RU2296417C2 - Method and device for manufacturing crystal elements - Google Patents

Abstract

FIELD: electrical and piezoelectric engineering; high-frequency resonators including precision ones.

SUBSTANCE: proposed method for manufacturing crystal elements includes chemical and dynamic etching of flat blank in liquid etchant while setting it in circular rotary motion at rotation frequency of 0.3 - 0.53 c^-1 and at the same time in reciprocation motion; angle of etchant flow attack relative to blank surface is chosen between 2 and 17 deg.; blank is fused primarily in horizontal plane while turning it through 270 to 300 deg. at circular rotation speed and at the same time rotated relative to symmetry axis normal to its plane. Device implementing proposed method has bowl holding liquid etchant and placed in thermostat, lifting-and-rotating mechanism incorporating electric motor whose shaft carries cam mechanically coupled with movable roller, as well as stacked magazine with cells to receive blanks; annular lobe of cam is slanting at angular length of 270 to 300 deg. so that angle of etchant flow attack between 1 and 17 deg. relative to blank surfaces and steep decent are ensured; specified height of magazine cells is 1.5 to 3.0 mm.

EFFECT: enhanced quality of polishing etching and facilitated manufacture.

2 cl, 10 dwg

Description

The invention relates to piezotechnics and can be used for the manufacture of crystalline elements (CE) of high-frequency resonators, including precision ones.

Known methods for shaping the FE of piezoresonance sensors, including chemical-dynamic etching of workpieces in a liquid etchant at a temperature of 353 ± 1 K by circular movement of the workpieces in a cassette with a frequency of 0.3 ÷ 3.0 rpm, as well as simultaneous rotation of the cassette links in the etchant stream [ one].

A constant processing speed of a large batch of workpieces is ensured, however, stagnant etching zones at the contact points between the workpiece and the cassette cannot be completely eliminated, which means that optimal surface quality is obtained. The closest analogue is a method of manufacturing quartz piezoelectric elements, including chemical etching of the workpieces at a solution temperature of (290 ÷ 368) ± 0.5K and moving them in solution by reverse circular motion with a frequency of 0.17 ÷ 0.75 r / s at angles of 180 ÷ 270 ° , as well as the reciprocating movement of the workpieces in a vertical plane [2]. The method has been successfully used in the production of RF cavities for the manufacture of FEs in the form of an inverse mesastructure. In this case, stagnant etching zones occur in non-working areas of FE. Obviously, the method does not fully realize the possibility of chemical polishing of FE for precision quartz resonators. It requires high quality processing over the entire surface of flat, and often lens FEs. In addition, the blanks during the etching process have different linear velocities relative to the etchant, which leads to a spread in the thickness of the FE at the end of the etching process.

A device for the manufacture of FE piezoresonance sensors by the method of chemical-dynamic etching [1]. The device comprises a container with a liquid etchant placed in a thermostat, a lifting and rotating mechanism, and a cassette of the floor type, each link of which rotates together with workpieces around its own axis on a shaft with turbines. In the process of etching, this design of the device provides an etcher supply from all sides of the workpiece along its perimeter. However, it is not possible to exclude stagnant zones at the contact points of the workpiece with cartridge elements.

In the technology of liquid polishing etching, devices (cartridges) are used to place CE in the etching solution [3, 4]. The cassette is a rigid cellular structure made of wire ties, staples and jumpers using spot welding. The cell sizes are chosen so that the workpieces being processed are in a free or fixed state, in contact with the cartridge elements only inoperative surface areas. The presence of stagnant etching zones on the FE is also obvious, which does not allow optimizing the surface of flat or lenticular FEs for thermostat resonators.

The closest analogue by design features is a device [2], containing a vessel with etching solution, placed in a thermostat, a lifting and rotating mechanism, including an electric motor, on the axis of which at least one cam mechanically connected to the movable roller is fixed, and a cartridge with cells for laying blanks. The device has these disadvantages of the method [2], which limits its use.

