Abstract:
An oscillating apparatus includes a driver generating a waveform signal based on a stored data for specifying a waveform so as to output the waveform signal to a transducer. A detector detects a phase difference between electric voltage and current supplied to the transducer. A memory unit holds gain data reflecting a characteristic of the transducer. The gain data specify gains corresponding to respective phase differences. An arithmetic unit calculates the frequency of the waveform based on the phase difference detected at the detector and a gain included in the gain data. The oscillating apparatus enables determination of a gain suitable to the transducer in view of the characteristic of the transducer. The frequency of the waveform signal is allowed to follow the change in the resonant frequency in a shorter period. The oscillation can thus be kept well.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an oscillating apparatus such as an ultrasonic oscillator. In particular, the invention relates to an ultrasonic oscillator applicable to an ultrasonic bonding machine.  
         [0003]     2. Description of the Prior Art  
         [0004]     An ultrasonic oscillator is well known as disclosed in Japanese Patent Application Publication No. 2001-340809. The ultrasonic oscillator utilizes a direct digital synthesizer, DSS, for generating a waveform signal. A digital phase lock loop (PLL) circuit is connected to the direct digital synthesizer. This structure allows the driving signal output from the direct digital synthesizer to follow the change in the resonant frequency of the transducer even if the resonant frequency varies. The oscillation of the transducer can in this manner be maintained. A larger gain of the phase lock loop circuit enables a quick response of the driving signal to the change in the resonant frequency.  
         [0005]     A so-called ultrasonic bonding machine is well known in the technical field of the circuit chip mounting. The phase lock loop circuit is connected to the transducer of a so-called ultrasonic head in the ultrasonic bonding machine. If the gain of the phase lock loop circuit is excessively larger, the ultrasonic head cannot follow the change in the frequency, so that the action of the ultrasonic head gets disordered. On the other hand, if the gain of the phase lock loop circuit gets smaller, the driving frequency for the ultrasonic head cannot reach the target resonant frequency in a shorter period. The driving signal for the ultrasonic head accordingly cannot be raised.  
       SUMMARY OF THE INVENTION  
       [0006]     It is accordingly an object of the present invention to provide an oscillating apparatus contributing to realization of a higher driving frequency applied to an ultrasonic head.  
         [0007]     According to the present invention, there is provided an oscillating apparatus comprising: a transducer; a driver connected to the transducer, said driver generating a waveform signal based on a stored data for specifying a waveform so as to output the waveform signal to the transducer; a detector designed to detect a phase difference between electric voltage and current supplied to the transducer; a memory unit holding gain data reflecting a characteristic of the transducer, said gain data specifying gains corresponding to respective phase differences; and an arithmetic unit designed to calculate the frequency of the waveform based on the phase difference detected at the detector and a gain included in the gain data.  
         [0008]     The oscillating apparatus enables determination of a gain suitable to the transducer in view of the characteristic of the transducer. The frequency of the waveform signal is allowed to follow the change in the resonant frequency in a shorter period. The oscillation can thus be kept well. Determination of a maximum gain leads to realization of a higher frequency of the waveform signal. If the oscillating apparatus is employed in an ultrasonic bonding machine, for example, the ultrasonic head is allowed to enjoy the driving signal of a higher frequency.  
         [0009]     The oscillating apparatus may further comprise a processing unit designed to update the gain data in the memory unit. Suitable gains can be set in view of the required resonant frequency in the oscillating apparatus of the type.  
         [0010]     Otherwise, the oscillating apparatus may allow employment of a bolt clamped Langevin type transducer as the transducer. The clamping force of the clamp may be utilized to set the resonant frequency in the bolt clamped Langevin type transducer. The stored data may be set in accordance with the set frequency. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment in conjunction with the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a perspective view schematically illustrating the entire structure of an ultrasonic bonding machine;  
         [0013]      FIG. 2  is a block diagram schematically illustrating the control system of the ultrasonic bonding machine; and  
         [0014]      FIG. 3  is a block diagram schematically illustrating the structure of an oscillator. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]      FIG. 1  schematically illustrates an ultrasonic bonding machine  11  according to an embodiment of the present invention. The ultrasonic bonding machine  11  includes a work table  12  defining the upper flat surface along a predetermined horizontal plane. The work table  12  is allowed to move within the horizontal plane. An ultrasonic head  13  is opposed to the upper flat surface of the work table  12 .  
