A packaging transfer method for LED

Abstract

The present invention belongs to the field of encapsulation and transfer of LEDs, and relates to an encapsulation transfer method for LEDs, which method includes the steps of cutting, stretching, filling, curing, grinding, segmenting and transferring, and optional welding and coating after fixing the wafer with an expansion grinding tape. The method provided by the present invention can improve the chip transfer efficiency and transfer accuracy, and at the same time, there is no need to perform bottom filling after transfer, and the transfer of small chip modules in batches is more stable when applying a transparent plastic film after welding, avoiding displacement during subsequent application of the transparent plastic film and causing screen distortion, solving the problem of uneven ink color of the display bottom plate, and the black liquid resin glue solidified before transfer prevents interference from the side light of Mini LED and Micro LED, and the black encapsulation glue with high insulation performance can prevent short circuits caused by metal migration between electrodes, etc.

Description

Technical Field

[0001] The invention belongs to the field of LED encapsulation and transfer, and in particular relates to an LED encapsulation and transfer method. Background Art

[0002] With the reduction of LED size and the application of new packaging technologies such as COB and flip-chip, the market potential of LED as a new backlight technology and display technology has gradually emerged. Mini LED has been gradually applied by well-known international consumer electronics companies such as Apple and Samsung in various terminals such as HDTVs and iPads. As a backlight source, Mini LED brings many advantages over traditional LCD or OLED displays, such as higher brightness and reliability, and the ability to control by partitions to increase display contrast and uniformity. As a direct display, Mini LED or Micro LED will bring revolutionary changes to the display industry, bringing significant improvements in contrast, power consumption, resolution, brightness and life. Whether it is penetrating into large-sized commercial applications in the short term, or being introduced into small-sized consumer electronics, automobiles and other fields in the future as costs decrease, the market space for Mini LED and Micro LED is broad.

[0003] According to forecasts, the output value of Mini LED chips alone will grow from about $100 million currently to $1 billion in 2025, with wafer production reaching 3 million pieces per year and display panel output reaching more than $2 billion. As Micro technology matures, it is foreseeable that it will bring about even larger growth. It is predicted that with the application of brighter and more energy-efficient display panels for smart devices and augmented reality / virtual reality helmets, global Micro LED will grow at a compound annual growth rate of 90%, reaching a production value of $20 billion by 2026.

[0004] However, to achieve large-scale commercialization, the industry is still facing many challenges. As the chip size shrinks to less than 200μm at the Mini level, and further shrinks to less than 50μm at the Micro level in the future, it poses a great challenge to the packaging process. The reduction in the size of a single chip means that more chips are integrated on the same size wafer area. The traditional process is to transfer chips from the wafer to the display backplane one by one, but when faced with smaller Mini LED and Micro LED, neither efficiency, accuracy nor yield can meet the requirements. For example, for P1.5 products, 440,000 lights need to be posted per square meter, while for P1.0 products, 1 million lights need to be posted per square meter. Not only has the number of patches increased by about 2 to 3 times, but due to higher precision requirements, the patch speed of the SMT machine also needs to be significantly reduced, and the overall production efficiency will be greatly affected. Therefore, a lot of research focuses on how to quickly transfer large quantities, that is, the mass transfer technology that is hotly debated in the industry, such as laser transfer, magnetic self-assembly technology, transfer technology, and traditional improved precision picking technology. All of these new technologies require a lot of money to be invested in equipment development, and even completely abandon existing technologies and materials to find new ways. However, there are still problems such as yield, accuracy, and transfer rate. The cost and effect are currently difficult to meet commercial requirements.

[0005] As chip size shrinks, whether it is wire bonding or flip-chip soldering, the contact points are getting smaller and smaller, and accurate alignment is becoming more and more difficult. Slight position deviations will cause many problems in subsequent processes and performance, such as chip soldering drift, which cannot meet the high-precision die bonding requirements of Mini LED. In addition, the subsequent plastic encapsulation will also cause chip drift due to shrinkage or stress changes, resulting in uneven display effects, commonly known as "flower screen". Some defects are as high as 20%, requiring a lot of rework, reducing efficiency and keeping costs high.

