Low-howling multilayer ceramic dielectric capacitor, preparation method thereof and end sealing tool

Abstract

The invention discloses a low-howling multilayer ceramic dielectric capacitor and a preparation method thereof, and an end sealing tool, and relates to the technical field of cleaning capacitor structures and preparation methods and end sealing, the capacitor comprises a positive end electrode, a negative end electrode and an inner electrode, and the inner electrode comprises a plurality of inner electrode layers stacked in the Z-axis direction; when current passes through the capacitor, the direction of the current is the horizontal X-axis direction; when the vertical direction is the Y-axis direction, the Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction; the inter-plate electrostriction stress transfer direction of the inner electrode layer is an XZ plane, and the electrostriction stress transfer direction between the positive end electrode and the negative end electrode is an XY plane. According to the invention, the direction of the terminal electrode is changed, so that the purpose of dispersing and guiding the electrostrictive stress of each component in the MLCC under the conditions that hardware is not changed, the space height is not influenced and the ceramic material is not changed is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of capacitor structures, their preparation methods, and capping technologies, and particularly relates to a low-whistling multi-layer ceramic capacitor, its preparation method, and a capping tooling. Background Art

[0002] Multi-layer ceramic capacitors (abbreviated as MLCC) are formed by laminating printed electrode ceramic dielectric films in a staggered manner, and then undergoing a one-time high-temperature sintering to form a ceramic chip. Metal layers are then sealed at both ends of the chip. The end electrodes (metal layers) of MLCC capacitors are composed of three parts: a silver or copper (Ag / Cu) bottom layer, a nickel (Ni) barrier layer, and a tin or lead-tin (Sn / PbSn) surface plating layer. The silver or copper bottom layer provides electrical connection for the internally stacked electrodes. Secondly, nickel plating is applied to play a role in blocking the thermal shock of soldering. Finally, a pure tin layer or a tin-lead alloy layer is plated on the surface to improve the solder wettability. The specific structure of traditional MLCC is as Figure 1 shown, including a ceramic dielectric 12, an internal electrode 18, a surface plating layer 15, a barrier layer 16, and a metal bottom layer 17.

[0003] From the perspective of the MLCC structure, due to the variable characteristics of the ceramic dielectric itself, high-precision and high-quality capacitors can be manufactured by adjusting the dielectric constant, particle structure, fineness of the ceramic layer, etc. The multi-layer pressing process also significantly reduces the volume of capacitors of the same specification. With the popularization and portability of mobile and portable products, the original tantalum capacitors and aluminum electrolytic capacitors have gradually been replaced by smaller ceramic capacitors. However, with the development of the multi-functionalization and quietness of electronic devices, in power supply circuits of notebook computers, mobile phones (smartphones), digital cameras, thin TVs, etc., the problem of the previously unnoticed ceramic capacitors making noise has attracted more and more attention.

[0004] Due to its specific structure and working principle, MLCC may exhibit a whistling phenomenon in some electrical devices, causing interference or discomfort to people's work and life. The following are some noise hazard phenomena caused by the use of ceramic capacitors:

[0005] (1) Switching power supplies (SMPS), which are widely used in TVs, computers, chargers, and other digital devices, often use ceramic capacitors for filtering and energy storage. During high-frequency switching, the capacitors may generate whistling sounds;

[0006] (2) Some LED lamps use ceramic capacitors to smooth the power input. Especially in the case of a large change in the driving current, it may cause the generation of whistling sounds;

[0007] (3) The motor drive circuit in an electric fan may use ceramic capacitors to stabilize the power supply. When the motor operates at high frequencies, the capacitors may emit a whistling sound.

[0008] (4) Air conditioners and refrigerators: The compressor circuits of these devices may use ceramic capacitors for high-frequency filtering and starting. Especially in variable-frequency air conditioners, the whistling phenomenon may be more obvious.

[0009] (5) In washing machines, when the control circuit or the motor drive circuit uses ceramic capacitors, especially in variable-frequency drive washing machines, it may cause a whistling sound during high-frequency operation.

[0010] (6) The high-voltage power supply part in a microwave oven may use ceramic capacitors to stabilize the current and achieve high-frequency signal conversion, and a whistling phenomenon may occur.

[0011] (7) In a high-fidelity audio system, the ceramic capacitors used for power filtering in amplifiers and other audio devices may cause a whistling sound.

[0012] The reason for the whistling is the piezoelectric effect of the dielectric ceramic material. The academic definition of the piezoelectric effect is: When pressure, tension, and shear forces are applied to a crystal without a center of symmetry, dielectric polarization proportional to the stress occurs, and positive and negative charges will appear on the two end faces of the crystal. This phenomenon is called the direct piezoelectric effect. Conversely, when an electric field is applied to the crystal and polarization is caused, a deformation or mechanical stress proportional to the electric field strength is generated. This phenomenon is called the inverse piezoelectric effect. These two direct and inverse piezoelectric effects are collectively called the piezoelectric effect. The whistling of MLCC belongs to the inverse piezoelectric effect. Generally speaking, under the action of an external electric field, the ceramic dielectric itself will undergo a telescopic deformation, so it is also called electrostriction.

