JPH0538801U - Positive characteristic thermistor element - Google Patents

Abstract

(57) [Abstract] [Purpose] A PTC that can realize stable characteristics regardless of the baking temperature of the Ag paste and that has excellent life characteristics in which the contact resistance between the electrode and the element hardly changes over time. Get the element. [Structure] First steps 3a and 3b made of Ni-B alloy plating layers are formed on both main surfaces of a PTC element body 2, and Ag paste is baked onto the first electrodes 3a and 3b to form a second step. A PTC element 1 on which electrodes 4a and 4b are formed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a positive characteristic thermistor element having electrodes formed on both main surfaces of a semiconductor ceramic, and more particularly to a low resistance type positive characteristic thermistor element having a low specific resistance of the semiconductor ceramic.

[0002]

[Prior Art]

 In recent years, the resistance of positive temperature coefficient thermistors (hereinafter referred to as PTC) elements has been reduced, and low resistance type PTC elements using a low resistance PTC element with a specific resistance of 15 Ω · cm or less have been developed. .. The following two types of electrodes are used as electrodes of this type of low resistance PTC element. (1) Electroless plating of Ni on both main surfaces of a semiconductor porcelain, Ag paste is applied on the formed Ni electrode, and baked to form an Ag electrode. (2) An electrode formed by baking an Ag paste containing an ohmic component such as Ga.

[0003]

[Problems to be solved by the device]

 However, in the electrode structure of (1) in which the Ni electrode and the Ag electrode are laminated, there is a problem that the contact resistance between the electrode and the element largely changes depending on the temperature at which the Ag paste is baked. That is, as shown in FIG. 2, for example, when the Ag paste is baked at a temperature of 550 ° C. or higher, there is a problem that the element resistance increases significantly. On the other hand, when the Ag paste is baked at a relatively low temperature of, for example, 500 ° C or less, the element resistance does not change so much as shown in Fig. 2, but the life of the Ag electrode is shortened, or There was a problem that solder erosion resistance deteriorates due to insufficient electrode sintering.

Therefore, when forming the electrode of (1), it is necessary to strictly control the temperature at which the Ag paste is baked, and it is very difficult to produce a PTC element with excellent reliability and stable characteristics. was difficult. When the ohmic component-containing Ag paste is applied and baked to form the electrode as in (2), the above-mentioned variation in the contact resistance between the electrode and the element is unlikely to occur. However, there is a problem that the electrode formed by baking the Ag paste containing the ohmic component does not have sufficient life characteristics and the contact resistance between the electrode and the element increases with time. In particular, in a low-resistance type PTC element, the resistance of the PTC element body is low, so that even if the contact resistance between the electrode and the element slightly increases over time, the resistance of the entire element tends to fluctuate significantly.

An object of the present invention is to obtain a PTC element having stable characteristics and excellent in life characteristics in which the contact resistance between the electrode and the element hardly changes over time.

[0006]

[Means for Solving the Problems]

 The present invention provides a positive temperature coefficient thermistor device in which electrodes are formed on both main surfaces of a semiconductor porcelain, wherein the electrodes are a first electrode made of a Ni-B alloy plating layer and a first electrode on the first electrode. And a second electrode formed by baking an Ag paste.

[0007]

[Action]

 In the present invention, the first electrode is made of a Ni-B alloy. Ni-B alloy is difficult to oxidize. Therefore, even if the Ag paste is baked on the upper surface, the Ni-B alloy surface itself is stable, so that the electrode resistance hardly changes depending on the baking temperature of the Ag paste. Therefore, it is possible to obtain a PTC element having stable characteristics without strictly controlling the baking temperature of the Ag paste. In addition, the electrode resistance of the first electrode made of the Ni-B alloy and the second electrode formed by baking the Ag paste hardly increases with time. Therefore, a PTC element having excellent life characteristics can be obtained.

[0008]

Description of Embodiments FIG. 1 is a sectional view showing a PTC element according to an embodiment of the present invention. The PTC element 1 is configured by using a PTC element body 2 made of a semiconductor ceramic such as a barium titanate-based semiconductor ceramic. The PTC element body 2 can be formed in any shape such as a disc shape or a square plate shape. First electrodes 3a and 3b made of a Ni-B alloy containing B in an amount of 1% by weight or less with respect to Ni are formed on both main surfaces of the PTC element body 2. The first electrodes 3a and 3b made of a Ni-B alloy are formed by electrolessly plating both main surfaces of the PTC element body 2 with a Ni-B alloy. In the PTC element 1 of this embodiment, the second electrodes 4a and 4b are formed by applying Ag paste on the first electrodes 3a and 3b and baking it. The second electrodes 4a and 4b are formed by a conventionally known electrode forming method in which Ag paste obtained by kneading Ag with an organic vehicle and a binder is applied and baked.

