Terminal electrode capable of improving bending resistance of ceramic dielectric capacitor

Abstract

The utility model discloses a terminal electrode capable of improving bending resistance of a ceramic dielectric capacitor, which relates to the field of terminal electrode structures and is arranged at two ends of a ceramic body of an MLCC (multilayer ceramic capacitor) structure, and the terminal electrode is connected with an inner electrode in the ceramic body to lead out the capacity of the capacitor. The end electrode comprises a bottom electrode and a flexible electrode, the bottom electrode is arranged on the porcelain body in a flanging mode, the flexible electrode wraps the outer side of the bottom electrode, the flanging width of the bottom electrode relative to the porcelain body is f1, and the flanging widths of the flexible electrode relative to the porcelain body are f2 and f2gt; f1. According to the utility model, the flexible electrode is arranged, and the flanging width of the flexible electrode is set to be greater than the flanging width of the bottom electrode, so that the purpose that the failure mode can be converted from short-circuit failure with serious consequences to open-circuit failure with slight severity even if the capacitor is subjected to the action of limit external stress is achieved.

Description

Technical Field

[0001] This utility model relates to the field of end electrode structure, specifically to an end electrode that can improve the bending resistance of ceramic capacitors. Background Technology

[0002] Surface-mount multilayer ceramic capacitors (MLCCs) are essential components of modern electronic systems, playing roles in filtering, decoupling, and coupling. For example... Figure 1 As shown, the MLCC structure mainly consists of three parts: a ceramic dielectric, a metal internal electrode, and metal terminal electrodes. The metal terminal electrodes provide capacitance leads at both ends of the core and serve to connect and fix the MLCC to the mounting plate. The MLCC ceramic body is hard and brittle. During assembly and service, due to the difference in thermal expansion coefficients between the ceramic, metal terminal electrodes, and printed circuit board materials, rapid temperature changes or abnormal welding thermal stress can cause tensile stress and cracks in the ceramic body, leading to MLCC failure. Furthermore, harsh operating environments such as vibration and acceleration can cause the MLCC to crack and fail due to shear mechanical stress generated by the bending of the printed circuit board (e.g., ...). Figure 2 (As shown).

[0003] Flexible electrode MLCCs consist of a conductive resin filler layer coated at both ends of the capacitor core, giving the traditional metal end electrodes a certain degree of toughness. This allows them to absorb or reduce welding thermal and mechanical stresses, enabling MLCCs to withstand higher bending stresses and certain thermal stresses during assembly and use. This is an effective means of preventing MLCC failure due to stress. The end electrode structure of flexible electrode MLCCs mainly has two directions: one is the same "three-layer end electrode" structure as ordinary MLCCs, except that the sintered bottom electrode is replaced with a flexible resin metal bottom layer (such as...). Figure 3 (as shown in a); another type is a "four-layer end electrode" (as shown in a diagram) that adds a flexible resin-metal layer to the sintered bottom electrode, based on the conventional end electrode structure design. Figure 3 (As shown in b). The three-layer electrode design, represented by Syfer products, has the advantage of avoiding thermal stress generated during the sintering of the bottom metal and ceramic body and simplifying the manufacturing process. However, this design is prone to poor contact between the inner and outer electrodes. The four-layer electrode design is adopted by foreign manufacturers such as AVX, Exxelia, and KEMET, as well as domestic MLCC manufacturers, and is the main technical route for manufacturing flexible electrode MLCCs. Overall, flexible electrode MLCCs have good resistance to plate bending and meet the development trend of miniaturization and large capacity. They can replace surface-mount capacitors in situ. Therefore, compared with other methods such as design structure optimization and replacement of support capacitors, flexible electrode MLCCs have better development prospects and have attracted widespread interest from the application side.

[0004] The mechanical properties of the end electrodes of MLCCs can be characterized by a "plate bending" test, such as... Figure 4 As shown, when the printed circuit board is bent to a certain height (H), stress may cause cracks in the ceramic body, leading to a decrease in capacitance. The bending resistance of the product is evaluated by detecting changes in capacitance. Test results show that the flexible electrode MLCC improves the bending resistance of the product from 1mm to over 4mm, significantly enhancing its bending performance. However, under ultimate bending stress, the main failure mode is still ceramic body cracking (e.g., ...). Figure 5 As shown in the figure, when a crack penetrates the effective area of ​​the inner electrode, it can easily cause a short circuit failure in the product, resulting in the burning of the entire circuit board and serious consequences.

