JPS6333282B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a temperature sensing element using semiconductor ceramic and a method for manufacturing the same, and its purpose is to improve the adhesion of lead wires and provide a highly reliable temperature sensing element. In recent years, in order to achieve challenges such as sophistication of control systems and energy conservation, many types of industrial and consumer electronic and electrical equipment have built-in microcomputers. There is a growing need for high performance temperature sensing elements that provide information. Thermistors are widely used as this type of temperature sensing element. However, thermistor elements vary widely and lack compatibility, so adjustments are made by connecting an external resistor to each element, or by providing an adjustment part in the connected circuit, which reduces the price of the element. This requires several times the adjustment costs. The present inventors have developed a high-precision thermistor that has fundamentally improved the shortcomings of these thermistors.
We have already proposed a method for manufacturing highly reliable temperature sensing elements. (Japanese Unexamined Patent Publication No. 56-36102 and patent application dated October 12, 1974) FIG. 1 shows a cross-sectional view of a temperature sensing element made according to this proposal. 1 is a thermistor chip, which is usually made of porcelain mixed with oxides of transition metals such as Mn, Co, and Ni and sintered. 2 and 3 are electrodes that usually have little migration.
Formed by printing and baking Ag-Pd paste or Au paste. Reference numerals 4 and 5 are lead wires, which are usually made of a composite wire that has excellent adhesion to glass. 6 is glass to protect the thermistor from corrosive gas and improve moisture resistance. 7 is a welded part, which has a shape when resistance heating is selected as the welding method. In general, thermistors made of transition metal oxides such as Mn-Ni-Co are manufactured carefully so that the raw materials are prepared, mixed, and the firing temperature and atmosphere are uniform.
Since sufficiently reproducible characteristics can be obtained, it is possible to keep the variation within ±1% by performing a very small amount of electrode trimming, and this value can be
It is fully compatible. however,
The resistance value changes when the lead wire is baked and fixed with heat-resistant paint or sealed in glass. This change is caused by thermal changes in the thermistor body, as well as frit components in the electrodes, frit in the heat-resistant paint, carbon from the decomposition of the organic binder, and evaporated components from the sealing glass, all of which act in a complex manner on the thermistor components. Therefore, even if the characteristics were once made uniform, variations would occur again, which was not desirable. Therefore, it is preferable to be able to attach the leads at as low a temperature as possible, and good results were obtained using the welding method. In this resistance heating method, electrodes A and B shown in Figure 4 are crimped onto the lead wires, and the
In this method, when a voltage of about 0.1 to 0.5 seconds is applied and electricity is passed, heat is generated, locally melting, and instantaneous bonding occurs. If the applied pulse width is long, the melting will be complete, but the electrode may peel off, so conditions should be determined depending on the thickness of the electrode layer.
Adhesion at multiple points yielded good results in improving mechanical strength and electrical bonding. Furthermore, it has been found that lead wires plated with Au or silver have good adhesive properties in addition to electrical contact. The present inventors further investigated this point in detail and discovered the following phenomenon. FIG. 2 is a cross-sectional view of a welded portion when only a conventional composite wire is used, and FIG. 3 is a cross-sectional view of a welded portion when a composite wire coated with at least one coating layer 9 according to the present invention is used. It is a diagram. FIG. 4 is a schematic diagram during resistance welding, and is shown for the purpose of understanding the basic concept. The major difference between FIG. 2 (conventional example) and FIG. 3 (invention) is in the molten state of the electrode layer. In other words, the welded part shown in Fig. 3 has less melting or damage to the electrode layer than that shown in Fig. 2.
On the contrary, the lead wire and coating layer melt to a large extent. This means that when the electrode layer and the composite wire are directly pressed together and energized for welding, the electrode layer, which has a relatively (relatively) low melting point, starts melting first.
In the case of using a diamond wire coated with Au or Ag, it is shown that the coating layer or the coating layer and the electrode layer are melted almost simultaneously. Furthermore, it is taught that it is preferable to configure the coating layer with a material having a low melting point. The present invention will be described in detail below with reference to Examples. Example Metal oxides such as manganese, nickel, and cobalt are mixed in a desired mixing ratio and sufficiently calcined at a temperature of 800 to 1000°C to make the mixture uniform. After that, it is pulverized in a vibrating mill, and then a binder such as ethyl cellulose or terpineol is added to form a paint. Next, this paint is formed into a sheet with a thickness of about 1 mm by a doctor blade method or the like. Punch out a square plate with a side of about 5cm to 10cm from this sheet.
The larger the dimensions of the square plate, the better the manufacturing efficiency, but
On the other hand, differences in the firing atmosphere inside the furnace occur during firing, leading to large variations in resistance values, increasing the number of non-standard items, and decreasing yields. It is necessary to determine the optimum dimensions. Next, after sintering the square plate at 1100 to 1300°C, both sides of the sintered square plate are plane-polished in parallel to obtain a desired thickness for accuracy. Next, as shown in FIG. 5a, on both sides of the square plate 1,
Ag-Pd is applied and baked at a temperature of 600 to 1000°C to form electrodes 2 and 3. Next, the dimensions of the thermistor element to be finally obtained are calculated from the dimensions and resistance value of the thermistor element 1, and according to the calculation results, the thermistor element 1 is
Dividing grooves S ₁ and S ₂ are cut into each side in a lattice pattern as shown in FIG. 5b. Next, the resistance value of each thermistor element T ₁ -Tn of this assembly of thermistor elements T ₁ -Tn is measured and recorded. The resistance value is normally measured in an atmosphere at room temperature of 25°C. If the resistance value is smaller than the desired standard value, trim the electrode 2 or 3 using a diamond cutter, ultrasonic cutter, laser, sandplast, etc. (Fig. 5c) to increase the resistance value and set it to the specified value. Match the value. If the resistance value is larger than the standard value, it is impossible to reduce the resistance value by trimming, so please burn it off with a laser or remove the electrode 2 with sandplast, etc. to prevent it from being sent to the next process by mistake. Make sure it doesn't get caught. Next, the thermistor element assembly is divided into thermistor chips using a wafer breaker. Prepare a composite wire as a lead wire, and apply Au, Ag, Ag solder (hard solder), solder (soft solder), Sn, Ni, Ag-Pd (same alloy composition as the electrode) to the welding part.
Coated with Pd, Pt, and Cu. Connect each lead wire to 1V, 0.1~ by the method shown in Figure 4.
Welded after passing 0.5 seconds. Table 1 shows the results of visual observation of the welded parts.

