Barreling medium and barreling method for improving appearance of MLCC (multilayer ceramic capacitor)

Abstract

The invention relates to the technical field of multi-layer ceramic capacitor manufacturing, in particular to a barreling medium and a barreling method thereof for improving the appearance of an MLCC (multilayer ceramic capacitor), and the barreling medium comprises the following components in percentage by mass: 78-82% of ceramic rods and 18-22% of 95% zirconia ceramic microspheres; the ceramic rod comprises 84-86% of aluminum oxide, 11-13% of magnesium oxide and 2-4% of aluminum borate, the diameter of the ceramic rod is 2.2-2.8 mm, the length of the ceramic rod is 6.0-10.0 mm, the Mohs hardness of the ceramic rod is larger than or equal to 8.5, and the surface roughness Ra of the ceramic rod is smaller than or equal to 0.1 micron. The tumbling medium has the advantages of high hardness, strong wear resistance, good chemical and thermal stability and excellent electrical insulating property, original tumbling point contact is changed into line contact, and stress concentration caused by point contact is effectively reduced, so that the bad phenomenon of the appearance of an MLCC is improved, damage to the MLCC can be reduced, stable performance of the MLCC can be ensured, and the tumbling medium has good adaptability with an MLCC material.

Description

Technical Field

[0001] This invention relates to the field of multilayer ceramic capacitor manufacturing technology, and in particular to a tumbling dielectric and a tumbling method for improving the appearance of MLCCs. Background Technology

[0002] MLCCs (multilayer ceramic capacitors) are one of the most basic and widely used passive components in electronic circuits, and their importance permeates almost all electronic information fields in today's society.

[0003] Tumbling is a crucial post-sintering process in MLCC (multilayer ceramic capacitors). Tumbling removes burrs and rough edges caused by shrinkage after sintering through the mechanical abrasive action of the tumbling media, preventing uneven plating thickness and pinholes caused by surface roughness during subsequent dip plating and electroplating. Furthermore, conventional automotive-grade processes require tumbling after the cutting process, followed by tumbling after sintering.

[0004] Currently, the grinding media used in tumbling are mainly zirconia balls. Zirconia balls have high hardness, wear resistance, and chemical stability, making them suitable for high-precision tumbling. However, their high density can easily damage ultra-thin MLCCs, poses a risk of nano-contamination, and is expensive (2-3 times that of alumina). On the other hand, high-purity alumina balls are used as grinding media. They have fewer impurities and are increasingly used in automotive-grade applications. However, their wear resistance and lifespan are not as good as zirconia balls, and their brittleness can easily lead to chipping at the edges and corners. Ordinary products cannot meet the radioactivity requirements of automotive-grade applications.

[0005] The current technical challenges mainly lie in the mainstream alumina / alumina balls. The point contact between the balls leads to uneven grinding, easily causing edge damage and deep surface scratches on the ceramic body. In terms of appearance, the yield rate is low (especially for small-sized products), making it difficult to meet the appearance standards of automotive-grade products. Current tumbling solutions, however, are prone to dimensional deviations due to adjustments in grinding time / frequency, and the addition of chemical abrasives increases costs and pollutes the environment.

[0006] Therefore, there is an urgent need to develop a new grinding media to improve the adverse effects on the appearance of MLCCs during the grinding process. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a tumbling media and a tumbling method for improving the appearance of MLCCs, so as to mitigate the adverse effects of the tumbling process on the appearance of MLCCs.

[0008] To achieve the above objectives, the present invention provides a grinding media comprising, by mass percentage, 78-82% ceramic rods and 18-22% ceramic microspheres; wherein the ceramic rods comprise 84-86% alumina, 11-13% magnesium oxide and 2-4% aluminum borate, and the ceramic rods have a diameter of 2.2-2.8 mm, a length of 6.0-10.0 mm, a Mohs hardness ≥ 8.5, and a surface roughness Ra ≤ 0.1 μm.

