JPH079368B2 - Circuit board inspection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board inspection apparatus, and more particularly to a circuit board inspection apparatus for detecting an external defect of a circuit board.

[Conventional technology]

The circuit board inspection apparatus generally captures a copper foil pattern as a two-dimensional image using a two-dimensional image sensor, or uses a one-dimensional image sensor to arrange the circuit board in a direction in which photoelectric conversion elements of the one-dimensional image sensor are arranged. After the temporal image information captured continuously while moving continuously in the perpendicular direction is replaced with the spatial image information (two-dimensional image information) in the memory, image processing such as noise processing and feature extraction is performed to obtain The identified features are compared to the master substrate or design constraints to detect pattern defects. Among the image detection methods of such a circuit board inspection device, Japanese Patent Application Laid-Open No. 59-232344
When a printed circuit board is printed with excitation light of a relatively short wavelength (about 500 mm or less) as described in Japanese Patent Publication, fluorescence having a wavelength longer than that of the excitation light is emitted from the substrate portion of the board, It is known that an extremely stable image detection can be performed without being affected by the surface properties of the copper foil by a fluorescence detection method that utilizes the fact that no fluorescence is generated from the foil portion. But,
In this fluorescence detection method, the amount of fluorescence generated with respect to the applied excitation light is small, and unlike reflected light, fluorescence is generated almost uniformly in all directions from the irradiation point, so the light collection efficiency is poor. The amount of light that can be focused on the surface is extremely small compared to the excitation light that is applied (one-thousandth to tens-thousandth)
In order to obtain a sufficient S / N ratio with the output of the one-dimensional image sensor, the amount of excitation light should be increased to increase the amount of fluorescence generated,
It is necessary to lengthen the charge accumulation time of the image sensor. Further, since the charge accumulation time is almost proportional to the inspection time, it is necessary to increase the amount of excitation light in order to shorten the inspection time. As a light source for obtaining this high illuminance excitation light, a laser that can be easily condensed is most suitable.
An argon ion laser is suitable because of its large output.
For example, when laser light is used as an excitation light source and a one-dimensional image sensor is used as a detector, laser light is guided from a laser oscillator onto a printed circuit board by changing the optical axis direction using several mirrors. ing. At this time, 1
In order to irradiate the position on the printed circuit board imaged by the dimensional sensor most efficiently in a straight line, the laser light is expanded in one direction by using two cylindrical lenses and is condensed in the direction perpendicular to the direction.

[Problems to be solved by the invention]

However, in the above-mentioned conventional circuit board inspection apparatus, the irradiation position on the circuit board changes due to the change over time of the emission angle of the laser emission beam, the change over time, and the change of the mirror attachment angle over time and change over temperature. , The image sensor is out of the imaging position. Therefore, there is a problem that a mechanism for detecting the irradiation position and making a correction is required, and the entire apparatus becomes complicated.

Further, when an abnormality appears in the brightness of the laser light source that generates the laser light, in the conventional circuit board device, the signal due to the light source abnormality in the output signal of the image sensor is output as a signal indicating the appearance defect of the circuit board. Therefore, in order to constantly stabilize the output of the laser light source, a special image processing device is required so that the defect of the circuit can be detected even when the anxiety occurs.

It is an object of the present invention to provide a circuit board inspection apparatus that can detect a visual defect of a circuit even when an abnormality appears in a light source without a mechanism for correcting an irradiation position.

[Means for Solving Problems] The above-described object is to detect an abnormality of the circuit board to be inspected by irradiating the circuit board to be inspected with light from a light source and detecting a light beam from the circuit board to be inspected. In the circuit board inspecting device, a laser light source having an oscillation mode of a transverse mode and a longitudinal mode is used as a light source, a means for dividing the laser light source from the laser light source into first and second optical paths, and the first optical path. A first optical fiber having an entrance for taking in the light, an exit for irradiating the taken-in laser beam to the first circuit board as the inspection target, and an entrance for taking in the second optical path, and the taken-in laser beam A second optical fiber having an emission port for irradiating a second circuit board, which is compared with the first circuit board, with respect to the first and second optical fiber emission ports, Circuit board Means for moving two-dimensionally while relatively synchronizing with each other, and first and second image sensors for detecting light rays from the first and second circuit boards, and first and second image sensors This is achieved by providing image signal processing means for comparing the signals from.

