JP2007301538A - Ultrasonic cleaner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic cleaner wherein roughly uniform ultrasonic vibration is generated in a cleaning solution in a cleaning tub and contamination of a cleaning object is evenly removed in a short time. <P>SOLUTION: A bottom plate 4 composing a bottom face of the cleaning tub 2 is made of a stainless steel (SUS316 ) plate of 236 mm square and 2 mm thick, and has 108 pieces of piezoelectric ceramics 9 jointed thereto with epoxy resin. One piece of the piezoelectric ceramic 9 is 58 mm in length, 2.0 mm in thickness and 3.0 mm in width. A polarization direction is in the thickness direction. Resonance frequency of a desired vibration mode of only one piezoelectric ceramic 9 is about 460 KHz, while resonance frequency of an ultrasonic vibrator composed by jointing the bottom plate 4 with 108 pieces of piezoelectric ceramics 9 is about 440 KHz. A. C. voltage of a frequency of about 415 KHz is applied to the piezoelectric ceramics via a lead wire from an ultrasonic drive circuit (not shown). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic cleaner.

  Ultrasonic cleaners are used for cleaning various articles such as daily necessities such as glasses and rings, precision mechanical parts used for cameras and watches, and wafers used for manufacturing semiconductor elements. The ultrasonic cleaner is an instrument that removes dirt adhered to an article by immersing the article to be cleaned in a cleaning liquid placed in a container (cleaning tank) and applying ultrasonic waves to the cleaning liquid. The ultrasonic cleaner is composed of a cleaning tank for storing a cleaning liquid, an ultrasonic vibrator for applying ultrasonic waves to the cleaning liquid, and the like. As the cleaning liquid, water, an organic solvent, an acidic solution, or an alkaline solution is used depending on the type of dirt applied to the article.

  1 to 3 are cross-sectional views illustrating a typical configuration of a conventional ultrasonic cleaner described in Non-Patent Document 1. FIG.

  The ultrasonic cleaner shown in FIG. 1 is called a cleaning tank type, and has a configuration in which an ultrasonic transducer 3 is fixed to the bottom surface of a cleaning tank 2 into which a cleaning liquid 1 is placed.

  The ultrasonic cleaner of FIG. 2 is called a cleaning plate type, and has a configuration in which the bottom plate 4 of the cleaning tank 2 is removable and the ultrasonic transducer 3 is fixed to the bottom plate 4. The bottom plate 4 of the cleaning tank is fixed to the bottom of the cleaning tank 2 by a fixture such as a bolt 6 or a nut 7. A packing 5 that prevents the cleaning liquid 1 from leaking is provided at the bottom of the cleaning tank 2.

  The ultrasonic cleaner shown in FIG. 3 is called a throwing vibrator type, and an ultrasonic applicator having a configuration in which the ultrasonic vibrator 3 is fixed to the inner surface of the watertight container 8 inside the cleaning tank 2. It has an arranged configuration.

  In addition to the ultrasonic cleaners shown in FIGS. 1 to 3, the non-patent document 1 includes ultrasonic cleaners having various configurations such as an ultrasonic vibrator attached to the side surface of the cleaning tank. Is described.

  In general, a plurality of ultrasonic vibrators are used in the ultrasonic cleaner except for a small one. For example, in the case of the above-described cleaning tank type ultrasonic cleaner, a plurality of ultrasonic vibrators are fixed to the bottom surface of the cleaning tank. In the case of an ultrasonic cleaner having such a configuration, in order to reduce the occurrence of uneven cleaning of articles, a plurality of ultrasonic vibrators are arranged at high density on the bottom surface of the cleaning tank, It is preferable to ultrasonically vibrate the whole as much as possible (vibrates in the vertical direction). However, in general, the upper limit of the number of ultrasonic transducers to be used is determined in consideration of the manufacturing cost of the ultrasonic cleaner.

  In the case of an ultrasonic cleaner equipped with a plurality of ultrasonic vibrators, each ultrasonic vibrator has a large contact area with the bottom surface in order to vibrate the entire bottom plate of the cleaning tank as uniformly as possible. That is, a horizontally long shape (eg, a plate-like piezoelectric vibrator) is considered suitable.

