JPS6348013B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention reduces displacement due to pressure of the diaphragm,
The present invention relates to a method of manufacturing a pressure sensor that detects changes in capacitance. Its characteristics are:
The sealing glass containing beads for setting the gap between the substrate and the diaphragm is printed and provided with the width of the sealing glass being successively reduced, and then the diaphragm is sealed and fixed. Capacitive pressure sensors, which detect the displacement of a diaphragm due to pressure as a change in capacitance via a counter electrode, are extremely reliable due to their principles and materials, and are therefore suitable for use in automobiles, which are forced to operate in harsh operating environments. It has been widely used as a pressure sensor for measuring air flow rate. The manufacturing method for this type of pressure sensor is to form a thin film electrode on a substrate typically made of alumina, and to provide a corresponding electrode on an insulating diaphragm with extremely uneven thickness and minimal warpage. Fix it with glass. At this time, the capacitance between the electrodes is inversely proportional to the gap between the electrodes, and since the capacitance value varies greatly depending on the gap of one inch, beads of a constant diameter are included in the glass, and a constant load is applied when the glass is sealed. By adding , the gap is prevented from narrowing further. Furthermore, the change in capacitance value when the pressure changes varies depending on the deflection state of the diaphragm used (Young's modulus of the diaphragm, diaphragm thickness, inner diameter of the glass portion), electrode area, and initial gap. The pressure sensor is used as an air flow meter for automobiles to quantitatively measure the pressure drop due to air flow in the manifold and determine the optimal fuel. Therefore, the target pressure is negative pressure (lower than atmospheric pressure). For this reason, there are two methods: one is to measure the relative pressure difference between atmospheric pressure and the manifold pressure, and the other is to measure the absolute pressure (negative pressure) inside the manifold, but the latter is considered to be more common in terms of measurement accuracy. . For this reason, after the pressure sensor is sealed around its periphery with glass, it is vacuum-sealed by some method to keep the pressure inside the gap at a vacuum. Therefore, a pressure sensor intended for absolute pressure measurement has a glass part of
Long-term confidentiality is also an important basic characteristic. As described above, a major problem in the process was how to accurately provide the gap and how to ensure the airtightness of the glass layer. The present invention has been developed based on experimental studies based on the above-mentioned viewpoints, and has significantly improved gap accuracy and airtightness using a glass printing structure. . Example 1 Diameter 33 with reduced surface roughness by polishing
After providing Au thin film electrodes with several diameters on an alumina substrate with a diameter of 3 mm and a thickness of 3 mm, an appropriate amount of high melting point beads with an average particle size of 10, 20, and 30 μm and a relatively small particle size distribution were placed in PbO glass. The impregnated glass paste was printed on a ring-shaped screen. At this time,
The width of the first glass layer is 1mm in order from 5mm to 1mm.
I prepared a smaller version every other time and printed it multiple times.
After this, after pre-baking at 400-700℃, diameter 33
An alumina diaphragm with a polished surface of 0.5 mm and a thickness of 0.5 mm with a thin Au film electrode provided on the polished surface was stacked on a substrate with the electrode surfaces facing each other, and heated at 400 to 700 °C under a constant load. The glass was sealed by passing it through a heat treatment electric furnace with a holding time of 10 minutes to 1 hour. After the sealing hole was sealed in a vacuum, two lead wires were attached, and the capacitance was measured while changing the pressure of the diaphragm. It is easy to determine whether there is a large leak in the glass part at the initial stage by examining the relationship between pressure and capacity, but in order to check for small leaks or the adhesion of the glass, 0 and 750 mmHg.
The change in capacity was also measured when 10 ⁶ pressure cycles were applied. Example 2 A glass paste that does not contain high melting point beads,
It was produced in the same manner as in Example 1, except that it was used for the second and subsequent glass layers, and the characteristics were evaluated in the same manner. A cross-sectional view and a partially cut away perspective view of a capacitive pressure sensor manufactured by such a manufacturing method are shown in the first part.
As shown in Fig. 2. In these figures, 1 is an alumina substrate, 2 is a diaphragm, 3 is an opposing inner surface electrode, 4 is a sealing glass, 5 is a vacuum sealing part, and 6 is a lead wire. FIG. 3 is an example of the glass layer printing structure of the present invention,
(a) is a glass layer printed on the substrate surface with successive narrowings. (b) is a print in which the glass layers are successively narrowed to fit the periphery. C is stacked with the insides aligned.
d indicates that a glass layer is also printed on the diaphragm side, and the same reference numerals as in Fig. 1 have the same contents.
4 and 4' are glass layers. Comparative Example As a typical example of the conventionally printed structure of the glass layer, Example 1 was prepared with the glass width kept constant.
I made it using the same procedure as before. At this time, the mesh paste viscosity of the screen and printing conditions were changed so that the amount of glass and beads were equal to those of the present invention. The table shows a comparison between the conventional method and the production method of the present invention, and the rate of change in capacity, with three types of bead average particle diameters and three types of counter electrode diameters changed accordingly. C _p750 is the capacitance measured when the pressure applied to the diaphragm is 750 mmHg, and is designed to be 50 pF. In addition, the capacitance change rate ΔC is C _p750 after sealing and 0 mm
The rate of change with C _p750 after 10 ⁶ pressure cycles between Hg and 750 mmHg is shown. Also, the number of leaks N is 0mm among the 30 pieces made.
After overpressure cycle test between Hg and 5Kg/ ^cm2 ,
Capacity when the capacitance value of C _p750 is p=0mmHg (C _p=O )
It shows the number of samples that became equal to (in other words, a leak occurred). Further, FIG. 4 shows typical characteristics of the printing structure of the present invention for Example 1 and Example 2.
Number of prints and pressure cycle (0→750mmHg)
This shows the relationship with the rate of change in capacity when ¹⁰⁶ times of addition. Note that the number of times of printing is one based on the conventional method.

