MLCC product and preparation method thereof

Abstract

The invention relates to the technical field of ceramic capacitors, in particular to an MLCC product and a preparation method thereof. The preparation method of the MLCC product comprises the following steps: carrying out drying treatment on an MLCC ceramic body subjected to chamfering treatment; in an annealing atmosphere containing nitrogen and / or inert gas, the dried MLCC body is subjected to multi-section annealing treatment, and the multi-section annealing treatment comprises a heating section, a heat preservation section and a cooling section which are conducted in sequence; wherein the annealing temperature of the heat preservation section ranges from 700 DEG C to 900 DEG C, and the annealing time of the heat preservation section ranges from 2 h to 5 h; and carrying out end sealing treatment on the MLCC ceramic body subjected to the multi-section annealing treatment. The MLCC product prepared by adopting the preparation method is good in leakage current stability in a high-temperature IR test, the internal stress is obviously reduced, and the MLCC product has higher reliability, stability and service life in long-term work, and can meet the special requirements of the industries of vehicle-mounted electronics, base stations, servers and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic capacitors, in particular to an MLCC product and a preparation method thereof. BACKGROUND

[0002] Multi-layer Ceramic Capacitors (MLCC) are also known as chip capacitors or monolithic capacitors, which are capacitors with ceramic as dielectric material and multi-layer stacked structure. MLCC has the advantages of small size, large capacity, high temperature resistance, good high frequency characteristics, etc., and can be applied to various circuits such as oscillation circuit, timing or delay circuit, coupling circuit, decoupling circuit, etc., and is widely used in consumer electronics, vehicle electronics, base stations, servers and security industries.

[0003] Some MLCC products need to be tested for long-period high-temperature insulation resistance (HotIR) after being manufactured: at the highest working temperature (T max ) of the product, 1~2 times the rated voltage (1U R ~2U R ) is applied, and the leakage current generated by the product is collected at a specified time interval for at least 168h, and the stability of the leakage current is observed to evaluate its reliability in long-term use. However, the leakage current stability of traditional MLCC products in HotIR test is poor, which is difficult to meet the demand of high-reliability MLCC products in vehicle electronics, base stations and servers industries. SUMMARY

[0004] Therefore, it is necessary to provide an MLCC product and a preparation method thereof to solve the problem of poor leakage current stability of traditional MLCC products in HotIR test.

[0005] The above-mentioned purpose of the present application is achieved by the following technical solutions: In a first aspect, the present application provides a preparation method of an MLCC product, comprising the following steps: drying the MLCC ceramic body after chamfering; performing multi-stage annealing treatment on the dried MLCC ceramic body in an annealing atmosphere containing nitrogen and / or inert gas, the multi-stage annealing treatment comprising a temperature rising stage, a temperature holding stage and a temperature falling stage performed in sequence; wherein the annealing temperature of the temperature holding stage is 700℃~900℃, and the annealing time of the temperature holding stage is 2h~5h; performing end sealing treatment on the MLCC ceramic body after multi-stage annealing treatment.

[0006] In one of the embodiments, the annealing atmosphere further contains water vapor, and the oxygen potential of the annealing atmosphere is 700mV-800mV.

[0007] In one of the embodiments, the annealing atmosphere is formed by the following method: nitrogen and / or inert gas is introduced into water, and then introduced into the annealing equipment at a flow rate of 200L / min-500L / min.

[0008] In one of the embodiments, the temperature rising section comprises the following steps: temperature rising annealing treatment is performed at 400℃-800℃, and the temperature rising annealing time is 1h-3h.

[0009] In one of the embodiments, the temperature falling section comprises the following steps: temperature falling annealing treatment is performed at 350℃-800℃, and the temperature falling annealing time is 1h-3h.

[0010] In one of the embodiments, the annealing equipment of the multi-section annealing treatment comprises a mesh belt annealing furnace, and the mesh belt conveying speed of the mesh belt annealing furnace is 10mm / min-100mm / min.

[0011] In one of the embodiments, the drying temperature of the drying treatment is 100℃-120℃, and the drying time is 20min-120min.

[0012] In one of the embodiments, before the drying treatment, the MLCC ceramic body after the chamfering treatment is further subjected to cleaning treatment, and the interval between the end time of the cleaning treatment and the start time of the drying treatment is not more than 180min.

[0013] In one of the embodiments, before the end sealing treatment, the MLCC ceramic body after the multi-section annealing treatment is further subjected to appearance inspection treatment.

[0014] In the second aspect of the present application, a MLCC product is provided, which is prepared by the method for preparing a MLCC product as described above.

[0015] The present application has at least the following beneficial effects: The leakage current stability of the traditional MLCC product in high temperature IR test is poor, and many researchers tend to believe that if the copper layer of the end has defects such as too thin thickness, holes or damage, insufficient compactness, etc., then hydrogen ions (H + ) will be introduced in the process of nickel plating and tin plating. +The movement into the interlayer dielectric leads to a decrease in insulation resistance. According to the formula I=U / R, with a constant applied voltage, a decrease in insulation resistance R results in an increase in leakage current I, thus failing to meet the requirement of stable current. However, the applicant discovered that even without electroplating, MLCC products still exhibit abnormally high leakage current during high-temperature IR testing.

