A method for manufacturing sintered tantalum blocks for tantalum capacitors

Abstract

This invention belongs to the field of tantalum capacitor manufacturing technology, specifically relating to a method for manufacturing sintered tantalum blocks for tantalum capacitors. The method involves placing the tantalum block in a sintering furnace, pre-firing and sintering under vacuum conditions, then lowering the temperature to 100-1000°C. After vacuuming, nitrogen is introduced into the furnace for heat treatment. Once the furnace temperature drops to ≤100°C, oxygen is introduced for surface passivation. This method is characterized by simple and easy-to-control process operation, making it suitable for industrial production. It also effectively reduces the oxygen content of the sintered tantalum block, inhibits oxygen migration from the dielectric oxide film to the tantalum substrate after formation, reduces leakage current in the tantalum capacitor, and improves the electrical performance stability of the tantalum capacitor.

Description

Technical Field

[0001] This invention belongs to the field of tantalum capacitor manufacturing technology, specifically relating to a method for manufacturing sintered tantalum blocks for tantalum capacitors. Background Technology

[0002] The tantalum anode block is the core component of a tantalum capacitor, and its manufacturing process generally includes powder mixing, pressing, binder removal, and sintering. As tantalum electrolytic capacitors develop towards miniaturization, thinning, and larger capacitance, the specific capacitance of the tantalum powder used to make the anode block is increasing. With increasing specific capacitance, the tantalum powder particle size becomes smaller, the specific surface area becomes larger, and the surface activity becomes higher, making it more prone to oxidation with oxygen. Ultrafine tantalum powder exhibits slow oxidation even at room temperature. The reaction between tantalum powder and oxygen forms an extremely thin tantalum oxide film, covering the surface of the tantalum powder and inhibiting further oxidation of the tantalum matrix—a process known as passivation. When the temperature rises, the reaction between tantalum and oxygen intensifies, and the heat released further accelerates the oxidation reaction, creating a vicious cycle that ultimately leads to the combustion of the tantalum powder, making production impossible.

[0003] When the oxygen content of the tantalum block is high after sintering, low-valence tantalum oxides will form on the surface of the tantalum powder. When forming the tantalum pentoxide dielectric oxide film in a tantalum capacitor, these low-valence tantalum oxides will induce crystallization of the tantalum pentoxide dielectric oxide film, increasing leakage current. Therefore, the oxygen content of the tantalum powder must be controlled within a certain range. Secondly, there is no stable thermodynamic equilibrium between the tantalum pentoxide dielectric oxide film and the tantalum substrate. Oxygen in the tantalum pentoxide dielectric oxide film tends to migrate into the tantalum substrate, entering the interatomic positions of tantalum atoms. This leads to oxygen deficiency in the tantalum pentoxide dielectric oxide film, forming oxygen vacancies and creating new conductive mechanisms, thus reducing the insulation performance of the tantalum pentoxide dielectric oxide film. With prolonged storage time, oxygen migration in the tantalum pentoxide dielectric oxide film increases, reducing its voltage withstand capability and lowering the reliability of the tantalum capacitor.

[0004] To reduce oxygen absorption by tantalum powder, prevent vigorous oxidation reactions, and facilitate storage, transportation, and use, passivation treatment is performed during tantalum powder manufacturing. This process generates a protective oxide film on the tantalum powder surface, maintaining its relative stability. The mixing, forming, and binder removal stages during the fabrication of the tantalum anode block for tantalum capacitors do not significantly alter the surface activity or chemical composition of the tantalum powder, keeping it relatively stable. However, the sintering process disrupts this equilibrium. Under high temperatures, oxygen migrates from the surface into the tantalum matrix or escapes from the surface under vacuum, reducing surface oxygen content, increasing purity, and enhancing activity. When the unpassivated tantalum block is exposed to air after sintering, the abundant oxygen in the air immediately triggers a vigorous and uncontrolled oxidation reaction. Therefore, passivation treatment is essential before the anode block is removed from the furnace. Traditional passivation methods involve slowly introducing air or oxygen-containing gas into the furnace, causing tantalum to slowly oxidize with a small amount of oxygen, forming a very thin oxide film. This film isolates the tantalum substrate from external oxygen, thus slowing down or reducing the oxidation reaction. The surface of the tantalum powder becomes less reactive, achieving passivation. However, because the tantalum block is highly reactive after sintering and has a strong oxygen absorption capacity, it is difficult to control the oxidation reaction rate. Even after passivation, the oxygen content remains high, especially when the specific capacitance of the tantalum powder reaches ≥50000 μF·V / g, the rate of increase in oxygen content becomes greater, which is detrimental to the control of leakage current and the improvement of stability of tantalum capacitors.

