JP2010040560A - Chip ptc thermistor and its manufacturing method - Google Patents

Abstract

A chip-type PTC thermistor that does not generate resistance at the interface between a thermistor element and an external electrode is provided.
For a PTC thermistor body 2 having a positive resistance temperature characteristic, first and second external electrodes 3 are respectively provided on first and second end faces 2a and 2b opposite to each other of the PTC thermistor body. 4 is a chip-type PTC thermistor 1 provided with
Each of the first and second external electrodes includes a plurality of electrode forming layers 21, 22, 23, and 24 that are stacked in a direction opposite to each other, and of the plurality of electrode forming layers, the first of the PTC thermistor element bodies An electrode forming layer joined to the first and second end faces is in ohmic contact as a first electrode layer, and the first electrode layer contains Zn in addition to Ag.
[Selection] Figure 2

Description

The present invention relates to a chip-type PTC thermistor used as an overheat protection element or an overcurrent protection element and a method for manufacturing the same.
In the chip-type PTC thermistor according to the present invention, PTC is an abbreviation display of positive temperature characteristic: hereinafter referred to as PTC throughout this specification.

In general, a chip-type thermistor is configured by providing first and second external electrodes on first and second end surfaces opposite to each other as described in Patent Document 1, respectively. .
In addition, what is described in Patent Document 1 is a chip-type NTC thermistor. NTC is an abbreviation for negative temperature characteristics: Negative Temperature Coefficient, and has temperature characteristics in the opposite direction to PTC.

  The first and second external electrodes in the chip-type thermistor described in Patent Document 1 are composed of a first base electrode layer in contact with the surface of the thermistor body, and the first base electrode layer As a result, an Ag electrode layer is formed. On the Ag electrode layer, a Ni film and a Sn film are formed as a second layer and a third layer by a wet method.

  However, as described in Patent Document 2, in a chip-type electronic component made of a semiconductor such as a PTC thermistor element, when the first base electrode layer is formed of Ag directly on the thermistor element, the thermistor element and the first Interfacial resistance is generated between the single base electrode layer. As a result, the resistance is higher than that of a thermistor element using an In—Ga simple electrode that is generally considered not to generate resistance at the interface.

JP 2004-319589 A JP 2004-143537 A

Thus, the reason why the resistance of the PTC thermistor element is higher than that of the thermistor element using the In—Ga simple electrode is considered as follows.
That is, it is considered that the PTC thermistor element has a lower resistance than the NTC thermistor element, and further, the specific resistance on the surface of the PTC thermistor element is lower than that of the NTC thermistor.

This will be described. The total resistance of the thermistor,
[Total resistance of thermistor] = [Internal resistance of thermistor element + Interface resistance between thermistor element and external electrode + Internal resistance of external electrode]
Assuming that the NTC thermistor has a relatively large total resistance, the interface resistance between the thermistor element and the external electrode is lower than the internal resistance of the thermistor element. For this reason, the interface resistance between the thermistor element and the external electrode is negligible in terms of total resistance.

  However, the total resistance of the PTC thermistor is lower than that of the NTC thermistor, and the interface resistance between the thermistor element and the external electrode is equal to or higher than the internal resistance of the thermistor element. For this reason, the total resistance is increased by the interface resistance due to the presence of the interface resistance. Further, the interface resistance itself may be higher because the specific resistance of the thermistor element surface is lower than that of the NTC thermistor.

  In view of the above problems, an object of the present invention is to provide a chip-type PTC thermistor that does not cause resistance at the interface between the thermistor element and the external electrode, and a method for manufacturing the same.

In order to achieve the above object, the present invention specifically relates to the PTC thermistor element body on the first and second end faces opposite to each other of the PTC thermistor element body, respectively. A chip type PTC thermistor provided with an electrode,
Each of the first and second external electrodes is composed of a plurality of electrode forming layers stacked in a reverse direction, and the first and second end faces of the PTC thermistor element body among the plurality of electrode forming layers. The electrode forming layer to be joined is in ohmic contact as a first electrode layer, and the first electrode layer includes Zn in addition to Ag, and constitutes a chip type PTC thermistor.

