JPH10172807A - Manufacture of thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erosion of a thermistor elementary body and an overhang of plating by forming a plated layer by a wet electric field plating method with a specific pH mainly composed of not less than one or two kinds to be selected from a group consisting of hydroxy carboxylic acid, polyoxylactone and its acid. SOLUTION: An Ag electrode 2A is formed by sticking Ag paste to both terminals of a chip-shaped thermistor 1 by an immersion method, and baking under an atmospheric pressure. Next, an Ni plated layer 2B, and an Sn/Pb solder-plated layer 2C are formed by using an Ni plating liquid (pH 6.0 to 9.0) mainly composed of citric acid which is a kind of hydroxy carboxylic acid, and an Sn/Pb (ratio 9/1) solder plating liquid (pH 6.0 to 9.0) mainly composed of tartaric acid and by an electrolytic barrel plating method. Thereby, erosion of the thermistor element body due to a plating liquid at the time of plated layer formation and an overhang of plating can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermistor surface-mounted on a printed circuit board or the like, and more particularly to a negative temperature coefficient thermistor whose resistance value decreases with an increase in temperature. The present invention relates to a method of manufacturing a thermistor for preventing overhang of plating and erosion of a thermistor body when forming a thermistor.

[0002]

2. Description of the Related Art As shown in FIG. 1, a chip-type thermistor surface-mounted on a printed circuit board or the like has solder heat resistance and solder adhesion on both end surfaces of a chip-like thermistor body 1 made of a sintered body of thermistor material. An external electrode composed of a baked terminal electrode 2A for improving the performance and a Ni plating layer 2B and a solder plating layer 2C covering the surface thereof is formed. The exposed surface of the element body 1 on which the external electrode is not provided may be covered with a protective film such as a glass layer. In addition, the chip-like thermistor body 1
Are provided with internal electrodes for adjusting the resistance value.

Conventionally, such a chip thermistor has
It is manufactured as follows.

That is, first, a ceramic sheet of a thermistor material is formed by a casting method or the like, and an internal electrode is formed on a part of the ceramic sheet as necessary. Then, a plurality of these ceramic sheets are laminated, pressed and cut into chips. Alternatively, a thin ceramic wafer manufactured by a block molding method or the like is cut into chips.
Thereafter, a chip-shaped thermistor body is prepared by performing barrel polishing, terminal electrodes are formed on both end surfaces of the chip-shaped thermistor body, and a plating layer is further formed.

When a protective film such as a glass layer is formed on the side surface of the chip-shaped thermistor element, a glass paste may be applied and baked before and after cutting into chips, or a sputtering method may be used. After a protective film such as a glass layer is formed on the chip-shaped thermistor body by means of a method such as described above, a terminal electrode and a plating layer are formed.
No. 05, 7-212516).

The plating layer is generally formed by a wet barrel electrolytic plating method, and an acidic plating solution having a pH of about 4.0 has been conventionally used as a plating solution.

That is, in the chip type thermistor, as a plating layer, a Ni plating layer is generally used as described above.
A Sn / Pb solder layer is formed. Conventionally, a Ni plating layer is formed using a Ni plating solution having a pH of about 4.0 containing sodium sulfamate or the like as a main component. And a plating solution containing carboxylic acid or the like as a main component and having a pH of about 4.0.

[0008]

The thermistor material constituting the thermistor body has a low durability against a plating solution. Therefore, if the glass layer is not formed on the side surface of the chip-like thermistor body, the Ni plating is not performed. The plating process uses an acidic plating solution for both the solution and the solder plating solution.
There is a problem that the chip-shaped thermistor body is eroded.

If the chip-shaped thermistor element is eroded by the plating solution, the resistance value, which is the basic characteristic of the thermistor, changes greatly, making it impossible to obtain a thermistor having the desired characteristics. For this reason, the product yield is low and the cost rises.

In particular, when the chip-shaped thermistor body is greatly eroded, its mechanical strength is reduced and its reliability against external stress such as resistance strength and substrate bending resistance is greatly impaired.

In addition, plating overhangs from the terminal electrode to the side surface of the chip-shaped thermistor body, resulting in poor appearance, which lowers the product yield and increases the cost. The overhang of the plating also causes the following problem.

That is, after mounting the thermistor on a substrate or the like,
When using with a voltage applied, migration failure may occur if the atmosphere contains moisture.
In a chip-type thermistor with overhanging plating, the distance between electrodes is narrowed by the overhang width, so that the possibility of occurrence of migration failure is extremely high.

