JPS587044B2 - Positive temperature coefficient thermistor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positive temperature coefficient thermistor made of barium titanate semiconductor ceramic having a positive temperature coefficient of resistance, and a method for manufacturing the same.

A positive temperature coefficient thermistor has a current control function that allows you to obtain any heat generation temperature by appropriately selecting the Curie temperature, and that the electrical resistance value increases rapidly when a specific temperature is reached, automatically controlling the current and heat generation temperature. Because it has features such as having a self-temperature control function, and is safe and reliable, it has been widely used as a current control element in electronic/electric circuits or as a heat source in various heat generating devices.

This positive temperature coefficient thermistor takes various forms and structures depending on its use, but when used as a heating element in a heating device for heating and drying copy paper in a copying machine or for fixing, for example, as shown in FIG. As shown in A and B, electrodes 3 and 4 are provided on both sides of a PTC thermistor body 2 formed in a disk shape with a through hole 1, and electrodes 3 and 4 are provided around the through hole 1. A device with a separating gap G1 is used.

The electrodes 3 and 4 include nickel layers 3a and 4a deposited on the surface of the PTC thermistor body 2 by electroless nickel plating, and improved oxidation resistance and solderability of the nickel layers 3a and 4a. Silver layer 3 printed and baked for the purpose of
It has a two-layer structure with silver layers 3b and 4b, and the silver layers 3b and 4b are printed so as to cover the entire surface of the nickel layers 3a and 4a.

The above-mentioned gap G1 is necessary because this positive temperature coefficient thermistor is manufactured according to the manufacturing process shown in FIG. 2 a1 to a4.

That is, as shown in FIG. 2 a1, a positive temperature coefficient thermistor body 2 formed in a donut disk shape with a through hole 1 is coated with nickel electroless on its entire surface, as shown in FIG. 2 a2. After depositing the nickel layer 5 by plating and performing necessary treatments such as heat treatment, a frit-containing silver paste or the like is applied to the entire surface of the nickel layer 5 on both sides in the thickness direction, as shown in FIG. A silver layer 6 is formed by printing and baking, and then, as shown in FIG. delete.

As a result, the nickel layer 5 becomes the positive temperature coefficient thermistor body 2.
is separated by a gap G1 on both sides in the thickness direction,
A positive temperature coefficient thermistor having electrodes 3 and 4 as shown in FIGS. 1A and 1B is obtained.

In this case, the nickel layer 5 in the through hole 1 cannot be removed and remains as it is, but the electrodes 3 and 4 are made independent of each other by the gap G1.

However, if the silver layer 6 is printed on the nickel layer 5, the third
As shown in the enlarged view in FIG. When the area around the through hole 1 is removed by sandblasting 7 or the like, the hanging portion a remains inside the through hole 1.

The through hole 1 is used to pass an insulating pipe, set screw, etc. through when fixing the PTC thermistor, and as mentioned above, if the sagging part a remains, the inner diameter will be reduced, and the insulating pipe This makes it very difficult to insert the set screw.

Furthermore, if an attempt is made to remove this sagging part a, the positive temperature coefficient thermistor element etc. will be scraped off, leading to variations in the characteristics. Also, if the area around the through hole 1 is ground by sandblasting, the outer periphery will be ground by centerless polishing. In either case, the nickel layer 5 and the silver layer 6 are ground at the same time, so the nickel layer 5 and the silver layer 6 become entangled with each other due to the malleability and adhesiveness of the silver layer 6, resulting in poor grindability. Moreover, it may also lead to electrode peeling.

If the nickel layer 5 is ground and the nickel layers 5 on both sides are separated from each other before the silver layer 6 is printed, the problem caused by the entanglement of the silver layer 6 can be solved, but in this case, the silver layer 6
The printing position of the silver layer 6 shifts and the distance of the gap G1 fluctuates, leading to a decrease in reliability such as a decrease in withstand voltage.In order to eliminate such defects, the printing position of the silver layer 6 must be positioned with high precision. This will result in poor workability.

Furthermore, in addition to the various drawbacks in the manufacturing process described above, when the positive temperature coefficient thermistor is actually used, there is also a serious drawback in that it is susceptible to short-circuit accidents between electrodes due to migration phenomena.

That is, FIG. 1A. When the edges of the silver layers 3b and 4b are on the edges of the nickel layers 3a and 4a as shown in B, and the electrode plates 8 and 9 are stacked on the electrodes 3 and 4 as shown in FIG.
The edges of the silver layers 3b and 4b are in direct contact with the outside air.

Therefore, when a potential difference is applied to the electrodes 3 and 4 via the electrode plates 8 and 9 to generate heat, the silver layer 3b
, 4b come into contact with moisture in the outside air, and a silver movement phenomenon, that is, a migration phenomenon occurs.

Moreover, as mentioned above, the gap G separating the electrodes 3 and 4
1 only has a relatively short surface distance, so
If the migration phenomenon described above occurs,
The electrodes 3 and 4 are easily short-circuited via the nickel layer 5 in the through hole 1.

In other words, the conventional positive temperature coefficient thermistor has the drawback that it has an electrode structure that is susceptible to migration phenomena, and when migration phenomena occur, it is likely to cause a short-circuit accident between the electrodes.

The present invention eliminates the above-mentioned drawbacks and provides a highly reliable positive temperature coefficient thermistor that is less prone to short-circuit accidents between electrodes due to migration phenomena, and in which the gap distance does not change even if the printing position of the silver layer is misaligned. In addition, when part of the electrode layer is removed to make it independent as a counter electrode, the electrode layer can be easily removed while maintaining the uniformity of the shape, and the electrode layer can be easily removed without causing electrode peeling accidents. An object of the present invention is to provide a method for manufacturing a characteristic thermistor.

In order to achieve the above object, the present invention provides a positive temperature coefficient thermistor having a gap separating a pair of electrodes on the electrode forming surface of the positive temperature coefficient thermistor element, wherein the electrode is made of nickel coated on the positive temperature coefficient thermistor element. and a silver layer deposited on the nickel layer, the gap-side edge being located inside the gap-side edge of the nickel layer.

Further, the manufacturing method according to the present invention is a method for manufacturing a positive temperature coefficient thermistor having a gap separating a pair of electrodes on the electrode forming surface of the positive temperature coefficient thermistor element, in which the entire surface of the positive temperature coefficient thermistor element is coated with a nickel electroless plating method. After depositing the nickel layer, a silver layer is deposited on the nickel layer outside the region where the gap is to be formed, and then the nickel layer in the region where the gap is to be formed is removed.

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

5A, B to 8A, B all show examples of positive temperature coefficient thermistors according to the present invention, and FIGS. 5A to 8A
5A to 8B are perspective views, and FIGS. 5B to 8B are sectional views taken along lines (XI-Xi) to (X4-X4) in FIGS. 5A to 8A.

First, FIGS. 5A and 5B show the same through-type thermistor as the PTC thermistor already explained in FIGS. 1A and 1B.

The feature of this embodiment is that the nickel layers 3a and 4a are deposited on both sides of the PTC thermistor body 2 with a gap G1.
Above, a silver layer 3 is placed inwardly from the inner end E1 and outer end E2 of the nickel layer 3a or 4a, with gaps W1 and W2 in between.
b, 4b are provided in an annular shape.

With such a structure, the gap G1 is close to the nickel layer 3.
a, 4a, and as long as the silver layers 3b, 4b are printed on the nickel layers 3a, 4a, the width of the gap G1 changes depending on the printing position shift of the silver layers 3b, 4b, since it is irrelevant to the printing position. This eliminates the occurrence of such situations, and it is possible to almost completely prevent a decrease in withstand voltage due to misalignment of printing positions and short-circuit accidents between electrodes.

In addition, since the distance from the edge of the silver layers 3b, 4b to the nickel layer 5 in the through hole 1 is expanded by the gap W1, short-circuit accidents between electrodes due to migration of the silver layers 3b, 4b are less likely to occur. Become.

Moreover, as shown in FIG. 9, an electrode plate 8 is placed on the electrodes 3 and 4.
, 9 are overlapped, the lower surfaces 8a, 9a of the electrode plates 8, 9,
A gap d corresponding to the layer thickness of the silver layers 3b and 4b is provided between the nickel layers 3a and 4a.

is formed. The thickness of the silver layers 3b and 4b is at most 10μ
Because the layer is so small that the silver layers 3b and 4b are substantially cut off from the outside air, even if there is a high temperature and humidity atmosphere around them, the silver layers 3b and 4b will not come into contact with it. .

As a result, the migration phenomenon of the silver layers 3b and 4b is effectively suppressed.

Therefore, according to this embodiment, by increasing the bath surface distance between the electrodes and suppressing the migration phenomenon, short-circuit accidents between the electrodes due to the migration phenomenon can be almost completely prevented.

Further, in the case shown in FIGS. 6A and 6B, a nickel layer 3a is formed in an annular shape on one surface of the PTC thermistor body 2, and a gap W is formed on the nickel layer 3a from its edges E3, E4.
3, W4 is taken to form a coaxial annular silver layer 3b, and a drawer conductively connected to the electrode 4 on the lower surface via the nickel layer 5 of the through hole 1 in the area surrounded by the electrode 3. The electrodes 10 are arranged to face each other with an annular gap G1 interposed therebetween.

