JPH02275331A - Weight sensor element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a weight sensor element that can be used in microwave ovens and the like, and particularly to a capacitive weight sensor element.

BACKGROUND OF THE INVENTION Conventionally, this type of weight sensor element has been disclosed, for example, in Japanese Patent Application Laid-Open No.
As shown in Japanese Patent No. 288616, it had a structure as shown in FIG.

That is, a pair of alumina flat plates 1.2 were fixed at their peripheries with spacers 3 made of glass or the like so that they were parallel to each other and spaced apart from each other by a certain distance.

A circular electrode 4.5 was provided on the inner surface of the pair of alumina flat plates 1 and 2 to serve as a capacitor. A bullet-shaped load point 6 is fixed at the center of the alumina plate 1, a load is applied to the load point 6, the alumina plate 1 is operated as a diaphragm, and the electrode 4.
It was used as a weight sensor element that detects the load from the capacitance value of the capacitor made of 5. At this time, in order to avoid deformation of the diaphragm due to changes in atmospheric pressure, the diaphragm (alumina flat plate 1) or the base (alumina flat plate 2)
) was provided with a through hole 7 or 8.

Problems to be Solved by the Invention However, with this type of structure, two alumina flat plates were fixed together using a spacer such as glass.
Since it is necessary to process at a high temperature of 600°C or higher, there is a problem in that productivity is extremely low. Furthermore, in integrating with a hybrid IC or the like using chip components, there is a problem that the degree of freedom in the manufacturing process is significantly restricted. In addition, since the alumina flat plate and the spacer such as glass were bonded together at high temperatures of over 600'C, it was necessary to precisely match the thermal expansion coefficients of the materials used, so there was some freedom in designing the temperature coefficient of the weight sensor element. It was not possible to do so.

In addition, through holes 7 or 8 are provided in the diaphragm or base.
However, since the system is used with a filter, there is a problem that condensation occurs due to contamination of water vapor, etc., and malfunctions are likely to occur.

Therefore, the first object of the present invention is to significantly lower the processing temperature when fixing alumina flat plates and to improve productivity. The second goal is that as a result of being able to significantly lower the processing temperature,
The purpose of this invention is to expand the degree of freedom in selecting the coefficient of thermal expansion of the material used, and by extension to make it possible to design the temperature coefficient of the weight sensor element with some degree of freedom. The third object is to provide a weight sensor element that does not malfunction due to condensation of water vapor or the like inside the element by making it possible to coat the inside of the weight sensor element with a hydrophobic resin as a result of significantly lowering the processing temperature. It is in.

Means for Solving the Problems In order to achieve the first object, the present invention uses an organic adhesive layer instead of a spacer such as glass to significantly lower the processing temperature and improve productivity. We aim to

In order to achieve the second objective, the range of selection of the thermal expansion coefficient of the organic adhesive layer has been expanded by significantly lowering the processing temperature, and it has become possible to design the temperature coefficient of the weight sensor element with some degree of freedom. . In order to achieve the third objective, a hydrophobic resin film was formed on the surface of the electrode in advance, and then fixed with an organic adhesive layer to prevent condensation due to moisture from forming on the inner surface of the element.

Function: Since the weight sensor element of the present invention fixes the pair of flat plates with an organic adhesive layer, the processing temperature for fixing with glass or the like requires a high temperature of 150"C to 800"C. This has become possible at temperatures as low as ``C~200''C.As the processing temperature has been significantly lowered, the productivity of weight sensor elements has been greatly improved.Hence, hybrid ICs using chip components, etc. When integrated with other devices, the degree of freedom in the manufacturing process is greatly expanded.

In addition, when bonding an alumina flat plate to a seal such as glass, the processing temperature is high, so it is generally said that the difference in thermal expansion coefficient must be less than 0.5X10-'/''C for bonding to occur. However, in the case of organic adhesive layer,
Partly because the processing temperature is low, it is said that it is possible to bond if the difference in thermal expansion coefficient is about 5 x 10-'/''C. By making a selection, it becomes possible to design the temperature coefficient of the weight sensor element to a certain extent.

In addition, because the processing temperature during fixation by the organic adhesive layer is low,
Even after the electrode surface is coated with a hydrophobic resin in advance, it can be fixed, making it less likely that condensation will occur even if water vapor or the like enters the inside of the element, and malfunctions will be less likely to occur.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. In FIG. 1, 11.12 is a pair of alumina flat plates with a thickness of 0.63 mm, and 13 is a pair of non-conductive flat plates.
12 is an organic adhesive layer for fixing and holding 12 in parallel. Its contents are φ24, outer diameter φ28, and height approximately 50 μm.114.15 is a circular electrode of φ12 formed on the inner surface of an alumina flat plate.
4' and 15' indicate respective lead electrodes. Reference numeral 16 indicates a φ4 bullet-shaped loading point fixed to the center of the alumina flat plate, and reference numeral 17 indicates a through hole provided in 11. As the organic adhesive layer 13, an epoxy resin was used because it satisfies the practically important characteristics of a weight sensor element and can achieve a significant improvement in productivity. Adhesive strength, moisture resistance of adhesive strength, and responsiveness were selected as the important properties.