[0016] The applicant's in-depth research revealed that traditional MLCC products have a high water content. When voltage is applied, the hydrogen in the water vapor ionizes into H₂. + And H + Movement under an electric field reduces insulation resistance, ultimately affecting the stability of leakage current. Therefore, before end-capping the MLCC ceramic body, this application first removes moisture from the ceramic body surface through drying, and then removes internal moisture through multi-stage annealing. This minimizes the hydrogen content inside the MLCC product, thereby improving leakage current stability and meeting the requirements of high-temperature IR testing.

[0017] In multi-stage annealing, using an annealing atmosphere containing nitrogen and / or inert gases can prevent oxidation or reduction reactions in the ceramic body during annealing. Holding at 700℃~900℃ for 2h~5h can effectively remove moisture from the ceramic body and prevent defects such as oxidative expansion of the internal electrodes due to prolonged annealing. In addition, multi-stage annealing helps to release internal stress in the ceramic body, improving the reliability and service life of MLCC products. Therefore, MLCC products prepared using this method exhibit good leakage current stability and significantly reduced internal stress in high-temperature IR testing, and demonstrate higher reliability, stability, and service life during long-term operation, meeting the special requirements of industries such as automotive electronics, base stations, and servers. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the preparation method of MLCC products in some embodiments; Figure 2 for Figure 1 The flowchart of step S100 is shown below; Figure 3 SEM images of protective caps for high-capacity, small-sized ceramic bodies in some embodiments; Figure 4A TDS test result graph for the MLCC product of Comparative Example 1; Figure 5 A TDS test result graph for the MLCC product of Example 1; Figure 6 A high temperature IR test result graph for the MLCC product of Comparative Example 1; Figure 7 A high temperature IR test result graph for the MLCC product of Example 1; Figures 8-9 A stress test result graph for the MLCC product of Comparative Example 1; Figures 10-11 A stress test result graph for the MLCC product of Example 1. DETAILED DESCRIPTION

[0020] In order to facilitate the understanding of the present application, further detailed description will be made to the present application in connection with specific embodiments. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, it is intended to cover all the possible forms of the present application falling within the scope of the disclosure.

[0021] Unless otherwise defined, all the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0022] In the present application, the meaning of "and / or" is to include any and all combinations of one or more of the associated listed items. The meaning of "at least one" is more than one, such as one, two, and more than two. The meaning of "a plurality of" or "several" is at least two, such as two, three, and the like, unless otherwise specifically defined. In the description of the present application, the meaning of "several" is at least one, such as one, two, and the like, unless otherwise specifically defined.

[0023] When a numerical range is disclosed in the present application, the above range is considered to be continuous and includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when a plurality of ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise indicated, all the ranges disclosed in the present application should be understood to include any and all sub-ranges falling within the range.

[0024] If not otherwise specified, all steps of the present application can be performed in sequence or randomly. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0025] In the present application, "above" or "below" includes the number itself. For example, 1 below includes 1.

[0026] In the present application, the temperature parameter, if not otherwise specified, allows for constant temperature treatment, and also allows for variation within a certain temperature range. It should be understood that the constant temperature treatment allows for fluctuations within the accuracy range controlled by the instrument. Fluctuations within a range of, for example, ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0027] In the present application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally, the range of room temperature can be any of the following temperature ranges: 23°C ± 2°C, 25°C ± 5°C or 20°C ± 5°C.

[0028] In the conventional technology, the MLCC product is usually prepared by the following method: (1) batching: ceramic powder, binder, additive and solvent are mixed in a certain proportion, and ball milling or sand milling is performed for a certain period of time to form a uniform and stable ceramic slurry.

[0029] (2) casting: the ceramic slurry is coated on the running silicone film through the casting port of the casting machine to form a uniform ceramic slurry thin layer, and then dried by heating to form a uniform ceramic film with a certain thickness and density.

[0030] (3) printing: the internal electrode slurry is printed onto the ceramic film through a silk screen, and a clear and complete dielectric film is obtained after drying.

[0031] (4) lamination: the printed dielectric films are stacked together in a certain order and staggered to form a bar with uniform thickness.

[0032] (5) lamination: the lamination film in the bar is tightly combined with each other by static water pressure lamination at a uniform temperature to improve the density of the ceramic body after sintering, so that they are more tightly combined together.

[0033] (6) Cutting: according to the design requirements of the product, using a sheet thin blade to cut the laminated bar in the horizontal and vertical directions according to the design size, so as to become a completely separated independent chip (ceramic green body).

[0034] (7) Desmear: after cutting the ceramic green body, heat treatment is carried out to remove organic matter such as adhesive.

[0035] (8) Sintering: using an atmosphere sintering furnace, high-temperature sintering is carried out at 1100°C to 1350°C. The ceramic green body after desmear becomes a ceramic body with intact internal electrodes, high density, qualified size, high mechanical strength and excellent electrical properties.

[0036] (9) Chamfering: also called grinding, the edges of the sintered ceramic capacitor body are sharp, and through chamfering, the curvature of the ceramic body is chamfered and the internal electrode is exposed, so as to facilitate the connection of the internal and external electrodes. The chamfering process is to put the ceramic chip, chamfering ball, water and grinding aid into a chamfering tank, and move through ball milling and planetary milling, etc. to remove the burrs on the surface of the ceramic chip, so that the surface of the chip is smooth, and at the same time, the end face internal electrode is fully exposed.

