A method for quickly detecting the status of LDI equipment

Abstract

The invention discloses a method for quickly detecting the state of an LDI device, and belongs to the technical field of PCB board exposure. A detection pattern containing M rows and N columns of matrix points is exposed by a software built-in tool, and the position of the exposure point is tested by an alignment camera to compare with the theoretical position, and the test data is automatically analyzed to detect whether there is a problem with the device, and quickly locate the problem point, such as whether there is a problem with the optical path, the positioning accuracy of the workpiece stage, the horizontal straightness, the YAW, etc., to save the time of shutdown inspection; further, by setting the matrix point to a solid circle or a ring, the detection of the correctness of the pattern and the alignment result of the pattern are respectively realized.

Description

Technical Field

[0001] The invention relates to a method for quickly detecting the state of an LDI device, and belongs to the technical field of PCB board exposure. Background Art

[0002] Laser direct imaging (LDI) is a device that can directly transmit the exposure data of PCB board to the dedicated graphics processing software. The graphics are processed by the graphics processing software and then sent to the LDI exposure software through the exposure system composed of DMD digital micromirror array, laser and optical path, and then the graphics are directly transferred on the board.

[0003] LDI equipment is mainly composed of a high-precision motion platform, an exposure system, an alignment system, etc. The high-precision motion platform includes a carrying platform and a control device that controls the precise movement of the carrying platform, etc. The exposure system includes a DMD digital micromirror array, multiple light sources and their corresponding optical path systems, etc. The alignment system includes an alignment camera, etc. The exposure principle is that multiple light sources cooperate with the digital micromirror DMD to realize the exposure of the pattern (hereinafter referred to as the exposure system). Therefore, there are multiple light sources to form a splicing of light spots, and the exposure system can be moving or fixed. A carrying platform (suction cup) for placing the product is fixed on the high-precision motion platform, and scanning exposure is achieved by moving the carrying platform. The exposure can be scanned once or multiple times.

[0004] Because the temperature and humidity of the environment in which the LDI equipment is exposed are unstable, or some sudden problems occur, such as collision with the lens, collision with the camera, card, etc., which will cause the hardware position or parameters of the equipment to change, which will directly affect the quality of the product, such as layer deviation problems and splicing problems. Due to its own structural complexity, when layer deviation problems and splicing problems occur during the exposure process, it is difficult to determine where the problem occurs. In particular, although layer deviation problems are often caused by abnormalities of high-precision motion platforms, there are also many parameters of high-precision motion platforms, such as YAW, horizontal straightness, positioning accuracy, etc. If layer deviation problems occur during production, the equipment needs to be shut down, and calibration plates or interferometers are used to measure and identify the causes and then make adjustments to avoid more defective parts in the future (considering the high price of calibration plates or interferometers, they are usually not equipped for every exposure equipment). This process takes a long time and requires professional personnel, and long downtime will naturally affect output; therefore, it is time-consuming and labor-intensive, and seriously reduces production, which will lead to increased costs for manufacturers.

[0005] As for the splicing problem, the existing method usually uses equipment to expose the splicing analysis graphics, and then uses a line width meter to measure the splicing data, but the line width meter also has the problem of high cost. The workpiece stage detection is calibrated with an interferometer or a calibration plate, which also has the problem of long detection time and high cost. Summary of the invention

[0006] In order to solve the above problem, the present invention provides a method for quickly detecting the status of an LDI device, the method comprising:

[0007] Using the LDI device to expose a preset detection pattern, wherein the preset detection pattern includes matrix points of M rows and N columns;

[0008] The actual coordinate values ​​of each matrix point on the detection pattern after exposure are collected by the alignment camera of the LDI device;

[0009] The difference between the actual coordinate value of each matrix point and the theoretical value is used to determine whether each component of the LDI device is in a normal state.

