Method for detecting undesired connection on printed circuit board

1 . A method for detecting an undesired connection forming a short circuit on a printed circuit board (PCB) based on an original image of the PCB, the PCB having a substrate on which a trace is formed, said method comprising steps of:

performing binarization on the original image to generate a binary image that has an external boundary;

identifying a trace area on the binary image, wherein the trace area corresponds to the trace of the PCB;

determining whether the trace area contacts the external boundary of the binary image at four places;

determining that the trace that corresponds to the trace area has an undesired connection forming a short circuit when it is determined that the trace area contacts the external boundary of the binary image at four places, wherein the trace area corresponding to the trace that has an undesired connection is a short-circuit trace area, and the trace corresponding to the short-circuit trace area has two trace segments interconnected by the undesired connection to form an H-shape;

converting the binary image to a converted image; and

determining, on the converted image, two substrate areas corresponding respectively to two portions of the substrate that are between the trace segments and that are separated by the undesired connection,

wherein for each of the substrate areas, the substrate area has a perimeter that is equal to a sum of a U-shape portion of a contour of the short-circuit trace area adjoining the substrate area and a straight-line portion of an external boundary of the converted image adjoining the substrate area, and the U-shape portion of the contour of the short-circuit trace is longer than the straight-line portion of the external boundary of the converted image.

2 . The method as claimed in claim 1 , wherein the step of identifying a trace area is to identify the trace area based on pixel values of the binary image.

3 . The method as claimed in claim 1 , wherein the step of identifying a trace area is to identify the trace area using edge detection to obtain a contour of the trace area.

4 . The method as claimed in claim 1 , wherein, in the step of performing binarization, the binary image has a plurality of pixels each having either a first pixel value or a second pixel value, and the trace area has a plurality of pixels each having the first pixel value, wherein:

the step of converting the binary image to a converted image is implemented when it is determined that the trace area contacts the external boundary of the binary image at four places, and is implemented by assigning the second pixel value to all of the pixels of the binary image except for the trace area.

5 . The method as claimed in claim 4 , further comprising a step of:

performing skeletonization procedure on the trace area in the converted image to obtain a topological skeleton of the trace area.

6 . The method as claimed in claim 5 , further comprising steps of:

determining two fork points in the topological skeleton, each of the fork points being an intersection of three branches of the topological skeleton; and

obtaining two coordinate sets respectively of the two fork points.

7 . The method as claimed in claim 6 , further comprising steps of:

connecting the two fork points to form a reference line segment;

determining a pair of first reference points respectively on two sides of one of the substrate areas in a manner that the first reference points form a first line segment having a central point spaced apart from a central point of the reference line segment by a predefined distance, the two sides of said one of the substrate areas respectively adjoining two portions of the trace area that correspond respectively to the trace segments;

determining a pair of second reference points respectively on two sides of the other one of the substrate areas in a manner that the second reference points form a second line segment having a central point spaced apart from the central point of the reference line segment by the predefined distance, the two sides of said the other one of the substrate areas respectively adjoining the two portions of the trace area;

determining a pair of first terminal points on the reference line segment in a manner that a distance between the first terminal points is equal to a distance between the first reference points and that a distance between the central point of the reference line segment and one of the first terminal points is equal to a distance between the central point of the reference line segment and the other one of the first terminal points;

determining a pair of second terminal points on the reference line segment in a manner that a distance between the second terminal points is equal to a distance between the second reference points and that a distance between the central point of the reference line segment and one of the second terminal points is equal to a distance between the central point of the reference line segment and the other one of the second terminal points; and

determining a short-circuit region that is defined by the first and second terminal points and the first and second reference points and that corresponds to the undesired connection.

8 . The method as claimed in claim 7 , wherein the predefined distance is one half the distance between the two fork points.

9 . The method as claimed in claim 7 , wherein the first line segment terminating at the first reference points is parallel to another side of said one of the substrate areas, said another side of said one of the substrate areas adjoining another portion of the trace area that corresponds to the undesired connection,

wherein the second line segment terminating at the second reference points is parallel to another side of said the other one of the substrate areas, said another side of said the other one of the substrate areas adjoining said another portion of the trace area.

10 . The method as claimed in claim 7 , further comprising a step of converting the converted image to a short-circuit image by assigning the second pixel value to each pixel of the converted image except for the short-circuit region.

11 . The method as claimed in claim 7 , further comprising a step of outputting a coordinate set of each pixel having the first pixel value in the short-circuit image.

12 . The method as claimed in claim 1 , further comprising a step of determining a short-circuit region that corresponds to the undesired connection.

13 . The method as claimed in claim 12 , wherein the step of determining a short-circuit region includes sub-steps of:

performing skeletonization procedure on the trace area to obtain a topological skeleton of the trace area;

determining two fork points in the topological skeleton, each of the fork points being an intersection of three branches of the topological skeleton; and

determining the short-circuit region according to the fork points.

14 . The method as claimed in claim 13 , wherein the sub-step of determining the short-circuit region includes

determining two substrate areas corresponding respectively to two portions of the substrate that are between the trace segments and that are separated by the undesired connection, and further includes:

connecting the two fork points to form a reference line segment;

determining a pair of first reference points respectively on two sides of one of the substrate areas in a manner that the first reference points form a first line segment having a central point spaced apart from a central point of the reference line segment by a predefined distance, the two sides of said one of the substrate areas respectively adjoining two portions of the trace area that correspond respectively to the trace segments;

determining a pair of second reference points respectively on two sides of the other one of the substrate areas in a manner that the second reference points form a second line segment having a central point spaced apart from the central point of the reference line segment by the predefined distance, the two sides of said the other one of the substrate areas respectively adjoining the two portions of the trace area;

determining a pair of first terminal points on the reference line segment in a manner that a distance between the first terminal points is equal to a distance between the first reference points and that a distance between the central point of the reference line segment and one of the first terminal points is equal to a distance between the central point of the reference line segment and the other one of the first terminal points;

determining a pair of second terminal points on the reference line segment in a manner that a distance between the second terminal points is equal to a distance between the second reference points and that a distance between the central point of the reference line segment and one of the second terminal points is equal to a distance between the central point of the reference line segment and the other one of the second terminal points; and

determining the short-circuit region that is defined by the first and second terminal points and the first and second reference points.

15 . The method as claimed in claim 14 , wherein:

in the step of performing binarization, the binary image has a plurality of pixels each having either a first pixel value or a second pixel value, and the trace area has a plurality of pixels each having the first pixel value;

the step of converting the binary image to a converted image is implemented when it is determined that the trace area contacts the external boundary of the binary image at four places, and is implemented by assigning the second pixel value to all of the pixels of the binary image except for the trace area;

the sub-steps of performing skeletonization procedure and determining the short-circuit region are implemented based on the converted image.

16 . The method as claimed in claim 15 , further comprising steps of:

obtaining a short-circuit image by assigning the second pixel value to each pixel of the converted image except for the short-circuit region; and

outputting a coordinate set of each pixel having the first pixel value in the short-circuit image.

17 . The method as claimed in claim 14 , wherein the predefined distance is one half the distance between the two fork points.

18 . The method as claimed in claim 14 , wherein the first line segment terminating at the first reference points is parallel to another side of said one of the substrate areas, said another side of said one of the substrate areas adjoining another portion of the trace area that corresponds to the undesired connection,

wherein the second line segment terminating at the second reference points is parallel to another side of said the other one of the substrate areas, said another side of said the other one of the substrate areas adjoining said another portion of the trace area.