JPH05308003A - Method of manufacturing chip type thermistor - Google Patents

Abstract

PURPOSE:To protect a glass film against damage when a chip type thermistor is mounted on the surface by a method wherein a thermistor base chip having rounded corners is used. CONSTITUTION:A wet barrel grinding is performed onto a thermistor base chip 11 to obtain a thermistor element chip 12 in which square parts of its square corner and ridgeline parts and the like are rounded. Electrode material paste is adhered to end parts on the both sides of this thermistor element chip 12 to form electrode material sintering films 13, 13. Next, glass paste is applied to the entire surface of the obtained chip to form a glass film 14. The wet barrel grinding is again performed. A part in which a glass layer projects is grinded and continued to grind until the electrode material sintering film 13 is exposed, then the thermistor groundwork part can still be in a condition that it is coated with the glass layer. Thereafter, plating is performed to obtain a chip type thermistor forming metallic plating layers 15, 15.

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 In a circuit board on which a semiconductor element is mounted, the function of the semiconductor element is impaired when the temperature thereof rises.
The temperature is detected so that the temperature does not rise. A chip type thermistor is used for temperature compensation such as detecting such temperature or controlling the temperature in a circuit manner.

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 adhere and dry this paste, and then baked to form terminal electrodes, thus completing a 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 of only Ag, the so-called solder erosion phenomenon occurs in which the terminal electrode is eroded by the molten solder particularly in the flow soldering, and the terminal electrodes formed on both ends of the thermistor base chip are The shortest distance is changed to change the resistance value of the chip thermistor. Since the thermistor characteristics are determined by the resistance value and the B constant (temperature coefficient), it is important to prevent the resistance value from changing. Therefore, conventionally, the terminal electrode contains an electrode material in which Pd is added to Ag. It is formed by using an electrode material paste. 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, the square thermistor substrate chip 1 manufactured as described above is stirred with alumina powder and water, so-called wet barrel polishing is performed to round the corners and the ridges. The polished thermistor base 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 applied to both ends of the thermistor base chip 2 by a dipping method, dried, and baked to form electrode material baking films 3 and 3, which are plated with nickel as described above. The plating films 4 and 4 are formed. 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 on the plating solution and prevent the thermistor substrate from being affected by the humidity of the atmosphere, a coating material containing glass powder is applied to the thermistor substrate portion and heated to form a glass layer. Chip-type thermistors are also used. For example, as shown in FIG. 3, a glass layer 5 is formed on the thermistor substrate chip 1, Ag-Pd electrode material baking films 6, 6 are formed on both ends thereof in the same manner as above, and further plated with nickel plating or the like. The films 7, 7 are formed.

[0007]

However, in the chip type thermistor having the glass layer formed, the corners and the ridges are sharp, and the glass layer is fragile. In the actual work line, many of them are accommodated in hoppers 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 in this way, the thermistor substrate is exposed and affected by the humidity in the air.If the chipped part is part of the terminal electrode, the resistance value of the chip-type thermistor of the product changes and There is a problem that the resistance value is different for each product. An object of the present invention is to provide a chip-type thermistor in which a thermistor substrate having a shape that does not chip is covered with a glass layer.

[0008]

In order to solve the above problems, the present invention provides a step of preparing a thermistor base chip with rounded corners, and forming an electrode material baking film on both ends of the thermistor base chip. Electrode material baking film forming step, step of forming a glass film on the surface of the chip obtained in this electrode material baking film forming step, and removing the glass film on the electrode material baking film to expose the electrode material baking film The present invention provides a method of manufacturing a chip type thermistor including a step of forming a metal plating layer on the electrode material baked film.

[0009]

[Function] Prepare a thermistor base chip with rounded corners,
Be careful of the electrode material baking film on both ends, further form a glass film on the whole, and remove the glass film on the electrode material baking film to expose the electrode material baking film. The formed state can be maintained, and the metal plating layer can be formed on the electrode material baking film without affecting this portion.

