JP3511456B2 - Pattern inspection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method for inspecting a pattern formed on a green sheet, a printed wiring board or the like. 2. Description of the Related Art A PGA (Pin Grid Array) has been conventionally known as a mounting technique suitable for a demand for increasing the number of pins of ICs and LSIs. In PGA, a ceramic substrate is used as a base of a package for attaching a chip, and wiring is performed up to a lead-out position. To make this ceramic substrate, a so-called green sheet made by kneading alumina powder with a liquid binder is used, and a paste containing a high melting point metal is screen-printed on the green sheet. By stacking and firing the required number of such sheets, so-called simultaneous firing, in which the green sheets are sintered and the paste is metallized, is performed. In such a green sheet or printed wiring board, a pattern is visually inspected by a human using a microscope after the pattern is formed. However, visually inspecting a fine pattern has a problem that skill is required and eyes are overworked. Therefore, as an alternative to the visual inspection, an inspection method has been proposed in which a pattern formed on a film carrier or the like is imaged by a TV camera and automatically inspected. In such an inspection method,
Defects in the pattern to be measured have been detected by comparing the pattern to be measured with the master pattern that is a reference for inspection. [0004] By the way, since a pattern such as a land and a hole in the land are usually formed in different processes, the center of the land coincides with the center of the hole in the master data. However, the hole position may be shifted due to a position shift at the time of drilling. According to the conventional inspection method, as shown in FIG. 8, when the position of the hole H of the pattern to be measured is largely shifted with respect to the master pattern M, it is detected as a defect. However, in such an inspection method, there is a problem that even if the distance (remaining pattern) between the outer edge of the land and the hole edge (remaining pattern) is sufficiently large and there is no electrical problem, it is detected as a defect. Was. Therefore, the conventional inspection method has a problem that the yield of products is reduced due to such overdetection. Further, if the hole position is not stable, the yield of the product is reduced for the above-mentioned reason. Therefore, a pattern having lands and holes is masked and not inspected. Therefore, in this case, there is a problem that the inspection of the land and the hole cannot be performed. The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a pattern inspection method that can prevent overdetection of a pattern defect and that is not affected by a change in a hole position. I do. According to the present invention, as described in claim 1, edge data indicating a pattern edge is extracted from pattern data at the time of designing a pattern to be measured, and this is extracted for inspection. As a first master pattern serving as a reference, edge data indicating a hole edge is extracted from the NC data at the time of designing the pattern to be measured, and this is used as a second master pattern. Edge data indicating a hole edge is extracted, a positional relationship between a predetermined positioning mark and a predetermined hole in the extracted pattern to be measured is obtained, and the positional relationship is calculated by comparing this with a reference amount. If the shift amount of the hole position is within the allowable range, the position of the second master pattern is shifted by the shift amount, and the first master pattern and the position are corrected. The pattern to be measured is inspected by comparing the second master pattern with the edge data of the pattern to be measured. As described above, the amount of deviation of the hole position in the pattern to be measured is calculated, and if the amount of deviation of the hole position is within the allowable range, the position of the second master pattern is shifted by the amount of the deviation. The deviation from the master pattern due to the positional deviation can be corrected. Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart illustrating a pattern inspection method according to an embodiment of the present invention, and FIG. 2 is a block diagram of a pattern inspection apparatus used in the inspection method. In FIG. 2, 1 is a printed wiring board,
Reference numeral 2 denotes an XY table on which the printed wiring 1 is placed. Reference numeral 3 denotes a line sensor camera for imaging the printed wiring board 1. Reference numeral 4 denotes edge data indicating an edge of the pattern to be measured from a grayscale image obtained by the camera 3. An image processing apparatus for calculating a shift amount of a hole position in a pattern to be measured and inspecting the pattern to be measured by shifting the position of the master pattern by the amount of the shift, a host computer for controlling the entire apparatus, a result of the inspection, and a result of the inspection Is a display device for displaying. First, a master pattern created in advance before inspection will be described. Host computer 5
Is read by a magnetic disk device (not shown) which reads pattern data of a printed wiring board created by a CAD (Computer Aided Design) system and written on a magnetic disk, for example (step 101 in FIG. 1). Then, edge data is extracted from the read pattern data,
This is set as the first master pattern (step 10
2). The edge data of the first master pattern is a set of pixels “1” indicating a pattern edge. Subsequently, the host computer 5 executes the above C
Numerical control (NC) data of the printed wiring board created by the AD system and written on the magnetic disk is read by the magnetic disk device (step 10).