[0005] On the other hand, the bending resistance of flexible electrode MLCCs mainly depends on the flexible electrode paste and the fabrication process. In terms of the fabrication process, the flexible layer is obtained by applying a further layer to the underlying electrode using a dip-coating process. Due to the relatively rough surface and high tension of the underlying electrode, there are difficulties in the wetting of the flexible paste and capillary action. Therefore, the resulting flexible layer flange width is generally less than or equal to the flange width of the underlying electrode (e.g., ...). Figure 6 As shown, f2≤f1), which means that the "toughness" function of the flexible layer cannot be fully utilized, thus hindering the improvement of the product's bending resistance.

[0006] In view of the above, this application is hereby submitted. Utility Model Content

[0007] The purpose of this invention is to provide an end electrode that can improve the bending resistance of ceramic capacitors. By setting a flexible electrode and setting the flange width of the flexible electrode to be greater than the flange width of the bottom electrode, the invention solves the problem that in the prior art, when capacitors are subjected to extreme external stress, the failure mode of the product is still mainly manifested as ceramic body cracks, which leads to short circuit failure and burnout of the entire circuit board.

[0008] This utility model embodiment is achieved through the following technical solution: This utility model embodiment provides an end electrode that can improve the bending resistance of ceramic capacitors. The end electrode is disposed at both ends of the MLCC structure ceramic body and is configured to lead out the capacitance of the capacitor after being connected to the internal electrode in the ceramic body.

[0009] The end electrode includes a bottom electrode and a flexible electrode. The bottom electrode is flanged and disposed on the ceramic body. The flexible electrode is wrapped around the outside of the bottom electrode. The flange width of the bottom electrode relative to the ceramic body is f1, and the flange width of the flexible electrode relative to the ceramic body is f2, where f2>f1.

[0010] Preferably, f1 <f2<2f1;

[0011] Preferably, the vertical projection of the flange of the bottom electrode falls into the flexible electrode;

[0012] Preferably, the connecting surface between the bottom electrode and the flexible electrode adopts a structure after sandblasting treatment, and the structure after sandblasting treatment can improve the adhesion between the flexible electrode and the bottom electrode.

[0013] Preferably, a nickel plating layer is coated outside the flexible electrode, and a solderable layer is coated outside the nickel plating layer. The solderable layer is set to be able to weld the MLCC structure on the circuit board, and the nickel plating layer is set to prevent the solderable layer from melting and damaging the flexible electrode or the bottom electrode during the welding process.

[0014] Preferably, the solderable layer is made of Sn or SnPb.

[0015] Preferably, the maximum flanging thickness of the flexible electrode is greater than 20 μm.

[0016] Preferably, under the action of the ultimate bending stress, the flexible electrode fractures and / or falls off, and the bottom electrode and the ceramic body remain intact.

[0017] Preferably, the Ra value of the roughness of the structure after sandblasting treatment is between 0.5 and 2 μm.

[0018] Preferably, the hole diameter on the flexible electrode is less than 1,50 μm.

[0019] Compared with the prior art, the embodiment of the present utility model has the following advantages and beneficial effects:

[0020] 1. The end electrode for improving the bending resistance of the ceramic capacitor provided by the embodiment of the present utility model wraps the flexible electrode outside the bottom electrode, limits its relative flanging width to the ceramic body as f2, and f2 is greater than f1. This enables the flexible electrode to better disperse stress when subjected to bending stress, reducing the direct pressure on the ceramic body, thereby improving the bending resistance of the MLCC. This structure helps to change the failure mode to reduce the severity of failure when the MLCC is subjected to extreme external stress, thereby improving the overall reliability of the MLCC. <​​​​​​

[0023] 4. This utility model embodiment obtains a four-layer end electrode structure by sequentially setting a "bottom electrode", a "flexible layer electrode", a "nickel plating layer" and a "solderable layer" at the chip end, which ensures that the end electrode has sufficient rigidity to maintain electrical connection and sufficient flexibility to absorb stress.

