JPS6035387B2 - Conductive paint for solid electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive paint for solid electrolytic capacitors that achieves cost reduction.

The element of a solid electrolytic capacitor is formed using a valve metal such as tantalum (Ta) or aluminum (A) as an anode material.

Figure 1 is a block diagram of a solid electrolytic capacitor,
The anode metal 1 is formed in a shape with an extremely enlarged surface area per unit volume, such as a sintered or etched body, and this surface is converted into an oxide film layer 2 having the necessary withstand voltage by electrolytic oxidation treatment. There is.

Next, 3 oxide semiconductors are added on top of this to increase insulation and breakdown voltage.
After forming a graphite layer 4 as a cathode, a conductive coating film 6 is applied thereon to reduce resistance and to take out a cathode lead wire 5, thereby forming a capacitor element.

Note that the cathode lead wire 5 is bonded to the conductive coating film 6 by solder 7. In this case, the conductive coating must be a non-oxidizing metal, have low resistivity, and have good solderability. In other words, the resistivity of the graphite layer that acts as a cathode is 1~
100 arc, which is extremely high compared to metal, so in order to reduce the spreading resistance of charging and discharging currents and to provide a cathode terminal, conductive paint made of metal with low resistivity, stable and solderable is used. A conductive coating is made by soaking a capacitor element and impregnating it with a graphite layer and then baking it.

The conductive paint is made of metal powder with an average particle size of about 0.5 mm, an organic polymer, and an organic solvent.The materials for the metal powder include gold (Au), silver (Ag), steel (Cu), etc. However, silver paint is commonly used from the viewpoint of resistivity, price, and stability over time.

Now, in the mass production of solid electrolytic capacitors, the work unit is a metal bar in which the lead wire ends of anode elements are welded in large numbers at regular intervals. However, a huge amount of coating film is consumed in the process of forming a conductive coating film, and therefore, there has been a desire to reduce this amount and reduce the cost.

The purpose of the present invention is to reduce the cost of conductive paint, and as a method to achieve this, solder powder of 150 mesh or more is added to silver paint to an extent that hardly affects the characteristics of solid capacitors, that is, to reduce the price of conductive paint. This is added when the mixing weight ratio is up to 1:3, and the effects of this addition will be explained below with reference to the drawings.

The resistivity of silver is the lowest among metals at 1.62
Although it varies depending on the composition ratio with (b), the resistivity increases by more than one order of magnitude. Therefore, when the amount of solder powder added to silver powder is increased, the equivalent series resistance of the capacitor increases. In the present invention, the content of the organic polymer constituting the paint is fixed, and the mixing ratio of solder powder to silver powder is changed.The specific composition ratio is 6% by weight of metal powder, 5% by weight of ethyl cellulose.
5% by weight, modified alkyd resin 15.5% by weight, turpentine oil 7% by weight, and cellosol pla by weight.
:0) to 1:5 (10:50) in six steps to make conductive paints.

FIGS. 2 and 3 are characteristic diagrams of an aluminum solid electrolytic capacitor element prototyped using such a conductive paint, and the rating of the prototype capacitor is 1 French F, 25 WV.

Figure 2A shows the dielectric support value at IKHZ with respect to the mixing weight ratio, and Figure 2B shows the ESR measured at 10MHZ.
(equivalent series resistance value), showing that the loss increases as the amount of solder powder added increases.

In this case, the present invention uses a mixing weight ratio of up to 1:3, and within this range there is almost no effect on the dielectric strength.

On the other hand, ESR increases as the mixing ratio increases, but the standard value at a measurement frequency of 10 MH2 is 1.50, and even the worst value when the mixing weight ratio is 1:3 does not exceed 0.80. Therefore, the mixing ratio within the claimed range has only a slight effect on the characteristics of the capacitor. On the other hand, FIG. 3 shows the relationship between the tensile strength of the lead wire and the mixing weight ratio, and as the mixing ratio increases, the tensile strength decreases.

Note that this test is based on the values obtained when the tips of the anode and cathode lead wires are fixed and pulled in opposite directions, and breakage occurs when the conductive coating to which the cathode lead wire 5 is soldered peels off as shown in Figure 1. This is caused by

In this case, the minimum value of the tensile strength is about 100 mm at the maximum mixing ratio of 1:3 as claimed in this patent, but the lead wire extraction part is substantially reinforced and protected by the molded exterior, and the mounting The strength of the lead wire terminal will not be insufficient in this case.

The present invention was made with the aim of reducing the price of conductive paint, and since it is a necessary condition for the conductive paint to be solderable, solder powder with a mesh size of 150 mesh or more was selected as the metal added to the paint. , this one) When the weight mixing ratio to silver powder was within 1:3, the material cost could be significantly lowered with almost no effect on the electrolytic and mechanical properties of the solid electrolytic capacitor.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a solid electrolytic capacitor, Figure 2 A is the dielectric loss tangent of the capacitor with respect to the mixture weight ratio, Figure B is a relationship diagram with the equivalent series resistance value, and Figure 3 is a lead wire diagram with respect to the mixture weight ratio. It is a relationship diagram with tensile strength. In the figure, 1 is an anode metal, 4 is a graphite layer, 5 is a cathode lead wire, 6 is a conductive coating film, and 7 is solder. Figure 3

Claims (1)

[Claims] 1 A valve metal such as aluminum or tantalum is used as an anode, an oxide layer of the metal produced by electrolytic oxidation is used as a dielectric, and an oxidizing semiconductor layer and a graphite layer are used as a cathode, and is coated on the graphite. In a solid electrolytic capacitor element in which a solder connection is made to a cathode lead wire through a conductive coating, the constituent metal of the conductive coating is a mixture of 150 mesh or more of silver powder and solder powder, and the metal powder has a weight ratio of up to 1:3. A conductive paint for solid electrolytic capacitors characterized by comprising: