KR20020041017A - Dielectic sensor and manufacture method and wheatstone bridge type dielectric circuit for the cure monitoring of the high temperature composites - Google Patents

Abstract

PURPOSE: A dielectric sensor and method for manufacturing the same is provided to achieve improved quality of product by measuring the degree of cure of composite material cured in a high temperature, while enhancing sensitivity. CONSTITUTION: A method for manufacturing dielectric sensor comprises a first step(S1) of producing a base substrate from a glass material; a second step(S2) of producing a metal mold; a third step(S3) of producing a sensor pattern by using the metal mold; a fourth step(S4) of grinding the produced sensor pattern; and a fifth step(S5) of plating the completed dielectric sensor with a chrome. A dielectric sensor comprises a base substrate made of a glass material, and a copper paste attached onto the base substrate.

Description

Dielectric sensor and manufacture method and wheatstone bridge type dielectric circuit for the cure monitoring of the high temperature composites}

The present invention relates to a Wheatstone bridge dielectric circuit for measuring the degree of cure of the composite material, a high temperature dielectric sensor, and a method for manufacturing the same. More specifically, the Wheatstone which can accurately measure a maximum error of ± 1% or less. The present invention relates to a bridge dielectric circuit, a high temperature dielectric sensor for measuring the degree of cure of a thermosetting resin composite material having good electrical properties without causing a change in base at high temperatures, and a method of manufacturing the same.

Conventional dielectric sensors have a low temperature dielectric sensor that can be used only at a low temperature of 150 ° C. or less based on epoxy or glass-epoxy series. Such a dielectric sensor of the prior art has a large error in measuring the dissipation coefficient of the composite resin because the epoxy generates its own electrical change at a temperature of 150 ℃ or more.

1 is a graph measuring the dissipation coefficient of the sensor by leaving the dielectric sensor in a 220 ° C. atmosphere for a long time, and after about 25 minutes, the base is carbonized to show very unstable characteristics.

Figure 2 is a graph measuring the dissipation coefficient of BMI (Matrimid 5292, CIBA-GEIGY) using a low temperature dielectric sensor, the curing temperature of the BMI resin is 220 ℃. As can be seen from the measured results, the BMI resin has a dissipation factor of 3.6 or more after about 3 minutes in a 220 ° C atmosphere and drops after about 10 minutes. However, after about 10 minutes, the dissipation factor is increased again, indicating unstable characteristics. Therefore, there was a problem with many errors in the measurement of the curing degree of the high temperature composite resin such as BMI resin.

On the other hand, in order to measure the degree of curing of the composite material, a dielectric circuit for measuring the signal from the dielectric sensor is required. The dissipation factor value of the resin was used to measure the curing process of the resin using the dielectric circuit. The dissipation factor D _f can be defined in terms of the equivalent resistance R _m of the resin and the equivalent capacitor C _m , and the following relationship holds.

(One)

In the prior art, there are various methods for measuring the equivalent resistance and equivalent capacitor value of a composite resin, but a direct method circuit is known as a general method.

FIG. 13 is a circuit configuration of a series system, in which the equivalent resistance R _m and the equivalent capacitor C _m of the composite resin can be measured using the resistance R measured in advance.

In the series circuit shown in Fig. 13, the dissipation coefficient of the resin is a voltage ratio. And phase difference It is defined as follows.

(2)

Voltage ratio as shown in equation (2) And phase difference By measuring, the dissipation factor D _f could be measured.

In the conventional series circuit, the measurement range of the equivalent resistance R _m is theoretically from 0 to infinity (∞), which causes a problem in that the measurement range is very large and the precision is lowered.

In order to solve the problems of the prior art, the equivalent resistance of the composite resin is usually a few MΩ or more, so that the resistance range of the resistance can be reduced from infinity to MΩ, and the dielectric circuit can improve the measurement accuracy, 200 ℃ It is an object of the present invention to provide a dielectric sensor having excellent electrical characteristics and a method of manufacturing the same without causing a change in base at the above temperature.

In order to achieve the above object, the present invention provides a base substrate manufacturing process for manufacturing a base substrate of a glass material, a metal mold manufacturing process for manufacturing a sensor pattern, and a sensor pattern manufacturing process using the metal mold; The high temperature dielectric sensor is manufactured by the polishing process of the fabricated sensor pattern, and the chrome plating process of the completed high temperature dielectric sensor, the Wheatstone bridge circuit equipped with the high temperature dielectric sensor, the differential amplifier circuit, and the multiple buffers. , Phase difference compensator and voltage compensator, 2 comparator, a converter connected in parallel to the two comparator, an exclusive OR gate, and a converter connected in parallel to the exclusive OR gate.