[0013] However, the electrostriction characteristics of different dielectrics also vary. The dielectric materials of multilayer ceramic capacitors mainly include two categories: paraelectric dielectrics and ferroelectric dielectrics.

[0014] Paraelectric dielectrics are also called Class I dielectrics, mainly including SrZrO3, MgTiO3, etc. The deformation generated by the electrostriction of paraelectric dielectrics is very small and is not sufficient to generate noise under the working voltage. Therefore, MLCCs made of paraelectric dielectric materials, such as NPO capacitors, do not produce obvious whistling during operation. However, it is difficult to fabricate MLCCs with large capacitance values using such dielectrics.

[0015] Ferroelectric dielectrics are also called Class II dielectrics, mainly including BaTiO3, BaSrTiO3, etc. The electrostriction characteristics of ferroelectric dielectrics are strong. Therefore, MLCCs made of ferroelectric dielectrics (Class II dielectrics), such as X7R / X5R products, will produce obvious whistling noise under the action of a relatively large alternating electric field strength. And the ceramic materials used to fabricate MLCCs with large capacitance values are all ferroelectric dielectrics.

[0016] As Figure 2 shown, due to the electrostrictive properties of ceramics, after applying an alternating current, the MLCC will undergo telescopic deformation in the direction perpendicular to the ceramic dielectric stack (Y-axis) and in the direction parallel to the positive and negative electrodes (X-axis). Since the ceramic capacitor is soldered to the circuit board, the deformation of the capacitor will pull the circuit board, resulting in vibrations on the surface of the circuit board. When the vibration frequency falls within the audible range of the human ear, the capacitor squeal phenomenon is heard. If the telescopic deformations in the direction perpendicular to the ceramic dielectric stack (Y-axis) and in the direction parallel to the positive and negative electrodes (X-axis) have a superimposed pulling effect on the circuit board, it will bring higher deformation amounts and squeal amplitudes. Generally speaking, for large-capacitance MLCCs such as X7R / X5R, when the voltage ripple on the capacitor is large enough and the ripple frequency is within the human audible range of 20 Hz to 20 kHz, obvious squealing may occur.

[0017] To improve the squeal problem of ceramic capacitors, the following measures are generally taken:

[0018] (1) Existing technology 1: Changing the capacitor type

[0019] Replace it with capacitors that do not have piezoelectric effects, such as electrostrictive ceramic capacitors, tantalum capacitors, and thin-film capacitors. The disadvantages of this technology are: it is necessary to adjust the circuit design and PCB layout, consuming a lot of time and labor costs, and it may affect other performance indicators of the entire circuit system, requiring a comprehensive retest and verification, increasing time costs and capital costs;

[0020] (2) Existing technology 2: Changing the capacitor body structure

[0021] Improve the ceramic capacitor body, generally by increasing the thickness of the bottom protective layer of the ceramic capacitor (see the bottom protective layer 13 in Figure 3 a) or increasing the metal bracket (see the metal bracket 14 in Figure 3 b). The disadvantages of this technology are: increasing the weight, which is not suitable for weight-sensitive devices; increasing the thickness of the component, which is not suitable for thin devices.

[0022] (3) Existing technology 3: Design and manufacture using dielectric materials with weak piezoelectric effects

[0023] This method generally changes the crystal structure, electric domain structure or conductivity of existing ceramic materials by further doping to reduce the piezoelectric effect. The doping methods include donor doping, acceptor doping and isovalent doping. For example, donor doping may introduce high-valent cations, increase the oxygen vacancy concentration, affect the domain wall movement, and thus reduce the piezoelectric response. Acceptor doping may introduce low-valent cations, reduce the oxygen vacancies, but may increase the dielectric loss. Although dielectric materials with greatly weakened piezoelectric effects can be obtained through doping, doping will affect other properties of the materials, such as reducing the dielectric constant, mechanical strength or temperature stability. Therefore, the weakly piezoelectric effect ceramic materials modified by doping are only applicable to specific capacitance values and voltage specifications, which limits the design flexibility and has limited improvement effect.

[0024] In view of this, the present application is specifically proposed. Summary of the Invention

[0025] The purpose of the present invention is to provide a low-whistling multi-layer ceramic capacitor, its preparation method and a capping tooling, which "disperse and direct", "break up into parts" and "offset positive and negative" the electrostrictive stresses of each component inside the MLCC by changing the direction of the end electrodes, so as to solve the problem of large whistling noise amplitude of capacitors in the prior art.

[0026] The embodiments of the present invention are realized through the following technical solutions: The embodiments of the present invention provide a low-whistling multi-layer ceramic capacitor, including a positive end electrode, a negative end electrode and inner electrodes, and the inner electrodes include a plurality of inner electrode layers stacked along the Z-axis direction;

[0027] When there is current passing through the capacitor, the direction of the current is the horizontal X-axis direction;

[0028] When the vertical direction is the Y-axis direction, the Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction;

[0029] The electrostrictive stress transfer direction between the inner electrode layers is the XZ plane, and the electrostrictive stress transfer direction between the positive end electrode and the negative end electrode is the XY plane.