[0005] Patent application number 202110348016.1 discloses a method for preparing a tantalum anode block for a low-oxygen-content solid electrolyte tantalum capacitor. Under the condition that the tantalum anode core effectively removes the binder, the oxygen in the tantalum anode block is brought close to or equal to its saturation solubility by lowering the pre-sintering temperature. The oxygen mainly dissolves in the metallic tantalum in a solid solution state, resulting in fewer surface oxides and sub-oxide layers. Under high-temperature conditions, the saturated oxygen reacts with impurities such as C and Si in the tantalum anode block, purifying the tantalum anode block, reducing the leakage current value after formation, and further improving the precision and quality of the solid electrolyte tantalum capacitor. Although this method purifies the tantalum powder and reduces the oxygen content during sintering, the surface activity also increases. After exiting the furnace, the reaction rate with oxygen in the air increases, causing the oxygen content to rise again.

[0006] Patent application number 202111342291.9 discloses a sintering method for a tantalum capacitor anode block, including the following steps: (1) loading the anode block to be sintered into a sintering furnace, making the vacuum degree inside the furnace ≤5×10 -3 pa; (2) First stage sintering; (3) Second stage sintering; (4) At the second stage sintering temperature, continuously fill the furnace with a reducing atmosphere for a period of time; (5) After the reducing atmosphere sintering is completed, make the vacuum degree in the furnace ≤2×10 -2pa, heat to the sintering temperature at the third heating rate and keep the temperature constant; (6) when the furnace temperature is reduced to below 50°C, a mixture of oxygen and inert gas is introduced into the furnace in multiple batches; (7) when the furnace temperature drops to room temperature, a cleaning and drying operation is performed; this method is to add magnesium vapor, aluminum vapor or calcium vapor, so that oxygen reacts with it to generate alkaline oxides, which are eventually discharged with inert gas, thereby reducing the oxygen content. However, magnesium, aluminum and calcium are solid metals, and special equipment is required to form vapor, which is costly and complicated to operate. Secondly, magnesium, aluminum and calcium atoms are large, and the vapor formed is difficult to enter the interior of the tantalum block, resulting in inconsistent reduction reactions on the surface and inside of the tantalum block. After the reaction, the oxygen content inside and on the surface of the tantalum block is inconsistent. Thirdly, the alkaline oxides generated by the reaction of magnesium, aluminum and calcium have large molecular weights, are difficult to discharge, and are easily deposited on the inner wall of the sintering furnace and in the vacuum pipe, which contaminates the sintering furnace and increases the difficulty of sintering furnace maintenance. In addition, magnesium, aluminum and calcium will leave some residue inside the tantalum block after the reaction, which needs to be removed by acid washing or other methods. However, it cannot be guaranteed that the residue will be 100% removed, which increases the risk of the tantalum block being contaminated by metallic impurities, leading to an increase in leakage current of the tantalum capacitor.

[0007] Patent application number 201710354394.4 discloses a method for complete passivation of tantalum powder, comprising the following steps: 1) transferring heat-treated and passivated tantalum powder, along with a crucible containing the tantalum powder, to a sealable tantalum powder passivation device; 2) evacuating the tantalum powder passivation device to a pressure of 10-100 Pa, and then filling it with inert gas to a pressure of approximately 0.1 kPa; 3) introducing oxygen-containing gas, controlling the oxygen concentration to be 1 vol% to 21 vol%, and the flow rate of the oxygen-containing gas to be 1 L / s to 3 L / s. At a speed of 0 liters / second, the tantalum powder that has formed clumps in the crucible is peeled off and crushed. The temperature of the tantalum powder is measured continuously, and the tantalum powder is dispersed to passivate it while the temperature rise is below 15°C. 4) The oxygen concentration is controlled at 20 vol% to 25 vol%, and the flow rate of the oxygen-containing gas is 0.1 liters / second to 1 liter / second. The crushed tantalum powder is sieved, and the dispersed tantalum powder is fully passivated while the temperature rise is below 15°C. The inert gas is one or more of nitrogen, argon, neon, and helium. This scheme discloses a method for introducing inert gas into the passivation process. However, the technology of this scheme belongs to the field of tantalum powder production and manufacturing, the object is tantalum powder, the technical link is the passivation stage, and the role of inert gas is to serve as a protective atmosphere or dilute oxygen, promote gas flow in the passivation device, and improve the uniformity of passivation. During the passivation process, the introduced inert gas does not chemically react with the tantalum powder and does not change the structure and composition of the tantalum matrix. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention proposes a method for manufacturing sintered tantalum blocks for tantalum capacitors.

[0009] Specifically, this is achieved through the following technical solutions:

[0010] A method for manufacturing sintered tantalum blocks for tantalum capacitors involves placing the tantalum blocks in a sintering furnace, pre-firing and sintering under vacuum conditions, cooling the furnace to 100-1000°C, stopping the vacuuming, and then filling the furnace with nitrogen for heat treatment. After the furnace temperature drops to ≤100°C, oxygen is then introduced for surface passivation.

[0011] A method for manufacturing a sintered tantalum block for a tantalum capacitor includes the following steps:

[0012] (1) Heating: After placing the tantalum block into the sintering furnace, a vacuum is drawn into the furnace, with the vacuum degree ≤9×10⁻⁶. -3 After Pa, start the heater to heat the tantalum block at a rate of 1–50 °C / min until it reaches 200–800 °C. Then stop heating and hold the temperature for 10–360 min. During the holding period, the vacuum degree inside the furnace should be ≤9 × 10⁻⁶. -3 Pa; Continue heating at a rate of 1–50 °C / min to the sintering temperature of the tantalum block, with a vacuum degree ≤9 × 10⁻⁶ during the heating process. -3 pa;

[0013] (2) Temperature control: Maintain the temperature at the sintering temperature of the tantalum block for 10–50 min, and the vacuum degree inside the furnace during the temperature control process should be ≤9×10⁻⁶. -3 pa;

[0014] (3) Cooling: Reduce the furnace temperature at a rate of 1–500℃ / min, and maintain a vacuum level of ≤9×10⁻⁶ during the cooling process. - 3 pa;

[0015] (4) Nitrogen heat treatment: When the temperature inside the furnace drops to 100℃~1000℃, stop the vacuuming inside the furnace, maintain the temperature for 5s~360min, and during the constant temperature process, fill the furnace with nitrogen until the nitrogen volume fraction of the furnace body is 0.1%~100%; after the constant temperature is completed, vacuum the furnace, and the furnace pressure is 0 to -100KPa; repeat this step 1~30 times;

[0016] (5) Passivation: When the temperature inside the furnace drops to ≤100℃, evacuate the furnace to make the pressure inside the furnace 0 to -100KPa; fill the furnace with oxygen until the oxygen volume fraction in the furnace body is 0.1% to 100%, and keep it constant for 5s to 360min; repeat this step 1 to 30 times; the oxygen-containing gas is one of oxygen or a mixture of oxygen and other gases;

[0017] (6) Unloading: Introduce air or a mixture of air and other gases into the furnace to make the furnace pressure ≥0 kPa, maintain for 5 s to 120 min, and then remove the tantalum block from the sintering furnace.

[0018] The nitrogen gas can also be replaced with a mixture of nitrogen gas and other gases.

[0019] The oxygen may also be replaced by a mixture of oxygen and other gases, such as air.

