Manufacturing method for mass transfer of MIP
Through blue film expansion and double adhesive packaging technology, combined with reflow soldering technology, the problems of low efficiency, thermal damage and insufficient accuracy in the huge transfer of Micro LEDs are solved, and efficient and reliable wafer transfer and bonding are achieved, which is suitable for mass production.
Patent Information
- Application Number
- CN202510516181.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-23
- Publication Date
- 2025-08-01
AI Technical Summary
The existing Micro LED massive transfer technology has problems such as inefficiency, risk of thermal damage, complex process and insufficient accuracy, making it difficult to meet the needs of efficient transfer.
The blue film expansion technology is used to combine double-adhesive packaging and reflow soldering technology. The wafer spacing is adjusted through the film expansion device, and the transparent A-adhesive layer and light-shielding B-adhesive layer are used for fixing and bonding. The reflow soldering process is combined to achieve high-precision arrangement and reliable bonding, avoid laser thermal damage and simplify the process flow.
It realizes efficient adjustment of wafer spacing, reduces costs and improves transfer efficiency, with the wafer offset rate below 0.3%, the process shortened by 50%, and the bond yield is as high as 98%, and the display effect is excellent.
Smart Images
Figure CN120417608A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of Micro LED display, and more specifically, to a manufacturing method for massive transfer of MIP. Background Art
[0002] Existing Micro LED massive transfer technologies mainly rely on stamp transfer or needle transfer to bond wafers to a glass carrier, and then transfer them to a BT board through laser bonding.
[0003] Stamp transfer uses an elastomeric material such as PDMS to make a microstructure stamp, the surface pattern of which matches the target pitch. The stamp picks up Micro LEDs from a temporary substrate through negative pressure adsorption or adhesion force, controls pressure and time to ensure reliable adhesion of single wafers, and then aligns the stamp with the glass carrier (pre-coated with a bonding layer such as temporary glue or metal pads), and completes the bonding by slowly releasing pressure or heating / UV curing the glue; Needle transfer uses a high-precision metal needle array (corresponding to the positions of Micro LEDs), picks up / releases through pneumatic or mechanical drive, and ensures alignment of the wafers with the marks on the glass carrier through real-time calibration by a vision system, and requires pitch control, so that the pitch of the wafers on the glass carrier needs to match the target circuit of the BT board.
[0004] Laser bonding transfers to the BT board, and laser selective heating: uses ultraviolet or infrared laser (such as 355nm wavelength) to irradiate the bonding area through the glass carrier (transparent to the laser); heats the bonding material (such as Au-Sn solder or conductive glue) at the bottom of the Micro LED to melt it and form a metallurgical connection with the pads on the BT board.
[0005] However, the above methods have the following defects: low efficiency: the stamp / needle transfer rate is low (hundreds per second), making it difficult to meet the massive transfer requirements; risk of thermal damage: the local high temperature of laser bonding is likely to burn out the pads and surrounding circuits on the BT board; complex process: requires injection molding and encapsulation, increasing the process cost and the risk of wafer tilt; insufficient accuracy: the reconstitution of solder paste is likely to cause wafer offset. Summary of the Invention
[0006] In view of this, in order to solve the above problems, the present invention proposes a manufacturing method for massive transfer of MIP, which precisely matches the pad pitch of the BT board 7 through the film expansion of the blue film 1, combines double glue encapsulation and reflow soldering technologies, realizes high-precision alignment and reliable bonding of the wafers 2, and at the same time avoids laser thermal damage and simplifies the process flow.
[0007] A manufacturing method for massive transfer of MIP, characterized by comprising the following steps:
[0008] (a) Invert the de-substrated wafer 2 on the blue film 1, and adjust the wafer 2 pitch to the target Pitch value through the film expansion device 3;
[0009] (b) Transfer the wafer 2 to the glass carrier 6 coated with the A glue layer 4. The A glue layer 4 is a transparent glue. Coat the black B glue layer 5 on the A glue layer 4 to cover the gaps between the wafers 2 and perform pre-curing. Apply pressure to make the wafer 2 penetrate through the B glue layer 5 and embed into the A glue layer 4. The wafer electrodes 21 of the wafer 2 are exposed outside the B glue layer 5 and are in direct contact with the pads of the subsequent BT board 7.
[0010] (c) Align and bond the glass carrier 6 with the pads of the pre-treated BT board 7. Bond the wafer electrodes 21 of the wafer 2 with the pads of the pre-treated BT board 7 through reflow soldering. At the same time, in the reflow soldering, at high temperature, the A glue layer 4 is completely cured, and the B glue layer 5 softens and adapts to the surface topography of the BT board 7, and is preliminarily cured to form a structure lock.
[0011] (d) Bake and harden the B glue layer 5, and cut to obtain single LEDs.
[0012] Furthermore, in step (a), the substrate-removed wafer 2 removes the original substrate through laser lift-off, chemical etching or mechanical grinding to obtain an independent wafer 2.
[0013] In some embodiments, the film expanding device 3 includes an asymmetric film expanding ring and an optical dynamic calibration system, and the film expanding force is 3–10 N / cm 2 , and the pitch error < ±1 μm.
[0014] Furthermore, calculate the film expanding magnification according to the pad Pitch value of the BT board 7, and design the structure of the asymmetric film expanding ring to ensure uniform stretching in the XY directions.
[0015] Furthermore, during the film expanding process, the position of the wafer 2 is real-time fed back through the optical dynamic calibration system, such as CCD + AI image recognition, and the film expanding force is fed back and adjusted to control the pitch error of the wafer 2 < ±1 μm.
[0016] In some embodiments, in step (a), the blue film 1 is a high-elastic UV blue film, and the shrinkage rate after film expanding < 0.5%, to avoid the displacement of the wafer 2.
[0017] Furthermore, the surface of the blue film 1 is microstructured to increase the contact area of the wafer 2, and the adhesion force of the wafer 2 after film expanding is insufficient.
[0018] In some embodiments, in step (b), the A glue layer 4 is an ultraviolet-curable polyurethane acrylate, and the light transmittance > 95%. After the wafer 2 is attached, the highly transparent A glue layer 4 is pre-cured to form a temporary fixing layer, and the temporary fixing layer is an adhesive surface with both hardness and viscosity.
[0019] Further, in step (b), the black B glue layer 5 is a high-temperature resistant epoxy resin containing carbon black filler, with a light shielding rate OD > 4, covering the gaps of the wafer 2, eliminating the traditional injection molding and pressing station, reducing the risk of wafer 2 breakage caused by thermal pressing stress. At the same time, the double glue layer is cured synchronously during reflow soldering, simplifying the process.
[0020] Further, the A glue layer 4 and the B glue layer 5 need to withstand a high temperature of 260 °C during reflow soldering without decomposition or yellowing.
[0021] In some embodiments, in step (c), the steps of preprocessing the pads of the BT board 7 include: pre-plating the electrodes with eutectic solder, and ensuring that the surface roughness Ra of the pads of the BT board 7 is < 0.1 μm through electroplating and reflow leveling processes.
[0022] Further, the peak temperature of the reflow soldering is 250–260 °C, and the molten solder forms an intermetallic compound bond with the wafer electrodes 21 of the wafer 2. The solder is a SnAgCu alloy with a thickness of 3–5 μm.
[0023] Further, the temperature of the A glue layer 4 in the initial stage of reflow is < 150 °C, maintaining viscoelasticity, and automatically correcting the position of the wafer 2 through surface tension; the temperature of the B glue layer 5 in the high-temperature stage is > 200 °C, and the fluidity decreases, locking the posture of the wafer 2.
[0024] Further, the BT board 7 is made of a high TG material to ensure no deformation at high temperatures.
[0025] Further, if the yield of tin bonding is low, low-temperature transient liquid-phase bonding can be adopted.
[0026] In some embodiments, in step (d), the cutting uses infrared laser stealth cutting, focusing the infrared laser inside the BT board 7 to modify the resin layer without damaging the LED.
[0027] Further, finally, bake in an oven at a temperature of 120–150 °C for 2 h to fully cure the B glue layer 5.
[0028] In some embodiments, in step (d), after cutting, perform supercritical CO2 cleaning to remove the glue residue without mechanical damage.
