Analysis method of density of MLCC basic external electrodes

Abstract

The present application provides a method for analyzing the compactness of MLCC base external electrodes, comprising the following steps: obtaining an MLCC product with sintered base external electrodes; placing the MLCC product in a sintering device for high-temperature oxidation treatment; performing metallographic sectioning on the oxidized MLCC product; observing the cross-section of the base external electrodes of the sliced ​​MLCC product using a metallographic microscope, and determining whether the MLCC base external electrodes have through-holes based on the color difference between the metal oxide and the unoxidized metal in the cross-section to assess their compactness. The method of this embodiment can efficiently assess the compactness of the base external electrodes without waiting for electroplating to be completed, nor does it rely on expensive and complex methods such as scanning electron microscopy. This significantly improves the timeliness and accuracy of sintering quality testing during the mass production of MLCC products, and effectively reduces potential reliability risks in subsequent electroplating processes.

Description

Technical Field

[0001] The present application relates to the technical field of MLCC product testing and analysis, and in particular to a method for analyzing the density of MLCC basic external electrodes. Background Art

[0002] The traditional chip-type multilayer ceramic capacitor (MLCC) manufacturing process involves applying a prepared ceramic slurry through a casting head to form a thin dielectric diaphragm. The dielectric diaphragm is then dried in an oven. A metal inner electrode is then printed on the dried ceramic dielectric diaphragm. A laminator then peels the ceramic dielectric diaphragms with metal inner electrodes layer by layer and stacks them together to form an unsintered laminated body. The unsintered laminated body undergoes lamination, cutting, binder removal, sintering, and chamfering to obtain a sintered ceramic body. Basic external electrodes are then attached to both ends of the sintered ceramic body. After high-temperature sintering, nickel and tin layers are electroplated on the basic external electrodes to produce the desired MLCC product.

[0003] If the density of the base external electrode is poor and there are many pores, hydrogen ions in the plating solution will enter through the pores / defects of the base external electrode during the MLCC electroplating process and be retained in the weak points inside the base external electrode. After being heated, some hydrogen ions may further diffuse into the interior of the ceramic body and migrate between the dielectric layers within the ceramic body under the action of external voltage, forming leakage paths in the dielectric layers, thereby reducing the insulation resistance of the MLCC product and affecting the reliability of the MLCC product. Under high temperature and high humidity power-on conditions, the performance of the MLCC product will also deteriorate further.

[0004] Therefore, it is crucial to quickly and accurately judge the density of the basic external electrode during the mass production and sintering of MLCC external electrodes.

[0005] In traditional technology, a scanning electron microscope (SEM) is usually used to perform microscopic morphology analysis on the surface of the basic external electrode of an MLCC to which the basic external electrode has been sintered or its DPA cross-section. However, although the pores inside the basic external electrode can be observed in the cross-section, it is impossible to determine whether the pores are through-holes and whether they are connected to the ceramic body. As a result, non-through pores (which generally do not affect product reliability) cannot be distinguished from through pores, resulting in a high misjudgment rate.

[0006] Other technologies use DPA to slice MLCC products after electroplating, and then observe and analyze the cross-sections using a metallographic microscope. This method uses multiple DPA analyses combined with the cross-section's plating solution penetration status to determine whether the density of the base external electrode meets design requirements. However, this analysis method requires the MLCC product to be electroplated before it can be performed, which is time-consuming. The entire electroplating process typically takes 2-3 working days. During continuous product production, it is impossible to monitor the density of the current product's base external electrode during the sintering process. This is a post-judgment method that can easily lead to batch quality defects and pose a high quality risk. Summary of the Invention

[0007] Based on this, the present application provides a method for analyzing the density of MLCC basic external electrodes that can solve the above-mentioned technical problems.

