JP2010175449A - Ultrasonically inspecting device and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonically inspecting device capable of more precisely detecting a defect of an object to be inspected including a multilayer structure with a simple method, clearly visualizing, and precisely inspecting, and a method therefor. <P>SOLUTION: The ultrasonically inspecting device 17 includes the steps of transmitting an ultrasonic wave to the object while scanning the object 15 with an ultrasonic probe 16 in the surface direction, receiving a reflected echo wave returned from the object to transform it to the waveform data of the reflected echo wave, transmitting the waveform data to an arithmetically processing means 41, and performing an arithmetic processing by the arithmetically processing means 41 to inspect a flaw. The arithmetically processing means contains an extracting means (steps S16 and S17) to extract a changed site caused by frequency power spectrum 206 of a received wave concerning the reflected echo wave when the plurality of reflected echo wave are interfered and an image creating means (steps S19 and S20) to create images 221-224 concerning a flaw based on the changed site extracted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic inspection apparatus and an ultrasonic inspection method, and more particularly to an ultrasonic inspection apparatus and an ultrasonic inspection method suitable for inspecting a subject having a multilayer structure.

  In general, in order to detect a defect of an object with ultrasonic waves, reflection characteristics due to differences in acoustic impedance are used. By detecting the intensity change or phase change of the reflected wave from the defect, it is possible to grasp the presence or absence of the defect present in the subject. In the subject, when an ultrasonic wave is incident on a substance having a low acoustic impedance from a substance having a high acoustic impedance, the ultrasonic wave is reflected at the boundary surface between the two substances. The phase of the reflected wave changes by 180 ° compared to the phase of the incident wave. For example, when an ultrasonic wave is incident on a substance having a low acoustic impedance such as water or air from a solid substance, the phase of a reflected signal corresponding to a reflected wave from delamination is 180 ° relative to an incident signal corresponding to the incident wave Shift and invert. By determining whether the phase of the reflected signal is inverted or non-inverted with respect to the phase of the incident signal, it is possible to detect the presence or absence of a defect in the subject using ultrasonic waves.

  In a defect inspection apparatus, the maximum value of the positive peak and the maximum value of the absolute value of the negative peak are usually detected from the non-inverted signal waveform and the inverted signal waveform in the waveform signal on the time axis, respectively, and these two maximum values are detected. Compare values. Then, when the maximum value of the absolute value of the negative peak corresponding to the inverted reflected wave is larger than the maximum value of the positive peak, it is determined that there is a defect inside the subject. The determination result is displayed as a two-dimensional image or the like on the screen of the display device.

  Moreover, there is a defect inspection apparatus described in Patent Document 1 as a conventional technique. In this defect inspection apparatus, an internal interface of a subject having a multilayer structure is inspected. The subject is a member having a three-layer structure in which, for example, two carbon steel plates are bonded with an epoxy adhesive. An interface that reflects ultrasonic waves exists between each of the two carbon steel plates and the epoxy adhesive. The computer that performs the defect determination stores a unique frequency corresponding to the reflected echo returning from the interface between the lowermost carbon steel plate and the epoxy adhesive. At the time of inspection, when a reflected echo signal is input from an ultrasonic flaw detector, the reflected echo signal is Fourier transformed to calculate a frequency spectrum and check whether the frequency spectrum includes the above-mentioned specific frequency. The quality of the adhesion state is determined. When a specific frequency is included, it is determined that the adhesion is good, and when it is not included, it is determined that the adhesion is poor. As described in paragraph 0020 of Patent Document 1, the intrinsic frequency (f) of the reflected wave by the ultrasonic wave incident on each layer of the three-layer structure member is “f = L / T, T = L / c”. It is calculated | required by the formula of ". Here, L is the propagation distance (plate thickness × 2), c is the speed of sound in the material, and T is the period.

Japanese Patent Laid-Open No. 9-5305

  According to the conventional ultrasonic flaw detection method, generally, a plurality of reflected waves (reflected echoes) are generated from each of a plurality of interfaces inside the subject, and a time difference is generated between these reflected echo signals due to a difference in propagation time. Therefore, the reflected echo signal at the specific interface can be extracted separately from the other reflected echo signals. Therefore, it is possible to inspect defects inside the subject by applying an imaging gate to the interface echo signal, cutting out an arbitrary time region, and detecting an interface image by detecting a peak in the imaging gate. it can.

