TW201434056A - Chip-type positive temperature coefficient thermistor element - Google Patents

Abstract

A chip-type positive temperature coefficient thermistor element (1) has an element volume of no more than 0.12 [mm<SP>3</SP>]. In order to improve responsiveness, the following are provided: a ceramic base material (2) which has end surfaces (Sa, Sb) that face one another in parallel in the X axis direction and side surfaces (Sc) that connect the end surfaces (Sa, Sb), and the inner resistance value of which changes according to a temperature change and a metal-containing first external electrode (4a) and second external electrode (4b) that are provided on the end surfaces (Sa, Sb). The distance (d [μm]) in the X axis direction between the end surfaces (Sa, Sb) is 300 ≤ d ≤ 700, and the maximum point thickness (tmax [μm]) of the thickness in the X axis direction of the first external electrode (4a) and the second external electrode (4b) is tmax ≥ 0.015 x d - 1.5.

Description

Wafer type positive characteristic thermistor element

The present invention relates to a wafer type positive characteristic thermistor element having a volume of 0.12 mm ³ or less.

As an example of the conventional wafer type positive characteristic thermistor element (hereinafter, simply referred to as a thermistor element), for example, the following Patent Document 1 is described. The thermistor element includes a ceramic base having a substantially rectangular parallelepiped shape and external electrodes disposed on both end faces of the thermistor element. Each of the external electrodes has a structure in which a conductive metal layer, a conductive resin layer, and a metal plating layer are laminated. Here, the conductive metal layer is formed directly above the both end faces of the ceramic substrate, and the metal plating layer is the outermost layer. Further, a glass layer is formed on the four side faces of the ceramic substrate in which the external electrodes are not provided to improve mechanical strength and the like.

Not only the one described in Patent Document 1, but the conventional thermistor element is typically used for overheat detection of a heat source. Specifically, the thermistor element is mounted adjacent to the heat source. When the temperature of the heat source (i.e., the ambient temperature) increases, the temperature of the ceramic substrate rises and the resistance value increases. Further, a supply voltage is supplied to the thermistor element. Then, a voltage indicating the ambient temperature is output between the output terminals of the thermistor element, and is supplied to the IC. The IC determines whether the heat source is in an overheated state based on the input voltage.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 10-092606

A thermistor element for overheat detection has been developed in recent years to be miniaturized (for example, a volume of 0.12 mm ³ or less). For such a small thermistor element, it is also required to respond at a high speed (for example, within 1 second) after the heat source is in an overheated state. The usual method for achieving this is to thermally couple the thermistor element to the heat source with a resin or the like. However, this method must cover the heat resistor element and the heat source with a resin or the like, so that the cost is high.

Accordingly, an object of the present invention is to provide a wafer type positive characteristic thermistor element having a volume of 0.12 [mm ³ ] or less, low cost, and excellent responsiveness.

In order to achieve the above object, an aspect of the present invention is a wafer type positive characteristic thermistor element having a volume of 0.12 [mm ³ ] or less, and comprising: a ceramic substrate having mutually parallel ground and a first end surface and a second end surface opposite to the specific direction, and a side surface connecting the first end surface and the second end surface, and the internal resistance value changes with temperature; and the first external electrode and the second external electrode And being disposed on the first end surface and the second end surface, and containing metal. a distance d [μm] between the first end surface and the second end surface in a specific direction is 300 ≦d ≦ 700, and a portion of the first external electrode and/or the second external electrode having the largest thickness in a specific direction The thickness tmax [μm] is tmax ≧ 0.015 × d - 1.5.

According to the above aspect, the metal-containing first external electrode and/or the second external electrode have a sufficient thickness of tmax ≧ 0.015 × d - 1.5 [μm]. Therefore, when the present resistor element is mounted in the vicinity of the heat source, the distance between the first external electrode and/or the second external electrode and the heat source is relatively close, so that heat from the heat source is transmitted to the ceramic substrate at a high speed. Thereby, a thermistor element excellent in responsiveness can be provided. Further, since it is not necessary to cover the heat resistor element and the heat source with a resin or the like, overheat detection can be performed at low cost.

1‧‧‧Thermistor component

2‧‧‧Ceramic substrate

3a, 3b‧‧‧ external electrodes

4a, 4b‧‧‧ base electrode

5a, 5b‧‧‧ first coated film

6a, 6b‧‧‧second plating film

10‧‧‧Oscilloscope

I‧‧‧current

M‧‧‧ Determination System

Sa, Sb‧‧‧ end face

Sc‧‧‧ side

Sv‧‧‧ extended face

Vout‧‧‧ voltage between two terminals

X, Y, Z‧‧‧ axes

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view showing a wafer type positive characteristic heat resistor element according to an embodiment of the present invention.

Fig. 2 is a schematic view showing the thickness of the external electrode of the edge portion of the ceramic substrate of Fig. 1 in the X-axis direction.

Fig. 3 is a view showing a circuit configuration for measuring characteristics of each sample of a wafer type positive characteristic thermistor element.