The epoxy resin used was one whose main components were a well-known bisphenol epoxy resin and hexahydrophthalic anhydride. Adhesive strength is 100kg/
C4 or higher was obtained, which was sufficient for practical use. In addition, its moisture deterioration resistance properties were measured after being left in an atmosphere of 60°C and 195%RH for 500 hours, and the adhesive strength was measured to be less than 10% of the initial value, that is, more than 90kg/c4, which is a practical problem. The value was not . Responsiveness was evaluated by weight fluctuation for 4 minutes from 30 seconds after ON-OFF of 5 kg load. As a result, it was within about 5 g. This value was a practically acceptable value for a weight sensor element normally used for detecting food weight in microwave ovens and the like. However, in applications that require higher responsiveness, such as detecting changes in the weight of food being cooked, it is somewhat insufficient in practice. The responsiveness could be improved by mixing filler into the epoxy resin. Figure 2 shows the results. In the figure, the horizontal axis represents alumina (AiO,), silica (S
The vertical axis shows the content of fine particles (spherical with a diameter of 40 μm or less), such as (ift), and the weight fluctuation. From the figure, it was possible to achieve a practically sufficient response of 2 g or less by containing the filler at 25 wt% or more. At this time, as shown in FIG. 3, it was observed that the adhesive strength was also improved by 10% to 30%. Next, the temperature characteristics of the weight sensor element will be explained. The capacitance C of the sensor element is determined by the electrode area S and the height of the organic adhesive layer dC = ...
・It is shown by (1).

If the temperature coefficient numbers of the weight sensor element, that is, the capacitance are α and , respectively, then the thermal expansion coefficient of the electrode area S is 2α, so if the temperature change is ΔT, then (1)
The formula is as shown in the following formula (2).

ΔS d (1+□・8T) ΔT ε. S (1+2・α,・8T) d (1+αE・ΔT) ε. S = −−+ 1 + (2, α, −α,)・ΔT) ・
...(2) ΔC The thermal expansion coefficient α of the alumina substrate is 7X10-6/'C
Then, in the case of conventional glass fixation at 600 to 800°C, the coefficient of thermal expansion is (6.5 to 7.5) Xl0-
It was 6 C to T. However, in the case of an organic adhesive layer treated at a low processing temperature in the present invention, its coefficient of thermal expansion is (2 to 12).
The temperature coefficient of the weight sensor element is (12~2)
It was found that it is possible to achieve a wide range of 10-'/'C. The coefficient of thermal expansion of the epoxy resin used in this example is
(6±1) I got it.

Furthermore, productivity was further improved by using a conductive flat plate, that is, a metal plate, as the flat plate facing the alumina flat plate that acts as a diaphragm.

FIG. 4 shows a cross-sectional view of a weight sensor consisting of a non-conductive flat plate and a conductive flat plate. A weight sensor element is shown in which an alumina flat plate 11 is fixed to a conductive flat plate, ie, a metal flat plate, with an organic adhesive layer 13. As seen in the figure, a conductive flat plate 18
There is no need to form the electrode 15 and lead portion 15' shown in FIG. 1 on the top, and the conductive flat plate 18 can be used as the electrode and lead portion. Therefore, not only does electrode formation become unnecessary, but also alignment of the upper and lower electrodes becomes unnecessary, which not only significantly reduces the manufacturing process cost, but also eliminates the drop in yield due to misalignment of the upper and lower electrodes, which increases productivity. Significantly improved. Furthermore, productivity was also improved by using a metal plate for one side.

That is, in FIG. 1, in order to hold the upper and lower flat plates in parallel, the flatness of the upper and lower flat plates is required to be approximately 1710 mm for the adhesive layer 13 (in this example, approximately 5 μm), so the alumina flat plate is polished and finished. However, in the case of a metal plate, the number of man-hours required for polishing was reduced to about 1,710 compared to the case of an alumina substrate, significantly lowering the manufacturing process cost and achieving an unexpected improvement in productivity.

In the above example, an alumina flat plate was used as the non-conductive flat plate, but any material that has excellent elastic properties, is thin, and has good flatness may be used. For example, zirconia, which has strong characteristics, etc. A mortarboard may also be used. Further, a glass plate made of quartz glass, borosilicate glass, etc., which can easily obtain flatness, may also be used.

In the above embodiments, epoxy resin was used as the organic adhesive layer, but thermosetting resins having a low curing temperature such as phenol and urea resins may also be used.

The materials for the metal flat plate include stainless steel (SUS), Kovar, and 426 alloy from the viewpoint of processability, cost, moisture resistance, coefficient of thermal expansion, adhesion with organic adhesive layer, compatibility with non-conductive flat plate, etc. etc. are suitable.

