JPH0134336Y2 - - Google Patents

Description

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

Demand for multilayer ceramic capacitors has been increasing in recent years as an essential component for promoting high speed and miniaturization of electronic devices and circuits with high reliability.

Multilayer ceramic capacitors are formed by stacking multiple elements with internal electrodes printed on ceramic green sheets, pressing them into one piece, and then going through steps such as sintering, baking external electricity, and attaching leads. It is usually constructed as 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 a function to protect 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 a fuse", which is a multilayer ceramic capacitor with a fuse added thereto, is sometimes required and has been developed.

In other words, the internal metal for multilayer ceramic capacitors is silver, silver, Metals mainly composed of noble metals such as palladium are used, metals equivalent to those for the internal electrodes are used for the external electrodes, and metals that can be easily attached to the external electrodes by soldering (for example, copper and tin) are used for the lead wires. The melting points of the metals that make up the laminated ceramic are as high as 900°C to 1500°C.

Therefore, if the multilayer ceramic capacitor built into the circuit breaks down and becomes short,
Until one of the metals constituting the laminated ceramic capacitor is burnt out and the two lead wires of the laminated ceramic capacitor are electrically disconnected, compared to when a metal with a low melting point is used as the metal constituting the laminated ceramic capacitor, A current exceeding the standard flows for a long time, which may impair the functions of circuits and components electrically connected to the multilayer ceramic capacitor.

An example of a "multilayer ceramic capacitor with a fuse" will be explained using FIG. Figure 2 a
is an external view of the "multilayer ceramic capacitor with fuse", where 9 is the ceramic part, 10, 11, 12
1 is an external electrode, 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 includes an element in which internal electrodes 18 are printed on a ceramic green sheet 17 (corresponding to b in FIG. 2) and a ceramic green sheet 19.
An element with internal electrodes 20 printed on it (c in Figure 2)
) are alternately laminated, then pressed and integrated, and then sintered. When the fuse is not attached, the electrode 18 is connected to the external electrode 12 and the end face d-d' of the electrode, and the electrode 20 is electrically connected to the electrode 10 at end faces e-e'. Fuse 1
As for No. 5, 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, and it is called a "multilayer ceramic capacitor with a fuse."
By using this, even if the capacitor becomes shorted, the 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 shorted 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=εoεrn/T×S...(1) n=Number of laminated layers εo=8.856×10 ^-12 F/m εr=Dielectric constant of ceramic S=Area of internal electrodes T= It is known that the greater the number of laminated layers, which is expressed as the thickness of the ceramic, the less the effect of electrically cutting a part of the electrode, and therefore, in many cases, it 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 this invention, part or all of the external electrodes constituting the multilayer ceramic capacitor are made of a metal that has a lower melting point than the internal electrodes and becomes an insulator when melted, and the lead wires are attached to the parts of the external electrodes that do not melt. In the multilayer ceramic capacitor of the present invention, only the internal electrodes in a short-circuited state can be electrically disconnected from the external electrodes, which was difficult with conventional multilayer ceramic capacitors. There are merits.

In other words, in a multilayer ceramic capacitor in which some of the internal electrodes are short-circuited, the part of the external electrode that reaches high temperature fastest due to the Joule heat is the part that contacts the internal electrode, and that part burns out and The desired purpose can be achieved if the thickness and material of the external electrodes are adjusted so that only the internal electrodes can be electrically disconnected from the external electrodes.

FIG. 3 is a diagram for explaining one embodiment of the present invention, in which a is a cross-sectional view including the internal electrodes and parallel to the internal electrodes, b is a cross-sectional view when viewed from the side, and FIG.
0 has a shape of 14mm x 12mm x 5mm, and the capacitance value is
200μF, multilayer ceramic capacitor with 160 layers, 31 is a silver external electrode, 32 is an internal electrode made of silver-palladium alloy, 33 is ceramic, 34
35 is a copper wire, and 35 is a 20 micron aluminum foil, and the aluminum foil, internal electrodes, and external electrodes are all electrically connected by thermocompression bonding. Also, the copper wire
Mold part 36 having a shape of 18 mm x 18 mm x 10 mm
It is taken out as a lead wire from.

The multilayer ceramic capacitor in this example is 200K
It was developed as a capacitor for use in the phase delay circuit of Hz band power supplies, and there were no problems when it was incorporated into the phase delay circuit. After using it for a certain period of time, I removed it from the phase delay circuit section, took out the aluminum foil surface to prevent damage, and examined it. I found that the part that contacted the internal electrode of the 51st layer was burnt out, and that the 51st layer was actually burnt out. Only the internal electrodes of the layers were short-circuited. 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, in the multilayer ceramic capacitor of the present invention, a part or all of the external electrodes constituting the multilayer ceramic capacitor are made of a metal that has a lower melting point than the internal electrodes and becomes an insulator when melted. By attaching the wire to a location where the external electrode will not melt and integrating it, it is possible to electrically disconnect only the shorted internal electrode from the external electrode, which was difficult with conventional multilayer ceramic capacitors, making this an excellent capacitor.

[Brief explanation of the drawing]

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 laminated ceramic capacitor.
31 is an external electrode, 32 is an internal electrode, 33 is a ceramic, 34 is a lead wire, 35 is an aluminum foil, and 36 is a molded portion.

Claims (1)

[Scope of utility model registration request] Part or all of the external electrodes that make up the multilayer ceramic capacitor are made of a metal that has a lower melting point than the internal electrodes and becomes an insulator when melted, and the lead wires are attached to the parts of the external electrodes that do not melt and are integrated. A multilayer ceramic capacitor characterized by: