JPH05283205A - Chip-type thermistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent a decrease in mechanical strength of a thermistor element and to increase a substrate mountability. CONSTITUTION:This device is constituted of a chip-type thermistor element 1, chief of which is one or more than two kinds of transition metal oxides, Mn oxides, and terminal electrodes 2 formed on both ends of the thermistor element 1. When a surface layer of the thermistor element 1 is mainly formed of a cubic spinel crystal phase and an internal layer is mainly formed of a tetragonal spinel crystal phase, the surface layer of the thermistor element is 10-50mum in thickness. The chip-type thermistor is obtained by baking the terminal electrodes 2 on the thermistor element 1 and then heat treating the thermistor element 1 in the air at 150-350 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type thermistor having surface mountability and a method of manufacturing the same. More specifically, the present invention relates to a chip type thermistor in which a thermistor element body is a bulk element and a manufacturing method thereof.

[0002]

2. Description of the Related Art As shown in FIG. 1, a chip type thermistor of this type has terminal electrodes 2 and 2 formed at both ends of a thermistor element body 1 formed in a chip shape. This chip type thermistor is directly mounted on the surface of a printed circuit board or the like. In order to manufacture such a chip-type thermistor, a thermistor material is pressure-molded into a cylindrical block using, for example, a die. This block is fired, the thermistor sintered body obtained by firing is sliced into a wafer with a diamond blade or the like, and the wafer is further cut to obtain a chip-shaped thermistor element body 1 having a predetermined size. Then, the terminal electrode 2 is formed on the chip-shaped thermistor body 1 by a method such as baking to obtain a chip-type thermistor. Since the thermistor body generally contains a transition metal layer oxide as a main component, the thermistor material has a stable crystal structure depending on the temperature at the time of firing and the partial pressure of oxygen in the surroundings, whereby the elastic modulus, the thermal expansion coefficient, etc. It is known that physical properties change.

[0003]

When the chip type thermistor element is manufactured by the above method, the crystal structure of the chip type thermistor element after cutting into wafers and the terminal electrode are formed depending on the composition of the thermistor material. The crystal structure of the later thermistor body may be different. For example, when a crystal phase different from the crystal phase before baking occurs in the surface layer of the element body due to the baking of the terminal electrode, residual tensile stress is generated on the surface of the element body. This tensile stress reduces mechanical strength such as bending strength of the chip thermistor body, and when the chip type thermistor is mounted on a printed circuit board or the like, the thermistor element is cracked or cracked. ..
In particular, as a material that causes this phenomenon, a compound having a tetragonal spinel crystal containing Mn as a main component can be mentioned. In addition to Mn, other components such as Co, Ni, Fe, Cu,
As the components such as Cr, Al, and Zn are increased, if these components exceed a certain composition range, the compound has a cubic spinel crystal. In such a region, the inside of the element body becomes a tetragonal spinel crystal, and the surface layer easily becomes a cubic spinel crystal, resulting in a decrease in mechanical strength and the like.

An object of the present invention is to provide a chip type thermistor which is excellent in substrate mountability and which prevents deterioration of mechanical strength of the thermistor element body, and a manufacturing method thereof.

[0005]

In order to achieve the above object, a chip type thermistor of the present invention comprises, as shown in FIG. 1, one or more transition metal oxides as a main component. The oxide is composed of a chip-shaped thermistor element body 1 whose main component is an oxide of Mn, and terminal electrodes 2 formed at both ends of the thermistor element body 1. When the surface layer of the thermistor body 1 is mainly composed of a cubic spinel type crystal phase and the inner layer of the thermistor body 1 is mainly composed of a tetragonal spinel type crystal phase, the thermistor body 1
The thickness of the surface layer is 10 to 50 μm. Further, the method for manufacturing the chip type thermistor of the present invention is a method in which the terminal electrode 2 is baked and then heat-treated in the temperature range of 150 to 350 ° C. in air.