         [0016]     Here, the xyz-coordinate system is established in the ultrasonic bonding machine  11 . They y-axis of the xyz-coordinate system extends in the direction perpendicular to the upper flat surface of the work table  12 , namely to the horizontal plane. The work table  12  is positioned within the horizontal plane based on the x-coordinate and the z-coordinate of the xyz-coordinate system. A relative position can in this manner be determined between the ultrasonic head  13  and the work table  12  along the horizontal plane.  
         [0017]     A pressure apparatus  14  is connected to the ultrasonic head  13 . The pressure apparatus  14  includes a support shaft  15  for supporting the ultrasonic head  13  at the tip or lower end. The support shaft  15  has the longitudinal axis in parallel with they y-axis of the xyz-coordinate system. The support shaft  15  may be made of a metallic material, for example. A first guide  16  is employed to support the support shaft  15  for relative movement therebetween in the vertical direction.  
         [0018]     The first guide  16  is a so-called non-contact guide, for example. The non-contact guide is designed to effect a predetermined force to the peripheral surface of the support shaft  15  from at least pairs of directions. The predetermined force may include force such as magnetic force based on atoms, static pressure based on fluid such as air, or the like. Here, the first guide  16  employs static pressure based on air.  
         [0019]     A movable member  17  is coupled to the support shaft  15 . Here, the movable member  17  includes a pair of guide shaft  18 ,  18 . The individual guide shaft  18  has the longitudinal axis in parallel with the y-axis of the xyz-coordinate system. The guide shafts  18  may be made of a metallic material, for example. Second guides  19  are employed to respectively support the guide shafts  18  for relative movement therebetween in the vertical direction. The second guides  19  are likewise a so-called non-contact guide. The first and second guides  16 ,  19  may be fixed to a common support member  21 . The support member  21  stays still even during the movement of the movable member  17 .  
         [0020]     A drive source or voice coil motor  22  is connected to the movable member  17 . The voice coil motor  22  includes a columnar permanent magnet  22   a  stationary to the movable member  17 , for example. A cylindrical coil  22   b  is fixed to the support member  21 . The coil  22   b  is designed to surround the outer cylindrical surface of the permanent magnet  22   a . When electric current is supplied to the coil  22   b , the movable member  17  and the support shaft  15  is driven to move in the direction of the y-axis.  
         [0021]     A force sensor  23  is interposed between the support shaft  15  and the movable member  17 . The force sensor  23  is designed to detect a force or load acting on the support shaft  15  from the movable member  17  in the direction of the y-axis. The load corresponds to a pressure transmitted to the work table  12  from the ultrasonic head  13 . A load cell, a piezoelectric element, or the like, may be employed as the force sensor  23 , for example.  
         [0022]     An image capturing apparatus  24  is related to the work table  12  and the pressure apparatus  14 . The image capturing apparatus  24  is supported on a base  25  for movement in the horizontal direction. The image capturing apparatus  24  includes a camera unit  26  designed to capture images. When the image capturing apparatus  24  moves in the horizontal direction, the camera unit  26  is positioned in a space between the ultrasonic head  13  and the work table  12 . The camera unit  26  thus serves to simultaneously capture an image of the ultrasonic head  13  and an image of the upper flat surface of the work table  12 .  
         [0023]     As shown in  FIG. 2 , the ultrasonic bonding machine  11  includes a main controller circuit  31 . The main controller circuit  31  is designed to control the operation of the ultrasonic bonding machine  11  in accordance with a predetermined software program. An ultrasonic oscillator  32  is connected to the main controller circuit  31 . The ultrasonic oscillator  32  serves to control the oscillation of the ultrasonic head  13 . The ultrasonic oscillator  32  will be described later in detail.  
         [0024]     A pressure apparatus controlling circuit  33  is connected to the main controller circuit  31 . The pressure apparatus controlling circuit  33  is designed to supply the coil  22   b  with electric current. The vertical movement of the movable member  17  is controlled in response to the supply of the electric current.  
