JPH0566537B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a strain sensor that receives the pressure of a liquid or the like with a diaphragm and converts the strain into an electrical signal using a strain-sensitive resistor set on the diaphragm.

BACKGROUND ART Conventionally, strain sensors have been widely used as pressure sensors for measuring the pressure of liquids, etc., which receive pressure with a diaphragm and extract strain as a change in electrical resistance using a strain-sensitive resistor formed on the diaphragm. A metal strain gauge or a semiconductor strain gauge is used as the strain-sensitive resistor, and this is adhered and fixed onto a diaphragm with an adhesive.

FIG. 6 shows an example of a conventional strain sensor, and is a sectional view of a main part in which a metal strain gauge is stuck on a diaphragm. In FIG. 6, strain gauge 1 is fixed onto diaphragm 2 with adhesive 3. In FIG. The diaphragm 2 is distorted by the pressure of the liquid introduced from the liquid inlet 7, and the distortion generated in the diaphragm 2 is transmitted to the strain-sensitive resistor 4 via the adhesive layer 3 and the resin substrate 5, and the strain-sensitive resistor 4, distortion occurs in accordance with the pressure of the liquid. This strain is detected by the lead wire 6 as a change in electrical resistance, and the pressure of the liquid can be determined. However, in sensors with such a structure, the characteristics deteriorate due to deterioration during use and bonding, and it takes considerable skill to evenly attach the metal strain gauge or semiconductor strain gauge to the diaphragm with adhesive. There were inherent problems such as the need for

In order to solve the above-mentioned problems, the applicant previously proposed a new strain sensor (Japanese Patent Laid-Open No. 58-232497).
To summarize, there is a strain-sensitive structural member (diaphragm), a plurality of strain-sensitive resistors formed directly on the diaphragm by vapor deposition and whose electrical resistance changes according to strain, and a strain-sensitive resistor formed on both ends of the strain-sensitive resistor. This is a strain sensor that extracts the strain generated in the diaphragm as an electrical signal. That is, it attempts to solve the above-mentioned problems by eliminating the adhesive that has conventionally caused various problems and forming a strain-sensitive resistor directly on the diaphragm.

FIG. 4 shows a sectional view of the main parts of the above-mentioned strain sensor. In Figure 4, diaphragm 2
An electrically insulating layer 9 is formed on the upper surface of the electrically insulating layer 9, and a strain-sensitive resistor 4 is provided on the electrically insulating layer 9.
Electrode portions 8 are formed at both ends of the strain-sensitive resistor 4 to extract changes in electrical resistance occurring in the strain-sensitive resistor 4. Specifically, the electrode portion 8 is formed from an electrode 8a on a strain-sensitive resistor and a conductor circuit portion 8b. 6 is a lead wire for taking out an electric signal from the conductive circuit portion 8b. Such a structure is usually used when the sensor is constructed into a bridge circuit as shown in FIG. In Fig _. 5 _, R ₁ , R ₂ , R _{3 ,} and _{R 4} are _{strain -} sensitive resistors _;
4b shows the resistance of the conductor circuit between the electrodes. Further, E indicates the input power supply section of the bridge, and V indicates the bridge output terminal section. Electrodes and conductor circuits of electrodes are usually formed by thin film forming means such as vapor deposition.

The lead wire 6 is connected to the electrode section 8 (normal conductor circuit section 8b)
However, since the electrode part is a thin film, it is usually difficult to directly join a thick lead wire to the electrode part, and it is difficult to connect the lead wire to the electrode part directly by wire bonding or soldering with a thin wire. There are problems such as breakage of lead wires, the reliability of the bonding is low, and the workability is also poor. Furthermore, the resistances γ _1a , γ _1b , γ _2a ,
There are variations in γ _2b , γ _3a , γ _3b , γ _4a , and γ _4b , which causes problems such as creating a cause of resistance value variation when bridge-forming a strain-sensitive resistor. When the other strain-sensitive resistors are made of a semiconductor such as silicon, the temperature coefficient of resistance is generally large, so it is desired to reduce the temperature difference between the respective strain-sensitive resistors.

Purpose of the Invention Therefore, the purpose of the present invention is to provide a thick solder layer directly on the electrode part to prevent lead wire breakage, improve bonding reliability, and improve workability.
Covering almost all surfaces of the conductor circuit connecting the electrode parts to reduce variations in resistance of the conductor parts, and furthermore, when the strain-sensitive resistor is a semiconductor such as silicon,
Since the temperature coefficient of resistance is generally large, the objective is to reduce the temperature difference between each strain-sensitive resistor.

Structure of the Invention The present invention provides a strain sensor in which a strain-sensitive resistor is bridge-formed on a diaphragm having an electrically insulating layer on at least a surface layer, and in which electrodes at both ends of the strain-sensitive resistor formed in a thin film shape and a conductor between the electrodes are provided. The present invention provides a strain sensor characterized in that a thick solder layer is formed on a circuit, and more preferably, the strain-sensitive resistor is protected with an insulating layer such as a heat-resistant resin.

Embodiment FIGS. 1 and 2 show an embodiment of the strain sensor of the present invention, with FIG. 1 being a sectional view and FIG. 2 showing the main part of the upper part of the diaphragm.

