JPS6055672A - Structure of pressure-electric converter - Google Patents

Abstract

PURPOSE:To contrive the simplification of the mounting of a pressure sensor chip by a method wherein a pedestal and said chip are sealed hermetically by application of silicon rubber on the pedestal formed by hardening silicon rubber. CONSTITUTION:The pedestal 8 formed by hardening of silicon rubber is hermetically fixed to a hermetic terminal 4 with silicon rubber, organic adhesive, etc. After the silicon rubber 9 is uniformly applied on the pedestal 8, the pressure sensor chip 1 is placed on the rubber 9. The chip 1 and the pedestal 8 are hermetically fixed with the rubber 9 and then sealed. The use of silicon rubber as a pedestal having a moderate thickness enables the absorption of stresses except the pressure displacement to the chip 1 such as the thermal strain from the hermetic terminal, and the mechanical strain of the terminal itself due to the installation of this converter, outer forces, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a pressure-electric transducer that converts pressure into an electrical signal by utilizing the piezoresistance effect of a semiconductor diffused resistor.

In recent years, with the development of IC manufacturing technology, pressure-electric transducers have been produced in which a semiconductor diffused resistor is formed on the surface of a single crystal silicon chip and the semiconductor diffused resistor is used as a strain gauge.

The pressure-electric transducer utilizes the piezoresistance effect in which electrical resistance changes due to the stress of an external force applied to a conductor or semiconductor, by configuring the strain gauge into a bridge type circuit.

It converts pressure changes into electrical resistance changes, which are then captured as voltage changes in a bridge-type circuit, and its performance is superior to that of conventional pressure gauges or pressure-electric transducers.
Because of its excellent properties, it has been developed, manufactured, and used primarily for industrial measurement.

Recently, it has become possible to mass produce products by making full use of IC manufacturing technology, including applications for automobiles.

Demand is also increasing for consumer use.

FIG. 1 is a sectional view showing the structure of a conventional piezoresistive pressure electric transducer developed in response to one or more of the following needs.

1 is a diaphragm-type semiconductor pressure sensor chip that converts pressure into an electrical signal using the piezoresistance effect of semiconductor diffused resistors; 2 is a pedestal; for example, the pressure sensor chip 1 and pedestal 2 are made of #7740 borosilicate glass; is hermetically sealed. 4 is an airtight terminal body, 5 is the pressure sensor chip 1
The stem 5 serves as a power supply terminal and an output terminal, and the stem 5 is hermetically fixed to the airtight terminal body 4 using a sealing glass 6.

The airtight terminal body 4 to which the stem 5 is fixed as described above and the pedestal 2 to which the pressure sensor chip 1 is fixed are airtightly fixed.
Further, the pressure sensor chip 1 and the stem 5 are electrically connected by wire bonding.

6 is a cap with a pressure introduction hole, and the pressure sensor chip 1
After the stem 5 and the stem 5 are electrically connected by wire bonding, they are hermetically fixed to the airtight terminal body 4, thereby forming a relative pressure (differential pressure) type pressure-electric transducer 10.

In the manufacturing process of the pressure-electric transducer 10 configured as described above, the most important process is to prepare the pressure sensor chip 1 and the pedestal 2.
The next important process is fixing the base 2 and the airtight terminal body 4.
It is a fixation with.

That is, the pressure sensor chip 1 is made of silicon.

Utilizing the anisotropy of the piezoresistance effect in each crystal axis direction of a single crystal with a diamond key-vic structure such as germanium, a very large value of gauge factor (more than 100 compared to 2 for a metal strain gauge) can be obtained. Since the strain gauge is formed on the surface of the chip, it is very sensitive to strain, and the influence of stress other than pressure displacement 1. For example, mechanical strain when fixing the pressure sensor chip 1, Alternatively, it is necessary to eliminate thermal distortion caused by the difference in coefficient of thermal expansion between the pressure sensor chip 1 and the pedestal 2.

Therefore, as mentioned above, the material for the pedestal 2 has a small difference in thermal expansion coefficient compared to the pressure sensor chip 1: #77
40 borosilicate glass, silicon single crystal which is the same material as the pressure sensor chip 1, etc. are selected.

Moreover, the pressure sensor chip 1 is connected to the airtight terminal body 4 via the pedestal 2.
The reason for this is to remove the influence of thermal strain from the airtight terminal body 4 or distortion of the airtight terminal body 4 itself due to mounting of the pressure-electric transducer 10 or external force. The minimum necessary thickness has been determined using the finite element method.

By carefully selecting the material and thickness of the pedestal 2 as described above, it is possible to remove a considerable amount of unnecessary strain. Alternatively, if the method of fixing the pedestal 2 and the airtight terminal body 4 is incorrect, no matter how good the pedestal 2 is, everything will be wasted. For this reason, various fixing methods have been studied, and a fixing method that meets the required accuracy and cost has been adopted. Here are some examples of fixing methods.

