Chip solid tantalum capacitor and coating process thereof

Abstract

The invention relates to a chip solid capacitor and a coating process thereof, the chip solid tantalum capacitor is composed of a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer and a plastic package layer, the cathode layer is a manganese dioxide layer, and the manganese dioxide layer is formed by thermal decomposition on the tantalum block on which the dielectric oxide layer grows through the coating process; the specific operation of the coating process is specifically limited, and the tantalum block is sequentially impregnated with thin-thick-thick-thin coating liquid, so that the prepared cathode layer is high in density, high in interlayer binding force and free of bubbling and delamination defects, the qualification rate and the moisture resistance of the product are greatly improved, meanwhile, parameters of all stages are controllable and adjustable, and the production cost is reduced. And the production requirements of high-specific-volume tantalum capacitors with different specific volume grades can be met, and the method has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of tantalum capacitor manufacturing, specifically relating to a chip solid capacitor and its coating process. Background Technology

[0002] Tantalum capacitors, with their superior characteristics such as high energy density, high reliability, and wide temperature range, are widely used in many key fields such as consumer electronics, automotive electronics, 5G communications, aerospace, and AI servers, and are an indispensable core energy storage component in high-end electronic devices. As electronic devices rapidly iterate towards miniaturization, lightweighting, and high performance, tantalum capacitors are developing towards smaller size and higher capacity, which places higher demands on the specific capacitance of tantalum powder and the compaction degree of tantalum blocks.

[0003] To achieve the above technical goals, it is necessary to further improve the specific capacitance of tantalum powder and increase the compactness of tantalum blocks. However, this results in a significant reduction in the internal porosity of the tantalum blocks, leading to difficulties in the impregnation process of manganese nitrate. This seriously affects the uniformity and compactness of the manganese nitrate film, thereby restricting the performance improvement of tantalum capacitors, which needs further improvement. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a chip solid tantalum capacitor and its coating process.

[0005] The present invention adopts the following technical solution: A coating process for preparing a chip solid tantalum capacitor, wherein the chip solid tantalum capacitor is composed of a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer, and a molding layer, wherein the cathode layer is a manganese dioxide layer, and the manganese dioxide layer is formed by thermal decomposition on the tantalum block on which the dielectric oxide layer has been grown through a coating process. The coating process specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution with added low-boiling-point surfactant, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-6 times. Step 2: Immerse the tantalum block that has completed Step 1 in a second coating solution containing low-boiling-point surfactant and high-boiling-point surfactant, and then send it into a decomposition furnace for high-temperature decomposition. Repeat 1-3 times. Step 3: Immerse the tantalum block that has completed step 2 in the third coating solution, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-4 times; Step 4: Immerse the tantalum block that has completed Step 3 in a coating solution containing low-boiling-point surfactant and high-boiling-point surfactant, and then send it into a decomposition furnace for high-temperature decomposition. Repeat this process 1-3 times to complete the coating process. The specific gravity of the first coating solution is 1.2-1.4, the specific gravity of the second coating solution is 1.5-1.7, the specific gravity of the third coating solution is 1.5-1.7, and the specific gravity of the fourth coating solution is 1.2-1.5.

[0006] Furthermore, in steps 1, 2, 3 and 4, after the tantalum block is impregnated with the coating solution, it is first dried at 60-130℃ for 5-15 minutes, and then sent to a decomposition furnace for high-temperature decomposition.

[0007] Furthermore, in step 1, the temperature of the decomposition furnace is 240-300℃, and in steps 2-4, the temperature of the decomposition furnace is 200-240℃.

[0008] Furthermore, the first coating solution includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, and catalyst, wherein the low-boiling-point surfactant accounts for 0.5-10 wt% of the mass of the first coating solution, the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution, and the amount of nitric acid added is controlled so that the pH of the first coating solution is less than 2.

[0009] Furthermore, the second coating solution includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the second coating solution, and the high-boiling-point surfactant accounts for 0.01-0.1 wt% of the mass of the second coating solution. The amount of nitric acid added is controlled so that the pH of the second coating solution is less than 2.

[0010] Furthermore, the third coating solution includes the following raw materials: manganese nitrate, water, nitric acid, and catalyst. The catalyst accounts for 0.5-4 wt% of the mass of the first coating solution, and the amount of nitric acid added is controlled so that the pH of the third coating solution is less than 2.