[0030] Optionally, the positive end electrode and the negative end electrode are located on the same side of the capacitor;

[0031] Among the multiple inner electrode layers, there are adjacent and co-directionally stacked first inner electrode layer and second inner electrode layer, and there are f1 staggered stacked inner electrode layers stacked outside the first inner electrode layer, and there are f2 staggered stacked inner electrode layers stacked outside the second inner electrode layer;

[0032] Wherein, f1 = f2, and both f1 and f2 are integers greater than zero.

[0033] Optionally, there is a gap between the positive end electrode and the negative end electrode, and the cross-section of the gap is an arc structure.

[0034] To better solve the above problems, an embodiment of the present invention further provides a method for preparing a low-whistling multi-layer ceramic capacitor, including the following steps:

[0035] S1: Prepare ceramic slurry, including ball-milling dielectric ceramic powder;

[0036] S2: Cast the ceramic slurry to prepare a ceramic film;

[0037] S3: Print electrodes on the ceramic film;

[0038] S4: Stack the films, punch holes, and cut them in sequence to obtain a green body of MLCC;

[0039] S5: Remove the binder from the green body of MLCC;

[0040] S6: Sinter the green body of MLCC after removing the binder together with a carrier plate to obtain a fired body of MLCC;

[0041] S7: Chamfer the fired body of MLCC;

[0042] S8: Seal the chamfered fired body of MLCC.

[0043] Optionally, the conditions for ball-milling in S1 include that the weight ratio of dielectric ceramic powder to zirconia balls is 1:5.5 to 7; the diameter of zirconia balls is 2.5 to 3.5 mm; the ball-milling time is 35 to 50 hours; the slow-rolling time is 14 to 18 hours; the rotation speed of the ball mill is 30 to 40 RPM; the rotation mode is alternating forward and reverse rotation; the particle sizes D10, D50, and D90 of the ball-milled dielectric ceramic powder are 0.3 to 0.4 μm, 0.7 to 0.8 μm, and 1.5 to 1.6 μm respectively.

[0044] Optionally, in S4, it includes printing a cutting line pattern on the uppermost ceramic film during each film stacking, punching holes along the punching line, and the cutting includes cutting along the cutting line.

[0045] Optionally, the conditions for removing the binder in S5 include that the highest temperature is 300 to 320 °C, and the duration at the highest temperature is 10 to 14 hours.

[0046] Optionally, the sintering process in S6 includes a first stage and a second stage. The sintering temperature T1 in the first stage is 1100 to 1200 °C; the sintering temperature T2 in the second stage is 1000 to 1100 °C, and the sintering environment is an oxygen-rich environment.

[0047] Finally, an embodiment of the present invention also provides a capping tooling for the capping operation in S8 above, including a first rubber plate and a second rubber plate which are overlapped. A plurality of first through holes are provided on the first rubber plate, and a plurality of second through holes are provided on the second rubber plate. A single first through hole and a single second through hole are overlapped, and the single first through hole is larger than the single second through hole. A rotating shaft is provided in the single first through hole;

[0048] The rotating shaft is configured to introduce the chamfered MLCC green body into the second through hole from the first through hole by flipping;

[0049] The first rubber plate and the second rubber plate are detachably connected.

[0050] Optionally, when the positive terminal electrode and the negative terminal electrode of the chamfered MLCC green body are arranged on the same side and there is a gap between the positive terminal electrode and the negative terminal electrode, the flipping drive of the rotating shaft has an anti-fooling installation effect on the installation direction of the chamfered MLCC green body in the single first through hole.

[0051] Compared with the prior art, the embodiment of the present invention has the following advantages and beneficial effects:

[0052] 1. The low-squeal multi-layer ceramic capacitor provided by the embodiment of the present invention adopts the technologies of "terminal electrode reorientation", "inner electrode horizontal arrangement" and "inner electrode polarity flipping", and through "dispersing and guiding", "breaking into pieces" and "positive and negative cancellation" of the electrostrictive stress of each component inside the MLCC, without hardware modification, without affecting the space height, without changing the ceramic material, with flexible design, and only by slightly adjusting the pad size, the original capacitor can be replaced in-situ, which can effectively ensure the development efficiency and response speed of the whole machine.

[0053] 2. The inner electrodes of the embodiment of the present invention are perpendicular to the current direction (X-axis direction) and perpendicular to the vertical direction (Y-axis direction), and are stacked horizontally (Z direction) along the horizontal plane. The electrostrictive stress transfer direction between the inner electrode plates is the XZ plane, and the electrostrictive stress transfer direction between the terminal electrodes is the XY plane, avoiding the stress superposition in the same plane. An equipotential stack is arranged in the middle part of the capacitor to divide the MLCC into two parts. The electrostrictive directions of the two groups of flat capacitors are designed to be opposite directions from the equipotential stack, and the telescopic stresses cancel each other out, thereby reducing the deformation amount. At the same time, the terminal electrodes are led out in the same direction perpendicular to the current direction, and the action direction and moment of the telescopic stress are changed by changing the telescopic deformation directions of the two terminal electrodes, thereby reducing the deformation amount.

