An LDI focusing system

Abstract

The application discloses an LDI focusing system and relates to the technical field of direct writing exposure technology.The method comprises a host computer, a motion platform, an alignment camera, an alignment lens barrel, a light source and a distance measuring sensor arranged on the motion platform.The top of the alignment lens barrel is connected with the alignment camera, the bottom of the alignment lens barrel is fixed with the light source, and the distance measuring sensor is fixed on the light source.The motion platform is used for carrying a PCB and driving the PCB to move along the z-axis direction, and the distance measuring sensor is used for detecting the distance of the PCB relative to the distance measuring sensor.The host computer is connected with the motion platform, the alignment camera and the distance measuring sensor, the host computer determines whether the mark of the current PCB is in the focal plane of the alignment lens barrel according to the data fed back by the distance measuring sensor, controls the motion platform to move when the mark is not in the focal plane, and focuses on the mark again until the alignment camera is focused on the mark again.The problem that the focal plane is not aligned due to the warping of the plate material or the deformation of the mechanical structure is solved, and the requirement of the PCB industry capacity is met.

Description

Technical Field

[0001] This invention relates to the field of direct-write exposure technology, and in particular to an LDI focusing system. Background Technology

[0002] LDI (Laser Direct Imaging) exposure machines consist of an alignment system, a motion platform, and an imaging system. Throughout the PCB manufacturing process, the accuracy of the alignment system in identifying mark coordinates plays a crucial role in the precision of the image formed by the exposure system. The PCB industry has stringent requirements for production capacity; therefore, it typically employs telecentric lenses with large depth of focus to increase throughput. This means that during production, the PCB can be directly moved to the focal plane position set during process debugging for alignment. As long as the PCB thickness error is within the depth of focus range of the telecentric lens, the exposure machine can image normally, thus eliminating the focusing step before aligning each PCB and accelerating production.

[0003] However, in actual production, occasional issues arise where the mark coordinates are not on the focal plane of the telecentric lens barrel, leading to particularly large exposure errors on some boards and resulting in their rejection. This is because, in addition to the thickness error of the board material itself, the warping of the board and the deformation of the mechanical structure over time can cause significant deviations in the mark coordinates identified by the alignment system, resulting in occasional large exposure imaging misalignments and thus rejecting boards—a problem unacceptable in the PCB industry. Therefore, there is an urgent need to solve the problem of incorrect focal planes caused by board warping or mechanical deformation, while also meeting the production capacity requirements of the PCB industry. Summary of the Invention

[0004] To address the aforementioned problems and technical requirements, the inventors have proposed an LDI focusing system. This system utilizes hardware-based focal plane detection technology combined with software image acquisition to accurately pinpoint the location of the mark, thus resolving the issue of incorrect PCB focal planes caused by PCB warping or mechanical deformation. The technical solution of this invention is as follows: An LDI focusing system includes a host computer, a motion platform, an alignment camera, an alignment tube, a light source, and a distance sensor. The top of the alignment tube is connected to the alignment camera, and the bottom of the alignment tube is fixed to the light source. The distance sensor is fixed to the light source. The motion platform carries a PCB and moves it along the z-axis. The distance sensor detects the distance of the PCB relative to itself. The host computer is connected to the motion platform, the alignment camera, and the distance sensor. When the host computer determines, based on data from the distance sensor, that the current mark on the PCB is not on the focal plane of the alignment tube, it controls the motion platform to move until the alignment camera refocuses on the mark.

[0005] A further technical solution involves fixing the ranging sensor to the light source via a sensor fixing structure.

[0006] A further technical solution is that the sensor fixing structure includes a support structure and a rotating structure; one end of the rotating structure is fixed to the light source, and the other end of the rotating structure is connected to the support structure, and the ranging sensor is installed on the support structure; the support structure rotates on the rotating structure to adjust the detection angle of the ranging sensor, so that the detection position of the ranging sensor coincides with the field of view center of the focal plane of the detection lens barrel of the camera.

