Method for reducing high-temperature leakage current of tantalum capacitor

Abstract

The invention belongs to the technical field of tantalum capacitors, and particularly relates to a method for reducing high-temperature leakage current of a tantalum capacitor, which comprises the following steps of: 1) passivating a microporous metal plate: passivating the microporous metal plate in concentrated nitric acid, cooling to room temperature and then taking out the microporous metal plate; 2) corrosion of the microporous metal plate: soaking the passivated microporous metal plate in a sodium hydroxide solution, and washing with water; (3) forming: taking the sintered tantalum core as an anode, taking the microporous metal plate treated in the step (2) as a cathode, adding a forming liquid into a forming tank, boosting to a capacity testing voltage at a constant current density of 0.01-0.06 A / g, and then keeping the voltage constant; (4) post-treatment; after the tantalum anode manufactured by the method is subjected to traditional coating, assembling and aging processes, high-temperature and low-leakage-current tantalum capacitor production is realized, and the product percent of pass is high. The microporous metal plate used in the invention has a large specific surface area, and has the effects of low electron density per unit area and uniform electric field distribution in the forming process of tantalum capacitor manufacturing.

Description

Technical Field

[0001] The invention belongs to the technical field of tantalum capacitors, and in particular relates to a method for reducing high-temperature leakage current of tantalum capacitors. Background Art

[0002] Tantalum capacitors are high-performance electronic components that are widely used in high-tech fields such as aviation, aerospace, military, and communications because of their high capacity, low leakage current, good temperature characteristics, and long life. In the manufacturing process of tantalum capacitors, the forming slot is a special equipment used to form the tantalum core. The forming equipment and process have a direct impact on the electrical parameters and performance of the tantalum core.

[0003] At present, the cathode plate of the tantalum capacitor is usually made of ordinary 304 metal plate. However, the high-voltage, large-capacity, and large-size capacitors prepared by the existing cathode slot have large leakage current and high scrap rate when measuring high-temperature leakage current, which has a great impact on the product qualification rate and production cost. There is little research on cathode slot materials in the prior art, and most of it is focused on the molding research of tantalum sheets. For example, Patent No. CN201810354215.1 discloses a method for preparing a porous tantalum sheet, which uses a tantalum sheet as an anode electrode and a stainless steel plate as a cathode electrode. The purity and preparation efficiency of the tantalum sheet are improved by adjusting the concentration of the electrolyte solution and the process parameters of the electrolytic corrosion, but it cannot solve the problem of large leakage current of the tantalum block.

[0004] Due to the uneven electric field distribution during the formation of tantalum blocks, the tantalum pentoxide dielectric films of different tantalum blocks are different, resulting in defects. In addition, the tantalum powder has a high impurity content. When the tantalum block is formed, the impurities are wrapped in the tantalum pentoxide layer, and a relaxation effect occurs under high temperature and electric field force. As a result, the parameters of tantalum capacitors are high when measuring high-temperature leakage current, which is not conducive to the production of tantalum capacitors. Therefore, it is very important to study methods to reduce the high-temperature leakage current of tantalum capacitors. Summary of the invention

[0005] The present invention aims at the deficiencies of the prior art and proposes a method for reducing the high temperature leakage current of a tantalum capacitor.

[0006] This is achieved specifically through the following technical solutions:

[0007] A method for reducing high temperature leakage current of a tantalum capacitor comprises the following steps:

[0008] 1) Passivation of the microporous metal plate: The microporous metal plate is placed in concentrated nitric acid at 50°C-80°C for passivation, and then taken out after cooling to room temperature;

[0009] 2) Microporous metal plate corrosion: The passivated microporous metal plate is immersed in a sodium hydroxide solution for 10-20 minutes, and then washed with deionized water until the pH value of the rinse solution is 6.9-7.1;

[0010] 3) Formation: Using the sintered tantalum core as the anode and the microporous metal plate treated in step 2) as the cathode, add the forming solution into the forming tank, and increase the voltage at a constant current density of 0.01 A / g - 0.06 A / g to the test capacitance voltage, and then keep the voltage constant for 60 min - 150 min;

[0011] 4) Post-treatment: Wash the formed tantalum core successively with deionized water, heat-treat, cool, and perform supplementary formation to obtain the anode.

