JPH05283207A - Chip-type thermistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a thermistor whose resistance value is not influenced by a difference in terminal electrodes to be formed and which has no loss by rounding the corner of a thermistor element housing an internal electrode. CONSTITUTION:A green sheet laminate housing internal electrodes 10a, 10b is cut to the specified size and is sintered to obtain a thermistor base chip 11. The thermistor base chip 11 is wet barrel polished for obtaining a polished thermistor base chip 12 whose corner and ridge are rounded. On the surface of the polished thermistor base chip 12, a glass film 13 and a baked electrode 14 are formed. Then, a metal plated layer 15 is formed by a usual method. By this method, a productivity is increased and an accuracy and a reliability of the chip are increased.

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, temperature compensation is performed in some circuits and automatic adjustment is performed so that the electrical characteristics do not change. A chip type thermistor is used as such a temperature compensation circuit component, a temperature detection sensor, and the like.

Conventionally, a surface mounting chip type thermistor for a circuit board is one in which terminal electrodes are formed at both ends of a fired body of a thermistor resistor material.
Oxides of manganese, nickel, cobalt, etc. are blended and mixed in the same way as when manufacturing conventional ceramic products,
Then, it is calcined, and this calcined product is crushed. The thermistor resistor material powder thus obtained is mixed with a binder composition comprising a resin and a solvent to prepare a viscous slurry, which is molded by a molding machine to form a green sheet of the thermistor resistor material. Create. This green sheet is cut into a certain size and fired to obtain a thermistor base chip of a thermistor resistor. Both ends of this chip are sequentially dipped in an electrode material paste to attach the paste, and dried and baked to form a terminal electrode.
Complete the chip type thermistor.

In order to surface-mount such a chip type thermistor on a printed circuit board, a solder paste is applied to a soldering land of the printed circuit board, and then a terminal electrode of the chip type thermistor is placed and heated to form a coating layer. Reflow soldering that melts and solders the solder, or soldering by temporarily fixing the chip type thermistor to the printed circuit board with an adhesive and jetting molten solder to the soldering land and connecting the terminal electrodes Yes Flow solder. At this time, if the terminal electrode is formed of a coating layer containing only Ag, the so-called solder erosion phenomenon occurs, in which the terminal electrode is attacked by the molten solder particularly in the flow soldering, and the shortest length of the terminal electrode formed on both ends of the thermistor base chip is generated. The resistance value of the chip type thermistor is changed by changing the distance. The thermistor characteristics are resistance value and B
Since it is determined by a constant (temperature coefficient), it is important not to change this resistance value.
The terminal electrode is formed using an electrode material paste containing an electrode material in which Pd is added to Ag. Recently, the thermistor resistance value is required to be highly accurate and highly reliable.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 is required. It is desired to improve the wettability with respect to solder, but if Pd is increased, the wettability is lowered and the solder adhesion is deteriorated.

In order to improve the solderability of the terminal electrodes and suppress the phenomenon of solder erosion, there is a method of applying nickel plating or solder plating to the terminal electrodes like a multilayer capacitor. For example, as shown in FIG. 2, a square thermistor chip 1 manufactured as described above is agitated with alumina powder and water, so-called wet barrel polishing is performed to round the corners and ridges, thereby forming a thermistor chip. 2 is formed so as to prevent chipping 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 on the electrode material baking films 3 and 3. However, in this method, when the plating is performed, the thermistor substrate containing manganese as the main component is eroded by the plating solution, resulting in wavy unevenness on the thermistor substrate as shown in the figure, or plating on the edge of the electrode material baking film. There is a problem that a phenomenon of so-called plating extension, in which the film is extended and formed, occurs, and the manufactured individual chip type thermistors have large variations in resistance value between their terminal electrodes.

In order to eliminate the influence of the plating solution and prevent the thermistor substrate from being affected by the atmosphere, a chip containing a glass coating formed by coating a coating material containing glass powder on the thermistor substrate and heating it. Type thermistors are also used. For example, as shown in FIG. 3, a glass film 5 is formed on the thermistor base chip 1, and Ag—Pd electrode material baking films 6, 6 are formed on both ends thereof in the same manner as described above, and a metal film is formed on the film by nickel plating or the like. The plated layers 7 and 7 are formed.