[0008] The above-mentioned purpose of this application is achieved through the following technical solutions:

[0009] The present application provides a method for analyzing the density of the external electrode of an MLCC, the method comprising the following steps:

[0010] Obtain MLCC products with basic external electrodes already fired;

[0011] Placing the MLCC product in a sintering device for high-temperature oxidation treatment; wherein the atmosphere in the sintering device is an air atmosphere or an oxidizing gas atmosphere with an oxygen volume concentration higher than that of air;

[0012] Performing metallographic sectioning on the MLCC product after oxidation treatment;

[0013] The cross section of the basic external electrode of the MLCC product after slicing is observed through a metallographic microscope. The color difference between the metal oxide and the unoxidized metal in the cross section is used to determine whether there are through pores in the basic external electrode of the MLCC, so as to evaluate its density.

[0014] In an optional embodiment, the process of placing the MLCC product in a sintering device for high-temperature oxidation treatment is as follows:

[0015] The temperature in the sintering device is raised to 500° C. to 800° C. within 30 to 120 seconds, and maintained at this temperature for 40 to 130 seconds.

[0016] In an optional embodiment, the cooling stage after holding at the temperature for 40 to 130 seconds comprises the following steps:

[0017] The first stage of cooling: the temperature in the sintering device is reduced from 500-800°C to 400-500°C at a rate of 50-100°C / second, and kept at this temperature for 3-10 seconds;

[0018] The second stage of cooling: the temperature in the sintering device is reduced from 400°C to 500°C to 200°C to 300°C at a rate of 20°C to 50°C per second, and kept at this temperature for 5 seconds to 15 seconds;

[0019] The third stage of cooling: the temperature in the sintering device is lowered from 200-300°C to room temperature at a rate of ≤10°C / second.

[0020] In an optional embodiment, when the base external electrode is a Cu external electrode, the second stage cooling process and the third stage cooling process further include the following steps:

[0021] Inert gas is introduced into the sintering device at a gas flow rate of 1-3 L / min, a gas purity of ≥99.99%, and the gas temperature is precooled to -20°C~0°C.

[0022] In an optional embodiment, the slicing direction of the metallographic slicing process is parallel to the length direction and height direction of the body of the MLCC product, and perpendicular to the width direction of the body of the MLCC product.

[0023] In an optional embodiment, when observing the cross section of the basic external electrode of the MLCC product after the slicing process through a metallographic microscope, the following steps are further included:

[0024] Polarized light with a wavelength of 400-550 nm is used to illuminate the cross section of the MLCC product to enhance the color difference contrast between the metal oxide and the unoxidized metal in the basic external electrode.

[0025] In an optional embodiment, after the MLCC product after the oxidation treatment is subjected to metallographic sectioning, the following steps are further included:

[0026] The cross section of the basic external electrode of the MLCC product after the slicing process is subjected to surface polishing, using a diamond suspension with a particle size of ≤0.1 μm.

[0027] In an optional embodiment, before placing the MLCC product in a sintering device for high-temperature oxidation treatment, the following steps are further included:

[0028] The MLCC product is plasma cleaned to remove organic residues on the surface of the MLCC product.

[0029] This application has the following beneficial effects:

[0030] This application provides a method for analyzing the density of MLCC base external electrodes. By subjecting unplated MLCC products to high-temperature oxidation, the metal material (such as nickel or copper) in the base external electrodes undergoes a significant oxidation reaction in an oxidizing atmosphere, forming a visible metal oxide layer within the pathways of the through-hole pores. Because oxygen can only enter through-hole pores connected to the outside and cannot enter closed, non-through-hole pores, after metallographic sectioning, the through-hole pores exhibit a distinct color difference from the unoxidized metal along their path (e.g., dark green for NiO and black for CuO), while non-through-hole pores show no noticeable color difference. This enables rapid, stable, and intuitive identification of through-hole pores. This method efficiently assesses the density of the base external electrodes without waiting for the MLCC product to be electroplated, nor does it rely on expensive or complex methods such as scanning electron microscopy. This significantly improves the timeliness and accuracy of sintering quality testing during mass production of MLCC products, effectively reducing potential reliability risks in subsequent electroplating processes.