[0012] The micropores of the microporous metal plate have a size of 30 - 150 μm and a porosity of 25% - 35%.

[0013] The microporous metal plate is selected from any one of 316L stainless steel microporous plates, titanium metal plates, and 316L metal fiber microporous felts.

[0014] The mass concentration of the concentrated nitric acid is 20% - 30%.

[0015] The concentration of the sodium hydroxide solution is 0.5 - 1 mol / L.

[0016] The time for the water washing is 30 min - 45 min.

[0017] The conductivity of the forming solution is 800 - 3000 μS / cm, and the temperature is 60 - 75 °C.

[0018] The temperature of the heat treatment is 340 °C - 380 °C.

[0019] Beneficial effects:

[0020] After the tantalum anode manufactured by the method of the present invention undergoes the traditional film coating, assembly, and aging processes, the production of tantalum capacitors with high temperature and low leakage current is realized, and the product qualification rate is high.

[0021] The passivation and corrosion treatment of the present invention endows the microporous metal plate with the following characteristics:

[0022] 1. A larger surface area, which is beneficial to increasing the path and area of electron transmission.

[0023] 2. A lower electron density per unit area. The low electron density helps to reduce the local electric field strength, thereby reducing the polarization effect of the electrode and improving the uniformity of the electrochemical reaction.

[0024] 3. A more uniform electric field distribution, enabling the electric field to be more evenly distributed on the surface of the tantalum core. This uniform electric field distribution helps to form a more uniform dielectric film, reducing the thickness difference of the dielectric film caused by the uneven electric field, and thus effectively improving the performance and reliability of the capacitor.

[0025] 4. Larger cathode area. The cathode area corresponding to each tantalum core is larger, further enhancing the uniformity of the electric field and the stability of the electrochemical reaction. Detailed implementation manners

[0026] The following further elaborates on the detailed implementation manners of the present invention. However, the present invention is not limited to these implementation manners. Any improvement or substitution based on the basic spirit of this embodiment still falls within the scope protected by the claims of the present invention.

[0027] Example 1

[0028] A method for reducing the high-temperature leakage current of tantalum capacitors includes the following steps:

[0029] 1) Passivation: Passivate the metal microporous plate formed and sintered from 316L stainless steel metal powder in 25% concentrated nitric acid at 60°C for 30 min, and take it out after cooling to room temperature. The micropore size of the microporous metal plate is about 50 μm, and the porosity is about 35%.

[0030] 2) Corrosion: Immerse it in 0.5 mol / L sodium hydroxide solution for 18 min, then rinse it with deionized water for 45 min, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1.

[0031] 3) Replace the ordinary cathode metal plate in the forming tank with the metal microporous plate obtained in step 2).

[0032] 4) Prepare the forming solution: Add 120 ml of phosphoric acid to 100 L of ethylene glycol aqueous solution with a volume fraction of 35%, add 70 g of citric acid, heat up to 65°C, and measure the conductivity to be 1120 μS / cm.

[0033] 5) Forming: Use the sintered tantalum core as the anode and the porous metal plate treated in step 2) as the cathode. Add the forming solution to the forming tank, and increase the voltage at a constant current density of 0.06 A / g to 220 V, and then keep the voltage constant for 70 min.

[0034] 6) After the forming of the tantalum core is completed, wash it successively with deionized water, heat-treat it at 340°C, cool it, and perform supplementary forming for 55 min to obtain a tantalum anode.

[0035] 7) Coating: After immersing the product in manganese nitrate solution, perform wet thermal decomposition at 230°C to obtain a manganese dioxide cathode.

[0036] 8) Strengthening: Immerse the product obtained in 7) in the manganese dioxide strengthening solution to fill the pores of the tantalum core and increase the roughness of the tantalum core at the same time.

