JPS5917510B2 - PTC heating element and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a barium titanate semiconductor ceramic heating element (hereinafter referred to as PTC thermistor) having a positive temperature coefficient of resistance.
This invention relates to a PTC heating element using.

Conventionally, PTC heating elements have been used as fixed-temperature heating elements in electronic mosquito repellents, electronic heat shields, etc., but recently they have been put to practical use in oil atomization heating systems to improve combustion efficiency, especially in oil and gas stoves. It is about to be reduced to 0.
A high output constant temperature heating element that takes advantage of the characteristics of such a PTC thermistor as a constant temperature heating element is attracting attention. However, in the conventional PTC heating element, as shown in Fig. 1, ohmic electrodes are formed by depositing silver electrodes 2, 2 on both ends of the PTC thermistor body 1 by printing silver alloy paste, etc. However, the structure is such that metal plates 3, 3 are brought into surface contact with the surfaces of the silver electrodes 2, 2.

However, with such an electrode structure, as shown in FIG. When a potential difference is applied between the silver electrodes 2 and 2, a silver migration phenomenon occurs in which silver migrates and is deposited along the outer peripheral surface of the PTC thermistor body 1, which often results in a short circuit between the electrodes. It was hot.

Such a silver migration phenomenon is called a silver migration phenomenon (indicated by reference numeral 4 in FIG. 2), and is particularly accelerated in a high temperature and high humidity atmosphere.

If the electrode is formed using a noble metal such as gold, platinum, or palladium instead of silver, the silver migration phenomenon will not occur, but this will increase the cost of the product and is not practical. There are also known methods of preventing silver migration by coating a silver electrode with a metal layer such as solder or configuring a barrier on parts with the same potential as a silver migration barrier, but this method is costly. In the case of a PTC heating element, it is necessary to select a metal layer to be coated due to the high temperature, which is difficult in terms of design.

The present invention completely prevents the above-mentioned silver migration phenomenon with a simple configuration, and at the same time stabilizes the characteristics by eliminating the thermal breakdown and imbalance of heat generation caused by local heat generation of the element body. It is an object of the present invention to provide a PTC heating element with reduced in-plane resistance and improved electrode conductivity, and a method for manufacturing the electrode.

In order to achieve the above object, the ℃ heating element according to the present invention has a metal other than silver as a main component on both end surfaces of a barium titanate-based semiconductor ceramic body having a positive temperature coefficient of resistance, and A first conductive layer is formed in ohmic contact with the barium titanate-based semiconductor ceramic body, and a conductive layer having a smaller planar area than the first conductive layer is formed on the entire outer circumference. A second conductive layer mainly composed of silver having a gap is formed therein.

Moreover, in order to obtain this PTC heating element, the PTC heating element according to the present invention
The manufacturing method of the C heating element is to use a metal other than silver as a main component on both end faces of a barium titanate semiconductor ceramic material having a positive temperature coefficient of resistance so as to be in ohmic contact with the material. After forming the metal coating layer, a conductive layer mainly composed of silver having a smaller planar area than the metal coating layer is formed on the metal coating layer by a screen printing method, and a gap is formed around the entire outer peripheral edge. It is characterized by being coated in a manner similar to the above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be specifically described below with reference to the accompanying drawings, which are examples.

FIG. 3A is a plan view of a PTC heating element according to the present invention, FIG. 3B is a front sectional view, and FIG. 4 is a perspective view.

In the figure, reference numeral 21 denotes a PTC thermistor element, which in this embodiment is formed into a disk shape with a diameter of 34 m/m, for example. On both opposing end surfaces of the element body 21, a first conductive layer 22, which is mainly composed of a metal other than silver and is in ohmic contact with the element body 21, is formed. In this way, in the present invention, since the first conductive layer 22 is made of a material whose main component is a metal other than silver, it is possible to prevent silver migration from occurring in the first conductive layer 22. Can be done. Furthermore, since the first conductive layer 22 is in ohmic contact with the element body 21, it is possible to directly bring out the positive resistance-temperature characteristics of the element body 21 itself. Moreover, since the first conductive layer 22 is formed on substantially the entire surface of both end surfaces of the element body 2, the current density from the first conductive layer 22 to the element body 21 is
It becomes uniform over the entire region of both end faces of the element body 21. For this reason, the element body 21 generates heat evenly over substantially the entire surface, heat destruction of the element body 21 due to localized heat generation, and heat generation imbalance are eliminated, and homogeneity is stabilized. The first conductive layer 22 may be formed as a metal plating layer using an electroless plating method.

That is, the element body 21 is immersed in an electroless nickel polishing solution, metal ions are chemically reduced and precipitated over the entire surface of the element body 21 using a reducing agent, and then unnecessary portions on the sides of the element body 21 are ground by centerless grinding. Alternatively, a metal plating layer made of nickel having approximately the same diameter, that is, a first conductive layer 22, is formed on both end surfaces of the element body 21 by dissolving and removing it with a resist.
Note that this first conductive layer 22 may be formed by a method other than the electroless plating method, such as an ion plating method or a sputtering method. Further, on the first conductive layer 22, a second conductive layer 23 whose planar area is smaller than that of the first conductive layer 22 and whose main component is silver is formed.

In order to form the second conductive layer 23, a frit-containing silver alloy paste is applied concentrically onto the first conductive layer 22 with a suitable gap G left on the outer periphery by screen printing, and Baking treatment. The gap G is suitably about 2 m/m for the material 21 having a diameter of 34 m/m, so that the second conductive layer 23 with a diameter of 30 m/m is formed on the first conductive layer 22 by baking. As mentioned above, since the first conductive layer 22 is made of a metal other than silver, such as an electroless nickel plating layer, it is effective in preventing silver migration and making the current density uniform. Internal resistance is large and conductivity is not very good.

