JPH0636904A - Positive characteristic thermister - Google Patents

Abstract

PURPOSE:To manufacture PTC (positive resistance temperature charac-terisctics) having the small nominal load resistance value and apparently narrow conductive area of elements while sustaining the breakdown voltage held by unit elements by a method wherein the laminated unit elements are electrically parallel-connected. CONSTITUTION:Adjacent inner electrodes 2 electrically connecting to outer electrodes 4 comprising Ag, Ni, Fe, etc., are to form the electrode non-formation parts 3. At this time, the unit elements of PTC thermistor mainly comprising barium titanate are laminated so as to electrically connect to the inner electrodes formed on adjacent electrodes while the outer electrodes 4 parallel- connecting respective unit elements are formed so that the PTC thermistor in the small nominal zero load resistance value having an arbitrary breakdown voltage in narrow conductive area may be manufactured.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thermistor having a positive resistance temperature characteristic (hereinafter referred to as PTC characteristic),
The present invention relates to an element structure in which a nominal zero load resistance value can be lowered and a withstand voltage value can be freely set without increasing a cross-sectional area of a current-carrying portion of the element.

[0002]

2. Description of the Related Art PTC characteristics above the Curie point are obtained by adding a small amount of a trivalent rare earth metal element such as Y and La or a pentavalent transition metal element such as Sb or Nb to barium titanate and firing it. It has been known. Originally, barium titanate is an insulator, and if it is simply made into a semiconductor, it will have a relatively high resistance value. However, as a recent field of use, an element having a resistance value as low as possible, such as an element for an overcurrent prevention circuit, is required. Therefore, the resistance has been lowered by methods such as highly purifying the raw material, changing the composition of the raw material in a complicated manner, and performing firing in a reducing atmosphere.

[0003]

However, the PTC element obtained by the method according to the prior art tends to have a reduced withstand voltage value as the nominal zero load resistance value decreases. This is a fatal problem in miniaturizing the device.
The withstand voltage value is generally related to the thickness of the element shape as represented by V / mm. Therefore, in order to increase the withstand voltage value, the thickness of the element shape is increased, but the increase in the thickness causes an increase in the resistance value. Therefore,
In order to reduce the resistance value, it is possible to increase the cross-sectional area of the current-carrying part, that is, the cross-sectional area of the element cut along a plane perpendicular to the current-carrying direction of the element. However, there was a limit to the miniaturization of low resistance and high withstand voltage devices.

An object of the present invention is to provide an element structure for obtaining a positive temperature coefficient thermistor which can solve the above problems without changing the conventionally used composition, firing conditions and the like.

[0005]

According to the present invention, electrodes of unit elements of a positive temperature coefficient thermistor having barium titanate as a main component and having the same shape and characteristics are laminated so as to be connected in parallel and are connected to each other. It is a low resistance element for high breakdown voltage in which an electrode for connecting the formed electrode to an external circuit is formed. When the unit element of the thermistor is disk-shaped, electrodes are formed on both sides of the current-carrying surface of the unit element, stacked so that the mutual electrodes are electrically connected, and each unit element is electrically connected in parallel. To reduce the electrical resistance without increasing the cross-sectional area of the current-carrying portion of the device.

[0006]

In the positive temperature coefficient thermistor of the present invention, since the unit elements are laminated and electrically connected in parallel, the nominal zero load resistance value is small while maintaining the withstand voltage of the unit elements, and the apparent energization of the elements. It is possible to obtain a PTC thermistor having a small sectional area.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a thermistor in which electrodes for electrical connection are formed. The unit element is a disk-shaped PTC thermistor unit element 1 containing barium titanate as a main component, and internal electrodes 2 made of Pd, Ag, Pd-Ag, Ni, Pt, Au, etc. are formed on both surfaces. Electrode non-formation portions 3 were provided at the ends of the internal electrodes on both sides of the unit element. The electrode non-formation portion of each surface is formed at a portion opposite to the internal electrode so as to be at the same position on the contact surface of the adjacent unit element.

