Patent Publication Number: US-11395081-B2

Title: Acoustic testing method and acoustic testing system thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 63/030,913, filed on May 27, 2020, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an acoustic testing method and acoustic testing system thereof, and more particularly, to an acoustic testing method and acoustic testing system thereof capable of increasing testing efficiency. 
     2. Description of the Prior Art 
     The design challenge for producing high-fidelity sound by the conventional speaker is its enclosure. Normally, a speaker cannot be used without installing it in the speaker enclosure (or an acoustic resonator). The speaker enclosure is often used to contain the back-radiating wave of the produced sound to avoid cancelation of the front radiating wave in certain frequencies where the corresponding wavelengths of the sound are significantly larger than the speaker dimensions. The speaker enclosure can also be used to help improving, or reshaping, the low-frequency response, for example, in a bass-reflex (ported box) type enclosure where the resulting port resonance is used to invert the phase of back-radiating wave and achieves an in-phase adding effect with the front-radiating wave around the port-chamber resonance frequency. On the other hand, in an acoustic suspension (closed box) type enclosure, the enclosure functions as a spring which forms a resonance circuit with the vibrating membrane. With properly selected speaker driver and enclosure parameters, the combined enclosure-driver resonance peaking can be leveraged to boost the output of sound around the resonance frequency and therefore improves the performance of resulting speaker. 
     The testing of the conventional speaker can bring various challenges and costs time, money and effort. Since the conventional speaker requires the speaker enclosure, the conventional speaker is tested and calibrated after the speaker has been installed in the speaker enclosure. A disadvantage of this approach is that a defective speaker is recognized only after installation/assembly. This causes a cost increase because the defective speaker must be discarded together with the speaker enclosure. Therefore, how to test a sound producing device is an important objective in the field. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the present invention to provide an acoustic testing method and acoustic testing system thereof capable of increasing testing efficiency. 
     An embodiment of the present invention provides an acoustic testing method. The acoustic testing method comprises providing an electrical signal to a wafer, wherein the wafer comprises a plurality of acoustic transducers, and the electrical signal is provided to an acoustic transducer within the wafer; and receiving a sound wave generated by the acoustic transducer according to the electrical signal, and generating a sensing result for determining an acoustic functionality of the acoustic transducer. 
     Another embodiment of the present invention provides an acoustic testing system. The acoustic testing system comprises a wafer, wherein a plurality of acoustic transducers is formed within the wafer, and an acoustic transducer within the wafer receives an electrical signal; and a sound sensing device, configured to receive a sound wave generated by the acoustic transducer according to the electrical signal, and generate a sensing result for determining an acoustic functionality of the acoustic transducer. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  to  FIG. 6  are schematic diagrams of acoustic testing systems according to embodiments of the present invention respectively. 
         FIG. 7  and  FIG. 8  are schematic diagrams of spectrum according to embodiments of the present invention respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic diagram of an acoustic testing system  10  according to an embodiment of the present invention. The acoustic testing system  10  comprises a wafer  100  and an acoustic testing apparatus  110 . The wafer  100  (also referred to as semiconductor wafer) comprises a plurality of acoustic transducers DUT (also referred to as die). Each acoustic transducer DUT may produce a sound/acoustic wave Wp after receiving an electrical signal Sd. The acoustic testing apparatus  110  may comprise a sound sensing device  116 , and is utilized to perform acoustic testing corresponding to the electrical signal Sd on the wafer  100 . 
     Briefly, each acoustic transducer DUT may be able to convert the electrical signal Sd into the sound wave Wp. The acoustic testing apparatus  110  may detect the sound wave Wp at wafer level (or before the conventional wafer dicing process), so as to verify the acoustic functionality of each of the acoustic transducer DUT. Therefore, cost in time, money and effort may be reduced. 
     Conventionally, a manufacturing process (by which a wafer is formed), a conventional wafer testing process (by which circuit behavior of each die on the wafer is electrically tested and measured), the conventional wafer dicing process, a conventional packaging process (by which each separated die is packaged), an conventional installation/assembly process (by which each separated die is mounted in an enclosure), and a conventional acoustic testing are performed and follow the sequence outlined above. The conventional acoustic testing must follow the conventional assembly process because only with the enclosure can the conventional acoustic testing be practical and worthwhile. 
