A method for preparing a multilayer ceramic capacitor

Abstract

The present invention discloses a method for preparing a multilayer ceramic capacitor, comprising the following steps: step S1. casting a dielectric slurry into a raw film sheet, and printing an internal electrode slurry on the raw film sheet to form an internal electrode layer; step S2. the internal electrode layer is laminated, pressed, cut, debonded, and sintered to obtain a fired laminate; step S3. covering the fired laminate with a terminal electrode copper slurry, firing the terminal, and forming the multilayer ceramic capacitor; the terminal electrode copper slurry comprises copper powder and glass powder; the glass powder comprises a metal oxide in a divalent or higher valence state; the oxygen potential value of the fired terminal is 600-800mv, the temperature of the fired terminal is 800-830℃, and the insulation time is 10-15min. On the one hand, the present invention introduces a conductive component into the glass component of the copper slurry so that the glass has a certain conductivity, and on the other hand, by controlling and adjusting the firing process, the above conductive component is partially reduced, further enhancing the conductivity of the conductive component and enhancing the terminal electrode bonding force.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials, and in particular to a method for preparing a multilayer ceramic capacitor. Background Art

[0002] Multilayer ceramic capacitors (MLCCs) are the most widely used chip components in electrical equipment and are widely used in laptops, mobile phones, automobiles, home appliances, drones and other fields. Existing multilayer ceramic capacitors include multiple stacked dielectric layers, internal electrodes arranged relative to each other with dielectric layers located between them, and terminal electrodes electrically connected to the internal electrodes. Usually, in order to form terminal electrodes, a conductive paste containing conductive powder is applied to the laminate, which is then sintered to form terminal electrodes.

[0003] The terminal electrode slurry is usually composed of copper metal phase, organic phase and glass phase. Its composition, ratio and sintering process determine the performance of the electrode after sintering. The performance of the copper slurry for the terminal electrode and the sintering process have an important influence on the appearance, basic electrical properties, reliability and solder resistance of the capacitor.

[0004] The terminal electrodes prepared by using the existing copper paste and sintering end process have the problem that the glass phase easily overflows, resulting in uneven electroplating and low electroplating efficiency, which ultimately leads to deterioration of the product's tensile properties and poor welding, and low product production efficiency. Summary of the invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the purpose of the present invention is to provide a method for preparing a multilayer ceramic capacitor, in which, on the one hand, a conductive component is introduced into the glass component of the copper paste so that the glass has a certain conductivity, and on the other hand, the above-mentioned conductive component is partially reduced by controlling and adjusting the firing process, thereby further enhancing the conductivity of the conductive component and enhancing the terminal electrode bonding force.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a multilayer ceramic capacitor comprises the following steps:

[0008] Covering the laminate with terminal electrode copper paste and firing the terminals to obtain the multilayer ceramic capacitor;

[0009] The terminal electrode copper paste includes copper powder and glass powder;

[0010] The glass powder includes metal oxides in divalent or higher valence states;

[0011] The oxygen potential value of the burning end is 600-800 mv, the temperature of the burning end is 800-830° C., and the insulation time is 10-15 minutes.

[0012] According to research, in the later stage of copper firing, the copper end gradually densifies, and a large amount of glass flows to the surface of the copper electrode. If the glass does not have conductive properties, it will cause the phenomenon of being unable to be electroplated during the subsequent electroplating process, affecting the performance of the MLCC product.

[0013] In order to avoid this situation, divalent or higher-valent metal oxides are added to the glass phase. In the high-temperature reducing atmosphere introduced during end firing, the metal oxides will be partially reduced, and the elements therein will undergo changes in valence and have a certain conductivity, thereby making the glass phase have a certain conductivity, which is beneficial to the electroplating process and enhancing the bonding strength of the end electrodes.

[0014] The present invention is to add divalent or higher valence metal oxides and then reduce them at high temperature instead of directly adding metals. This is to allow specific metal elements to be incorporated into the glass system in the form of oxides, and then to convert the valence state under specific conditions, wherein low-valent oxides exhibit better conductivity. Simply adding metal elements cannot become a component of glass, and cannot make the glass present a uniform conductive state, while high-valent metal oxides have poor conductivity and cannot make the glass have good conductivity.