[0009] By using ceramic rods and leveraging their line contact characteristics to expand the grinding area, combined with physical properties such as Mohs hardness ≥8.5 (higher than MLCC ceramic bodies) and surface roughness Ra≤0.1μm, efficient grinding is ensured while avoiding secondary scratches.

[0010] The ceramic rod is a cylindrical ceramic rod with a length-to-diameter ratio greater than 2.

[0011] The ceramic microspheres are 95% pure zirconia ceramic microspheres with a diameter of 0.08-0.12 mm.

[0012] Preferably, the ceramic rod has a diameter of 2.5 mm and a length of 8 mm.

[0013] A tumbling method for improving the appearance of MLCCs using the aforementioned tumbling media involves loading tumbling media and MLCCs at a mass ratio of 2.5-3.5:1, with a roller filling capacity of 60-70%. After tumbling and cleaning, the MLCCs are dried. Maintaining the mass ratio of tumbling media to MLCCs between 2.5:1 and 3.5:1 ensures sufficient contact and interaction between the grinding media and the MLCCs, achieving efficient tumbling. If the ratio is too low, insufficient grinding media will result in poor tumbling performance; if the ratio is too high, it will increase costs and may affect tumbling efficiency due to collisions between the grinding media. Therefore, this ratio range is the optimal choice balancing effectiveness and cost. This tumbling media and method are suitable for tumbling processes that do not require post-cutting tumbling and are performed only after sintering.

[0014] Preferably, the mass ratio of the grinding media to the MLCC is 3:1.

[0015] The grinding frequency is 25-35Hz, and the time is 45-75 minutes. Controlling the grinding frequency to 25-35Hz ensures the grinding media has sufficient kinetic energy for effective grinding of the MLCC, while avoiding excessive impact and damage to the MLCC due to excessive frequency. The optimal grinding time is preferably set to 50-60 minutes, which is the optimal time range determined after comprehensively considering the MLCC's material, size, and grinding effect. This ensures thorough grinding of the MLCC within this time while avoiding the adverse effects of over-grinding.

[0016] The cleaning process uses water circulation.

[0017] The grinding media mixing scheme uses 78-82% ceramic rods as the main media to undertake the main grinding task, and 18-22% of 95% zirconia ceramic microspheres with a diameter of 0.08-0.12mm to fill the gaps, eliminating grinding dead corners. The three work together to form a complete system of "structural innovation - process adaptation - media complementarity", which is particularly suitable for ultra-fine grinding scenarios such as MLCC with extremely high requirements for precision and purity.

[0018] The cleaning agent used is a neutral ceramic cleaner specifically designed for MLCC manufacturing. Its core components are a nonionic surfactant (such as fatty alcohol polyoxyethylene ether), a complexing agent (such as aminotrimethylenephosphonic acid), and deionized water. The pH value is controlled between 6.5 and 7.5, and the dosage is 4-6 ml. This facilitates efficient dissolution and removal of grinding debris (ceramic rod dust, zirconia microspheres) and sintering residues adhering to the MLCC surface, preventing pinholes or uneven plating thickness caused by residual microparticles. Adding 2-4 ml of defoamer suppresses the excessive foam generated by surfactants during water circulation cleaning, preventing foam from encapsulating the MLCC surface and creating cleaning dead zones. This ensures that grinding impurities are fully removed from the product. Its main component is a polyether-based high-efficiency defoamer.

[0019] The significant difference between this invention and conventional automotive-grade processes is that conventional automotive-grade processes require tumbling after the cutting process, followed by tumbling after sintering; while this invention eliminates the tumbling step after cutting, and can meet the performance and appearance requirements of automotive-grade products through only the tumbling process after sintering.

