Anodic oxidation method for improving uniformity of dielectric layer of capacitor

Abstract

The invention discloses an anodic oxidation method for improving the uniformity of a dielectric layer of a capacitor. The anodic oxidation method comprises the following steps that a tantalum block is pretreated and then placed in an electrolytic bath; adding electrolyte into the electrolytic bath, and performing oscillation circulation through an oscillator; a tantalum block is sequentially subjected to a pre-oxidation procedure, a main oxidation procedure, a stabilization procedure, heat treatment and constant-pressure treatment, the tantalum block is taken out after treatment is finished, and the tantalum block is cleaned and dried to finish anodic oxidation. The ultrasonic oscillator is additionally arranged in the electrolytic bath, so that the electrolyte concentration gradient can be eliminated, and the thickness uniformity of the dielectric layer is improved. And by adding ammonium dihydrogen phosphate, micropores are filled, the surface of the tantalum block is passivated, and the performance of a capacitor prepared from the tantalum block is improved. Through a staged dynamic oxidation method and a composite electrolyte formula, the uniformity and reliability of a tantalum oxide dielectric layer are remarkably improved, and the method is suitable for industrial production of a high-reliability tantalum capacitor.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic component manufacturing, and particularly relates to an anodization method for improving the uniformity of the dielectric layer of a capacitor. Background Art

[0002] Tantalum capacitors are widely used in fields such as aerospace, communication equipment, and automotive electronics due to their advantages of small size, large capacitance, and high stability. Their core structure is to form a dense tantalum oxide (Ta2O5) dielectric layer on the surface of tantalum metal through anodization, and then form a capacitor structure through cathode materials such as graphite / silver paste. In the existing capacitor processing technology, the anodization process has the following problems: 1. The thickness of the dielectric layer is uneven. Due to the uneven concentration and temperature distribution of the electrolyte, local defects in the oxide layer are caused; 2. There are micropores and cracks in the tantalum block. High-voltage rapid oxidation is likely to cause microcracks in the dielectric layer, reducing the breakdown voltage performance.

[0003] The patent application document with the publication number JP2000331884A discloses a manufacturing method of a tantalum solid electrolytic capacitor capable of simultaneously forming a dielectric oxide film layer and a solid electrolyte layer through a simple method. An anode body containing a sintered layer of tantalum powder is anodized in a solution containing a conductive polymer monomer and an additive, thereby simultaneously forming a dielectric oxide film layer and a solid electrolyte layer. This manufacturing method can obtain an electrode body, and can significantly improve productivity and stabilize the characteristics. The anode body prepared from the tantalum powder used in this method is anodized in a phosphoric acid solution, but it does not solve the technical problems of uneven thickness of the dielectric layer and the existence of micropores and cracks in the tantalum block during anodization. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides an anodization method for improving the uniformity of the dielectric layer of a capacitor.

[0005] The present invention is achieved through the following technical solutions.

[0006] An anodization method for improving the uniformity of the dielectric layer of a capacitor provided by the present invention includes the following steps:

[0007] S1: Place the tantalum block in the electrolytic cell after pretreatment;

[0008] S2: Add electrolyte to the electrolytic cell and perform oscillating circulation through an oscillator;

[0009] S3: Perform a pre-oxidation process on the oscillated tantalum block;

[0010] S4: Perform a main oxidation process on the pre-oxidized tantalum block;

[0011] S5: Perform a stabilization process on the main-oxidized tantalum block;

[0012] S6: Heat-treat the stabilized tantalum block;

[0013] S7: Perform constant voltage treatment on the heat-treated tantalum block, take out the tantalum block after the treatment, and perform cleaning and drying to complete anodization.

[0014] Preferably, in step S2, an ultrasonic oscillator is used to circulate for 5 - 20 minutes at a frequency of 25 ± 5 kHz.

[0015] Preferably, the electrolyte in step S2 includes one or more of phosphoric acid, polyethylene glycol, and sodium dodecyl sulfate.

[0016] Preferably, the electrolyte in step S2 includes 0.1 - 0.4 wt% phosphoric acid, 0.01 - 0.09 wt% polyethylene glycol, and 0.005 - 0.02 wt% sodium dodecyl sulfate.

[0017] Preferably, the pre-oxidation process steps include raising the voltage to 10 - 30 V at a rate of 5 V / min after the tantalum block is energized, and maintaining a constant voltage for 5 - 20 minutes.

[0018] Preferably, the main oxidation process steps include raising the voltage to 50 - 100 V at a rate of 2.5 V / min after the tantalum block is energized, and maintaining a constant voltage for 5 - 20 minutes.