[0031] The present application also reduces the residence time of the metal surface of the basic external electrode in the low temperature stage by rapidly increasing the temperature, thereby accelerating the oxidation rate of the metal surface in the pores, preventing the full formation of a dense oxide film, and resulting in a looser or more porous oxide film. Oxygen can quickly penetrate into the pores through the gaps in the oxide layer, ensuring that the inner wall of the pore deep in the pore is fully oxidized and the degree of oxidation inside and outside the pore is consistent.

[0032] This application also uses gradient cooling and introduces inert gas during the third stage of cooling, which on the one hand increases the overall cooling rate, shortens the processing time, and improves detection efficiency; on the other hand, it inhibits the secondary oxidation reaction in the medium and low temperature stages, prevents the diffusion and blurring of the oxidation area, and effectively improves the clarity of the color development layer boundary, thereby enhancing the ability to identify the through-pore path. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the steps of a method for analyzing the density of an MLCC basic external electrode in an exemplary embodiment of the present application;

[0034] Figure 2 This is a schematic diagram of the structure of an MLCC product with basic external electrodes already attached;

[0035] Figure 3 Schematic diagram of an MLCC product with a basic external electrode already attached in one embodiment;

[0036] Figure 4 A schematic diagram of an MLCC product with attached basic external electrodes after high-temperature oxidation treatment in one embodiment;

[0037] Figure 5 This is a partial image of a cross-section of an MLCC product taken using a metallographic microscope in one embodiment;

[0038] Figure 6 This is a partial image of a cross-section of an MLCC product taken using a metallographic microscope in one embodiment. DETAILED DESCRIPTION

[0039] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] In view of the technical problems in the background technology, this application provides a method for analyzing the density of the external electrode of MLCC. Figure 1 As shown, in one embodiment, the method for analyzing the density of the MLCC basic external electrode of the present application includes the following steps:

[0043] S101: Obtain MLCC products with basic external electrodes already fired.

[0044] The base external electrode refers to the metal layer formed on both ends of the MLCC during the pre-electroplating stage through a sintering process. It is commonly formed by curing a metal paste such as nickel or copper at high temperature. This electrode has not yet been electroplated with Ni / Sn and is in an intermediate process after sintering. The purpose of this embodiment is to analyze whether the base external electrode has through-holes to more accurately analyze its density.

[0045] like Figure 2 As shown, Figure 2The schematic diagram of the structure of the MLCC product with basic external electrodes on both ends is shown in FIG. The basic external electrodes 20 are burned on both ends of the MLCC ceramic body 10. Figure 2 In the figure, the length direction of the ceramic body 10 is the x direction, the width direction is the y direction, and the height direction is the z direction. In the ceramic body 10, the stacking direction of the dielectric diaphragms is the height z direction.

[0046] The basic external electrode (metal layer, usually Ni, Cu, etc.) formed by sintering is usually a sintered body formed by slurry printing + sintering. Due to factors such as sintering temperature, slurry quality, debinding residue, and particle accumulation morphology, the following two types of pores are often formed inside it:

[0047] 1. Through-hole pores, that is, channel-type pores that are directly connected from the outermost surface of the base external electrode to the interior, and even to the interface area (the connection part with the metal internal electrode / ceramic dielectric diaphragm of the ceramic body). The channel-type pores connected to the interface area can become the penetration path of hydrogen ions, electrolyte or plating solution, which are usually in the shape of slender tunnels or cracks.

[0048] Through pores extending to the interface area will seriously affect the electroplating quality. This type of through pores is a key defect type that reduces the reliability of MLCC products. The extension direction of the through pores can be in any direction, that is, from Figure 1 Any upper, lower, left, or right surface of the basic external electrode 20 extends to the inside of the basic external electrode 20 along the length direction, width direction or height direction of the ceramic body 10.

[0049] 2. Non-through pores: These are isolated pores located within the base external electrode and not connected to the surface. These pores are often caused by incomplete sintering, particle aggregation, or residual gas. While they don't directly cause penetration or short circuits, they may affect local conductivity and, in most cases, have a minimal impact on reliability.