When the heat treatment temperature is lower than 150 ° C., the surface layer of the thermistor element, that is, the thickness of the cubic spinel type crystal phase becomes less than 10 μm, and the tensile stress when the terminal electrode is baked on this surface layer. It still remains. On the other hand, when the heat treatment temperature exceeds 350 ° C., the thickness of the cubic spinel type crystal phase exceeds 50 μm, the thickness of the tetragonal spinel type crystal phase in the inner layer decreases, the crystal structure balance is lost, and the strength decreases. It is not preferable because it is seen. As the transition metal element constituting the transition metal oxide of the present invention, Ti, V, C
IIIA to VII of the periodic table of r, Mn, Co, Ni, Cu, etc.
The elements of Group A, Group VIII and Group IB are mentioned, but especially M
It is preferable to include each oxide of n, Co, and Cu because the mechanical strength can be improved. In this case, the composition of the transition metal oxide is such that Mn is 45 mol% or more and 72.5 mol% or less, Co is 0 mol% or more and 15 mol% or less, and Cu is 27.
It is preferably 5 mol% or more and 40 mol% or less.

[0007]

[Function] Depending on the composition of the thermistor body, when the chip type thermistor body is obtained by cutting the thermistor sintered body, the crystal structure of the body is composed mainly of the tetragonal spinel type crystal phase. However, when the terminal electrode is formed by baking or the like, the surface of the element body is oxidized to form a surface layer having a cubic spinel type crystal phase of about 5 μm as a main crystal phase. At this time, the cubic spinel-type crystal phase generated on the surface of the element body by baking the terminal electrode has a thermal expansion coefficient generally larger than that of the tetragonal spinel-type crystal phase inside the unoxidized element body. In the process, residual tensile stress is generated on the device surface. This tensile stress reduces the mechanical strength of the element body such as the bending strength of the chip type thermistor. These mechanical strength reductions are about 5 when the terminal electrode is baked.
The cause is the formation of a surface layer by the oxidation of the thermistor body of μm. After the terminal electrode is formed, thermistor is 150-350 ℃
When the thickness of the surface layer is increased to 10 to 50 μm by annealing at the temperature of 1, the residual tensile stress is eliminated and the mechanical strength is improved.

[0008]

EXAMPLES Next, the present invention will be described with reference to examples. The invention is not limited by these examples. Example 1 First, commercially available manganese carbonate, cobalt carbonate, and copper oxide were used as starting materials, and their metal atomic ratio was Mn:
It was weighed so that Co: Cu = 5: 1: 4, mixed with a ball mill for 16 hours, and then dehydrated and dried. Next, this mixture was calcined at 900 ° C. for 2 hours, mixed again in a ball mill and dehydrated and dried. 1% by weight of polyvinyl alcohol was added to the raw material after the calcination, and pressure molding was performed using a mold to produce a columnar block of 50 mmφ × 10 mm.
This block was fired at 1000 ° C. for 5 hours to obtain a sintered body. This sintered body was cut using a diamond blade, and the length was 1.9 mm, the width was 1.2 mm, and the thickness was 0.65 mm.
I got the thermistor body. The thermistor body in this state was used as sample A.

After the silver paste was applied to the thermistor element and dried, the terminal electrode was baked by baking in air at 800 ° C. for 10 minutes. The chip type thermistor thus obtained was designated as Sample B. After baking the terminal electrode 2, in the air, 150 ° C, 200 ° C, 250 ° C, 300 ° C, 35 ° C.
Annealing treatment (heat treatment) was performed for 24 hours at each of 6 stages of temperature of 0 ° C. and 400 ° C. These heat-treated products were used as samples C, D, E, F, G and H in order of temperature.

With respect to the thermistor bodies of the obtained samples A to H, the respective crystal structures on the surface and inside were examined, and the thickness of the surface layer was measured. Specifically, first the crystal structure of the surface of the element body is examined by X-ray diffraction, then the surface of the element body is polished and examined again by X-ray diffraction, and the thickness of the sample when the crystal structure starts to change is measured. The layer thickness was measured with a micrometer. The results are shown in Table 1. (Hereafter, margins on this page)

[0011]

[Table 1]

A bending strength test was conducted on the obtained thermistor bodies of Samples A to H. That is, both ends of each sample in the length direction are placed on two tables arranged with a gap of 1.2 mm, and the sample is pushed down to an intermediate position between the two tables at a speed of 20.
A force was applied at mm / min, and the load applied when the thermistor element body was broken was measured. The results are shown in Table 2. Table 2
The value of the breaking load of is the average value of 20 pieces of each sample.

