JPH0982505A - Chip type thermistor and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: A chip type thermistor having a wide range of thermistor characteristics is manufactured easily and at low cost by preventing defects such as microcracks in a cutting process. A chip type thermistor 10 having surface electrodes 2 on four side surfaces. After forming the surface electrodes on both plate surfaces of the thin plate thermistor body, it is cut into strips, and then the surface electrodes are formed on the remaining two side surfaces, and then the glass layers are formed on the four side surfaces. This is cut into chips, and external electrodes are formed on both end surfaces of the chip thermistor element body. [Effect] Since the surface electrodes are provided on the four side surfaces and the effect of reducing the resistance value is great, the range of thermistor characteristics (resistance value and B constant) is expanded. Since the glass layer is formed after cutting into strips, defects during cutting are prevented. A product with high mechanical strength and high reliability can be manufactured.

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 surface-mounted on a printed circuit board or the like and a method for manufacturing the same, and more particularly to a negative characteristic thermistor whose resistance value decreases as temperature rises. The present invention relates to a chip thermistor having a wide range and a method for easily manufacturing such a chip thermistor without impairing mechanical strength and reliability.

[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, as shown in FIG. 9, a pair of side surfaces of a chip-shaped thermistor element body 1 are provided with surface electrodes 2 for resistance value adjustment. (2A, 2B), 2 (2A, 2B) are formed, and the external terminals 3 are formed on both end surfaces as the external electrodes 3 and the baking terminal electrodes 3A for improving solder heat resistance and solder adhesion and a plating layer 3B covering the surfaces thereof. Is provided, and the structure other than the surface on which the external electrode 3 is formed is covered with the glass layer 4.

Conventionally, such a chip type thermistor 5 has been used.
Is manufactured as follows. That is, first, conductive surface electrodes for resistance value adjustment are formed on both plate surfaces of a thin plate thermistor element body (hereinafter also referred to as “thermistor wafer”) made of a ceramics sintered body, An insulating glass layer is formed by printing a glass paste on the plate surface and baking it. Next, a thermistor wafer whose both surfaces are covered with a glass layer is cut into strips, and thereafter, a glass paste is printed on the cut surface and baked in the same manner as described above to form a glass layer. The thus obtained prismatic thermistor body having glass layers on four sides is cut in a direction perpendicular to the longitudinal direction (a direction perpendicular to the cut surface) to obtain a chip-like thermistor body.
A conductive paste is applied to the cut surfaces (both end surfaces) of the chip-shaped thermistor body and baked to form baked terminal electrodes. Further, a plating layer is formed on the surface of this terminal electrode to obtain a chip type thermistor.

[0004]

In the conventional manufacturing method described above, the surface electrodes for adjusting the resistance value are derived from the surface electrodes formed on both plate surfaces of the thermistor wafer, that is, the surface electrodes are chip-shaped thermistor bodies. Since the structure is formed on only two side faces, there is a limit to the effect of reducing the resistance value by the surface electrode, and the range of thermistor characteristics (combination of the resistance value and B constant) that can be obtained is relatively narrow, and it is generally obtained. Has been a problem in realizing a thermistor having a low resistance and a high B constant, which is difficult to achieve.

Further, according to the conventional method, after the glass layer is formed on the thermistor wafer, the thermistor element body and the glass layer are cut into strips in a bonded state. Due to the interaction between the internal residual stress of thermal stress during firing and the stress generated in the element body during cutting, defects such as microcracks occur in the thermistor element body or the glass layer. As a result, there is a problem that the mechanical strength of the product cannot be sufficiently obtained and sufficient performance cannot be obtained even in a reliability test relating to the product strength such as substrate bending resistance and temperature cycle.

In order to solve this problem, attempts have conventionally been made to optimize the thermal expansion coefficients of the thermistor element body and the glass layer, but the problem has not been completely solved.

The present invention solves the above-mentioned problems of the prior art, and prevents chip defects such as microcracks in the cutting process when manufacturing a chip thermistor having a wide range of thermistor characteristics and such a chip thermistor. Then, it is an object of the present invention to provide a method for manufacturing a highly reliable chip type thermistor having excellent mechanical strength and temperature cycle performance characteristics relatively easily and at low cost.

[0008]

A chip type thermistor of the present invention comprises a rectangular parallelepiped chip thermistor body made of a ceramics sintered body, and external electrodes formed on both end faces of the chip thermistor body. It is characterized by having a surface electrode for resistance value adjustment formed on four side surfaces other than the both end surfaces and a glass layer covering the surface electrode.