  However, in the conventional ultrasonic flaw detection method described above, when the subject has a multilayer structure composed of thin layers, or in the case of low-frequency ultrasonic measurement at the expense of waveform separation due to the influence of attenuation, etc. A problem arises in that reflected echo signals from the interface of each layer are close in the time domain and the waveforms interfere with each other. In such a case, it is impossible to obtain a plane image in which each layer is separated, and even if there is a defect, the waveform including the information on the part is distorted or buried, so that an accurate inspection can be performed. The problem of not being raised is raised.

  Therefore, the present inventors previously proposed a new defect detection method (Japanese Patent Application No. 2008-1111148, filed on April 22, 2008). This defect detection method is a method of extracting a feature of a defect from a change characteristic generated in a frequency domain by performing Fourier transform on a waveform formed by interference of a plurality of echo signals. The present invention further develops a technique that utilizes a change characteristic in the frequency domain, and proposes a technique that can detect a defect more easily even for an object including the multilayer structure.

  Moreover, according to the inspection method of the defect inspection apparatus described in Patent Document 1, a specific frequency corresponding to the interface between the lowermost carbon steel sheet and the epoxy adhesive is obtained in the frequency spectrum obtained by Fourier transform from the reflected echo signal. Whether or not the two carbon steel sheets are bonded is determined based on whether they are included. This point is shown in the flowchart of FIG. 4 or FIG. On the other hand, the defect inspection method disclosed in Patent Document 1 does not disclose the concept of visualizing (imaging) the inspection result with a defect inspection apparatus and expressing the presence or absence of a defect as an image.

  An object of the present invention is to detect internal defects such as an object including a multilayer structure accurately and with good reproducibility based on a simple method, and can clearly image the object. An object of the present invention is to provide an ultrasonic inspection apparatus and an ultrasonic inspection method that can be inspected well.

  The ultrasonic inspection apparatus and the ultrasonic inspection method according to the present invention are configured as follows in order to achieve the above object.

The ultrasonic inspection apparatus according to the present invention sends ultrasonic waves from the ultrasonic probe toward the subject while scanning the ultrasonic probe in a plane direction parallel to the surface of the subject, and returns from the subject. The reflected echo wave is received by the ultrasonic probe, the signal related to the reflected echo wave is converted into digital waveform data, the digital waveform data is sent to the arithmetic processing means, and the arithmetic processing means performs the arithmetic processing to perform the processing. Inspect the specimen for internal defects. When the plurality of reflected echo waves returning from the subject and interfering with each other, the arithmetic processing means described above performs waveform characteristics (frequency power spectrum) of the received waveform related to the plurality of reflected echo waves that interfered with each other. Extraction means for extracting a change part (a part having a dip frequency or interference frequency) generated by the characteristic) and an image creation means for creating an image related to an internal defect based on the extracted change part. Based on the image thus created, the user inspection operator inspects internal defects.
The above extraction means performs processing by Fourier transform (FFT, etc.) on the data related to the received waveform, and calculates the power spectrum, and the power spectrum value decreases on the power spectrum calculated by the Fourier transform processing. And calculating means for calculating at least one dip frequency and band setting means for setting a band for the dip frequency.
The image creating means includes a value detecting means for detecting a power value of a band or a peak value of a waveform obtained by inverse Fourier transform, and a two-dimensional image by converting the detected power value or peak value data into luminance. And an image creating means for creating the image.
In the above configuration, the subject includes a multilayer structure having a plurality of interfaces, dip frequencies are calculated corresponding to each of the plurality of interfaces, and a plurality of two-dimensional images are created according to each of the plurality of dip frequencies. It is characterized by that.
With respect to the above dip frequency (f _d ), the dip frequency (f _di ) relating to the i-th layer is obtained by the following equation (1).

The ultrasonic inspection method according to the present invention sends an ultrasonic wave from the ultrasonic probe toward the subject while scanning the ultrasonic probe in a plane direction parallel to the surface of the subject, and returns from the subject. This is a method of receiving the reflected echo wave coming from the ultrasonic probe, converting the signal related to the reflected echo wave into digital waveform data, processing the digital waveform data, and inspecting the internal defect of the subject. An extraction step for extracting a change site generated in the waveform characteristics in the frequency domain of the received waveform related to the plurality of reflected echo waves that interfered with each other when there are a plurality of reflected echo waves returning from And an image creation step of creating an image related to the internal defect based on the changed part.
The extraction step includes a conversion processing step of performing Fourier transform processing on the data related to the received waveform to calculate a power spectrum, and at least one dip frequency having a reduced power spectrum value on the power spectrum calculated by the Fourier transform. A calculation step for calculating and a band setting step for setting a band for the dip frequency are included.
The image creating step includes a value detecting step for detecting a band power value or a peak value of a waveform obtained by inverse Fourier transform, and converting the detected power value or peak value data into luminance to a two-dimensional image. And an image creating step for creating the image.
The subject includes a multilayer structure and has a plurality of interfaces, and dip frequencies are calculated corresponding to each of the plurality of interfaces, and a plurality of two-dimensional images are created according to the plurality of dip frequencies. To do.
As described above, with respect to the dip frequency (f _d ), the dip frequency (f _di ) relating to the i-th layer is obtained by the above equation (1).

The ultrasonic inspection apparatus and ultrasonic inspection method according to the present invention have the following effects.
The frequency power spectrum is obtained by performing Fourier transform on the waveform data obtained at multiple measurement points in the measurement range in the inspection of the internal defect of the subject in which multiple echo echoes are mixed to cause an interference state. Since the ultrasonic image for each layer is obtained using the spectrum and the structure information related to the multilayer structure of the subject, it is possible to easily and reliably inspect for the presence or absence of defects at each interface.
In addition, since an image of each interface between layers of a multilayer structure is created and displayed, ultrasonic inspection with excellent visibility and high defect detection can be performed for the user.
Furthermore, since each image to be created corresponds to the interface of each depth of the multilayer structure, it is possible to obtain depth information on the defect position with higher resolution.

It is an external view which shows the whole apparatus structure of the ultrasonic inspection apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structure of the control system and signal processing system of the ultrasonic inspection apparatus which concern on this embodiment. It is a figure for demonstrating the multilayer structure of a test object. It is a figure which shows the measurement range on a subject. It is a flowchart which shows the flow of a process of the test | inspection method implemented with the ultrasonic inspection apparatus which concerns on this embodiment. It is a conceptual explanatory diagram for conceptually explaining the contents of the procedure of the ultrasonic inspection method according to the present embodiment.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  The basic configuration of the ultrasonic inspection apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an external view showing the entire mechanical structure of the ultrasonic inspection apparatus. FIG. 2 is a system configuration diagram showing an electrical system, a control system, and a signal processing system.

  In FIG. 1, reference numeral 10 indicates a coordinate system of three orthogonal axes of X, Y, and Z. Reference numeral 11 denotes a scanner base, 12 denotes a water tank provided on the scanner base 11, and 13 denotes a scanner device provided on the scanner base 11 so as to straddle the water tank 12. The scanner base 11 is a base that is installed almost horizontally. Water 14 is injected into the water tank 12, and the subject 15 is placed in the water 14 in a submerged state. The water 14 in the water tank 12 is a medium necessary for efficiently propagating the ultrasonic wave radiated from the opening surface at the lower end of the ultrasonic probe 16 to the inside of the subject 15.

  In the ultrasonic inspection apparatus 17, it is necessary to interpose the water 14 between the subject 15 and the ultrasonic probe 16. The subject 15 is placed at the bottom of the water tank 12, for example. The subject 15 is a semiconductor package including, for example, a multilayer structure (or a stacked structure). The ultrasound probe 16 is disposed at a position above the subject 15, and the opening surface at the lower end faces the surface of the subject 15. The ultrasonic probe 16 transmits ultrasonic waves from the opening surface (ultrasonic wave emitting portion at the tip), and receives reflected echo waves (or reflected echoes) returning from the subject 15 at the opening surface. The ultrasonic probe 16 is supported by a holder 18 and installed. The holder 18 is attached to the X-axis scanner 19, and the X-axis scanner 19 is further attached to the Y-axis scanner 20. The arm-shaped X-axis scanner 19 has a function of moving the holder 18 in the X-axis direction, and the Y-axis scanner 20 has a function of moving the X-axis scanner 19 in the Y-axis direction. The X-axis scanner 19 and the Y-axis scanner 20 constitute the scanner device 13 described above. The ultrasonic probe 16 can be freely moved in the XY directions by the scanner device 13. Based on this moving operation, the ultrasonic probe 16 scans a predetermined measurement range on the surface of the subject 15, transmits and receives ultrasonic waves, and reflects at a plurality of measurement points set in advance within the measurement range. It is possible to receive an echo wave and inspect a defect of an internal structure included in the measurement range. The ultrasonic probe 16 is connected to a flaw detector (not shown) or the like via a cable 21.

  In the ultrasonic inspection apparatus 17 described above, an internal plane image is created by imaging the internal structure based on the reflected echo waves obtained at a plurality of measurement points, and defects such as defects are generated based on the image content of the internal plane image. Inspect (or measure) the defective part.

  As shown in FIG. 2, the ultrasonic inspection apparatus 17 is a digital ultrasonic inspection apparatus. The ultrasonic flaw detector 31 is driven by applying a pulse signal to the ultrasonic probe 16, and sends an ultrasonic wave U 1 from the ultrasonic probe 16 to the subject 15. Further, the ultrasonic flaw detector 31 receives the reflected echo wave U2 returning from the surface of the subject 15 or a plurality of internal interfaces, and converts it into an electric signal (reflected signal). The reflected signal is then amplified and filtered. The reflected signal that has undergone the necessary processing in the reception path of the ultrasonic flaw detector 31 is further converted into a digital signal, that is, digital waveform data (or reception waveform data) by the A / D converter 32. The digital waveform data is transmitted from the A / D converter 32 to the memory 33 and stored in the data storage unit 34 of the memory 33. The memory 33 further stores a mechanical scanning program 35, a measurement condition setting program 36, and a waveform calculation processing program 37. Thereafter, the digital waveform data is used as an arithmetic processing target when the waveform arithmetic processing program 37 stored in the memory 33 is executed, converted into two-dimensional image data by the waveform arithmetic processing, and stored in the image memory 38. Stored. The image data stored in the image memory 38 is displayed on a display device (LCD or the like) 40 via the display circuit 39. In addition, the waveform of the captured reflection signal is also displayed on the screen of the display device 40.

  The mechanical scanning program 35, the measurement condition setting program 36, and the waveform calculation processing program 37 stored in the memory 33 are read and executed by the microprocessor 41 via the bus 42 as necessary. The mechanical scanning program 35 is a program for controlling the scanning operation of the scanner device 13. The measurement condition setting program 36 is a program for setting measurement conditions according to the subject 15. The waveform calculation processing program 37 is a program that performs calculation processing on the obtained digital waveform data and creates two-dimensional image data for imaging.

  The waveform calculation processing program 37 performs image creation processing using a reflected wave returning from the surface and each interface of the multilayer structure in a predetermined measurement range of the subject 15 to extract defects and the like. The processing function is executed.

  The ultrasonic probe 16 fixed to the holder 18 is mechanically scanned in the biaxial direction (XY direction) by the scanner device 13. The scanner device 13 is controlled via a scanner control circuit 43 and an interface 44. As a result, the ultrasonic probe 16 can perform a scanning operation, move to an arbitrary position, and can stand still. An input device 45 is connected to the bus 42 via an interface 46.

  Even if the subject 15 has a multi-layer structure, when the surface or interface where the reflected wave is generated has a sufficient interval, the reflected signal from each interface has a time difference due to the difference in propagation time. Can be separated and extracted. If the reflected echo signal can be extracted, an arbitrary time region can be cut out by applying an imaging gate to a desired time region of the reflected echo signal, and a peak value in the imaging gate can be detected and imaged. . However, when the subject 15 is a thin multi-layer structure or low frequency ultrasonic measurement sacrifices waveform separation due to the influence of attenuation, reflected echo signals from each interface and the like are close in the time domain, and the waveform interferes. Resulting in. In this case, it is not possible to obtain a planar image in which each interface is separated. The present invention proposes a method for producing a planar image and inspecting a defect by this method particularly suitable for such a case.

FIG. 3 shows an example of a multilayer structure of the subject 15 and an example of a state of generation of reflected waves (or “reflected echo waves”) on the surface and each interface of the subject 15. In the example of the multilayer structure of the subject 15, for convenience of explanation, for example, at least four layers 51, 52, 53, 54 are shown. The materials of the four layers 51 to 54 are different. A surface 60 and four interfaces 61, 62, 63, 64 are formed. In FIG. 3, for each of the layers 51 to 54, the thickness is indicated by l ₁ to l ₄ , the sound velocity is indicated by ν _{1 to} ν ₄ , and the phase constant is indicated by β ₁ to β ₄ . . In the example shown in FIG. 3, the ultrasonic wave 71 incident from the surface side of the subject 15 is reflected by the reflected wave 72 reflected by the surface 60 and the interface 63 located at the third depth position from the surface 60. A reflected wave 73 is shown. In this reflection example, it is assumed that the interface 63 has a defect. The reflected wave 72 and the reflected wave 73 interfere with each other, and one reflected wave 74 returns to the ultrasonic probe 16 as an echo.

The ultrasonic wave 71 corresponds to the ultrasonic wave U1 shown in FIG. 2, and the reflected wave 74 that has interfered corresponds to the reflected echo wave U2 shown in FIG. In addition, bold “r _A ”, “r _B ”, and “R” shown in FIG. 3 represent the reflected waves 72, 73, and 74 as vectors, respectively.

  As described above, when reflected echo waves (72, 73) interfere with each other from the multilayer structure of the subject 15, it is not easy to separate and detect the reflected echo signal to be obtained in the time domain. Therefore, information related to the defect is extracted by paying attention to a change in characteristics in the frequency domain, not in the time domain. That is, the present inventors have found a characteristic that when interference occurs with a reflected echo wave returning due to a defect, a dip (a portion where power is weakened) occurs in the frequency power spectrum. Such a dip does not occur in the frequency power spectrum of the reflected echo wave from the normal part. Therefore, if attention is paid to the presence or absence of the dip in the frequency power spectrum, the presence or absence of a defect can be determined, and the depth of the defect can be estimated from the frequency (dip frequency or interference frequency) where the dip occurs. I found out.

  When the reflected wave 74 generated by interference between the reflected wave 72 from the surface 60 of the subject 15 and the reflected wave 73 from the interface 63 is mathematically expressed, the following equation (2) is obtained.

Here, π of the phase term (−2β ₁ l ₁ −β ₂ l ₂ −β ₃ l ₃ + π) means that the phase is inverted by 180 ° due to a defect. The condition that the phase is reversed is that the ultrasonic wave propagates from a material having a high acoustic impedance to a material having a low acoustic impedance. In particular, the acoustic impedance of the void that becomes a defect is very low.

The condition that the dip occurs in the frequency power spectrum is when the amplitude of the reflected wave 74 becomes weak and the expression “−2β ₁ l ₁ −β ₂ l ₂ −β ₃ l ₃ + π = −π (3)”. Is true. This means that the phase difference between the reflected wave 72 from the surface 60 and the reflected wave 73 from the interface 63 is shifted by 180 ° (π). Further, the dip frequency (f _d3 ) at this time is calculated by the following equation (4).

  The presence / absence of a defect is determined from the presence / absence of the dip frequency, and the depth of the defect is estimated from the dip frequency.

  With respect to the reflected echo wave returning from the subject 15 to the ultrasonic probe 16, the reflected echo wave returning from the normal part and the reflected echo wave returning from the defective part are Fourier-transformed, and the frequency at which the difference occurs is obtained. Extract the band and visualize it. As a result, the three-dimensional position of the defective portion can be visualized more clearly.

  Next, with reference to FIGS. 4-6, the procedure of the defect inspection method implemented with the ultrasonic inspection apparatus 17 which concerns on this embodiment is demonstrated.

  FIG. 4 shows a flowchart of a procedure of a defect inspection method performed in the ultrasonic inspection apparatus 17 based on the mechanical scanning program 35 and the waveform calculation processing program 37 described above. FIG. 5 conceptually shows a measurement range, a scanning path, and a large number of measurement points set in advance on the surface of the subject 15. These measurement ranges, scanning paths, and the like are set according to the measurement condition setting program 36. FIG. 6 is a diagram conceptually explaining the defect inspection method performed by the procedure shown in FIG.

  The ultrasonic inspection method according to the present invention automatically calculates the interference frequency of the reflected echo wave returning from the surface or each interface of the subject 15 having a multilayer structure, calculates the frequency power spectrum, and An imaging process is performed based on several predetermined bands in the frequency power spectrum, and a defect is inspected. In other words, the multi-gate video method using the frequency domain.

