JPH10106809A - Chip type thermistor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chip thermistor which exhibits excellent mountability and thermistor characteristics and few variations in characteristics such as element size and resistance. SOLUTION: A thermistor element 1 is covered with a protective film 2. Both ends of the thermistor element 1 are subjected to cutting. Terminal electrodes 3A are formed on the cut surfaces 1A and 1B. By this method, the cutting can be performed with a high precision and variations in element size can be reduced. Variations in resistance due to variations in size are also reduced and taping workability and characteristics for implementation can be improved. Since terminal electrodes can be joined directly to the exposed surface of the terminal electrodes, there is no need to limit with a high precision the thickness of the protective film. A chip thermistor exhibiting a desired resistance can be obtained by ensuring an electrical junction between the thermistor element and the terminal electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip thermistor surface-mounted on a printed circuit board or the like and a method of manufacturing the same, and more particularly to a negative thermistor whose resistance value decreases with an increase in temperature. The present invention relates to a chip-type thermistor having small variations in characteristics such as body dimensions and resistance values and excellent in mounting performance and characteristics, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a typical product of a chip-type thermistor surface-mounted on a printed circuit board or the like, a protective coating is formed on the outer surface of a chip-shaped thermistor element formed of a ceramic sintered body and then formed on both end surfaces. A structure in which terminal electrodes are formed is provided.

Conventionally, such a chip thermistor has
It is manufactured as follows.

[0004] First, a ceramic green sheet of a thermistor material is prepared by a casting method, a required number of such sheets are laminated, pressed, cut into chips, baked, and then barrel-polished, as shown in FIG.
A chip thermistor body 1 as shown in FIG. The outer surface of the chip-like thermistor body 1 is shown in FIG.
After forming the protective film 2 by a sputtering method or the like as shown in FIG. 3B, the terminal electrode 3A is formed as shown in FIG.
Is further baked to form a Ni plating layer 3B and a solder plating layer 3C.

The protective coating 2 is formed on the entire outer surface of the thermistor body 1, and the terminal electrode 3A is formed on the protective coating 2. However, when the terminal electrode 3A is baked, the glass frit in the terminal electrode 3A is removed. The glass component in the protective coating 2 reacts and melts, the melt is absorbed in the terminal electrode, and the protective coating disappears, so that the terminal electrode 3A and the thermistor element 1
Continuity with the terminal is ensured.

As shown in FIG. 4, there is a chip thermistor in which internal electrodes 4A and 4B are formed in a thermistor body 1. Such a chip thermistor is provided at a predetermined position on a ceramic green sheet. Are printed and laminated in the same manner as described above.

Further, there is also provided a thermistor element in which a surface electrode for adjusting a resistance value is formed on the surface of the thermistor body, and then a protective film and a terminal electrode are formed.

When such a chip thermistor is shipped as a product, a taping process is performed to facilitate mounting process by a user.

As described above, the protective film is formed on the entire outer surface of the thermistor body, and the terminal electrode is formed by reacting the glass component in the protective film with the glass frit in the terminal electrode at the time of baking. Electrical connection with the thermistor body is obtained by the absorption of the protective film and the loss of the protective coating.However, in order to absorb the reaction melt into the terminal electrode and secure good electrical connection, However, there is an upper limit to the thickness of the protective coating, and if the thickness of the protective coating is too large, the electrical connection cannot be obtained.

The upper limit of the thickness of the protective film varies depending on the presence or absence of the surface electrode of the element body, but is usually 1-2 μm.

[0011]

The above-mentioned conventional chip type thermistor has the following disadvantages.

In producing the thermistor body, the barrel of the chip is polished. However, since this barrel polishing is not a processing method with high dimensional accuracy, the dimensions of the body obtained in a manufacturing lot vary.

Variations in the dimensions of the thermistor element cause variations in resistance, which is a main characteristic of a chip thermistor.

