JPH02196939A - Pressure sensor and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the sensor having high burst pressure, high sensitivity and satisfactory heat stability by forming a diaphragm and a base as one body, and forming a bridge circuit and a thick film pressure sensitive element in its recessed part by a transfer technique. CONSTITUTION:A diaphragm 2 is formed as one body with a base plate 4, and made of alumina ceramics or enameled SUS. A bridge circuit 6 containing a thick film pressure sensitive element 8 is formed on the bottom face of the inside of a recessed part 10 of the diaphragm 2. In such a case, at the time of forming the bridge circuit 6 in the diaphragm 2, the circuit 6 containing the element 8 is transferred and formed in the recessed part 10 of the diaphragm 2 by using transfer paper 16. The transfer paper 16 consists of a water absorptive mount 18, and by forming a water soluble paste applied layer 20 consisting of dextrin, etc. on the mount 18, a pattern is printed and dried, an electrode pattern 22 and a thick film pressure sensitive element pattern 24 are printed there on and dried in the same way, and thereafter, overcoating is executed for the purpose of protection.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is based on the fact that the resistance value of a pressure sensitive element (hereinafter referred to as a thick film pressure sensitive element) made of a thick film resistor on a diaphragm changes due to pressure. The present invention relates to a pressure sensor for detecting pressure using the present invention and a method for manufacturing the pressure sensor.

(Prior Art) The diaphragm 40 of the first conventional example in which a thick film is used as the pressure-sensitive element of a pressure sensor is shown in FIGS. 8(A) and 8(B). A thick film pressure sensitive element made of enamel made of stainless steel or the like with an insulating layer is bonded to the base plate 44 4B.

A bridge circuit 50 is constructed in the deformable portion of the diaphragm 40 on the bottom surface of the recess 48 provided in the base plate 44. Normal pressure P is applied to the upper surface of the diaphragm 40 on the opposite side from the inside of the recess 48.

FIGS. 9A and 9B illustrate a second conventional example. The diaphragm 52 in this example is formed integrally with the base plate, and is made of enamel made of ceramic, iron, stainless steel, or the like with an insulating layer applied, as in the first conventional example. A thick-film pressure-sensitive element 56 is separated by a recess 54 provided in the diaphragm 52 (also serving as a base plate), and a bridge circuit 58 including the thick-film pressure-sensitive element is formed on the outer surface of the recess 54 . is added inward.

(Question III that the invention seeks to solve) In the prior art described above, FIG. 8(A).

In the first conventional example (B), the diaphragm 40 on which the thick-film pressure-sensitive element is formed and the base plate 44 are bonded 46 with a bonding agent, so there is no stress concentration when pressure is applied from the outside of the four parts 48. Since the bonding layer 46 has low strength and Young's modulus, a creep phenomenon occurs. (See FIG. 7) Furthermore, there were other problems in the manufacturing process, such as the fact that forming the bonding layer 46 was time consuming.

There are large manufacturing variations in the dimensions, shapes, etc. of the deformable 1XH (distorted portion) of the diaphragm 40, and in order to maintain the joint strength of the joint, the joint area must be large, resulting in a small pressure sensor. There were also problems such as difficulty in optimizing the system.

Next, in the second conventional example, since the diaphragm and the base plate are integrally formed, unlike the first conventional example, there is less leap phenomenon, but since the pressure P is received from the inside of the recess 54, the four corners 54 This has drawbacks such as tension and shear stress concentration, which may cause the diaphragm 52 to break. Therefore, the diaphragm does not have sufficient strength and breaking strength, making it unsuitable for pressure sensors used for high pressure applications, and making it difficult to miniaturize.

(Means for Solving the Problems) The present invention provides the following means for solving the above-mentioned problems.

The diaphragm integrated with the base plate is made of powder molded ceramics or machined metal enamel, and a thick film pressure sensitive element is formed on the inner surface of the recess provided in the base plate. This invention discloses a method of forming elements and bridge circuits using a transfer method and post-baking them.

(Function) According to the present invention, since the pressure P can be received by the outer two-lat surface of the diaphragm, tensile stress concentration does not occur at the corners of the recess.

Therefore, the burst pressure can be increased, the safety design of the diaphragm is easy, and the design of a pressure sensor for high pressure is possible.

Furthermore, since the diaphragm and the base plate are integrated and made of ceramic or metal, the sensor characteristics are such that creep phenomenon can be suppressed and a stable output can be obtained.

In addition, after forming the concave portion of the diaphragm with high precision in advance using a mold or machining, a thick film pressure-sensitive element is placed on the inner bottom surface of the concave portion.
Since the bridge circuit is formed using a transfer technique or the like, it is easy to align the electrodes, resistance patterns, etc. with the center line of the diaphragm as a reference.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a top view. The diaphragm 2 is formed integrally with the base plate 4, and is made of alumina ceramics or enamel-coated SUS.

Reference numeral 6 denotes a bridge circuit including a thick-film pressure-sensitive element 8, which is formed on the inner bottom surface of the recess IO of the diaphragm 2 by a method described later. 12 is a wiring, and 14 is a terminal portion. A power source (not shown) is electrically connected from the bridge circuit 6 to four terminal portions 14 disposed on the inner bottom surface of the recessed portion of the diaphragm 2 via wiring 12 .