[0037] (10) End sealing: through the end sealing machine, the end electrode paste is coated on the two ends of the exposed internal electrode of the ceramic body after chamfering, and the internal electrodes on the same side are connected to form the external electrode.

[0038] (11) End firing: under high temperature conditions, the organic binder in the end electrode paste is fully burned, the glass powder is melted and infiltrated into the copper powder, so that the end is solidified and forms a good connection with the ceramic body and the internal electrode.

[0039] (12) Electroplating: in an electroplating solution containing nickel ions and / or tin ions, the end electrode of the MLCC is used as the cathode, and through a certain low-voltage direct current, a nickel layer and a tin layer are respectively deposited on the cathode.

[0040] (13) Testing and inspection: for the capacity, loss, insulation and voltage resistance of the capacitor product, 100% testing and sorting are carried out on the product, and the defective products are removed, and at the same time, after being sorted according to different capacity ranges, appearance inspection is carried out.

[0041] For high-capacity small-size products ≥1 μF, high-temperature IR testing is usually required to evaluate its reliability. With the increase of testing time, the leakage current of traditional MLCC products will abnormally increase greatly, which is difficult to meet the requirements of high-temperature IR testing, and therefore is difficult to be applied to industries with special requirements for product reliability and stability, such as base stations, servers and vehicle-mounted electronics.

[0042] Based on this, the first aspect of the present application provides a preparation method of an MLCC product, aiming to improve the leakage current stability of the MLCC product in high-temperature IR testing, and to obtain a high-reliability MLCC product.

[0043] In some embodiments, as shown in Figure 1 The preparation method of the MLCC product comprises the following steps: S100: drying treatment is performed on the MLCC ceramic body after the chamfering treatment; S200: multi-stage annealing treatment is performed on the MLCC ceramic body after the drying treatment in an annealing atmosphere containing nitrogen and / or inert gas, the multi-stage annealing treatment comprising a temperature rising stage, a temperature holding stage and a temperature decreasing stage performed in sequence; wherein the annealing temperature of the temperature holding stage is 700-900℃, and the annealing time of the temperature holding stage is 2-5h; S300: end sealing treatment is performed on the MLCC ceramic body after the multi-stage annealing treatment.

[0044] The conventional MLCC product has poor leakage current stability in high-temperature IR testing, and many researchers tend to believe that, in the electroplating process, if the copper layer of the end has defects such as too thin thickness, holes or damage, and insufficient compactness, then hydrogen ions (H + ) will be introduced in the process of nickel plating and tin plating, and the movement of H + to the dielectric layer causes the insulation resistance to decrease. According to the formula I=U / R, if the applied voltage remains unchanged and the insulation resistance R decreases, then the leakage current I increases, and thus the requirement for stable current cannot be met. However, the applicant found that even if the MLCC product has not been subjected to electroplating treatment, it will still exhibit abnormal increase in leakage current in high-temperature IR testing.

[0045] The applicant found through in-depth research that the conventional MLCC product has a high water content, and when the voltage is applied, the hydrogen element in the water vapor will ionize into H + , and the movement of H + under the electric field will reduce the insulation resistance, which ultimately affects the stability of the leakage current. Based on this, the present application removes the water on the surface of the ceramic body through drying treatment before end sealing treatment of the MLCC ceramic body, and then removes the water inside the ceramic body through multi-stage annealing treatment, so as to reduce the content of hydrogen elements inside the MLCC product as much as possible, and thus to improve the stability of the leakage current and to meet the requirements of high-temperature IR testing.

[0046] In the multi-stage annealing process, the annealing atmosphere containing nitrogen and / or inert gas can avoid oxidation or reduction of the ceramic body during the annealing process. The ceramic body is kept at 700-900 DEG C for 2-5 hours, which can not only remove the moisture inside the ceramic body, but also prevent the internal electrode of the product from expanding due to oxidation for a long time. In addition, the multi-stage annealing process is also beneficial to release the internal stress of the ceramic body, improve the reliability and service life of the MLCC product. Therefore, the MLCC product prepared by the preparation method has good leakage current stability in high temperature IR test, the internal stress is obviously reduced, and has higher reliability, stability and service life in long-term work, which can meet the special requirements of vehicle-mounted electronics, base stations and servers and other industries.

[0047] The preparation method of the MLCC product is described step by step as follows. Figure 1 and Figure 2 The preparation method of the MLCC product is described step by step as follows.

[0048] S100: drying treatment is performed on the MLCC ceramic body after chamfering treatment.

[0049] In some embodiments, the chamfering treatment comprises the following steps: S110: chamfering treatment is performed on the MLCC ceramic body after high-temperature sintering treatment by using a chamfering machine.

[0050] The main purpose of chamfering is to chamfer the curvature of the MLCC ceramic body and expose the internal electrode. Adding an appropriate amount of water during chamfering can ensure the flowability of the ceramic body during chamfering and the uniformity of the chamfering effect, reduce the collision between the ceramic body and the grinding medium, and also play a certain heat dissipation effect. The ceramic body after high-temperature sintering is brittle, and if water is not added during chamfering, the mutual collision between the ceramic bodies and between the ceramic body and the chamfering ball during high-speed chamfering will cause the ceramic body to break. If the amount of water is too small during chamfering, the ceramic body is prone to edge collapse and corner collapse, i.e. porcelain damage; if the amount of water is too large, the chamfering grinding effect cannot be achieved, and the production efficiency is reduced. The chamfering machine can be a planetary chamfering machine or a rolling chamfering machine, and is preferably a planetary chamfering machine.

