthermore, after step 2 and before step 3, The method further includes performing a cleaning process on the capacitor body to wash away the seed metal ions adhering to the first internal electrode, the second internal electrode, and the outer surface of the protective film. [Effects of the Invention]

[0033] The beneficial effects of the present invention are as follows: The seed layer of the multilayer ceramic capacitor of the present invention facilitates plating of the metal electrode layer, and the metal electrode layer formed by plating has a uniform and thin thickness, which uniformly distributes stress and prevents cracks from occurring in the external electrodes. In addition, because the metal electrode layer is formed by plating, sintering is avoided, and the high density prevents penetration of nickel liquid, etc., and prevents cracks from occurring in the capacitor body. [Brief explanation of the drawings]

[0034] The above-mentioned objects, technical means and beneficial effects of the invention can be realized by the following attached drawings.

[0035] [Figure 1] 1 is a flowchart of forming external electrodes of a multilayer ceramic capacitor according to the prior art. [Figure 2] 1 is a perspective view of a multilayer ceramic capacitor according to the present invention; [Figure 3] FIG. 3 is a cross-sectional view of the multilayer ceramic capacitor shown in FIG. [Figure 4] FIG. 4 is an enlarged view of the structure within the circle in FIG. 3. [Figure 5] 3 is a schematic diagram of the structure formed in step 2 of the method for producing the multilayer ceramic capacitor of the present invention. FIG. [Figure 6] FIG. 2 is a schematic diagram of the structure formed in step 3 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 7] FIG. 2 is a schematic diagram of the structure formed in step 4 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 8] FIG. 5 is a schematic diagram of the structure formed in step 5-6 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 9] FIG. 2 is a schematic diagram of the structure formed in step 7 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 10] FIG. 2 is a schematic diagram of the structure formed in step 8 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 11] FIG. 10 is a schematic diagram of the structure formed in step 9 of the method for producing the multilayer ceramic capacitor of the present invention. [Figure 12] FIG. 2 is a schematic diagram of the structure formed in step 10 of the method for producing a multilayer ceramic capacitor of the present invention. [Figure 13] FIG. 13 is an enlarged view of the structure within the circle in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will now be described in more detail with reference to the accompanying drawings of examples.

[0037] Please refer to Figures 2 to 7 at the same time. A first preferred embodiment of the present invention provides a multilayer ceramic capacitor 100 including a capacitor body 10, two external electrodes 20 provided on two end faces 13 of the capacitor body 10 that face each other in the longitudinal direction, and a protective film 30 that covers the capacitor body 10 and is located on the outer surface between the two external electrodes 20.

[0038] The capacitor body 10 includes a plurality of laminated dielectric layers 14 and alternatingly laminated internal electrodes, including first and second internal electrodes 151 and 153. The dielectric layers 14 are typically made of a ceramic dielectric material. The outer end surfaces of the first and second internal electrodes 151 and 153 are exposed from two end surfaces 13 of the capacitor body 10, respectively. The first and second internal electrodes 151 and 153 are alternately spaced apart, and the dielectric layers 14 are interposed between adjacent first and second internal electrodes 151 and 153, forming the active area of ​​the multilayer ceramic capacitor 100 together with the first and second internal electrodes 151 and 153. The first and second internal electrodes 151 and 153 may be metal electrodes made of nickel, silver, or copper. The capacitor body 10 has an outer peripheral surface 11 connecting the two opposing end surfaces 13. The external electrode 20 includes at least a two-layer electrode layer structure consisting of an electrode metal layer 27 located in the inner layer and a weld metal layer 28 located in the outermost layer.

[0039] The two external electrodes 20 cover the corresponding end faces 13 and at least a part of the outer peripheral surface 11, respectively, and are electrically connected to the outer end faces of the first internal electrode 151 and the second internal electrode 153, respectively.