  In the flowchart of FIG. 4, in the first step S <b> 11, the ultrasonic probe 16 irradiates the surface of the subject 15 placed in the water 14 of the water tank 12 with ultrasonic waves from above. The ultrasonic probe 16 is scanned within a required measurement range on the XY plane set on the surface of the subject 15 based on the X-axis scanner 19 and the Y-axis scanner 20 (step S11). An example of the measurement range is shown in FIG. In this measurement range 101, reflection is performed at a large number of measurement points 103 (k = 1, 2, 3,..., N: n is the total number of pixels) set along the scanning movement path 102 of the ultrasonic probe 16. A wave echo wave (U2) is received, and a reflected echo signal is extracted. The reflected echo signal is a waveform signal of a reflected wave. In step S11, normal subject measurement is performed. Based on the reflected echo signal obtained at each measurement point 103, the reflected echo data in digital format is calculated and obtained. The reflected echo data is waveform data. The obtained n reflected echo data are stored in the data storage unit 34 of the memory 33.

  Next, using the n reflected echo data stored in the memory 33, the measurement range 101 is imaged once (step S12). The algorithm for performing the imaging is a conventional imaging algorithm. That is, an imaging gate is applied to the waveform data related to the acquired reflected echo signal in a desired time region, and a conventional normal ultrasound image is acquired based on the intensity of the maximum peak value. An image 201 shown in FIG. 6 is a normal ultrasonic image obtained by the above imaging process. The image 201 is an image created from the waveform data of the reflected echo wave obtained at each of the n measurement points 103. However, since the reflected echo wave at each measurement point 103 has interference, the defect is clear. The image is not displayed on the screen.

  An image 201 in FIG. 6 is displayed on the screen of the display device 40. The user inspection operator can recognize the image 201 on the screen of the display device 40. The inspection operator calls the waveform data 203 at a desired position (for example, the position of the point 202 in the image 201 in FIG. 6) while viewing the obtained image 201, and selects a time region 205 for performing Fourier transform (FFT, etc.) 204. To set (step S13). The calling position is a position where the reflected echo waves returning from the surface 60 of the subject 15 and the interfaces 61 to 64 are expected to be in a better interference state. The Fourier transform 204 is executed on the waveform data included in the selected time region 205, and the frequency power spectrum 206 is acquired and displayed on the screen of the display device 40 (step S14).

In the next step S <b> 15, the examination operator inputs data related to the multilayer structure of the subject 15 using the input device 45. Regarding the multilayer structure of the subject 15, the structure information is known to the user's inspection operator in advance. For example, when the user is a semiconductor device manufacturer, the user can know the multilayer structure or the laminated structure of various semiconductor devices handled by the user on the design drawing. As shown in the multilayer structure 207 of the subject 15 in FIG. 6, the structural information is the thicknesses l _{1 to} l ₄ and the sound speeds ν _{1 to} ν for each of the four layers 51 to 54 and the four interfaces 61 to 64 described above. ₄ and phase constants β _{1 to} β ₄ . Thus, in the ultrasonic inspection method according to the present embodiment, information related to the multilayer structure 207 of the subject 15 is input in advance to the processing system of the system as a parameter. The subject 15 is different for each user, and the multilayer structure is also different for each user. Therefore, in the automatic calculation of the dip frequency (interference frequency) in the obtained frequency power spectrum 206, information on the multilayer structure for each user is obtained. Is provided to the system in advance. In the multilayer structure 207 shown in FIG. 6, it is assumed that a defect 208 exists at the interface 62 and at least two defects 209 exist at the interface 64.

In the next step S16, the dip frequency (f _d ) of each of the four layers 51 to 54 is automatically calculated for the multilayer structure of the subject 15 based on the input information (parameters) related to the multilayer structure. The dip frequency of each layer 51-54 is the dip frequency corresponding to each interface 61-64. In this case, the dip frequencies corresponding to the reflected echo waves returning from the interfaces 61 to 64 are calculated on the assumption that an interference state has occurred. In the automatic calculation of the dip frequency, an expression similar to the expression (3) described above is used. In this example, the dip frequency (f _d1 ) of the first interface 61 is given by the following equation (5), and the dip frequency (f _d2 ) of the second interface 62 is given by the following equation (6): 3 The dip frequency (f _d3 ) of the fourth interface 63 is calculated by the aforementioned equation (4), and the dip frequency (f _d4 ) of the fourth interface 64 is calculated by the following equation (7). The equation shown in block 218 of FIG. 6 shows a general equation for automatically calculating the dip frequency. When the number of layers is 5 or more (the number of layers is i), the denominator term (2l _i / ν _i : i = 5, 6,...) Added.