The objective of the proposed technical solution is to expand the field of application of the technology of chemical polishing of CE to serial production of high-frequency resonators of a precision class with a simultaneous simplification of the technology.

The problem is solved in that in the method of manufacturing FE, including chemical-dynamic etching of a flat or lenticular preform in a liquid etchant with circular movement of the preform with a frequency of 0.3 ÷ 0.53 s ^-1 and simultaneous reciprocating movement, the angle of attack of the etchant stream relative to the surface of the workpiece, choose within 2 ÷ 17 ° and ensure the workpiece is swimming mainly in the horizontal plane during a rotation of 270 ÷ 300 ° for each revolution of circular rotation and simultaneous rotation of the workpiece relative to the symmetry axis normal to its plane.

In addition, the task is solved by the fact that in the device for the manufacture of FE containing a vessel with a liquid etchant, placed in a thermostat, a lifting and rotating mechanism including an electric motor, on the axis of which a cam is mechanically connected to the movable roller, and a cassette of the floor type with cells for laying blanks, the circular protrusion of the cam has a gentle slope at an angular length of 270 ÷ 300 ° so that an angle of attack of 2 ÷ 17 ° of the etchant flow relative to the surface of the workpiece is provided, and a steep slope, and I have cassette cells height of 1.5 ÷ 3.0 mm.

Figure 1 and 2 shows the movement patterns of the workpiece during the etching process.

Figure 3 shows a diagram of an etching device.

Figure 4 - sketch of a four-link cassette for laying blanks in two projections.

Figure 5 shows the sweep of the trajectory of movement of the workpieces in a circular and reciprocating motion of the cartridge.

Figure 6-9 shows the graphical dependence of the movement L of the workpiece in the etchant stream on the rotation frequency of the cartridge ν for various angles of attack α.

Figure 10 shows the calculated dependence of the angle of rotation of the round billets on the viscosity of the etchant.

A method of manufacturing crystalline elements is implemented in this sequence, see Figs. 1 and 2. A flat preform 1 after machining and washing is placed in a liquid etchant 2 (acidic, alkaline solutions). Provide simultaneous reciprocating and circular movement of the workpiece 1 with a frequency of 0.3 ÷ 0.53 s ^-1 and the angle of attack of the etchant stream 2 relative to the surface of the workpiece 1 within 2 ÷ 17 ° at an angular length of 270 ÷ 300 ° in each cycle of circular movement . In this way, the free-floating mode of the workpiece 1 is predominantly set in the horizontal plane during a rotation of 270–300 ° in each cycle and the workpiece is simultaneously rotated about the axis of symmetry, its normal plane, and etched in this mode at a temperature of, for example, 353 K until the specified thickness of the FE.

The claimed method is implemented using a device that is proposed as a stand-alone invention, figure 3 and 4.

A device for manufacturing CE (Fig. 3) contains a vessel 3 with a liquid etch 2 placed in a thermostat 4, a lifting and rotating mechanism 5, including an engine 6, on the axis of which a cam 7 is placed, mechanically connected to the movable roller 8, and a cartridge 9 ( Fig. 4) a bookcase type with cells 10 for stacking blanks 1. A multi-link cartridge 9 is connected to the axis of the engine 6 through a rod 11 and a standard lock 12. Parts of the cartridge 9 and rod 11 are made of materials resistant to aggressive etchants, for example, nickel and fluoroplastic .

The device is used in this sequence. First, the temperature control of the vessel 3 with the liquid etchant 2 in the thermostat 4 is performed and at the same time the blanks 1 are loaded into the cartridge 9. To load the cartridge 9, the shutter 13 is removed, the necessary number of blanks 1 is placed in the cells 10 between the ties 14 and the jumpers 15 (one in each cell 10 ) and install the shutter 13 in the socket 16 on the base 17. Next, the cartridge 9 is connected to the rod 11, placed in a vessel with a liquid etchant, the rod 11 is fixed in the lock 12, the engine 6 is turned on and the workpieces 1 are etched in dynamic mode for a predetermined time . After etching, the cartridge 9 is removed from the vessel with the etchant, releasing the lock 12, washed and dried by known methods, the shutter 13 is removed and the finished CEs are unloaded.

