JP2002033576A - Method and device for examining appearance of cream solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome a problem such that it can not be conventionally detected whether a cream solder is normal or not from the form of the cream solder. SOLUTION: Concerning this method for examining appearance of cream solder, the cream solder is irradiated through an illuminating means 3, which is installed almost in the lateral direction of a cream solder 2, capable of alternately switching and emitting light from at least two confronted directions, reflected light from the cream solder is photographed by a camera 4, at least two light and dark images are differentiated, the side face inclined part of the cream solder is found from the luminance value thereof, the value of the side face inclined part is compared with the preset reference value for propriety decision and propriety in the form of the cream solder is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting whether or not cream solder previously applied to a printed circuit board is applied in a normal shape in order to solder electronic components to the printed circuit board. Method and apparatus.

[0002]

2. Description of the Related Art A conventional cream solder inspection method is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-296746. This is achieved by irradiating a cream solder formed on an electrode made of a copper foil on a printed circuit board with light having a wavelength of 600 nm or less from an obliquely upward direction, and causing the reflected light reflected from the printed circuit board to enter an upper camera to increase or decrease the brightness. The image is obtained, and the quality of the application area of the cream solder is determined based on the bright and dark images.

[0003] In the above-mentioned publication, the quality of the application area of the cream solder is determined irrespective of the presence or absence of a solder coating portion such as a solder leveler, that is, the quality is determined based on two-dimensional information of the cream solder. It does not inspect the three-dimensional shape of the cream solder.

As a method of applying cream solder to a printed circuit board, a metal screen having small holes formed at positions corresponding to positions where cream solder is applied is used. Then, cream solder is applied to the printing surface through the holes from above the screen. Then, when the application is completed, the screen is lifted, and the cream solder printed through the holes of the screen is left at the application position, thereby completing the application of the cream solder.

In such a method of applying cream solder, when the screen is lifted, the cream solder having a small soldering area as shown in FIG.
(B), the upper peripheral surface is shaved off by the inner peripheral surface of the hole of the screen as shown in FIG.

[0006]

Even if cream solder having such a shape is inspected by employing the technique disclosed in the above-mentioned publication, that is, even if the printed board does not have a solder coating portion such as a solder leveler, There is a problem that it is impossible to detect the lack of cream solder.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to ensure that the shape of the cream solder can be reliably formed even if the circumferential portion above the cream solder is cut off. It is an object of the present invention to provide a cream solder appearance inspection method and apparatus which can detect the cream solder shortage by detecting the appearance.

[0008]

SUMMARY OF THE INVENTION A method for inspecting the appearance of cream solder according to the present invention is intended to achieve the above object.
That means is to irradiate the cream solder alternately with light from at least two opposite directions through illuminating means arranged in a substantially horizontal direction of the cream solder, and to use a camera in which reflected light from the cream solder is arranged upward. Photographing, calculating the difference between the at least two light and dark images, obtaining a side slope portion of the cream solder from the brightness value, comparing the value of the slope portion with a preset reference value for quality determination, and determining the shape of the cream solder. Is determined.

Further, the cream solder appearance inspection apparatus of the present invention comprises: a camera disposed above a printed circuit board to be inspected;
Illuminating means arranged in a substantially horizontal direction of the cream solder applied to the printed board and configured to irradiate light to the cream solder alternately from two opposing directions, and switching the illuminating means and photographing with the camera A calculating unit that calculates a difference between the at least two images and obtains a side slope portion of the cream solder from the difference brightness value, and a value of the side slope portion obtained by the calculation unit and a preset reference value for pass / fail determination A determination unit for performing a comparison and determining the quality of the shape of the cream solder.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cream solder shape inspection apparatus according to the present invention will be described below with reference to the drawings. Figure 1
In the figure, reference numeral 1 denotes a printed circuit board on which pads 1a, which are conductive patterns, are formed, and cream solder 2 is applied on the pads 1a by screen printing as in the conventional case. The printed board 1 is configured to move in the XY directions by an XY stage (not shown).

3 is approximately 5 to 5 mm above the upper surface of the printed circuit board 1.
As illumination means fixed at positions spaced apart by 10 mm, a number of light sources such as LEDs are arranged opposite to each other in a ring shape so as to emit light in a substantially horizontal direction. Further, the light sources disposed opposite to each other are configured so that only light sources located at both ends of the ring, which are obtained by dividing a ring into three equal lines by three parallel straight lines by a switching circuit 5 described later, are alternately turned on.

Reference numeral 4 denotes a camera such as a video camera, which is fixed at a distance of about 100 mm from the upper surface of the printed circuit board 1 and whose optical axis is set to coincide with the center of the illuminating means 3. In addition, they have an integral structure. Incidentally, the movement by the XY stage may be changed to the printed circuit board 1, and the integrated structure (the illumination means 3 and the camera 4) may be moved by the XY stage.

Next, the block diagram of FIG. 2 will be described. 1 denote the same members, and a description thereof will be omitted. Reference numeral 5 denotes an image memory for storing an image from the camera 4 described above. Reference numeral 6 denotes a switching circuit for alternately switching on and off light sources facing each other in the illuminating means 3, and each time the illuminating means 3 is switched by the switching circuit 6. The image memory 5 is configured to store an image from the camera 4.

Reference numeral 7 denotes the cream solder 2 in a state where the light sources at both ends of the illuminating means 3 are alternately lit and illuminated.
The arithmetic unit 8 calculates the difference between the luminance values of the two images of the image memory 5 that have photographed the part, and calculates the area and length of the high luminance value part. This is a determination unit that compares with a reference value and determines whether the shape of the cream solder 2 is normal.

Next, the operation will be described based on the above configuration. First, FIG. 3A shows an image obtained by photographing an image with all the light sources in the lighting unit 3 turned on by the camera 4. As described above, when the illumination is applied to the truncated cone-shaped cream solder 2 from almost the side and photographed with the camera 4 directly above, the brightness of the side inclined portion of the cream solder becomes high.
It should be possible to judge the shape of the cream solder 2 from this information. However, since the cream solder 2 is a particle of several tens of microns and the upper surface is not a perfect flat surface, diffuse reflection is caused by light from almost right beside and the solder from the side of the cream solder 2 The difference in brightness between the reflected light and the reflected light from the upper surface cannot be sufficiently obtained.

Therefore, in the present invention, the light sources at both ends of the illuminating means 3 are alternately turned on by the switching circuit 6, and an image from the camera 4 is stored in the image memory 5 every time the switching is turned on (FIG. 3). (B)). Next, when the two images are differentiated in the arithmetic unit 7, the upper surface portions that always cause irregular reflection due to illumination from both directions are canceled out, and an image as shown in FIG.

The value of the sloping portion having a high luminance value in the image is compared with a predetermined reference value, for example, an area value, in the judgment section 8, that is, the area of the high luminance portion is equal to or more than the reference value. Means that the side inclined portion of the cream solder 2 is gently inclined and the amount of solder is insufficient. Therefore, the area value and the length of the inclined portion at which degree of inclination the luminance value is determined to be normal. Is set as a reference value, and a comparison is made with this reference value.

If the determination unit 8 determines that the cream solder 2 is defective, it is notified by various known methods that a defect has occurred in the shape of the cream solder 2.

In the above-described embodiment, the angle of the optical axis from the light source differs between the cream solder 2 near the light source of the lighting means 3 and the cream solder 2 far from the light source of the lighting means 3 in the image obtained by switching the lighting means 3. As a result, the brightness values are different, and thus, by performing the correction based on the difference between the optical axes, a more accurate pass / fail determination can be performed.

In the above embodiment, the LED
Although the method using the illuminating means 3 formed in a ring shape has been exemplified, it is also possible to execute the same cream solder appearance inspection as described above by using the illuminating means formed with LEDs in a straight line.

[0021]

As described above, according to the present invention, it is determined that the cream solder is normally applied. Therefore, the cream solder is alternately switched from at least two opposing directions provided substantially in the lateral direction of the cream solder. Irradiate the cream solder via a light irradiating means, photograph the reflected light from the cream solder with a camera, determine the difference between the brightness values in at least two of the captured images, and obtain a certain value or more based on the difference. Since the shape of the cream solder was determined by comparing the value of the side inclined portion having the luminance value with a preset reference value, the upper portion of the cream solder at the time of screen printing was scraped off and was determined to be defective. The determination can be made reliably.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an arrangement of lighting means in an embodiment of a cream solder appearance inspection apparatus according to the present invention.

FIG. 2 is a block diagram of the inspection device according to the first embodiment;

3A and 3B show images taken by a camera, wherein FIG. 3A is an image when light is irradiated from above, FIG. 3B is an image when light is irradiated from right and left, and an image when a difference is obtained.

4A and 4B are side views showing normal and defective cream solders, where FIG. 4A shows a normal state and FIG. 4B shows a defective state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Cream solder 3 Lighting means 4 Camera 5 Image memory 6 Switching circuit 7 Operation part 8 Judgment part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C035 AA06 2G051 AA65 AB14 AC15 BA01 BA20 BC06 CA03 CA04 CB01 CD06 DA07 EA08 EA14 EA16 EB01 EB02 5E319 AA03 AC01 BB05 CD04 CD29 CD53 GG03 GG20

Claims (2)

[Claims] 1. A camera in which light is alternately radiated to cream solder from at least two opposite directions via illuminating means arranged substantially in the horizontal direction of the cream solder, and reflected light from the cream solder is arranged upward. Photographed with the at least 2
The difference between the two bright and dark images is obtained, the side slope portion of the cream solder is obtained from the luminance value, and the value of the slope portion is compared with a predetermined reference value for quality determination to determine the quality of the shape of the cream solder. A method for inspecting the appearance of cream solder, characterized in that: 2. A camera disposed above a printed circuit board to be inspected, and a cream solder applied to the printed circuit board is arranged substantially in the horizontal direction and alternately emits light to the cream solder from two opposing directions. Illuminating means, and at least two of the illuminating means being switched and photographed by the camera
A calculating unit that calculates a difference between the two images and obtains a side inclined portion of the cream solder from the difference luminance value, and compares the value of the side inclined portion obtained by the calculating unit with a preset reference value for pass / fail determination. A determination unit for determining the quality of the shape of the cream solder, and a visual inspection device for cream solder.