JPH0417375B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas sensor in which a thick-film detection element and an element support substrate are firmly adhered, and a method for manufacturing the same. Conventionally, as shown in FIG. 1, a gas sensor with a thick-film detection element formed on the surface of a substrate has electrode patterns 2a and 2b of a desired shape formed by thick-film printing on the surface of an insulating ceramic substrate 1 that supports the detection element. However, it has been known to print a thick film of paste containing a gas-sensitive metal oxide as a main component thereon in the shape of an element, and then bake it to form the detection element 3. This type of sensor has good response due to its thin element, and the heater, which is essential for many gas sensors, can be formed on the same substrate as the detection element by thick film printing, simplifying the structure. , has many advantages. However, in this type of sensor, as can be seen from the cross-sectional view taken along the line in FIG. 1-' shown in FIG. When the sensing element is used in a harsh environment with a low temperature and severe thermal cycles such as automobile exhaust, the sensing element may peel off from the substrate due to thermal strain caused by the difference in thermal expansion coefficient between the substrate material and the element material. I was afraid. In order to eliminate this fear, it is possible to use large ceramic particles as a raw material for the substrate itself to make the substrate surface rough, but on the other hand, such coarse graining may affect the insulation, mechanical strength, etc. of the substrate itself. This results in deterioration of the required properties. As a result of intensive study, the inventors determined that particles were adhered to the element forming surface of the substrate in advance to create irregularities.
It has been found that by forming a thick film detection element thereon, the adhesive strength between the detection element and the support substrate is increased and the possibility of peeling is extremely reduced. Based on the above knowledge, the inventors filed a patent application in 1983-
Invention No. 20322 "Gas sensor and method for manufacturing the same", a support substrate made of insulating sintered ceramics and having a thick film electrode formed on its surface, and a sintered material that is integrally fixed to the support substrate near the thick film electrode. The size of the previous granulated particle state is the maximum average particle size of 5 μm or more
It is characterized by comprising a group of sintered ceramic particles of 500 μm or less and a thick film detection element formed on the support substrate, electrically connected to the thick film electrode, and adhered to the particle group. gas sensor,
In addition, an electrode pattern of a desired shape is formed on the surface of a green sheet made of insulating ceramic powder and an organic binder by thick film printing, and an average particle size of 5 μm is formed on the surface of the green sheet near the electrode pattern.
A gas sensor characterized in that a group of granulated ceramic particles having a maximum particle size of 500 μm or more is dispersed, then fired, and then a thick film of a paste mainly consisting of a gas-sensitive metal oxide is printed thereon and baked. A manufacturing method was proposed. The present invention improves the above invention and increases the adhesive strength between the detection element and the support substrate by embedding the ceramic particle group within the support substrate by 1/20 to 1/4 of the average particle size. . Hereinafter, the present invention will be explained in detail with reference to the drawings. First, FIG. 3 is a sectional view showing the state of adhesion between the detection element and the support substrate in the gas sensor of the present invention. Support substrate 11 made of insulating sintered ceramic
Thick film electrodes 12a and 12b are formed on the surface of
In the vicinity of the electrodes 12a, 12b, the ceramic particle groups 4, 4, . are electrically connected to the electrodes 12a, 12b and are formed by thick film printing so as to adhere to the particle groups 4, 4...4. The first reason why the adhesive strength between the detection element and the support substrate of the gas sensor of the present invention is high is that the adhesive area becomes large due to the unevenness formed by the integrated particle groups 4, 4...4 on the substrate surface. The second reason is that the respective spherical particles constituting the particle groups 4, 4...4 are in the depressions 13a, 13a on the detection element side.
...It is thought that it mutually fulfills the hook function with 13a. Here, the particle group means a group of particles starting from unsintered secondary particles granulated into granules, and the particle size range limited above is the average particle size range of these unsintered secondary particles. It is. Therefore, the unevenness created by this is much larger than the unevenness caused by normal substrate surface roughness. In the state before sintering, the average particle size of particle groups 4, 4...4 must be 5 μm or more and the maximum particle size is 500 μm or less, and if the average particle size is less than 5 μm, the unevenness effect that increases adhesive strength will be poor. , if the thickness exceeds 500 μm, it becomes difficult to uniformly form the detection element by thick film printing, and the variation becomes large. The most desirable range of average particle size is 50 to 200 μm. The reason why the particle groups 4, 4...4 are buried inside the substrate 11 by 1/20 to 1/4 of the average particle diameter is that this increases the adhesion area between the particle groups and the substrate, thereby increasing the bonding area between the particles and the substrate. This is due to the increased adhesive strength; if the burying ratio is less than 1/20, the effect is poor; if it exceeds 1/4, it is difficult to bury, and the hook function effect is reduced for thick films. The amount of the particle group depends on the exposed area of the substrate and the particle group when the surface of the substrate before or after sintering on which the particle group is provided before printing the detection element is viewed from above in a direction perpendicular to the surface. The ratio (hereinafter abbreviated as "coverage ratio") to the area where the view is blocked (projected area of particle group) is 4/