[0054] 3. The capacitor preparation method provided by the embodiment of the present invention combines the "fine crystallization ball milling" process to greatly reduce the deformation stress of the capacitor, thereby reducing or even eliminating the squeal noise amplitude of the capacitor.

[0055] Generally speaking, the low-squeal multi-layer ceramic capacitor provided by the embodiments of the present invention redirects the end electrodes to achieve the purpose of dispersing and guiding the electrostrictive stress of each component inside the MLCC without hardware modification, without affecting the space height, and without changing the ceramic material. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0057] Figure 1 is a schematic structural diagram of a traditional MLCC;

[0058] Figure 2 is a schematic diagram of the generation of squeal in a traditional MLCC;

[0059] Figure 3 is an improved structure of an existing ceramic capacitor, where Figure 3 a is a schematic diagram of increasing the thickness of the bottom protective layer of the ceramic capacitor, Figure 3 b is a schematic diagram of adding a metal support structure;

[0060] Figure 4 is a schematic diagram of the external shape structure of a traditional MLCC;

[0061] Figure 5 is a schematic diagram of the capacitor structure provided by the embodiments of the present invention;

[0062] Figure 6 is a schematic diagram of the internal expansion and contraction stress transfer direction of the capacitor provided by the embodiments of the present invention;

[0063] Figure 7 is a schematic diagram of the internal electrode stack of the capacitor provided by the embodiments of the present invention;

[0064] Figure 8 is a process chart of the preparation of the capacitor provided by the embodiments of the present invention;

[0065] Figure 9 is a schematic diagram of the internal electrode pattern of the capacitor provided by the embodiments of the present invention;

[0066] Figure 10 is a schematic diagram of the cutting line pattern of the capacitor provided by the embodiments of the present invention;

[0067] Figure 11 is a schematic diagram of the shape of the green body after cutting provided by the embodiments of the present invention;

[0068] Figure 12 Schematic diagram of the capping tooling structure provided by the embodiment of the present invention;

[0069] Figure 13 Schematic diagram of the implantation principle of the special-shaped capacitor provided by the embodiment of the present invention, where Figure 13 a is the state diagram with the correct installation direction of the MLCC green body, Figure 13 b is the state diagram with the wrong installation direction of the MLCC green body.

[0070] Marks in the drawings and corresponding component names:

[0071] 1 - Positive terminal electrode, 2 - Negative terminal electrode, 3 - First inner electrode layer, 4 - Second inner electrode layer, 5 - Gap, 6 - Cutting line, 7 - Punching line, 8 - First rubber plate, 9 - Second rubber plate, 10 - First through hole, 11 - Rotating shaft, 12 - Ceramic dielectric, 13 - Bottom protective layer, 14 - Metal bracket, 15 - Surface coating, 16 - Barrier layer, 17 - Metal bottom layer, 18 - Inner electrode, 19 - Alignment mark point, 20 - Electrode pattern area. Detailed implementation manners

[0072] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations.

[0073] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0074] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0075] In the description of the present invention, it should be noted that the terms "first", "second", "third", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0076] Embodiment

[0077] Embodiment 1: The embodiment of the present invention provides a low - crosstalk multi - layer ceramic capacitor, such as Figure 5 , Figure 6 and Figure 7As shown, it includes a positive terminal electrode 1, a negative terminal electrode 2, and an internal electrode 18. It is characterized in that the internal electrode 18 includes a plurality of internal electrode layers stacked along the Z-axis direction; when current passes through the capacitor, the direction of the current is the horizontal X-axis direction; when the vertical direction is the Y-axis direction, the Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction; the direction of the electrostrictive stress transfer between the plates of the internal electrode layer is the XZ plane, and the direction of the electrostrictive stress transfer between the positive terminal electrode 1 and the negative terminal electrode 2 is the XY plane.

[0078] The positive terminal electrode 1 and the negative terminal electrode 2 are located on the same side of the capacitor; among the plurality of internal electrode layers, there are adjacent and co-directionally stacked first internal electrode layer 3 and second internal electrode layer 4. There are f1 staggered stacked internal electrode layers stacked outside the first internal electrode layer 3, and f2 staggered stacked internal electrode layers stacked outside the second internal electrode layer 4; wherein, f1 = f2, and both f1 and f2 are integers greater than zero. There is a gap 5 between the positive terminal electrode 1 and the negative terminal electrode 2, and the cross-section of the gap 5 is an arc structure.

[0079] The two terminal electrodes of the traditional MLCC are axially opposite and led out along the current direction (as Figure 4 shown), and the telescopic deformation occurring in the direction perpendicular to the ceramic dielectric stack and parallel to the positive and negative terminal electrodes will be superimposed, resulting in a relatively high deformation amount and noise amplitude. In the embodiment of the present invention, the terminal electrodes are designed to be led out in the same direction perpendicular to the current direction (as Figure 5 shown), and by changing the telescopic deformation direction of the two terminal electrodes, the acting direction and moment of the telescopic stress are changed, thereby reducing the deformation amount.