The proposed technical solutions and the boundaries of their use were established by model calculations and pilot testing in a production environment.

The calculations were performed for blanks in the form of round plates of crystalline quartz. According to [5] in the dynamic mode of rotational and reciprocal motion, the force of attraction mg, the Archimedes force F _A and the force of the dynamic pressure F of the etchant flow act on the plate along the y axis, see FIG. 1:

where a is the acceleration of the plate under the action of these forces;

α is the angle of attack of the etchant stream at the displacement stage shown in FIG. 1;

m is the mass of the plate.

Over time t, the plate moves to a distance L

because the initial velocity of the plate along the y axis, ν ₀ = 0.

We will write forces

where ρ _Tr is the density of the liquid etchant;

V _PL = S · h is the volume of the plate;

v is the speed of movement of the etchant stream relative to the plate;

h is the plate thickness;

S is the plate area (S = π · r ² );

r is the radius of the plate.

окончательно получим формулу для расчета перемещения пластины вдоль оси у на указанном этапеGiven that the density of quartz

finally, we obtain the formula for calculating the movement of the plate along the y axis at the indicated stage

In addition, the plate, rotating with the cartridge relative to the center O around the circumference, experiences the force of internal friction F _century [5] from the side of the liquid etcher, Fig.2.

From the Newton equation, the value of the internal friction force

where η is the viscosity of the liquid etchant;

- изменение линейной скорости пластины вдоль оси х;

- a change in the linear velocity of the plate along the x axis;

S is the area of the plate.

The near and far halves of the plate relative to the center of rotation experience internal friction F ₁ and F ₂ :

where v ₀ , v ₁ , v ₂ are the linear velocities of the plate at the indicated points.

With sufficient accuracy, we can assume that these forces are applied in the center of symmetry of each half, then the rotational moments for these halves

According to the calculation model (figure 2) under the action of internal friction forces, the indicated half of the plate must rotate with different angular accelerations; the plate should roll along an imaginary plane (upward from point 1 in figure 2). However, actually being in the cells between the cassettes of the cassette, the plate will rotate around its axis, overcoming friction - sliding in places of contact with the screeds. This is also confirmed by practical experiments.

The resulting torque giving the plate an acceleration of rotation is

- момент инерции пластины;Where

- moment of inertia of the plate;

m is the mass of the plate;

r is the radius of the plate.

Find the angular acceleration

After substituting 5 expressions 3 and 4, taking into account the relationship between the linear and angular velocity v = 2πRν, we obtain the final formula for accelerating the rotation of the plate around the central axis, its normal plane:

where ν is the angular velocity of rotation of the plate together with the cartridge around the center O, see figure 2.

Essentially, the beneficial effect is due to free swimming and rotation of the workpiece in the etchant stream for a certain time. In this mode, the work surface of the workpiece does not come into contact with structural elements, in addition, the rotation of the workpiece leads to a constant change of the contact points of the working and non-working sections and the structure in sliding mode. This virtually eliminates the appearance of stagnant etching zones in places where the etchant stream is screened by structural elements.

It is known that chemical polishing etching is used to fabricate high-frequency resonators from 10 MHz to 100 MHz and higher. As a rule, flat or lens FEs are used up to 30 MHz, and for higher frequencies, in the form of an inverse mesostructure. Moreover, blanks for such CEs have a thickness of ≥50 μm after mechanical grinding or polishing. The blanks for flat FEs at 10 MHz in the first harmonic, for example, for an AT-slice quartz, have a thickness of 0.18 mm, for a BT-slice - 0.28 mm. Here, the tolerance on the thickness of the workpieces, which is removed at the stage of polishing etching, is taken into account. Such an analysis allows us to establish the boundaries of the use of the proposed technical solution associated with the thickness of the blanks: 0.05 ÷ 0.28 mm To solve the practical problems of piezotechnics at selected frequencies, usually round FEs with diameters of 5–10 mm are used.