[0010] Optionally, determining whether each component of the LDI device is in a normal state according to the difference between the actual coordinate value of each matrix point and the theoretical value includes:

[0011] Obtain the horizontal coordinate difference Δx and the vertical coordinate difference Δy between the actual coordinate value and the theoretical value of each matrix point respectively;

[0012] If the horizontal coordinate difference Δx of the matrix points in the same row is ≥ 5 μm, it is judged that the position relationship of each DMD in the LDI device is in an abnormal state;

[0013] If the horizontal coordinate difference Δx of the matrix points in the same column is ≥ 10μm, it is judged that the horizontal straightness of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state;

[0014] If the vertical coordinate difference Δy of the matrix points in the same column is ≥15μm, it is judged that the positioning accuracy of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state;

[0015] If the vertical coordinate difference Δy of the matrix points in the same row is ≥5 μm, it is determined that the debugging state of the splicing in the LDI device is in an abnormal state.

[0016] Optionally, the method further includes:

[0017] The state of the platform YAW is determined by detecting the curve difference of the vertical coordinates Y1~Yn of multiple rows of matrix points on the graph.

[0018] Optionally, the method comprises:

[0019] If the curve difference of the vertical coordinates Y1 to Yn of the matrix points in multiple rows on the detection graph exceeds 10 μm, it is determined that the state of the platform YAW is abnormal.

[0020] Optionally, the matrix points are solid circles or rings.

[0021] Optionally, when the method is used to detect the correctness of the exposure pattern, the matrix points are filled circles.

[0022] Optionally, when the method is used to detect the alignment result of the exposure pattern, the matrix points are in the form of circular rings.

[0023] The beneficial effects of the present invention are:

[0024] Use the software's built-in tools to expose a test graphic containing M rows and N columns of matrix points, use the alignment camera to test the position of the exposure points and compare them with the theoretical position, and automatically analyze the test data to detect whether there are problems with the equipment and quickly locate the problem points, such as whether there are problems with the optical path, the positioning accuracy of the workpiece stage, the horizontal straightness, YAW, etc., saving time for downtime inspection; further, by setting the matrix points to solid circles or rings, the graphics correctness and graphics alignment results can be detected respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 is a schematic diagram of a detection pattern used in one embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of a ring in a detection pattern used in one embodiment of the present invention;

[0028] Figure 3A It is a schematic diagram showing that the curves of the vertical coordinates Y1 to Yn of multiple rows of matrix points on a detection graph are greatly different in one embodiment of the present invention;

[0029] Figure 3B It is a schematic diagram showing that the curves of the vertical coordinates Y1 to Yn of multiple rows of matrix points on a detection graph have small differences in one embodiment of the present invention;

[0030] Figure 4A It is a schematic diagram of the state of the graphics projected by the DMD before the splicing and debugging of the LDI device disclosed in one embodiment of the present invention;

[0031] Figure 4B It is a schematic diagram of the state of the graphics projected by the DMD after the LDI device is spliced ​​and debugged according to one embodiment of the present invention;

[0032] Figure 5A It is a schematic diagram of a graphic exposure when the Y axis moves normally along a straight line in the motion mode of the LDI device disclosed in one embodiment of the present invention;

[0033] Figure 5B It is a schematic diagram of a graphic exposure when the Y axis does not move along a straight line in the LDI device motion mode disclosed in one embodiment of the present invention;

[0034] Figure 6 It is a graphic diagram that is exposed by scanning when the LDI equipment fails to splice and debug;

[0035] Fig. 7A This is a diagram showing the normal exposure of the YAW value in the motion mode of the LDI device;

[0036] Figure 7B This is a graphic diagram of the exposure when the YAW value is abnormal in the motion mode of the LDI device. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] To facilitate understanding of the technical solution of this application, some technical terms involved in this application are explained as follows:

[0039] A calibration board is a flat plate with a pattern array at fixed spacing. To correct lens distortion, it is necessary to determine the conversion relationship between physical size and pixels, as well as the relationship between the three-dimensional geometric position of a point on the surface of a spatial object and its corresponding point in the image. By photographing the calibration board with a camera and calculating with a calibration algorithm, the geometric model of the camera can be obtained, thereby obtaining high-precision measurement and reconstruction results.

[0040] Stitching: refers to the connection between adjacent strips during the scanning process.

[0041] Splicing misalignment: In this application, it specifically refers to the presence of a discontinuity in the Y direction at the connection between different scanning strips during DMD scanning.

[0042] Splicing overlap: refers to the anomaly in the X direction at the splicing point, where two strips overlap.