[0006] As the chip size shrinks to the Micro LED size level and when used as a direct display, the dot pitch reaches below 0.1mm, which not only brings challenges to the packaging process, but also causes problems such as light mixing and light uniformity, and uneven bottom plate ink color. At present, some international companies use complex methods of dividing the area or even using glue to build dams on a single chip to prevent interference from side light, and the process is extremely complicated.

[0007] In summary, the current LED market faces the following major challenges:

[0008] (1) Mass transfer - a single chip is transferred from a wafer to a substrate. As the chip size becomes smaller, the transfer becomes more difficult and the transfer efficiency becomes lower.

[0009] (2) After the chip is transferred to the substrate, subsequent operations may cause relative displacement of the chip, resulting in the problem of "flower screen", and the defective rate may even be as high as more than 20%;

[0010] (3) As pixels become smaller and smaller, direct display and mixed light problems will arise, and there is currently no economical and effective solution. Summary of the invention

[0011] The purpose of the present invention is to overcome the defects of the existing LED market, such as low chip transfer efficiency and transfer accuracy, and the subsequent plastic sealing that easily leads to "flower screen" and easy interference with side light emission, and to provide a new encapsulation transfer method for LED. The method can improve the chip transfer efficiency and transfer accuracy, and at the same time, there is no need to perform bottom filling after the transfer, and the transfer of small chip modules in batches is more stable when the transparent plastic film is applied after welding, which avoids displacement during the subsequent application of the transparent plastic film and causes flower screen, solves the problem of uneven ink color of the display base plate, and the black liquid resin glue solidified before the transfer prevents interference with the side light emission of MiniLED and Micro LED.

[0012] Specifically, the present invention provides an encapsulation transfer method for LEDs, wherein the method comprises the following steps:

[0013] (1) Cutting: The sapphire base layer of the wafer is fixed by an expanded polishing tape and then cut. The top surface of the wafer is an electrode layer and the bottom surface is a sapphire base layer. The electrode layer is provided with bump contacts. The expanded polishing tape has a stretchable property. During cutting, the electrode layer of the wafer is cut into and through the sapphire base layer but not through the expanded polishing tape, forming a plurality of transverse and / or longitudinal cutting grooves. At this time, the wafer is actually divided into a plurality of chips.

[0014] (2) Stretching: The expanded polishing tape is stretched according to the preset contact spacing on the PCB substrate to be transferred to adjust the distance between chips so that the bump contacts on all chips can be subsequently aligned with the preset contacts on the PCB substrate to be transferred;

[0015] (3) Glue filling: Fill the black liquid resin glue from the surface of the electrode layer into the cutting groove and overflow the cutting groove and cover the electrode layer and the bump contact to obtain a glue-filled part;

[0016] (4) Curing: The glue filling part is heated to cure the black liquid resin glue to obtain a cured part, at which time the chip spacing is fixed;

[0017] (5) Grinding: Grinding the surface of the cured part having the bump contact for the first time until at least the bump contact is exposed, and removing the expanded grinding tape to obtain a polished part;

[0018] (6) Splitting and transfer: Flip the polished wafer and fix the electrode layer with polishing tape, cut it into several small chip modules along the cutting groove, and then transfer the several small chip modules to the PCB substrate to be transferred.

[0019] In a preferred embodiment, each chip obtained in step (1) has two bump contacts.

[0020] In a preferred embodiment, in step (3), the black liquid resin glue is filled into the cutting groove by printing, dispensing or spin coating.

[0021] In a preferred embodiment, the printing method is steel mesh or screen printing.

[0022] In a preferred embodiment, the dispensing method is to first apply the black liquid resin glue to one side of the electrode layer of the wafer through pneumatic, screw, solenoid valve or spraying, and then promote the black liquid resin glue to flow into the cutting groove by heating and pressurizing.

[0023] In a preferred embodiment, the spin coating method is to pre-place the black liquid resin glue on one side of the electrode layer of the wafer, and then rotate the wafer to cause the black liquid resin glue to flow into the cutting groove and be evenly distributed on the wafer surface.

[0024] In a preferred embodiment, the first grinding in step (5) is horizontal grinding.

