JP2967221B2 - Positive thermistor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC thermistor element compatible with soldering, and more particularly to a PTC thermistor element having an improved electrode structure.

[0002]

2. Description of the Related Art A positive temperature coefficient thermistor element is formed by forming electrodes on both main surfaces of a plate-shaped positive temperature coefficient thermistor element made of, for example, a barium titanate-based semiconductor ceramic. Since the PTC thermistor body is made of semiconductor porcelain, it is necessary that the electrode does not form a barrier between the PTC thermistor body and the surface of the PTC thermistor body. there were. However, Ni has a high specific resistance so as to increase conductivity, and in an element to be soldered to an electrode, to increase solderability.
A structure in which a second electrode layer is formed is used.

However, when Ag is used as an electrode material in a positive temperature coefficient thermistor element, thermal migration occurs between the electrodes on both main surfaces, and a short circuit accident occurs. Therefore, conventionally, the following positive temperature coefficient thermistor elements have been proposed as a structure for preventing migration. The conventional positive temperature coefficient thermistor element 1 shown in FIG. 1 has a structure in which electrodes 3 and 4 are formed on both main surfaces of a disk-shaped positive temperature coefficient thermistor body 2. In this structure,
The electrodes 3 and 4 include inner electrode layers 3a and 4a made of Ni,
And outer electrode layers 3b and 4b made of Ag so as to have a smaller diameter so as to leave a gap region around the inner electrode layers 3a and 4a. That is, by providing the gap region g around the outer electrode layers 3b and 4b made of Ag, migration between the outer electrode layers 3b and 4b is prevented.

On the other hand, the positive temperature coefficient thermistor element 5 shown in FIG.
Is the outer electrode layer 3 in the thermistor element 1
It has a structure in which the entire surface exposed outside b, 4b is covered with solder coating layers 3c, 4c. That is, by covering the entire surface exposed to the outside of the outer electrode layers 3b and 4b made of Ag with the solder coating layers 3c and 4c having excellent solderability, the solderability is further improved and migration between the electrodes is achieved. Is more reliably prevented.

[0005]

In the positive temperature coefficient thermistor element 1 shown in FIG. 1, since the inner electrode layers 3a and 4a are made of a Ni thin film, as shown in FIG. There is a film resistance R. Therefore, a slight potential difference occurs due to the film resistance, and the gap region g
Is provided, migration between the electrodes may still occur. Therefore, in the positive temperature coefficient thermistor element 1, the thicknesses of the inner electrode layers 3a and 4a serving as bases are increased,
Attempts have been made to lower the film resistance. However, since the internal stress of the Ni thin film is large, the adhesion strength to the surface of the positive temperature coefficient thermistor element body 2 made of semiconductor porcelain decreases as the thickness increases. Therefore,
In the positive temperature coefficient thermistor element 1 scheduled to be soldered to the electrodes 3 and 4, the adhesion strength of the electrodes 3 and 4 is reduced, which is a fatal problem.

On the other hand, in the positive temperature coefficient thermistor element 5 shown in FIG. 2, although the outer electrode layers 3b, 4b made of Ag are covered with the solder coating layers 3c, 4c, migration between the electrodes is surely prevented. Sn, Pb or Sn constituting the solder coating layers 3c and 4c
-Pb alloy has low thermal conductivity. For this reason, there has been a problem that the thermal response and the heat recovery speed of the positive temperature coefficient thermistor element 5 are deteriorated, and the characteristics of the positive temperature coefficient thermistor element are deteriorated.

An object of the present invention is to provide a positive temperature coefficient thermistor element compatible with soldering, which has a structure which can not only prevent the occurrence of migration between electrodes but also hardly cause deterioration of electrode adhesion strength and characteristics. Is to provide things.

[0008]

The present invention is characterized in that a positive temperature coefficient thermistor element having electrodes formed on both main surfaces of a positive temperature coefficient thermistor body has the following configuration. That is, the first electrode layer is in ohmic contact with the main surface of the positive temperature coefficient thermistor body, and a region of a predetermined width is left on the first electrode layer near the periphery of the first electrode layer. Alternatively, a second electrode layer which is formed to have the same size as the first electrode layer and has a lower specific resistance than the first electrode layer and made of a material containing Al as a main component; And a third electrode layer formed of a material having better solderability than the first and second electrode layers, the third electrode layer being formed leaving a region of a predetermined width near the periphery of the second electrode layer. It is characterized by the following.

