JP3391364B2 - Manufacturing method of tantalum solid electrolytic capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tantalum solid electrolytic capacitor, and more particularly to a method for manufacturing a tantalum solid electrolytic capacitor which does not require a silver layer as a cathode extraction layer.

[0002]

2. Description of the Related Art FIG. 2 shows a partially enlarged sectional view of a tantalum solid electrolytic capacitor element. According to this, the capacitor element is provided with the sintered pellet 1 obtained by sintering tantalum powder, and first, the conversion coating 2 made of Ta ₂ O ₅ is formed on the surface of the sintered pellet 1.

Then, a manganese dioxide layer 3 as a solid electrolyte is formed on the chemical conversion film 2, and a carbon layer 4 as a cathode extraction layer is further formed on the manganese dioxide layer 3.
And the silver layer 5 are sequentially formed.

[0004]

The carbon layer 4 is formed by immersing the sintered pellet 1 on which the manganese dioxide layer 3 is formed in a graphite suspension aqueous solution, pulling it up and firing it at a predetermined temperature. Since the manganese dioxide layer 3 and the carbon layer 4 have different properties,
Due to the thermal stress applied at the time of soldering, peeling easily occurs at the joint surface between the manganese dioxide layer 3 and the carbon layer 4.

In particular, most of the surface of the manganese dioxide layer 3 has unevenness of 0.5 μm or less, whereas
Conventionally, the graphite has a particle size of 0.3 to 2
Since scale-like particles having a size of about μm are used, it has been difficult to evenly attach the carbon layer 4 to the surface of the manganese dioxide layer 3 also from this fact.

Further, in the dip type, which has been the main production in the past, the cathode lead is soldered to the capacitor element. However, since the manganese dioxide layer 3 and the carbon layer 4 have poor solderability, the carbon layer 4 is formed with a silver layer 5, and a cathode lead is soldered to the silver layer 5.

For the same reason, when a resin package is formed around the capacitor element by resin molding to form a chip type, the silver layer 5 is formed on the carbon layer 4 and the silver layer 5 is formed. The cathode terminal plate 7 of the lead frame is attached via a conductive adhesive material (adhesive silver) 6.

However, the silver layer 5 has a problem that, when a voltage is applied under high temperature and high humidity, electromigration occurs, and often LC (leakage current) defects and short circuits associated therewith occur.

The present invention has been made in order to solve the above-mentioned conventional drawbacks, and its purpose is to bring a carbon layer into close contact with a manganese dioxide layer at a high density and to cause a silver layer which causes electromigration. It is an object of the present invention to provide a method for manufacturing a tantalum solid electrolytic capacitor in which the cathode terminal plate of the lead frame can be directly attached to the carbon layer of the capacitor element by omitting.

[0010]

In order to achieve the above object, the present invention provides a method for forming a chemical conversion coating on tantalum sintered pellets, and then dipping in a manganese nitrate aqueous solution and thermal decomposition a plurality of times to form a chemical conversion coating on the chemical conversion coating. In forming a manganese dioxide layer as a solid electrolyte in, to mix carbon black in the manganese nitrate aqueous solution at least in the final stage, to mix the high adhesion carbon layer of carbon black in the manganese dioxide layer formed on the outermost, It is characterized in that the cathode terminal plate is attached to the high adhesion carbon layer via adhesive silver.

In this case, the carbon black content in the manganese nitrate aqueous solution in the final step is 1-10.
It is preferably wt%. If it is less than 1 wt%,
Adhesion to the manganese dioxide layer formed in the previous step is poor, and the interface resistance may increase. On the other hand,
If it exceeds 10 wt%, cracking tends to occur during drying shrinkage.

The carbon black preferably has a particle size of 0.1 to 0.5 μm. this is,
This is because it is considered that the size of the fine irregularities on the surface of the manganese dioxide layer is almost 0.5 μm or less.

Further, it is desirable to mix a water-soluble adhesive such as polyvinyl alcohol (PVA) in the range of 0.1 to 2 wt% with the manganese nitrate aqueous solution at the final stage. According to this, the adhesiveness between the manganese dioxide layer and the carbon layer is further enhanced. In addition, 0.1 wt%
If the amount is less than the above, the adhesive effect is not recognized. On the other hand, if the adhesive is added in excess of 2 wt%, the resistance value increases correspondingly, which is not preferable.

