JPS6127892B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to electronic components, and particularly to improvements in electrode extension layers in solid electrolytic capacitors. In general, this type of solid electrolytic capacitor is manufactured by forming a capacitor element A in advance, which is made by press-molding metal powder having a valve action such as tantalum, niobium, or aluminum into a cylindrical shape and sintering it, as shown in Fig. 1. Connect the metal wire with valve action to the anode lead B
A first external lead member C bent in an L shape is welded to the protruding portion of the anode lead B from the capacitor element A, and a straight second external lead member D is attached to the capacitor element. A solder member F is used to connect to the electrode lead layer E formed on the circumferential surface of capacitor element A via an oxide layer and a semiconductor layer, and then the entire circumferential surface of capacitor element A is covered with resin material G. It is configured. By the way, the graphite layer of the electrode lead layer E in the capacitor element A shows almost no wettability to the solder member F, and it is almost impossible to solder the second external lead member D to the graphite layer. In view of this, the electrical
It is made of a conductive material that has excellent mechanical connectivity and excellent wettability with respect to the solder member F. This conductive member contains silver powder with an average particle size of 2 to 3 μm and a resin, and is configured such that the ratio of the silver powder to the whole is set to 70% by weight. Incidentally, the conductive member is usually constituted as a conductive suspension consisting of silver powder, an inorganic material, a resin, and a solvent, and the electrode lead layer E is formed by adding the capacitor element A to this conductive suspension.
It is formed by dipping it in water, pulling it up, and then heating it to about 150℃. The silver powder is fixed to the circumferential surface of the capacitor element A by thermosetting the resin, and good electrical connection between the silver powder and the graphite layer is maintained. By the way, the second external lead member D is soldered to the electrode lead layer E.
This is done by immersing the capacitor element A in a molten solder bath controlled at a temperature of about 250°C while making contact with the external lead member D of the capacitor element A, and then pulling it up. When immersed in the solder bath, a phenomenon occurs in which the silver in the electrode lead-out layer E is eaten by the solder member (alloying phenomenon of silver with the solder member). This phenomenon occurs from the outer surface of the electrode lead layer E that comes into contact with the molten solder, and migrates to the graphite layer side with the passage of time. In this way, when the eating phenomenon caused by the silver solder material in the electrode lead layer reaches the interface with the graphite layer, good contact with the graphite layer is established at the reached part by the silver solder material. Correspondingly, the contact resistance increases. For this reason, capacitor characteristics such as dielectric loss and impedance are significantly impaired. For example, in a 3V 100μF capacitor element made by press-molding tantalum powder into a 3.5φ x 4mm cylinder and sintering it, the dielectric loss at 120Hz is normally 4%.
Not only will cases where the difference between the front and back exceeds 10% occur, but the variation will also increase. Moreover, although the entire circumferential surface of the capacitor element A is covered with the thermosetting resin material G, stress acts on the electrode lead layer E, the graphite layer, the semiconductor layer, etc. when it is thermoset. In particular, if the silver eating phenomenon has progressed to the interface between the electrode lead layer E and the graphite layer, or if the thickness of the silver has become extremely thin, the stress described above may cause the electrode lead layer E to Peeling may occur locally between the graphite layer or between the graphite layer and the semiconductor layer, or in extreme cases over a wide area. If such peeling occurs, the contact resistance between the electrode lead layer E and the graphite layer will ultimately increase significantly, and as mentioned above, dielectric loss and
This poses a problem in that not only capacitor characteristics such as impedance are significantly impaired, but also variations in characteristics during the manufacturing process become large, making it difficult to perform sufficient process control. For example, in the case of the above-mentioned 3V100μF capacitor element, after forming the electrode lead layer,
Dielectric loss of around 4% at 120Hz becomes 10% after exterior
(usually around 4%) or more. For this reason, the rate of process failures is about 1% at most immediately after the formation of the electrode lead layer, but it can reach 50% after resin packaging, making process control extremely difficult. Therefore, in order to solve this problem, conventionally, the electrode lead layer E in the capacitor element A is configured to have a thick coating. For example, the weight of the conductive material attached to the 3V100μF capacitor element mentioned above.
Figure 2 shows the relationship with dielectric loss at 0KHz. In the figure, black dots indicate average values, and straight lines extending vertically through the black dots indicate dispersion. As is clear from this figure, the weight of the conductive material attached is
Above 380μg/ ^mm2 , not only dielectric loss but also
Although the variation has become smaller, 380μg/
All values become larger below mm ² . Therefore, the weight of the conductive member attached to the electrode lead layer E is set to be as thick as 380 μg/mm ² or more. According to this configuration, although a phenomenon in which the silver solder material eats away at the surface layer of the electrode lead-out layer E occurs when the second external lead member D is soldered, it is not only possible to prevent the silver solder material from reaching the graphite layer.
A sufficient thickness of silver can also be ensured. For this reason, it is possible to reduce the influence of various factors in the manufacturing process as much as possible, and also to obtain good electrical connectivity to the graphite layer of the electrode extraction layer E.
The variation in dielectric loss at 1KHz is reduced to 20 to 40
This can be improved from about 20% to 30%. However, as mentioned above, the electrode extraction layer E is
As the thickness of the capacitor itself increases, the amount of silver powder used also increases significantly, which, combined with the recent rise in the price of precious metal powder, poses a problem in that the cost of the capacitor becomes extremely high. In view of these points, the present invention aims to reduce the cost by reducing the amount of precious metal powder, such as silver, in the conductive member constituting the electrode lead layer, but the characteristics due to the phenomenon of being eaten by the silver solder member are not affected. The objective is to provide a solid electrolytic capacitor that can minimize the effects of In FIG. 3, 1 is a capacitor element (component body) made of a metal member having a valve action, and is formed by, for example, press-molding metal powder having a valve action into a cylindrical shape and sintering it. There is. An oxide layer as a dielectric layer, a semiconductor layer such as manganese dioxide, and a graphite layer are sequentially formed on the circumferential surface of the capacitor element 1 by chemical conversion treatment. Also, capacitor element 1
A metal wire having a valve action is planted as an anode lead 2 at the center of the anode lead 2 prior to pressure molding of the metal powder. Incidentally, the anode lead 2 can also be welded to the circumferential surface of the capacitor element 1 and led out prior to the formation of the oxide layer. On the graphite layer of this capacitor element 1, a first electrode lead layer 3 is formed of a conductive material having a specific resistance of 1×10 ⁻¹ to 3×10 ⁻⁴ Ω gold·cm. This conductive member is made of, for example, a part or most of the silver powder, tin powder,