[0015] By controlling the process conditions during end firing, the degree of reduction of the metal elements in the electrode after firing and the density of the end electrode can be controlled. If the degree of reduction of the metal elements is small, the conductivity of the glass phase is weak, which is insufficient to achieve the beneficial effects of this solution; if the degree of reduction of the metal elements is too large, it means that the atmosphere in the furnace is highly reducing, which will lead to reduced fluidity of the glass and poor density of the end electrode.

[0016] In some embodiments of the present invention, the terminal electrode copper paste includes the following components in percentage by weight: 65-75% copper powder and 7-15% glass powder.

[0017] In some embodiments of the present invention, the glass powder includes 9-15% by weight of divalent or higher valent metal oxides.

[0018] The glass powder of the present invention includes 9-15% by weight of divalent or higher valent metal oxides. If the content of metal oxides in the glass powder is too little, the conductivity will be less than ideal, and the technical effect to be achieved by the present solution cannot be well achieved; if the content of metal oxides in the glass powder is too much, when the melt is cooled, the number of crystal nuclei increases and the crystal nuclei are easy to grow, and the system is easy to crystallize but not easy to form glass.

[0019] In some embodiments of the present invention, the divalent or higher-valent metal oxide includes at least one of CuO, Fe3O4, SnO2, MnO2, TiO2, V2O5, ZnO, RuO2, and Ni3O4.

[0020] In some embodiments of the present invention, the divalent or higher valent metal oxide is selected from CuO.

[0021] The present invention prefers CuO because CuO has better conductivity after being partially reduced and has better compatibility with glass.

[0022] In some embodiments of the present invention, the glass powder further comprises the following components in percentage by weight: 45-60% ZnO, 20-35% B2O3, 8-15% SiO2, 0-5% Na2O, 0-5% CaO, and 0-5% Al2O3.

[0023] In some embodiments of the present invention, the preparation of the laminate comprises the following steps:

[0024] Step S1. Casting the dielectric slurry into a green film sheet, and printing the internal electrode slurry on the green film sheet to form an internal electrode layer;

[0025] Step S2: The inner electrode layers are stacked, pressed, cut, debonded and sintered to obtain a laminate.

[0026] In some embodiments of the present invention, the terminal electrode copper paste further comprises the following components in percentage by weight: 5-10% resin, 10-18% solvent, and 1-5% thixotropic agent.

[0027] In some preferred embodiments of the present invention, the resin includes at least one of ethyl cellulose, acrylic resin, epoxy resin, nitrocellulose resin, styrene resin, and phenolic resin.

[0028] In some preferred embodiments of the present invention, the thixotropic agent includes at least one of polyamide wax, fumed silica, hydrogenated castor oil, and organic bentonite.

[0029] In some preferred embodiments of the present invention, the organic solvent includes at least one of terpineol, hydrogenated terpineol, butyl carbitol, butyl carbitol acetate, tributyl citrate, and dipropylene glycol propyl ether.

[0030] In some preferred embodiments of the present invention, the copper powder includes at least one of flake copper powder and spherical copper powder.

[0031] In some preferred embodiments of the present invention, D50 of the copper powder is 2-6 μm.

[0032] Another object of the present invention is to provide a method for preparing a terminal electrode copper slurry, comprising the following steps:

[0033] S1. The components of the glass powder are mixed and sieved, melted, cooled, crushed, sieved, and ground to obtain the glass powder;

[0034] S2. adding the resin to the solvent, heating and stirring until the resin is completely dissolved to obtain glue;

[0035] S3. The copper powder and the glass powder are mixed uniformly to obtain a mixed powder;

[0036] S4. Add the glue to the mixed powder, stir, add a thixotropic agent, mix evenly, and obtain the terminal electrode copper slurry.

[0037] Another object of the present invention is to provide a multilayer ceramic capacitor, which is manufactured by the method for manufacturing the multilayer ceramic capacitor.

