A method for calibrating a rotation axis of a die bonder head

Abstract

The application relates to the field of semiconductor packaging equipment, and particularly discloses a die bonding head rotating shaft calibration method, which comprises the following steps: S1, nozzle center alignment and coordinate recording: the nozzle center of the die bonding head is respectively aligned with the center of an Up-look camera and the center of a Wafer camera; S2, wafer center detection and coordinate recording: the wafer center is detected through machine vision, the corresponding rotating shaft encoder coordinates are recorded, and an Up-look camera pixel calibration conversion matrix is acquired; S3, wafer rotation and angle calculation: the wafer is rotated by 10 degrees as a step to 360 degrees, and the plane angle is calculated; S4, linear relationship establishment and fitting step: the linear relationship between the rotating shaft coordinates and the plane angle coordinates in the die bonding head coordinate system is established, and the rotating angle coefficient and the offset are fitted; S5, compensation and re-detection: the wafer angle is detected through the Wafer camera, the actual coordinates of the rotating shaft are converted according to the coefficient, the rotating center and the nozzle center are not consistent, and compensation is carried out; the wafer center after re-scanning and compensation should coincide with the original position.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor packaging equipment, and in particular relates to a method for calibrating the rotation axis of a die bonder. Background Technology

[0002] In current die bonding processes, the commonly used method is to use the world coordinate system as a medium to calculate the coordinates of various components. While this method can achieve coordinate transformation between different devices to a certain extent, it has some significant limitations, especially in applications requiring high precision.

[0003] The world coordinate system is a global reference frame that provides a unified coordinate benchmark for all participating devices and tools. However, this approach ignores the minute mechanical errors that may exist between devices, especially the mechanical errors of the rotation axis. Specifically, existing methods do not consider the problem of the mechanical errors of the rotation axis causing the nozzle center and rotation center of the die bonder to misalign. This can lead to a series of problems in practical applications:

[0004] 1. Error Propagation: Since the world coordinate system is a global reference frame, any local mechanical error will be amplified within this frame and propagated to the entire system. For example, if the center of the die bonder's nozzle is not aligned with the rotation center, this deviation will gradually accumulate during the entire rotation process, eventually affecting the accuracy of wafer placement.

[0005] 2. Lack of targeted compensation: Existing methods fail to compensate for the specific mechanical characteristics of each device. Each die bonder, rotary axis, and other component has its unique mechanical errors, which cannot be corrected by simple coordinate conversion. Therefore, in applications requiring high precision, such as semiconductor packaging, this method struggles to meet the required accuracy standards. Summary of the Invention

[0006] This invention provides a patent title and solves the above-mentioned problems.

[0007] To solve the above problems, the present invention provides the following technical solution: a method for calibrating the rotation axis of a die bonder, comprising the following steps:

[0008] Step S1: Nozzle center alignment and coordinate recording

[0009] Align the center of the die bonder nozzle with the center of the up-look camera and the center of the wafer camera, respectively, and record the corresponding die bonder coordinates;

[0010] Step S2: Wafer Center Detection and Coordinate Recording

[0011] After the die bonder picks up the wafer, it moves to the Up-look camera. The center of the wafer is detected by machine vision, the corresponding rotary axis encoder coordinates are recorded, and the Up-look camera pixel calibration conversion matrix is ​​obtained at the same time.

[0012] Step S3: Wafer Rotation and Angle Calculation

[0013] Rotate the chip to 360° in 10° increments, and use the pixel calibration transformation matrix to transform the image coordinates to the die bond head coordinate system to calculate the planar angle.

[0014] Step S4: Establishing and Fitting Linear Relationships

[0015] The linear relationship between the rotation axis coordinates and the plane angle coordinates in the die bond head coordinate system is determined, and the rotation angle coefficient and offset are fitted using the least squares method.

[0016] Step S5: Compensation and Re-detection

[0017] The wafer angle is detected by a Wafer camera, converted into the actual coordinates of the rotation axis according to the coefficient, and necessary compensation is made to account for the inconsistency between the rotation center and the nozzle center; the wafer center after rescanning and compensation should coincide with the original position.

[0018] Preferred step; Step S2: Wafer center detection and coordinate recording: The die bonder picks up the wafer and moves it to align with the up-look camera. The wafer center is then determined using machine vision. Record the corresponding rotary axis encoder coordinates Up-look camera pixel calibration conversion matrix for:

[0019]

[0020] Preferably, in step S3, the wafer rotates and the angle is calculated: the wafer rotates to 360° in 10° increments, and the image coordinates are calculated using the pixel-calibrated transformation matrix. Converted to the corresponding coordinate system of the die bonder

[0021]

[0022] because On the XOY plane of the die bonder coordinate system, using Find Angle in the XOY plane

[0023] Preferred step; Step S4: Establishing and fitting linear relationship: Calibrating the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die bonding head coordinate system, and fitting the rotation angle coefficient and offset using the least squares method;

[0024] Calibrate rotation axis coordinates and the XOY plane angular coordinates within the die-bonding head coordinate system The relationship between them is linear, which can be expressed by the following formula:

[0025]

[0026] A series The least squares fitting polynomial method uses η and b, where η is the rotation angle coefficient and b is the rotation angle offset.

[0027] Preferably, the sample points are fitted into a circle, and the center of rotation is described by the center and radius. Let the center of the circle be O(A,B) and the radius be R, then the equation of the circle can be written as:

[0028] R 2 =(xA) 2 +(yB) 2 =x 2 -2Ax+A 2 +y 2 -2By+B 2

[0029] Transform the above formula into:

[0030] X 2 +Y 2 +aX+bY+c=0

[0031] in:

[0032] a = -2A, b = -2B, c = A 2 +B 2 -R 2

[0033] X, the sample set captured by the camera i Y i Substituting (i = 1, 2, 3, ..., n) into the above formula, we get the following formula.

[0034]

[0035] Write it in matrix form.

[0036]

[0037] That is, it must meet the following format,

[0038] Ax = B

[0039] The X matrix is ​​obtained by solving using the least squares method.

[0040] x=(AT A) -1 A T B

[0041] Given a, b, and c, the radius and center of the circle can be calculated.

[0042]

[0043] At this point, the rotation center O(A, B) and the angular coefficient η have been determined.

[0044] Preferred step; Step S5: Compensation and re-detection; including Wafer camera detection, using a Wafer camera to detect the angle of the wafer already attached to the die bonder; at this time, through step S4, the wafer angle θ′ detected by the Wafer camera is converted into the actual coordinates of the rotation axis; record the wafer angle detected by the Wafer camera and the corresponding rotation axis encoder coordinates;

[0045] The Wafer camera detects the angle θ′ of the wafer and converts it into the actual coordinates of the rotation axis using a coefficient.

[0046] θ = η·θ′ + b.

[0047] Preferred; Step S5: Compensation and re-inspection also includes calculating the compensation amount; The die bonder picks up and lifts up. During this process, the rotation axis -θ needs to be rotated to straighten the wafer. Since the rotation center and the die bonder nozzle center are not consistent, the wafer center P(x,y) will be offset, and this offset needs to be compensated.

[0048] The rotation matrix is:

[0049]

[0050] Preferably, step S5: compensation and re-detection also includes linear interpolation compensation; compensation is performed using a linear interpolation method, rotating from 0° to 360° within the field of view, taking intervals of 10°, and setting θ as... i ≤θ<θ j The scaling factor is:

[0051]

[0052] Integrate the linear interpolation compensation into the rotation matrix:

[0053]

[0054] The offset wafer center P′(x′, y′) is obtained as follows:

[0055]

[0056] After the compensation for the die bonding head movement is ΔP = P′ - P, the wafer center coincides with the original position, and the entire process is completed.

[0057] Preferably; Step S5: Compensation and re-inspection also includes actual compensation. Based on the calculated compensation amount, the position of the die bonder is adjusted so that the center of the wafer can still coincide with the original position after rotation. After the compensation is completed, the wafer position is confirmed again using a Wafer camera or other inspection equipment to ensure that its position is accurate.

[0058] Compared to existing technologies, the advantages of this invention, using the above-described scheme, are that in high-precision applications such as die bonders, it utilizes a local coordinate system of the die bonder head as a medium to calibrate and calculate the rotation coefficient and rotation center of the die bonder head, preventing error propagation. In the rotation calibration, not only is a rotational model of the rotation axis generated, but linear interpolation is also used to further improve accuracy and reduce the impact of errors. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments or prior art, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 This is a schematic diagram illustrating the calibration of the Up-look camera center and the die bonder center in this invention.

[0061] Figure 2 This is a schematic diagram illustrating the calibration of the Wafer camera center and the die bonding head center in this invention.

[0062] Figure 3 This is a schematic diagram of the wafer rotation structure of the present invention;

[0063] Figure 4 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0064] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0065] It should be noted that when a component is described as being "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is described as being "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "fixed," "integral," "left," "right," and similar expressions used in this specification are for illustrative purposes only, and in the figures, structurally similar units are labeled with the same reference numerals.

[0066] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0067] One embodiment of the present invention is a method for calibrating the rotation axis of a die bonder, the steps of which are as follows:

[0068] Step S1: Nozzle center alignment and coordinate recording

[0069] Align the center of the die bonder nozzle with the center of the up-look camera and the center of the wafer camera, respectively, and record the corresponding die bonder coordinates;

[0070] Step S2: Wafer Center Detection and Coordinate Recording

[0071] After the die bonder picks up the wafer, it moves to the Up-look camera. The center of the wafer is detected by machine vision, the corresponding rotary axis encoder coordinates are recorded, and the Up-look camera pixel calibration conversion matrix is ​​obtained at the same time.

[0072] Step S3: Wafer Rotation and Angle Calculation

[0073] Rotate the chip to 360° in 10° increments, and use the pixel calibration transformation matrix to transform the image coordinates to the die bond head coordinate system to calculate the planar angle.

[0074] Step S4: Establishing and Fitting Linear Relationships

[0075] The linear relationship between the rotation axis coordinates and the plane angle coordinates in the die bond head coordinate system is determined, and the rotation angle coefficient and offset are fitted using the least squares method.

[0076] Step S5: Compensation and Re-detection

[0077] The wafer angle is detected by a Wafer camera, converted into the actual coordinates of the rotation axis according to the coefficient, and necessary compensation is made to account for the inconsistency between the rotation center and the nozzle center; the wafer center after rescanning and compensation should coincide with the original position.

[0078] It should be noted that existing methods use a world coordinate system as a medium to calculate the coordinates of each component, and do not consider the mechanical errors of the rotation axis that cause the nozzle center and rotation center of the die bonder to not coincide. The above solution uses the local coordinate system of the die bonder as a medium to calibrate the rotation coefficient and rotation center of the die bonder, preventing error propagation. In the rotation calibration, not only is a rotation model of the rotation axis generated, but linear interpolation is also used to further improve accuracy and reduce the impact of errors.

[0079] Step S1: Nozzle center alignment and coordinate recording

[0080] Align the center of the die bonder nozzle with the center of the up-look camera and the center of the wafer camera, respectively, and record the corresponding die bonder coordinates;

[0081] It should be noted that step 1 requires preliminary work, as follows:

[0082] 1. Preparation

[0083] Equipment preparation: Ensure that the die bonder, up-look camera, and wafer camera are all in normal working order.

[0084] Environmental preparation: Ensure the work surface is clean and tidy, and avoid external factors that may interfere with the alignment process.

[0085] 2. Align the die bonder with the up-look camera.

[0086] Initial position setting: Move the die bonder to a known initial position, ensuring that the center of its nozzle is within the field of view that can be clearly captured by the up-look camera.

[0087] Visual alignment:

[0088] Use an up-look camera to capture an image of the center of the die bond nozzle.

[0089] The die bonder nozzle center is perfectly aligned with the optical center of the up-look camera using machine vision algorithms or manual adjustments. This process may require fine-tuning the die bonder's position until the two are perfectly aligned in the image.

[0090] Record coordinates: Once alignment is complete, record the precise coordinates of the die bonder at this point. These coordinates include, but are not limited to, the position information of the X-axis, Y-axis, and Z-axis.

[0091] 3. Align the die bonder with the wafer camera.

[0092] Move the die bonder from the up-look camera to the wafer camera's field of view. Similarly, ensure the center of the nozzle is clearly captured by the wafer camera.

[0093] Visual alignment:

[0094] Use a Wafer camera to capture an image of the center of the die bond nozzle.

[0095] Similarly, through machine vision algorithms or manual adjustments, the center of the die bonder nozzle is made to perfectly align with the optical center of the wafer camera. This step also involves fine-tuning the position of the die bonder.

[0096] Record coordinates: After alignment, record the precise coordinates of the die bonder again. Note that these coordinates should reflect the position of the die bonder relative to the wafer camera.

[0097] 4. Verification and Confirmation

[0098] Double check: To ensure alignment accuracy, it is recommended to perform multiple re-alignment and coordinate recording to reduce errors.

[0099] Data saving: Properly save all recorded coordinate information for use in subsequent steps. This coordinate information is crucial for establishing the local coordinate system of the die bonder.

[0100] 5. Technical Details

[0101] Camera pixel calibration transformation matrix: During alignment, the camera's pixel calibration transformation matrix may be used. This matrix is ​​used to convert image coordinates into actual spatial coordinates (i.e., coordinates in the die bond coordinate system). This transformation process ensures an accurate correspondence between different coordinate systems.

[0102] Error control: Throughout the alignment process, mechanical errors must be strictly controlled to ensure that every movement and adjustment is minute and precise in order to avoid cumulative errors affecting the final result.

[0103] By eliminating the dependence on the world coordinate system through the above methods, alignment is performed directly in the local coordinate system of the die bonder, rather than relying on the world coordinate system, which effectively avoids error propagation and improves the overall calibration accuracy.

[0104] Establishing reference points: This step establishes two important reference points (the center of the up-look camera and the center of the wafer camera), which will serve as the basis for subsequent rotation calibration and other operations.

[0105] Step S1 precisely aligns the center of the die bonder's nozzle with the centers of the Up-look and Wafer cameras, respectively, and records the corresponding die bonder coordinates, providing a reliable reference for subsequent rotational calibration. This process not only requires high-precision mechanical adjustments but also relies on advanced machine vision technology and coordinate transformation algorithms to ensure that the starting point of the entire die bonder process is accurate.

[0106] Preferred step; Step S2: Wafer center detection and coordinate recording: The die bonder picks up the wafer and moves it to align with the up-look camera. The wafer center is then determined using machine vision. Record the corresponding rotary axis encoder coordinates Up-look camera pixel calibration conversion matrix for:

[0107]

[0108] It should be noted that step S2 is a crucial part of the entire calibration method, ensuring the accurate acquisition of wafer position information; it includes the following aspects:

[0109] 1. The die bonder holds the wafer.

[0110] • Pick up the wafer: Use the nozzle on the die bonder to pick up the wafer to be processed, ensuring that the wafer is stably attached to the nozzle and does not slip or fall off.

[0111] • Initial position confirmation: After picking up the wafer, move the die bonder to a safe position to prevent collisions with any other equipment.

[0112] 2. Move to the Up-look camera view.

[0113] • Move the die bonder head: Move the die bonder head from its current safe position to within the field of view of the up-look camera to ensure that the chip can be clearly captured by the up-look camera.

[0114] • Adjust position: Fine-tune the position of the die bonder as needed to position the wafer in the optimal shooting area of ​​the up-look camera.

[0115] 3. Machine Vision Inspection Chip Center

[0116] • Image acquisition: Images of the wafer are captured using an up-look camera, and the center position of the wafer is identified and determined using machine vision algorithms.

[0117] • Coordinate system transformation: The position of the wafer center in the image coordinate system needs to be converted to its actual spatial coordinates in the die bonding head coordinate system. This step requires the use of the pixel calibration transformation matrix of the up-look camera.

[0118] 4. Pixel calibration transformation matrix

[0119] • Definition: Transformation matrix This is used to convert coordinates in the image coordinate system to coordinates in the die bonding head coordinate system. Its form is as follows:

[0120]

[0121] Where A, B, C, DA, B, C, D are transformation coefficients used for linear transformation;

[0122] οTx,Ty are translation parameters, representing the offset of the origin of the image coordinate system relative to the die bonding head coordinate system.

[0123] The machine vision algorithm used in this paper is used to identify the specific location of the chip center. It may involve technologies such as edge detection and template matching to ensure the accuracy and reliability of the identification.

