System and method for automatic alignment of BGA (ball grid array) ball mounter screen

Abstract

The invention discloses a system and a method for automatically aligning a BGA (ball grid array) ball mounter screen plate. The system comprises a rotary carrying table, an upper camera, a lower camera, a control unit, a compensation module and an execution mechanism. The upper camera is used for acquiring the coordinate of a mark point on the rotary carrying table and carrying out coordinate system calibration with the rotary carrying table; and the lower camera is used for shooting a plurality of calibration points of the screen, extracting coordinate information and calibrating with a world coordinate system. The control unit calculates the rotation center of the rotary carrying table according to coordinate data obtained by the upper camera and the lower camera, and meanwhile dynamic alignment compensation is achieved by combining the compensation value of the compensation module. The execution mechanism receives an instruction of the control unit, accurately controls the rotation angle of the rotary carrying table and the movement amount of the X-axis and the Y-axis, and achieves high-precision automatic alignment of the screen plate. According to the method, a nine-point calibration method and rotation center calculation are adopted, and through a conversion matrix between an image coordinate and a physical coordinate system, the problems that traditional manual alignment is insufficient in precision and low in efficiency are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chip ball planting detection, and more specifically to a system and method for automatic alignment of a stencil of a BGA ball planting machine. Background Art

[0002] BGA is a technology widely used in semiconductor chip packaging, with advantages such as high density and low loss. BGA ball planting process is a crucial part of this packaging technology, and its quality directly affects the subsequent welding reliability and product performance. In actual operation, factors affecting the quality of BGA ball planting process include the quality of raw materials, the control of process conditions and the accuracy of operating equipment.

[0003] In terms of raw materials, the properties of solder balls, solder paste and substrates play a decisive role in the ball planting effect. For example, solder balls need to be kept clean and prevented from oxidation, substrates need to prevent coating from falling off, and the storage and use conditions of solder paste also need to be strictly managed. In process design, the ball planting process usually improves quality by adjusting the properties of solder paste or flux, optimizing the process temperature curve, and improving the protective atmosphere. The traditional ball planting process relies on manual or semi-automatic operations, such as aligning the steel mesh template with the BGA device through a microscope to spread and adjust the solder balls. However, this method is not only time-consuming and labor-intensive, but also easily affected by operational errors and process limitations, and it is difficult to meet the needs of modern high-precision manufacturing.

[0004] With the rapid development of the electronics industry, the requirements for ball planting accuracy in BGA packaging are constantly increasing. However, there are still many technical bottlenecks in the positioning accuracy of current ball planting machines. Especially in the high-precision alignment process, due to the lack of flexibility of the detection mechanism, the limitation of the depth of field of the lens, the inconsistency of the surface characteristics and color of the stencil, etc., the detection effect is often difficult to achieve the ideal level. These problems lead to the alignment error between the stencil and the device, which affects the implantation accuracy of the solder ball, and then reduces the production efficiency and quality consistency of the product. Summary of the invention

[0005] In order to meet the challenges of the existing technology, the present invention proposes a system and method for automatically aligning the BGA ball planting machine stencil and unifying the three coordinate systems into the world coordinate system. By integrating advanced automated alignment technology and coordinate system unification algorithm, the invention can not only overcome the limitations of traditional hardware, but also significantly improve the detection accuracy and alignment efficiency. The development of this system will provide the industry with an efficient and reliable solution, greatly improving the automation level and production quality of the BGA ball planting process. The specific plan is as follows:

[0006] A system for automatic alignment of a stencil of a BGA ball implanter, the system comprising a rotating stage for placing incoming products; an upper camera for acquiring coordinates of marking points on the rotating stage, calibrating the coordinate system with the rotating stage, and calibrating with the world coordinate system; a lower camera for photographing multiple calibration points on the stencil, extracting coordinate information of the calibration points, and calibrating with the world coordinate system; a control unit connected to the upper camera, the lower camera and the rotating stage, and calculating the rotation center of the rotating stage according to coordinate data acquired by the upper camera and the lower camera; a compensation module for adding a rotation angle compensation value and X-axis and Y-axis offset compensation amounts; and an actuator connected to the control unit for controlling the rotation angle of the rotating stage and the movement amounts of the X-axis and Y-axis according to instructions of the control unit to complete automatic alignment of the stencil.

