KR100402369B1 - Chip thermistors and methods of producing same - Google Patents

Abstract

First, a green sheet containing a thermistor ceramic material and an organic binder is prepared, and then, a resistive paste is applied to at least one green sheet, an internal electrode paste is applied to the remaining few green sheets, and a predetermined number of these green sheets are laminated. By pressing to form a multilayer structure, a chip thermistor is produced. Thereafter, a firing treatment is performed on the multilayer structure, and external electrodes are formed on a pair of opposite outer end faces of the multilayer structure.

The chip thermistor thus produced includes: a body made of thermistor ceramic material having predetermined resistance-temperature characteristics; A pair of external electrodes formed on the cross section of the body; At least one resistor having a resistance greater than 1 kΩ; And a pair of internal electrodes facing each other apart from each other with the thermistor ceramic material therebetween. The resistor and the inner electrode pair are connected in series between the pair of outer electrodes.

Description

Chip thermistors and methods of manufacturing the same

The present invention relates to a chip thermistor and a method of manufacturing the same. More particularly, the present invention relates to a composite electronic device comprising a resistor and a chip thermistor, and a method of manufacturing the same.

Recently, surface mounted chip thermistors have been widely used. As is well known, chip thermistors include PTC and NTC types, and the B constant (resistance temperature coefficient) of the NTC thermistor is determined by the composition of the thermistor ceramic material used and is difficult to control freely. For this reason, in order to adjust the B constant of each circuit to be used, connecting a resistor in series or in parallel with the thermistor is normally performed. This not only adversely affects the mobility, but also has the problem that a large area is required to separately mount the resistors and thermistors as individual electronic components on the circuit board.

In view of the foregoing, Japanese Patent Laid-Open No. 64-1206 discloses a chip thermistor in which a resistor layer is formed between an external electrode on an outer surface and a thermistor and a resistor layer are connected in parallel. According to this, the surface mount area can be reduced because the thermistor and the resistor are on a single chip, and the B constant of the thermistor can be freely adjusted by changing the resistance of the resistor layer.

However, the chip thermistor thus constructed is not reliable because the resistor layer is exposed to the outside. In addition, an error tends to occur at the time of mounting, that is, a resistor layer is likely to be incorrectly mounted on the circuit board side.

Accordingly, it is an object of the present invention to provide a compact and reliable chip thermistor which can easily adjust the B constant and can avoid errors in mounting.

Another object of the present invention is to provide a method for manufacturing such a chip thermistor.

1 is a cross-sectional view of a chip thermistor according to a first embodiment of the present invention.

2 is a cross-sectional view taken along the line 2-2 of FIG.

3 is a cross-sectional view taken along the line 3-3 of FIG.

4 is an equivalent circuit diagram of the chip thermistor of FIG. 1.

5 is an exploded perspective view illustrating a layer structure of the chip thermistor of FIG. 1.

FIG. 6A is a chip thermistor according to a second embodiment of the present invention, which is a cross-sectional view along the line 6A-6A of FIG. 6B, and FIG. 6B is a cross-sectional view along the line 6B-6B of FIG. 6A.

FIG. 7 is an exploded perspective view illustrating a layer structure of the chip thermistor of FIG. 6.

FIG. 8A is a chip thermistor according to a third embodiment of the present invention, which is a sectional view along the 8A-8A line in FIG. 8B, and FIG. 8B is a sectional view along the 8B-8B line in FIG. 8A.

9 is an equivalent circuit diagram of the chip thermistor of FIG. 8.

FIG. 10A is a chip thermistor according to a fourth embodiment of the present invention, which is a sectional view along the line 10A-10A of FIG. 10B, and FIG. 10B is a sectional view along the line 10B-10B of FIG. 10A.

FIG. 11 is an equivalent circuit diagram of the chip thermistor of FIG. 10.

(Explanation of the code in the main part of the drawing)

1: ceramic body

3: resistor

5a, 5b: internal electrode

6, 7: external electrode

In order to achieve the above and other objects, the chip thermistor according to the present invention comprises a body made of a thermistor ceramic material having predetermined resistance-temperature characteristics, an external electrode formed on an outer cross section, and at least one high resistance conductor (or "). Resistors) and internal conductors formed inside the thermistor ceramic body, wherein at least one pair of internal electrodes spaced apart from each other with the resistor and the thermistor ceramic material interposed therebetween is electrically connected in series or in parallel. . According to the present invention, since the thermistor and the resistor are formed in one chip, it is possible to obtain a compact chip thermistor capable of freely adjusting the B constant. Since the resistor is formed inside the thermistor ceramic without being exposed to the outside, there is no fear of erroneous contact with an external circuit when the chip thermistor is mounted. That is, since only the external electrode is exposed to the outside, the reliability is improved. For the purposes of the present invention, "high resistance conductor" or "resistor" is defined as an electronic device having a much higher resistance than the internal electrode, or a device having a resistance greater than 1 kΩ, and the resistance of the internal electrode is usually in the milliohm range. .

