JPS61223540A - Lighting system for optical type printed circuit board - Google Patents

Abstract

PURPOSE:To obtain a quality image pickup output easy to binary code, by preventing direct entry of an illumination light passing through a through hole of a printed circuit board into a camera. CONSTITUTION:A lighting unit 20 forms a linear light source as a whole and is arranged parallel with the scanning direction of a lien sensor camera 10. The tip of a light shielding plate 28 sticks out by a proper length from an emission end face 26b of a photoconductive plate 26 and the radial expanse of the emission light from the end face 26b in regulated with the light shielding plate 28. Light from the lighting device 20 exists on the left from a limit line R and little on the right. The tilt angle alpha of the lighting device 20 is almost a half theta as much as the width-wise view angle 2theta of the camera 10 viewed from an object S. Thus, the light from the light unit 20 is prevented from the directly entering the view of the camera 10 even if traveling straight through the through hole 14c.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention provides a line sensor camera (-
Regarding an optical printed circuit board inspection device that inspects the condition of conductor patterns and mounted components on a printed circuit board by using a 11-dimensional (11-dimensional) image device), an improvement in the method of illuminating the printed circuit board from the side opposite to the camera. Regarding.

[Background Art of the Invention and Problems thereof] Figures 3 (A) and 3 (B) show the configuration of a conventional general optical printed circuit board inspection device, and Figure 3 (C) shows the imaging output waveform of this device. ing.

10 is a line sensor camera, which combines a line sensor 10a such as COD with an mR lens system 10b. 1
Reference numeral 2 denotes an illumination device, which is a linear light source that combines a straight tube type fluorescent lamp and a reflector, and is placed in front of the camera 10 at regular intervals and parallel to the scanning direction of the camera 10. There is.

14 is a printed circuit board to be inspected, and camera 1
The camera 10 is placed at a predetermined photographing position between the camera 10 and the illumination device 12.
is arranged perpendicular to the optical axis of the

The light from the illumination device 12 falls on the lower surface side of the printed circuit board 14, and a transmitted and scattered light image of the light is captured by the camera 10 as an image Ii.

In the printed circuit board 14, 14a is a base material part where a base material such as glass epoxy is exposed, 14b is a conductor pattern part formed of copper or the like on the surface of the base material, and 14C is a part that penetrates the base material from the front and back. The through holes 14d each represent a mounted component. Figure 3 (C) shows each of these parts 1
The image output when the portion including 4a to 14d is imaged by the camera 10 is shown.

Since the base member 14a is semitransparent, the light from the illumination device 12 is transmitted and scattered and reaches the camera 10, so that a high output that can be distinguished from a bright level is obtained (portion A in the figure). Since the conductive pattern portion 14b and the mounting component 14d substantially block the light from the illumination device 12, the Wi image output of this portion becomes a low output that can be distinguished from the dark level (portion B in the figure). Further, the light from the illumination device 12 passes through the through hole 14c and directly enters the camera 10. Therefore, the imaging output corresponding to the through-hole portion 14c becomes an extremely high-level pulse-like output (portion indicated by C in the figure).

The wa image output of the camera 10 has a dark level corresponding to the base material part 14a, a conductor pattern part 14b and a mounted component 14d.
Level discrimination is performed to binarize the dark level corresponding to the dark level. In order to increase the difference between the bright level and the dark level during image pickup output, it is effective to increase the amount of light from the illumination device 12, but in this case, the level of direct incident light corresponding to the through hole 14c becomes extremely large. This will saturate the direct light incident portion of the line sensor 10a.

In a semiconductor image sensor such as a COD, if light strong enough to saturate a pixel is incident on a localized area, surrounding pixels will be adversely affected due to blooming phenomenon, etc.
There is a problem that the resolution of image data deteriorates. Therefore, the amount of light from the illumination device 12 must be kept low to some extent so that the pixels of the in-sensor 10a are no longer saturated at the level of direct incident light corresponding to the through-hole portion 14C.

Then, the level difference between the bright level corresponding to the base material N14a and the dark level corresponding to the conductive pattern portion 14b and the mounted component 14d becomes smaller, and the bright level and dark level can be accurately discriminated (binarized). becomes difficult to do. In other words, the S/N ratio decreases.