As a material for forming the first electrode layer, an appropriate material which makes ohmic contact with the semiconductor porcelain, for example, Ni, Cr, Ti, W or the like can be used. Further, as a material forming the third electrode layer, a material having better solderability than Ni, for example, Ag, Cu, Au, or the like can be used. The above-mentioned second electrode layer is preferably made of Japanese Patent Application No. 2-34086.
As disclosed in No. 0, Al and Si are mixed at a weight ratio of 4%.
It is composed of an Al-Si alloy containing at a ratio of 8 to 96: 4 to 52, thereby preventing migration between the electrodes more reliably without lowering the adhesion strength of the electrodes to the PTC thermistor body. obtain.

[0010]

In the positive temperature coefficient thermistor element of the present invention, the second electrode layer is made of a material mainly composed of Al having a lower specific resistance than the material of the first electrode layer. Therefore, since the film resistance of the second electrode layer is small, it is possible to reduce the potential difference near the periphery of the third electrode layer even when the third electrode layer having excellent solderability is made of Ag. Therefore, the occurrence of migration can be prevented.

In addition, even if the thickness of the electrode material containing Al as a main component is increased, the adhesion strength of the electrode does not easily decrease. Therefore, even when the thickness of the second electrode layer is increased and the film resistance is further reduced to thereby more reliably prevent the occurrence of migration, the adhesion strength of the electrode is maintained at a sufficient level. That is, according to the present invention, the second electrode layer is made of a material mainly composed of Al having a small specific resistance, and the second electrode layer is connected to the first electrode layer having ohmic contact with a solder such as Ag. By being interposed between the third electrode layer and the third electrode layer having an excellent property, the occurrence of migration is prevented without lowering the electrode adhesion strength.

[0012]

The present invention will be clarified by the following non-limiting examples. A positive-characteristic thermistor body made of a barium titanate-based semiconductor porcelain having a disk-like shape with a diameter of 14 mm x a thickness of 2 mm and a resistance value between both main surfaces of 7 Ω is prepared, and electrodes are formed in the following manner. The positive temperature coefficient thermistor elements of Examples and Comparative Examples 1 to 3 were produced.

[0013] As shown in the example Figure 3 (a) and (b), N on the entire surface of both main surfaces of the PTC thermistor element 11 prepared as described above
i is formed to a thickness of 1.5 μm, and the first electrode layer 12a,
13a was formed. Next, the first electrode layers 12a and 13a
Above, a diameter of 13 m concentric with the first electrode layers 12a and 13a
m-Al-Si paste (Al and S
i) in a weight ratio of 84:16) to a thickness of 10 μm, and a second electrode layer 12b,
13b. Further, on the second electrode layers 12b and 13b, an Ag paste is applied to a circular region having a diameter of 6 mm concentric with the second electrode layers 12b and 13b to a thickness of 3.0 μm, and the third electrode layers 12c and 13b are coated with Ag paste. 13c. Note that the second electrode layers 12b and 13b and the third electrode layers 12c and 13c
Was applied to each of the above pastes and baked at 600 ° C. to complete electrodes.

Comparative Example 1 As shown in FIG. 4, Ni was plated on both main surfaces of the positive temperature coefficient thermistor body 11 to a thickness of 1.5 μm to form inner electrode layers 22a and 23a. , 23a, an Ag paste was applied to a circular region having a diameter of 11 mm concentric with the first electrode layers 22a, 23a, and baked at a temperature of 600 ° C. to form outer electrode layers 22b, 23b.

COMPARATIVE EXAMPLE 2 The PTC thermistor element prepared in Comparative Example 1 was immersed in molten solder to form outer electrode layers 22b and 23b as shown in FIG.
Was coated with the solder coating layers 22c and 23c.

COMPARATIVE EXAMPLE 3 In the positive temperature coefficient thermistor element of Comparative Example 1, except that the thickness of the inner electrode layer made of Ni was changed to 5 μm.
In the same manner as in Comparative Example 1, an electrode of a positive temperature coefficient thermistor element was manufactured. Example and Comparative Example 1 prepared as described above
A soldered iron lead wire having a diameter of 0.65 mm is soldered to the electrodes of each of the positive temperature coefficient thermistor elements (1) to (3) using a soldering iron, and the characteristics and lead wire tensile strength of each positive temperature coefficient thermistor element are measured. It was measured in the following manner. The results are shown in Table 1 below.

Interelectrode resistance value: Each positive temperature coefficient thermistor element was left at 25 ± 1 ° C. for 1 hour or more, and then the interelectrode resistance value was measured. Withstand voltage: A voltage of 100 V was applied to the positive-characteristic thermistor element, the voltage was further increased slowly, and the voltage value when the positive-characteristic thermistor element was broken was recorded as the withstand voltage. Migration test: 200V in 220 ° C atmosphere
Was applied, and the time until spark due to migration occurred was recorded. The maximum value of the recording time was set to 10,000 hours, and if no spark occurred even after 10,000 hours, no migration was performed.

