Calibration method for rotating shaft of die bonding head

Abstract

The invention 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, aligning the center of a suction nozzle and recording coordinates: aligning the center of the suction nozzle of a die bonding head with the center of a Up-look camera and the center of a Wafer camera respectively; s2, wafer center detection and coordinate recording: detecting the center of the wafer through machine vision, recording a corresponding rotating shaft encoder coordinate, and obtaining a Up-look camera pixel calibration conversion matrix; s3, wafer rotation and angle calculation: enabling the wafer to rotate to 360 degrees by taking 10 degrees as a step length, and solving a plane angle; s4, a linear relation establishment and fitting step: calibrating a linear relation between a rotating shaft coordinate and a plane angle coordinate in a die bonding head coordinate system, and fitting a rotating angle coefficient and an offset; s5, compensation and re-detection: detecting the angle of the wafer through a Wafer camera, converting the angle into the actual coordinate of a rotating shaft according to a coefficient, and compensating if the rotating center is inconsistent with the center of the suction nozzle; and the center of the re-scanned and compensated wafer should coincide with the original position.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor packaging equipment, and in particular relates to a method for calibrating a rotation axis of a die bonding head. Background Art

[0002] In the current die bonding process, the commonly used method is to use the world coordinate system as a medium to convert the coordinates of each component. Although this method can achieve coordinate conversion between different devices to a certain extent, it has some significant limitations, especially in application scenarios with high precision requirements.

[0003] The world coordinate system is a global reference frame that provides a unified coordinate reference for all devices and tools involved in the operation. However, this approach ignores the small mechanical errors that may exist between devices, especially the mechanical errors of the rotation axis. Specifically, the existing method does not consider the problem that the nozzle center and the rotation center of the die bonding head do not coincide with each other due to the mechanical error of the rotation axis. This will 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 nozzle center of the die bonding head is inconsistent with the rotation center, then during the entire rotation process, this deviation will gradually accumulate and eventually affect the accuracy of wafer placement.

[0005] 2. Lack of targeted compensation: Existing methods fail to compensate for the mechanical characteristics of specific equipment. Each device such as a die bonding head and a rotating axis has its own unique mechanical errors, which cannot be corrected by simple coordinate conversion. Therefore, in high-precision application scenarios, such as the semiconductor packaging field, this method is difficult to meet the required accuracy standards. Summary of the invention

[0006] The present invention provides a patent name to solve the above-mentioned problems.

[0007] To solve the above problems, the present invention provides a technical solution as follows: a method for calibrating the rotation axis of a die bonding head, the steps of which are as follows:

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

[0009] Align the nozzle center of the die bonding head with the center of the Up-look camera and the center of the Wafer camera respectively, and record the corresponding coordinates of the die bonding head;

[0010] Step S2: Wafer center detection and coordinate recording

[0011] After the die bonding head holds the wafer, it moves to the Up-look camera, detects the wafer center through machine vision, records the corresponding rotary axis encoder coordinates, and obtains the Up-look camera pixel calibration conversion matrix at the same time;

[0012] Step S3: Wafer rotation and angle calculation

[0013] The wafer is rotated to 360° in steps of 10°, and the image coordinates are converted to the die bonding head coordinate system using the pixel calibration transformation matrix to calculate the plane angle;

[0014] Step S4: Linear relationship establishment and fitting

[0015] Calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die-bonding head coordinate system, and use the least squares method to fit the rotation angle coefficient and offset;

[0016] Step S5: Compensation and re-detection

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

[0018] Preferably; Step S2 Wafer center detection and coordinate recording: The wafer is sucked by the wafer head, and the wafer head is moved to align with the Up-look camera, and the wafer center is detected by machine vision. Record the corresponding rotary axis encoder coordinates Pixel calibration transformation matrix for up-look cameras for:

[0019]

[0020] Preferably, in step S3, the chip is rotated and the angle is calculated: the chip is rotated to 360° in steps of 10°, and the image coordinates are converted to Convert to the corresponding coordinate system of the die bonding head

[0021]

[0022] because On the XOY plane of the die bonding head coordinate system, use Find Angle in XOY plane

[0023] Preferably; Step S4 linear relationship establishment and fitting: calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the solid crystal head coordinate system, and use the least squares method to fit the rotation angle coefficient and offset;

