JP3277292B2 - Chip type thermistor and manufacturing method thereof - Google Patents

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 for surface mounting such as a temperature sensor and a circuit board used for temperature compensation.

[0002]

2. Description of the Related Art When the temperature of a circuit board on which a semiconductor element is mounted rises, the mounted semiconductor element is affected, and the electrical characteristics of the circuit change. Therefore, depending on the circuit, temperature compensation is performed, and automatic adjustment is performed so that the electrical characteristics do not change. A chip-type thermistor is used as such a temperature compensating circuit component or a temperature detecting sensor.

Conventionally, a chip type thermistor for surface mounting of a circuit board has terminal electrodes formed on both ends of a fired body of a thermistor resistor material.
Mix and mix oxides of manganese, nickel, cobalt, etc. in the same way as in the case of manufacturing conventional ceramic products,
Then, it is calcined, and the calcined product is pulverized. The thus obtained thermistor resistor material powder is mixed with a binder composition comprising a resin, a solvent and the like to prepare a viscous slurry, which is molded by a molding machine to form a green sheet of the thermistor resistor material. Make it. The green sheet is cut into a predetermined size and fired to obtain a thermistor base chip of a thermistor resistor. Both ends of the chip are sequentially immersed in an electrode material paste to adhere the paste, and dried and baked to form terminal electrodes,
Complete a chip-type thermistor.

In order to mount such a chip-type thermistor on a printed circuit board, a solder paste is applied to the soldering lands of the printed circuit board, and then the terminal electrodes of the chip-type thermistor are placed and heated to form a coating layer. Reflow soldering, in which the solder is melted and soldered, or soldering, by temporarily fixing the chip-type thermistor to the printed circuit board with an adhesive, and then contacting the soldering land and the connection between the terminal electrodes with the jetted molten solder Flow soldering. At this time, if the terminal electrode is formed of a coating layer of Ag alone, the terminal electrode is eroded by the molten solder, particularly in flow soldering, so-called solder erosion occurs, and the shortest terminal electrode formed at both ends of the thermistor base chip is formed. The distance is changed to change the resistance value of the chip thermistor. The thermistor characteristics include resistance value and B
Since it is determined by a constant (temperature coefficient), it is important that this resistance value does not change.
The terminal electrode is formed using an electrode material paste containing an electrode material obtained by adding Pd to Ag. Recently, high accuracy and high reliability have been required for thermistor resistance value.Accordingly, in order to improve the solderability of the terminal electrode of the chip type thermistor to the soldering land on the printed circuit board, the melting of the terminal electrode has been required. It is desired to improve the wettability with respect to solder. However, when Pd is increased, the wettability decreases and the solder adhesion deteriorates.

[0005] In order to improve the solderability of the terminal electrode and to suppress the solder erosion phenomenon, there is a method of applying nickel plating or solder plating to the terminal electrode like a multilayer capacitor. For example, as shown in FIG. 2, the square thermistor chip 1 manufactured as described above is stirred with alumina powder and water, that is, a so-called wet barrel polishing is performed to round the corners and ridges of the polishing thermistor chip. 2 is formed, and it is hard to be chipped when it becomes a product so that the resistance value does not change. Then, an electrode material paste of Ag @ Pd is attached to both ends of the thermistor chip 2 by a dipping method and dried. The electrode material baking films 3 and 3 are formed by baking, and the plating films 4 and 4 are formed thereon by the nickel plating or the like. However, in this method, when performing plating, the thermistor base mainly composed of manganese is eroded by the plating solution, and as shown in the figure, wavy irregularities are formed on the thermistor base, or the end of the electrode material baking film is plated. The so-called plating elongation phenomenon occurs in which the film is extended, and the individual chip-type thermistor manufactured has a problem that the resistance value between the terminal electrodes varies greatly.

In order to eliminate the influence of the plating solution and to prevent the thermistor substrate from being affected by the atmosphere, a chip containing a glass powder is applied to the thermistor substrate and heated to form a glass coating. Type thermistors have also been used. For example, as shown in FIG. 3, a glass coating 5 is formed on the thermistor base chip 1, and electrode material baking films 6, 6 of Ag @ Pd are formed on both ends of the glass coating 5 in the same manner as described above. The plating layers 7 are formed.

[0007]

However, the chip type thermistor having the glass film formed thereon has sharp corners and ridges, and the glass film is brittle. Then, in the actual working line, many are stored in the hopper,
Each piece is taken out and carried to a printed circuit board and soldered.When it is rubbed together with other things with a hopper, it is taken out with a suction chuck and placed on a printed circuit board, etc. The ridge may be missing. If it is chipped in this way, the thermistor substrate will be exposed and will be affected by the temperature and humidity in the air.If the chipped part is part of the terminal electrode, the resistance of the chip thermistor of the product will change. This causes a problem that the resistance value differs for each product.