The extraction electrode 10 is composed of a nickel layer 10a and a silver layer 10b formed inside by a gap W5 from the gap side edge E5 of the nickel layer 10a.

Further, the electrode 4 on the lower surface side also has a silver layer 4b formed inside the outer edge E6 of the nickel layer 4a by a gap W6.

In this example as well, it is possible to avoid fluctuations in the width of the gap G1 due to misalignment of the printing positions of the silver layers 3b and 10b, and it is possible to prevent short-circuit accidents between the electrodes due to the migration phenomenon by increasing the surface distance between the electrodes. There are other effects.

Note that this embodiment has the advantage that the electrode 3 and the extraction electrode 10 are present on the same side, and the electrodes 3 and 4 can be drawn out from the same side.

7A and 7B show a structure in which a pair of electrodes 3 and 4 are provided on one surface of the PTC thermistor body 2, and an intermediate electrode 11 is provided on the other surface.

This embodiment also has the advantage that the electrodes 3 and 4 can be drawn out from the same side.

The electrodes 3 and 4 have a structure in which silver layers 3a and 4b are formed on the nickel layers 3a and 4a formed in a semicircular arc shape with a gap G1 separated from the edges E7 and E8 by gaps W7 and W8. The intermediate electrode 11 also has a two-layer structure including a nickel layer 11a and a silver layer 1lb formed on the nickel layer 11a from the edge E to the gap W and inside the nickel layer 11a.

Further, in the case shown in FIGS. 8A and 8B, gaps W1o and W11 are formed on the nickel layer 3a from the edges EIO and Ell.
A silver layer 3b is formed on the inner side, and the lead electrode 12 of the lower electrode 4 is disposed on the same surface as the electrode 3, facing each other with a gap G1 in between.

The extraction electrode 12 is electrically connected to the lower electrode 4 by an outer nickel layer 14 in a recess 13 provided on the outer periphery of the PTC thermistor body 2, and on a nickel layer 12a extending from this nickel layer 14, A silver layer 12b is provided inside the edge E12 by a gap W12.

Both of the embodiments shown in FIG. 7 and FIG.
It is possible to obtain the same effect as shown in FIGS.

Next, a method for manufacturing a positive temperature coefficient thermistor according to the present invention will be described with reference to FIGS. 10 a1 to a4.

This example shows a method for manufacturing the positive temperature coefficient thermistor shown in FIG. 5, but it can be similarly applied to the manufacturing method for the positive temperature coefficient thermistor shown in FIGS. 6 to 8. .

First, as shown in FIG. 10a1, a nickel layer 15 is deposited on the entire surface of the PTC thermistor body 2 by electroless nickel plating.

Next, after performing necessary treatments such as heat treatment, a frit-containing silver paste is printed on the sea urchin and nickel layer 15 to form a silver layer 16, as shown in FIG. 10, and baked.

When printing the silver layer 16, the edge E of the nickel layer 15
The edges E15 and E16 of the silver layer 16 are located inside the gaps W13 and W14 from the nickel layer 13 and E14.
Printing is performed so that the exposed portion 17 of No. 5 remains.

This prevents sagging.

Next, as shown in FIG. 10a3, the exposed portion 17 of the nickel layer 15 formed around the through hole 1 is removed by a gap G1 by sandblasting or the like.

In this case, the silver layer 16 is not removed and its edges El5, E1
6 is removed so that it is located inside the edges E17, E18 of the nickel layer 15 by re-gaps W17, W18.

In this way, only the nickel layer 15, which has good polishing properties, can be polished without causing various drawbacks associated with polishing the silver layer 16, such as deterioration of polishing workability due to entanglement of the silver layer 16, electrode peeling accidents, etc. can do.

Next, as shown in Figure 10 a4, the nickel layer 1 on the outer periphery
5 is removed by Senkless polishing.

As a result, a positive temperature coefficient thermistork as shown in FIGS. 5A and 5H is completed, but since the silver layer 16 is not polished during this cenless polishing, it is different from the polishing by sandblasting described above. Similarly, polishing can be easily performed without causing accidents such as electrode peeling.

As described above, the present invention provides a positive temperature coefficient thermistor having a gap separating a pair of electrodes on the electrode formation surface of the positive temperature coefficient thermistor element, in which the electrodes are connected to a nickel layer deposited on the positive temperature coefficient thermistor element. , the silver layer is deposited on the nickel layer and the edge on the gap side is located inside the edge on the gap side of the nickel layer, so the following effects can be obtained. be.

(1) The distance between the electrodes is expanded, making it difficult for short-circuit accidents between the electrodes to occur due to migration.

