JP2005172530A - Load sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load sensor which avoids the change of a resistance value of a distortion resistance element at the time of calcination, as well as maintains moisture-proof effect sufficiently. <P>SOLUTION: The load sensor is equipped with: an origin distortion body 1 formed from the metal base substrate; an insulated glass layer 6 provided in the upper surface of this origin distortion body 1; a circuit pattern 9 provided in the upper surface of this insulated glass layer 6; distortion resistance elements 2, 3, 4, 5 electrically connected to this circuit pattern 9; and a coating layer 10 for covering the upper surface of these distortion resistance elements 2, 3, 4, 5, while this coating layer 10 is formed by the moisture-proof coating material consisting of fluororesin. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a load sensor used for a seat of an automobile, and more particularly to a structure of a load sensor that converts strain of a strain resistance element into a weight value.

  The structure of the conventional load sensor includes a metal base substrate 28 as a sensor substrate, an insulating glass layer 29 provided on the upper surface of the metal base substrate 28, and a pair of electrodes provided on the upper surface of the insulating glass layer 29. 30, 30, a strain resistance element 31 electrically connected to these electrodes 30, 30, and a protective layer 34 that protects the strain resistance element 31 are known (for example, Patent Document 1).

FIG. 5 is a side sectional view showing this conventional load sensor.
In the figure, the sensor substrate is formed by printing a glass paste on the upper surface of the metal base substrate 28 and baking it in a heating furnace at about 850 ° C. for about 45 minutes to form the insulating glass layer. Next, an electrode paste made of silver is printed on the upper surface of the metal base substrate 28 provided with the insulating glass layer 29 on the upper surface, and baked in a heating furnace at about 850 ° C. for about 45 minutes to form the electrode 30.

  Next, a resistance paste is printed on the upper surface of the metal base substrate 28 provided with the insulating glass layer 29 and the electrode 30 so as to be electrically connected to the electrode 30, and is heated in a heating furnace at about 850 ° C. for 45 minutes. The strain resistance element 31 is formed by baking. Next, although not described in detail, generally, a protective layer 34 made of glass or an organic resin such as a phenol resin or an epoxy resin is formed on the upper surface of the strain resistance element 31.

  Next, the operation will be described. When a bending moment is generated in the sensor substrate, the resistance value of the strain resistance element 31 changes in proportion to the deformation amount of the sensor substrate that is deformed in accordance with the bending moment. This change in resistance value is amplified by an electronic circuit and output as an output signal to an external device.

JP-A-11-258075

  However, in the structure of the conventional load sensor described above, when glass is used as the protective layer covering the upper surface of the strain resistance element, the moisture-proof effect as the protective layer is sufficiently satisfactory. Due to the high temperature applied, the resistance value of the strain resistance element changes and the performance as the strain resistance element deteriorates. In addition, when an organic resin such as a phenol resin or an epoxy resin is used, since the temperature during firing is relatively low, the resistance value of the strain resistance element does not deteriorate, but on the other hand, a sufficient moisture-proof effect is obtained. There was no problem.

  Accordingly, an object of the present invention is to provide a load sensor that solves the above-described problems and that provides a sufficient moisture-proof effect and that does not cause a change in the resistance value of the strain resistance element during firing.

In order to solve the above problems, in the present invention, as a first solution, a strain generating body made of a metal base substrate, an insulating glass layer provided on the top surface of the strain generating body, and an upper surface of the insulating glass layer are provided. A wiring pattern provided, a strain resistance element electrically connected to the wiring pattern, and a coating layer covering the upper surface of the strain resistance element were provided, and the coating layer was formed of a fluororesin.
As a second solution, the coating layer made of the fluororesin is formed on the upper surface of the wiring pattern including the strain resistance element.

Further, as a third solving means, the coating layer has a configuration in which a plurality of layers are formed by being applied a plurality of times.
As a fourth solution, an insulating glass layer having an opening exposing the strain resistance element is formed on the upper surface of the wiring pattern, and the opening is filled with the fluororesin to form the coating layer. It was set as the structure which formed.