[0025] In a preferred embodiment, in step (6), each small chip module has at least one chip. When several small chip modules are transferred to the PCB substrate to be transferred, the bump contacts on the chip are aligned with the preset contacts on the PCB substrate to be transferred and then placed.

[0026] In a preferred embodiment, the encapsulation transfer method for LEDs provided by the present invention further includes step (7) welding: aligning the bump contacts on the chip in each small chip module with the preset contacts on the PCB substrate to be transferred and then welding them to obtain a welded part.

[0027] In a preferred embodiment, the encapsulation transfer method for LED provided by the present invention further comprises the following step (8) coating: providing a transparent plastic sealing layer on the side of the soldering part away from the PCB substrate.

[0028] The present invention has the following beneficial effects:

[0029] (1) The method provided by the present invention can maximize the use of the existing mature equipment production line capacity, can realize batch transfer of small chip modules, realize low-cost, large-scale and efficient transfer of Mini LEDs and Micro LEDs, and improve the transfer efficiency and transfer accuracy. In addition, the method provided by the present invention can adjust the distance between chips by controlling the stretching amplitude of the expansion polishing tape to adapt to various PCB substrates to be transferred, thereby realizing the encapsulation transfer of different LEDs;

[0030] (2) The method provided by the present invention does not require bottom filling after transfer (in the existing method, the chips need to be transferred one by one, and then bottom filled together by self-filling after the transfer is completed, while the method provided by the present invention is actually equivalent to the glue filling operation before the chip is formed, which is equivalent to both playing the role of chip connection and providing the role of bottom filling), and can ensure that the subsequent welding and transparent plastic film coating operations are more stable, solve the problem of uneven ink color of the display bottom plate, and avoid the problem of chip position drifting and screen distortion during subsequent welding and transparent plastic film coating after the size of the chip and substrate contacts is greatly reduced;

[0031] (3) As mentioned above, when LED develops into Mini LED and Micro LED, the distance between chips is very small, which will cause mutual light interference. If light interference is to be avoided by building dams between chips based on the existing process, it is difficult and the process is complicated. However, the method provided by the present invention requires filling the cutting groove with black liquid resin before chip transfer. After curing, the black liquid resin can prevent the side light interference of the chip. That is, the black liquid resin glue cured before transfer in the method provided by the present invention can effectively prevent the interference of the side light of Mini LED and Micro LED and ensure the angle and uniformity of the emitted light. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic flow chart of the encapsulation transfer method for LEDs provided by the present invention. DETAILED DESCRIPTION

[0033] like Figure 1 As shown, the encapsulation transfer method for LED provided by the present invention includes cutting, stretching, filling, curing, first grinding, segmentation and transfer, and optionally also includes welding and coating after the segmentation and transfer.

[0034] In step (1) (cutting), before cutting, the top surface of the wafer to be cut is an electrode layer and the bottom surface is a sapphire base layer, and the surface of the electrode layer has a bump contact. The bump contact serves to connect to the outside world for electrical conduction. The electrode layer serves to generate current. The sapphire base layer serves to provide a substrate and physical support for lattice growth. When cutting, the electrode layer of the wafer is cut into and through the sapphire base layer but not through the expanded polishing tape to form a plurality of transverse and / or longitudinal cutting grooves inside the wafer. In the present invention, the term "transverse" refers to a direction parallel to the radial direction of the wafer. When cutting transversely, the wafer is cut vertically downward from the electrode layer side of the wafer along the transverse direction of the wafer; the term "longitudinal" refers to a direction perpendicular to the "transverse". When cutting longitudinally, the wafer is cut vertically downward from the electrode layer side of the wafer along the longitudinal direction of the wafer. That is, the terms "transverse" and "longitudinal" refer to the direction of entry from the surface of the electrode layer, and the two are relative directions. Whether it is horizontal cutting or vertical cutting, the cutting depth direction is vertically downward, and the cutting grooves formed thereby are in the shape of a grid alternating vertically and horizontally. After the cutting is completed, the wafer is actually divided into a number of chips, and the bottom of each chip is connected together by an expanded polishing tape, and the spacing between the chips can be controlled by the stretching amplitude of the expanded polishing tape. In addition, after cutting, each chip preferably has two bump contacts.