[0043] Splice tearing: refers to the abnormality in the X direction at the splicing point, with a distance between the two strips.

[0044] Inner layer alignment: After laminating on the diazo film, use a mark to mark the target on the A side and expose the pattern. When exposing the B side, grab the two alignment target points lit by Smark on the B side and expose them. At this time, the deviation of the images on the two sides is the inner layer alignment.

[0045] Outer layer alignment: During exposure, the two layers of the printed circuit board use the same alignment target hole, generally 4 points. At this time, the deviation value of the two layers of exposure images is the outer layer alignment.

[0046] High-precision motion platform Stage: In this system, it generally refers to the electric-controlled translation stage, which carries the substrate for exposure. It is usually square and has two axes, which can realize forward and backward movement of the X axis and forward and backward movement of the Y axis;

[0047] Orthogonality: Orthogonality of the X & Y axes of the workpiece table;

[0048] YAW: The yaw angle of the workpiece table Y axis during linear motion.

[0049] Positioning accuracy: Positioning is performed sequentially at certain intervals in one direction from the reference point (end point), and the difference between the measured value (actual position moved from the reference point) and the command value (actual position to be moved after the command is issued) of each positioning point is measured within the moving range of the worktable. The maximum difference is taken as the cumulative error (positioning accuracy).

[0050] Horizontal straightness: Position in one direction from the reference position, measure the difference between the vertical and horizontal offsets and the reference position, connect the starting and end points of the measured values ​​to get a straight line, and take the maximum difference in offset from the straight line as the straightness. Straightness has vertical and horizontal components. The maximum value of each component is taken as the straightness of the platform.

[0051] Embodiment 1:

[0052] This embodiment provides a method for quickly detecting the status of an LDI device. The method controls an exposure system through exposure software to expose a detection pattern on a PCB board with a dry film. The detection pattern is as follows: Figure 1 The matrix points shown in the figure contain M rows and N columns. The matrix points are solid circles or rings, which are used to detect different items. For example, when detecting the correctness of the exposure pattern, the matrix points are solid circles, which are used to compare the difference between the actual exposure pattern and the original image. The smaller the difference, the better the correctness of the pattern. When detecting the alignment result of the exposure pattern, the matrix points are rings, with the solid circle as the upper layer and the ring as the exposure layer. The deviation value of the center between the solid circle and the ring is detected to confirm the alignment effect. The schematic diagram of the ring is as follows Figure 2 shown.

[0053] The size of the graphics and the number of matrix points can be configured according to actual needs, and the exposure layer, alignment type, etc. can be controlled. After configuring the parameters, the software tool automatically generates the graphics in GDS format and exposes according to the configured exposure conditions.

[0054] The actual coordinates of the matrix points on the image are collected by the alignment camera of the LDI device, and compared with the coordinates in the original image in GDS format using the coordinate comparison method. The obtained data is analyzed in rows and columns to determine whether the current status of the device is normal.

[0055] The size of the detection pattern and the number of matrix points can be configured according to actual needs. The small tools included in the exposure software can be used to configure various parameters, control the exposure system, graphic data database, etc. to achieve graphic generation and exposure, control the alignment camera for data collection, and process and analyze the data.

[0056] The coordinate comparison method means that when the GDS graph is generated, the coordinates of each matrix point are known (i.e., the theoretical value of X, the theoretical value of Y). After the exposure is completed, the color of the exposed area of ​​the dry film becomes darker, forming an obvious color difference with the surrounding unexposed areas, and the contrast is very high. The actual position (actual value of X, actual value of Y) is calculated by aligning the camera and the existing publicly available image recognition algorithm. The software automatically calculates the difference between the two coordinate positions and automatically outputs the calculated difference data.

[0057] Determine whether the hardware of the LDI device is faulty based on the difference between the actual value and the theoretical value of each matrix point on the detection graph after exposure:

[0058] 1. Determine the state of the DMD position relationship by detecting the coordinate difference of the horizontal coordinates X1~Xn of each row of matrix points on the graph;

[0059] 2. Determine the horizontal straightness state of the Y axis of the high-precision motion platform by detecting the coordinate difference of the horizontal coordinates X1~Xm of each column of matrix points on the graph;

[0060] 3. Determine the positioning accuracy of the Y axis of the high-precision motion platform by detecting the coordinate difference of the vertical coordinates Y1~Ym of each column of matrix points on the graph;

[0061] 4. Determine the debugging status of splicing by detecting the coordinate difference of the vertical coordinates Y1~Yn of each row of matrix points on the graph;

[0062] 5. The state of the platform YAW is determined by detecting the curve difference of the vertical coordinates Y1~Yn of multiple rows of matrix points on the graph.