It is constructed by replacing it with additives such as zinc powder, glass powder, aluminum powder, and niobium powder. On this first electrode lead layer 3, there is further a second electrode lead layer 4 made of a conductive material having a resistivity of 1×10 ⁶⁴ Ω·cm or less and containing silver powder as a main component and having sufficient wettability to the solder member. is formed. Further, these extraction layers are formed by, for example, immersing the capacitor element 1 in a conductive suspension consisting of silver powder, an inorganic additive, a resin, and a solvent, pulling it up, and then subjecting it to heat treatment. On the other hand, on the anode lead 2 led out from the capacitor element 1, there is a first external lead member 5 formed by bending it into an L shape using a metal member with excellent solderability, and the bent portion 5a of the first external lead member 5 is a protruding portion. 2a, and then welded. Further, the second electrode lead layer 4 of the capacitor element 1 has a second electrode formed in a straight shape from a metal member with excellent solderability.
An external lead member 6 is connected by a solder member 7. Note that the second external lead member 6
For soldering to the electrode lead layer 4, for example, one end of the second external lead member 6 is brought into contact with the outer surface of the second electrode lead layer 4, and the temperature is controlled together with the capacitor element 1 to around 250°C. This is done by dipping it into a bath of molten solder and pulling it up. Further, the entire circumferential surface of the capacitor element 1 is simply covered with a resin material 8 such as epoxy resin or phenol resin. In addition to the molding method, this packaging can also be done by a dipping method, a powder coating method, or the like. In this way, the electrode lead layers in the capacitor element 1 are each made of a conductive member having a specific resistance within a specified range. In other words, the upper limit of the specific resistance of the first electrode extraction layer 3 is 1×10 ^-1 Ω・If the upper limit value of the resistivity is exceeded, the dielectric loss and its dispersion will increase and electrical connectivity will be lost.
cm, and if the lower limit is 3×10 ^-4 , the silver powder ratio cannot be reduced and costs cannot be reduced substantially.
The specific resistance of the second electrode lead layer 4 is set to 1×10 ^-4 Ω·cm or less so that the wetting properties of the second electrode lead layer 4 are not impaired and the soldering can be performed well. Conductive members are selected for each. Therefore, when the second external lead member 6 is soldered to the second electrode lead layer 4, the surface layer of the second electrode lead layer 4 is eaten away by the silver solder member. The electrode extraction layer 3 prevents it from reaching the graphite layer. Therefore, the electrical connection of the first electrode lead layer 3 to the graphite layer can be maintained well, desired capacitor characteristics can be obtained, and process variations can also be suppressed. In particular, the first electrode lead layer 3 is disposed between the graphite layer and the second electrode lead layer 4 of the capacitor element 1, and is electrically conductive to the graphite layer and the second electrode lead layer 4. Solderability is not required as long as a good connection can be made. Therefore, since the resistance of the graphite layer in particular is as high as about 20 Ω・cm, the resistance of the first electrode lead layer itself is also 1×10 ^-4 to 1×10 ^-5 of a conductive material mainly made of silver powder.
A value as low as Ωcm is not required. For example, when tin powder is used as an additive in a conductive member containing silver powder, additives, and resin, the specific resistance of the conductive member is As shown in FIG. 4, it varies greatly depending on the additive content. Therefore, even if the specific resistance of the first electrode extraction layer 3 is set to a value larger than, for example, 3×10 ^-4 Ω·cm, the graphite layer and the second electrode extraction layer 4
In contrast, not only can sufficient electrical connectivity be obtained, but also the cost of the capacitor can be effectively reduced by reducing the proportion of silver powder in the conductive member. However, since the specific resistance of the first electrode extraction layer 3 has a close relationship with characteristics such as dielectric loss and impedance, its value cannot be increased indefinitely. For example, using a 3V 100μF capacitor element made by press-molding tantalum powder into a 3.5φ x 4mm column and sintering it, find the relationship between the resistivity of the first electrode extraction layer 3 and the dielectric loss at 1KHz. As a result, the results shown in FIG. 5 were obtained. In the figure, the black dots indicate the average value, and the straight lines extending vertically through the black dots indicate the amount of variation. As is clear from this figure, the dielectric loss is 25% in the resistivity range of 2.5×10 ^-5 to 5×10 ^-2 Ωcm.
Not only is it stable, but its fluctuation is also 10
It has decreased to about %. And the specific resistance is 5
When it becomes larger than ×10 ^-2 Ω·cm, the dielectric loss increases. In particular, when the resistivity exceeds 1×10 ^-1 Ω・cm, not only dielectric loss but also its dispersion occur.
It has become extremely large, exceeding 40%. Therefore, the specific resistance of the first electrode extraction layer 3 must be set to 1×10 ^-1 Ω・cm or less, and from 3×10 ⁻⁴ to 1×10 ⁻¹ Ω・in economical consideration. It is desirable to regulate it within the cm range. Furthermore, since the second electrode lead layer 4 is formed of a conductive material mainly composed of silver powder and has a specific resistance of 1×10 ^-4 Ω·cm or less, it exhibits sufficient wettability to the solder material. The second external lead member 6 can be soldered well. In particular, part of the silver powder in this conductive member can be replaced with metal powder such as tin as long as the wettability to the solder member is not impaired. For example, when using tin powder, the proportion of tin powder in the total amount of silver powder and tin powder can be replaced up to 35% by weight, so the proportion of silver powder in the conductive member can be reduced as in the first electrode extraction layer 3. The cost of capacitors can be further reduced. Next, specific examples will be described. Example 1 A 35V 10 μF capacitor element made by press-molding tantalum powder into a cylinder shape and sintering it, is coated with silver powder and about 100 meshes of lead borate on the circumference of a 35V 10μF capacitor element through an oxide layer and a manganese dioxide layer (semiconductor layer). The first electrode extraction layer is formed using a conductive material containing glass powder as an additive and the additive content including resin is set to 43% by weight, and on top of that, a conductive material consisting mainly of silver powder containing no additives is formed. to form a second electrode lead layer. A tantalum solid electrolytic capacitor is manufactured using the following conventional method. In this case, the specific resistance value of each electrode extraction layer is 8×
10 ^-4 Ω・cm, second electrode extraction layer is 1.5×10 ^-5
It was Ω・cm. In addition, for comparison with the product of the present invention, a conventional product was prepared that had an electrode lead layer constructed by using a conductive member made of silver powder and 30% of the weight of a resin material through a two-time dipping process. When we measured the dielectric loss of this capacitor at 120Hz and 1KHz, we obtained the results shown in Table 1.

