JPH021855Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a multilayer ceramic capacitor.

Multilayer ceramic coders are highly reliable and play a role in speeding up and downsizing electronic devices and circuits.
As an essential component, the demand for it has been increasing in recent years.

Multilayer ceramic capacitors are formed by laminating multiple elements with internal electrodes printed on ceramic green sheets, then pressing them into one piece, and then going through steps such as sintering, baking the external electrodes, and attaching leads. It usually has the configuration shown in FIG.
In FIG. 1, 1 is a ceramic, 2 is an internal electrode, 3 is an external electrode, and 4 is a lead wire.

However, the type of multilayer ceramic capacitor shown in Figure 1 does not have the function of protecting the circuits and components electrically connected to the capacitor when the multilayer ceramic capacitor fails and enters the short state. A so-called "multilayer ceramic capacitor with fuse", which is a multilayer ceramic capacitor with a fuse added to the multilayer ceramic capacitor shown in the figure, is sometimes required and has been developed. In other words, the internal metal of a multilayer ceramic capacitor is integrated with the ceramic and sintered (sintering temperature 900°C to 1500°C).
Metals, mainly noble metals such as silver and palladium, are used to prevent them from oxidizing or melting and impairing their function as capacitors.
The metal for the external electrode is usually the same as that for the internal electrode, and the lead wire is a metal that can be easily attached to the external electrode by soldering (for example, tinned copper). The melting points of the metals that make up ceramics are all between 900℃ and 1500℃.
As high as ℃. Therefore, if a multilayer ceramic capacitor built into a circuit breaks down and enters a shorted state, one of the metals that make up the multilayer ceramic capacitor will burn out, causing an electrical disconnect between the two lead wires of the multilayer ceramic capacitor. Until a low melting point metal is used as the metal constituting a multilayer ceramic capacitor, a current exceeding the standard will flow for a longer period of time than when a metal with a low melting point is used as the metal constituting the multilayer ceramic capacitor. may impair its functionality. An example of a "multilayer ceramic capacitor with a fuse" will be explained using FIG. Figure 2a is an external view of a "multilayer ceramic capacitor with a fuse", and 9
is a ceramic part, 10, 11, 12 are external electrodes,
13 and 14 are leads, and 15 is a fuse, and the leads and the external electrode and the fuse and the external electrode are electrically connected using solder 16. The ceramic part is an element in which internal electrodes 18 are printed on a ceramic green sheet 17 (corresponding to b in Fig. 2).
After the elements (corresponding to c in Fig. 2) in which internal electrodes 20 are printed on ceramic green sheets 19 are laminated alternately, they are pressed and integrated, and then sintered, and a fuse is attached. In the state where the electrode 18 is not connected to the outer electrode 12 and the end surface d-
d', and electrode 20 is electrically connected to electrode 10 at end face e-e'. As Fuse 15,
The material and dimensions of the fuse should be selected so that the external electrodes 11 and 12 are electrically opened when a current exceeding the standard flows.If a "multilayer ceramic capacitor with a fuse" is used, Even if the capacitor becomes shorted, circuits and components electrically connected to the capacitor will be protected.

By the way, most of the shorted states of multilayer ceramic capacitors are caused by electrical short-circuiting between some adjacent internal electrodes (metal ions that make up the internal electrodes move to adjacent internal electrodes and short-circuit them). It is known that in many cases, if the short-circuited internal electrode can be electrically disconnected from the external electrode, it can function satisfactorily as a capacitor. In other words, the capacitance value C of a multilayer ceramic capacitor is C= _E0 Ern/T×S...(1) n=Number of laminated layers _E0 =8.856×10 ^-12 F/m Er=Dielectric constant of ceramic S=Area of internal electrode T is expressed as the thickness of the ceramic, and it is known that the greater the number of laminated layers, the less the effect of electrically cutting a part of the electrode, and therefore, in many cases, the ceramic can function satisfactorily as a capacitor.

Since the conventional "multilayer ceramic capacitor with a fuse" has the structure shown in FIG. 2, even if some internal electrodes are electrically shorted, the fuse will be cut and the capacitor function will be lost, which is not desirable.

In the present invention, a metal electrode part separate from the external electrode is provided in a part of the ceramic block part constituting the multilayer ceramic capacitor for one or both of the external electrodes, and one or both of the external electrodes are electrically connected. It is composed of m electrode parts that are not connected to each other, the m electrode parts and the metal electrode part provided for the external electrode are connected by a fuse, and a lead wire is connected to the metal electrode part. In the multilayer ceramic capacitor of the present invention, even if some of the internal electrodes are short-circuited, the short-circuited internal electrodes are more easily connected than the external electrodes. It has the advantage of being able to operate after being electrically disconnected.

