Abstract:
A scanning acoustic microscope, comprising an ultrasonic transducer, a motor assembly on which the ultrasonic transducer is mounted, a controller that is electrically connected to the transducer and the motor assembly, the controller being adapted to cause the rotor and transducer to be moved along a path in a predetermined sequence of movements with respect to a sample; and wherein the controller is adapted to cause the ultrasonic transducer to emit one or more pulses of acoustic energy and to generate profile measurements of the sample by processing signals from the transducer that are representative of pulses of acoustic energy that are reflected by the sample.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The content of U.S. provisional application Ser. No. 60/979,021, filed Oct. 10, 2007 and 61/038,460, filed Mar. 21, 2008 is incorporated by reference into this application as if fully set forth herein. The following US patents and applications are assigned to Sonoscan, and generally relate to various aspects of scanning acoustic microscopy: U.S. Pat. Nos. 4,518,992, 4,781,067, 4,866,986, 5,351,544, 5,684,252, 6,357,136, 6,460,414, 6,880,387, 6,890,302, 6,895,820, 6,981,417, and 7,000,475, as well as Ser. No. 11/626,177 filed Jan. 23, 2007. All such patents and applications are incorporated by reference as if fully set forth herein. 
     
    
     DESCRIPTION OF RELATED ART 
       [0002]    As is well known in the art a scanning acoustic microscope typically comprises a transducer which is driven by voltage pulses which may have amplitudes of, for example, 100 volts or more and are typically in the frequency range of tens of megahertz to 100 megahertz or higher. 
         [0003]    The pulsed acoustic beam penetrates the target, which may be an IC package, for example. A fraction of the energy passes through the target, and the remainder is absorbed, scattered, or reflected. In many applications sufficient energy is returned to the transducer (after a delay) to be sensed. Acoustic energy is almost totally reflected by an air gap. Thus acoustic microscopes have proven to be extremely useful in locating disbonds (air gaps) between internal layers of a device such as an IC package. 
         [0004]    The return signal is an echo composed of a range of frequencies centered around the transducer&#39;s resonant frequency. As described further in U.S. Pat. No. 6,981,417, the return signal is commonly known as the “A” waveform or “A-scan”, and in practice contains a great deal of information about acoustic impedance perturbations or features in the body of the IC package. 
         [0005]    As is well known in the art, a time domain signal received by the acoustic microscope during a scanning session is conventionally gated by a gating process. During the gating process, a gate isolates a pixel-representative signal segment associated with a single pixel. 
         [0006]    Gating of the signal permits a user to examine any chosen level in the target simply by selecting an appropriate delay time for the gate. For example, a single pixel segment might be captured with a gate 100 nanoseconds wide set at a delay of 384-484 nanoseconds. If a deeper level were to be visualized, a longer delay would be employed. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In accordance with the invention, there is provided a scanning acoustic microscope capable of collecting and displaying any profile image of a sample including a surface profile, an internal profile or any combination of the two. 
         [0008]    In accordance with another aspect of the invention, the scanning acoustic microscope may also be capable of simultaneously collecting and displaying an internal acoustic image of a sample. 
         [0009]    In accordance with yet another aspect of the invention, the scanning acoustic microscope may be configured to simultaneously display a surface profile, a time domain signal representation, a frequency domain signal representation, or any representation of features on or within a sample. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of an acoustic imaging microscope. 
           [0011]      FIG. 2  is a schematic illustration of an alternative acoustic imaging microscope. 
           [0012]      FIGS. 3A and 3B  illustrates alternative transducer assemblies which may be implemented in certain applications of the present invention. 
           [0013]      FIG. 4A  is an illustration of a profile scan of an integrated chip useful in understanding an aspect of the present invention. 
           [0014]      FIG. 4B  is a 3-dimensional illustration of an integrated chip. 
           [0015]      FIG. 5A  illustrates a side view of an ultrasonic pulse that is directed towards a tilted part. 
           [0016]      FIG. 5B  is a schematic diagram showing how an exemplary tilt fixture can be rotated about two different axes. 
           [0017]      FIG. 5C  is an annotated perspective view of an exemplary tilt fixture shown with exemplary roll and pitch axes. 
           [0018]      FIG. 6  is a flowchart showing the steps of manually adjusting a tilt fixture. 