[0035] In step (2) (stretching), the expanded polishing tape is stretched according to the preset contact spacing on the PCB substrate to be transferred to adjust the distance between chips so that the bump contacts on all chips can be subsequently placed in alignment with the preset contacts on the PCB substrate to be transferred.

[0036] In step (3) (filling glue), the black liquid resin glue is filled from the surface of the electrode layer into the cutting groove and overflows the cutting groove and covers the electrode layer and the bump contacts. The present invention does not specifically limit the filling method, and can be specifically carried out by conventional methods such as printing, dispensing or spin coating. Among them, the printing method can be, for example, steel mesh printing, screen printing, etc. The dispensing method can be, for example, first applying the black liquid resin glue to one side of the electrode layer of the wafer through air pressure, screw, solenoid valve or spraying, and then heating and pressurizing the black liquid resin glue to flow into the cutting groove. The spin coating method can be, for example, first pre-setting the black liquid resin glue on one side of the electrode layer of the wafer, and then rotating the wafer to cause the black liquid resin glue to flow into the cutting groove and evenly distribute on the surface of the wafer. In addition, preferably, the black liquid resin glue contains 20 to 80 parts by weight of epoxy resin, 20 to 80 parts by weight of epoxy curing agent, 0.1 to 10 parts by weight of catalyst, 0.1 to 10 parts by weight of colorant, and optionally 0 to 400 parts by weight of filler, 0 to 10 parts by weight of adhesion promoter, 0 to 5 parts by weight of leveling agent, 0 to 5 parts by weight of dispersant, and 0 to 100 parts by weight of toughening agent. Among them, the specific selection of each component is well known to those skilled in the art and will not be repeated here. At this time, the black liquid resin glue has a high degree of insulation, and the black encapsulation glue formed by it can block the metal migration between electrodes and prevent electromigration short circuits in harsh environments such as high temperature and high humidity. The black liquid resin glue can be a ready-made black resin glue in liquid state, or it can be obtained by heating and melting a black glue film, and there is no special limitation on this.

[0037] In step (4) (curing), the filler is heated to cure the black liquid resin glue to obtain a cured part, at which time the chip spacing is fixed. The heating conditions can be adjusted according to the specific selection of the black liquid resin glue so that the black liquid resin glue is fully cured. For example, the heating temperature can be 80-200°C and the heating time can be 5-60 minutes.

[0038] In step (5) (grinding), the cured part is still fixed by the expanded grinding tape, and the surface of the cured part with the bump contact is first ground until at least the bump contact is exposed, and then the expanded grinding tape is peeled off to obtain a polished part. The first grinding is preferably horizontal grinding, so that the bump contacts at various positions on the surface of the polished part obtained are located at the same horizontal position, which is more conducive to subsequent transfer and welding. The surface of the first polished part with the bump contact is preferably fixed by grinding tape.

[0039] In step (6) (i.e., splitting and transferring), the wafer of the polished piece is turned over and the electrode layer side is fixed with polishing tape, and then cut into several small chip modules along the cutting groove, and then the several small chip modules are transferred to the PCB substrate. Each small chip module obtained in this process preferably has at least one chip independently. After the first polished piece is turned upside down, one side of the sapphire base layer is located on the top, and the electrode layer and the bump contact side are located on the bottom. In addition, before cutting, the sapphire base layer side surface of the first polished piece can be polished a second time, or it can be cut directly without any polishing. Figure 1 As shown, the wafer can be cut into independent single chips, in which case each chip module only includes a single chip; the wafer can also be cut into several groups of multiple chips, in which case each chip module includes multiple chips; mixed cutting can also be adopted, that is, some chip modules include a single chip, and the remaining chip modules include multiple chips. In addition, when several small chip modules are transferred to the PCB substrate, the bump contacts on the chip are aligned with the preset contacts on the PCB substrate to be transferred and then placed.

[0040] In step (7) (i.e. welding), the bump contacts on the chip in each small chip module are aligned with the pre-set contacts on the PCB substrate to be transferred and then welded to obtain a welded part. The welding method can be carried out in a conventional manner in the art, which is known to those skilled in the art and will not be described in detail here.