[0029] Further, add a CTE buffer layer, such as a polyimide film, between the BT board 7 and the glass carrier 6 to reduce thermal mismatch warping.
[0030] Advantages of the present invention: The present invention provides a manufacturing method for massive transfer of MIP, including the processes of reverse molding blue film 1, double-sided glue coating of glass carrier 6 and wafer 2 fixation, alignment of glass carrier 6 and BT board 7, reflow soldering, cutting, and post-treatment; blue film 1 film expansion technology, through an asymmetric film expansion ring and a dynamic calibration system, realizes efficient adjustment of the spacing between wafers 2, reducing costs by 70%; double-sided glue collaborative encapsulation: A glue layer 4 provides optical transparency and temporary fixation, B glue layer 5 shields light and locks the posture of wafer 2, replacing injection molding; solder paste reflow soldering: directly bonding with pre-plated eutectic solder pads, combined with the self-correction of the surface tension of A glue layer 4, the offset rate of wafer 2 < 0.3%; adding a CTE buffer layer, such as a polyimide film, between BT board 7 and glass carrier 6 to reduce thermal mismatch warping. High hardness of epoxy resin may cause chipping, so the cutting process needs to be optimized. Process integration: omitting the laser bonding and injection molding processes, shortening the process by 50%. Description of the Drawings
[0031] Figure 1 Schematic diagram of the reverse molding blue film 1 to the film expansion ring of the manufacturing method for massive transfer of MIP of the present application.
[0032] Figure 2 Schematic diagram of adjusting the spacing by film expansion of the manufacturing method for massive transfer of MIP of the present application.
[0033] Figure 3 Schematic diagram of carrier preparation of the manufacturing method for massive transfer of MIP of the present application.
[0034] Figure 4 Schematic diagram of massive transfer of the manufacturing method for massive transfer of MIP of the present application.
[0035] Figure 5 For Figure 4 Enlarged view.
[0036] Figure 6 Schematic diagram of the alignment of glass carrier 6 and BT board 7 of the manufacturing method for massive transfer of MIP of the present application.
[0037] Figure 7 For Figure 6 Enlarged view.
[0038] Figure 8 Partial schematic diagram of reflow soldering of the manufacturing method for massive transfer of MIP of the present application.
[0039] Figure 9 Schematic diagram of cutting of the manufacturing method for massive transfer of MIP of the present application.
[0040] Description of the Main Component Symbols
[0041] Blue film 1, chip 2, chip electrode 21, film expanding device 3, A glue layer 4, B glue layer 5, glass carrier plate 6, BT board 7.
[0042] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Specific embodiments
[0043] Example 1:
[0044] The present invention provides a manufacturing method for mass transfer of MIP, including the following steps:
[0045] (a) Invert the substrate-removed Micro LED chip 2 onto the blue film 1, and adjust the pitch value of the chip 2 to the target Pitch value through the film expanding device 3;
[0046] (b) Transfer the chip 2 to the glass carrier plate 6 coated with the A glue layer 4. The A glue layer 4 is a transparent glue. Coat the black B glue layer 5 on the A glue layer 4 to cover the gaps between the chips 2 and perform pre-curing. Apply pressure to make the chip 2 penetrate the B glue layer 5 and embed into the A glue layer 4. The chip electrode 21 of the chip 2 is exposed outside the B glue layer 5. The chip electrode 21 of the chip 2 is combined with the blue film 1 to prevent pollution of the B glue layer 5, and the chip electrode 21 of the chip 2 is in direct contact with the pads of the subsequent BT board 7;
[0047] (c) Align and bond the glass carrier plate 6 with the pads of the pre-treated BT board 7, and bond the chip electrode 21 of the chip 2 with the pads of the pre-treated BT board 7 through reflow soldering. At the same time, in the reflow soldering, at high temperature, the A glue layer 4 is completely cured, and the B glue layer 5 softens and adapts to the surface topography of the BT board 7, and is preliminarily cured to form a structure lock;
[0048] (d) Bake and harden the B glue layer 5, and cut to obtain single Micro LEDs.