In this embodiment, the first electrodes 3a and 3b are made of a Ni—B alloy that is difficult to oxidize. Therefore, since the electrodes of the first electrodes 3a and 3b made of the Ni-B alloy are stable, even if the Ag paste is baked, the variation of the contact resistance between the electrodes and the element is unlikely to occur. The reason for this will be described based on the following experimental examples. As the PTC element body 2, a disc-shaped barium titanate-based ceramics having a diameter of 14 mm × a thickness of 0.45 mm and a specific resistance of 7 Ω · cm was prepared. Ni-B alloys containing 99% by weight and 1% by weight of Ni and B, respectively, were electroless plated on both main surfaces of the PTC element 2 to form a first electrode having a thickness of 1.5 μm. 3a and 3b were formed on the entire surfaces of both main surfaces of the PTC element body 2. Next, an Ag paste is applied on the first electrodes 3a and 3b and baked at various temperatures to form a second electrode having a thickness of 4.5 μm, and both main surfaces of the PTC element depending on the baking temperature. The change in inter-electrode resistance of was measured. Results are shown in FIG. As is clear from FIG. 3, the resistance of the PTC element is kept substantially constant regardless of the baking temperature of the Ag paste.

Using the same PTC element body as the PTC element body used in the above experiment, a PTC element formed by forming electrodes by the conventional method of (1) and (2) described above is respectively prepared in the conventional example (1). And prepared as a conventional example (2). With respect to the PTC elements of the above-mentioned examples and the PTC elements of the conventional examples (1) and (2), resistance values were measured and life characteristics were evaluated. The life characteristics were evaluated by performing the following high temperature storage test, wet storage test, and room temperature intermittent load test.

High-temperature storage test: This was left for 1000 hours at 150 ° C. and normal humidity, and the rate of change in element resistance before and after storage was measured. Humidity storage test: The product was left for 1000 hours in an environment of 60 ° C. and relative humidity of 90 to 96%, and the change rate of the element resistance value before and after the storage was measured. Room temperature intermittent load test: The process of applying a voltage of 15 V for 1 minute and leaving it for 5 minutes at 25 ° C. and a relative humidity of 65 to 75% was repeated for 1000 hours, and the change rate of the element resistance value before and after the test was measured. .. The results of the element resistance value and life characteristic evaluation are shown in Table 1 below.

[0012]

[Table 1]

As is clear from Table 1, the PTC element of the embodiment has a much smaller variation in element resistance value than the PTC elements of the conventional examples (1) and (2). Regarding the life characteristics, in the conventional example (2), the element resistance greatly changed after 1000 hours in all of the high temperature standing test, the humidity standing test and the room temperature intermittent load test, whereas It can be seen that in the PTC element of 1 and the PTC of the conventional example (1), the element resistance value hardly changes. In the PTC element of the above-described embodiment, the first electrodes 3a and 3b made of Ni-B alloy are formed on the entire surfaces of both main surfaces of the PTC element body 2, and Ag is formed on the entire surfaces of the first electrodes 3a and 3b. Although the paste was baked to form the second electrodes 4a and 4b, as shown in FIG. 4, the second electrode 4a (the second electrode 4b on the lower surface side is not shown) is surrounded. It may be formed to have a diameter smaller than that of the first electrode 3a so as to leave the gap region 5 having a predetermined width x. In this way, the second electrode 4a is made smaller than the first electrode 3a, and the gap region 5 is left on the periphery, so that the migration between the second electrodes on both main surfaces made of Ag is surely prevented. be able to.

[0014]

[Effect of the device]

 As described above, the present invention has an electrode structure in which the second electrode formed by baking the Ag paste is formed on the first electrode made of the Ni—B alloy plating layer, and thus the baking temperature of the Ag paste is high. It is possible to obtain a PTC element having stable characteristics without strict control of the temperature, and it is particularly suitable for a low resistance type PTC element. Further, since the PTC element of the present invention comprises the first electrode made of the Ni-B alloy plating layer and the second electrode made by baking the Ag paste, the electrode resistance also changes with time. It is difficult to obtain a PTC element having excellent life characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of a PTC element according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a baking temperature of an Ag paste and a resistance value of a PTC element in a conventional technique.

FIG. 3 shows the baking temperature and P of Ag paste in Examples.
The figure which shows the relationship with the resistance value of TC element.

FIG. 4 is a perspective view illustrating a PTC device having another shape to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... PTC element 2 ... PTC element body 3a, 3b ... 1st electrode 4a, 4b ... 2nd electrode

Claims (1)

[Scope of utility model registration request] 1. A positive temperature coefficient thermistor element having electrodes formed on both main surfaces of a semiconductor porcelain, wherein the electrodes are formed on a first electrode made of a Ni—B alloy plating layer, and formed on the first electrode. And a second electrode formed by applying and baking an Ag paste, and a positive temperature coefficient thermistor element.