1 is a graph measuring the dissipation factor of a sensor by leaving a conventional dielectric sensor at 220 ° C. for a long time;

2 is a graph measuring the dissipation factor of BMI (Matrimid 5292, CIBA-GEIGY) resin using a conventional dielectric sensor,

3 is a process chart showing the manufacturing method of the high temperature dielectric sensor of the present invention;

Figure 4 is a photograph showing a metal mold manufactured to manufacture a pattern of the high temperature dielectric sensor of the present invention,

5 is a photograph showing a state of the high-temperature dielectric sensor of the present invention,

Figure 6 is a perspective view showing a finite element model for analyzing the thermal residual stress around the high temperature dielectric sensor of the present invention,

7 is a graph showing the maximum stress value acting on the base portion and the sensor pattern portion according to the height of the sensor pattern;

8 is a photograph showing a state that the sensor is destroyed after the curing test of the BMI resin,

9 is a simplified diagram showing an experimental apparatus for forming a chromium plating layer having excellent electrical properties on the sensor surface;

10 is a photograph showing a high temperature dielectric sensor after forming a chromium plating layer of the present invention;

Figure 11 is a graph showing the result of leaving the high-temperature dielectric sensor of the present invention for a long time in 250 ℃ atmosphere,

12 is a graph showing the results of monitoring the curing of the BMI resin using the high temperature dielectric sensor of the present invention;

13 is a series circuit diagram,

14 is a Wheatstone bridge circuit diagram,

15 is a circuit diagram showing a Wheatstone bridge dielectric circuit of the present invention;

16 is a photograph showing a Wheatstone bridge circuit of the present invention;

17 is a graph comparing the error of the resistance of the series circuit and the Wheatstone bridge circuit,

Fig. 18 is a graph comparing errors of a capacitor of a series power circuit and a Wheatstone bridge circuit.

Explanation of symbols on the main parts of the drawings

8: high temperature dielectric sensor 9, 10, 12, 14: buffer

11: differential amplifier circuit 13: voltage compensator

15: phase difference compensator 17, 18: comparator

16, 19, 21: converter 20: exclusive OR gate

Hereinafter, a configuration according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.

As shown in Figure 3, the manufacturing method of the high-temperature dielectric sensor for measuring the degree of cure of the composite material of the present invention includes a base substrate manufacturing process (S1) for manufacturing a glass base substrate; A metal mold fabrication process (S2) for fabricating the sensor pattern; A sensor pattern manufacturing process (S3) using the metal mold; Polishing process (S4) of the produced sensor pattern; It is configured to include a chrome plating process (S5) of the completed high-temperature dielectric sensor.

Hereinafter, a method of manufacturing a high temperature dielectric sensor for measuring the degree of curing of the composite material of the present invention will be described in detail for each process.

First step: base substrate manufacturing process (S1)

The dielectric sensor may be divided into a copper foil and a base substrate supporting the copper foil, which form the sensor pattern. To use the dielectric sensor at a high temperature, the material of the base substrate should be replaced for a high temperature.

The material of such a high temperature base substrate has a low coefficient of thermal expansion, has a stable structure at high temperatures, and can use high temperature thermosetting resins, glass and ceramics, which are electrical insulators. Ceramic-based products, such as glass, which are not easily produced and are easily obtained, are used as the base substrate material.

Second Process: Metal Mold Manufacturing Process (S2)

Since it is almost impossible to bond a copper foil on a glass base substrate, a copper paste composed of a mixture of epoxy and fine copper particles is used instead of the copper film.

The copper paste is ACP-060, ASAHI Co., Ltd., coated on a glass base substrate, and then cured at a temperature of 150 ° C. for about 1 hour to have conductivity, and other properties are shown in Table 1 below.

Viscosity (ps at 25 ° C) 400-600 Specific gravity (g / cc at 25 ° C) 3.2 Curing condition 150 ℃ x 30min Hardness (H) 3 Humidity(%) ± 30 Coupling Resistance (%) ± 30

In order to apply the copper paste to the sensor pattern, a method using a metal mold is applied.

Here, the metal mold was manufactured as shown in FIG. 4 using the discharge wire cutting method for the accuracy of the sensor pattern.