In the case where a protective film such as a glass layer is formed on the side surface of the chip-like thermistor body, erosion of the chip-like thermistor body and overhang of plating are prevented. However, when a protective film such as a glass layer is formed on the side surface of the chip-shaped thermistor element, the number of manufacturing steps is considerably increased, and there is a problem that the manufacturing cost increases.

An object of the present invention is to solve the above-mentioned conventional problems and to provide an easy and inexpensive method for manufacturing a thermistor that prevents erosion of the thermistor body and plating overhang during plating.

[0015]

A method for manufacturing a thermistor according to the present invention comprises the steps of forming terminal electrodes on both end surfaces of a thermistor body made of a ceramic sintered body, and forming a plating layer on the terminal electrodes. In the method for producing a chip-type thermistor, the plating layer may be composed of one or more selected from the group consisting of hydroxycarboxylic acids, polyoxylactones and salts thereof, and have a pH of 6.0 to 9.0.
It is formed by a wet electrolytic plating method using a plating solution of No. 0.

If the plating solution is mainly composed of hydroxycarboxylic acid, polyoxylactone and salts thereof,
Even with a neutral or alkaline plating solution having a pH of 6.0 to 9.0, metal ions of a plating material such as Ni or Sn / Pb can be dissolved at a high concentration, and efficient wet electrolytic plating can be performed. I can do it.

In the present invention, such pH 6.0 to 9.0.
Since a neutral or alkaline plating solution is used, erosion of the chip-like thermistor body and overhang of plating during plating are prevented.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a thermistor according to the present invention will be described below in detail.

First, the plating solution according to the present invention will be described.

In the present invention, the plating solution used for forming the plating layer contains at least one selected from the group consisting of hydroxycarboxylic acids, polyoxylactones and salts thereof, and has a pH of 6.0 to 6.0. 9.0. If the pH is 9.0 or higher, Sn and Pb ions cannot be stably present in the plating solution, which is not desirable in performing the plating operation.

Next, a method of manufacturing a chip thermistor according to the present invention will be described.

In the present invention, first, a rectangular parallelepiped chip-shaped thermistor element made of a ceramic sintered body is manufactured. This chip-shaped thermistor body is obtained by cutting a thin plate-shaped thermistor body (thermistor wafer) made of a ceramic sintered body into a strip shape to obtain a prismatic thermistor body.
The prismatic thermistor body can be manufactured by cutting it in a direction orthogonal to its longitudinal direction and performing barrel polishing. Alternatively, a thermistor sheet is manufactured by a casting method or the like, and a plurality of the sheets are laminated and pressed,
It can be manufactured by cutting into chips, firing, and barrel polishing.

Next, terminal electrodes are formed on both end faces of the chip-shaped thermistor body. This terminal electrode can be formed by attaching a conductive paste to both end surfaces of the chip-shaped thermistor body by an immersion method or the like, and baking and baking it. Ag, Pd
And the like, but are not limited to noble metal electrodes.

The terminal electrode is not limited to the above-mentioned burn-in electrode, but may be a conductive resin electrode using a thermosetting resin.

Next, a Ni plating layer and a solder plating layer are formed on the terminal electrodes by a wet electrolytic barrel plating method using the above-mentioned Ni plating solution and Sn / Pb solder plating solution in a conventional manner. I do.

Normally, the Ni plating layer has a thickness of 0.5 to
It is preferable that the solder plating layer is formed to a thickness of about 1 to 10 μm.

In the present invention, the metal component of the plating layer on the terminal electrode is not limited to Ni or Sn / Pb at all.
/ Ag, Sn / Bi, Cr, Zn, etc.

In this case, as the plating solution, one or two or more selected from the group consisting of hydroxycarboxylic acids, polyoxylactones and salts thereof, having a pH of 6.0 to 9.0 is used. And a plating solution containing these metal ions is used.

In the present invention, the structure of the thermistor body is not limited to the chip type, but may be another type such as a disk type. In the case of the chip type, the structure of the thermistor body is not limited, and may include an internal electrode.

In the method of the present invention, the pH is 6.0 to 6.0.
Since the erosion of the thermistor body is prevented by using the plating solution of 9.0, it is not necessary to particularly form a protective film on the thermistor body, but a protective film such as a glass layer is formed on the thermistor body. Needless to say, there is no problem.

[0031]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A chip-type thermistor shown in FIG. 1 was manufactured according to the method of the present invention.

Commercially available manganese carbonate, cobalt carbonate and iron oxide were used as starting materials, each of which was weighed so that the metal atomic ratio became a predetermined ratio, mixed uniformly in a ball mill for 16 hours, and then dehydrated and dried. Next, this mixture was calcined at 900 ° C. under atmospheric pressure for 2 hours, and the calcined product was again pulverized by a ball mill and dehydrated and dried.