[0063] Specifically, the horizontal coordinate difference Δx and the vertical coordinate difference Δy between the actual coordinate value and the theoretical value of each matrix point are obtained respectively;

[0064] If the horizontal coordinate difference Δx of the matrix points in the same row is ≥ 5 μm, it is judged that the position relationship of each DMD in the LDI device is in an abnormal state;

[0065] If the horizontal coordinate difference Δx of the matrix points in the same column is ≥ 10μm, it is judged that the horizontal straightness of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state;

[0066] If the vertical coordinate difference Δy of the matrix points in the same column is ≥15μm, it is judged that the positioning accuracy of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state;

[0067] If the vertical coordinate difference Δy of the matrix points in the same row is ≥5 μm, it is determined that the debugging state of the splicing in the LDI device is in an abnormal state.

[0068] Furthermore, the state of the platform YAW is determined by detecting the curve difference of the vertical coordinates Y1 to Yn of the multiple rows of matrix points on the graph; the curve refers to the X&Y orthogonal curve at different positions of the Y axis. If the curve difference of the vertical coordinates Y1 to Yn of the multiple rows of matrix points exceeds 10μm, it is determined that the state of the platform YAW is abnormal, such as Figure 3A and Figure 3B The cases where the curve difference exceeds 10μm and does not exceed 10μm are given respectively.

[0069] The judgment principles are introduced as follows:

[0070] 1. The exposure system is composed of multiple DMDs and imaging optical paths. The light spots of multiple optical paths are spliced ​​together to form an exposure optical path. Regardless of whether it is a single scan or multiple scans, there is splicing between optical paths. Figure 4A This is the state of the DMD before splicing and debugging. There is misalignment in the Y direction or tearing and overlap in the X direction. Figure 4B To adjust the splicing state, the overlap and tearing in the X direction and the misalignment in the Y direction are controlled within a certain range. During continuous production, the splicing needs to maintain this qualified state. If there is misalignment in the X and Y directions, it will cause product quality problems.

[0071] By exposing dense matrix points, each light source can expose n (n ≥ 1) points to represent the position of the light source. After adjusting the stitching, the distance between the points that can be exposed by adjacent light sources is fixed. Therefore, the exposure system software obtains the coordinates of the n points that can be exposed by each light source and compares them with the theoretical values ​​to confirm whether the current DMD position relationship is normal. If the actual position is tested to be different from the theoretical position by more than the set threshold, the exposure system software will give a prompt to check the stitching status.

[0072] 2. The motion mode of the LDI device during exposure is as follows Figure 5A and Figure 5BAs shown, the suction cup with the PCB board is moved along the Y-axis direction, which is perpendicular to the exposure light path (fixed or moving), and the alignment axis where the camera is located is also perpendicular to the Y-axis. Because the suction cup moves linearly along the Y-axis during exposure, the X coordinate of the exposed figure should be kept within a certain range, that is, the exposed figure is a rectangle. If the suction cup does not move in a straight line, the exposed figure is a parallelogram, which is too different from the original image, resulting in quality problems such as alignment layer deviation and inconsistent figure size. Therefore, the movement of the platform can be determined from the difference in matrix point coordinates. If the difference in X1~Xm coordinates does not exceed the set threshold, it is considered that the horizontal straightness of the Y-axis is in normal state. If it exceeds the threshold, the software will prompt professionals to check the status of the platform.

[0073] 3. The positioning accuracy of the workpiece stage is an important guarantee to ensure the correct exposure pattern. Its accuracy is determined by the grating ruler of the workpiece stage. The temperature and humidity of the working environment will affect the grating ruler, resulting in inaccurate positioning accuracy. After exposing the matrix point, it can be determined from each column of Y coordinates Y1~Ym whether its positioning accuracy has changed. If the difference between the actual exposure position and the theoretical position is within the set threshold range, it is considered that the platform Y-axis positioning accuracy is normal. If it exceeds the threshold, the exposure system software will give a prompt to check the positioning accuracy of the platform and compensate according to the test data.

