JPH1070002A - Ptc ceramic thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTC ceramic thermistor which has a low resistance and high safety, does not produce a rise in resistance value at after heating due to an overecurrent and can be made a low cost. SOLUTION: A device has a laminate of PTC ceramic sheets with electrodes formed thereon. At least one of two terminal electrode plates is previously branched at one end so that they are alternately inserted between the ceramic sheets, and the electrode plastes are disposed from two side faces so as to electrically parallel connect the ceramic sheets. The main part of this structure is covered with a thermally shrinkable tube t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-resistance PTC ceramic thermistor used for protecting circuits such as batteries.

[0002]

2. Description of the Related Art A PTC thermistor exhibits a characteristic in accordance with Ohm's law in which a current is proportional to a voltage up to a certain current, as in a normal resistor. It has the characteristic of suppressing current,
Utilizing this characteristic, it is widely used for applications such as overcurrent protection such as short circuit protection and transformer protection of circuits.

[0003]

Among them, a small and low-resistance PTC thermistor is required to protect the circuit of a battery or the like because the load resistance of the circuit must be as small as possible. As such a PTC thermistor, an organic PTC thermistor using an organic polymer material, in which conductive particles such as carbon black are mixed and dispersed, as a base material, is usually put into practical use. And there is a problem with safety. Further, the organic PTC thermistor has a drawback that when a heat generation state due to an overcurrent continues for 5 minutes or more, the subsequent resistance value changes to about twice the initial resistance value.

[0004] The above-mentioned problems can be solved by using ceramics for the body of the PTC thermistor.
Simply forming electrodes on ceramics is not practical because the element shape becomes too large to obtain the required characteristics. Therefore, in order to obtain a small and low-resistance PTC thermistor using PTC ceramics, a structure in which a plurality of PTC ceramics on which electrodes having ohmic contact are formed are alternately stacked so as to be electrically connected in parallel. Has been proposed.

[0005] For example, Japanese Patent Application Laid-Open No. 6-5402 discloses a laminated PTC ceramic thermistor of integral firing type. Generally, in PTC ceramics, an electrode having ohmic contact must be formed, and since its component is based on a base metal such as Ni, it must be fired in a reducing atmosphere. In the integral firing type, since the ceramic is fired in a reducing atmosphere, a PTC thermistor having sufficient characteristics cannot be generally obtained due to a reduction in PTC characteristics due to reduction of the ceramic.

In Japanese Patent Application Laid-Open No. 6-36904,
Plural PTs formed with electrodes having ohmic contact
An example is disclosed in which a C thermistor is formed by laminating C ceramics themselves and electrically connecting each PTC ceramic in parallel. As methods for electrically connecting ceramics in parallel, electrode baking and bonding with a conductive adhesive or cream solder described in the above publications are known, all of which are disadvantageous in cost or excessive. If there is a risk of melting the adhesive due to heat generation at the time of electric current,
No suitable connection method has been found.

[0007]

SUMMARY OF THE INVENTION The present invention uses a flame-retardant material that has low resistance and at the same time has sufficient PTC characteristics, hardly increases the resistance after overheating due to overcurrent. To provide a thermistor that can be manufactured relatively inexpensively.

That is, the gist of the present invention is to provide an element in which two or more PTC ceramic plates having electrodes having ohmic contact on both main surfaces are stacked in parallel with the main surfaces, Two terminal electrode plates each having one end branched in advance so as to be sandwiched between them alternately are arranged and configured from two side surfaces so that each PTC ceramic plate is electrically connected in parallel. A PTC ceramic thermistor, wherein a main part of the structure is covered with a heat-shrinkable tube.

In the thermistor according to the present invention, if a step is formed at the other end of each terminal electrode plate, a distance can be provided between the PTC ceramic plate and the mounting substrate.
Even if the TC ceramic plate is in a heating state due to overcurrent,
The solder in the surface mount does not melt.

Hereinafter, the present invention will be described specifically. As for the PTC ceramic plate used in the present invention, a material may be selected as the PTC ceramic according to the desired characteristics. However, from the viewpoint that low resistance and sufficient PTC characteristics can be obtained, a barium titanate-based semiconductor material is fired. PTC ceramics are preferably used. Various shapes such as a circle, an ellipse, a rectangle, and a square can be selected according to the purpose.
Further, since it is covered with a heat-shrinkable tube, a shape having corners, for example, a rectangle is preferable.