■ Fixing using electrostatic force: A method that can be used to airtightly seal metal and glass. When the metal and glass are heated and a DC voltage is applied between the metal and glass, static electricity is generated at the interface between the metal and glass. A force is generated, and the electrostatic force hermetically seals the metal and glass.

■ Method of fixing with low melting point glass ■　Method of fixing with organic adhesive etc.

(2) The method of airtight sealing using electrostatic force or energy is because there are no inclusions such as adhesives between the metal and glass.

Although this is an ideal fixing method, it is extremely difficult because the fixing technology itself is not yet common and is not completely understood in conjunction with the theoretical aspects.

The method of fixing with low melting point glass (2) is a method often used in the pressure-electric converter 10 as shown in Fig. The difference in thermal expansion coefficient with the sensor chip 1 cannot be eliminated, and the problem of thermal distortion inevitably remains. In addition, low melting point glass is
The binder must be disassembled through a process called temporary sintering, and it takes a very long time for it to solidify.

The method of fixing with an organic adhesive can be easily and quickly fixed, but due to the low rigidity of the organic adhesive, stable properties cannot be obtained, and the reliability of the adhesive itself due to changes over time and airtightness etc. The problem remains.

The pressure sensor chip 1 and the pedestal 2 can be sealed in various ways, such as by hermetically sealing them with solder. Alternatively, the pedestal 2 and the airtight terminal body 4 are fixed together.

Each has its own advantages and disadvantages, and the current state of the art is that pressure-electric transducer manufacturers have accumulated know-how through long-term independent research and development to produce products.

Regarding the processing of the pedestal 2, when configuring a relative pressure type pressure electric transducer, it is necessary to drill holes in the pedestal 2, and if the thickness of the pedestal 2 needs to be a certain degree as described above, then Processing takes time, resulting in an increase in the price of each part.

As described above, in the conventional pressure-electric transducer 10 configured using the pedestal 2 made of borosilicate glass, silicon single crystal, etc., which has a small difference in thermal expansion coefficient compared to the pressure sensor chip 1, the pressure sensor chip 1 Since it is necessary to accumulate sufficient technical know-how and knowledge regarding fixing the chip 1 and the pedestal 2, or the pedestal 2 and the airtight terminal body 4, it is not only difficult to manufacture it, but also the number of manufacturers is limited. This is pedestal 2
This caused the unit price of the product to increase due to processing costs.

The present invention obviates one or more such drawbacks.

A pedestal made of hardened silicone rubber is prepared in advance, and silicone rubber is further applied onto the pedestal to airtightly seal the pedestal and the pressure sensor chip. This is due to the simplification of mounting the sensor chip.

A detailed explanation will be given below based on the drawings.

FIG. 2 is a cross-sectional view of a pressure-electric transducer showing one embodiment of the present invention, and FIG. 3 is a cross-sectional view of a pressure-electric converter showing another embodiment of the present invention. A pressure-electric transducer of relative pressure (differential pressure) type, and FIG. 3 shows a pressure-electric transducer of absolute pressure type. FIG. 4 is a perspective view of the main parts of the pressure-electric transducer shown for explaining the method of manufacturing the pressure-electric transducer of FIG. 2. FIG.

The same numbers as in FIG. 1 indicate the same members.

As shown in the example of FIG. 4(A), 8 is a pedestal formed by curing silicone rubber using a mold or the like to ensure a constant thickness. It is hermetically fixed to the airtight terminal body 4 with adhesive or the like. This state is shown in FIG. 4(B), but the pedestal 8 may of course be formed by molding and curing silicone rubber directly on the airtight terminal body 4. In Fig. 4 (CB), 16 is a car in which silicone rubber is injected, and 9 is silicone rubber that is uniformly applied on the pedestal 8. Fig. 4 (B) shows the process. In the meaning shown, silicone rubber 9 is cartridge 1.
I have shown the state where it is being squeezed out from 6.

After the silicone rubber 9 is uniformly applied onto the base 8 in this way, the pressure sensor chip 1 is placed on the silicone rubber 9 in a first step before the silicone rubber 9 is cured. As a result, the pressure sensor chip 1 and the pedestal 8 are hermetically fixed and sealed by the silicone rubber 9.

Also, in Fig. 3, 7 is soldered to the airtight terminal body 14.

A pressure introduction pipe is airtightly fixed using adhesive bonding or the like, 16 is a sealing tube, and 15 is a stem.

What is constructed through the above steps is the relative pressure type pressure electric transducer 11 shown in FIG. 2, and the absolute pressure type pressure electric converter 12 shown in FIG. 3. The absolute pressure type pressure electric transducer 12 shown in FIG. The space surrounded by the sensor chip 1 is evacuated, and the reference pressure is absolute pressure.