According to the present invention, the first and second external electrodes are provided on the first and second end surfaces of the PTC thermistor body opposite to each other, respectively. Each of the two external electrodes is a manufacturing method of a chip-type PTC thermistor composed of a plurality of electrode forming layers laminated in the opposite direction,
A first step of forming a first electrode layer containing Zn in addition to Ag so as to make ohmic contact with the first and second end faces of the PTC thermistor body;
A second step of forming a second electrode layer made of Ag and a bonding agent on each of the first electrode layers;
A third step of forming a third electrode layer comprising at least one substance component containing Ni on each of the second electrode layers;
A fourth step of forming a fourth electrode layer comprising at least one substance component containing Sn on each of the third electrode layers;
A method for manufacturing a chip-type PTC thermistor is provided.

By adopting the above configuration (chip-type PTC thermistor and manufacturing method thereof), first electrode layers containing Ag in Zn are formed on the first and second end faces of the PTC thermistor body, and the end faces and the ohmic contacts are formed. Because of the contact, the generation of interface resistance can be suppressed.
Here, since Zn is used as the metal contained in Ag, an increase in internal resistance of the external electrode can be suitably suppressed while the thermistor body and the first electrode layer are in ohmic contact.

Furthermore, the present invention is characterized in that, among the plurality of electrode forming layers, the electrode forming layer formed on each first electrode layer is composed of Ag and a bonding agent as the second electrode layer. is there.
By adopting the above configuration, a second electrode layer made of Ag and a bonding agent is formed on the first electrode layer containing Ag in Zn. Therefore, the electrode layer (first electrode) is formed of Ag and the bonding agent. Compared with the case of forming (layer + second electrode layer), the following advantageous effects can be obtained.

  That is, when the resistance value of the electrode layer itself is taken into consideration, it is preferable that the electrode layer is composed of Ag and the bonding agent because of the low resistance value. However, when an electrode layer is composed of Ag and a bonding agent, non-ohmic contact is made with the thermistor element as described above, and interface resistance is generated. On the other hand, according to the above configuration, since the first electrode layer contains Zn in Ag, the second electrode layer and the thermistor element are brought into ohmic contact while suppressing generation of interface resistance. By forming the electrode layer with Ag and the bonding agent, an increase in the resistance value of the electrode layer itself can be suppressed.

Furthermore, the present invention is characterized in that the plurality of electrode forming layers are formed of at least one kind of substance containing Ni as a third electrode layer, the electrode forming layer formed on each second electrode layer. It is what.
By adopting the above configuration, Ag migration can be prevented because the third electrode layer is formed of a substance containing Ni.

Furthermore, the present invention is characterized in that the plurality of electrode formation layers are made of at least one kind of substance containing Sn as the fourth electrode layer.
By adopting the above configuration, the fourth electrode layer is made of a substance containing Sn, so that the solder wettability at the time of mounting can be improved.

Furthermore, the present invention is characterized in that the first electrode layer contains 35 to 55% by weight of Zn, 40 to 60% by weight of Ag, and 2 to 8% by weight of a bonding agent (glass frit or the like). Is.
By adopting the above configuration, the first electrode layer containing Zn in Ag is formed on the first and second end faces of the PTC thermistor body, and preferably makes ohmic contact with the end faces, thereby generating interface resistance. Can be suppressed.

Furthermore, the present invention is characterized in that the second electrode layer contains 50 to 90% by weight of Ag among inorganic components.
By taking the above configuration, the bonding strength between the second electrode layer formed of Ag and the bonding agent and the first electrode layer containing Ag in Zn can be sufficiently maintained, and the electrode The resistance value of the layer itself can also be suppressed.