[0050] S102: placing the MLCC product in a sintering device for high-temperature oxidation treatment; wherein the atmosphere in the sintering device is an air atmosphere or an oxidizing gas atmosphere with an oxygen volume concentration higher than that of air.

[0051] In this embodiment, the sintering device refers to a high-temperature processing device that can achieve controlled heating and atmosphere adjustment, such as a box-type electric furnace, an infrared rapid sintering furnace, etc., and has temperature adjustment and heat preservation capabilities.

[0052] In this step, one or more MLCC products with attached basic external electrodes are placed in a sintering boat or ceramic tray, placed in a sintering device, and a suitable oxidizing atmosphere (such as air or an oxygen-rich environment) is selected. If it is an oxygen-rich environment, oxygen-rich gas needs to be introduced into the sintering device. If it is an air atmosphere, the air atmosphere in the sintering device can be maintained. During the sintering process of this embodiment, the gas in the sintering device can be maintained stable, or gas can be continuously introduced during the sintering process to improve the efficiency of the oxidation reaction when a large number of MLCC products are sintered. The participation of oxygen will promote the oxidation reaction on the surface of the basic external electrode of the MLCC product.

[0053] During the high-temperature oxidation treatment in this embodiment, the high-temperature oxidation reaction mainly occurs in the area where the metal surface is fully exposed to oxygen, and the reaction generates metal oxides (such as NiO and CuO), which appear as darker colors.

[0054] For the basic outer electrode surface, it will directly undergo oxidation reaction with oxygen.

[0055] For through-hole pores: During the high-temperature oxidation process, oxygen will enter the pores along the through-hole path and react with the metal inner wall of the pores, and the metal inner wall of the pores will be oxidized; the oxides generated by the reaction form a continuous oxide layer along the extension direction of the pores.

[0056] For non-through pores: oxygen cannot enter the isolated pores, and the metal inside the isolated pores will not be oxidized.

[0057] S103: performing metallographic sectioning on the MLCC product after the oxidation treatment.

[0058] Metallographic sectioning involves cutting open an MLCC product by mechanical grinding or cutting to expose its internal structure and end faces. The sectioning direction is usually perpendicular to the width of the MLCC product, ensuring that the observation area spans multiple internal and external electrode layers.

[0059] In an optional embodiment, when metallographic sectioning is performed on the MLCC product after oxidation treatment, the sample is first fixed by cold embedding with epoxy resin (to avoid the oxide layer from falling off due to high temperature), and then sliced ​​along the set direction by a precision DPA grinder, and coarse grinding and fine grinding are carried out with 240# to 2400# silicon carbide sandpaper in sequence to remove excess material and refine the surface, and then polished with 1μm and 0.1μm diamond suspension and polishing cloth until the surface is free of scratches (roughness ≤ 0.1μm); finally, ultrasonic cleaning (deionized water) and ethanol dehydration and drying are performed to ensure that there are no residual contaminants on the cross section; the integrity and flatness of the cross section are verified by initial microscopic inspection and roughness detection, providing a clear morphology of the basic external electrode pores for subsequent metallographic microscope observation.

[0060] In this embodiment, the MLCC product after oxidation treatment is subjected to metallographic sectioning to expose the interface area between the basic external electrode, the internal electrode and the dielectric layer, so as to clearly observe possible through pores.

[0061] During the specific operation process, the number of slices can be performed once or multiple times according to needs.

[0062] S104: Observe the cross section of the basic external electrode of the MLCC product after slicing through a metallographic microscope, and judge whether there are through pores in the basic external electrode of the MLCC based on the color difference between the metal oxide and the unoxidized metal in the cross section, so as to evaluate its density.

[0063] A metallographic microscope is a microscopic device used to observe the metal structure of materials. It can magnify the microscopic differences between metals and oxides in the visible light range.