  In patent document 1, the ultrasonic cleaner of the structure by which the plate-shaped ultrasonic vibrator was fixed to the bottom face of the washing tank made from porcelain via the acoustic matching layer was disclosed, and by forming the washing tank from porcelain It is said that cleaning using a chemical solution using a corrosive chemical solution can be realized.

  In Patent Document 2, an ultrasonic transducer having a structure in which a plurality of prismatic piezoelectric bodies are aligned in a synthetic resin and sandwiched between a pair of electrodes on a bottom surface of a cleaning tank is fixed. A sonic cleaner is disclosed, and the above-mentioned prismatic piezoelectric body has higher electromechanical conversion efficiency than a plate-like piezoelectric body, and an ultrasonic vibrator provided with this piezoelectric body has a high-frequency superhigh frequency of about 1 MHz or more. It is said that since the sonic wave can be oscillated in the cleaning tank, the submicron dirt can be easily cleaned. However, when the ultrasonic radiation area exceeds 25 square centimeters, it is very difficult to manufacture the ultrasonic vibrator, and naturally it becomes expensive. In addition, it becomes more difficult to manufacture an ultrasonic transducer having a frequency of 500 KHz or less.

Patent Document 3 discloses a piezoelectric vibrator in which an acoustic vibration control material having a configuration in which high-elastic fibers are arranged and arranged in a base material resin is bonded. The highly elastic fiber of the acoustic vibration control material transmits acoustic vibration that vibrates in a direction orthogonal to the length direction. For this reason, it is supposed that the vibration direction of the piezoelectric vibrator can be controlled in a direction orthogonal to the length direction of the highly elastic fiber of the acoustic vibration control material.
Hiroyuki Futahashi, “Latest Powerful Ultrasonic Technology”, first edition, General Technology Center, Inc., September 1987, p. 223-224, p. 228-232 JP 2001-29907 A (FIG. 1) Japanese Patent Publication No. 5-83313 JP 7-284198 A

  As described above, the bottom surface of the cleaning tank is uniformly superposed to some extent by a plurality of ultrasonic vibrators or a plurality of vibration parts (parts having respective piezoelectric bodies) of the ultrasonic vibrator described in Patent Document 3. Since the sound waves can be vibrated, the occurrence of uneven cleaning can be reduced. However, efficient cleaning cannot be performed unless the resonance frequency of the ultrasonic transducer is accurately tracked. However, when there are a plurality of ultrasonic transducers, since the natural frequencies of the ultrasonic transducers are different, it is not possible to operate all the ultrasonic transducers efficiently. Furthermore, since ultrasonic vibration nodes are generated in the cleaning liquid, a place having a small cleaning ability is created depending on the place.

  In particular, in an ultrasonic cleaner exceeding 100 KHz, the ultrasonic vibrator generates a large amount of heat, and the temperature of the cleaning liquid may increase. Furthermore, there is a problem that power is consumed greatly.

  Since the ultrasonic cleaner is used for cleaning an article that needs to be cleaned extremely uniformly, such as a wafer for manufacturing a semiconductor element, it is desirable to further reduce the occurrence of cleaning unevenness.

  Accordingly, an object of the present invention is to provide an ultrasonic cleaner that consumes less power and can reduce the occurrence of cleaning unevenness.

  In the piezoelectric ceramic bonded to the elastic plate that applies ultrasonic vibration to the cleaning liquid, the shape of the surface that radiates ultrasonic waves is rectangular, and the rectangular long side of the piezoelectric ceramic is perpendicular to the thickness of the piezoelectric ceramic. The length is 2 times or more of the thickness direction, the width direction is less than 1 time, and there are a plurality of piezoelectric ceramics bonded to the elastic plate, and the elastic plate is made of metal and its thickness is 5 mm or less. This is an ultrasonic cleaning apparatus.