Therefore, in the present invention, by providing the second conductive layer 23 mainly composed of silver with high conductivity on the first conductive layer 22, the in-plane resistance can be lowered and the above-mentioned drawbacks of the first conductive layer 22 can be reduced. I was able to solve it. However, since the second conductive layer 23 is mainly composed of silver, the occurrence of silver migration becomes a problem again.

As a measure to prevent silver migration in the second conductive layer 23, in the present invention, the planar area of the second conductive layer 23 is formed to be smaller than that of the first conductive layer 22. With such a structure, when an electrode plate etc. is stacked on the second conductive layer 23, the second conductive layer 22 and the electrode plate stacked on the second conductive layer 23 are separated. conductive layer 2
A gap is formed based on the layer thickness of 3.3 and the gap G between the first conductive layer 22 and the second conductive layer 22. Due to these voids, the second conductive layer 23, which is mainly composed of silver, is substantially cut off from the outside air, and even if there is a high temperature and humid atmosphere around it, the second conductive layer 23 cannot be touched. Therefore, silver migration in the second conductive layer 23 is prevented from occurring, and short circuits between electrodes along the outer periphery of the element body 21 are prevented. Next, electrode plates are brought into close contact with both end surfaces of the PTC thermistor, covering the gap G, thereby completing the PTC heating element of the present invention.

FIG. 5 is an exploded perspective view of a high-output heating element for oil atomization heating as a specific example. In this embodiment, a PTC heating element 51 is provided with a first conductive layer made of a metal plating layer on both end faces, and a second conductive layer 52 made of a silver alloy based on which a gear G is provided on the outer periphery on the first conductive layer. I am using it.

The gap G has a width of about 1 to 3 m/m.
Two electrode plates 53 are brought into close contact with both end surfaces of the PTC thermistor 51 so as to cover the gap G. Furthermore, two alumina porcelain plates 5
A positioning mechanism is provided between the electrode plate 53 and the alumina porcelain plate 54, and includes a projection 58 and a recess 5r that fit into the mutual contact surfaces of the electrode plate 53 and the alumina porcelain plate 54. Next, lug pieces 55 having through holes through which electrode lead wires 56 are inserted are protruded from both sides in the radial direction of the alumina porcelain plate 54, and the PTC thermistor is inserted between the lug pieces of the two alumina porcelain plates. 51 and the electrode plate 53 are interposed therebetween, and an elastic hook piece 55 is hooked thereon so that the electrode plate 53 is elastically supported. Next, Table 1 shows the results of comparison between the present invention and conventional products.

The sample is 34TEL in diameter as shown in Figures 1 and 3.
Thickness: 2.5 m/m (7) Using a PTC thermistor body with a single point at 240°C and having the same dimensions as in the previous example, it was placed in a test chamber as a high-temperature continuous load test at 350°C, A.
The test was carried out for 234 hours (HR) with ClIO applied.

In Table 1, R2O of the sample indicates the resistance value of the PTC thermistor at 20°C. As shown in Table 1, compared to conventional products, the electrode structure of the present invention effectively prevents short-circuiting of both electrodes due to silver migration of the silver alloy electrode due to energization at high temperatures and under humid loads. It is possible.
As described above, the PTC heating element according to the present invention reliably prevents the occurrence of silver migration phenomenon, prevents short circuit between electrodes, and generates constant temperature heat especially for oil atomization heating method which generates a large amount of heat. This has the effect of significantly improving reliability in physical systems, etc.

In addition, it is possible to stabilize the characteristics by eliminating thermal breakdown and imbalance in heat generation due to localized heat generation in the element body, and also to reduce the in-plane resistance of the electrode surface and improve the conductivity of the electrode. Moreover, the silver-based electrode, which is the second conductive layer of the PTC thermistor, can be formed by an extremely easy method of screen printing, and by making its plane area smaller than the metal plating layer, which is the first conductive layer, product costs can be reduced. Therefore, there are great industrial benefits.

[Brief explanation of drawings]

FIG. 1 is a plan view and a structural cross-sectional view of a conventional PTC thermistor, FIG. 2 is a view showing the state of silver migration, FIG. The figure is a perspective view of the same, and FIG. 5 is an exploded perspective view of a PTC heating element showing an embodiment of the present invention. 2... Barium titanate based semiconductor ceramic body having a positive temperature coefficient of resistance, 22... Metal plating layer, 23... Silver based electrode layer, G... ... Gap.

Claims (1)

[Claims] 1. Both end faces of a barium titanate-based semiconductor porcelain body having a positive temperature coefficient of resistance contain a metal other than silver as a main component,
A first conductive layer is formed in ohmic contact with the barium titanate-based semiconductor ceramic body, and the first conductive layer has a smaller planar area than the first conductive layer and has an outer circumferential edge. A second silver-based material with a gap around the periphery.
A PTC heating element characterized in that a conductive layer is formed. 2. The PTC heating element according to claim 1, wherein the first conductive layer is made of a metal plating layer. 3. The PTC heating element according to claim 2, wherein the first conductive layer is a nickel plating layer. 4. Forming a metal coating layer containing a metal other than silver as a main component on both end faces of a barium titanate semiconductor ceramic element having a positive temperature coefficient of resistance so as to be in ohmic contact with the element. After that, on top of this metal coating layer, a conductive layer mainly composed of silver, which has a smaller planar area than the metal coating layer, is deposited by a screen printing method so that a gap is formed around the entire outer periphery. A method for producing a PTC heating element, characterized in that: 5. The PT according to claim 4, wherein the metal coating layer is formed by electroless plating.
C. Manufacturing method of heating element.