JP3277291B2 - Manufacturing method of chip type thermistor - 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 A circuit board on which a semiconductor element is mounted may lose its function when the temperature thereof rises.
The temperature is detected to prevent the temperature from rising. A chip thermistor is used for temperature compensation for detecting such a temperature or controlling the temperature in a circuit.

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. The both ends of the chip are sequentially immersed in an electrode material paste to adhere and dry the paste, and then baked to form terminal electrodes, thereby completing 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, so-called wet barrel polishing is performed to round the corners of the corners and ridges. A polished thermistor chip 2 is formed, and is hardly chipped when the product is formed, 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. The electrode material baking films 3 and 3 are formed by drying and 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 on the plating solution and prevent the humidity of the atmosphere from affecting the thermistor substrate, a coating containing glass powder is applied to the thermistor substrate 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 base chip 1 and electrode material baking films 6, 6 of Ag-Pd are formed on both ends of the glass layer 5 in the same manner as described above. The films 7, 7 are formed.

[0007]

However, the chip type thermistor having the glass layer formed thereon has sharp corners and ridges, and the glass layer is brittle.
If this is to be surface-mounted on a printed circuit board, in the actual working line, many of them are stored in a hopper, taken out one by one, transported to a printed circuit board, and soldered, so that the hopper together with other things When it is rubbed, the corners and ridges may be chipped when it is taken out by a suction chuck and placed on a printed circuit board. If it is chipped in this way, the thermistor substrate will be exposed and will be affected by the humidity in the air.If the chipped part is part of the terminal electrode, the resistance of the chip-type thermistor of the product will change, A problem arises that the resistance value differs for each product. An object of the present invention is to provide a chip type thermistor in which a thermistor body is covered with a glass coating having a shape that does not chip.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a step of preparing a thermistor base chip having rounded corners, and a step of forming a sharp corner or a sharp corner on the entire surface of the thermistor base chip. A glass coating forming step of forming a glass coating having no ridge line portion, a step of attaching electrode materials to both ends of the chip obtained in the glass coating forming step, and a step in which the glass coating is higher than the working point temperature of the glass. so
Forming conductive electrodes connected material baked film on the thermistor matrix chip by the a process temperature and the <br/> electrode material and a glass fluidizing been heat-treated is heat-treated at a processing temperature at which the mixed state An object of the present invention is to provide a method of manufacturing a chip type thermistor including an electrode material baking film forming step and a step of forming a metal plating layer on the electrode material baking film obtained in the electrode material baking film forming step.

[0009]

[Function] A thermistor base chip having rounded corners is coated with a glass coating, and when the electrode material baking film is formed on both ends of the chip, the glass coating is adjusted to the working point temperature of the glass.
Heat treatment is performed at a higher temperature to fluidize and mix the electrode material and glass to form a terminal electrode conductively connected to the thermistor base chip. The thermistor substrate has sharp ridges and rounded corners.

[0010]

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. Thermistor resistor material powder mixed with a binder composition made of resin, water, etc.,
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, baked, and as shown in FIG. 1, a 3.2 mm × 1.6 mm × 1.0 mm NTC is formed.
The thermistor base chip 11 is obtained. The thermistor base 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 thermistor base chip 12 having rounded corners and ridges.

The thermistor base chip 12 is immersed in a glass paste containing a glass having a working point temperature of 400 to 1000 ° C. and lower than the baking temperature of the electrode material baking film described later, for example, a working point temperature of 700 ° C. After being adhered by the method, it is dried, and further heat-treated at 800 ° C. for 10 minutes to form a glass coating 13 of about 10 μm.
The working point temperature is a temperature at which the viscosity becomes 10,000 poise units. Specific examples of the material corresponding to the working point temperature are described in the IWF frit varieties and characteristics list in the catalog of Iwaki Glass Co., Ltd. 300-800 ° C at softening point temperature
Is preferred. The composition includes silicon oxide, boron oxide, and barium oxide-based ones. In addition, Li, K, N
Examples thereof include those containing ions such as a, 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 made of a powder of Ag-Pd, a binder, or the like is attached to both end portions of the thermistor base chip 12 having the glass coating formed thereon by dipping, dried, and baked at 850 ° C. for 10 minutes. At the time of this baking, the glass coating fluidizes, and the electrode material and the glass are mixed and the electrode material glass baking films 14 and 14 having a thickness of about 20 μm are formed at both end portions. Can contact the end face of At this time, the distance between the opposite ends of the electrode material glass baking films 14 on both sides is determined so as to have a predetermined resistance value. The electrode material paste was Ag-Pd (7:
3) The powder was prepared using ethyl cellulose as a binder resin and butyl carbitol acetate as a solvent.

Thereafter, a chip-type thermistor tap 16 on which metal plating layers 15 and 15 are formed by performing nickel plating and solder plating by an ordinary method 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.

Comparative Example A chip-type thermistor was prepared in the same manner as in Example 1 except that the glass layer was not provided, and 100 of the thermistors were visually inspected.

[0016]

According to the present invention, the entire surface of the thermistor base chip whose rounded corners and ridges are rounded is coated with a glass coating, and an electrode material baking film is coated on the end of the glass coating. The glass working point temperature higher than the temperature
The glass coating has no sharp corners or ridges, and the glass coating is less likely to be chipped during surface mounting of chip-type thermistors, etc. . In addition, since the electrode material is mixed with the glass and can be brought into contact with the end face of the thermistor base chip, a metal plating layer can be formed thereon to form a terminal electrode, and the terminal electrode is rarely chipped. If the thermistor base chip can be covered with the electrode material glass baking films at both ends and the other parts can be covered with the glass coating in this way, even if plating is performed, the thermistor base part will not be eroded by the plating solution. In addition, plating extension in the thermistor base can be prevented. Further, since the plated terminal electrode can prevent the solder erosion phenomenon, a chip type thermistor using a flow soldering method can be provided, and the productivity can be improved and the solderability is good. It is possible to provide a highly accurate and highly reliable chip thermistor in addition to the fact that there is no obstacle in performing the plating.

[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]

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (1)

(57) [Claims] A step of preparing a thermistor base chip having rounded corners ; a glass coating forming step of forming a glass coating having no sharp corners or ridges on the entire surface of the thermistor base chip; A step of attaching electrode materials to both ends of the chip obtained in the glass film forming step, and the glass film is formed at a temperature higher than the working point temperature of the glass.
Forming conductive electrodes connected material baked film on the thermistor matrix chip by the a process temperature and the <br/> electrode material and a glass fluidizing been heat-treated is heat-treated at a processing temperature at which the mixed state A method for manufacturing a chip type thermistor, comprising: an electrode material baked film forming step; and a step of forming a metal plating layer on the electrode material baked film obtained in the electrode material baked film forming step.