3). Then, edge data is extracted from the read NC data, and is used as a second master pattern (step 104). The edge data of the second master pattern is a set of pixels “1” indicating a hole edge. It goes without saying that the pattern of the printed wiring board 1 is printed and etched based on the pattern data, and the printed wiring board 1 is drilled based on the NC data. Next, the inspection of the pattern to be measured will be described. First, the printed wiring board 1 is imaged by the camera 3. Then, the image processing device 4 digitizes the grayscale image output from the camera 3 and temporarily stores it in an internal image memory (not shown) (step 105). Since the camera 3 is a line sensor in which pixels are arranged in the X direction, two-dimensional image data is stored in the image memory by moving the XY table 2 or the camera 3 in the Y direction. The image processing apparatus 4 aligns the positioning marks of the pattern to be measured stored in the image memory with the positioning marks of the first and second master patterns sent from the host computer 5 to obtain the pattern to be measured and the second pattern. First, alignment with the second master pattern is performed (step 106). Since the positional relationship between the first master pattern and the second master pattern is determined at the time of creation, the alignment between the master pattern and the pattern to be measured is one.
Just go around. After the alignment, the image processing device 4
Binarizes the grayscale image of the pattern to be measured (step 107). The grayscale image data of the pattern to be measured includes the pattern and the other background (substrate), but there is a density difference between the pattern and the background. Is set as the threshold,
The pattern is converted to "1" and the background is converted to "0". Thus, the pattern edge and the inside thereof are pixel “1”.
Can be obtained. Subsequently, the image processing device 4 extracts edge data indicating the edge coordinates of the pattern to be measured by performing a labeling process for giving the same label (name) to the connected pixels in the binary image (step 108). FIG. 3 is a diagram for explaining the labeling process. Here, the pattern is represented by white circles, and the background (base material) is represented by black circles. For example, when extracting edge data from a binary image as shown in FIG. 3, the binary image is sequentially scanned in the TV raster direction (left to right in FIG. 3), and the boundary is still traced. An unbounded boundary point is found, this is set as a new tracking start point n1, and its X and Y coordinates are stored.
Then, for example, a boundary point connected in a clockwise direction is searched from the tracking start point n1, and storing the X and Y coordinates of the boundary point is repeated until returning to the tracking start point n1. When the boundary points of n1, n2, n3,... Are extracted and the boundary tracing of one pattern is completed, a boundary point whose boundary tracing has not been performed is searched again, and the boundary of the next pattern is traced. Thus, the patterns to be measured are labeled one after another. In this embodiment, when scanning in the raster direction, a white pixel is defined as the boundary point when rising from black to white, and a black pixel is defined as a boundary point when falling from white to black. Next, the image processing apparatus 4 obtains a shift amount of the hole position of the printed wiring board caused at the time of drilling (step 109). FIG. 4 is a diagram for explaining a method for obtaining the amount of deviation of the hole position. In FIG. 4, R1 is a positioning mark formed on the printed wiring board 1 by etching, R2 is a land also formed on the printed wiring board 1, H is a hole formed in the land R2 by drilling, and n1 is Edge data indicating the edge of the positioning mark R1, n2 being edge data indicating the edge of the land R2,
n3 is edge data indicating the edge of the hole H. When the printed circuit board 1 is imaged by the camera 3, the position of the positioning mark R1, land R2, and hole H is
The edge data n1, n2, and n3 of the pattern to be measured are obtained. The image processing device 4 obtains the center of gravity G1 of the positioning mark R1 from the edge data n1, and obtains the center of gravity G2 of the hole H from the edge data n3. Thereby, the distance X in the X direction between the center of gravity G1 of the positioning mark R1 and the center of gravity G2 of the hole H is obtained.
The distance YG in the G and Y directions can be calculated. The reference amount XGref of the distance XG and the reference amount YGref of the distance YG are determined in advance based on a master pattern or a good printed wiring board. Therefore,
Difference X between reference amounts XGref, YGref and distances XG, YG
By calculating Gref-XG and YGref-YG,
X, X of the hole position of the printed wiring board 1 generated at the time of drilling
The shift amount in the Y direction can be obtained. The image processing device 4 determines whether the calculated shift amount is within a preset allowable range (step 11).
0) If it is out of the allowable range, it is determined to be defective. Also,
If the calculated shift amount is within the allowable range, the image processing apparatus 4 shifts the position of the second master pattern in the X direction by the amount of shift XGref-XG in the X direction, and shifts the shift amount in the Y direction YGref-XG. Y of the second master pattern by YG
The position of the second master pattern is corrected by shifting the position in the direction (step 111). When the master pattern is created, as shown in FIG. 5A, the center C1 of the land in the first master pattern M1 and the center C2 of the hole in the second master pattern M2 have the same position. However, the position is shifted as shown in FIG. 5B by performing the position correction of the second master pattern M2. Subsequently, the image processing apparatus 4 obtains an error amount of a land between the first master pattern and the pattern to be measured, and obtains an error amount of a hole between the second master pattern and the pattern to be measured (step 112). . FIG. 6 is a diagram for explaining a method for obtaining the error amount of the land and the hole, and n4
Is the edge data indicating the outer edge of the pattern to be measured, and n5 is the edge data indicating the hole edge in the pattern to be measured. First, in the land portion of FIG. 6A, the center C1 of the land in the first master pattern M1 and the edge data n4 are connected by a straight line as shown in FIG. 6B. The error amount Δd of the edge data n4 is obtained by subtracting the distance between the master pattern M1 and the center C1, that is, the radius R of the land in the pattern M1, from the length L of the straight line.
R. The other error amounts of the land edge data can be similarly obtained. Similarly, the error Δe of the edge data n5
When the center C2 of the hole in the second master pattern M2 and the edge data n5 are connected by a straight line, the distance from the length Le of the straight line to the center C2 of the master pattern M2, that is, the radius r of the hole in the pattern M2 Le minus the value
−r. Next, the image processing apparatus 4 determines whether the land and the hole of the pattern to be measured are normal based on the land error Δd and the hole error Δe (step 113).
That is, the image processing device 4 determines that the image is normal when the error amount Δd is smaller than the predetermined threshold value D and the error amount Δe is smaller than the predetermined threshold value E. When the error amount Δd is equal to or greater than the threshold value D or the error amount Δe is equal to or greater than the threshold value E, the image processing apparatus 4 determines that there is a defect. When the edge of the land overlaps the hole and the land edge of the pattern P to be measured is cut as shown in FIG. 7, it is determined that the edge is cut in the labeling process. When the edge of the land is cut in this way, it is an electrical problem, so that it is determined that there is a defect even if the amount of displacement of the hole position is within the allowable range. According to the present invention, the shift amount of the hole position in the pattern to be measured is calculated, and if the shift amount of the hole position is within the allowable range, the second master is shifted by the shift amount. Since the position of the pattern is shifted, a shift from the master pattern due to a position shift at the time of drilling can be corrected, and the inspection according to the actual product can be performed without being affected by a change in the hole position. In addition, if the deviation of the hole position is within the allowable range and the distance between the outer edge of the land and the hole edge is sufficient, the pattern to be measured is regarded as normal, so that overdetection can be prevented and the product yield can be reduced. Can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a pattern inspection method according to an embodiment of the present invention. FIG. 2 is a block diagram of a pattern inspection apparatus. FIG. 3 is a diagram for explaining labeling processing of a pattern to be measured. FIG. 4 is a diagram for explaining a method of obtaining a shift amount of a hole position. FIG. 5 is a diagram showing a state of position correction of a second master pattern. FIG. 6 is a diagram for explaining a method of obtaining an error amount of a land and a hole. FIG. 7 is a diagram showing a state in which a land edge has been cut by overlapping of a land edge and a hole. FIG. 8 is a view for explaining a conventional inspection method. [Description of Signs] 1 ... Printed wiring board, 2 ... XY table, 3 ... Line sensor camera, 4 ... Image processing device, 5 ... Host computer, 6 ... Display device.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 21/84-21/958 H05K 3/00

Claims (1)

(57) [Claims 1] Edge data indicating a pattern edge is extracted from pattern data at the time of designing a pattern to be measured,
This is used as a first master pattern as a reference for inspection, edge data indicating a hole edge is extracted from NC data at the time of designing the pattern to be measured, and this is used as a second master pattern. The edge data indicating the pattern edge and the hole edge is extracted from, and the positional relationship between the predetermined positioning mark and the predetermined hole in the extracted pattern to be measured is obtained, and this is compared with the reference amount, thereby displacing the hole position. If the shift amount of the hole position is within an allowable range, the position of the second master pattern is shifted by the shift amount, and the first master pattern and the position-corrected second master pattern are shifted. A pattern inspection method, wherein a pattern to be measured is inspected by comparing edge data of the pattern to be measured.