In the taping process at the time of shipping of the chip type thermistor, if there is a variation in the element size, especially in the longitudinal direction of the element, it is difficult to insert the element body into the element insertion hole for taping or reverse. In addition, the displacement of the body in the body insertion hole is likely to occur, and the body is less likely to be sucked by the body suction nozzle of the taping apparatus.

[0015] The variation in the body dimensions directly results in the variation of the chip-type thermistor dimensions as a product. However, if there is variation in the dimensions of the chip-type thermistor, there is a high possibility that a mounting failure will occur upon mounting on a substrate.

Another problem is that the formation of a protective film is not easy. That is, there is an upper limit to the thickness of the protective coating in order to ensure electrical connection between the terminal electrode and the thermistor body. For this reason, when the protective film is formed by a method in which the control of the film thickness is relatively difficult, such as the sol-gel method, the protective film becomes too thick and electrical connection between the element body and the terminal electrode cannot be obtained. In addition, since the protective coating remains as an insulating layer between the terminal electrode and the thermistor element, a chip-type thermistor having a desired resistance value may not be obtained. For this reason, in forming the protective film, it is necessary to control the film thickness with high precision after selecting the formation method, and it is not easy to form the protective film.

The present invention solves the above-mentioned conventional problems, has small variations in characteristics such as element size and resistance value, and has a high mounting performance.
An object of the present invention is to provide a chip type thermistor excellent in taping workability and thermistor characteristics, and a method of manufacturing the same.

[0018]

A chip-type thermistor according to the present invention comprises a thermistor element made of a rectangular parallelepiped ceramic sintered body and terminal electrodes provided on a pair of parallel end faces of the thermistor element. In a chip thermistor having the same, a protective coating is formed on the outer surface of the thermistor body, and then both end faces of the body are cut, and then terminal electrodes are formed on the cut surface.

The method of manufacturing a chip-type thermistor of the present invention comprises the steps of: forming a protective coating on the outer surface of a rectangular parallelepiped thermistor body made of a ceramic sintered body; and forming terminal electrodes on both end surfaces of the thermistor body. A method for manufacturing a mold thermistor is characterized in that both end surfaces of a thermistor body on which a protective coating is formed are cut, and a terminal electrode is formed on the cut surface.

In the present invention, after forming a protective coating on the outer surface of the thermistor body, both end faces of the body, that is, both ends in the longitudinal direction are cut. Since the cutting can be performed with high precision using a dicing saw or the like having high dimensional accuracy, the lengths of the element bodies in the longitudinal direction can be made uniform, and variations in the dimensions can be reduced. For this reason, it is possible to suppress the variation in the resistance value due to the variation in the dimensions, and to improve the taping workability and the mounting performance.

Further, since the surface of the element body can be exposed at the end face by cutting both end faces of the element body on which the protective film is formed, the terminal electrode is directly joined to the exposed surface of the terminal electrode. be able to. For this reason, it is not necessary to limit the thickness of the protective film with high precision, and electrical connection between the element body and the terminal electrode can be ensured, and a chip thermistor having a desired resistance value can be obtained.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A chip type thermistor and a method for manufacturing the same according to the present invention will be described below in detail with reference to the drawings.

FIGS. 1A to 1C are sectional views showing one embodiment of a procedure for manufacturing a chip type thermistor of the present invention.

In the present invention, the production of the thermistor body and the formation of the protective film can be performed in the same manner as in the prior art.

That is, first, a ceramic green sheet of a thermistor material is prepared by a casting method, a required number of such sheets are laminated, pressed, cut into chips, baked, and then barrel-polished to obtain chips. A thermistor body 1 is obtained, and a protective coating 2 is formed on the entire outer surface of the chip-like thermistor body 1 (FIG. 1).
(A)).

The method of forming the protective film 2 is not particularly limited, and any method such as a physical vapor deposition method such as sputtering, and a wet film forming method such as a sol-gel method can be employed.