[0037] 9) Graphite, silver paste, spot welding: Immerse the product obtained in step 8) in graphite emulsion, dry it, then immerse it in silver paste, dry it again, cut it to a height suitable for the outer shell, and spot weld the cut product to the nickel lead wire.

[0038] 10) Assembly: Load the tinned copper outer shell with an appropriate amount of HH60 tin-lead solder. After the solder melts, load the product obtained in step 9) and install the insulator. Finally, seal it with high-temperature tin.

[0039] 11) Aging: Age the product obtained in step 10) at 85°C and 60V for 96 hours, and then age it at 125°C and 40V for 4 hours.

[0040] 12) Screening: Measure the leakage current of the product obtained in step 11) at 125°C and 40V.

[0041] Example 2

[0042] A method for reducing the high-temperature leakage current of tantalum capacitors, comprising the following steps:

[0043] 1) Passivation: Passivate the metal microporous plate after forming and sintering titanium alloy powder in 25% concentrated nitric acid at 60°C for 40 minutes, and take it out after cooling to room temperature; the micropore size of the microporous metal plate is about 30μm, and the porosity is about 25%.

[0044] 2) Cleaning: Immerse it in a 0.5mol / L sodium hydroxide solution for 18 minutes, then rinse it with deionized water for 45 minutes, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1.

[0045] 3) Replace the ordinary cathode metal plate in the forming tank with the metal microporous plate obtained in step 2).

[0046] 4) Prepare the forming solution: Add 130ml of phosphoric acid to 100L of an ethylene glycol aqueous solution with a volume fraction of 35%, add 70g of citric acid, heat it to 65°C, and measure the conductivity to be 1213μS / cm.

[0047] 5) Forming: Use the sintered tantalum core as the anode and the porous metal plate treated in step 2) as the cathode. Add the forming solution to the forming tank, and increase the voltage to 220V at a constant current density of 0.06A / g, and then keep the voltage constant for 70 minutes.

[0048] 6) After the forming of the tantalum core is completed, wash it with deionized water, heat-treat it at 340°C, cool it, and perform supplementary forming for 55 minutes to obtain a tantalum anode.

[0049] 7) Coating: After immersing the product in manganese nitrate solution, perform wet thermal decomposition at 230°C to obtain a manganese dioxide cathode.

[0050] 8) Strengthening: Immerse the product obtained in 7) in a manganese dioxide strengthening solution to fill the pores of the tantalum core and increase the roughness of the tantalum core at the same time.

[0051] 9) Graphite, silver paste, spot welding: Immerse the product obtained in 8) in a graphite emulsion, dry it, then immerse it in silver paste, dry it again, cut it to a height suitable for the outer shell, and spot weld the cut product to a nickel lead.

[0052] 10) Assembly: Load a suitable amount of HH60 tin-lead solder into the tinned copper outer shell. After the solder melts, load the product obtained in 9) and load an insulator, and finally seal it with high-temperature tin.

[0053] 11) Aging: Age the product obtained in 10) at 85 °C and 60 V for 96 h, and then age it at 125 °C and 40 V for 4 hours.

[0054] 12) Screening: Measure the leakage current of the product obtained in 11) at 125 °C and 40 V.

[0055] Example 3

[0056] A method for reducing the high-temperature leakage current of tantalum capacitors, comprising the following steps:

[0057] 1) Passivation: Passivate a 316L stainless steel metal fiber microporous felt in 25% concentrated nitric acid at 60 °C for 30 min, and take it out after cooling to room temperature; the micropore size of the 316L stainless steel metal fiber microporous felt is about 100 μm, and the porosity is about 40%.

[0058] 2) Cleaning: Immerse it in a 0.5 mol / L sodium hydroxide solution for 18 min, then rinse it with deionized water for 45 min, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1.

[0059] 3) Replace the ordinary cathode metal plate in the forming tank with the metal fiber microporous felt obtained in step 2).