FIG. 5 is a sectional view and a perspective view of essential parts of a pressure-electric transducer showing still another embodiment of the present invention.

24 is an airtight terminal body made of zircon (ZrO2.5in2) ceramics, and its linear expansion coefficient is 40 to 400.
The temperature is kept below 3.7 x 10-'/'C, and electrodes 25 are formed on the surface by printing technology. Reference numeral 28 denotes a pedestal formed by applying silicone rubber directly onto the airtight terminal body 24 to a certain thickness using a printing technique or the like, and curing it in advance.
8 is hermetically fixed to the airtight terminal body 24.

21 is a diaphragm type semiconductor pressure sensor chip;
After the silicone rubber 9 is uniformly applied onto the base 28 as in FIG. 4(B), the pressure sensor chip 21 is placed on the silicone rubber 9 before the silicone rubber 9 hardens.

As a result, the pressure sensor chip 21 and the pedestal 28 are hermetically fixed and sealed by the silicone rubber 9. After this, the pressure sensor chip 21 and the electrode 25 are electrically connected by wire bonding.

27 is a pressure introduction pipe, and 23 is a cap.

The pressure introduction pipe 27 is airtightly fixed to the cap 23 by brazing, adhesive, or the like.

Airtight terminal body 24 and camp 26 with completed wire bonding
In this state, the pressure-electric transducer 2o is configured by being hermetically fixed with low melting point glass, organic adhesive, or the like.

The silicone rubber used in the present invention is, for example, a material with excellent heat and cold resistance that maintains rubber elasticity over a wide temperature range of -50°C to +250°C, and has appropriate elongation.

It also has excellent strain recovery properties and has the property of absorbing vibrations and shocks.

Therefore, as shown in the embodiments of the present invention, if silicone rubber is used as a pedestal with an appropriate thickness, thermal strain from the airtight terminal body or mounting of a pressure-electric transducer can be prevented.
It becomes possible to absorb stress other than pressure displacement on the pressure control knob 1 or 21, such as mechanical strain of the airtight terminal body itself due to external force, etc., with the pedestal made of silicone rubber.

Of course, as the airtight terminal body, the pressure sensor chip 1 or 210, such as zircon-based ceramics with a linear expansion coefficient of 3.7 x 10-'/'c or less, as shown in the embodiment shown in FIG.
It is clear that if a material with a small difference in coefficient of linear expansion is selected, excess thermal strain can be more effectively removed.

Similarly, silicone rubber 9 is applied to the pedestal in order to fix the pedestal and the pressure sensor chip.

Naturally, since it has the properties described above, the influence of thermal strain caused by the difference in linear expansion coefficient between the pressure sensor chip and the silicone rubber is eliminated.

Furthermore, since silicone rubber can be printed using conventional printing techniques, pedestals of the same quality can be easily formed in large quantities by printing.

In addition, since there is no need to use a pedestal made of #7740 borosilicate glass, silicon single crystal, etc., the material and processing costs for one pedestal are eliminated, making it possible to substantially reduce costs and make the product thinner. can.

As described above, according to the structure of the pressure-electric transducer of the present invention,
Even if you do not have sufficient technical know-how regarding fixing the pressure sensor chip and the pedestal, or the pedestal and the airtight terminal body,
Since it can be produced easily and in large quantities, there are no restrictions on manufacturers, and it has the effect of being able to supply pressure-electric transducers at low manufacturing costs.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the structure of a conventional pressure-electric transducer, Fig. 2 is a cross-sectional view of a pressure-electric transducer showing one embodiment of the present invention, and Fig. 3 is a cross-sectional view showing another embodiment of the present invention. FIG. 4 is a perspective view of the main parts of the pressure-electric transducer shown in FIG. 2, and FIG. 5 is a cross-sectional view of the pressure-electric converter showing still another embodiment of the present invention. FIG. 3 is a perspective view of main parts. 1.21...Diaphragm type semiconductor pressure sensor chip. 8.28...Pedestal. 9...Silicone rubber. 11.12.20... Pressure electric transducer. Figure 1 Figure 2 Figure 3 Figure 4 (A) Figure 5 (A) So (B)

Claims (1)

[Claims] A pressure-electric transducer having a diaphragm-type semiconductor pressure sensor chip that converts pressure into an electrical signal using the piezoresistance effect of a semiconductor diffused resistor, and a pedestal for protecting the pressure sensor chip from distortion other than pressure displacement, 1. A structure of a pressure-electric transducer, characterized in that a pedestal made of hardened silicone rubber is provided, and the pressure sensor chip and the pedestal are hermetically sealed with a silicone rubber adhesive.