[0024] 5. By setting the bottom electrode sandblasting structure and limiting the width of the flexible layer flange, the adhesion between the flexible layer and the bottom electrode is enhanced. At the same time, when the MLCC is subjected to extreme external stress, the severity of failure is reduced by the peeling of the flexible layer and the bottom electrode, thereby improving the overall reliability of the MLCC.

[0025] In general, the end electrode provided by the embodiments of this utility model, which can improve the bending resistance of ceramic capacitors, achieves the purpose of changing the failure mode from a severe short-circuit failure to a minor open-circuit failure even when the capacitor is subjected to extreme external stress by setting a flexible electrode and setting the flange width of the flexible electrode to be greater than the flange width of the bottom electrode. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of an MLCC structure in the prior art;

[0028] Figure 2 This is a schematic diagram of stress cracking in the prior art;

[0029] Figure 3 This is a schematic diagram of a flexible electrode MLCC structure in the prior art, in which... Figure 3 a is a three-layer flexible electrode MLCC, and 3b is a four-layer flexible electrode MLCC;

[0030] Figure 4 This is a schematic diagram of a plate bending test;

[0031] Figure 5 This is a schematic diagram of short-circuit failure caused by cracks in the ceramic body in the prior art;

[0032] Figure 6 This is a schematic diagram of the terminal electrode dimensions and structure of a flexible electrode MLCC in the prior art;

[0033] Figure 7 This is a schematic diagram of the end electrode structure provided in an embodiment of the present utility model;

[0034] Figure 8 Enlarged schematic diagrams of the structure before and after sandblasting treatment are provided for embodiments of this utility model, wherein... Figure 8 a is a schematic diagram of the state before the sandblasting structure was installed. Figure 8 b is a schematic diagram of the state after the sandblasting structure is set;

[0035] Figure 9 This is a schematic diagram of the flexible layer pores in an embodiment of the present invention;

[0036] Figure 10 This is a schematic diagram showing the state of open circuit failure after the flexible layer of the end electrode in this embodiment of the present invention breaks and falls off.

[0037] The attached diagram shows the markings and corresponding component names:

[0038] 1-Ceramic body, 2-Internal electrode, 3-Bottom electrode, 4-Flexible electrode, 5-Nickel plating, 6-Solderable layer. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can typically be arranged and designed in various different configurations.

[0040] 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 invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0041] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0042] In the description of this utility model, it should be noted that the terms "first", "second", "third", etc. are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0043] Example

[0044] like Figure 7As shown, an end electrode for improving the bending resistance of a ceramic capacitor according to an embodiment of the present utility model is provided at both ends of the ceramic body 1 of the MLCC structure, and is configured to lead out the capacitance of the capacitor after being connected to the internal electrode 2 in the ceramic body 1; the end electrode includes a bottom electrode 3 and a flexible electrode 4. The bottom electrode 3 is flanged on the ceramic body 1, and the flexible electrode 4 is coated on the outside of the bottom electrode 3. The flanging width of the bottom electrode 3 relative to the ceramic body 1 is f1, and the flanging width of the flexible electrode 4 relative to the ceramic body 1 is f2, and f2 > f1. Specifically, the end electrode is provided at both ends of the ceramic body 1 of the MLCC structure, and the flexible electrode 4 is coated on the outside of the bottom electrode 3, which helps to improve the bending resistance of the MLCC because the flexible electrode 4 can provide additional flexibility and strength to resist external stress. The setting of f2 > f1 helps to provide a larger adhesion area, reduce the stress intensity per unit area of the ceramic body 1, avoid stress concentration, and thus improve the bending resistance of the MLCC. As a preferred embodiment of the present utility model, f1 < f2 < 2f1, which ensures that the flexible electrode 4 has enough space to absorb and disperse stress without overly restricting its flexibility, and at the same time ensures that there is enough contact area between the bottom electrode 3 and the ceramic body 1 to maintain the stability of the electrical connection. By precisely controlling the ratio of f1 and f2, the bending resistance of the MLCC can be optimized, and the severity of failure can be reduced when subjected to extreme external stress.

