CN1306244C - On-the-spot printing circuit board test based on digital image - Google Patents

Abstract

The present invention relates to a printing circuit board on-the-spot test method based on digital images, which belongs to the technical field of measurement. The present invention comprises the following steps that (1) the image matching test of the integrity of a PCB board structure is carried out, the corresponding areas of a target image and a standard picture are compared, and the matching test of the integrity of the PCB board structure is realized; (2) the test technique of a rectangular frame of the size of a PCB board wire is adopted, according to the difference of grey scale after the wire and the base board are imaged, greyscale processing and edge positioning are carried out to the target image in a rectangular test frame, and the geometric size of the wire is calculated; (3) the high-precision edge position of the target image is realized, an LOG operator is adopted for fast edge localization, and the image edge positioning of minor pixel level is realized by using a gray-scale value in a neighboring region of a fitting edge of a cubic polynomial. The present invention adopts the technique of high-precision minor pixel edge test to realize the target detection of a PCB board, and simultaneously, a test data report is made.

Description

Field Test Method of Printed Circuit Board Based on Digital Image

technical field

The invention relates to a testing method in the technical field of printed circuit boards, in particular to a digital image-based on-site testing method for printed circuit boards.

Background technique

In recent years, with the transfer of foreign PCB (printed circuit board) manufacturing to China, my country's PCB industry has achieved vigorous development, and at the same time it has brought higher requirements for PCB testing. From the perspective of the development of PCB products, today's testing technology is developing towards full automation and high reliability to reduce the influence of human and environmental factors. Among them, visual inspection, dimensional inspection, wire accuracy, structural integrity, etc. are the quality appraisal items stipulated in the IPC (International Association of Connecting Electronics Industry) standards. At present, automatic optical inspection has been widely used in the online inspection of PCB boards. This method uses the difference in the reflection effect of light on different materials to obtain the image information of PCB through the optical scanning system. For complex PCB boards, the amount of image information is large, the production status is relatively unstable, and the image error is large. The automatic optical inspection system will report many false errors when judging defects. According to the operator's experience, when inspecting complex PCBs, the automatic optical inspection system has a certain degree of missed detection.

After searching the existing technical documents, it is found that the Chinese patent application number is: 02139916.6, and the patent name is: image measurement system and method. According to the measurement method provided by the invention, it can be seen that the method obtains the size data of the object by processing the image data of the object. However, for the specific detection requirements of the PCB board, this method cannot guarantee the detection accuracy of the target on the PCB board, the structural integrity test and other requirements, and at the same time cannot issue a detection report to the production department to guide production.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, provide a kind of on-the-spot testing method for printed circuit board based on digital image, make it utilize stepper motor to drive pulley to adjust optical lens magnification according to test needs, to PCB target Image acquisition is carried out in a specific area, and high-precision sub-pixel edge detection technology is used to realize the target detection of the PCB board, and a detection data report is issued at the same time.

The present invention is realized through the following technical solutions, and the present invention comprises the following steps:

(1) Carry out image matching detection of the structural integrity of the PCB board, compare the target image with the corresponding area of the standard image, and realize the matching detection of the structural integrity of the PCB board:

(2) Using the rectangular frame test technology of PCB board wire size, according to the difference in grayscale between the wire and the substrate after imaging, the grayscale processing and edge positioning of the target image are carried out in the rectangular test frame, and the geometric size of the wire is calculated;

(3) To achieve high-precision edge positioning of the target image, the LOG operator (Laplacian Gaussian operator) is used for fast edge positioning, and the cubic polynomial is used to fit the gray value in the edge neighborhood to achieve a sub-pixel-level image Edge positioning.

The image matching detection of the structural integrity of the PCB board refers to: in order to improve the accuracy of detection, the test system directly produces the standard image data of the PCB board from CAD/CAM (Computer Aided Design and Manufacturing System); The magnification of the lens is adjusted by the stepping motor to drive the pulley. According to the size and distribution density of the target on the PCB, adjust the magnification of the optical system to collect and store the image of the target area of the PCB board under test, and move the X axis and Y axis of the horizontal worktable. Axis, to realize the image acquisition and storage of the entire PCB board; according to the magnification of the optical system, the standard image is enlarged or reduced, and the collected target image is compared with the corresponding area of the standard image, so as to realize the defect detection of the structural integrity of the PCB board.

The rectangular frame testing technology of the PCB board wire size refers to: according to the requirements of PCB design and manufacturing process, the items of PCB board wire size measurement include: wire width, wire spacing, wire average width, drilling maximum diameter, solder The maximum diameter of the pad, the deviation between the center of the drill hole and the center of the pad. In the detection process, according to the difference in the gray level of the wire and the substrate after imaging, the geometric size of the wire is calculated by using the sub-pixel edge positioning algorithm of the image.

Conductor width, line spacing of parallel conductors and average conductor width are measured using a rectangular test frame, that is, a rectangular mark frame is established in the image test area with the mouse, and the size of the test frame is adjusted according to the image size of the measurement target. The system is within the test frame Perform grayscale processing and edge positioning, calculate the currently tested line width, and mark it on the image.