On the other hand, when the cathode terminal plate is attached to the high adhesion carbon layer via the adhesive silver, it is preferable to previously form an organic solvent-based carbon layer on the high adhesion carbon layer.

[0015]

With the above structure, since carbon black is contained in the manganese nitrate aqueous solution in the final stage of the solid electrolyte forming step, the outermost manganese dioxide layer is formed and at the same time, the carbon layer formed by carbon black is formed. It is formed. Since this carbon layer is naturally formed integrally with the manganese dioxide layer, it does not peel off due to thermal stress during soldering. In this sense, this carbon layer is called a high adhesion carbon layer.

Further, according to this, there is no need to newly form the carbon layer thereafter, and therefore the carbon layer forming step which has been conventionally prepared after the solid electrolyte forming step becomes unnecessary, and the carbon layer is adhered to the high adhesion carbon layer. Since the cathode terminal plate of the lead frame can be connected via silver, the silver layer is also unnecessary. Therefore, even if the adhesive silver is present, the electromigration phenomenon of the silver layer in the cathode extraction layer is suppressed, and a highly reliable tantalum solid electrolytic capacitor can be obtained.

[0017]

EXAMPLE FIG. 1 is a partially enlarged sectional view of a tantalum solid electrolytic capacitor manufactured according to the present invention. First, a conversion coating film 2 made of Ta ₂ O _{5 is} formed on the surface of a tantalum sintered pellet 1 as in the conventional case. Is formed.

Next, the manganese dioxide layer 3A as a solid electrolyte is formed by repeating immersion in an aqueous solution of manganese nitrate and thermal decomposition a plurality of times. Carbon black is added to the aqueous solution of manganese nitrate at the final stage. As a result, the carbon layer of the carbon black, that is, the high adhesion carbon layer 4A is naturally formed integrally in the manganese dioxide layer formed by being mixed and formed on the outermost side.

Then, the conventional carbon layer forming step and silver layer forming step are omitted, and the cathode terminal plate 7 of the lead frame is electrically and mechanically connected to the high adhesion carbon layer 4A via the adhesive silver 6. It Then, a resin exterior body is formed by resin molding around the solid electrolytic capacitor element.

In this embodiment, carbon black is mixed in the manganese nitrate aqueous solution at the final stage of solid electrolyte formation, but carbon black may be mixed before or after the previous stage. Well, in that case, it is preferable to gradually increase the amount of carbon black mixed. Further, before attaching the cathode terminal plate 7, an organic solvent-based carbon layer may be formed on the high adhesion carbon layer 4A, and the cathode terminal plate 7 may be attached to the carbon layer via the adhesive silver 6. Good.

Example 1 [Chemical conversion step] Tantalum sintered pellets of 1 mm cubic size were immersed in a 0.01 wt% phosphoric acid aqueous solution, and a DC voltage of 18 V was applied for 4 hours to form a chemical conversion film. [Solid Electrolyte Forming Step] (1) After immersing in a 10 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (2) The above (1) was repeated. (3) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 10 V was applied for 10 minutes for re-formation. (4) After immersing in a 20 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (5) After immersing in a 40 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (6) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 9 V was applied for 10 minutes for re-formation. (7) After immersing in a 70 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (8) The above (7) was repeated. (9) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 8 V was applied for 10 minutes for re-formation. (10) 2 as the final stage of the manganese dioxide formation process
An average particle size of about 0.
5 wt% of 28 μm carbon black, PVA
(Water-soluble adhesive) soaked in a mixture of 1 wt%,
The layer was pulled up and thermally decomposed at 240 ° C. to form a layer in which manganese dioxide and carbon (high adhesion carbon layer) were mixed. (11) After that, it was immersed in organic solvent-based carbon (for example, PC-403 manufactured by Fujikura Kasei Co., Ltd.), pulled up, and cured at 180 ° C. Then, the anode terminal plate of the lead frame is welded to the anode lead rod planted in the tantalum sintered pellet, and the cathode of the lead frame is bonded to the carbon layer formed in the above (11) via the adhesive silver. The terminal board was attached, and the resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rated voltage of 4V and 10 μF were produced, and the temperature was set to 85.
When a humidity resistance load test was performed for 2000 hours by applying a rated voltage of 4 V in an atmosphere of ° C and relative humidity of 85%, the number of defective products was 0 out of 100. In addition, regarding the above 100 products, the temperature is 121 ° C and the pressure is 2
When a PCT (pressure cooker test) was performed for 96 hours in an atmosphere of 026 hPa (hectopascals) and a relative humidity of 100%, the number of defective products was 0 out of 100.

