JPH0379844B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a thermistor with improved heat resistance so as to be suitable for use in a high temperature atmosphere. (Prior Art) Thermistors are used in a wide range of applications for temperature measurement for temperature control. There is a need to downsize the thermistor to reduce the thermal time constant, there is a need to improve heat resistance to enable measurement of higher temperatures and expand the operating temperature range, and there is also a need to make it possible to use large quantities. There is a demand for a structure that is suitable for mass production. Glass-coated thermistors are typically used up to about 300°C and require stability at high temperatures. FIG. 2 is a cross-sectional view of a well-known bead-shaped thermistor. Manganese oxide on two noble metal wires 11 such as platinum,
A thermistor bead 12 is formed by sintering a mixed powder of metal oxide such as nickel oxide. One end of the noble metal wire 11 is connected to a composite wire 13 and sealed with a glass tube 14. Furthermore, as another type of thermistor, a thermistor called PSB type (Pellet type Small Bead) is known. The structure and manufacturing method of this type of thermistor are described in detail in Japanese Patent Publication No. 52-7535. FIG. 3 is a partially cutaway view of the PSB type thermistor described above. This thermistor chip 15 is made by molding a thermistor metal oxide powder into a wafer shape, firing it, providing electrode layers on both sides, and then cutting it into small pieces. Electrode layer of thermistor chip 15 and lead wire 16
are connected with a heat-resistant conductive paint 17 and sealed with a glass tube 18. Yet another form of thermistor, DHT
(Double Heat sink Thermister) type is known. FIG. 4 is a cross-sectional view of a DHT type thermistor. The thermistor chip 19 is manufactured in the same manner as the PSB type thermistor described above. The electrode layers on both sides of the thermistor chip 19 and the slug lead wires 20, 20 are firmly connected by thermocompression bonding. The heads of the slug lead wires 20, 20 are sealed with a glass tube 21. The bead-shaped thermistor shown in FIG. 2 has the characteristic that it can be made very small. However, since the density of the thermistor beads 12 cannot be increased, the resistance value varies widely and the yield is extremely low. Furthermore, due to its structure, many parts are manually operated, making it difficult to mass-produce. The PSB type thermistor shown in FIG. 3 can increase the density of thermistor chips 15,
Variations in resistance values can be made extremely small. Additionally, it has the advantage of being structurally suitable for relatively miniaturization and good mass production. However, during glass sealing, the heat-resistant conductive paint 17 and oxides of the lead wires are dispersed in the glass, resulting in deterioration of withstand voltage and large change in resistance value during high-temperature operation, resulting in a lack of reliability. The DHT type thermistor shown in Fig. 4 is extremely suitable for mass production. However, miniaturization is not possible, and the welded portion 22 between the head of the slug lead wire and the lead wire is easily oxidized during high-temperature operation, and this oxidation may cause the problem that the lead may come off. (Problems to be Solved by the Invention) The above-mentioned prior art examples all have a structure in which the thermistor bead portion or chip portion is covered with glass to protect it. The glass used for this coating is 300 to 500
At a high temperature of 0.degree. C., the movement of internal ions becomes active, causing electrical instability. Furthermore, near the transition point or softening point of glass, it becomes mechanically unstable, leading to the generation of micro-cracks. Furthermore, even if lead wires that can withstand high temperatures and glass that has a high softening point are used to melt the glass at high temperatures, the temperature will approach the transformation point of the thermistor bead and chip, resulting in instability of the thermistor itself. An object of the present invention is to solve the above-mentioned problems caused by the glass coating that occur during high-temperature processing or high-temperature operation, and to provide a thermistor that has excellent heat resistance, can be miniaturized, and is suitable for mass production. become. (Means for Solving the Problems) In order to achieve the above object, the thermistor according to the present invention connects metal lead wires to electrode layers formed on both sides of a thermistor chip with a heat-resistant conductive paint, and covers the connection portions. In the thermistor, the coating is constructed as a ceramicized sintered body of a mixture of an organosilicon polymer and a metal oxide filler containing glass frit. (Example) Hereinafter, the present invention will be described in more detail with reference to the drawings and the like. FIG. 1 is a sectional view showing an embodiment of a thermistor according to the present invention. Thermistor chip 1 is made of manganese, nickel,
Pressure molded aluminum oxide into wafer shape, 1250
The wafer was baked at approximately 800°C, then coated with silver palladium paste on both sides, baked at approximately 800°C, and then cut into 0.5 mm x 0.5 mm x 0.3 mm (thickness). The thermistor chip 1 has electrode layers 2 on both sides.
is formed. As lead wires 3 and 3, the diameter is 0.2 mm and the length is
25mm [Inconel-600 Sumitomo Electric product number]
Use Inconel wire. Inconel wire is an alloy of Ni, Cr, Fe, and Al and is suitable for use at high temperatures. The lead wires 3, 3 are adhesively connected to the electrode layer 2 of the thermistor chip 1 using silver/palladium paste 4, and are fixed by baking at about 800°C. The electrical characteristics of the thermistor at this time were: B (150 to 250°C) = 5500K R (200°C) = 20KΩ. The thermistor to which the lead wires are connected in this manner is coated with a mixture of an organic silicon polymer and a filler having the following composition. Γ Mixture 1 Silicone resin (silica mixed type)
100 parts by weight Al ₂ O ₃ 10 MgO 10 KMC80 from Shin-Etsu Chemical Co., Ltd. was used as the silicone resin. Γ Mixture 2 Silicone resin (silica mixed type)
100 parts by weight Al ₂ O ₃ 10 〃 MgO 5 〃 Glass frit (cover glass) 10 〃 Γ mixture 3 Polybolysiloxane resin 100 parts by weight Ladder type silicone resin 25 〃 Al ₂ O ₃ 10 〃 Γ mixture 4 Polybolysiloxane resin 100 Ladder type silicone resin (parts by weight) 25 〃 Al ₂ O ₃ 10 〃 Glass frit (cover glass) 10 〃 Adjust each of the above mixtures to an appropriate viscosity with a solvent such as xylene, and place the thermistor chip and its lead wire connection part in it. Dip into mixture solution until well coated. In this way, the area covered with the mixture solution is
Dry at 100℃ for 4 hours, then dry at 350℃ for 1 hour, then at 650℃ for 1 hour.
After firing for a certain period of time, the mixture becomes a ceramic sintered body, and the chip portion is covered with a coating layer 5 of the ceramic sintered body. The following tests were conducted on the four types of thermistors thus obtained, and the results are summarized in a table. ΓHigh temperature storage: Store at 500℃ for 1000 hours. Γ Cooling cycle: 0℃ (20 minutes) and 200℃ (20 minutes)
Five cooling/heating cycles are performed with a 5-minute room temperature period in between. The change in resistance value at 200°C and the occurrence of cracks in the fired ceramic body are examined.