[0040] In this embodiment, the electrode layers of the external electrodes 20 specifically include an electrode metal layer 27 and a weld metal layer 28, each of which includes an end wall 21 and a peripheral wall 23 connected to the periphery of the end wall 21 and extending toward the same side of the end wall 21. The end wall 21 covers the corresponding end face 13 of the capacitor body 10, and the peripheral walls 23 of the two external electrodes 20 cover opposite ends of the outer circumferential surface 11. The electrode metal layer 27 may be a chemically plated copper metal layer. In other embodiments, the electrode metal layer 27 may be a chemically plated nickel metal layer, and the weld metal layer 28 is a chemically plated or electroplated tin metal layer to facilitate electric welding. It is understood that an additional layer, such as a conductive resin electrode layer, may be provided between the two layers of the external electrode 20 to reduce mechanical shock, etc. In this embodiment, one end of the peripheral wall 23 of the external electrode 20, away from the end wall 21, forms the boundary edge 25.

[0041] When a voltage is applied between the two outer electrodes 20, the outer electrodes 20 cause the first inner electrode 1 51 and the second internal electrode 153 are electrically connected, and a voltage is applied to the plurality of dielectric layers 14 between the first internal electrode 151 and the second internal electrode 153, thereby storing charge in the multilayer ceramic capacitor 100 and generating a capacitance value.

[0042] To uniformly form the electrode metal layer 27 of the external electrode 20 and prevent cracks from occurring in the external electrode 20 or internal cracks from occurring in the capacitor body 10, in this embodiment, the external electrode 20 includes, from inside to outside, a seed layer 26 (or catalyst layer), the electrode metal layer 27, and a weld metal layer 28. The seed layer 26 contains at least one seed metal 310 selected from gold, silver, and platinum-group metals (e.g., ruthenium, rhodium, palladium, osmium, iridium, and platinum). The seed layer 26 is thin and distributed at intervals. After replacing the electrode metal (copper or nickel) in the electrode metal layer 27, the amount of seed metal 310 in the seed layer 26 is further reduced, and the seed metal 310 is distributed over the roughened surface layer 29 of the capacitor body 10 and the first and second internal electrodes 151 and 153. The electrode metal layer 27 is formed by chemical plating using the seed layer 26 as a base. The thickness of the electrode metal layer 27 formed by chemical plating can be significantly reduced. When the electrode metal layer 27 formed by chemical plating is a copper metal layer, the thickness of the copper metal layer can be 7-8 μm, and at its thinnest, 0.5-0.6 μm. This significantly reduces the thickness of the external electrode 20 and reduces internal stress within the electrode metal layer 27. The electrode metal layer 27 formed by chemical plating has a uniform thickness, which uniformly distributes stress rather than concentrating near the end surface 13 of the capacitor body 10, preventing cracks from occurring in the capacitor body 10. Furthermore, the electrode metal layer 27 formed by chemical plating is highly dense, making it resistant to the penetration of moisture and welding metals (e.g., nickel solution). A protective film 30 is formed on the capacitor body 10 between the external electrodes 20, and the protective film 30 can further prevent moisture and welding metal (e.g., metals such as tin and nickel) from seeping into the external electrodes 20 at the boundary edges 25 of the electrode metal layer 27, and can also prevent short circuits between the external electrodes 20 at two opposite ends.

[0043] In this embodiment, the electrode layer of the external electrode 20 includes at least a three-layer structure of an electrode metal layer 27 formed by plating (specifically, a chemically plated copper layer is used in this embodiment), a protective layer 33 of a metal protective material (specifically, an electroplated nickel layer is used in this embodiment), and a weld metal layer 28 formed by plating (specifically, a chemically plated / electroplated tin layer is used in this embodiment), or includes at least a two-layer structure of an electrode metal layer 27 formed by plating (specifically, a chemically plated nickel layer may be used in this embodiment) and a weld metal layer 28 formed by plating (specifically, a chemically plated / electroplated tin layer is used in this embodiment).

[0044] In this embodiment, the seed layer 26 is not formed on the portion of the internal electrode exposed from the end face 13 , and the electrode metal layer 27 is directly connected to the portion of the internal electrode exposed from the end face 13 .

[0045] In this embodiment, the thickness of the protective film 30 may be equal to or greater than the thickness of the electrode metal layer 27 , and in other embodiments, the thickness of the protective film 30 may be equal to or greater than the thickness of the external electrode 20 .