           [0019]      FIG. 7  is a schematic block diagram of a system that allows a scanning acoustic microscope to perform tilt adjustment measurements under automatic control. 
           [0020]      FIG. 8  is a normalized profile scan of the IC illustrated in  FIG. 4A . 
           [0021]      FIG. 9  is an illustration of a profile tilt adjust screen used to manually normalize a profile image. 
           [0022]      FIGS. 10A and 10B  is an illustration of excessive warpage of a part. 
           [0023]      FIG. 11  illustrates a graphical user interface allowing a user to specify warpage information. 
           [0024]      FIG. 12  is a flowchart that shows program steps that are followed to allow a scanning acoustic microscope to collect acoustic profile information. 
           [0025]      FIG. 12A  is a flow chart used in conjunction with  FIG. 12  to allow a scanning acoustic microscope to simultaneously collect internal and profile acoustic information. 
           [0026]      FIG. 13A-13C  is an illustration of a profile image, time domain image, and frequency domain image capable of being displayed simultaneously. 
           [0027]      FIG. 14  is a flow chart illustrating how a user can cause visual indication of surface profile data to be simultaneously displayed with a time domain signal representation and/or a frequency domain signal representation. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  illustrates in highly schematic form an acoustic imaging microscope, shown as being adapted to inspect a sample, for example, an integrated circuit (“IC”) package  94  submerged in a coupling medium  96 . Although an IC is used in the example, the sample may be any of a variety of tangible objects and is not restricted to an IC. A sample may be, for example, a ceramic plate, a diamond, a medical device, a machine plate, or an electrical component such as a capacitor or a transistor. A pulser  98 , under the control of a motion controller  100  excites a transducer  102  to generate a pulsed ultrasonic probe  104 , typically at frequencies ranging from 10 MHz or lower to 230 MHz or higher. The transducer  102  is scanned in X, Y, and Z coordinates by an X-Y-Z stage  106  through an X-Y-Z stage driver  108  under the control of motion controller  100 . 
         [0029]    Acoustic reflections from impedance features in the IC package  94  are sensed by a receiver  110 . Acoustic reflectance signals developed by receiver  110  may be in analog form. The analog acoustic reflectance signals developed by receiver  110  are supplied to an automatic or computer-driven gain control (“AGC”) circuit  120 . The AGC circuit  120  may sometimes be employed to adjust the retrieved acoustic reflectance signal to correct or reduce signal amplitude errors such as may be caused by acoustic energy absorption by the examined sample. The output of the AGC  120  is supplied to a digitizer  112  where the analog signals are quantized, for example by a 2 GHz analog-to-digital converter, into digital bytes for storage in a 4D space-time memory  114 . 
         [0030]    As explained in U.S. Pat. No. 6,981,417, the 4D space-time memory  114  is of a type adapted to store time-space data corresponding to three spatial dimensions, and associated with each point in 3D space, a set of data corresponding to A-scans associated with each point in space. In accordance with the present invention, for each point in a 3D volume, a sequence of data bytes are stored. The data bytes describe the time-dependent amplitude fluctuations of an acoustic reflectance signal returned upon interrogation of a particular point in sample space. The length of the stored acoustic reflectance signal is a function of the width of a capture gate that is set by the operator or generated by a program or algorithm. 
         [0031]    As will become evident from a more detailed description to follow, to create a display, the stored space-time data stored within memory  114  is, in one method, gated and peak detected in a gate and detect component  116  which may be a software algorithm or hardware signal processor. A conventional peak-detected output signal from component  116  is processed in a post processor  125 . The post processor  125  comprises an aspect of the present invention and will be described at length below. 
         [0032]    After being processed in post processor  125 , the acquired data signals are employed to modulate a display  118 , which may be CRT monitor, for example. Alternatively, as is well known, time-of-flight data may also be displayed. 