<Comparative Example 1> [Chemical conversion step] The same as in Example 1 above. [Solid Electrolyte Forming Step] (1) to (9) are the same as in Example 1 above. (10) 3% by weight of carbon black having an average particle diameter of about 2.0 μm and 0.5% of methyl cellulose (water-soluble adhesive)
The first carbon layer was formed by immersing in a carbon black suspension aqueous solution with wt% and the balance being water, and then firing at 180 ° C. (11) Graphite 10 wt%, methyl cellulose 1
After dipping in a carbon black suspension aqueous solution containing wt% and the balance being water, the second carbon layer was formed by firing at 180 ° C. Then, after forming a silver layer on the second carbon layer, the anode terminal plate of the lead frame is welded to the anode lead rod implanted in the tantalum sintered pellets, and the adhesive silver is adhered on the silver layer. The cathode terminal plate of the same lead frame was attached via the above, and a resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rating of 4V and 10 μF were produced and the temperature was set to 85.
When a humidity resistance load test was performed for 2000 hours by applying a rated voltage of 4 V in an atmosphere of ° C and relative humidity of 85%, the number of defective products was 3 out of 100. In addition, regarding the above 100 products, the temperature is 121 ° C and the pressure is 2
When PCT was performed for 96 hours in an atmosphere of 026 hPa and relative humidity of 100%, the number of defective products was 10
It was 3 out of 0.

Example 2 [Chemical conversion step] Tantalum sintered pellets of 1 mm cube size were immersed in a 0.01 wt% phosphoric acid aqueous solution, and a DC voltage of 64 V was applied for 4 hours to form a chemical conversion film. [Solid Electrolyte Forming Step] (1) After immersing in a 10 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (2) The above (1) was repeated. (3) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 30 V was applied for 10 minutes for re-formation. (4) After immersing in a 20 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (5) After immersing in a 40 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (6) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 28 V was applied for 10 minutes for re-formation. (7) After immersing in a 70 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (8) The above (7) was repeated. (9) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 26 V was applied for 10 minutes for re-formation. (10) 2 as the final stage of the manganese dioxide formation process
An average particle size of about 0.
5 wt% of 28 μm carbon black, PVA
(Water-soluble adhesive) soaked in a mixture of 1 wt%,
It was pulled up and thermally decomposed at 240 ° C. to form a layer in which manganese dioxide and carbon were mixed. (11) After that, it was immersed in organic solvent-based carbon (for example, PC-403 manufactured by Fujikura Kasei Co., Ltd.), pulled up, and cured at 180 ° C. Then, the anode terminal plate of the lead frame is welded to the anode lead rod planted in the tantalum sintered pellet, and the cathode of the lead frame is bonded to the carbon layer formed in the above (11) via the adhesive silver. The terminal board was attached, and the resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rated voltage of 16V and 3.3 μF were manufactured, and the temperature was 8
When a humidity resistance load test for 2000 hours was performed by applying a rated voltage of 16 V under an atmosphere of 5 ° C. and a relative humidity of 85%, the number of defective products was 0 out of 100.
Further, when 100 pieces of the above-mentioned products were subjected to PCT for 96 hours in an atmosphere of a temperature of 121 ° C., a pressure of 2026 hPa and a relative humidity of 100%, the number of defective products was 0 out of 100.

