JP3402994B2 - Solder paste quality judgment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recognizing a solder paste provided on a surface of a board by distinguishing the paste from other elements of the board.
And to a method for determining the quality of the solder paste. 2. Description of the Related Art Various solder paste recognizing methods have been proposed for inspecting defects such as chipping, thinning, bleeding, and bridges of a solder paste provided on the surface of a substrate. As an example, there are a method using a difference in luminance and a method using a slit light by a laser (light cutting method). [0003] In the former method, a camera is arranged so as to face an inspection area on the surface of a substrate, and the inspection area is photographed by a camera while illuminating the inspection area with a lighting device. By performing image processing based on the change, the solder paste provided in the inspection area is recognized separately from other elements (pattern, base material) of the substrate. In the latter method, an illuminating device for irradiating a slit light by a laser is arranged to face an inspection region on the surface of the substrate, and the illumination device irradiates the inspection region with the slit light to illuminate the surface of the substrate. The image is taken with a camera from an oblique position, and the solder paste is recognized by utilizing the fact that the slit light appears to be bent by the height of the solder paste. [0005] However, the above-mentioned conventional method for recognizing a solder paste has the following problems. That is, in the former method, since the brightness of the solder paste, the base material, and the pattern are similar to each other, it is difficult to accurately recognize the solder paste with a single illumination. In the latter method, a special illuminating device for irradiating slit light is required, so that there is a problem that the solder paste inspection device becomes expensive. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to accurately distinguish and recognize a solder paste on the surface of a substrate from other elements of the substrate .
To provide a solder paste quality determination method capable of soldering quality of the paste can be determined, and inexpensively constitute the solder paste inspection apparatus. [0009] [Means for Solving the Problems] To achieve the above object, a solder paste quality determination method of the present invention, a camera
A first step of photographing the inspection area irradiated with light parallel to the optical axis of the camera with a camera, and irradiating the inspection area with light inclined to the optical axis of the camera.
The image obtained by the second step of photographing the inspection area obtained by the camera and the first step is set to a value capable of distinguishing a pattern portion from a solder paste portion. A third step of performing a binarization process based on the first density threshold value, and an image obtained by the second step, wherein a pattern portion, a solder paste portion, and a base portion can be distinguished from each other. a fourth step of binarizing the second concentration threshold set to, extracts the third and the solder paste portions from an image obtained by the fourth step, the shape of the solder paste portions Recognize and calculate area
Fifth step to issue and reference area stored in advance
And the difference between the first determination threshold value and the difference calculated in the fifth step.
And compare the area of the solder paste portion
If it is larger, the sixth step to determine that there is thinness or chipping
And the reference area stored in advance and the second determination threshold
And the solder pace calculated in the fifth step.
Compare the area of the part and if the sum is smaller,
The seventh step of determining that there is bleeding, and the fifth step
Whether there is a bridge based on the shape of the solder paste recognized
And an eighth step of determining Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a solder paste inspection apparatus employing the solder paste recognition method of the present invention, FIG. 2 is a plan view of one inspection area of a substrate, and FIG. 3 explains the principle of the solder paste recognition method of the present invention. FIGS. 4 and 5 are flowcharts showing a procedure for inspecting the solder paste by the solder paste inspection apparatus of FIG. The solder paste inspection apparatus shown in FIG. 1 is mounted on a screen printing machine and inspects for defects such as chipping, thinning, bleeding, and bridges of the solder paste on the surface of the substrate. , Substrate support table 1
And a camera 2 arranged above the camera and taking an image of the surface of a substrate PB mounted horizontally on the substrate support table 1.
A first illuminating device 3 provided at the lower end of the illuminator, a ring-shaped second illuminating device 4 disposed between the first illuminating device 3 and the substrate PB, and an image processing means connected to the camera 2 5 and
Determining means 6 connected to the image processing means 5;
And a display 7 connected to the display. The substrate support table 1 has an X extending in the horizontal direction.
It moves in the axial direction and the Y-axis direction and rotates in a horizontal plane. By moving the substrate support table 1 in the XY directions, a plurality of inspection areas set on the surface of the substrate PB can be sequentially positioned directly below the taking lens 2a of the camera 2. The first illumination device 3 comprises a cylindrical case 3a attached to the lower end of the camera 2 so as to be coaxial with an optical axis L extending in the vertical direction of the taking lens 2a of the camera 2,
And an LED (not shown) mounted inside the case 3a. The LED is connected to a power supply (not shown), emits light vertically downward as indicated by an arrow B, and uniformly irradiates the inspection area of the substrate PB facing the camera 2 with light. The second illuminating device 4 has a ring-shaped frame 4a arranged coaxially with the extension of the optical axis L of the taking lens 2a of the camera 2, and a lower part of the frame 4a has a full circumference. And a number of LEDs (not shown) mounted over the same. The LED is connected to a power supply (not shown), emits light radially downward as indicated by an arrow C, and transmits an optical axis from the periphery of the inspection area of the substrate PB facing the camera 2 toward the inspection area. Light is uniformly irradiated in a direction inclined with respect to L. The image processing means 5 is constituted by a microcomputer. The memory of the microcomputer converts a grayscale image photographed by the camera 2 while irradiating the substrate PB with light by the first lighting device 3. A first density threshold for processing, and a second density threshold for binarizing a grayscale image captured by the camera 2 while irradiating the substrate PB with light by the second illumination device 4 Are stored. As shown in FIG. 2, a plurality of patterns P are provided on the surface of a substrate M of a substrate PB, and a solder paste SP is screen-printed on each pattern P.