Now we analyze the conditions for free swimming of workpieces with the indicated dimensions in the etchant stream according to formula (1).

First, we establish additional conditions. For example, a workpiece with a diameter of 5 mm does not fall out of the cassette cell 10 (see FIG. 4) and does not stop between the jumpers 15 and the ties 14 if the cassette cell height is l≤3.0 mm. This was shown by 15 years of experience using the installation [2] in the production of quartz resonators. On the other hand, it is advisable that workpieces with any of the selected diameters be able to move freely between the jumpers of the cassette cells at the free-floating stage by at least 0.5 l. So we choose the height of the cassette cell 1,5 ÷ 3,0 mm.

Secondly, practical operating experience [2] made it possible to optimize the value of the reciprocating movement of the cartridge with the workpieces in the vessel with the etchant. Two critical points can be distinguished here:

- the consumption of the etchant and the size of the vessel in which the etching is carried out;

- the reliability of operation and the service life of the mechanical pair of the cam 7 and the movable roller 8 in figure 3.

It is established that the coordination of these conditions takes place for the height of the circular protrusion of the cam 7 within 7 ÷ 20 mm

For the proposed technical solution, the reliability of the specified mechanical pair is provided only under the condition that the steep slope of the circular protrusion on the cam 7 (see figure 3 and 5) has an angular length of 60 ° or more. When the angular length of the steep slope of the cam 7 is less than 60 °, the surfaces of the cam 7 and the roller 8 are generated and the device malfunctions. The upper boundary of the angular length of the steep slope of the cam 7, taking into account the smooth transition from the steep slope to the gentle and the accuracy of the manufacture of such an eccentric cam, it is advisable to choose equal to 90 °. Thus, when the rotation of the cartridge with the workpieces at an angular length within 270 ÷ 300 ° is ensured, such an angle of attack of the etchant α (Fig. 1), at which the etchant flow puts the workpieces into free-floating mode.

и 300°, когда

см. формулу (1). Фиг.8 и 9 аналогичны, но соответствуют толщине пластины кварца 0,28 мм.Let us show the reliability of such a statement and determine the boundary values of α in the technological conditions for the fabrication of CE of high-frequency resonators. Figure 6-9 shows graphs of the dependence of the displacement L of the quartz plate (billet) in the etchant stream on the rotation frequency of the cartridge v for various α, calculated by the formula (1). In the calculations, the standard values ρ _sq = 2.65 g / cm ³ and g = 9.8 m / s, as well as the value ρ _tr = 1.12 g / cm ³ obtained in the experiment by weighing the dosed volume of the etchant V _tr at temperature 353K, ρ _sq = m _tr / V _tr , where m _tr is the mass of the etchant. In the experiments, a solution of hydrofluoric acid and butanol - 1 was used in the experiments [6]. 6 and 7 correspond to a plate thickness of 0.05 mm, but the graphs are obtained for two extreme values of the angular length of the workpiece free-floating mode: 270 °, when

and 300 ° when

see formula (1). Figs. 8 and 9 are similar, but correspond to a quartz plate thickness of 0.28 mm.

The analysis of the graphs in Fig.6-9 shows that the theoretical model of the claimed technical solutions is operational in the range of ν = 0.17 ÷ 0.75 s ^-1 and α = 2 ÷ 45 °. However, the boundaries of the movement of the cartridge with the plates vertically 7 ÷ 20 mm and the boundaries of the cells of the cartridge 1,5 ÷ 3,0 mm were set above. Obviously, when moving the cartridge by 20 mm, the maximum movement of the plate will be L = (20-1.5) = 18.5 mm. When moving the cartridge by 7 mm, the minimum movement of the plate will be L = (7-3) = 4 mm. These boundaries are shown in Fig.6-9.