The resistance value of the high resistance conductor can be freely changed by connecting internal electrodes facing each other in series and / or in parallel with thermistor ceramic material therebetween. In order to obtain a large resistance value, the resistor may be formed in a coil shape. This method is preferable because it is possible to increase the resistance value without being affected by the thermistor characteristics between the conductors.

Thermistors with negative thermistor-resistance characteristics (NTC thermistors) are widely used for temperature compensation and temperature detection of circuit elements. The B constant of this NTC thermistor is determined by the material composition of the thermistor ceramic. The B constant represents the magnitude of the change in the no-load resistance value with respect to temperature and can be obtained from two arbitrary temperatures T and T ₀ as follows.

Formula (1): B = {log (R / R ₀ )} / {(1 / T)-(1 / T ₀ )}

In the above formula, T and T ₀ are units of absolute temperature (K), and R and R ₀ are no-load resistance values (값) at these temperatures. Since the R / R ₀ ratio changes, the B constant can change even though the thermistor ceramics are the same.

A method of manufacturing a chip thermistor according to the present invention is to prepare a green sheet and an organic binder containing a thermistor ceramic material having a characteristic of becoming a thermistor ceramic by firing, and to include a resist paste on at least one green sheet, The internal electrode paste is applied to several green sheets. In the above, " resistance paste " refers to a paste having the property of being a resistor within the meaning of the present invention as defined above when firing is performed, and " internal electrode paste " Refers to a paste having properties. A predetermined number of green sheets are laminated and crimped to form a multilayer structure, and then firing is performed. External electrodes are formed on the cross sections of the multilayer structure that face each other. This method has the advantage that both the green sheet to which nothing is applied and the green sheet to which the paste is printed are subjected to the firing process all at once. That is, the manufacturing process includes fewer steps, which preferably works for manufacturing costs. The resistance value of the resistor can be changed by easily adjusting the number of laminated sheets of the green sheet on which the resistor is printed in the multilayer structure.

The internal electrodes and resistors can be connected in series simply by connecting the ends of the resistors and the internal electrodes to the corresponding external electrodes. If they are connected in series, the resistor and the internal electrode must be electrically connected in the ceramic body. This can be achieved by forming a through hole inside the thermistor ceramic and filling this through hole with the conductor material. This method is also applicable to the case of forming a coil-shaped resistor.

The accompanying drawings illustrate embodiments of the invention and are used to explain the principles of the invention. In the drawings, the same or similar components are denoted by the same reference numerals even if they are components of different chip thermistors, and no duplicate description is given.

Hereinafter, the present invention will be described by way of example.

Fig. 1 shows a chip thermistor according to a first embodiment of the present invention, in which the chip thermistor is a planar rectangular resistor 3 having a resistance of 1 kΩ or more and a thermistor having a desired resistance-temperature characteristic as shown in Fig. 2. It has a plurality of planar rectangular internal electrodes (first internal electrodes 5a and second internal electrodes 5b) formed in the ceramic body 1 made of a material and extending in opposite directions to each other. The body 1 is parallel and facing each other and has a planar shape with an upper and a lower surface extending between two mutually opposing cross sections .. Both ends of each resistor 3 are external to the cross section of the ceramic body 1. One end of each first inner electrode 5a is exposed at one end face of the ceramic body 1, and one end of each second inner electrode 5b is exposed at the other end face. 1 and more The secondary electrode 6 and the second external electrode 7 have one end of each resistor 3 and the exposed end of the first internal electrode 5a electrically connected to the first external electrode 6, The other end of each resistor 3 and the exposed end of the second external electrode 5b are respectively formed in the cross section of the ceramic body 1 so as to be electrically connected to the second external electrode 7. Thus, the first And thermistor characteristics between the second internal electrodes 5a, 5b and the resistor 3 are connected in parallel via the external electrodes 6, 7, the equivalent circuit diagram of which is as shown in FIG.

As shown in Fig. 5, the ceramic body 1 and a predetermined number of ceramic layers 8 having a resistor 3 longer than the ceramic body 1 and longer like a belt are stacked on each other, and the upper part of the laminate And at the bottom, a cover sheet 9 comprising at least one ceramic layer having no resistor. In addition, several ceramic layers 10 having a first internal electrode 5a or a second internal electrode 5b extending from one intermediate end or the other end in an intermediate position are laminated to each other, and the first is viewed perpendicularly to the layer. And the second internal electrodes 5a and 5b partially overlap. Under the lowermost ceramic layer 10, another cover sheet 9 including at least one ceramic layer in which no electrode is formed is disposed to form a composite multilayer structure. The chip thermistor is formed by forming the external electrodes 6, 7 on opposite sections of the composite multilayer structure in which the resistors and the internal electrodes 5a, 5b are exposed to the outside.

Next, the manufacturing method of such a chip thermistor is demonstrated. First, oxides of Mn, Ni, and Co are mixed in a ratio of 52:12:32 (wt%), and then the mixture is prebaked, and an organic binder, water, a dispersant, a surfactant is added, and a sheet shape is obtained. The green sheet is manufactured by molding. A sheet of a predetermined size was punched out from the green sheet, a resist paste containing PdO and Pd in a weight ratio of 10: 0 to 50:50, and an internal electrode paste in which Pd and Ag were mixed in a weight ratio of 70:30 were formed in a sheet form. Print on Thereafter, the sheets are laminated and pressed.

A plurality of unit cells are formed on each green sheet. As described above, after the layers are laminated and pressed, the laminated structure is appropriately cut and individual chip bodies are obtained. These chip bodies are fired to obtain a fired body. The surface of each fired body is polished to expose the resistor 3 and the internal electrodes 5a and 5b, and then the external electrodes 6 and 7 are formed. The external electrodes 6 and 7 are formed using conventionally known methods such as firing Ag, plating (Ni-Sn, Ni-Sn-Sn / Pb), and sputtering (Monel-Ag-solder, Ag-solder). Can be. The parallel circuit as shown in FIG. 1 of the resistor and the inner electrode through the outer electrode is used to form the equivalent circuit shown in FIG. 4, after these resistors and the inner electrode are previously connected through a through hole inside the thermistor ceramic. It may be drawn to the end face so that it may be connected to an external electrode.

Table 1 shows the total resistance and total B constants of the composite including NTC thermistor monoliths (300 kV and 100 kV) and the resistor and NTC thermistor shown in FIG. The dimensions are 2 mm in length, 1.20 mm in width, 0.9 mm in thickness, and 0.8 mm in width of the belt-shaped resistor.

Examples of thermistor materials forming the green sheet include oxides of Mn, Ni, Co, Cu, Al and Fe. The material of the resistor includes PdO, Pd, Lu ₂ O ₃ , SiC and mixtures thereof. Examples of internal electrode pastes include Ag, Ag-Pd, Pt and Pb.

Table 2 shows the resistance value of each resistor 3, which is 2 mm long, 0.8 mm wide, and 0.001 to 0.1 mm thick, as shown in FIG.

PdO or Pd: PdO ratio in the resistor Number of resistors Resistance of the resistor; Pd: PdO NTC resistance NT constant B (K) Total resistance at 25 ℃ Total resistance at 50 ℃ Total B Constant b25 / 50 (K) 0: 100 One 1000 300 3450 230.77 109.61 2869 25:75 One 500 300 3450 187.50 98.78 2470 25:75 One 250 300 3450 136.36 82.49 1937 40:60 One 125 300 3450 88.24 62.02 1359 0: 100 One 1000 100 3450 90.91 39.42 3220 25:75 One 500 100 3450 83.33 37.92 3034 25:75 2 250 100 3450 71.43 35.25 2722 40:60 One 125 100 3450 55.56 30.89 2262 40:60 2 62.5 100 3450 38.46 24.77 1696

material Content in Paste Resistance Pd: PdO 0: 100 100 Pd: PdO 10:90 700 Pd: PdO 25:75 500 Pd: PdO 40:60 125 Pd: PdO 50:50 10 Pd: PdO 75:25 5 Pd: PdO 90:10 2 Pd: Cu 25:75 2500 Pd: Ni 25:75 Pd: SiC 25:75 200 Ni 100 30k Cr 100 150k SiC 100 1500 Pd: Strontium titanate 25:75 700 Pd: Barium titanate 25:75 3000

The materials shown in Fig. 2 are used to prepare the paste by mixing 70% by weight of the solid component, 23% by weight of the resin component and 7% by weight of the solvent, respectively. Each paste is applied by the screen printing method by selecting the viscosity of the paste and the type of printing screen so that the thickness of the printed matter after drying becomes 10 to 100 µm. The firing treatment is performed at 1000 to 1250 ° C for 1 to 5 hours and cooled at 200 ° C. PdO does not have electrical conductivity, but is reduced during the calcination process, and part of the PdO becomes metallic Pd to exhibit electrical conductivity. Therefore, the resistor can be obtained even by using a paste containing only PdO, but the resistance value can be more easily controlled by using a mixture of Pd and PdO as the paste. In the case of Ni, Cr or Cu, depending on the conditions of the firing process and the oxygen density, a part of the oxide can be oxidized to produce oxides such as NiO, Cr ₂ O ₃ and CuO, and thus a significantly high resistance value can be obtained. have. The resistance value can be further controlled by mixing Pd. According to SiC, strontium titanate and barium titanate, the elements in the thermistor diffuse and cause a large change in the resistance value. In particular, Mn and Fe react sensitively, increasing the resistance value.

From Table 1, it can be clearly seen that the B constant 3450K of the thermistor monolith can be significantly changed by changing the resistance of the resistor 3. Although the B constant obtainable by a thermistor material normally exists in the range of 2500K-4500K, by making a composite with a resistor, it is possible to obtain low B constant values, such as 1359K previously unobtainable. Since the resistance value can be changed freely by changing the shape, the number of layers and the material of the resistor 3, the B constant value can be changed greatly. Depending on the combination of the resistance of the resistor material and the resistance of the NTC thermistor, the B constant can be as small as the temperature coefficient of the resistor.

6A, 6B and 7 show another chip thermistor according to a second embodiment of the present invention, in which the resistor 3 is formed in a coil shape and in parallel with the internal electrodes 5a, 5b. Connected. As shown in FIG. 7, a plurality of ceramic layers 8 having L-shaped resistors 3 formed thereon are stacked on the upper surface, and resistors 3 on other ceramic layers 8 are embedded in the through-holes 11. It connects through a conductor and forms a spiral coil. When forming such a coil-shaped resistor 3, the ends (represented by 3a and 3b) such that only the resistors 3 at the top and bottom of the plurality of ceramic layers 8 are connected to the external electrodes 6, 7). Extends. In this embodiment, the resistor, the shape of the high resistance conductor 3 and the number of ceramic layers 8 are determined according to the target resistance of the chip thermistor. The internal electrodes 5a and 5b and the cover sheet 9 are as described with reference to the first embodiment of the present invention shown in FIG.

In this embodiment, since the resistor 3 is formed in a coil shape, there is an advantage that a higher resistance value can be obtained than in the first embodiment of the present invention. The high resistance value can be obtained, for example, by forming the resistor 3 in a zigzag pattern or by reducing the width, but resistance conductors with too small a width are fragile, and the zigzag pattern is shorted if the separation between the zigzag lines is too small. Easy to cause By forming the resistor 3 in a coil shape, the resistance value can be increased without causing a broken line or a short circuit.

8A and 8B show another chip thermistor according to a third embodiment of the present invention, and FIG. 9 is an equivalent circuit diagram thereof. This embodiment is similar to the second embodiment of the present invention in that the resistor 3 is formed in a coil shape, and differs in that the resistor 3 and the internal electrodes 5a and 5b are connected in series. That is, one end 3a of one resistor 3 is connected to the first external electrode 6, the other end 3b is connected to the first internal electrode 5a, and the second internal electrode 5b is connected. It is connected to the second external electrode 7. It is evident from Figs. 8A and 8B that the first internal electrode 5a is not connected to the first external electrode 6, and the equivalent circuit diagram of this chip thermistor is as shown in Fig. 9. As can be seen from the general formula (1), in the present embodiment, the ratio R / R ₀ can be changed by connecting the resistor 3 in series with the internal electrodes 5a, 5b, and thus the B constant. Can be adjusted.

