JPS6239701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a substrate with a built-in heater for a gas sensor, which is suitable as a substrate for a gas sensor such as an oxygen sensor.

The oxygen sensor described above is used to measure the oxygen concentration in a fluid, for example, to measure the oxygen concentration in the exhaust gas of an automobile internal combustion engine to realize air-fuel ratio control, and is used for various combustion It is used to control the combustion of equipment and the atmosphere inside the furnace.

In many such oxygen sensors, the oxygen concentration detection section is supported by a substrate with a built-in heater, and when manufacturing the substrate, the steps shown in FIGS. 1a to 1f, for example, have been adopted. In other words, first
As shown in Figures a and d, two substrate materials 1 are prepared by cutting raw ceramic sheets mainly composed of alumina or the like into appropriate sizes (for example, 9 x 5 x 0.7 mm).
A and 1b are prepared, and on one substrate material 1a, a conductive paste using platinum powder is used to form the pattern shown in Fig. 1b.
The heater layer 3 in a dry and unfired state is laminated by screen printing in the pattern shown in FIG. Then the first
As shown in Figure c, the diameter of platinum etc. is
Connect and place lead wires 4a and 4b with a length of 0.2 mm and a length of 10 mm. Further, in the other substrate material 1b, as shown in FIG. 1e, through holes 2a and 2b are formed at positions corresponding to the terminal portions 3a and 3b. Then,
The other substrate material 1b is placed on the one substrate material 1a.
The substrate 1 with a built-in heater as shown in FIG. Thereafter, the material is fired at a stage corresponding to the manufacturing process of the oxygen concentration sensing portion to maintain its strength as a structural base.

However, in such a conventional method for manufacturing a substrate with a built-in heater, when connecting the lead wires 4a and 4b, the lead wires 4a and 4b are placed at a depth exceeding the through holes 2a and 2b, as shown in FIG. As shown, the through holes 2a, 2
Parts 2c and 2d beyond b and through holes 2a and 2b
Since each lead wire 4a, 4b was fixed at both the portions 2e, 2f between the side and the side,
Terminal portions 3a and 3b of the heater layer 3 shown in FIG. 1b
However, after the substrate materials 1a, 1b are bonded under heat and pressure, the lead wires 4a, 4b are pushed into the lead wires 4a, 4b, resulting in frequent damage. This situation will be explained in more detail.

FIG. 2 is an enlarged explanatory view of the through-holes 2a and 2b portions (the through-hole 2b portion is omitted) of the substrate 1 after being bonded under heat and pressure. A part of the terminal portion 3a of No. 3 and a part of the lead wire 4a are exposed. Further, although the portion buried inside the substrate 1 is shown by a broken line, the lead wire 4a is inserted and fixed to a position beyond the through hole 2a. Note that the same applies to the through hole 2b.

FIG. 3 is a cross-sectional view taken along line A-A' in FIG. 2, and since the tip of the lead wire 4a is inserted beyond the through hole 2a, the heater layer 3 It is bent very sharply and is a very thin film. Further, the heater layer 3 is likely to receive strong shearing force at the tip portion of the lead wire 4a.

Furthermore, FIG. 4 is a cross-sectional view taken along the line B-B' in FIG. The heater layer 3 is pushed left and right by the line 4a. Therefore, in the conventional case, the electrical contact portion between the lead wire 4a and the heater layer 3 was only a small portion on the left and right sides. Further, in the cross section taken along the line C-C' in FIG. 2 shown in FIG. 5, the thickness of the heater layer 3 is about 0.3
mm, and the diameter of the lead wire 4a is about 0.2 mm, so when the heater layer 3 is pushed left and right by the lead wire 4a, it is in a state where it is in contact only at a very small portion on the left and right. Ta.