         [0033]    A second embodiment of a scanning acoustic microscope is shown in  FIG. 2 .  FIG. 2  illustrates a schematic form of an acoustic imaging microscope implementing the principles of the invention. Similar to  FIG. 1 , the acoustic imaging microscope of  FIG. 2  is shown as being adapted to inspect an IC  200  submerged in a coupling medium  204  in a tank  206 . A pulser/receiver  208  under the control of a host computer  210  upon receiving a trigger from a motion controller  212 , excites a transducer  214  to generate a pulsed ultrasonic probe  216 . The transducer  214  is scanned in the X and Y axis using an X and Y axis actuator, and in the Z axis using a Z axis actuator  220  through the scanning system  222  under the control of motion controller  212   
         [0034]    The motion controller  212 , during an image scanning mode, upon moving the actuators  218 ,  220  to a location to be scanned, provides a trigger to the host computer  210  and a depth selection gate detector  224 . Within the host computer  210 , upon receiving a trigger from motion controller  212  a waveform acquisition sequence  226  begins and waits for an analog acoustic reflectance signal developed by the pulser/receiver  208 . Similarly, depth selection gate detector  224  upon receiving a trigger from motion controller  212  begins an amplitude peak acquisition sequence. 
         [0035]    Acoustic reflections from impedance features in the IC  200  are sensed by the pulser/receiver  208 . Acoustic reflectance signals developed by the pulser/receiver  208  may be in analog form. The analog acoustic reflectance signals developed by the pulser/receiver  208  are supplied to the depth selection gate detector  224  and the host computer  210 . Waveform data  228  is collected by the host computer  210  during the waveform acquisition sequence  226  and may be displayed on monitors  230 . Waveform data  228  is processed using a surface profile echo detection algorithm  232  and surface profile image data  234  may be displayed on monitors  230 . 
         [0036]    A user may choose to detect internal images at multiple depths within a sample. Depth selection gate controller  224 , upon receiving the acoustic reflection signals may develop a plurality of signals corresponding to each depth selection gate selected by the user. Amplitude peak detection data  236  is processed using an amplitude peak acquisition algorithm  238  and internal image data  240  corresponding to each depth selection gate selected by the user may be displayed on monitors  230 . All surface and internal image data may be stored on a computer network or in internal memory  242  and/or sent to a printer  244  coupled to the host computer  210 . 
         [0037]      FIG. 3A  illustrates an alternative to the transducer shown in  FIG. 1 .  FIG. 3A  illustrates a “waterfall” transducer  300  wherein pulses of ultrasonic energy are emitted through a flow of coupling fluid  302 . The “waterfall” transducer, as illustrated may be useful when scanning a circuit board that may include both waterproof parts and parts susceptible to damage if it came in contact with the fluid  302 . The transducer  300  may be positioned above only those parts that are waterproof, thus, protecting the non-waterproof parts. A liquid pump  304  having an inlet  306  is shown positioned within the liquid coupling medium  302  in a tank  308 . The outlet of the liquid pump  304  is connected by flexible conduit  310  to a housing  312  of transducer  314 . The flow of fluid  302  will only contact the selected portion of the part  316 . A tray  318  is adapted to hold the part  318  above the tank  308 . As illustrated, the coupling fluid  302  is collected in the tank  308  and may be recirculated through the inlet  306 . 
         [0038]    In another alternative, the transducer system of  FIG. 1-FIG .  3 A may be implemented using a transducer array  350  as illustrated in  FIG. 3B . The term “the system” as referenced herein will refer to the transducer system of  FIG. 1-3A . Where the transducers of  FIG. 1-FIG .  3 A must physically move to scan each point of a part, the transducer array  350  may be used to minimize or completely eliminate any physical movement of the transducer while scanning a part. The array  350  may be positioned over a part  352 . The beams  354  may simultaneously scan the part  352  greatly reducing the scanning time. If the area of the part  352  is greater than the area of the array  350 , the array  350  may be configured to move to the next position and scan the rest of the part  352 . Although the configuration shown is a square array of transducers, other configurations may be used such as a linear, rectangular, triangular, circular, or semi-circular array. 
         [0039]    In accordance with an exemplary embodiment of the invention, acoustic surface data is collected and then displayed as a color-coded image in which each color corresponds to a topographical distance measurement as, for example, shown in  FIG. 4A . The sensitivity of the acoustic software module is in the micron range, and is not dependant upon the surface smoothness, color or optical characteristics.  FIG. 4A  shows a profile image of an integrated chip (IC)  402 . A graph  404  along the Y axis of  FIG. 4A  shows the variation of height across the surface of the IC  402  along a vertical line  406 . A ruler  408  may be imposed on the graph  404  to give an indication of the height along the vertical line  406  referenced to a zero point. Similarly, a graph  410  along the X axis of  FIG. 4A  shows the variation of height across the surface of the IC  402  along a horizontal line  412 . Similar to the ruler  408 , a ruler  414  may be imposed on the graph  410  to give an indication of the height along the horizontal line  412  as referenced to a zero point. Of course, the graphs of the profile image are not limited to the vertical and horizontal lines. The graphs may be a collection of data between other points such as a diagonal line from one corner of the IC  402  to another corner of the IC  402 , a curved line, or a user modifiable line. 