[0007]

However, the chip-type thermistor having the glass coating formed thereon has sharp corners and ridges, and the glass coating is fragile. Then, in the actual work line, many of them are accommodated in the hopper, and
Since they are individually taken out and carried to the printed circuit board and soldered, when they are rubbed together by other things in the hopper, when they are taken out by the suction chuck and placed on the printed circuit board, etc. The ridge may be missing. If it is chipped like this, the thermistor substrate is exposed and is affected by the temperature and humidity in the air.If the chipped part is part of the terminal electrode, the resistance value of the chip type thermistor changes. However, there arises a problem that the resistance value is different for each product.

In order to solve this problem, the inventors of the present invention polished the thermistor base chip to round the corners and ridges, and the polished thermistor base chip contained glass powder. The paste is applied and the thermistor base chip is covered with a glass film by heating, and then a baking film of the electrode material is formed on both ends of this chip. By selecting the working temperature of the glass powder when forming the baking film, the glass material can be fluidized so that the electrode material penetrates into the glass film, thereby forming the thermistor base chip and the electrode material baking film. Proposed a method of contacting.

However, according to this method, even if the electrode material coating film is made to penetrate into the fluidized glass film, it is difficult to make the degree of penetration uniform for each product. There is a variation in the contact state with the thermistor base chip, which causes a problem that the variation in the resistance value, which is a characteristic value of the product, tends to be large.

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

[0011]

In order to solve the above-mentioned problems, the present invention provides a thermistor element body having at least a pair of spaced internal electrodes and having rounded corners.
The glass coating on the outer peripheral surface of the thermistor body and one of the pair of internal electrodes is led to different outer surfaces of the chip-shaped resistor to form the respective inner electrodes. The present invention provides a chip type thermistor having a terminal electrode connected to.

The present invention also provides a thermistor element chip through 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 firing the green sheet laminated body. To obtain, the step of polishing the thermistor element chip, the step of forming a glass coating on the polished thermistor element chip, and the electrode material is attached to both ends of the thermistor element chip on which the glass coating is formed. And a step of forming an electrode material baking film conductively connected to the internal electrodes by performing heat treatment at a temperature higher than the working point temperature of the glass film, and forming a metal plating layer on the electrode material baking film. The present invention provides a method for manufacturing a chip type thermistor including the steps of:

[0013]

Since the resistance value is determined by the distance between the internal electrodes by incorporating at least a pair of internal electrodes separated in the layer of the chip thermistor resistor, these internal electrodes are placed on the outer surface of the chip thermistor resistor. By leading out and forming a terminal electrode on this outer surface and connecting to each internal electrode, this connection is a connection between conductors, so the resistance value of the characteristic value of the product is less affected by the connection state .. On the other hand, when the thermistor element body is polished and then coated with glass coating, and the electrode material baking film is formed on both ends of the thermistor element, it is heat-treated at a temperature higher than the working temperature of the glass film, so the electrode material baking film is formed. During baking, the glass coating fluidizes and the electrode material and glass are mixed to form a terminal electrode that is conductively connected to the internal electrode.

[0014]

EXAMPLE An example of the present invention will be described below with reference to FIG. Example 1 Manganese, nickel and cobalt oxide thermistor resistor raw materials were mixed, mixed and calcined as in the case of producing a normal ceramic product, and the calcined product was pulverized,
Obtain the thermistor resistor material powder. This thermistor resistor material powder is mixed with a binder composition composed of resin, water, etc., and this mixture is molded by a molding machine to produce a thermistor resistor green sheet. An electrode material paste made of Ag-Pd, resin, solvent, etc. is applied to the thermistor resistor green sheet to obtain a green sheet with an internal electrode coating film. These two sheets are stacked so that the internal electrode coating films face each other with the thermistor resistor green sheet interposed therebetween, and the thermistor resistor green sheets are further stacked to embed the internal electrode coating film to obtain a green sheet laminate. This green sheet laminate is cut into a certain size and fired,
3.2, which has internal electrodes 10a and 10b.
A square thermistor element chip 11 having a size of mm × 1.6 mm × 1.0 mm is obtained. This thermistor element chip 11 is stirred with alumina powder having an average particle size of 30 μm and water to perform wet barrel polishing to obtain a polished thermistor element chip 12 with rounded corners and ridges.

