JPH04307365A - Method and apparatus for inspecting soldered part - Google Patents

Abstract

PURPOSE:To inspect the flaw of a soldered part by an electron converging and scanning system even with respect to a printed circuit board having an internal structure heterogeneous to an ultrasonic wave. CONSTITUTION:A whole control part 11 calculates the propagation state of an ultrasonic wave in a printed circuit board 1 on the basis of the board structure model preliminarily stored in a board structure memory 12 to calculate a condition for converging an ultrasonic wave to a soldered part 2 and a condition for detecting the ultrasonic wave reflected from the soldered part 2. A plurality of predetermined transducers 6 are controlled on the basis of those conditions to converge an ultrasonic wave to the specific soldered part 2 and the ultrasonic wave reflected from the soldered part 2 is detected to judge the presence of the flaw in a connected part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for inspecting the quality of soldered joints on a circuit board on which electronic components are mounted.

0002

2. Description of the Related Art Generally, when various electronic components are mounted on a circuit board, electrical connections are made by soldering. However, defects such as poor wetting and bridges often occur in these soldered parts, causing disconnections and short circuits. The method for inspecting such soldering defects is as follows:
Conventionally, in addition to visual inspection methods, various inspection methods using visible light, X-rays, ultrasonic waves, etc. are known.

An example of a method for inspecting the joint state of soldered parts on a circuit board using ultrasonic waves is described in, for example, Japanese Patent Laid-Open No. 61-93950. In this method, an ultrasonic vibrator generates ultrasonic waves, irradiates the soldered parts on a circuit board, and measures the intensity of the transmitted or reflected ultrasonic waves to inspect the bonding state. Generally, a portion of the ultrasonic wave is reflected at an interface between media having different acoustic impedances, and the greater the difference in acoustic impedance, the greater the reflected intensity. If there is a layer of air at the joint interface of the soldered part due to poor wetting, etc., strong reflected waves will occur, but this is because the acoustic impedance of air is significantly smaller than that of the circuit board or solder. be. Based on this principle, defects in soldered parts can be detected by measuring the reflected intensity of ultrasonic waves.

By the way, when detecting minute defects using ultrasonic waves as described above, a method is generally used in which the ultrasonic beam is focused with an acoustic lens and then mechanically scanned for inspection. ing. On the other hand, a method is known in which an ultrasound beam is electronically focused and scanned. For example, "Nondestructive Testing" Vol. 38 No. 12 pp. 10
Nos. 72 to 1078 describe electronic scanning ultrasonic flaw detection devices for the purpose of inspecting electronic components. This device uses a transducer with multiple ultrasonic transducers arranged in an array, and electronically controls the phase of the ultrasonic waves generated from each transducer to focus the ultrasound beam and drive the transducers. The beam is scanned by switching as appropriate. This electronic scanning/focusing method enables faster inspection than the mechanical scanning method.

[0005]

The ultrasonic detection methods described above are all based on the premise that the propagation medium existing between the transducer and the part to be inspected is uniform. In other words, assuming that ultrasonic waves do not exhibit complex behavior such as reflection or refraction inside the medium, if an ultrasonic wave is emitted from a transducer, this ultrasonic wave will reach the inspection target part in a certain amount of time depending on the distance. I think we will reach it.

However, in general, in a circuit board, the material of the internal wiring layer is different from that of the other parts.
This cannot be treated as a uniform medium. For example, when ultrasonic waves are propagated through a circuit board, the speed of sound is different between the wiring layer and other parts, so the time it takes for the ultrasonic waves to reach the soldered area varies depending on the internal structure of the circuit board. do. Therefore, in such a circuit board, reliable inspection cannot be performed using the conventional method assuming a uniform medium.

[0007] For the above reasons, when inspecting the soldered parts on the back side of a circuit board, there is a problem in that the conventional electron focusing/scanning method cannot be applied as is.

An object of the present invention is to use ultrasonic electron focusing and electronic scanning to determine the quality of the bonding state of soldered parts even when the circuit board is made of a plurality of materials and cannot be considered a homogeneous medium for ultrasonic waves. It is an object of the present invention to provide a method and apparatus for inspecting a soldered part, which can be inspected by a method.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention is achieved by the following means. That is, first, the structure of a circuit board that propagates ultrasonic waves is modeled and stored based on its design information, and the propagation state of ultrasonic waves in the circuit board is calculated based on the model. Find the transducer driving conditions necessary to focus the ultrasonic waves on the soldered part. Then, based on the conditions, the transducer is controlled to generate ultrasonic waves, and the ultrasonic waves are focused on a specific soldering part. The ultrasonic waves reflected from the soldered portion are detected by the transducer and converted into electrical signals. In order to determine the defect from the detected signal, first, a signal due to the reflected wave from the soldered part is extracted from the detection signal of the transducer based on the ultrasonic propagation state calculated based on the model. , the defect is determined based on the strength of the signal.

[0010] Furthermore, the present invention can also employ the following method in order to determine defects from the detection signal. first,
Based on the model, a signal that should be detected by the transducer when there is no defect in the soldered part is calculated in advance and stored, and the detected signal of the transducer and the stored signal are directly connected. A difference signal is extracted by comparison, and a defect is determined based on the strength of this difference signal.

[0011]

[Effect] If the structure of the circuit board is modeled based on the design information and the propagation state of ultrasonic waves in the circuit board is calculated, the time required for the ultrasonic waves generated by the transducer to reach the soldered part to be inspected can be calculated. can be predicted. Therefore, if the transducer is controlled based on this so that the generated ultrasonic waves reach the soldering area at a certain time, the ultrasonic waves can be focused on the target soldering area regardless of the structure of the circuit board. be able to.

On the other hand, the signals detected by the transducer also include ultrasonic signals reflected from areas other than the soldered parts. However, by calculating the propagation state using the above model, it is possible to predict the time it takes for the ultrasonic wave reflected from the soldered part to reach the transducer. Therefore, by extracting the detection signal of the transducer at that time, it is possible to detect the intensity of the ultrasonic wave reflected at the soldered part, and it is possible to determine the defect based on this.

[0013] Furthermore, based on the above model, a detection signal that should be observed when there is no defect in the soldered part is obtained in advance, and when this result is directly compared with the actually detected signal, it is found that the soldered part If there is a defect in the sample, there will be a difference in the comparison results. Thereby, defects can be determined.

[0014]

[Example] Before explaining the example of the present invention, first, FIG.
An example of a ceramic substrate to be inspected will be explained below. In the figure, a large number of minute spherical soldering parts 2 are arranged in a grid pattern on a ceramic substrate 1, and an IC chip 3 is mounted and connected thereto. Defects such as poor wetting may occur in these soldering parts 2, but since they are sandwiched between the ceramic substrate 1 and the IC chip 3, they cannot be visually confirmed from the outside. The ceramic substrate 1 has a multilayer structure, and a wiring pattern 4 made of metal such as copper or tungsten is formed in each layer. Further, on the back surface of the ceramic substrate 1, IO pins 5 for electrical connection with the outside are arranged in a grid pattern.

Next, the electron focusing method employed in the present invention will be explained with reference to FIG. In the figure, this electron focusing method irradiates an ultrasonic wave from the back side of a ceramic substrate 1 to a soldering part 2, and detects defects based on the reflected intensity of the ultrasonic wave. Although not shown in the figure, a structure such as a heat sink for cooling the IC chip 3 is placed on the top surface of the IC chip 3, so ultrasonic waves are irradiated from the top surface of the ceramic substrate 1 to detect defects. It is difficult to do so. For this reason, here, as shown in the figure, a predetermined number of transducers 6 for transmitting and receiving ultrasonic waves are inserted into the gaps between the IO pins 5 on the back surface of the ceramic substrate 1, and brought into direct contact with the surface of the ceramic substrate 1. Although the transducers 6 need to be arranged two-dimensionally, they do not necessarily have to be arranged regularly. However, when the IO pins 5 are arranged in a grid pattern, it is appropriate to arrange them in a grid pattern in the gaps between them. As will be described later, each transducer 6 generates a pulsed ultrasonic wave, and a spherical wave spreads radially around the contact point between the transducer 6 and the ceramic substrate 1. The situation is equivalent to placing a point sound source on the surface of the substrate.