         [0040]    The acoustic surface data collected may also be used to generate a 3-dimensional image of the IC  402  as shown, for example, in  FIG. 4B . Using mathematical and graphical rendering programs such as MATLAB, the acoustic surface data may be transformed and projected as a 3-D image as shown in  FIG. 4B . 
         [0041]    External factors may induce errors to the acoustic surface data. Factors such as unevenness of the floor on which the machine stands, or the table on which the tank sits may cause a “tilting” of the image as shown in  FIG. 5A . One aspect of the present invention concerns the use of a universal tilting fixture that allows 2-axis orthogonal tilt adjustments to be made with, for example, a matching tank. This utility assists the user in removing tilt from the part being scanned. For general scanning and especially for surface flatness inspection and main bang imaging, the best data is obtained when the part surface is parallel to the scanner. The gating setup for surface flatness inspection and main bang imaging is greatly simplified when the part is parallel to the scanner. The tilt of the tilting fixture can be adjusted with two orthogonal tilt adjustments (e.g. Roll and Pitch) and a fixed pivot. 
         [0042]      FIG. 5B  is a schematic diagram showing how an exemplary tilt fixture can be rotated about two different axes. Referring to  FIG. 5C , an annotated perspective view of an exemplary tilt fixture  500  is shown with exemplary roll and pitch axes. The tilt fixture  500  includes thumbscrews  502 ,  504  that are used to raise and lower each corner of the fixture  500 . On the top of the fixture is a knurled knob for rotating the screw by hand. Underneath the tilt fixture is a ball end screw tip (not shown) that rests on the tank bottom (with kinematic coupling). 
         [0043]    Regarding the shape of the tilt fixture, the exact shape can change. The illustrated design of  FIG. 5C  keeps the center of gravity close to the fixed ball in the corner of the fixture so there is no need to use springs. By removing the corner away from the from the fixed ball, the center of gravity moves to a stable position between the three balls. If a rectangular fixture is used, a spring or other means of providing stability may be utilized. 
         [0044]      FIG. 6  is a flowchart showing the steps to manually adjust the tilt fixture shown in  FIG. 5C . At step  600  the transducer is placed over the 2-axis tilt fixture. The transducer then proceeds to the Pivot Measurement Position at step  602 . In the case of the fixture  500  shown in  FIG. 5C  the Pivot Measurement Position will be located at the lower left corner. At step  604  an average TOF is measured. The average TOF may be used as a reference value to calibrate each corner of the fixture  500 . At step  606  the transducer is moved to the Roll Measurement Position, the lower right corner of the fixture as referenced to  FIG. 5C . An average TOF is measured for the Roll Measurement Position. The system compares the Roll Measurement Position TOF to the reference TOF measured in step  604 . At step  610 , based on the difference of the TOF measurement at step  604  and  608 , the velocity of the coupling medium, and the pitch of the Roll tilt screw, the user may be told to rotate the Roll tilt knob x.x amount of turns clockwise or counterclockwise. For a more precise adjustment an indicator light may be displayed on the display screen. As the user is turning the knob, when the Roll TOF matches the Pivot Position TOF the indicator light may change colors, for example, from red to green. Of course, the indicator may also be a physical light on the device, or an audible indicator alerting the user when the positions are balanced. 