[Action]

The laser beam passes through the optical fiber and reaches the vicinity of the circuit board. If the position of the exit end of the optical fiber does not change, the irradiation position does not change even if the position of the fiber in the middle changes, and since the circuit board is very close to the exit end of the optical fiber, Even if there is a deviation again, the change in irradiation position is very small. However, when a high-coherency laser beam is passed through the optical fiber,
Since a phase difference occurs between the light propagating through the fiber, a speckle due to interference occurs on the surface where the emitted beam hits, and as a result, locally high illuminance and low illuminance, that is, the illuminance distribution is localized. Creates non-uniformity. Generally, when transmitting a laser beam using an optical fiber in optical communication, the total amount of received light is used, so local unevenness in the amount of light does not pose a problem. In such a case, the amount of fluorescence generated varies locally depending on the local non-uniformity of illuminance, which causes a change in the level of the detection signal of the image sensor. Moreover, if the optical fiber is swung or swung at an intermediate portion between the entrance end and the exit end, the local nonuniformity of the illuminance distribution greatly changes, and it is extremely difficult to correct this. That is, the local non-uniformity of the illuminance distribution is the same as the noise in the detection signal, and the S / N ratio of the signal is reduced, so that the reliability of the detection result is significantly reduced, which is a serious problem. In order to solve this problem, the laser emission mode is set to the multi-transverse mode and the multi-longitudinal mode to significantly reduce the laser beam coffee coffee. As a result, the generation of speckles is reduced, the local non-uniformity of the illuminance distribution is reduced, the S / N ratio is improved, and the reliability of the detection result can be significantly increased. In addition, the laser beam from the same light source is divided and one of the laser beams is applied to the first circuit board to be inspected, and the other laser beam is used as a symmetrical reference circuit different from the first circuit board. It irradiates the treated circuit board and detects the light rays from each circuit board, so even if there is an abnormality in the brightness of the light source, etc., the signal from the circuit board to be inspected and the circuit board from the reference will be used. Since the signal also changes, it is possible to detect the true abnormality of the circuit board without erroneously recognizing the abnormality of the light source as the abnormality of the circuit board.

〔Example〕

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

The beam emitted from the argon laser 1 is a half mirror 2.
Is split into 50% reflected light and 50% transmitted light. The transmitted light is condensed by the condensing lens 4A, and the reflected light is changed in direction by the total reflection mirror 3 and then similarly condensed by the condensing lens 4B to enter the optical fibers 5A and 5B, respectively. The optical fiber used here is a single-core step-index type or graded type, and the optimum material is quartz. The light emitted from the optical fibers 5A and 5B is expanded in the horizontal direction by the first cylindrical lenses 6A and 6B, and is vertically condensed by the second cylindrical lenses 7A and 7B, and the cold mirror 8A. , 8B is reflected and is irradiated linearly on the printed circuit boards 9A, 9B. The fluorescence image generated by this excitation light passes through the cold mirrors 8A and 8B, and the imaging lens 10
It is incident on A and 10B. At this time, most of the excitation light reflected by the printed boards 9A, 9B used as a circuit board is reflected by the cold mirrors 8A, 8B, and only a small part enters the imaging lenses 10A, 10B. The imaging lenses 10A and 10B have a focal length and a positional relationship so that the irradiation portion on the printed circuit board is imaged at a predetermined magnification on the photoelectric conversion surface on the one-dimensional image sensors 12A and 12B via the shear cut filters 11A and 11B. It is set.
Cold mirror 8 with a shear cut filter 11A, 11B
A part of the excitation light transmitted through A and 8B is blocked, and only fluorescence reaches the image sensors 12A and 12B. Image sensor 1
Although not shown here, the output signals from 2A and 12B are sent to the image processing unit.

One of the printed circuit boards 9A and 9B may be a master and the other may be an inspection target, or both may be inspection targets. The printed circuit boards 9A and 9B are mounted on a stage 12 and 13 which is movable in the X and Y directions.
It is mounted on top and the entire surface can be inspected by scanning this stage.

