JPH0335820B2 - - Google Patents

Description

[Detailed description of the invention]

Recently, in addition to the miniaturization and high density of electronic devices, the demand for safety has increased, and the majority of failures in electrolytic capacitors in particular are short-circuit failures, so one of the countermeasures is to incorporate fuses into capacitors. is used. For example, in tantalum solid electrolytic capacitors, if a short-circuit failure occurs, the tantalum metal is highly oxidized and combustible, and the silver paint inside the capacitor is a combustible material, so it may sometimes catch fire.
There are commercially available products that are equipped with an internal fuse mechanism to prevent ignition in the event of a failure. However, with conventional fuses, depending on the size of the capacitor element and the type (rating) of the element, the fusing current is not necessarily the same even if the same fuse is used, and even if the same fault current flows, the fusing time is different, and the mold There are drawbacks such as the surface temperature of the resin rising abnormally and affecting adjacent parts. The present invention aims to improve these drawbacks. In general, capacitors with a built-in fuse mechanism are
This is based on the principle that when a short circuit occurs, the fuse is blown by the heat generated by the capacitor element, but conventionally, if the leakage current of the capacitor increases for some reason, the capacitor has resistance. This resistance generates heat,
This heat increases the temperature of the capacitor element, further accelerating the increase in leakage current, and deteriorating the capacitor with a large leakage current. Therefore, by rapidly dissipating the generated heat to the outside, leakage is reduced. ^In order to prevent deterioration of capacitors due to increased current, it is common to use a resin with good heat dissipation, that is, good thermal conductivity, as a molding resin. ℃・sec・cm
Above, generally 20 to 50×10 ^-4 cal/℃・sec・cm
are often used. However, even if a capacitor molded with a resin with good thermal conductivity has a built-in fuse, if the capacitor is short-circuited for some reason, there will be large variations in the current when the fuse blows and the time it takes for the fuse to blow. can be,
Furthermore, even if the surface temperature of the capacitor's exterior increases, the current cannot be cut off easily, and if the surface temperature of the exterior increases too much, it may cause ignition and the effect of having a built-in fuse will be diminished. In the present invention, in order to blow the fuse without abnormally increasing the surface temperature of the exterior resin, it is important to make maximum use of the generated heat. Focusing on the need to reduce thermal conductivity as much as possible, this method uses a material with low thermal conductivity for the exterior resin that protects the capacitor element and fuse, contrary to conventional methods. rate is 10×10 ^-4 cal/
The temperature below ℃・sec・cm is used.
Such resins include, for example, alumina, which is added as a filler to epoxy resins or silicone resins;
It can be easily obtained by controlling the type and amount of filler materials of inorganic metal compounds such as calcium oxide, silica, and mica. The figure shows an embodiment of the solid electrolytic capacitor of the present invention having a built-in fuse. In the figure, 1 is a metal with a valve action such as tantalum or aluminum as an anode, a dielectric oxide is formed on the surface of the anode, and an electrolyte layer such as manganese dioxide, a carbon layer, a cathode, etc. are further formed on the anode. A capacitor element constructed by stacking, an anode lead wire 3 is welded to the anode lead wire 2, and a fuse 6 is connected between the cathode 4 of the element and the cathode lead wire 5 by welding, soldering, or thermocompression bonding. Top, so that lead wires 3 and 5 are drawn out to the outside, the thermal conductivity is 10×10 ^-4 cal/℃・sec・
The exterior 7 is formed by molding with a resin containing a filler smaller than cm. As mentioned above, the thermal conductivity is 10×10 ^-4 cal/℃・
When using a resin of sec/cm or less as the exterior resin, the surface temperature of the exterior resin is kept below 100°C, and the temperature of the capacitor element is rapidly raised in a short period of time with a small short-circuit current, and the built-in fuse is The solid electrolytic capacitor can be quickly melted down, and when a short circuit accident occurs, a solid electrolytic capacitor can be obtained that has uniform melting characteristics. Additionally, it has been experimentally confirmed that the thicker the exterior resin is, the more effective it is to prevent heat radiation, and that it is desirable for the resin wall thickness to be 0.5 mm or more. Next, Tables 1 and 2 show the experimental results of actually measuring the surface temperature of the exterior and the time until the fuse is cut off when the thermal conductivity of the exterior resin was varied. Table 1 shows the thermal conductivity of the exterior resin when a 35V, 1μF tantalum solid electrolytic capacitor element is exteriorized with molding resins with different thermal conductivities, and a short-circuit failure occurs by passing a reverse current of 2A, and the thermal conductivity of the exterior resin 10 times after failure. This is an actual value obtained by measuring the relationship between the surface temperature of the exterior resin after a few seconds. This table demonstrates that the higher the thermal conductivity of the resin, the higher the surface temperature, and the lower the thermal conductivity of the resin, the lower the surface temperature. Table 2 also shows that a 35V, 1μF tantalum solid electrolytic capacitor element has a built-in fuse that melts depending on the temperature as shown in the figure, and is molded and exteriorized with various resins with different thermal conductivities. The time it takes for a short circuit to occur by flowing a reverse current, and for the built-in fuse to blow and the circuit to become open is calculated as follows:
It shows the width of variation and time value when measuring 10 pieces each under the same conditions. From the table, it can be seen that the lower the thermal conductivity of the resin used, the shorter the time it takes to reach the open state, and the smaller the time width of the variation. From these tables, in order to keep the surface temperature of the exterior resin as low as possible (below 100℃) and blow out the fuse in a short time in the event of a failure, 10×
It can be seen that it is desirable to use a resin with a thermal conductivity of 10 ^-4 cal/℃・sec・cm or less.

【table】

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a perspective view showing the internal structure of an embodiment of an electrolytic capacitor with a built-in fuse according to the present invention. 1... Capacitor element, 2... Anode lead wire, 3
... Anode lead wire, 4 ... Cathode, 5 ... Cathode lead wire, 6 ... Fuse, 7 ... Resin mold exterior.

Claims (1)

[Claims] 1. A fuse is connected to a capacitor element in which a metal with valve action such as tantalum or aluminum is used as an anode, a dielectric oxide film is formed on the surface of the anode, and an electrolyte such as manganese dioxide, a carbon layer, and a cathode are laminated on top of the anode. In solid electrolytic capacitors that are packaged with a resin mold, the package resin contains a filler and the thermal conductivity is 10×10 ^-4 cal/°C・sec・cm.
A solid electrolytic capacitor with a built-in fuse, characterized by the use of the following resins.