KR20100039044A - Method for optical test of pcb - Google Patents

Abstract

PURPOSE: A method for an optical test of a PCB is provided to secure the quality of a test by expressing the brightness and deviation of an image of the surface of PCB, copper foil, and a solder ball numerically. CONSTITUTION: When an image of PCB mounted on a test bed of an optical inspection system is obtained, a test is prepared(S105-S111). The surface brightness of the PCB, the brightness difference between a copper foil and a solder ball, and brightness data are obtained(S117). Reference image data is read(S119). It is determined whether the PCB has a defect by comparing the detected data with a reference data.

Description

Optical test method for printed circuit boards {Method for Optical Test of PCB}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical inspection method of a printed circuit board (PCB), wherein the surface brightness and illuminance variation of a copper foil after image acquisition using a camera, an illumination, and a frame grabber are calculated and counted. The data relates to a method of optical inspection of a PCB that generates standard data according to the PCB and solder ball manufacturers, and thereby improves productivity by reducing errors in determining the quality of the PCB.

In general, PCB surface, copper foil, and PCB mold surface marking and solder ball attaching processes are produced in the back end of the line process during semiconductor memory manufacturing process. Due to the change in the brightness of the solder ball, problems occur in precision inspection and detection of defects.Because many companies manufacture and mass-produce PCBs, the brightness and illuminance of each company must be varied, and there is a need for leveling by companies. .

For example, the phenomenon occurring in the manufacturing line is formed by recognizing the name of the material engraved on the PCB and the characteristics of the material with copper foil in the semiconductor processing line, and identifying the specific material by recognizing the material name to prevent PCB mixing. It is then sent to the material transport equipment and other equipment on which the interface is built.

In this case, the optical inspection system analyzes by acquiring an image, and there are often false recognition and non-recognition due to the difference in brightness of the copper foil, which may obviously hinder the operation and production of the equipment.

In addition, the solder balls are placed on copper foil, melted in an oven (Reflow M / C), and the PCB paste and solder balls are attached. Extra, etc.) is difficult to detect.

In this way, the brightness and roughness difference of the surface of PCB, copper foil of PCB, solder ball, etc. should be leveled and a suggestion can be made to improve product quality and productivity.

Presenting the collected data using a method of measuring illuminance and brightness values will increase the productivity and the potential of the optical inspection system.

As described above, the PCB provided by various companies that manufacture and mass-produce the PCB has a problem in precision inspection and defect detection due to various brightness and roughness of the surface, copper foil, and solder balls, which causes a decrease in productivity. There was a problem.

Therefore, in order to solve the problems according to the related art, the present invention generates standard data by counting and quantifying brightness and roughness deviations of images of PCB surface, copper foil, and solder balls for each manufacturer, thereby improving quality of inspection in an optical inspection system. It is an object of the present invention to provide an optical inspection method of a PCB to ensure the quality, and to improve the defect detection of the PCB and the productivity in the production line.

Optical inspection process of the PCB to achieve the object of the present invention is obtained by analyzing the image of the surface of the printed circuit board (PCB), strip (line), solder ball (Solder Ball) through the optical inspection device and different for each manufacturer A PCB optical inspection method for inspecting a PCB state, the method comprising: an inspection preparation process of checking an inspection preparation state by acquiring an image of the PCB located on an inspection table of the optical inspection apparatus; PCB image detection process of detecting the roughness difference and brightness data of the surface of the PCB, copper foil and solder balls by inspecting the PCB when the inspection preparation is completed; A PCB reference data access process of accessing and recalling previously stored reference image data to be compared with the image detected through the PCB image detection process; And a non-defective product determination process of comparing the detected roughness and brightness data of the surface of the PCB, copper foil, and solder balls with reference data to determine whether the good quality of the PCB is determined.

Here, the PCB image detection process is a step in which the PCB image analysis process is a step in which the light emitted from the light source of the PCB optical inspection device is irradiated to the PCB surface through the diffusion plate; Maintaining a predetermined angle between the light source and the PCB surface to steer the light difference between the solder ball and the coated PCB surface; Maintaining the light source and the PCB surface at a predetermined angle to steal the light difference between the copper foil and the PCB surface; 4 steps of collecting the reflected light from the PCB surface, solder ball, copper foil surface with a camera; Converting the collected reflected light into a digital signal and converting the reflected light into an image having a series of brightnesses; Selecting the PCB surface, solder balls, and copper foil surfaces according to a series of brightness differences from the PCB image; And extracting and collecting the brightness of the PCB surface, the roughness difference between the solder ball and the copper foil surface, and the brightness data.

The PCB optical inspection method according to the present invention made as described above generates standard data by counting and quantifying the brightness and roughness deviation of the image of the PCB surface, copper foil, and solder ball for each manufacturer, thereby ensuring a better inspection quality in the optical inspection system. In addition, there is an effect that can increase the accuracy of the failure detection of the PCB, thereby improving the productivity.

First, the present invention uses the PCB optical inspection device (camera, lighting, frame grabber) to detect the illuminance difference and the brightness of the PCB surface. In other words, if you examine the roughness and brightness of the copper foil on the PCB, where the copper foil is located. Or, the gray value of each pixel exists around it.

As shown in FIG. 3, a remarkable difference occurs between the pixel gray value of the subject and the surroundings, and the position and size of the subject, an average brightness value, and the like may be calculated using edge and labeling techniques. The position of all copper foils on the PCB and the solder ball position in the subsequent solder ball attaching process are obtained from the coordinates on the PCB fabrication drawing, and the positions of the roughness, size, and average of each copper foil and solder ball are used using the positions. After collecting the brightness, the data is digitized.

Hereinafter, with reference to the accompanying Figures 1 to 11 with respect to a specific embodiment of the present invention will be described in detail.

1 is a schematic configuration diagram of a PCB optical inspection apparatus for implementing a PCB optical inspection method according to an embodiment of the present invention, the central computer 100 for controlling the image acquisition and inspection results of the PCB 110, and the PCB A camera 130 for acquiring and capturing an image of the camera, an illumination 120 providing a light source to provide an even image to the PCB, and supplying power to the still image and the illumination 120 of the PCB 110, An image control algorithm for synchronizing between the camera 130 and the illumination 120 and the image acquired by the camera 130 are converted into a computer language so that the user can check the image and an image algorithm. Frame grabber 102 to be applied, and the monitor 140 for displaying the operation state of each part and the PCB optical inspection process on the screen.

Figure 2 is a flow chart of the PCB optical inspection process according to an embodiment of the present invention, the PCB for inspection is placed on the inspection table (not shown in the figure) of the PCB optical inspection device to obtain a PCB image (S101).

The PCB image is inspected before the start of the acquisition inspection and whether the PCB presetting for the inspection is completed. (S103) Pre-inspection presetting is the PCB position correction inspection tool setting, PCB surface brightness and roughness inspection tool setting, unit position. Calibration inspection tool setting and PCB copper foil, solder ball roughness difference and brightness inspection tool setting work will be performed. (S105 ~ S111)

PCB optical inspection preparation is completed through the above process, and starts the PCB optical inspection. (S113)

The illumination 120 is controlled by the control of the illumination control unit 101 to acquire the image of the PCB so that the light emitted from the light source is irradiated onto the PCB surface through a diffuser plate (not shown). The PCB surface adjusts and maintains a predetermined angle so that the light difference between the solder ball and the PCB surface is raised, and the light source and PCB surface adjusts and maintains at a constant angle so that the copper difference between the copper foil and the PCB surface is raised.

The light beam reflected by the light source irradiated onto the PCB surface is collected by the camera 130, and image processed through the frame grabber 102, and then sorted into the PCB surface, solder ball, and copper foil surface according to a series of brightness differences. do.

To this end, first, the gray value of each pixel is measured at the position where the brightness of the PCB surface except for the copper foil existing on the PCB is to be measured. (S115)

 Here, the PCB surface brightness detection is to calculate the average brightness by using the edge, labeling technique and histogram (Histogram: graph of the brightness value of each pixel) and obtain the difference value of brightness by manufacturer.

8 and 9 are monitor screens showing brightness values of the same kind of PCB surface of different manufacturers, even if the same product, it can be seen that the products of different manufacturers have different gray values of each pixel.

7 is a histogram showing the gray values of the PCB surface on a monitor.

FIG. 10 shows the brightness of the surface and the copper foil as an image of the PCB to be inspected. FIG. 11 shows an image for inspecting the brightness of the surface and the solder ball as the solder balls are placed on the copper foil instead of the copper foil inspection. This is the figure shown.

The brightness and degree of the PCB copper foil and solder balls are measured, and there are two cases in which there is only a copper foil as shown in FIG. 10, and a solder ball is adhered onto the copper foil as shown in FIG. 11. The gray value of and has a group of pixels with a value above or below.

That is, in order to obtain the shape of the copper foil and the solder ball, the brightness difference between the background pixel and the object (the copper foil and the solder ball) is generated. For this, the lighting is adjusted to have a significant difference between the copper foil and the solder ball and the peripheral pixel. Will be

Subsequently, in the image measurement step, the brightness difference setting value of the pixel is set to separate the surrounding pixels and the objects (copper and solder balls).

When the pixel corresponding to the setting value is formed by using the setting value, it is recognized as an object (copper and solder ball).

5 and 6 are display diagrams of the monitor screen representing the gray values of the copper foil and the solder ball of the PCB.

In order to discriminate the configuration of the pixel group as the subject, an edge and a labeling method are used.

Groups of the plurality of subjects gather to form a semiconductor chip, and the brightness values of each subject unit are measured and collected and expressed as subject image data, which is specifically, a difference between gray values and illuminance for each subject. Value, gray value and illuminance difference value per unit, the size of the subject (size of the pixel) and the position data of the subject (S117).

The stored reference data is loaded in order to determine whether the gray value of the pixel on the PCB surface and the image data of the subject which are measured and collected through the above process are good or defective (S119).

By comparing the PCB image data of the same type of the same manufacturer loaded with the reference data with the brightness and roughness difference data of the PCB surface, copper foil and solder ball collected through the above process is determined as good or bad (S121).

The reference data for the determination is inputted and stored from the corresponding manufacturer as PCB image data of the same type of the same manufacturer, or if there is no previously stored reference data, the reference image data is currently measured and collected through the inspection process. Since it is generated and stored, it is used as reference data for PCB inspection of the same type in the future. (S123)

1 is a schematic configuration diagram of a PCB optical inspection device for implementing the present invention,

2 is a flow chart of a PCB optical inspection process according to an embodiment of the present invention,

3 and 4 are display diagrams of screens representing gray values of a subject to be detected according to an embodiment of the present invention;

5 and 6 are display diagrams of the screen representing the gray value of the copper foil and the solder ball of the PCB,

7 is a screen display diagram of a histogram showing a gray value of a subject;

8 and 9 are screen views showing differences in brightness values on the same PCB for the same product of different manufacturers,

10 is a display diagram when there is only copper foil on the PCB,

11 is a screen display of a PCB with a solder ball attached to a copper foil.

Claims (7)

In the PCB optical inspection method for inspecting different PCB status by manufacturer by acquiring and analyzing the surface of the printed circuit board (PCB), the strip line, the solder ball (Solder Ball) through the optical inspection device, An inspection preparation process of checking an inspection preparation state by acquiring an image of the PCB located on an inspection table of the optical inspection device; A PCB image detection process of inspecting the PCB to detect surface brightness of the PCB, roughness difference between the copper foil and solder balls, and brightness data when the test preparation is completed; A PCB reference data access process of accessing and recalling previously stored reference image data to be compared with the image detected through the PCB image detection process; And An optical inspection method for determining whether the PCB is good or bad by comparing the detected roughness and brightness data of the surface of the PCB, copper foil, and solder balls with reference data; . The method of claim 1, The inspection preparation process sets the PCB position correction tool, sets the PCB surface brightness and roughness inspection tool, sets the unit position correction inspection tool, and sets the PCB copper foil and solder ball roughness and brightness inspection tool. Optical inspection method of a printed circuit board comprising a. The method of claim 1, The PCB image detection process is a step in which the PCB image analysis process is a step in which the light emitted from the light source of the PCB optical inspection device is irradiated onto the PCB surface through the diffusion plate; Maintaining a predetermined angle between the light source and the PCB surface to steer the light difference between the solder ball and the coated PCB surface; Maintaining the light source and the PCB surface at a predetermined angle to steal the light difference between the copper foil and the PCB surface; 4 steps of collecting the reflected light from the PCB surface, solder ball, copper foil surface with a camera; Converting the collected reflected light into a digital signal and converting the reflected light into an image having a series of brightnesses; Selecting the PCB surface, solder balls, and copper foil surfaces according to a series of brightness differences from the PCB image; And And extracting and collecting the brightness of the PCB surface, the roughness difference between the solder ball and the copper foil surface, and the brightness data. 7. An optical inspection method of a printed circuit board, the method comprising: The method of claim 1, The PCB image detection process may include: calculating a minimum, maximum, and average value of gray values of a range to be measured after extracting gray values of each pixel by measuring brightness of PCB surface areas except for copper foil and solder ball areas of the PCB; Calculating a gray value for the subject determined according to the gray value difference between the gray value of the subject composed of the copper foil and the solder ball and the peripheral PCB surface pixels extracted in step 1, and a unit composed of the plurality of subjects; Optical inspection method of a printed circuit board comprising a. The method of claim 1, Subject image data calculated through the PCB image detection process includes a gray value and an illuminance difference value for each subject; Gray value and illuminance difference value per unit; The size of the subject; And the position of the subject; including, The calculation method is an optical inspection method of a printed circuit board, characterized in that the calculation using the edge and the labeling (Blob) technique and histogram (Histogram) according to the difference between the gray value of the subject and the surrounding pixels. The method according to claim 1 or 5,  Printed circuit, characterized in that further comprising the step of storing the PCB image data calculated by the PCB image detection process as reference data, if the same PCB data of the manufacturer previously stored in the PCB reference data access process is not registered. Optical inspection method of the substrate. The method of claim 1, If the pre-stored homogeneous PCB data of the manufacturer in the PCB reference data access process is not registered, further comprising the step of inputting the image data of the PCB received from the manufacturer, the optical inspection method of the printed circuit board .

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