[0060] 4) Prepare the forming solution: Add 125 ml of phosphoric acid to 100 L of an ethylene glycol aqueous solution with a volume fraction of 35%, add 70 g of citric acid, heat it to 65 °C, and measure the conductivity to be 1174 μS / cm.

[0061] 5) Forming: Use the sintered tantalum core as the anode and the porous metal plate treated in step 2) as the cathode. Add the forming solution to the forming tank, and increase the voltage at a constant current density of 0.06 A / g to 220 V, and then keep the voltage constant for 70 min.

[0062] 6) After the forming of the tantalum core is completed, wash it with deionized water, heat-treat it at 340 °C, cool it, and perform supplementary forming for 55 min to obtain a tantalum anode.

[0063] 7) Coating: After the product is immersed in the manganese nitrate solution, it is wet-thermally decomposed at 230 °C to obtain a manganese dioxide cathode.

[0064] 8) Strengthening: Immerse the product obtained in 7) in a manganese dioxide strengthening solution to fill the pores of the tantalum core and increase the roughness of the tantalum core at the same time.

[0065] 9) Graphite, silver paste, spot welding: Immerse the product obtained in 8) in a graphite emulsion, dry it, then immerse it in silver paste, dry it again, cut it to a height suitable for the outer shell, and spot-weld the cut product to a nickel lead.

[0066] 10) Assembly: Load a suitable amount of HH60 tin-lead solder into the tinned copper outer shell. After the solder melts, load the product obtained in 9) and install an insulator. Finally, seal it with high-temperature tin.

[0067] 11) Aging: Age the product obtained in 10) at 85 °C and 60 V for 96 h, and then age it at 125 °C and 40 V for 4 h.

[0068] 12) Screening: Measure the leakage current of the product obtained in 11) at 125 °C and 40 V.

[0069] Example 4

[0070] A method for reducing the high-temperature leakage current of tantalum capacitors, comprising the following steps:

[0071] 1) Passivation: Passivate a metal microporous plate formed and sintered from 316L stainless steel metal powder in 25% concentrated nitric acid at 60 °C for 30 min, and take it out after cooling to room temperature; the micropore size of the metal microporous plate is about 50 μm, and the porosity is about 35%.

[0072] 2) Cleaning: Immerse it in a 0.5 mol / L sodium hydroxide solution for 18 min, then rinse it with deionized water for 45 min, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1.

[0073] 3) Replace the ordinary cathode metal plate in the forming tank with the metal microporous plate obtained in step 2).

[0074] 4) Prepare a forming solution: Add 120 ml of phosphoric acid to 100 L of an ethylene glycol aqueous solution with a volume fraction of 35%, add 70 g of citric acid, heat it to 65 °C, and measure the conductivity to be 1120 μS / cm.

[0075] 5) Forming: Use the sintered tantalum core as the anode and the porous metal plate treated in step 2) as the cathode. Add the forming solution to the forming tank, and increase the voltage at a constant current density of 0.04 A / g to 270 V, and then keep the voltage constant for 70 min.

[0076] 6) The formed tantalum core is successively washed with deionized water, heat-treated at 340 °C, cooled, and post-formed for 55 min to obtain a tantalum anode.

[0077] 7) Coating: After the product is immersed in the manganese nitrate solution, it is wet-thermally decomposed at 230 °C to obtain a manganese dioxide cathode.

[0078] 8) Strengthening: The product obtained in 7) is immersed in the manganese dioxide strengthening solution to fill the pores of the tantalum core and increase the roughness of the tantalum core at the same time.

[0079] 9) Graphite, silver paste, spot welding: The product obtained in 8) is immersed in the graphite emulsion, dried, then immersed in the silver paste, dried again, cut to a height suitable for the shell, and the cut product is spot-welded to the nickel lead.

[0080] 10) Assembly: The tinned copper shell is filled with an appropriate amount of HH60 tin-lead solder. After the solder melts, the product obtained in 9) is loaded and an insulator is loaded. Finally, it is sealed with high-temperature tin.

[0081] 11) Aging: The product obtained in 10) is aged at 85 °C and 75 V for 96 h, and then aged at 125 °C and 50 V for 4 h.

[0082] 12) Screening: The product obtained in 11) is measured for leakage current at 125 °C and 50 V.

[0083] Comparative Example 1

[0084] The differences from Example 1, Example 2, and Example 3 are as follows: The cathode of Comparative Example 1 uses a 304 stainless steel metal plate, and the treatment methods in steps 1) and 2) are respectively:

[0085] 1) Immersion: After cleaning and pickling the 304 stainless steel metal plate to remove oil, it is immersed in 15% nitric acid for passivation for 30 min, taken out after cooling to room temperature;

[0086] 2) Cleaning: Rinse with deionized water for 60 min, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1;

[0087] Comparative Example 2

[0088] The difference from Example 4 is as follows: The cathode of Comparative Example 1 uses a 304 stainless steel metal plate; the treatment methods in steps 1) and 2) are respectively:

[0089] 1) Immersion: After cleaning and pickling the 304 stainless steel metal plate to remove oil, it is immersed in 15% nitric acid for passivation for 30 min, taken out after cooling to room temperature;

[0090] 2) Cleaning: Rinse with deionized water for 60 min, and measure the pH value of the rinsing solution with a pH meter to be 6.9 - 7.1.

[0091] Table 1. Comparison of data between examples and comparative examples

[0092]

[0093] As can be seen from Examples 1, 2 and 3 in Table 1, for the products prepared with the microporous metal plate with a large surface area as the cathode plate, the high-temperature leakage current performance is better, and the number of products with unqualified DLC (greater than 0.1 URC) and the number of qualified products with large leakage current (0.1 URC ≥ DLC > 0.01 URC) are fewer. Compared with the improved forming groove cathode plate in Comparative Example 1, the advantages are obvious; as can be seen from Comparative Example 2 and Example 4, the microporous metal plate with a large surface area significantly improves the leakage current of the 63V-47μF products. The metal plate with a large surface area as the forming groove cathode plate improves the quality of the tantalum pentoxide dielectric oxide film and significantly improves the high-temperature leakage current parameters of high-voltage and large-capacity products.

Claims

1. A method for reducing the high-temperature leakage current of tantalum capacitors, characterized in that, It includes the following steps: 1) Passivate the microporous metal plate: Place the microporous metal plate in concentrated nitric acid and passivate it at 50°C - 80°C, then take it out after cooling to room temperature; 2) Corrode the microporous metal plate: Immerse the passivated microporous metal plate in sodium hydroxide solution for 10 min - 20 min, and then wash it with deionized water until the pH value of the rinsing solution is 6.9 - 7.1; 3) Formation: Use the sintered tantalum core as the anode and the microporous metal plate treated in step 2) as the cathode. Add the formation solution to the formation tank, and increase the voltage at a constant current density of 0.01 A / g - 0.06 A / g to the test capacitance voltage, and then keep the voltage constant for 60 min - 150 min; 4) Post-treatment: Boil the formed tantalum core successively with deionized water, perform heat treatment, cool it, and perform supplementary formation to obtain the anode.

2. The method for reducing the high-temperature leakage current of a tantalum capacitor according to claim 1, characterized in that, The micropore size of the microporous metal plate is 30 - 150 μm, and the porosity is 25% - 35%.

3. A method for reducing the high-temperature leakage current of tantalum capacitors as described in claim 1, characterized in that, The mass concentration of the concentrated nitric acid is 20% - 30%.

4. A method for reducing the high-temperature leakage current of tantalum capacitors according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 0.5 - 1 mol / L.

5. A method for reducing the high-temperature leakage current of tantalum capacitors according to claim 1, characterized in that The time for the water washing is 30 min - 45 min.

6. The method for reducing the high-temperature leakage current of a tantalum capacitor according to claim 1, wherein The conductivity of the formation solution is 800 - 3000 μS / cm, and the temperature is 60 - 75°C.

7. A method for reducing the high-temperature leakage current of tantalum capacitors according to claim 1, characterized in that, The temperature of the heat treatment is 340°C - 380°C.

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