[0024] Calibrate the rotation axis coordinates And the XOY plane angle coordinates in the die bonding head coordinate system There is a linear relationship between them, and the following formula can be obtained:

[0025]

[0026] By a series of The least squares polynomial method η and b is used, 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 and radius are used to describe the center of rotation. Assuming the center of the circle is O(A, B) and the radius is R, 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] The sample set X collected by the camera i , Y i Substituting (i=1, 2, 3, ..., n) into the above formula, we get the following formula:

[0034]

[0035] Written in matrix form,

[0036]

[0037] That is, it satisfies the following format,

[0038] Ax=B

[0039] Solve using the least squares method to obtain the X matrix,

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

[0041] That is, if we get a, b, and c, we can find the radius and center of the circle:

[0042]

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

[0044] Preferably, step S5: compensation and re-detection; including wafer camera detection, using the wafer camera to detect the angle of the wafer adsorbed on the die bonding head; at this time, through step S4, the wafer angle θ′ detected by the wafer camera is converted into the actual coordinate of the rotation axis; the wafer angle detected by the wafer camera and the corresponding rotation axis encoder coordinate are recorded;

[0045] The wafer camera detects the angle θ′ of the wafer and converts it into the actual coordinates of the rotation axis through the coefficient;

[0046] θ=η·θ′+b.

[0047] Preferably; step S5: compensation and re-detection also includes calculating the compensation amount; the solid crystal head is sucked and lifted, and during this process, the rotation axis -θ needs to be rotated to align the wafer. Since the rotation center is inconsistent with the center of the solid crystal head nozzle, 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; use linear interpolation method to compensate, to the field of view, rotate from 0° to 360°, take an interval of 10°, set θ i ≤θ<θ j , the scaling factor is:

[0051]

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

[0053]

[0054] The chip center P'(x', y') after the offset is obtained as:

[0055]

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

[0057] Preferably; step S5: compensation and re-detection also includes actual compensation. According to the calculated compensation amount, the position of the die bonding head is adjusted so that the center of the wafer can still coincide with the original position after rotation; after completing the compensation, the wafer position is confirmed again using a wafer camera or other detection equipment to ensure that its position is accurate.

[0058] Compared with the prior art, the beneficial effect is that, by adopting the above scheme, the present invention uses the local coordinate system of the die bonding head as a medium in the scenario where high precision is required, and calibrates and calculates the rotation coefficient and the rotation center of the die bonding head to prevent error diffusion. In the rotation calibration, not only a rotation model of the rotation axis is generated, but also linear interpolation is used to further improve the precision and reduce the impact of errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0060] Figure 1 This is a schematic diagram of the calibration between the center of the Up-look camera and the center of the die bonding head of the present invention;

[0061] Figure 2 It is a schematic diagram of calibration between the wafer camera center and the die bonding head center of the present invention;

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

[0063] Figure 4 It is a schematic diagram of the overall process of the present invention. DETAILED DESCRIPTION

[0064] In order to facilitate the understanding of the present invention, the present invention is described in more detail below in conjunction with the accompanying drawings and specific embodiments. Preferred embodiments of the present invention are provided in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0065] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "fixed", "integrally formed", "left", "right" and similar expressions used in this specification are for illustrative purposes only. In the drawings, units with similar structures are marked with the same reference numerals.

[0066] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

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

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

[0069] Align the nozzle center of the die bonding head with the center of the Up-look camera and the center of the Wafer camera respectively, and record the corresponding coordinates of the die bonding head;

[0070] Step S2: Wafer center detection and coordinate recording

[0071] After the die bonding head holds the wafer, it moves to the Up-look camera, detects the wafer center through machine vision, records the corresponding rotary axis encoder coordinates, and obtains the Up-look camera pixel calibration conversion matrix at the same time;

[0072] Step S3: Wafer rotation and angle calculation

[0073] The wafer is rotated to 360° in steps of 10°, and the image coordinates are converted to the die bonding head coordinate system using the pixel calibration transformation matrix to calculate the plane angle;

[0074] Step S4: Linear relationship establishment and fitting

[0075] Calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die-bonding head coordinate system, and use the least squares method to fit the rotation angle coefficient and offset;

[0076] Step S5: Compensation and re-detection

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

[0078] It should be noted that the existing method uses the world coordinate system as a medium to convert the coordinates of each component, and does not take into account the mechanical error of the rotation axis that causes the nozzle center of the die bonding head and the rotation center to not coincide. The above solution uses the local coordinate system of the die bonding head as a medium to calibrate and calculate the rotation coefficient and rotation center of the die bonding head to prevent error diffusion. In the rotation calibration, not only a rotation model of the rotation axis is generated, but also linear interpolation is used to further improve accuracy and reduce the impact of errors.

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

[0080] Align the nozzle center of the die bonding head with the center of the Up-look camera and the center of the Wafer camera respectively, and record the corresponding coordinates of the die bonding head;

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

[0082] 1. Preparation

[0083] Equipment preparation: Make sure the die bonding head, Up-look camera, and Wafer camera are in normal working condition.

[0084] Environmental preparation: Ensure the work surface is clean and tidy to avoid external factors interfering with the alignment process.

[0085] 2. Align the die bonding head with the Up-look camera

[0086] Initial position setting: Move the die bonding head to a known initial position, making sure 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 the Up-look camera to capture an image of the center of the die bonding head nozzle.

[0089] Through machine vision algorithms or manual adjustments, the center of the die bonding head nozzle is completely aligned with the optical center of the Up-look camera. This process may require fine-tuning the position of the die bonding head until the two are perfectly aligned in the image.

[0090] Record coordinates: When the alignment is completed, record the precise coordinates of the die-bonding head at this time, including but not limited to the position information of the X-axis, Y-axis and Z-axis.

[0091] 3. Align the die bonding head with the wafer camera

[0092] Move to the Wafer camera field of view: Move the die bonding head from the Up-look camera to the Wafer camera field of view. Also, make sure the center of the nozzle can be clearly captured by the Wafer camera.

[0093] Visual Alignment:

[0094] Use a wafer camera to capture an image of the center of the die bonding head nozzle.

[0095] Similarly, through machine vision algorithms or manual adjustments, the center of the die bonding head nozzle is completely aligned with the optical center of the wafer camera. This step also involves fine adjustment of the position of the die bonding head.

[0096] Record coordinates: After alignment is completed, record the precise coordinates of the die bonding head again. Note that the coordinates here should reflect the position of the die bonding head relative to the wafer camera.

[0097] 4. Verification and Validation

[0098] Double check: To ensure the accuracy of the alignment, it is recommended to repeat the alignment and coordinate recording several times to reduce errors.

[0099] Data preservation: All recorded coordinate information should be properly saved for use in subsequent steps. These coordinate information are crucial for establishing the local coordinate system of the die bonding head.

[0100] 5. Technical Details

[0101] Camera pixel calibration conversion matrix: During the alignment process, the camera pixel calibration conversion matrix may be used, which is used to convert image coordinates into real space coordinates (i.e., coordinates in the die bonding head coordinate system). This conversion process ensures the accurate correspondence between different coordinate systems.

[0102] Error control: During the entire alignment process, mechanical errors must be strictly controlled to ensure that each movement and adjustment is small and precise to avoid cumulative errors affecting the final result.

[0103] Through the above content, the dependence on the world coordinate system is eliminated: by directly aligning in the local coordinate system of the die bonding head instead of relying on the world coordinate system, error propagation is effectively avoided and the overall calibration accuracy is improved.

[0104] Establish reference points: This step establishes two important reference points (up-look camera center and wafer camera center), which will become the basic reference points for subsequent rotation calibration and other operations.

[0105] In step S1, the nozzle center of the die bonding head is precisely aligned with the center of the Up-look camera and the center of the Wafer camera, and the corresponding die bonding head coordinates are recorded, providing a reliable reference for subsequent rotation calibration. This process not only requires high-precision mechanical adjustment, but also relies on advanced machine vision technology and coordinate conversion algorithms to ensure that the starting point of the entire die bonding process is accurate.

[0106] Preferably; Step S2 Wafer center detection and coordinate recording: The wafer is sucked by the wafer head, and the wafer head is moved to align with the Up-look camera, and the wafer center is detected by machine vision. Record the corresponding rotary axis encoder coordinates Pixel calibration transformation matrix for up-look cameras for:

[0107]

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

[0109] 1. The bonding head holds the chip

[0110] ·Suction the wafer: Use the nozzle on the wafer bonding head to suck the wafer to be processed, and ensure that the wafer is stably adsorbed on the nozzle without sliding or falling off.