[0046] In this embodiment, the boundary edges 25 of the electrode metal layer 27 on the upper and lower surfaces of the capacitor body 10 are linear along the width direction perpendicular to the longitudinal direction, thereby increasing the insulation distance L2 between the two external electrodes 20 and preventing electrical interruption or short circuit between the external electrodes 20.

[0047] The shape of the capacitor body 10 is not limited to the rectangular parallelepiped of this embodiment. For example, the surface of the capacitor body 10 may be curved, the shape of the capacitor body 10 may be cylindrical as a whole, or the eight corners of the capacitor body 10 may be rounded or chamfered. It is understood that this is also acceptable.

[0048] It will be understood that in other embodiments, the number of internal electrodes and the thickness of the dielectric layer 14 can be determined depending on the size and performance requirements of the capacitor 100 .

[0049] The second preferred embodiment of the present invention further provides a method for forming the multilayer ceramic capacitor 100, and the specific method is as follows.

[0050] Step 1: A pre-processing step including cleaning is performed on the capacitor body 10.

[0051] Step 2: The entire outer surface 11 and end faces 13 of the capacitor body 10 are coated with a layer of protective film 30 (see FIG. 5 for details). Specifically, the capacitor body 10 is immersed in an insulating chemical solution to form the protective film 30, and the outer surface 11 of the capacitor body 10 is coated with a thin layer of protective film 30. The thickness of the protective film 30 may be 0.3-5 μm, but is not limited to this and can be adjusted according to the thickness of the electrode metal layer 27 or the external electrode 20. The protective film 30 has characteristics such as waterproofness, high-temperature resistance, and insulating properties. In one embodiment, the protective film is a silicone oil material layer. Silicone oil has properties such as high hydrophobicity, a small temperature-dependent viscosity coefficient, excellent high- and low-temperature resistance, anti-oxidation, a high flash point, low volatility, high insulating properties, low surface tension, and is non-corrosive and non-toxic to metals. Silicone oils include methylsilicone oil, methylphenylsilicone oil, various functional silicone oils, and modified silicone oils. In a preferred embodiment of the present invention, the protective film 30 is specifically made of the most widely used methylsilicone oil (also known as dimethylsilicone oil, with the chemical formula (CH3)3SiO[(CH3)2SiO]n·Si(CH3)3). Methylsilicone oil is a colorless, transparent, novel synthetic polymer material available in a variety of viscosities ranging from 5 cps to 8 million cps, and can be in the form of a highly flowable liquid or a thick semi-solid. Methylsilicone oil has excellent water repellency, chemical stability, excellent electrical insulation, and high and low temperature resistance. It has a high flash point, a low freezing point, and can be used for long periods at temperatures from -50°C to +200°C. It also has a small temperature-dependent viscosity coefficient, a high compressibility, low surface tension, excellent water repellency and moisture resistance, and a low specific heat and thermal conductivity, all of which contribute to the excellent protective properties of the multilayer ceramic capacitor 100.A layer of insulating chemical material (specifically, in this embodiment, a layer of methyl silicone oil is used to form the protective film 30) is applied to the surface of the capacitor body 10 of the multilayer ceramic capacitor 100 by immersion, and then heat treatment is performed at 250-300°C, so that the insulating chemical material layer penetrates into the gaps formed on the surface after the capacitor body 10 is sintered, and a single semi-permanent protective film 30 is formed that is further excellent in waterproofness, mildew resistance, insulation, high temperature resistance, and stability.

[0052] Step 3: To facilitate the modification and roughening treatment of the corresponding regions of the capacitor body 10, the protective film 30 in the region where the external electrode 20 is to be formed is processed and removed using a laser device, see Fig. 6 for details. In other embodiments, step 3 may be performed simultaneously with the subsequent surface roughening treatment, i.e., after the surface roughening treatment, the portion of the protective film 30 corresponding to the capacitor body 10 where the external electrode 20 is to be formed is removed, and the portion of the protective film 30 corresponding to the capacitor body 10 where the external electrode 20 is not to be formed remains.

[0053] Step 4: Using a laser irradiation device, sandblasting, laser beam irradiation, or heating is performed to treat the portion of the capacitor body 10 where the external electrode 20 will be formed, modifying the outer surface of the corresponding portion of the capacitor body 10 and simultaneously performing surface roughening treatment, thereby forming a roughened surface layer 29 with an uneven surface, the depth of the roughened surface layer 29 is about 1 μm, and the adsorption ability of the outer surface of the capacitor body 10 is improved, which is in turn compatible with the electrode metal layer 27 formed later by chemical plating. This increases the contact area and helps strengthen the bonding strength of the electrode metal layer 27 to the capacitor body 10 (see FIG. 6 for details). Because the first internal electrode 151 and the second internal electrode 153 are made of metal, the exposed portions of the first internal electrode 151 and the second internal electrode 153 at the end faces 13 are not roughened, whereas the portions of the dielectric layer 14 are roughened. It is understood that the roughness of the roughened surface layer 29 is greater than the roughness of the outer surface of the capacitor body 10 where the external electrode 20 is not provided. Because they are not roughened, the exposed portions or outer edges of the first internal electrode 151 and the second internal electrode 153 protrude from the roughened surface layer 29, i.e., the first internal electrode 151 and the second internal electrode 153 are not lower than the most protruding portion of the uneven surface of the roughened surface layer 29, which facilitates subsequent direct connection between the electrode metal layer 27 of the external electrode 20 and the first internal electrode 151 and the second internal electrode 153. In order to more suitably perform the surface roughening treatment on the dielectric layer 14, the laser irradiation device for performing the processing can be appropriately selected depending on the type of material used for the dielectric layer 14.

[0054] Step 5: After the modification and roughening treatments, the capacitor body 10 having the roughened surface layer 29 is immersed in an activation chemical solution to perform a surface activation treatment, thereby further improving the adsorption ability of the capacitor body 10 for the ion catalyst. The activation chemical solution may be a solution suitable for surface activation treatment of the dielectric layer 14, such as a sodium hydroxide solution.

[0055] Step 6: The capacitor body 10 is immersed in a solution of an ion catalyst containing at least one seed metal ion 31 selected from gold, silver, or platinum-group metal ions (e.g., ruthenium, rhodium, palladium, osmium, iridium, and platinum), and the seed metal ions 31 in the ion catalyst are adsorbed onto the modified and roughened surface layer 29 (see FIG. 8 for details). Seed metal ions 31 are also present on the exposed portions of the internal electrodes at the end faces 13, which are the outer surfaces that have not been modified or roughened, and on the outer surface of the protective film 30, but they are not firmly adsorbed. In this embodiment, the ion catalyst preferably contains palladium ions.

[0056] Step 7: The capacitor body 10 is washed to remove the seed metal ions 31 adhering to the exposed end faces 13 of the internal electrodes and the outer surface of the protective film 30, which are the outer surfaces that have not been subjected to the modification or roughening treatment. The capacitor body 10 is then immersed in a reducing chemical solution to reduce the adsorbed ion catalyst to seed metal 310 (catalytic metal). As described above, the ion catalyst is firmly fixed to the roughened surface layer 29 after the roughening treatment, so the reduced seed metal 310 is also firmly fixed to the roughened surface layer 29. See FIG. 9 for details. It should be understood that the seed metal 310 is not fixed to the outer surfaces of the capacitor body 10 that have not been roughened (the exposed end faces 13 of the internal electrodes 20 and the outer surface of the protective film 30). In this embodiment, the ion catalyst specifically contains palladium ions. Therefore, when the capacitor body 10 is immersed in the reducing chemical solution, the ion catalyst containing palladium ions is reduced to palladium metal, i.e., seed metal 310, which is firmly fixed to the roughened surface layer 29. Furthermore, step 7 may include a step of immersing the capacitor body 10 to which the seed metal 310 is adsorbed in a surfactant-containing aqueous solution, thereby removing the oxide layer on the outer surface of the adsorbed seed metal 310 (specifically palladium metal in this embodiment) and activating it, thereby facilitating the progress of the subsequent chemical plating process of the electrode metal layer 27.

[0057] Step 8: The capacitor body 10 is immersed in an electrode metal solution, and the seed metal 310 on the outer surface of the capacitor body 10 becomes the seed layer 26 (also called a catalyst layer). In addition, since the portions exposed from the end faces 13 of the first internal electrode 151 and the second internal electrode 153 are made of a metal material, the electrode metal in the electrode metal solution is precipitated and plated onto the seed layer 26 and the portions exposed from the end faces 13 of the first internal electrode 151 and the second internal electrode 153 to form an electrode metal layer 27. In addition, since the electrode metal replaces the seed metal 310, a small amount of seed metal is deposited on the capacitor body 10. The remaining metal 310 connects the electrode metal layer 27 to the exposed end surfaces 13 of the first and second internal electrodes 151 and 153 through direct contact therewith, i.e., the electrode metal layer 27 of the external electrode 20 is directly electrically connected to the first and second internal electrodes 151 and 153, improving electrical conductivity (see FIG. 10 for details). The border 25 of the electrode metal layer 27 is connected to and shielded by the remaining protective film 30, preventing moisture from seeping into the external electrode 20 through the border 25. In this embodiment, the electrode metal solution is a chemical plating copper metal solution, and the seed metal 310 on the outer surface of the capacitor body 10 is palladium metal. The palladium metal seed layer 26 (or catalyst layer) precipitates copper metal in the chemical plating copper metal solution and plates it onto the palladium metal, the first internal electrode 151, and the second internal electrode 153. The copper metal replaces the palladium metal, leaving only a small amount of palladium metal on the capacitor body 10. This copper metal layer forms the electrode metal layer 27 of the external electrode 20. The copper metal layer of the electrode metal layer 27 may have a minimum thickness of 0.5-0.6 μm, and a maximum thickness of 7-8 μm when chemical plating efficiency is highest. A thickness greater than 10 μm results in poor chemical plating efficiency. In other embodiments, if the thickness of the electrode metal layer 27 needs to be further increased, further chemical plating or electroplating can be performed to thicken the electrode metal layer 27 to a thickness of 10-15 μm or higher, as needed. The electrode metal layer 27 has a uniform thickness, and the thickness is thin at the edge of the end surface 13 of the electrode metal layer 27, but there is no phenomenon of the thickness being thick at the end, so stress is uniformly distributed and cracks are prevented from occurring in the external electrode 20.

[0058] Step 9: A protective layer 33 made of a metal material may be further formed on the outer surface of the electrode metal layer 27 by chemical plating or electroplating, and the protective layer 33 can prevent oxidation of the electrode metal layer 27 and penetration of the weld metal layer 28. For details, see Figure 11. In this embodiment, the specific protective layer 33 is a nickel metal layer protective layer 33, and the thickness of the metal protective layer 33 formed by chemical plating is 2-5 μm.

[0059] Step 10: To facilitate welding of the external electrodes 20 of the multilayer ceramic capacitor 100, a weld metal layer 28 is further formed on the outer surface of the protective layer 33 by chemical plating or electroplating. For details, see Figures 12 and 13. Figures 12 and 13 are consistent with Figures 3 and 4, and it should be understood that Figures 12 and 13 are schematic diagrams of the forming step, intended to provide a clearer understanding of the present invention. In this embodiment, the specific weld metal layer 28 is a tin metal layer, and the thickness of the weld metal layer 28 formed by chemical plating is 2-5 μm.

[0060] It is understood that in the method for forming the multilayer ceramic capacitor 100 of the present invention, step 1 is a cleaning step, steps 2 and 3 are steps for treating the protective film 30, step 4 is a roughening treatment step, and step 5 is an activation step. In other embodiments of the present invention, any combination of steps 1, 2 and 3, and step 5 may be selectively omitted, and the roughening treatment of step 4 and the ion catalyst solution immersion process of step 6 may be directly performed.

[0061] In the method for forming the multilayer ceramic capacitor 100 of the present invention, step 9 is the step of forming the protective layer 33, and it is understood that in other embodiments of the present invention, step 9 may be selectively omitted and the step of forming the weld metal layer 28 in step 10 may be directly performed.

[0062] The external electrode of the multilayer ceramic capacitor 100 of the present invention includes, from the inside to the outside, a seed layer 26 and an electrode layer, and the electrode layer includes at least a two-layer structure of an electrode metal layer 27 and a weld metal layer 28. The seed layer 26 can facilitate plating of the electrode metal layer 27, and the thickness after plating can be 7-8 μm, and the thinnest case can be 0.5-0.6 μm. In addition, when the seed metal 310 of the seed layer 26 replaces the electrode metal in the electrode metal solution, the seed layer 26 By using a forming method in which the seed metal 310 is reduced to a certain extent, leaving only a small amount of seed metal 310 remaining, and the seed layer 26 is then replaced to form the external electrode 20 of the electrode metal layer 27, the thickness of the external electrode 20 can be significantly reduced, and the overall size of the multilayer ceramic capacitor 100 can be further reduced. In addition, after the electrode metal layer 27 (e.g., a copper metal layer) formed by chemical plating is formed, it is uniformly distributed over the capacitor body 10, and the thickness distribution of the electrode metal layer 27 is uniform on the end face 13 and the outer peripheral surface 11, so that stress does not concentrate on the end face 13, thereby preventing cracks from occurring in the external electrode 20 and inside the capacitor body 10. The electrode metal layer 27 (e.g., a copper metal layer) formed by plating (formed by a chemical plating method) is highly dense, and can effectively prevent moisture and the welding metal solution used for subsequent plating from seeping into the space between the external electrode 20 and the capacitor body 10, and further prevents cracks from occurring inside the capacitor body 10, thereby improving the performance and lifespan of the product.

[0063] In the present invention, the electrode metal layer 27 formed by plating has boundary edges 25 on the upper and lower surfaces of the capacitor body 10 that are linear in the width direction perpendicular to the longitudinal direction. This increases the insulation distance L2 between the external electrodes 20 located at the two opposing ends, compared to the arc-shaped contracted rims formed by sintering in the prior art, and further prevents electrical interruption or short circuit between the external electrodes 20.

[0064] The present invention performs roughening and modification treatments on the outer surface portion of the capacitor body 10 where the external electrode 20 is provided, thereby forming a roughened surface layer 29, thereby improving the adhesion ability of the seed layer 26 and the electrode metal layer 27 (e.g., a copper metal layer) to the capacitor body 10, increasing the contact area for the subsequent plating formation of the electrode metal layer 27 (e.g., a copper metal layer), and improving the bonding ability between the electrode metal layer 27 (e.g., a copper metal layer) and the capacitor body 10. The seed layer 26 can later promote the stable and uniform adhesion of the electrode metal layer 27 (e.g., a copper metal layer) to the capacitor body 10.

[0065] In the present invention, a protective film 30 is formed on the outer surface of the capacitor body 10 where the external electrode 20 is not formed. The specific thickness of the protective film 30 is equal to or greater than the thickness of the electrode metal layer 27 (e.g., copper metal layer). In this way, the protective film 30 can shield the boundary edge 25 of the electrode metal layer 27 (e.g., copper metal layer) and prevent moisture and subsequent welding metal solution from seeping in through the boundary edge 25 of the electrode metal layer 27.

[0066] The technical features of the above embodiments can be combined in any way, and for the sake of simplicity, not all possible combinations of the technical features in the above embodiments are listed, but as long as the combinations of these technical features are not contradictory, they should be included in the scope of the present specification.

[0067] The above examples merely represent embodiments of the present invention and have been described in detail, but should not be construed as limiting the scope of the claims of the present invention. It should be noted that a person skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and all of these are included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be governed by the appended claims. [Explanation of symbols]

[0068] 100 multilayer ceramic capacitor, 10 capacitor body, 11 outer peripheral surface, 13 end surface, 14 dielectric layer, 151 first internal electrode, 153 second internal electrode, 30 protective film, 20 external electrode, 21 end wall, 23 peripheral wall, 25 boundary edge, 26 seed layer, 27 electrode metal layer, 28 weld metal layer, 29 surface roughening layer, 31 seed metal ion, 33 protective layer, 310 seed metal.