In order to solve this problem, the present inventors polished a thermistor base chip to round corners and ridges, and made the polished thermistor base chip contain glass powder. In a method of manufacturing a chip-type thermistor, a paste is applied, and the thermistor base chip is covered with a glass coating by heating, and then a baking film of an electrode material is formed on both ends of the chip, and further plated. By selecting the working point temperature of the above glass powder when forming the baked film, the glass film can be fluidized so that the electrode material penetrates into the glass film, and thereby the thermistor base chip, the electrode material baked film and A method of contacting was proposed.

[0009] However, in this method, even if the electrode material coating is penetrated into the fluidized glass coating, it is difficult to make the degree of penetration uniform for each product. Variations occur in the state of contact with the thermistor base chip, causing a problem that the variation in the resistance value, which is the characteristic value of the product, tends to increase.

An object of the present invention is to provide a chip-type thermistor coated with a glass coating having a shape such that the resistance value is not affected by a difference in terminal electrodes formed and is not chipped, and a method of manufacturing the same.

[0011]

In order to solve the above-mentioned problems, the present invention provides a thermistor element having at least a pair of spaced-apart internal electrodes and having rounded corners and ridges, and a thermistor element. A glass coating that has no sharp corners or ridges coated on the outer peripheral surface of the body, and one end of the pair of internal electrodes is led out to different outer surfaces of the thermistor body to form these outer surfaces. The above glass cover
The membrane was heat treated at a temperature above its glass working point
An object of the present invention is to provide a chip-type thermistor having terminal electrodes connected to respective internal electrodes formed by mixing an electrode material and the glass of the glass film by forming an electrode material baked film .

Further, the present invention provides a thermistor element chip through a step of laminating a green sheet with an internal electrode coating formed by forming an internal electrode coating on a thermistor resistor green sheet and a step of firing this green sheet laminate. And grinding the thermistor body chip to make the corners and ridges round, and the gas thermistor body chip having no sharp corners and ridges throughout the polished thermistor body chip. /> forming a lath coating, a step of depositing an electrode material on both ends of the thermistor element chips forming the glass coating, the glass coating than the working point temperature of the glass
The processing temperature at which it is processed and fluidized at a high temperature,
And a step of forming a conductive electrode connected to the material baked film on the inner electrode by the electrode material and the glass is heat treated at a processing temperature at which the mixed state, the step of forming a metal plating layer on the electrode material baked film It is intended to provide a method for manufacturing a chip type thermistor having:

[0013]

Since the resistance value is determined by the distance between the internal electrodes by providing at least a pair of internal electrodes separated in the layer of the chip-shaped thermistor resistor, these internal electrodes are attached to the outer surface of the chip-shaped thermistor resistor. By deriving and forming terminal electrodes on the outer surface and connecting to the respective internal electrodes, since this connection is a connection between conductors, the resistance of the characteristic value of the product is less affected by the connection state. . On the other hand, the thermistor body is polished to make the corners and ridges round, and then coated with a glass coating. At the time of baking when forming the electrode material baking film on both ends, the glass coating works on the glass. Temperature higher than point temperature
As a result, the glass film is fluidized, and the electrode material and the glass are mixed to form a terminal electrode conductively connected to the internal electrode.

[0014]

Next, an embodiment of the present invention will be described with reference to FIG. Example 1 As in the case of manufacturing a normal ceramic product, manganese, nickel and cobalt thermistor resistor raw materials were mixed, mixed and calcined, and the calcined product was pulverized.
A thermistor resistor material powder is obtained. A binder composition comprising a resin, water, and the like is mixed with the thermistor resistor material powder, and the mixture is molded by a molding machine to produce a thermistor resistor green sheet. An electrode material paste composed of Ag @ Pd, a resin, a solvent and the like is applied to the thermistor resistor green sheet to obtain a green sheet with an internal electrode coating film. These two sheets are overlapped so that the internal electrode coatings face each other with the thermistor resistor green sheets interposed therebetween, and the thermistor resistor green sheets are further stacked to embed the internal electrode coatings to obtain a green sheet laminate. This green sheet laminate was cut into a certain size, fired, and
As shown in 3.2, 3.2 having internal electrodes 10a and 10b
The thermistor body chip 11 having a square chip shape of mm × 1.6 mm × 1.0 mm is obtained. This thermistor element chip 11 is stirred with alumina powder having an average particle diameter of 30 μm and water to perform wet barrel polishing to obtain a polished thermistor element chip 12 having rounded corners and ridges.

The polishing thermistor element chip 12 is applied to a glass paste containing glass having a working point temperature of 400 to 1000 ° C. and a working point temperature lower than the baking temperature of the electrode material baking film described later, for example, 700 ° C. Is adhered by a dipping method, and then dried.
Heat treatment is performed for 0 minutes to form a glass coating 13 of about 10 μm. The working point temperature is a temperature at which the viscosity reaches 10,000 poise units. Specific materials corresponding to this temperature are described in the IWF frit varieties and characteristics list in the catalog of Iwaki Glass Co., Ltd. 300 to 800 at softening point temperature
C is preferred. In terms of composition, silicon oxide, boron oxide, and barium oxide-based ones can be mentioned.
Examples include those containing ions such as Na, Mg, Sr, Zn, Cd, Pb, and Al. For example, lead borosilicate glass is preferable. The glass paste was prepared using glass powder (working point temperature: 700 ° C.), nitrocellulose as a binder resin, and butyl carbitol acetate as a solvent.