[Table] This table shows that products mixed with glass frit do not crack when stored at high temperatures. This is because the thermistors using Mixtures 1 and 3 have many small holes in the ceramic fired body, whereas the thermistors using Mixtures 2 and 4 (mixed with glass frit) have many small holes. This is thought to be due to the fact that the small pores are blocked and a dense coating layer is formed. This seems to prevent the progress of oxidation of the lead wires buried and protected in the coating layer, thereby suppressing the occurrence of cracks. (Effects of the Invention) As explained above, in the thermistor according to the present invention, the connection portion between the thermistor chip to which the metal lead wire is connected and the lead wire is coated and fired with a mixture of an organic silicon polymer and a filler, Covered with ceramic fired body. Therefore, there are the following effects. (1) Since high-density thermistor chips can be used, a thermistor with uniform characteristics and less variation in resistance value can be obtained. It is also suitable for miniaturization. (2) The temperature at which the mixture of organosilicon polymer and filler is fired is similar to that for low-melting glass;
The temperature is much lower than the thermistor's transformation point, so it does not cause deterioration of the thermistor itself. (3) When firing the mixture to form a ceramic,
Unlike glass, the oxides of the heat-resistant conductive paint and lead wires are extremely unlikely to disperse into the fired coating, and there is no deterioration in withstand voltage. (4) Since the fired coating is made of ceramic, its transformation point is higher than that of glass, and even when operated at a high temperature of 300 to 500°C, there is little movement of ions, and it is electrically stable and mechanically stable. Strong and highly reliable. (5) Lead wire connections are made in the same way as for the PSB type described in the second example of the thermistor structure, but the formation of the fired coating is much easier than covering and melting a glass tube, so mass production is high. As described above, since the thermistor according to the present invention has excellent heat resistance, it can be widely used in combustion control sensors and the like.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a thermistor according to the present invention. FIG. 2 is a cross-sectional view of a conventional bead-shaped thermistor. Figure 3 shows the conventional
FIG. 3 is a cross-sectional view of a PSB type thermistor. Figure 4 shows
FIG. 2 is a cross-sectional view of a conventional DHT type thermistor. DESCRIPTION OF SYMBOLS 1...Thermistor chip, 2...Electrode layer, 3...Lead wire, 4...Heat-resistant conductive paint (silver/palladium paste), 5...Coating layer (ceramic fired body).

Claims (1)

[Scope of Claims] 1. A thermistor in which metal lead wires are connected to electrode layers formed on both sides of a thermistor chip using a heat-resistant conductive paint, and the connection portion is covered, wherein the coating is made of a metal containing an organic silicon polymer and glass frit. A thermistor characterized in that it is constructed as a ceramic fired body of a mixture with an oxide filler. 2. The thermistor according to claim 1, wherein the organosilicon polymer is a silica-mixed silicone resin. 3. The thermistor according to claim 1, wherein the organosilicon polymer is a polybolysiloxane resin and a ladder-type silicone resin. 4 The metal oxide is Al ₂ O ₃ or Al ₂ O ₃ and MgO
The thermistor according to claim 1, which is a mixture of.