<Comparative Example 2> [Chemical conversion step] Same as Example 2 above. [Solid Electrolyte Forming Step] From (1) to (9), the same as in Example 2 above. (10) As in Comparative Example 1 above, the average particle size is about 2.0.
After immersing in a carbon black suspension aqueous solution containing 3 wt% of carbon black of 3 μm, 0.5 wt% of methylcellulose (water-soluble adhesive), and the balance being water, baking is performed at 180 ° C. to form a first carbon layer. did. (11) 10 wt% of graphite as in Comparative Example 1
%, 1% by weight of methyl cellulose, and the remainder was water, and the resultant was immersed in a carbon black suspension aqueous solution and then baked at 180 ° C. to form a second carbon layer. And this second
After forming a silver layer on the carbon layer, the anode terminal plate of the lead frame is welded to the anode lead rod planted in the tantalum sintered pellet, and the lead is formed on the silver layer via adhesive silver. Attach the cathode terminal plate of the frame,
A resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rated voltage of 16V and 3.3 μF were manufactured, and the temperature was 8
When a humidity resistance load test for 2000 hours was performed by applying a rated voltage of 16 V in an atmosphere of 5 ° C. and a relative humidity of 85%, the number of defective products was 5 out of 100.
Moreover, when 100 pieces of the above-mentioned products were subjected to PCT for 96 hours in an atmosphere of a temperature of 121 ° C., a pressure of 2026 hPa and a relative humidity of 100%, the number of defective products was 1
The number was 2 out of 00.

Example 3 [Chemical conversion step] Tantalum sintered pellets of 1 mm cubic size were immersed in a 0.01 wt% phosphoric acid aqueous solution, and a DC voltage of 140 V was applied for 4 hours to form a chemical conversion film. [Solid Electrolyte Forming Step] (1) After immersing in a 10 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (2) The above (1) was repeated. (3) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a direct current voltage of 56 V was applied for 10 minutes for re-formation. (4) After immersing in a 20 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (5) After immersing in a 40 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (6) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a DC voltage of 54 V was applied for 10 minutes for re-formation. (7) After immersing in a 70 wt% manganese nitrate aqueous solution,
It was pyrolyzed at 240 ° C. to form manganese dioxide. (8) The above (7) was repeated. (9) It was immersed in a 0.001 wt% phosphoric acid aqueous solution, and a direct current voltage of 52 V was applied for 10 minutes for re-formation. (10) 2 as the final stage of the manganese dioxide formation process
An average particle size of about 0.
5 wt% of 28 μm carbon black, PVA
(Water-soluble adhesive) soaked in a mixture of 1 wt%,
It was pulled up and thermally decomposed at 240 ° C. to form a layer in which manganese dioxide and carbon were mixed. (11) After that, it was immersed in organic solvent-based carbon (for example, PC-403 manufactured by Fujikura Kasei Co., Ltd.), pulled up, and cured at 180 ° C. Then, the anode terminal plate of the lead frame is welded to the anode lead rod planted in the tantalum sintered pellet, and the cathode of the lead frame is bonded to the carbon layer formed in the above (11) via the adhesive silver. The terminal board was attached, and the resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rating of 35V and 1 μF were manufactured and the temperature was set to 85.
When a humidity resistance load test for 2000 hours was performed by applying a rated voltage of 35 V in an atmosphere of ° C and relative humidity of 85%, the number of defective products was 0 out of 100. In addition, regarding the above 100 products, the temperature is 121 ° C and the pressure is 2
When PCT was performed for 96 hours in an atmosphere of 026 hPa and 100% relative humidity, the number of defective products was 0 out of 100.

<Comparative Example 3> [Chemical conversion step] The same as in Example 3 above. [Solid Electrolyte Forming Step] From (1) to (9), the same as in Example 3 above. (10) As in Comparative Example 1 above, the average particle size is about 2.0.
After immersing in a carbon black suspension aqueous solution containing 3 wt% of carbon black of 3 μm, 0.5 wt% of methylcellulose (water-soluble adhesive), and the balance being water, baking is performed at 180 ° C. to form a first carbon layer. did. (11) 10 wt% of graphite as in Comparative Example 1
%, 1% by weight of methyl cellulose, and the remainder was water, and the resultant was immersed in a carbon black suspension aqueous solution and then baked at 180 ° C. to form a second carbon layer. And this second
After forming a silver layer on the carbon layer, the anode terminal plate of the lead frame is welded to the anode lead rod planted in the tantalum sintered pellet, and the lead is formed on the silver layer via adhesive silver. Attach the cathode terminal plate of the frame,
A resin exterior body was formed by resin molding.

In this way, 100 tantalum solid electrolytic capacitors having a rating of 35V and 1 μF were manufactured and the temperature was set to 85.
When a humidity resistance load test for 2000 hours was performed by applying a rated voltage of 35 V in an atmosphere of ° C and relative humidity of 85%, the number of defective products was 6 out of 100. In addition, regarding the above 100 products, the temperature is 121 ° C and the pressure is 2
When PCT was performed for 96 hours in an atmosphere of 026 hPa and relative humidity of 100%, the number of defective products was 10
It was 2 out of 0.