[0020] Beneficial effects:

[0021] The method of this invention is characterized by its simple and easy-to-control process, making it suitable for industrial production. It can also effectively reduce the oxygen content of sintered tantalum blocks, inhibit oxygen migration from the dielectric oxide film to the tantalum matrix after formation, reduce leakage current in tantalum capacitors, and improve the electrical performance stability of tantalum capacitors.

[0022] This invention first removes most of the adsorbed oxygen and other low-temperature impurities by heating, preventing the formation of tantalum compounds under high-temperature, high-vacuum conditions that would remain in the tantalum block. Second, nitrogen heat treatment is performed before passivation, causing nitrogen atoms to occupy oxygen atom positions, reducing the probability of oxygen migration into the tantalum matrix during passivation. This reduces the oxygen content of the tantalum block, improves the quality of the dielectric oxide film after formation, and reduces the leakage current of the tantalum capacitor. Finally, a certain nitrogen content in the tantalum matrix inhibits oxygen migration from the tantalum pentoxide dielectric oxide film into the tantalum matrix, improving the stability of the dielectric oxide film and thus enhancing the electrical performance stability of the tantalum capacitor.

[0023] This invention effectively reduces the oxygen content of tantalum powder by controlling the pre-firing process, and also effectively controls the oxidation reaction after exiting the furnace, thereby achieving the goal of reducing the oxygen content of tantalum blocks.

[0024] This invention incorporates nitrogen, a beneficial substance, before passivation. Nitrogen is added in gaseous form, allowing for easy diffusion and uniform distribution within the tantalum block. This nitrogen doping within the tantalum matrix alters its structure and composition, making it difficult for oxygen to oxidize during passivation and reducing the oxygen content of the tantalum block after passivation. Furthermore, the introduced nitrogen gas does not cause any contamination to the equipment; excess nitrogen can be directly discharged through vacuuming. The operation is simple and does not introduce other impurities, eliminating the need for additional processing steps and further reducing the risk of secondary contamination of the tantalum block. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below. However, the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0026] Example 1

[0027] A method for manufacturing a sintered tantalum block for a tantalum capacitor involves pressing tantalum powder with a CV value of 50000 μF·V / g into a tantalum block weighing 252 mg and measuring 2.7 mm x 3.4 mm x 5.0 mm. The prepared tantalum capacitor has a specification of 10V 330 μF. The method includes removing the internal binder of the tantalum block before sintering, and includes the following steps:

[0028] (1) Heating: After placing the tantalum block into the sintering furnace, a vacuum is drawn into the furnace, with the vacuum degree ≤9×10⁻⁶. -3 After Pa, the heater is started to heat the tantalum block at a rate of 30℃ / min until it reaches 500℃. Heating is then stopped, and the temperature is held constant for 30 minutes. During this holding period, the vacuum level inside the furnace is ≤9×10⁻⁶. -3 Pa; Continue heating at a rate of 30℃ / min to the sintering temperature of the tantalum block, with a vacuum degree ≤9×10 during the heating process. -3 pa;

[0029] (2) Temperature control: Maintain the temperature at the sintering temperature of the tantalum block for 30 minutes. During the temperature control process, the vacuum degree in the furnace should be ≤9×10⁻⁶. -3 pa;

[0030] (3) Cooling: Reduce the furnace temperature at a rate of 50℃ / min, and maintain a vacuum level of ≤9×10⁻⁶ during the cooling process. -3 pa;

[0031] (4) Nitrogen heat treatment: When the temperature inside the furnace drops to 400℃, stop the vacuuming inside the furnace, maintain the temperature for 30 minutes, and during the constant temperature process, fill the furnace with high-purity nitrogen until the nitrogen content in the furnace body is 0.5% by volume; after the constant temperature is completed, vacuum the furnace and the furnace pressure is -90KPa; repeat this step once; the purity of the high-purity nitrogen is greater than 99%;

[0032] (5) Passivation: When the temperature inside the furnace drops to 50℃, evacuate the furnace to make the pressure inside the furnace ≤ -90KPa; fill the furnace with air until the air volume fraction inside the furnace is 40%, and keep it constant for 10 minutes; repeat this step 3 times.

