JPS5842614B2 - Denkai capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electrolytic capacitor, and in particular to a method for manufacturing tantalum electrodes thereof.

. In the manufacture of tantalum capacitor anodes from tantalum powder, a portion of the tantalum is used only as a contact and does not play an active role in the capacitance formation mechanism.

Since alloys such as tantalum, button and niobium, and even niobium and tantalum alloys, are expensive, it is an object of the present invention to replace contactless tantalum with cheaper materials.

The present invention provides an electrode for an electrolytic capacitor comprising a shaped porous body of tantalum coated particles, the particle core being non-conductive and non-flammable, the initial thickness of the tantalum coating being determined by the required voltage rating of the capacitor. When anodizing the body (porous body) at an anodizing voltage, the average thickness of the non-anodized tantalum coating does not exceed 0.5 microns (10-6) meters.

The present invention also provides an electrode for an electrolytic capacitor comprising a shaped porous anodized body of tantalum coated particles, the particle core being a non-conductive, non-flammable material, and the thickness of the anodized portion of the coating being adjusted to meet the requirements of the capacitor. The average thickness of the non-anodized portion of the coating is 0.5 microns (10-
') Do not exceed meters.

Tantalum coating on the particle cores is carried out by any suitable means, typically in the case of tantalum by gas phase reduction of tantalum pentachloride in hydrogen with substrate particles on a fluidized bed.

Ceramic materials such as alumina are suitable as non-conductive, non-flammable particle core materials.

As explained below, the particle core (matrix) size typically ranges from 30 microns to 2.5 microns.

The tantalum thickness remaining after anodization is limited to that required for the anode contact, and the resulting configuration offers the possibility of realizing capacitors with self-healing breakdown properties.

The result of the modification process is to convert the thin layer of tantalum into an oxide, effectively isolating the fracture area.

If this step occurs before oxide recrystallization, the tendency of the breakdown to propagate throughout the capacitor is reduced.

Another advantage of using tantalum is that the low tantalum content makes the capacitor much more non-flammable than conventional capacitors.

The encapsulation of special flame retardant reactants becomes less important apart from the need to prevent the encapsulation from burning.

The basic manufacturing steps for producing capacitor anodes include providing tantalum-coated particles with a suitable substrate size depending on the dimensions of the anode and the thickness of the tantalum coating depending on the required anodizing voltage, and forming a shaped porous body. The steps include shaping and sintering the particles to form the capacitor, and anodizing the final product based on the required maximum operating voltage of the capacitor, ie, the rated voltage of the capacitor.

Other processes for manufacturing electrolytic capacitors from anode bodies, namely:
Attachment of the electrolyte (liquid or solid), cathode, leads, housing and/or provision of encapsulation is done in a known manner.

The invention will be better understood from the following description made with reference to the accompanying drawings.

The core particles of the matrix are not spherical but irregularly shaped.

This has the advantage of providing a larger surface area than a spherical shape.

The core particles are selected by passing through a mesh of a certain size, the dimensions of which will be described in terms of radius or diameter as a measure of size for purposes described below.

As shown in Figure 1, the tantalum coating 1 on the core 2 is not of uniform thickness, but is considered to have an average thickness as shown by the dotted line 3, and this average thickness will be referred to hereinafter. .

Density of tantalum (dTa): 16.65 Density of tantalum oxide (dTa205); 8.2 Density of alumina (dAI□03); 3.97 Typical apparent density of tank compacts (dB); 9. 41 Ratio (α) of the typical surface of tantalum powder maintained after sintering at 450° C. to the surface of tantalum powder before sintering (α) 20.

Typical dB of R5 tantalum sintered at 571450°C
: dTa ratio (β): 0.57 (where R5 indicates that the average grain diameter is 5 microns.

) 17λ/volt dielectric constant Ta2O, corresponding to 8.5 people/volt of the insulation resistance of tantalum (Ta) of Ta205: 28 For pure tantalum powder (theoretical radius of the average particle r centimeters) where C is the nominal electrostatic In the capacity, ■ is the rated voltage, °, tantalum; product of C = 14.5 surface (μC) 1st
The table shows the variation in the apparent volume of the capacitor moldings and the use of commonly available quality tantalum materials with respect to substrate diameter and tantalum coating thickness.

It can be seen from the value of the product C/unit weight of tantalum that the diameter of the substrate has only a small influence.

A major factor for efficient use of tantalum is coating thickness.

For example, a 1 micron thick tantalum layer on a 30 micron and 2.5 micron diameter substrate each has a thickness of 5303 μm.
O/,! yielding li' tantalum and 8012 μO/11 tantalum.

Therefore, a reduction of more than an order of magnitude in the diameter of the substrate is (available tantalum surface)/,! 9 only yields a 50% increase.

However, the particle size of the matrix directly affects the total volume occupied by the capacitor compact, with a reduction from 30 microns to 2.5 microns being 11.32 m'' to 1.59 m8 for a 1 micron tantalum coating. to volume/10
000 μC.

To further elaborate tantalum coatings, for example, 0.1 micron coating on 30 micron - 10,68 m8.2.
The effect becomes even more pronounced at 96 mB - 0.1 micron coating on top of 5 microns.

Among the relationships shown in Table 1, Figure 2 shows the relationship between the volume of the molded body per unit clone and the size of the substrate particles.
The figure shows the relationship between the product of C2 per unit duram of tantalum and the thickness of the coating.

From these figures, it is possible to independently optimize the size of the capacitor molded body and the use of tantalum material.