     Different from the conventional acoustic testing, coming after the conventional wafer dicing process and the conventional assembly process, the acoustic testing apparatus  110  of the present invention performs the acoustic testing, along with the conventional wafer testing process, at wafer level to increase testing efficiency and smoothen overall process. 
     The acoustic testing (or the conventional acoustic testing) may involve sound intensity, sound power, sound quality, or sound spectral measurement. The conventional wafer testing process focuses on circuit behavior such as connectivity, sensitivity, capacitance, resonance frequency, −3 dB frequency, frequency response, and quality factor. The conventional wafer testing process may include, for instance, wafer sort, wafer final test, electronic die sort, and circuit probe. 
       FIG. 2  is a schematic diagram of an acoustic testing system  20  according to an embodiment of the present invention. In  FIG. 2 , the sound sensing device  116  of the acoustic testing system  20  may be a microphone. The sound sensing device  116  may measure the sound wave Wp produced by the acoustic transducer DUT within the wafer  100  and convert the sound wave Wp into an electrical signal Ss (also referred to as a second electrical signal). The acoustic testing apparatus  110  may analyze the electrical signal Ss to verify acoustic functionality of the acoustic transducer DUT. For example, the acoustic testing apparatus  110  may check whether the acoustic transducer DUT within the wafer  100  is able to produce sound. Alternatively, the acoustic testing apparatus  110  may determine whether the sound pressure level (SPL) of the sound wave Wp produced by the acoustic transducer DUT within the wafer  100  exceeds certain threshold, such as 55 decibel (dB). 
     Optionally, the acoustic testing apparatus  110  may compare voltage or current of the electrical signal Ss with a reference value. Optionally, the acoustic testing apparatus  110  may determine whether distortion is created or increased. Optionally, the SPL or waveform of the sound wave Wp may be assessed according to factory specifications to determine whether to pass or fail the acoustic transducer DUT. 
     In  FIG. 2 , each of the acoustic transducers DUT may be a sound producing device (SPD) (for example, a speaker). The acoustic transducer DUT may have high acoustic quality even if an enclosure or an acoustic resonator is absent from the acoustic transducer DUT. For example, the SPL of the sound wave Wp produced by the acoustic transducer DUT alone is high enough. Alternatively, the acoustic transducer DUT produces the sound wave Wp with little or no distortion. Therefore, the acoustic testing apparatus  110  performs acoustic testing on the acoustic transducer DUT at wafer level, or before the acoustic transducer DUT is assembled in an enclosure or an acoustic resonator. When the acoustic transducer DUT passes the acoustic testing at wafer level, the acoustic transducer DUT may be delivered to an end consumer without further acoustic testing. The acoustic testing apparatus  110  does not perform acoustic testing on the acoustic transducer DUT mounted in an enclosure or an acoustic resonator. 
     To overcome the design challenges of speaker driver and enclosure within the sound producing industry, applicant provides the sound producing micro-electrical-mechanical-system (MEMS) device in U.S. application Ser. No. 16/125,761, so as to produce sound in an air pulse rate/frequency, where the air pulse rate is higher than the maximum human audible frequency, sometimes reaching an ultrasonic frequency. 
     A force-based sound producing apparatus/device and a position-based sound producing apparatus/device are provided in U.S. application Ser. No. 16/420,141 and Ser. No. 16/420,190, which can be used as a realization of the acoustic transducer of the present invention and are incorporated herein by reference. In the force-based sound producing apparatus, the force-based SPD is directly driven by a pulse amplitude modulated (PAM) driving signal. In the position-based apparatus, a MEMS SPD is utilized and a summing module therein is utilized to convert the PAM driving signal to the driving voltage to drive the membrane within the MEMS SPD to achieve a certain position. 
     To enhance sound quality, an SPD disclosed by U.S. application Ser. No. 16/920,384, which may be also used as a realization of the acoustic transducer of the present invention and is incorporated herein by reference. A MEMS chip configured to produce sound wave is formed of a silicon wafer by at least one semiconductor process. 