FIGS. 4 and 5 each show a specific example of a transducer that realizes the equivalent point sound source as described above. The transducer shown in FIG.
A concave diaphragm 22a fixed to 3 is attached to the surface of the circuit board, and ultrasonic waves are output from the diaphragm 22a and focused on the surface of the circuit board. Inside the circuit board, ultrasonic waves propagate radially around a focal point. Therefore, this focal point can be regarded as an equivalent point sound source. Instead of using a concave diaphragm, the transducer shown in FIG.
Acoustic lenses 24a and 24b are constructed using two types of media with different ultrasonic propagation velocities, and these are used to focus the ultrasonic waves from the diaphragm 22b onto the surface of the circuit board. In this case, a planar diaphragm 22b can be used as the transducer.

In FIG. 2, it is assumed that there is no wiring layer inside the circuit board and that it can be assumed to be a uniform medium for ultrasonic waves.

When a voltage pulse is applied from a pulse source 8 to a transducer 6 disposed on the back surface of the ceramic substrate 1, a pulsed ultrasonic wave is generated and propagates radially through the circuit board as a spherical wave. As a result, each soldering part 2 has
The ultrasound waves arrive after a certain amount of time depending on the distance. By making the timing of the trigger pulse that triggers the pulse source 11 different for each pulse source 8 using the delay circuit 7a, the generation time of the voltage pulse applied to the transducer 6 is adjusted, and the ultrasonic waves generated from each transducer 6 are adjusted. By reaching a particular soldering point 2 at the same time, each transducer 6 at that soldering point 2
The phases of the ultrasonic waves from the two are aligned, and a strong ultrasonic wave is generated. In this way, the intensity of the sound field can be concentrated on a specific soldered portion 2.

On the other hand, if a defect exists in a particular soldered portion 2, a strong reflected wave is generated from the focused ultrasonic waves and returns to each transducer 6. Each transducer 6 detects this reflected wave and converts it into an electrical signal. At this time,
In each transducer 6, reflected waves are detected with a certain time difference depending on the distance to the respective soldering part 2. This time difference is equal to the delay time difference of the voltage pulses applied by the delay circuit 7a during transmission. Therefore, the output signal of each transducer 6 is amplified by the amplifier circuit 9, this time difference is corrected by the delay circuit 10b to eliminate the time difference, and then added by the adder circuit 10. It is possible to detect waves by superimposing them.

However, as shown in FIG. 3, if there is a wiring layer 4 inside the circuit board and the sound speed between this layer and the surrounding parts is greatly different, the ultrasonic waves will be refracted inside and reach the soldered parts. 2, and the arrival time is different from that in the case where no wiring layer exists. Therefore, if the method shown in FIG. 2 is applied as is, the phases of the ultrasonic waves from each transducer 6 at the soldering part 2 will not be aligned and will not be focused there.

[0021] In this way, the present invention determines in advance the change in propagation time when there is a wiring layer inside the circuit board, and by this, the generation timing of ultrasonic waves from each transducer can be set appropriately. As shown in FIG. 6, the ultrasonic wave is focused on a predetermined soldering part.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a soldered joint inspection method and apparatus according to the present invention, in which 11 is an overall control section, 12 is a memory, 13 is a trigger pulse generator, and 14a
, 14b is a transducer selection section, 15 is a gate section,
16 is a peak detection section, 17 is a defect determination section, and parts corresponding to those in the previous drawings are given the same reference numerals.

In the figure, the entire inspection apparatus is controlled by an overall control section 11. This overall control section 11 is constituted by a computer programmed with control procedures and processing methods. First, the overall control unit 11 determines one of the soldering parts 2 to be inspected, determines some transducers 6 to be used for inspection from among all the transducers 6, and transducer selection units 14a, 14b. The determined transducers 6 are connected to the corresponding pulse sources 8 and amplifier circuits 9, respectively. Such selection of transducers 6 can be realized by selecting the necessary number of transducers in descending order of distance from the soldered portion 2 to be inspected.

Next, the overall control unit 11 controls the process from each selected transducer 6 to the soldering part 2 based on the board structure model of the illustrated circuit board to be inspected, which is stored in advance in the memory 12. Calculate the propagation distance of the ultrasonic wave and find the time required for its propagation. Here, in order to simplify the explanation, it is assumed that one wiring layer 4 exists in the circuit board, but the propagation time in this case is as shown in FIG. Considering a model in which there is a wiring layer 4 with a thickness d, the following equation is obtained. That is, in the figure, the sound velocities of the ceramic substrate 1 and the wiring layer 4 are now v1 and v2, respectively, the transmitting point of the ultrasonic wave is O, the coordinates are taken with point O as the origin, and the receiving point is R.
(x, D), the incident angle of the ultrasonic wave at the interface of the wiring layer 4 is α, and the outgoing angle is β, then Equations 1 and 2 shown in FIG. 8 hold. Also, the propagation time T of the ultrasonic wave from point O to point R
is given by Equation 3 in FIG. 8, and by solving Equations 1 and 2 numerically to obtain α and β, and substituting these into Equation 3, the propagation time T can be obtained.

If the propagation time T for each transducer selected as described above is determined and C is a suitable constant, then the delay required for the ultrasonic waves from each transducer 6 to concentrate on a predetermined soldering part 2 is determined. The delay time τ of the circuits 7a and 7b is determined as shown in Equation 4 of FIG.

Next, the overall control section 11 instructs the trigger pulse generating section 13 to generate a trigger pulse. This trigger pulse is simultaneously supplied to each delay circuit 7a, delayed by a set time, and drives the pulse source 8. As a result, each pulse source 8 generates a high voltage pulse at a predetermined timing, and the transducer selection unit 14
a to the transducer 6. Such voltage pulses cause the selected transducer 6 to generate and radiate ultrasonic pulses into the circuit board. The emitted ultrasonic waves are focused on the soldered portion 2 to be inspected according to the principle described above, and reflected waves are generated depending on the state of the defect. The reflected ultrasound waves reach the transducer 6 again and are converted into electrical signals. These electrical signals pass through the transducer selection section 14b, are supplied to the amplifier circuit 9, and are amplified. The output signals of the amplifier circuit 9 are delayed by the delay circuit 7b by the same delay time as at the time of transmission based on instructions from the overall control section 11, and added by the addition section 10. Under the control of the overall control section 11, the gate section 15 selects the output signal of the addition section 10 in a fixed time width, and extracts only the signal due to the reflected wave generated at a predetermined soldering section 2. The peak detection section 16 detects the peak value of the output signal of the gate section 15. This peak value represents the reflection intensity at the soldered portion 2, and the defect determining section 17 determines that it is a defect when this peak value is equal to or greater than a certain value.

By sequentially performing the above-described procedures and processing on each soldered portion 2, each soldered portion 2 is inspected for defects.

In this embodiment, the delay time of the trigger pulse was explained to be calculated and inspected for each soldered part, but the delay time to be set for each soldered part should be calculated in advance. By calculating all the information and storing them in the overall control unit 11, the processing time during inspection can be shortened.

In this embodiment, while electron focusing is performed, inspection is performed by electronically changing the position of the focusing point depending on the soldered area. Since mechanical beam scanning is not performed in this way, high-speed inspection is possible.

FIG. 9 is a block diagram showing another embodiment of the soldering part inspection method and apparatus according to the present invention, in which 18 is a reference signal calculation section, 19 is a reference signal storage section, and 20 is a comparison section. , parts corresponding to those in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

In the figure, when detecting a signal by a reflected wave, the output signal of each transducer 6 is directly compared with a reference signal stored in advance, and the same processing as in FIG. 1 is performed based on the difference. This point differs from the embodiment shown in FIG. This reference signal is the output waveform of the transducer 6 that should be detected when there is no defect in the soldered portion 2, and is calculated in advance by the reference signal calculation unit 18 based on the board structure model in the memory 12 and is referred to as the output waveform of the transducer 6. Signal storage unit 1
It is stored in 9. The comparator 20 reads out the reference signal from the reference signal storage 19 and directly compares it with the output signal of the transducer 6.

Note that it is also possible to provide a waveform obtained by detecting a sample with no defects as the reference signal stored in the reference signal storage section 19. According to this embodiment, since a large difference signal appears only when a defect exists, there is an advantage that the accuracy of defect determination can be improved.

FIG. 10 is a block diagram showing another embodiment of the soldering part inspection method and apparatus according to the present invention, and includes
1 is an image storage unit, and parts corresponding to those in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

In this embodiment, defects are detected by detecting a two-dimensional distribution of reflection intensity as an image and analyzing it. This is similar to the embodiment.

In FIG. 10, the focal position of the ultrasonic waves is two-dimensionally scanned by an electronic scanning method, and the distribution of reflection intensity is detected as an image, which is stored in the image storage section 21. The defect determination unit 17 analyzes the characteristics of the image and determines defects based on the characteristics. For example, if the joint area of the soldered portion 2 is measured, a joint failure can be determined based on the size. This embodiment has the advantage that it is possible to perform more detailed classification regarding the size and type of defects.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
Even in cases where the circuit board is made of multiple materials and cannot be considered as a uniform medium for ultrasonic waves, the quality of the soldered joints can be inspected using ultrasonic waves using electronic focusing and electronic scanning methods. . Therefore, an excellent effect can be obtained in that defect inspection can be performed even on the soldered portion on the back side of the circuit board, which has conventionally been difficult to inspect.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a soldering part inspection method and apparatus according to the present invention.

FIG. 2 is an explanatory diagram of the principle of the electron concentration method.

FIG. 3 is a sectional view showing an example of a ceramic substrate.

FIG. 4 is a configuration diagram showing a specific example of a point source transducer.

FIG. 5 is a configuration diagram showing another specific example of a point source transducer.

FIG. 6 is an explanatory diagram of an electron focusing method when a wiring layer is present on the circuit board.

FIG. 7 is an explanatory diagram of an ultrasound propagation model.

FIG. 8 is a diagram showing a calculation formula for the model of FIG. 7;

FIG. 9 is a configuration diagram showing another embodiment of the soldering part inspection method and apparatus according to the present invention.

FIG. 10 is a configuration diagram showing still another embodiment of the soldering part inspection method and apparatus according to the present invention.

[Explanation of symbols]

1 Ceramic substrate 2 Soldering section 3 IC chip 4 Wiring layer 5 IO pin 6 Transducer 7a, 7b Delay circuit 8 Pulse source 9 Amplification circuit 10 Adding section 11 Overall control section 12 Board structure model 13 Trigger pulse generation section 14a, 14b Transducer Selection unit 15 Gate unit 16 Peak detection unit 17 Defect determination unit 18 Reference signal calculation unit 19 Reference signal storage unit 20 Comparison unit 21 Image storage unit

Claims (4)

[Claims] 1. A soldering part inspection method in which a circuit board is irradiated with ultrasonic waves to inspect the quality of the joints of soldered parts on the circuit board, wherein the structure of the circuit board is modeled based on its design information. calculate the propagation state of ultrasonic waves in the circuit board based on the model, and use the results to determine the driving conditions of the transducer necessary to focus the ultrasonic waves on the soldered part. , by controlling the transducer based on the conditions, ultrasonic waves are generated and focused on the specific soldering area, and the ultrasonic waves reflected from the soldering area are detected by the transducer and converted into electrical signals. , from the propagation state of the ultrasound calculated based on the model, predict the time at which the ultrasound reflected from the soldering part should be detected by the transducer, and predicting the time at which the ultrasound reflected from the soldering part should be detected from the output signal of the transducer. 1. A method for inspecting a soldered joint, which comprises extracting a signal caused by a wave and determining a defect based on the intensity of the signal. 2. In claim 1, a signal output from the transducer when there is no defect in the soldered portion is calculated and stored in advance based on the model, and the signal is calculated and stored in advance as the detection signal of the transducer. Directly compare the stored signal to extract a difference signal,
A method for inspecting a soldered joint, characterized in that a defect is determined based on the intensity of the difference signal. 3. A soldering part inspection device that irradiates ultrasonic waves onto a circuit board to inspect the quality of the joints of the soldered parts on the circuit board, in which a model of the structure of the board is created based on the design information. a storage means for storing, and a calculation means for calculating the propagation state of the ultrasonic waves in the circuit board based on the model, and calculating from the results the drive conditions of the transducer necessary for focusing the ultrasonic waves on the soldering part. and,
A control means for controlling the transducer to generate and detect ultrasonic waves based on the conditions, and a propagation state of the ultrasonic waves calculated based on the model. a calculation means for predicting the time to be detected by the transducer; a means for extracting a signal due to a reflected wave from the soldering part from the output signal of the transducer based on the output of the calculation means; and an intensity of the signal. 1. A soldering part inspection device comprising: a defect determining means for determining a defect based on. 4. An arithmetic means for predicting a signal to be detected by the transducer when there is no defect in the soldered portion, from a propagation state of the ultrasonic wave calculated based on the model, according to claim 3; A storage means for storing the prediction result by the calculation means, and a comparison means for directly comparing the signal detected by the transducer and the signal stored in the storage means to extract a difference signal, A soldering part inspection device characterized in that means determines a defect based on the intensity of the difference signal from the comparing means.