[0020] The beneficial effects of this invention are: 1. The grinding media of this invention possesses high hardness, strong wear resistance, good chemical and thermal stability, and excellent electrical insulation. It changes the point contact of traditional grinding to line contact, effectively reducing stress concentration caused by point contact, thereby improving the appearance of MLCCs, reducing MLCC damage, ensuring stable performance, and exhibiting excellent compatibility with MLCC materials. This invention limits the main grinding media to a cylindrical ceramic rod with specific aspect ratio, hardness, diameter, and length. The aspect ratio > 2 enhances the cutting and grinding effect of the ceramic rod during grinding, ensuring uniform treatment of the MLCC. The Mohs hardness exceeds the requirement of the MLCC ceramic body hardness, preventing the grinding media from being worn down and contaminating the MLCC during grinding, thus ensuring product quality. The specified range of diameter and length is the optimal range verified through extensive experiments, adaptable to different MLCC specifications, achieving efficient and high-quality grinding processing.

[0021] 2. The ceramic rod and the MLCC matrix are both ceramic materials, avoiding metal contamination (such as the risk of Fe ion migration) and achieving a breakthrough in material compatibility.

[0022] 3. The lifespan of the medium is extended by 5 times (actual measurement > 200 hours), saving 370,000 yuan per production line per year in consumable costs (based on a production capacity of 100,000 pieces per hour). Attached Figure Description

[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Images showing the morphology of zirconia spheres and high-purity alumina spheres; Figure 2 This is a morphological diagram of the ceramic rod of the present invention; Figure 3 A schematic diagram illustrating stress concentration caused by point contact of a sphere. Figure 4 This is a schematic diagram illustrating the uniform grinding achieved by the rod body through line contact in this invention. Figure 5 Electron micrographs of the MLCC surface after tumbling using existing techniques; Figure 6 Electron micrograph of the MLCC surface after using a ceramic rod as the main grinding medium; Figure 7 The design flowchart for obtaining the optimal rolling conditions for this invention is shown below. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0026] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "comprising" or "including," and similar words used in this invention, mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0027] Taking 0402 specification MLCC as an example, using a φ2.5mm×8mm YSZ ceramic rod and a roller frequency of 30Hz for 55 minutes, a surface roughness Ra≤0.1μm is obtained, which fully meets the automotive standard.

[0028] To compare the effects of different primary grinding media on the appearance of 0402 specification MLCCs after sintering, this experiment divided the same batch of MLCCs of this specification into six smaller batches, and used zirconia balls, high-purity alumina balls, and four different sizes of ceramic rods as primary grinding media for tumbling. The ceramic rods in Examples 1-3 had a composition and content of approximately 85% alumina, approximately 12% magnesium oxide, and approximately 3% aluminum borate. The number of MLCCs in each smaller batch was fixed at 200K pieces, and the mass ratio of grinding media to MLCCs was set at 3:1, with the mass ratio of primary grinding media to ceramic microspheres at 8:2. The filling amount of each roller was controlled within the range of 60%-70%, the tumbling frequency was 35Hz, and the grinding time was set at 40 minutes. After tumbling, the MLCC products were cleaned with DL water circulation and dried before use. The cleaning agent used is a neutral ceramic cleaner specifically designed for MLCC manufacturing. Its core components are a nonionic surfactant, fatty alcohol polyoxyethylene ether, a complexing agent, aminotrimethylene phosphonic acid, and deionized water. The pH value is controlled between 6.5 and 7.5, and the dosage is 5ml. This facilitates efficient dissolution and removal of grinding debris (ceramic rod dust, zirconia microspheres) and sintering residues adhering to the MLCC surface, preventing pinholes or uneven coating thickness caused by residual microparticles. 3ml of defoamer is added to suppress the excessive foam generated by the surfactant during water circulation cleaning. Its main component is a polyether-based high-efficiency defoamer.