Third process: sensor pattern manufacturing process (S3)

The processed metal mold is subjected to a release treatment, and then copper paste is applied to the surface of the sensor pattern and cured at 120 ° C. for about 2 hours.

Since the copper paste is completely cured at 150 ° C., the sensor pattern manufactured by the metal mold is not completely cured and then cured at 150 ° C. for about 30 minutes.

Fourth Step: Polishing Sensor Pattern (S4)

The sensor pattern separated from the metal mold shown in FIG. 5 cannot be used as it is because it has an uneven surface, and the non-uniform surface becomes a uniform surface and is ground to have a suitable height.

The release material on the glass base substrate has a bad effect on the sensor, so wipe it off with acetone.

The higher the height of the sensor pattern, the better the sensitivity. However, the excessive height of the sensor pattern is the most suitable sensor pattern because it cannot act as a sensor by destroying the glass base substrate in contact with the resin due to thermal residual stress caused by curing of the resin. Should be determined.

The height of the sensor pattern was determined through the following examples.

Example

In the present invention, thermal stress analysis using an finite element program, Ansys, was performed to determine the optimal height of the sensor pattern.

FIG. 6 illustrates a finite element model for calculating thermal residual stress around a sensor. The temperature difference before and after curing was assumed to be 180 ℃, and the height of the sensor pattern was 35 m, 100 m, 150 m, 200 m, 250 The thermal residual stress around the sensor was analyzed by changing to m. 7 shows the maximum stress values acting on the base portion and the sensor pattern portion according to the height of the sensor pattern. The shear strength of the copper paste pattern used in the experiment was about 15 MPa, which was lower than the fracture strength value as shown in FIG. 7. However, the stress acting on the underlying glass has a height of 250 When m was reached, the glass had a breaking strength of 35 MPa, indicating that the glass was broken. In order to verify the results of the finite element analysis described above, the BMI resin was cured on the sensor pattern by changing the height of the sensor pattern. At this time, the curing temperature of the BMI resin was selected as 220 ℃. Experimental Results The sensor pattern height is 250 Above m, it was observed that the breakage of the sensor pattern occurred. FIG. 8 is a photograph showing a state in which the sensor is broken after the curing test of the BMI resin, and it can be seen that the base portion made of glass is broken.

From the above results, the height of the sensor pattern is about 200 to prevent breakage of the sensor due to thermal residual stress. We could conclude that it should be less than m.

5th process: chrome plating process of high temperature dielectric sensor (S5)

As described above, in the high temperature dielectric sensor manufactured by the metal mold, since the sensor pattern is formed of copper paste, the surface of the sensor may be electrically uneven.

In order to stabilize this electrically non-uniform sensor surface, the sensor surface was metal-coated using the electroplating method.

The experimental apparatus as shown in FIG. 9 was configured to obtain optimum conditions for forming a chromium plating layer having excellent electrical characteristics on the sensor surface. The plating solution used is a standard plating solution, consisting of 250 g of hexavalent chromium powder per liter of water and sulfuric acid with 1% of chromium mass. Since 1 g of sulfuric acid had a volume of 1.84 ml, sulfuric acid was added to the dropper by calculating the volume corresponding to the mass. The DC power supply used can be used from 0 to 100V and 0 to 20A. Insoluble lead was used for the positive electrode, copper was used for the high conductivity, and the negative electrode was not touched with the plating solution except for the plating part so that chromium did not precipitate on the electrode. The temperature of the plating liquid was room temperature (25 ° C.), and the experiment was performed while changing the operating current to 0.2, 0.4, 0.6, 0.8, 1.0 A. Table 2 is a table showing the results of experiments in the resistance change of the sensor pattern according to the current used.

Current (A) Resistance of the sensor Before plating (M Ω) After plating (M Ω) 0.2 34 0 0.4 34 20 × 10-6 0.6 34 42.75 0.8 34 - 1.0 34 -

As shown in Table 2, when the operating current is 0.2A, the electrical resistance is almost zero, and the electrical characteristics are excellent. In addition, when the use current is more than 0.8A, it could be observed that the plating layer was not formed due to cracking of the sensor pattern.

10 is a photograph showing a state of the high temperature dielectric sensor in which the chromium plating layer is formed.

In order to confirm the properties and effects of the high temperature dielectric sensor for measuring the degree of cure of the composite material of the present invention was evaluated through the following experimental example.