FIG. 2A is a cross-sectional view in which the thermistor unit elements are laminated, but the adjacent internal electrodes 2 are electrically connected to each other, the electrode non-forming portion 3 is formed, and the internal electrodes are also formed. An external electrode 4 made of Ag, Ni, Fe, or the like is connected to and has an electric circuit as shown in FIG.

FIG. 3 is a plan view showing the external appearance of the high-voltage low-resistance element of the present invention, in which the lead wire 5 is connected to the external electrode and covered with resin.

EXAMPLE Internal electrodes 2 made of ohmic silver electrodes were formed on both surfaces of five disc-shaped PTC thermistor unit elements 1 having a diameter of 4.5 mm and a thickness of 0.5 mm, which contained barium titanate as a main component. . The internal electrodes on each surface had 0.
The electrode non-formation part 3 was provided in the part of 5 mm. The non-formation portions of the electrodes on each surface were formed at the opposite portions of each unit element so as to be at the same position on the contact surface of the adjacent unit elements.

The electrical characteristics of the unit element used are shown in Table 1 as a value expressed by the nominal zero load resistance value, the temperature coefficient, and the ratio of the common logarithm of the maximum resistance value when the temperature is changed and the nominal zero load resistance value. (Ψ), and withstand voltage.

[0013]

[Table 1]

Then, as shown in FIG. 2, the unit elements are laminated so that the electrode non-formed portions of the adjacent unit elements are overlapped with each other, and then silver paste is applied to the two places on the both sides of the laminated body where the electrode non-formed portions are located. After coating, the silver paste was heat-treated at 600 ° C. and baked to form a conductive connection between the internal electrode and the external electrode. The lead wire 5 was joined to the obtained external electrode 4, and the element was covered with the insulating heat-resistant resin 6.

FIG. 4 shows a logarithmic change in the resistance value with respect to the temperature of the element laminated with the unit element. The element according to the present invention was obtained by moving the resistance temperature characteristic of the unit element to the low resistance side as it was, and no change in the characteristic curve was observed due to the combination of the unit elements in parallel.

Further, FIG. 5 shows a graph of the number of unit elements and the change in resistance value of the elements.

With respect to the withstand voltage value, the value held by one unit element becomes the value of the element of the present invention as it is. Therefore, the withstand voltage value can be controlled by changing the thickness direction of the element.
At this time, the increase in the resistance value of the unit element caused by the thickness can be solved by increasing the number of unit elements. You can make various choices.

[0018]

According to the present invention, the unit electrodes of the positive temperature coefficient thermistor containing barium titanate as a main component are laminated and the internal electrodes formed on the adjacent unit electrodes are electrically connected to each other, and the unit electrodes are connected to each other. Form external electrodes connected in parallel,
The nominal zero load resistance value with any withstanding voltage value is small,
A PTC thermistor having a small energization area can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a thermistor in which electrodes for electrical connection are formed.

2A and 2B are a cross-sectional view and an electric circuit in which thermistor unit elements are laminated.

FIG. 3 is a plan view showing the appearance of a high-voltage low-resistance element of the present invention.

FIG. 4 is a diagram showing a change in resistance value with respect to temperature of an element laminated with a unit element.

FIG. 5 is a diagram illustrating the number of stacked unit elements and resistance value changes.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... PTC thermistor unit element, 2 ... Internal electrode, 3 ... Electrode non-formation part, 4 ... External electrode, 5 ... Lead wire, 6 ... Insulating heat resistant resin

Claims (1)

[Claims] 1. A unit element in which electrodes are formed on both surfaces of a positive temperature coefficient thermistor is laminated, adjacent electrodes are electrically connected, and each unit element is electrically connected in parallel. A positive temperature coefficient thermistor characterized in that an external electrode is formed to take out the electrodes formed on both sides to the outside.