JP2003121381A - Printed circuit board inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the inspection time of an optical automatic inspection device for printed circuit board by reducing the number of processed image data. SOLUTION: The time required by the optical automatic inspection device for comparison and acceptance/rejection discrimination when the device performs image processing is shortened by reducing the data volume of a circuit pattern shape, by not comparing the image of a printed circuit board which is an object to be inspected directly with a model image in the unit of picture elements, but extracting the outline of the circuit pattern of the printed circuit board and obtaining data from an aggregate of extremely short segments of sub-pixel accuracy.

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an inspection apparatus for inspecting a circuit pattern of a printed circuit board for defects such as circuit defects, circuit fatness, and foreign matter. 2. Description of the Related Art As a method of inspecting a printed circuit board before mounting components, there are provided a continuity test for actually checking the presence or absence of a disconnection or a short circuit by passing electricity through a circuit, and a circuit defect or foreign matter which cannot be detected by the continuity test. There are optical inspections that are inspected by an inspector or detected by an optical automatic inspection device by image processing. [0003] Inspection methods in an optical automatic inspection apparatus by image processing are roughly classified into two types, a feature extraction method and a comparative inspection method. In the feature extraction method, it is checked whether the features of the circuit pattern of the printed circuit board conform to the design rules. The design rules include whether the circuit width is larger than the specified minimum circuit width, whether the circuit interval is larger than the specified minimum circuit interval, whether the circuit end is a terminal, and the curvature of the circuit contour. Is smaller than the given maximum curvature. Typically,
The feature extraction method can process even a small-sized inspection device and has a short inspection time, but the inspection reliability is lower than the comparative inspection method. The comparative inspection method includes an actual pattern comparison method of comparing printed circuit boards using non-defective samples as a model for comparison with a printed circuit board to be inspected,
There are two types of design pattern comparison methods for modeling design information such as CAD data. In either method, a printed circuit board pattern image to be inspected is superimposed on a model, and a pass / fail judgment is made by comparing the two. The comparative inspection method requires a large amount of calculation for image processing and the like, so the apparatus scale is large and the inspection time is long, but the reliability of the inspection is higher than that of the feature extraction method. In the comparative inspection method, a pattern image of a printed circuit board to be inspected is generally compared with CAD data or a model image generated from a non-defective product. If the size of the smallest portion of the printed circuit slope that needs to be determined based on the size is referred to as the minimum size, the minimum circuit width or minimum circuit interval is usually the minimum size. In the appearance inspection, it is necessary to inspect a chip or a protrusion of a circuit. Therefore, the pattern image or the model image needs to have a resolution sufficient to determine whether or not the circuit appearance of the smallest dimension portion is acceptable. If the pixels in the image are used as the unit of the size measurement, and if the pixel size is about 1/10 of the minimum size, the pixel size is 10 μm if the minimum size is 100 μm.
Need to be about. However, when the minimum dimension is 100 μm,
In the case of inspecting a 00 mm square printed circuit board, if the pixel size is 10 μm, the number of pixels on one side of the pattern image to be inspected is as large as 10,000 pixels. Such a huge image,
There is a problem that it is difficult to handle the image capturing means for capturing an image and the image processing means for processing an image after capturing, and it takes time to process even if the handling is possible. SUMMARY OF THE INVENTION The present invention has been made to solve such a problem of a conventional method for automatically inspecting a circuit pattern of a printed circuit board, and its object is to maintain the inspection accuracy. Another object of the present invention is to provide a printed circuit board pattern automatic inspection method in which the amount of pattern image data to be inspected is reduced and the processing time is reduced. SUMMARY OF THE INVENTION The present invention provides a printed circuit board pattern inspection apparatus for comparing a model data generated from design information or a non-defective image with a printed circuit board product to determine whether the product is acceptable or not. A printed circuit board that converts the circuit pattern contour shape of a printed circuit board product into a group of minute line segments having sub-pixel accuracy, and compares the position and orientation of each minute line segment with the outline of the model data to determine the acceptability of the product. It is a board inspection device. Next, an embodiment of the present invention will be described. FIG. 1 is a schematic diagram of a printed circuit board inspection method using an actual pattern comparison method. The printed circuit board 1 to be inspected and the printed circuit board 2 serving as a non-defective model are imaged by the imaging means 3