  By using the external electrode, it is possible to provide a chip-type PTC thermistor that does not generate resistance at the interface between the thermistor element and the external electrode.

Hereinafter, a chip type PTC thermistor according to the present invention will be described in detail based on a specific embodiment shown in the drawings.
FIG. 1 is a perspective view of a chip-type PTC thermistor 1 according to an embodiment of the present invention. FIG. 2 is a chip-type PTC thermistor according to the present invention, and a first external electrode is provided on one end face of the thermistor body. FIG. 2 is a schematic cross-sectional view showing a basic configuration example in which a second external electrode is provided on the other end face.
FIG. 3 shows a chip-type PTC thermistor according to the present invention, in which the first external electrode and the second external electrode provided for the thermistor body cover a part of the four side surfaces of the thermistor body. It is a schematic sectional drawing which shows an example.

  The chip-type PTC thermistor 1 according to the present invention has a PTC thermistor element body 2 and a first external electrode 3 with respect to the first end face 2a and the second end face 2b opposite to each other of the PTC thermistor element body 2, respectively. The second external electrode 4 is provided. The first and second external electrodes 3 and 4 are each composed of a plurality of electrode forming layers 21, 22, 23, and 24 that are laminated in the opposite directions.

Of the plurality of electrode forming layers, the first electrode layer 21 is in ohmic contact with the first and second end faces 2a and 2b of the PTC thermistor body 2, and contains Zn in addition to Ag. Yes.
The second electrode layer 22 is formed of Ag and a bonding agent on each of the first electrode layers 21 (on the opposite surface opposite to the bonding surface bonded to the PTC thermistor body 2). ,
The third electrode layer 23 is composed of at least one kind of substance containing Ni on each second electrode layer 22 (on each contralateral surface opposite to the bonding surface bonded to the first electrode layer 21). The fourth electrode layer 24 is composed of at least one kind of substance containing Sn on each third electrode layer 23 (on each contralateral surface opposite to the bonding surface bonded to the second electrode layer 22). Being done.

  In the present invention, the first electrode layer 21 in the plurality of electrode forming layers constituting the first and second external electrodes 3 and 4, in one example, includes 35 to 55 wt% Zn and Ag as an inorganic component. It is preferable to contain 40 to 60% by weight and 2 to 8% by weight of a bonding agent (glass frit or the like).

  Further, the second electrode layer 22 in the plurality of electrode forming layers constituting the first and second external electrodes 3 and 4 preferably contains 50 to 90% by weight of Ag among the inorganic components.

Next, a specific example of a manufacturing method of the chip-type PTC thermistor 1 according to the present invention will be described.
First, as a ceramic thermistor material containing barium titanate as a main component, BaTiO ₃ (Ba _0.90 Sr _0.10 ) is used as a main component, and with respect to this main component, SiO ₂ , MnO ₂ , Y ₂ as subcomponents. Each O ₃ was weighed, wet-mixed in a ball mill and dried.

Next, this thermistor material was heat-treated in air at 1100 ° C. for 2 hours, and then wet-pulverized again with a ball mill and dried. This pulverized powder was granulated by adding a binder made of polyvinyl alcohol, and formed into a square plate shape having a length of 50 mm, a width of 20 mm, and a thickness of 1.5 mm at a pressure of 800 kg per cm ² . Next, this molded body was fired at 1300 ° C. for 2 hours to obtain a sintered body.

  Next, the sintered body was polished and cut to obtain a thermistor body 2 having a shape of 2.0 mm in length, 1.2 mm in width, and 0.9 mm in thickness.

[Comparison of Configuration of External Electrode] Example 1, Comparative Examples 1 to 3, Conventional Example [Example 1]
On the 1.2 mm × 0.9 mm end faces 2 a and 2 b of the thermistor body 2, a paste containing a binder (glass frit), Zn and Ag in an organic binder (Zn / Ag / glass frit = 45/50 / 5 and a weight% ratio) were uniformly applied by screen printing or tampo printing, and dried at 150 ° C. for 15 minutes to form the first electrode layer 21 (first step).