[0051] In some embodiments, the chamfering treatment of step S110 comprises the following steps: S111: the MLCC ceramic body, the chamfering ball and water are loaded into the chamfering tank. The water can be tap water, deionized water, pure water, ultrapure water or distilled water, etc.; in some specific examples, grinding aids such as silicon carbide (SiC) powder can also be used during chamfering, which can play a fine grinding role and reduce the mutual collision between the ceramic bodies and between the ceramic body and the chamfering ball. If SiC powder is added or not added, porcelain damage is easy to occur, and the chamfering effect is poor.

[0052] S112: The chamfering tank is placed in the planetary chamfering machine, and the protruding corner and edge of the rolling ceramic body are rounded and formed into an arc through planetary motion, while the inner electrode of the end surface is fully exposed to ensure the connection of the subsequent inner and outer electrodes.

[0053] S113: The arc and inner electrode exposure rate of the MLCC ceramic body after chamfering are detected.

[0054] In some embodiments, before the drying treatment, the following steps are further included: S120: The MLCC ceramic body after chamfering is subjected to cleaning treatment, and the interval between the end time of the cleaning treatment and the start time of the drying treatment is not more than 180 min. If not cleaned in time, the SiC powder added during chamfering will adhere to the surface of the ceramic body and is not easy to clean. The residual SiC powder will cause poor connection of the inner and outer electrodes, affecting the capacity and loss.

[0055] In some embodiments, the cleaning treatment includes one or more of manual cleaning and ultrasonic cleaning, and the cleaning medium includes one or more of tap water, deionized water, pure water, ultrapure water, and distilled water.

[0056] As an example, the manual cleaning can include the following steps: adjusting the opening of the faucet valve to less than 1 / 2 of the total opening, and flushing the ceramic body in the chamfering tank into the screen with filter cloth with tap water; completely opening the valve of the faucet, and continuously cleaning the ceramic body in the screen with tap water until the water droplets dropped by lifting the ceramic body are not turbid.

[0057] As an example, the ultrasonic cleaning can include the following steps: flushing the ceramic body in the chamfering tank into the screen with filter cloth with water; transferring the ceramic body in the filter cloth to a container, and then placing it on the holding rack in the ultrasonic cleaning machine tank; adding pure water until the water level is 0.1 cm to 0.5 cm higher than the container, and then ultrasonic cleaning for 5 min to 30 min. The container for the ceramic body can be a drying barrel to facilitate subsequent drying treatment.

[0058] In some embodiments, the drying treatment includes the following steps: S130: The cleaned MLCC ceramic body is dried at 100°C to 120°C for 20 min to 120 min.

[0059] In some embodiments, the drying temperature of the drying treatment is 100°C to 120°C, for example, it can be 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C, or 120°C, etc.

[0060] In some embodiments, the drying time of the drying treatment is 20 min to 120 min, for example, can be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc.

[0061] In some embodiments, the drying treatment is performed in a drying furnace.

[0062] It can be understood that the purpose of the drying treatment is to remove the moisture of the MLCC ceramic body and the chamfered ball surface. After the drying is completed, it is checked whether the drying is sufficient. If the moisture of the ceramic body and the chamfered ball surface is not sufficiently dried, the ceramic body and the chamfered ball surface will be adhered together to form a wet sticky mass. If there is a wet sticky mass, the wet sticky mass is dried again at 100°C to 120°C for 20 min to 120 min. In addition, due to the low temperature and short time of the drying treatment, the water vapor inside the ceramic body cannot be completely removed, and therefore a multi-stage annealing treatment needs to be added.

[0063] In some embodiments, after the drying treatment, the following steps are further included: S140: performing a screening treatment, and then performing a piece arrangement treatment on the screened MLCC ceramic body.

[0064] As an example, the screening treatment can include the following steps: transferring the dried MLCC ceramic body and the chamfered ball to a vibrating screening machine for screening to separate the MLCC ceramic body and the chamfered ball; during the screening, the number of stacked screens can be 2, and the material drop height is ≤8 cm, so as to reduce the screening time and ensure accurate screening; a receiving tray is arranged at the outlet of the vibrating screening machine to receive the material, and a sponge pad and a filter cloth are placed in the receiving tray as a buffer to prevent the MLCC ceramic body from falling and being damaged to affect the appearance yield.

[0065] As an example, the piece arrangement treatment includes the following steps: laying the MLCC ceramic body on a metal mesh for subsequent annealing treatment. The metal mesh can be a nickel mesh, a copper mesh, an aluminum mesh, etc., and the number, size and mesh size of the metal mesh are not specially limited, and a person skilled in the art can adjust them according to the processing conditions and performance requirements. Specifically, a nickel mesh with a length and width of 150 mm x 150 mm can be selected, 4 nickel meshes are arranged in order and placed in the center on a stainless steel support, and the nickel meshes are not pressed and overlapped; a quantitative spoon is used to transfer the MLCC ceramic body to the nickel mesh, one spoon per mesh; a brush is used to evenly brush the MLCC ceramic body until the ceramic bodies are evenly stacked and the laying area is consistent, and there is no foreign matter on the nickel mesh.