  An ultrasonic cleaning device in which the frequency of the voltage applied to the piezoelectric ceramic is smaller than the resonance frequency of the ultrasonic vibrator of the ultrasonic cleaning device containing the cleaning liquid, and the driving frequency is 85% to 98% of the resonance frequency; To do.

  The ultrasonic cleaning apparatus in which the voltage applied to the piezoelectric ceramic is an alternating current of 100 KHz or more.

  First, an ultrasonic cleaner having a configuration of the present invention will be described with reference to the drawings. FIG. 4 is a plan view of the bottom plate of the ultrasonic cleaner having the configuration of the present invention, which is a cleaning plate type in which the bottom plate is removable. A piezoelectric ceramic is bonded to the bottom plate. FIG. 5 is a side view thereof. FIG. 6 is a perspective view of the piezoelectric ceramic bonded to the bottom plate. FIG. 7 is a side view of an ultrasonic cleaner using the bottom plate shown in the plan view of FIG.

  The bottom plate 4 constituting the bottom surface of the cleaning tank 2 is a stainless steel (SUS316) plate having a 236 mm square and a thickness of 2 mm. Then, 108 piezoelectric ceramics 9 are joined to a stainless steel (SUS316) plate using an epoxy resin. One piezoelectric ceramic 9 has a length of 58 mm, a width of 2.0 mm, and a thickness of 3.0 mm. The polarization direction is the thickness direction. The resonance frequency of the desired vibration mode of only one piezoelectric ceramic 9 is about 460 KHz. However, the resonance frequency of the ultrasonic vibrator configured by joining the bottom plate 4 and 108 piezoelectric ceramics 9 is about 440 KHz. is there.

  Silver electrodes are provided on both sides of the piezoelectric ceramic 9 in the plate thickness direction. The surface of the piezoelectric ceramic 9 in contact with the stainless steel plate is connected to the ground. Connect the opposite side in parallel with all lead wires.

  The bottom plate having the above structure is attached to the cleaning tank with bolts with a packing interposed therebetween. Then, the cleaning solution is put into a cleaning tank.

  Next, an AC voltage from 400 KHz to 500 KHz was applied to the ultrasonic transducer through a lead wire with a constant current value from an ultrasonic drive circuit (not shown), and the sound pressure was measured. As a result, the sound pressure was highest at about 415 KHz and 475 KHz as indicated by the solid line in FIG.

  However, as indicated by the dotted line in FIG. 8, the input power at about 415 KHz is about 200 W, but at 475 KHz it is about 1100 W. From this, it can be seen that the ultrasonic wave was most efficiently applied to the cleaning liquid at about 415 KHz.

  FIG. 9 shows the result of measuring the frequency characteristics of the ultrasonic vibrator of the ultrasonic cleaner when the cleaning liquid is added. The resonance frequency at that time is about 440 KHz, and the anti-resonance frequency is about 475 KHz. there were.

  Here, looking at the relationship between the frequency and the sound pressure in FIG. 8 once again, the peak indicated by B in the figure almost coincides with the resonance frequency. In addition, the peak indicated by C in the figure almost coincides with the antiresonance frequency. In the peak of about 415 KHz of A in the figure, it is considered that vibration that can excite longitudinal vibration in the cleaning liquid very efficiently is generated in the stainless steel plate. In order to obtain the same magnitude as the sound pressure indicated by A at the resonance frequency of B, it is necessary to apply a power of 600 W or more, which is approximately three times or more. In addition, the peak indicated by C in the figure requires 1100 W at the antiresonance frequency, and 5 times or more of power is required for A.

  The vibration mode at the resonance frequency of about 440 KHz of the ultrasonic transducer is considered to be as shown in FIG. The vibration displacement of the piezoelectric ceramic is considered to be the largest. On the other hand, the vibration mode of about 415 KHz that can impart ultrasonic vibration to the cleaning liquid most efficiently is considered to be the mode in which the stainless steel plate vibrates most in the direction perpendicular to the surface as shown in FIG. At the resonance frequency of about 440 KHz of the ultrasonic vibrator of the ultrasonic cleaning device, the admittance is the maximum and the most current flows, but the sound pressure is not the maximum. This indicates that the longitudinal vibration is not efficiently excited on the stainless steel plate in contact with the cleaning liquid. On the other hand, at about 415 KHz, the power is less than half compared to about 440 KHz, but the sound pressure is maximized. This is presumed that the stainless steel plate mainly vibrates.

  Here, the vibration mode of the resonance frequency of the ultrasonic vibrator and the frequency of the mode in which the stainless steel plate vibrates most in the direction perpendicular to the surface are not greatly different. This is because vibration displacement cannot be imparted to the stainless steel plate at a frequency that is significantly different from the resonance frequency. From this, the frequency of the mode in which the stainless steel plate vibrates most in the direction perpendicular to the surface is considered to be 85% to 98% of the resonance frequency.

  The resonance frequency of the ultrasonic vibrator of the ultrasonic cleaning device is about 440 KHz, and an inductance value is determined so that the resonance frequency including this inductance is about 415 KHz by connecting the inductance in series with the ultrasonic vibrator. . An equivalent circuit near the resonance frequency of the ultrasonic transducer is shown in FIG. In FIG. 12, Cd represents a braking capacity, Rm represents an equivalent resistance, Cm represents an equivalent capacity, and Lm represents an equivalent inductance. The equivalent circuit of the ultrasonic transducer is described in detail in Non-Patent Document 2. As shown in FIG. 13, the inductance value for setting the resonance frequency to about 415 KHz is about 3.6 μH. This inductance also reduces the braking capacity of the ultrasonic transducer. This can reduce reactive power. For reference, the inductance value for canceling the braking capacity is about 7.4 μH, and the resonance frequency including the inductance at this time is about 400 KHz. Accordingly, the frequency becomes too low to be driven at a desired level of about 415 KHz and cannot be employed.

Takuro Ikeda, “Basics of Piezoelectric Materials”, Ohm Co., Ltd., November 1984, p. 99-102

  The frequency characteristics of the equivalent circuits shown in FIGS. 12 and 13 are shown in FIG. The frequency characteristics of the equivalent circuit shown in FIG. 12 are indicated by solid lines, and the frequency characteristics of the equivalent circuit shown in FIG. 13 are indicated by dotted lines. It can be seen from this frequency characteristic that impedance is further reduced and power consumption is reduced by connecting an inductance in series with the ultrasonic transducer.

  The frequency at which the sound pressure is highest is smaller than the resonance frequency, and the magnitude is desirably 85% to 98% of the resonance frequency. This is because when it is smaller than 85%, the inductance connected to the ultrasonic transducer is too large to cancel the braking capacity. If the resonance frequency exceeds 98%, the resonance mode of the ultrasonic transducer is expected to be excited, and if the resonance mode is excited, a large amount of power is required.

  On the other hand, the conventional ultrasonic cleaning apparatus has the highest sound pressure at the resonance frequency of the ultrasonic vibrator, and therefore the resonance frequency is reduced when the damping capacity is canceled or the inductance to be reduced is connected in series. It becomes impossible to drive at the highest frequency of sound pressure. For this reason, since there is no choice but to drive at the resonance frequency of the ultrasonic vibrator and the braking capacity cannot be canceled or reduced, the power efficiency is lowered because invalid power must be supplied.

  When the above circuit configuration is used for the configuration of the ultrasonic cleaning device of the present invention, the efficiency of applying ultrasonic vibration to the cleaning liquid is enhanced along with the effect of the vibration mode of the ultrasonic vibrator of the ultrasonic cleaning device. The damping capacity of the ultrasonic transducer is reduced and the electrical efficiency is improved. Therefore, since the required electric capacity of the ultrasonic drive circuit is reduced, the ultrasonic drive circuit can be manufactured at low cost. Moreover, since the electric power supplied to the ultrasonic transducer can be reduced, it becomes an energy saving measure.

  That is, the resonance frequency of the ultrasonic transducer and the frequency with the highest sound pressure are different, and the frequency with the highest sound pressure is lower than the resonance frequency of the ultrasonic transducer.

  In order to achieve such a configuration, it is necessary that the thickness of the stainless steel plate is small and easy to bend, and the thickness of the stainless steel plate is 10 mm or less, preferably 5 mm or less.

  Further, it is possible to approximate the waveform applied to the ultrasonic transducer to a sine wave by connecting a capacitance to the inductance.

  Although the interval between adjacent piezoelectric ceramics is not shown in FIG. 4, the length direction is about 4 mm and the width direction is about 3 mm. Piezoelectric ceramics and piezoelectric ceramic stainless plates are susceptible to bending vibration.

  Further, at least 5 or more, preferably 10 or more piezoelectric ceramics are arranged on the same ultrasonic radiation surface, and the resonance frequency of the ultrasonic vibrator depends on the shape and arrangement of the piezoelectric ceramic and the material and shape of the bottom plate. The frequency with the highest sound pressure is different, and the frequency with the highest sound pressure is smaller than the resonance frequency of the ultrasonic transducer.

  Such an ultrasonic cleaning device having different resonance frequencies of the ultrasonic transducers and the highest frequency of the sound pressure has a completely new configuration.

  As described above, by controlling the thickness of the metal plate to which the piezoelectric ceramic is bonded and the shape and arrangement of the piezoelectric ceramic, it is possible to propagate ultrasonic vibrations almost uniformly in the liquid in the cleaning tank, and to the piezoelectric ceramic. An ultrasonic cleaner capable of reducing the applied power can be provided.

  The ultrasonic cleaner of the present invention can be used for cleaning various objects.

  It is sectional drawing which shows the structural example of the conventional ultrasonic cleaner.   It is sectional drawing which shows another structural example of the conventional ultrasonic cleaner.   It is sectional drawing which shows another structural example of the conventional ultrasonic cleaner.   It is a top view which shows the baseplate of the ultrasonic cleaner of this invention.   It is a side view which shows the baseplate of the ultrasonic cleaner of this invention.   It is a perspective view of the piezoelectric ceramic joined to the bottom plate of the ultrasonic cleaner of the present invention.   It is a side view of the ultrasonic cleaner of the present invention.   It is a figure which shows the frequency characteristic of the sound pressure of the ultrasonic cleaner of this invention, and input electric power.   It is a figure which shows the frequency characteristic of the ultrasonic transducer | vibrator of the ultrasonic cleaner of this invention.   It is the schematic which shows the vibration displacement of about 440 KHz stainless steel plate.   It is the schematic which shows the vibration displacement of the stainless steel plate of about 415 KHz.   It is a figure which shows the equivalent circuit of the resonance frequency vicinity of an ultrasonic transducer | vibrator.   It is a figure which shows the equivalent circuit which connected the inductance to the ultrasonic transducer | vibrator.   It is a figure which shows the frequency characteristic of the equivalent circuit shown in FIG. 12, FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cleaning liquid 2 Cleaning tank 3 Ultrasonic vibrator 4 Bottom plate 5 Packing 6 Bolt 7 Nut 8 Watertight container 9 Piezoelectric ceramic 10 Bolt hole 11 Vibration displacement of stainless steel plate

Claims (3)

  In the piezoelectric ceramic bonded to the elastic plate that applies ultrasonic vibration to the cleaning liquid, the shape of the surface that radiates ultrasonic waves is rectangular, and the rectangular long side of the thickness of the piezoelectric ceramic orthogonal to the radiation surface is The length is 2 times or more of the thickness direction, the width direction is less than 1 time, and there are a plurality of piezoelectric ceramics bonded to the elastic plate, and the elastic plate is made of metal and its thickness is 5 mm or less. An ultrasonic cleaning apparatus characterized by being:   The frequency of the voltage applied to the piezoelectric ceramic is smaller than the resonance frequency of the ultrasonic vibrator of the ultrasonic cleaning apparatus containing the cleaning liquid, and the drive frequency is 85% to 98% of the resonance frequency. Item 2. The ultrasonic cleaning apparatus according to Item 1.   The ultrasonic cleaning apparatus according to claim 1 or 2, wherein a voltage applied to the piezoelectric ceramic is an alternating current of 100 KHz or more.

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