[0033] (6) Unloading: Introduce air into the furnace to make the pressure inside the furnace 0 kPa, maintain for 10 minutes, and then remove the tantalum block from the sintering furnace.

[0034] Example 2

[0035] A method for manufacturing a sintered tantalum block for a tantalum capacitor involves pressing tantalum powder with a CV value of 70000 μF·V / g into a tantalum block weighing 135 mg and measuring 1.6 mm x 3.4 mm x 4.6 mm. The prepared tantalum capacitor has a specification of 10V 220 μF. The method includes removing the internal binder of the tantalum block before sintering, and comprises the following steps:

[0036] (1) Heating: After placing the tantalum block into the sintering furnace, a vacuum is drawn into the furnace, with the vacuum degree ≤ 6×10⁻⁶. -3 After Pa, the heater is started to heat the tantalum block at a rate of 20℃ / min until it reaches 300℃. Heating is then stopped, and the temperature is held constant for 40 minutes. During this holding period, the vacuum level inside the furnace is ≤9×10⁻⁶. -3 Pa; Continue heating at a rate of 20℃ / min to the sintering temperature of the tantalum block, with a vacuum degree ≤9×10 during the heating process. -3 pa;

[0037] (2) Temperature control: Maintain the temperature at the sintering temperature of the tantalum block for 20 minutes. During the temperature control process, the vacuum degree in the furnace should be ≤9×10⁻⁶. -3 pa; constant temperature:

[0038] (3) Cooling: Reduce the furnace temperature at a rate of 40℃ / min, and maintain a vacuum level of ≤9×10⁻⁶ during the cooling process. -3 pa;;

[0039] (4) Nitrogen heat treatment: When the temperature inside the furnace drops to 300℃, stop the vacuuming inside the furnace, maintain the temperature for 20 minutes, and during the constant temperature process, fill the furnace with high-purity nitrogen until the nitrogen content in the furnace body is 1% by volume; after the constant temperature is completed, vacuum the furnace, and the pressure inside the furnace is ≤-90KPa; repeat this step 3 times; the purity of the high-purity nitrogen is greater than 99.9%;

[0040] (5) Passivation: When the temperature inside the furnace drops to 40℃, evacuate the furnace to make the pressure inside the furnace ≤ -90KPa; fill the furnace with air until the air volume fraction inside the furnace is 30%, and keep it constant for 5 minutes; repeat this step 5 times.

[0041] (6) Unloading: Introduce air into the furnace to make the pressure inside the furnace 0 kPa, maintain for 30 minutes, and then remove the tantalum block from the sintering furnace.

[0042] Example 3

[0043] A method for manufacturing a sintered tantalum block for a tantalum capacitor involves pressing tantalum powder with a CV value of 100,000 μF·V / g into a tantalum block weighing 59 mg and measuring 1.3 mm x 2.5 mm x 3.6 mm. The prepared tantalum capacitor has a specification of 10V 150 μF. The method includes removing the internal binder of the tantalum block before sintering, and comprises the following steps:

[0044] (1) Heating: After placing the tantalum block into the sintering furnace, a vacuum is drawn into the furnace, with the vacuum degree ≤ 4×10⁻⁶. -3 After Pa, the heater is started to heat the tantalum block at a rate of 10℃ / min until it reaches 200℃. Heating is then stopped, and the temperature is held constant for 60 minutes. During this holding period, the vacuum level inside the furnace is ≤9×10⁻⁶. -3Pa; Continue heating at a rate of 10℃ / min to the sintering temperature of the tantalum block, with a vacuum degree ≤9×10 during the heating process. -3 pa;

[0045] (2) Temperature control: Maintain the temperature at the sintering temperature of the tantalum block for 20 minutes. During the temperature control process, the vacuum degree in the furnace should be ≤9×10⁻⁶. -3 pa;