According to the chip type thermistor of the present invention as described above, the resistance value is adjusted, that is, the resistance value is reduced, because the chip thermistor body has the surface electrodes for adjusting the resistance value on the four side surfaces. It is possible to easily realize a chip-type thermistor having a low resistance and a high B constant, which has been difficult to obtain in the past, because the thermistor characteristics (resistance value and B constant) that are obtained are expanded. .

A method for manufacturing a chip-type thermistor according to the present invention comprises a rectangular parallelepiped chip-like thermistor body made of a ceramics sintered body, external electrodes formed on both end surfaces of the chip-like thermistor body, and both end surfaces thereof. In the method for producing a chip-type thermistor having a resistance-value-adjusting surface electrode formed on four side surfaces other than the above, and a glass layer covering the surface electrode, a thin plate thermistor element body made of a ceramic sintered body is used. A step of forming a surface electrode on the plate surface, a step of cutting the thin plate thermistor element body on which the surface electrode is formed into a rectangular shape to form a prismatic thermistor element, which extends in the longitudinal direction of the prismatic thermistor element A step of forming a surface electrode on two of the four side surfaces where the surface electrode is not formed,
A step of forming a glass layer on the four side surfaces of a prismatic thermistor element body having surface electrodes formed on the four side surfaces, and cutting the prismatic thermistor element body on which the glass layer is formed in a direction orthogonal to the longitudinal direction to form a chip thermistor. A step of forming a body, and
The chip-like thermistor element is characterized in that it has a step of forming external electrodes on both end surfaces which are not covered with the glass layer.

In the method of the present invention, the thermistor wafer is cut into strips, and then the glass layers are formed on the four side surfaces of the prismatic thermistor body. It is possible to eliminate defects such as microcracks that occur when cutting into a strip shape. As a result, the mechanical strength of the product can be improved, and the performance can be improved even in reliability tests related to the product strength such as substrate bending resistance and temperature cycle. Further, in the present invention, the glass layer can be formed once.

Further, the resistance value of the chip type thermistor is mainly determined by the distance between the surface electrodes, but since the method of the present invention is a method of forming the surface electrode on the thermistor sintered body, the dimension due to firing shrinkage is obtained. Precision variations are avoided,
The resistance value can be adjusted with high accuracy, and a chip type thermistor with a small resistance value distribution can be obtained.

[0013]

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.

FIG. 8 is a sectional view showing an embodiment of the chip type thermistor of the present invention. As shown in the figure, the chip type thermistor 10 of the present invention comprises a rectangular parallelepiped chip thermistor body 1 made of a ceramics sintered body, and external electrodes 3 (terminal electrodes) formed on both end surfaces of the chip thermistor body 1. 3A and plating layer 3B), and surface electrodes 2 (2A, 2B) for resistance value adjustment formed on four side surfaces other than the both end surfaces.
And a glass layer 4 provided so as to cover the surface electrode 2.

A method for manufacturing such a chip type thermistor 10 of the present invention according to the method of the present invention will be described below with reference to FIGS.

FIG. 1 is a perspective view of the thermistor wafer, and FIG.
5 is a perspective view of a thermistor wafer having surface electrodes formed on both plate surfaces, FIG. 3 is a perspective view of a prismatic thermistor element body, FIG. 4 is a perspective view of a prismatic thermistor element body having surface electrodes formed on four side surfaces, and FIG. 6 is a perspective view showing a method for forming a glass layer, FIG. 6 shows a prismatic thermistor body on which a glass layer is formed, and FIG.
6A is a perspective view, FIG. 6B is an enlarged view of a cross section taken along line BB of FIG. 6A, and FIG. 6C is a cross section taken along line CC of FIG. 6A. FIG. FIG. 7 is an internal perspective view showing a state where the prismatic thermistor body is cut into chips.

In the method of this embodiment, first, on both plate surfaces 11A and 11B of a thin plate thermistor element body (thermistor wafer) 11 made of a ceramics sintered body shown in FIG.
As shown in FIG. 2, a band-shaped pattern is printed with an appropriate interval 2a by a screen printing method using a conductive paste, and then dried and baked to form the surface electrode 2. Then, the thermistor wafer 11 on which the surface electrode 2 is formed is
A prismatic thermistor element body 13 shown in FIG. 3 after being cut into strips.
And Next, of the four side surfaces 13A, 13B, 13C, 13D extending in the longitudinal direction of the prismatic thermistor body 13, the two side surfaces 13B, 1 on which the surface electrode 2 is not formed are formed.
Also in 3D, as shown in FIG. 4, the surface electrodes 2 are formed at intervals so as to be continuous with the surface electrodes 2 formed on the side surfaces 13A and 13C.