[0080] At the same time, the stacking direction of the internal electrode layers of the traditional MLCC is perpendicular to the current direction (X-axis direction) and parallel to the vertical direction (Y-axis direction). The electrostrictive stress direction between the internal electrode plates and the electrostrictive stress direction between the terminal electrodes will be superimposed in the plane perpendicular to the current direction (as Figure 2 shown). In the embodiment of the present invention, the internal electrodes are designed to be perpendicular to the current direction (X-axis direction) and perpendicular to the vertical direction (Y-axis direction), and are stacked horizontally along the Z-axis direction. The direction of the electrostrictive stress transfer between the internal electrode plates is the XZ plane, and the direction of the electrostrictive stress transfer between the terminal electrodes is the XY plane, avoiding the superposition of stress in the same plane (as Figure 6 shown).

[0081] The stacking order of the internal electrode layers of the traditional MLCC is staggered stacking of positive and negative alternately, forming a structure in which a plurality of flat capacitors are connected in parallel. The electrostrictive directions of each flat capacitor are the same, and will be superimposed in the direction perpendicular to the horizontal plane (Y-axis direction). In the embodiment of the present invention, an equipotential stack is provided in the middle part of the capacitor (see Figure 7The first inner electrode layer 3 and the second inner electrode layer 4) in it divide the MLCC into two parts. From the equipotential lamination, the electrostrictive directions of the two groups of planar capacitors are designed to be opposite, and the telescopic stresses cancel each other out, thereby reducing the deformation amount.

[0082] Embodiment 2: The embodiment of the present invention provides a preparation method of a low-whistling multi-layer ceramic capacitor, as Figure 8 shown, including the following content:

[0083] 1. Prepare ceramic slurry: The main component of the ceramic powder used in the embodiment of the present invention is barium titanate, with a temperature characteristic of X7R and a dielectric constant of about 2800. Different from the conventional process of preparing ceramic slurry, this patent innovatively formulates the slurry. By the "fine-grained ball milling" process, the particle size of the original powder is reduced to reach sub-micron powder, and a fine-grained structure is formed after sintering. The fine-grained treatment can increase the grain boundary density of the ceramic, hinder the domain wall flipping or the phase transition propagation path. At the same time, the grain boundaries with high surface area lead to a more complex local electric field distribution, which can weaken the polarization efficiency. By controlling the microstructure (grain size) of the ceramic material through the "fine-grained ball milling" process, the domain wall activity and the piezoelectric polarization response are restricted, so as to suppress the piezoelectric effect of the ceramic to achieve the purpose of reducing whistling.

[0084] Specific method for preparing ceramic slurry: The dielectric ceramic powder and zirconia balls are put into a ball mill tank according to a specific weight ratio. The binder, solvent and additives used in the prior art can be added in turn. According to the ceramic classification, the ratio of zirconia balls and the size of zirconia balls, the ball milling time and rotation speed are set. By the rotation of the ball mill, the agglomerated ceramic powder is broken up, and all raw materials are evenly mixed. The "fine-grained ball milling" process has the following differences from the conventional ceramic slurry preparation process as shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] After sufficient ball milling by the "fine-grained ball milling" process, the required ceramic slurry powder has a smaller and more concentrated particle size. The D50 is reduced from 1.09 μm to 0.75 μm, and the powder particle size is reduced from the micron level to the sub-micron level.

[0089] 2. Cast ceramic membrane: Inject the above-mentioned ceramic slurry into a stainless steel tank, and then use a vacuum pressure pump to inject the prepared slurry from the slurry tank into the casting head of the casting equipment. Then, spray the slurry in the casting head onto a 50μm * 200mm PET carrier tape to form a uniform layer of ceramic slurry. Finally, obtain a ceramic membrane with a certain width, thickness, and strength through heating and drying. Control the deposition amount of the ceramic slurry by controlling the flow rate of the casting head and the winding speed of the PET carrier tape, thereby controlling the thickness of the ceramic membrane. The thickness of the cast ceramic membrane in this patented technology should be 15μm, and the width should be 180mm.