[0007] A further technical solution is that the mating surface of the bracket structure is provided with a boss and a rotation angle fixing hole, and the mating surface of the rotating structure is provided with a boss positioning groove and an arc-shaped positioning groove. The boss is inserted into the boss positioning groove to realize the mating of the bracket structure and the rotating structure. The screw is inserted into the arc-shaped positioning groove and connected to the rotation angle fixing hole. The rotating bracket structure makes the detection angle of the ranging sensor meet the measurement requirements. The screw is tightened to fix the detection angle.

[0008] A further technical solution is that the support structure includes a sensor fixing surface and a first docking surface that are perpendicular to each other; the rotating structure includes a light source fixing surface and a second docking surface, wherein the light source fixing surface is an L-shaped plane, and the second docking surface is perpendicular to the first side of the L-shaped plane; the sensor fixing surface is provided with a sensor fixing hole, and the ranging sensor is fixed to the support structure through the sensor fixing hole; the second side of the L-shaped plane is provided with a light source fixing hole, and the rotating structure is fixed to the light source through the light source fixing hole.

[0009] The further technical solution is that the motion platform includes a suction cup for carrying the PCB and a moving mechanism for controlling the suction cup to move along the z-axis. When the system is working, the host computer is used to open the suction cup to adsorb the PCB and control the moving mechanism to move the PCB to the adjusted fixed focal plane position. The fixed focal plane position is the position where the mark of the standard PCB is located on the focal plane of the lens barrel.

[0010] The further technical solution is that when the PCB moves to the fixed focal plane position after debugging, the host computer determines whether the current position of the PCB is within the set sensing range of the ranging sensor based on the data fed back by the ranging sensor. If it is within the range, the PCB mark is determined to be on the focal plane of the alignment lens barrel, and the alignment camera is directly instructed to capture the coordinates of the mark and perform exposure imaging. Otherwise, the PCB mark is determined to be not on the focal plane of the alignment lens barrel, and the alignment camera is instructed to refocus, capture the coordinates of the mark, and perform exposure imaging.

[0011] A further technical solution involves using a standard PCB to determine the set sensing range of the ranging sensor.

[0012] A further technical solution is that when the host computer determines that the current PCB position exceeds the set sensing range frequency by more than the preset value, the fixed focal plane position needs to be readjusted using a standard PCB.

[0013] The further technical solution is as follows: Before the system operates, a standard PCB without warping is placed on the motion platform. The host computer controls the motion platform to move along the z-axis until the camera focuses on the mark on the standard PCB at the focal plane of the lens barrel, which is used as the fixed focal plane position. Starting from this position, the host computer controls the motion platform to move the standard PCB upwards until the mark pattern in the field of view of the camera is about to blur, at which point the feedback value 'a' of the range sensor is recorded. The host computer controls the motion platform to return to the starting point and moves the standard PCB downwards until the mark pattern in the field of view of the camera is about to blur, at which point the feedback value 'b' of the range sensor is recorded. The range between 'a' and 'b' is used as the set sensing range of the range sensor and stored in the host computer.

[0014] The beneficial technical effects of this invention are: The aforementioned LDI focusing system can determine whether the current PCB mark is on the focal plane of the alignment lens barrel detected by the alignment camera's field of view using feedback data from the ranging sensor. Only when it is outside the focal plane range is the motion platform controlled to move along the z-axis until the alignment camera refocuses on the mark. This process takes milliseconds, and its impact on the production time of each PCB is negligible. This not only solves the problem of focal plane misalignment caused by occasional warping or mechanical deformation of the PCB, reducing scrap, but also meets PCB production capacity requirements. The system can also infer whether the initial fixed focal plane position has been permanently changed based on the frequency of focal plane misalignment and promptly readjust the fixed focal plane position using a standard board. Furthermore, the designed sensor fixing structure is easy to install and allows for free adjustment of the ranging sensor's detection position to meet measurement needs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the LDI focusing system provided in this application.

[0016] Figure 2 This is a schematic diagram of the alignment module in the LDI focusing system provided in this application.

