Ultrasonic Apparatus

1. Field of the Invention

This invention relates to an ultrasonic apparatus provided with an autofocusing function.

2. Description of the Prior Art

Heretofore, in defect inspection of electronic components and the like by ultrasonic waves, one practical system uses a so-called pulse-echo method in which, for the purpose of increasing the resolution, ultrasonic pulses are emitted toward an object to be inspected in water using a focusing-type probe which focuses an ultrasonic beam into a narrow beam, and nondestructive inspection of the object is performed by analyzing signals reflected from the object. This method is described in detail in, for example, Japanese Patent Public Disclosure (Kokai) No. 63-47658 (1988).

In this method, the focus of the ultrasonic beam must exactly coincide with a desired depth to be inspected. The focal length of the probe is usually fixed, and focusing is performed by changing the distance between the probe and the object to be inspected. If the depth to be inspected within the object from the surface of the object is represented by d, the velocity of sound in water by V.sub.w, the velocity of sound within the object to be inspected by V.sub.s, and the focal length of the ultrasonic beam in water by F, then the target distance W.sub.p in water from the probe to the object to be inspected is expressed by

Hence, it can be understood that the probe should be disposed at a position which is at a distance equal to the target distance W.sub.p in water from the surface of the object to be inspected.

In general, however, the velocity of sound V.sub.s within the object to be inspected is unknown, and the velocity of sound V.sub.w in water and the focal length F in water change mainly due to changes in water temperature. Moreover, there exists an inherent deviation from a nominal value in the focal length F in water for every probe.

Accordingly, in the conventional method, it is necessary to separately measure or estimate the above-described values before starting inspection. Furthermore, since there exists no means for automatically adjusting the position of the probe to the target length W.sub.p in water, the operator himself must perform any adjusting operation while measuring the distance in water. Consequently, this inspection method is troublesome, causes many misoperations, and is not an efficient method.

It is an object of the present invention to provide an ultrasonic apparatus capable of making the focus of an ultrasonic beam automatically coincide with a desired depth within an object to be inspected.

It is another object of the present invention to provide an ultrasonic inspection apparatus in which the focus of an ultrasonic beam can automatically be made to coincide with a desired depth to be inspected within an object to be inspected in order to perform the inspection of a plane to be inspected at the desired depth, and the result can be obtained as an ultrasonic image.

FIG. 1 is a block diagram of the circuit configuration of an ultrasonic apparatus according to a first embodiment of the present invention; and

FIG. 2 is a partial configurational circuit diagram of a second embodiment of the present invention.

FIG. 1 shows a configurational block diagram of an ultrasonic measuring apparatus according to a first embodiment of the present invention. The apparatus of the present embodiment is used for inspection of electronic components, such as semiconductor-device packages, multilayer ceramic capacitors, high-density-mounted ceramic substrates and the like, performs nondestructive inspection of defects within an object to be inspected by ultrasonic wave, and provides the result as image information.

In FIG. 1, an object S to be inspected is, for example, an electronic component, such as an integrated circuit, a large scale integrated circuit or the like. The object S to be inspected is sunk within a medium which transmits ultrasonic waves, for example a water tank filled with water. For some applications, a liquid other than water, for example oil, may be used. A probe 1 for performing transmission and reception of ultrasonic wave is mounted to a vertical moving unit 2 and a horizontal moving unit 3 with its front end immersed in the water. A pulser/receiver 4, which has the function of generating high-voltage pulses for transmitting ultrasonic wave and amplifying received signals, is connected to the probe 1. The amplified output from the pulser receiver 4 is connected to a surface-signal processing circuit 5 and an internal-signal processing circuit 6. The output from the surface-signal processing circuit 5 branches to three outputs. The first and second outputs are connected to a distance-in-water calculation circuit 9 via a maximum-value detection circuit 7 and a surface-reflection counting circuit 8, respectively. The third output is connected to an internal-reflection counting circuit 10 together with the output from the internal-signal processing circuit 6. The output from the internal-reflection counting circuit 10 is connected to a target-distance-in-water evaluation circuit 12 via a calculation circuit 11 which calculates the sonic velocity in an object to be inspected together with the output from the distance-in-water calculation circuit 9. The output from the target-distance-in-water evaluation circuit 12 is connected to a distance-in-water comparison circuit 13 together with the output from the distance-in-water calculation circuit 9. The output from the distance-in-water comparison circuit 13 is connected to the vertical moving unit 2 via a vertical-driving-signal generation circuit 14. Further provided are an apparatus-synchronizing-signal generator 15 and a timing-reference-signal generation circuit 16. The output from the generator 15 is connected to the pulser/receiver 4 and the surface-reflection counting circuit 8. The output from the generation circuit 16 is connected to the surface-reflection counting circuit 8 and the internal-reflection counting circuit 10.

Setting conditions, including a desired depth d for focus within the object to be inspected, the thickness L.sub.s of the object and the velocity of sound V.sub.w in water are input and set by the operator from a depth input unit 17, a thickness input unit 18 and a sonic-velocity-in-water input unit 19, respectively. The outputs from the depth input unit 17, the thickness input unit 18 and the sonic-velocity-in-water input unit 19 are connected to the target-distance-in-water evaluation circuit 12, the calculation circuit 11 of the sonic velocity in an object to be inspected, and the distance-in-water calculation circuit 9 and the target-distance-in-water evaluation circuit 12, respectively.

Furthermore, outputs from the horizontal moving unit 3 and a phase detection circuit 20 connected to the internal-signal processing circuit 6 are input to an image processing circuit 21, the output from which is connected to an image display unit 22, such as CRT or the like, and a printing unit 23, such as a printer or the like.

The operation of the present invention in the above-described configuration will now be explained.

In synchronization with the apparatus-synchronizing signal, which may be, for example, a clock signal, the pulser/receiver 4 generates high-voltage pulses which are applied to the probe 1. The probe 1 transmits an ultrasonic beam which is irradiated onto the object S to be inspected via water. Each ultrasonic echo as reflected by the surface, by the inner portion or by the base of the object S to be inspected is received again by the probe 1, amplified by the pulser receiver 4, and transmitted to the surface-signal processing circuit 5 and the internal-signal processing circuit 6. These two signal processing circuits 5 and 6 have time-gating and threshold-discriminating functions, and extract only a received signal exceeding a predetermined threshold value within a predetermined time gate based on the apparatus-synchronizing signal to extract the signal as a surface signal, an internal signal or a bottom signal, respectively. That is, the time required for the pulses to be reflected from the relevant portion of the object and returned is calculated and used to establish the time gate. The surface-reflection counting circuit 8 counts a timing reference signal, which is advantageously a sufficiently fine clock signal having a period t.sub.w, between the apparatus-synchronizing signal and the surface signal, that is, a time difference, and outputs the result N.sub.w. The distance-in-water calculation circuit 9 calculates the distance L.sub.w in water from the value N.sub.w obtained from the surface-reflection counting circuit 8, the input value V.sub.w from the sonic-velocity-in-water input unit 19, and the output from the timing-reference-signal generation circuit 16, that is, the time t.sub.w corresponding to one period of the timing reference signal according to the following formula.

The above-described operation is repeated while moving the probe 1 slightly in the vertical direction by the vertical moving unit 2. During this process, the maximum-value detection circuit 7 outputs a detection signal when it detects the maximum value of the amplitude of the surface signal. The amplitude of the surface signal has its maximum value when the ultrasonic beam is focused onto the surface of the object S to be inspected, and the distance in water when the detected maximum value signal is output is the measured focal length F in water of the probe 1.

On the other hand, the internal-reflection counting circuit 10 counts the timing reference signal between the surface signal and the internal signal or between the surface signal and the bottom signal, that is, the time difference, and outputs the corresponding result of counting t.sub.s. The velocity of sound V.sub.s within the object S to be inspected is calculated from the result of counting t.sub.s, the thickness L.sub.s of the object S to be inspected, which was input to the thickness input unit 18 and the input value N.sub.s of the depth from the surface of the object S to be inspected to an internal reflective source within the object S to be inspected. V.sub.s is calculated according to the following formula.

From the values of the focal length F in water of the probe 1, the sonic velocity V.sub.s of the object to be inspected and the desired depth d to be inspected obtained in the above-described process, the target distance W.sub.p in water is evaluated in the target-distance-in-water evaluation circuit 12 according to the following formula.

It is readily apparent that if one of the focal length or the sonic velocity of the object is known in advance from prior measurement or other sources, it is only necessary to determine the other.

The result is input to the distance-in-water comparison circuit 13, which compares the input target distance W.sub.p in water with the distance L.sub.w in water from the probe 1 to the object to be inspected at that moment, and outputs a differential signal which is proportional to the difference between the two distances. The differential signal is input to the vertical-driving-signal generation circuit 14, and is transmitted to the vertical moving unit 2 as a driving signal for driving the probe 1 in the direction to reduce the value of the differential signal. As a result, the distance in water gradually approaches the target distance W.sub.p in water, and finally, the focus of the ultrasonic beam exactly coincides with the desired depth d.

After the above-described focusing process has been completed, ultrasonic inspection of the object to be inspected is performed. Ultrasonic waves are emitted toward the object to be inspected while the probe 1 is being moved substantially two-dimensionally in horizontal directions over the object S to be inspected by the horizontal moving unit 3, and reflected signals of the ultrasonic waves reflected by the object to be inspected are received. The internal-reflection counting circuit 10, the internal-signal processing circuit 6 and the phase detection circuit 20 detect information about the depth, strength and phase relative to the received reflected signals. By providing time gate for the reflected signals, it is possible to take out only reflected signals from the desired depth within the object to be inspected, to detect an air layer (a detached layer) within the object to be inspected at the desired depth from the directions of the phases of the taken-out reflected signals from the desired depth, and to detect the degree of detachment of the detached layer from the strengths of the signals. More particularly, the obtained strengths have attached thereto positive or negative signs in accordance with the phases and are then provided as the detected data. By performing the detection two-dimensionally, an ultrasonic image visualized by image contrast or colors in accordance with the values of the detected data is formed by the image processing circuit 21, and the result is output to the image display unit 22 or the printing unit 23. The ultrasonic image of the object to be inspected at the desired depth can thus be obtained. A more detailed explanation relative to the above-described processing is provided, for example, in Japanese Patent Public Disclosure (Kokai) No. 63-47658 (1988).

As described above, according to the present invention in the first embodiment, since inspection is performed by automatically making the focus of a focusing-type ultrasonic probe coincide with a desired depth within an object to be inspected, the present invention has the advantages that troublesome human operation becomes unnecessary, misoperation decreases, and efficiency in inspection can be increased.

Suitable examples of inspection by the apparatus in the present embodiment are as follows.

Detection of cracks and voids within IC's in molded packages, and inspection of the adhesion state at the boundary between a chip and a lead frame.

Inspection of delamination in ceramic multilayer capacitors.

Soldering quality inspection of chip components on a high-density-mounted ceramic substrate.

Inspection of internal defects in new materials, composite materials and the like.

Next, a further improved second embodiment of the present invention will be explained.

In the above-described first embodiment, there was adopted a method in which the operator inputs the velocity of sound in water. The velocity of sound in water which includes few impurities has the property of depending substantially only on temperature. FIG. 2 shows the partial configurational diagram of an ultrasonic apparatus of the second embodiment. In FIG. 2, the output from a water-temperature sensor 31 provided in water is input to a sonic-velocity-in-water conversion unit 32, the output from which is input to the distance-in-water calculation circuit 9 and the target-distance evaluation circuit 12.

In this configuration, the sonic-velocity-in-water conversion unit 32 obtains the velocity of sound V.sub.w in water by conversion, and this value is used in place of the input value used in the first embodiment.

Thus, according to the present embodiment, it is possible to omit the operation in which the operator inputs the velocity of sound V.sub.w in water.

Although the embodiments described above have been applied to ultrasonic inspection apparatuses which are suitable for inspection of electronic components, objects to be inspected may be other than electronic components. Furthermore, the present invention is not limited to ultrasonic inspection apparatuses, but may also be widely used as an autofocusing mechanism for various apparatuses utilizing ultrasonic wave, for example, ultrasonic heating therapeutic apparatuses, ultrasonic calculus-breaking apparatuses and the like in the medical field.