10A and 10B show another chip thermistor according to a fourth embodiment of the present invention, and FIG. 11 is an equivalent circuit diagram thereof. This embodiment is characterized in that a resistor 3 'is formed inside the ceramic body 1, one end of which contacts the first external electrode 6 and the other end of which contacts the second external electrode 7. 8A, 8B and 9 are different from the third embodiment described with reference to FIG. That is, this resistor 3 'is connected in parallel with the series connection of the above-mentioned resistor 3 and internal electrodes 5a and 5b. Therefore, the equivalent circuit diagram of this chip thermistor is as shown in FIG. It goes without saying that the chip thermistor according to the fourth embodiment of the present invention has the features of the chip thermistor according to the first and third embodiments of the present invention.

While the invention has been described with reference to a limited number of embodiments, these embodiments do not limit the scope of the invention. While the above has described embodiments with only one serial or parallel connection, a plurality of serial and / or parallel connections can be provided. Although the present invention has been described based on embodiments using NTC thermistors, PTC thermistors may be used. With PTC thermistors, the resistance increases with increasing temperature, but the manner of increasing the resistance (or increasing the characteristic) can be changed by connecting the resistors in series or in parallel. PTC materials that can be used in the manufacture of the chip thermistors of the invention can be obtained, for example, by adding oxides of yttrium, Mn or Pb to barium titanate.

In the said manufacturing method, although the different types of layers were laminated | stacked mutually and the baking process was performed, after baking these layers individually, you may join together using the glass paste containing lead borosilicate, for example. Thereafter, the thus obtained laminated composite structure is cut to a desired chip size to obtain an individual chip body.

In the case where a plurality of green sheets having internal electrodes formed on the upper surface are laminated, and then the firing treatment is performed, charges of the electrode material move to the ceramic material, thereby generating a voltage difference. As a result, a barrier layer that functions as an electric wall may be formed, and thus it may be difficult to obtain a desired resistance. In order to avoid such a problem, it is preferable to form internal electrodes on the ceramic plate which has already been subjected to the firing treatment, and to laminate and join each other through the resistor layer.

In the above embodiment, the internal electrodes 5a and 5b are arranged so as to be superimposed on each other in a perpendicular view to the plane, but this does not limit the scope of the present invention. These internal electrodes 5a and 5b may be on the same plane so as to face each other with a gap therebetween on the same plane, or may be arranged in a stepped form, although not separately shown.

As mentioned above, although this invention was disclosed, this indication should be interpreted widely, and those skilled in the art will recognize that various deformation | transformation are possible within the scope of this invention.

According to the present invention, there is provided a compact and reliable chip thermistor which can easily adjust the B constant and can avoid errors in mounting.

Claims (10)

A body made of a thermistor ceramic material having predetermined resistance-temperature characteristics and having a pair of outer cross sections facing each other; A first external electrode formed on one of the external cross sections; A second external electrode formed on the other one of the external cross sections; And A chip thermistor comprising: at least one resistor and at least one pair of internal electrodes having a resistance greater than 1 kV formed inside the body. The pair of inner electrodes face each other with the thermistor ceramic material interposed therebetween, wherein the one resistor and the inner electrode pair are electrically connected between the first outer electrode and the second outer electrode. Chip thermistor. 2. The apparatus of claim 1, wherein the one resistor has a first end in contact with the first external electrode, a second end in contact with the second external electrode, and the pair of inner electrodes in contact with the first external electrode. And a second inner electrode in contact with the first inner electrode and the second outer electrode. 2. The resistor of claim 1 wherein the one resistor is in contact with the first external electrode at one end and the inner electrode pair is in contact with the first and second external electrodes in contact with the other end of the resistor. And a second internal electrode. The chip thermistor of claim 1, wherein the thermistor ceramic material has negative resistance-temperature characteristics. The chip thermistor of claim 2, wherein the thermistor ceramic material has negative resistance-temperature characteristics. 4. The thermistor of claim 3, wherein the thermistor ceramic material has negative resistance-temperature characteristics. The chip thermistor of claim 1, wherein the one resistor has a coil shape. The chip thermistor of claim 2, wherein the one resistor has a coil shape. 4. The chip thermistor of claim 3, wherein the one resistor has a coil shape. Preparing a green sheet containing a thermistor ceramic material to be a thermistor ceramic and an organic binder by firing; Applying a resist paste, which becomes a resistor by firing, to at least one green sheet; Applying an internal electrode paste to another green sheet; Stacking and compressing a predetermined number of the green sheets, the at least one green sheet, and the other green sheets to form a multilayer structure having cross sections facing each other; Calcining the multilayer structure to form one or more resistors having a resistance of greater than 1 kΩ; And Forming an external electrode on the external cross section; and a method of manufacturing a chip thermistor.