FIG. 3 shows a method of forming the zero-order bridge circuit 6 on the diaphragm 2. FIG. 4 illustrates a transfer paper 1B for transferring and forming a bridge circuit 6 including a thick film pressure-sensitive element 8 into a recess 10 of a diaphragm 2. The transfer paper 16 is made of a water-absorbing mount 18, and a water-soluble glue coating layer 20 made of dextrin or the like is applied on the mount 18.
form. For the transfer paper, first, a pattern is printed on a water-absorbing mount 18 by screen printing or the like with a water-soluble glue coating layer 20 made of dextrin or the like, and then dried. Thereon, an electrode pattern 22 and a thick film pressure sensitive element pattern 24 are similarly printed and dried. Finally, the mount is overcoated to protect the electrode and thick-film pressure-sensitive element patterns, and to facilitate the transfer (transfer) and slide pasting of the design onto the transfer target.The overcoating material is ethyl cellulose, methyl Adopt a material whose main component is methacrylic. Transfer paper is completed through this series of processes.
Next, regarding the case of transferring this, when the completed transfer paper 16 is immersed in water, the dextrin of the water-soluble glue coating layer 20 is dissolved, and the electrode pattern 22 is separated from the mount 18. The peeled electrode pattern 22 is pasted on the transferred portion, that is, the inner bottom surface of the four parts 10 of the diaphragm 2, and then dried and fired to form an electrode pattern.

Next, FIG. 5 illustrates a transfer paper 26 having only 24 patterns of pressure sensitive elements.

Normally, if the electrode and the thick-film pressure-sensitive element are fired at the same time, there will be a lot of diffusion of the electrode into the pressure-sensitive element, so to prevent this, each is fired separately. The transfer paper 2B for the thick film pressure sensitive element 8 is made of the same material as the transfer paper 16 for the electrode pattern described above, and has a water-soluble glue coating layer 30 formed on its upper surface, and further has the thick film pressure sensitive element pattern 24 on its upper surface. form.

First, only the electrode pattern 22 shown in FIG. 4 is transferred, then dried and fired, and the thick film pressure-sensitive element pattern 24 shown in FIG. 5 is transferred thereon at a predetermined position, followed by drying and firing.

Although the water-applying method was adopted as the transfer method described above, there are other methods such as heat transfer (H, R) and HR-OFF, and the transfer method is not limited to the above-mentioned method.

Further, in the present invention, the diaphragm has a cylindrical shape, but it may be square or rectangular, and the thick film pressure sensitive element is arranged such that two opposite sides are compressed and the other two are expanded in response to pressure. If the position is such that the extent of the damage is maximized, it is not necessarily necessary to arrange it as shown in FIG.

Next, comparisons between the characteristics of the embodiment shown in #I1 and FIG. 2 of the present invention and the conventional example are shown in FIGS. 6 and 7, respectively.

FIG. 6 shows the pressure and fracture characteristics, and FIG. 7 shows the creep characteristics.

As is clear from the drawings, the examples of the present invention exhibit better fracture characteristics and creep characteristics than the conventional examples (first and second examples).

(Effects of the Invention) As described in detail above, according to the present invention, the diaphragm is integrated with the base, the bridge circuit and the thick film pressure-sensitive element are formed in the recessed part of the diaphragm by transfer technology, and pressure is applied on the flat surface. The following effects can be expected since the structure is designed to receive

0) There is no stress concentration and the fracture pressure is high.

(2) Creep phenomenon is less likely to occur.

(3) Since it does not have a joint structure unlike the conventional example, the shape and size of the deformable portion (distorted portion) of the diaphragm have good accuracy.

(4) The bursting pressure is high, and the structure makes it easy to make the sensor smaller and higher pressure.

(5) A flush type diaphragm is possible.

Further, the pressure sensor according to the present invention described above can be applied to any case requiring strain sensing with high sensitivity and good thermal stability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment according to the present invention, FIG. 2 is a plan view, FIG. 3 is a bridge circuit diagram, and FIGS. The pattern diagram of the transfer paper, FIGS. 6 and 7 show the fracture characteristics of the present invention and the conventional pressure sensor, respectively. It is a graph showing creep characteristics. Figure 8 (A) is a sectional view of a conventional pressure sensor, and Figure 8 (B)
9(A) is a sectional view of another conventional pressure sensor, and FIG. 9(CB) is a plan view. 2...Diaphragm, 4...Base plate. 6... Bridge circuit, 8... Thick film pressure sensitive element, lO.
... recess, 16 ... transfer paper, 18 ... water absorbent mount,
20... Water-soluble glue coating layer, 22... Electrode pattern, 2
4... Thick film pressure sensitive element pattern, 26... Transfer paper, 3
0...Water-soluble glue coating layer. Applicant Delphi Co., Ltd. Agent Patent Attorney Sakae Kobayashi

Claims (1)

[Scope of Claims] 1. A base body in which a thick-film pressure-sensitive element resistor is formed in a deformable portion, and an electric circuit that senses a change in resistance of the pressure-sensitive element as a function of deformation of the base body. In the pressure measuring device, the base body includes a deformable part and a non-deformable part integrally formed, and the deformable part formed inside a recess that is not exposed to pressure of the base body is configured with a thick film pressure sensitive element. Features of pressure sensor. 2. A method for manufacturing a pressure sensor comprising the steps of forming a bridge circuit pattern on transfer paper by screen printing or the like, transferring the circuit pattern to the inner bottom surface of the recess of the diaphragm, and firing the transferred pattern. 3. Separately forming the electrode pattern of the bridge circuit and the thick film pressure sensitive element pattern on transfer paper by screen printing or the like, and sequentially applying the electrode pattern and the thick film pressure sensitive element pattern to the inner bottom surface of the recess of the diaphragm. 2. The method of manufacturing a pressure sensor according to claim 1, further comprising the steps of transferring and then firing each image.