As described above, the load sensor of the present invention includes a strain body made of a metal base substrate, an insulating glass layer provided on the top surface of the strain body, a wiring pattern provided on the top surface of the insulating glass layer, Since the strain resistance element electrically connected to the wiring pattern and the coating layer covering the upper surface of the strain resistance element are provided and the coating layer is formed of a fluororesin, the temperature at the time of firing the fluororesin is relatively low Therefore, a change in the resistance value of the strain resistance element when the coating layer is baked can be suppressed, and a sufficient moisture-proof effect can be obtained because the fluororesin has a moisture-proof property.
In addition, since the coating layer made of fluororesin is formed on the upper surface of the wiring pattern including the strain resistance element, the wiring pattern and the strain resistance element can be coated at a time, so that workability is good.

Further, since the coating layer is formed by overlapping a plurality of layers by applying a plurality of times, the uneven surface of the wiring pattern is flattened, and the occurrence of pinholes and the like can be prevented.
In addition, an insulating glass layer having an opening that exposes the strain resistance element is formed on the upper surface of the wiring pattern, and a fluororesin is filled in the opening to form a coating layer. Since the fluororesin coating layer having a sufficient thickness can be formed simply by filling, the moisture-proof effect can be improved with a simple configuration.

  Embodiments of the load sensor of the present invention are shown in FIGS. FIG. 1 is a plan view showing a load sensor according to an embodiment of the present invention, FIG. 2 is a sectional view of an essential part of the load sensor, FIG. 3 is a plan view showing another embodiment of the coating layer of the load sensor, and FIG. It is principal part sectional drawing which shows the other Example of the coating layer of a load sensor.

  In FIG. 1, the strain body 1 is made of a metal plate such as stainless steel, and is a flat plate having a certain thickness and is formed in a substantially T shape. The strain body 1 includes a base 1a provided with a fixing portion 1b having a mounting hole 1c in the center, and a pair of load receiving portions 1d and 1d provided in a wing shape on both sides of the fixing portion 1b. A pair of arm portions 1e and 1e are provided between the pair of load receiving portions 1d and 1d and the fixed portion 1b. The pair of arm portions 1e and 1e has a cross-sectional area at the center. It is formed to be thin. The pair of load receiving portions 1d and 1d are provided with round holes 1f and 1f, and the base 1a is provided with a pair of screw holes 1g and 1g.

  When the strain body 1 is attached to a seat such as an automobile, an attachment screw (not shown) is inserted into the attachment hole 1c of the fixing portion 1b to be fixed to the vehicle body, and the load receiving portion. A lever (not shown) that comes into contact with a part of the seat is engaged with the 1d round hole 1f. The arm portion 1e is appropriately bent by the load applied to the lever, and load detection is performed by applying strain stress to the strain resistance elements 2 to 5 described later disposed on the arm portion 1e. .

  Thus, since the strain body 1 is formed of a flat plate having a constant thickness and has flexibility, the generation of a constant strain can be obtained. Further, the strain body 1 has a fixed portion 1b formed on a central base 1a, and a pair of arm portions 1e and 1e provided on both sides of the fixed portion 1b. The pair of arm portions 1e and 1e. Since the load receiving portion 1d is formed at the tip of each, the load can be detected at both positions opposed to the fixed portion 1b, and the load can be stably detected for loads from all directions. ing.

  Further, on one coplanar surface of the strain generating body 1, strain resistance elements 2 to 5 are provided on the arm portion 1e on the fixed portion 1b side and the load receiving portion 1d side, respectively. The strain resistance elements 2 to 5 respectively disposed on the arm portion 1e on the fixed portion 1b side and the load receiving portion 1d side are provided in pairs on both sides with the fixed portion 1b of the strain body 1 in between. . Among these, the strain resistance elements 3 and 4 on the fixed portion 1b side are disposed near the base portion of the arm portion 1e, and the strain resistance elements 2 and 5 on the load receiving portion 1d side are the arm portions. 1e is disposed near the border between the details and the thick part.

  As described above, the strain resistance elements 2 to 5 on the fixed portion 1b side and the load receiving portion side 1d are provided in pairs on both sides with the fixed portion 1b of the strain generating body 1 interposed therebetween. Thus, balanced detection can be performed and detection errors with respect to loads can be reduced.