[Object of the Invention] This invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an apparatus for imaging a printed circuit board with a line sensor camera by illuminating it from behind. 1. Prevents the illumination light passing through the section from directly entering the camera. To provide an illumination method for an optical printed circuit board inspection device that can prevent a sensor from becoming saturated and can obtain an imaging output with a good S/N ratio that is easy to binarize. It is in.

[Summary of the Invention] Therefore, in this invention, a linear light source is used as an illumination device, and this is arranged in parallel with the scanning line of a line sensor camera, and the emitted light of the linear light source is spread in the width direction. is regulated at least on one side in the width direction, and the emission direction limit line created by this regulation is tilted at an appropriate angle with respect to the optical axis of the camera, so that the emitted light from the linear light source directly enters the field of view of the camera. I tried to suppress it.

[Embodiments of the Invention] FIGS. 2(A) and 2(B) schematically show the configuration of an optical printed circuit board inspection apparatus to which the illumination method of the present invention is applied.
C) shows the imaging output waveform in this device. Also the first
The figure shows the configuration of the main parts of this device and the details of the illumination method. Note that in FIGS. 1 and 2, the same parts as those in FIG. 3 described above are given the same reference numerals.

In FIG. 2, reference numeral 14 denotes a printed circuit board to be inspected, a line sensor camera 10 is disposed on the upper surface thereof, and an illumination device 20 is installed on the lower surface thereof.

The structure and arrangement of this lighting device 20 are the features of the present invention.

As shown in FIG. 1, the lighting device 20 includes a straight tube type fluorescent lamp 22, a light-shielding box 24 that is housed to cover the lamp 22, and a slit on the top surface of the light-shielding box 24. It is composed of a light guide plate 26 and a light shielding plate 28 attached to one side of the light guide plate 26.

A reflecting mirror 25 is formed on the inner surface of the light shielding box 24, and efficiently supplies light from the lamp 22 to the light guide plate 26.

The light guide plate 26 is a rectangular plate made of transparent plastic or the like, and its length is approximately equal to that of the lamp 22, and its one end surface 2
6a faces the inside of the light-shielding box 24 and faces the lamp 22 in close proximity. Light from the lamp 22 enters the light guide plate 26 from this end surface 26a and exits from the opposite end surface 26b. That is, the illumination device 20 as a whole is a linear light source, and is arranged parallel to the scanning direction of the line sensor camera 10.

The tip portion of the light shielding plate 28 protrudes by an appropriate length from the output end face 26b of the light guide plate 26, and the light shielding plate 28 restricts the spread of the emitted light from the end face 26b in the width direction. Figure 1 (
As shown in B), out of the light emitted from the end surface 26b of the light guide plate 26, the emission direction to the right in the width direction in the figure is restricted. R in the figure indicates the emission direction limit line created by this regulation. Light from the lighting device 20 exists on the left side of this limit line R, and almost no light exists on the right side.

The illumination device 2o configured as described above is installed tilted to the left in the figure so that the emission direction limit line R passes through the subject point S and forms a predetermined angle α with the optical axis P of the camera 10. There is.

The above-mentioned inclination angle α is approximately equal to half the viewing angle 2θ of the camera 10 in the width direction as viewed from the subject point S. This viewing angle 2θ means that the light generated from the object point S is
b is the angle of the range where light is focused on the light receiving section of the line sensor 1Qa. This is determined by the width of the light receiving section of the line sensor 10a and the effective diameter of the lens system 10b.

Therefore, assuming that the printed circuit board 14 does not exist at the subject point S, the emission direction limit line R passes through the point S and is tilted to the left by α=θ, so that the light emitted from the end surface 26b of the light guide plate 26 Most of the light is outside the viewing angle 2θ of the camera 10, and the light from the output end face 26b does not directly enter the camera 10 and is not received by the line sensor 10a. This does not have to be perfect; the object of the present invention is achieved as long as the amount of direct light incident on the camera 10 is sufficiently small. Therefore, the angle α needs only to be larger than or approximately equal to the angle θ. , the emission direction limit line R does not need to be a boundary that completely demarcates the presence or absence of emitted light.