The measurement of the maximum diameter of drill holes and pads adopts a rectangular test frame. The size of the test frame is adjusted according to the image size of the drill holes or pads. The system performs grayscale processing and edge positioning in the test area; at the initial position, the system It will detect the two best tangent lines of the drilling hole or pad circumference along the parallel direction of the test frame, and calculate the diameter at this position; the test frame rotates one equivalent around its center position, and the rotation equivalent is determined according to the measurement accuracy. The primary system will detect the two optimal tangent lines of the drill hole or pad circumference along the parallel direction of the test frame, and obtain the diameter at this position; after rotating 180°, compare all the obtained diameter values to obtain the maximum The diameter value and the corresponding inclination angle are marked on the image along the direction of the maximum diameter.

The measurement of the deviation between the center of the drill hole and the center of the pad adopts two rectangular test frames. The size of the two test frames is adjusted according to the size of the drill hole and the pad respectively. The system performs grayscale processing and edge positioning in the two test frames respectively. ;Same as the method of testing the diameter, calculate the maximum diameter position of the drill hole and pad respectively, then calculate the center position of the drill hole and pad, and use the distance between two points to calculate the center deviation value.

The system generates a data report from the test results of each image, and issues a test report through the printer to guide the staff to improve the process.

The high-precision edge positioning of the target image refers to: in order to improve the detection accuracy of the test system, two measurement fields of view are set according to the density of the PCB board wires and the thickness of the lines; when the wires are thinner and the density is larger When using a smaller measurement field of view to improve detection accuracy; when the wire is thicker and requires more targets to be measured at the same time, a larger measurement field of view is used; the size of the field of view is adjusted by a stepping motor.

In the case of a certain measurement field of view and a certain resolution of the CCD camera, the key to improving the detection accuracy of the test system is how to improve the edge positioning accuracy of the target image. If the feature target on the image can be positioned at the sub-pixel level, it is equivalent to improving the measurement accuracy. system precision. Therefore, the present invention proposes to use LOG operator for fast edge location and cubic polynomial to fit the gray value of the edge, so as to realize sub-pixel level image edge location. The specific implementation is as follows:

First, the original image is convolved with the Gaussian function, and the zero-crossing point after the discretized LOG template is convolved with the image is the edge of the image, so as to realize the fast edge positioning of the LOG operator;

Secondly, in the edge neighborhood of fast positioning, use the cubic polynomial to fit the gray value of the edge, take its inflection point as the edge position, and realize the method of sub-pixel positioning accuracy.

The invention applies the digital image detection technology to the production site test of the printed circuit board, solves the defects of the traditional automatic optical test system, and at the same time issues a test report for the staff to improve the manufacturing process and the like. The method adopts the image matching detection technology of the structural integrity of the PCB board, the rectangular frame testing technology of the wire size of the PCB board, and uses the LOG operator for fast edge location and the algorithm of the cubic polynomial to fit the gray value of the edge. Edges are positioned at the sub-pixel level. The test system not only has high detection accuracy, but also has a very low missed detection rate.

Detailed ways

Provide following embodiment in conjunction with content of the present invention:

This embodiment is carried out on a self-developed digital image detector, and the specific implementation process is as follows:

The target to be tested is the geometric size of the wires on the inner layer of the PCB. The test items are wire width, wire spacing and the maximum diameter of the drilled hole. The hardware configuration of the test system is as follows: CCD camera COSTAR C400, 1/2"Color CCD 752×582 optical lens Navitar Zoom 6000, C-Mount, 1X Adapter frame grabber Imagenation PCX200 Frame Grabber Card light source Ose Vision Light Source, BIN-50-2R-60G, BT68*118FR stepper motor 35BYG007 computer Pentium(R)4, CPU 2.00GHz, 256M RAM

(1) According to the thickness and distribution density of the PCB board wires, the measurement field of view is determined to be 12mm×9mm, and the size of the field of view is realized by adjusting the magnification of the optical lens by driving the pulley with a stepping motor.

(2) The target area is imaged by the image acquisition subsystem, and the imaged video signal is stored in the computer through the image acquisition card.

(3) Carry out convolution operation on the collected original image with Gaussian function, the zero crossing point after discretized LOG template and image convolution is the edge of the image, so as to realize the fast edge location of LOG operator; In the edge neighborhood of fast positioning, the gray value of the edge is fitted by a cubic polynomial, and the inflection point is taken as the edge position to realize the sub-pixel edge positioning of the image.

(4) The measurement of the wire width and the line spacing of parallel wires adopts a rectangular test frame, that is, a rectangular mark frame is established in the image test area with the mouse, and the size of the test frame is adjusted according to the image size of the measurement target. Grayscale processing and edge positioning, calculate the currently tested line width, and mark it on the image.