  These strain resistance elements 2 to 5 are composed of a binder made of a low-melting glass material or the like and a metal or metal oxide as a conductive material dispersed therein, and are subjected to stresses such as compressive force and tensile force. The absolute resistance value is changed by changing the density of the conductive material dispersed by. In addition, the resistance value of each distortion resistance element 2-5 is formed in the same value.

  These strain resistance elements 2 to 5 are connected to the input electrode, ground electrode, first output electrode, and second output electrode of the wiring connector (not shown) attached to the screw hole 1g of the base 1a by the wiring pattern 9, respectively. They are connected to form a bridge circuit. When no stress is applied to the strain resistance elements 2 to 5, the resistance value is constant and the bridge is in an equilibrium state.

  In this state, when a load is applied to the load receiving portion 1d, the arm portion 1e of the strain generating body 1 is deflected, and the strain resistance elements 2 to 5 disposed on the arm portion 1e are compressed and pulled. The resistance value of each strain resistance element changes in proportion to. A voltage applied to the bridge circuit from an input electrode (not shown) is divided by the respective strain resistance elements 2 to 5 and appears as a deviation voltage between the first output electrode and the second output electrode. The deviation voltage is converted into a weight value by a desired circuit, and a signal is transmitted to a display element (not shown).

Next, the manufacturing method of the strain body 1 is demonstrated using FIG.
First, undercoat layers 6a, 6b and 6c made of insulating glass are laminated and formed in three times on the upper surface of the strain generating body 1 made of a metal base substrate. In this case, a glass paste is applied to the upper surface of the strain generating body 1 by printing and baked in a heating furnace at about 850 ° C. for about 45 minutes to form the undercoat layers 6a, 6b, 6c, respectively.

  Next, a silver paste made of cermet-based silver is applied to the upper surface of the undercoat layer 6c by printing, and fired in a heating furnace in the same manner as described above to form the ground layer 7. Then, the middle coat layers 8a, 8b, and 8c made of insulating glass are again laminated in a manner similar to the above in a state where a part of the upper surface of the ground layer 7 has an opening. .

  Next, a silver paste made of cermet silver is applied on the upper surface of the middle coat layer 8c by printing, and baked in the same manner as described above to form the wiring pattern 9. In this case, a part of the wiring pattern 9 is electrically connected to the ground layer 7 through the opening. Then, a resistance paste is applied by printing so as to be electrically connected to the electrode portion on the upper surface of the wiring pattern 9, and is baked by the same method as described above, so that the strain resistance elements 2, 3, 4, 5 are Form.

  Next, on the upper surface of the wiring pattern 9 including the strain resistance elements 2, 3, 4, and 5, a resin made of a fluororesin is formed except for the solder land portion 9 a (the portion indicated by the hatching in FIG. 1). The paste is printed and the coating layer 10 is formed. In this case, a resin paste is applied to the upper surface of the wiring pattern 9 by printing, and is baked for about 10 minutes in a heating furnace at about 200 ° C. to form the coating layer 10a. The coating layer 10b is baked in a heating furnace, and the coating layers 10c and 10d are repeatedly formed four times in the same manner. Finally, the coating layer is baked for 10 minutes in a heating furnace at 250 ° C. 10 is formed.

In this embodiment, the fluororesin of a fluorine moisture-proof coating material is used as the resin paste to form the coating layer 10, and an amorphous fluororesin is used as the fluororesin.
Conventionally, this fluororesin has been used for a semiconductor passivation film, an anti-fogging coating such as a lens, and the like, and the film forming method has been performed by spin coating or dipping. For this reason, it is difficult to increase the coating film thickness by the conventional coating method.

In this example, the fluororesin film could be formed with a thickness of 5 to 8 μm by the method described above. By forming the coating film thick in this way, the uneven surface of the wiring pattern 9 is covered and flattened, and the occurrence of pinholes can be prevented, so that the reliability can be improved.
Also, the wiring layer 9 and the strain resistance elements 2, 3 are formed by forming the coating layer 10 made of a fluororesin on the upper surface of the wiring pattern 9 including the strain resistance elements 2, 3, 4, 5. Since 4, 4 and 5 can be coated at a time, workability is improved.

