Bonding type high-transmittance transparent screen based on Mini LED COB direct display technology

Abstract

The utility model discloses a binding type high-transmittance transparent screen based on Mini LED COB direct display technology, which comprises a base material, more than one driving chip, more than one LED wafer, a positive electrode power line, a negative electrode power line and a signal line, the positive electrode power line, the negative electrode power line and the signal line are respectively and fixedly arranged on the base material, the driving chip and the LED wafer are fixed on the base material, and the LED wafer is fixed on the base material. The positive power supply end of the driving chip is bound with the positive power line through a metal wire, the grounding end of the driving chip is bound with the negative power line through a metal wire, the signal end of the driving chip is bound with the signal line through a metal wire, and the LED wafer is bound with the driving chip through a metal wire. According to the utility model, the driving chip and the LED wafer are fixed on the base material by adopting a direct bonding mode, so that the area of the base material occupied by the LED and the driving chip can be reduced to the greatest extent, the light transmittance of the whole product is improved, and the cost of the product can be reduced at the same time.

Description

Technical Field

[0001] This utility model discloses a transparent screen, particularly a bonded high-transparency transparent screen based on Mini LED COB direct display technology, which can be widely used in various fields such as outdoor advertising, indoor display, stage performance, museums, exhibition halls, science and technology museums, multimedia teaching, smart windows, indoor partitions, and LCD backlights. Background Technology

[0002] LED transparent screen is a new type of display screen that uses LED dot matrix technology. It forms images and text by controlling the on / off state and color changes of LED beads. These LED beads are arranged in a matrix, and each bead can be controlled independently to achieve various complex display effects.

[0003] The substrate of a transparent screen is typically made of transparent materials, such as transparent glass or acrylic, to ensure light transmission. LED beads are mounted on the transparent substrate, and through special structural designs, such as arranging the beads along the edges of the substrate or using perforations or grids, light obstruction is reduced, thus achieving the transparent effect. Alternatively, a circuit board with a conventional substrate can be used, with perforations created in the substrate to achieve the same transparency.

[0004] Transparent screens can be installed in key locations such as shop windows, entrances, or inside brand stores in shopping malls, department stores, and brand boutiques to dynamically display product advertisements, promotional information, or brand stories, attracting customer attention and enhancing brand awareness and sales. They can also be seamlessly integrated into architectural elements such as glass curtain walls, windows, and columns, beautifying the building's appearance and enhancing its technological and modern feel. Custom designs can be tailored to the building's style and characteristics, achieving a perfect fusion with the architecture. Alternatively, in museums, science and technology museums, and art galleries, they can be used to display images and videos of cultural relics, artworks, or technological products, allowing viewers to clearly see the details behind the exhibits, enhancing the interactivity and engagement of the exhibition. They can also be used in stage performances, entertainment venues, public spaces, and transportation hubs, with extremely wide applications.

[0005] In the existing technology, transparent screens are all made by soldering LED beads onto a substrate. On the one hand, the finished LED beads are expensive, making the entire transparent screen expensive. On the other hand, the packaged finished LED beads, whether they have a driving function or are just LED beads, inevitably include a lamp holder and lamp cover structure, which occupy a large space. After soldering, they will occupy a large substrate area, thus affecting the light transmittance of the transparent screen to a certain extent. Summary of the Invention

[0006] In view of the shortcomings of the above-mentioned existing transparent screens, which are made by welding pre-packaged LED beads onto a substrate, resulting in high cost and poor light transmission, this utility model provides a bonding-type high-transparency transparent screen based on Mini LED COB direct display technology. It uses a direct bonding method to fix the driver chip and LED wafer onto the substrate, which can minimize the area occupied by the LED and driver chip on the substrate.

[0007] The technical solution adopted by this utility model to solve its technical problem is: a bonding-type high-transparency transparent screen based on Mini LED COB direct display technology. The transparent screen includes a substrate, one or more driver chips, one or more LED chips, a positive power line, a negative power line, and a signal line. The positive power line, negative power line, and signal line are respectively fixed on the substrate. The driver chip and the LED chip are fixed on the substrate. The positive power terminal of the driver chip is bonded to the positive power line through a metal wire. The ground terminal of the driver chip is bonded to the negative power line through a metal wire. The signal terminal of the driver chip is bonded to the signal line through a metal wire. The LED chip is bonded to the driver chip through a metal wire.

[0008] The technical solution adopted by this utility model to solve its technical problem further includes:

[0009] A display unit consists of a driver chip and a set of LED chips.

[0010] The driver chip is a four-pin driver chip, including a positive power terminal, a ground terminal and two signal terminals. Both signal terminals have I / O functions, and each signal terminal is bonded to a signal line through a metal wire.