[0019] Preferably, the stabilization process includes putting the tantalum block into the electrolyte used in step S2, adding a stabilizer to the electrolyte, and using an ultrasonic oscillator to circulate for 10 min at a frequency of 25 ± 5 kHz, and maintaining a constant voltage for 60 min at 80 V.

[0020] Preferably, the stabilizer is 0.01 - 0.2% ammonium dihydrogen phosphate.

[0021] Preferably, the heat treatment step includes holding the tantalum block at 340 - 450 °C for 20 - 45 minutes, and then taking it out and air-cooling.

[0022] Preferably, the constant voltage treatment step includes putting the heat-treated tantalum block into the electrolyte used in step S2, adding a 0.01 - 0.2% ammonium dihydrogen phosphate solution to the electrolyte, performing constant voltage treatment at 70 - 90 V for 60 minutes, taking out the tantalum block after the treatment, cleaning it with deionized water, and drying it at 120 °C to complete anodization.

[0023] The beneficial effects of the present invention are as follows:

[0024] By adding an ultrasonic oscillator in the electrolytic cell, the present invention can eliminate the electrolyte concentration gradient and improve the uniformity of the dielectric layer thickness. By adding ammonium dihydrogen phosphate, the micropores are filled and the surface of the tantalum block is passivated, improving the performance of the capacitor prepared therefrom. Through the staged dynamic oxidation method and the composite electrolyte formula, the uniformity and reliability of the tantalum oxide dielectric layer are significantly improved, which is applicable to the industrial production of high-reliability tantalum capacitors. Detailed implementation manners

[0025] The technical solution of the present invention will be further described below, but the scope of protection claimed is not limited thereto.

[0026] Example 1:

[0027] An anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor, comprising the following steps:

[0028] S1: Take 1000 pieces of 25V 47μF-E tantalum blocks, pre-treat them and place them in an electrolytic cell. An ultrasonic oscillator is added in the electrolytic cell. The pre-treatment step is to soak the tantalum blocks in a 5% hydrogen peroxide solution for 15 minutes, then boil and wash them with deionized water at 85°C for 30 minutes, and then dry them at 120°C;

[0029] S2: Add electrolyte to the electrolytic cell, and circulate for 5 minutes at a frequency of 20 kHz by using the ultrasonic oscillator to eliminate the electrolyte concentration gradient;

[0030] S3: Perform a pre-oxidation process on the oscillated tantalum blocks: After the tantalum blocks are energized, raise the voltage to 10V at a rate of 5V / min, keep the voltage constant for 5 minutes, and form a dense bottom layer of 5-20 nm on the surface of the tantalum blocks;

[0031] S4: Perform a main oxidation process on the pre-oxidized tantalum blocks: After the tantalum blocks are energized, raise the voltage to 50V at a rate of 2.5V / min, and keep the voltage constant for 5 minutes;

[0032] S5: Perform a stabilization process on the main-oxidized tantalum blocks: Put the tantalum blocks into the electrolyte used in step S2, add 0.01% ammonium dihydrogen phosphate to the electrolyte, and circulate for 10 min at a frequency of 20 kHz by using the ultrasonic oscillator, and keep the voltage constant at 80V for 60 min to fill the micropores and passivate the surface of the tantalum blocks;

[0033] S6: Perform heat treatment on the stabilized tantalum blocks: Keep the tantalum blocks at 340°C for 20 minutes, and then take them out and air-cool;

[0034] S7: Perform constant voltage treatment on the heat-treated tantalum blocks: Put the heat-treated tantalum blocks into the electrolyte used in step S2, add a 0.01% ammonium dihydrogen phosphate solution to the electrolyte, or the electrolyte with ammonium dihydrogen phosphate solution added in step S5 can also be used. Perform constant voltage treatment at 70V for 60 minutes. After the treatment, take out the tantalum blocks, wash them with deionized water, and dry them at 120°C to complete anodization.

[0035] The electrolyte in step S2 includes 0.1 wt% phosphoric acid, 0.01 wt% polyethylene glycol (molecular weight 2000), and 0.005 wt% sodium dodecyl sulfate. Polyethylene glycol and sodium dodecyl sulfate are added to inhibit crystallization.