As described above, according to the present invention, since there is no silver layer as the cathode extraction layer, the migration phenomenon of silver does not occur under high temperature and high humidity, and a highly reliable tantalum solid electrolytic capacitor can be obtained. . Further, according to the present invention, the steps of forming the silver layer and the carbon layer can be omitted, so that the steps can be simplified. For reference, the above-mentioned Example 1
Table 3 shows the test results of Comparative Examples 1 to 3 and Comparative Examples 1 to 3.

[0034]

[Table 1]

[0035]

As described above, according to the present invention,
The following effects are achieved. That is, carbon black is mixed with the manganese nitrate aqueous solution at least at the final stage of the solid electrolyte forming step, and the high adhesion carbon layer of carbon black is mixed in the manganese dioxide layer formed on the outermost side, and adhered to the high adhesion carbon layer. According to the invention as set forth in claim 1, wherein the cathode terminal plate is attached via silver, not only the carbon layer forming step but also the silver layer forming step can be omitted, and the silver migration also occurs under high temperature and high humidity. Provided is a highly reliable tantalum solid electrolytic capacitor in which no phenomenon occurs.

Further, according to the invention of claim 2, the carbon black content in the manganese nitrate aqueous solution at the final stage of manganese dioxide formation is 1 to 10 wt%.
The adhesion between the manganese dioxide layer and the carbon layer becomes stronger, and the effect of claim 1 is further enhanced.

The particle size of the carbon black mixed with the manganese nitrate aqueous solution is 0.1 to 0.5 μm.
According to the invention described in (1), since the carbon black can penetrate even into the inside of the fine irregularities on the surface of the manganese dioxide layer, a tighter adhered state can be obtained.

Further, according to the invention of claim 4, wherein 0.1 to 2 wt% of a water-soluble adhesive such as polyvinyl alcohol is mixed in the manganese nitrate aqueous solution, the manganese dioxide layer and the carbon layer are adhered even after drying. The long-life tantalum solid electrolytic capacitor having stable heat resistance and stable heat resistance is provided.

Similarly, according to the invention of claim 5, wherein an organic solvent-based carbon layer is further formed on the high adhesion carbon layer, the electrical connection between the high adhesion carbon layer and the cathode terminal plate is achieved. Connection status is guaranteed for a long time.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view of a tantalum solid electrolytic capacitor element as one embodiment manufactured by the present invention.

FIG. 2 is a partially enlarged sectional view of a tantalum solid electrolytic capacitor element as a conventional example.

[Explanation of symbols]

1 Tantalum sintered pellet 2 Chemical conversion film 3A Manganese dioxide layer 4A carbon layer 5 silver layers

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-63-31107 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/04 H01G 9/032

Claims (5)

(57) [Claims] 1. A manganese dioxide layer as a solid electrolyte is formed on the chemical conversion film by forming a chemical conversion film on the tantalum sintered pellet, dipping it in an aqueous solution of manganese nitrate, and then repeating thermal decomposition a plurality of times. The carbon black is mixed with the manganese nitrate aqueous solution in the step, the high adhesion carbon layer is mixed with the carbon black in the manganese dioxide layer formed on the outermost side, and the cathode terminal plate is bonded to the high adhesion carbon layer through the adhesive silver. A method for manufacturing a tantalum solid electrolytic capacitor, which is characterized by being attached. 2. The method for producing a tantalum solid electrolytic capacitor according to claim 1, wherein the carbon black content in the manganese nitrate aqueous solution at the final stage is 1 to 10 wt%. 3. The method for producing a tantalum solid electrolytic capacitor according to claim 1, wherein the carbon black has a particle size of 0.1 to 0.5 μm. 4. The water-soluble adhesive such as polyvinyl alcohol (PVA) is mixed with the manganese nitrate aqueous solution at the final stage in the range of 0.1 to 2 wt%. 2. The method for producing a tantalum solid electrolytic capacitor as described in 2. 5. The method for producing a tantalum solid electrolytic capacitor according to claim 1, further comprising forming an organic solvent-based carbon layer on the high adhesion carbon layer.