[0011] The driving chip is a three-pin driving chip, including a positive power terminal, a ground terminal and a signal terminal. Positive power line, negative power line and signal line are respectively arranged on the substrate. The signal terminal of each driving chip is bonded to the signal line through a metal wire.

[0012] The driver chip is a five-pin driver chip, including a positive power terminal, a ground terminal, and three signal terminals. All three signal terminals have I / O functions. One signal terminal is provided on one side and two signal terminals are provided on the other side. One or two signal lines are provided between adjacent display units. If only one signal line is provided, the signal terminal is bonded to the signal line by a metal wire if only one signal line is provided on one side, and the two signal lines are bonded to the signal line by a metal wire if only one signal line is provided on one side. If only two signal lines are provided, the signal terminal is bonded to the signal line by a metal wire if only one signal line is provided on one side, and the two signal lines are bonded to the signal line by a metal wire if only one signal line is provided on one side.

[0013] The driver chip is a six-pin driver chip, including a positive power terminal, a ground terminal and four signal terminals. Each of the four signal terminals has I / O function. Each of the four signal terminals is bonded to a signal line through a metal wire. Two of the signal lines are connected to the front-end driver chip, and the other two signal lines are connected to the rear-end driver chip.

[0014] A set of LED chips includes a blue LED chip, a green LED chip, and a red LED chip. The blue LED chip, green LED chip, and red LED chip are arranged in a straight line or in a triangular pattern on the substrate.

[0015] The blue, green, and red LED chips are driven by a common anode. The anodes of the blue, green, and red LED chips are bonded to the positive power line via a metal wire, and the cathodes of the blue, green, and red LED chips are bonded to the corresponding pins of the driver chip via a metal wire.

[0016] The display units are arranged in rows and columns on the substrate, with two rows or two columns forming a group. The signal line of the last display unit in each row or column is connected to the signal line of the adjacent display unit in the same group through an adapter cable.

[0017] The substrate material is selected from transparent glass, transparent soft PC or FR4.

[0018] The beneficial effects of this invention are: This invention uses a direct bonding method to fix the driver chip and LED wafer onto the substrate, which can minimize the area occupied by the LED and driver chip on the substrate, improve the overall light transmittance of the product, and reduce product cost. Compared with other packaging technologies, COB technology is inexpensive (only about 1 / 3 the cost of the same chip), space-saving, and has a mature process.

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the circuit structure of this utility model.

[0021] Figure 2 for Figure 1 A partial enlarged structural diagram of A.

[0022] Figure 3 This is a flowchart of the processing of this utility model.

[0023] In the diagram, 1-substrate, 2-driver chip, 3-LED chip, 31-blue LED chip, 32-green LED chip, 33-red LED chip, 4-positive power line, 5-negative power line, 6-signal line, 7-adapter cable, 8-metal wire. Detailed Implementation

[0024] This embodiment is a preferred embodiment of the present invention. All other embodiments that are the same as or similar to this embodiment in principle and basic structure are within the protection scope of the present invention.

[0025] Please refer to the appendix for details. Figure 1 and attached Figure 2 This utility model primarily protects a bonded high-transparency transparent screen based on Mini LED COB direct display technology. COB, or Chip on Board, is a technology that directly mounts integrated circuit chips onto a circuit board. This involves directly fixing the bare chip onto the circuit board using specific processes and achieving electrical connection between the chip and the circuitry on the circuit board through methods such as wire bonding. The transparent screen mainly includes a substrate 1, one or more driver chips 2, one or more LED chips 3, a positive power line 4, a negative power line 5, and a signal line 6. The positive power line 4, negative power line 5, and signal line 6 are respectively fixed on the substrate 1. The driver chip 2 and the LED chip 3 are fixed on the substrate 1. The positive power terminal of the driver chip 2 is bonded to the positive power line 4 via a metal wire 8, the ground terminal of the driver chip 2 is bonded to the negative power line 5 via a metal wire 8, the signal terminal of the driver chip 2 is bonded to the signal line 6 via a metal wire 8, and the LED chip 3 is bonded to the driver chip 2 via a metal wire 8.

[0026] In this embodiment, a driver chip 2 and a group of LED chips 3 constitute a display unit.

[0027] In this embodiment, the driver chip 2 and the LED chip 3 are located on the same side of the substrate 1, and preferably the driver chip 2 and the LED chip 3 are arranged side by side.