[0041] In step (8) (i.e., coating), after the chiplet module is fixed on the PCB substrate, a transparent plastic layer is provided on the side of the obtained soldering part away from the PCB substrate. The method of providing the transparent plastic layer is not particularly limited, and generally, a transparent plastic composition is applied to the side of the soldering part away from the PCB substrate, and then the transparent plastic composition is cured by heating and / or UV irradiation according to its physicochemical properties to obtain a transparent plastic layer.

[0042] The product obtained by the encapsulation transfer method for LED provided by the present invention includes a PCB substrate, a chip, a black insulating encapsulation glue and a transparent plastic sealing layer, wherein the preset contacts on the PCB substrate are connected to the bump contacts on the chip, and the transparent plastic sealing layer is located on the side of the chip away from the bump contacts.

[0043] The present invention will be described in detail below through examples.

[0044] The black liquid resin glue used in the following examples and comparative examples is composed of 40 parts by weight of bisphenol A epoxy resin (EPICLON EXA-850CRP of DIC Corporation), 40 parts by weight of epoxy curing agent (pentaerythritol tetrakis (3-mercaptopropionate), PEMP of SC Organic Chemical Co., Ltd.), 0.5 parts by weight of catalyst (NOVACURE HXA9322HP of Asahi Kasei Corporation), 0.5 parts by weight of colorant (carbon black), 18 parts by weight of filler (silicon dioxide) and 1 part by weight of leveling agent (γ-mercaptopropyltrimethoxysilane).

[0045] Example 1

[0046] A method for encapsulation transfer of LEDs, the method comprising the following steps:

[0047] (1) Cutting: Select a 4-inch wafer with a preset chip size of 100μm×100μm and a cutting groove width of 100μm. Fix the sapphire base layer of the wafer with an expanded polishing tape before cutting. The top surface of the wafer is the electrode layer and the bottom surface is the sapphire base layer. The electrode layer is provided with bump contacts. The expanded polishing tape has a stretchable property. When cutting, cut along the preset cutting groove from one side of the electrode layer of the wafer until the sapphire base layer is cut through but the expanded polishing tape is not cut through. All chips on the wafer are electrically separated. Each chip has two bump contacts. At this time, the wafer contains approximately 170,000 independent chips.

[0048] (2) Stretching: The expanded polishing tape is stretched according to the preset chip spacing on the PCB substrate to be transferred to adjust the distance between the chips so that the bump contacts on all the chips can be subsequently aligned with the preset contacts on the PCB substrate to be transferred;

[0049] (3) Glue filling: black liquid resin glue is applied to the electrode layer of the wafer by air pressure, and then the black liquid resin glue is caused to penetrate into and overflow the cutting groove by heating and pressurizing. The black liquid resin glue covers the bump contacts to obtain a glue-filled part;

[0050] (4) Curing: The filled part is heated to 150°C and maintained for 30 minutes to allow the black liquid resin glue to cure and obtain a cured part. At this time, the chip spacing is fixed by bonding with the black liquid resin glue;

[0051] (5) Grinding: Grinding the surface of the cured part having the bump contact point horizontally until at least the bump contact point is exposed, and removing the expanded grinding tape to obtain a first-grinded part;

[0052] (6) Split and transfer: Turn the first polished piece upside down, and then fix the electrode layer on the first polished piece with polishing tape. Cut the wafer into several small chip modules along the middle line of the solidified black resin glue in the cutting groove. Each small chip module has one or more chips. Transfer the several small chip modules to the PCB substrate. At this time, align the bump contacts on the chip with the preset contacts on the PCB substrate and place them.

[0053] (7) Welding: Align the bump contacts on the chip in each small chip module with the preset contacts on the PCB substrate and then weld them to obtain a welded part;

[0054] (8) Coating: After the chiplet module is fixed on the PCB substrate, a transparent plastic sealing layer is applied to the side of the resulting welded part away from the PCB substrate.

[0055] Example 2

[0056] A method for encapsulation transfer of LEDs, the method comprising the following steps:

[0057] (1) Cutting: Select a 4-inch wafer with a preset chip size of 50μm×50μm and a cutting groove width of 100μm. Fix the sapphire base layer of the wafer with an expanded polishing tape before cutting. The top surface of the wafer is the electrode layer and the bottom surface is the sapphire base layer. The electrode layer is provided with bump contacts. The expanded polishing tape has a stretchable property. When cutting, cut along the preset cutting groove from one side of the electrode layer of the wafer until the sapphire base layer is cut through but the expanded polishing tape is not cut through. All chips on the wafer are electrically separated. Each chip has two bump contacts. At this time, the wafer contains approximately 300,000 independent chips.