[0017] Figure 3 This is a schematic diagram of the support structure provided in this application.

[0018] Figure 4 This is a schematic diagram of the rotating structure provided in this application.

[0019] Figure 5 This is a flowchart of the LDI focusing system provided in this application. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0021] Combination Figure 1 and Figure 2 As shown in the figure, this application embodiment provides an LDI focusing system, including a host computer (not shown), a base 1, a motion platform mounted on the base 1, an alignment module 2, and an imaging module 3. The alignment module 2 is mounted on a camera moving axis 4, and a moving mechanism controls the camera moving axis 4 to move along a crossbeam in the x-direction. The alignment module 2 includes an alignment camera 201, an alignment lens barrel 202, a light source 203, and an additionally provided range sensor 204. The connection relationship is as follows: the alignment camera 201 is rotatably fixed to the top of the alignment lens barrel 202 by a C-shaped thread; the light source 203 is fixed to the bottom of the alignment lens barrel 202 using a snap-fit ​​clamp; and the range sensor 204 is fixed to the snap-fit ​​clamp via a sensor fixing structure, and thus fixed to the light source 203. The motion platform includes a suction cup 5 for carrying a PCB and a moving mechanism for controlling the suction cup 5 to move along the y-axis and z-axis. The host computer is connected to the imaging module 3, the suction cup 5, the moving mechanism, the alignment camera 201, the light source 203, and the range sensor 204. Optionally, the light source 203 used in this embodiment is preferably a ring light source, which does not hinder the camera 201 from capturing the mark on the PCB below.

[0022] The range sensor 204 is used to detect the distance between the PCB and itself, and uploads the detected displacement data to the host computer for position determination via analog signal or serial port. To meet the requirements of focal plane measurement, the point 'a' of the measuring beam from the range sensor 204 landing on the focal plane of the alignment lens barrel must coincide with the center of the field of view of the alignment camera 201. That is, the position detected by the range sensor 204 must be the center of the field of view of the focal plane of the alignment camera. Figure 2 As shown, the dashed line represents the focal plane aligned with the lens barrel 202.

[0023] To meet the detection position requirements of the ranging sensor 204, a sensor fixing structure was designed, such as... Figure 2 As shown, the system includes a support structure 6 and a rotating structure 7. One end of the rotating structure 7 is fixed to the light source 203, and the other end of the rotating structure 7 is connected to the support structure 6. The range sensor 204 is mounted on the support structure 6. The support structure 6 rotates on the rotating structure 7 to adjust the detection angle of the range sensor 204, so that the position detected by the range sensor coincides with the field of view center of the focal plane of the camera's detection lens barrel.

[0024] like Figure 3As shown, the bracket structure 6 includes a sensor fixing surface 601 and a first mating surface 602 that are perpendicular to each other. The sensor fixing surface 601 has a sensor fixing hole 611, and the first mating surface 602 has a rotation angle fixing hole 621 and a boss 622. Optionally, four rotation angle fixing holes 621 are arranged around the boss 622. Figure 4 As shown, the rotating structure 7 includes a light source fixing surface 701 and a second mating surface 702. The light source fixing surface 701 is an L-shaped plane, and the second mating surface 702 is perpendicular to the first side of the L-shaped plane. A light source fixing hole 711 is provided on the second side of the L-shaped plane, and an arc-shaped positioning groove 721 and a boss positioning groove 722 are provided on the second mating surface 702. Optionally, the two arc-shaped positioning grooves 721 are arranged around the boss positioning groove 722. During assembly, screws are used to fix the ranging sensor 204 to the sensor fixing hole 611 of the bracket structure 6 through its mounting hole. The boss 622 is inserted into the boss positioning groove 722 to achieve docking between the bracket structure 6 and the rotating structure 7. Screws are inserted into the arc-shaped positioning groove 721 to connect with the rotation angle fixing hole 621. The rotating bracket structure 6 is rotated so that the detection angle of the ranging sensor 204 meets the measurement requirements. The screws are then tightened to fix the detection angle.

