WO2003051542A1 - Ultrasound cleaning using cyclically-variable static pressure and subsequent drying - Google Patents

Abstract

The method and corresponding device serve to carry out efficient ultrasound cleaning of solid material (8) for cleaning, located in a gas-tight sealable ultrasound vessel, in the form of a vacuum/pressure recipient (20), along with the cleaning agent (6). In a cyclical process said recipient (20) is evacuated and pressurised. Under reduced pressure, generated by means of a vacuum pump (26), the material (8) for cleaning, which can optionally be located within a frame (9), is freed of gas bubbles. The latter may be stuck in nooks with only one entrance and hidden structures within the material for cleaning. On pressurisation, generated by means of a compressor pump (23), an efficient ultrasound cleaning is carried out as a result of an increased cavitation effect and simultaneous compression of the residual gas in the inaccessible nooks. The ultrasound transducer (2, 2'), mounted on the vacuum/pressure recipient (20), may optionally be operated in the reduced pressure phase to increase the clearance of the gas bubbles. The evacuation and pressurisation of the vacuum/pressure recipient (20) can optionally be repeated several times under control of control means (29). Exchange of the material (8) for cleaning, optionally located within a frame (9), can optionally be carried out automatically, by means of an automated device (27) on the lid (21) of the vacuum/pressure recipient (20) and an unlatching mechanism (28) on the device (7) for exchange of material (7) for cleaning and a corresponding unlatching mechanism (28') on the frame (9). The construction of the cyclically-operated vacuum/pressure recipient (20) permits the gas volume above the cleaning agent (6) to be replaced after the last cleaning cycle with a solvent vapour for reducing surface tension. The possibility of rapidly and efficiently drying the material (8) for cleaning after removal from the cleaning agent as a result of the Marangoni effect is thus provided.

Description

 Ultrasonic cleaning with cyclically variable static pressure and subsequent drying

introduction

The invention relates to a method and an apparatus for

Ultrasonic cleaning of mechanical, electronic and optical components and subsequent drying of the same. It is based on the basics of

Ultrasonic cleaning technology, conveyor technology, pneumatics, vacuum technology and marangoni drying.

The method of ultrasonic cleaning is well known. It is particularly successfully used where sensitive surfaces have to be cleaned efficiently and gently. In particular, ultrasonic cleaning brings great advantages in removing very small particles with sizes below 10 nm compared to most other cleaning processes, such as mechanical or chemical particle separation.

The cleaning effect of ultrasound treatment is based on several mechanisms. The increase in the mobility of the cleaning agent along the surface to be cleaned and the acceleration of the items to be cleaned in the ultrasonic field lead to an increase in the cleaning effect compared to the stationary sample. The so-called cavitation is mainly responsible for the cleaning effect. This means the formation and imploding of solvent bubbles in the ultrasonic field: during the negative pressure phase of the ultrasonic signal, the vapor pressure of the cleaning agent is briefly fallen below, which leads to the formation of boiling-like vapor bubbles. (This effect has an analogy to foaming when opening a CO ₂ -containing mineral water bottle.) They fall during the positive ultrasound pressure phase Bubbles back together to form shock waves. These bubble implosions in the vicinity of the contaminated surface exert a force on the particles and thus cause them to lift off. The bladder implosion is therefore primarily responsible for the cleaning effect.

It is due to the work of O.V. Sukhar'-kov, "Effect of the Temperature of an Aqueous Caustic Solution on the Duration of Cleaning in the Field of a Hydrodynamic Reactor", Russ-Ultrason. Vol. 18, No. 4, p. 197-199, (1988) This publication explains that an increase in the temperature leads to a decrease in the erosion activity, and this strange result - if the temperature was expected to have a better cleaning effect - is caused by the fact that the bubbles form as the temperature increases It is clear that lowering the static pressure above the solvent can also promote the formation and disappearance of the bubbles. Consequently, lowering the static pressure leads to a weakening Conversely, increasing this static pressure, that is, the stationary pressure above the Detergent, an increase in the cavitation-related cleaning effect. The principle of ultrasonic cleaning is detailed by L.D. Rozenberg discussed. The two-volume Russian work is by J.S. Wood has been translated into English ("Physical Principles of Ultrasonic Technics, Plenum Press, New York, 1973). Especially in the article by B.A. Agranat et al. (p. 246) in Volume I, Part III, "Ultrasonic Cleaning", the influence of cavitation on the size of the bubbles, the temperature and the static pressure above the cleaning agent is treated. An increase in pressure to 0.3 bar leads to an increase in the Cavitation It should be noted, however, that if the pressure increases further, the cavitation effect will decrease again, which is due to the prevention of blistering.

An ultrasonic cleaning method is known in which work is carried out not under an open but under a vacuum-tight vessel under reduced pressure. By lowering the pressure, the air is removed from hidden structures of the items to be cleaned, so that the surface of the items to be cleaned Cleaning agents can come into better contact. Thus, this measure means that good wetting of the items to be cleaned by the cleaning agent can be achieved even if, for example, finely structured bulk goods or components with niches which are only accessible on one side. Mention should be made of U.S. Patent No. 4,193,818 to Jack H. Joung et al. on "Combined Ultrasonic Cleaning and Biocidal Treatment in a Single Pressure Vessel" from 1980. In addition to ultrasonic cleaning (ultrasonic clean), the patent mentioned also works under reduced pressure even at elevated pressure, but not in combination with the effect of ultrasound, but independently of which, as a bacteria-killing heat treatment of the cleaned goods (biocidal treatment).

The drying of the items to be cleaned is usually accomplished by removing the latter from the detergent bath. It is also possible in single-bath systems to lower the level of the solvent instead of removing the items to be cleaned.

In addition to the conventional drying of the items to be cleaned by applying heat and the action of dry gas, this is a very efficient one

Drying process well known. It is the so-called Marangoni

Effect. The same is based on a reduction in the surface tension in the area of

Detergent-gas interface during the extraction of the items to be cleaned. Under

The action of a surface tension reducing substance on the so-called meniscus completely detaches the detergent skin on the items to be cleaned from the surface. It is due to the theoretical work of O. Ziranov et al. "A model for the thermal Marangoni drying" in Journal of Engineering Mathematics, Vol. 40, p.

249 (2001) and by O.K. Matar and R.V. Craster "Model for Marangoni drying" in

Physics of Fluids, vol. 13, p. 1869 (2001). The process results in an ultra-dry surface for semiconductor wafers. A drying of the

Cleaning items are no longer required.

The applicability of the Marangoni effect presupposes that a chemical substance is used in the area of the meniscus, which in the Detergent is readily soluble and leads to an efficient reduction of the surface tension. Isopropanol or ethanol, for example, is well suited as a surface tension-reducing substance (hereinafter referred to as solvent vapor).

The effect of the solvent vapor on the meniscus is caused, for example, by spraying or by establishing an appropriate gas atmosphere. It should be noted that the cleaning agent bath is not significantly contaminated with the solvent. This can be achieved by using the solvent locally precisely in the area of the meniscus (US Pat. No. 5,660,642 (1997) "Moving zone Marangoni drying of wet objects using naturally evaporated solvent vapor" by JABritten; European Patent Application No. 1 039 506 A2 (2000) "Apparatus for cleaning and drying substrates" by B. Fishkin and M. Sherrard; US Patent No. 6,170,495 Bl (2001) "Apparatus for treating Substrates using the Marangoni effect" by AFM Leenaars and JJ Van Oekel). Another possibility is that the evaporated solvent, optionally together with a carrier gas, is in a closed gas space above the cleaning bath with the cleaning agent (US Pat. No. 5,807,439 (1998) "Apparatus and method for improved washing and drying of semiconductor wafers" by H. Akatsu and R. Ramachandran). The gas space can additionally be separated from the bath by a plate (US Pat. No. 6,273,100 B1 (2001) "Surface cleaning apparatus and method", M.T. Andreas and M.A. Walker).

task

For economic reasons, it is important to achieve the most efficient cleaning effect possible with minimal ultrasound power and little time. It is also important to carry out the subsequent drying as efficiently as possible. It is an object of the invention to provide a method and a device which, in this respect, are compared to existing ultrasonic cleaning methods

Brings advantages and can be integrated into an efficient drying process.

The object is achieved by the method described in claim 1 by means of a device as shown in claim 9.

Description of the invention

The invention will be described with reference to the following drawings:

Fig. 1 shows the structure of conventional ultrasonic bath

Fig. 2 shows an example of an embodiment of the inventive vacuum pressure recipient with an integrated ultrasound device.

3 illustrates a cleaning product arrangement with a niche which is only accessible from one side and a hidden structure.

A conventional ultrasonic bath consists, as shown in FIG. 1, of an open, trough-shaped vessel 1, which is provided on the bottom with one or more powerful ultrasonic transducers 2, 2 ', the latter being connected to an oscillator 3 with power level 4. A cleaning agent exchange device 5 for the automatic or manual change of the cleaning agent 6 is optionally present, as well as a cleaning item exchange device 7 for the automatic or manual change of the cleaning item 8. The latter may be located in a basket-like frame 9.

In contrast to the conventional ultrasonic bath with a trough-shaped vessel 1, the inventive device in the form of a vacuum pressure recipient 20, as described with reference to FIG. 2, is not open, but can be closed gas-tight with a lid 21. The same is further via a pressure line 22 and one Pressure pump 23 or one or more pressure bottles 24, 24 'to increase the static pressure above the cleaning agent 6 with the items to be cleaned 8 in connection. The vacuum pressure recipient 20 is also connected to a vacuum pump 26 via a vacuum line 25. The latter devices allow a lowering of the static pressure above the cleaning agent 6. To control or handle the pressure pump 23, respectively. of the pressure bottles 24, 24 ', and the vacuum pump 26, means 29 are present which permit an optional operation of these elements 23, 26, respectively. 24, 24 'allow and if necessary additionally allow the control of the ultrasonic transducers 2, 2'.

The cleaning agent may be water, an aqueous solution or an organic solvent, optionally with additives.

The device described allows, after filling the cleaning agent 6 with the help of the cleaning agent exchange device 5 and the

Immersing the items to be cleaned 8 with the aid of the items to be exchanged for items to be cleaned 7 and after the vacuum pressure recipient 20 has been closed by the cover 21, initially to lower the static pressure. As already mentioned, the

Air is removed from hidden structures of the items to be cleaned 8, so that the surface thereof can come into better contact with the cleaning agent 6. However, it must be ensured that the pressure does not fall below the vapor pressure of the

Detergent is reduced, otherwise boiling starts. It is also important that the pressure is reduced slowly in order to prevent the foam from foaming

Detergent because of the release of dissolved gases, on the other hand to prevent hypothermia or even freezing of the detergent 6.

After the items 8 to be cleaned are practically completely wetted, the pressure above the cleaning agent is raised to the pressure range for efficient ultrasound cleaning: the effectiveness of the ultrasound cleaning is increased by more intensive cavitation. The pressure increase not only has the advantage of more efficient ultrasonic cleaning. In addition, the residual gas remaining in niches 31 (blind holes) and hidden structures 32 (FIG. 3) of the items to be cleaned that are only accessible on one side is compressed despite the vacuum treatment, so that the contact area between the items 8 to be cleaned and the cleaning agent 6 is increased. It may be appropriate to switch on the ultrasonic transducer 2 already in the negative pressure phase, since although the simultaneous effects of vacuum and ultrasound do not favor the cavitation, the expulsion of gas bubbles in hidden structures of the items to be cleaned 8 is supported.

The one-time evacuation of the vacuum pressure recipient 20 and its one-time increase in pressure may well lead to a satisfactory cleaning result in certain cases. As a rule, however, it will be advantageous to repeat the vacuum pressure treatment in several cycles. It may also be appropriate to replace the cleaning agent 6 one or more times. This cleaning agent exchange can also be carried out during the vacuum or pressure phase, but in particular this exchange should be carried out during the normal pressure intermediate phase.

The cyclical change in the static pressure in the vacuum pressure recipient 20 brings the following advantage: Because the residual gas can be compressed in hidden structures 32 - and primarily in recesses 31 that are only accessible from one side - the cleaning agent 6, which was contaminated in the previous cleaning phase, becomes expelled during the renewed negative pressure phase. In the subsequent overpressure phase, it is replaced by new cleaning agent 6. This process is particularly effective if the cleaning agent is completely or at least partially replaced via the cleaning agent exchange device 5 before the printing phase. If necessary, a flood valve 5 'allows flooding of the vacuum pressure recipient 20 when the cleaning agent is replaced.

It is also conceivable that the cleaning agent in the vacuum pressure recipient 20 does not have to be replaced during the cleaning process. This is particularly true when the original contamination of the items 8 to be cleaned is only slight and consequently the cleaning agent is only slightly contaminated. In this case, it is advisable to evacuate the vacuum pressure recipient 20 only once, namely after immersing the items 8 to be cleaned in the cleaning agent 6 to expel the residual gas from only one side Niches 31 and hidden structures 32 (Fig. 3). On the other hand, it makes sense to use the pressure several times, since in the printing phase the cleaning agent 6 is compressed in the niches 31, which are only accessible from one side, and then expelled from the niches 31 again as contaminated cleaning agent in the non-pressurized phase.

The ultrasound exposure by means of the ultrasound transducers 2, 2 ′, which are attached to the vacuum pressure recipient 20, can take place during one or more overpressure phases or additionally during at least one underpressure phase. According to the article by B.A. Agranat et al. in volume I of the work of L.D. Although Rozenberg only leads to increased cavitation due to the static overpressure, the use of ultrasound also has advantages in the negative pressure phase: Adhesion-related bubbles adhering to hidden structures of the items to be cleaned 8 when wetted by the cleaning agent 6 become, as already mentioned, under the action of ultrasound more easily detached, although the cavitation effect is reduced compared to that at normal static pressure.

The device initially appears to be similar to that described in U.S. Patent No. 4,193,818. In that document, as in the present invention, there is a closable ultrasound vessel which can be operated both in the negative pressure range and in the case of excess pressure. According to US Pat. No. 4,193,818, the removal of gas inclusions in hidden structures of the items to be cleaned is carried out under reduced pressure. However, it is obviously accepted that the efficiency of the cavitation effect is reduced. The subsequent overpressure phase in the recipient is not used to increase cavitation in any way, but only to kill bacteria (biocidal treatment). In contrast to that method, in the present case the vacuum phase is used in a cyclical method for the efficient removal of gas inclusions, while the efficient ultrasonic cleaning is carried out in the phase of increased pressure. US Pat. No. 4,193,818 shows that the batch change is carried out manually. An indirect batch change would hardly make sense for cleaning and sterilizing medical cutlery. In the present case, however, an automatic batch change is indicated. For this reason, a release mechanism 28 for the automatic opening and closing of the vacuum pressure recipient 20, as well as for automatic handling of the items to be cleaned 8 on the items to be cleaned, and a corresponding release mechanism 28 'on the frame 9 are provided as a variant ,

It should be noted that both the vacuum phase and the overpressure phase do not place high demands on the pump devices 23, 26. Because of the risk of the cleaning agent 6 boiling, the pressure during the evacuation phase must not be reduced below its vapor pressure, which is 15 mbar in water, for example. Furthermore, it does not make sense to let the pressure rise significantly in the overpressure phase, since it is known that the efficiency of the cavitation is reduced again at high pressure. It is therefore not necessary to make high demands on the tightness and pressure resistance of the system. These conditions are important for the creation of an inexpensive, automatically controlled vacuum pressure recipient (20).

In addition to effective cleaning, the cyclically operable vacuum pressure recipient 20 also allows the items to be cleaned 8 to be dried quickly and efficiently. For this purpose, the gas space 10 above the surface of the cleaning agent 6 is first pumped off after the last cleaning phase and then by the vapor of a surface tension lowering substance (hereinafter referred to as solvent vapor), for example isopropanol or ethanol. The solvent vapor is optionally contained in a carrier gas, for example in air or an inert gas such as nitrogen. After the gas exchange, either the detergent level is lowered by pumping out via the detergent exchange device 5, respectively. the items to be cleaned 8 are lifted out of the detergent 6 for drying by lifting by means of the items to be exchanged for items to be cleaned. The lid 21 of the vacuum pressure recipient 20 remains closed during this drying phase. The The presence of the surface tension-reducing solvent vapor in the area of the detergent-gas space boundary, in the so-called meniscus, causes the items to be cleaned to dry quickly and efficiently 8 due to the Marangoni effect.

The Marangoni effect is based on a local reduction in the

Surface tension in the meniscus and thus causes the wetting to withdraw into the cleaning agent. As already mentioned, care must be taken to ensure that the solvent vapor is either very local to the meniscus or only briefly in contact with the cleaning agent. Otherwise, the cleaning agent is contaminated by the solvent vapor and thus the Marangoni effect is reduced, respectively. prevented. The pressure pump 23 already present in the presented vacuum pressure recipient 20, respectively. Pressure bottles 24, 24 ', and the vacuum pump 26 enable the solvent vapor to be introduced quickly into the vacuum pressure recipient 20 before and the solvent vapor to be removed quickly after drying. For this purpose, in the pressure line 22, which connects the pressure pump 23 to the vacuum pressure recipient 20, there is a supply device 33 for the solvent vapor or in one of the gas bottles 24, 24 'a gas corresponding to the solvent vapor. There is also the possibility of connecting a gas bottle 24 'or the flood valve 5' upstream or downstream of a solvent vapor supply device 34, for example in the form of a gas washing bottle. It may be advantageous to remove the solvent vapor from the gas which exits the vacuum pressure recipient 20 by means of a solvent vapor trap 35 by condensation or adsorption. It could protect the vacuum pump 26 and the environment. Since the solvent vapor is small amounts, this collecting device 35 can be dispensed with if necessary.

Claims

claims 1. A method for cleaning solid items to be cleaned by means of the ultrasound method by sonicating the items to be cleaned and mixed with cleaning agents, characterized in that the items to be cleaned are enclosed in a gas-tightly sealable vacuum pressure recipient, which alternates in a cyclical process evacuated and pressurized. 2. A method for cleaning solid items to be cleaned according to claim 1, characterized in that - The items to be cleaned are immersed under reduced pressure after immersion or re-immersion in the cleaning agent, so that gas bubbles which adhere in niches which are only accessible from one side and to hidden structures of the items to be cleaned can be expelled and - The pressure above the cleaning agent is increased in the overpressure area and the cleaning items are sonicated with ultrasound, so that efficient ultrasound cleaning takes place. 3. A method for cleaning solid items to be cleaned according to claim 1, characterized in that - the items to be cleaned after immersion in the cleaning agent are placed under reduced pressure and simultaneously sonicated with ultrasound, so that gas bubbles in only one-sided niches and hidden structures of the items to be cleaned cling, can be expelled efficiently and - the pressure above the cleaning agent in the overpressure area is increased and the cleaning items are sonicated with ultrasound, so that an efficient ultrasound cleaning can take place. 4 A method for cleaning solid items to be cleaned according to one of claims 1, 2 or 3, characterized in that the change of the items to be cleaned is carried out automatically. 5 A method for cleaning solid items to be cleaned according to one of claims 1, 2, 3 or 4, characterized in that the cleaning agent is filled or replaced at least once. 6 A method for cleaning solid items to be cleaned according to one of claims 1, 2 3, 4 or 5, characterized in that the cyclical process for alternately evacuating and pressurizing the vacuum pressure recipient consists of a single vacuum pressure cycle. 7. The method for cleaning solid items to be cleaned according to one of claims 1, 2 3, 4 or 5, characterized in that the cyclic process for alternately evacuating and pressurizing the vacuum pressure recipient from a single vacuum, but several pressure Cycle exists. 8. The method for cleaning solid items to be cleaned according to one of claims 1, 2 3, 4, 5, 6 or 7, characterized in that after the last cleaning phase, the vacuum pressure recipient is mixed with a surface tension-reducing solvent vapor, so that on the ground the Marangoni effect dries the items quickly and efficiently after removing them from the detergent. 9. Device for performing a method according to one of claims 1 to 8 for the cleaning of solid, optionally in a frame (9) located, items to be cleaned (8), which can be closed in a gas-tight manner with a lid (21) in the form of an ultrasound vessel vacuum pressure Recipient (20) with attached or inserted ultrasonic transducers (2, 2 '), characterized in that the vacuum-pressure recipient (20) - Is connected via a pressure line (22) to a pressure pump (23) or pressure bottles (24, 24 ') and additionally - via a vacuum line (25) to a vacuum pump (26) Connection is established so that the vacuum pressure recipient (20) can alternately be pressurized and evacuated with the solid items to be cleaned (8), ultrasound transducers (2, 2 ') attached or inserted to sonicate the items to be cleaned (8) a cleaning material exchange device (7) with a notching device (28) and the frame (9) with a corresponding notching device (28 ') and - In addition, a device (29) for cycling the pressure pump (23), respectively. the pressure bottles (24, 24 ') and the vacuum pump (26) and optionally the ultrasonic transducer (2, 2') is present. 10. Device for cleaning solid items to be cleaned (8) according to claim 9, characterized in that means (4, 5, 29) are present which allow the ultrasonic transducers (2, 2 ') both during the phase of the increased pressure in Vacuum pressure recipient (20), which by means of the pressure pump (23), respectively. of the pressure bottles (24, 24 '), is generated and maintained - as well as during the evacuation phase by means of the vacuum pump (26) generated and maintained to put into operation. 11. Device for cleaning solid items according to one of the Claims 9 or 10, characterized in that the exchange of the items to be cleaned (8), which may be located in a basket-like frame (9) within the vacuum pressure recipient (20), - By means of a lid (21) on the vacuum pressure recipient (20), which in turn can be had automatically by means of an opening-closing device (27) and - Can be automatically exchanged by means of a release mechanism (28 '), which is optionally attached to the frame (9), by a cleaning material exchange device (7) with a corresponding release device (28). 12. Device for cleaning solid items according to one of the Claims 9, 10 or 11, characterized in that the device (29) allows the vacuum pressure recipient (20) to be automatically evacuated and pressurized several times in succession in a cyclical process, optionally additionally and in particular with normal Pressure the cleaning agent (6) is replaced. 13. Device for cleaning solid items to be cleaned according to one of claims 9, 10 or 11, characterized in that the device (29) makes it possible to automatically the one after the other in a single cycle Evacuating vacuum pressure receivers (20) and putting them under pressure, the cleaning agent (6) possibly being replaced, in particular and in particular at normal pressure. 14. Device for cleaning solid items to be cleaned according to one of claims 9, 10 or 11, characterized in that the device (29) allows the vacuum pressure recipient (20) to be evacuated only once, but pressurized several times and if necessary additionally and in particular at normal pressure the cleaning agent (6) is exchanged. 15. Device for cleaning solid items to be cleaned according to one of claims 9 to 14, characterized in that a solvent vapor supply device (33, 34) is present, which allows the gas space above the cleaning agent (7) with a after the last cleaning phase to remove surface tension-reducing solvent vapor. 16. Device for cleaning solid items to be cleaned (8) according to claim 15, characterized in that a solvent vapor collecting device (35) is present, which removes the solvent vapor from the gas pumped by means of the vacuum pump (26) above the Cleaning agents (6) allowed.