Experimental Example 1

In order to compare the performance of the existing low-temperature dielectric sensor with the high-temperature dielectric sensor of the present invention, the following conditions were used in each experiment.

Initial temperature: Room temperature (25 ℃)

Measuring circuit: Wheatstone bridge dielectric circuit

Dielectric Sensor: Low Temperature Sensor, High Temperature Sensor, High Temperature Sensor with Chrome Plating

Experimental resin: 0.08g of BMI resin (Matrimid 5292 of CIBA-GEIGY)

Experiment temperature: 200 ℃ at 10 ℃ / min

Experiment time: about 120 minutes

Figure 2 is a graph measuring the dissipation coefficient of BMI (Matrimid 5292, CIBA-GEIGY) using a low temperature dielectric sensor, the curing temperature of the BMI resin is 220 ℃. As can be seen from the measured results, the BMI resin has a dissipation factor of 3.6 or more after about 3 minutes in a 220 ° C atmosphere and drops after about 10 minutes. However, after about 10 minutes, the dissipation factor is increased again, indicating unstable characteristics.

In order to investigate the characteristics of the fabricated high temperature dielectric sensor, the characteristics of the sensor itself were investigated by leaving it in a high temperature atmosphere for a long time. 11 is a diagram showing the result of leaving the high temperature dielectric sensor in a 250 ° C. atmosphere for a long time, and it can be seen that the dissipation coefficient has a constant value of almost zero.

Curing monitoring of high temperature resin, BMI resin, was carried out to examine the applicability of high temperature dielectric sensor. Curing temperature was maintained for a long time at 200 ℃ same as the experiment of low temperature dielectric sensor. 12 is a diagram showing the results of curing monitoring of the BMI resin, it can be seen that the dissipation factor value reaches a maximum after about 3 minutes. Also, after about 10 minutes, the dissipation coefficient value has a constant value, so it can be seen that the curing is completed. From the above results, it was confirmed that the fabricated high temperature dielectric sensor can be applied to the curing monitoring of the high temperature composite material.

As a result of the above experiment, the high temperature dielectric sensor has no influence on the curing monitoring of the resin cured at high temperature, so it can be useful for the study of the properties of other resins and the manufacture of molded products of composite materials.

In order to precisely measure the signal from the dielectric sensor manufactured as described above, the present invention configures a Wheatstone bridge type measurement circuit, and compares and evaluates the performance of the conventional measurement circuit.

First, in order to improve the accuracy of the measurement by reducing the measurement range of the equivalent resistance R _m from infinity to MΩ, a Wheatstone bridge type circuit as shown in FIG. 14 was constructed. The bridge circuit is largely divided into a balanced bridge method and an unbalanced bridge method, and the present invention uses an unbalanced bridge circuit because it is necessary to measure the resistance and capacitor values of the sensor portion that change over time.

Predetermined resistance R _2, R _3, R ₄ impedance Z _2, Z _3, Z ₄ ask the impedance Z _m of the resin and the composite of,

(3)

to be. The voltage applied to the resin is expressed as follows.

(4)

here,

(5)

This is the difference between the output voltage of the sensor part minus the output voltage on the opposite side. The above equation can be summarized as follows.

(6)

Voltage ratio between V _i and V _m in equation (6) And phase difference If you find

(7)

(8)

to be. At this time, if R = R ₂ = R ₄ , and substituted by the formula (7) and (8) in the formula (6) as follows.

(9)

A =

B =

C =

Therefore, solving equation (9) above, the equivalent resistance R _m and equivalent capacitor C _m values of the resin are as follows.

10

(11)

The dissipation factor D_f of the resin is defined by

(12)

to be. Therefore, by substituting Equations (10) and (11) into Equation (12), the dissipation coefficient of the composite resin can be measured.

In the Wheatstone bridge circuit as described above, the resistors R and R ₃ should be selected properly to improve the accuracy of the measurement. In the present invention, the circuit was configured by selecting R = R ₂ = R ₄ = 10 MΩ and R ₃ = 1 MΩ.

Next, in order to measure the dissipation coefficient of the composite material, as shown in equations (10) and (11), the voltage ratio V _r and the phase difference Should be measured.

15 is a voltage difference V _r and a phase difference A circuit configuration diagram for measuring.

