JPH0580070A - Strain gauge element and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a protective film which enables complete prevention of the infiltration of water. CONSTITUTION:A strain gauge element has a strain gauge section which is bonded on a beam 2 sensing a distortion on a beam plate 1 in an acceleration sensor device to play a role of an electric resistance. A silicon dioxide thin film 8 is provided on the surface of a gauge and a resin coating film 9 comprising a mixture of cyclic rubber and a photosensitive crosslinking agent on the surface of the silicon dioxide thin film 8. With the silicon dioxide thin film on the surface of the gauge and the resin coating film mainly composed of the photosensitive cyclic rubber on the surface thereof, there is no possibility of a pinhole, cracking and the like in a protective film, which eliminates fear of infiltration of water achieving excellent resistance to moisture. In this production method, the minimum thin protective film is formed by a dip coating or the like least affecting dynamic distortion characteristics of the strain gauge element. A cyclic rubber resist used as photosensitive coating resin can be obtained inexpensively with ease with a high quality thereby enabling the production of a high quality strain gauge element at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain gauge element used in various sensors such as a pressure sensor and an acceleration sensor, and a manufacturing method thereof.

[0002]

2. Description of the Related Art As the prior art relating to the present invention, Japanese Patent Laid-Open Publication No. 62-222137 and Japanese Utility Model Laid-Open No. 2-146372
The one shown in Japanese Patent Publication is known. In the former, Ni is sputtered on a diaphragm made of glass.
-Si-B amorphous alloy thin film is adhered to the surface of the pressure sensor in order to improve heat resistance, and a protective film mainly composed of silicon dioxide having excellent adhesiveness is adhered to the surface by sputtering. It is a strain gauge element. On the other hand, the latter is
As shown in FIG. 3, an insulating film 11 is attached to the surface of a metal base 10 by sputtering, and a conductive pattern 12 is formed on the surface of the base 10 to improve heat resistance. This is a strain gauge element of an acceleration sensor in which a silicon dioxide thin film 14 containing silicon dioxide as a main component, which has excellent adhesiveness, is attached by sputtering.

[0003]

However, the protective film 16 containing silicon dioxide as a main component, which is used for the above-mentioned two types of strain gauge elements and is formed by a vacuum film forming method such as sputtering, is Upon contact, as shown in FIG. 4, there are pinholes due to the breakage of the protective film and cracks due to insufficient adhesion to the stepped portion of the protective film 16, so that water penetrates and corrodes. It will be easier. further,
Gauge film 1 such as Ni-Si-B amorphous alloy thin film in the pressure sensor device or conductive pattern 12 in the acceleration sensor device 1
In No. 5, the voltage is applied in the use state, so that the electrolytic corrosion due to the inflow of current and the intrusion of water is very likely to occur.

Therefore, the present invention has as its technical problem the formation of a protective film that completely prevents the intrusion of moisture.

[0005]

[Means for Solving the Problems] The technical means for solving the above-mentioned technical problems includes a strain acting as an electric resistance, which is adhered to a beam for sensing a strain on a beam plate in an acceleration sensor device. In a strain gauge element having a gauge portion, a strain gauge element having a silicon dioxide thin film on the gauge surface and a resin coating film made of a mixture of a cyclized rubber and a photosensitive crosslinking agent on the surface of the silicon dioxide thin film and an acceleration A conductive film is attached on the surface of the beam that detects the strain on the beam plate in the sensor device by a vacuum film forming method, and a photosensitive resist is used to dissolve and remove unnecessary portions not covered with the resist. Then, the conductive film is processed into a predetermined shape to form a conductive pattern, the electrode portion is masked, and then the oxide film is formed on the surface of the strain gauge portion and the wiring portion by a vacuum film forming method. Depositing a Lee-containing film, coated dried photosensitive cyclized rubber resist on the surface of the silicon dioxide thin film and the electrode portions, by exposing,
The resist film applied on the surface of the silicon dioxide thin film is cured as a pattern, and then developed and rinsed to expose only the electrode portion, and finally baked to form a film on the surface of the silicon dioxide thin film. It is a manufacturing method of a strain gauge element which forms a resin coating film.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged plan view of the beam plate in the acceleration sensor device of the present invention, and FIG. 2 is a sectional view taken along line XX of the beam plate of FIG.