In this way, the number of direct incident light beams from the illumination device 20 to the camera 10 is extremely reduced, so that the through hole 14C of the printed circuit board 14 is located at the object point S, and the illumination device Even if the light from 20 goes straight through this hole 140 and passes through, of course, the light will not directly enter the field of view of the camera 10.

Therefore, as shown in FIG. 2(C), the image carrier output level corresponding to the through hole 14c is significantly lower than that of the conventional one (portion C in the figure). Since the imaging output level corresponding to the through-hole portion 14C becomes lower as the inclination angle α is increased, the angle α may be determined depending on the level of this output level.

Further, when the base portion 14a of the printed circuit board 14 exists at the object point S, the light from the illumination bag @20 enters the base portion 14a and is scattered and refracted, and the scattered and refracted light enters the camera 10. As a result, as shown in FIG. 2(C), the base material portion 14a
The image carrier output level corresponding to is a high value that should be discriminated as a bright level (portion A in the figure).

Also, the conductor pattern portion 1 of the printed plate 14 is placed at the subject point S.
4b or the mounted component 14d, the scattered and refracted light at the base material portion on the lower surface side is reflected by the conductor pattern portion 14b.
The light is blocked by the mounting components 14d and does not come out on the upper surface side. As a result, as shown in FIG. 2(C), the conductor pattern portion 14
The layer image output level corresponding to b and the mounted component 14d is a very low value that should be recognized as a dark level (portion B in the figure).

Here, since the amount of light that passes through the through hole 14c and directly enters the camera 10 is very small, if the illumination light m from the illumination device 20 is made sufficiently large, the in-sensor 10a will no longer be saturated. The corresponding bright level can be increased, and E can be increased to the difference between the dark level and the bright level. Therefore, the binarization process of the image pickup output can be performed very easily and accurately.

[Effects of the Invention] As explained in detail above, according to the illumination method of the optical printed circuit board inspection device according to the present invention, the illumination light directly enters the camera through the through hole of the printed circuit board, resulting in an excessive level of illumination. This eliminates the conventional disadvantage of producing an Ii image output, eliminates the saturation phenomenon of the line sensor, and provides high-quality imaging output that is easy to perform binarization processing with a large difference in brightness and darkness.

[Brief explanation of the drawing]

FIGS. 1A and 1B are diagrams showing the detailed configuration and illumination method of a lighting device according to an embodiment of the present invention, and FIGS.
) are a front view and a side view showing a schematic configuration of an inspection device to which this invention is applied, FIG. 2(C) is a diagram showing an imaging output waveform in this device, and FIGS. 3(A) and (B) are a diagram showing a conventional inspection device. A front view and a side view showing a schematic configuration of the device, and FIG. 3(C) are waveform diagrams of imaging output in this conventional device. 10...Line sensor camera 12...Lighting device (conventional) 14...Printed circuit board 14a...Base material part 1
4b...Conductor pattern part 14G...Through hole part 14
d... Mounted component 20... Lighting device (present invention) 22... Lamp 24... Light shielding box 2
6...Light guide plate 28...Light shielding plate P・
...Optical axis R... Output direction limit line Fig. 1 Fig. 2 (A) (8,
) (C) 3rd (A) (B)

Claims (1)

[Claims] (1) A printed circuit board to be inspected is placed at a predetermined position between a line sensor camera and an illumination device, perpendicular to the optical axis of the camera, and a transmitted and scattered light image of the printed circuit board is captured by the camera; In this optical printed circuit board inspection device that obtains image data that separates the bright part of the semi-transparent base material of the printed circuit board and the dark part that is shielded from light by the conductor pattern or mounted components, a linear light source is used as the lighting device. This is arranged parallel to the scanning line of the camera, and the spread of the emitted light from the linear light source in the width direction is regulated at least on one side in the width direction, and the limit in the emission direction caused by this regulation is Tilt the line at an appropriate angle with respect to the optical axis of the camera,
An illumination method for an optical printed circuit board inspection apparatus, characterized in that the emitted light from the linear light source is suppressed from directly entering the field of view of the camera.