[0124] • Coordinate transformation: The image coordinate system is transformed to the die bonding head coordinate system through the pixel calibration transformation matrix. This is a key step to ensure the accuracy of subsequent calibration.

[0125] • Error control: Throughout the process, mechanical and visual recognition errors must be strictly controlled to ensure that each operation is precise in order to avoid cumulative errors affecting the final result.

[0126] Step S2 uses machine vision to detect the center position of the wafer and transforms it into the die bond head coordinate system, while simultaneously recording the coordinates of the rotary axis encoder. This process provides the basic data for subsequent rotational calibration, ensuring that the wafer position information at each rotation angle is accurate, thereby improving the accuracy and reliability of the entire calibration method.

[0127] Preferably, in step S3, the wafer rotates and the angle is calculated: the wafer rotates to 360° in 10° increments, and the image coordinates are calculated using the pixel-calibrated transformation matrix. Converted to the corresponding coordinate system of the die bonder

[0128]

[0129] because On the XOY plane of the die bonder coordinate system, using Find Angle in the XOY plane It should be noted that step S3 is a crucial part of the entire calibration method, involving the gradual rotation of the wafer and precise angle calculation. The detailed steps are as follows:

[0130] Chip rotation settings

[0131] • Initial position setting: Starting from a known initial position, ensure that the chip has been accurately picked up through step S2 and that its center position has been recorded.

[0132] • Rotation step size setting: Set the rotation axis to rotate in 10° steps, from 0° to 360°. This means a total of 36 rotations are required (including 0°).

[0133] Successive rotation and image acquisition

[0134] • Image captured after each rotation: After each 10° rotation increment, an image of the wafer is captured using an up-look camera. This step ensures that the wafer's position at each rotation angle is captured and recorded.

[0135] • Visual inspection: Identifying and determining the new position P of the chip center using machine vision algorithms. i C (x,y,1) are the coordinates of the image coordinate system.

[0136] coordinate transformation

[0137] • Applying a pixel calibration transformation matrix: Utilizing the pixel calibration transformation matrix of an up-look camera The center position P of the wafer in the image coordinate system i C (x, y, 1) is converted to coordinates P in the die bonding head coordinate system. i B (x′,y′,1).

[0138] Assume the center coordinates of the wafer in the image coordinate system are P. i C (x,y,1), then its coordinates P in the die-bonding head coordinate system. i B It can be calculated using the following formula:

[0139]

[0140] Right now:

[0141]

[0142] The calculation result is:

[0143] x′=Ax+Cy+T x

[0144] y′=Bx+Dy+T y

[0145] Angle calculation

[0146] Solving for plane angles On the XOY plane of the die bonder coordinate system, using the transformed coordinate P i B The angle between the center of the wafer and the origin is calculated using (x′, y′, 1).

[0147] The angle can be calculated using the arctangent function (atan2):

[0148] ο

[0149] The `atan2` function returns the angle from the positive X-axis to the point (x′, y′), ranging from -π to π. To adjust the angle range to 0 to 2π, an appropriate conversion can be performed.

[0150]

[0151] Step S3 involves successively rotating the wafer and obtaining the wafer center position at each rotation angle. Using a pixel calibration transformation matrix, the image coordinates are converted to coordinates in the die-bonding head coordinate system. Finally, the angle between the wafer center and the origin of the die-bonding head coordinate system at each rotation angle is calculated. This process provides the foundational data for subsequent linear relationship establishment and fitting, ensuring the accuracy and reliability of the rotation axis calibration.

[0152] Preferred step; Step S4: Establishing and fitting linear relationship: Calibrating the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die bonding head coordinate system, and fitting the rotation angle coefficient and offset using the least squares method;

[0153] Calibrate rotation axis coordinates and the XOY plane angular coordinates within the die-bonding head coordinate system The relationship between them is linear, which can be expressed by the following formula:

[0154]

[0155] A series The least squares fitting polynomial method uses η and b, where η is the rotation angle coefficient and b is the rotation angle offset. 。

[0156] It should be noted that step S4, through assuming a linear relationship, collecting data, applying the least squares method for fitting, and verifying the fitting effect, determined the linear relationship between the rotation axis coordinates and the angular coordinates in the X0Y plane within the die-bonding head coordinate system, and solved for the rotation angle coefficient and offset. This process provides a reliable mathematical foundation for subsequent rotation compensation, ensuring the accuracy and stability of the die-bonding process.