The polishing thermistor body chip 12 is added 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 applied by the dipping method and then dried, and then at 800 ° C for 1
A heat treatment is performed for 0 minutes to form a glass film 13 of about 10 μm. The working point temperature is a temperature at which the viscosity becomes 10,000 poise units, and specific materials corresponding to this are described in the IWF frit type and characteristics list in the catalog of Iwaki Glass Co., Ltd. 300-800 at softening point temperature
C is preferred. In terms of composition, silicon oxide, boron oxide, and barium oxide-based ones are listed, and in addition to these, Li, K,
Examples thereof include those containing ions such as Na, Mg, Sr, Zn, Cd, Pb and Al, and 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.

Electrode material paste consisting of Ag--Pd powder, binder, etc. is applied by dipping to both side ends of the polished thermistor element chip 12 having the glass layer formed thereon, dried, and baked at 850 ° C. for 10 minutes. .. During this baking, the glass layer was fluidized to form a mixture of electrode material and glass, and baking electrodes 14, 14 with a thickness of about 20 μm were formed at both ends, and these electrodes contacted the ends of the internal electrodes. However, the two are connected. The internal electrodes 10a,
The distance between 10b is determined so as to have a predetermined resistance value. The electrode material paste was prepared using Ag-Pd (7: 3) powder, ethyl cellulose as the binder resin, and butyl carbitol acetate as the solvent.

After that, nickel plating and solder plating are applied by a usual method to form metal plating layers 15 and 15 to obtain a chip type thermistor chip 16 having a terminal electrode in which a baking electrode and a plating film are laminated.

In the visual inspection of 100 chip-type thermistors thus obtained, the plating was extended and no abnormality such as corrosion of the thermistor substrate was observed.

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

Reference Example In Example 1, the thermistor resistor green sheet on which the internal electrode coating film was not formed was cut into a piece having a predetermined size of 3.2 m.
A chip-type thermistor was produced in the same manner except that an NTC thermistor base chip in the form of a square chip of m × 1.6 mm × 1.0 mm was used, and this was used instead of the thermistor body.
Table 1 shows the results of measuring 100 of them in the same manner as in Example 1.

Comparative Example In the same manner as in Example 1, except that the glass coating was not provided, chip type thermistors were manufactured in the same manner, and the appearance inspection was performed on 100 of them.

[0018]

According to the present invention, a thermistor element body having inner electrodes and inner corners and rounded corners is coated with a glass film, and then the glass film is fluidized to form an electrode material baking film. Since the terminal electrode provided with the plated film is provided, the internal electrode and the terminal electrode are connected to each other, 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, the chip-type thermistor does not have sharp corners or ridges, and the corners of the thermistor body are less likely to be chipped when the chip-type thermistor is surface-mounted. In this way, if the thermistor body chip can be covered with the electrode material glass baking film on both ends and the other parts can be covered with the glass layer, the thermistor body part will not be eroded by the plating solution even if plating is performed. In addition, it is possible to prevent the plating extension in the thermistor body part. Also, the plated terminal electrodes can prevent solder erosion from occurring,
It is possible to provide a chip-type thermistor using the flow soldering method, which can improve the productivity, and also has good solderability and no obstacles when performing the plating described above, with high precision and high accuracy. It is possible to provide a reliable chip type thermistor.

[Brief description of drawings]

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

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

FIG. 3 is another manufacturing process explanatory diagram of the 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 Thermistor

[Table 1]

Claims (2)

[Claims] 1. A thermistor element body having at least a pair of spaced internal electrodes and having rounded corners, and a glass film coated on the outer peripheral surface of the thermistor element body.
A chip-type thermistor having terminal electrodes connected to respective internal electrodes formed by leading one end of one of the pair of internal electrodes to different outer surfaces of the chip-shaped resistor. 2. A step of stacking a green sheet with an internal electrode coating film formed by forming an internal electrode coating film on a thermistor resistor green sheet, and a step of obtaining a thermistor element chip through a step of firing the green sheet laminated body. , A step of polishing the thermistor element chip, a step of forming a glass coating on the polished thermistor element chip, and a step of attaching an electrode material to both ends of the thermistor element chip having the glass coating formed, And a step of forming an electrode material baking film conductively connected to the internal electrodes by heat treatment at a temperature higher than the working point temperature of the glass film, and a step of forming a metal plating layer on the electrode material baking film. Manufacturing method of chip type thermistor.