     As shown in  FIG. 2 , the acoustic transducer DUT may comprises a sound producing membrane  202 , an actuator  204  attached to the sound producing membrane  202 , or circuit(s). The actuator  204  is configured to receive an electrical signal (for example, the electrical signal Sd), such that the acoustic transducers DUT is able to produce a plurality of air pulses at an air pulse rate, where the air pulse rate is higher than a maximum human audible frequency, like what U.S. application Ser. No. 16/125,761 does. More specifically, the plurality of air pulses and the air pulse array produced by the acoustic transducer DUT of the present application would inherit the air pulse characteristics of U.S. applications Ser. Nos. 16/125,761, 16/420,141, 16/420,190 and 16/420,184, in which each one of the plurality of air pulses generated by the acoustic transducer DUT of the present application would have non-zero offset in terms of SPL, where the non-zero offset is a deviation from a zero SPL. The amplitude of each air pulse and its non-zero offset may be proportional to amplitudes of the electrical signal Sd sampled at the said air pulse rate. In addition, the plurality of air pulses generated by the acoustic transducer DUT of the present application is aperiodic over a plurality of pulse cycles. Details of the “non-zero SPL offset” and the “aperiodicity” properties may be referred to U.S. application Ser. No. 16/125,761, which are not narrated herein for brevity. 
     The acoustic testing mentioned above on the acoustic transducers DUT is initiated after the manufacturing process is completed. The acoustic transducers DUT may be manufactured using thin film techniques or micromachining fabrication techniques such as typical MEMS processes at wafer level similar to those used for integrated circuits. The acoustic transducers DUT may be a lead zirconate titanate (PbZr (x) Ti (1-x) O 3  or PZT) actuated MEMS device, which may be fabricated from an silicon on insulator (SOI) wafers with silicon (Si) thickness as 3˜6 μm and a PZT layer of thickness of 1 to 2 micrometer (μm), for example. All the acoustic transducers DUT are simultaneously fabricated on the wafer  100 . To manufacture one of the acoustic transducers DUT, each sound producing membrane  202  may be formed during the manufacturing process of the circuit(s). That is to say, the sound producing membrane  202 , the actuator  204 , and the circuit(s) are integrated together instead of being fabricated from individual discrete parts, and this monolithic nature ensure higher yield and lower cost. 
       FIG. 3  is a schematic diagram of an acoustic testing system  30  according to an embodiment of the present invention. As shown in  FIG. 3 , the acoustic testing apparatus  110  of the acoustic testing system  30  may comprise a plurality of sound sensing devices  116 , a probe card  311 , and a frame  318 . In some embodiments, the acoustic testing apparatus  110  may further comprise a wafer prober, a tester, or a microscope. The sound sensing devices  116  configured to detect the sound wave Wp produced by the acoustic transducer DUT within the wafer  100  may be arranged in an array and disposed on the frame  318  above the probe card  311 . Alternatively, the sound sensing devices  116  may be randomly distributed on the frame  318 . The more the sound sensing devices  116 , the higher the testing efficiency, coverage, or accuracy may be. The frame  318  is configured to provide electrical connections and mechanical support. In some embodiments, the frame  318  may be another probe card different from the probe card  311 . 
     The probe card  311  is configured to provide the electrical signal Sd to the wafer  100 . The probe card  311  configured to test the wafer  100  may comprise a plurality of probes  311   g  that extend downwards from the probe card  311 . The probes  311   g  may be microscopic electronic contacts for making electrical contact with electronic pads of the acoustic transducers DUT on the wafer  100  to allow signal transmission. Before, when, or after the probe card  311  triggers one of the acoustic transducers DUT within the wafer  100  by the electrical signal Sd, the probe card  311  may perform the conventional wafer testing process on the acoustic transducer DUT at wafer level to check whether the acoustic transducer DUT meets (electrical characteristics) requirements. In the conventional wafer testing process, the probe card  311  may input electrical signal(s) (which may be the electrical signal Sd or another electrical signal) to and receive electrical feedback(s), which belong to electrical signal(s), from the acoustic transducer DUT being tested on the wafer  100  via the probes  311   g  so as to identify faults in the acoustic transducer DUT (namely, for electrical measurements). 
     While all the acoustic transducers DUT are still on/within the wafer  100 , the acoustic transducers DUT are tested (electrically checked by the conventional wafer testing process and acoustic checked by the acoustic testing) and nonfunctional/malfunctional acoustic transducer(s) DUT are identified. In other words, during testing, the sound sensing device  116  may keep detecting the sound wave Wp produced from the sound producing membrane  202  being triggered to vibrate, and the probe card  311  may keep detecting the electrical feedback(s) from the probe(s)  311   g . Subsequently, the wafer  100  is sliced into individual acoustic transducers DUT. Nonfunctional acoustic transducer(s) DUT are discarded; functional acoustic transducer(s) DUT are sent on to be assembled into (plastic) packages and then delivered to an end consumer. Because the testing takes place before the acoustic transducers DUT are split by, for instance, a diamond saw, it can be easier and more accurately for an processing circuit of the acoustic testing apparatus  110  to localize all the acoustic transducers DUT on the same wafer  100  and for the probe  311   g  to contact the electronic pads of the acoustic transducers DUT. Instead of performing the conventional wafer testing process and the acoustic testing separately, the acoustic testing apparatus  110  of the present invention performs the acoustic testing, along with the conventional wafer testing process, at wafer level to increase testing efficiency. 