[0007] Furthermore, the control unit fixes the camera, rotates the stage and photographs the trajectory of the marking points on the screen; calculates the rotation trajectory coordinates of the marking points, thereby determining the rotation center coordinates of the rotating stage; simultaneously calculates the rotation angle change between the initial position and the final fixed position of the screen; and calculates the X and Y axis offsets of the rotating stage through the coordinates of the rotation center and the two marking points.

[0008] Furthermore, the system includes an adjustable light source and an additional front array light source.

[0009] A method for automatically aligning a stencil of a BGA ball planting machine, the method comprising the following steps:

[0010] S1. Rotation center calibration: rotate the rotating stage and capture the trajectory of the marking points; extract the coordinates of the marking points and calculate the rotation center of the rotating stage according to the trajectory of the marking points;

[0011] S2, nine-point calibration of the lower camera: extract the center coordinates of the nine marking points and establish the transformation matrix between the image coordinates and the world coordinates;

[0012] S3, upper camera and lower camera calibration: perform similar calibration on the upper camera, extract the coordinates of the marker points, calculate the transformation matrix of the upper camera; transform the coordinates of the upper and lower cameras into a unified world coordinate system;

[0013] S4, four-point coordinate extraction: obtain the coordinates of the four reference points of the stencil through the lower camera; calculate the actual stencil coordinates according to the calibration matrix;

[0014] S5, alignment calculation: compare the difference between the incoming product and the target position; calculate the required rotation angle, X-axis offset and Y-axis offset;

[0015] S6, add fixed compensation value: add the fixed compensation value of the rotation angle, X-axis offset and Y-axis offset required by PLC;

[0016] S7, calibrate and realize alignment: send the calibrated data to the PLC control system; determine the rotation angle and the movement of the X / Y axis according to the compensation amount to complete the precise alignment of the screen.

[0017] Furthermore, S1 also includes the following sub-steps:

[0018] S101: Take one or more fixed circles on the calibration plate;

[0019] S102: Keep the camera fixed and rotate the stage;

[0020] S103: Obtaining the trajectory coordinates of the center of the marking circle during the rotation process;

[0021] S104: Calculate the coordinates x0, y0 of the rotation center o through the trajectory coordinates;

[0022] S105: If there are multiple circles, calculate them separately and take the average value as the final rotation center coordinate.

[0023] Furthermore, before the correction is performed in S5, the stage is moved to a fixed correction position for correction, and then moved to the final position according to the calculated rotation angle offset.

[0024] Furthermore, S3 also includes the following sub-steps:

[0025] S301: placing the marking plate on the stage and obtaining an image containing 9-12 marking circles;

[0026] S302: extracting and calculating the center coordinates of the marked circle on the image and the world coordinates automatically given;

[0027] S303: Calculate a conversion matrix from image coordinates to world coordinates and a conversion matrix from world coordinates to image coordinates through the image coordinates and world coordinates of the nine points;

[0028] S304: The upper camera and the lower camera are calibrated at nine points respectively, and finally a conversion matrix between the image coordinates of the upper camera and the world coordinates and a conversion matrix between the image coordinates of the lower camera and the world coordinates are obtained.

[0029] Beneficial effects:

[0030] The present invention provides a system and method for automatic alignment of a BGA ball planting machine stencil, which has the following beneficial effects compared with the prior art:

[0031] (1) The upper camera and the lower camera are combined with the calibration method to ensure that the coordinates of the stencil accurately match the actual physical coordinates. The nine-point calibration method and rotation center calculation are used to effectively reduce the angle error and position offset error. The final alignment accuracy reaches 2.46μm, meeting the needs of high-precision production.