[0049] As Figure 1-2 shown, in step (a), the substrate-removed Micro LED chip 2 removes the original substrate through laser lift-off, chemical etching or mechanical grinding to obtain an independent Micro LED chip 2; Invert the blue film 1: The MicroLED chips 2 (RGB three colors) after substrate peeling are evenly dispersed and temporarily fixed on the blue UV blue film 1 through vacuum adsorption or centrifugal force. The initial pitch of the chips 2 is dense; Expand the film and adjust the pitch: Use a film expanding ring to mechanically stretch the blue film 1 to expand the pitch of the chips 2 to match the electrode Pitch value designed for the BT board 7. The film expansion should be uniform to avoid displacement or detachment of the chips 2 caused by local stress; Verify the pitch consistency through optical detection; RGB integration: Invert and expand the film three times (R / G / B are operated independently), and transfer the three-color chips 2 to the same glass carrier plate 6 according to the designed layout, and strict alignment is required to ensure accurate color arrangement.
[0050] In step (b), the glass carrier 6 is double-coated and fixed to the wafer 2, including the following steps:
[0051] As Figure 3 shown, the glue system design: The highly transparent layer A of glue 4: As the underfill glue to fix the Micro LED wafer 2, it requires a high light transmittance of > 95% to reduce light loss. Coating method: Spin coating or slit coating, with the thickness controlled at 5 - 10 μm, covering the entire surface of the glass carrier 6. The black layer B of glue 5: As the encapsulation glue to shield light crosstalk and protect the circuit, it requires high light shielding property with OD > 3 and high temperature resistance. Coating method: Spray or print after the layer A of glue 4 is semi-cured, covering the upper surface of the layer A of glue 4, with the thickness of 20 - 30 μm.
[0052] As Figure 4-5 shown, the curing process: The layer A of glue 4 is pre-cured, such as by UV irradiation or heating at 80 °C for 10 minutes. Wait until the layer A of glue 4 is semi-cured to form a temporary fixing layer. The temporary fixing layer is an adhesive surface with both hardness and viscosity. The black layer B of glue 5 is coated on the upper surface of the layer A of glue 4 to cover the gaps between the wafers 2, eliminating the traditional injection molding and pressing stations, reducing the risk of wafer 2 breakage caused by thermal stress. At the same time, the double-glue layer is cured synchronously during reflow soldering, simplifying the process.
[0053] As Figure 6-8 shown, the alignment and reflow soldering of the glass carrier 6 and the BT board 7 include the following steps:
[0054] Pretreatment of the BT board 7: The pads are electroplated with tin, such as SnAgCu solder, with a thickness of 3 - 5 μm, and patterned pads are formed through photolithography or spray tin process;
[0055] Alignment and bonding: Use a high-precision mounter to place the glass carrier 6 with Micro LED and the glue layer into the carrier and align it with the BT board 7, ensuring that the wafer electrodes 21 of the wafer 2 coincide with the pads, and applying a slight pressure to make the bottom of the wafer 2 contact the pads;
[0056] Reflow soldering bonding: Temperature curve: Heating zone: Preheat from 2 - 3 °C / s to 150 °C; Reflow zone: The peak temperature is 250 - 260 °C, maintaining the peak temperature above the melting point of tin for 60 - 90 seconds to melt the solder and form a metal bond with the Micro LED electrodes; Cooling zone: Control the cooling rate at 1 - 2 °C / s to reduce thermal stress. At high temperatures, the layer A of glue 4 is completely cured, and the layer B of glue 5 softens and adapts to the surface topography of the BT board 7, and is initially cured to form a structure lock;
[0057] Secondary curing of epoxy resin: After reflow soldering, the whole is placed in an oven at 120 - 150 °C and baked for 2 h to completely harden the black layer B of glue 5 and enhance the mechanical strength.
[0058] As Figure 9As shown, cutting and post-processing include the following steps: Single-particle separation: The BT board 7 is cut into the designed size using a laser cutter or a diamond dicing machine to obtain independent Micro LED units. The cutting parameters are a laser wavelength of 355 nm and a power of 5–10 W to avoid carbonization of the glue layer. Residual debris in the cutting channels is cleaned, such as by plasma cleaning;
[0059] Inspection and repair: Defective bonded products are screened by AOI (Automated Optical Inspection) and repaired by re-soldering or replacing the wafer 2.