As shown in FIG. 15, a Wheatstone bridge circuit with a high temperature dielectric sensor 8 of the present invention, a differential amplifier circuit 11, and a plurality of buffers for measuring the values of V _m and V _i 9, 10, 12, and 14, the phase difference compensator 15 and the voltage compensator 13 were installed, and the phase difference ( Two comparators 17 and 18, a transducer 16 and 19 connected in parallel to the two comparators 17 and 18, an exclusive OR gate 20 and the exclusive OR gate And a converter 21 connected in parallel with (20).

The comparators 17 and 18 output square signals by + 5V when the input AC signal is positive voltage and 0 V when the negative voltage is negative, and the two comparators 17 and 18 function. Square wave of V _i and V _m passes through the exclusive OR gate 20. If you convert this signal to an RMS value, the phase difference Can be obtained. The defining formula of RMS is as follows.

V _rms (13)

Equation (13) is converted to the following equation because of the characteristic of the square wave passing through the exclusive OR gate, that is, only the phase difference is detected as the square wave.

V _rms (14) Phase difference in equation (14) If we derive the equation

(15)

Becomes

FIG. 16 is a photograph showing a Wheatstone bridge type circuit manufactured to measure the dissipation coefficient of a composite resin.

In order to confirm the characteristics and effects of the Wheatstone bridge dielectric circuit for measuring the degree of cure of the composite material of the present invention was evaluated through the following experimental example.

Experimental Example 2

The optimum input frequency and input voltage should be selected to improve the accuracy of the measurement in the dissipation factor measurement circuit.

The frequency of 1kHz and the voltage of 1V were used for the direct method circuit, and the most suitable value was selected through the experiment for the Wheatstone bridge circuit.

In the present invention, an input frequency of 400 Hz and an input voltage of 3 V are selected. The performance of the direct method circuit and the Wheatstone bridge circuit was compared and evaluated using five previously measured resistors and capacitors. FIG. 17 is a graph comparing the resistance error. The direct method circuit is about ± 1%. While the Wheatstone bridged circuit exhibited an error of ± 0.5%.

On the other hand, Figure 18 is a graph measuring the error of the capacitor, the error of the direct method circuit is ± 2%, the error of the Wheatstone bridge circuit is ± 1%. Therefore, the Wheatstone bridge circuit has a maximum error of ± 1% or less, and thus has better precision than the conventional direct method circuit.

As confirmed through the above examples and experimental examples, the high-temperature dielectric sensor and the Wheatstone bridge circuit for measuring the degree of cure of the composite material of the present invention have a stable structure even at high temperature, and the electrical insulator is used as the base substrate material. This improves the quality of the product by measuring the degree of cure of the composite material cured at high temperature without causing any change in the base even at high temperature, and improves the value of the dissipation coefficient by chromium plating on the surface of the sensor. This is a very useful invention in the field of dielectric sensor manufacturing because it has the effect of improving the sensitivity and the effect of reducing the measurement error to a maximum of 1% or less to make more accurate measurements.

Claims (5)

A base substrate fabrication process (S1) for fabricating a glass substrate base substrate; A metal mold fabrication process (S2) for fabricating the sensor pattern; A sensor pattern manufacturing process (S3) using the metal mold; Polishing process (S4) of the produced sensor pattern; Method for producing a high-temperature dielectric sensor for measuring the degree of cure of the composite material, characterized in that the chromium plating process (S5) of the completed high-temperature dielectric sensor. A high temperature dielectric sensor for measuring the degree of cure of a composite material, characterized in that consisting of a glass base substrate and a copper paste fixed on the base substrate. The high temperature dielectric sensor for measuring the degree of cure of a composite material according to claim 2, wherein the surface of the high temperature dielectric sensor is chromium plated. A Wheatstone bridge circuit with a high temperature dielectric sensor 8, a differential amplifier circuit 11 and a plurality of buffers 9, 10, 12, 14 are connected, and a phase difference compensator 15 and a voltage compensator 13 ), And the phase difference ( Two comparators 17 and 18, a transducer 16 and 19 connected in parallel to the two comparators 17 and 18, an exclusive OR gate 20 and the exclusive OR gate A Wheatstone bridge type dielectric circuit for measuring the degree of cure of a composite material, comprising a converter 21 connected in parallel to the 20. 5. The Wheatstone for measuring the degree of cure of the composite material according to claim 4, wherein the Wheatstone bridge circuit is composed of a circuit in which R = R ₂ = R ₄ = 10 MΩ and R ₃ = 1 MΩ. Bridged dielectric circuit.