In other words, in a multilayer ceramic capacitor having the above structure, even if some of the internal electrodes become short-circuited, the fuse connected to the internal electrodes is simply disconnected, so only the internal electrodes are more electrically connected than the external electrodes. It will work after being disconnected.

By the way, when capacitors are used for the purpose of blocking inrush current to various circuits and devices, even if the capacitance value fluctuates, it is often not a problem as long as the capacitance value does not fall below the allowable capacitance value.

Therefore, the multilayer ceramic capacitor of the present invention is
If the probability that the internal electrodes will be short-circuited is properly estimated and the value of m is selected so that the capacitance value in the event of a short-circuit does not fall below the allowable capacitance value, when used for the above-mentioned purposes, the conventional type of laminated It can operate as a highly reliable capacitor for a longer period of time than ceramic capacitors.

Figure 3 is for explaining one embodiment of the present invention, where a is a cross-sectional view when viewed from the side, b is a cross-sectional view when viewed from the front, and 30 is 14 mm x 12 mm x 5 mm.
A multilayer ceramic capacitor having the shape of , a capacitance of 200 μF, and a number of laminated layers of 160, 31 is an electrode that constitutes the multilayer ceramic capacitor, 32 is a fuse,
33 is solder, 37 is an internal electrode, 34 is a copper wire, 35
is an electrode for attaching a lead wire and a fuse, and a copper wire 34 is taken out as a lead wire from a molded part 36 having a shape of 18 mm x 18 mm x 10 mm. In this embodiment, one of the external electrodes 31 is composed of eight electrode parts that are not electrically connected to each other, and the eight electrode parts and the electrode part 35 are connected by eight fuses 32. .

The multilayer ceramic capacitor in this example is 200K
It was developed as a capacitor used to absorb noise in power supply circuits in the Hz band, and has a capacitance value of 40μF more than the required capacitance value of 160μF for noise absorption in power supply circuits. The reason why one electrode part was divided into eight parts is that, based on past usage records, most of the internal electrodes of this type of multilayer ceramic capacitor are short-circuited due to a short-circuit between only two internal electrodes. In addition, consideration was given to ensuring that even if one of the fuses were to blow, the required capacitance would not fall below 160μF. After using this multilayer ceramic capacitor in a 200KHz power supply circuit for a certain period of time, I removed it from the circuit, disassembled it to avoid damaging the fuses and internal electrodes, and examined the eight fuses. The fuse was broken, and only the internal electrode on the 31st layer was actually shorted. However, when it was mounted on a circuit, it worked without any problems, and the desired purpose was achieved.

As is clear from the above embodiments, the multilayer ceramic capacitor of the present invention has a metal electrode separate from the external electrodes provided in a part of the ceramic block portion constituting the multilayer ceramic capacitor for one or both of the external electrodes. , one or both of the external electrodes is composed of m electrode parts that are not electrically connected to each other, and the m electrode parts and the metal part provided for the external electrode are connected by a fuse, and Because it has a structure in which a lead wire is connected to the metal electrode part, it is an excellent capacitor because it can electrically disconnect short-circuited internal electrodes from the external electrodes, which was difficult with conventional multilayer ceramic capacitors. .

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a multilayer ceramic capacitor.
FIG. 2 is an explanatory diagram of a laminated ceramic capacitor with a fuse, and FIG. 3 is an explanatory diagram of an embodiment of the present invention. In FIG. 1, 1 is a ceramic part, 2 is an internal electrode, 3 is an external electrode, and 4 is a lead wire. In FIG. 2, 9 is a ceramic part, 10, 11, 12
13 and 14 are external electrodes, 13 and 14 are lead wires, 15 is a fuse, 16 is solder, 17 and 19 are ceramic green sheets, 18 and 20 are internal electrodes, and in Fig. 3, 30 is a multilayer ceramic capacitor, and 31 is a multilayer ceramic capacitor. 32 is a fuse, 33 is a solder, 34 is a lead wire, 35 is an external electrode, 36 is a mold part, and 37 is an internal electrode.

Claims (1)

[Scope of utility model registration request] A metal electrode part separate from the external electrodes is provided in a part of the ceramic block part constituting the multilayer ceramic capacitor for one or both of the external electrodes, and one or both of the external electrodes are electrically connected to each other. It is composed of m electrode parts with no
1. A multilayer ceramic capacitor characterized in that each electrode part and a metal electrode part provided for the external electrode are connected by a fuse, and a lead wire is connected to the metal electrode part so as to be integrated.