JP7784612B2 - Multilayer ceramic capacitor and its manufacturing method - Google Patents

Description

The present invention relates to the technical field of capacitors, and in particular to multilayer ceramic capacitors and methods for manufacturing the same.

As an example of a conventional multilayer ceramic capacitor, Chinese invention patent application CN114078634A discloses a multilayer ceramic capacitor having a capacitor body that is a sintered body formed by alternately laminating and sintering dielectric layers and internal electrodes, with external electrodes provided on each end 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 material in copper paste and sintering it to obtain a copper layer, then electroplating to form a nickel layer, and finally electroplating to form a tin layer. As a result, the innermost copper layer is a sintered copper layer, which is thick and uneven in thickness. Furthermore, 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 can lead to increased electrode size and larger capacitors.

Referring to FIG. 1, when manufacturing the copper layer of the external electrode, the capacitor body 10 is placed vertically, and the end of the capacitor body 10 to which the copper paste 200 is to be attached is immersed in the copper paste 200 with the end pointing 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 layer of the external electrode can be formed at the end of the capacitor body 10. However, the multilayer ceramic capacitor obtained by this manufacturing method has the following drawbacks: 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, causing stress in the copper layer to concentrate near the edges of the copper layer and making the external electrodes prone to cracking; 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; and because the distance extending along the length of the capacitor body 10 between the external electrodes at both ends of the capacitor body 10 is small, making it easy for the external electrodes to short-circuit.

While internal cracking is unlikely to occur in the capacitor body 10 when external electrodes are not formed on the multilayer ceramic capacitor, the bonding stress between the copper layer and the capacitor body 10 during the copper layer sintering process often releases residual stress, causing the sintered copper layer to crack the capacitor body 10. 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 subsequent application of the multilayer ceramic capacitor, 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, leaving nickel remaining in 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.

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 and a method for manufacturing the same that can suppress the occurrence of cracks in the capacitor body and external electrodes.

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.

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

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

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

Furthermore, the electrode metal layer is formed on the outer surface of the seed layer using a chemical plating method.

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 roughened surface layer.

Furthermore, the seed metal is palladium metal.

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 μm to 8 μm.

Furthermore, the seed metal of the seed layer is replaced by the electrode metal solution to deposit the electrode metal layer, and 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 that are exposed from the outer surface of the roughened surface layer.

Furthermore, 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.

Furthermore, the protective layer is made of nickel metal.

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 covering 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 each exposed from 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.

Furthermore, the outer peripheral surface of the capacitor body where the external electrode is not provided is covered with a layer of protective film, the thickness of which 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.

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

Furthermore, the protective film is methyl silicone oil, and the thickness of the protective film is 0.3-5 μm.

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.

Furthermore, after step 4 and before step 5, the method further includes forming a protective layer of a metallic 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.

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.

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.

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

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.

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.

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

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

Furthermore, after the surface roughening treatment, the portions of the protective film corresponding to the locations of the external electrodes of the capacitor body are removed, leaving portions of the protective film corresponding to the locations of the capacitor body where the external electrodes are not provided.

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

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.

The beneficial effects of the present invention are as follows: The seed layer of the multilayer ceramic capacitor of the present invention makes it easy to plate the electrode metal layer, and the plated electrode metal layer has a uniform, thin thickness, which distributes stress evenly and prevents cracks from occurring in the external electrode. In addition, because the electrode metal layer is formed by plating, it is possible to avoid forming using a sintering method, and the high density prevents the penetration of nickel liquid, etc., and prevents cracks from occurring in the capacitor body.

The above-mentioned objectives, technical means, and beneficial effects of the invention can be realized by the attached drawings below.

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

The present invention will now be described in further detail with reference to the accompanying drawings of the embodiments.

Referring simultaneously to Figures 2 to 7, 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.

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, constituting the effective 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 has at least a two-layer electrode structure consisting of an electrode metal layer 27 located in the inner layer and a weld metal layer 28 located in the outermost layer.

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

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 nickel metal layer formed by chemical plating, and the weld metal layer 28 is a tin metal layer formed by chemical plating or electroplating 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.

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.

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, or a platinum-group metal (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 metal or nickel metal) 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 dispersed throughout 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 face 13 of the capacitor body 10, thereby 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 penetration by 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 further prevents moisture and welding metals (e.g., tin and nickel) from penetrating 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 the two opposing ends.

In this embodiment, the electrode layer of the external electrode 20 includes at least a three-layer structure consisting of a plated electrode metal layer 27 (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 plated weld metal layer 28 (specifically, a chemically plated/electroplated tin layer is used in this embodiment), or includes at least a two-layer structure consisting of a plated electrode metal layer 27 (specifically, a chemically plated nickel layer may be used in this embodiment) and a plated weld metal layer 28 (specifically, a chemically plated/electroplated tin layer is used in this embodiment).