  According to the embodiment described above, since the coating layer 10 covering the upper surfaces of the strain resistance elements 2, 3, 4, and 5 is formed of a fluororesin, the temperature at the time of firing the fluororesin is the insulating glass. Since the temperature is relatively low compared to the firing temperature, it is possible to suppress changes in the resistance values of the strain resistance elements 2, 3, 4, and 5 when the coating layer 10 is fired, and the fluororesin is moisture-proof. Therefore, a sufficient moisture-proof effect can be obtained.

3 and 4 show another embodiment of the configuration of the coating layer 10 of the present invention.
In this case, the configuration is different from the above embodiment in that the coating layer is partially formed not only on the entire upper surface of the wiring pattern 9 but only on the upper surfaces of the strain resistance elements 2, 3, 4, and 5. .

  That is, in this embodiment, a silver paste made of cermet-based silver is printed on the upper surface of the middle coat layer 8c and baked to form the wiring pattern 9, which is electrically connected to the electrode portion on the upper surface of the wiring pattern 9. The structure is the same as that of the above-described embodiment until the resistor paste 2, 3, 4, 5 is formed by printing and baking the resistor paste so as to be connected, but after that, on the upper surface of the wiring pattern 9 An overcoat layer 12 made of insulating glass having an opening 11 exposing the strain resistance elements 2, 3, 4, and 5 is formed, and a fluororesin is filled in the opening 11 to form a coating layer 13. It is the composition to do.

  In this case, the overcoat layer 12 is formed by stacking the overcoat layers 12a and 12b, for example, by repeating printing and baking in a plurality of times as in the formation of the undercoat layer 6. Then, the opening 11 formed in the overcoat layer 12 is filled with a resin paste made of a fluororesin and baked to form the coating layer 13. In this case, since the resin paste can be filled by the thickness of the opening 11 of the overcoat layer 12, the coating layer 13 made of a fluororesin film having a large coating thickness can be easily obtained at one time. .

  As described above, according to the present embodiment, the overcoat layer 12 made of insulating glass having the opening 11 that exposes the strain resistance elements 2, 3, 4, and 5 on the upper surface of the wiring pattern 9. Since the coating layer 13 is formed by filling the opening 11 with the fluororesin, the fluororesin coating layer having a sufficient thickness can be obtained simply by filling the opening 11 with the fluororesin. Therefore, the moisture-proof effect can be improved with a simple configuration.

It is a top view which shows the load sensor which is one Example of this invention. It is principal part sectional drawing which shows the load sensor of this invention. It is a top view which shows the other Example of the coating layer of the load sensor of this invention. It is principal part sectional drawing which shows the other Example of the coating layer of the load sensor of this invention. It is a sectional side view which shows the conventional load sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Strain body 1a: Base 1b: Fixed part 1c: Mounting hole 1d: Load receiving part 1e: Arm part 1f: Round hole 1g: Screw hole 2: Strain resistance element 3: Strain resistance element 4: Strain resistance element 5 : Strain resistance element 6: Undercoat layer 6a: Undercoat layer 6b: Undercoat layer 6c: Undercoat layer 7: Ground layer 8: Middle coat layer 8a: Middle coat layer 8b: Middle coat layer 8c: Middle coat layer 9: Wiring pattern 9a: Solder land portion 10: Coating layer 10a: Coating layer 10b: Coating layer 10c: Coating layer 10d: Coating layer 11: Opening portion 12: Overcoat layer 12a: Overcoat layer 12b: Overcoat layer 13: Coating layer

Claims (4)

  A strain body made of a metal base substrate, an insulating glass layer provided on the top surface of the strain body, a wiring pattern provided on the top surface of the insulating glass layer, and an electrical connection to the wiring pattern A load sensor comprising a strain resistance element and a coating layer covering an upper surface of the strain resistance element, wherein the coating layer is formed of a fluororesin.   2. The load sensor according to claim 1, wherein a coating layer made of the fluororesin is formed on an upper surface of the wiring pattern including the strain resistance element.   The load sensor according to claim 1, wherein the coating layer is formed by stacking a plurality of layers by applying the coating layer a plurality of times. The insulating glass layer having an opening for exposing the strain resistance element is formed on the upper surface of the wiring pattern, and the coating layer is formed by filling the opening with the fluororesin. Item 1. The load sensor according to Item 1.

Images