[0036] Example 2:

[0037] An anodization method for improving the uniformity of the dielectric layer of a capacitor, comprising the following steps:

[0038] S1: Take 1000 pieces of 25V 47μF-E tantalum blocks, pre-treat them and place them in an electrolytic cell. An ultrasonic oscillator is added to the electrolytic cell. The pre-treatment steps are to soak the tantalum blocks in a 5% hydrogen peroxide solution for 15 minutes, then boil and wash them with deionized water at 85°C for 30 minutes, and then dry them at 120°C;

[0039] S2: Add electrolyte to the electrolytic cell, and circulate for 5 minutes at a frequency of 30 kHz using the ultrasonic oscillator to eliminate the electrolyte concentration gradient;

[0040] S3: Perform a pre-oxidation process on the oscillated tantalum blocks: After the tantalum blocks are energized, raise the voltage to 30V at a rate of 5V / min and keep the voltage constant for 20 minutes to form a 20nm dense bottom layer on the surface of the tantalum blocks;

[0041] S4: Perform a main oxidation process on the pre-oxidized tantalum blocks: After the tantalum blocks are energized, raise the voltage to 100V at a rate of 2.5V / min and keep the voltage constant for 20 minutes;

[0042] S5: Perform a stabilization process on the main-oxidized tantalum blocks: Put the tantalum blocks into the electrolyte used in step S2, add 0.2% ammonium dihydrogen phosphate to the electrolyte and use the ultrasonic oscillator to circulate for 10 min at a frequency of 30 kHz, and keep the voltage constant at 80V for 60 min to fill the micropores and passivate the surface of the tantalum blocks;

[0043] S6: Perform heat treatment on the stabilized tantalum blocks: Keep the tantalum blocks at 450°C for 45 minutes, and then take them out and air-cool;

[0044] S7: Perform constant voltage treatment on the heat-treated tantalum block: Place the heat-treated tantalum block into the electrolyte used in step S2, add a 0.2% ammonium dihydrogen phosphate solution to the electrolyte, or the electrolyte with ammonium dihydrogen phosphate solution added in step S5 can also be used. Perform constant voltage treatment at 90V for 60 minutes. After the treatment, take out the tantalum block, wash it with deionized water, and dry it at 120°C to complete anodic oxidation.

[0045] The electrolyte in step S2 includes 0.4wt% phosphoric acid, 0.09wt% polyethylene glycol (molecular weight 2000), and 0.02wt% sodium dodecyl sulfate. Adding polyethylene glycol and sodium dodecyl sulfate is used to inhibit crystallization.

[0046] Example 3:

[0047] An anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor, comprising the following steps:

[0048] S1: Take 1000 pieces of 25V 47μF-E tantalum blocks, pre-treat them and place them in an electrolytic cell. An ultrasonic oscillator is added to the electrolytic cell. The pre-treatment steps are to soak the tantalum blocks in a 5% hydrogen peroxide solution for 15 minutes, then boil and wash them with deionized water at 85°C for 30 minutes, and then dry them at 120°C;

[0049] S2: Add electrolyte to the electrolytic cell, and circulate for 10 minutes at a frequency of 25kHz by using the ultrasonic oscillator to eliminate the electrolyte concentration gradient;

[0050] S3: Perform a pre-oxidation process on the oscillated tantalum blocks: After the tantalum blocks are powered on, raise the voltage to 20V at a rate of 5V / min and keep the voltage constant for 10 minutes to form a dense bottom layer of 5 - 20nm on the surface of the tantalum blocks;

[0051] S4: Perform a main oxidation process on the pre-oxidized tantalum blocks: After the tantalum blocks are powered on, raise the voltage to 80V at a rate of 2.5V / min and keep the voltage constant for 10 minutes;

[0052] S5: Perform a stabilization process on the main-oxidized tantalum blocks: Place the tantalum blocks into the electrolyte used in step S2, add 0.1% ammonium dihydrogen phosphate to the electrolyte and use the ultrasonic oscillator to circulate for 10 min at a frequency of 25kHz, keep the voltage constant at 80V for 60 min to fill the micropores and passivate the surface of the tantalum blocks;

[0053] S6: Perform heat treatment on the stabilized tantalum blocks: Keep the tantalum blocks at 380°C for 30 minutes, then take them out and air-cool;

[0054] S7: Perform constant voltage treatment on the heat-treated tantalum blocks: Put the heat-treated tantalum blocks into the electrolyte used in step S2, add a 0.1% ammonium dihydrogen phosphate solution to the electrolyte, or the electrolyte with ammonium dihydrogen phosphate solution added in step S5 can also be used. Perform constant voltage treatment at 80V for 60 minutes. After the treatment, take out the tantalum blocks, wash them with deionized water, and dry them at 120°C to complete anodic oxidation.

[0055] The electrolyte in step S2 includes 0.2 wt% phosphoric acid, 0.05 wt% polyethylene glycol (molecular weight 2000), and 0.01 wt% sodium dodecyl sulfate. Polyethylene glycol and sodium dodecyl sulfate are added to inhibit crystallization.

[0056] Comparative Example 1:

[0057] The anodic oxidation method of the existing capacitor includes the following steps:

[0058] S1: Take 1000 pieces of 25V 47μF - E tantalum blocks, pre-treat them and place them in an electrolytic cell. The pre-treatment steps are to soak the tantalum blocks in a 5% hydrogen peroxide solution for 15 minutes, then boil and wash them with deionized water at 85°C for 30 minutes, and then dry them at 120°C;

[0059] S2: Add an electrolyte containing 0.2 wt% phosphoric acid and 0.05 wt% polyethylene glycol to the electrolytic cell, and circulate for 10 min at a frequency of 25 kHz;

[0060] S3: Main oxidation process: After the tantalum blocks are energized, raise the voltage to 80V at a rate of 2V / min and keep the voltage constant for 120 minutes;

[0061] S4: Heat treatment: Keep the tantalum blocks at 360°C for 30 min, and then air-cool;

[0062] S5: Constant voltage treatment: Put the tantalum blocks into the solution used in step S2, and perform constant voltage at 80V for 60 min;

[0063] S6: Take out the tantalum blocks, wash them with deionized water, and dry them at 120°C to complete anodic oxidation.

[0064] Randomly select 10 tantalum blocks processed by the methods of Examples 1 - 3 and Comparative Example 1 respectively and process them into finished capacitors, and test the leakage current and breakdown voltage of the capacitors. The comparison is shown in Table 1 and Table 2.

[0065] Table 1 Leakage Current Detection Table

[0066]

[0067] Table 2 Breakdown Voltage Detection Table

[0068]

[0069] As can be seen from Tables 1 and 2, the leakage current of the tantalum blocks prepared by using the method of the present invention is reduced by more than 60%, and the breakdown voltage is increased by about 30%.

[0070] 188 tantalum blocks processed by the methods of Examples 1-3 and Comparative Example 1 were randomly selected and processed into finished capacitors, and then the above capacitors were aged at 85 °C for 1000 hours. None of the capacitors in Examples 1-3 failed, while 8 capacitors in Comparative Example 1 failed. Thus, it can be seen that the present invention can improve the reliability of tantalum capacitors.

Claims

1. An anodization method for improving the uniformity of the dielectric layer of a capacitor, characterized in that, It includes the following steps: S1: Place the tantalum block in the electrolytic cell after pretreatment; S2: Add electrolyte to the electrolytic cell and perform oscillating circulation through an oscillator; S3: Perform a pre-oxidation process on the oscillated tantalum block; S4: Perform a main oxidation process on the pre-oxidized tantalum block; S5: Perform a stabilization process on the main-oxidized tantalum block; S6: Perform heat treatment on the stabilized tantalum block; S7: Perform constant voltage treatment on the heat-treated tantalum block. After the treatment is completed, take out the tantalum block, clean and dry it to complete anodic oxidation.

2. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, wherein: In step S2, an ultrasonic oscillator is used to circulate for 5 - 20 minutes at a frequency of 25 ± 5 kHz.

3. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: In step S2, the electrolyte includes one or more of phosphoric acid, polyethylene glycol, and sodium dodecyl sulfate.

4. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 3, characterized in that: In step S2, the electrolyte includes 0.1 - 0.4 wt% phosphoric acid, 0.01 - 0.09 wt% polyethylene glycol, and 0.005 - 0.02 wt% sodium dodecyl sulfate.

5. The anodization method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: The pre-oxidation process steps include raising the voltage to 10 - 30 V at a rate of 5 V / min after the tantalum block is electrified, and maintaining a constant voltage for 5 - 20 minutes.

6. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: The main oxidation process steps include raising the voltage to 50 - 100 V at a rate of 2.5 V / min after the tantalum block is electrified, and maintaining a constant voltage for 5 - 20 minutes.

7. An anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: The stabilization process includes putting the tantalum block into the electrolyte used in step S2, adding a stabilizer to the electrolyte and using an ultrasonic oscillator to circulate for 10 min at a frequency of 25 ± 5 kHz, and maintaining a constant voltage of 80 V for 60 min.

8. The anodization method for improving the uniformity of the dielectric layer of a capacitor according to claim 7, wherein: The stabilizer is 0.01 - 0.2% ammonium dihydrogen phosphate.

9. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: The heat treatment steps include maintaining the tantalum block at 340 - 450 °C for 20 - 45 minutes, and then taking it out and air-cooling.

10. The anodic oxidation method for improving the uniformity of the dielectric layer of a capacitor according to claim 1, characterized in that: The constant voltage treatment steps include putting the heat-treated tantalum block into the electrolyte used in step S2, adding a 0.01 - 0.2% ammonium dihydrogen phosphate solution to the electrolyte, performing constant voltage treatment with a voltage of 70 - 90 V for 60 minutes. After the treatment is completed, take out the tantalum block, clean it with deionized water, and dry it at 120 °C to complete anodic oxidation.

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