[0011] Furthermore, the fourth coating solution includes the following raw materials: manganese acid, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the fourth coating solution, the high-boiling-point surfactant accounts for 0.002-0.03 wt% of the mass of the fourth coating solution, and the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the fourth coating solution is less than 2.

[0012] Furthermore, the low-boiling-point surfactant is one or more of ethanol, propanol, ethylene glycol, ethylene glycol methyl ether, diethylene glycol monomethyl ether, ethylene glycol ethyl ether, diethylene glycol ethyl ether, propylene glycol monomethyl ether, ethylene glycol mono-n-propyl ether, 2-isopropoxyethanol, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and glyceryl monoacetate.

[0013] Furthermore, the high-boiling-point surfactant is one or more of the following: fatty alcohol polyoxyethylene ether, 2-octyl alcohol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether, isomeric alcohol polyoxyethylene ether, nonylphenol polyoxyethylene ether, Tween 20, Tween 40, polyethylene glycol, and perfluorohexylethanol polyoxyethylene ether.

[0014] A chip solid tantalum capacitor comprises a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer, and a molding compound layer. The cathode layer is a manganese dioxide layer, which is formed by thermal decomposition on the tantalum block on which the dielectric oxide layer is grown through any of the above-described coating processes.

[0015] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention, by limiting the specific operation of the coating process, uses four coating solutions of dilute-concentrated-concentrated-dilute to impregnate the tantalum block in sequence, so that the prepared cathode layer has high density, strong interlayer bonding force, no bubbling or delamination defects, and the product qualification rate and moisture resistance are greatly improved. At the same time, the parameters of each stage are controllable and adjustable, which can adapt to the production needs of high specific capacitance tantalum capacitors of different specific capacitance grades, and has good prospects for industrial application. It fundamentally improves the manufacturing pain points of high specific capacitance products, reduces the scrap rate in the production process, and has significant economic benefits. Specifically, the specific gravity and raw material composition of the first coating solution are limited. A dilute coating solution with added low-boiling-point surfactants is used to fully wet and penetrate the interior. After thermal decomposition, there are no impurities or surfactant residues, ensuring a high capacity extraction rate. The specific gravity and raw material composition of the second coating solution are also limited. A concentrated coating solution with added low-boiling-point and high-boiling-point surfactants is used. During thermal decomposition, the low-boiling-point surfactants gradually evaporate with the water, while the high-boiling-point surfactants gradually concentrate. The surface tension of the coating solution remains stable, alleviating the bubbling problem caused by excessive surfactants. The concentrated coating solution penetrates the interior and rapidly generates manganese dioxide simultaneously in both the inner and outer layers, creating a nail effect that greatly enhances the bonding force between the inner and outer layers and reduces delamination during the coating process. Specifically, the specific gravity and raw material composition of the third coating solution are limited. Using a concentrated coating solution without surfactants can increase the amount of immersion solution and improve the deposition and growth efficiency of the outer manganese dioxide layer. Specifically, the specific gravity and raw material composition of the fourth coating solution are limited. Using a medium-concentration coating solution with added low-boiling-point and high-boiling-point surfactants repairs the voids in the outer manganese dioxide layer, smooths the surface, and improves density. Detailed Implementation

[0016] The present invention will be further described below through specific embodiments.

[0017] A surface-mount solid tantalum capacitor comprises a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer, and a molding compound. The cathode layer is a manganese dioxide layer, formed by thermal decomposition on the tantalum block with the grown dielectric oxide layer using a coating process. Specifically, the tantalum block is prepared as follows: tantalum powder with a specific capacitance of 70000 uF•V / g is mixed with tantalum wire at a ratio of 6 g / cm³. 2 The tantalum block is pressed into a tantalum blank with a diameter of 1.8mm*2.4mm*1.2mm, and then sintered to obtain the tantalum block. The dielectric oxide layer is formed as follows: the sintered tantalum block is placed in a forming tank of 0.02-0.3wt% phosphoric acid or 0.05-1wt% nitric acid electrolyte to carry out electrochemical formation so that the thickness of the generated dielectric oxide layer meets the design requirements.

[0018] A coating process for fabricating a chip-type solid tantalum capacitor specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution with added low-boiling-point surfactant, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-6 times. Step 2: Immerse the tantalum block that has completed Step 1 in a second coating solution containing low-boiling-point surfactant and high-boiling-point surfactant, and then send it into a decomposition furnace for high-temperature decomposition. Repeat 1-3 times. Step 3: Immerse the tantalum block that has completed step 2 in the third coating solution, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-4 times; Step 4: Immerse the tantalum block that has completed Step 3 in a coating solution containing both low-boiling-point and high-boiling-point surfactants, and then send it to a decomposition furnace for high-temperature decomposition. Repeat this process 1-3 times to complete the coating process.