         [0045]    Once the Roll TOF matches the Pivot Position TOF, at step  612 , the transducer moves to the Pitch measurement position, the top left corner as referenced to  FIG. 5C . At step  614 , the average TOF is measured for the Pitch measurement position. Based on the difference of the TOF measurement at step  604  and  614 , the velocity of the coupling medium, and the pitch of the Pitch tilt screw, at step  616 , the user may be told to rotate the Roll tilt knob x.x turns clockwise or counterclockwise. An indicator light similar to the light described above may be used for a more precise adjustment. At step  618 , the user may be prompted to check each of the positions again for accuracy of the adjustment. If a check is not chosen to be performed, at step  620 , the user may be prompted to save the positions of the Pitch and Roll knobs for future reference. If the user decides to save the positions the system proceeds to step  622 . If the user does not decide to save the positions then the manual tilt adjust is finished at step  624 . If the user chooses to perform the check, at step  626 , the transducer may proceed to the Pivot measurement position and measure the average TOF. The transducer may then proceed to the Roll measurement position at step  628  and measure the TOF of the Roll position. At step  630 , the Pivot TOF is compared to the Roll TOF. If the TOFs do not match then the system will proceed back to step  610 . If the TOFs do match then the transducer may proceed to the Pitch position and measure the TOF at step  632 . The TOF at the Pitch position will be compared to the TOF at the Pivot position from step  626  at step  634 . If the TOFs do not match the system will proceed back to step  616  where the Pitch position will be readjusted. If TOFs match then the system proceeds to step  620  where the steps of saving the positions are the same as described above. 
         [0046]    The system may also be adapted to remove tilt from a part already placed on the fixture  500 . To remove tilt from a part installed on the fixture  500  the steps are essentially the same as described above. Instead of placing the transducer at the corners of the fixture  500  the transducer may be placed at a corner of the part and the TOFs measured and compared and the fixture tilt adjusted accordingly. 
         [0047]    The system of  FIG. 5C  may also be motorized to allow the tilt correction to be done automatically.  FIG. 7  is a schematic block diagram of a system that allows a scanning acoustic microscope to perform tilt adjustment measurements under automatic control. A controller  650  is used to control a roll motor  652  and a pitch motor  654 . The roll motor  702  and the pitch motor  704  are connected to a tilt fixture  656  to automatically adjust the tilt of the fixture. Instead of the user manually adjusting the knobs as described in steps  610  and  616  above, the Roll motor  652  and the Pitch motor  654  respectively, automatically adjust the tilt fixture  656  so the measured TOF matches the reference TOF. 
         [0048]    Physical correction of the tilt may, at times, be cumbersome and time consuming. Thus, one aspect of the invention may allow the user to “normalize” the data virtually adjusting for tilt after collecting the acoustic surface data. Referring back to  FIG. 4A , the graphs  404  and  410  show substantial tilt to the right and the bottom of the IC  402 . The user may choose to normalize the acoustic surface data in a variety of manners. One option may be to select three points on the profile image of the part, usually three corners of the part. An average of the three corners may be determined, and the image may be adjusted accordingly as shown in  FIG. 8 . As illustrated in  FIG. 8 , the end points on the graphs  670 ,  672  are now normalized compared to the end points of the graphs in  FIG. 4A . Correspondingly, the color-coded image has also been changed due to the tilt adjustment giving a more precise profile height deviation image. 
         [0049]    A second option to normalize the acoustic surface data may be to use the Rotational Tilt Adjust from the Profile Tilt Adjust screen shown in  FIG. 9 . To manually normalize the data the user must first select a pivot point on the profile image. The pivot point may be any point the user determines to need adjustment such as the low points on the graphs  404  and  410  of  FIG. 4A . The user may then enter an amount of rotation in the Horizontal and Vertical text boxes  680 ,  682 . Alternatively, the user may use the arrows  684  to incrementally change the tilt adjustment. 
         [0050]    A profile image may be useful in detecting, among other things, warpage in a part. As illustrated in  FIG. 10A  and  FIG. 10B , excessive warpage of a part may result in weak or even failed soldering of bonds to a substrate or circuit board. A severely convex part, as shown in  FIG. 10A  may have ends that weak of no contact with the bonding surface of a substrate. Additionally,  FIG. 10B  illustrates a severely concave part. In this case, the bonds in the middle of the part may have weak or no contact with the bonding surface of a substrate. 
         [0051]    A user may choose to manually check for warpage by selecting two points on a profile image to calculate a deviation in height between the two points. If the deviation is out of an acceptable range, the user may choose to discard the part. Warpage may also be automatically checked during an acoustic surface scan. The user may select, before performing a scan, to gather the maximum and minimum height of a part or of a portion of the part during an acoustic surface scan. The user may also define a tolerance in which parts with a difference between the maximum and minimum above the tolerance may be discarded. After an acoustic surface scan of a part, the system will automatically display to the user the maximum and minimum height, the deviation, and a recommendation to accept or reject the part based on either a user defined tolerance level or a built in tolerance level. 
         [0052]      FIG. 11  is a screen shot which shows a graphical user interface that allows a user to enter data, such as maximum warpage, into the system. If the curvature of a part is out of an acceptable range, then the part can be rejected. This can be accomplished by, for example, a visual indication being given to an operator to put the faulty part into a reject bin or an indication to accept the part. Alternatively, the part reject process can be controlled by means of a robot. 
         [0053]      FIG. 12  is a flowchart that shows program steps that are followed to allow the scanning acoustic microscope shown in  FIG. 2  to generate acoustic profile data. At step  700  the system is initiated to begin an acoustic surface image scan. At step  702 , the system places the transducer at a position corresponding to the position of the pixel to be scanned. At step  704 , a pixel trigger is generated to start the pixel acquisition sequence. At step  706 , the Pulser creates an acoustic pulse. Concurrently, at step  708  the waveform acquisition is initialized. As the waveforms are received the waveform data is stored in memory of the computing device as shown in  FIG. 2 . The storage of data may occur continuously, buffered by a line, bus or some other similar means. At step  710 , the surface reflection echo is received. At step  712  the waveform acquisition ends. The waveform acquisition is then reset and ready for the next pixel trigger corresponding to the next pixel to be scanned. At step  714 , the surface echo TOF is determined relative to the pixel trigger set by the user. At step  716 , the surface echo time value is stored in the Image Data. At step  718  the image data is displayed on the image display monitor as it is acquired. At step  720  the system checks if all pixels have been acquired. If all pixels have not been acquired the system proceeds back to step  702  where the next pixel position will be scanned. This process is performed until all pixels have been acquired. 
         [0054]    After all pixels have been acquired, the system proceeds to step  722  where the raster scan ends. The system then checks, at step  724 , if the user has enabled the surface curvature measurement. If the surface curvature measurement is not enabled the scan is completed. If the surface curvature measurement is enabled, then at step  726  the surface curvature is calculated using the acoustic surface data collected. The curvature may be defined along a vertical and a horizontal line across the part being scanned or along any other user definable lines as described with reference to  FIG. 4A  and  FIG. 8  above. As also described above, the curvature may also be calculated between two user definable points of an average curvature may be calculated. The results may be displayed on the Image Display Monitor, printed, or saved in memory as shown in  FIG. 2 . At step  728 , the system checks if the surface curvature accept and reject thresholds have been enabled. If the threshold is not been enabled then the raster scan will end. If the threshold is enabled then at step  730  the upper and lower bounds which may be defined by the user is retrieved. At step  732 , the part is checked if the surface curvature is within the limits set by the user. If the surface curvature is outside of the acceptable range, then at step  734  the monitor may display a reject indicator and the raster scan will end. If the surface curvature is within the acceptable range, then at step  736  the monitor will display an accept indicator. 
         [0055]    One aspect of the present invention is a new capability for acoustic microscopes such as, for example, C-SAM® acoustic microscopes. In accordance with this aspect of the invention, the external surface topography of a device can be revealed, if desired, at the same time as its internal features or by itself. The acoustic surface profile software module can be used, for example, to measure warpage of plastic integrated circuits, flip chips, substrates, circuit boards, etc., without any sample preparation. The module can be loaded onto an existing microscope or can be incorporated into a new microscope. 
         [0056]    In addition to causing bonding issues, warpage, at the surface of a part is often associated with internal problems such as cracks and delamination that can cause electrical failures. For example, the surface profile of a plastic encapsulated IC may show warpage in one quadrant. Internally, the same quadrant may reveal lead-frame delaminations. Having both images makes it easier, for example, to identify the processes that are causing the problem. 
         [0057]    One advantage of the acoustic surface profile module is that it displays both the surface profile and the internal features on a single instrument, eliminating the need to buy a second instrument, and requires no additional scanning time, as the profile data is taken at the same time as the acoustic image data. 