[0025] Before normal board fabrication, it is necessary to determine the set sensing range of the rangefinder 204 using a standard PCB. The process is as follows: A standard PCB without warping is placed on the suction cup 5 of the motion platform. The host computer first controls the moving mechanism of the motion platform to move the mark on the standard PCB to the center of the camera's field of view. Then, the host computer controls the moving mechanism of the motion platform to move the suction cup 5 along the z-axis until the camera 201 focuses on the mark on the standard PCB at the focal plane of the lens barrel, which is used as the fixed focal plane position. Starting from this position, the host computer controls the moving mechanism to move the standard PCB upwards until the mark pattern in the camera's field of view is about to blur, and records the feedback value 'a' of the rangefinder 204. The host computer controls the moving mechanism to move the standard PCB back to the starting point and then moves it downwards until the mark pattern in the camera's field of view is about to blur, and records the feedback value 'b' of the rangefinder 204. The range between 'a' and 'b' is used as the set sensing range of the rangefinder 204 and stored in the host computer.

[0026] like Figure 1The range sensor 204 is mounted on the alignment module 2, and its relative position to the alignment camera 201 remains constant. Therefore, after adjusting the set sensing range of the range sensor 204 using a standard plate, subsequent changes in the range sensor's value correspond to platform mechanical deformation or board warping. Thus, the feedback value from the range sensor 204 can be used to determine whether the current mark is on the calibrated focal plane. If it is, the alignment module 2 can directly capture the mark's coordinates; if it is not on the focal plane, z-axis focusing is performed before capturing the mark's coordinates. This method can resolve the issue of occasional board warping or mechanical deformation causing incorrect focal planes.

[0027] like Figure 5 As shown, the workflow of the LDI focusing system is as follows: During normal board fabrication, the PCB is placed on the suction cup 5. The host computer activates the suction cup to adsorb the PCB. First, it controls the moving mechanism of the motion platform to move the PCB's mark to the center of the camera's field of view. Then, it controls the moving mechanism to move the PCB along the z-axis to the fixed focal plane position that has been adjusted. The host computer determines whether the current position of the PCB is within the set sensing range of the ranging sensor 204 based on the data received from the ranging sensor 204. If it is within the range, the host computer determines that the PCB's mark is on the focal plane of the alignment lens barrel 202 and directly instructs the alignment camera 201 to capture the mark coordinates, calculate the image data, and transmit it to the imaging module 3 for exposure imaging. Otherwise, the host computer determines that the PCB's mark is not on the focal plane of the alignment lens barrel 202. The host computer controls the moving mechanism to move the PCB along the z-axis until the alignment camera 201 refocuses, captures the mark coordinates, calculates the image data, and transmits it to the imaging module 3 for exposure imaging.

[0028] Optionally, based on the frequency at which the current PCB position exceeds the set sensing range as determined by the host computer, it can also be determined whether the initial fixed focal plane position has been permanently changed due to the mechanical deformation of the motion platform and other components. If the error rate of the host computer in determining the PCB position reaches one percent or higher, it is considered that the initial fixed focal plane position has been permanently changed, and the fixed focal plane position needs to be readjusted in a timely manner using a standard PCB.

[0029] Because the host computer-controlled moving mechanism to move the PCB along the z-axis for focusing consumes a significant amount of time, approximately one-fifth of the production time for a single PCB, and because board warping is an occasional phenomenon—not every PCB warps—focusing every time alignment is required would severely impact production capacity. In the above process, determining whether the PCB position is within the set sensing range based on the feedback value from the ranging sensor 204 takes only milliseconds, and its impact on the production time of each PCB is negligible. Therefore, the problem of occasional PCB misalignment can be resolved without affecting production capacity, reducing the generation of scrap boards.