[0038] The multilayer ceramic capacitor comprises a plurality of stacked dielectric layers, internal electrodes arranged opposite to each other with the dielectric layer located therebetween, and terminal electrodes electrically connected to the internal electrodes respectively, wherein the terminal electrodes are made of the copper paste. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0040] Example 1

[0041] This embodiment provides a multilayer ceramic capacitor, and the specific process is as follows:

[0042] Weigh the glass powder according to the ratio of 45% ZnO, 25% B2O3, 8% SiO2, 2% Na2O, 15% CuO, 0% CaO, and 5% Al2O3, mix them evenly in a V-type mixer, and then sieve them to obtain a mixed material B;

[0043] The mixed material B is added into a crucible, and after being kept at 1100° C. for 1 hour, the molten glass liquid is rapidly cooled, wherein the rapid cooling operation is to cool from 1100° C. to 25° C. within 2 seconds, the crucible used for the heat preservation is a quartz crucible, and the cooling treatment method is rolling mill cooling, thereby obtaining glass;

[0044] The glass is crushed, sieved, the sieve is 80 mesh, and then the glass powder particle size is reduced to 0.5-1.0 μm by jet milling to obtain the glass powder;

[0045] The copper paste is prepared in the proportion of 65% copper powder, 15% glass powder, 5% resin, 10% solvent and 5% additive. The resin is first added to the organic solvent, heated and stirred at 80°C until the resin is completely dissolved, and the stirring frequency is 10-20Hz to obtain glue; the resin is ethyl cellulose, and the organic solvent is pine alcohol;

[0046] Weigh copper powder and glass powder, mix them evenly, and obtain mixed powder;

[0047] The glue is added to the mixed powder, stirred to make the glue preliminarily wet the mixed powder until no dry powder exists, and a thixotropic agent is added during the stirring process to obtain a mixed material A; the thixotropic agent is fumed silica;

[0048] The mixed material A is rolled using a three-roll rolling mill to be evenly mixed to obtain the terminal electrode copper slurry.

[0049] The dielectric slurry is prepared and cast into a raw film, and the internal electrode slurry is printed on it. After lamination, cutting, debinding, sintering and other steps, a fired laminate is obtained. The terminal electrode copper slurry is covered on the fired laminate. During the terminal firing process, the oxygen potential value in the furnace is controlled at 600mv, the temperature during the terminal firing is controlled at 800℃, and the holding time is controlled at 10min. After the terminal firing, electroplating is performed to obtain a multilayer ceramic capacitor.

[0050] Example 2

[0051] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the content of each component in the copper paste:

[0052] The copper paste is prepared according to the ratio of 70% copper powder, 11% glass powder, 5% resin, 12% solvent and 2% additive.

[0053] Example 3

[0054] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the content of each component in the copper paste:

[0055] The copper paste is prepared according to the ratio of 75% copper powder, 9% glass powder, 5% resin, 10% solvent and 1% additive.

[0056] Example 4

[0057] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the content of each component in the copper paste:

[0058] The copper paste is prepared according to the ratio of 65% copper powder, 7% glass powder, 9% resin, 18% solvent and 1% additive.

[0059] Example 5

[0060] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0061] Glass powder was weighed according to the ratio of 45% ZnO, 20% B2O3, 15% SiO2, 5% Na2O, 9% CuO, 5% CaO, and 1% Al2O3.

[0062] Example 6

[0063] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0064] The glass powder was weighed according to the ratio of 60% ZnO, 20% B2O3, 8% SiO2, 0% Na2O, 9% CuO, 0% CaO, and 3% Al2O3.

[0065] Example 7

[0066] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0067] The glass powder was weighed according to the ratio of 45% ZnO, 35% B2O3, 8% SiO2, 1% Na2O, 10% CuO, 1% CaO, and 0% Al2O3.

[0068] Example 8

[0069] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0070] Glass powder was weighed according to the ratio of 45% ZnO, 35% B2O3, 8% SiO2, 1% Na2O, 10% SnO2, 1% CaO, and 0% Al2O3.

[0071] Example 9

[0072] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0073] The glass powder was weighed according to the ratio of 45% ZnO, 35% B2O3, 8% SiO2, 1% Na2O, 10% RuO2, 1% CaO, and 0% Al2O3.