[0111] Initial position confirmation: After sucking the wafer, move the die bonding head to a safe position to prevent collision with any other equipment.

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

[0113] Move the die bonding head: Move the die bonding head from its current safe position to the field of view of the Up-look camera to ensure that the wafer can be clearly captured by the Up-look camera.

[0114] Adjust position: Fine-tune the position of the die bonding head as needed to place the wafer in the best shooting area of ​​the Up-look camera.

[0115] 3. Machine vision inspection wafer center

[0116] Image acquisition: Use an up-look camera to capture an image of the wafer and use a machine vision algorithm to identify and determine the center position of the wafer.

[0117] Coordinate system conversion: The position of the wafer center in the image coordinate system needs to be converted to the actual space coordinates in the die bonding head coordinate system. This step requires the pixel calibration conversion matrix of the Up-look camera.

[0118] 4. Pixel calibration transformation matrix

[0119] Definition: Transformation Matrix It is used to convert the coordinates in the image coordinate system into the coordinates in the die bonding head coordinate system. Its format is as follows:

[0120]

[0121] Among them, A, B, C, D A, B, C, D are conversion coefficients used for linear transformation;

[0122] οTx,TyTx,Ty is a translation parameter, which represents the offset of the origin of the image coordinate system relative to the die bonding head coordinate system.

[0123] The machine vision algorithm in this article is used to identify the specific location of the center of the chip, which may involve edge detection, template matching and other technologies to ensure the accuracy and reliability of recognition.

[0124] Coordinate conversion: The pixel calibration conversion matrix is ​​used to convert the image coordinate system to the die-bonding head coordinate system, which is a key step to ensure the accuracy of subsequent calibration.

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

[0126] In step S2, the center position of the wafer is detected by machine vision and converted to the die bonding head coordinate system, while the coordinates of the rotary axis encoder are recorded. This process provides basic data for subsequent rotation 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 chip is rotated and the angle is calculated: the chip is rotated to 360° in steps of 10°, and the image coordinates are converted to Convert to the corresponding coordinate system of the die bonding head

[0128]

[0129] because On the XOY plane of the die bonding head coordinate system, use Find Angle in XOY plane It should be noted that the S3 step is a very critical part of the entire calibration method, which involves the gradual rotation of the wafer and the precise calculation of the angle. The following are the detailed steps:

[0130] Wafer rotation setting

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

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

[0133] Successive rotation and image acquisition

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

[0135] Visual inspection: Use machine vision algorithms to identify and determine the new position P of the wafer center i C (x,y,1) is the coordinate in the image coordinate system.

[0136] Coordinate transformation

[0137] Apply pixel calibration transformation matrix: Use the pixel calibration transformation matrix of the Up-look camera The chip center position P in the image coordinate system i C (x, y, 1) is converted to the coordinate P in the solid crystal head coordinate system i B (x′,y′,1).

[0138] Assume that the center coordinate of the chip in the image coordinate system is P i C (x,y,1), then its coordinate P in the solid crystal head coordinate system i B It can be calculated by the following formula:

[0139]

[0140] Right now:

[0141]

[0142] The calculation results are:

[0143] x′=Ax+Cy+T x

[0144] y′=Bx+Dy+T y

[0145] Angle calculation

[0146] Solving plane angles On the XOY plane of the die bonding head coordinate system, use the converted coordinate P i B (x′,y′,1) to solve the angle of the chip center relative to the origin

[0147] The angle ο can be calculated using the inverse tangent function (atan2):

[0148] ο

[0149] The atan2 function returns the angle from the positive X axis to the point (x′, y′)(x′, y′), ranging from -π to π. If you need to adjust the angle range to 0 to 2π, you can do the appropriate conversion:

[0150]

[0151] Step S3 rotates the wafer one by one and obtains the center position of the wafer at each rotation angle. Combined with the pixel calibration conversion matrix, the image coordinates are converted into coordinates in the die bonding head coordinate system. Finally, the angle of the wafer center relative to the origin of the die bonding head coordinate system at each rotation angle is calculated. This process provides basic data for the subsequent establishment and fitting of linear relationships, ensuring the accuracy and reliability of the rotation axis calibration.

[0152] Preferably; Step S4 linear relationship establishment and fitting: calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the solid crystal head coordinate system, and use the least squares method to fit the rotation angle coefficient and offset;

[0153] Calibrate the rotation axis coordinates And the XOY plane angle coordinates in the die bonding head coordinate system There is a linear relationship between them, and the following formula can be obtained:

[0154]

[0155] By a series of The least squares polynomial method η and b is used, where η is the rotation angle coefficient and b is the rotation angle offset.

[0156] It should be noted that step S4 determines the linear relationship between the rotation axis coordinates and the X0Y plane angle coordinates in the die bonding head coordinate system by assuming a linear relationship, collecting data, applying the least squares method to fit, and verifying the fitting effect, and solves the rotation angle coefficient and offset. This process provides a reliable mathematical basis for subsequent rotation compensation and ensures the accuracy and stability of the die bonding process.

[0157] Preferably, the sample points are fitted into a circle, and the center and radius are used to describe the center of rotation; assuming that the center of the circle is 0 (A, B) and the radius is R, the equation of the circle can be written as:

[0158] R 2 =(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] The sample set X collected by the camera i , Y i Substituting (i=1, 2, 3, ..., n) into the above formula, we get the following formula:

[0164]

[0165] Written in matrix form,

[0166]

[0167] That is, it satisfies the following format,

[0168] Ax=B

[0169] Solve using the least squares method to obtain the X matrix,

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

[0171] That is, if we get a, b, and c, we can find the radius and center of the circle:

[0172]

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

[0174] Preferably, step S5: compensation and re-detection; including wafer camera detection, using the wafer camera to detect the angle of the wafer adsorbed on the die bonding head; at this time, through step S4, the wafer angle θ′ detected by the wafer camera is converted into the actual coordinate of the rotation axis; the wafer angle detected by the wafer camera and the corresponding rotation axis encoder coordinate are recorded;

[0175] The wafer camera detects the angle θ′ of the wafer and converts it into the actual coordinates of the rotation axis through the coefficient;

[0176] θ=η·θ′+b.

[0177] Preferably; step S5: compensation and re-detection also includes calculating the compensation amount; the solid crystal head is sucked and lifted, and during this process, the rotation axis -θ needs to be rotated to align the wafer. Since the rotation center is inconsistent with the center of the solid crystal head nozzle, 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; use linear interpolation method to compensate, to the field of view, rotate from 0° to 360°, take an interval of 10°, set θ i ≤θ≤θ j The scaling factor is:

[0181]

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

[0183]

[0184] The chip center P'(x', y') after the offset is obtained as:

[0185]

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

[0187] Step S5: Compensation and re-detection also include actual compensation. According to the calculated compensation amount, the position of the die bonding head 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 detection equipment to ensure that its position is accurate.

[0188] In the scenario of a die bonder that requires high precision, the present invention uses the local coordinate system of the die bonder as a medium to calibrate and calculate the rotation coefficient and rotation center of the die bonder to prevent error diffusion. In the rotation calibration, not only a rotation model of the rotation axis is generated, but also linear interpolation is used to further improve the precision and reduce the impact of errors.

[0189] It should be noted that the above-mentioned technical features are further combined with each other to form various embodiments not listed above, which are all deemed to be within the scope of the present invention; and, for ordinary technicians in this field, they can be improved or transformed according to the above description, and all these improvements and transformations should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for calibrating a 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 nozzle center of the die bonding head with the center of the Up-look camera and the center of the Wafer camera respectively, and record the corresponding coordinates of the die bonding head; Step S2: Wafer center detection and coordinate recording After the die bonding head holds the wafer, it moves to the Up-look camera, detects the wafer center through machine vision, records the corresponding rotary axis encoder coordinates, and obtains the Up-look camera pixel calibration conversion matrix at the same time; Step S3: Wafer rotation and angle calculation The wafer is rotated to 360° in steps of 10°, and the image coordinates are converted to the die bonding head coordinate system using the pixel calibration transformation matrix to calculate the plane angle; Step S4: Linear relationship establishment and fitting Calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the die-bonding head coordinate system, and use the least squares method to fit the rotation angle coefficient and offset; Step S5: Compensation and re-detection The wafer angle is detected by the wafer camera, converted into the actual coordinates of the rotation axis according to the coefficient, and necessary compensation is performed considering the inconsistency between the rotation center and the nozzle center. The center of the wafer after rescanning and compensation should coincide with the original position, completing the rotation calibration.

