Abstract:
An apparatus and method for measuring cavitation energy of a device placed in a cleaning bath tank of ultrasonic and megasonic cleaning systems. Probe apparatus having an array of probes positioned within the bath detects formation of bubbles at various locations within the bath that are generated by ultrasonic and megasonic vibrations applied to the bath with each probe of the array generating an electrical waveform in response to the detection of the bubbles. Apparatus coupled to each probe of the probe array analyzes the probe-generated voltages and determines cavitation energy profiles occurring on surfaces of a device located in the bath.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to apparatus and method for measuring cavitation energy profiles on devices placed in ultrasonic and megasonic cleaning systems. 
     2. Field of the Invention 
     Ultrasonic and megasonic cleaning systems are well known and are used in a wide variety of applications to clean various types of devices. Typically, a cleaning system has a tank with a cleaning bath that may consist of water with a cleaning material such as a detergent recommended and selected for use in cleaning particular types of devices. Ultrasonic and megasonic systems, sometimes referred to as agitation systems, have a transducer designed to generate high frequency vibrations in the cleaning tank in response to an electric input top the transducer. An ultrasonic cleaning system may operate in a range of 20 kHz to 400 kHz while a megasonic system may operate in a range of 500 kHz to 3 MHz. 
     In operation, the transducer vibrations are introduced into the cleaning tank containing the bath and the device or devices to be cleaned. The introduced vibrations generate pressure gradients within the bath, which form cavitation bubbles in low-pressure areas. The bubbles begin to grow until entering a high-pressure region and then collapse against a surface of the device to be cleaned thereby dislodging contaminants. The implosion of the bubbles creates a strong force over a period of time to clean devices such as memory disks, semiconductor wafers, LCD and other like devices. 
     Ultrasonic energy is a series of pressure points, or rather a series of compression and rarefaction. If the energy is of sufficient intensity, the cleaning liquid of the bath will actually be pulled apart and small bubbles or cavities will be formed. The bubbles collapse or implode throughout the cleaning fluid creating an effective force, which is uniquely suited to cleaning. This process is known as cavitation. Although the energy released from a single cavitation bubble is extremely small, the collapse of millions of bubbles produces an intense scrubbing action of the surface of the device to be cleaned. In many cleaning processes the control of cavitation energy is one of the most critical parameters affecting product yield. A problem arises in that if not enough energy is present on a surface location, the device will not be cleaned. Another problem arises in that if too much energy is present in one location the excessive force may damage the device being cleaned. One method of measuring cavitation is an indirect method that consists of exposing aluminum foil to the cavitation process and then examining the foil for dents and holes caused by the cavitation process. The current technology is limited to the measurement of the ultrasonic sound waves energy by the use of instructions called hydrophones. A problem with hydrophones systems arises in that they are limited to detecting only very low frequencies typically in the range of 40 kHz to 68 kHz. Thus, hydrophone systems act as a low-pass filter, which automatically filters out and removes the higher frequency cavitation energy. Neither of these methods measure the cavitation process at various locations within the cleaning bath. Accordingly, a need exists in the art for apparatus and a method for actively measuring the cavitation process at various locations in the cleaning bath during operation of removing contaminants from devices placed in the bath. 
     SUMMARY OF THE INVENTION 
     Apparatus solves the foregoing problem by measuring the cavitation process at various locations in a cleaning bath during ultrasonic and megasonic sonic cleaning of devices placed in the cleaning bath. 
     It is an object of this invention to provide apparatus for measuring the cavitation activity occurring in various locations in an ultrasonic and megasonic cleaning bath and for generating a profile of the cavitation process occurring at various locations on the surface of a device resident in the cleaning bath. 
     It is also an additional object of this invention to provide probe apparatus having a plurality of probe sensors for measuring cavitation energy appearing at various locations in an ultrasonic and megasonic cleaning bath. 
     It is also an additional object of this invention to provide apparatus coupled to each probe of the probe array immersed in an ultrasonic and megasonic cleaning bath for analyzing the voltage waveform generated by each probe and determining a cavitation energy profile occurring on surfaces of a device located in the bath. 
     In the preferred embodiment of the invention apparatus for measuring cavitation energy of a bath resident in a tank of ultrasonic and megasonic cleaning systems has probe apparatus having an array of probes positioned within the bath for detecting the pressure formed by the collapse of bubbles at various locations within the bath that are generated by ultrasonic and megasonic vibrations applied to the bath and with each probe of the array generating an electrical waveform in response to the detection of the bubbles. Apparatus coupled to each probe of the probe array analyzes the voltage generated each probe and determines a cavitation energy profile occurring on surfaces of a device located in the bath. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a further understanding of the objects and advantages of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawing, in which like parts are given like reference in numerals and wherein; 
     FIG. 1 is a view of an ultrasonic and megasonic cleaning system having apparatus for actively and continuously measuring profiles of a cavitation processes on devices being cleaning in the ultrasonic and megasonic cleaning bath in accordance with principles of the invention. 
     FIG. 2 is a view of a probe apparatus in FIG. 1 for measuring profiles of an ultrasonic and megasonic cavitation process. 
     FIG. 3 is an typical waveform generated by a probe of the probe apparatus of FIGS. 1 and 2 in response to a cavitation process occurring in the cleaning bath, 
     FIG. 4 is a waveform of the ultrasonic and megasonic generated by the transducer of FIG.  1  and applied to the cleaning bath, 
     FIG. 5 is a typical waveform of the cavitation process energy occurring in the cleaning tank FIG. 1 as a result of ultrasonic and megasonic signals applied to the cleaning tank by the transducer of FIG. 1, and 
     FIG. 6 is a block diagram of the apparatus of the cavitation sensor system set forth in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     System  10  set forth in FIG. 1 of the drawing may be either an ultrasonic or megasonic system for use in cleaning a device  207  in accordance with principles of the invention and having cleaning apparatus  200  consisting of a tank  202  associated with a transducer  201 . The tank  202  contains a cleaning solution  205 , typically, although not limited thereto, which may be water having a detergent suitability recommended for cleaning devices  207  which may be memory disks, semiconductors, LCDs or other similar devices. In operation, device  207  is placed in the cleaning bath and transducer  201  enabled to generate transducer vibrations of a value in a selected range of 20 kHz to 400 kHz for an ultrasonic cleaning system and of 500 kHz to 3 MHz for a megasonic cleaning system and to introduce the vibrations into the cleaning tank  202 . In a typical example, for example, cleaning memory disks, the disks are cleaned in a cassette of disks wherein all of the disks sit side by side with only a few millimeters between them in the tank  202 . The introduced vibrations generate pressure gradients within the bath  205 , which form cavitation bubbles, such as bubbles  206  in low-pressure areas. The bubbles begin to grow until entering a high-pressure region and then collapse against a surface of device  207  thereby dislodging contaminants. 
     Probe apparatus  204 , FIG. 2, may be a quartz disk  208  having a plurality of sensors  209  mounted on an inside surface of the disk  208 . Various configurations of the sensors  209  may be positioned at various positions on the quartz disk  208  at the option of the user. The quartz disk  208  functions as quartz lens for interfacing the probe apparatus  204  with the cavitation process occurring in the cleaning system tank  202 . Each of the sensors  209  is a piezoelectric device formed of piezoelectric material affixed to the inside surface of the quartz lens disk  208  at the predetermined locations. The sensors  209  may vary in number and location of the quartz lens disk  208  and each sensor  209  is responsive to the cavitation energy occurring in the bath at the location of the sensor  209  for generating an electrical waveform in response to the cavitation energy occurring at the sensor  209  location in the cleaning bath  205 . Although only eight sensors  209  are shown in FIG. 2, it is to be understood that they are only representative to show typical probe apparatus  204  and various numbers and positions of sensors  209  may be used in accordance with the invention depending upon the types of devices to be cleaned. 
     A support structure of a generally circular hollow member  212  attached to quartz lens disk  208  by members  213  supports the probe apparatus quartz lens  208  and the plurality of sensors  209  affixed thereto in the cleaning bath tank  202  adjacent the devices  207  to be cleaned. A waterproof housing is formed and mounted on a side of the quartz lends disk  208  adjacent the plurality of sensors  206  forming a water tight seal around an edge of the quartz lens disk  208  while interfacing the quartz lens disk  208  with the cavitation energy occurring in the cleaning bath  205 . A plurality of wires  210  conductors of cable  211  extending from cavitation sensor system  100 , FIG. 1, and terminated in hollow member  212 , FIG. 2, are located in the hollow member  212  with one of wires  210  forming a common ground lead for all of the piezoelectric sensors  209 . Each of the other wires  210  are individually attached to one of the piezoelectric sensors  209  and interconnected to each of the piezoelectric sensors  209  with analyzing apparatus of cavitation sensor system  100 . A pair of contact elements are affixed to each piezoelectric sensor  209  to connect the common ground lead and one of the other wires  210  to the piezoelectric sensor  209 . In operation, probe apparatus  204  generates an electrical waveform  2048 , FIG. 3 at each location of a probe sensor  209  in cleaning bath  205  characterizing the specific cavitation energy occurring at the sensor location. The electrical waveform  2048  is a combination of the transducer induced vibration energy superimposed on the cavitation energy occurring at the location of the probe sensor  209 . 
     Cavitation sensor system  100 , FIG. 1 is coupled to each probe  206  of the probe array apparatus  204  and analyzes the ultrasonic and megasonic frequency induced in the cleaning bath  205  by transducer  201  and the probe generated electrical waveforms to determine a cavitation energy profile occurring on the surfaces of a device  207  located in the cleaning bath  205 . Each of the probe apparatus  204  wires  210 , FIG. 2 in addition to the ground lead, form a channel individual to each sensor  209  and is connected, FIG. 1, to cavitation sensor system  100 , FIG.  6 . The electrical low-pass filter  101 , connected to a wire  210  of probe sensor  209  and identified as channel  1 , attenuates the cavitation energy frequencies in the input combined waveform  2408 , FIG. 3, such that the output waveform  2050 , FIG. 4 of low-pass filter  101  is essentially the ultrasonic and megasonic frequency generated by the transducer  201 , FIG.  1 . Upon receiving the sinusoidal waveform  2050  output of low-pass filter  101 , FIG. 6 voltage comparator  105  converts sinusoidal waveform  2050  into a square wave of the same period and having a plus and minus value selected by user adjustment of voltage comparator  105 . The square wave output of voltage comparator  105  is applied as input to frequency divider  106  wherein the frequency of the input wave is divided by a user selected multiple of two such as  128 ,  256  or the like. The output of frequency divider  106  is then applied to a frequency input of data acquisition board  301 . Data acquisition board  301  may be any one of a number of commercially available circuit boards and serves to interconnect cavitation sensor system  100  with a digital computer or profile meter  300 , FIG.  1 . Thus, computer or profile meter  300  is enabled by data acquisition board  301 , to display the frequency of the vibrations introduced into cleaning bath  205 , FIG. 1 by transducer  201 . 
     Each of filters  102  through  104  individually connected to a probe channel wire  201 , has an output connected to a corresponding RMS to DC converter  107  through  109 . RMS to DC converts  107  through  109  calculates the root-mean square (RMS) value  2051 , FIG. 5, of the cavitation energy electrical RMS into a varying  2051  waveform detected by each probe sensor  209  and converts the calculated RMS into a varying DC voltage representative of the probe sensor detected cavitation energy input to the RMS to DC converter  117 . The output of each RMS to DC converter  107  through  109  is connected to a corresponding channel input of the data acquisition board  301  so that the varying DC voltage appearing on each channel input is converted into digital information that can be displayed on computer or profile meter  300 , FIG.  1 . 
     Each of filters  102  through  104  individually connected to a probe channel wire  201 , has an output connected to a corresponding RMS to DC converter  107  through  109 . RMS to DC converts  107  through  109  calculates the root-mean square (RMS) value  2051 , FIG. 5, of the cavitation energy electrical RMS into a varying  2051  waveform detected by each probe sensor  209  and converts the calculated RMS into a varying DC voltage  2052  representative of the probe sensor detected cavitation energy input to the RMS to DC converter  107 . The output of each RMS to DC converter  107  through  109  is connected to a corresponding channel input of the data acquisition board  301  so that the varying DC voltage appearing on each channel input is converted into digital information that can be displayed on computer or profile meter  300 , FIG.  1 . 
     The channel information is the characteristic of the cavitation energy occurring in the cleaning bath  205  at each probe sensor  209  location and thereby enables the computer or probe meter  300  to display the probe sensor characteristics as a profile of the cavitation energies appearing at surfaces of the devices being cleaned in cleaning bath  205 . 
     The detailed logic circuitry of the circuit apparatus set forth in FIG. 6 of the drawing is performed by filters, voltage comparators, frequency dividers, digital acquisition cards, computer and the like, the operation of which are well known in the art and the details of which need not be disclosed for an understanding of the invention. Typical examples of the logic circuitry are described in numerous textbooks. For example, such types of logic circuitry, among others, are described by J. Millman and H. Taub in Pulse, Digital and Switching Waveforms, 1965, McGraw-Hall, Inc., H. Alex Romanowitz and Russell E. Pucket in Introduction of Electronics, 1968, John Wiley &amp; Sons, Inc. and in the TTL Data Book of Design Engineers, Second Edition, 1976, Texas Instruments Incorporated. 
     It is obvious from the foregoing that the facility, economy and efficiently of ultrasonic and megasonic cleaning systems are improved by apparatus for profiling individual cavitation process occurring at surfaces of devices immersed in a cleaning bath of the cleaning system and for displaying a profile of the cavitation process on a monitor. 
     While the foregoing detailed description has described an embodiment of Invention having a specific configuration of probe sensors and monitors for displaying a profile of probe sensor cavitation energy it is to be understood that other configurations are within the scope and spirit of this invention. Thus, the invention is to be limited only by the claims set forth below.