[0074] Example 10

[0075] This embodiment provides a multilayer ceramic capacitor, which is different from the embodiment 1 only in that the contents of various oxides in the glass powder are different:

[0076] The glass powder was weighed according to the ratio of 45% ZnO, 35% B2O3, 8% SiO2, 1% Na2O, 10% Ni3O4, 1% CaO, and 0% Al2O3.

[0077] Embodiment 11

[0078] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the process conditions of the firing end:

[0079] During the firing process, the oxygen potential in the furnace was controlled at 700 mv, the temperature during firing was controlled at 820°C, and the holding time was controlled at 11 minutes.

[0080] Example 12

[0081] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the process conditions of the firing end:

[0082] During the firing process, the oxygen potential in the furnace was controlled at 800 mv, the temperature during firing was controlled at 830°C, and the holding time was controlled at 15 min.

[0083] Example 13

[0084] This embodiment provides a multilayer ceramic capacitor, which differs from the embodiment 1 only in the process conditions of the firing end:

[0085] During the firing process, the oxygen potential in the furnace was controlled at 600 mv, the temperature at the firing was controlled at 810°C, and the holding time was controlled at 14 minutes.

[0086] Comparative Example 1

[0087] This comparative example prepares a multilayer ceramic capacitor, which is different from Example 1 in that the contents of various oxides in the glass powder are different. The specific process is as follows:

[0088] The glass powder was weighed according to the ratio of 53% ZnO, 30% B2O3, 9% SiO2, 3% Na2O, and 5% Al2O3.

[0089] Comparative Example 2

[0090] This comparative example prepares a multilayer ceramic capacitor, which is different from Example 1 in that the contents of various oxides in the glass powder are different. The specific process is as follows:

[0091] The glass powder was weighed according to the ratio of 50% ZnO, 28% B2O3, 9% SiO2, 3% Na2O, 5% CuO, and 5% Al2O3.

[0092] Comparative Example 3

[0093] This comparative example prepares a multilayer ceramic capacitor, which is different from Example 1 in that the contents of various oxides in the glass powder are different. The specific process is as follows:

[0094] The glass powder is weighed according to the ratio of 45% ZnO, 20% B2O3, 8% SiO2, 2% Na2O, 20% CuO, and 5% Al2O3.

[0095] Comparative Example 4

[0096] This comparative example prepares a multilayer ceramic capacitor, which is different from Example 1 in that the contents of various oxides in the glass powder are different. The specific process is as follows:

[0097] The glass powder was weighed according to the ratio of 45% ZnO, 20% B2O3, 8% SiO2, 2% Na2O, 20% Cu, and 5% Al2O3.

[0098] Comparative Example 5

[0099] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0100] During the firing process, the oxygen potential in the furnace is controlled at 400mv, the temperature during firing is controlled at 800℃, and the holding time is controlled at 10min.

[0101] Comparative Example 6

[0102] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0103] During the firing process, the oxygen potential in the furnace is controlled at 1000mv, the temperature during firing is controlled at 800℃, and the holding time is controlled at 10min.

[0104] Comparative Example 7

[0105] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0106] During the firing process, the oxygen potential in the furnace is controlled at 600mv, the temperature during firing is controlled at 750℃, and the holding time is controlled at 10min.

[0107] Comparative Example 8

[0108] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0109] During the firing process, the oxygen potential in the furnace is controlled at 600mv, the temperature during firing is controlled at 850℃, and the holding time is controlled at 10min.

[0110] Comparative Example 9

[0111] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0112] During the firing process, the oxygen potential in the furnace is controlled at 600mv, the temperature during firing is controlled at 800℃, and the holding time is controlled at 5min.

[0113] Comparative Example 10

[0114] This comparative example prepares a multilayer ceramic capacitor, which differs from Example 1 only in the different firing process conditions. The specific process is as follows:

[0115] During the firing process, the oxygen potential in the furnace is controlled at 600mv, the temperature during firing is controlled at 800℃, and the holding time is controlled at 20min.