[0019] In steps 1, 2, 3 and 4, after the tantalum block is impregnated with the coating solution, it is first dried at 60-130℃ for 5-15 minutes, and then sent to a decomposition furnace for high-temperature decomposition. Specifically, in step 1, the temperature of the decomposition furnace is 240-300℃, and in steps 2-4, the temperature of the decomposition furnace is 200-240℃.

[0020] Furthermore, the specific gravity of the first coating solution is 1.2-1.4, and it includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 0.5-10 wt% of the mass of the first coating solution, and the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the first coating solution is less than 2.

[0021] The specific gravity of the second coating solution is 1.5-1.7, and it includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the second coating solution, and the high-boiling-point surfactant accounts for 0.01-0.1 wt% of the mass of the second coating solution. The amount of nitric acid added is controlled so that the pH of the second coating solution is less than 2.

[0022] The specific gravity of the third coating solution is 1.5-1.7, and it includes the following raw materials: manganese nitrate, water, nitric acid, and catalyst. The mass percentage of the catalyst in the first coating solution is 0.5-4 wt%, and the amount of nitric acid added is controlled so that the pH of the third coating solution is less than 2.

[0023] The specific gravity of the fourth coating solution is 1.2-1.5, and it includes the following raw materials: manganese acid, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the fourth coating solution, the high-boiling-point surfactant accounts for 0.002-0.03 wt% of the mass of the fourth coating solution, and the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the fourth coating solution is less than 2.

[0024] Among them, the low-boiling-point surfactant is one or more of ethanol, propanol, ethylene glycol, ethylene glycol methyl ether, diethylene glycol monomethyl ether, ethylene glycol ethyl ether, diethylene glycol ethyl ether, propylene glycol monomethyl ether, ethylene glycol mono-n-propyl ether, 2-isopropoxyethanol, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and glycerol monoacetate.

[0025] The high-boiling-point surfactant is one or more of the following: fatty alcohol polyoxyethylene (3) ether (AEO-3), fatty alcohol polyoxyethylene (5) ether (AEO-5), octyl alcohol polyoxyethylene ether (JFC-2), isooctyl alcohol polyoxyethylene ether (JFC-3), isomeric alcohol polyoxyethylene ether (JFC-E), nonylphenol polyoxyethylene ether (NP-4 / NP-6), Tween 20, Tween 40, polyethylene glycol (PEG-200 / PEG-400), and perfluorohexyl ethanol polyoxyethylene ether. Example 1

[0026] In this embodiment, the preparation method of the first coating solution is as follows: 5 wt% ethanol and 2 wt% urea are added to a manganese nitrate solution with a specific gravity of 1.25, and then nitric acid solution is added dropwise until the solution pH=1. The solution is stirred evenly to obtain the first coating solution for later use.

[0027] The preparation method of the second coating solution is as follows: Add 8 wt% ethanol, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.55, and then add nitric acid solution dropwise until the solution pH=1. Stir evenly to obtain the second coating solution for later use.

[0028] The preparation method of the third coating solution is as follows: add 2wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution dropwise until the solution pH=1, stir evenly, and the third coating solution is ready for use.

[0029] The preparation method of the fourth coating solution is as follows: Add 8 wt% ethanol, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.38, and then add nitric acid solution dropwise until the solution pH=1. Stir well to obtain the fourth coating solution for later use.

[0030] A coating process for fabricating a chip-type solid tantalum capacitor specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution with added low boiling point surfactant for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 270°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 4 times. Step 2: Immerse the tantalum block that has completed Step 1 in a second coating solution containing low-boiling-point surfactant and high-boiling-point surfactant for 5 minutes. First, pre-dry it at 75°C for 8 minutes, then transfer it to an oven at 220°C and thermally decompose it in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process twice. Step 3: Immerse the tantalum block from Step 2 in the third coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 3 times. Step 4: Immerse the tantalum block from Step 3 in a coating solution containing both low-boiling-point and high-boiling-point surfactants for 5 minutes. First, pre-dry it at 75°C for 8 minutes, then transfer it to an oven at 250°C for thermal decomposition in steam for 5 minutes. Repeat the immersion and thermal decomposition process 4 times to complete the coating process.