[0058] (2) Stretching: The expanded polishing tape is stretched according to the preset chip spacing on the PCB substrate to be transferred to adjust the distance between the chips so that the bump contacts on all the chips can be subsequently aligned with the preset contacts on the PCB substrate to be transferred;

[0059] (3) Glue filling: black liquid resin glue is applied to the electrode layer of the wafer by air pressure, and then the black liquid resin glue is caused to penetrate into and overflow the cutting groove by heating and pressurizing. The black liquid resin glue covers the bump contacts to obtain a glue-filled part;

[0060] (4) Curing: The glue-filled part is heated to 80°C and maintained for 60 minutes to allow the black liquid resin glue to cure, thereby obtaining a cured part. At this time, the chip spacing is fixed by bonding with the black liquid resin glue;

[0061] (5) Grinding: Grinding the surface of the cured part having the bump contact point horizontally until at least the bump contact point is exposed, and removing the expanded grinding tape to obtain a first-grinded part;

[0062] (6) Split and transfer: Turn the first polished piece upside down, and then fix the electrode layer on the first polished piece with polishing tape. Cut the wafer into several small chip modules along the middle line of the solidified black resin glue in the cutting groove. Each small chip module has one or more chips. Transfer the several small chip modules to the PCB substrate. At this time, align the bump contacts on the chip with the preset contacts on the PCB substrate and place them.

[0063] (7) Welding: Align the bump contacts on the chip in each small chip module with the preset contacts on the PCB substrate and then weld them to obtain a welded part;

[0064] (8) Coating: After the chiplet module is fixed on the PCB substrate, a transparent plastic sealing layer is applied to the side of the resulting welded part away from the PCB substrate.

[0065] Example 3

[0066] A method for encapsulation transfer of LEDs, the method comprising the following steps:

[0067] (1) Cutting: Select a 4-inch wafer with a preset chip size of 200μm×200μm and a cutting groove width of 200μm. Fix the sapphire base layer of the wafer with an expanded polishing tape before cutting. The top surface of the wafer is the electrode layer and the bottom surface is the sapphire base layer. The electrode layer is provided with bump contacts. The expanded polishing tape has a stretchable property. When cutting, cut along the preset cutting groove from one side of the electrode layer of the wafer until the sapphire base layer is cut through but the expanded polishing tape is not cut through. All chips on the wafer are electrically separated. Each chip has two bump contacts. At this time, the wafer contains approximately 40,000 independent chips.

[0068] (2) Stretching: The expanded polishing tape is stretched according to the preset chip spacing on the PCB substrate to be transferred to adjust the distance between the chips so that the bump contacts on all the chips can be subsequently aligned with the preset contacts on the PCB substrate to be transferred;

[0069] (3) Glue filling: black liquid resin glue is applied to the electrode layer of the wafer by air pressure, and then the black liquid resin glue is caused to penetrate into and overflow the cutting groove by heating and pressurizing. The black liquid resin glue covers the bump contacts to obtain a glue-filled part;

[0070] (4) Curing: The glue-filled part is heated to 200°C and maintained for 5 minutes to allow the black liquid resin glue to cure and obtain a cured part. At this time, the chip spacing is fixed by bonding with the black liquid resin glue;

[0071] (5) Grinding: Grinding the surface of the cured part having the bump contact point horizontally until at least the bump contact point is exposed, and removing the expanded grinding tape to obtain a first-grinded part;

[0072] (6) Split and transfer: Turn the first polished piece upside down, and then fix the electrode layer on the first polished piece with polishing tape. Cut the wafer into several small chip modules along the middle line of the solidified black resin glue in the cutting groove. Each small chip module has one or more chips. Transfer the several small chip modules to the PCB substrate. At this time, align the bump contacts on the chip with the preset contacts on the PCB substrate and place them.