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

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

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, increasing the insulation distance L2 between the two external electrodes 20 and preventing electrical interruption or short circuit between the external electrodes 20.

It is understood that the shape of the capacitor body 10 is not limited to the rectangular parallelepiped of this embodiment, and that, for example, the surface of the capacitor body 10 may be curved, the shape of the capacitor body 10 may be cylindrical overall, or the eight corners of the capacitor body 10 may be rounded corners, chamfered corners, etc.

It is 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.

Specifically, the second preferred embodiment of the present invention further provides a method for forming the multilayer ceramic capacitor 100, the specific method being as follows:

Step 1: Pre-processing, including cleaning, is performed on the capacitor body 10.

Step 2: The entire outer surface 11 and end faces 13 of the capacitor body 10 are coated with a single 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 to match 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 methyl silicone oil (also known as dimethyl silicone oil, with the chemical formula (CH3)3SiO[(CH3)2SiO]n.Si(CH3)3). Methyl silicone 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 fluid liquid or a thick semi-solid. Methyl silicone oil has good water repellency, chemical stability, excellent electrical insulation, and high and low temperature resistance. It has a high flash point, a low freezing point, can be used for long periods at temperatures from -50°C to +200°C, a small temperature-dependent viscosity coefficient, a high compressibility, low surface tension, excellent water and moisture repellency, and a low specific heat 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 by immersion to the surface of the capacitor body 10 of the multilayer ceramic capacitor 100, and then heat treatment is performed at 250-300°C. The insulating chemical material layer permeates into the gaps that form on the surface after the capacitor body 10 is sintered, forming a single, semi-permanent protective film 30 that is waterproof, mildew-resistant, insulating, high-temperature resistant, and stable.

Step 3: To facilitate modification and roughening of the corresponding areas of the capacitor body 10, the protective film 30 in the area where the external electrode 20 will 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; that is, after the surface roughening treatment, the portion of the protective film 30 corresponding to the capacitor body 10 where the external electrode 20 will be formed is removed, leaving the portion of the protective film 30 corresponding to the capacitor body 10 where the external electrode 20 will not be formed.

Step 4: Using a laser irradiation device, sandblast, laser beam irradiation, or heating is performed to treat the portion of the capacitor body 10 where the external electrode 20 will be formed, thereby modifying the outer surface of the corresponding portion of the capacitor body 10 and simultaneously roughening the surface, thereby forming a roughened surface layer 29 with an uneven surface. The roughened surface layer 29 has a depth of about 1 μm, which improves the adhesion ability of the outer surface of the capacitor body 10, increases the contact area with the electrode metal layer 27 formed later by chemical plating, and helps strengthen the bonding force 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 portions of the first internal electrode 151 and the second internal electrode 153 exposed from the end face 13 are not roughened, while the portions of the dielectric layer 14 are roughened. It can be seen 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. Since the dielectric layer 14 has not been 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 on the uneven surface of the roughened surface layer 29, and in this way it becomes easy to later directly connect the electrode metal layer 27 of the external electrode 20 to 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.

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.

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 electrode end faces 13, which are the outer surface portions not subjected to the modified and roughened treatment, and on the outer surface of the protective film 30, but it should be understood that the seed metal ions 31 are not firmly adsorbed. In this embodiment, the ion catalyst preferably contains palladium ions.

Step 7: The capacitor body 10 is washed, and the seed metal ions 31 adhering to the exposed portions of the internal electrode at the end faces 13, which are the outer surface portions that have not been subjected to the modification treatment or roughening treatment, and to the outer surface of the protective film 30 are washed away. The capacitor body 10 is immersed in a reducing chemical solution to reduce the adsorbed ion catalyst to seed metal 310 (catalytic metal). As described above, since the ion catalyst is firmly fixed to the roughened surface layer 29 after the roughening treatment, the reduced seed metal 310 is also firmly fixed to the roughened surface layer 29. See Figure 9 for details. It is understood that the seed metal 310 is not fixed to the outer surface of the capacitor body 10 that has not been roughened (the exposed portions of the internal electrode 20 at the end faces 13 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 reduces the ion catalyst to palladium metal, i.e., the seed metal 310, which is firmly fixed to the roughened surface layer 29. Furthermore, step 7 may include immersing the capacitor body 10 with the adsorbed seed metal 310 in an aqueous solution containing a surfactant. This removes the oxide layer on the outer surface of the adsorbed seed metal 310 (specifically palladium metal in this embodiment), activating it and facilitating the subsequent chemical plating process of the electrode metal layer 27.