[Table] As can be seen from the table, it can be seen that the pressure sensor obtained by the present invention has extremely high reliability. This is thought to be because the printed structure of the glass layer according to the present invention sufficiently reacts with the diaphragm surface during glass sealing to form a strong glass film, and because the number of bubbles in the glass is reduced. It will be done. In conventional glass layers, after the glass is pre-baked, the glass surface is flat, with leveling protrusions remaining on the edges. For this reason, the initial contact surface between the surfaces of the object to be sealed is small, and the air bubbles contained in the glass cannot escape even at high temperatures and remain, forming a weak glass layer. On the other hand, the cross section of the glass layer obtained by the present invention after pre-firing is as follows:
It has a mountain-like shape, which not only makes it easier for air bubbles in the glass to escape during sealing, but also smoothly promotes reactions at the glass interface. Therefore, a strong glass layer with less leakage can be obtained. In addition, this method has the advantage that the minimum required glass amount can be adjusted by varying the glass width. Therefore, in the examples, PbO-based glass was used,
Although sealing was performed at 400 to 700°C, there is no difference in the type of glass or whether the glass is provided on the diaphragm side or the substrate side. Basically, the effects of the present invention can be obtained by providing a mountain-shaped glass cross section.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a capacitive pressure sensor made according to the present invention, FIG. 2 is a partially cut away perspective view of the pressure sensor of FIG. 1, and FIG. FIG. 4, a diagram illustrating an example of a layered printing structure, is a diagram illustrating the characteristics of a sensor according to the invention. DESCRIPTION OF SYMBOLS 1... Alumina substrate, 2... Diaphragm, 3... Opposing inner surface electrode, 4, 4'... Glass layer, 5... Vacuum sealing part, 6... Lead wire.

Claims (1)

[Scope of Claims] 1. A gap between a diaphragm sealed by a glass layer containing a small amount of beads at the periphery of the alumina sintered substrate and the substrate changes depending on the pressure applied to the diaphragm, For this purpose, in a method for manufacturing a capacitive pressure sensor that utilizes the change in capacitance between inner facing electrodes provided in advance on the gap side surfaces of both, the width of the sealing glass containing beads is A method for manufacturing a capacitive pressure sensor, which is characterized by printing a pattern smaller than the size multiple times and then sealing the sensor. 2. The method for manufacturing a capacitive pressure sensor according to claim 1, wherein a glass layer containing no beads is printed from the second time onward.