[0060] In this application, through the film expansion technology, the pitch adjustment of the wafer 2 is achieved at low cost, and high-density transfer is compatible; through the double-glue encapsulation technology, the high transparency of the A glue layer 4 ensures the light extraction efficiency, the B glue layer 5 blocks light to improve the display contrast, and the epoxy resin integrated encapsulation enhances the anti-mechanical shock resistance; through the reflow soldering compatibility, the reliability of the tin bond is high, which is suitable for mass production. The test results are as follows: the bonding strength of the wafer 2 > 15 MPa, the yield > 98%, and the offset rate 0.2%.
[0061] The above embodiments merely represent several implementation manners of the present invention. The descriptions thereof are relatively specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.
Claims
1. A manufacturing method for massive transfer of MIP, characterized in that Including the following steps: (a) Invert the substrate-removed wafer (2) onto the blue film (1), and adjust the spacing between wafers (2) to the target Pitch value through the film expanding device (3); (b) Transfer the wafer (2) to the glass carrier (6) coated with the A glue layer (4). The A glue layer (4) is a transparent glue. Coat the black B glue layer (5) on the A glue layer (4) to cover the gaps between wafers (2) and perform pre-curing. Apply pressure to make the wafer (2) penetrate the B glue layer (5) and embed into the A glue layer (4). The wafer electrode (21) of the wafer (2) is exposed outside the B glue layer (5) and is in direct contact with the pads of the subsequent BT board (7); (c) Align and bond the glass carrier (6) with the pads of the pretreated BT board (7). Bond the wafer electrode (21) of the wafer (2) with the pads of the pretreated BT board (7) through reflow soldering. At the same time, in the reflow soldering, at high temperature, the A glue layer (4) is completely cured, and the B glue layer (5) softens and adapts to the surface topography of the BT board (7), and is preliminarily cured to form a structure lock; (d) Bake and harden the B glue layer (5), and cut to obtain single LEDs.
2. The manufacturing method of massive transfer of MIP according to claim 1, characterized in that: In step (a), the substrate-removed wafer (2) removes the original substrate through laser lift-off, chemical etching or mechanical grinding to obtain an independent wafer (2).
3. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: The film expanding device (3) includes an asymmetric film expanding ring and an optical dynamic calibration system, and the film expanding force is 3-10 N / cm 2 , and the pitch error < ±1 μm.
4. The manufacturing method of massive transfer of MIP according to claim 1, characterized in that: In step (a), the blue film (1) is a high-elasticity UV blue film, and the shrinkage rate after film expansion is <0.5%, to avoid the displacement of the wafer (2).
5. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: In step (b), the A glue layer (4) is an ultraviolet-curable polyurethane acrylate with a light transmittance >95%. After the wafer (2) is attached, the highly transparent A glue layer (4) is pre-cured to form a temporary fixing layer, and the temporary fixing layer is an adhesive surface with both hardness and viscosity.
6. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: In step (b), the black B glue layer (5) is a high-temperature-resistant epoxy resin containing carbon black filler, with a light-shielding rate OD >4, covering the gaps between wafers (2), eliminating the traditional injection molding and pressing station, reducing the risk of wafer (2) breakage caused by thermal compression stress. At the same time, the double glue layers are cured synchronously in reflow soldering, simplifying the process.
7. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: In step (c), the steps for the pretreatment of the pads of the BT board (7) include: pre-plating the electrodes with eutectic solder, and ensuring that the surface roughness Ra of the pads of the BT board (7) is <0.1μm through electroplating and reflow leveling processes.
8. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: The peak temperature of the reflow soldering is 250–260°C. The molten solder forms an intermetallic compound bond with the wafer electrode (21) of the wafer (2). The solder is a SnAgCu alloy with a thickness of 3–5μm.
9. The manufacturing method of the massive transfer of MIP according to claim 1, characterized in that: In step (d), the cutting uses infrared laser stealth cutting, focusing the infrared laser inside the BT board (7) to modify the resin layer without damaging the LEDs.
10. The manufacturing method of massive transfer of MIP according to claim 1, characterized in that: In step (d), after cutting, it is cleaned with supercritical CO2 to remove the glue residues without mechanical damage.