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 serves as a seed layer 26 (also called a catalyst layer). Since the portions of the first internal electrode 151 and the second internal electrode 153 exposed at the end faces 13 are made of metal, the electrode metal in the electrode metal solution is precipitated and plated onto the seed layer 26 and the portions of the first internal electrode 151 and the second internal electrode 153 exposed at the end faces 13, thereby forming an electrode metal layer 27. Since the electrode metal replaces the seed metal 310, a small amount of seed metal 310 remains on the capacitor body 10, and the electrode metal layer 27 directly contacts and connects with the portions of the first internal electrode 151 and the second internal electrode 153 exposed at the end faces 13. That is, the electrode metal layer 27 of the external electrode 20 is directly electrically connected to the first internal electrode 151 and the second internal electrode 153, improving the electrical conductivity. See FIG. 10 for details. The boundary edge 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 boundary edge 25. In this embodiment, the electrode metal solution is a chemical plating copper metal solution, the seed metal 310 on the outer surface of the capacitor body 10 is palladium metal, and the palladium metal seed layer 26 (or catalyst layer) causes copper metal in the chemical plating copper metal solution to precipitate and plate the palladium metal onto 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, and the copper metal layer becomes the electrode metal layer 27 of the external electrode 20. The thickness of the copper metal layer of the electrode metal layer 27 may be 0.5-0.6 μm at its thinnest, and 7-8 μm at its thickest at its thickest when the chemical plating efficiency is highest. If the thickness exceeds 10 μm, the chemical plating efficiency will be poor. In other embodiments, if the thickness of the electrode metal layer 27 needs to be further increased, the electrode metal layer 27 can be thickened by further chemical plating or electroplating as needed to achieve a thickness of 10-15 μm or more. 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 does not become thick at the end portion, which distributes stress uniformly and prevents cracks from occurring in the external electrode 20.

Step 9: A protective layer 33 made of a metal material may be formed on the outer surface of the electrode metal layer 27 by chemical plating or electroplating. The protective layer 33 can prevent oxidation of the electrode metal layer 27 and penetration of the weld metal layer 28. See FIG. 11 for details. In this embodiment, the protective layer 33 is specifically a nickel metal layer, and the thickness of the metal protective layer 33 formed by chemical plating is 2-5 μm.

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, please refer to 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 and are intended to provide a clearer understanding of the present invention. In one embodiment, the 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.

In the method for forming the multilayer ceramic capacitor 100 of the present invention, it is understood that 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 performed directly.

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. 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, step 10, may be performed directly.

The external electrodes of the multilayer ceramic capacitor 100 of the present invention include, 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 thickness 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 further replacing the seed layer 26 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 on the end face 13 and outer peripheral surface 11 is uniform, 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 subsequent welding metal solution for plating from seeping into the gap between the external electrode 20 and the capacitor body 10, and further can prevent cracks from occurring inside the capacitor body 10, thereby improving the performance and lifespan of the product.

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 conventional technology, and further prevents electrical interruptions or short circuits between the external electrodes 20.

The present invention performs roughening and modification treatments on the outer surface of the capacitor body 10 where the external electrode 20 is provided, forming a roughened surface layer 29, which improves the adhesion ability of the seed layer 26 and electrode metal layer 27 (e.g., a copper metal layer) to the capacitor body 10, increases the contact area for the subsequent plating of the electrode metal layer 27 (e.g., a copper metal layer), and improves 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 stable and uniform adhesion of the electrode metal layer 27 (e.g., a copper metal layer) to the capacitor body 10.

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 shields the boundary edge 25 of the electrode metal layer 27 (e.g., copper metal layer) and prevents moisture and subsequent welding metal solution from seeping in through the boundary edge 25 of the electrode metal layer 27.

The technical features of the above embodiments can be combined in any way. For the sake of simplicity, not all possible combinations of the technical features of the above embodiments are listed. However, as long as these combinations of technical features are consistent, they should be considered to be within the scope of the present specification.

The above examples merely represent embodiments of the present invention and have been described in detail and specifically, 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 may make various modifications and improvements without departing from the concept of the present invention, and all such modifications and improvements are within the scope of the present invention. Therefore, the scope of the present invention should be determined in accordance with the appended claims.

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 Roughened surface layer, 31 Seed metal ion, 33 Protective layer, 310 Seed metal.

Claims (13)

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. 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. 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. 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. 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. 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. 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. 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. 8. The method for manufacturing a multilayer ceramic capacitor according to claim 7 , wherein the protective film is made of methyl silicone oil. 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. 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. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein the seed metal of the seed layer is dispersed and distributed at intervals on the roughened surface layer. 2. The method for manufacturing a multilayer ceramic capacitor according to claim 1, wherein 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 μm to 8 μm.