[0028] In this embodiment, the driver chip 2 is a four-pin driver chip, including a positive power terminal, a ground terminal, and two signal terminals. Both signal terminals have I / O functions. In this embodiment, they are marked DL and DR respectively. The two signal terminals are bonded to a signal line 6 through a metal wire 8. One signal line 6 is connected to the front-end (i.e., the display unit set at the front end) driver chip 2, and the other signal line 6 is connected to the rear-end (i.e., the display unit set at the rear end) driver chip 2. If the signal line 6 is set in the display unit at the very front or the very back end, it is connected to the controller, thus forming a connection method of parallel power supply and series communication control.

[0029] In practice, the driver chip 2 can also be designed with three, five, or six pins.

[0030] When the driver chip 2 adopts a three-pin design, it includes a positive power supply terminal, a ground terminal, and a signal terminal. The substrate 1 is provided with a positive power supply line 4, a negative power supply line 5, and a signal line 6. The signal terminals of each driver chip 2 are bonded to the signal line 6 through a metal wire 8. The signal line 6 is connected to the controller, thereby forming a connection method of parallel power supply and parallel communication control.

[0031] The driver chip 2 is a five-pin design, including a positive power supply terminal, a ground terminal, and three signal terminals. All three signal terminals have I / O functions. One signal terminal is located on one side, and two signal terminals are located on the other side. One or two signal lines 6 can be provided between adjacent display units. If only one signal line 6 is provided, and one signal terminal is provided on one side, this terminal is bonded to the signal line 6 via a metal wire 8. If two signal lines 6 are provided, each signal terminal is bonded to the signal line 6 via a metal wire 8. If two signal lines 6 are provided, and one signal terminal is provided on one side, this terminal... The signal line 6 is bonded to the signal line 6 by a metal wire 8. Each of the two signal lines is bonded to the signal line 6 by a metal wire 8. The signal line 6 adopts a redundant design to improve the stability of signal control. In this embodiment, the signal line 6 on one side is connected to the front-end (i.e., the display unit set at the front end) driver chip 2, and the signal line 6 on the other side is connected to the rear-end (i.e., the display unit set at the rear end) driver chip 2. If the signal line 6 is set in the display unit at the very front or the very back end, it is connected to the controller, thus forming a connection method of parallel power supply and series communication control.

[0032] The driver chip 2 is a six-pin design, including a positive power terminal, a ground terminal, and four signal terminals. All four signal terminals have I / O functions. Each of the four signal terminals is bonded to a signal line 6 via a metal wire 8. Two of the signal lines 6 are connected to the front-end (i.e., the display unit at the front end) driver chip 2, and the other two signal lines 6 are connected to the rear-end (i.e., the display unit at the rear end) driver chip 2. If the signal line 6 is located in the display unit at the very front or the very back end, it is connected to the controller, thus forming a parallel power supply and series communication control connection. The signal line 6 adopts a redundant design, which can improve the stability of signal control.

[0033] In this embodiment, a set of LED chips 3 includes a blue LED chip 31, a green LED chip 32, and a red LED chip 33. The blue LED chip 31, green LED chip 32, and red LED chip 33 are arranged in a straight line on the substrate 1. In specific implementation, the blue LED chip 31, green LED chip 32, and red LED chip 33 can also be arranged in a triangular shape.

[0034] In this embodiment, the blue LED chip 31, green LED chip 32, and red LED chip 33 adopt a common anode driving method to improve their light emission effect and increase brightness. The anodes of the blue LED chip 31, green LED chip 32, and red LED chip 33 are electrically connected to the positive power line 4, and the cathodes of the blue LED chip 31, green LED chip 32, and red LED chip 33 are electrically connected to the corresponding pins of the driver chip 2. In specific implementation, the blue LED chip 31, green LED chip 32, and red LED chip 33 can also adopt a common cathode driving method.

[0035] In this embodiment, the anode and cathode of the blue LED chip 31 and the green LED chip 32 are respectively bonded to the corresponding power lines via a metal wire 8. The anode of the red LED chip 33 is directly attached to the positive power line 4 via conductive adhesive, and the cathode of the red LED chip 33 is bonded to the negative power line 5 via a metal wire 8. In a specific implementation, the anode and cathode of the red LED chip 33 can also be respectively bonded to the corresponding power lines via a metal wire 8, and the anodes of the blue LED chip 31 and the green LED chip 32 can also be directly attached to the positive power line 4 via conductive adhesive.

[0036] In this embodiment, the blue LED chip 31, green LED chip 32 and red LED chip 33 typically have sizes between 100 micrometers and 300 micrometers, and can even have a chip size of 90 micrometers, which is referred to as Mini LED.

[0037] In this embodiment, the display units are arranged in rows and columns on the substrate 1, or in a matrix arrangement. The spacing between adjacent display units is 5 to 20 times the size of the LED chip. Two rows or two columns form a group. The signal line 6 of the last display unit in each row or column is connected to the signal line 6 of the adjacent display unit in the same group through the adapter line 7. Thus, the control signals of the two rows or two columns of display units in a group form a redundant structure. When the driver chip in one of the display units is damaged, the control signal can be transmitted from the other side, which only affects the normal display of the one display unit and does not affect the display of the entire row or column.