In FIGS. 1 and 2, 2 is a metal diaphragm made of stainless steel, 9 is an electrical insulating layer made of resin, ceramics, glass, etc., and 4 is a thin film-like strain-sensitive film formed of silicon semiconductor or the like on the insulating layer. As shown in Figure 2, four resistors are formed with a thickness of about 1 μm on an electrical insulating layer 9, and they are connected by a conductive circuit to form a bridge circuit (the two strain-sensitive resistors in the center). is the tensile force, and the two strain-sensitive resistors at the ends are the compressive force). Further, 8 is a thin film electrode portion (thickness approximately 0.5 μm) made of a well-known conductive material such as nickel or copper, which is formed on both ends of the strain-sensitive resistor.
Reference numeral 8a indicates an electrode on the strain-sensitive resistor, and 8b indicates a conductive circuit portion between the strain-sensitive resistors. 10 is a thick solder layer (about 0.4 mm thick) formed on the electrode 8a and the interelectrode conductor circuit section 8b, covering each electrode and the entire conductor circuit section in the bridge circuit. The diaphragm 2 is strained by the pressure from the liquid inlet 7, and each strain-sensitive resistor on the diaphragm 2 causes a change in electrical resistance due to the strain, and this change is taken out to the outside through the lead wire 6 as a bridge output voltage change. (The applied power supply section is omitted from the figure).

The solder layer 10 is obtained by immersing the upper surface of the diaphragm in a solder melt after forming the strain-sensitive resistor 4, the electrode portion 8, and the insulating layer 11, or by incinerating the diaphragm after screen printing with solder paste. The insulating layer 11 is made of a heat-resistant resin such as polyesteramide, and prevents surface deterioration of the strain-sensitive resistor (short-circuiting of the resistor if the strain-sensitive body is made of metal) when forming the solder layer, and also protects against external damage. It functions as a moisture intrusion prevention layer. Note that the insulating layer 11 is between mutual electrodes,
Alternatively, if the width between mutually conductive circuit parts is narrow and there is a risk of a short circuit due to solder, it may be possible to cover a certain range in advance.

In addition to silicon, semiconductors such as Ge, C (diamond), Ga, As, and GaP, as well as Ni, can be used as strain-sensitive resistors.
-Metals such as Cu and Ni-Cr can be used.

Although the diaphragm must have an electrically insulating layer on its surface as shown in FIG. 1, it is also possible to construct the entire diaphragm from an insulating or semi-insulating material. FIG. 3 shows another embodiment of the invention. Figure 3 shows a bridge circuit similar to Figure 2, but the area of the conductor circuit between the electrodes is increased to increase the heat capacity of the solder layer and improve heat conduction. This makes the temperature more uniform.

Effects of the Invention As described above, the present invention provides a strain sensor in which a strain-sensitive resistor is bridge-formed on a diaphragm having an electrically insulating layer on at least the surface layer, and a strain-sensitive resistor on an electrode at both ends of the strain-sensitive resistor and a conductor circuit between the electrodes. This strain sensor has a thick solder layer formed on the thin film electrode and conductor circuit, making the lead wire connection work extremely quick and easy, which was difficult to apply in the past. It is now possible to directly solder connect even relatively thick lead wires, which eliminates problems such as soldering of thin wire leads and breakage of lead wires that occur during wire bonding. In addition, the resistance value of the conductor circuit part varied from several ohms to several + ohms in the configuration shown in FIG. Variations can be eliminated. Furthermore, we have increased the heat capacity of the electrodes and conductor circuits to improve heat conduction, so the temperature difference between the strain-sensitive resistors can be minimized even during thermal transient states such as rapid heating and cooling, resulting in improved thermal balance. We provide a sensor with further improved performance and stable performance. Furthermore, the insulating layer made of heat-resistant resin or the like on the strain-sensitive resistor prevents surface deterioration of the strain-sensitive resistor during formation of the solder layer.

As described above, the strain sensor according to the present invention has various excellent effects and is of great industrial value.

[Brief explanation of the drawing]

1 and 2 are embodiments of the strain sensor of the present invention, and FIG. 1 is a sectional view of the main part. FIG. 2 shows a plan view of the main part of the upper part of the diaphragm. FIG. 3 shows another embodiment of the strain sensor of the present invention, and shows a plan view of the main part of the upper part of the diaphragm. FIG. 4 is a sectional view of the main parts of the strain sensor of the earlier application. FIG. 5 shows an electrical circuit diagram of the bridge circuit of FIG. FIG. 6 shows a sectional view of the main parts of an example of a conventional strain sensor. 2...Diaphragm, 4...Strain-sensitive resistor, 6...
... Lead wire, 8 ... Thin film electrode portion, 10 ... Solder layer, 11 ... Insulating layer.

Claims (1)

[Scope of Claims] 1. A strain sensor in which a strain-sensitive resistor is bridge-formed on a diaphragm having an electrically insulating layer on at least a surface layer, which includes electrodes at both ends of the strain-sensitive resistor and a first conductor circuit of the electrode. A strain sensor characterized in that the layer is made of a thin film-like conductive metal material such as nickel or copper, and further thereon is formed a second conductive layer having a solder layer on substantially all surfaces of the first layer. 2. The strain sensor according to claim 1, wherein the strain-sensitive resistor is protected by an insulating layer such as a heat-resistant resin.