Next, in this way, the surface electrodes 2 are formed on the four side surfaces.
A glass layer is formed on the four side surfaces (or the entire surface) of the prismatic thermistor element body 14 having the above-mentioned structure.

For forming the glass layer, a thin film forming technique such as sputtering can be adopted. For example, as shown in FIG.
As shown in, a stainless steel basket 16 containing a plurality of prismatic thermistor bodies 14 is installed in a sputtering device having a target 15 of glass having a predetermined composition, and the basket 16 is swung by a shaft 17. Then, by performing the sputtering while rotating the prismatic thermistor element body 14, as shown in FIGS. 6A to 6C, the glass layer 4 is formed on the four side surfaces or the entire surface of the prismatic thermistor element body 14 with surface electrodes. Can be formed.

Next, the prismatic thermistor element body 14 with a surface electrode on which the glass layer 4 is formed is cut in a direction orthogonal to the longitudinal direction to form a chip-like thermistor element body 1 as shown in FIG. External electrodes 3 are formed on both end surfaces of the chip-like thermistor body 1 which are not covered with the glass layer 4 by a conventional method.

According to such a method of the present invention, it is possible to manufacture a chip type thermistor having surface electrodes for resistance value adjustment on four side surfaces. Moreover, since the thermistor wafer is cut into strips before forming the glass layer, defects such as microcracks at the time of cutting are prevented, and a high-strength and highly reliable chip-type thermistor can be manufactured.

In the above description, the glass layer is formed by the sputtering method, but the glass layer may be formed by a usual printing method.

[0023]

The present invention will be described more specifically with reference to the following examples.

Example 1 A chip type thermistor of the present invention shown in FIG. 8 was manufactured according to the method of the present invention shown in FIGS.

Commercially available manganese carbonate, cobalt carbonate, and copper carbonate were used as starting materials, and these were weighed so that the metal atomic ratio was a predetermined ratio, uniformly mixed in a ball mill for 16 hours, and then dehydrated and dried. Next, this mixture was calcined at 900 ° C. under atmospheric pressure for 2 hours, and the calcined product was again pulverized by a ball mill and dehydrated and dried. An organic binder and the like were added to the pulverized product, granulated to have a particle size of about 60 μm by a spray drier, and compression-molded into a rectangular parallelepiped by a hydraulic press. This molded product was fired at 1100 ° C. for 4 hours under atmospheric pressure to produce a thermistor sintered block having a length of 35 mm, a width of 50 mm and a thickness of 10 mm. Next, this block is cut into a thin plate with a band saw, and the length is 35 mm, the width is 50 mm,
A thermistor wafer having a thickness of 0.40 mm was obtained (FIG. 1).

Commercially available conductive paste (Ag) was printed on both plate surfaces of the thermistor wafer by screen printing so as to form a belt-like pattern with an interelectrode distance of 200 μm as shown in FIG. 2, and after drying, It was baked at 820 ° C.

Next, the thermistor wafer was adjusted to a width of 0.
It was cut into 42 mm strips (Fig. 3).

Further, similar surface electrodes with an interelectrode distance of 200 μm were printed on the two side surfaces of the obtained prismatic thermistor element body on which the surface electrodes were not formed by a screen printing method, and after drying, at 820 ° C. It was baked (Fig. 4).

An insulating glass layer was formed on the four side surfaces of the prismatic thermistor element on which the surface electrodes were formed by the following method.

Formation of Glass Layer by Screen Printing Method On one side surface of the prismatic thermistor element on which the surface electrode is formed,
Insulating glass was printed by a screen printing method and dried. This was repeated for the four side surfaces. afterwards,
By baking at 850 ° C., an insulating glass layer having a thickness of 15 μm was formed on the four side faces of the prismatic thermistor element body (FIG. 6).

Formation of Glass Layer by Sputtering Method It was carried out using the sputtering apparatus shown in FIG. That is,
A stainless steel basket in which a large number of prismatic thermistor bodies with surface electrodes are placed in a sputtering device targeting insulating glass made of oxides such as SiO ₂ , Al ₂ O ₃ , MgO and ZrO _2. Was installed, and sputtering was performed for about 10 hours while rocking the cage to form a glass layer with a thickness of about 2 μm on the entire surface of the prismatic thermistor body.

Then, each prismatic thermistor element body with a surface electrode coated with the glass layer was cut out into a chip shape having a length of 0.92 mm by a dicing machine according to the pattern of the surface electrode (FIG. 7).