When alumina is used as the non-conductive flat plate, it is most suitable to use the 426 alloy as the metal flat plate because the coefficient of thermal expansion of the 426 alloy is the closest to that of alumina among the metals.

Furthermore, by combining the alumina diaphragm and the metal flat plate, the following new productivity improvements were obtained. That is, in FIG. 1, the extraction lead electrode 14'
, 15', if the sensor element was made of alumina flat plates on both the top and bottom, it would be necessary to invert and solder the element for each lead, but in the case of the element shown in Fig. Since it consists of a flat plate 18, one lead wire could be connected, for example, to the back surface of the element 18 without inverting the element.

A second embodiment of the present invention will be described with reference to FIG. 5(a).

FIG. 5(a) shows the same structure as FIG.
) formed a hydrophobic resin film 20 before fixing the alumina flat plate 11 and the metal flat plate 18. In conventional fixing using spacers such as glass, the processing temperature is 600 to 800°C.
Due to the extremely high temperatures, it was impossible to form such a resin film on the inner surface of the element. Note that 21 indicates a hydrophobic resin film formed on the outer surface of the element, which was formed after fixing the upper and lower flat plates.

FIG. 6 shows the results of moisture resistance when the hydrophobic resin film 20 is coated with polyimide amide resin or fluorocarbon resin to a thickness of about 0.2 to 5 μm. In the same figure, the horizontal axis is 3
Relative humidity at 0°C, vertical axis is phase C.

The results for the sensor element are indicated by an X mark, and the results for the weight sensor element according to the present invention are indicated by a Q mark. From the same figure, 95% is on the verge of condensation.
It can be seen that the moisture resistance properties are significantly improved in the head area.

Effects of the Invention As described above, the present invention uses an organic adhesive layer instead of fixing the pair of flat plates with a spacer such as glass, so that the processing temperature ranges from as high as 600 to 800°C to as high as 150 to 150°C.
It was possible to lower the temperature to as low as 200°C, significantly improving productivity such as manufacturing process costs.

Furthermore, in the case of fixation using an organic adhesive layer, it has become possible to use materials with a wide range of thermal expansion coefficients, and it has become possible to design the temperature coefficient with some degree of freedom.

Furthermore, a hydrophobic resin coating could be formed on the inner surface of the sensor element, and a weight sensor element with good moisture resistance could be provided.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a weight sensor element according to an embodiment of the present invention, Figs. 2 and 3 are characteristic diagrams of the same weight sensor element, and Fig. 4 is a sectional view of a weight sensor element of an embodiment with the same color. , FIG. 5(a) (bl is a cross-sectional view of a weight sensor element based on yet another embodiment, FIG. 6 is a characteristic diagram of the weight sensor element in FIGS. 5(a) and (b), and FIG. 7 is a conventional weight sensor element. It is a partially cutaway perspective view of the weight sensor element. 11.12... Alumina flat plate, 14.15...
...Electrode, 13...Organic adhesive layer, 16...
...Load point, 18...Metal flat plate. Name of agent: Patent attorney Shigetaka Awano 1 person 11.12
・- I415--- 16~・- Alumina flat plate 1 stitch s/! t Polar mother blind spot diagram filler word quantity (uIt, '/,) 1!5 5o75 Fu (Boo containing chrysanthemum amount (resistant-A) diagram G) Book diagram diagram

Claims (8)

[Claims] (1) Consisting of a pair of non-conductive plates, the pair of plates are arranged parallel to each other with a certain space between them, and their peripheral parts are fixed with an organic adhesive layer, and A weight sensor element in which electrodes are provided on mutually facing planes of arranged plate bodies to form a capacitance, and at least one of the plate bodies operates as an elastic diaphragm depending on the weight. (2) Consisting of a pair of plates, a non-conductive plate and a conductive plate, the pair of plates are arranged parallel to each other with a certain space between them, and their peripheral parts are covered with an organic adhesive layer. and an electrode is provided on a plane facing the conductive plate of the non-conductive plate arranged in parallel, and a capacitance is formed between the electrode and the conductive plate. A weight sensor element in which at least one of the plates operates as an elastic diaphragm depending on the weight. (3) The weight sensor element according to claim 1 or 2, wherein the organic adhesive layer is an epoxy resin adhesive layer. (4) The epoxy resin adhesive layer is made of silica (SiO_
2) Alternatively, the weight sensor element according to claim 3, which contains 25 wt% or more of a filler made of fine particles of alumina (AlO_3). (5) The weight sensor element according to claim 1 or 2, wherein the outer and inner surfaces of the pair of plates are coated with a hydrophobic resin. (6) The weight sensor element according to claim 1 or 2, wherein the non-conductive plate is made of glass such as alumina or zirconia or glass such as quartz glass or borosilicate glass. (7) The conductive plate is made of stainless steel, Kovar, 42
The weight sensor element according to claim 2, which is made of a 6-alloy metal. (8) The weight sensor element according to claim 2, wherein the non-conductive plate is made of alumina, and the conductive plate is made of a 426 alloy metal.