JPH11307308A - Chip thermister and printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and accurately detect a rise in temperature of a printed wiring board, by forming an electrode on both ends of a thermister device and swelling a non-electrode portion thicker than the electrode on both ends so that one face of the thermister device abuts on the printed wiring board. SOLUTION: In a chip thermister device 11, electrodes 13 and 14 are formed on both ends of a negative temperature coefficient thermister device 12, and non-electrode portions on a pair of opposite faces in the negative temperature coefficient thermister device 12 are lumped thicker than the electrodes 13 and 14 on both ends. A green sheet lamination is obtained by laminating and attaching by pressure a specific number of inner layer green sheets 20 between the upper and the lower outer layer green sheets 19. After cutting the green sheet lamination so that a frame 21 of the outer layer green sheet 19 forms the lumped portion 12a of the negative temperature coefficient thermister 12, the negative temperature coefficient thermister 12 is obtained by firing. Accordingly, heat of the printed wiring board is conducted to both ends and the central portion of the thermister device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip thermistor mounted on a board and a circuit board on which the chip thermistor is mounted.

[0002]

2. Description of the Related Art FIG. 7 shows a general structure of a chip type thermistor 1 for detecting a substrate temperature and an example of mounting on a substrate 5. The chip-type thermistor 1 includes a thermistor element 2
Electrodes 3 and 4 are formed at both ends of the
Is Cu connected by solders 7 and 8 and formed on substrate 5
It is electrically connected to the lands 6a and 6b of the wiring pattern made of foil or the like.

[0003]

In recent years, the temperature of a circuit board in a device has been regulated in the IEC standard, and a chip thermistor has been used as a temperature detecting element of the board. As shown in FIG. 7, a conventional chip thermistor 1
When the electrode 3 is mounted on the substrate 5 for detecting the substrate temperature,
4 and the thickness of the lands 6a and 6b, the thermistor element 2
Since the gap 9 is formed between the substrate 5 and the substrate 5, the detection accuracy of the substrate temperature is reduced and the detection time is delayed. This is because the heat flow from the substrate 5 is blocked by the gap 9 and the heat is not directly conducted from the substrate 5 to the central portion of the thermistor element 2, but from one land 6a via the electrode 3 and the other land 6
This is because heat is conducted from both ends of the thermistor element 2 to the center from the electrode b through the electrode 4.

To solve this problem, there is a method of applying an adhesive or an insulating resin so as to fill the gap 9 when the chip thermistor 1 is mounted on the substrate 5. However, there is a problem that a coating process such as the above is necessary.

An object of the present invention is to use no adhesive or the like,
An object of the present invention is to provide a chip thermistor capable of eliminating a gap between a thermistor element after mounting and a substrate.

[0006]

According to a first aspect of the present invention, there is provided a chip type thermistor in which electrodes are formed at both ends of a thermistor element, and one surface of the thermistor element is formed without an electrode so as to contact a substrate. The portion is raised thicker than the electrodes at both ends.

A chip type thermistor according to a second aspect of the present invention is characterized in that the thermistor element has a negative resistance temperature characteristic.

The chip thermistor according to the third aspect of the invention is characterized in that the thermistor element has an internal electrode.

According to a fourth aspect of the present invention, there is provided a circuit board having the chip-type thermistor according to any one of the first to third aspects mounted on a substrate, and electrodes at both ends of the chip-type thermistor. Are connected to the lands on the substrate by solder, and the raised portion of the chip type thermistor is in contact with the substrate.

Thus, in the chip-type thermistor of the present invention, the heat flow from the substrate is simultaneously conducted from the three ends, that is, both ends and the center of the thermistor element, and the temperature rise of the substrate can be detected quickly and accurately.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the mounting diagram of a chip type thermistor 11 on a substrate shown in FIG.

In the chip type thermistor 11, electrodes 13 and 14 are formed at both ends of a negative characteristic thermistor element 12, and a pair of opposing surfaces of the negative characteristic thermistor element 12 where no electrodes are formed have electrodes 13 and 14 at both ends. It is thicker and swelling.