[0010]

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. Mix the resin composition of the thermistor resistor material powder with a binder composition consisting of water,
This mixture is molded by a molding machine to produce a thermistor resistor green sheet. This thermistor resistor green sheet is cut into a certain size and fired to obtain a JISC3216-shaped NTC thermistor base chip 11, as shown in FIG.

This thermistor base chip 11 is agitated with alumina powder having an average particle size of 30 μm and water to perform wet barrel polishing to obtain a thermistor base chip 12 having rounded corners such as corners and ridges. An electrode material paste made of Ag-Pd powder, a binder, etc. is adhered to both end portions of this thermistor base chip 12 by dipping and then dried, and baked at 850 ° C. for 10 minutes to have a thickness of about 20 μm at both end portions. The electrode material baking films 13 and 13 are formed. At this time, the distance between the opposite ends of the electrode material baking films 13 on both sides is determined so as to have a predetermined resistance value. The electrode material paste is Ag
-Pd (7: 3) powder, prepared using nitrocellulose as the binder resin and butyl carbitol acetate as the solvent.

Next, a glass paste consisting of glass powder, a binder, etc. is adhered to the entire surface of the obtained chip by a dipping method, dried, and baked at 800 ° C. for 10 minutes to obtain a thickness over the entire surface of the chip. Bake 10μ
m to form a glass film. Examples of the glass composition include silicon oxide, boron oxide, and barium oxide particles, and in addition, Li, K, Na, Mg, Sr, Zn, C
Examples thereof include those containing ions such as d, Pb and Al, and for example, lead borosilicate glass is preferable. The glass paste was prepared using glass powder, nitrocellulose as a binder resin, and butyl carbitol acetate as a solvent.

The chips coated with the glass layer thus obtained are again subjected to wet barrel polishing in the same manner as above. Since the glass layer provided thereon by the thickness of the electrode material baking film protrudes from other parts, polishing the protruding part and stopping the polishing when the electrode material baking film is exposed , The thermistor substrate part can remain covered with the glass layer. After that, nickel-plating and solder-plating are applied by a usual method to obtain the chip type thermist tap 16 on which the metal plating layers 15 and 15 are formed.

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.

Comparative Example In the same manner as in Example 1, except that the glass layer was not provided, chip type thermistors were manufactured in the same manner, and 100 pieces of the thermistors were inspected for appearance.

[0016]

According to the present invention, since the electrode material baking film and the glass film are formed by using the thermistor base chip with rounded corners, the glass film has no sharp corners or ridges, and the chip type The glass coating is less likely to be chipped during the surface mounting of the thermistor. Further, since the electrode material baking film is not formed on the glass film, it is possible to reduce chipping of the terminal electrode formed of the metal plating layer thereon. In this way, if the other parts can be covered with the glass film except the electrode material baking film on both ends of the thermistor base chip, the thermistor base part will not be corroded by the plating solution even if plating is performed. ,
It is possible to eliminate the plating extension in the thermistor base portion. In addition, since the plated terminal electrode can prevent solder erosion from occurring, it is possible to provide a chip type thermistor using the flow soldering method,
It is possible to provide a highly accurate and highly reliable chip-type thermistor, which can improve its productivity, have good solderability, and have no obstacles when performing the above plating.

[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 a view for explaining another manufacturing process of the conventional chip type thermistor.

[Explanation of symbols]

 11 Thermistor base chip 12 Thermistor base chip with rounded corners 13 Electrode material baking film 14 Glass coating 15 Metal plating layer 16 Chip type thermistor

Claims (1)

[Claims] 1. A step of preparing a thermistor base chip with rounded corners, an electrode material baking film forming step of forming electrode material baking films on both ends of the thermistor base chip, and an electrode material baking film forming step. Forming a glass film on the surface of the obtained chip; removing the glass film on the electrode material baking film to expose the electrode material baking film; and forming a metal plating layer on the electrode material baking film. A method of manufacturing a chip type thermistor including the steps of: