JPH01214756A - Acoustic coupling method of body to be checked and piezoelectric element - Google Patents

Abstract

PURPOSE:To match acoustic impedance, by bringing the surface of a body to be checked facing a piezoelectric element into contact with the piezoelectric element tightly by sucking with vacuum, making it possible to communicates a vacuum sucking system with atmosphere, and making it possible to bring the body to be checked and the piezoelectric element into contact or separation. CONSTITUTION:Energy such as an optical beam is concentrated and inputted into a body to be checked 1 as shown by an arrow. Then, an ultrasonic wave that is propagating in the body to be checked 1 is generated. The generated ultrasonic wave is received with a piezoelectric element 2 as an acoustic signal and transduced into an electric signal. At this time, the quality of the receiving efficiency in the element 2 directly affects whether the transduced electric signal becomes useful checking data or not. Therefore, the pressure in a vacuum sucking device 4 is adjusted to a negative pressure conforming to the shape of the body to be checked 1 before the checking is started. The negative pressure is applied under the state wherein the body to be checked 1 is mounted on the element 2. At this time, the amount of air to be sucked is small. The body to be checked 1 is instantaneously sucked with vacuum through a hole 7 in the element 2. The contact surfaces of both parts are brought into contact tightly and acoustically coupled. After the check is finished, a leak valve 6 is opened and the inside is communicated to atmosphere. Thus, the close contact state is released, and the body to be checked 1 can be removed from the element 2 simply.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the connection between an object and a piezoelectric element when inspecting the surface condition or internal defects of the object using acoustic signals generated in the object. The present invention relates to an acoustic coupling method, and particularly relates to an acoustic coupling method suitable for inspecting a test object such as a semiconductor product, which requires prevention of adhesion of other substances and contamination thereof.

[Conventional technology]

When time-continuous energy (for example, light beams, electromagnetic waves including laser beams, electron beams, ultrasonic waves, etc.) is modulated and concentrated at an arbitrary frequency and is incident on the surface of the object, the The vicinity of the surface is excited to locally excite heat waves, and this excitation generates ultrasonic waves that propagate inside the object. Although the acoustic signal generated by the generated ultrasonic waves is a weak signal, it has information corresponding to the condition of the object to be examined, and is used for inspecting the surface condition of the object, internal defects, etc. In this case, the ultrasonic waves generated in the subject are received using a piezoelectric element, but as mentioned above, the energy of the received signal is weak, so it is necessary to receive it efficiently. It is necessary to improve signal transmission efficiency by matching the acoustic impedances of the signals and minimizing loss due to mismatching. In order to match the above-mentioned acoustic impedance and improve signal transmission efficiency, water was conventionally used between the subject and the piezoelectric element.

This has been dealt with by applying one of the coupling media such as mineral oil such as machine oil, grease, paste, glycerin, water glass, amalgam, etc., and bringing the two into close contact to prevent air or bubbles from entering. These various coupling media are in liquid or fairly viscous liquid form, and depend on the type and properties of the test object, such as whether the test object is an electronic component or a welded structure, the degree of roughness of the test surface, and the test surface. The material is selectively used as an adhesive for the object or the piezoelectric element depending on whether it is a flat surface, a curved surface, or an inclined surface. However, these coupling media usually require a lot of time to apply and remove the coupling media attached to the specimen or piezoelectric element after use, especially when a large number of specimens are sequentially attached and detached. Moreover, this is one of the bottlenecks in inspection efficiency when inspecting at high speed. At the same time, the specimen is easily susceptible to rust and contamination by the coupling medium, which is due to
This is a problem that must be avoided especially in electronic components such as semiconductor products, but since the conventional method of acoustically coupling the object and piezoelectric element uses the coupling medium described above, it is a problem that must be avoided. This had become an unavoidable problem.

[Problem to be solved by the invention]

In view of the above-mentioned problems, the present invention provides the following features when testing a subject by receiving ultrasound generated in the subject using a piezoelectric element.
It is possible to match the acoustic impedance of the piezoelectric element to the test object without adhering to or contaminating other substances such as rust, and the acoustic impedance can be easily and arbitrarily attached and detached between the test object and the piezoelectric element. It is an object of the present invention to provide a method for acoustically coupling a piezoelectric element to a subject, which enables the acoustic coupling between a subject and a piezoelectric element, thereby improving inspection efficiency.

[Means to solve the problem]

In order to achieve the above object, a method of acoustically coupling a subject and a piezoelectric element according to the present invention provides a method for acoustic coupling between a subject and a piezoelectric element when an acoustic signal generated in the subject is received using the piezoelectric element. In the acoustic coupling method, the surface of the subject facing the piezoelectric element is suctioned by a vacuum suction system to bring it into close contact with the piezoelectric element, and the vacuum suction system is made to be able to freely communicate with the atmosphere, thereby connecting the subject and the piezoelectric element. It is characterized in that the close contact between the parts is made removable.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment, and FIG. 2 shows a second embodiment, both of which show examples of methods for acoustically coupling a subject and a piezoelectric element in direct contact with each other. In FIG.

1 is a solid object to be examined; 2 is a piezoelectric element that receives an acoustic signal generated by the object 1, and is in direct contact with the inspection surface of the object 1; Reference numeral 3 denotes an inspection table on which the surface of the piezoelectric element 2 that is not in contact with the subject 1 is placed. A vacuum suction device 4 generates a vacuum for suctioning the subject 1, and the negative pressure caused by the vacuum can be adjusted. 5 is a tube connecting the vacuum suction device 4 and the piezoelectric element 2;
6 is a leak valve provided in the middle of the pipe 5, 7 is a piezoelectric element 2
One side is connected to the tube 5, and the other side is open to the surface that comes into contact with the subject 1, and the number, arrangement, etc. are arbitrary depending on the size and shape of the subject 1. can be decided. Vacuum suction device r! 14. Tube 5. The leak valve 6 and the hole 7 form a vacuum suction system. Now, when energy such as a light beam is concentratedly incident on the object 1 as shown by the arrow in the figure, an ultrasonic wave is generated that propagates inside the object 1, and the generated ultrasonic wave is received by the piezoelectric element 2 as an acoustic signal. and converted into electrical signals. The electrical signal is sent to a signal processing device (not shown) and processed into test information. In this case, the reception efficiency of the piezoelectric element 2 directly affects whether the converted electrical signal becomes useful inspection information. It is necessary to improve the signal transmission efficiency by matching the acoustic impedance between the two. Therefore, before the start of the test, the vacuum suction device 4 is adjusted to a negative pressure according to the dimensions, shape, etc. of the subject 1, and the adjusted negative pressure is applied with the subject 1 placed on the piezoelectric element 2. . Since the amount of air to be aspirated is small,
is instantly vacuumed through the hole 7 of the piezoelectric element 2, and the contact surfaces of the two are brought into close contact and acoustically coupled. In this case, if an acoustic coupling material, such as a thin rubber plate, having holes similar to the holes 7 (not necessarily the same size and number) is sandwiched between the contact surfaces of the two, the piezoelectric element of the object 1 can be Even if the roughness of the contact surface with 2 is relatively large, the adhesion is good, the mixture of air into the vacuum is more reliably prevented, and a vacuum suction state is ensured. Further, even if there is a difference in acoustic impedance between the subject 1 and the piezoelectric element 2, the acoustic impedance can be matched more uniformly by using an acoustic coupling material having an intermediate acoustic impedance. The contact surface is brought into close contact with an appropriate pressure, and after the inspection is completed, the leak valve 6 is closed.
By opening and communicating with the atmosphere, the close contact state is instantly released, and the subject 1 can be easily removed from above the piezoelectric element 2. In this way, the test in this embodiment is performed without any adhesion or contamination by substances other than air, such as conventional coupling media, and moreover, the acoustic impedance between the object 1 and the piezoelectric element 2 is reduced. On the other hand, since the subject 1 and the piezoelectric element 2 can be acoustically coupled in a detachable manner at any time and instantaneously, the process can be performed with high accuracy and efficiency. .

Next, a second embodiment shown in FIG. 2 will be described. This embodiment is an example of ultrasonic flaw detection, and the same reference numerals as in FIG. 1 indicate the same parts or the same functions. In the figure, reference numeral 8 denotes an ultrasonic probe for both transmission and reception, which has a piezoelectric element built into its case, and is brought into contact with the flaw detection surface la of the object 1. Reference numeral 9 denotes a hose, and a certain length of the tube 5 on the ultrasonic probe 8 side is made of a flexible material such as a rubber tube so that the ultrasonic probe 8 can freely scan the deep wound surface la. 6 Ultrasonic probe 8
In the same way as the piezoelectric element 1 shown in FIG. 1, there is a hole 7 for vacuum suction.
is provided, and when negative pressure is generated by the vacuum suction device 4, the ultrasonic probe 8 passes through the tube 5 and the leak valve 6. It is instantly attracted to the flaw detection surface 1a via the hose 9 and the hole 7. In this case, the negative pressure generated by the vacuum suction device 4 is adjusted to the dimensions, weight, and roughness of the flaw detection surface 1a of the ultrasonic probe 8 so that the ultrasonic probe 8 is attracted to the flaw detection surface 1a with an appropriate pressure. However, in this embodiment, as in the first embodiment, an acoustic coupling material is sandwiched between the contact surface of the ultrasonic probe 8 and the flaw detection surface 1a to further improve the acoustic performance. Impedance matching can be achieved.

Acoustic coupling is performed more effectively. When moving the ultrasonic probe 8 for scanning, the suction state is instantly released by opening the leak valve 6, so that the ultrasonic probe 8 can be moved freely. As can be seen from this example, the present invention can be used in cases where the test surface 1a is inclined, or where the ultrasonic probe 8 falls when one hand is removed, where the lower or back surface of the object is to be inspected. is particularly effective.

Next, the third embodiment shown in FIG. 3 and the fourth embodiment shown in FIG. 4 will be explained. Both embodiments are examples in which an object to be examined is placed on an examination table, and an acoustic signal generated by the object is received via the table by a piezoelectric element placed opposite to the object for examination. be. In the drawings, the same reference numerals as in FIGS. 1 and 2 indicate the same components or components with the same function.

In FIG. 3, 10 is a piezoelectric element that receives acoustic signals generated by the subject 1, 11 is an examination table, and its upper surface 11
The subject 1 is placed on the bottom surface 11b, and the bottom surface 11b is formed to be substantially parallel to the top surface 11a so that the piezoelectric element 10 can be moved in the # direction in the figure, facing the subject 1. Reference numeral 12 designates holes for vacuum suction provided in the table 11, one end of which is connected to the tube 5, and the other end of which is a plurality of vertical holes that open to the upper surface 11a.

The number, arrangement, etc. of the vertical holes opened in the upper surface 11a are determined depending on the dimensions, weight, etc. of the subject 1. The piezoelectric element lO shown in the figure
is configured so that it can be supported and scanned by the inspector's hand without providing the hole 7 shown in FIG. In that case, it is not necessary to support the piezoelectric element 10 by hand. Further, as in the first and second embodiments, acoustic coupling materials may be sandwiched between the subject 1 and the upper surface 11a and between the piezoelectric element 10 and the lower surface 11b, respectively. In this embodiment, the table 11 of the subject 1
Since the mounting surface of the piezoelectric element IO is removably vacuum-suctioned through the stand 11, and the piezoelectric element IO is made freely movable, in addition to the effects of the above embodiments, the size is larger than that of the piezoelectric element 10. This has the effect that the subject 1 can be tested.

FIG. 4 shows a fourth embodiment, which is an example in which the method according to the present invention is applied to a basic inspection device.

Similar to the third embodiment, this embodiment is an example in which an object to be inspected and a piezoelectric element are placed opposite to each other via an inspection table to be inspected. In the drawings, the same reference numerals as in FIGS. 1 to 3 indicate the same components or components with the same function. In the figure, 13 is a piezoelectric element that receives acoustic signals (photoacoustic signals in this example) generated in the subject 1, 14 is an examination table, and an acoustic cup made of a thin rubber plate is attached to the top surface 14a of the table. A ring material 15 is adhered, and a piezoelectric element I3 is adhered to the lower surface 14b. In this case, the piezoelectric element 13 may be bonded to the lower surface 14b with an acoustic coupling material 15 interposed therebetween. The piezoelectric element 13 is provided with a hole 16 for vacuum suctioning the subject 1, and one end is connected to the tube 5. The other end of the hole 16 is connected to a hole 17 provided in the stand 14 and a hole 18 provided in the acoustic coupling material 15 so as to communicate with the hole 16.
, and is configured to suction the surface of the subject 1 placed on the table 14 side. 20 is a laser.

21 is a modulator that modulates a temporally continuous laser beam outputted from the laser 20, indicated by the broken line in the figure, at an arbitrary frequency and converts it into pulses. The pulsed beam is sent to the optical system 22
The beam is then focused on the surface of the subject 1 via the beam scanning system 23, and the focused position is two-dimensionally scanned. Due to the irradiation of the pulse beam, an ultrasonic wave due to the photoacoustic effect, that is, a photoacoustic signal shown by the dotted line in the figure, is generated near the surface of the subject 1, and the generated photoacoustic signal is transmitted to the acoustic coupling material 1.
5 and the stage I4, the signal is received by the piezoelectric element 13, and simultaneously converted into an electric signal and sent to the signal processing device 24, which processes the signal and outputs inspection information of the subject 1.

In the inspection of objects using the above-mentioned photoacoustic signals, the objects to be tested are usually minute parts, such as semiconductor devices, and even the slightest amount of contamination by other substances often degrades their functionality. Many are produced in large quantities.

On the other hand, the photoacoustic signal is weak and does not provide effective inspection information unless the signal transmission efficiency is improved. For these inspection conditions, the fourth embodiment is capable of transmitting microscopic signals without contaminating the subject 1 in any way. The object 1 to be inspected can be easily and reliably vacuum-suctioned and fixed to minute positions on parts, so the pulse beam can be easily focused on the desired position, and it can be attached to and removed from a large number of objects 1. This can be done instantly, making it easy to respond.

Furthermore, regarding the transmission efficiency of weak signals,
' is vacuum-suctioned onto the acoustic coupling material 15 and brought into close contact with the piezoelectric element 13 through the table 14, and the acoustic impedance matching with the piezoelectric element 13 is improved, resulting in effects such as being able to obtain effective inspection information. have

〔Effect of the invention〕

As described above, the method of acoustically coupling a subject and a piezoelectric element according to the present invention involves applying vacuum suction to the surface of the subject facing the piezoelectric element using a vacuum suction system to bring them into close contact with each other; Since the close contact between the subject and the piezoelectric element is made removable by allowing communication with the atmosphere at will, the subject is free from adhesion of other substances such as rust and is completely free from contamination by such substances and is free from acoustic interference with the piezoelectric element. Impedance matching can be achieved, and the piezoelectric element can be acoustically coupled to the piezoelectric element in a simple and optionally attachable/detachable manner, which dramatically shortens the time required to attach and detach the subject, thereby increasing inspection efficiency. It has a remarkable efficiency in practice that can be improved.

[Brief explanation of the drawing]

The drawings are all explanatory diagrams of embodiments according to the present invention, and the first
The figure shows the first embodiment in which the object to be inspected and the piezoelectric element are brought into direct contact, Figure 2 is the second embodiment and shows an example of ultrasonic flaw detection, and Figure 3 shows the object to be inspected and the piezoelectric element. FIG. 4 is a diagram of the third embodiment in which the
FIG. 3 is a diagram showing an example in which the present invention is applied to a specific inspection device.

Claims (1)

[Claims] 1. In a method of acoustic coupling between a subject and a piezoelectric element when an acoustic signal generated in the subject is received using a piezoelectric element, a surface of the subject facing the piezoelectric element is A subject characterized in that the subject is brought into close contact with a piezoelectric element by suction with a vacuum suction system, and the vacuum suction system is made to communicate with the atmosphere at will, and the close contact between the subject and the piezoelectric element is made detachable. Acoustic coupling method with piezoelectric element. 2. The method of acoustically coupling a subject and a piezoelectric element according to claim 1, wherein the surface of the subject facing the piezoelectric element is sucked using a vacuum suction hole provided in the piezoelectric element. 3. The object of claim 1, wherein an acoustic coupling material is interposed between the object and the piezoelectric element, and the surface of the object facing the piezoelectric element is attracted and brought into close contact with the piezoelectric element through the acoustic coupling material. Acoustic coupling method between specimen and piezoelectric element. 4. When a subject is placed on an examination table and an acoustic signal generated in the subject is received using a piezoelectric element placed opposite to the subject via the table, the subject and the piezoelectric In the acoustic coupling method with the element, the surface of the subject to be placed on the table is suctioned by a vacuum suction system to bring it into close contact with the table, and the vacuum suction system is arbitrarily enabled to communicate with the atmosphere. A method of acoustic coupling between a subject and a piezoelectric element, characterized in that the piezoelectric element can be attached to and removed from the table. 5. The method of acoustic coupling between a subject and a piezoelectric element according to claim 4, wherein the surface of the subject on which the subject is placed on the table is suctioned using a vacuum suction hole provided in the table. 6. The subject according to claim 4, wherein an acoustic coupling material is interposed between the subject and the table, and the surface of the subject on which the subject is placed on the table is sucked and brought into close contact with the table via the acoustic coupling material. A method of acoustic coupling between a piezoelectric element and a piezoelectric element.