An electrode material paste composed of a powder of Ag @ Pd, a binder, or the like is adhered to both end portions of the polishing thermistor element chip 12 having the glass layer formed thereon by dipping, dried, and baked at 850 ° C. for 10 minutes. . At the time of this baking, the glass layer fluidizes and becomes a mixture of electrode material and glass, and baking electrodes 14 and 14 having a thickness of about 20 μm are formed at both ends, and the electrodes contact the ends of the internal electrodes. Then, both are connected. The internal electrodes 10a,
The distance between 10b is determined to have a predetermined resistance value. The electrode material paste was prepared using Ag @ Pd (7: 3) powder, ethyl cellulose as a binder resin, and butyl carbitol acetate as a solvent.

Thereafter, nickel plating and solder plating are performed by a usual method to form metal plating layers 15 and 15, and a chip type thermistor chip 16 having terminal electrodes in which a baked electrode and a plating film are laminated is obtained.

In the appearance inspection of 100 chip type thermistors thus obtained, plating was elongated, and no abnormality such as erosion of the thermistor substrate was observed.

Further, these chip type thermistors 100
Table 1 shows the results of determining the variation 3σ (three times the standard deviation of 100 resistance values) of the resistance values at 25 ° C.

REFERENCE EXAMPLE In Example 1, the thermistor resistor green sheet on which the internal electrode coating film was not formed was cut into a predetermined size, and was cut to 3.2 m.
A chip type thermistor was prepared in the same manner except that a square chip-shaped NTC thermistor base chip of mx 1.6 mm x 1.0 mm was obtained, and this was used instead of the thermistor body.
Table 1 shows the measurement results of the 100 samples in the same manner as in Example 1.

Comparative Example A chip-type thermistor was prepared in the same manner as in Example 1 except that no glass coating was provided, and 100 of the thermistors were examined for appearance. As a result, erosion by the plating solution was observed for all of them.

[0018]

According to the present invention, a glass film is coated on a thermistor element having an internal electrode and rounded corners, and then the electrode film is baked while fluidizing the glass film. Since the terminal electrode provided with the plated film is provided, the internal electrode and the terminal electrode are connected, and the resistance value determined by the distance between the internal electrodes can be set to a predetermined value,
The variation can be reduced. Further, there is no sharp corner or ridge of the chip-type thermistor, and the corner of the thermistor body is less likely to be chipped at the time of surface mounting work of the chip-type thermistor. If the thermistor body chip is covered with the electrode material glass baking films at both ends and the other parts can be covered with the glass layer in this way, the plating does not erode the thermistor body part even when plating is performed. In addition, plating extension in the thermistor body can be prevented. Also, plated terminal electrodes can prevent solder erosion,
It is possible to provide a chip type thermistor using a flow soldering method, which can improve the productivity, as well as having good solderability and no obstruction in performing the above plating, as well as high accuracy and high precision. A reliable chip-type thermistor can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of a chip type thermistor according to one embodiment of the present invention.

FIG. 2 is an explanatory view of a manufacturing process of a conventional chip thermistor.

FIG. 3 is an explanatory view of another manufacturing process of a conventional chip-type thermistor.

[Explanation of symbols]

 10a, 10b Internal electrode 11 Thermistor element chip 12 Polished thermistor element chip 13 Glass coating 14 Electrode material glass baking film 15 Metal plating layer 16 Chip type thermistor

[Table 1]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-251210 (JP, A) JP-A-62-122103 (JP, A) JP-A-64-65825 (JP, A) 120102 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (2)

(57) [Claims] 1. A thermistor element having at least a pair of spaced-apart internal electrodes and having rounded corners and ridges, and a sharp corner that is coated on the entire outer peripheral surface of the thermistor element. A glass coating without ridges ,
One end of one of the pair of internal electrodes is led to a different outer surface of the thermistor body, and the outer surface of the thermistor body is provided with the gas.
Heat treatment of the lath coating at a temperature higher than the glass working point temperature.
A chip-type thermistor having terminal electrodes connected to respective internal electrodes formed by mixing an electrode material and the glass of the glass film by forming a baked film of the electrode material. 2. A step of laminating a green sheet with an internal electrode coating film in which an internal electrode coating film is formed on a thermistor resistor green sheet, and a step of obtaining a thermistor element chip through a step of firing the green sheet laminate. Grinding the thermistor body chip to have rounded corners and ridges; and forming a glass coating without sharp corners and ridges on the entire polished thermistor body chip. Depositing electrode material on both ends of the thermistor body chip with the glass coating formed thereon, and treating the glass coating at a temperature higher than the working point temperature of the glass.
Forming a conductive electrode connected to the material baked film on the inner electrode by is the a treatment temperature and the electrode material and the glass fluidized to a heat treatment at a processing temperature at which the mixed state, the electrode material A method for manufacturing a chip type thermistor, comprising a step of forming a metal plating layer on a baked film.