(2) Even if the printing position of the silver layer is misaligned, the width of the gap does not change, so the distance between the electrodes is maintained at a constant distance determined by the width of the gap, improving reliability.

(3) Printing and forming the silver layer is easy.

(4) In the case of a type in which an electrode plate is stacked on top of an electrode, the occurrence of silver layer migration phenomenon can be suppressed, and short-circuit accidents between electrodes due to migration can be almost completely eliminated.

Further, in the manufacturing method according to the present invention, in order to obtain the above-mentioned PTC thermistor, a nickel plating layer is deposited on the entire surface of the PTC thermistor element by electroless nickel plating, and then nickel is coated on the outside of the region where the gap is formed. The method is characterized in that a silver layer is deposited on the layer, and then the nickel layer in the area where the gap is to be formed is removed.When forming the gap separating the pair of electrodes, a part of the electrode is removed by sandblasting or centerless polishing. When removing the nickel layer, it is necessary to polish only the nickel layer, which has good polishability, and it is possible to avoid the various drawbacks caused by polishing the silver layer, such as poor polishability and electrode peeling accidents.

In addition, since the silver layer is printed inside the nickel layer, there is no dripping of the silver paste during printing, and there is no need for a process to remove dripping, so the uniformity of the shape is maintained and the characteristics are stable. Things can be manufactured efficiently.

[Brief explanation of the drawing]

Figures 1A and B are a perspective view and a sectional view of a conventional positive temperature coefficient thermistor, Figures 2 a1 to a4 are manufacturing process diagrams, and Figure 3 a
1, a2 are diagrams explaining the defects in the manufacturing process of FIGS. 2 a1 to a4, FIG. 4 is a diagram explaining the defects when using the positive temperature coefficient thermistor shown in FIGS. B
~ Figures 8A and 8B both show respective embodiments of the positive temperature coefficient thermistor according to the present invention, Figures 5A to 8A are perspective views thereof, and Figures 5B to 8B are perspective views of the positive temperature coefficient thermistor according to the present invention. Figures A to 8 are cross-sectional views taken along lines (X1 - Xt) to (X4 - , FIG. 10 is a process diagram of a method for manufacturing a positive temperature coefficient thermistor according to the present invention. 1... Through hole, 2... Positive temperature coefficient thermistor, 3, 4... Electrode, 3a, 4a...
Nickel layer, 3b, 4b...Silver layer, 5...
...Nickel layer, G1...gap.

Claims (1)

[Scope of Claims] 1. A positive temperature coefficient thermistor having a gap separating a pair of electrodes on the electrode forming surface of the positive temperature coefficient thermistor element, wherein the electrode includes a nickel layer deposited on the positive temperature coefficient thermistor element, and a nickel layer deposited on the positive temperature coefficient thermistor element. A positive temperature coefficient thermistor comprising a silver layer deposited on a nickel layer, the edge on the gap side being located inside the edge on the gap side of the nickel layer. 2. A positive temperature coefficient thermistor body formed in a flat plate shape with a through hole has a pair of electrodes on both sides thereof, and the pair of electrodes is formed between the inner circumferential surface of the through hole and each electrode. A positive temperature coefficient thermistor according to claim 1, characterized in that the positive temperature coefficient thermistor is separated by a gap. 3. A positive temperature coefficient thermistor element formed in a flat plate shape with a through hole has a pair of electrodes on both sides, and one of the pair of electrodes is connected to the same electrode as the other of the pair of electrodes through the through hole. A positive temperature coefficient thermistor according to claim 1, characterized in that the positive temperature coefficient thermistor has an extraction electrode drawn out on a surface, and has the gap between the extraction electrode and the other of the pair of electrodes. . 4 A positive temperature coefficient thermistor formed in a flat plate has a pair of electrodes on both sides, and one of the pair of electrodes is connected to the same electrode as the other of the pair of electrodes through a recess provided in the outer periphery of the positive temperature coefficient thermistor. The positive characteristic according to claim 1, characterized in that the positive characteristic has an extraction electrode drawn out on a surface, and has the gap between the extraction electrode and the other of the pair of electrodes. thermistor. 5. The PTC thermistor according to claim 1, wherein the pair of electrodes are provided on the same surface of the PTC thermistor. 6 In a method for manufacturing a positive temperature coefficient thermistor having a gap separating a pair of electrodes on the electrode forming surface of a positive temperature coefficient thermistor element, after depositing a nickel layer on the entire surface of the positive temperature coefficient thermistor element by nickel electroless plating method. . A method for producing a positive temperature coefficient thermistorc, comprising depositing a silver layer on the nickel layer outside the region where the gap is to be formed, and then removing the nickel layer in the region where the gap is to be formed.