As in the conventional case, as shown in FIG. 1, the beam plate 1 includes a beam 2 for sensing strain, strain gauge portions 3a to 3h bonded to the beam 2, wiring portions 4a, and an electrode portion to which a voltage is applied. 4b. Since the beam 2 is a metal having a thickness of about 0.1 mm, the beam 2 has a structure that is easily affected by an external force, and the strain gauge portions 3a to 3h serve as a gauge resistance.

The present invention has a mechanism in which the strain gauge portions 3a to 3h in contact with the beam 2 sense the strain generated by the inertial force applied by the pendulum, act as gauge resistance, and detect the acceleration by changing the electrical resistance. I'm running.

As shown in FIG. 2, the strain gauge element of the present invention comprises a metal base 5, an insulating film 6, and a conductive pattern 7.
And a silicon dioxide thin film 8 serving as a protective film and a resin coating film 9 serving as a protective film. That is, the present invention is characterized in that the two-layer protective film is formed.

A method of manufacturing a beam plate will be described with reference to FIGS.
The explanation will be as follows.

An insulating film 6 was attached to the cleaned surface of the base 5 by a vacuum film forming method such as sputtering. Next, a conductive film is attached to the surface of the insulating film 6 by a vacuum film forming method, and a photosensitive resist (solvent of resin material) is used to etch and remove unnecessary portions not covered with the resist (photo). The conductive film was processed into a desired shape by etching to form the conductive pattern 7. Then, in order to prevent the thin film from adhering to the surface of the electrode portion 4b,
After protecting b with a resist film, strain gauge parts 3a to 3h
Then, a silicon dioxide thin film 8 of about 1 μm was deposited on the surface of the wiring portion 4a by the vacuum film forming method. After that, a photosensitive cyclized rubber resist (trade name “OM” manufactured by Tokyo Ohka Kogyo Co., Ltd.
R-83 ") by dipping in silicon dioxide thin film 8
The surface of the electrode portion 4b was coated with a photosensitive cyclized rubber resist to a thickness of about 2 μm and dried (prebaked) at 100 ° C. for 25 minutes in order to enhance the adhesion to the base.

By the way, the photosensitive cyclized rubber resist is
It is a mixture of a cyclized rubber and a photosensitive cross-linking agent as shown in FIGS. 7 and 8, and has an advantage that it has strong adhesiveness and can be easily patterned by general photo-etching. Here, the expansion and contraction of the protective film due to the temperature change may distort the beam 2 or change the dynamic strain characteristics of the beam 2, so that the protective film formed on the gauge surface needs to be thinned to the minimum. Therefore, the dip coating method of immersing in the photosensitive cyclized rubber resist was used so as not to affect the beam 2.
Also, here, when the coating film is spread by the dip coating or the like, the coating film spreads over the entire surface of the sample, but since the coating film of the electrode portion 4b needs to be removed, a photosensitive cyclized rubber resist is used. I was there.

The resist film coated on the surface of the silicon dioxide thin film 8 is hardened in a pattern by exposing it to light through a mask (exposure), and then developed using an OMR developing solution, and then using an OMR rinse solution. By rinsing, the resist film applied on the surface of the electrode portion 4b is completely removed, only the electrode portion 4b is exposed, and finally, baking is performed at 150 ° C. for 30 minutes (post-baking) to leave no residue. The solvent component contained therein is evaporated, a crosslinking reaction further occurs, the adhesion to the base is strengthened, and the resin coating film 10 is formed on the surface of the silicon dioxide thin film 8.

The strain gauge element and the silicon dioxide thin film 14 according to the present embodiment having the two-layer protective film purified as described above.
FIG. 5 shows the relationship between the leaving time and the rate of change in gauge resistance when a high temperature / high humidity test was performed under conditions of 80 ° C. and 95% RH in a conventional strain gauge element having only a protective film. During the high-temperature and high-humidity test, a predetermined voltage was applied to the gauge to energize it. As can be seen from FIG. 5, in the conventional example, the gauge resistance started to change about 20 hours after the start of the test and then changed remarkably, and when the gauge part was observed, cracks, pinholes, etc. existed, It can be said that moisture intrudes from there and only corrodes, so that it is not excellent in moisture resistance. On the other hand, in this example, the gauge resistance value is almost the same as that at the start of the test even after 200 hours, so it can be said that the moisture resistance is excellent.