[0031] The tantalum block after coating is processed with graphite silver paste and encapsulation to obtain a transition layer and an encapsulation layer, respectively. After aging and screening, a chip solid tantalum capacitor is obtained. Example 2

[0032] The preparation method is basically the same as in Example 1, with the main difference being: the preparation method of the second coating solution is as follows: 8 wt% ethanol, 0.01 wt% perfluorohexyl ethanol polyoxyethylene ether, and 2 wt% urea are added to a manganese nitrate solution with a specific gravity of 1.65, and then nitric acid solution is added dropwise until the solution pH=1. The mixture is stirred evenly to obtain the second coating solution for later use. Example 3

[0033] The preparation method is basically the same as in Example 1, with the main difference being: the preparation method of the second coating solution is as follows: add 8 wt% ethanol, 0.01 wt% EPG400 and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution until the solution pH=1, stir evenly, and the second coating solution is obtained for later use. Example 4

[0034] The preparation method is basically the same as that in Example 1, the main difference being: the preparation method of the second coating solution is as follows: add 8 wt% ethylene glycol methyl ether, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution until the solution pH=1, stir evenly, and the second coating solution is obtained for later use. Example 5

[0035] The preparation method is basically the same as in Example 1, with the main difference being: the preparation method of the second coating solution is as follows: 5 wt% ethanol, 0.02 wt% JFC-E, and 2 wt% urea are added to a manganese nitrate solution with a specific gravity of 1.55, and then nitric acid solution is added dropwise until the solution pH=1. The solution is stirred evenly and set aside to obtain the second coating solution for later use. Example 6

[0036] The preparation method is basically the same as in Example 1, with the main difference being: the preparation method of the second coating solution is as follows: 12wt% ethanol, 0.005wt% JFC-E, and 2wt% urea are added to a manganese nitrate solution with a specific gravity of 1.55, and then nitric acid solution is added dropwise until the solution pH=1. The mixture is stirred evenly to obtain the second coating solution for later use. Example 7

[0037] The preparation method is basically the same as that in Example 1, the main difference being: the preparation method of the first coating solution is as follows: add 3wt% ethanol and 2wt% urea to a manganese nitrate solution with a specific gravity of 1.25, then add nitric acid solution dropwise until the solution pH=1, stir evenly, and the first coating solution is obtained for later use. Example 8

[0038] The preparation method is basically the same as that in Example 1, the main difference being: the preparation method of the first coating solution is as follows: 10wt% ethanol and 2wt% urea are added to a manganese nitrate solution with a specific gravity of 1.25, and then nitric acid solution is added dropwise until the solution pH=1. The solution is stirred evenly to obtain the first coating solution for later use. Example 9

[0039] The preparation method is basically the same as in Example 1, with the main difference being: the preparation method of the second coating solution is as follows: add 8 wt% ethanol, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.65, and then add nitric acid solution until the solution pH=1. Stir evenly to obtain the second coating solution for later use. Example 10

[0040] The preparation method is basically the same as that in Example 1, the main difference being: the preparation method of the second coating solution is as follows: add 8wt% ethanol, 0.01wt% JFC-E and 2wt% urea to a manganese nitrate solution with a specific gravity of 1.50, then add nitric acid solution until the solution pH=1, stir evenly, and the second coating solution is obtained for later use.

[0041] Comparative Example 1 In this comparative example, the preparation method of the first coating solution is as follows: 2 wt% urea is added to a manganese nitrate solution with a specific gravity of 1.25, and then nitric acid solution is added dropwise until the solution pH=1. The mixture is stirred evenly to obtain the first coating solution for later use.

[0042] The preparation method of the second coating solution is as follows: add 2wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution dropwise until the solution pH=1, stir evenly, and the second coating solution is ready for use.

[0043] A coating process for fabricating a chip-type solid tantalum capacitor specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 270°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 8 times. Step 2: Immerse the tantalum block from Step 1 in the second coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 6 times to complete the coating process.

[0044] The tantalum block after coating is processed with graphite silver paste and encapsulation to obtain a transition layer and an encapsulation layer, respectively. After aging and screening, a chip solid tantalum capacitor is obtained.