In the present invention, since the cutting process is performed, there is no restriction on the thickness of the protective coating for securing the electrical connection between the element body and the terminal electrode, and the thickness of the protective coating 2 can be arbitrarily set. It is adjustable.

A protective coating 2 is formed on the entire outer surface of the thermistor body 1.
Is formed, the terminal electrode forming end face of the element body 1 is
Cutting is performed at the position indicated by the broken line in FIG.
(B)). This cutting process can be performed with high accuracy using a cutting device such as a dicing saw with high dimensional accuracy or a polishing device such as a lapping machine. By this cutting process, the surface 1 of the body 1 is attached to the terminal electrode forming end face of the thermistor body 1.
A and 1B appear.

After the terminal electrode forming end faces of the thermistor body 1 are cut, the end faces 1A and 1B are formed on the end faces 1A and 1B in the same manner as in the prior art.
Terminal electrode 3A, Ni plating layer 3B, solder plating layer 3C
Is formed to obtain a chip thermistor. This terminal electrode 3
Since A is directly formed on the exposed end faces 1A and 1B of the element body 1, electrical connection between the element body 1 and the terminal electrode 3A can be reliably obtained.

The chip-type thermistor obtained in this way is one in which the longitudinal dimension, which is the most important for the resistance value, taping, and mounting performance, of the chip-type thermistor is adjusted by cutting. There is little dimensional variation, and the problem of conventional taping is solved.
In addition, the mounting performance is good and the variation in the resistance value is small.

As shown in FIG. 2, the chip type thermistor of the present invention has internal electrodes 4A, 4B inside a thermistor body 1.
May be formed, or a surface electrode may be formed on the surface of the thermistor body 1. As shown in FIG. 2, in the case of having the internal electrodes 4A and 4B, the element body 1
The ends of the internal electrodes 4A, 4B are reliably exposed on the terminal electrode forming end surfaces of the element body 1 by cutting the both end surfaces of the element body 1, and the electrical connection between the internal electrodes 4A, 4B and the terminal electrode 3A can be easily and easily performed. This is extremely advantageous because it can be performed reliably.

Although the illustrated chip type thermistor is provided with a Ni plating layer 3B and a solder plating layer 3C as plating layers, the Ni plating layer may be omitted and only the solder plating layer may be used.

[0033]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A chip-type thermistor of the present invention was manufactured by the method shown in FIGS. 1 (a) to 1 (c).

Manganese carbonate, cobalt carbonate and copper oxide were used as starting materials, each of which was weighed so that the metal atomic weight became a predetermined ratio, uniformly mixed in a ball mill for 16 hours, and then dehydrated and dried. Next, the mixture is brought to atmospheric pressure.
The calcined product was calcined at 900 ° C. for 2 hours. To the obtained raw material powder, an organic solvent, a binder component, a dispersant and the like are added to prepare a slurry,
A ceramic green sheet having a thickness of 40 μm was prepared by a casting method.

After stacking a predetermined number of the ceramic green sheets, the sheets were pressed by a hydrostatic pressing method. Thereafter, the press-bonded sheet was cut into chips by using a cutting machine to obtain chips having a length of 2.0 mm, a width of 1.1 mm, and a thickness of 0.8 mm. This chip is heated at 1100 ° C under atmospheric pressure for 4 hours.
After firing for a time, a barrel polishing treatment was performed to produce a thermistor body.

A protective glass film mainly composed of SiO ₂ was formed on the outer surface of the obtained element by a sputtering method to a thickness of 5 μm.
Then, both ends in the longitudinal direction of the element were cut by 0.1 mm using a dicing saw.

Next, an Ag paste (D
uPont 1176J) was attached by an immersion method and baked to form an Ag terminal electrode. After that, a Ni plating layer and a solder plating layer were formed and used as a sample.
The results are shown in Table 1.

