JPH08138905A - Positive temperature coefficient(ptc) thermistor - Google Patents

Abstract

PURPOSE: To provide a chip type PTC thermistor as a highly reliable excessive current protecting element and a temperature sensor element by reducing the influence of heat conduction to a circuit board of the heat generated by the PTC thermistor. CONSTITUTION: A PTC thermistor element 12 is composed of the main body and leg parts provided on both ends of the main body. Electrodes 13 are provided on both edge faces of the PTC thermistor element 12 and in the vicinity of both edge faces, leg part and on the main body in the vicinity of the leg part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type positive temperature coefficient thermistor used in electronic circuits such as overcurrent protection and temperature sensors.

[0002]

2. Description of the Related Art A conventional chip type positive temperature coefficient thermistor 1
As shown in FIG. 5, electrodes 3, 3 are formed on both ends of a substantially rectangular ceramic body 2 having a positive resistance temperature characteristic. Generally, the thickness of the electrodes 3 and 3 is several to one.
It is 0 μm, and the electrodes 3 and 3 serving as the installation bottom surface and the PTC thermistor element body 2 are substantially flush with each other.

The positive temperature coefficient thermistor 1 is fixed to a circuit board (not shown) by, for example, soldering the electrodes 3 to form a part of the circuit configuration.

[0004]

However, since the lower surface of the PTC thermistor element body 2 is flat, the surface of the circuit board and the lower surface of the PTC thermistor element body 2 are almost in contact with each other. As a result, heat generated by the ceramic body 2 due to overcurrent flowing through the PTC thermistor 1 or heat transmitted from the outside to the PTC thermistor 1 is directly transmitted to the circuit board.

Therefore, when the PTC thermistor 1 is used as an overcurrent protection element, there is a problem that the decay start time becomes long and the temperature of the circuit board rises. On the other hand, when it is used as a temperature sensor, the heat capacity of the temperature sensor increases and the thermal response deteriorates. Further, when an overcurrent flows in a circuit including the temperature sensor due to a short circuit or the like, the temperature sensor itself generates heat to raise the temperature of the circuit board.

The object of the present invention is to eliminate the above-mentioned problems, and prevents the heat generated from the positive temperature coefficient thermistor from being directly conducted to the circuit board, thereby providing a highly reliable overcurrent protection circuit. It is to provide a chip-type positive temperature coefficient thermistor used for devices, temperature sensor devices, etc.

[0007]

In order to achieve the above object, in the positive temperature coefficient thermistor of the present invention, the positive temperature coefficient thermistor body has a main body and legs provided at both ends of the main body. Electrodes are provided on both end faces of the PTC thermistor element body, in the vicinity of both end faces, and on the legs and the main body near the legs.

Further, the step between the main body of the PTC thermistor element body and the substrate installation surface of the leg portion is 0.1 mm or more.

The lower layer of the electrode is made of nickel and the upper layer is made of silver. The upper layer is provided at least on the substrate mounting surface of the leg portion, and the lower layer is exposed outside the end portion of the upper layer. Characterize.

[0010]

In the present invention, the leg portions are provided at both ends of the main body of the positive temperature coefficient thermistor body and the electrodes are provided so as to extend from the leg portions to the main body as described above. The central portion serves as a heat generating portion, and the electrode portion having the electrodes including the legs is a non-heat generating portion that does not generate heat. A gap is formed between the heat generating portion and the circuit board, and heat conduction to the circuit board is reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described in detail with reference to FIGS. Positive characteristic thermistor 1
Reference numeral 1 is composed of a positive temperature coefficient thermistor body 12 and electrodes 13 and 13 provided at both ends thereof.

In FIG. 2, the positive temperature coefficient thermistor body 12 is shown.
Is a single plate type ceramic having a positive resistance temperature characteristic, and has a main body 15 and leg portions 16 and 1 provided at both ends thereof.
It consists of 6.

The electrodes 13, 13 are connected to each other across both the end faces of the PTC thermistor element body 12 and in the vicinity of the both end faces, and the legs 16 including the substrate mounting surface and the main body 15 near the legs 16. It is provided without any. The electrode 13 has a two-layer structure in which a lower layer 18 is, for example, a nickel electrode provided by electroless plating, and an upper layer 19 is, for example, a silver electrode provided by baking a paste. The lower layer 18 is provided from the end portion of the main body of the PTC thermistor element body 12 to the both end surfaces including the leg portions 16 except for the central portion of the main body.
The upper layer 19 is provided from the end surface to the substrate mounting surface which is the bottom surface of the leg portion 16, and as shown in the figure, the outer end portion of the lower layer 18 is exposed without being covered with the upper layer 19.

The PTC thermistor 11 having such a structure has a step S between the main body 15 of the PTC thermistor element body 12 and the substrate installation surface of the legs 16 and 16, and the PTC thermistor 11 is provided on a circuit board (not shown). ) With solder etc.,
Between the main body 15 and the installation surface of the circuit board, the legs 16, 1
6 creates a gap. On the other hand, since the electrodes 18, 18 are formed on the substrate installation surface which is the bottom surface of the legs 16, 16 and a part of the main body 15, when a current flows through the positive temperature coefficient thermistor 11, the shortest distance between the electrodes 18, 18 occurs. The central part of a certain main body 15 becomes the heat generating part H, and the legs 16, 16 having the board mounting surface
Both ends of the positive temperature coefficient thermistor on which the electrodes 13, 13 including the are formed are non-heat generating parts.