         [0025]     The force sensor  23  is connected to the pressure apparatus controlling circuit  33 . The pressure apparatus controlling circuit  33  controls the supply of the electric current to the coil  22   b  of the voice coil motor  22  based on the electric signal output from the force sensor  23 . The load of the support shaft  15  is in this manner maintained at a set value. Servo control may be realized in the pressure apparatus controlling circuit  33  based on the output from the force sensor  23 .  
         [0026]     An image processing circuit  34  is connected to the main controller circuit  31 . The image processing circuit  34  is designed to supply the camera unit  26  with a predetermined control signal. The camera unit  26  is designed to capture images in response to the supply of the control signal. The image processing circuit  34  analyzes the images output from the camera unit  26 . A predetermined control signal may be supplied to the image processing circuit  34  from the main controller circuit  31  so as to realize the supply of the control signal from the image processing circuit  34 .  
         [0027]     An image capturing apparatus driving circuit  35  is connected to the main controller circuit  31 . The image capturing apparatus driving circuit  35  is designed to supply a predetermined electric signal to an electric motor incorporated within the image capturing apparatus  24 , for example. A predetermined control signal may be supplied to the image capturing apparatus driving circuit  35  from the main controller circuit  31  so as to realize the supply of the electric signal. The image capturing apparatus  24  is allowed to move in the horizontal direction based on the supplied electric signal.  
         [0028]     A work table driving circuit  36  is connected to the main controller circuit  31 . The work table driving circuit  36  is designed to supply a predetermined electric signal to an electric motor incorporated within the work table  12 , for example. A predetermined control signal may be supplied to the work table driving circuit  36  from the main controller circuit  31  so as to realize the supply of the electric signal. The work table  12  is allowed to move in the horizontal direction based on the supplied electric signal.  
         [0029]     A brief description will be made on the operation of the ultrasonic bonding machine  11 . A printed circuit board is placed on the upper flat surface of the work table  12 . A circuit chip is held on the ultrasonic head  13 . Ball bumps are arranged on the lower surface of the chip. Conductive pads are likewise arranged on the upper surface of the printed circuit board in an array identical to that of the ball bumps. The ball bumps and conductive pads may be made of an electrically conductive material such as copper, for example. A position mark is printed on the lower surface of the chip. A position mark is likewise printed on the upper surface of the printed circuit board so as to identify the expected position of the chip.  
         [0030]     The camera unit  26  is driven to move into a space between the ultrasonic head  13  and the work table  12 . The camera unit  26  is positioned between the chip and the printed circuit board. The image capturing apparatus driving circuit  35  outputs a predetermined electric signal based on a control signal supplied from the main controller circuit  31 .  
         [0031]     When the camera unit  26  has been positioned, the camera unit  26  is forced to capture images in response to the supply of the control signal from the image processing circuit  34 . The camera unit  26  simultaneously captures the images of the printed circuit board and the chip. The image data is then supplied to the image processing circuit  34 . The image processing circuit  34  then analyzes the supplied image data. The image processing circuit  34  thus detects the position marks on the chip and the printed circuit board based on the analysis of the image data. The position of the printed circuit board and the chip can in this manner be identified within the xyz-coordinate system.  
         [0032]     The printed circuit board is then positioned relative to the chip. The work table  12  is driven to move in the horizontal direction so as to align the work table  12 . The work table driving circuit  36  outputs an electric signal based on a control signal from the main controller circuit  31 . The main controller circuit  31  generates the control signal based on the output from the image processing circuit  34 .  
         [0033]     When the printed circuit board has been aligned with the chip, the ultrasonic head  13  is lowered. The ball bumps are received on the corresponding conductive pads. The ultrasonic head  13  serves to urge the chip against the printed circuit board. The coil  22   b  of the voice coil motor  22  receives an electric signal from the pressure apparatus controlling circuit  33  in this case. The pressure apparatus controlling circuit  33  serves to keep the urging force constant.  
         [0034]     While the ultrasonic head  13  is urged against the upper flat surface of the work table  12 , the ultrasonic oscillator  32  induces the ultrasonic vibration of the ultrasonic head  13 . The chip is caused to move in the horizontal direction relative to the printed circuit board by a minute amplitude. The ultrasonic energy allows exchanged metallic atoms to diffuse into the ball bumps and the conductive pads at the contacts between the ball bumps and the conductive pads. The ball bumps are in this manner bonded to the corresponding conductive pads.  