[0064] In this step, by adjusting the light source, magnification, and focal length of the metallographic microscope, the color changes of the base external electrode in the cross-section of the MLCC product slice can be observed. Oxidized areas are typically black or dark (e.g., black for CuO and dark green-gray for NiO), while unoxidized metals are metallic or bright. If the inner side of the cross-section of the base external electrode of the sliced ​​MLCC product is black or dark green, it can be roughly determined that there are through-holes there. Even if the black or dark color extends to the interface area (the connection area with the metal internal electrode of the ceramic body / ceramic dielectric diaphragm), these through-holes have a significant impact on the reliability of the MLCC product.

[0065] This application provides a method for analyzing the density of MLCC base external electrodes. By subjecting unplated MLCC products to high-temperature oxidation, the metal material (such as nickel or copper) in the base external electrodes undergoes a significant oxidation reaction in an oxidizing atmosphere, forming a visible metal oxide layer within the pathways of the through-hole pores. Because oxygen can only enter through-hole pores connected to the outside and cannot enter closed, non-through-hole pores, after metallographic sectioning, the through-hole pores exhibit a distinct color difference from the unoxidized metal along their path (e.g., dark green for NiO and black for CuO), while non-through-hole pores show no noticeable color difference. This enables rapid, stable, and intuitive identification of through-hole pores. This method efficiently assesses the density of the base external electrodes without waiting for the MLCC product to be electroplated, nor does it rely on expensive or complex methods such as scanning electron microscopy. This significantly improves the timeliness and accuracy of sintering quality testing during mass production of MLCC products, effectively reducing potential reliability risks in subsequent electroplating processes.

[0066] The oxidation reaction of copper usually starts at around 200°C in air to produce copper oxide (CuO). The oxidation temperature of nickel is higher and starts to oxidize at about 400°C to produce nickel oxide (NiO). The high-temperature oxidation treatment of this application can be set with reference to the high-temperature oxidation temperature of the actual base external electrode. For example, for the copper base external electrode, the oxidation temperature is higher than 200°C, and for the nickel base external electrode, the oxidation temperature is higher than 400°C.

[0067] In actual application, the applicant discovered that during high-temperature oxidation treatment, if the temperature is only slightly higher than the oxidation temperature, the inner wall of the pore deep within the narrow, through-hole pores will be less oxidized, and the color change will not be obvious, making it difficult to identify after sectioning. This is because when metals (such as copper and nickel) are slowly heated at low temperatures, the surface will preferentially oxidize to form a dense oxide film (such as CuO or NiO). The dense oxide film has a compact structure and uniform thickness. The dense oxide film hinders the diffusion of oxygen into the metal and deep into the pores, resulting in insufficient oxidation within the pores. In particular, in areas with narrow pores, if the surface oxide film is too thick, oxygen will have difficulty penetrating during the subsequent high-temperature stage, affecting the accuracy of pore penetration analysis.

[0068] In order to solve this technical problem, in a preferred embodiment, the process of placing the MLCC product in a sintering device for high-temperature oxidation treatment is as follows:

[0069] The temperature in the sintering device is raised to 500° C. to 800° C. within 30 to 120 seconds, and maintained at this temperature for 40 to 130 seconds.

[0070] In this embodiment, by rapidly heating up, the metal surface of the basic external electrode stays in the low-temperature stage for a very short time. At high temperatures of 500°C to 800°C, the oxidation rate of the metal surface is accelerated, and a dense oxide film cannot be fully formed. The generated oxide film is looser or more porous, and oxygen can quickly penetrate into the pores through the gaps in the oxide layer, ensuring that the inner walls of the pores deep in the pores are fully oxidized, so that the oxidation degree inside and outside the through pores is consistent, and the black or dark oxide forms a high contrast with the metallic glossy area, which can be clearly distinguished under visible light conditions; avoiding misjudgment caused by the obstruction of the dense oxide film generated by low temperature.

[0071] This embodiment significantly improves the uniformity of the oxidation reaction and the reliability of the analysis by controlling the heating and holding parameters, and can also significantly shorten the time of the high-temperature oxidation treatment.

[0072] After high-temperature oxidation, MLCC products face thermal shock from rapid cooling. The ceramic body and the base external electrodes have different coefficients of thermal expansion. An improper cooling process can easily lead to microcracks, metal delamination, or oxide layer shedding, compromising structural integrity and subsequent microscopic observation.