[Table] As is clear from the above table, although the product of the present invention exhibits slightly higher characteristic values than the conventional product, this does not pose any problem in practice. In addition, the failure rate due to dielectric loss at 120Hz after the formation of the first and second electrode lead layers and after the resin coating is approximately the same for both the inventive product and the conventional product, which is the highest for so-called high-voltage products. No effect of suppressing process variations by the electrode lead layer 1 was observed. On the other hand, the product of the present invention has
The capacitor cost was reduced by 2.8% compared to conventional products. Example 2 In Example 1, the content of the lead borate glass powder was increased to 58% by weight, and the results shown in Table 2 were obtained. In this case, the specific resistance value of each lead-out layer was 2×10 ⁻² Ω·cm for the first electrode lead-out layer and 1.5×10 ⁻⁵ Ω·cm for the second electrode lead-out layer.

[Table] As is clear from the table above, in the product of the present invention, the resistivity of the first electrode extraction layer is considerably larger than that of Example 1, so the dielectric loss is also slightly larger than that of Example 1. ing. However, there is no problem at all in practice. Furthermore, good results similar to those in Example 1 were obtained regarding process variations. On the other hand, in the product of the present invention, the additive content was further increased compared to Example 1, and thus the cost of the capacitor could be reduced by 3.4%. Example 3 The circumferential surface of a 3V 100 μF capacitor element using tantalum powder contains silver powder, tin powder (additive), and resin via an oxide layer and a manganese dioxide layer, and the additive content is set to 80% by weight. A first electrode extraction layer was formed using the conductive material obtained above, and a second electrode extraction layer was further formed thereon using the same conductive material as in Example 1 (additive content: 0% by weight). In addition, the specific resistance of the first and second electrode extraction layers is
2.5× ^10.2 , 1.5×10 ^-5 Ω・cm. The dielectric loss of this capacitor is shown in Table 3, and the process variation (defective incidence of dielectric loss at 120 Hz) is shown in Table 4.