Therefore, even if the positive temperature coefficient thermistor 11 generates heat, since the step S exists between the heat generating portion H and the circuit board, the heat is not easily transferred to the circuit board. In addition, the board mounting surface of the positive temperature coefficient thermistor 11 is a non-heat generating portion, and the circuit board does not become hot. Therefore, it is possible to reduce the possibility that the solder portion of the PTC thermistor 11 attached to the circuit board is melted and the PTC thermistor 11 is displaced.

The upper layer 19 and the positive temperature coefficient thermistor element body 12
Since the exposed lower layer 18 is interposed between the exposed portion and the exposed portion, silver migration does not occur. When soldering the PTC thermistor 11 to the circuit board, the upper layer 19
It is possible to prevent the solder from flowing into the main body 12 from the leg portion 16 in which the solder is not formed.

Next, a second embodiment according to the present invention will be described in detail with reference to FIG. However, the same parts as those in the first embodiment described above are designated by the same reference numerals and detailed description thereof will be omitted.
In this embodiment, the shape of the PTC thermistor element body is different.

The PTC thermistor 21 is composed of a PTC thermistor element body 22 and electrodes 13, 13 provided at both ends thereof. The PTC thermistor element body 22 is the main body 2
The leg portions 26, 26 are provided on the opposite sides of the substrate installation surface at both ends of 5. This positive temperature coefficient thermistor body 22
An electrode 13 composed of a lower layer 18 and an upper layer 19 at both ends of the electrode 13
Are formed. With this structure, the positive temperature coefficient thermistor 21 does not have the vertical direction and the mounting on the circuit board is simple. Further, although not shown, the leg portions 26, 26 may be provided on the left and right side surfaces of the substrate mounting surface at both ends of the main body 25 of the PTC thermistor element body 22.

Next, a third embodiment according to the present invention will be described in detail with reference to FIG. However, the same parts as those in the first embodiment described above are designated by the same reference numerals and detailed description thereof will be omitted.
In this example, the electrodes are different.

The PTC thermistor 31 is composed of the PTC thermistor body 12 and electrodes 33, 33 provided at both ends thereof. The electrode 33 is composed of two layers, a lower layer 18 and an upper layer 39. The upper layer 39 is provided on the end face side and both end faces that are a part of the substrate installation face that is the bottom face of the leg portion 16. Therefore, the lower layer 18 is exposed on a part of the substrate mounting surface.

Although not shown, the third embodiment is also provided at both ends of the positive temperature coefficient thermistor element body 22 in which legs 26, 26 are provided on the opposite side of the substrate mounting surface shown in the second embodiment. The electrode 33 including the two layers of the lower layer 18 and the upper layer 39 shown in FIG.

The main body 1 of the above-mentioned positive temperature coefficient thermistor element body
2,22 and leg parts 16,1 provided at both ends of the main body
If the step S between the substrate mounting surface of 6, 26, 26 is 0.1 mm or more, it is possible to prevent the contact between the heat generating portion H of the PTC thermistor 11 and the PTC thermistor 11 due to the unevenness or the deflection of the substrate and the circuit board. it can.

Further, although the above-mentioned upper layers 19 and 39 are formed on the ends of the positive temperature coefficient thermistor elements 12 and 22, they are for soldering to the circuit board and are formed at least on the board mounting surface. It may have been done.

[0024]

As described above, in the positive temperature coefficient thermistor according to the present invention, since the legs are provided at both ends of the main body of the positive temperature coefficient thermistor body, the substrate mounting surface and the heat generating portion of the positive temperature coefficient thermistor element are There is a step between. Therefore, the heat can be prevented from being directly conducted to the circuit board to which the positive temperature coefficient thermistor is attached.

Therefore, when the positive temperature coefficient thermistor is used as an overcurrent protection element, the attenuation start time becomes short. When used as a temperature sensor, the heat capacity is determined by the size of the positive temperature coefficient thermistor, so that the thermal response is improved. Further, when an overcurrent flows in a circuit including the temperature sensor due to a short circuit or the like, even if the temperature sensor itself generates heat, the temperature rise of the circuit board can be prevented.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of a positive temperature coefficient thermistor according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a side perspective view showing a second embodiment of the positive temperature coefficient thermistor according to the present invention.

FIG. 4 is a side sectional view showing a third embodiment of the positive temperature coefficient thermistor according to the present invention.

FIG. 5 is a conventional perspective view.

[Explanation of symbols]

 11,21,31 Positive characteristic thermistor 12,22 Positive characteristic thermistor body 13,33 Electrode 15,25 Main body 16,26 Leg 18 Lower layer 19,39 Upper layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Namikawa 2 26-10 Tenjin Tenjin, Nagaokakyo City, Kyoto Murata Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A PTC thermistor element body has a main body and legs provided at both ends of the main body. The positive characteristic thermistor element body has both end faces and the vicinity of both end faces, and the leg portions and the leg parts. A positive temperature coefficient thermistor, which is characterized in that an electrode is provided on a main body in the vicinity. 2. The positive temperature coefficient thermistor according to claim 1, wherein the step between the main body of the positive temperature coefficient thermistor body and the substrate mounting surface of the leg is 0.1 mm or more. 3. The electrode comprises a lower layer made of nickel and an upper layer made of silver, and the upper layer is provided at least on a substrate mounting surface of the leg portion, and the lower layer is exposed outside an end portion of the upper layer. The positive temperature coefficient thermistor according to claim 1 or 2.