As a method for forming an electrode having ohmic contact on the PTC ceramic plate, N
A method usually used for PTC ceramics, such as an i-plating method or a method of baking an ohmic silver electrode, is employed. At this time, in order to prevent a short circuit between the electrode portion having ohmic contact and the terminal electrode plate on the counter electrode side, it is preferable that the electrode having ohmic contact is not formed over the entire PTC ceramic main surface. For example, it is preferable to provide a gap portion in a range of about 0.1 mm or more and 0.5 mm or less from each side of the ceramic plate.

As the material of the terminal electrode plate used in the present invention, any conductive material that can withstand heat of 200 ° C. can be used. For example, a tin-plated brass or copper plate,
Ti-Cu alloy, beryllium-copper alloy and the like are preferable.

As the structure of the terminal electrode plate, two or more P
The two terminal electrode plates may be arranged so as to be alternately sandwiched between the main surfaces of the ceramic plates so that the TC ceramic plates can be electrically connected in parallel. To do this,
One end of at least one terminal electrode plate needs to be branched in advance. For example, when the PTC ceramic thermistor of the present invention is formed by using two PTC ceramic plates, one end of one terminal electrode plate is formed by a surface formed by a1 and a2, as shown in FIG. It is preferable that the terminal electrode plate is processed into a three-branched shape so that it can be sandwiched between two surfaces, and the other terminal electrode plate is arranged without branching (b)
1).

Similarly, when three PTC ceramic plates are used, each of the two terminal electrode plates is processed into a branched shape so that one end thereof can be sandwiched between two surfaces. The number of surfaces formed by the electrode plate is three on one side and two on the other side. As described above, when the PTC ceramic thermistor of the present invention is configured using N PTC ceramic plates,
The sum of the surfaces formed by the two terminal electrode plates is N + 1. That is, assuming that the number of surfaces formed by the two terminal electrode plates is L and M, respectively, the relationship of (L + M) = N + 1 holds, and when N is an even number, L = M + 1
And L = M when N is an odd number.

Regarding the shape of the terminal electrode plate at the point of contact with the PTC ceramic plate, the contact resistance between the electrode having ohmic contact formed on the PTC ceramic and the terminal electrode plate is smaller than the resistance value of the PTC thermistor. It is acceptable if it is within a range that can be ignored. The dimensions of the terminal electrode plate at this contact portion must be set smaller than the length and width of the PTC ceramic plate, and care must be taken not to protrude from the ceramic plate.

The other outer ends of the terminal electrode plates located outside the ceramic plate are, as shown in FIGS.
A step is formed, and the distance between the PTC ceramic plate and the mounting board is preferably 1 mm or more, more preferably 3 mm or more. The formation of the step prevents the solder of the surface mounting portion from melting due to heat generation of the PTC ceramic plate due to an overcurrent after mounting on the circuit board.

As shown in FIG. 2, two terminal electrode plates (a, b) are formed from two sides of a PTC ceramic plate (c) having electrodes (d) having ohmic contacts on both main surfaces. ) So that they can be electrically connected in parallel. In the drawings of the present invention, an example in which the terminal electrode plates are arranged from the front is described, but in the side direction when each terminal electrode plate is arranged and configured, a distance is set so that the terminal electrode plates are not short-circuited, or the ceramic plate is disposed. The terminal electrode plate itself may be disposed from any direction as long as the terminal electrode plate itself is subjected to insulation treatment.

Further, as shown in FIG. 3, a heat-shrinkable tube (f) is put on a main part of the structure on which the terminal electrode plate is arranged, and a heat treatment is performed so that the heat-shrinkable tube (f) is intimately coated on the structure. This makes the connection between the PTC ceramic plate and the terminal electrode plate stronger. As a heat shrink tube,
It is preferable to use those made of flame-retardant Teflon or silicon. In order to further strengthen the connection between the PTC ceramic plate and the terminal electrode plate, a heat-resistant and flame-retardant adhesive may be used as needed in the arrangement and configuration process.

FIG. 4 is a cross-sectional view when the PTC ceramic thermistor of the present invention is configured in the arrangement of FIG. 3 and is cut perpendicular to the main surface of the PTC ceramic plate.
The drawing shows a case where the terminal electrode plate is cut along the direction in which the terminal electrode plates mesh (upper figure) and a case where the terminal electrode plate is cut vertically (lower figure). FIG. 5 is a side view of the PTC ceramic thermistor of the present invention in the arrangement of FIG. 3 when viewed from the outer end side of each terminal electrode plate, when viewed from the terminal electrode plate a in FIG. 1 ( (Upper figure) and the case when viewed from the terminal electrode plate b (lower figure).