[0157] Preferably, the sample points are fitted into a circle, and the center of rotation is described by the center and radius. Let the center of the circle be O(A, B) and the radius be R, then the equation of the circle can be written as:

[0158] R2 =(xA) 2 +(yB) 2 =x 2 -2Ax+A 2 +y 2 -2By+B 2

[0159] Transform the above formula into:

[0160] X 2 +Y′ 2 +aX+bY+c=0

[0161] in:

[0162] a = -2A, b = -2B, c = A 2 +B 2 -R 2

[0163] X, the sample set captured by the camera i Y i Substituting (i = 1, 2, 3, ..., n) into the above formula, we get the following formula.

[0164]

[0165] Write it in matrix form.

[0166]

[0167] That is, it must meet the following format,

[0168] Ax = B

[0169] The X matrix is ​​obtained by solving using the least squares method.

[0170] x=(A T A) -1 A T B

[0171] Given a, b, and c, the radius and center of the circle can be calculated.

[0172]

[0173] At this point, the rotation center O(A, B) and the angular coefficient η have been determined.

[0174] Preferred step; Step S5: Compensation and re-detection; including Wafer camera detection, using a Wafer camera to detect the angle of the wafer already attached to the die bonder; at this time, through step S4, the wafer angle θ′ detected by the Wafer camera is converted into the actual coordinates of the rotation axis; record the wafer angle detected by the Wafer camera and the corresponding rotation axis encoder coordinates;

[0175] The Wafer camera detects the angle θ′ of the wafer and converts it into the actual coordinates of the rotation axis using a coefficient.

[0176] θ = η·θ′ + b.

[0177] Preferred; Step S5: Compensation and re-inspection also includes calculating the compensation amount; The die bonder picks up and lifts up. During this process, the rotation axis -θ needs to be rotated to straighten the wafer. Since the rotation center and the die bonder nozzle center are not consistent, the wafer center P(x,y) will be offset, and this offset needs to be compensated.

[0178] The rotation matrix is:

[0179]

[0180] Preferably, step S5: compensation and re-detection also includes linear interpolation compensation; compensation is performed using a linear interpolation method, rotating from 0° to 360° within the field of view, taking intervals of 10°, and setting θ as... i ≤θ≤θ j The scaling factor is:

[0181]

[0182] Integrate the linear interpolation compensation into the rotation matrix:

[0183]

[0184] The offset wafer center P′(x′, y′) is obtained as follows:

[0185]

[0186] After the compensation for the die bonding head movement is ΔP = P′ - P, the wafer center coincides with the original position, and the entire process is completed.

[0187] Step S5: Compensation and re-inspection also includes actual compensation. Based on the calculated compensation amount, the position of the die bonder is adjusted so that the center of the wafer can still coincide with the original position after rotation. After the compensation is completed, the wafer position is confirmed again using a Wafer camera or other inspection equipment to ensure that its position is accurate.

[0188] In high-precision applications such as die bonders, this invention uses a local coordinate system of the die bonder head as a medium to calibrate and calculate the rotation coefficient and rotation center of the die bonder head, preventing error propagation. The rotation calibration not only generates a rotation model of the rotation axis but also uses linear interpolation to further improve accuracy and reduce the impact of errors.

[0189] It should be noted that the above-mentioned technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of this invention specification; and, for those skilled in the art, improvements or modifications can be made based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for calibrating the rotation axis of a die-bonding head, characterized in that; The steps are as follows: Step S1: Nozzle center alignment and coordinate recording: Align the center of the die bonder nozzle with the center of the up-look camera and the center of the wafer camera, respectively, and record the corresponding die bonder coordinates; Step S2: Wafer Center Detection and Coordinate Recording After the die bonder picks up the wafer, it moves to the Up-look camera and uses machine vision to detect the center of the wafer, record the corresponding rotary axis encoder coordinates, and simultaneously obtain the Up-look camera pixel calibration conversion matrix. Step S3: Wafer rotation and angle calculation: Rotate the chip to 360° in 10° increments, and use the pixel calibration transformation matrix to transform the image coordinates to the die bond head coordinate system to calculate the planar angle. Step S4: Establishing and fitting linear relationships: The linear relationship between the rotation axis coordinates and the plane angle coordinates in the die bond head coordinate system is determined, and the rotation angle coefficient and offset are fitted using the least squares method. Step S5: Compensation and Re-inspection: The wafer angle is detected by a Wafer camera, converted into the actual coordinates of the rotation axis according to the coefficient, and the necessary compensation is made to account for the inconsistency between the rotation center and the nozzle center. The wafer center after rescanning and compensation should coincide with the original position to complete the rotation calibration. Step S2: Wafer Center Detection and Coordinate Recording: The die bonder picks up the wafer and moves it to align with the up-look camera. The wafer center is then determined using machine vision. Record the corresponding rotary axis encoder coordinates Up-look camera pixel calibration transformation matrix for: ; ； A, B, C, and D are transformation coefficients used for linear transformations; Tx , Ty It is a translation parameter, representing the offset of the origin of the image coordinate system relative to the die bonding head coordinate system; Step S3: Wafer Rotation and Angle Calculation: The wafer is rotated to 360° in 10° increments. The image coordinates are then calculated using the pixel-calibrated transformation matrix. Converted to the corresponding coordinate system of the die bonder , ； because On the XOY plane of the die bonder coordinate system, using Find exist Angle of the plane ; Step S4: Establishing and fitting linear relationships: Calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die-bonding head coordinate system, and fit the rotation angle coefficients and offsets using the least squares method; Calibrate rotation axis coordinates and the XOY plane angular coordinates within the die-bonding head coordinate system The relationship between them is linear, resulting in the following formula: ； A series Least squares fitting polynomial method and ,in This is the rotation angle coefficient. This represents the rotation angle offset.

2. The die bonding head rotation axis calibration method according to claim 1, characterized in that; The sample points are fitted to a circle, and the center of rotation is described by the center and radius. Let the center of the circle be O(A,B) and the radius be R, then the equation of the circle can be written as: ； Transform the above formula into: ； in: ； The sample set captured by the UpLook camera Substituting into the above formula, we get the following formula. ； Write it in matrix form. ； That is, it must meet the following format, ； Solving using the least squares method, we obtain... x matrix, ； That is, get a, b, c Then the radius and center can be calculated: ； ； ； At this point, the center of rotation O(A,B) and angle coefficient All of these have already been calculated.

3. The die bonding head rotation axis calibration method according to claim 1, characterized in that; Step S5: Compensation and Re-inspection; This includes wafer camera inspection, using a wafer camera to detect the angle of the wafer already attached to the die bonder; at this point, the wafer angle detected by the wafer camera is adjusted according to step S4. Convert to the actual coordinates of the rotation axis; record the wafer angle detected by the Wafer camera and the corresponding rotation axis encoder coordinates; Wafer camera detects the angle of the wafer. The actual coordinates of the rotation axis are converted using coefficients. 。 4. The die bonding head rotation axis calibration method according to claim 3, characterized in that; Step S5: Compensation and re-inspection also includes calculating the compensation amount; the die bonder is held and lifted, during which the rotating shaft needs to be rotated. To align the wafer, the misalignment between the rotation center and the die bonder nozzle center will cause the wafer to be centered. P(x, y) The offset needs to be compensated. The rotation matrix is: 。 5. The die bond head rotation axis calibration method according to claim 3, characterized in that; Step S5: Compensation and re-detection also includes linear interpolation compensation; compensation is performed using linear interpolation, rotating from 0° to 360° within the field of view, with intervals of 10°. The scaling factor is: ； Integrate the linear interpolation compensation into the rotation matrix: ； Find the offset wafer center for: ； The compensation for the die bonding head to be moved is Afterwards, the center of the chip coincides with the original, and the whole process is complete.

6. A method for calibrating the rotation axis of a die-bonding head according to any one of claims 1, 3, 4, and 5, characterized in that; Step S5: Compensation and re-inspection also includes actual compensation. Based on the calculated compensation amount, the position of the die bonder is adjusted so that the center of the wafer can still coincide with the original position after rotation. After compensation is completed, the wafer camera or other inspection equipment is used again to confirm the position of the wafer to ensure that its position is accurate.

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