[0073] (7) Welding: Align the bump contacts on the chip in each small chip module with the preset contacts on the PCB substrate and then weld them to obtain a welded part;

[0074] (8) Coating: After the chiplet module is fixed on the PCB substrate, a transparent plastic sealing layer is applied to the side of the resulting welded part away from the PCB substrate.

[0075] Comparative Example 1

[0076] Select a 4-inch wafer, preset the chip size to 100μm×100μm and the cutting groove width to 100μm. Cut the wafer directly into about 170,000 chips, and then transfer the chips one by one to the PCB substrate. At this time, the bump contacts on the chip need to be aligned with the preset contacts on the PCB substrate, placed and welded, and then along the rows of chips, dot the black bottom filler back and forth row by row and wait for the black bottom filler to self-fill (the black bottom filler is liquid at this time and will flow, so the height of the side of the chip cannot be accurately controlled, and a concave surface will be formed between the chips, and some may climb to the sapphire luminous surface), solidify, and then apply a transparent plastic layer.

[0077] When the method of Example 1 is used for encapsulation transfer, the first cutting also requires cutting 170,000 chips, but the second cutting only cuts them into small chip modules, which contain multiple chips and are connected by resin, greatly reducing the number of chips transferred from the wafer to the PCB board. If they are transferred one by one, it takes about 170,000 times, but if each chip module contains 1,000 chips, it only needs to be transferred 170 times, and the spacing between these 1,000 chips is fixed in advance. That is, the method provided by the present invention can significantly improve the transfer efficiency.

[0078] Test Case

[0079] (1) Transfer efficiency: Chips were transferred according to the methods of Examples 1 to 3 and Comparative Example 1, and the number of chips transferred per minute was measured. The results are shown in Table 1.

[0080] (2) Transfer accuracy: If the chips are picked up and transferred one by one, and the positioning accuracy deviation is 5%, then the chip module transfer accuracy can be improved by 5%.

[0081] (3) Uniformity of ink color of the bottom plate: With the traditional bottom filling method, due to the narrow spacing between the electrodes under the chip, the glue does not flow smoothly, and the fillers contained in the glue will accumulate, resulting in uneven bottom color. However, with the method provided by the present invention, there is no problem of flow obstruction, and the glue evenly covers the electrodes and the sapphire surface, and the bottom color is very uniform.

[0082] (4) Screen smear rate: The chip was transferred 1000 times according to the methods of Examples 1 to 3 and Comparative Example 1, and the screen smear situation after each transfer was observed and the screen smear rate ε was calculated, ε=A / 1000, A is the number of screen smears. The results are shown in Table 1.

[0083] (5) Side light interference: As mentioned above, the method provided by the present invention needs to fill the cutting groove with black liquid resin before chip transfer. After curing, the black liquid resin can prevent the side light interference of the chip. That is, the black liquid resin glue cured before transfer in the method provided by the present invention can effectively prevent the side light interference of Mini LED and Micro LED. However, if the chip is transferred one by one, the distance between the chips is very small, which will cause mutual light interference.

[0084]

[0085] It can be seen from the results in Table 1 that the method provided by this embodiment can maximize the use of the existing mature equipment production line capacity, realize batch transfer of small chip modules, realize low-cost, large-scale and efficient transfer of Mini LED and Micro LED, and improve transfer efficiency and transfer accuracy. Furthermore, the method provided by the present invention does not require bottom filling after transfer, and is more stable when coated with a transparent plastic film after welding, which solves the problem of uneven ink color on the display bottom plate and avoids the problem of chip position drifting and screen distortion when the transparent plastic film is subsequently coated after the size of the chip and substrate contacts is greatly reduced. In addition, the black liquid resin used in the method provided by the present invention has been solidified before transfer, which can prevent interference from the side light of Mini LED and Micro LED.

[0086] From the comparison between Examples 1 to 3 and Comparative Example 1, it can be seen that the existing encapsulation transfer method of gradually transferring a single chip is inefficient and difficult to accurately align. When applying the transparent plastic sealing layer, displacement is likely to occur, resulting in a flowery screen, and mixed light interference is likely to occur between adjacent MiniLEDs / Micro LEDs.