  Next, as the second electrode layer 22 which is an external electrode, a paste (Ag 70 wt%) containing Ag and a bonding agent is applied onto the first electrode layer 21 like the first electrode layer 21 at 150 ° C. After drying for 15 minutes, baking was performed at 550 ° C. for 10 minutes to form the second electrode layer 22 (second step).

  Next, Ni was plated on the surface of the second electrode layer 22 by an electrolytic plating method in a neutral Ni plating solution to form a third electrode layer 23 (third step).

  Next, Sn was plated on the surface of the third electrode layer 23 by electrolytic plating to form a fourth electrode layer 24 (fourth step), thereby obtaining a chip-type PTC thermistor.

(Comparative Examples 1-3)
As shown in Table 1, the configurations of the first to fourth electrode layers are different. However, the PTC thermistor sample was produced in the same manner as in Example 1 in forming the electrode layer having the same composition.

(Conventional example)
As shown in Table 1, a PTC thermistor sample was prepared in the same manner as in Example 1 except that the In—Ga electrode, which is generally considered not to generate resistance at the interface, was changed to the first electrode (without the second to fourth electrode layers). Produced.

For each of the above PTC thermistor samples, the resistance values were compared on the basis of a conventional example that does not generate interface resistance.
Table 1 below shows the measurement results of the resistance value with respect to the electrode configuration. It can be seen that Comparative Examples 1 to 3 in which the configuration of the external electrode is outside the scope of the present invention have a higher resistance value than the conventional example, and Example 1 is equivalent to the conventional example.

[Comparison of composition of first electrode layer] Examples 1 to 11 and conventional example Table 2 below shows resistance values and adhesiveness with respect to the composition (% by weight) of the first electrode layer. In Examples 2 to 11, PTC thermistor samples were prepared in the same manner as in Example 1 except that the composition (% by weight) of the first electrode layer was different.
About each said PTC thermistor sample, resistance value and adhesiveness were compared on the basis of the prior art example which does not generate | occur | produce interface resistance.
Adhesion was evaluated by an electrode strength test [Cellotape (registered trademark) test]. Specifically, the peel strength of the first electrode layer with respect to the surface of the PTC thermistor element was evaluated.

  As can be seen from Table 2, the composition of the first electrode layer is such that the resistance value is small when the Zn content is 35 to 55 wt%, the Ag content is 40 to 60 wt%, and the glass frit is 2 to 8 wt%. Is also excellent.

[Comparison of composition of second electrode layer] Examples 1, 12 to 17, conventional example Table 3 below shows the relationship between the composition (weight%) of Ag and bonding agent contained in the second electrode layer 22 and the resistance value. Is quantitatively shown. In addition, about Examples 12-17, the sample was produced on the conditions similar to Example 1 except having changed the composition (weight%) of Ag of a 2nd electrode layer, and a bonding agent.
About each said PTC thermistor sample, resistance value and adhesiveness were compared on the basis of the prior art example which does not generate | occur | produce interface resistance.
Adhesion was evaluated by an electrode strength test [Cellotape (registered trademark) test]. Specifically, the peel strength of the first electrode layer with respect to the surface of the PTC thermistor element was evaluated.

  As can be seen from Table 3, the composition of the second electrode layer in the plurality of electrode forming layers constituting the first and second external electrodes is such that the resistance value and adhesiveness are in the case of containing 50 to 90% by weight of Ag. It is preferable from both viewpoints.

  The external electrode first and second layers are formed by applying paste by screen printing or tampo printing, drying and baking in the above embodiment, but may be formed by other methods such as sputtering.

  Further, in the above embodiment, the external electrode third and fourth layers are formed of Ni and Sn by the electrolytic plating method. However, other methods such as a sputtering method and a screen printing method may be used.