[0090] 3. Printing electrodes: Different from the rectangular internal electrode pattern of traditional MLCCs, the embodiment of the present invention innovatively designs a "C"-shaped internal electrode pattern (as shown in Figure 9 ). The structure of traditional MLCCs is axially lead-out, and two adjacent capacitors on the left and right share 1 cutting line. The embodiment of the present invention is designed for radial lead-out, and two adjacent capacitors above and below share 1 cutting line. After cutting along the cutting line, the internal electrode pattern inside a single capacitor is an "L" shape (as shown in Figure 7 ). Table 2 shows the information of capacitors with different sizes corresponding to those in the preparation method of the embodiment of the present invention. Figure 9

[0091] Table 2

[0092] Product Dimensions a (mm) b (mm) c (mm) d (mm) r (mm) L (mmm) H (mm) 0402 0.4 0.4 0.4 0.6 0.2 1.3 0.65 0603 0.55 0.56 0.56 0.8 0.28 2.0 1.0 0805 0.66 0.76 0.76 1.1 0.38 2.3 1.35 1210 0.76 0.76 0.76 1.8 0.38 3.7 2.6 1812 1.0 0.76 0.76 2.7 0.38 5.5 3.1 2220 1.0 1.0 1.0 3.3 0.5 6.7 4.3

[0093] The screen printing equipment designed and manufactured according to the embodiment of the present invention has a mesh count of 400 - 500 meshes, a tension of 22N, and a latex thickness of 15μm. When printing electrodes, first put about 70g of silver-palladium internal electrode slurry into the screen printing equipment. The silver-palladium ratio of the internal electrode slurry is 9:1, and the viscosity is 28 Pa·s. Then, use a plastic squeegee to extrude the internal electrode slurry to penetrate the screen, and form an internal electrode layer with a thickness of about 3μm on the blank ceramic membrane under the screen. The pattern of this internal electrode layer is consistent with the screen printing pattern designed in this patented technology, and should be clear, complete, without showing the bottom, and the edges should be neat. Then, perform high-temperature baking at about 90°C to remove the organic matter in the internal electrode slurry, so that the printed internal electrode slurry is dry enough, preferably ensuring that the internal electrode slurry will not contaminate the back of the PET carrier tape during membrane tape winding.

[0094] 4. Laminating, punching, and cutting: Cut the blank ceramic membrane and the ceramic membrane printed with internal electrodes into squares of about 180mm * 180mm. Set the pressure table temperature to 30°C to soften the ceramic membrane, and then apply a pressure of 7000 kgf to stack the ceramic membranes in a certain order with misalignment to form a green ceramic block.

[0095] In the embodiment of the present invention, the middle two layers of the internal electrode membranes of the capacitor are not misaligned during lamination, and an equipotential stack is set, so that two sets of internal electrodes with opposite arrangement directions can be formed.​

[0096] Different from the existing MLCC cutting process, in the embodiments of the present invention, the top layer of each film stacking of the capacitor adopts a cutting line 6 pattern printed as shown in Figure 10 to accurately align the punching position.

[0097] After the ceramic block after film stacking is first subjected to warm isostatic pressing, it is then punched according to the punching line 7 described in Figure 10 , and then the MLCC green body shown in Figure 11 can be obtained after cutting along the cutting line.

[0098] 5. Excluding the binder: Place the capacitor green body prepared in the previous process on a zirconia ceramic carrier plate, lay it flat in a single layer, and then place the carrier plate in a programmable debinding furnace. Using a certain heating curve, at a high temperature for a long time, the organic substances such as the binder and additives in the green body are discharged. This process is called excluding the binder. According to the differences in the ceramic slurry formula and the number of internal electrode layers of the capacitor, the optimal debinding temperature curve is determined by thermogravimetric analysis (TGA). The capacitor green body is heated or cooled with time at a controlled temperature, and at the same time, the change in its mass is measured in real time. The green body loses weight at a certain temperature, so the temperature near this is the decomposition temperature, and based on this, a suitable debinding curve is formulated. If the debinding is not sufficient, it will lead to too much residual organic matter. When sintering, the temperature is rapidly increased, and the organic matter decomposes too fast, resulting in delamination of the porcelain body and the formation of holes. If the debinding is excessive, the binder is discharged very cleanly and cannot fix the porcelain powder, resulting in a very fragile porcelain body that is easy to break. The whole process of debinding the capacitor produced by the patented technology lasts for 84 hours, the highest temperature is 310 °C, and the high temperature lasts for 12 hours.

[0099] 6. Sintering: The capacitor green body after debinding together with the carrier plate is placed in a box furnace for sintering, and the capacitor after sintering is called a fired body. Since the sintering curves of ceramic capacitors with different ceramic materials, different outer dimensions, and different numbers of internal electrode layers are different, the capacitor green body after debinding needs to determine the sintering temperature curve through differential thermal analysis (DTA), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA). Differential thermal analysis (DTA) can evaluate the thermal stability of materials in a high-temperature environment, and by monitoring the shape and characteristics of the curve, it can be judged whether there is thermal degradation or thermal decomposition of the materials. Thermogravimetric analysis (TGA) is tested under different atmospheres (air, nitrogen, etc.) and different heating rates to evaluate the influence of these conditions on the decomposition and reaction characteristics of the materials. Using thermomechanical analysis (TMA), it can be found that the green body will shrink at a certain temperature, so the temperature near this is the sintering temperature to form porcelain. Based on the analysis curves obtained through the above steps, suitable sintering temperature conditions are formulated.