         [0035]     Next, description will be made on the structure of the ultrasonic oscillator  32 . As shown in  FIG. 3 , for example, the ultrasonic oscillator  32  includes a transducer  37  incorporated within the ultrasonic head  13 . A bolt clamped Langevin type transducer, BLT, is employed as the transducer  37 , for example. As conventionally known, the bolt clamped Langevin type transducer comprises a layered piezoelectric elements. The bolt is used to clamp the piezoelectric elements.  
         [0036]     A direct digital synthesizer, DDS,  38  is connected to the transducer  37 . The direct digital synthesizer serves as a driver of the present invention. The direct digital synthesizer  38  is designed to output a waveform signal such as a sine wave signal, for example, based on a look-up table, not shown. When the frequency of the waveform signal coincides with the resonant frequency of the transducer  37 , the transducer  37  oscillates. The waveform signal, namely the driving signal is amplified at an amplifier  41  after regulation at a low-pass filter, LPF,  39 . The driving signal is input into the transducer  37  after the amplification.  
         [0037]     A digital phase lock loop circuit  42  is connected to the direct digital synthesizer  38 . The digital phase lock loop circuit  42  includes a voltage phase detector  43  and a current phase detector  44 . The voltage phase detector  43  is designed to detect the phase of the voltage from the driving signal for the transducer  37 . The current phase detector  44  is likewise designed to detect the phase of the current from the driving signal for the transducer  37 . If the frequency of the driving signal coincides with the resonant frequency of the transducer  37 , the phase of the voltage coincides with the phase of the current. The phase difference is thus removed between the phase of the voltage and the phase of the current.  
         [0038]     A digital phase difference detecting circuit  45  is connected to the voltage and current phase detectors  43 ,  44 . The digital phase difference detecting circuit  45  is designed to calculate the phase difference between the phase of the voltage and the phase of the current based on the outputs from the voltage phase detector  43  and the current phase detector  44 . A digital phase shift amount determining circuit  46  serves to modify the phase difference calculated at the digital phase difference detecting circuit  45 . The digital phase shift amount determining circuit  46  is designed to modify the phase difference based on a predetermined amount of phase shift. The amount of phase shift is set unique to the voltage phase detector  43  and the current phase detector  44 , for example.  
         [0039]     A gain table RAM  47  is connected to the digital phase difference detector  46 . The gain table RAM  47  holds gain data at the individual addresses. The gain data represents the loop gain of the phase lock loop circuit  42 . The magnitude of the loop gain depends on the amount of phase difference. When the address is designated based on the phase difference, the corresponding gain data is output from the gain table RAM  47 . The gain table RAM  47  in this manner functions as a so-called look-up table.  
         [0040]     A frequency setting circuit  48  is connected to the gain table RAM  47 . The frequency setting circuit  48  is designed to calculate the driving frequency of the transducer  37  based on the gain data output from the gain table RAM  47 . The frequency setting circuit  48  adds the gain data to the current frequency. The target driving frequency is in this manner determined. The determined target driving frequency is supplied to the direct digital synthesizer  38 . The frequency of the driving signal output form the direct digital synthesizer  38  is in this manner changed.  
         [0041]     A zero-cross detecting circuit  49  is connected to the frequency setting circuit  48 . The zero-cross detecting circuit  49  detects the position of the zero-cross of the driving signal. The detected timing of the zero-cross is reported to the frequency setting circuit  48 .  
         [0042]     A central processing unit, CPU,  51  is connected to the digital phase shift amount determining circuit  46 , the gain table RAM  47  and the frequency setting circuit  48 . The central processing unit  51  supplies the digital phase shift amount determining circuit  46  with an amount of phase shift. The central processing unit  51  is allowed to update the gain data stored in the gain table RAM  47 . The gain data is prepared for each of the ultrasonic heads  13  or the each kind of the ultrasonic heads  13 , for example. The central processing unit  51  supplies a reference frequency to the frequency setting circuit  48 . The reference frequency corresponds to the initial value of the driving signal. The direct digital synthesizer  38  starts generating the driving signal based on the reference frequency.  