[0032] (2) The system automatically completes the rotation center calibration, coordinate conversion and angle calculation of the screen, eliminating the instability of traditional manual alignment. Through the PLC automatic compensation function, dynamic compensation of the rotation angle and X / Y axis offset is achieved, reducing manual debugging errors.

[0033] (3) This method automatically completes the alignment and compensation of the screen, reduces tedious manual operation steps, and significantly shortens the production cycle. It effectively reduces the downtime in the production process and improves the equipment utilization rate.

[0034] (4) Dynamic coordinate transformation matrix and rotation compensation algorithm are used to adapt to stencils of different sizes and models without the need for additional hardware replacement. The adjustable design of the light source and camera system, including angle, brightness, and focal length, can adapt to different types of marking points and workpiece materials.

[0035] (5) The stability of the rotation center and coordinate compensation results is ensured through multiple image acquisitions and average calculations of the rotating stage. Even when the equipment is running for a long time, the alignment accuracy and compensation data can be kept highly consistent.

[0036] In summary, the present invention effectively solves the problems of insufficient positioning accuracy, frequent manual intervention, low production efficiency, etc. in the prior art through automated visual calibration, coordinate transformation and dynamic compensation methods, and has significant economic value and market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The present invention is a flow chart of a method for automatically aligning a stencil of a BGA ball planting machine.

[0038] Figure 2 Schematic diagram of the rotation center calibration of the embodiment.

[0039] Figure 3 It is a schematic diagram of the alignment calculation of the embodiment.

[0040] Figure 4 This is a working status diagram of the automatic alignment of the stencil of a BGA ball planting machine. DETAILED DESCRIPTION

[0041] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0042] Example:

[0043] The present invention discloses a system and method for automatically aligning a stencil of a BGA ball planting machine, wherein the system comprises a rotating stage for placing incoming products; an upper camera for acquiring the coordinates of marking points on the rotating stage, calibrating the coordinate system with the rotating stage, and calibrating with the world coordinate system; a lower camera for photographing multiple calibration points on the stencil, extracting the coordinate information of the calibration points, and calibrating with the world coordinate system; a control unit connected to the upper camera, the lower camera and the rotating stage, and calculating the rotation center of the rotating stage according to the coordinate data acquired by the upper camera and the lower camera; a compensation module for adding a rotation angle compensation value and an X-axis and Y-axis offset compensation amount; an actuator connected to the control unit, and controlling the rotation angle of the rotating stage and the movement amount of the X and Y axes according to the instructions of the control unit to complete the automatic alignment of the stencil. Compared with traditional light sources and detection devices:

[0044] The traditional detection method of fixed light source, fixed angle and fixed focus is improved to:

[0045] Variable light source: adjustable brightness.

[0046] Adjustable Angle: The light source angle can be adjusted from 0° to 45°.

[0047] Adjustable focal length: The focal length is dynamically adjusted according to the target height, ranging from 50mm to 200mm.

[0048] Add front array light source: achieve uniform illumination of the stencil and improve image quality.

[0049] Figure 1 The flowchart of the method for automatic alignment of the stencil of a BGA ball planting machine is as follows: Figure 1 As shown, the flowchart includes the following steps:

[0050] S1. Rotation center calibration: rotate the rotating stage and capture the trajectory of the marking points; extract the coordinates of the marking points and calculate the rotation center of the rotating stage according to the trajectory of the marking points;

[0051] The specific steps are as follows:

[0052] S101: Take one or more (four in this embodiment) fixed circles on the calibration plate;

[0053] S102: Keep the upper camera fixed and rotate the stage;

[0054] S103: Obtain the trajectory coordinates of the center of the marked circle during the rotation process (in this embodiment, take 40 times, from -20 degrees to 20 degrees, once for every rotation of 1 degree);

[0055] S104: Calculate the coordinates (x0, y0) of the rotation center o through the trajectory coordinates;

[0056] S105: Calculate the four circles separately and take the average as the final rotation center coordinate.