The pattern P is made of metal, the surface of which is coated with molten solder (solder leveler) and is in a mirror-like state. When light is applied to the surface, the light is specularly reflected. On the other hand, the solder paste SP includes a large number of solder ball groups having a diameter of several tens of μm, and when light is applied to the surface thereof, the light is irregularly reflected. The surface of the base material M is colored dark green or the like, and the solder paste SP and the pattern P have a silver color. Since the first lighting device 3 irradiates light vertically downward, when the first lighting device 3 irradiates light to the substrate PB, most of the light hitting the pattern P is reflected vertically upward, The light enters the photographic lens 2a of the camera 2. on the other hand,
Light hitting the solder paste SP is irregularly reflected in all directions, and the amount of light incident on the photographing lens 2a is smaller than that of the pattern P. Further, since the base material M is colored, the amount of light reflected on the base material M and incident on the photographing lens 2a is smaller than that of the pattern P. Accordingly, in an image obtained by photographing the substrate PB with the camera 2 while irradiating light with the first lighting device 3, the density difference between the solder paste SP and the portion of the base material M and the portion of the pattern P is large, and The density difference between the portion and the portion of the substrate M is reduced. The first density threshold value in this embodiment is set to a value that allows the portion of the solder paste SP and the base material M in this image to be distinguished from the portion of the pattern P. Therefore, when this image is binarized using the first density threshold, as shown in FIG. 3A, an image in which the portion of the solder paste SP and the base material M is black and the portion of the pattern P is white Is obtained. Further, since the light emitted from the second lighting device 4 is obliquely incident on the surface of the substrate M, the light reflected on the pattern P as in the case of the first lighting device 3 Most of the light does not enter the photographing lens 2a of the camera 2, but is reflected by the pattern P and is taken
And the amount of light reflected on the solder paste SP and the substrate M and incident on the photographing lens 2a is small.
Therefore, in an image obtained by photographing the substrate PB with the camera 2 while irradiating light with the second lighting device 4, a density difference due to a difference in the color of the solder paste SP, the pattern P, and the base material M appears. As described above, the solder paste SP
Since the pattern P has a silver color and the base material M is colored dark green or the like, in this image, the density difference between the portion of the solder paste SP and the portion of the pattern P is small. The density difference between the portion and the portion of the substrate M increases. The second density threshold value in this embodiment is determined by the solder paste SP and the pattern P in this image.
Is set to a value that can be distinguished from the portion of the base material M. Therefore, when this image is binarized by the second density threshold, an image in which the solder paste SP and the pattern P are white and the base M is black as shown in FIG. Is obtained. The image processing means 5 divides the image processed by the first density threshold as shown in FIG. 3A into a solder paste SP and a substrate M portion and a pattern P portion. The image processed by the second density threshold as shown in FIG. 3 (b) is divided into a portion of the solder paste SP and the pattern P and a portion of the substrate M, and from these, as shown in FIG. 3 (c). An image is generated by extracting only the solder paste SP. A plane image of each inspection area of the substrate PB before screen printing is input to the memory of the image processing means 5 in advance, and the image processing means 5
A processing area is set for each solder paste portion of the solder paste extraction image, the shape of the solder paste SP in the area is recognized, and the recognized solder paste S is recognized.
A process of calculating the area by counting the number of pixels in the P portion is performed. The judging means 6 is constituted by a microcomputer, and the memory of the microcomputer has a reference area of the solder paste to be printed on each pattern P and the solder paste recognized by the image processing means 5. A first judgment threshold value for judging whether or not there is a hook and a second judgment threshold value for judging whether or not the solder paste is blurred are stored. The determining means 6 calculates the difference between the reference area of the solder paste and the first determination threshold value and the sum of the reference area of the solder paste and the second determination threshold value, and calculates these by the image processing means 5. Pass / fail is determined by comparing the area of the solder paste. The determining means 6 determines the presence or absence of a bridge from the shape of the solder paste recognized by the image processing means 5. Camera 2, first and second lighting devices 3, 4
Power supply, image processing means 5, determination means 6, display 7
Is connected to control means (not shown) composed of a microcomputer, and operates based on a command from the control means. Next, the operation of the above-mentioned solder paste inspection apparatus will be described with reference to the flowcharts of FIGS. First, the substrate support table 1 on which the substrate PB to be inspected is mounted moves, and when one of the inspection areas set on the surface of the substrate PB is located directly below the taking lens 2a of the camera 2, the substrate support table 1 is moved. 1 stops. Next, the first
Of the lighting device 3 is turned on (the second lighting device 4 is not turned on), and the camera 2 takes an image of the substrate PB (step # 5,
# 10). This image is sent to the image processing means 5 and stored in the memory. Then, the first lighting device 3 is turned off, the second lighting device 4 is turned on, and the camera 2 captures an image of the substrate PB (Steps # 15 and # 20). This image is also sent to the image processing means 5 and stored in the memory. Next, the image processing means 5 executes step # 10
Are binarized using the first density threshold, and the image obtained in step # 20 is binarized using the second density threshold. Generate an image by extracting only (Step # 2)
5 to # 35). When this is completed, the substrate support table 1
Moves, and the above-described steps are performed for other inspection areas. When it is confirmed that the above-described steps have been repeated for the number of inspection areas registered in the control means in advance (step # 40), the image processing means 5 sets each solder paste in each solder paste extracted image. A processing area is set for each part, the solder paste in the processing area is recognized, and the area is calculated (steps # 45 and # 5).