[0045] Comparative Example 2 (without low-boiling-point surfactant) The preparation method is basically the same as that in Example 1, the main difference being: the preparation method of the second coating solution is as follows: add 0.05wt% JFC-E and 2wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution until the solution pH=1, stir evenly, and the second coating solution is obtained for later use.

[0046] Comparative Example 3 The preparation method is basically the same as that in Example 1, the main difference being that the formulations of the second coating solution and the third coating solution are the same.

[0047] Comparative Example 4 In this comparative example, the preparation method of the first coating solution is as follows: 5 wt% ethanol and 2 wt% urea are added to a manganese nitrate solution with a specific gravity of 1.25, and then nitric acid solution is added dropwise until the solution pH=1. The solution is stirred evenly to obtain the first coating solution for later use.

[0048] The preparation method of the second coating solution is as follows: Add 8 wt% ethanol, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.55, and then add nitric acid solution dropwise until the solution pH=1. Stir evenly to obtain the second coating solution for later use.

[0049] The preparation method of the third coating solution is as follows: add 2wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution dropwise until the solution pH=1, stir evenly, and the third coating solution is ready for use.

[0050] A coating process for fabricating a chip-type solid tantalum capacitor specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 270°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 4 times. Step 2: Immerse the tantalum block from Step 1 in the second coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process twice. Step 3: Immerse the tantalum block from Step 2 in the third coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 3 times to complete the coating process.

[0051] The tantalum block after coating is processed with graphite silver paste and encapsulation to obtain a transition layer and an encapsulation layer, respectively. After aging and screening, a chip solid tantalum capacitor is obtained.

[0052] Comparative Example 5 In this comparative example, the preparation method of the first coating solution is as follows: 5 wt% ethanol and 2 wt% urea are added to a manganese nitrate solution with a specific gravity of 1.25, and then nitric acid solution is added dropwise until the solution pH=1. The solution is stirred evenly to obtain the first coating solution for later use.

[0053] The preparation method of the second coating solution is as follows: add 2wt% urea to a manganese nitrate solution with a specific gravity of 1.55, then add nitric acid solution dropwise until the solution pH=1, stir evenly, and the second coating solution is ready for use.

[0054] The preparation method of the third coating solution is as follows: Add 8 wt% ethanol, 0.01 wt% JFC-E, and 2 wt% urea to a manganese nitrate solution with a specific gravity of 1.38, and then add nitric acid solution dropwise until the solution pH=1. Stir evenly to obtain the third coating solution for later use.

[0055] A coating process for fabricating a chip-type solid tantalum capacitor specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 270°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 8 times. Step 2: Immerse the tantalum block from Step 1 in the second coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process 6 times. Step 3: Immerse the tantalum block from Step 2 in the third coating solution for 5 minutes, pre-dry it at 75°C for 8 minutes, and then transfer it to an oven at 220°C for thermal decomposition in water vapor for 5 minutes. Repeat the immersion and thermal decomposition process twice to complete the coating process.

[0056] The tantalum block after coating is processed with graphite silver paste and encapsulation to obtain a transition layer and an encapsulation layer, respectively. After aging and screening, a chip solid tantalum capacitor is obtained.

[0057] Experimental Test The chip solid tantalum capacitors prepared in the examples and comparative examples were subjected to corresponding electrical performance tests, wherein: 1. Process pass rate = (Quantity of finished products / Quantity put into production) x 100%.

[0058] 2. 500-hour humidity resistance test: Place the capacitor in a constant temperature and humidity chamber at 85℃ and 85% relative humidity for 500 hours. After storage, remove the capacitor and allow it to cool down for 2 hours at room temperature. Then test the leakage current of the capacitor for 10 seconds.

[0059] Table 1 Performance data of the examples and comparative examples

[0060] In summary, the yield and moisture resistance of the chip solid tantalum capacitors prepared in the examples are significantly improved. At the same time, the parameters at each stage are controllable and adjustable, which can meet the production needs of high specific capacitance tantalum capacitors with different specific capacitance levels and has good prospects for industrial application.

[0061] This application provides a segmented synergistic control method that synergistically regulates the type and concentration gradient of surfactants. Tantalum blocks are sequentially impregnated with four coating solutions: dilute-concentrated-concentrated-dilute. This results in a high-density cathode layer with strong interlayer adhesion, free from bubbling and delamination defects, significantly improving product yield and moisture resistance. First, a dilute coating solution containing low-boiling-point surfactants is used for thorough wetting, ensuring dense filling of the inner layer and eliminating surfactant residue, thus improving capacity extraction. Next, a concentrated coating solution combining low- and high-boiling-point surfactants is used to generate a "nail effect," strengthening the adhesion between the inner and outer manganese dioxide layers and reducing delamination. The third stage uses a surfactant-free concentrated coating solution to enhance the growth efficiency of the manganese dioxide layer. Finally, a medium-concentration coating solution containing two surfactants is used to smooth and densify the outer manganese dioxide layer.