[0046] (3) Cooling: Reduce the furnace temperature at a rate of 30℃ / min, and maintain a vacuum level of ≤9×10⁻⁶ during the cooling process. -3 pa;

[0047] (4) Nitrogen heat treatment: When the temperature inside the furnace drops to 200℃, stop the vacuuming inside the furnace, maintain the temperature for 1 minute, and during the constant temperature process, fill the furnace with high-purity nitrogen until the nitrogen in the furnace accounts for 2% of the volume of the furnace body; after the constant temperature is completed, vacuum the furnace and the furnace pressure is -90KPa; repeat this step 5 times; the purity of the high-purity nitrogen is greater than 99.99%;

[0048] (5) Passivation: When the temperature inside the furnace drops to 30°C, evacuate the furnace to make the pressure inside the furnace -90KPa; fill the furnace with air until the air volume fraction inside the furnace is 20%, and keep it constant for 1 minute; repeat this step 7 times.

[0049] (6) Unloading: Introduce air into the furnace to make the pressure inside the furnace 0 kPa, maintain for 30 minutes, and then remove the tantalum block from the sintering furnace.

[0050] Comparative Example 1

[0051] Tantalum powder with a CV value of 50000 μF·V / g was pressed into tantalum blocks with a powder weight of 252 mg and a size of 2.7 mm x 3.4 mm x 5.0 mm. The tantalum blocks were prepared according to the design and requirements in Example 1. After removing the internal binder of the tantalum blocks, they were sintered according to the prior art. The sintering process included heating, isothermal treatment, cooling and passivation treatment.

[0052] Comparative Example 2

[0053] Tantalum powder with a CV value of 70000 μF·V / g was pressed into tantalum blocks with a powder weight of 135 mg and a size of 1.6 mm x 3.4 mm x 4.6 mm. The tantalum blocks were prepared according to the design and requirements in Example 2. After removing the internal binder of the tantalum blocks, they were sintered according to the prior art. The sintering process included heating, isothermal treatment, cooling and passivation treatment.

[0054] Comparative Example 3

[0055] Tantalum powder with a CV value of 100000 μF·V / g was pressed into tantalum blocks with a powder weight of 59 mg and a size of 1.3 mm x 2.5 mm x 3.6 mm. The tantalum blocks were prepared according to the design and requirements in Example 3. After removing the internal binder of the tantalum blocks, they were sintered according to the prior art. The sintering process included heating, isothermal treatment, cooling and passivation treatment.

[0056] The oxygen and nitrogen content of sintered tantalum blocks from Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were randomly sampled and tested. The oxygen and nitrogen content was determined using an oxygen-nitrogen-hydrogen combined analyzer. The test results are shown in Table 1.

[0057] The remaining tantalum blocks were processed under the same conditions, including forming a dielectric oxide film and coating with cathode manganese dioxide, to prepare tantalum capacitors. Thirty finished products were randomly selected and tested according to the following procedure: initial leakage current test at room temperature → aging at 85℃ with 1.2 times the rated voltage for 1000 hours → final leakage current test at room temperature. The leakage current test used a DC regulated power supply with a test voltage of 1.2 times the rated voltage and a charging time of 30 seconds. The results are shown in Table 2.

[0058] As shown in Table 1, the oxygen content of the example samples was lower than that of the comparative examples, indicating that the measures taken in the examples were effective and reduced the oxygen content of the anode tantalum block. The nitrogen content of the example samples was higher than that of the comparative examples, indicating that a certain amount of nitrogen was added to the anode tantalum block, achieving the purpose of nitrogen doping.