In this way, in the conventional case, since the heater layer 3 is more likely to be destroyed by the lead wires 4a, 4b, the heater layer 3 and the lead wires 4a, 4 are damaged after firing.
b, and even if the wire does not break, the resistance value of the heater layer 3 tends to vary greatly, and the temperature characteristics and responsiveness of the gas concentration detection section such as the oxygen sensor formed on this substrate 1 are likely to occur. However, the production yield of gas sensors is extremely low, which has become a major problem.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, form a heater layer on the surface of one of two unfired substrate materials, and connect lead wires to the terminals of the heater layer. After that, when the other substrate material is laminated to produce a gas sensor substrate incorporating the heater layer, it is possible to prevent the occurrence of disconnection between the heater layer and the lead wire, and also to reduce the electrical resistance value of the heater layer. An object of the present invention is to provide a method for manufacturing a substrate with a built-in heater for a gas sensor that can reduce variations in the temperature. , After positioning the lead wire connected to the heater layer so that the tip of the lead wire can be terminated in the through hole when both substrate materials are laminated, the other substrate material is laminated on the one substrate material and unfired. The advantage is that the substrate is created and then fired in accordance with the manufacturing process of the gas sensor detection section to maintain the strength of the substrate.

Examples of the present invention will be described in more detail below.

Figure 6 shows an example of the manufacturing process of a substrate with a built-in heater for a gas sensor based on the present invention, in which a raw ceramic sheet containing approximately 72% by weight alumina and the remainder talc, polyvinyl butyral, dibutyl phthalate, a dispersant, etc. size (9 x 5 x 0.7
Prepare two substrate materials 11a and 11b as shown in FIG. , screen printed in the pattern shown in Figure 6b using a conductive paste containing a surfactant, etc.
A dry, unfired heater layer 13 is laminated.
The thickness of the heater layer 13 obtained after drying is approximately 10 μm.
The membrane width is approximately 0.3 mm, and the terminal portions 13a,
The diameter of 13b is approximately 1.0 mm. Next, as shown in FIG. 6c, conductive lead wires 14a, 14b, 14c made of platinum or the like having a diameter of 0.2 mm and a length of 10 mm are attached to the terminal portions 13a, 13b and approximately in the center thereof.
At this time, each lead wire 14
Detailed positioning of a, 14b, and 14c will be described later. Further, as shown in FIG. 6e, the other substrate material 11b has the terminal portions 13a, 13b.
Three through holes 12a, 12b, and 12c are formed in accordance with the positions of the lead wires 14b. At this time, the diameters of the through holes 12a, 12b, 12c are approximately
It is 0.8mm. After that, the one substrate material 11
The other substrate material 11b is laminated on top of the substrate material 11b, and the substrate material 11b with a built-in heater is fabricated as shown in FIG. 6f by heat-pressing. At this time, when stacking, the center of both terminal portions 13a, 13b and the through hole 12a,
They are each positioned so that the centers of 12c substantially coincide with each other. Further, as shown in FIG. 6c, three lead wires 14a, 14b, 14c are connected to one substrate material 1.
When placing the two lead wires 14a and 14c on the heater layer 1a, the tips of the lead wires 14a and 14c are positioned approximately at the center of the thirteen terminal portions 13a and 13b of the heater layer. Position. At this time, as shown in FIG. 6c, another lead wire 14b is placed at a position approximately midway between the lead wires 14a and 14c so as not to come into contact with the heater layer 13.

Next, one substrate material 11a shown in FIG. 6c
At the top, through holes 12a, 12b, 1 shown in FIG.
The other substrate material 11b provided with 2c is laminated, and then heat and pressure bonding is performed. In this state, as shown in FIG. 6f, the lead wires 14a, 14c are positioned so that the tips of the lead wires 14a, 14c are located approximately at the center of the through holes 12a, 12c, and the lower heater layer 13 is Terminal parts 13a, 13b
so that the top of the screen is exposed.

On the other hand, regarding the lead wire 14b, in the example shown in FIG.
However, since this lead wire 14b has nothing to do with the heater layer 13, its tip ends at the through hole 1 as in the conventional case.
The substrate materials 11a, 1 exceed 2b.
There is no problem even if it falls within 1b. The subsequent heat and pressure bonding was carried out at 100° C. for 3 minutes and at 4 kg/cm ² . Next, the unfired substrate 11 bonded under heat and pressure was fired in the atmosphere at 1500° C. for 2 hours. Note that, depending on the manufacturing process of the gas concentration sensing section attached to the substrate 11, it is possible that the substrate 11 is fired during the manufacturing of the gas concentration sensing section.