Further, external electrodes were formed on both end faces of each chip-shaped thermistor element by the following method. First, a conductive paste (commercial Ag paste) was attached to both end surfaces of the chip-like thermistor body by a dipping method, and baked at 820 ° C. under atmospheric pressure (at that time, the surface electrode and the terminal electrode were electrically connected to each other. can get.). Next, a Ni plating layer having a thickness of 2 to 5 μm was formed on the surface of this electrode layer by the electrolytic barrel method, and a solder plating layer having a thickness of 3 to 7 μm was formed thereon (FIG. 8).

The electrical characteristics (resistance value) of the chip type thermistor thus manufactured were measured, and the results are shown in Table 1. Incidentally, even if the glass layer was formed by the printing method, the results were the same whether the glass layer was formed by the sputtering method, but according to the sputtering method, one treatment is sufficient, Moreover, there is an advantage that the glass layer can be formed thin. Table 1
9 also shows the resistance measurement results of the conventional chip type thermistor having two surface electrodes and the chip type thermistor having no surface electrode shown in FIG.

From Table 1, it can be seen that the chip type thermistor of the present invention can significantly reduce the resistance value as compared with the conventional chip type thermistor.

[0036]

[Table 1]

[0037]

As described in detail above, according to the chip type thermistor of the present invention, the surface electrodes are provided on the four side surfaces and the effect of reducing the resistance value is great, so that the thermistor characteristics (resistance value and B
The range of (constant) is expanded, and it is possible to realize a chip type thermistor having a low resistance and a high B constant, which has been difficult to realize in the past.

Further, according to the method of manufacturing the chip type thermistor of the present invention, such a chip type thermistor of the present invention can be manufactured relatively easily and inexpensively with a good yield, and has high mechanical strength and reliability. It is possible to provide a high chip type thermistor.

[Brief description of drawings]

FIG. 1 is a perspective view of a thermistor wafer.

FIG. 2 is a perspective view of a thermistor wafer having surface electrodes formed thereon.

FIG. 3 is a perspective view of a prismatic thermistor body.

FIG. 4 is a perspective view of a prismatic thermistor element body having surface electrodes formed on four side surfaces.

FIG. 5 is a perspective view showing a glass layer forming method.

6 (a) is a perspective view of a prismatic thermistor element body with a surface electrode on which a glass layer is formed, and FIG. 6 (b) is FIG.
6A is an enlarged view of a cross section taken along line BB of FIG. 6A, and FIG. 6C is an enlarged view of a cross section taken along line CC of FIG. 6A.

FIG. 7 is an internal perspective view showing a state in which a prismatic thermistor body is cut into chips.

FIG. 8 is a sectional view showing an embodiment of the chip type thermistor of the present invention.

FIG. 9 is a cross-sectional view of a conventional chip type thermistor.

[Explanation of symbols]

 1 Chip Thermistor Element 2 Surface Electrode 3 External Electrode 3A Terminal Electrode 3B Plating Layer 4 Glass Layer 10 Chip Thermistor 11 Thermistor Wafer 13 Prism Thermistor Element 14 Target Prism Thermistor Element 15 Target 16 Stainless Steel Basket

Claims (2)

[Claims] 1. A rectangular parallelepiped chip-shaped thermistor element made of a ceramic sintered body, external electrodes formed on both end faces of the chip-shaped thermistor element, and four electrodes other than the both end faces.
A chip type thermistor having a surface electrode for adjusting a resistance value formed on a side surface and a glass layer covering the surface electrode. 2. A rectangular parallelepiped chip-shaped thermistor element made of a ceramic sintered body, external electrodes formed on both end faces of the chip-shaped thermistor element, and four electrodes other than the both end faces.
In a method for manufacturing a chip type thermistor having a surface electrode for resistance value adjustment formed on a side surface and a glass layer covering the surface electrode, a thin plate thermistor element body made of a ceramic sintered body is formed on both plate surfaces. The step of forming the surface electrode, the step of cutting the thin plate thermistor element body on which the surface electrode is formed into a rectangular shape to form a prismatic thermistor element, and the four side surfaces extending in the longitudinal direction of the prismatic thermistor element body. Among them, a step of forming a surface electrode on two side surfaces where a surface electrode is not formed, a step of forming a glass layer on the four side surfaces of a prismatic thermistor element body having a surface electrode formed on four side surfaces, and a glass layer were formed. A step of cutting the prismatic thermistor element body in a direction orthogonal to the longitudinal direction to form a chip-like thermistor element, and an outer surface of the tip-like thermistor element body not covered with a glass layer. A method for manufacturing a chip type thermistor, which has a step of forming electrodes.