JP3169096B2 - Positive thermistor - Google Patents

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 (hereinafter referred to as a PTC element), and more particularly to an electrode structure thereof.

[0002]

2. Description of the Related Art Conventionally, a PTC element is known to have a characteristic that when a large current flows when a voltage is applied, the resistance increases due to the heat generated by a thermistor element, which is a porcelain. Detection, overheat detection, temperature control, motor start, degaussing, etc. For example, in an automatic degaussing circuit for erasing residual magnetism of a TV cathode ray tube, as shown in a simplified manner in FIG.
The configuration in which the C element 10 is connected in series between the cathode ray tube coil 20 and the AC power supply 21 is adopted. That is, the automatic degaussing circuit performs degaussing by first applying an AC current larger than the remanence to the CRT coil 20 from the AC power supply 21 and then gradually attenuating the current to bring the magnetic flux density close to zero. In this automatic degaussing circuit, the current is controlled and attenuated by the PTC element 10.

As shown in FIG. 3, a metal plating layer 12 made of nickel (Ni) or the like is formed on both main surfaces of a disc-shaped thermistor element 11 as shown in FIG. After being formed, it is common to apply and bake an electrode layer 13 containing silver (Ag) as a main component on each metal plating layer 12. The metal plating layer 12 functions as an ohmic layer, and is usually formed with a very small thickness.

Then, for example, a degaussing PTC element 10
In such cases, the thickness of the thermistor body 11 is increased, for example, to 3.8 m, in order to adjust the demagnetization time or to improve the static withstand voltage characteristics (destruction characteristics when voltage is gradually applied).
m or more. Furthermore, when the electrode layer 13 containing Ag as a main component is used, silver migration may occur due to the influence of the atmosphere in the place where the PTC element 10 is used, for example, moisture or a flux gas generated during solder mounting. It is easy to cause and risk of destruction. Therefore, in order to prevent such inconvenience from occurring, the electrode layer 1
The occupied area of the thermistor element 3 is set smaller than the surface area of the main surface of the thermistor element body 11, and the gap portion 14 is left on the periphery of the main surface of the thermistor element body 11.

[0005]

However, the PTC element 10 having the above-mentioned conventional structure, in particular, a PTC element used for degaussing or motor starting in which a large current flows when a voltage is applied.
In the element 10, if the thickness of the metal plating layer 12 is too thin despite the thickness of the thermistor body 11 being as thick as 3.8 mm or more, the flash withstand voltage characteristics (F withstand voltage characteristics: destruction against inrush current) As a result, degradation (characteristics) is caused, and a destruction (shown by a phantom line in FIG. 3) occurs in which a portion corresponding to the electrode layer 13 of the thermistor body 11 is cut off.
This would lead to a decrease in the reliability for the zero. It is considered that such deterioration of the F breakdown voltage characteristic is caused by a difference in current density between a portion of the metal plating layer 12 in contact with the edge 13a of the electrode layer 13 and another portion when limiting the current. Can be

The present invention has been made in view of such inconvenience, and it is an object of the present invention to provide a PTC element capable of preventing deterioration of the F breakdown voltage characteristic and improving reliability. And

[0007]

According to the present invention, a metal plating layer is formed on both main surfaces of a thermistor body having a thickness of 3.8 mm or more, in order to achieve the above object. A PTC element in which an electrode layer containing silver as a main component is formed on each metal plating layer, wherein the thickness of the metal plating layer is 2 μm or more.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an external perspective view schematically showing a specific structure of a PTC element according to the present embodiment. In this figure, reference numeral 1 denotes a PTC element.

In this PTC element 1, a metal plating layer 3 made of Ni or the like is formed on both main surfaces of a disc-shaped thermistor body 2 having a thickness of 3.8 mm or more, respectively.
Further, the electrode layer 4 mainly composed of Ag is applied and baked on each metal plating layer 3, and the thickness t of each metal plating layer 3 is 2 μm or more. Each electrode layer 4 is formed such that a gap portion 5 remains on the periphery of the main surface of the thermistor element body 2. By providing the gap portion 5, silver migration is prevented from occurring. ing.

Next, the inventors of the present invention prepared a PTC element 1 of this embodiment and a PTC element 10 of a conventional example, each of which had a different specification from each other, and conducted a characteristic comparison experiment. As a result, the results shown in Table 1 were obtained. In addition, PTC as a sample used in this experiment
Each element has a metal plating layer made of Ni formed on both main surfaces of a disc-shaped thermistor body having a diameter of 18 mm made of ceramics prepared at a predetermined component ratio, and a metal plating layer made of Ni is formed on each metal plating layer. And an electrode layer mainly composed of Ag and having a predetermined thickness. The resistance value (R25) in Table 1 indicates the resistance value of the sample at 25 ° C., and the sample marked with * in Table 1 is out of the scope of the present invention.

[0012]

[Table 1]

That is, according to these Tables 1, in Samples 1 to 8 in which the thickness of the thermistor body is as thin as less than 3.8 mm, good F breakdown voltage characteristics can be obtained regardless of the thickness of the metal plating layer. Samples 9 and 10 and Sample 1 both having a body thickness of 3.8 mm and different thicknesses of metal plating layers
When compared with Samples 1 and 12, Samples 9 and 10 outside the range of the present invention were broken at a lower voltage than Samples 11 and 12 outside the range of the present invention, and the thickness of the metal plating layer was reduced. 2
It can be seen that the improvement of the F breakdown voltage characteristics due to the thickness of not less than μm is remarkably exhibited. Furthermore, the element body thickness is 3.8
Even when comparing samples 13 to 20 thicker than 1 mm, samples 13 and 17 outside the scope of the present invention break at a lower voltage than samples 14 to 16 and 18 to 20 within the scope of the invention. Also, the thickness of the metal plating layer is 2 μm
The improvement in the F withstand voltage characteristic can be seen by the above.

[0014]

As described above, according to the present invention, P
According to the TC element, a metal plating layer having a thickness of 2 μm or more is formed on each of both main surfaces of the thermistor body having a thickness of 3.8 mm or more, and an electrode mainly composed of silver is formed through the metal plating layer. Since the layer is formed, it is possible to prevent deterioration of the flash withstand voltage characteristic, and to improve the flash withstand voltage characteristic. As a result, the effect of improving the reliability of the PTC element can be obtained.

[Brief description of the drawings]

FIG. 1 is an external perspective view schematically showing a PTC element according to an embodiment.

FIG. 2 is an explanatory diagram illustrating an example of an automatic degaussing circuit.

FIG. 3 is a side view schematically showing a PTC element according to a conventional example.

[Explanation of symbols]

 Reference Signs List 1 PTC element (positive characteristic thermistor) 2 Thermistor body 3 Metal plating layer 4 Electrode layer

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-305404 (JP, A) JP-A-1-236602 (JP, A) JP-A-54-44797 (JP, A) 34048 (JP, U) JP-B 53-29386 (JP, B2) JP-B 51-20716 (JP, B1) JP-B 49-8379 (JP, B1)

Claims (1)

(57) [Claims] 1. A metal plating layer (3) is formed on both main surfaces of a thermistor body (2) having a thickness of 3.8 mm or more, and silver is formed on each metal plating layer (3). A positive temperature coefficient thermistor formed by forming an electrode layer (4) as a main component, wherein a thickness (t) of said metal plating layer (3) is 2 μm or more.