[0030] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. An LDI focusing system, characterized in that, The system includes a host computer, a motion platform, an alignment camera, an alignment lens barrel, a light source, and a distance sensor. The top of the alignment lens barrel is connected to the alignment camera, and the bottom of the alignment lens barrel is fixed to the light source. The distance sensor is fixed to the light source via a sensor fixing structure. The motion platform carries the PCB and moves it along the z-axis. The distance sensor detects the distance of the PCB relative to itself. The host computer is connected to the motion platform, the alignment camera, and the distance sensor. When the host computer determines, based on data from the distance sensor, that the current mark on the PCB is not on the focal plane of the alignment lens barrel, it controls the motion platform to move until the alignment camera refocuses on the mark. The sensor fixing structure includes a bracket structure and a rotating structure; one end of the rotating structure is fixed to the light source, and the other end of the rotating structure is connected to the bracket structure. The ranging sensor is mounted on the bracket structure; the bracket structure rotates on the rotating structure to adjust the detection angle of the ranging sensor, so that the detection position of the ranging sensor coincides with the field of view center of the focal plane of the camera's detection lens barrel. The bracket structure has a boss and a rotation angle fixing hole on its mating surface. The rotating structure has a boss positioning groove and an arc-shaped positioning groove on its mating surface. The boss is inserted into the boss positioning groove to achieve the mating of the bracket structure and the rotating structure. The screw is inserted into the arc-shaped positioning groove and connected to the rotation angle fixing hole. The bracket structure is rotated so that the detection angle of the ranging sensor meets the measurement requirements. The screw is tightened to fix the detection angle.

2. The LDI focusing system according to claim 1, characterized in that, The support structure includes a sensor fixing surface and a first docking surface that are perpendicular to each other; the rotating structure includes a light source fixing surface and a second docking surface, wherein the light source fixing surface is an L-shaped plane, and the second docking surface is perpendicular to the first side of the L-shaped plane; the sensor fixing surface is provided with a sensor fixing hole, and the ranging sensor is fixed to the support structure through the sensor fixing hole; the second side of the L-shaped plane is provided with a light source fixing hole, and the rotating structure is fixed to the light source through the light source fixing hole.

3. The LDI focusing system according to claim 1, characterized in that, The motion platform includes a suction cup for carrying the PCB and a moving mechanism for controlling the suction cup to move along the z-axis. When the system is working, the host computer is used to activate the suction cup to adsorb the PCB and control the moving mechanism to move the PCB to the adjusted fixed focal plane position. The fixed focal plane position is the position where the mark of the standard PCB is located on the focal plane of the lens barrel.

4. The LDI focusing system according to claim 1, characterized in that, When the PCB moves to the fixed focal plane position after debugging, the host computer determines whether the current position of the PCB is within the set sensing range of the ranging sensor based on the data received from the ranging sensor. If it is within the range, the PCB mark is determined to be on the focal plane of the alignment lens barrel, and the alignment camera is directly instructed to capture the coordinates of the mark and perform exposure imaging. Otherwise, the PCB mark is determined to be not on the focal plane of the alignment lens barrel, and the alignment camera refocuses, captures the coordinates of the mark, and performs exposure imaging.

5. The LDI focusing system according to claim 4, characterized in that, The set sensing range of the ranging sensor is determined using a standard PCB.

6. The LDI focusing system according to claim 4, characterized in that, When the host computer determines that the current PCB position exceeds the preset value at frequencies exceeding the set sensing range, the fixed focal plane position needs to be readjusted using a standard PCB.

7. The LDI focusing system according to claim 5 or 6, characterized in that, Before the system operates, a standard PCB without warping is placed on the motion platform. The host computer controls the motion platform to move along the z-axis until the camera focuses on the mark on the standard PCB at the focal plane of the lens barrel, which is the fixed focal plane position. Starting from this position, the host computer controls the motion platform to move the standard PCB upwards until the mark pattern in the camera's field of view is about to blur, at which point the feedback value 'a' of the ranging sensor is recorded. The host computer then controls the motion platform to return to the starting point and moves the standard PCB downwards until the mark pattern in the camera's field of view is about to blur, at which point the feedback value 'b' of the ranging sensor is recorded. The range between 'a' and 'b' is used as the set sensing range of the ranging sensor and stored in the host computer.

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