[Table] Melting point (1425℃) of Fe-Ni alloy, which is the core wire of the composite wire, and Ag-Pd used as the electrode layer.
It can be seen that the electrode layer melts less when coated with a material that has a melting point lower than the melting point of the alloy, approximately 1100°C (the exact value is unknown due to pulverization).
Therefore, more ideal welding is possible. In the case of Cu, it seems that the effect was low because it easily generates Cu ₂ O and CuO. Furthermore, solder (soft wax) is more likely to be eaten away by solder than other coating materials with a low melting point, and as a result there is a large possibility that variation in resistance value will occur, so this was avoided. Furthermore, if these metal layers are coated with a component to facilitate welding (commonly called flux, which consists of a reducing agent that removes the oxidized layer on the surface). More preferred. These low melting point metals are also molten and alloyed with lead wires and metal materials, so their melting point becomes high after melting, so they will not peel off during the glass sealing process (400 to 800°C) in the subsequent process. Ta. Further, these coating layers should be limited to only the adhesive portion and should not extend to the lead wire portion (8 in FIG. 1) sealed with glass. This is because this part maintains airtightness and adhesiveness by absorbing stress due to the plastic flow of the copper layer of the composite wire. Note that the present invention can be applied not only to a thermistor having a negative temperature coefficient of resistance, but also to a temperature sensing element using a barium titanate-based thermistor having a positive temperature coefficient of resistance.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional temperature sensing element, Figure 2 is a sectional view of a welded part of a conventional temperature sensing element, and Figure 3 is a sectional view of a welded part of a conventional temperature sensing element.
FIG. 4 is a cross-sectional view of a welded portion of a temperature sensing element according to the present invention, FIG. 4 is a sketch showing a welding method, and FIG. 5 is a diagram illustrating a manufacturing method of an embodiment. 1... Thermistor element body, 2, 3... Electrode, 4,
5...Lead wire, 6...Glass, 7...Welded part,
8...Sealing part, 9...Coating layer.

Claims (1)

[Claims] 1 A composite lead wire with at least one coating layer selected from silver solder, Au, Ag, Ag solder, and Ag-Pd alloy on one end is heated on the electrode provided on the surface of the thermistor body using a resistance heating method. 1. A temperature sensing element characterized in that the welded portion of the lead wire, the thermistor and the electrode are sealed with glass.