When the dip frequencies f _d1 , f _d2 , f _d3 , and f _d4 are calculated, necessary bands 211, 212, 213, and 214 are set for the respective dip frequencies. In the diagram 219 of FIG. 6, four bands 211, 212, 213, and 214 set in the waveform diagram showing the frequency power spectrum 206 are overlapped. On the horizontal axis of the diagram 219, the right side direction corresponds to the shallow side in the multilayer structure 207, and the left side direction corresponds to the deep side in the multilayer structure 207.

In the frequency power spectrum 206 displayed on the screen of the display device 40, four bands 211, 212, 213 set based on the four dip frequencies f _d1 , f _d2 , f _d3 , and f _d4 obtained by calculation 214 is displayed (step S17).

  In the next step S18, it is determined whether or not to start imaging. This imaging is performed by using each part of the frequency power spectrum 211 corresponding to each of the four bands 211, 212, 213, and 214 corresponding to the four dip frequencies obtained as described above. Is what you do. The start of imaging may be performed based on a start command signal by an inspection operator via the input device 45, or may be performed in response to an automatic start command signal. When the start command signal is generated, step S19 of the next iteration process is executed. In step S19 of the iterative process, for example, first, the power value or inverse Fourier transform (inverse FFT or the like) is performed on all reflected echo data of k = 1,. ) To detect the peak value of the waveform. When the peak values of the waveform data are obtained for all the measurement points 103, the peak values are converted into luminance to create a two-dimensional image in the band 211 (step S20). In this way, an image as shown by reference numeral 221 in FIG. 6 is created and converted into an image.

  Next, in determination step S21, it is determined whether or not there is a remaining band to be visualized. At this stage, since the bands 212, 213, and 214 still remain, the iterative processing step S19 and the two-dimensional image creation step S20 are repeated, and the two-dimensional images 222, 223, and 224 are also obtained for the bands 212, 213, and 214, respectively. Create and visualize. When it is determined NO in determination step S21, the process ends.

  Regarding the two-dimensional images 221 to 224 thus obtained, the two-dimensional image 221 is an image of the interface 61, the two-dimensional image 222 is an image of the interface 62, and the two-dimensional image 223 is an image of the interface 63. Image 224 is an image of interface 64. In the two-dimensional image 222, a black region (dark region) is drawn, which represents the defect 208 described above. Similarly, in the two-dimensional image 224, two black areas are generated, which represent the two defects 209 described above.

  As described above, if there is a defect at any interface or the like of the multilayer structure 207 in the subject 15, the frequency power spectrum of the reflected echo wave reflected at the location and returning to the ultrasonic probe 16 is weak. Since a portion is generated, when a visualization process is performed using the waveform data, a dark display portion is drawn in the obtained image. In this way, for example, by obtaining the four images 221 to 224 shown in FIG. 6 and confirming visually by the inspection operator, the occurrence state of the defect in the multilayer structure 207 of the subject 15 can be accurately grasped.

  The user's inspection operator can obtain an ultrasonic image (image) with high defect detectability that avoids the influence of waveform interference between reflected echo waves only by inputting structural information about the multilayer structure to the subject 15 as a parameter. it can. According to the ultrasonic inspection method based on this invention, the imaging which isolate | separated the layer which was difficult with the conventional ultrasonic inspection method which images using a time domain can be performed. Furthermore, a plurality of images for each interface can be obtained in one inspection operation, and the inspection time can be shortened.

  Furthermore, according to the inspection method of the ultrasonic inspection apparatus according to the present invention, it can be used to detect the presence or absence of the interference frequency between the surface echo wave and the bottom surface echo wave in the subject 15. If there is a defect at any interface in the multilayer structure 207 of the subject 15, the ultrasonic wave does not propagate to the bottom surface of the subject 15, so that interference with the bottom surface echo wave does not occur. In the inspection method using the ultrasonic inspection apparatus according to the present invention, the structure information related to the multilayer structure of the subject 15 is input, and imaging of a portion where a defect may occur in the frequency power spectrum is performed. Interference frequency can be predicted. By providing this detection mode as a defect determination function, it is possible to perform defect determination with higher reliability.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented, and the numerical values and the compositions (materials) of the respective components Is just an example. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  In the ultrasonic inspection apparatus according to the present invention, when an object having a multilayer structure is to be imaged based on a reflection signal from a defect in the multilayer structure, interference occurs in the reflection signal. It can be used effectively in imaging at times.

DESCRIPTION OF SYMBOLS 10 Coordinate system 11 Scanner stand 12 Water tank 13 Scanner apparatus 14 Water 15 Subject 16 Ultrasonic probe 17 Ultrasonic inspection apparatus 18 Holder 19 X-axis scanner 20 Y-axis scanner 31 Ultrasonic flaw detector 32 A / D converter 33 Memory 34 Data storage unit 35 Mechanical scanning program 36 Measurement condition setting program 37 Waveform calculation processing program 38 Image memory 39 Display circuit 40 Display device 41 Microprocessor 51-54 Layer 60 Surface 61-64 Interface 101 Measurement range 102 Scanning path 103 Measurement point 201 Image 203 Waveform data 204 Fourier transform (FFT)
205 Time domain 206 Frequency power spectrum 207 Multi-layer structure 211-214 Band 221-224 Image

Claims (10)

While scanning the ultrasonic probe in a plane direction parallel to the surface of the subject, ultrasonic waves are sent from the ultrasonic probe toward the subject, and reflected echo waves returning from the subject are The signal received by the ultrasonic probe, the signal related to the reflected echo wave is converted into digital waveform data, the digital waveform data is sent to the arithmetic processing means, the arithmetic processing means performs the arithmetic processing, and the inside of the subject In ultrasonic inspection equipment for inspecting defects,
The arithmetic processing means includes:
Extraction that extracts a change site that occurs in the waveform characteristics in the frequency domain of the received waveform related to the plurality of reflected echo waves that interfere with each other when there are a plurality of reflected echo waves that return from the subject and interfere with each other Means,
An image creating means for creating an image related to the internal defect based on the extracted changed portion;
An ultrasonic inspection apparatus that inspects the internal defect based on the created image. The extraction means includes
Conversion processing means for calculating a power spectrum by performing a Fourier transform on the data related to the received waveform;
Computing means for calculating at least one dip frequency at which a power spectrum value is lowered on the power spectrum calculated by the Fourier transform process;
Band setting means for setting a band for the dip frequency;
The ultrasonic inspection apparatus according to claim 1, further comprising: The image creating means includes
A value detecting means for detecting a peak value of a waveform obtained by the power value of the band or the inverse Fourier transform;
Image creating means for creating a two-dimensional image by converting the detected power value or peak value data into luminance;
The ultrasonic inspection apparatus according to claim 2, further comprising:   The subject includes a multilayer structure having a plurality of interfaces, the dip frequencies are calculated corresponding to the plurality of interfaces, and a plurality of the two-dimensional images are created according to the plurality of dip frequencies. The ultrasonic inspection apparatus according to claim 3. The ultrasonic inspection apparatus according to claim 4, wherein the plurality of dip frequencies (f _di : dip frequency of the i-th layer) are obtained by the following equation (1).

While scanning the ultrasonic probe in a plane direction parallel to the surface of the subject, ultrasonic waves are sent from the ultrasonic probe toward the subject, and reflected echo waves returning from the subject are An ultrasonic inspection method for receiving an ultrasonic probe, converting a signal related to the reflected echo wave into digital waveform data, calculating the digital waveform data, and inspecting an internal defect of the subject,
Extraction that extracts a change site that occurs in the waveform characteristics in the frequency domain of the received waveform related to the plurality of reflected echo waves that interfere with each other when there are a plurality of reflected echo waves that return from the subject and interfere with each other Steps,
An image creating step of creating an image related to the internal defect based on the extracted changed portion;
An ultrasonic inspection method characterized by the above. The extraction step includes
A transform processing step for calculating a power spectrum by performing a Fourier transform on the data related to the received waveform;
A calculation step of calculating at least one dip frequency having a reduced power spectrum value on the power spectrum calculated by the Fourier transform;
A band setting step for setting a band for the dip frequency;
The ultrasonic inspection method according to claim 6, further comprising: The image creating step includes
A value detection step of detecting a peak value of the waveform obtained by the power value of the band or the inverse Fourier transform;
An image creation step of creating a two-dimensional image by converting the detected data of the power value or the peak value into luminance;
The ultrasonic inspection method according to claim 7, further comprising:   The subject includes a multilayer structure and has a plurality of interfaces, the dip frequency is calculated corresponding to each of the plurality of interfaces, and a plurality of the two-dimensional images are created according to the plurality of dip frequencies. The ultrasonic inspection method according to claim 8. The ultrasonic inspection method according to claim 9, wherein the plurality of dip frequencies (f _di : dip frequency of the i-th layer) are obtained by the following equation (1).

Images