[0116] Performance Test:

[0117] Reduction of copper oxide: The test method is to characterize the valence state of the copper element in the terminal electrode through XPS. The indicator is: the valence state distribution of copper oxide in the glass after reduction is: Cu(0):Cu(Ⅰ):Cu(Ⅱ)=0:(1~5):1.

[0118] Distribution of glass elements: The test method is to grind the LT surface of the sample to the 1 / 2 position and characterize the degree of glass overflow at the end through EPMA; indicator: glass overflow 40-60%.

[0119] Density of copper end: The test method is to place the LT surface of the sintered copper sample in a plastic mold, solidify the resin solvent, grind it on a metallographic grinder to the 1 / 2 position of the sample, and use SEM to observe the proportion of non-dense holes at the copper end to the copper end cross-section; indicator: non-dense voids cannot be less than 90%.

[0120] Coating continuity: The test method is to characterize the connection of the electroplating layer through a metallographic microscope; indicators: the coating continuity cannot be less than 95%, and the discontinuous length cannot be higher than 20μm.

[0121] Solder resistance test: evaluate whether the product has defects after welding. Indicator: after the solder resistance test, the coating surface is smooth and has no voids. 500 samples were tested and the yield rate was as high as 100%.

[0122] Table 1. Performance test results of multilayer ceramic capacitors.

[0123]

[0124] Table 1 is the test results of various embodiments and comparative examples. According to comparative examples 1 to 4, when no CuO is added or too little CuO is added, the glass has no conductivity or insufficient conductivity after overflowing, resulting in poor solder resistance test and coating continuity; when too much CuO is added, the glass cannot be formed and the proportion of non-dense voids is large; according to comparative examples 5 to 10, when the oxygen potential value is too low, the temperature is too low or the insulation time is too short during the firing process, less copper oxide is reduced, the glass conductivity is insufficient, and the solder resistance test and coating continuity are poor; and when the oxygen potential value is too high, the temperature is too high or the insulation time is too long, the copper oxide is excessively reduced to metallic copper, resulting in the glass cannot be formed and the proportion of non-dense voids is large.

[0125] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a multilayer ceramic capacitor, characterized in that: The steps include: Covering the laminate with a terminal electrode copper paste and firing the terminals to obtain the multilayer ceramic capacitor; The terminal electrode copper paste includes the following components in percentage by weight: 65-75% copper powder and 7-15% glass powder; The glass powder includes 9-15% by weight of a divalent or higher valence metal oxide; the divalent or higher valence metal oxide is selected from CuO; the glass powder also includes the following components by weight: 45-60% ZnO, 20-35% B2O3, 8-15% SiO2, 0-5% Na2O, 0-5% CaO, and 0-5% Al2O3; The oxygen potential value of the burning end is 600-800 mv, the temperature of the burning end is 800-830° C., and the insulation time is 10-15 min.

2. The method for preparing a multilayer ceramic capacitor according to claim 1, wherein: The terminal electrode copper paste also includes the following components in percentage by weight: 5-10% resin, 10-18% solvent, and 1-5% thixotropic agent; the resin includes at least one of ethyl cellulose, acrylic resin, epoxy resin, nitrocellulose resin, styrene resin, and phenolic resin; the thixotropic agent includes at least one of polyamide wax, fumed silica, hydrogenated castor oil, and organic bentonite.

3. The method for preparing a multilayer ceramic capacitor according to claim 1, wherein: The copper powder includes at least one of flaky copper powder and spherical copper powder; and the D50 of the copper powder is 2-6 μm.

4. The method for preparing a multilayer ceramic capacitor according to claim 2, wherein: The method for preparing the terminal electrode copper slurry comprises the following steps: S1. The components of the glass powder are mixed and sieved, melted, cooled, crushed, sieved, and ground to obtain the glass powder; S2. adding the resin to the solvent, heating and stirring until the resin is completely dissolved to obtain glue; S3. The copper powder and the glass powder are mixed uniformly to obtain a mixed powder; S4. Add the glue to the mixed powder, stir, add a thixotropic agent, mix evenly, and obtain the terminal electrode copper slurry.

5. A multilayer ceramic capacitor, characterized in that: The multilayer ceramic capacitor is prepared by the preparation method according to any one of claims 1 to 4.

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