Method for carrying out mass transfer by utilizing blue membrane expansion

Abstract

The invention discloses a method for carrying out mass transfer by utilizing blue film expansion, and relates to the technical field of mass transfer, and the method comprises the following steps: loading equidistantly distributed chip blue films to a blue film expansion mechanism, and carrying out blue film expansion according to the difference of thermal expansion coefficients; transferring the chip to a preset carrier by adopting a reverse mold process, wherein a PDMS transfer film is attached to the surface of the chip; a reference point of a preset carrier is acquired through a CCD image sensor, a coordinate offset is calculated based on an SURF feature matching algorithm, and a piezoelectric micro-motion platform is driven to implement sub-pixel compensation; in the vacuum cavity, pressure is applied in stages through a three-stage pressure cylinder component; a pulse laser is adopted for chip welding, and single-time transfer is completed; the steps are repeatedly executed to complete mass transfer of the RGB chips, and the position deviation of the chips is detected through the laser interferometer after each time of transfer. By adopting the method, the mass transfer quality of mass transfer by utilizing blue film expansion can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of mass transfer, and in particular to a method for mass transfer using blue film expansion. Background Art

[0002] With the rapid development of Micro LED display technology, mass transfer technology has become a key bottleneck restricting its industrialization. Micro LED chips are tiny (typically less than 50μm), requiring the high-precision transfer of millions or even tens of millions of chips onto target substrates. This places extremely high demands on the accuracy, efficiency, and yield of the transfer process. Currently, the display industry is upgrading from traditional LCD and OLED to Micro LED technology, but the shortcomings of mass transfer technology have severely constrained the mass production progress and cost control of Micro LED.

[0003] Existing mass transfer technologies primarily include pick-and-place, laser transfer, and stamp transfer. Among these, transfer technology based on blue film expansion has attracted considerable attention due to its ability to process chips in batches. This technology adjusts the chip spacing on a blue film through mechanical or thermal expansion, then transfers the chips to the target substrate via a transfer film. However, in practical applications, issues such as precise control of chip spacing, positioning accuracy during the transfer process, and repeated alignment of multi-color chips remain unresolved, resulting in transfer yields and efficiency that are difficult to meet mass production requirements.

[0004] However, traditional blue film expansion technology has three major defects: first, imprecise thermal expansion control leads to large errors in chip spacing adjustment; second, unstable transfer film performance causes chips to fall off or shift in position during transfer; third, there is a lack of an effective multi-level precision compensation mechanism, making it difficult to achieve nano-level alignment of RGB chips. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention aims to provide a mass transfer method of Micro LED chips, aiming to improve the mass transfer quality of mass transfer using blue film expansion.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for mass transfer using blue film expansion, comprising:

[0008] The blue film of the chips with equal spacing is loaded onto the blue film expansion mechanism, and the expansion ratio is adjusted by the thermal expansion coefficient difference compensation mechanism to make the chip spacing match the point spacing of the target pads;

[0009] The chip is transferred to a pre-set carrier using a reverse molding process, the surface of which is affixed with a 50-100 μm thick PDMS transfer film;

[0010] The reference points of the preset vehicle are collected by a CCD image sensor, the coordinate offset is calculated based on the SURF feature matching algorithm, and the piezoelectric micro-motion platform is driven to implement sub-pixel compensation;

[0011] In a vacuum chamber with a vacuum degree of ≤10-3Pa, pressure is applied in stages through a three-stage booster cylinder assembly;

[0012] Using a pulsed laser, chip welding is performed under process parameters of a spot diameter of 10-15 μm, a pulse frequency of 100-200 kHz, and an overlap rate of 30-50% to complete a single transfer;

[0013] Repeat the above steps to complete the mass transfer of three-color RGB chips, and use a laser interferometer to detect chip position deviation after each transfer.

[0014] According to one aspect of the above technical solution, the step of adjusting the expansion ratio by using a thermal expansion coefficient difference compensation mechanism includes:

[0015] Controlling the temperature change of different material layers in the blue film expansion mechanism to generate deformation by utilizing the difference in thermal expansion coefficient;

[0016] Monitor the chip spacing changes in real time and dynamically adjust the temperature compensation through the PID control algorithm;

[0017] When the error between the chip spacing and the target pad spacing is ≤±2μm, the current temperature parameter is locked.

[0018] According to one aspect of the above technical solution, the step of transferring the chip to a predetermined carrier using a reverse molding process includes:

[0019] Align the chip blue film with the preset carrier and apply a uniform pressure of 0.1MPa-0.3MPa;

[0020] The PDMS transfer film is irradiated with ultraviolet light to change its viscosity, thereby achieving chip selective transfer;

[0021] After the transfer is completed, the chip blue film and the preset carrier are gradually separated at a speed of 0.05 mm / s-0.1 mm / s.

