JPH07142204A - Positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a short-circuit between heat radiating plates due to a solder flow by making the outside dimensions of the heat radiating plates smaller than those of both main surfaces of a positive temperature coefficient thermistor element and forming gaps between the outer peripheral edges of the heat radiating plates and the outer peripheral edges of the main surfaces of the thermistor element. CONSTITUTION:Heat radiating plates 13 are formed by successively plating copper plates having nearly square shapes with nickel and silver. The outside dimensions of the plates 13 are made smaller than that of a positive temperature coefficient thermistor element 12 so that first gaps G1 can be formed between them. In addition, the outside dimensions of the plates 13 are made larger than those of second electrodes 16 so that second gaps G2 can be formed between them. Therefore, no short-circuit occurs between the two heat radiating plates 13, because no solder fills up the space between the outer peripheral edges of the plates 13 and no solder flows between the plates 13 on both main surfaces of the element 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor device having a positive temperature coefficient thermistor element having a positive resistance temperature characteristic and used for overcurrent protection of a motor or the like.

[0002]

2. Description of the Related Art Regarding a conventional positive temperature coefficient thermistor device,
A description will be given based on FIG. The PTC thermistor device 1 is
The heat dissipation plates 3 and 3 made of copper plates are formed on both main surfaces of the positive temperature coefficient thermistor element 2 so that their centers are aligned and conductively and mechanically joined via solder.

The positive temperature coefficient thermistor element 2 is formed on both main surfaces of a barium titanate-based semiconductor ceramic of a substantially rectangular plate having a positive resistance temperature characteristic that the resistance increases at high temperatures.
At least a first electrode 4 made of chromium having ohmic contact in the lower layer, a nickel electrode 5 in the middle layer, and a second electrode 6 made of silver having solderability in the upper layer are formed as a multi-layered electrode. It was done. Moreover, the heat sink 3 is
The positive characteristic thermistor element 2 is made of a substantially rectangular copper plate having an outer dimension slightly larger than that of the thermistor element 2. Then, both main surfaces of the positive temperature coefficient thermistor element 2 and the heat sink 3,
An appropriate amount of cream solder or plate-like solder (not shown) is sandwiched between the two and the PTC thermistor device 1 to heat the entire PTC thermistor device 1. To attach.

The positive temperature coefficient thermistor device 1 having such a structure is
It is built in a motor or the like (not shown) so as to be connected in series, and when an overcurrent flows to the motor or the like, the overcurrent also flows to the positive temperature coefficient thermistor device 1 to generate heat. When the PTC thermistor device 1 generates heat, the internal resistance of the PTC thermistor element 2 rapidly increases to limit the current and stop the motor or the like. That is, the PTC thermistor device 1 is used for overcurrent protection of a motor or the like.

[0005]

In the PTC thermistor device 1 having such a structure, the PTC thermistor device 1 has a thickness of 1 mm or less because the PTC thermistor device 1 is connected in series to a motor or the like to protect an overcurrent during operation. The one having a low resistance of 0.5Ω or less and the radiator plate 3 having an outer dimension slightly larger than that of the positive temperature coefficient thermistor element 2 were used.

However, when the PTC thermistor element 2 and the heat dissipation plate 3 are joined via solder, if the PTC thermistor element 2 is thin and has a thickness of 1 mm or less, the PTC thermistor element 2 is soldered to the side end portion thereof. When the heat sink 7 flows out, as shown in FIG. 2, the heat sinks 3 and 3 joined to both main surfaces with solder 7 as shown in FIG.
They had a problem that they were short-circuited.

The object of the present invention is to eliminate the above-mentioned problems, and when two heat radiation plates are joined to both main surfaces of a positive temperature coefficient thermistor element having a small thickness by soldering or the like, it is unnecessary. It is an object of the present invention to provide a positive temperature coefficient thermistor device which does not short-circuit between heat sinks even if solder flows out.

[0008]

Therefore, in the present invention, at least the first electrode having ohmic contact on the lower layer and the upper layer on both main surfaces of the plate-shaped positive temperature coefficient thermistor element have solderability. In a positive temperature coefficient thermistor device in which a second electrode is provided and a heat sink is joined to the second electrode,
The outer dimension of the heat sink is smaller than the outer dimensions of both main surfaces of the positive temperature coefficient thermistor element, and the outer peripheral edge of the heat sink,
A first gap is provided between the positive temperature coefficient thermistor element and the outer peripheral edge of the main surface.

Further, the second electrode is composed of an electrode containing silver as a main component, and the outer dimension of the second electrode is smaller than the outer dimension of the heat sink, and the outer peripheral end of the second electrode and It is characterized by having a second gap between it and the outer peripheral edge of the heat sink.

[0010]

That is, according to the present invention, due to the above-mentioned configuration, the positive temperature coefficient thermistor element, which is larger than the outer dimension of the heat sink, is present between the two heat sinks. Since this positive temperature coefficient thermistor element has no solder, it prevents the electrodes on both main surfaces from being short-circuited.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the attached FIG. The positive temperature coefficient thermistor device 11 is configured by radiating the heat radiation plates 13 and 13 made of metal plates on both main surfaces of the positive temperature coefficient thermistor element 12 so as to be conductively and mechanically bonded to each other through solder with their centers aligned. Is.