Furthermore, in the above embodiment, as a chip-type ceramic thermistor material mainly composed of barium titanate _were used BaCO _3, SrCO _3, TiO ₂ as a main component _{(Ba 0.90 Sr} 0.10) TiO ₃ Although there was BaTiO ₃ and formation, the main component is no problem even a rare earth element such as CaCO _3, PbO component and used in the perovskite-type products such as, Al ₂ O ₃ as an auxiliary component, _La 2 _{O 3} .

  In FIG. 2, the first and second external electrode layers are formed only on the 1.2 mm × 0.9 mm surface of the thermistor element 1, but if the two external electrodes are not short-circuited, the 2.0 mm × 0.9 mm surface Alternatively, it may be formed on a 2.0 mm × 1.2 mm surface.

1 is a schematic perspective view showing a chip-type PTC thermistor in an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a basic configuration example of the chip-type PTC thermistor according to the present invention, in which a first external electrode is provided on one end face of the thermistor body, and a second external electrode is provided on the other end face. 1 is a chip type PTC thermistor according to the present invention, in which a first external electrode and a second external electrode provided for a thermistor element body cover a part of four side surfaces of the thermistor element body. It is typical sectional drawing.

Explanation of symbols

1 Chip-type PTC Thermistor 2 PTC Thermistor Element 2a First End Face 2b of Thermistor Element Second End Face 2c, 2d, 2e, 2f Thermistor Element Four Sides 3 First External Electrode 4 Second External electrode

21 1st electrode layer 22 2nd electrode layer 23 3rd electrode layer 24 4th electrode layer

Claims (7)

A chip-type PTC thermistor in which first and second external electrodes are provided on the first and second end surfaces of the PTC thermistor element opposite to each other with respect to the PTC thermistor element,
Each of the first and second external electrodes is composed of a plurality of electrode forming layers stacked in a reverse direction, and the first and second end faces of the PTC thermistor element body among the plurality of electrode forming layers. A chip-type PTC thermistor in which an electrode forming layer to be joined is in ohmic contact as a first electrode layer, and the first electrode layer contains Zn in addition to Ag.   2. The chip type according to claim 1, wherein among the plurality of electrode formation layers, the electrode formation layer formed on each first electrode layer is made of Ag and a bonding agent as the second electrode layer. PTC thermistor.   2. The electrode forming layer formed on each of the second electrode layers among the plurality of electrode forming layers is formed of at least one substance containing Ni as a third electrode layer. Or a chip-type PTC thermistor according to 2;   The electrode forming layer formed on each of the third electrode layers among the plurality of electrode forming layers is composed of at least one kind of substance containing Sn as a fourth electrode layer. The chip-type PTC thermistor of any one of 1-3.   The said 1st electrode layer contains 35 to 55 weight% of Zn among inorganic components, 40 to 60 weight% of Ag, and 2 to 8 weight% of bonding | jointing agents, The 1-4 characterized by the above-mentioned. The chip type PTC thermistor according to any one of the above.   The chip-type PTC thermistor according to any one of claims 1 to 5, wherein the second electrode layer contains 50 to 90% by weight of Ag. For the PTC thermistor element having a positive resistance temperature characteristic, first and second external electrodes are provided on the first and second end surfaces of the PTC thermistor element opposite to each other,
Each of the first and second external electrodes is a manufacturing method of a chip-type PTC thermistor comprising a plurality of electrode forming layers laminated in a reverse direction,
Forming a first electrode layer containing Zn in addition to Ag so as to make ohmic contact with the first and second end faces of the PTC thermistor body;
A second step of forming a second electrode layer made of Ag and a bonding agent on each of the first electrode layers;
A third step of forming a third electrode layer comprising at least one substance component containing Ni on each of the second electrode layers;
A fourth step of forming a fourth electrode layer comprising at least one substance component containing Sn on each of the third electrode layers;
A method for manufacturing a chip-type PTC thermistor, comprising:

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