[0059] Table 2 shows that the initial leakage current of the embodiment at room temperature was lower than that of the comparative example, indicating that reducing the oxygen content improved the leakage current. After aging at 1.2 times the rated voltage at 85°C for 1000 hours, the leakage current of the embodiment did not change significantly, while the leakage current of the comparative example increased slightly, indicating that the dielectric oxide film of the embodiment had better stability. The leakage current of a tantalum capacitor is a macroscopic manifestation of the insulation performance of the dielectric oxide film. A small leakage current indicates good insulation performance and strong voltage withstand capability of the dielectric oxide film. Aging the tantalum capacitor at 1.2 times the rated voltage at 85°C for 1000 hours was to verify the long-term stability and reliability of the tantalum capacitor. Under the combined effect of electric field and temperature stress during the aging process, oxygen in the dielectric oxide film may migrate into the tantalum matrix, resulting in "oxygen vacancies" in the dielectric oxide film and reducing its withstand voltage performance, thus increasing the leakage current. The final leakage current test results at room temperature in Table 2 show that the leakage current of the embodiment did not increase significantly after aging, while the comparative example showed a slight increase, indicating that the dielectric oxide film of the embodiment had better stability than that of the comparative example.

[0060] Table 1 Comparison of oxygen and nitrogen content in samples

[0061]

[0062] Table 2 Comparison of Sample Leakage Current Tests

[0063] sample Tantalum capacitor specifications Preliminary Leakage Current Measurement (μA) Leakage current final measurement (μA) Example 1 10V 330μF 5.2～8.7 5.1～8.7 Comparative Example 1 10V 330μF 9.3～13.5 10.2～14.7 Example 2 10V 220μF 3.9～6.2 3.9～6.1 Comparative Example 2 10V 220μF 6.4～8.9 7.9～10.1 Example 3 10V 150μF 2.7～4.7 2.8～4.5 Comparative Example 3 10V 150μF 5.1～8.6 7.6～10.3

Claims

1. A method of manufacturing a sintered tantalum block for a tantalum capacitor, characterized by, The method comprises the following steps: (1) Heating: After the tantalum block is put into the sintering furnace, vacuum is drawn in the furnace, and the vacuum degree in the furnace is ≤ 9 × 10 -3 pa; the heater is started to heat the tantalum block, and when the temperature is raised to 200-800℃, the heating is stopped, and the temperature is kept constant for 10-360 minutes; during the constant temperature process, the vacuum degree in the furnace is ≤ 9 × 10 -3 pa; the heating is continuously carried out until the sintering temperature of the tantalum block is reached, and during the heating process, the vacuum degree is ≤ 9 × 10 -3 pa; (2) Constant temperature: keep the temperature of tantalum block sintering for 10-50 min, the vacuum degree in the furnace is less than 9*10 -3 Pa during the constant temperature process. (3) Cooling: cool down to room temperature at a rate of 1-5°C / min. (3) Cooling: reducing the temperature in the furnace, and the vacuum degree in the furnace is ≤ 9 x 10 -3 pa during the cooling process. (4) Heating: heating the furnace to the normal temperature, and the vacuum degree in the furnace is ≤ 9 x 10 <000 (4) Nitrogen heat treatment: when the temperature in the furnace is lowered to 100-1000℃, stop vacuumizing the furnace, keep the temperature constant for 5-360 minutes and fill nitrogen; after the constant temperature ends, vacuumize the furnace, the pressure in the furnace is 0 to -100 KPa; repeat the step 1-30 times; (5) Passivation: when the temperature in the furnace is lowered to ≤100℃, vacuumize the furnace, the pressure in the furnace is 0 to -100 KPa, and fill oxygen into the furnace, keep constant for 5-360 minutes; repeat the step 1-30 times; (6) Take out the furnace: fill air or a mixture of air and other gases into the furnace, so that the pressure in the furnace is ≥0 KPa, keep for 5-120 minutes, and then take out the tantalum block from the sintering furnace.

2. A method of producing a sintered tantalum block for a tantalum capacitor as defined in claim 1, wherein The heating rate is 1-50℃ / min.

3. The method of producing a sintered tantalum block for a tantalum capacitor as claimed in claim 1, wherein The cooling rate is 1-500℃ / min.

4. The method of producing a sintered tantalum block for a tantalum capacitor as claimed in claim 1, wherein The volume fraction of nitrogen in the furnace is 0.1%-100%.

5. The method of producing a sintered tantalum block for a tantalum capacitor of claim 1, wherein The volume fraction of oxygen in the furnace is 0.1%-100%.

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