[0057] S2, nine-point calibration of the lower camera: extract the center coordinates of the nine marking points and establish the transformation matrix between the image coordinates and the world coordinates;

[0058] S3, upper camera and lower camera calibration: perform similar calibration on the upper camera, extract the coordinates of the marker points, calculate the transformation matrix of the upper camera; transform the coordinates of the upper and lower cameras into a unified world coordinate system;

[0059] The specific steps are as follows:

[0060] S301: placing a marking plate (the marking plate in this embodiment is from Sibotron) on the stage, and obtaining an image containing 9-12 (12 in this embodiment) marking circles;

[0061] S302: extracting and calculating the center coordinates (image coordinates) of 12 marked circles on the image and the center coordinates (world coordinates) given automatically;

[0062] S303: Calculate a conversion matrix from image coordinates to world coordinates and a conversion matrix from world coordinates to image coordinates through the image coordinates and world coordinates of the nine points;

[0063] S304: The upper camera and the lower camera are calibrated at nine points respectively, and finally a conversion matrix between the image coordinates of the upper camera and the world coordinates and a conversion matrix between the image coordinates of the lower camera and the world coordinates are obtained.

[0064] S305: Four-point coordinate extraction: The coordinates of the four reference points of the stencil are obtained through the upper camera and the lower camera respectively; the actual stencil coordinates are calculated according to the calibration matrix of the upper camera and the lower camera;

[0065] S4, four-point coordinate extraction: obtain the coordinates of the four reference points of the stencil through the lower camera; calculate the actual stencil coordinates according to the calibration matrix;

[0066] S5, alignment calculation: compare the deviation between the actual coordinates of the product and the target position; calculate the required rotation angle, X-axis offset and Y-axis offset;

[0067] Figure 3 Schematic diagram of the alignment calculation of the embodiment, the calculation steps are as follows:

[0068] S501: Before correction, the stage will move to a fixed correction position for correction;

[0069] S502: Given the coordinates of the rotation center o (x0, y0), the coordinates of the two marking points m1 and m2 are (x1, y1) and (x2, y2) respectively, the slope and angle of the straight line m1m2 and the coordinates of the midpoint position z of the line segment m1m2 (x3, y3) can be calculated;

[0070] S503: according to the above method, the angles of the initial position and the final fixed position are respectively obtained, and then the angle change ΔU can be calculated;

[0071] S504: Finally, the coordinate offsets ΔX and ΔY can be calculated based on the coordinates of the center position z after the initial position is rotated and the coordinates (x4, y4) of the center point position z' of the final position.

[0072] Taking the stage rotation center o(x0, y0) as the rotation center, rotate ΔU, and the rotation transformation matrix from the initial position center point z(x3, y3) to the final position center point z'(x4, y4) is as follows:

[0074]

[0078] S6, add fixed compensation value: add the fixed compensation value of the rotation angle, X-axis offset and Y-axis offset required by PLC;

[0079] S7, calibrate and realize alignment: send the calibrated data to the PLC control system; determine the rotation angle and the movement of the X / Y axis according to the compensation amount to complete the precise alignment of the screen.

[0080] result:

[0081] ①Positioning accuracy:

[0082] The coordinates of the upper and lower cameras are unified to the world coordinate system to achieve precise alignment.

[0083] The alignment accuracy reaches 2.46μm.

[0084] ②Compatibility:

[0085] For ball implant boards of different sizes, the vision module can automatically adapt to multiple sizes to ensure that the ball implant board information is fully captured.

[0086] ③Production efficiency:

[0087] The system automatically completes stencil alignment, reduces manual intervention, and improves production efficiency and product quality.

[0088] As a further improvement, the above 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 principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A system for automatic alignment of a BGA ball placement machine stencil, characterized in that: The system includes a rotating stage for placing incoming products; an upper camera for acquiring the coordinates of the marking points on the rotating stage, calibrating the coordinate system with the rotating stage, and calibrating with the world coordinate system; a lower camera for photographing multiple calibration points on the screen, extracting the coordinate information of the calibration points, and calibrating with the world coordinate system; a control unit connected to the upper camera, the lower camera and the rotating stage, and used to calculate the rotation center of the rotating stage according to the coordinate data acquired by the upper camera and the lower camera; The compensation module is used to add the rotation angle compensation value and the X-axis and Y-axis offset compensation amount; the actuator is connected to the control unit and is used to control the rotation angle of the rotating stage and the movement amount of the X and Y axes according to the instructions of the control unit to complete the automatic alignment of the screen.

2. The automatic alignment system of the BGA ball planting machine stencil according to claim 1 is characterized in that: The control unit fixes the camera, rotates the stage and shoots the trajectory of the marking points on the screen; calculates the rotation trajectory coordinates of the marking points, thereby determining the rotation center coordinates of the rotating stage; simultaneously calculates the rotation angle change between the initial position and the final fixed position of the screen; and calculates the X and Y axis offsets of the rotating stage through the coordinates of the rotation center and the two marking points.

3. The automatic alignment system of the BGA ball planting machine stencil according to claim 1 is characterized in that: The system comprises an adjustable light source and an additional frontal array light source.

4. A method for automatically aligning a stencil of a BGA ball placement machine, characterized in that: The method comprises the following steps: S1. Rotation center calibration: rotate the rotating stage and capture the trajectory of the marking points; extract the coordinates of the marking points and calculate the rotation center of the rotating stage according to the trajectory of the marking points; S2, nine-point calibration of the lower camera: extract the center coordinates of the nine marking points and establish the transformation matrix between the image coordinates and the world coordinates; S3, upper camera and lower camera calibration: perform similar calibration on the upper camera, extract the coordinates of the marker points, calculate the transformation matrix of the upper camera; transform the coordinates of the upper and lower cameras into a unified world coordinate system; S4, four-point coordinate extraction: obtain the coordinates of the four reference points of the stencil through the lower camera; calculate the actual stencil coordinates according to the calibration matrix; S5, alignment calculation: compare the difference between the incoming product and the target position; calculate the required rotation angle, X-axis offset and Y-axis offset; S6, add fixed compensation value: add the fixed compensation value of the rotation angle, X-axis offset and Y-axis offset required by PLC; S7, calibrate and realize alignment: send the calibrated data to the PLC control system; determine the rotation angle and the movement of the X / Y axis according to the compensation amount to complete the precise alignment of the screen.

5. The method for automatic alignment of a BGA ball planting machine stencil according to claim 4, characterized in that: S1 also includes the following sub-steps: S101: Take one or more fixed circles on the calibration plate; S102: Keep the camera fixed and rotate the stage; S103: Obtaining the trajectory coordinates of the center of the marking circle during the rotation process; S104: Calculate the coordinates x0, y0 of the rotation center o through the trajectory coordinates; S105: If there are multiple circles, calculate them separately and take the average value as the final rotation center coordinate.

6. The method for automatic alignment of a BGA ball placement machine stencil according to claim 4, characterized in that: S5 Before correction, the stage moves to a fixed correction position for correction, and then moves to the final position according to the calculated rotation angle offset.

7. The method for automatic alignment of a BGA ball planting machine stencil according to claim 4, characterized in that: S3 also includes the following sub-steps: S301: placing the marking plate on the stage and obtaining an image containing 9-12 marking circles; S302: extracting and calculating the center coordinates of the marked circle on the image and the world coordinates automatically given; S303: Calculate a conversion matrix from image coordinates to world coordinates and a conversion matrix from world coordinates to image coordinates through the image coordinates and world coordinates of the nine points; S304: The upper camera and the lower camera are calibrated at nine points respectively, and finally a conversion matrix between the image coordinates of the upper camera and the world coordinates and a conversion matrix between the image coordinates of the lower camera and the world coordinates are obtained.

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