[0013]

[Table 2]

Compared with the sample A before baking the terminal electrode, the sample B after baking the terminal electrode shows a remarkable decrease in breaking load (strength). On the other hand, among the heat-treated Samples C to H, the strength of the sample H was much lower than that of the sample B, but the strength improvement effect was recognized in the samples C to G. From Table 1, Samples C to G have a heat treatment temperature of 150 ° C to 350 ° C,
The surface layer was constituted with the cubic spinel type crystal phase as the main crystal phase, and the thickness of the surface layer was about 10 to 40 μm.

<Example 2> The metal atom ratio of the starting material is M
A sample was prepared in the same manner as in Example 1 except that the weight was adjusted to n: Co: Cu = 6: 1: 3, and the same test was performed. Table 3 shows the crystal structures and surface layer thicknesses of the surface and inside of the obtained sample body, and Table 4 shows the results of measurement of the fracture load.
Are shown respectively. (Hereafter, margins on this page)

[0016]

[Table 3]

[0017]

[Table 4]

Also in Example 2, similarly to Example 1, in Samples C to G, the effect of improving the strength was recognized. From Table 3, in Samples C to G, the heat treatment temperature was 150 ° C. to 350 ° C., the surface layer was constituted with the cubic spinel type crystal phase as the main crystal phase, and the thickness of the surface layer was about 10 to 50 μm. ..

[0019]

As described above, in the present invention, after the terminal electrode is formed, the thermistor body is heat-treated at a predetermined temperature so that the cubic spinel type crystal phase is formed on the surface of the thermistor body as the main crystal phase. 10-5 composed surface layer
A chip-type thermistor having a thickness of 0 μm and having an inner layer composed of a tetragonal spinel-type crystal phase as a main crystal phase can be obtained. As a result, the degree of freedom in the design of the thermistor body is increased, the design is facilitated, and the reduction in strength is improved, so there is less risk of destruction during board mounting, its handling is easy, and mounting is easy. Automation can be easily realized.

[Brief description of drawings]

FIG. 1 is a sectional view of a chip type thermistor.

[Explanation of symbols]

 1 Thermistor body 2 Terminal electrode

Front page continuation (72) Inventor Koji Oi 2270 Yokoze, Yokose-cho, Chichibu-gun, Saitama Sanryo Materials Co., Ltd. Ceramics Research Institute Co., Ltd.

Claims (3)

[Claims] 1. A chip-like thermistor body (1) containing one or more kinds of transition metal oxides as a main component and the transition metal oxide containing an oxide of Mn as a main component, and the thermistor body. (1) provided with terminal electrodes (2) formed at both ends, the surface layer of the thermistor element body (1) is mainly composed of a cubic spinel type crystal phase, and the inner layer of the thermistor element body (1) In a chip type thermistor mainly composed of a tetragonal spinel type crystal phase, wherein the surface layer of the thermistor body (1) has a thickness of 10 to 50 μm.
m is a chip thermistor. 2. The transition metal oxide contains oxides of Co and Cu in addition to the oxide of Mn, and the composition of the transition metal is such that Mn is 45 mol% or more and 72.5 mol% or less, and Co is 0 mol. % To 15 mol% and Cu, 27.5 mol% to 4 Cu
The chip type thermistor according to claim 1, wherein the content is 0 mol% or less. 3. One or two containing Mn oxide as a main component.
A chip-shaped molded body is produced from at least one kind of transition metal oxide,
After obtaining the thermistor body (1) by firing the molded body, in a method for manufacturing a chip-type thermistor in which terminal electrodes (2) are baked on both ends of the thermistor body (1), the terminal electrodes (2) 150-350 in air after baking
A method for manufacturing a chip type thermistor, characterized by performing heat treatment in a temperature range of ° C.