【table】

[Table] As is clear from Table 3, even in so-called low-voltage products, the specific resistance of the electrode lead layer is higher than that of conventional products, resulting in a slightly higher dielectric loss. No problem at all. However, as shown in Table 4, the incidence of defects due to dielectric loss immediately after forming the electrode extraction layer and after being covered with epoxy resin fluctuates greatly in the conventional product, whereas it does not fluctuate at all in the product of the present invention. No significant changes were observed, indicating a significant improvement effect on process variations. This means that even if silver is eaten away on the surface of the second electrode extraction layer, the first electrode extraction layer prevents it from reaching the graphite layer and resists stress from the exterior resin material. This is thought to be due to the fact that it exhibits a buffering effect. In addition, the product of the present invention was able to reduce the cost of the capacitor by 4.3% compared to the conventional product. Example 4 The circumferential surface of a 16V22μF capacitor element using tantalum powder contained silver powder, zinc (additive), and resin via an oxide layer and a manganese dioxide layer, and the additive content was set to 72% by weight. A first electrode extension layer is formed using a conductive member, and a second electrode extension layer is further formed thereon using the same conductive member as in Example 1. Note that the specific resistance of the first electrode lead layer is 3×10 ⁻³ Ω·cm. As shown in Table 5, the dielectric loss of this capacitor was approximately the same for both the inventive product and the conventional product.

[Table] In addition, the product of the present invention was able to reduce the cost of the capacitor by 4.0% compared to the conventional product. In addition, in the embodiment of the present invention, the electrode lead layer is composed of the first and second electrode lead layers, but
Further conductive layers can also be interposed between them. Furthermore, as the noble metal powder in the conductive member constituting the electrode extraction layer, in addition to silver powder, gold powder or the like can also be used. Particularly when applied to a solid electrolytic capacitor, the graphite layer can be made of a conductive material other than graphite, and the shapes of the capacitor element, external lead members, etc. can be set as appropriate. As described above, according to the present invention, by adding additives to the conductive member constituting the first electrode extraction layer formed on the component main body side, the cost of the product can be effectively reduced. By adding , it is possible to minimize the influence on the properties caused by the phenomenon of the noble metal powder being eaten away by the solder member.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a conventional solid electrolytic capacitor, FIG. 2 is a diagram showing the relationship between the attached weight of the conductive member constituting the electrode extraction layer and the dielectric loss, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between additive content and specific resistance of the conductive member.
FIG. 5 is a diagram showing the relationship between specific resistance and dielectric loss.

Claims (1)

[Claims] 1. In an electrode lead-out member formed via an oxide layer and a semiconductor layer on the circumferential surface of a capacitor element made by pressure-molding and sintering metal powder having a valve action, the electrode lead-out member has a specific resistance of 1×10 ^{− 1} to 3
A first electrode lead layer made of a conductive material with a resistance of ×10 ^-4 Ω・cm, and a specific resistance formed on the first electrode lead layer of 1×10 ⁻⁴ Ω·cm or less, which has sufficient wettability for the solder member. What is claimed is: 1. A solid electrolytic capacitor comprising a second electrode lead layer made of a conductive material mainly composed of silver powder exhibiting the following characteristics.