To make an image, and the image processing means 4 makes a comparison to make a pass / fail decision. FIG. 2 is a schematic diagram of a printed circuit board inspection method using a design pattern comparison method. Printed circuit board 1 to be inspected
It is compared with a design pattern 5 generated from CAD data or the like, and a pass / fail judgment is made. In either method, a CCD is mainly used as the imaging means 3. Further, as the image processing unit 4, an image to be inspected and a model image are subjected to hardware processing by a dedicated circuit, software processing by a microprocessor, or the like. In the image pickup means 3, the image of the printed circuit board 1 is approximated to a finite set of pixels having a certain size. FIG.
FIG. 2 is an explanatory diagram of a problem of such an inspection method in units of pixels. 3 is a schematic diagram of a printed circuit board,
The black part indicates the substrate serving as the insulating part, and the white part indicates the circuit. FIG. 3 is a graph on the upper right of FIG. 3 in which the brightness of the AA ′ cross section of the printed circuit board is represented in a graph. Graphs of brightness when imaged by the imaging means 3 are the middle right and lower right figures in FIG. When the contour position of the circuit of the printed circuit board matches the grid position of the pixels of the image, the position of the contour can be accurately represented as shown in the middle right of FIG. However, in most cases, the contour position of the circuit does not match the pixel grid position.
Therefore, when a portion where each pixel in the image is larger than a certain threshold value is considered as a circuit portion, the result is that the true contour position is different from the apparent contour position on the image. This error is called a space quantization error, and it is necessary to make the space quantization error sufficiently smaller than the size of a defect to be detected in the inspection when setting the resolution of the imaging unit 3. This leads to an increase in the number of pixels of a printed circuit board image, that is, an amount of data, and an increase in processing time in the image processing means. In the printed circuit board inspection apparatus according to the present invention, instead of comparing the image of the printed circuit board 1 to be inspected with the model image as it is, as shown in FIG. After extracting and converting the contour into data with a group of line segments of minute length about the pixel size,
The position and direction of each line segment are compared with the circuit contour of the model, and pass / fail judgment is made. In the method of separating a circuit part and a part that is not so by comparing with a threshold value for each pixel, there is a possibility that a maximum of ± 0.5 pixel shift may occur as a spatial quantization error,
By using a contour extraction filter that estimates the position of the contour from the value of a certain pixel and its surrounding pixels, it is possible to determine which position in the pixel the contour passes through by a fraction to several tenths of the pixel size. , So-called sub-pixel accuracy. That is, according to the present invention, even if an image having a pixel size several times as large as that of the conventional method is used, the inspection can be performed with approximately the same accuracy. When the same area is inspected by the conventional apparatus and the apparatus of the present invention, the number of pixels of the image can be inspected with a fraction of a square, that is, a tenth of a pixel. Since the number of pixels in the image is small, the amount of image processing data required for inspection is also reduced, and the number of minute lines representing contours is even smaller than the number of pixels, so that the amount of data processing can be reduced. It is possible to hope for a higher speed. According to the method of the present invention, it is possible to provide an inspection apparatus in which the inspection time is reduced by reducing the data amount of image processing while maintaining the inspection accuracy in the inspection of a printed circuit board. Becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a printed circuit board inspection method using an actual pattern comparison method. FIG. 2 is a schematic diagram of a printed circuit board inspection method using a design pattern comparison method. FIG. 3 is an explanatory diagram of a problem of an inspection method in units of pixels. FIG. 4 is an explanatory diagram of a method for expressing a circuit contour of a printed circuit board according to the present invention. [Description of Signs] 1 Printed circuit board to be inspected 2 Printed circuit board 3 serving as a non-defective model 3 Imaging means 4 Image processing means 5 for comparison 5 Design pattern 6 Printed circuit board image 7 Fine line segment group of circuit outline

Claims (1)

Claims: 1. A printed circuit board pattern inspection apparatus for comparing a model data generated from design information or a non-defective image with a printed circuit board product to determine whether the product is acceptable or not. A printed circuit board inspection device that converts the circuit pattern contour shape of a product into a group of minute line segments having sub-pixel accuracy, and compares the position and orientation of each minute line segment with the contour of the model data to determine the acceptability of the product.