Figure 5 shows the trajectory of the movement of the plate in a circular and reciprocating motion of the cartridge. Here R is the radius on which the plate is placed from the center of rotation O (see figure 2). A similar view has a scan of the cam 7 with a circular protrusion, but with other values of R and α (figure 3). In Fig. 5, a “gentle slope” corresponds to the stage of free swimming of the plate in the etchant at each revolution of the cartridge. At the “steep slope” stage, the cassette quickly moves up and the plate at some point lays on the cassette jumpers, and then again emerges at the “gentle slope” stage. For practical R values within 15–40 mm, the boundary values of the angle α = 2–17 ° are established according to the data in FIG.

Thus, from the graphs in Fig.6-9, you can set the boundary values of the frequency of rotation of the cartridge with the blanks: 0.23 ÷ 0.53 s ^-1 ; 0.24 ÷ 0.58 s ^-1 ; 0.28 ÷ 0.61 s ^-1 and 0.30 ÷ 0.67 s ^-1, respectively. Common to all graphs is the range of values ν = 0.3 ÷ 0.53 s ^-1 , which is selected in the restrictive part of the claims.

The proposed technical solutions were tested in the technological route for manufacturing FE for experimental batches of precision resonators of the AT-cut at a frequency of 10 MHz. The experiments used flat quartz blanks with a diameter of 7.5 mm and a thickness of 0.12 mm after grinding on corundum M5 or mechanical polishing.

We used the basic setup [2] without turning on the reverse, but with a modernized cam 7 (see FIG. 2): a cam 12 mm high, a gentle slope at an angular length of 270 ° with an average diameter of the cam working plane of 30 mm. Chemical etching of the workpieces was carried out at a stabilized temperature of 353 ± 0.5 K in the mode of rotational and reciprocal movement with a frequency of 0.4 s ^-1 in solutions [6]. It should be noted that this mode provides high quality polishing etching, because and when rotating the cartridge with the blanks in one direction, the blanks have additional degrees of freedom - they rotate around the axis of symmetry normal to the planes.

For the first time, this effect was discovered experimentally, and, in addition to the previously indicated ones, it has positive aspects: the rotation of the workpieces around its own axis in swimming conditions is comparable to their cyclic movement along the diameter line, the linear velocities of differently spaced sections of the workpieces from the center of rotation of the cassette O are also aligned, see , for example, points 1 and 2 in figure 2. All this leads to a decrease in the frequency run. In batches of 20 quartz plates for 40 minutes of etching, the frequency spread was 6.5 kHz when etching with 20 microns by the proposed method and 10 kHz in the prototype process [2]. FEs were obtained for resonators at 10 MHz with a roughness of ≤0.03 μm in both cases. However, the level of CE activity in the first case is 15% higher than in the second, under the same measurement conditions. It can be noted that at a frequency of 65 MHz, the frequency spread instead of 10 kHz already exceeds 200 kHz and requires additional sorting of workpieces. In such experiments, stagnant sites are visually observed at the points of contact of the polished workpieces with cartridge elements for the conditions of the prototype in the first 10 minutes of etching. Stagnant areas were not detected during etching by the proposed method.