(5) The measurement of the maximum diameter of the borehole adopts a rectangular test frame. The size of the test frame is adjusted according to the image size of the borehole. The system performs grayscale processing and edge positioning in the test area; at the initial position, the system will Detect the two best tangent lines of the drilling circle in the parallel direction of the frame, and calculate the diameter at this position; the test frame rotates around its center position by an equivalent, and the rotation equivalent is 1°, and the system will parallel the test frame every time it rotates Detect the two boundary best tangents of the drilling circle in the direction of the drill hole, and obtain the diameter at this position; after rotating 180°, compare all the obtained diameter values to obtain the maximum diameter value and the corresponding inclination angle, and display it in the image Labeled along the direction of the largest diameter.

(6) Through the analysis of the test report issued by the test system, it can be concluded that the on-site test system for printed circuit boards based on digital images has high detection accuracy, which solves the defects of traditional automatic optical inspection systems and greatly reduces the cost of printed circuit boards. The missed detection rate, and the detection results provide a reference for the staff to improve the manufacturing process and design.

Claims (3)

1. printed wiring board on-the-spot test method based on digitized video, it is characterized in that, may further comprise the steps: the images match that (1) carries out the pcb board structural intergrity detects, and the corresponding region of target image and standard picture compares, and realizes the matching detection of pcb board structural intergrity; (2) adopt the rectangle frame measuring technology of pcb board conductor size, different according to gray scale after lead and the substrate imaging carry out to target image in the test rectangle frame that gray scale is handled and the location, edge, the physical dimension of calculating lead; (3) locate at the high precision edge of realizing target image, adopts the LOG operator to carry out the rapid edge location, and utilize the gray-scale value in the cubic polynomial match edge neighborhood, realizes that the image border of sub-pixel is located;

The images match of described pcb board structural intergrity detects, and is meant: test macro directly produces the standard image data of pcb board from CAD/CAM; The multiplying power of optical lens is regulated by the step motor drive belt wheel in the test macro, size and distribution density according to target on the pcb board, regulate the optical system multiplying power image acquisition and storage are carried out in the target area of detected PCB, the X-axis of mobile and horizontal worktable and Y-axis realize the image acquisition and the storage of whole pcb board; Standard picture is amplified or dwindle according to the multiplying power of optical system, the corresponding region of target image that collects and standard picture relatively, thereby realize the defects detection of pcb board structural intergrity;

The rectangle frame measuring technology of described employing pcb board conductor size, be meant: the distance between centers of tracks of conductor width, parallel wire and lead mean breadth are measured and are adopted the test rectangle frame, promptly set up a rectangle sign frame in the image measurement zone with mouse, the size of test block is regulated according to the picture size size of measurement target, system carries out gray scale processing and location, edge in test block, calculate the current line thickness of testing, and on image, mark;

The location, high precision edge of described realization target image, its method is: according to the density size of pcb board lead and the thickness of lines, set two and measure the visual field; When thin and density is big when lead, adopt the less measurement visual field with the raising accuracy of detection; Thick and require simultaneously-measured target more for a long time when lead, adopt the bigger measurement visual field; The size in the visual field is regulated by stepper motor;

Described employing LOG operator carries out the rapid edge location, its method is: original image is carried out convolution algorithm with Gaussian function, LOG template and the zero cross point after the image convolution after the discretize promptly are edge of image, thereby realize the rapid edge location of LOG operator;

The described gray-scale value that utilizes in the cubic polynomial match edge neighborhood, its method is: in the edge neighborhood of locating fast, utilize cubic polynomial to come the gray-scale value at match edge, getting its flex point is marginal position, realizes the method for sub-pixel positioning precision.

2. the printed wiring board on-the-spot test method based on digitized video according to claim 1, it is characterized in that, the rectangle frame measuring technology of described employing pcb board conductor size, be meant: the test rectangle frame is adopted in the measurement of boring and pad maximum gauge, the size of test block is regulated according to the picture size size of boring or pad, and system carries out gray scale processing and location, edge in test zone; In initial position, system can detect the best tangent line in two borders of boring or pad circumference, the diameter when calculating this position along the parallel direction of test block; Test block is around equivalent of its center rotation, and the rotation equivalent determines that according to measuring accuracy every rotation primary system can detect the best tangent line in two borders of boring or pad circumference, the diameter when drawing this position along the parallel direction of test block; Behind the Rotate 180 °, all diameter values that obtain are compared, draw maximum gauge value and corresponding inclination angle, and mark in image upper edge maximum gauge direction.

3. the printed wiring board on-the-spot test method based on digitized video according to claim 1 and 2, it is characterized in that, the rectangle frame measuring technology of described employing pcb board conductor size, be meant: two test rectangle frames are adopted in the measurement of the deviation of drill center and pad center, according to the size adjustment of boring and pad, system carries out gray scale processing and location, edge respectively to the size of two test block in two test block respectively; Identical with the method for test diameter, obtain the boring and the maximum gauge position of pad respectively, calculate again and hole and the pad home position, utilize distance between two points to calculate the centre deviation value.