[0100] To avoid effective control of the grain size of barium titanate ceramics after fine-grain treatment, while ensuring high density and suppressing abnormal grain growth, the embodiments of the present invention adopt a special sintering process: (1) Two-step sintering method. The first sintering temperature T1 is selected at the critical point of densification mainly caused by grain boundary diffusion (slightly lower than the conventional sintering temperature); the second sintering temperature T2 is set at a temperature that suppresses grain boundary migration but allows volume diffusion to reduce the oxygen vacancy concentration through reaction; (2) Oxygen atmosphere compensation mechanism, sintering in a rich oxygen environment in the second step, reducing the oxygen vacancy concentration to 3x10 17 cm -3 (conventional sintering is 1x10 19 cm -3 ), and the specific implementation methods are shown in Table 3 below:

[0101] Table 3

[0102]

[0103] 7. Chamfering: Put the sintered capacitor green body together with 500 ml of aluminum oxide balls and 1000 ml of 1500-mesh aluminum oxide powder into a planetary chamfering machine, and then add 600 ml of water as a medium, and chamfer for 48 h at a rotation speed of 50 rpm to 80 rpm. Through the rotation of the capacitor green body, chamfering medium and water in the chamfering machine, mutual grinding is carried out to grind the chip edges and corners smoothly, achieving the following three purposes:

[0104] (1) Fully lead out the inner electrode to enhance the tight connection between the inner and outer electrodes after capping;

[0105] (2) Round the corners of the capacitor ceramic body to eliminate the corner stress and reduce the collision damage during subsequent processing and transportation;

[0106] (3) Increase the wetting angle to facilitate the uniform application of the end electrode during subsequent capping and increase the firmness of the connection between the end electrode and the ceramic body.

[0107] 8. Capping: The next step for the capacitor green body after chamfering is capping. For the existing manual coating end equipment of ordinary multi-layer ceramic capacitors, first, the capacitor chip sieve plate is used. After the capacitor enters the capping plate hole, through the capping needle bed pressing plate, one end of the capacitor is exposed, while the other end is inside the capping plate. Then, use a leveling machine to make the exposed MLCC end electrode flat and consistent, and then the capping plate can be lowered into the slurry, so that the capping of one end electrode is completed. Place the entire capping plate flat in a tunnel drying furnace. After drying, press out the un-capped end on the other side through the needle bed, and complete the capping and drying process of the other end electrode according to the same operation, thus completing the entire capping process.

[0108] However, the capacitor of this patent is not a regular-shaped capacitor with axial leads, but a special-shaped structure with radial leads, and the prior art cannot seal the ends. Therefore, a sealing process technology is innovatively designed according to the shape deconstruction characteristics of the capacitor of this patent. First, a tooling composed of two layers of rubber plates is designed. Each cavity in the upper half is equipped with a turning shaft, and the aperture of the cavity in the lower half is slightly smaller than that in the upper half, as Figure 12 shown.

[0109] Before end coating, the capacitor is implanted into the upper half of this rubber plate, and the capacitor is pushed by a thimble. Since the surface with grooves of the capacitor in the embodiment of the present invention has a smaller rotation radius than the other three surfaces, as Figure 13 shown, when the direction is correct, the flipping can be successfully completed and implanted into the lower half of the rubber plate through the cavity, and when the direction is incorrect, it cannot pass through. After the capacitor is implanted, the upper and lower parts of the rubber plate are separated, and then the lower half of the rubber plate is put into the dipping equipment to carry out end electrode paste coating.

[0110] After that, a pure silver end electrode paste with a viscosity of 28 Pa·s is used. Utilizing the wetting property and capillary phenomenon of the end electrode paste, the silver paste is coated on the surfaces of the two ends of the capacitor green body, so as to connect each inner electrode layer exposed at the end, and the inner electrodes of each end are connected in parallel. Then, silver sintering is completed through three stages of 280 °C / 3 h → 710 °C / 2 h → 600 °C / 1 h, the organic matter in the silver paste is completely decomposed, and the end silver is densified.

[0111] Using this method has high end coating efficiency, easy control of dipping depth, and the products obtained by end coating have high consistency in end width and good appearance quality.

[0112] Finally, electroplating is carried out. A layer of nickel is plated on the end electrode, and then a layer of tin / tin-lead is plated on the nickel layer. The nickel layer is a thermal barrier layer, and the tin / tin-lead layer is to increase its solderability.

[0113] Embodiment 3: As Figure 12 shown, the embodiment of the present invention provides a sealing tooling for the above-mentioned sealing operation, including an overlapping first rubber plate 8 and a second rubber plate 9. A plurality of first through holes 10 are provided on the first rubber plate 8, and a plurality of second through holes are provided on the second rubber plate 9. A single first through hole 10 and a single second through hole are overlapped, and a single first through hole 10 is larger than a single second through hole. A rotating shaft 11 is provided in a single first through hole 10; the rotating shaft 11 is arranged to introduce the chamfered MLCC green body into the second through hole from the first through hole by flipping; the first rubber plate 8 and the second rubber plate 9 are detachably connected.

[0114] As Figure 13As shown, when the positive terminal electrode 1 and the negative terminal electrode 2 of the chamfered MLCC green body are arranged on the same side and there is a gap 5 between the positive terminal electrode 1 and the negative terminal electrode 2, the flipping drive of the rotating shaft 11 has an anti-fooling installation effect on the installation direction of the chamfered MLCC green body in a single first through hole 10.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. It should be noted that the structures or components illustrated in the drawings are not necessarily drawn to scale, and the present invention omits the description of well-known components and processing technologies and processes to avoid unnecessarily limiting the present invention.

Claims

1. A low-whistle multilayer ceramic capacitor, comprising a positive terminal electrode (1), a negative terminal electrode (2) and an inner electrode, characterized in that: The inner electrode comprises a plurality of inner electrode layers stacked along the Z-axis direction; When current flows through the capacitor, the direction of the current is in the horizontal X-axis direction; When the vertical direction is the Y-axis direction, the Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction; The inter-plate electrostrictive stress transmission direction of the inner electrode layer is the XZ plane, and the electrostrictive stress transmission direction between the positive terminal electrode (1) and the negative terminal electrode (2) is the XY plane.

2. The low-whistle multilayer ceramic capacitor according to claim 1, characterized in that: The positive terminal electrode (1) and the negative terminal electrode (2) are located on the same side of the capacitor; The plurality of internal electrode layers include a first internal electrode layer (3) and a second internal electrode layer (4) which are adjacent and stacked in the same direction, f1 internal electrode layers stacked in an alternating manner are stacked outside the first internal electrode layer (3), and f2 internal electrode layers stacked in an alternating manner are stacked outside the second internal electrode layer (4); Wherein, f1=f2, and f1 and f2 are both integers greater than zero.

3. The low-whistle multilayer ceramic capacitor according to claim 2, characterized in that: There is a gap (5) between the positive terminal electrode (1) and the negative terminal electrode (2), and the cross section of the gap (5) is an arc-shaped structure.

4. A method for preparing a low-whistle multilayer ceramic capacitor according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: preparing ceramic slurry, including ball milling dielectric ceramic powder; S2: Casting the ceramic slurry to prepare a ceramic diaphragm; S3: printing electrodes on the ceramic diaphragm; S4: laminating, punching and cutting are performed in sequence to obtain MLCC green sheets; S5: removing the adhesive from the MLCC green body; S6: sintering the MLCC green body without the binder together with the carrier to obtain the MLCC cooked body; S7: chamfering the MLCC blank; S8: Cap the ends of the chamfered MLCC blank.

5. The method for preparing a low-whistle multilayer ceramic capacitor according to claim 4, characterized in that: The ball milling conditions in S1 include a weight ratio of dielectric ceramic powder to zirconia balls of 1:5.5-7; a diameter of the zirconia balls of 2.5-3.5 mm; a ball milling time of 35-50 hours; a slow rolling time of 14-18 hours; a ball mill speed of 30-40 RPM; a rotation mode of alternating forward and reverse rotation; and particle sizes D10, D50 and D90 of the dielectric ceramic powder after ball milling are 0.3-0.4 μm, 0.7-0.8 μm and 1.5-1.6 μm, respectively.

6. The method for preparing a low-whistle multilayer ceramic capacitor according to claim 4, characterized in that: S4 includes printing a cutting line (6) pattern on the topmost ceramic membrane of each stack, and punching holes along the punching lines (7), wherein the cutting includes cutting along the cutting lines (6).

7. The method for preparing a low-whistle multilayer ceramic capacitor according to claim 4, characterized in that: The conditions for removing the adhesive in S5 include a maximum temperature of 300 to 320° C. and a maximum temperature duration of 10 to 14 hours.

8. The method for preparing a low-whistle multilayer ceramic capacitor according to claim 4, characterized in that: The sintering process in S6 includes a first stage and a second stage. The sintering temperature of the first stage is T1 = 1100-1200°C; the sintering temperature of the second stage is T2 = 1000-1100°C, and the sintering environment is an oxygen-rich environment.

9. A sealing tool, used for the sealing operation of S8 in claim 4, characterized in that: The invention comprises a first rubber plate (8) and a second rubber plate (9) which are arranged in an overlapping manner, wherein the first rubber plate (8) is provided with a plurality of first through holes (10), the second rubber plate (9) is provided with a plurality of second through holes, a single first through hole (10) is arranged in an overlapping manner with a single second through hole, and a single first through hole (10) is larger than a single second through hole, and a rotating shaft (11) is arranged in a single first through hole (10); The rotating shaft (11) is configured to guide the chamfered MLCC blank from the first through hole (10) into the second through hole by turning over; The first rubber plate (8) and the second rubber plate (9) are detachably connected.

10. The end-sealing tool according to claim 9, characterized in that: When the positive terminal electrode (1) and the negative terminal electrode (2) of the chamfered MLCC blank are arranged on the same side and there is a gap (5) between the positive terminal electrode (1) and the negative terminal electrode (2), the flipping drive of the rotating shaft (11) has an anti-mistake installation effect on the installation direction of the chamfered MLCC blank in the single first through hole (10).

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