A method for improving the die bonding yield of a COB package of small-pitch LEDs and a packaging system

Abstract

The application relates to the technical field of semiconductor light-emitting diode packaging, in particular to a COB packaging die bonding yield improvement method and packaging system for small-pitch LED, which comprises the following steps: S1, substrate pretreatment and deformation compensation, obtaining a PCB substrate to be packaged, S2, partition pre-bonding and in-situ detection, S3, laser-assisted in-situ repair, and S4, overall eutectic solidification. The application obtains PCB substrate warping distribution data through three-dimensional topography scanning, and generates a six-axis motion compensation track of a die bonding head, can compensate the two-dimensional deviation and three-dimensional height deviation of the substrate in real time, significantly improves the die bonding position precision of LED chips under small-pitch conditions, avoids batch deviation defects caused by substrate warping, simultaneously, a glass temporary carrier is introduced to assist in shaping, and the initial warping of the substrate is physically corrected, which not only has the low-cost advantage of the existing PCB industry chain, but also obtains high flatness close to the glass substrate, and provides a feasible engineering path for ultra-micro-pitch COB packaging.

Description

Technical Field

[0001] This invention relates to the field of semiconductor light-emitting diode packaging technology, specifically to a method and packaging system for improving die-bonding yield in COB packaging of small-pitch LEDs. Background Technology

[0002] In fine-pitch LED display technology, when the pixel pitch is reduced to below P1.0, COB packaging technology is widely used. This packaging structure involves directly transferring and soldering multiple micron-sized LED chips onto predetermined electrodes on a PCB substrate using a die-bonding process. Subsequently, a protective adhesive layer is applied to the entire assembly, forming a seamless and continuous light-emitting module. Its working principle is that the chips and substrate are electrically interconnected and mechanically fixed through a metal eutectic layer or conductive adhesive layer, and an external driver IC controls the brightness and grayscale of each chip.

[0003] In the aforementioned COB packaging, the die bonding process is a critical step: the die bonding equipment's nozzle picks up the LED chip, positions the substrate pads using a vision system, and places the chip onto the pads with specific pressure and temperature, completing pre-fixation or direct soldering. As display technology advances towards ultra-high definition, pixel pitch is compressed to below P0.9 or even P0.4, and chip size is simultaneously shrinking to below 50 micrometers. Under this miniaturization trend, traditional COB die bonding processes have the following problems: During conventional PCB substrate manufacturing, inherent warping occurs due to thermal stress and material shrinkage, with warping amplitude reaching 0.5%~1% of the substrate diagonal length. However, the positional accuracy requirement for small-pitch pads is within ±10 micrometers. This warping leads to… When the die bonding head moves along a preset planar trajectory, the actual landing point of the chip will have a two-dimensional planar offset and a three-dimensional height deviation. The die bonding process adopts open-loop control, and inspection is only carried out after batch placement. When a chip with excessive offset is found, the subsequent eutectic curing has already formed a permanent solder joint. Removing the offset chip can easily damage the surrounding normal chips and circuits, resulting in high repair costs or even scrapping the entire module. The above-mentioned insufficient accuracy and difficulty in repair combined mean that when the chip is smaller than 3mil and the pitch is smaller than P1.2, the first-pass yield of traditional COB die bonding is less than 85%, which seriously restricts the mass production of ultra-small pitch COB modules. To this end, this invention proposes a method and packaging system for improving the die bonding yield of small pitch LED COB packaging. Summary of the Invention

[0004] In view of this, the present invention provides a method and packaging system for improving die bonding yield of COB packaging for small-pitch LEDs, so as to solve or alleviate the technical problems existing in the prior art, and at least provide a beneficial option.

[0005] The technical solution of this invention is implemented as follows: A method for improving die-bonding yield of COB packaging for small-pitch LEDs, comprising the following steps:

[0006] S1: Substrate preprocessing and deformation compensation: Obtain the PCB substrate to be packaged, obtain the warpage distribution data of the PCB substrate through three-dimensional topography scanning, and generate the six-axis motion compensation trajectory of the die bonder based on the warpage distribution data.

[0007] S2: Partition pre-bonding and in-situ detection: The PCB substrate is divided into multiple die bonding partitions. In each die bonding partition, multiple LED chips are pre-bonded to the PCB substrate in sequence according to the motion compensation trajectory using the die bonding head. After the pre-bonding of each die bonding partition is completed, optical in-situ detection is performed on all LED chips in the partition to identify abnormal chips whose position offset exceeds the first threshold.

[0008] S3: Laser-assisted in-situ repair. For the abnormal chip, the pre-bonding material under the abnormal chip is softened by laser heating, and the abnormal chip is removed by applying a lifting force in a direction perpendicular to the substrate using a vacuum nozzle. Then, a new LED chip is placed in the same position.

[0009] S4: Overall eutectic curing. After pre-bonding and repair of all die bonding zones, the PCB substrate is heated and pressurized as a whole to simultaneously complete eutectic bonding of all LED chips, forming a COB package.

[0010] More preferably, in step S1, the six-axis motion compensation trajectory includes: position compensation in the X-axis and Y-axis directions parallel to the substrate plane, height compensation in the Z-axis direction perpendicular to the substrate plane, and rotation angle compensation around the X-axis, Y-axis, and Z-axis; the height compensation is calculated in real time based on the difference between the actual height of each point in the warp distribution data and the reference height.

[0011] More preferably, in step S2, the pre-bonding temperature is 150°C-200°C lower than the eutectic bonding temperature, and the pressure is 30%-50% of the eutectic bonding pressure, so that the LED chip is temporarily fixed on the PCB substrate and can be removed by the vacuum nozzle in step S3.

[0012] More preferably, in step S2, the optical in-situ detection employs a sub-pixel-level image processing algorithm to extract the deviation value between the actual center coordinates and the theoretical center coordinates of each LED chip, and generates a marker map of the abnormal chip based on the deviation value.

[0013] Further preferably, it also includes a glass temporary carrier plate auxiliary shaping step, which is located before S1: a glass temporary carrier plate with a flatness better than the PCB substrate is provided, and the PCB substrate is adsorbed and attached to the glass temporary carrier plate to physically correct the initial warpage of the PCB substrate; the warpage distribution data in S1 is obtained in this corrected state.

[0014] More preferably, a pyrolytic adhesive layer is provided between the glass temporary carrier and the PCB substrate. After the overall eutectic curing of S4 is completed, the glass temporary carrier is separated by heating to the dissociation temperature of the pyrolytic adhesive layer.

[0015] This invention provides a system for improving die-bonding yield in COB packaging of small-pitch LEDs, comprising:

[0016] A 3D appearance scanning module is used to acquire warpage distribution data of the PCB substrate;

[0017] The motion operation module, connected to the three-dimensional appearance scanning module, is used to generate and output the six-axis motion compensation trajectory of the die bonder based on the warp distribution data.

[0018] The die bonding head module has a six-axis micro-motion mechanism for pre-bonding the LED chip to the PCB substrate according to the motion compensation trajectory;

[0019] The partitioned optical inspection module is used to perform optical in-situ inspection on all LED chips in each die-bonding partition after pre-bonding is completed, and to identify abnormal chips.

[0020] The laser repair module includes a laser heating unit and a vacuum nozzle unit, used to heat and soften the pre-bonding material under the abnormal chip and remove the abnormal chip;

[0021] The eutectic curing chamber is used to heat and pressurize the PCB substrate as a whole to achieve eutectic bonding after pre-bonding and repair of all die bonding zones.

[0022] More preferably, the partitioned optical detection module includes a high-resolution line scan camera and an image processing unit. The image processing unit is configured to run a sub-pixel-level edge detection algorithm, calculate the center offset of each LED chip, and mark the coordinates of chips with offsets exceeding a first threshold to the laser repair module.

[0023] More preferably, the six-axis micro-motion mechanism of the die-bonding head module includes: an XY-axis voice coil motor, a Z-axis piezoelectric ceramic actuator, and a micro-motion universal joint for rotation angle compensation; the response frequency of the Z-axis piezoelectric ceramic actuator is not less than 1kHz.

[0024] A further preferred embodiment includes a substrate fixing stage, with a partitioned vacuum structure provided below the substrate fixing stage, used to apply differentiated adsorption forces to different areas of the PCB substrate during the overall eutectic curing of the PCB substrate, so as to suppress thermal deformation during the eutectic process.

[0025] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions:

[0026] I. This invention obtains PCB substrate warpage distribution data through three-dimensional topography scanning and generates a six-axis motion compensation trajectory for the die bonder. It can compensate for the two-dimensional offset and three-dimensional height deviation of the substrate in real time, significantly improve the die bonder position accuracy of LED chips under small pitch conditions, and avoid batch offset defects caused by substrate warpage.

[0027] II. This invention adopts a closed-loop control strategy of "partition pre-bonding + in-situ detection + laser-assisted in-situ repair": First, the chip is temporarily fixed by low-temperature and low-pressure pre-bonding. After each partition is completed, optical detection is performed to identify abnormal chips with excessive deviation. Then, the pre-bonding material is softened by laser heating and removed non-destructively by vacuum nozzle. Then, a new chip is placed. This process is completed before eutectic curing, avoiding the problem of damage to surrounding circuits caused by removing the chip after permanent soldering in traditional processes. This significantly reduces maintenance costs and module scrap rate, and improves the die bonding yield to over 95% when the chip size is less than 3mil and the pitch is less than P1.2.

[0028] Third, this invention introduces a glass temporary carrier to assist in shaping, physically correcting the initial warpage of the substrate. It not only retains the low-cost advantages of the existing PCB industry chain, but also achieves high flatness close to that of a glass substrate, providing a feasible engineering path for ultra-fine pitch COB packaging. At the same time, the various modules of the system work together to achieve fully automated closed-loop control, making it suitable for large-scale industrial production.

[0029] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating the steps of a method for improving die-bonding yield in COB packaging of small-pitch LEDs according to an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the module structure of the COB packaging die-bonding yield improvement system for small-pitch LEDs according to an embodiment of the present invention. Detailed Implementation

[0033] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] like Figure 1 As shown, this embodiment of the invention provides a method for improving die-bonding yield in COB packaging of small-pitch LEDs, including the following steps:

[0036] S1: Substrate preprocessing and deformation compensation: Obtain the PCB substrate to be packaged, acquire the warpage distribution data of the PCB substrate through three-dimensional topography scanning, and generate the six-axis motion compensation trajectory of the die bonder based on the warpage distribution data.

[0037] S2: Partition pre-bonding and in-situ detection. The PCB substrate is divided into multiple die-bonding partitions. In each die-bonding partition, multiple LED chips are pre-bonded to the PCB substrate sequentially using the die-bonding head according to the motion compensation trajectory. After the pre-bonding of each die-bonding partition is completed, optical in-situ detection is performed on all LED chips in the partition to identify abnormal chips whose position offset exceeds the first threshold.

[0038] S3: Laser-assisted in-situ repair. For the abnormal chip, the pre-bonding material under the abnormal chip is softened by laser heating, and the abnormal chip is removed by applying a lifting force in a direction perpendicular to the substrate using a vacuum nozzle. Then, a new LED chip is placed in the same position.

[0039] S4: Overall eutectic curing. After pre-bonding and repair of all die bonding zones, the PCB substrate is heated and pressurized as a whole to simultaneously complete eutectic bonding of all LED chips, forming a COB package.

[0040] In one embodiment, in step S1, the six-axis motion compensation trajectory includes: position compensation in the X-axis and Y-axis directions parallel to the substrate plane, height compensation in the Z-axis direction perpendicular to the substrate plane, and rotation angle compensation around the X-axis, Y-axis, and Z-axis; the height compensation is calculated in real time based on the difference between the actual height of each point in the warp distribution data and the reference height; for example, when the three-dimensional topography scan measures a protrusion height of +30 micrometers in a certain area of ​​the substrate, the Z-axis motion trajectory of the die bonder in that area is automatically shortened by 30 micrometers, so that the chip just contacts the pad surface without overvoltage or poor soldering.

[0041] In one embodiment, in step S2, the pre-bonding temperature is 150°C-200°C lower than the eutectic bonding temperature, and the pressure is 30%-50% of the eutectic bonding pressure, so that the LED chip is temporarily fixed on the PCB substrate and can be removed by the vacuum nozzle in step S3; taking gold-tin eutectic bonding (eutectic temperature about 280°C) as an example, the pre-bonding temperature is selected as 160°C-180°C, and the pressure is selected as 40% of the original eutectic pressure. At this time, a brittle and peelable intermetallic compound layer is formed between the chip and the pad, which can resist slight vibration and does not hinder subsequent laser removal.

[0042] In one embodiment, in step S2, the optical in-situ detection employs a sub-pixel-level image processing algorithm to extract the deviation between the actual center coordinates and the theoretical center coordinates of each LED chip, and generates a marker map of the abnormal chip based on the deviation value. Specifically, a sub-pixel edge positioning method based on grayscale gradient is adopted to improve the pixel-level accuracy to below 0.1 pixels, corresponding to an actual physical accuracy of ±1 micrometer, which is far higher than the tolerance requirement of ±10 micrometers for small-pitch pads.

[0043] In one embodiment, a glass temporary carrier plate auxiliary shaping step is further included, which is located before S1: a glass temporary carrier plate with a flatness better than the PCB substrate is provided, and the PCB substrate is adsorbed and attached to the glass temporary carrier plate to physically correct the initial warpage of the PCB substrate; the warpage distribution data in S1 is obtained in this corrected state; preferably, the flatness of the glass temporary carrier plate is better than ±5 micrometers / meter, and the warpage amplitude can be reduced from 0.5%~1% to below 0.05% through vacuum adsorption holes.

[0044] In one embodiment, a pyrolytic adhesive layer is provided between the glass temporary carrier and the PCB substrate. After the overall eutectic curing in step S4 is completed, the glass temporary carrier is separated by heating to the dissociation temperature of the pyrolytic adhesive layer. The pyrolytic adhesive layer can be made of acrylic pyrolytic adhesive tape, which maintains strong adhesion below 150°C and its adhesion drops sharply to zero above 180°C, thus automatically losing adhesion after eutectic curing (approximately 250°C-300°C), achieving non-destructive separation.

[0045] like Figure 2 As shown, this embodiment of the invention provides a COB packaging die-bonding yield improvement system for small-pitch LEDs, comprising:

[0046] A 3D appearance scanning module is used to acquire warpage distribution data of the PCB substrate. This module can employ laser triangulation or structured light 3D scanners, with a resolution better than ±5 micrometers.

[0047] The motion operation module, connected to the three-dimensional appearance scanning module, is used to generate and output the six-axis motion compensation trajectory of the die bonding head based on the warp distribution data. This module has a built-in trajectory interpolator, which can discretize the continuous warped surface into coordinate compensation values ​​of the die bonding path points.

[0048] The die bonding head module has a six-axis micro-motion mechanism for pre-bonding the LED chip onto the PCB substrate according to the motion compensation trajectory.

[0049] The partitioned optical inspection module is used to perform optical in-situ inspection on all LED chips in each die-bonding partition after pre-bonding is completed, and to identify abnormal chips.

[0050] The laser repair module includes a laser heating unit and a vacuum nozzle unit, used to heat and soften the pre-bonded material beneath the defective chip and remove the defective chip.

[0051] The eutectic curing chamber is used to heat and pressurize the PCB substrate as a whole to achieve eutectic bonding after pre-bonding and repair of all die bonding zones.

[0052] In one embodiment, the partitioned optical detection module includes a high-resolution line scan camera and an image processing unit. The image processing unit is configured to run a sub-pixel-level edge detection algorithm, calculate the center offset of each LED chip, and mark the coordinates of chips with offsets exceeding a first threshold to the laser repair module. The resolution of the line scan camera is not less than 16k pixels, and with the telecentric lens, the physical size of a single pixel can reach 1.5 micrometers.

[0053] In one embodiment, the six-axis micro-motion mechanism of the die-bonding head module includes: an XY-axis voice coil motor, a Z-axis piezoelectric ceramic actuator, and a micro-motion universal joint for rotation angle compensation; the response frequency of the Z-axis piezoelectric ceramic actuator is not less than 1kHz; the voice coil motor provides millimeter-level stroke and submicron-level resolution, and the piezoelectric ceramic actuator achieves micron-level high-speed height compensation with a response delay of less than 0.5 milliseconds, enabling it to follow changes in warped surfaces in real time.

[0054] In one embodiment, a substrate fixing stage is further included, with a partitioned vacuum structure provided below the substrate fixing stage. This structure is used to apply differentiated adsorption forces to different areas of the PCB substrate during the overall eutectic curing of the PCB substrate, so as to suppress thermal deformation during the eutectic process. For example, a higher adsorption force is applied to the edge area of ​​the substrate, and a lower adsorption force is applied to the center area to compensate for the warping tendency caused by the difference in the coefficient of thermal expansion.

[0055] When this invention is in operation:

[0056] First, the operator or automated feeding device places the PCB substrate to be packaged onto a temporary glass carrier. Vacuum adsorption physically straightens the substrate to a flat state. A 3D appearance scanning module scans the straightened substrate, acquiring precise warp distribution data and transmitting it to the motion control module.

[0057] The motion operation module generates a six-axis motion compensation trajectory for the die bonder based on the warpage data. Subsequently, the die bonder module follows this trajectory and uses low temperature and low pressure (e.g., 160℃, eutectic pressure 40%) to pre-bond the LED chips sequentially to the pads of each die bonder partition. After each partition is pre-bonded, the partition optical detection module immediately performs sub-pixel level image acquisition and offset calculation for that partition, identifying abnormal chips whose positional offset exceeds the first threshold.

[0058] If an abnormal chip is detected, the laser repair module is activated: the laser heating unit locally heats the area below the abnormal chip to the softening temperature of the pre-bonding material (approximately 200℃-250℃), the vacuum nozzle vertically lifts and removes the chip, and the die bonding head immediately places a new chip at the same coordinate. After all abnormal chips in this zone are repaired, the system automatically enters the pre-bonding-detection-repair cycle of the next zone.

[0059] After all partitions have been pre-bonded and repaired, the PCB substrate carrying all the LED chips is sent into the eutectic curing chamber. The chamber is heated and pressurized as a whole according to the preset temperature rise curve. At the same time, the partition vacuum structure of the substrate fixing stage applies differentiated adsorption force to suppress thermal deformation. After the eutectic bonding is completed, the chamber is cooled down, the pyrolysis adhesive layer automatically loses adhesion at high temperature, the glass temporary carrier separates from the COB package, and finally a COB display module with high die bonding yield is obtained.

[0060] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for improving die-bonding yield in COB packaging of small-pitch LEDs, characterized in that, Includes the following steps: S1: Substrate preprocessing and deformation compensation: Obtain the PCB substrate to be packaged, obtain the warpage distribution data of the PCB substrate through three-dimensional topography scanning, and generate the six-axis motion compensation trajectory of the die bonder based on the warpage distribution data. S2: Partition pre-bonding and in-situ detection: The PCB substrate is divided into multiple die bonding partitions. In each die bonding partition, multiple LED chips are pre-bonded to the PCB substrate in sequence according to the motion compensation trajectory using the die bonding head. After the pre-bonding of each die bonding partition is completed, optical in-situ detection is performed on all LED chips in the partition to identify abnormal chips whose position offset exceeds the first threshold. S3: Laser-assisted in-situ repair. For the abnormal chip, the pre-bonding material under the abnormal chip is softened by laser heating, and the abnormal chip is removed by applying a lifting force in a direction perpendicular to the substrate using a vacuum nozzle. Then, a new LED chip is placed in the same position. S4: Overall eutectic curing. After pre-bonding and repair of all die bonding zones, the PCB substrate is heated and pressurized as a whole to simultaneously complete eutectic bonding of all LED chips, forming a COB package.

2. The method for improving die-bonding yield of COB packaging for small-pitch LEDs according to claim 1, characterized in that, In S1, the six-axis motion compensation trajectory includes: position compensation in the X-axis and Y-axis directions parallel to the substrate plane, height compensation in the Z-axis direction perpendicular to the substrate plane, and rotation angle compensation around the X-axis, Y-axis, and Z-axis; the height compensation is calculated in real time based on the difference between the actual height of each point in the warp distribution data and the reference height.

3. The method for improving die-bonding yield of COB packaging for small-pitch LEDs according to claim 1, characterized in that, In step S2, the pre-bonding temperature is 150°C-200°C lower than the eutectic bonding temperature, and the pressure is 30%-50% of the eutectic bonding pressure, so that the LED chip is temporarily fixed on the PCB substrate and can be removed by the vacuum nozzle in step S3.

4. The method for improving die-bonding yield of COB packaging for small-pitch LEDs according to claim 1, characterized in that, In step S2, the optical in-situ detection employs a sub-pixel-level image processing algorithm to extract the deviation between the actual center coordinates and the theoretical center coordinates of each LED chip, and generates a marker map of the abnormal chip based on the deviation value.

5. The method for improving die-bonding yield of COB packaging for small-pitch LEDs according to claim 1, characterized in that, It also includes a glass temporary carrier plate auxiliary shaping step, which is located before S1: a glass temporary carrier plate with a flatness better than the PCB substrate is provided, and the PCB substrate is adsorbed and attached to the glass temporary carrier plate to physically correct the initial warpage of the PCB substrate; the warpage distribution data in S1 is obtained in this corrected state.

6. The method for improving die-bonding yield of COB packaging for small-pitch LEDs according to claim 5, characterized in that, A pyrolytic adhesive layer is provided between the glass temporary carrier and the PCB substrate. After the S4 overall eutectic curing is completed, the glass temporary carrier is separated by heating to the dissociation temperature of the pyrolytic adhesive layer.

7. A COB packaging die-bonding yield improvement system for small-pitch LEDs, used to perform the method according to any one of claims 1 to 6, characterized in that, include: A 3D appearance scanning module is used to acquire warpage distribution data of the PCB substrate; The motion operation module, connected to the three-dimensional appearance scanning module, is used to generate and output the six-axis motion compensation trajectory of the die bonder based on the warp distribution data. The die bonding head module has a six-axis micro-motion mechanism for pre-bonding the LED chip to the PCB substrate according to the motion compensation trajectory; The partitioned optical inspection module is used to perform optical in-situ inspection on all LED chips in each die-bonding partition after pre-bonding is completed, and to identify abnormal chips. The laser repair module includes a laser heating unit and a vacuum nozzle unit, used to heat and soften the pre-bonding material under the abnormal chip and remove the abnormal chip; The eutectic curing chamber is used to heat and pressurize the PCB substrate as a whole to achieve eutectic bonding after pre-bonding and repair of all die bonding zones.

8. The COB packaging die-bonding yield improvement system for small-pitch LEDs according to claim 7, characterized in that, The partitioned optical detection module includes a high-resolution line scan camera and an image processing unit. The image processing unit is configured to run a sub-pixel-level edge detection algorithm, calculate the center offset of each LED chip, and mark the coordinates of chips with offsets exceeding a first threshold to the laser repair module.

9. The COB packaging die-bonding yield improvement system for small-pitch LEDs according to claim 7, characterized in that, The six-axis micro-motion mechanism of the die bonding head module includes: an XY-axis voice coil motor, a Z-axis piezoelectric ceramic actuator, and a micro-motion universal joint for rotation angle compensation; the response frequency of the Z-axis piezoelectric ceramic actuator is not less than 1kHz.

10. The COB packaging die-bonding yield improvement system for small-pitch LEDs according to claim 7, characterized in that, It also includes a substrate fixing stage, under which a partitioned vacuum structure is provided, which is used to apply differentiated adsorption forces to different areas of the PCB substrate during the overall eutectic curing of the PCB substrate, so as to suppress thermal deformation during the eutectic process.

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