Further, in the strain gauge element according to the present embodiment having a two-layer protective film and the strain gauge element according to the conventional example having only the silicon dioxide thin film 14 as a protective film, 120 ° C.
FIG. 6 shows the relationship between the leaving time and the rate of change in gauge resistance when a high temperature test was performed for 1000 hours. During the high temperature test, a predetermined voltage was applied to the gauge to make it conductive. As shown in FIG. 6, in this embodiment, the gauge resistance is 10 as in the conventional example.
It can be said that it is also excellent in heat resistance because it is almost the same as when the test was started even after the lapse of 00 hours.

As the photosensitive coating resin,
Polyimide can also be used, but in this case, since the firing temperature in the final step must be set to 300 to 400 ° C., the characteristics of the strain gauge may change, and cracks easily form in the coating film and moisture invades. Polyimide is very expensive. Therefore, in this example, an inexpensive photosensitive cyclized rubber resist was used as the photosensitive coating resin.

[0018]

The present invention has the following effects.

In the present invention, since the silicon dioxide thin film is provided on the gauge surface and the resin coating film containing photosensitive cyclized rubber as a main component is provided on the surface of the silicon dioxide thin film, pinholes, cracks, etc. are formed in the protective film. There is no risk of water getting in, there is no risk of water entering, and it has excellent moisture resistance. Further, in the manufacturing method according to the present invention, since the minimum protective film is formed by dip coating or the like, it does not affect the dynamic strain characteristics of the strain gauge element. Since the cyclized rubber resist used as the photosensitive coating resin is of high quality and can be easily obtained at low cost, a high-quality strain gauge element can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is an enlarged plan view of a beam plate in an acceleration sensor device of the present invention.

2 is a cross-sectional view taken along line XX of the beam plate of FIG.

FIG. 3 is a sectional view of a beam plate in a conventional acceleration sensor device.

FIG. 4 is an explanatory diagram of problems in the conventional technique.

FIG. 5 shows a strain gauge element according to this embodiment and a strain gauge element according to a conventional example under the conditions of 80 ° C. and 95% RH.
It is a figure which shows the relationship between the leaving time and the gauge resistance change rate at the time of performing a high temperature and high humidity test.

FIG. 6 is a diagram showing a relationship between a leaving time and a rate of change in gauge resistance when a high temperature test is performed at 120 ° C. for 1000 hours in the strain gauge element according to the present example and the strain gauge element according to the conventional example.

FIG. 7 is an explanatory diagram showing the chemical structure of cyclized rubber.

FIG. 8 is an explanatory diagram showing the chemical structure of bisdiazide, which is a photosensitive crosslinking agent.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Beam plate 2 Beams 3a-3h Strain gauge part 4a Wiring part 4b Electrode part 5,10 Base part 6,11 Insulating film 7,12 Conductive pattern 8,13 Silicon dioxide thin film 9 Resin coating film 14 Insulating substrate 15 Gauge film 16 Protection film

Claims (2)

[Claims] 1. A strain gauge element having a strain gauge portion bonded to a strain sensing beam on a beam plate in an acceleration sensor device and serving as an electric resistance, wherein a silicon dioxide thin film and the silicon dioxide are provided on the gauge surface. A strain gauge element characterized in that a resin coating film made of a mixture of cyclized rubber and a photosensitive cross-linking agent is provided on the surface of a thin film. 2. A conductive film is attached to the surface of a beam that detects strain on a beam plate in an acceleration sensor device by a vacuum film forming method, and a photosensitive resist is used, which is not covered with the resist. The conductive film is processed into a predetermined shape by etching away a portion, a conductive pattern is formed, the electrode portion is masked, and then a vacuum film forming method is performed on the surface of the strain gauge portion and the wiring portion. By depositing a silicon dioxide thin film on the surface of the silicon dioxide thin film and the electrode portion, coating a photosensitive cyclized rubber resist on the surface of the silicon dioxide thin film, drying, and exposing the resist. The film is cured as a pattern, and then developed and rinsed to expose only the electrode portion, and finally baked to form a resin coat on the surface of the silicon dioxide thin film. A method for manufacturing a strain gauge element, which comprises forming a coating film.