[0029] By comparing the tumbling effects of different primary grinding media on MLCCs, including indicators such as edge breakage rate, surface roughness, automotive-grade appearance compliance rate, and grinding media consumption, the results showed that: zirconia balls (Comparative Example 1) caused an MLCC edge breakage rate of 1.2% and a self-consumption of 15g / 1000 pieces; high-purity alumina balls (Comparative Example 2) caused an MLCC edge breakage rate of 1.0% and a self-consumption of 23g / 1000 pieces. Both resulted in higher edge breakage rates and greater self-consumption. Comparative Example 3, a ceramic rod mainly composed of 90% alumina and 10% magnesium oxide, showed higher alumina content and roughness compared to ceramic rods with added aluminum borate, leading to a higher edge wear rate for MLCCs. The absence of aluminum borate increased the brittleness of the ceramic rod and resulted in greater grinding media consumption. Through the synergistic effect of "Al2O3 wear resistance - MgO toughening - aluminum borate densification," the performance contradictions of existing technologies were resolved, and the MLCCs met automotive-grade standards.

[0030] For ceramic rods of different sizes (1.3*3mm in Example 1, 2.5*8mm in Example 2, and 4*14mm in Example 3), the smaller size of the ceramic rod in Example 1 (1.3*3mm) increased the surface roughness of the MLCC to 0.16μm, while the larger size of the ceramic rod in Example 3 (4*14mm) increased the edge breakage rate of the MLCC to 1.1%. Comprehensive analysis shows that the 2.5*8mm ceramic rod in Example 2 can achieve a surface roughness as low as 0.08μm for the MLCC, a 96.4% automotive-grade appearance pass rate, and a grinding media consumption of only 3g / thousand pieces, making it more suitable for the tumbling treatment of 0402 sintered MLCCs.

[0031]

[0032] When using ceramic rods (2.5*8mm) as the main grinding media for 0402 specification MLCCs, the test quantity for each batch was 200Kpcs, with the following fixed parameters. The frequency and time were optimized. First, comparing the appearance pass rate of general-grade and automotive-grade MLCCs with the frequency at the same time, it can be seen that when the frequency is 30Hz, both general-grade and automotive-grade products can achieve a very high pass rate. Further optimization of the time was carried out on this basis. The results show that when the grinding parameters are finally 30Hz and 50min, the product pass rate is the highest, with a pass rate of 99.3% for general-grade products and 98.9% for automotive-grade products.

[0033]

[0034]

[0035] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A grinding media, characterized in that, By mass percentage, the grinding media comprises 78-82% ceramic rods and 18-22% ceramic microspheres; the ceramic rods comprise 84-86% alumina, 11-13% magnesium oxide and 2-4% aluminum borate, and the ceramic rods have a diameter of 2.2-2.8 mm, a length of 6.0-10.0 mm, a Mohs hardness ≥8.5, and a surface roughness Ra ≤0.1 μm.

2. The milling medium according to claim 1, characterized in that, The ceramic rod is a cylindrical ceramic rod with a length-to-diameter ratio greater than 2.

3. The milling medium according to claim 1, characterized in that, The ceramic microspheres are zirconia ceramic microspheres with a purity of 95%.

4. The milling medium according to claim 1, characterized in that, The diameter of the ceramic microspheres is 0.08-0.12 mm.

5. The milling medium according to claim 1, characterized in that, The ceramic rod has a diameter of 2.5 mm and a length of 8 mm.

6. A tumbling method for improving the appearance of MLCCs using the tumbling media described in any one of claims 1-5, characterized in that, The method involves loading tumbling media and MLCCs at a mass ratio of 2.5-3.5:1, with the roller filling amount being 60-70%. After tumbling and cleaning, the media is dried.

7. The tumbling method according to claim 6, characterized in that, The mass ratio of the grinding media to the MLCC is 3:

1.

8. The tumbling method according to claim 6, characterized in that, The rolling frequency is 25-35Hz, and the time is 45-75min.

9. The tumbling method according to claim 6, characterized in that, The cleaning process uses water circulation.

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