The amount is preferably within the range of 1 to 1/4, and the optimal amount is the amount where the above ratio is approximately 1/1. It is preferable that the material of the particle group be the same as that of the support substrate 11 from the viewpoint of preventing distortion due to the difference in thermal expansion and sinterability, but it is also possible to use a different insulating ceramic as long as the effects of the present invention are achieved. In terms of mechanical strength, heat resistance, insulation, cost, etc., the most suitable insulating ceramic to be used in the present invention is alumina, followed by mullite, zirconia, and spinel. Next, a method of manufacturing the gas sensor of the present invention will be explained. An insulating ceramic powder and an organic binder are mixed in an organic solvent to form a slurry, and the slurry is formed into a sheet to become the supporting substrate 11 using a doctor blade. Pt, Pd, Rh,
An electrode pattern in a desired shape such as a comb shape or a spiral shape is thick-film printed using a metal paste such as Au or an alloy thereof. Separately, secondary particles made of ceramic powder (primary particles) to form particle groups 4, 4...4 are granulated, and these are dispersed near the electrode pattern on the surface of the sheet, and the particle groups are separated by pressure. After embedding 1/20 to 1/4 of the average particle size inside the green sheet, it is fired, and mainly TiO ₂ ,
The gas sensor of the present invention is obtained by printing a thick film of a paste made of a gas-sensitive metal oxide such as SnO ₂ , ZnO, Fe ₂ O ₃ , etc. and optionally containing noble metal powder, and baking the paste. The paste made of gas-sensitive metal oxide becomes the detection element 13 after baking. As described above, in the gas sensor of the present invention, a detection element is bonded onto a substrate having large irregularities formed by a group of particles, and since the group of particles is partially embedded in the substrate, the substrate, the group of particles, and the detection element are bonded together. The adhesive strength of the three bodies is extremely high. In addition, in the manufacturing method, the above-mentioned irregularities are formed by molding or granulating the substrate and the particle group separately according to conventional methods, and then baking them into one piece. Therefore, it can be manufactured by a simple process without requiring any special equipment. There is an advantage that As shown in FIG. 4, the gas sensor of the present invention may have a structure in which a protective substrate 6 having an opening 5 is laminated on a supporting substrate 11, and the detection element 13 is printed with a thick film so as to fill the opening 5. . In this case, since the dispersion area of the granulated ceramic particles to form the particle groups 4, 4...4 is limited by the bottom area of the opening 5, uniform dispersion to a predetermined portion is facilitated, and the adhesive strength of the detection element 13 is can be further increased. Examples will be described below. Example 12 parts by weight of butyral resin and 6 parts by weight of DBP were added to 100 parts by weight of a mixed powder consisting of 92% by weight of Al ₂ O ₃ , 4% by weight of SiO _{2 ,} 2% by weight of CaO, and 2% by weight of MgO with an average particle size of 1.5 μm. The mixture was mixed in an organic solvent to form a slurry, and a green sheet 2 with a thickness of 1 mm in the shape shown in Figures 5 and 6 was prepared using a doctor blade.
Green sheets 1 and 7 with a thickness of 0.2 mm were prepared.
On the surface of the green sheet 21, a heating resistor pattern 8 and an electrode pattern 22a having the shape shown in FIG.
22b is thickly printed with platinum paste, and platinum lead wires 9a, 9b, 9 with a diameter of 0.3 mm are attached to the ends of each pattern.
c was placed. On the other hand, after punching out openings 5 at positions where the tips of the electrode patterns 22a and 22b can be exposed when the green sheet 7 is stacked on the green sheet 21, these two green sheets are laminated and thermocompressed. did. Separately, add 40% to the same powder with the same composition as the mixed powder used for the above sheet.
Parts by weight of polyvinyl alcohol were added, the particles were granulated into spherical shapes using a spray dryer, and then sieved into the particle size range shown in Table 1 to form ceramic granulated particles 4, 4...
...Granules that should be graded 4 were obtained. These granules are dispersed in the opening 5 so that the coverage ratio is about 1, and then the granules are placed on top at a temperature of 50°C and a pressure of 8°C through a cushioning sheet.
After suppressing the granules to Kg/cm ² and partially embedding the granules in a green sheet, the granules were fired together with two crimped sheets at a temperature of 1500° C. in the atmosphere for 2 hours. As for the hardness of the granules before sintering, it is possible to obtain sufficiently hard granules by increasing the amount of binder.
Further, in order to improve the handling properties of the granules, they may be heat-treated at a temperature lower than the sintering start temperature and temporarily solidified by a small amount of the vitreous component contained therein. Next, 1 mole part of platinum black was added to TiO ₂ powder with an average particle size of 1.2 μm, and 3 parts by weight of ethyl cellulose was added to the total powder, mixed in butyl carbitol, and the viscosity was adjusted to 300 poise. A thick TiO ₂ paste was printed to fill the opening 5 and adhere to the tips of the electrode patterns 22a and 22b to form the detection element 13.
Gas sensors No. 1 to No. 8 shown in FIG. 7 were manufactured by baking under the conditions of temperature and holding time of 1 hour. However, gas sensor No. 1 has aperture 5 for comparison.
In this case, the detection element 13 is formed without dispersing the ceramic particles. The internal resistance of gas sensors No. 1 to No. 8 was measured at 350℃ using a propane burner.
The stoichiometric air-fuel ratio λ>
1, all values were 200 MΩ or more, but when λ = 0.9, the values changed to those shown in Table 1, indicating that the sensor function was maintained. A thermal shock test was repeatedly conducted in which the gas sensor was exposed to exhaust gas with a maximum temperature of 800°C from a 2000cc engine under full load for 5 minutes, and then idling for 5 minutes, until the detection element 13 peeled off. Table 1 shows the results of time measurements.