In the circuit board inspection device having such a configuration, the optical fibers 5A, 5
The emission part of B is arranged near the printed boards 9A and 9B. With such an arrangement, even if the optical axis angle of the emitted beam from the argon laser 1 changes or the mounting angle of the mirrors changes, the deviation of the irradiation position on the printed circuit board can be made extremely small. Further, since the optical fiber is very flexible, instead of scanning the printed circuit boards 9A, 9B in the X direction by the stage 13, light sources of 2 to 7A and 7B and 8A,
The size of the device can be easily reduced by scanning the detecting portions of 8B to 12A and 12B in the X direction. Further, the argon laser 1 and the mirrors 2 and 3 can be attached at arbitrary positions, so that the degree of freedom in manufacturing the device can be extremely increased.

However, if the optical fiber is simply used in the above configuration,
There are the following major problems. That is, since the laser light generally has a very high coffee latency, a phase difference is generated as it propagates through the optical fiber while repeatedly undergoing total reflection, resulting in local nonuniformity of the illuminance distribution due to interference as described above.

The higher the monochromaticity and the lower the order of the transverse modes, the higher the coffee latency of the laser. Therefore, in the present invention, conversely, the laser output is reduced in monochromaticity, that is, in the multi-longitudinal mode, and the order of the transverse mode is increased, that is, in the multi-transverse mode, to reduce the coffee currency. When applying this to a general argon laser,
The multi-longitudinal mode can be achieved by removing the prism for wavelength selection inside the laser resonator, and the multi-longitudinal mode can be realized by changing the curvature of the resonance mirror of the laser resonator. is there. With this method, the coherence length of laser light was 100 m or more in single longitudinal mode and single lateral mode, but after changing to multi-longitudinal mode and multi-horizontal mode, it will be about 60 mm or less and drastically reduce coffee currency. You can By reducing the coffee latency as described above, the laser light approaches the general illumination light, the interference due to the phase difference in the optical fiber is reduced, and the local unevenness of the illuminance distribution of the illumination part due to the emitted light is reduced. The output of the one-dimensional image sensor with less noise can be obtained.

〔The invention's effect〕

According to the present invention, since the laser light is propagated to the vicinity of the printed circuit board by using the optical fiber, the change of the irradiation position can be made very small, and the generation of speckle due to the interference can be reduced, so that the image with a small noise can be obtained. A sensor output is obtained, and as a result, a printed circuit board pattern detection device having extremely high reliability can be configured. In addition to the sensor output signal from the inspection circuit board, the sensor output signal from the circuit board as the reference target using the same light source can be obtained, so the light source abnormality signal is detected in the sensor signal detected when the light source abnormality occurs. Even if "is present", it is possible to detect an abnormal signal due to the fact that an abnormality actually occurs in the circuit board from the signal.

[Brief description of drawings]

The drawing is a block diagram of a circuit board inspection apparatus according to the present invention. 1 ... Argon laser, 5A, 5B ... Optical fiber, 6A, 6B
...... First cylindrical lens, 7A, 7B …… Second cylindrical lens, 9A, 9B …… Printed circuit board, 10A, 10B
…… Imaging lens, 11A, 11B …… Optical filter, 12A, 12B…
… One-dimensional image sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiro Akabira 882, Imo, Katsuta-shi, Ibaraki Hitachi Ltd. Naka factory (56) References JP-A-59-232344 (JP, A) JP-A-58- 25735 (JP, A)

Claims (1)

[Claims] 1. A circuit board inspection apparatus for detecting an abnormality of a circuit board to be inspected by irradiating a circuit board to be inspected with light from a light source and detecting a light beam from the circuit board to be inspected. Oscillation mode is transverse mode,
A laser light source having a longitudinal mode is used, a means for dividing a laser beam from the laser light source into first and second optical paths, an entrance for taking in the first optical path, and the laser beam taken in are the inspection object. A first optical fiber having an emission port for irradiating the first circuit board as an input port, an entrance port for taking in the second optical path, and a second optical fiber for comparing the taken-in laser beam with the first circuit board. A two-dimensional optical fiber having an emission port for irradiating the circuit board, and the first and second circuit boards relative to the first and second optical fiber emission ports. Image signal for comparing the signals from the first and second image sensors and the first and second image sensors that detect the light rays from the first and second circuit boards. Circuit board characterized by comprising processing means Inspection equipment.