2. A method for calibrating a rotation axis of a die bonding head according to claim 1, characterized in that: Step S2 Wafer center detection and coordinate recording: The wafer is sucked by the bonding head and moved to align with the Up-look camera. The wafer center is detected by machine vision. Record the corresponding rotary axis encoder coordinates Pixel calibration transformation matrix for up-look cameras for: A, B, C, and D are conversion coefficients used for linear transformation; T x ,T y is the translation parameter, which indicates the offset of the origin of the image coordinate system relative to the die-bonding head coordinate system.

3. According to the method for calibrating the rotation axis of a die bonding head as described in claim ****, it is characterized by: Step S3: Rotate the chip and calculate the angle: Rotate the chip to 360° in steps of 10°, and use the pixel-calibrated transformation matrix to convert the image coordinates to Convert to the corresponding coordinate system of the die bonding head because On the XOY plane of the die bonding head coordinate system, use Find Angle in XOY plane 4. A method for calibrating a rotation axis of a die bonding head according to claim 1, characterized in that: Step S4: Linear relationship establishment and fitting: calibrate the linear relationship between the rotation axis coordinates and the plane angle coordinates in the solid crystal head coordinate system, and use the least squares method to fit the rotation angle coefficient and the offset; Calibrate the rotation axis coordinates And the XOY plane angle coordinates in the die bonding head coordinate system There is a linear relationship between them, and the following formula can be obtained: By a series of The least squares polynomial method η and b is used, where η is the rotation angle coefficient and b is the rotation angle offset.

5. A method for calibrating a rotation axis of a die bonding head according to claim 4, characterized in that: Fit the sample points into a circle, and use the center and radius to describe the center of rotation; assuming the center of the circle is O(A, B) and the radius is R, the equation of the circle can be written as: R 2 =(x-A) 2 +(y-B) 2 =x 2 -2Ax+A 2 +y 2 -2By+B 2 Transform the above formula into: X 2 +Y 2 +aX+bY+c=0 in: a=-2A,b=-2B,c=A 2 +B 2 -R 2 The sample set X collected by the camera i , Y i Substituting (i=1, 2, 3, ..., n) into the above formula, we get the following formula: Written in matrix form, That is, it satisfies the following format, Ax=B Solve using the least squares method to obtain the x matrix, x=(A T A) -1 A T B That is, if we get a, b, and c, then the radius and center of the circle can be found: At this point, the rotation center O(A, B) and the angle coefficient η have been calculated.

6. A method for calibrating a rotation axis of a die bonding head according to claim 1, characterized in that: Step S5: compensation and re-detection; including wafer camera detection, using the wafer camera to detect the angle of the wafer adsorbed on the die bonding head; at this time, through step S4, the wafer angle θ′ detected by the wafer camera is converted into the actual coordinate of the rotation axis; the wafer angle detected by the wafer camera and the corresponding rotation axis encoder coordinate are recorded; The wafer camera detects the angle θ′ of the wafer and converts it into the actual coordinates of the rotation axis through the coefficient; θ=η·θ′+b.

7. A method for calibrating a rotation axis of a die bonding head according to claim 6, characterized in that: Step S5: Compensation and re-detection also include calculating the compensation amount; the die bonding head is sucked and lifted up. During this process, the rotation axis -θ needs to be rotated to align the wafer. Since the rotation center is inconsistent with the center of the die bonding head nozzle, the wafer center P(x, y) will be offset, and this offset needs to be compensated; the rotation matrix is:

8. A method for calibrating a rotation axis of a die bonding head according to claim 6, characterized in that: Step S5: Compensation and re-detection also include linear interpolation compensation; use the linear interpolation method to compensate, within the field of view, rotate from 0° to 360°, take an interval of 10°, and set θ i ≤θ<θ j , the scaling factor is: Integrate the linear interpolation compensation into the rotation matrix: The chip center P'(x', y') after the offset is obtained as: After the compensation of the movement of the die bonding head is ΔP=P′-P, the center of the wafer coincides with the original one, and the whole process is completed.

9. A method for calibrating a rotation axis of a die bonding head according to any one of claims 1, 6, 7 and 8, characterized in that: Step S5: compensation and re-detection also includes actual compensation, and adjusting the position of the die bonding head according to the calculated compensation amount 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.

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