[0087] Economic benefit calculation

[0088] Take 2025, when LEDs are widely used, as an example. Assuming that the output value of LED panels in 2025 is 2.5 billion US dollars, the current median assembly defect rate is 15%, of which 90% can be repaired but requires additional labor and production lines, increasing costs by more than 10%. The adoption of the OSTMC process method will bring the following savings to the industry:

[0089] 25×15%×(1-90%)+25×15%×90%×10%=US$71 million

[0090] At the same time, the method can also improve the transfer efficiency by at least 50%. For example, in the past, it was necessary to pick up a single particle and then transfer it to the substrate. With the method provided by the present invention, multiple particles can be picked up and transferred in groups. At the same time, the method provided by the present invention can also improve the uniformity and reliability of the light output of the display panel, thereby increasing the market value of the product. Due to the different processes of various companies in the market and their high confidentiality, the panel prices vary greatly. It is difficult to find a benchmarking process to measure the economic benefits of this part.

[0091] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for encapsulation transfer of LED, characterized in that: The method comprises the following steps: (1) Cutting: The sapphire base layer of the wafer is fixed by an expanded polishing tape and then cut. The top surface of the wafer is an electrode layer and the bottom surface is a sapphire base layer. The electrode layer is provided with bump contacts. The expanded polishing tape has a stretchable property. During cutting, the electrode layer of the wafer is cut into and through the sapphire base layer but not through the expanded polishing tape, forming a plurality of transverse and / or longitudinal cutting grooves. At this time, the wafer is divided into a plurality of chips. (2) Stretching: The expanded polishing tape is stretched according to the preset contact spacing on the PCB substrate to be transferred to adjust the distance between chips so that the bump contacts on all chips can be subsequently aligned with the preset contacts on the PCB substrate to be transferred; (3) Glue filling: Fill the black liquid resin glue from the surface of the electrode layer into the cutting groove and overflow the cutting groove and cover the electrode layer and the bump contact to obtain a glue-filled part; (4) Curing: The glue filling part is heated to cure the black liquid resin glue to obtain a cured part, at which time the chip spacing is fixed; (5) Grinding: Grinding the surface of the cured part having the bump contact for the first time until at least the bump contact is exposed, and removing the expanded grinding tape to obtain a polished part; (6) Splitting and transfer: Flip the polished wafer and fix the electrode layer with polishing tape, cut it into several small chip modules along the cutting groove, and then transfer the several small chip modules to the PCB substrate to be transferred.

2. The encapsulation transfer method for LED according to claim 1, characterized in that: Each chip obtained in step (1) has two bump contacts.

3. The encapsulation transfer method for LED according to claim 1, characterized in that: In step (3), the black liquid resin glue is filled into the cutting groove by printing, dispensing or spin coating.

4. The encapsulation transfer method for LED according to claim 3, characterized in that: The printing method is steel mesh or screen printing.

5. The encapsulation transfer method for LED according to claim 3, characterized in that: The dispensing method is to first fill the black liquid resin glue on one side of the electrode layer of the wafer by air pressure, screw, solenoid valve or spraying, and then promote the black liquid resin glue to flow into the cutting groove by heating and pressurizing.

6. The encapsulation transfer method for LED according to claim 3, characterized in that: The spin coating method is to pre-place the black liquid resin glue on one side of the electrode layer of the wafer, and then rotate the wafer to make the black liquid resin glue flow into the cutting groove and evenly distribute it on the surface of the wafer.

7. The encapsulation transfer method for LED according to claim 1, characterized in that: The first grinding in step (5) is horizontal grinding.

8. The encapsulation transfer method for LED according to claim 1, characterized in that: In step (6), each small chip module has at least one chip. When several small chip modules are transferred to the PCB substrate to be transferred, the bump contacts on the chip are aligned with the preset contacts on the PCB substrate to be transferred and then placed.

9. The encapsulation transfer method for LED according to claim 1, characterized in that: The method also includes step (7) welding: aligning the bump contacts on the chip in each small chip module with the preset contacts on the PCB substrate to be transferred and then welding them to obtain a welded part.

10. The encapsulation transfer method for LED according to claim 9, characterized in that: The method further comprises step (8) coating: providing a transparent plastic sealing layer on the side of the welding part away from the PCB substrate.

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