[Table] As can be seen from Table 1, the present invention gas sensor No. 3
- No. 6 had extremely high adhesive strength compared to gas sensors No. 1 to No. 2 of comparative examples. Comparative example gas sensors No. 7 to No. 8 showed adhesive strength comparable to that of the inventive example, but the printing state of the detection element was non-uniform. In order to withstand exposure to intense thermal cycles and vibrations such as automobile exhaust, the substrate is provided with concavities and convexities that function as hooks, which are formed by granulated particles that are integrated and fixed on the substrate. This is due to the fact that a thick-film thin detection element is formed on the substrate. Moreover, the unevenness with the hook function could be constructed by sprinkling spherical granulated particles at predetermined positions on the substrate and firing them, without applying compressive force that would cause damage to the substrate. . Next, the manufacturing process is the same as that of gas sensor No. 4, except that the conditions for embedding the granules in the green sheet are the temperature and pressure shown in Table 2, and that the detection element 13 is not formed in the opening 5 after firing the green sheet. After that, we manufactured simulated sensors No. 1 to No. 6 and passed JISB8081.
Table 2 shows the results of conducting an impact test as specified in 1974 and investigating the relationship between the burying rate and falling rate of particle groups.

[Table] As you can see from Table 2, the burial rate is 1/20 to 1/4
Simulated sensors No. 3 to No. within the range of (5 to 20%).
No. 5 had a low rate of falling off and good adhesion, but
A large amount of simulated sensors No. 1 and No. 2, which had a burial rate of less than 1/20 (5%), fell off. In addition, the burial rate is 1/4
(25%), most of the granules were destroyed during burial, making it difficult to work.

[Brief explanation of drawings]

Figure 1 is a perspective view of a conventional gas sensor; Figure 2 is a perspective view of a conventional gas sensor;
The figure is an enlarged cross-sectional view taken along the line -' in FIG. 1, FIG. 3 is a cross-sectional view showing one embodiment of the gas sensor of the present invention, and FIG. 4 is a cross-sectional view showing another embodiment of the gas sensor of the present invention.
FIG. 5 is a plan view showing the initial stage of the gas sensor manufacturing method of the present invention, FIG. 6 is a plan view showing the middle stage, and FIG. 7 is a plan view showing the same embodiment as FIG. 4. 11... Support substrate, 12a, 12b... Electrode,
4... Ceramic particle group, 13... Detection element, 2
1... Green sheet, 22a, 22b... Electrode pattern.

Claims (1)

[Scope of Claims] 1. A support substrate made of insulating sintered ceramics on which a thick film electrode is formed, and the granulated particles that are integrated and fixed in the vicinity of the thick film electrode and have an average size before firing. Sintered ceramic particles having a particle size of 5 μm or more and a maximum particle size of 500 μm or less, and a thick film type detection formed on the support substrate, electrically connected to the thick film electrode, and attached to the particle group. 1. A gas sensor comprising an element, wherein the ceramic particle group is embedded in the supporting substrate by 1/20 to 1/4 of the average particle diameter. 2. An electrode pattern of a desired shape is formed on the surface of a green sheet made of insulating ceramic powder and an organic binder by thick film printing, and an average particle size of 5 μm is formed on the surface of the green sheet near the electrode pattern.
Granulated ceramic particles having a maximum particle size of 500 μm or less are dispersed, and the ceramic particles are embedded within the green sheet by 1/20 to 1/4 of the average particle size by pressure, and then fired, A method for manufacturing a gas sensor, which comprises then printing a thick film of paste mainly consisting of a gas-sensitive metal oxide thereon and baking it.