Claims

1. A method for manufacturing a multilayer ceramic capacitor including a capacitor body and two external electrodes provided on the capacitor body and facing each other with a gap therebetween, wherein the capacitor body includes a plurality of first internal electrodes, a plurality of second internal electrodes, and a dielectric layer separating the first internal electrodes and the second internal electrodes, and one end of the first internal electrodes and one end of the second internal electrodes are exposed from an outer surface of the capacitor body, a step 1 in which a surface roughening treatment is performed on a part of the outer surface of the capacitor body where the external electrodes are provided, to form a roughened surface layer having an uneven surface with a roughness greater than that of the outer surface of the part of the capacitor body where the external electrodes are not provided, and the parts of the first internal electrodes and the second internal electrodes exposed from the outer surface of the capacitor body are not roughened, so that the first internal electrodes and the second internal electrodes are exposed from the roughened surface layer and the exposed parts of the first internal electrodes and the second internal electrodes protrude from the roughened surface layer; Step 2: immersing at least the outer surface of the capacitor body, on which the roughened surface layer is provided, in a solution of an ion catalyst containing at least one seed metal ion selected from gold, silver, and platinum group metal ions, and after cleaning the capacitor body, allowing the seed metal ions in the ion catalyst to be adsorbed only on the outer surface of the roughened surface layer; Step 3: immersing the capacitor body in a reducing chemical solution to reduce the adsorbed seed metal ions to seed metal, and the reduced seed metal is fixed on the outer surface of the surface roughening layer to form a seed layer; Step 4: plating the seed layer to form an electrode metal layer, and exposing the first internal electrode and the second internal electrode from the seed layer to directly connect them to the electrode metal layer; and step 5, wherein plating is applied to the outside of the electrode metal layer to form a welding metal layer.

2. After step 4 and before step 5, 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, further comprising the step of forming a protective layer of a metal material, which is a nickel metal layer and has a thickness of 2-5 μm, on an outer surface of the electrode metal layer by chemical plating or electroplating.

3. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein the weld metal layer is a tin metal layer formed by chemical plating or electroplating, and the tin metal layer has a thickness of 2-5 μm.

4. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein in the plating method of step 4, at least the outer surface of the capacitor body on which the roughened surface layer is provided is immersed in an electrode metal solution, and the electrode metal in the electrode metal solution replaces a part of the seed metal, and the electrode metal is precipitated and plated onto the seed layer and the first internal electrode and the second internal electrode portions exposed from the outer surface of the capacitor body, thereby forming the electrode metal layer.

5. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein the surface roughening treatment is performed by sandblasting, laser beam irradiation, or heating.

6. After step 1 and before step 2, 6. The method for manufacturing a multilayer ceramic capacitor according to claim 5, further comprising the step of immersing the roughened surface layer of the capacitor body in an activation chemical solution to perform a surface activation treatment, thereby improving the adsorption ability of the capacitor body to the ion catalyst.

7. Before step 1, 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, further comprising a pre-treatment step 2 of immersing the capacitor body in an insulating chemical solution to cover the entire outer surface of the capacitor body with a layer of a protective film formed of an insulating chemical material.

8. 8. The method for manufacturing a multilayer ceramic capacitor according to claim 7, wherein when the protective film is heat-treated, the insulating chemical material in the protective film permeates into gaps formed on the outer surface of the sintered capacitor body.

9. 8. The method for manufacturing a multilayer ceramic capacitor according to claim 7, wherein the protective film is made of methyl silicone oil.

10. 8. The method for manufacturing a multilayer ceramic capacitor according to claim 7, wherein, after the surface roughening treatment, portions of the protective film corresponding to the locations of the capacitor body where the external electrodes are to be provided are removed, and portions of the protective film corresponding to the locations of the capacitor body where the external electrodes are not provided are left.

11. Before the pre-treatment step 2, 8. The method for manufacturing a multilayer ceramic capacitor according to claim 7, further comprising a pre-treatment step 1 in which the entire capacitor body is subjected to a cleaning treatment.

12. A method for manufacturing a multilayer ceramic capacitor as described in claim 1, characterized in that the seed metal of the seed layer is distributed at intervals in the roughened surface layer.

13. A method for manufacturing a multilayer ceramic capacitor as described in claim 1, characterized in that the electrode metal layer is a copper metal layer or a nickel metal layer, and the thickness range of the electrode metal layer is 0.5 um to 8 um.

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