     As shown in  FIG. 3 , the acoustic transducers DUT may comprise a plurality of cells CLL. Each cell CLL may comprise a membrane layer, a bottom electrode layer, an actuator layer, and a top electrode layer, which may be stacked in sequence. The actuator layer sandwiched between the bottom electrode layer and the top electrode layer may comprise a piezoelectric layer. The bottom electrode layer, the actuator layer, and the top electrode layer may constitute the actuator  204  and may be disposed on the membrane layer, which may serve as the sound producing membrane  202 , by means of, for instance, chemical vapor deposition (CVD), physical vapor deposition (PVD) sputtering or sol-gel spin coating. The electrical signal (for example, the electrical signal Sd) is applied between the bottom electrode layer and the top electrode layer to cause a deformation of the piezoelectric layer. Deformation of the actuator  204  may cause the membrane layer to deform and result in its surface moving upwards or downwards, particularly to a specific position according to the electrical signal. Moreover, the specific position of the membrane layer is proportional to the electrical signal applied to the actuator  204 . 
     In some embodiments, provided the response time of membrane movements is significant shorter than a pulse cycle time, such movements of the membrane layer over a plurality of pulse cycles would produce a plurality of air pulses at an air pulse rate, which is the inverse of the pulse cycle time. 
       FIG. 4  is a schematic diagram of an acoustic testing system  40  according to an embodiment of the present invention. Distinct from the acoustic testing system  30 , the sound sensing devices  116  of the acoustic testing system  40  are located on the probe card  311  to capture the sound wave Wp produced by the acoustic transducer DUT within the wafer  100 . In other words, the frame  318  of the acoustic testing system  30  is optional and may/can be removed. The probe card  311  alone may provide electrical connections and mechanical support for the sound sensing devices  116 . Because the sound sensing devices  116  of the acoustic testing system  40  is disposed closer to the wafer  100 , the sound sensing devices  116  of the acoustic testing system  40  may hear/receive the sound wave Wp more clearly. 
       FIG. 5  is a schematic diagram of an acoustic testing system  50  according to an embodiment of the present invention. Besides the sound sensing devices  116 , the probe card  311 , and the frame  318 , the acoustic testing apparatus  110  of the acoustic testing system  50  may comprise a probe chuck  515 , a probe card holder  517 , and a noise isolation cover  519 . The wafer  100  may be enclosed by the probe chuck  515 , the probe card holder  517 , and the noise isolation cover  519 . The acoustic testing apparatus  110  may not be sealed by the noise isolation cover  519 . The noise isolation cover  519  is configured to surround the wafer  100  or close off the acoustic testing apparatus  110  on several sides so as to achieve noise isolation and increase signal to noise ratio. The noise isolation cover  519  may comprise soundproofing material  519   m , such that ambient acoustic noise and vibration as seen by the acoustic transducer DUT are reduced. The soundproofing material  519   m  may have a structure of periodic solids, for example, a saw-tooth-shaped or pyramid array structure. The structural periodicity of the soundproofing material  519   m  may cause destructive interference between transmitted and reflected waves, thereby preventing specific wave types from propagating. The probe card holder  517  may form a part of the wafer prober. The probe card  311  may be fastened to the probe card holder  517  so as to be held in place during testing. 