[0073] Therefore, in an optional embodiment, a three-stage gradient cooling strategy is adopted for the cooling process after the high-temperature oxidation treatment to avoid ceramic cracks or metal delamination due to sudden cooling and to ensure stable formation of the oxide layer.

[0074] Specifically, the cooling stage after holding at the temperature for 40 to 130 seconds includes the following steps:

[0075] The first stage of cooling: the temperature in the sintering device is reduced from 500-800°C to 400-500°C at a rate of 50-100°C / second, and kept at this temperature for 3-10 seconds;

[0076] The second stage of cooling: the temperature in the sintering device is reduced from 400°C to 500°C to 200°C to 300°C at a rate of 20°C to 50°C per second, and kept at this temperature for 5 seconds to 15 seconds;

[0077] The third stage of cooling: the temperature in the sintering device is lowered from 200-300°C to room temperature at a rate of ≤10°C / second.

[0078] In this embodiment, the cooling process can be completed by natural cooling combined with the introduction of low-temperature gas into the sintering device.

[0079] This embodiment employs a three-stage gradient cooling scheme, gradually reducing the temperature at varying rates and providing short, insulated buffer zones within critical temperature zones to gradually release thermal stress between the ceramic and metal. This effectively suppresses structural stress concentration caused by sudden cooling, preventing ceramic cracking or interfacial cracking. It also prevents cracking or shedding of the oxide layer due to overcooling, ensuring that oxidation products remain intact within the through-pores, thus ensuring the stability and accuracy of subsequent color difference recognition.

[0080] During the second and third stages of cooling, due to the low oxidation temperature of Cu, the long-term air atmosphere cooling process will continue to oxidize the Cu metal external electrode, resulting in abnormal thickening of the CuO layer, forming a continuous surface area with low reflectivity, thereby obscuring the boundary contours of the through pores under the microscope and reducing the discrimination accuracy.

[0081] This is because under normal circumstances, the unoxidized portion of the metal is bright, and a continuous oxide band (dark) forms along the through-hole path. This visual feature, visible through the metallographic microscope, can be observed as a black line penetrating the metal layer, and thus identified as a through-hole pore. If the oxidation time is too long, resulting in comprehensive oxidation, such as the entire surface and interior of the Cu outer electrode turning into black CuO, the pore path and the surrounding black areas of similar color no longer have a sense of channel or boundary, making it impossible to distinguish between the through-hole path and some non-porous areas or some ordinary oxide layers produced by oxidation of semi-closed pores.

[0082] Therefore, in a preferred embodiment, when the base external electrode is a Cu external electrode, the second and third stage cooling processes further include the following steps:

[0083] Inert gas is introduced into the sintering device at a gas flow rate of 1-3 L / min, a gas purity of ≥99.99%, and the gas temperature is precooled to -20~0°C.

[0084] In this embodiment, a high-purity inert gas (such as nitrogen or argon) pre-cooled to -20°C to 0°C is introduced into the sintering device to remove heat in a stable, uniform, and controllable airflow, and to dilute or replace residual oxygen. On the one hand, this improves the overall cooling rate, shortens the processing time, and improves the detection efficiency; on the other hand, it inhibits the secondary oxidation reaction in the medium and low temperature stages, prevents the oxidation area from diffusing and blurring, and effectively improves the clarity of the color layer boundary, thereby enhancing the ability to identify the through-pore path.

[0085] In a specific embodiment, the slicing direction of the metallographic slicing process is parallel to the length direction and height direction of the body of the MLCC product, and perpendicular to the width direction of the body of the MLCC product. Figure 2 As shown, the slicing direction is parallel to the x-direction and the z-direction, and perpendicular to the y-direction.

[0086] In a preferred embodiment, when observing the cross section of the basic external electrode of the MLCC product after the slicing process through a metallographic microscope, the following steps are also included:

[0087] Polarized light with a wavelength of 400-550 nm is used to illuminate the cross section of the MLCC product to enhance the color difference contrast between the metal oxide and the unoxidized metal in the basic external electrode. This band corresponds to the green-blue region of visible light. The reflectivity of oxides (such as CuO and NiO) in this band is significantly lower than that of metallic Cu and Ni. Polarized light helps to weaken background scattering and enhance the reflection difference between materials, thereby improving the clarity of interface imaging and facilitating the accurate identification of the oxidized color band structure of the through path.

[0088] The mechanical cutting process will produce scratches, burrs and unevenness on the slice surface. These surface defects will interfere with the true color difference information of the microscopic image and even be mistaken for pore channels. Therefore, in a preferred embodiment, after the metallographic sectioning of the MLCC product after oxidation treatment, the following steps are also included:

[0089] The cross section of the basic external electrode of the MLCC product after slicing is subjected to surface polishing treatment, using a diamond suspension with a particle size of ≤0.1 μm to eliminate the interference of grinding scratches on color difference analysis.

[0090] This processing can effectively remove interfering stripes and processing marks, improve the consistency of the slice surface and the accuracy of edge contour recognition, and ensure stable and reliable image quality under polarized light or ordinary light.

[0091] After sintering, impurities such as organic matter, additives, and fingerprints may remain on the surface of the base external electrode. These contamination layers will hinder the contact reaction between oxygen and metal, resulting in uneven distribution of the oxide layer. Therefore, before placing the MLCC product in a sintering device for high-temperature oxidation treatment, the following steps are also included:

[0092] Plasma cleaning is performed on MLCC products to remove organic residues on the surface of MLCC products and ensure the uniformity and accuracy of the oxidation reaction.

[0093] In this embodiment, the cleanliness and reaction activity of the outer electrode surface can be significantly improved, making the oxidation reaction more uniform and controllable, while reducing the color spots or regional errors caused by subsequent uneven oxidation, thereby enhancing the overall image interpretability and the accuracy of density judgment.

[0094] like Figure 3-Figure 6 As shown, Figure 3 This is a schematic diagram of an MLCC product with a Cu-based external electrode attached, as observed through a visual microscope. Figure 4 This is a schematic diagram of the product after being placed in a sintering device for high-temperature oxidation treatment observed through a visual microscope. Figure 3 After the high temperature oxidation treatment, the surface of the metallic Cu-based external electrode becomes Figure 4 Black CuO is shown. Figure 5 and Figure 6 This is a partial cross-sectional image of the MLCC product after slicing, taken through a metallographic microscope. Figure 5 and Figure 6 In the local cross-sectional image, the left side is the ceramic body of the MLCC, and the right side is the basic external electrode layer, where Figure 5 The left side of the partial slice cross-sectional image shows a protective cover formed by a ceramic layer, without a metal inner electrode. Figure 6 The image of the metal inner electrode on the left side of the local slice cross-sectional image is blurred.

[0095] exist Figure 5 and Figure 6 In the figure, most of the bright colors in the basic external electrode area are Cu. The basic external electrode area is also mixed with glass powder and organic matter, while a layer of CuO is formed in the surface area on the far right of the basic external electrode.

[0096] exist Figure 4The reason why the basic outer electrode appears black when observed under a visual microscope is that the CuO layer on the surface of the basic outer electrode is thicker after the end is burned, a large amount of light is absorbed, and less light is reflected, so it appears black visually (the absorption of light by the oxide layer is dominant).

[0097] exist Figure 5 and Figure 6 The CuO layer in the cross-section of the base external electrode appears blue under a metallographic microscope. This is primarily due to the thickness of the oxide layer and the interference of light. The reason for this blue color under a metallographic microscope is that metallographic microscopes typically use reflected light for observation. When the oxide layer thickness reaches a certain nanometer level (e.g., tens to hundreds of nanometers), light of different wavelengths interferes with the reflections between the oxide layer surface and the metal substrate. The wavelength of blue light matches the interference conditions created by the oxide layer thickness, enhancing reflection and resulting in a blue appearance (the interference effect emphasizes specific wavelengths).