[0074] 4. The splicing between multiple light paths exists in two directions, X and Y. During exposure, the Y-axis movement direction of the workpiece stage is perpendicular to the axis of the exposure light path, and scanning exposure is performed. In order to ensure that the exposed pattern is a rectangle, it is necessary to pay attention to the debugging of the splicing Y direction to ensure that the Y coordinates Y1~Yn of each row are not much different, that is, the scanned image is a straight line perpendicular to the Y axis, not a diagonal line. If there is a tilt, it will cause the exposed pattern to be deformed, such as Figure 6 If the difference between the test coordinates Y1 to Yn is too large and exceeds the threshold, the exposure system software will give a prompt to check the stitching and re-debug.

[0075] 5. YAW is the left-right deflection of the platform during movement. This deflection will cause the image to deform. The conventional method is to use a laser interferometer or a calibration plate plus a camera to test the YAW situation. However, the laser interferometer is very expensive and requires professional personnel to set up and test, and the results cannot be obtained quickly. The calibration plate plus camera solution requires adding a camera and a moving axis to the exposure system, which is relatively expensive. Because this deflection will cause the orthogonality of the Y axis and the X axis to change, such as Fig. 7A and Figure 7BAs shown, this feature can be used to reversely determine the state of YAW through the exposure pattern. If the YAW is in a qualified state, the difference between the Y coordinates of each row is not large. If the YAW value exceeds the standard, the difference between the Y coordinates of each row is large. The Y coordinates of each row can be extracted by testing the coordinates of the entire matrix point, and the difference between the Y coordinates of each row can be compared to see if it exceeds the threshold. If it exceeds the set threshold, the exposure system software will give a prompt to determine that the YAW value of the workpiece stage is abnormal and needs further confirmation or debugging.

[0076] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quickly detecting the status of an LDI device, characterized in that: The method comprises: Using the LDI device to expose a pre-set detection pattern, the pre-set detection pattern is a pattern in GDS format automatically generated by the software tool after the parameters are configured, and includes matrix points of M rows and N columns; The actual coordinate values ​​of each matrix point on the detection pattern after exposure are collected by the alignment camera of the LDI device; Determine whether each component of the LDI device is in a normal state based on the difference between the actual coordinate value of each matrix point and the theoretical value, including: The state of the platform YAW is determined by detecting the curve difference of the vertical coordinates Y1~Yn of multiple rows of matrix points on the graph.

2. The method according to claim 1, characterized in that Determining whether each component of the LDI device is in a normal state according to the difference between the actual coordinate value of each matrix point and the theoretical value includes: Obtain the horizontal coordinate difference Δx and the vertical coordinate difference Δy between the actual coordinate value and the theoretical value of each matrix point respectively; If the horizontal coordinate difference Δx of the matrix points in the same row is ≥ 5 μm, it is judged that the position relationship of each DMD in the LDI device is in an abnormal state; If the horizontal coordinate difference Δx of the matrix points in the same column is ≥ 10μm, it is judged that the horizontal straightness of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state; If the vertical coordinate difference Δy of the matrix points in the same column is ≥ 15 μm, it is judged that the positioning accuracy of the Y axis of the high-precision motion platform in the LDI equipment is in an abnormal state; If the vertical coordinate difference Δy of the matrix points in the same row is ≥5 μm, it is determined that the debugging state of the splicing in the LDI device is in an abnormal state.

3. The method according to claim 2, characterized in that The method comprises: If the curve difference of the vertical coordinates Y1 to Yn of the matrix points in multiple rows on the detection graph exceeds 10 μm, it is determined that the state of the platform YAW is abnormal.

4. The method according to claim 1, characterized in that: The matrix points are solid circles or rings.

5. The method according to claim 4, characterized in that When the method is used to detect the correctness of the exposure pattern, the matrix points are filled circles.

6. The method according to claim 4, characterized in that When the method is used to detect the alignment result of the exposure pattern, the matrix points are circular rings.

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