Here, the positive temperature coefficient thermistor element 12 is made of a barium titanate based semiconductor ceramic of a substantially rectangular plate having a positive resistance temperature characteristic that the resistance increases at high temperature, and the size is, for example, 10.0 mm wide × long. 7.0m
On both main surfaces of the PTC thermistor element body having a thickness of 0.3 mm and a thickness of 0.3 mm, for example, a first electrode 14 made of a chromium electrode, a nickel electrode 15 and a second electrode made of a silver electrode are arranged in this order from the lower layer.
The three-layer electrode 16 of the electrode 16 is formed by sputtering or the like, and has a resistance value of 0.15Ω, for example. First electrode 1
4, the outer dimensions of the three layers of the nickel electrode 15 and the second electrode 16 are substantially the same, and the outer dimensions of the three layers of electrodes are smaller than those of the positive temperature coefficient thermistor element 12. It was formed.

The heat radiating plate 13 is made of a substantially rectangular copper plate having, for example, nickel plating as a base and silver plating on the surface thereof. The heat radiating plate 13 has outer dimensions of the positive temperature coefficient thermistor element 12. It is smaller and has a first gap G1 between the two outer dimensions. Further, the outer dimension of the heat dissipation plate 13 is larger than the outer dimension of the second electrode, and the second gap G is provided between the outer dimensions of both.
It has two. That is, the relationship among the three external dimensions is the external dimension of the second electrode 16 <the external dimension of the heat dissipation plate 13 <the external dimension of the positive temperature coefficient thermistor element 12.

Next, for example, an appropriate amount of cream solder or plate solder (not shown) is sandwiched between the second electrode 16 and the heat radiating plate 13 to heat the entire PTC thermistor device 11, thereby The heat dissipation plate 13 is reflow-soldered on both main surfaces of the PTC thermistor element 12 to form the PTC thermistor device 11.

The positive temperature coefficient thermistor device 11 having such a configuration is connected to a motor or the like in series and built therein. The internal resistance of the PTC thermistor device 11 increases due to self-heating due to overcurrent. Since this internal resistance blocks the current, it is used as an overcurrent protection element for the motor.

Since the basic structure of the positive temperature coefficient thermistor element 12 uses the conventional technique, its shape is not limited to the rectangular plate but may be a circular plate or the like. Further, the material of the heat dissipation plate 13 is not limited to copper having a high heat conductivity, and a material of a metal plate such as stainless steel or nickel silver having a low heat conductivity can be appropriately used according to the amount of heat dissipation. . When the surface of the heat dissipation plate 13 has poor solderability, both surfaces of the heat dissipation plate 13 can be soldered to the positive temperature coefficient thermistor element 12 by subjecting both surfaces to surface treatment with good solderability.

The electrodes formed on both main surfaces of the positive temperature coefficient thermistor element 12 are not limited to those in the above-mentioned embodiments, but the lower layer has a metal layer having ohmic contact and the upper layer has solderability. Any metal layer may be used. In particular, in the case where the upper layer is an electrode containing silver as a main component, if the outer dimensions of the heat dissipation plate 13 are larger than the outer dimensions of the electrode, silver migration is prevented.

[0018]

As described above, in the positive temperature coefficient thermistor device according to the present invention, since the outer dimension of the heat sink is smaller than the outer dimension of the positive temperature coefficient thermistor element, the solder is placed between the outer peripheral ends of the two heat sinks. There is a positive temperature coefficient thermistor element made of ceramic that does not stick. Therefore, the solder does not flow between the heatsinks on both main surfaces, and the two heatsinks are not short-circuited.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of a positive temperature coefficient thermistor device according to the present invention.

FIG. 2 is a vertical cross-sectional view of a PTC thermistor device according to a conventional example.

[Explanation of symbols]

 11 Positive Characteristic Thermistor Device 12 Positive Characteristic Thermistor Element 13 Heat Sink 14 First Electrode 16 Second Electrode G1 First Gap G2 Second Gap

Claims (2)

[Claims] 1. A plate-shaped positive temperature coefficient thermistor element is provided on both main surfaces thereof with at least a first electrode having ohmic contact as a lower layer and a second electrode having solderability as an upper layer. In a positive temperature coefficient thermistor device in which a heat sink is joined to an electrode, the outer dimension of the heat sink is smaller than the outer dimensions of both main surfaces of the positive temperature coefficient thermistor element, and the outer peripheral edge of the heat sink,
A positive temperature coefficient thermistor device having a first gap between the positive temperature coefficient thermistor element and the outer peripheral edge of the main surface. 2. The second electrode is composed of an electrode containing silver as a main component, and the outer dimension of the second electrode is smaller than the outer dimension of the heat sink, and the outer peripheral edge of the second electrode and The positive temperature coefficient thermistor device according to claim 1, wherein the positive temperature coefficient thermistor device has a second gap between the heat dissipation plate and the outer peripheral end.