Hereinafter, a wafer type positive characteristic thermistor element (hereinafter, simply referred to as a thermistor element) according to an embodiment of the present invention will be described with reference to the drawings.

(preface)

First, the X-axis, the Y-axis, and the Z-axis shown in Fig. 1 are defined for the convenience of the following description. The X-axis, the Y-axis, and the Z-axis indicate the left-right direction, the front-rear direction, and the up-and-down direction of the thermistor element 1.

(Composition of thermistor element)

In Fig. 1, the thermistor element 1 comprises a ceramic substrate 2 and two pairs of external electrodes 3a, 3b.

The ceramic substrate 2 is formed, for example, of a ceramic material to which a specific additive is added in BaTiO ₃ (barium titanate). Here, the additive is a rare earth, typically Sm (钐). In addition to this, Nd (钕) or La (镧) or the like may be used as an additive.

The ceramic base 2 may have any one of a single plate structure and a laminated structure. In Fig. 1, a veneer builder is exemplified. Further, the ceramic base 2 has a substantially rectangular parallelepiped shape elongated in the left-right direction, and has a first end surface Sa and a second end surface Sb, and at least one side surface Sc connecting the first end surface Sa and the second end surface Sb. The end faces Sa and Sb are parallel to each other and face each other in the X-axis direction. Here, in the present embodiment, both end faces Sa and Sb have substantially rectangular shapes. In this case, the side surface Sc includes the first side surface Sc1 to the fourth side surface Sc4 each having a substantially rectangular shape.

Next, an example of the size of the ceramic base 2 will be described. The length of the ceramic base 2 in the X-axis direction (hereinafter referred to as L dimension) is defined as the distance d [μm] between the end faces Sa and Sb. d is selected from 300≦d≦700. The width W in the Y-axis direction and the thickness T in the Z-axis direction are not particularly limited. However, the size of the ceramic base 2 is set such that the volume V of the entire thermistor element 1 is 0.12 [mm ³ ] or less.

Here, as described above, the ceramic base 2 has a substantially rectangular parallelepiped shape. However, the edge portion of the actual ceramic substrate 2 is not completely right angle but curved. The distance d is not the distance between the arcuate portions of the end faces Sa and Sb, but is the distance between the planar portions occupying most of the both end faces Sa and Sb.

The external electrodes 3a and 3b are formed on the end faces Sa and Sb, and include the base electrodes 4a and 4b, the first plating films 5a and 5b, and the second plating films 6a and 6b.

The base electrodes 4a and 4b contain, for example, an Ag-Zn (silver-zinc) alloy and Ag (silver). Specifically, an Ag-Zn alloy layer is ohmically bonded to each of the end faces Sa and Sb, and an Ag (silver) layer is formed on the Ag-Zn alloy layer.

Further, the first plating films 5a and 5b contain, for example, Ni, and are formed on the base electrodes 4a and 4b. The second plating films 6a and 6b contain, for example, Sn (tin), and are formed on the first plating films 5a and 5b.

One or both of such external electrodes 3a, 3b have a maximum thickness tmax as follows. The maximum thickness tmax is basically the thickness of the portion of the external electrodes 3a and 3b to be the largest in the X-axis direction (in other words, the normal directions of the end faces Sa and Sb). As described above, the edge portion of the ceramic base 2 is not completely right angle but curved. Further, as is well known, the external electrodes 3a, 3b are also formed on the arcuate portions of the end faces Sa, Sb. The thickness of the portion in the X-axis direction is defined by an arrow on the plane of the end faces Sa and Sb (imaginary surface) Sv as indicated by an arrow in FIG. 2 .

For the maximum thickness tmax as defined above, at least the lower limit value is specified. Specifically, when the above distance d [μm] is 300 ≦ d ≦ 700, the maximum thickness tmax is specified. The value is tmax ≧ 0.015 × d - 1.5, and the details will be described later. In addition, the upper limit of the maximum thickness tmax is set to 120 [μm] in order to prevent the occurrence of a tombstone phenomenon when the present heat resistor element 1 is mounted.

(An example of the method of manufacturing a resistor element)

An example of the manufacturing steps of the above-described thermistor element 1 roughly includes the following steps.

First, a BaTiO ₃ -based ceramic powder having a desired property can be press-formed into a size of 150 [mm] × 150 [mm]. Thereafter, the pressure-molded ceramic powder is subjected to specific degreasing and calcination treatment. Thereby, the mother substrate is obtained. The mother substrate is polished until its thickness (corresponding to the thickness T) becomes a specific value. Thereafter, a short strip substrate having a specific width (corresponding to the width W in the front-rear direction) is obtained by cutting.

Then, the short strip substrate is diced again so that the L size is 300 [μm] or more and 700 [μm] or less (for example, 500 [μm]).

The ceramic substrate 2 is produced in a large amount by the above steps.

Next, an Ag-Zn-based slurry which can be ohmically bonded to the ceramic is applied to each of the end faces Sa and Sb of the ceramic base 2. Thereafter, the ceramic substrate 2 coated with the Ag-Zn-based slurry is subjected to a baking treatment. Thereafter, a thermosetting Ag paste is applied onto the Ag-Zn alloy layer, and then the Ag slurry is heated and cured. Thereby, the base electrodes 4a and 4b are formed. In this case, the base electrodes 4a and 4b are applied to the maximum thickness tmax [μm] of the external electrodes 3a and 3b so as to be 0.015 × d - 1.5 ≦ tmax ≦ 120 (for example, about 80 [μm]). On the end faces Sa and Sb. More specifically, the ceramic base 2 is moved in the vertical direction, and the end faces Sa and Sb are partially immersed in the electrode slurry. For example, the thickness of the base electrodes 4a, 4b is adjusted by controlling the speed of the vertical movement. Further, the thickness of the base electrodes 4a and 4b may be adjusted by adjusting the viscosity of the electrode paste or by scraping off the electrode paste temporarily applied to the end faces Sa and Sb.

Finally, on the surface of the base electrodes 4a, 4b, the first plating films 5a, 5b of Ni are first formed by electric field plating, and then the second plating film of Sn is formed on the first plating films 5a, 5b. 6a, 6b. The thermistor element 1 is completed by the above steps.

(Relationship between component volume V, L dimension d and maximum thickness tmax and response time)

The inventors of the present invention changed the element volume V, the L dimension d, and the maximum thickness tmax, and produced the heat resistor elements of the sample numbers 1 to 15 shown in Table 1 below (hereinafter, simply referred to as samples 1 to 15), and borrowed them. The response time was confirmed by the measurement system shown in FIG. 2.

As shown in Table 1, with respect to the element volume V, the samples 1 to 9, 14, 15 were 0.12 [mm ³ ], and the samples 10 to 13 were 0.18 [mm ³ ].

Further, regarding the L size d, the samples 1 to 3 and 14 are 700 [μm], the samples 4 to 6, 12, 13, and 15 are 500 [μm], and the samples 7 to 9 are 300 [μm]. 10 and 11 are 1000 [μm].

Further, regarding the maximum thickness tmax, the samples 1, 10, and 12 were 9 [μm], the samples 2, 5, and 8 were 15 [μm], and the samples 3, 6, 9, 11, and 13 were 120 [μm]. Sample 4 was 6 [μm], and Samples 7, 14, and 15 were 3 [μm].

In the samples 1 to 15, the component volume V, the L dimension d, and the maximum thickness tmax of the above-described thermistor element 1 were samples 1 to 9. Samples 10 to 15 are listed in Table 1 for comparison with Samples 1 to 9.

Here, the measurement system M shown in Fig. 3 will be described. The measurement system M includes any of the samples 1 to 15 and the oscilloscope 10.

A current I having a predetermined fixed value is supplied to each of the samples 1 to 15. Corresponding to this, the temperature of the ceramic substrate of each of the samples 1 to 15 increased, and the resistance value increased. The oscilloscope 10 measures the voltage Vout between the two terminals of each of the samples 1 to 15.

The applicant of the present invention previously measured the initial voltage Vout when the current I was supplied to each of the samples 1 to 15 by the measurement system M. Then, the time from when the current I is supplied to when the measurement voltage Vout becomes, for example, 100 times the initial voltage Vout is measured as the response time Tres. According to the measurement results of the inventors of the present invention, it is found that the samples 1 to 9 have an excellent response time of 1 second or shorter. That is, as long as the L size d [μm] is 300 ≦d ≦ 700 and 0.015 × d - 1.5 ≦ tmax, the wafer type positive characteristic thermistor element 1 excellent in responsiveness can be provided. As described above, since the thermistor element 1 has an excellent response time of 1 second or less in a single element, it is not necessary to thermally couple the thermistor element 1 to the heat source by using a resin or the like in actual use. As a result, overheat detection can be performed at low cost.

[Industrial availability]

The wafer type positive characteristic thermistor element of the present invention is excellent in responsiveness, and is useful in heat source detection or overcurrent protection of the heat source.

1‧‧‧Thermistor component

2‧‧‧Ceramic substrate

3a, 3b‧‧‧ external electrodes

4a, 4b‧‧‧ base electrode

5a, 5b‧‧‧ first coated film

6a, 6b‧‧‧second plating film

Sa, Sb‧‧‧ end face

Sc‧‧‧ side

X, Y, Z‧‧‧ axes

Claims (2)

A wafer type positive characteristic thermistor element having a volume of 0.12 [mm ³ ] or less, and comprising: a ceramic substrate having first and second end faces facing each other in parallel and facing in a specific direction And a side surface connecting the first end surface and the second end surface, wherein the internal resistance value changes with temperature; and the first external electrode and the second external electrode are disposed on the first end surface and the first a second end surface and containing a metal; a distance d [μm] between the first end surface and the second end surface in a specific direction is 300≦d≦700, and the first external electrode and/or the second external electrode are The thickness tmax [μm] of the portion having the largest thickness in a specific direction is tmax ≧ 0.015 × d - 1.5. The wafer type positive characteristic thermistor element of claim 1, wherein the above tmax [μm] is tmax ≦ 120.