Considering prior art tantalum powder with a diameter of 5 microns as the standard for comparison (top row in Table 1), savings require the use of tantalum with a coating thickness of less than 1 micron.

The target thickness is about 0.2 microns, which is at least a 4x reduction for tantalum material.

If a 10 micron diameter substrate is adopted, the volume/100OOXμC will be doubled compared to 5 micron tantalum, and therefore the linear increase in compaction size will only be increased by 2i; It is 1.25 compared to 1.85 for a 30 micron diameter substrate.

A layer of 0.2 micron tantalum is applied at 2000/8.5 volts before the layer is insulated by full anodization.
That is, it should be possible to anodize at 235 volts.

Experiments today 1 showed that before the anode contact became open circuit with full anodization, a tantalum layer of nominally O,X microns was
This shows that anodization can be performed at 0.08 volt 1.

Therefore, a 0.2 micron tantalum layer can be applied to capacitors with at least 35 rated voltage ranges by anodizing the tantalum layer.

The objective is, of course, to use the minimum lintal thickness for a given voltage rating.

This concept ensures maximum utilization of tantalum.

Table 2 shows the minimum tantalum thickness required to provide a tantalum pentoxide dielectric at different rated voltages.

For the purposes of anode contact, it is possible to design the coating powder for each rated voltage, assuming that a tantalum thickness of 50oAi is required, for example, and to form the anode based on the desired rated voltage. The thickness of tantalum remaining after treatment is 0
．． Not exceeding 5 microns.

Dimensional standards for capacitors for consumer applications are less stringent than those for capacitors for professional applications.

Currently, Ta powder (6000μO/
A typical 1 μF (microfarad) 35 volt consumer device capacitor using 11) is 1.8
71m length, 1.5 station diameter, 207'2fi'
Adopts an anode with weight and dimensions of .

If this anode were to become twice as large and linear), then
There is no significant increase in the cost of the process, and there is an advantage of ease of handling.

Moreover, its application is not affected by such an increase in volume.

It is therefore conceivable that larger particle substrates can be used with the benefit of improved manganization (pyrolysis of manganese nitrate to produce a coating of manganese dioxide).

FIG. 4 shows an electrolytic capacitor having an anode 1 which is a compressed porous anodized body of tantalum coated particles, the particle core being a non-conductive, non-flammable material, for example a ceramic such as alumina.

The thickness of the tantalum coating after anodization is sufficient to ensure anodic contact.

This thickness ranges from about 10 to 2 ooo At, and initially it is possible to obtain powder coated with tantalum on a non-conductive, non-flammable material, with tantalum coatings of 0.5 micrometers (10'rrL). By compression and subsequent anodization with the required rated voltage of the capacitor, the tantalum anode contact layer remains within the thickness range mentioned above.

The capacitor further includes an anode lead 2 inserted into the coating powder before its compaction.

The cathode includes a case 3 from which a cathode lead 4 extends and there is a general encapsulation 5.

Breakdown tests were carried out on a capacitor having the configuration of FIG. 4 (tantalum coated alumina particles) and its properties were found to be superior to conventional all tantalum capacitors.

For tantalum-coated alumina anodes, the insulation fraying process is nondestructive because the damaged area is an open circuit and not a short circuit, and the failed area is also an open circuit (whereas all tantalum capacitors are short circuits). ), the number of permissible fracture points has increased by at least two orders of magnitude.

70,000 with our 15 volt capacitor tested with a 500 ohm series resistance and an applied voltage of 60V.
After dielectric breakdown at so and ooo locations, an "open circuit" (op
en circuit) J condition has occurred.

This is because the heat generated by the breakdown area breaks down the intergranular tantalum connections around this breakdown area, thereby insulating the rest of the capacitor from the parts around the breakdown area. Seem.

The term "open circuit" is used to indicate that the associated capacitor of several hundred picofarads actually has a resistance state of more than 108 ohms at 15 volts DC.

Under the same test conditions, a group of conventional all-tantalum capacitors withstood an average of 230 failure points before reaching short terminal mode.

It is to be understood that the above description of embodiments of the invention is illustrative only and is not intended to limit the scope of the invention.

[Brief explanation of drawings]

FIG. 1 is a partial illustration of a tantalum coated core or matrix. FIG. 2 is a graph showing the relationship between compressed volume and matrix particle size. FIG. 3 is a graph showing the relationship between the product of C/grams of tantalum and the thickness of the tantalum coating. FIG. 4 is a sectional view of an electrolytic capacitor embodying the present invention. In Fig. 1, 1... tantalum coating, 2...
...Core (substrate), as shown in Figure 4, 1...
・Anode, 2... Anode lead, 3... Case, 4... Cathode lead, 5... Capsule.

Claims (1)

[Claims] 1 Alumina substrate particles are coated with tantalum, pressure-molded and sintered to form a compressed porous body, and the compressed porous body is anodized to replace the tantalum coating with tantalum oxide. Converting to a method of preparing electrolytic capacitor electrodes from tantalum and making electrolytic capacitors, the tantalum has an irregular shape and a rough surface and has an average diameter ranging from 30 microns to 2.5 microns. preparing matrix particles of alumina; placing these particles in a fluidized bed state to produce a tantalum coating by vapor phase reduction of tantalum pentachloride in hydrogen; the thickness of the anodized part of the tantalum coating determines the rated voltage of the capacitor, while the rated voltage determines the anodizing voltage used to anodize the tantalum coating; The tantalum coating formed has an irregular surface due to the shape of the particles, and the average thickness of the unanodized tantalum coating does not exceed 0.5 microns. .