JP3121430B2 - Ultrasonic flaw detection method and ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe which generates an ultrasonic focused beam and is used for detecting a defect in a test material, and more particularly to an improved ultrasonic beam focusing characteristic using a transverse wave. It relates to an ultrasonic probe.

[0002]

2. Description of the Related Art Conventionally, as an ultrasonic probe of this kind,
For example, there is one as shown in FIG.

In this ultrasonic probe, to generate an ultrasonic focused beam, a damper 42 for attenuating the generated ultrasonic wave is provided on one side of a vibrator 41, and a damper 42 is provided on the other ultrasonic wave emitting surface. An acoustic lens 43 is provided for beam forming the ultrasonic waves.

The ultrasonic probe is immersed in a medium I, which is an acoustic coupling agent for transmitting generated ultrasonic waves, and
And medium I (acoustic coupling agent) 2 and medium II (test material)
The ultrasonic wave is transmitted toward 3, and the reception is also performed in the opposite direction through the same path.

[0005] The ultrasonic wave from the transducer 41 is a longitudinal wave. When the ultrasonic wave enters the medium II3 from the medium I2 via the acoustic lens 43, the ultrasonic wave is refracted and focused by the longitudinal ultrasonic wave in the test material. The beam is formed and focused at the focal position.

[0006] A reflected wave from a defect in the test material is received by the vibrator through the focused beam.

[0007]

In such a conventional ultrasonic probe, a vibrator immersed in a medium I2 vertically extends through an acoustic lens toward a medium II3 of a test material. Wave ultrasonic waves are emitted.

[0008] Since the incident angle of the longitudinal wave ultrasonic wave from the medium I2 to the medium II3 is smaller than the longitudinal wave critical angle, longitudinal wave ultrasonic waves are generated in the test material and refracted at the critical surface of both media as follows. I do.

[0009]

## EQU1 ## sin θ1 / sin θ2 = Cw / Ce θ1: incident angle, θ2: refraction angle, Cw: sound velocity of medium I2, Ce
... The sound velocity of the medium II3. Then, for example, the medium I2
Is water and the medium II3 is an epoxy resin.

If the incident angle .theta.1 changes, a focused beam is not formed in the test material due to the sound velocity ratio between the two, and the beam is dispersed, so that a sharp focused beam cannot be formed. Therefore, the resolution is reduced, and it becomes impossible to detect a minute defect in the test material, for example, a defect such as a crack in an IC package or a peeling of a chip inside.

If the frequency of the ultrasonic wave is increased to form a sharp focused beam, the propagation loss of the ultrasonic wave in the test material increases, the level of the received signal decreases, and it becomes difficult to detect minute defects. Become.

When the aperture of the acoustic lens is enlarged to form a sharp beam, the incident angle θ1 of the longitudinal ultrasonic wave changes over a wide range, so that a longitudinal wave and a transverse wave are generated at the same time, and the two interfere with each other, resulting in stable operation. There was a problem that was not obtained.

An object of the present invention is to provide an ultrasonic flaw detection method for transmitting ultrasonic waves that can be focused on a medium II via a medium I by using transverse ultrasonic waves.

[0014]

Means for Solving the Problems To solve the above problems,
Therefore, the present invention provides a method of transmitting ultrasonic waves through a medium I to a medium II.
Ultrasonic flaw detection method using transmitting ultrasonic probe
And cut a hollow sphere in two planes parallel to each other
The ultrasonic waves radiated from one ring-shaped vibrator
Obliquely incident on medium II at an angle greater than the longitudinal wave critical angle
That, after refraction of the transverse wave generated inside the medium II, the focal position
To provide an ultrasonic flaw detection method characterized by focusing on
You.

[0015]

According to the ultrasonic flaw detection method using an ultrasonic probe for transmitting ultrasonic waves toward the medium II via the medium I, the ultrasonic waves radiated from the vibrator are set to be larger than the longitudinal wave critical angle. Since the light is obliquely incident on the medium II at an angle, a transverse wave is generated inside the medium II. After the generated transverse wave is refracted and then incident in an annular shape and focused at the focal position, the ultrasonic wave is focused and becomes a sharp beam, and a focal point with a high degree of convergence is formed at a predetermined position. By changing the relative position between the oscillator and the medium II, the focal position in the medium II can be adjusted.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. FIG. 2 is a top view of FIG. FIG. 5 is an explanatory diagram showing the appearance of one embodiment of the vibrator of the present invention. First, the configuration will be described. 1 is a vibrator (made of PZT, lead titanate, lead metaniobate, PVDF, etc.), 2 is a medium I as an acoustic coupling agent, 3 is a medium II as a test material, 5 Indicates a focus. The vibrator 1 is made of a piezoelectric ceramic material and cuts a hollow sphere at two surfaces parallel to each other to form an annular shape. The vibrator 1 is immersed in a medium I2, that is, for example, water as an acoustic coupling agent, and is ultrasonically transmitted from a circular spherical surface to a medium II3 as a test material at a predetermined incident angle, that is, an incident angle larger than the longitudinal wave critical angle. And is disposed with respect to the medium II3 such that a focus of the focused beam is formed at a predetermined position in the medium II3. As shown in FIG. 5, the curvature of the vibrator 1 is set so that the propagation times of the sound emitted from the vibrator 1 to the focal point are the same.

Next, the operation of the above embodiment will be described. FIG. 3 is an intensity distribution diagram of longitudinal waves and transverse waves due to oblique incidence. A longitudinal wave generated in the medium II3 when a longitudinal wave is radiated from the vibrator 1 in the water to the medium II3 by changing the incident angle by the water immersion method. The reciprocal passage rates of the wave and the shear wave are shown as T _D and T _S , respectively. If the round trip rate is Ti,

[0019]

[Equation 2] Ti = P '/ P0 , P0 … Incident wave,
P ': reflected wave.

In the range where the incident angle is smaller than the critical angle of the longitudinal wave, a part of the transverse wave is also generated, but the longitudinal wave has a large reciprocal passage rate and the longitudinal wave is dominant. Incident angle increases and exceeds longitudinal wave critical angle,
In the range up to the shear wave critical angle, only the shear wave appears.
The incident angle is about 90% (about 1%)
This is a range that is lower than the maximum value by dB. In terms of the incident angle, for example, when the medium I is water and the medium II is epoxy, the curvature of the vibrator 1 is determined so as to output a sound wave in the range of 41 to 52 degrees. This is because if a sound wave in a wider range is output, a longitudinal wave may be generated), the cutting position of the hollow sphere is selected, and the shape of the vibrator is determined. Transducer 1 and medium II3
Can be adjusted to adjust the focal position formed by the focused beam in the medium II3.

When water is used for the medium I2 and epoxy resin is used for the medium II3, the refractive index is close to 1 and the shape of the vibrator is determined so that the reciprocal transmissivity of the transverse wave becomes an appropriate value. And a sharply focused beam is formed without increasing the aperture size, thereby increasing the degree of convergence.

Therefore, a sufficient level of reflected signal can be obtained from a minute defect in the medium II3, and the sensitivity is improved. Further, it is easy to identify defects adjacent to each other, and the resolution can be improved. Therefore, cracks generated in an IC package made of a plastic material and peeling of a chip inside can be detected with high resolution.

As described above, according to the present invention, the following effects can be obtained.

Since the ultrasonic waves are radiated from the vibrator having a spherical surface to the medium II at an incident angle larger than the longitudinal wave critical angle, only the transverse ultrasonic waves are included in the medium II. Can form a focus with a high degree of convergence, so that high sensitivity can be obtained.

Further, if the frequency is the same, a high resolution can be obtained even at a low frequency with a small attenuation since a transverse wave ultrasonic wave having a wavelength shorter than that of the longitudinal wave ultrasonic wave is used by about half. Becomes larger).

As a result, the probe has improved sensitivity and resolution, and can detect minute defects.

[0027]

As described above, according to the present invention, it is possible to provide an ultrasonic flaw detection method for transmitting ultrasonic waves that can be focused on the medium II via the medium I using the transverse ultrasonic waves. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a vibrator according to the present invention.

FIG. 2 is a top view of the vibrator of the present invention.

FIG. 3 is a graph showing the intensity distribution of longitudinal waves and transverse waves due to oblique incidence.

FIG. 4 is a cross-sectional view of a conventional ultrasonic probe.

FIG. 5 is an explanatory diagram of a sound propagation path in one embodiment of the vibrator of the present invention.

FIG. 6 is an explanatory view showing the appearance of one embodiment of the vibrator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... vibrator 41 ... vibrator 42 ... damper 43 ... acoustic lens

────────────────────────────────────────────────── ─── Continuation of the front page Examiner Naoji Kamiya (56) References JP-A-59-157560 (JP, A) JP-A-61-286747 (JP, A) Jikai Sho 62-140450 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (4)

(57) [Claims] In an ultrasonic flaw detection method using an ultrasonic probe for transmitting ultrasonic waves toward a medium II via a medium I, when a hollow sphere is cut on two planes parallel to each other.
The ultrasonic wave radiated from one vibrating ring is obliquely incident on the medium II at an angle larger than the critical angle of the longitudinal wave. The transverse wave generated inside the medium II is focused at the focal point after refraction. ultrasonic flaw detection method characterized by be. 2. An ultrasonic probe for transmitting an ultrasonic wave toward a medium II via a medium I , wherein the ultrasonic wave is formed in an annular shape at an angle larger than a longitudinal critical angle.
An ultrasonic probe having one vibrator at an annular position formed when a spherical surface is cut by two planes parallel to each other so as to be obliquely incident on II . 3. An ultrasonic probe for transmitting an ultrasonic wave toward a medium II via a medium I , wherein the ultrasonic wave is formed into an annular shape at an angle larger than a longitudinal wave critical angle.
To be incident obliquely to II, the ultrasonic probe and having a first vibrator annular capable when cut hollow sphere with two parallel planes to each other. 4. The ultrasonic probe according to claim 2 , wherein said ultrasonic probe has a function of receiving an ultrasonic wave.