         [0043]     Now, assume that the transducer  37  is driven to oscillate. The central processing unit  51  previously supplies the reference frequency to the frequency setting circuit  48 . The frequency setting circuit  48  reports the direct digital synthesizer  38  of the reference frequency. The direct digital synthesizer  38  thus generates the waveform signal based on the reference frequency. The generated waveform signal, namely the driving signal, is supplied to the transducer  37 . The transducer  37  oscillates at the frequency of the driving signal. The reference frequency corresponds to the resonant frequency of the ultrasonic head  13 , so that the ultrasonic head  13  oscillates.  
         [0044]     When the chip held on the ultrasonic head  13  contacts with the printed circuit board, the resonant frequency of the ultrasonic head  13  changes. This change generates a phase difference between the phase of the voltage and the phase of the current in the driving signal. The digital phase difference detecting circuit  45  detects the phase difference. The detected phase difference is utilized to designate the address of the gain table RAM  47 . The loop gain is extracted from the designated address. The frequency setting circuit  48  adds the frequency of the extracted loop gain to the current frequency. The target driving frequency is in this manner calculated.  
         [0045]     When the target driving frequency has been calculated, the frequency setting circuit  48  sets a new driving frequency for the direct digital synthesizer  38 . Here, the frequency setting circuit  48  detects the point of zero-cross and simultaneously sets the driving frequency. The point of zero-cross is reported from the zero-cross detecting circuit  49 . The frequency of the waveform signal is changed right after the zero-cross. The transducer oscillates at the new frequency. These operations are repeated so that the frequency of the vibration of the transducer follows the change in the resonant frequency of the ultrasonic head  13 . The ultrasonic head  13  keeps oscillating. The amplitude of the oscillation is kept constant at the ultrasonic head  13 .  
         [0046]     A larger loop gain contributes to a quicker response of the driving signal to the change in the resonant frequency. The oscillation of the ultrasonic head  13  thus gets stabilized in a shorter period. On the other hand, if the loop gain is excessively large, the ultrasonic head  13  cannot follow the change of the frequency. The ultrasonic head  13  gets disordered. The ultrasonic head  13  cannot be controlled well. If the loop gain is smaller, the driving frequency of the ultrasonic head  13  cannot reach the target frequency in a shorter period. In this case, the driving frequency cannot be raised for the ultrasonic head  13 . A larger loop gain is preferably set in the gain table RAM  47 . The driving frequency can thus be raised for the ultrasonic head  13 .  
         [0047]     Now, assume that the ultrasonic head  13  is replaced with new one. The central processing unit  51  selects a loop gain most suitable for the new ultrasonic head  13 . The selected loop gain is written into the gain table RAM  47  at a predetermined address for the respective phase differences. The gain table RAM  47  is in this manner updated. The aforementioned processes are effected based on the updated gain table RAM  47 . As a result, the oscillation of the ultrasonic head  13  is maintained well. The amplitude of the oscillation of the ultrasonic head  13  is kept constant. If a common loop gain is set for all of the ultrasonic heads  13 , the loop gain must take the smallest value. Accordingly, the resonant frequency of the ultrasonic head  13  cannot be improved. The driving frequency cannot be raised.  
         [0048]     The loop gain is prepared for each of the ultrasonic heads  13 . When the loop gain is to be determined, a driving frequency is supplied to the ultrasonic head  13  for realizing a predetermined amplitude. The driving frequency is composed of the direct component of the electric current. The alternating component of a predetermined frequency is superimposed on the direct component. One should observe whether or not the oscillation of the ultrasonic head  13  follows the alternating component. As long as the oscillation of the ultrasonic head  13  follows the alternating component, the frequency of the alternating component can be determined as the loop gain. The observation reveals a loop gain set for each of the ultrasonic heads  13 .  
         [0049]     The central processing unit  51  may calculate a loop gain based on a linear function, a quadric, or the like, for example. In this case, a predetermined coefficient may be set between the phase difference and the loop gain. Increase of the coefficient leads to an increase in the loop gain. The central processing unit  51  is thus allowed to use the maximum coefficient for the respective ultrasonic heads  13  in calculation of the loop gain.