         [0058]      FIG. 12A  is a flowchart that shows program steps that are followed to allow the scanning acoustic microscope shown in  FIG. 2  to simultaneously generate acoustic profile data while simultaneously generating data regarding internal acoustic impedance features. The steps of generating acoustic profile data along with the checking of the surface curvature are identical to the steps described in  FIG. 12  above. Thus, the steps of  FIG. 12  are incorporated herein. While the pulser is creates an acoustic pulse at step  706  in  FIG. 12 , at step  738 , amplitude peak acquisition begins. At step  740 , either one or both the reflection echo and the transmitted echo are received depending on the user settings. For example, a void in a part may have a strong reflection but no transmission. A user may choose to detect either a reflection or a transmission or try and detect both to give a more positive internal image. At step  743  the system checks one or both of the received echoes and selects a peak signal located within the user defined gate. The peak signal value gate is stored in the corresponding image data in step  744 . At step  746  the peak amplitude acquisition ends and resets for the next trigger. The system then proceeds to step  718  as in  FIG. 12  and displays the image data on the image display monitor. At step  720  the system checks if all pixels have been acquired. If all pixels have not been acquired then the system proceeds to block  702  in  FIG. 12  where the next pixel location will be scanned. 
         [0059]    One aspect of the invention concerns an acoustic micro imaging method that is useful in the inspection of a target. One step of the method is to scan the target with a focused pulsed acoustic beam, preferably in the ultrasonic range. The pulsed beam is sensed after it has been modified by interaction with the target, the modified pulsed beam being representative of acoustic impedance features inside of the target, as well as the surface topography of the target. A time-domain signal indicative of the modifications is generated, and then processed to produce a frequency domain representation of frequency selective modifications to the pulsed acoustic beam produced by said interaction with said target. The time-domain signal, the frequency domain signal representation and the surface topography data are displayed to provide two different visual indications of acoustic impedance features inside of the target together with surface topography data. 
         [0060]    As described in greater detail in U.S. Pat. No. 6,890,302, surface and internal acoustic data collected may be subjected to a frequency domain conversion, preferably a Fourier transform, fast Fourier transform, discrete Fourier transform, of other such well known signal processing techniques. 
         [0061]      FIG. 13A  shows a color coded surface topography of an IC similar to the surface profile image of  FIG. 4A .  FIG. 13B  shows a time domain image of the IC.  FIG. 13C  shows a frequency domain representation of the IC. Displaying any combination of the images of  FIG. 13A-13C  may provide a user a better understanding of how defects on any one of the three views may affect the others. 
         [0062]      FIG. 14  is a flowchart that illustrates how a user can cause a visual indication of surface profile data to be simultaneously displayed with, for example, a time domain signal representing internal acoustic impedance features, and/or a frequency domain representation. It should be understood that any combination of these three visual representations can be generated and displayed while the data is being generated. Alternatively, any combination of these three signals can be displayed by operation with a “virtual sample” of previously obtained data about a part. 
         [0063]    At step  800  profile and internal data may be collected as described above. At step  802 , the system checks whether the user has selected the frequency domain representation to be displayed. If the frequency domain representation is not selected to be displayed the system proceeds to step  810 . If the frequency domain representation is selected to be displayed, then at step  804  the computer collects the user selected data. The user selected data of step  804  refers to the frequency related characteristics or ranges in which a user is interested in analyzing a part. For example, a user may be interested in seeing a visual indication of how a part looks with respect to a particular band of frequencies. To accomplish this, the user selected data (e.g., a band of frequencies) is input into the system, which then applies a Fourier transfer at step  806  using the frequency data on a time domain signal. The resulting transformed signal is then displayed at step  808  on a display either by itself or in combination with a time domain signal and a surface topography image if the time domain representation is selected by the user at step  810 . 
         [0064]    At step  810 , if the time domain representation is not selected to be displayed, the system proceeds to step  814 . If the time domain representation is selected to be displayed then at step  812  the resulting time domain representation is displayed either by itself or in combination with the frequency domain representation and/or the surface topography image. 
         [0065]    At step  814  if the surface topography is not selected to be displayed the process ends. If the surface topography is selected to be displayed then at step  816  the surface topography image may be displayed in combination with either or both of the frequency domain representation of the time domain signal representation. 
         [0066]    While the present invention has been described with reference to specific examples, which are intended to be illustrative only and not to be limiting of the invention, it will be apparent to those of ordinary skill in the art that changes, additions or deletions in addition to those explicitly described above may be made to the disclosed embodiments without departing from the spirit and scope of the invention.