Evaluation of Initial Characteristics (Measurement of Resistance Value: Number of Samples n = 100) The resistance values of the obtained samples were measured, and the variation of the resistance values was evaluated by the standard deviation (σ). If the variation is extremely large, it is considered that electrical continuity between the terminal electrode and the element cannot be secured. Measurement of Product Dimensions in the Longitudinal direction (Gradation of Dimensional Variation: Number of Samples n = 100) Using a micrometer, the lengthwise dimensions of the sample were measured, and the degree of the variation was evaluated by a standard deviation (σ). Mounting defect occurrence rate when mounting taping products (number of samples n
= 10000 pieces) Each sample was 1 mm thick, square hole size 1.65 × 40 mm
After mounting on a taping reel, a mounting test was performed on a glass epoxy substrate using an automatic mounting machine, and the occurrence rate of mounting defects (for example, the automatic machine could not mount a sample) was confirmed.

Comparative Example 1 A chip-type thermistor shown in FIG. 3C was prepared in the same manner as in Example 1 except that the element was not cut by a dicing saw, and the same evaluation was performed. 1 is shown.

[0041]

[Table 1]

Example 2 In Example 1, Ag was added to the ceramic green sheet.
/ Pd paste (Ag: Pd = 70: 30) was used to form internal electrodes by printing, and the other steps were performed in the same manner to produce a chip thermistor having internal electrodes as shown in FIG. However, the thickness of the protective glass film is 2 μm.
A lapping machine was used for cutting both ends in the longitudinal direction of the element body.

The obtained chip-type thermistor was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 2 A chip-type thermistor shown in FIG. 4 was produced in the same manner as in Example 2 except that the element was not cut by a lapping machine, and the same evaluation was performed. The results are shown in Table 2. Was.

[0045]

[Table 2]

Example 3 A chip-type thermistor was manufactured in the same manner as in Example 1, except that the protective glass film was formed by the sol-gel method according to the following procedure. The results are shown in Table 3.

A sol containing Si was prepared, and the thermistor element obtained by barrel polishing was coated by a dipping method. The coated device was dried and baked at 800 ° C. for 1 hour to form a SiO ₂ glass protective film having a thickness of 10 μm.

Comparative Example 3 A chip-type thermistor was manufactured in the same manner as in Example 3 except that the element was not cut with a dicing saw, and the same evaluation was performed. The results are shown in Table 3.

[0049]

[Table 3]

From the above results, it is clear that the chip-type thermistor of the present invention has no conventional problems and has good characteristics and mounting performance.

[0051]

As described above in detail, according to the chip-type thermistor and the method of manufacturing the same according to the present invention, a chip-type thermistor having small variations in characteristics such as element dimensions and resistance values and excellent in mounting performance and thermistor characteristics is provided. Provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing procedure of a chip thermistor according to an embodiment of the present invention.

FIG. 2 is a sectional view showing another embodiment of the chip type thermistor of the present invention.

FIG. 3 is a cross-sectional view illustrating a conventional manufacturing method.

FIG. 4 is a sectional view showing a conventional chip thermistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermistor body 2 Protective coating 3A Terminal electrode 3B Ni plating layer 3C Solder plating layer 4A, 4B Internal electrode

Claims (2)

[Claims] 1. A chip type thermistor having a thermistor body made of a rectangular parallelepiped ceramic sintered body and terminal electrodes provided on a pair of parallel end faces of the thermistor body, wherein the outer surface of the thermistor body is provided. A chip thermistor characterized in that after forming a protective coating on the base body, both end faces of the element body are cut and then terminal electrodes are formed on the cut face. 2. A method for manufacturing a chip-type thermistor by forming a protective coating on the outer surface of a rectangular parallelepiped thermistor element made of a ceramic sintered body and then forming terminal electrodes on both end faces of the thermistor element. Cutting both end faces of the thermistor body with the coating formed,
A method for manufacturing a chip type thermistor, comprising forming a terminal electrode on the cut surface.