     The probe chuck  515  is configured to support the wafer  100 . The wafer  100  may be held onto the probe chuck  515 , for example, via vacuum pressure. The prober chuck  515  may control and limit movement of the wafer  100  and thus enable sequential wafer-level testing (namely, the acoustic testing and the conventional wafer testing process) from one acoustic transducer DUT to the next. After one acoustic transducer DUT has been tested, the probe chuck  515  may move the wafer  100  vertically or laterally to the next acoustic transducer DUT with respect to the probe card  311  to start next testing. For example, the wafer  100  may move downwards away from tips of the probes  311   g , then move towards the left (or right) with respect to the probe card  311 , and then move upwards and back to the tips of the probes  311   g . In this case, one acoustic transducer DUT receives the electrical signal Sd from the probe card  311  before the next acoustic transducer DUT receives the electrical signal Sd from the probe card  311 . That is, all the acoustic transducers DUT receive the electrical signal Sd respectively in sequence (one by one) according to movement of the wafer  100 . In an embodiment, the probe chuck  515  may be positioned by an optical device such that the probes  311   g  is able to contact the electronic pads of the acoustic transducers DUT on the wafer  100  precisely. The sound sensing devices  116  and the probe card  311  are firmly fixed without moving to ensure consistent test quality. 
       FIG. 6  is a schematic diagram of an acoustic testing system  60  according to an embodiment of the present invention. The acoustic transducers DUT constituting the wafer  100  as shown in  FIG. 1  may be named as acoustic transducers DUT 1 -DUTn. Distinct from the acoustic testing system  10 , the testing (namely, the acoustic testing and the conventional wafer testing process) of several acoustic transducers (for example, the acoustic transducers DUT 1 -DUTx) of the acoustic testing system  60  may take place in parallel on the wafer  100 . Specifically, a processing circuit  112  of the acoustic testing apparatus  110  or the probe card  311  may transmit electrical signals Sd 1 -Sdx, which correspond to different frequencies, to the acoustic transducers DUT 1 -DUTx respectively at a time. The acoustic transducers DUT 1 -DUTx may receive the electrical signals Sd 1 -Sdx respectively at the same time, and produce sound waves Wp 1 -Wpx corresponding to the electrical signals Sd 1 -Sdx respectively. The sound sensing devices  116  may detect the sound waves Wp 1 -Wpx, which correspond to frequencies different from each other, at a time. The parallelization of testing the acoustic transducers DUT 1 -DUTx may reduce the testing cost and time in an efficient manner. Before, when, or after the acoustic transducers DUT 1 -DUTx within the wafer  100  are triggered by the electrical signals Sd 1 -Sdx, the conventional wafer testing process may be performed on the acoustic transducers DUT 1 -DUTx at wafer level respectively as well. 
     After the acoustic transducers DUT 1 -DUTx have been tested, the probe chuck  515  may move the wafer  100  vertically or laterally to the next the acoustic transducers DUT(x+1)-DUT 2   x  to start next testing. Because more than one acoustic transducers (for instance, the acoustic transducers DUT 1 -DUTx) are tested at a time, testing efficiency is improved. By providing electrical signals of different frequencies (namely, the electrical signal Sd 1 -Sdx) to the acoustic transducers DUT 1 -DUTx, the processing circuit  112  or the sound sensing devices  116  can distinguish each of the sound waves Wp 1 -Wpx, because the sound waves Wp 1 -Wpx produced from the acoustic transducers DUT 1 -DUTx have different frequencies respectively. In this way, audio performance of each of the acoustic transducers DUT 1 -DUTx can be determined. The acoustic testing apparatus  110  may check whether the acoustic transducers DUT 1 -DUTx within the wafer  100  are able to produce sound by detecting the sound waves Wp 1 -Wpx. The acoustic testing apparatus  110  may detect the sound waves Wp 1 -Wpx by, for example, determining what component frequencies are present in the electrical signals Ss from the sound sensing device(s)  116 . 
     When a sound wave (for example, the sound wave Wp 1 ) is generated, it may produce its own fundamental and some harmonic due to nonlinear behavior. In other words, the output of the acoustic transducer (for example, the acoustic transducer DUT 1 ) has not only a component at the fundamental frequency, which is present at the input of the acoustic transducer, but also some of its harmonic. Therefore, each of the electrical signals Sd 1 -Sdx may have a frequency different from a harmonic frequency or a fundamental frequency of another of the electrical signals Sd 1 -Sdx. By the same token, each of the sound waves Wp 1 -Wpx may have a frequency different from a harmonic frequency or a fundamental frequency of another of the sound waves Wp 1 -Wpx. Alternatively, each of the electrical signals Sd 1 -Sdx (or the sound waves Wp 1 -Wpx) may have a frequency corresponding to a prime number respectively. 