[0062] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A coating process for fabricating a chip solid tantalum capacitor, wherein the chip solid tantalum capacitor comprises a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer, and a molding compound layer, characterized in that: The cathode layer is a manganese dioxide layer, which is formed by thermal decomposition on a tantalum block with a dielectric oxide layer grown by a coating process. The coating process specifically includes the following steps: Step 1: Immerse the tantalum block with the grown dielectric oxide layer in the first coating solution with added low-boiling-point surfactant, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-6 times. Step 2: Immerse the tantalum block that has completed Step 1 in a second coating solution containing low-boiling-point surfactant and high-boiling-point surfactant, and then send it into a decomposition furnace for high-temperature decomposition. Repeat 1-3 times. Step 3: Immerse the tantalum block that has completed step 2 in the third coating solution, and then send it into the decomposition furnace for high-temperature decomposition, repeating 2-4 times; Step 4: Immerse the tantalum block that has completed Step 3 in a coating solution containing low-boiling-point surfactant and high-boiling-point surfactant, and then send it into a decomposition furnace for high-temperature decomposition. Repeat this process 1-3 times to complete the coating process. The specific gravity of the first coating solution is 1.2-1.4, the specific gravity of the second coating solution is 1.5-1.7, the specific gravity of the third coating solution is 1.5-1.7, and the specific gravity of the fourth coating solution is 1.2-1.

5.

2. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: In steps 1, 2, 3 and 4, after the tantalum block is impregnated with the coating solution, it is first dried at 60-130℃ for 5-15 minutes, and then sent to a decomposition furnace for high-temperature decomposition.

3. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: In step 1, the temperature of the decomposition furnace is 240-300℃, and in steps 2-4, the temperature of the decomposition furnace is 200-240℃.

4. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The first coating solution includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 0.5-10 wt% of the mass of the first coating solution, and the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the first coating solution is less than 2.

5. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The second coating solution includes the following raw materials: manganese nitrate, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the second coating solution, and the high-boiling-point surfactant accounts for 0.01-0.1 wt% of the mass of the second coating solution. The amount of nitric acid added is controlled so that the pH of the second coating solution is less than 2.

6. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The third coating solution includes the following raw materials: manganese nitrate, water, nitric acid, and catalyst. The catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the third coating solution is less than 2.

7. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The fourth coating solution comprises the following raw materials: manganese acid, water, nitric acid, low-boiling-point surfactant, high-boiling-point surfactant, and catalyst. The low-boiling-point surfactant accounts for 3-15 wt% of the mass of the fourth coating solution, the high-boiling-point surfactant accounts for 0.002-0.03 wt% of the mass of the fourth coating solution, and the catalyst accounts for 0.5-4 wt% of the mass of the first coating solution. The amount of nitric acid added is controlled so that the pH of the fourth coating solution is less than 2.

8. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The low-boiling-point surfactant is one or more of ethanol, propanol, ethylene glycol, ethylene glycol methyl ether, diethylene glycol monomethyl ether, ethylene glycol ethyl ether, diethylene glycol ethyl ether, propylene glycol monomethyl ether, ethylene glycol mono-n-propyl ether, 2-isopropoxyethanol, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and glyceryl monoacetate.

9. The film coating process for preparing a chip solid tantalum capacitor according to claim 1, characterized in that: The high-boiling-point surfactant is one or more of the following: fatty alcohol polyoxyethylene ether, 2-octyl alcohol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether, iso-octyl alcohol polyoxyethylene ether, nonylphenol polyoxyethylene ether, Tween 20, Tween 40, polyethylene glycol, and perfluorohexylethanol polyoxyethylene ether.

10. A surface-mount solid tantalum capacitor, comprising a tantalum block, a dielectric oxide layer, a cathode layer, a transition layer, a silver layer, and a molding compound layer, characterized in that: The cathode layer is a manganese dioxide layer, which is formed by thermal decomposition on a tantalum block with a dielectric oxide layer grown by the film coating process described in any one of claims 1 to 9.

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