The negative temperature coefficient thermistor element 12 can be obtained as follows. As shown in FIG. 2, a predetermined number of inner layer green sheets 20 are laminated and pressed between upper and lower outer layer green sheets 19, 19 to obtain a green sheet laminate 22 as shown in FIG. This green sheet laminate 22 is connected to the crosspiece 21 of the outer layer green sheet 19.
Is cut in the dashed-dotted lines X and Y directions shown in FIG. 3 so that is a raised portion 12a of the negative characteristic thermistor element 12, and the negative characteristic thermistor element 1 before firing as shown in FIG.
Get 2. By further firing, the negative characteristic thermistor element 12 can be obtained.

The outer layer green sheet 19 is formed into a sheet shape using a ceramic material having a negative resistance temperature characteristic, and is cut out at a predetermined pitch so that a predetermined number of strip-shaped bars 21 parallel to the sheet remain. Is formed.
Since the thickness of the outer layer green sheet 19, that is, the thickness of the bar 21, constitutes the height of the raised portion 12a of the negative characteristic thermistor element 12, the electrodes 13, 14 and the lands 16a, 16b are formed after firing of the negative characteristic thermistor element 12. Is formed so as to have a thickness substantially equal to the total thickness. In this embodiment, the thickness of the electrodes 13 and 14 is 3 to 5 μm,
Since the thickness of each of a and 16b is approximately 35 μm, one or two outer layer green sheets 19 are stacked one on top of the other, and the thickness after firing, that is, the raised portion 12a
Had a thickness of about 40 μm.

The inner layer green sheet 20 is formed into a sheet shape using a ceramic material having a negative resistance temperature characteristic.

The raised portion 12a of the negative temperature coefficient thermistor element 12 does not necessarily need to be formed on a pair of opposing surfaces of the negative temperature coefficient thermistor element 12, but is mounted on one surface so as to come into contact with the substrate when mounted on the substrate. What is necessary is just to be formed. In this case, the outer layer green sheet 19 is formed on one surface of the green sheet laminate 22.

The electrodes 13 and 14 are formed by applying Ag paste to both ends of the negative temperature coefficient thermistor element 12 and then baking. As shown in FIG. 1, the electrodes 13 and 14 do not necessarily need to be formed at both end faces and near the both end faces of the negative characteristic thermistor element 12, but may be formed at least on both end faces.

When the electrodes 13 and 14 are formed, the electrodes 13 and 14 are fired in the state shown in FIG. 3 and cut in the direction of the dashed-dotted line Y to form a strip. By cutting in the direction of the dashed line X, individual chip thermistors may be formed. The electrodes 13 and 14 may be baked electrodes or plated electrodes.

The chip-type thermistor 11 having such a configuration
When the electrodes 13 and 14 are mounted on the substrate 15, the electrodes 13 and 14 come into contact with the lands 16 a and 16 b formed on the substrate 15, and the raised portion 12 a, which is a non-electrode-formed portion on one surface of the negative characteristic thermistor element 12, contacts the substrate 15. Touch

The chip thermistor 11 of the present invention
Can be applied to a positive characteristic thermistor element other than the negative characteristic thermistor element. However, the resistance of the positive temperature coefficient thermistor changes quickly in response to a change in temperature of a part of the element, whereas the resistance of the negative temperature coefficient thermistor changes quantitatively with respect to temperature change. Therefore, the present invention is effective particularly for a negative characteristic thermistor in which a heat flow is simultaneously transmitted to the thermistor element from three places at both ends and a central part of the thermistor element and the entire thermistor element is heated almost simultaneously.

Next, a chip type thermistor according to another embodiment having an internal electrode therein will be described with reference to FIGS. 5 (a) to 5 (e).
This will be described with reference to FIG. Chip type thermistors 11a, 11
“b” indicates the formation of the internal electrodes 23 and 24.