     Specifically,  FIG. 7  and  FIG. 8  are schematic diagrams of spectrum according to embodiments of the present invention. As shown in  FIG. 7 , a fundamental frequency f 11  and harmonic frequencies f 12 , f 13  are related to each other by simple whole number ratios. For example, the harmonic frequencies f 12  (also referred to as the frequency of the second harmonic) is two times the fundamental frequency f 11  (also referred to as the frequency of the first harmonic). However, fundamental frequencies f 21 , fx 1  and harmonic frequencies f 22 , f 23 , fx 2 , fx 3  are unrelated to the fundamental frequency f 11  or the harmonic frequencies f 12 , f 13 . By properly assigning frequencies to the electrical signals Sd 1 -Sdx (or the sound waves Wp 1 -Wpx), the processing circuit  112  or the sound sensing devices  116  can distinguish between the sound waves Wp 1 -Wpx, because the harmonic frequencies of each of the sound waves Wp 1 -Wpx produced from the acoustic transducers DUT 1 -DUTx respectively would not be the same as the fundamental frequency or the harmonic frequencies of another of the sound waves Wp 1 -Wpx so as to avoid interference. 
     As shown in  FIG. 8 , a harmonic frequency F 21  (also referred to as second harmonic frequency) corresponding to a fundamental frequency F 21  may be equal to a harmonic frequency F 13  (also referred to as third harmonic frequency) corresponding to a fundamental frequency F 11 . However, within a frequency range RNG of the acoustic testing, fundamental frequencies F 11 , F 21 , Fx 1  and harmonic frequency F 12  are unrelated to one another. Harmonic frequencies outside the frequency range RNG (for example, harmonic frequency F 13 , F 22 , Fx 2 ) may not be analyzed by the processing circuit  112 . The processing circuit  112  would not be confused by the harmonic frequency F 21  corresponding to the fundamental frequency F 21  and the harmonic frequency F 13  corresponding to the fundamental frequency F 11 . By properly assigning frequencies to the electrical signals Sd 1 -Sdx (or the sound waves Wp 1 -Wpx), the processing circuit  112  or the sound sensing devices  116  can distinguish between the sound waves Wp 1 -Wpx, because the harmonic frequencies of each of the sound waves Wp 1 -Wpx produced from the acoustic transducers DUT 1 -DUTx respectively would not be the same as the fundamental frequency or the harmonic frequencies of another of the sound waves Wp 1 -Wpx within the frequency range RNG so as to avoid interference. 
     In  FIG. 6 , the processing circuit  112  may control the operation of the probe card  311  or the sound sensing devices  116 . For example, the processing circuit  112  may instruct the probe card  311  to send the electrical signal Sd out. The processing circuit  112  may initiate the detection operation of the sound sensing devices  116  and receive the electrical signal Ss from the sound sensing devices  116 . The processing circuit  112  may be coupled to the probe card  311  or the sound sensing devices  116 . Alternatively, the processing circuit  112  may be integrated into the probe card  311 , the frame  318 , or any of the sound sensing devices  116 . 
     As shown in  FIG. 6 , the processing circuit  112  may comprise an audio recording circuit  612 R, a digital signal processing circuit  612 P, a determining circuit  612 D, a signal generating circuit  612 G, and an amplifier  612 M. The audio recording circuit  612 R may receive and record the electrical signal(s) Ss from the sound sensing device(s)  116 . After the digital signal processing circuit  612 P analyzes the output of the audio recording circuit  612 R, the determining circuit  612 D may evaluate the audio performance of the acoustic transducers DUT 1 -DUTx. The digital signal processing circuit  612 P may be a digital signal processor (DSP), and the determining circuit  612 D may be a processor or a micro-controller (MCU). The determining circuit  612 D may instruct the signal generating circuit  612 G to generate signals, which are then converted into the electrical signals Sd 1 -Sdx by the amplifier  612 M. In some embodiments, the processing circuit  112  may further comprise a simple multiplexer-type (MUX-type) addressing circuit so that merely one acoustic transducer is turned on at a time. 
     In summary, the acoustic testing apparatus of the present invention may detect a sound wave so as to verify acoustic functionality of an acoustic transducer at wafer level before the conventional wafer dicing process. Unlike the conventional acoustic testing always performed after the conventional wafer dicing process, the acoustic testing apparatus of the present invention may perform both the acoustic testing and the conventional wafer testing process at wafer level (before the conventional wafer dicing process) to increase testing efficiency and smoothen overall process. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.