Next, 100 substrates 11 with built-in heaters according to the present invention were selected after being fired, and the resistance of the heater layer 13 was measured between the lead wires 14a and 14c, and the results shown in FIG. 7 were obtained. In other words, 91% of the resistance values are within 5.0Ω±0.1Ω,
98% fall within 5.0Ω±0.2Ω.

Next, 10 of the heater built-in boards 11 that were within the 5.0Ω ± 0.1Ω were randomly selected, and a DC voltage of 10V was applied to them, and a power durability test was conducted in a cycle of 2 minutes of power on and 2 minutes of power outage. After 5000 cycles, no problems such as disconnection occurred.

As a comparative example, FIG. 8 shows a measurement example of the heater built-in substrate 1 by a conventional manufacturing method. Here too, 100 heater built-in substrates 1 were selected, and the resistance of the heater layer 3 was measured between the lead wires 4a and 4b.
Only 46% of the samples fell within the target value of 5.0Ω±1.0Ω, and only 72% fell within the target value of 5.0Ω±0.2Ω.

Next, we randomly selected 10 of the heater built-in boards 1 that were within the 5.0Ω±0.1Ω range, applied a DC voltage of 10V, and conducted a power durability test in a cycle of 2 minutes of power on and 2 minutes of power outage. As a result, the results shown in FIG. 9 were obtained. That is, three wires broke during the first 1,000 cycles, and as shown in the figure below, they gradually fell off, and after 5,000 cycles, there were only five, which was half the number.

As can be seen from the above comparison, in the present invention, variations in the resistance of the heater layer 13 of the heater-embedded substrate 11 (variations in the resistance measured between the lead wires 14a and 14c) are compared with variations in the resistance of the heater layer 13 itself. We were able to reduce the amount of electricity to about the same level, while also significantly improving the current durability.

The reason for this can be explained as follows. That is,
Lead wires 14a, 14 placed to establish electrical connection with terminal portions 13a, 13b of heater layer 13
This is because the tips of the lead wires 14a and 14c are positioned so as to terminate within the through holes 12a and 12c, so that the heater layer 13 will not be damaged by the tips of the lead wires 14a and 14c.

FIG. 10 is an enlarged explanatory view of the through hole 12a portion in FIG. 6 f, and the same is true for the other through hole 12c. As shown in the figure, a portion of the printed terminal portion 13a of the heater layer 13 and a portion of the lead wire 14a are visible in the through hole 12a of the substrate 11. At this time, the lead wire 14a (14c)
is the portion 12d (12f) between the through hole 12a (12c) and one side shown in FIG. 6f, that is,
It is fixed only at a portion 12d shown in FIG. 10, and the tip of the lead wire 14a terminates approximately at the center of the through hole 12a.

Furthermore, FIG. 11 shows a cross section taken along the line D-D' in FIG. When it is sandwiched in between, the tip becomes slightly raised. Therefore, the degree to which the lead wire 14a crushes the heater layer 13 is considerably reduced, and the tip of the lead wire 14a is placed on the terminal portion 13a of the heater layer 13, so that the contact between the heater layer 13 and the lead wire 14a is reduced. A fairly good electrical connection can be made between the two.

In this way, the heater-embedded substrate 11 according to the present invention
In this case, since the degree to which the lead wires 14a and 14c damage the heater layer 13 is very small, the heater layer 13
The electrical connection between the lead wires 14a and 14c can be made quite good, even when the lead wires 14a and 14c are connected to the heater layer 13 and then both the substrate materials 11a and 11b are bonded under heat and pressure. Since the resistance of the heater layer 13 itself can be directly used as the resistance between the lead wires 14a and 14c, the variation in the resistance value of the heater layer 13 measured between the lead wires 14a and 14c can be considerably reduced. This makes it possible to almost ignore variations in the resistance value based on the degree of contact between the heater layer 13 and the lead wires 14a and 14c, and in addition, it becomes possible to significantly improve the current carrying durability.