[0022] According to one aspect of the above technical solution, the preset carrier is a borosilicate glass carrier.

[0023] According to one aspect of the above technical solution, the step of calculating the coordinate offset based on the SURF feature matching algorithm includes:

[0024] Five reference marking points are set at the four corners and the center area of ​​the preset vehicle;

[0025] Extracting SURF feature descriptors of each of the reference markers and establishing a feature matching model;

[0026] The sub-pixel offset is calculated using a Gaussian fitting interpolation algorithm, with a fitting error of ≤0.02 pixels.

[0027] According to one aspect of the above technical solution, the step of applying pressure in stages through the three-stage booster cylinder group includes:

[0028] During the initial contact phase, maintain a pressure of 0.05MPa-0.1MPa for 3 seconds to make contact between the chip and the pad;

[0029] During the main pressing stage, the pressure is increased at a rate of 0.1MPa / s-0.2MPa / s, and the pressure change curve is monitored at the same time;

[0030] When the pressure reaches 0.5MPa-1.2MPa, it enters the pressure holding stage and maintains the pressure fluctuation ≤±5%.

[0031] According to one aspect of the above technical solution, the steps of using a pulsed laser to perform chip welding include:

[0032] Automatically adjust the laser spot diameter according to the chip size so that the spot diameter covers 80-120% of the pad area;

[0033] Welding is performed using a spiral scanning path with a scanning pitch of 30-50% of the spot diameter;

[0034] The reflection intensity of the welding area is monitored in real time, and the laser power of the pulse laser is dynamically adjusted according to the reflection intensity.

[0035] According to one aspect of the above technical solution, the steps of repeatedly performing the above steps to complete the mass transfer of three-color RGB chips include:

[0036] When transferring the red chip for the first time, a position deviation of ±3μm is allowed;

[0037] When transferring the green chip for the second time, compensation is performed based on the previous transfer result to control the deviation within ±1.5μm;

[0038] When the blue chip was transferred for the third time, the deviation was reduced to ±0.8 μm in combination with the pre-determined compensation data.

[0039] Compared with the prior art, the method of using blue film expansion to perform mass transfer as shown in the present invention has the following beneficial effects:

[0040] In the present invention, blue films of chips with equal spacing are loaded onto a blue film expansion mechanism, and the expansion ratio is adjusted through a thermal expansion coefficient difference compensation mechanism to match the chip spacing with the point spacing of the target pads; a reverse molding process is used to transfer the chips to a preset carrier, and a 50-100μm thick PDMS transfer film is attached to the surface of the preset carrier; the reference points of the preset carrier are collected by a CCD image sensor, the coordinate offset is calculated based on the SURF feature matching algorithm, and the piezoelectric micro-motion platform is driven to implement sub-pixel compensation; in a vacuum chamber with a vacuum degree of ≤10-3Pa, pressure is applied in stages through a three-stage booster cylinder assembly; a pulsed laser is used to perform chip welding under process parameters of a spot diameter of 10-15μm, a pulse frequency of 100-200kHz, and an overlap rate of 30-50% to complete a single transfer; the above steps are repeated to complete the mass transfer of three-color RGB chips, and the chip position deviation is detected by a laser interferometer after each transfer. This invention utilizes a unique heterogeneous material stacking structure combined with an intelligent temperature control system to significantly improve the accuracy of chip spacing adjustment, effectively resolving the positioning deviation problem caused by thermal expansion differences in traditional methods. Furthermore, an optimized plasma surface treatment process significantly enhances the performance of the transfer film, significantly improving the chip transfer success rate while avoiding the environmental pollution risks associated with traditional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0042] Figure 1 FIG. 1 is a flow chart of a method for performing mass transfer using blue film expansion according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] To make the objectives, features, and advantages of the present invention more readily apparent, the following detailed description of specific embodiments of the present invention is provided in conjunction with the accompanying drawings. The accompanying drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] Example 1

[0046] See also Figure 1 The first embodiment of the present invention provides a method for mass transfer using blue film expansion, the method comprising steps S10 to S50:

[0047] In step S10 , the blue film of the chips distributed evenly is loaded onto the blue film expansion mechanism, and the expansion ratio is adjusted by the thermal expansion coefficient difference compensation mechanism to make the chip spacing match the point spacing of the target pads.

[0048] In this embodiment, the step of adjusting the expansion ratio by using the thermal expansion coefficient difference compensation mechanism includes:

[0049] Controlling the temperature change of different material layers in the blue film expansion mechanism to generate deformation by utilizing the difference in thermal expansion coefficient;

[0050] Monitor the chip spacing changes in real time and dynamically adjust the temperature compensation through the PID control algorithm;

[0051] When the error between the chip spacing and the target pad spacing is ≤±2μm, the current temperature parameter is locked.

[0052] Specifically, a blue film with equidistantly distributed Micro LED chips is taken, where the chip spacing is 100μm, and then loaded onto the blue film expansion mechanism. The blue film expansion mechanism is composed of alternating layers of SUS304 stainless steel and Invar alloy. The SUS304 stainless steel layer is 0.5mm thick and has a thermal expansion coefficient of 17.3×10 -6 / K, the thickness of the Invar alloy layer is 1.2 mm, and the thermal expansion coefficient is 1.5×10 -6 / K. The PID temperature control system is then activated, heating the SUS304 stainless steel layer to 85°C while the Invar layer remains at 25°C. This creates differential thermal expansion and deformation between adjacent layers. A laser displacement sensor is then used for real-time monitoring, locking the temperature parameters when the chip pitch reaches the target value of 150μm ± 2μm.

[0053] More specifically, the blue film expansion mechanism is an alternating stacking structure of 5 layers of SUS304 stainless steel layers and 4 layers of Invar alloy layers, where the single layer thickness of the SUS304 stainless steel layer is 0.5 mm, and the single layer thickness of the Invar alloy layer is 1.2 mm. A temperature sensor is embedded between the SUS304 stainless steel layer and the Invar alloy layer, with a total of 9 temperature measuring points. The control system adopts a three-loop PID algorithm with a proportional coefficient Kp = 1.2, an integral time Ti = 8 s, and a differential time Td = 2 s.

[0054] The operation process of using the blue film expansion mechanism to expand the chip blue film by a multiple of the thermal expansion coefficient includes:

[0055] (1) The cut blue film (initial chip spacing 100±1μm) is fixed on the surface of the expansion mechanism by vacuum adsorption, with an adsorption pressure of -65kPa.

[0056] (2) Start the step-by-step heating program:

[0057] Stage 1: 30°C → 60°C (heating rate 5°C / min, duration 6 minutes);

[0058] The second stage: 60°C → 85°C (heating rate 2°C / min, duration 12.5 minutes).

[0059] In this embodiment, a heterogeneous material stacking structure of a SUS304 stainless steel layer and an Invar alloy layer is combined with a closed-loop PID temperature control system to achieve high-precision compensation for thermal expansion differences, solving the adjustment error problem caused by the single thermal expansion coefficient of the material in the traditional method.

[0060] In step S20 , the chip is transferred to a predetermined carrier by using a mold-reversing process. A PDMS transfer film with a thickness of 50-100 μm is attached to the surface of the predetermined carrier.

[0061] In this embodiment, the steps of transferring the chip to a predetermined carrier using a reverse molding process include:

[0062] Align the chip blue film with the preset carrier and apply a uniform pressure of 0.1MPa-0.3MPa;

[0063] The PDMS transfer film is irradiated with ultraviolet light to change its viscosity, thereby achieving chip selective transfer;

[0064] After the transfer is completed, the chip blue film and the preset carrier are gradually separated at a speed of 0.05 mm / s-0.1 mm / s.

[0065] Specifically, the preset carrier is a borosilicate glass carrier with a thickness of 1 mm. The borosilicate glass carrier is aligned and bonded to the chip blue film, and the PDMS transfer film on the surface of the borosilicate glass carrier is plasma treated. After 80W plasma treatment for 45 seconds, a uniform pressure of 0.2 MPa is applied, and then ultraviolet light with a wavelength of 365 nm is used for 30 seconds to reduce the viscosity of the PDMS transfer film. The chip blue film is separated at a speed of 0.08 mm / s to achieve chip selective transfer.

[0066] More specifically, the PDMS transfer film was mixed with the substrate and the curing agent in a ratio of 10:1. When the PDMS transfer film was spin-coated onto the surface of a borosilicate glass carrier, a staged spin-coating method was adopted, wherein the spin-coating parameters of the first stage were 500 rpm / 10 s, and the spin-coating parameters of the second stage were 2000 rpm / 30 s, ultimately making the thickness of the PDMS transfer film 80±5 μm.

[0067] When the PDMS transfer film is subjected to plasma treatment, a plasma cleaning machine is used for treatment, wherein the radio frequency power is 80 W, the argon flow rate is 20 sccm, the oxygen flow rate is 5 sccm, and the treatment time is 45 seconds.

[0068] This embodiment uses a specific power and duration for plasma treatment to reduce the contact angle of the PDMS transfer film from 110° to 25°, significantly improving the reliability and yield of chip transfer.

[0069] Step S30 , collecting the reference points of the preset vehicle through a CCD image sensor, calculating the coordinate offset based on a SURF feature matching algorithm, and driving the piezoelectric micro-motion platform to implement sub-pixel compensation.

[0070] In this embodiment, the step of calculating the coordinate offset based on the SURF feature matching algorithm includes:

[0071] Five reference marking points are set at the four corners and the center area of ​​the preset vehicle;

[0072] Extracting SURF feature descriptors of each of the reference markers and establishing a feature matching model;

[0073] The sub-pixel offset is calculated using a Gaussian fitting interpolation algorithm, with a fitting error of ≤0.02 pixels.

[0074] Specifically, a high-pixel CCD image sensor captures fiducial markers at the four corners and center of a borosilicate glass carrier. Specifically, a 50μm diameter gold dot is placed on the carrier. A SURF algorithm is then used to build a feature model and calculate the X / Y offsets, which are +0.12μm and -0.08μm, respectively. Sub-pixel compensation is then performed by driving the piezoelectric micro-motion stage based on these coordinate offsets.

[0075] In this embodiment, nanometer-level alignment is achieved through gradient pressure control of the three-stage booster cylinder group and sub-pixel compensation of the SURF algorithm + piezoelectric micro-motion platform.

[0076] Step S40, when the vacuum degree is less than 10 -3 Pa vacuum chamber, pressure is applied in stages through a three-stage booster cylinder group.

[0077] Specifically, in 5×10-4 Under the Pa vacuum environment, the initial contact stage maintains a pressure of 0.05MPa-0.1MPa for 3 seconds to make the chip contact the pad; in the main pressing stage, the pressure is increased at a rate of 0.1MPa / s-0.2MPa / s, and the pressure change curve is monitored at the same time; when the pressure reaches 0.5MPa-1.2MPa, it enters the pressure holding stage and maintains the pressure fluctuation ≤±5%.

[0078] Step S50 , using a pulsed laser, performing chip bonding under process parameters of a spot diameter of 10-15 μm, a pulse frequency of 100-200 kHz, and an overlap rate of 30-50%, to complete a single transfer.

[0079] In this embodiment, the steps of using a pulsed laser to perform chip welding include:

[0080] Automatically adjust the laser spot diameter according to the chip size so that the spot diameter covers 80-120% of the pad area;

[0081] Welding is performed using a spiral scanning path with a scanning pitch of 30-50% of the spot diameter;

[0082] The reflection intensity of the welding area is monitored in real time, and the laser power of the pulse laser is dynamically adjusted according to the reflection intensity.

[0083] Specifically, a 532 nm pulsed laser (spot size 12 μm, frequency 150 kHz) was used for spiral scanning welding (overlap rate 40%), with a real-time power adjustment range of ±10%.

[0084] Step S60 , repeating the above steps to complete the mass transfer of the three-color RGB chips, and detecting the chip position deviation by a laser interferometer after each transfer.

[0085] In this embodiment, the above steps are repeated to complete the mass transfer of three-color RGB chips, including:

[0086] When transferring the red chip for the first time, a position deviation of ±3μm is allowed;

[0087] When transferring the green chip for the second time, compensation is performed based on the previous transfer result to control the deviation within ±1.5μm;

[0088] When the blue chip was transferred for the third time, the deviation was reduced to ±0.8 μm in combination with the pre-determined compensation data.

[0089] Compared with the prior art, the method of using blue film expansion to perform mass transfer as shown in this embodiment has the following beneficial effects:

[0090] In this embodiment, the blue film of the chips distributed at equal intervals is loaded into the blue film expansion mechanism, and the expansion ratio is adjusted by the thermal expansion coefficient difference compensation mechanism to match the chip spacing with the point spacing of the target pads; the chip is transferred to a preset carrier using a reverse molding process, and the surface of the preset carrier is attached with a PDMS transfer film with a thickness of 50-100μm; the reference point of the preset carrier is collected by a CCD image sensor, the coordinate offset is calculated based on the SURF feature matching algorithm, and the piezoelectric micro-motion platform is driven to implement sub-pixel compensation; in a vacuum chamber with a vacuum degree of ≤10-3Pa, pressure is applied in stages by a three-stage booster cylinder assembly; a pulsed laser is used to perform chip welding under process parameters of a spot diameter of 10-15μm, a pulse frequency of 100-200kHz, and an overlap rate of 30-50% to complete a single transfer; the above steps are repeated to complete the mass transfer of three-color RGB chips, and the chip position deviation is detected by a laser interferometer after each transfer. This embodiment utilizes a unique heterogeneous material stacking structure combined with an intelligent temperature control system, significantly improving the accuracy of chip spacing adjustment and effectively resolving the positioning deviation problem caused by thermal expansion differences in traditional methods. Furthermore, an optimized plasma surface treatment process significantly enhances the performance of the transfer film, significantly improving the success rate of chip transfer while avoiding the environmental pollution risks associated with traditional processes.

[0091] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0092] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for mass transfer using blue film expansion, characterized in that: The method comprises: The blue film of the chips with equal spacing is loaded onto the blue film expansion mechanism, and the expansion ratio is adjusted by the thermal expansion coefficient difference compensation mechanism to make the chip spacing match the point spacing of the target pads; The chip is transferred to a pre-set carrier using a reverse molding process, the surface of which is affixed with a 50-100 μm thick PDMS transfer film; The reference points of the preset vehicle are collected by a CCD image sensor, the coordinate offset is calculated based on the SURF feature matching algorithm, and the piezoelectric micro-motion platform is driven to implement sub-pixel compensation; In a vacuum chamber with a vacuum degree of ≤10-3Pa, pressure is applied in stages through a three-stage booster cylinder assembly; Using a pulsed laser, chip welding is performed under process parameters of a spot diameter of 10-15 μm, a pulse frequency of 100-200 kHz, and an overlap rate of 30-50% to complete a single transfer; Repeat the above steps to complete the mass transfer of three-color RGB chips, and use a laser interferometer to detect chip position deviation after each transfer.

2. The method for mass transfer using blue film expansion according to claim 1, characterized in that: The steps of adjusting the expansion ratio by using the thermal expansion coefficient difference compensation mechanism include: Controlling the temperature change of different material layers in the blue film expansion mechanism to generate deformation by utilizing the difference in thermal expansion coefficient; Monitor the chip spacing changes in real time and dynamically adjust the temperature compensation through the PID control algorithm; When the error between the chip spacing and the target pad spacing is ≤±2μm, the current temperature parameter is locked.

3. The method for mass transfer using blue film expansion according to claim 1, characterized in that: The steps of transferring the chip to the pre-set carrier using the mold reversing process include: Align the chip blue film with the preset carrier and apply a uniform pressure of 0.1MPa-0.3MPa; The PDMS transfer film is irradiated with ultraviolet light to change its viscosity, thereby achieving chip selective transfer; After the transfer is completed, the chip blue film and the preset carrier are gradually separated at a speed of 0.05 mm / s-0.1 mm / s.

4. The method for mass transfer using blue film expansion according to claim 3, characterized in that: The preset carrier is a borosilicate glass carrier.

5. The method for mass transfer using blue film expansion according to claim 3, characterized in that: The steps for calculating the coordinate offset based on the SURF feature matching algorithm include: Five reference marking points are set at the four corners and the center area of ​​the preset vehicle; Extracting SURF feature descriptors of each of the reference markers and establishing a feature matching model; The sub-pixel offset is calculated using a Gaussian fitting interpolation algorithm, with a fitting error of ≤0.02 pixels.

6. The method for mass transfer using blue film expansion according to claim 1, characterized in that: The steps of applying pressure in stages through the three-stage booster cylinder group include: During the initial contact phase, maintain a pressure of 0.05MPa-0.1MPa for 3 seconds to make contact between the chip and the pad; During the main pressing stage, the pressure is increased at a rate of 0.1MPa / s-0.2MPa / s, and the pressure change curve is monitored at the same time; When the pressure reaches 0.5MPa-1.2MPa, it enters the pressure holding stage and maintains the pressure fluctuation ≤±5%.

7. The method for mass transfer using blue film expansion according to claim 1, characterized in that: The steps for chip welding using pulsed laser include: Automatically adjust the laser spot diameter according to the chip size so that the spot diameter covers 80-120% of the pad area; Welding is performed using a spiral scanning path with a scanning pitch of 30-50% of the spot diameter; The reflection intensity of the welding area is monitored in real time, and the laser power of the pulse laser is dynamically adjusted according to the reflection intensity.

8. The method for mass transfer using blue film expansion according to any one of claims 1 to 7, characterized in that: Repeat the above steps to complete the mass transfer of three-color RGB chips, including: When transferring the red chip for the first time, a position deviation of ±3μm is allowed; When transferring the green chip for the second time, compensation is performed based on the previous transfer result to control the deviation within ±1.5μm; When the blue chip was transferred for the third time, the deviation was reduced to ±0.8 μm in combination with the pre-determined compensation data.

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