The chip type thermistor 1 shown in FIG.
1a, the internal electrodes 23 and 24 have one end facing each other on the same plane. In the chip-type thermistor 11b shown in FIG. 5B, the internal electrodes 23 and 24 partially overlap each other via the thermistor. Such chip type thermistors 11a and 11b are shown in FIG.
As shown in (c), the thermistor elements 26... Formed by the internal electrodes 23 and 24 electrically connected to the external electrodes 13 and 14 are connected in parallel, and the heat flow 25 from the circuit board 15 is The lowermost thermistor element 26 of the thermistor element is directly heated, and the change in the resistance value of the thermistor element 26 determines the change in the resistance value of each of the thermistor elements.

The chip type thermistor 1 shown in FIG.
1c is a hollow electrode 2 based on the one shown in FIG.
The internal electrodes 23 and 24 are electrically connected to the external electrodes 13 and 14, respectively. FIG. 5 (e) shows an equivalent circuit diagram of the chip thermistor 11c, which has the same effect as the chip thermistors 11a and 11b.

The outer layer green sheet 19 is different from the inner layer green sheet 20 in that the outer layer green sheet 19 has excellent thermal conductivity.
It may be made of an insulating material such as l2O3.

Further, the chip type thermistor 11 shown in FIG. 1 is not limited to the above-mentioned sheet laminating method, but is shown in FIG.
As shown in FIG. 6A, electrodes 13b and 14b are formed at predetermined positions corresponding to both ends of a rod-shaped thermistor element 12b obtained by extruding and sintering a thermistor material. As shown in ()), it can be obtained by cutting into chips.

[0026]

According to the chip-type thermistor of the present invention, the heat flow from the substrate is simultaneously transmitted to the thermistor element from three places at both ends and the center of the thermistor element, and the temperature change of the substrate is detected quickly and accurately. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a circuit board on which a chip thermistor according to an embodiment of the present invention is mounted.

FIG. 2 is an exploded perspective view showing a laminated state of an outer layer green sheet and an inner layer green sheet constituting a thermistor element.

FIG. 3 is a front view showing a cut portion of the sheet laminate.

FIG. 4 is a perspective view showing a thermistor element cut into chips.

5A and 5B show a chip-type thermistor provided with internal electrodes according to the present invention, wherein FIG. 5A is a cross-sectional view of a chip-type thermistor in which ends of the internal electrodes face each other, and FIG. Sectional view of a chip type thermistor that overlaps with an interposition, (c) is an equivalent circuit diagram thereof, (d) is a sectional view of a chip type thermistor having a hollow electrode in which ends of internal electrodes face each other, and (e) is an equivalent circuit thereof. FIG.

6A and 6B are perspective views showing another method of manufacturing the chip-type thermistor of the present invention, wherein FIG. 6A is a rod-shaped thermistor element on which electrodes are formed, and FIG. 6B is a chip-type thermistor cut into chips. is there.

FIG. 7 is a cross-sectional view of a circuit board on which a conventional chip thermistor is mounted.

[Description of Signs] 11 Chip type thermistor 12 Negative characteristic thermistor element 12a Raised portion 13, 14 electrode 15 Substrate 16a, 16b Land 17, 18 Solder 23, 24 Internal electrode

Claims (4)

[Claims] 1. A chip characterized in that electrodes are formed at both ends of a thermistor element, and one surface of the thermistor element is thicker than an electrode at both ends so that an electrode-free portion is in contact with a substrate. Type thermistor. 2. The chip thermistor according to claim 1, wherein said thermistor element has a negative resistance temperature characteristic. 3. The chip thermistor according to claim 1, wherein said thermistor element includes an internal electrode. 4. A chip-type thermistor according to claim 1, which is mounted on a substrate,
A circuit board, characterized in that electrodes at both ends of the chip thermistor are connected to lands on the board by solder, and the raised portions of the chip thermistor are in contact with the board.