[0098] Simply put, the color difference is caused by the different optical effects caused by the different thickness of the oxide layer. What you see visually is the absorption effect of the thick oxide layer, and what you see under a metal microscope is the interference color development of the thin oxide layer.

[0099] exist Figure 5 In the figure, there is a more obvious blue area (red circle) inside the basic outer electrode, which means that there is CuO in this area and there are through pores in this area.

[0100] exist Figure 6 In the figure, there are multiple blue areas of varying sizes within the base external electrode, some of which are marked by red circles. This indicates that multiple areas within the base external electrode contain CuO and have through-holes. One through-hole even approaches the MLCC ceramic body on the left.

[0101] In this example, the more blue the area, the worse the density of the MLCC product's base external electrode. If the blue area extends to the junction with the internal electrode, this through-hole pore will seriously affect the electroplating quality and is a key defect type that reduces the reliability of MLCC products.

[0102] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patented invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims, and the specification may be used to interpret the content of the claims.

Claims

1. A method for analyzing the density of MLCC basic external electrodes, characterized in that: The method comprises the steps of: Obtain MLCC products with basic external electrodes already fired; The MLCC product is placed in a sintering device for high-temperature oxidation treatment; wherein the atmosphere in the sintering device is an air atmosphere or an oxidizing gas atmosphere with an oxygen volume concentration higher than that of air; the high-temperature oxidation treatment process is as follows: within 30 seconds to 120 seconds, the temperature in the sintering device is raised to 500°C to 800°C, and maintained at this temperature for 40 seconds to 130 seconds; the first stage of cooling: the temperature in the sintering device is reduced from 500°C to 800°C to 400°C to 500°C at a rate of 50°C to 100°C per second, and maintained at this temperature for 3 seconds to 10 seconds; the second stage of cooling: the temperature in the sintering device is reduced from 400°C to 500°C to 200°C to 300°C at a rate of 20°C to 50°C per second, and maintained at this temperature for 5 seconds to 15 seconds; the third stage of cooling: the temperature in the sintering device is reduced from 200°C to 300°C to room temperature at a rate of ≤10°C per second; Performing metallographic sectioning on the MLCC product after oxidation treatment; The cross section of the basic external electrode of the MLCC product after slicing is observed through a metallographic microscope. The color difference between the metal oxide and the unoxidized metal in the cross section is used to determine whether there are through pores in the basic external electrode of the MLCC, so as to evaluate its density.

2. The method for analyzing the density of the MLCC basic external electrode according to claim 1, characterized in that: When the basic external electrode is a Cu external electrode, the cooling process in the second stage and the cooling process in the third stage further includes the following steps: Inert gas is introduced into the sintering device at a gas flow rate of 1-3 L / min, a gas purity of ≥99.99%, and the gas temperature is precooled to -20°C~0°C.

3. The method for analyzing the density of the MLCC basic external electrode according to claim 1, characterized in that: The slicing direction of the metallographic sectioning process is parallel to the length and height directions of the MLCC product body, and perpendicular to the width direction of the MLCC product body.

4. The method for analyzing the density of the MLCC basic external electrode according to claim 3, characterized in that: When observing the cross section of the basic external electrode of the MLCC product after the slicing process through a metallographic microscope, the following steps are also included: Polarized light with a wavelength of 400-550 nm is used to illuminate the cross section of the MLCC product to enhance the color difference contrast between the metal oxide and the unoxidized metal in the basic external electrode.

5. The method for analyzing the density of the MLCC basic external electrode according to claim 3, characterized in that: After the MLCC product after oxidation treatment is subjected to metallographic sectioning, the following steps are further included: The cross section of the basic external electrode of the MLCC product after the slicing process is subjected to surface polishing, using a diamond suspension with a particle size of ≤0.1 μm.

6. The method for analyzing the density of the MLCC basic external electrode according to claim 3, characterized in that: Before placing the MLCC product in a sintering device for high-temperature oxidation treatment, the following steps are also included: The MLCC product is plasma cleaned to remove organic residues on the surface of the MLCC product.

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