[0045] More preferably, the projection of the flanging of the bottom electrode 3 in the vertical direction can be set to fall within the flexible electrode 4, ensuring good mechanical and electrical connection between the bottom electrode 3 and the flexible electrode 4. The projection of the flanging of the bottom electrode 3 falling within the flexible electrode 4 can provide a larger contact area and enhance the adhesion between the two. Since the flexible electrode 4 layer contains resin, it is equivalent to an elastic layer, so it can more effectively absorb external stress, prevent the stress of the circuit board from being transmitted to the rigid ceramic body 1, and make the capacitor still not damaged under the condition of PCB board bending deformation caused by the manufacturing process and external environmental influences (such as vibration and temperature changes, etc.), improving the reliability of the product.

[0046] Furthermore, a structure after sandblasting treatment is adopted on the connection surface between the bottom electrode 3 and the flexible electrode 4. The structure after sandblasting treatment can improve the adhesion between the flexible electrode 4 and the bottom electrode 3. After sandblasting, the surface of the bottom electrode becomes rough and the surface area increases. On the one hand, it increases the contact area between the flexible electrode and the bottom electrode, and on the other hand, a "rivet" biting structure is formed between the two, significantly improving the adhesion between the flexible electrode 4 and the bottom electrode 3, thereby improving the reliability and durability of the MLCC.

[0047] In a preferred embodiment of this invention, a nickel plating layer 5 is provided on the outer side of the flexible electrode 4, and a solderable layer 6 is provided on the outer side of the nickel plating layer 5. The solderable layer 6 is configured to enable the MLCC structure to be soldered onto the circuit board, and the nickel plating layer 5 is configured to prevent the solderable layer 6 from melting and damaging the flexible electrode 4 or the bottom electrode 3 during the soldering process. Specifically, the nickel plating layer 5 mainly serves as a barrier layer, its function being to protect the flexible electrode 4 and the bottom electrode 3 from damage during the soldering process. Due to the good high-temperature resistance of nickel, it can prevent the solderable layer 6 (usually a tin plating layer) from melting and damaging the flexible electrode 4 or the bottom electrode 3 during the soldering process. This helps to maintain the integrity of the electrodes and improves the reliability and durability of the MLCC. The solderable layer 6 can be a tin (Sn) plating layer, exemplarily Sn or SnPb, and its function is to provide the metal layer required for soldering the MLCC structure onto the circuit board. Due to its good soldering performance, the tin plating layer can ensure a good electrical and mechanical connection between the MLCC and the circuit board. During the welding process, the nickel layer acts as a barrier, preventing the molten tin plating from dripping onto the flexible electrode 4 or the bottom electrode 3, thus avoiding potential welding damage. The combination of the flexible electrode 4, nickel plating 5, and tin plating ensures the stability of the MLCC during welding, further reducing cracks and damage caused by welding.

[0048] Furthermore, the maximum flange thickness of the flexible electrode 4 is greater than 20 μm. The thicker flexible electrode 4 provides better mechanical strength, which is particularly important for resisting bending stress. The thicker flexible electrode 4 can disperse stress, reducing the force transmitted to the ceramic body 1, thereby reducing the risk of the ceramic body 1 cracking. This structure can significantly improve the mechanical strength, bending resistance, thermal stability, and welding reliability of the MLCC. Under ultimate bending stress, the flexible electrode 4 may fracture and / or detach, while the bottom electrode 3 and the ceramic body 1 remain intact, protecting the bottom electrode 3 and the ceramic body 1 from damage. Preferably, the roughness Ra value of the structure after sandblasting is between 0.5 and 2 μm, and the diameter of the pores on the flexible electrode 4 is less than 150 μm. Roughness within this range provides good surface characteristics to enhance the bonding force between the flexible layer and the bottom electrode. The smaller pore diameter reduces potential defects and weaknesses during electrode use, thereby improving the overall reliability and performance of the MLCC.