PTC recovery time: After applying a voltage of 250 V to each of the positive temperature coefficient thermistor elements for 10 minutes, the PTC is allowed to stand in an atmosphere of a temperature of 25 ° C. and has a resistance within a range of a normal electrode resistance value of ± 10% at 25 ° C. The time required for the values to return was measured. Lead wire tensile strength: As shown in FIG. 6, one lead wire 31 is bent into an L-shape, and the bent tip side is moved away from the electrode 30 (the electrode laminated structure is omitted) on the positive temperature coefficient thermistor body 11. When the wire was pulled in the direction, the maximum load until the lead wire 31 came off was measured as the lead wire tensile strength. In Table 1 below, for comparison, an In-Ga alloy was applied to both principal surfaces of the positive-characteristic thermistor body 11, and the measured values of resistance, withstand voltage, and PTC recovery time were positive. The characteristics of the thermistor element itself are shown together to show the characteristics.

[0019]

[Table 1]

As apparent from Table 1, in the positive temperature coefficient thermistor elements of Comparative Examples 1 and 3, migration between electrodes occurred after 1230 hours and after 8560 hours, respectively. This is presumably because in Comparative Example 1, migration occurred due to film resistance because the inner electrode layer made of Ni was relatively thin. Further, in Comparative Example 3, although the migration generation time is delayed by the thickness of the inner electrode layer made of Ni as compared with Comparative Example 1, migration between the electrodes is also avoided. I couldn't.

Furthermore, in Comparative Example 2, although the occurrence of migration between the electrodes was not observed because the solder coating layers 22c and 23c were formed, the PTC recovery time was extremely long at 430 seconds, and the solder coating layer 22c , 23c indicate that the withstand voltage characteristic was also deteriorated probably because the heat dissipation was reduced. Furthermore, in the positive temperature coefficient thermistor element of Comparative Example 3, the lead wire tensile strength was as low as 0.8 kg. On the contrary,
In the positive temperature coefficient thermistor element of the embodiment, there is no difference between the characteristics of the positive temperature coefficient thermistor element itself and any of the resistance value, the withstand voltage and the PTC return time, and furthermore, no migration occurs and the lead wire tensile strength is sufficient Value.

[0022]

According to the present invention, between the first electrode layer in ohmic contact with the main surface of the positive temperature coefficient thermistor body and the third electrode layer made of a material having excellent solderability. Since the second electrode layer mainly composed of Al having a small specific resistance is interposed and the size of the first to third electrode layers has the above-described specific relationship, the occurrence of migration between the electrodes is reduced. This can be reliably prevented, and the adhesion strength of the electrode to the main surface of the positive temperature coefficient thermistor body is effectively increased.

Thus, according to the present invention, it is possible to provide a positive temperature coefficient thermistor element which is unlikely to cause migration between electrodes and has excellent electrode adhesion strength without causing deterioration of electric characteristics.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a conventional PTC thermistor element, and FIG. 1B is a partially enlarged side view for explaining a problem of the conventional PTC thermistor element.

FIG. 2 is a side view showing another example of the conventional positive temperature coefficient thermistor element.

FIG. 3A is a plan view of a PTC thermistor element according to an embodiment, and FIG. 3B is a side view.

FIG. 4 is a side view showing a positive temperature coefficient thermistor element of Comparative Example 1.

FIG. 5 is a side view showing a positive temperature coefficient thermistor element of Comparative Example 2.

FIG. 6 is a side view for explaining a method for measuring a lead wire tensile strength.

[Explanation of symbols]

 11 Positive characteristic thermistor element 12, 13 ... Electrode 12a, 13a ... First electrode layer 12b, 13b ... Second electrode layer 12c, 13c ... Third electrode layer

Claims (1)

(57) [Claims] 1. A positive temperature coefficient thermistor element comprising electrodes formed on both main surfaces of a positive temperature coefficient thermistor body, wherein said electrode is in ohmic contact with a main surface of the positive temperature coefficient thermistor body. An electrode layer, formed on the first electrode layer and leaving a region of a predetermined width near the periphery of the first electrode layer or the same size as the first electrode layer; A second electrode layer made of a material containing Al as a main component and having a lower specific resistance than the second electrode layer, and a region having a predetermined width is formed around the second electrode layer on the second electrode layer. And a third electrode layer made of a material having better solderability than the first and second electrode layers.