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail by way of examples. The lowercase letters a to f in parentheses respectively correspond to the symbols in the figure. BaC
O ₃ : 0.62 mol, SrCO ₃ : 0.26 mol,
PbO: 0.12 mol, TiO ₂ : 1 mol, Mn
_{(NO 3) 2 · 6H 2} O: 0.00015mol, Y
_{(NO 3) 3 · 6H 2} O: 0.0015mol, SiO
₂ : Each of ₂ mol was blended, wet-mixed in a ball mill, calcined, pulverized, molded and calcined to a size of 12.5 mm.
A PTC ceramic of × 5 mm × 0.3 mm was obtained. An ohmic silver electrode and a cover silver electrode were baked on both main surfaces of these PTC ceramics to form electrodes (d) having ohmic contact. At this time, a gap portion (e) where an electrode having a width of 0.3 mm was not formed from the side of each end of the PTC ceramics was provided. The resistance value of the obtained PTC ceramic plate at 25 ° C.
It was 0.20Ω as a result of measurement by a four-terminal method using a resistance meter manufactured by AX-110A.

The two PTC ceramic plates (c) are
It is sandwiched between two terminal electrode plates (a, b) made of a Sn-plated brass plate having a thickness of 0.1 mm and processed into the structure shown in FIG. 1 (FIG. 2), and a portion corresponding to the PTC ceramic plate is made of Teflon. And heat treated to obtain a PTC ceramic thermistor (FIG. 3). The external dimensions of the main part of the PTC ceramic thermistor (excluding the protruding part of the terminal electrode plate) thus obtained were 12.5 mm × 5.4 mm × 1.3 mm.
The resistance at 5 ° C. was 0.10Ω. Next, this PT
A voltage of 12 V DC was applied to the C ceramic thermistor for 10 minutes to generate heat in an overcurrent state, but no change in appearance was observed. Then, after the voltage application was completed, the device was left at 25 ° C. for 1 hour, and the resistance value was measured. As a result, it was 0.10 Ω, and there was no change in the resistance value before and after the operation. Further, the device was broken by applying a voltage higher than the withstand voltage of the thermistor itself, but it did not burn.

[0022]

The PTC ceramic thermistor of the present invention has low resistance and uses all flame-retardant materials, so that even if a voltage higher than the rated voltage is applied, the thermistor may break. Even if any abnormalities occur, it does not burn and has high safety. In addition, since ceramics are used as the PTC element, there is no increase in resistance after heat generation due to overcurrent as seen in organic polymer materials. Furthermore, the use of a heat-shrinkable tube eliminates the need for the bonding step, thereby enabling relatively inexpensive manufacturing costs.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a terminal electrode plate used in the present invention.

FIG. 2 is a perspective view showing an example of a case where stacked PTC ceramic plates are sandwiched between terminal electrode plates from two side surfaces so that they can be electrically connected in parallel.

FIG. 3 is a perspective view of a PTC ceramic thermistor showing an example of the present invention.

4 is a cross-sectional view of the arrangement configuration of FIG. 3 when cut perpendicular to the main surface of the PTC ceramic plate.

5 is a side view of the arrangement configuration of FIG. 3 when viewed from the outer end side of each terminal electrode plate.

[Explanation of symbols]

a, b: terminal electrode plate, c: PTC ceramic, d: electrode having ohmic contact, e: gap, f: heat shrinkable tube

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Minoru Ishihara 1-33, Funamachi, Taisho-ku, Osaka

Claims (2)

[Claims] 1. An element comprising two or more PTC ceramic plates having electrodes having ohmic contacts formed on both main surfaces thereof stacked in parallel with the main surfaces, alternately between the main surfaces of the ceramic plates. At least one terminal electrode plate having at least one end preliminarily branched so as to be sandwiched between each PTC
A PTC ceramic thermistor characterized in that ceramic plates are electrically connected in parallel and arranged from two sides, and a main part of the structure is covered with a heat-shrinkable tube. 2. The PTC ceramic thermistor according to claim 1, wherein a step is formed at the other external end of each terminal electrode plate.