[0049] To enable those skilled in the art to better understand the technical solution of this utility model, the following description is provided as an example:

[0050] The purpose of this invention is to improve the bending resistance of MLCCs while transforming the failure mode of the capacitor under extreme external stress from a severe short-circuit failure to a less severe open-circuit failure. Exemplarily, during the manufacturing process, the chamfered capacitor core is coated with a bottom electrode 3 paste. After firing, the surface of the bottom electrode 3 is roughened using a process such as sandblasting. After cleaning to remove the sandblasting medium, a flexible electrode 4 is coated. After curing, the next step is nickel plating and tin (lead) plating, thus completing the complete fabrication of the flexible electrode 4 MLCC end electrode. By employing a sandblasting treatment on the connection surface between the bottom electrode 3 and the flexible electrode 4, the surface roughness of the bottom electrode 3 is increased, improving the adhesion between the flexible layer and the bottom electrode 3, and enhancing the soldering heat resistance of the flexible layer electrode MLCC. This allows the capacitor to withstand a 260°C, 10s soldering thermal shock (solder bath method, Sn63Pb37 solder) while maintaining good adhesion between the flexible layer and the bottom electrode 3. The surface roughness of the bottom electrode 3 before and after sandblasting is as follows: Figure 8 As shown.

[0051] During the preparation process, vacuuming can be performed on the product coated with the flexible electrode 4 slurry to reduce residual microbubbles in the slurry, improve the density of the flexible layer, and reduce the risk of residual nickel plating solution seeping in during electroplating. The resulting flexible electrode 4 structure has pore diameters as shown in the figure. Figure 9 As shown. By controlling the flange width of the bottom electrode 3 and the flange width of the flexible electrode 4, the flange width of the flexible electrode 4 can completely cover the bottom electrode 3. By increasing the viscosity of the flexible electrode 4 slurry, the flange thickness of the flexible layer can be increased, thereby comprehensively improving the bending resistance of MLCC by 2-3mm. The bending resistance of 0805-2225 size capacitors can reach more than 6mm.

[0052] Overall, by optimizing the end electrode structure, the adhesion between the flexible layer and the bottom electrode is improved. However, the adhesion between the flexible electrode 4 and the bottom electrode 3 remains the weakest link of the end electrode. This allows the product to "self-destruct" by breaking and detaching the flexible layer when subjected to extreme bending stress, thus avoiding stress-induced cracks in the ceramic body 1 and achieving the purpose of protecting the circuit.

[0053] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model. It should be noted that the structures or components illustrated in the accompanying drawings are not necessarily drawn to scale, and descriptions of well-known components, processing techniques, and processes are omitted to avoid unnecessarily limiting the utility model.

Claims

1. A terminal electrode that can improve the bending resistance of a ceramic capacitor, characterized in that, The terminal electrode is set at both ends of the MLCC structure ceramic body (1) and is configured to lead out the capacitance of the capacitor after being connected to the internal electrode (2) in the ceramic body (1). The end electrode includes a bottom electrode (3) and a flexible electrode (4). The bottom electrode (3) is flanged and disposed on the ceramic body (1). The flexible electrode (4) is disposed on the outside of the bottom electrode (3). The flange width of the bottom electrode (3) relative to the ceramic body (1) is f1, and the flange width of the flexible electrode (4) relative to the ceramic body (1) is f2, where f2>f1.

2. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 1, characterized in that, f1 <f2<2f1。 3. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 2, characterized in that, The projection of the flange of the bottom electrode (3) in the vertical direction falls into the flexible electrode (4).

4. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 3, characterized in that, The connection surface between the bottom electrode (3) and the flexible electrode (4) adopts a sandblasted structure, which can improve the adhesion between the flexible electrode (4) and the bottom electrode (3).

5. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 1, characterized in that, The flexible electrode (4) is covered with a nickel plating layer (5), and the nickel plating layer (5) is covered with a solderable layer (6). The solderable layer (6) is configured to enable the MLCC structure to be soldered onto the circuit board. The nickel plating layer (5) is configured to prevent the solderable layer (6) from melting and damaging the flexible electrode (4) or the bottom electrode (3) during the soldering process.

6. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 5, characterized in that, The solderable layer (6) is made of Sn or SnPb.

7. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 1, characterized in that, The maximum flange thickness of the flexible electrode (4) is greater than 20 μm.

8. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 1, characterized in that, Under extreme bending stress, the flexible electrode (4) breaks and / or falls off, while the bottom electrode (3) and the ceramic body (1) remain intact.

9. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 4, characterized in that, The roughness Ra value of the structure after sandblasting is between 0.5 and 2 μm.

10. The terminal electrode for improving the bending resistance of a ceramic capacitor according to claim 1, characterized in that, The diameter of the holes on the flexible electrode (4) is less than 150 μm.

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