[0066] S200: performing multi-stage annealing treatment on the MLCC ceramic body after the drying treatment in an annealing atmosphere containing nitrogen and / or inert gas, the multi-stage annealing treatment including a temperature rising stage, a temperature holding stage and a temperature falling stage performed in sequence, the annealing temperature of the temperature holding stage being 700-900℃, and the annealing time of the temperature holding stage being 2-5h.

[0067] To explore the reason for the unstable leakage current of the traditional MLCC product, the applicant compares and analyzes the high-capacity small-size ceramic body and the large-size ceramic body, and finds that the sintering temperature of the small-size ceramic body is low, which leads to very poor density of the ceramic body, especially the thin thickness and many pores of the protective cover. As shown in the scanning electron microscope (SEM), the surface of the small-size ceramic body has a lot of pores. In the process of chamfering and cleaning, water vapor is easy to enter the inside of the ceramic body through the pores, thereby introducing a large amount of hydrogen element. Therefore, the multi-stage annealing treatment can completely remove the water vapor in the inside of the MLCC ceramic body, so that the high-capacity small-size MLCC product meets the requirements of the high-temperature IR test. Figure 3

[0068] In some embodiments, the annealing atmosphere of the multi-stage annealing treatment includes nitrogen and / or inert gas. The inert gas includes one or more of helium, neon, argon, krypton and xenon. Preferably, the annealing atmosphere of the multi-stage annealing treatment uses nitrogen, which can not only form a protective atmosphere to avoid oxidation or reduction side reactions of the ceramic body, but also reduce the preparation cost of the MLCC product.

[0069] In some embodiments, the annealing atmosphere of the multi-stage annealing treatment also contains water vapor, and the oxygen potential of the annealing atmosphere is 700-800mV, for example, it can be 700mV, 720mV, 740mV, 760mV, 780mV or 800mV.

[0070] A certain amount of water vapor is introduced, which will decompose into hydrogen and oxygen under high-temperature annealing conditions, which can supplement the oxygen vacancies formed in the sintering process of the ceramic body, and help the insulation and reliability of the MLCC product, further ensuring the stability of the leakage current of the MLCC product in the high-temperature IR test. Under the same annealing conditions, the obtained MLCC product has lower leakage current and better stability in the high-temperature IR test.

[0071] ​The more the water vapor is introduced, the higher the oxygen content of the annealing atmosphere is. If the oxygen content of the annealing atmosphere is too high, it is easy to cause oxidation of the internal electrode and produce defects such as cracking. In the embodiments of the present application, the oxygen potential measured in the annealing atmosphere is controlled in the range of 700 mV to 800 mV, which effectively prevents the negative effects of too high oxygen content in the annealing atmosphere. In the embodiments of the present application, the oxygen content in the annealing atmosphere can be directly and conveniently characterized by the oxygen potential. Specifically, the oxygen potential can be measured by online real-time monitoring or offline measurement of the annealing atmosphere by an oxygen probe, a gas analyzer or the like.

[0072] In some embodiments, the annealing atmosphere of the multi-stage annealing process is composed of a combination of nitrogen and / or inert gas and water vapor, and is mainly composed of nitrogen and / or inert gas. That is, the annealing atmosphere is mainly a protective atmosphere composed of nitrogen, inert gas or a combination of both, and contains a small amount of water vapor for supplementing oxygen elements. For example, the annealing atmosphere can be humidified nitrogen composed of nitrogen and a small amount of water vapor, humidified argon composed of argon and a small amount of water vapor, humidified helium composed of helium and a small amount of water vapor, etc.

[0073] In some embodiments, the annealing atmosphere of the multi-stage annealing process is formed by introducing nitrogen and / or inert gas into water and then introducing the gas into the annealing equipment at a flow rate of 200 L / min to 500 L / min. In this way, by continuously introducing and exhausting the gas, the water vapor and other gases desorbed from the ceramic body can be timely removed, avoiding the re-adsorption of the desorbed gas on the surface of the ceramic body, and further reducing the water content of the ceramic body.

[0074] It can be understood that the humid gas can be introduced into the annealing equipment through one or more gas inlets (or gas inlets). If the number of gas inlets is one, the flow rate of the humid gas introduced into the annealing equipment through the single gas inlet is 200 L / min to 500 L / min; if the number of gas inlets is more than one, the sum of the flow rates of the humid gas introduced into the annealing equipment through each gas inlet is 200 L / min to 500 L / min, i.e. the total gas flow rate = the sum of the flow rates of each gas inlet.

[0075] For example, nitrogen and / or inert gas can be introduced into a humidification barrel containing water, and the water vapor content in the annealing atmosphere can be adjusted by adjusting the temperature of the humidification barrel. Those skilled in the art can adjust the temperature according to the actual annealing conditions and product performance requirements.

[0076] For example, the flow rate of the humid gas introduced into the annealing equipment can be 200 L / min, 250 L / min, 300 L / min, 350 L / min, 400 L / min, 450 L / min or 500 L / min, etc.