An organic solvent, a binder, a dispersant and the like were added to the obtained raw material powder to prepare a slurry, and a 40 μm-thick ceramic sheet was prepared by a casting method.

A predetermined number of the ceramic sheets were stacked, and the sheets were pressed by a hydrostatic pressing method. Thereafter, the sheet is cut into chips using a cutting machine.
A chip having a thickness of 0 mm, a width of 1.2 mm, and a thickness of 0.8 mm was obtained. This chip was baked at 1050 ° C. for 4 hours under atmospheric pressure, and then subjected to barrel polishing to produce a chip thermistor body.

Next, an Ag paste was adhered to both end surfaces of the chip-shaped thermistor body by an immersion method,
By baking while holding at 850 ° C for 10 minutes, a thickness of 1
A 00 μm Ag terminal electrode was formed.

Next, a Ni plating solution (pH 8.0) containing citric acid, which is a kind of hydroxycarboxylic acid, as a main component, and a Sn / Pb (ratio 9/1) solder plating solution containing tartaric acid as a main component (pH 9: 1). 0), a Ni plating layer having a thickness of 2 μm and a thickness of 3 μm by electrolytic barrel plating, respectively.
Was formed to obtain a chip-type thermistor.

The obtained chip type thermistor was subjected to the following performance evaluation tests, and the results are shown in Table 1.

(1) Evaluation of Initial Characteristics (Measurement of Resistance Value) The resistance value of each of the sample before plating and the sample of the final product was measured, and the rate of change in resistance before and after plating (Δ
R) was evaluated by the average value (the number of samples n = 100). (2) Observation of appearance properties The appearance properties of the obtained device were observed with an optical microscope, and the overhang of plating and the element erosion rate were confirmed (number of samples n = 1).
00). (3) Element polishing cross-section observation The obtained element was embedded in a curable resin and polished,
The structure of the cross section was observed with an electron microscope, and the degree of elementary body erosion (the amount eroded) was confirmed (number of samples = 100).
Pieces).

COMPARATIVE EXAMPLE 1 Ni containing sulfamic acid as a main component was used as a Ni plating solution.
Using a plating solution (pH 4.2), as a Sn / Pb solder plating solution, trade name Soldalon SG manufactured by Meltex Co., Ltd.
The chip type thermistor was manufactured in the same manner as in Example 1 except that the Sn / Pb solder plating solution (pH 3.8) was used, and the evaluation was performed in the same manner. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that sulfuric acid was added to the plating solution of Example 1 to adjust the pH of both the Ni plating solution and the Sn / Pb solder plating solution to pH 5.8. A chip-type thermistor is manufactured in the same manner as in
The results are shown in Table 1.

[0042]

[Table 1]

It is apparent from Table 1 that the method of the present invention can provide a good thermistor with little element erosion or the like.

[0044]

As described above in detail, according to the method for manufacturing a thermistor of the present invention, the erosion of the thermistor body and the overhang of the plating by the plating solution during the formation of the plating layer are prevented.

Therefore, a change in resistance value due to erosion of the thermistor body is prevented, and a thermistor having desired characteristics can be obtained with good yield. Further, a decrease in mechanical strength due to erosion of the thermistor body is prevented, and a thermistor with high reliability against external stress can be provided.

In addition, the appearance failure due to the overhang of the plating is prevented, and the occurrence of the migration failure is also prevented.

Moreover, there is no need to take any special treatment for preventing the erosion of the thermistor body and the overhang of the plating, so that it can be manufactured easily and at low cost.

Therefore, according to the present invention, a high-performance and highly-reliable thermistor having desired characteristics can be manufactured with good yield, easily and at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a chip thermistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Chip-shaped thermistor body 2A Terminal electrode 2B Ni plating layer 2C Solder plating layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takuya Yamazaki 2270 Yokoze, Yokoze-machi, Chichibu-gun, Saitama Prefecture Inside the Electrotechnical Laboratory, Mitsubishi Materials Corporation (72) Inventor Wataru Ito 2270 Yokoze, Yoji, Yokoze-cho, Chichibu-gun, Saitama Mitsubishi Materials Corporation

Claims (1)

[Claims] 1. A method for manufacturing a chip-type thermistor, comprising: forming terminal electrodes on both end surfaces of a thermistor body made of a ceramic sintered body; and forming a plating layer on the terminal electrodes. One or two selected from the group consisting of hydroxycarboxylic acids, polyoxylactones and salts thereof
A method for producing a thermistor, characterized by being formed by a wet electrolytic plating method using a plating solution having a pH of 6.0 to 9.0 and containing at least a seed as a main component.