JPH02133885A - Inspecting method for pattern - Google Patents

Abstract

PURPOSE:To exactly execute the pattern inspection by projecting a direction code of a density gradient in an arbitrary part of an edge image in the X axis direction or in the Y axis direction and deriving a histogram of the direction code. CONSTITUTION:A video signal obtained by executing an image pickup by a TV camera 2 from the upper part of a printed circuit board 1 is converted to a digital signal through an A/D converter 3, differentiated by a differentiating circuit 4, and an absolute value of a differential for showing a density gradient and a direction code for showing the direction of the density gradient are obtained. Subsequently, the absolute value of the differential which is obtained is binarized by a binarization processing circuit 5, and also, brought to line thinning processing by a line thinning processing circuit 6, and obtained edge image data is written in a frame memory 7. A decision processing part 9 projects only the direction code of a part to be taken notice of in the axial direction for showing satisfactorily information to be desired to obtain, and from the statistic of a code histogram obtained by the projection, an inspection of a circuit pattern P is executed. In such a way, it becomes unnecessary to execute a complicated data setting work in advance, and also, the measurement of a pattern can be executed correctly irrespective of existence of a misalignment of an image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pattern inspection method for automating visual inspection of the appearance of printed circuit boards.

[Prior Art] As seen in Japanese Patent Application Laid-open No. 15380/1983, the address of the pattern is measured at a preset position for each repeated pattern on a binary image or a grayscale image, and the addresses of the repeated patterns are measured. There is a method to check the average position and alignment.

[Problems to be Solved by the Invention] However, in the conventional method, it is necessary to measure and set the fixed position for each individual pattern in advance, so when a plurality of patterns exist, there is a problem that the setting work becomes complicated. Furthermore, if a positional shift occurs due to a shift when setting the workpiece or a deformation of the pattern itself, the measurement will be performed at a location that is shifted from the original measurement position, making it impossible to obtain accurate measurement results.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a pattern inspection method that does not require complicated data setting work in advance and can perform pattern inspection correctly regardless of the presence or absence of image positional shift. is to provide.

[Means for Solving the Problems] The present invention provides a method for creating a grayscale image consisting of a pattern of repeated shapes.
Obtain an edge image by converting it into a differential line, and calculate the direction code of the density gradient at any point in this edge image in the X-axis direction,
Alternatively, the histogram of the direction code is obtained by projecting it in the Y-axis direction.

[Operation] According to the method of the present invention, it is determined in advance which direction code to focus on and which axis to project, the X-axis or the Y-axis.

Next, a histogram of the projected direction code is obtained, and detection is determined based on this histogram. As described above, according to the method of the present invention, the preliminary setting work is simple, and measurement errors due to individual pattern deviations do not occur.

[Example code] The present invention will be explained below with reference to Examples.

FIG. 1 shows the configuration of an embodiment of a pattern inspection apparatus using the method of the present invention. In this embodiment, a video signal obtained by imaging with a TV camera 2 from above a printed circuit board 1 is
/D converter 3 to convert it into a digital signal.

The digitally converted signal is differentiated by a differentiating circuit 4 to obtain the absolute value of the differential representing the density gradient and a direction code representing the direction of the density gradient. The absolute value of the obtained differential is binarized in a binarization processing circuit 5 so as to represent the shape of the pattern, and further thinned in a line thinning processing circuit 6 to obtain edge image data. The edge image data obtained by this thinning processing circuit 6 is written into the frame memory 7.

Further, the direction code is stored in the direction code memory 8.

The above edge image clearly represents the shape of the pattern as shown in FIG. 2(a). Here, Figure 2 (a
), the arrow at the tip of the circuit pattern P indicates the direction of the direction code and indicates a part of the pattern shape.

Next, a method of creating a direction code histogram in the determination processing section 9 will be explained based on FIGS. 2 to 4.

First, determine the part of the pattern of interest on the obtained image. For example, if you want to know the shift in the X-axis direction of the image, focus on the tip of the circuit pattern P.

Next, the direction code of the part of interest is examined, and only the direction code of the part of interest is projected in the axis direction that best represents the information desired. In FIG. 2(a), if it is desired to know the positional deviation in the X-axis direction, the direction code at the tip of the circuit pattern P is projected in the X-axis direction. The code histogram obtained by this projection is shown in FIG. 2(b).

FIG. 4 shows the flow of this projection process, and the frame memory 7
The upper edge image is scanned, and when an edge image is detected, the direction code value in the direction code memory 8 corresponding to the address on the edge image is referred to, and if it is the direction code of interest, it is added to the histogram.

Once a histogram of direction codes is obtained, statistics such as the median value and distribution width of this histogram are calculated. The circuit pattern P is inspected based on these statistics.

For example, from the median value, the position of the circuit pattern P in the X-axis direction can be obtained as shown in FIG. 2(b), and from the width of the distribution, for example, the width of the distribution as shown in FIG. If so, it can be seen that the tips of the circuit pattern P are not aligned in a straight line as shown in FIG. 3(a). That is, the degree of alignment of the tips of the circuit pattern P can be inspected based on the width of the distribution.

[Effects of the Invention] The present invention can create a grayscale image consisting of a pattern of repeated shapes,
Obtain an edge image by converting it into a differential line, and calculate the direction code of the density gradient at any point in this edge image in the X-axis direction,
Alternatively, since the histogram of the direction code is obtained by projecting it in the Y-axis direction, there is no need for complicated data setting work in advance, and the pattern can be accurately measured regardless of the presence or absence of positional deviation of the image.

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram of an embodiment using the method of the present invention,
Figure 2 (a) is the side view of the edge image obtained by the same method as above, Figure 2 (b) is the side view of the direction code histogram of Figure 2 (a) obtained by the same method, and Figure 3 (a) is the same as above. FIG. 3(b) is another side view of the edge image obtained by the above process, and FIG. 4 is a flowchart of the projection process of the above process. 1 is a printed circuit board, 2 is a TV camera, 3 is an A/D converter,
4 is a differentiation circuit, 5 is a binarization processing circuit, 6 is a thinning processing circuit, 7 is a frame memory, 8 is a direction code memory, 9 is a determination processing section, and P is a circuit pattern. Agent Patent Attorney Ishi 1) Chief Voluntary author of amendments to Figure 4 procedures)

Claims (1)

[Claims] (1) Obtain an edge image by converting a grayscale image consisting of a pattern of repeated shapes into differential thin lines, and projecting the direction code of the density gradient at any location of this edge image in the X-axis direction or Y-axis direction. 1. A pattern inspection method characterized by determining a histogram of direction codes.