Further, a conductive substance 15 (15a, 15b) such as platinum paste is dropped into the through holes 12a, 12c of the unfired substrate 11 with a built-in heater according to the present invention, and then fired in accordance with the manufacturing process. For example, as shown in FIGS. 13 and 14,
Since the lead wire 14a (14c) is surrounded by the heater layer 13 and the conductive material 15a (15b), the heater layer 13 and the lead wire 14a (14c) are surrounded by the heater layer 13 and the conductive material 15a (15b).
c) The electrical connection can be made even more reliable. If you do this,
For example, when a stacked oxygen sensor detection section is formed on the heater-embedded substrate 11 and used as an oxygen sensor for measuring the oxygen concentration in the exhaust gas of an automobile internal combustion engine, it is placed under severe conditions of high temperature and high vibration. Even when the heater layer 13 and lead wires 14 are
The electrical connection between the electrodes a and 14c can be made quite reliable, and an oxygen sensor having the heater layer 13 with good heat generation characteristics can be obtained. Note that the same effect can be obtained by dropping the conductive material 15 such as platinum paste into the through hole 12b as needed.

Next, as an application example of the heater-embedded substrate 11 according to the present invention, a case will be shown in which oxygen sensor detection sections using an oxygen ion conductive solid electrolyte are stacked. Therefore, as shown in FIG. 15a, platinum paste was printed on the heater-embedded substrate 11 in the unfired state shown in FIG. 6f and then dried to form the reference side electrode layer 16 in the unfired state. At this time, the reference side electrode layer 1
The film thickness of No. 6 was approximately 20 μm. Subsequently, as shown in FIG. 15b, a solid electrolyte paste using 5 mol % Y ₂ O ₃ -95 mol % ZrO ₂ solid electrolyte powder is printed on the reference side electrode layer 16, and then dried and left untreated. A solid electrolyte layer 17 in a fired state was formed. During printing, the film thickness after drying was set to 20 to 22 μm. Further, as shown in FIG. 15c, a platinum paste was printed on the solid electrolyte layer 17 and then dried to form a measurement side electrode layer 18 in an unfired state. At this time, the thickness of the measurement side electrode layer 18 after drying was about 20 μm. At the same time, the through hole 12
The platinum paste was also poured into the holes 15a, 12b, and 12c to form conductive portions 15a, 15b, and 15c. Regarding the conductive parts 15a and 15c, in order to make a good electrical connection between the heater layer 13 and the lead wires 14a and 14c and to ensure sufficient durability at the connection part, Regarding the conductive parts 15b and 15c,
This is provided to improve the electrical connection between each electrode layer 16, 18 and the lead wires 14b, 14c. In this case, the lead wire 14c serves as an electrically conductive portion for both the heater layer 13 and the electrode layer 18, but of course, four lead wires may be used to separate them.

Next, the unfired laminate (including the substrate 11) produced as described above was heated to 1500°C in the atmosphere.
Co-firing was performed for 2 hours. Next, Figure 15d
As shown in FIG. 2, a porous protective layer 19 was formed by plasma spraying calcium zirconate (CaO-ZrO ₂ ) over the entire surface.

The oxygen sensor 20 manufactured in this way was attached to the exhaust pipe of a propane gas combustor, and the output voltage was measured while changing the ratio of propane gas to air (air permeability) while maintaining the exhaust gas at 400°C. . The results are shown in FIG. Above 400℃
This is the temperature at which almost no output voltage is generated in the case of an oxygen sensor without a heater layer, but in the case of this application example, as shown in Figure 16, the exhaust gas temperature is
Even when the temperature was as low as 400° C., good output voltage characteristics were exhibited, and it was confirmed that heat generation by the heater layer 13 was being performed well.

In addition to the oxygen ion conductive solid electrolyte described above, there are also oxygen sensors using oxide semiconductors such as CoO and TiO ₂ as oxygen sensors, and the present invention can also be used as a substrate for this oxygen sensor. Alternatively, it can also be applied as a substrate for a gas sensor that detects the concentration of gases other than oxygen, such as hydrogen, carbon monoxide, hydrocarbons, methane, and ethane.