0). The shape and area of the obtained solder paste are sent to the judging means 6. The judging means 6 calculates the area D of the solder paste SP sent from the image processing means 5 by the difference E between the reference area of the solder paste SP stored in the memory and the first judgment threshold value. If D <E, a message to that effect is sent to the control means, and the display 7 is made thin and a message indicating the presence of a chip is displayed (steps # 55 and # 60). Next, the judging means 6 compares D with the sum F of the reference area of the solder paste SP and the second judgment threshold value, and when D> F, the fact is transmitted to the control means. Then, a display indicating that there is bleeding is made on the display 7 (steps # 65 and # 70). Next, the judging means 6 judges from the shape of the solder paste SP sent from the image processing means 5 whether or not there is a bridge between the adjacent solder pastes. This is transmitted and a display indicating that a bridge is present is displayed on the display 7 (step #).
80, # 85). Since the above solder paste inspection apparatus does not require a special illuminating device such as a slit light, the illumination used for photographing the position recognition mark provided on the surface of the substrate for positioning the substrate. The apparatus and the camera can be used, and can be configured at low cost. In this embodiment, the case where the camera position is fixed and the substrate is moved in the X and Y directions to perform photographing has been described. Instead, the position of the substrate is fixed. Alternatively, the camera may be moved in the X-Y direction to perform shooting. As described above, according to the method for judging the acceptability of the solder paste according to the present invention, the property that the pattern portion of the substrate reflects light regularly and the solder paste portion reflects light irregularly is used.
The pattern portion and the solder paste portion are distinguished from each other, and the pattern portion and the solder paste portion are distinguished by using the density difference due to the difference between the color of the pattern portion and the solder paste portion and the color of the base portion. This allows the solder paste portion to be accurately distinguished and recognized from other elements of the substrate. Recognizes the shape of the solder paste part and
Calculate the product, thin the solder paste from the shape and area,
Chips, bleeds, bridges can be determined
You. Further, the solder paste recognition method of the present invention
Since a special lighting device such as a slit light is not required, a solder paste inspection device can be configured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a solder paste inspection device employing a solder paste recognition method of the present invention. FIG. 2 is a plan view of one inspection area of the substrate. FIG. 3 is an explanatory diagram for explaining the principle of the solder paste recognition method of the present invention. FIG. 4 is a flowchart showing a procedure for inspecting a solder paste by the solder paste inspection apparatus of FIG. 1; FIG. 5 is a flowchart showing a procedure for inspecting a solder paste by the solder paste inspection apparatus of FIG. 1; [Description of Signs] 1 Substrate support table 2 Camera 2a Photographing lens 3 First illumination device 4 Second illumination device 5 Image processing means 6 Judgment means 7 Display L Optical axis M of photography lens of camera 2 Base material P Pattern PB Substrate SP Solder paste

Claims (1)

(57) [Claims] [Claim 1] A detector irradiated with light parallel to the optical axis of a camera.
A first step of photographing an inspection area with a camera, and the inspection area irradiated with light inclined to the optical axis of the camera.
A second step of photographing with the camera; and an image obtained in the first step, the first density threshold value being set to a value capable of distinguishing between the pattern portion and the solder paste portion. 3rd value processing
And binarizing the image obtained in the second step by a second density threshold value set to a value that can distinguish the pattern portion, the solder paste portion, and the base portion. Extracting the solder paste portion from the images obtained in the third and fourth steps, and recognizing the shape of the solder paste portion.
A fifth step of calculating the area, a reference area stored in advance and a first determination threshold value.
And the solder paste portion calculated in the fifth step
Compare with the area of the minute, if the difference is larger,
A sixth step of determining that there is a chip, a reference area stored in advance, and a second determination threshold value.
And the solder paste portion calculated in the fifth step
Compare with the area of the minute, if the sum is smaller,
A seventh step of determining that there is only a solder paste, and whether the shape of the solder paste recognized in the fifth step is
Solder paste quality determination method characterized by including an eighth step of determining whether the Luo bridge.