. Согласно [7] вязкость воды при 80°С равна η=355·10^-6 Па·с. Таким образом, заготовка диаметром 7,5 мм за один оборот кассеты повернется вокруг своей оси на 53°, см. фиг.10. Опыт дает значения угла поворота 32±5°. Разницу можно объяснить наличием трения скольжения в местах касания заготовки со стяжками кассеты, а также наличием внутреннего трения в жидкости.Also in the experiments, the rotation angles φ of the workpieces around their own axis of symmetry were measured. A comparative analysis was carried out for distilled water at a temperature of 353K. Figure 10 shows the dependences of the rotation angle φ of the round billets obtained by the formula (6) at various viscosity values. In this case, the angular length of rotation

. According to [7], the viscosity of water at 80 ° C is η = 355 · 10 ^-6 Pa · s. Thus, the workpiece with a diameter of 7.5 mm in one revolution of the cartridge will rotate around its axis by 53 °, see figure 10. The experiment gives a rotation angle of 32 ± 5 °. The difference can be explained by the presence of sliding friction at the points of contact of the workpiece with cassette ties, as well as the presence of internal friction in the liquid.

In the etching solution [6], the measured values of the angle of rotation for similar conditions are φ = 40 ± 7 °. However, in experiments over 5 turns of the cartridge, the angle of rotation of the workpieces φ exceeds 360 °. It can be assumed that the viscosity of water and acid solution is close at 80 ° C. Unfortunately, it was not possible to obtain exact viscosity values for complex acid solutions.

Thus, the proposed technical solutions provide free swimming and simultaneous rotation of the workpiece relative to the axis of symmetry, its normal plane. This leads to a simplification of the technology and device for its implementation. The operation of sorting workpieces at the etching stages is significantly reduced, as well as the measurement operation during the rejection of finished CE and products, because the spread of their dynamic parameters decreases. The latter provides the use of inventions in the manufacture of precision class resonators.

In the device for manufacturing FE excluded the mechanism of reverse circular motion. The engine here is single-sided and does not require an additional cam pair to control it. The shelf-type cassette, in addition to having a large loading capacity with comparable diameters, is less labor intensive to manufacture. In the manufacture of cassettes, the number of complex folds and new spots for spot welding is reduced. The service life is increased due to the weakening of corrosion in places of stressed joints and the number of such places is reduced.

Information sources

1. Development of technology for the formation of crystalline elements of piezoresonance sensors. Report of the Macrolon Research Institute T-44191, Central Research Institute "Electronics", 1986

2. Patent 1679940, Russia, MKI N 03 N 3/02.

3. Cassette TsL 7803-4041, development of the Research Institute of Instrument Engineering, 04/28/90, Omsk.

4. Patent 2169985, Russia, 7 Н 03 Н 3/02.

5. Trofimova T.I. Physics Course: Textbook for university students. - M .: Higher. school 1985, p. 45-47, 76.

6. Kibirev S.N., Resnenko O.A., Yarosh A.M. Unified technologies of chemical etching in the production of quartz resonators // Radio communication technology. - 1998. Issue 4. - p.148.

7. Enokhovich A.S. Handbook of Physics. M., "Enlightenment", 1978, p.98.

Claims (2)

1. A method of manufacturing crystalline elements, including chemical-dynamic etching of a flat workpiece in a liquid etchant with a circular rotation of the workpiece with a frequency of 0.3 ÷ 0.53 s ^-1 and simultaneous reciprocating movement, characterized in that the angle of attack of the etchant flow relative to the surface the workpieces are selected within 2 ÷ 17 ° and provide the workpiece swimming mainly in the horizontal plane during a rotation of 270 ÷ 300 ° for each revolution of circular rotation and simultaneous rotation of the workpiece relative the symmetry axis normal to the plane. 2. The device for the manufacture of crystalline elements according to claim 1, containing a vessel with a liquid etchant, placed in a thermostat, a lifting and rotating mechanism, including an electric motor, on the axis of which a cam is mechanically connected to the movable roller, and a shelf-type cartridge with stacking cells blanks, characterized in that the circular protrusion of the cam has a gentle slope on an angular length of 270 ÷ 300 ° so that an angle of attack of 2 ÷ 17 ° of the etchant flow relative to the surface of the blanks is provided, and a steep slope, and the cassette cells adayut height of 1.5 ÷ 3.0 mm.

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