[0077] In some embodiments, the multi-stage annealing process includes a temperature rising stage, a temperature holding stage and a temperature decreasing stage performed in sequence.

[0078] The temperature increasing section includes the following steps: temperature increasing annealing treatment is performed at 400-800℃, and the temperature increasing annealing time is 1-3h. For example, the annealing temperature of the temperature increasing section can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, and the temperature increasing annealing time can be 1h, 1.5h, 2h, 2.5h or 3h.

[0079] The temperature holding section includes the following steps: temperature holding annealing is performed at 700-900℃ for 2-5h. The annealing temperature of the temperature holding section can be 700℃, 750℃, 800℃, 850℃ or 900℃, and the annealing time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0080] The temperature decreasing section includes the following steps: temperature decreasing annealing treatment is performed at 350-800℃, and the temperature decreasing annealing time is 1-3h. For example, the annealing temperature of the temperature decreasing section can be 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, and the temperature decreasing annealing time can be 1h, 1.5h, 2h, 2.5h or 3h.

[0081] It can be understood that in the temperature increasing section, the annealing temperature can be increased at a certain temperature increasing rate, or the ceramic body can be transferred to a higher temperature zone at a certain transfer speed for annealing. Similarly, in the temperature decreasing section, the annealing temperature can be decreased at a certain temperature decreasing rate, or the ceramic body can be transferred to a lower temperature zone at a certain transfer speed for annealing.

[0082] For the temperature holding section, if the annealing time is too short, the water vapor removal is insufficient, and the leakage current stability cannot be improved; if the annealing time is too long, the internal electrode (such as a nickel electrode) of the ceramic body is easily oxidized and expanded at 700-900℃, which causes poor structural continuity and low surface flatness of the internal electrode, and leads to easy connection between two adjacent electrodes and short circuit. Therefore, by accurately controlling the annealing temperature and annealing time of the high temperature section, not only can the water vapor inside the ceramic body be completely desorbed, but also the oxidation and expansion of the internal electrode of the ceramic body can be prevented, thereby ensuring the yield of the MLCC product. By sequentially performing the temperature increasing section, the temperature holding section and the temperature decreasing section, the internal stress can be better released, and the reliability and stability of the MLCC product can be further improved.

[0083] In some embodiments, the annealing equipment of the multi-stage annealing process includes a mesh belt annealing furnace. However, the present application is not limited thereto, and in other specific examples, a single or multiple annealing furnaces with a precise temperature control system and an air inlet and outlet system can also be used, and the same annealing effect can be achieved by setting the heating rate, cooling rate, annealing time, and the like.

[0084] In some embodiments, the heating mode of the mesh belt annealing furnace is continuous resistance heating, the heating plate is a micro-exposed resistance heating plate, the maximum heating temperature is 400-1000℃, and the mesh belt conveying speed is 10-100 mm / min. As an example, the mesh belt conveying speed can be 10 mm / min, 20 mm / min, 30 mm / min, 40 mm / min, 50 mm / min, 60 mm / min, 70 mm / min, 80 mm / min, 90 mm / min, or 100 mm / min.

[0085] In some embodiments, the mesh belt annealing furnace is provided with multiple temperature zones, and the annealing temperatures of each temperature zone can be the same or different. As an example, the heating section is provided with 1-4 temperature zones, the set value of the annealing temperature of each temperature zone gradually increases along the conveying direction, and the temperature range in the same temperature zone is the set value ± (80-120)℃; the holding section is provided with 5-10 temperature zones, the set value of the annealing temperature of each temperature zone is the same, and the temperature range in the same temperature zone is the set value ± (20-50)℃; and the cooling section is provided with 3-5 temperature zones, the set value of the annealing temperature of each temperature gradually decreases along the conveying direction, and the temperature range in the same temperature zone is the set value ± (80-120)℃.

[0086] By setting the number of temperature zones of the heating section, the holding section, and the cooling section, and adjusting the mesh belt conveying speed, the annealing time of each section can be precisely controlled, and better annealing effect can be achieved.

[0087] Specifically, if the heating section is provided with 3 temperature zones, the holding section is provided with 8 temperature zones, and the cooling section is provided with 5 temperature zones, the mesh belt conveying speed can be controlled at 14-35 mm / min to ensure that the holding time of the holding section is 2-5 h.

[0088] S300: performing end sealing treatment on the MLCC ceramic body after the multi-stage annealing process.

[0089] In some embodiments, before the end sealing treatment, the following steps are further included: S310: performing appearance inspection treatment on the MLCC ceramic body after the multi-stage annealing process.

[0090] In some embodiments, after the multi-stage annealing process, the following steps are further included: placing a sponge pad at the bottom of the bowl unloading box as a buffer to reduce the occurrence of porcelain damage; using a fixing clamp to fix the filter cloth in the bowl unloading box, and pouring the MLCC ceramic body on the nickel mesh into the filter cloth to play a role in collecting and heat dissipation; and then pouring the ceramic body on the filter cloth into a product bag.

[0091] In some embodiments, the appearance inspection process is carried out by a sampling detection method. Specifically, 10,000 samples are taken from the product bag and placed on an inspection paper, and an optical microscope with 20 or 40 times magnification is used for appearance inspection. If there is no abnormality, the MLCC ceramic body in the product bag can be transferred to the end sealing process to produce an MLCC product.