In the above embodiment, alumina is used as the material for the substrate 11, but other known ceramic materials or cermet materials such as mullite, spinel, forsterite, steatite, beryllia, titania, etc. can be used.
At this time, by making the thermal conductivity of one substrate material 11a smaller than that of the other substrate material 11b, more of the calorific value of the heater layer 13 is transferred to the other substrate material 11b side, that is, to the gas concentration. It is also possible to transmit the information to the detection unit side.

Furthermore, as a material for the heater layer 13, a single platinum group element such as platinum or an alloy thereof, or an electrical resistance material such as tungsten or molybdenum can be used. Furthermore, lead wires 14a, 14
In addition to platinum, nickel and other known conductive materials can be used as materials for b and 14c.

As described above, according to the present invention, when manufacturing a substrate with a built-in heater layer, a through hole is provided in the other substrate material at a position corresponding to the heater layer terminal portion of one substrate material, and both substrate materials are After positioning the lead wire so that the tip of the lead wire connected to the heater layer can be terminated in the through hole during lamination, the one substrate material is laminated with the other substrate material to create an unfired substrate. Since the firing is then performed in accordance with the manufacturing process of the gas sensor detection section, it is possible to prevent the heater layer from being significantly damaged by the lead wires after laminating both substrate materials, and the above-mentioned state after firing can be prevented. It is possible to ensure a good electrical connection between the heater layer and the lead wires, and the variation in the resistance value of the heater layer measured between the lead wires almost matches the variation in the resistance value of the heater layer itself. This brings about very excellent effects such as being able to significantly reduce the variation in the resistance value and significantly improving the current carrying durability.

[Brief explanation of the drawing]

1a to 1f are explanatory diagrams showing an example of the manufacturing process of a conventional substrate with a built-in heater for a gas sensor; FIG. 2 is an enlarged explanatory diagram of one through-hole portion of the substrate shown in FIG. 1f; Figures 4 and 5 are the second
Figure A-A' line sectional view, B-B' line sectional view and C-
C' line cross-sectional view, FIGS. 6 a to 6 f are explanatory diagrams showing an example of the manufacturing process of a substrate with a built-in heater for a gas sensor according to the present invention, and FIGS. 7 and 8 are diagrams showing the heater of the substrate according to the present invention and the conventional example, respectively. A graph showing the results of measuring the resistance value of the layer, Figure 9 is a graph showing the relationship between the energization-outage cycle and the remaining quantity.
0 is an enlarged explanatory view of one of the through-hole portions of the substrate shown in FIG. 6f, and FIGS. Figure 13 and Figure 14 are respectively Figure 10 D- after the conductive substance has been dropped into the through hole.
D' line sectional view and E-E' line sectional view, Figure 15a
-d are explanatory diagrams of the manufacturing process of the oxygen sensor detection section in one application example of the present invention, and FIG. 16 is a graph showing the relationship between excess air ratio and output voltage of the oxygen sensor of FIG. 15. 11...Substrate, 11a, 11b...Substrate material,
12a, 12b, 12c...Through hole, 13...Heater layer, 13a, 13b...Terminal part, 14a, 1
4b, 14c...Lead wires.

Claims (1)

[Claims] 1. After forming a heater layer on the surface of one of the two unfired substrate materials and connecting a lead wire to the terminal portion of the heater layer, the other substrate material is laminated. In manufacturing a gas sensor substrate incorporating the heater layer, a through hole is provided in the other substrate material at a position corresponding to the terminal portion of the heater layer, and a lead connected to the heater layer is formed when both substrate materials are laminated. After positioning the lead wire so that the tip of the wire can be terminated within the through hole, the one substrate material is laminated with the other substrate material to create an unfired substrate, and the gas sensor is then fired. A method for manufacturing a substrate with a built-in heater. 2. The method of manufacturing a substrate with a built-in heater for a gas sensor according to claim 1, wherein a conductive substance is dropped into the through hole.