[0092] In the end sealing process, it is usually necessary to use a drying oven to simply dry the external electrode paste to solidify the external electrode paste. The drying temperature is 80-120°C, and the drying time is 15-25 min, and water vapor cannot be removed. If the drying temperature is too high and the drying time is too long, the external electrode paste will be severely oxidized. Therefore, the present application needs to remove the water in the MLCC product through a multi-stage annealing process after the chamfering process and before the end sealing process.

[0093] In the second aspect, the present application provides an MLCC product prepared by the method for preparing an MLCC product as described above. Thanks to the drying process and the multi-stage annealing process, the water vapor in the MLCC product is completely removed, the leakage current is more stable in high-temperature IR testing, and the internal stress is effectively reduced, so that the MLCC product can exhibit high reliability, high stability and long service life in long-term use, and is very suitable for use in industries such as base stations, servers and vehicle-mounted electronics.

[0094] The following will be further described in conjunction with specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, if not specifically stated, can be sourced from the market. The instruments used, if not specifically stated, can be sourced from the market. The processes involved, if not specifically stated, are routinely selected by those skilled in the art.

[0095] Example 1 The method for preparing the MLCC product of the present embodiment is as follows: (1) Chamfering process: MLCC ceramic bodies cut into blocks after high-temperature sintering, chamfered balls, tap water and grinding aid SiC powder are loaded into a chamfering tank, and then the chamfering tank is loaded into a planetary chamfering machine. Through planetary motion, the protruding corners and edges of the rolling ceramic bodies are rounded and form an arc, and the inner electrodes of the end surface are fully exposed to ensure the connection of the subsequent inner and outer electrodes.

[0096] (2) cleaning treatment: the ceramic body in the chamfered tank is flushed into the screen with filter cloth laid on it with tap water; the ceramic body in the filter cloth is transferred to the drying barrel, and then placed on the supporting frame in the ultrasonic cleaning machine tank; pure water is added until the water level is 0.5 cm higher than the drying barrel, and then ultrasonic cleaning is performed for 20 minutes.

[0097] (3) drying treatment: after the ultrasonic cleaning is completed, the pure water in the drying barrel is poured out, and within 180 minutes, it is transferred to the drying oven, dried at 120°C for 100 minutes; after drying is completed, the ceramic body and chamfered ball are checked, and if the surface is not wet with sticky mass, the next process is performed.

[0098] (4) screening treatment: the ceramic body and chamfered ball in the drying barrel are transferred to the vibrating screening machine for screening to separate the ceramic body and chamfered ball; during the screening process, the number of screen stacks is 2, the material drop height is ≤8 cm, and at the same time, the outlet of the vibrating screening machine is provided with a material receiving tray to receive the material, and a sponge pad and filter cloth are placed in the receiving tray as a buffer to prevent porcelain damage.

[0099] (5) sheet arrangement treatment: nickel mesh with a size of 150 mm x 150 mm is selected, and 4 pieces of nickel mesh are placed on the stainless steel support in the middle and in order, without pressing and overlapping between the nickel meshes; a quantitative spoon is used to transfer the ceramic body to the nickel mesh, one spoon per mesh; a brush is used to evenly brush the ceramic body until the ceramic bodies are evenly stacked and have consistent areas, and there is no foreign matter on the nickel mesh.

[0100] (6) multi-stage annealing treatment: the nickel mesh after sheet arrangement on the stainless steel support is placed on the mesh belt of the mesh belt annealing furnace, conveyed to the furnace with the mesh belt, nitrogen gas is introduced into the water in the humidification barrel, and then humidified nitrogen gas is introduced into the mesh belt annealing furnace at a flow rate of 500 L / min; the mesh belt conveying speed is set to 20 mm / min, and then multi-stage annealing treatment is performed according to the annealing conditions shown in Table 1.

[0101] Table 1. Annealing conditions for multi-stage annealing treatment of Example 1 (7) collection treatment: after annealing is completed, a sponge pad is placed at the bottom of the unloading material box as a buffer to reduce porcelain damage; a filter cloth is fixed in the unloading material box with a fixed clamp, the ceramic body on the nickel mesh is poured into the filter cloth, and then the ceramic body on the filter cloth is poured into a product bag.

[0102] (8) appearance inspection treatment: 10,000 samples are taken from the product bag and placed on the inspection paper, and appearance inspection is performed using a 40x optical microscope; if there is no abnormality, it is transferred to the next process.

[0103] (9) end sealing process: end sealing treatment is performed on both ends of the ceramic body to form an external electrode, so that the internal and external electrodes are connected to obtain an MLCC product.

[0104] Example 2 This example is basically the same as Example 1, except that the annealing temperatures of the multi-stage annealing process are different, as shown in Table 2: Table 2. Annealing conditions of the multi-stage annealing process of Example 2 Example 3 This example is basically the same as Example 1, except that the web conveying speed is 25 mm / min, so that the annealing time of the multi-stage annealing process is different, and the annealing time of the heating stage, the holding stage and the cooling stage is 2.2 h, 2.8 h and 2.0 h, respectively.

[0105] Example 4 This example is basically the same as Example 1, except that the inlet flow rate of the humidified nitrogen is 200 L / min.

[0106] Example 5 This example is basically the same as Example 1, except that the annealing atmosphere is pure nitrogen, instead of humidified nitrogen.

[0107] Comparative Example 1 This comparative example is basically the same as Example 1, except that there is no piece sorting and multi-stage annealing process, i.e. after the drying treatment, the MLCC product is collected, appearance inspected and end-capped in sequence.

[0108] Test Example (1) The MLCC products of Example 1 and Comparative Example 1 were tested by Thermal Desorption Spectroscopy (TDS), and the results are shown in Figure 4 and Figure 5 .

[0109] As can be seen from Figure 4 and Figure 5 , the MLCC product of Comparative Example 1 has an abrupt desorption peak in the range of 100℃-200℃, while the desorption peak intensity of the MLCC product of Example 1 is significantly weakened, indicating that the multi-stage annealing process can remove the water vapor inside the MLCC ceramic body, so that the water content is greatly reduced. In addition, the TDS test results also show that the water vapor in the MLCC product can be completely removed only above 400℃, and cannot be removed by simple drying treatment.

[0110] (2) High temperature IR test: at the highest working temperature (T max ) of the MLCC product, 1.5 times the rated voltage (1.5U R), and the leakage current generated by the MLCC product was collected every 5 min for 168 h, and the stability of the leakage current was observed. The results are shown in Table 3. Figure 6 、 Figure 7 and Table 3.

[0111] Table 3. Test results of high-temperature IR test From Figure 6 、 Figure 7 and Table 3, it can be seen that, compared with Comparative Example 1, the peak leakage current of the MLCC product of Examples 1-5 in the high-temperature IR test is lower, and the leakage current is more stable, and the peak leakage current of Example 1 is the lowest and the leakage current stability is the best. Therefore, by multi-stage annealing treatment, the water content of the MLCC product is greatly reduced, and the phenomenon of H + moving to the interlayer medium to weaken the insulation resistance, meeting the requirement of current stability in the high-temperature IR test.

[0112] (3) Stress test: the stress test was performed on the MLCC product of Example 1 and Comparative Example 1 by using a nanoindenter, and the crack length on the surface of the porcelain body was observed by using a 40 times optical microscope. The results are shown in Figures 8 to 11 .

[0113] Figures 8-9 The stress test result graph of the MLCC product of Comparative Example 1 can be seen that there are very obvious long cracks on the surface of the product, indicating that the internal stress of the MLCC product is high. Figures 10-11 The stress test result graph of the MLCC product of Example 1 can be seen that, compared with Comparative Example 1, the cracks on the surface of the product of Example 1 are short and not obvious, indicating that the internal stress of the MLCC product is greatly reduced. Therefore, the multi-stage annealing treatment is beneficial to releasing the internal stress while improving the stability of the leakage current, further improving the reliability level of the MLCC product.

[0114] The technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, it should be considered that it is within the scope of the present application.

[0115] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the protection scope of the present application. It should be noted that, for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing an MLCC product, characterized in that, Includes the following steps: The chamfered MLCC ceramic body is then dried. In an annealing atmosphere containing nitrogen and / or inert gas, the dried MLCC ceramic body is subjected to a multi-stage annealing process, which includes a heating stage, a holding stage, and a cooling stage performed sequentially; wherein the annealing temperature of the holding stage is 700℃~900℃, and the annealing time of the holding stage is 2h~5h. The MLCC ceramic body after multi-stage annealing is then end-capped.

2. The method for preparing the MLCC product as described in claim 1, characterized in that, The annealing atmosphere also contains water vapor, and the oxygen potential of the annealing atmosphere is 700mV~800mV.

3. The method for preparing the MLCC product as described in claim 2, characterized in that, The annealing atmosphere is formed using the following method: Nitrogen and / or inert gas are introduced into the water, and then introduced into the annealing equipment at a flow rate of 200 L / min to 500 L / min.

4. The method for preparing the MLCC product according to any one of claims 1 to 3, characterized in that, The heating section includes the following steps: heating and annealing at 400℃~800℃ for 1h~3h.

5. The method for preparing the MLCC product according to any one of claims 1 to 3, characterized in that, The cooling section includes the following steps: cooling annealing at 350℃~800℃ for 1h~3h.

6. The method for preparing the MLCC product according to any one of claims 1 to 3, characterized in that, The annealing equipment for the multi-stage annealing process includes a mesh belt annealing furnace, wherein the mesh belt conveying speed of the mesh belt annealing furnace is 10mm / min to 100mm / min.

7. The method for preparing the MLCC product according to any one of claims 1 to 3, characterized in that, The drying temperature for the drying process is 100℃~120℃, and the drying time is 20min~120min.

8. The method for preparing the MLCC product as described in claim 6, characterized in that, Prior to the drying process, the following steps are also included: The MLCC ceramic body after beveling is cleaned, and the interval between the end time of the cleaning process and the start time of the drying process does not exceed 180 minutes.

9. The method for preparing the MLCC product according to any one of claims 1 to 3, characterized in that, Prior to the end-sealing process, the following steps are also included: The MLCC ceramic body after the multi-stage annealing treatment is subjected to visual inspection.

10. An MLCC product, characterized in that, It is manufactured using the preparation method of the MLCC product as described in any one of claims 1 to 9.

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