[0038] In this embodiment, the material of the substrate 1 can be transparent glass, transparent soft PC or FR4.

[0039] The aforementioned Mini LED bonding structure can be used in direct-display transparent screens. In the field of transparent displays, "direct display" refers to a display technology that directly utilizes light-emitting elements as pixels to achieve image display, without the need for additional backlighting or other auxiliary means to illuminate the pixels. Mini LED direct-display technology uses Mini LED beads directly as pixels. Based on the electroluminescence effect of light-emitting diodes, when current passes through a semiconductor material, electrons and holes recombine to generate photons, releasing energy to achieve self-emissive display. Each Mini LED can be independently controlled, enabling local dimming, thus making blacks purer, significantly improving contrast, and enhancing the three-dimensionality and depth of the image. Using self-emissive technology, each pixel can emit light independently. Compared to some display technologies that require backlighting, this achieves higher brightness and contrast, making the displayed image clearer and more vivid, brighter in bright areas and darker in dark areas. It can achieve pixel-level pure black display, making the black parts of the image deeper, resulting in higher overall contrast, better display effects, and richer image layering and detail. Mini LED direct-view technology typically uses a smaller current drive, reducing power consumption. At the same time, due to the good thermal stability and other characteristics of Mini LED itself, it also improves the lifespan of the display screen.

[0040] This invention can be used in direct-display transparent screen terminal products such as vehicle screens, shopping mall displays, advertising screens, and queuing screens. In addition, it can also be used as a backlight module for LCD screens, which provides more uniform light emission and better lighting effect.

[0041] Please refer to the appendix for details. Figure 3 The present invention is manufactured using a die bonder and mainly includes the following steps:

[0042] Step S1, substrate loading, which includes the following sub-steps:

[0043] Step S1-1, Substrate feeding: The substrate 1 to be processed is fed into the working position of the die bonder;

[0044] Step S1-2, Substrate identification: The substrate 1 is identified and judged to ensure the accuracy of feeding. In this embodiment, the substrate is identified by scanning a code, which is fast and accurate. The scanning method can be a QR code or a barcode.

[0045] Step S1-3, Solder joint identification: Identify the solder joints on the substrate 1 to ensure that there are no missing solder joints, bridging solder joints, or misaligned solder joints. In this embodiment, machine vision can be used for solder joint identification.

[0046] Step S1-4, Platform XY Correction: Adjust the position of substrate 1 to ensure the accuracy of substrate 1. In this embodiment, the accuracy of the XY position is guaranteed to be within ±20μm.

[0047] Step S2, chip loading, includes the following sub-steps:

[0048] Step S2-1, Chip Feeding: Feed the chips or wafers to be processed, including driver chips and LED wafers;

[0049] Step S2-2, Chip Ring Identification: When loading chips or wafers, the entire tray is loaded. The chip ring can be identified to ensure that the chips are correct. In this embodiment, the chip ring is identified by scanning a code, which is fast and accurate. The scanning method can be a QR code or a barcode.

[0050] In this embodiment, steps S1 and S2 can be performed simultaneously without conflict.

[0051] Step S3, Die Expansion: The entire LED wafer film / chip film is uniformly expanded using an expansion machine, which pulls apart the LED wafers / chips that are tightly packed on the film surface, forming a "die expansion ring", which facilitates subsequent die piercing operations;

[0052] Step S4, Back Adhesive: Place the expanded die ring on the back adhesive machine surface with the silver paste layer already applied, and apply silver paste to the back of the LED wafer / chip. The back adhesive operation is applicable to the whole LED wafer / chip, while the silver paste application operation is applicable to the bulk LED wafer / chip. At the same time, in this step, a dispensing machine is also used to apply an appropriate amount of silver paste to the pads on the substrate.

[0053] Step S5, Crystal Attachment: Place the prepared silver paste-filled expansion ring into the crystal attachment frame, and attach the LED chip to the substrate using a crystal attachment pen. In this embodiment, the crystal attachment step includes the following sub-steps:

[0054] Step S5-1, Crystal Removal: The chip or wafer is removed from the chip ring using the vacuum suction head of the crystal removal pen. In this embodiment, the crystal is removed using a vacuum suction head, and the suction pressure of the vacuum suction head is between 30g and 100g.

[0055] Step S5-2, Chip Identification: Identify the chip or wafer to determine its polarity;

[0056] Step S5-3, Crystal Ring Angle Correction: The wafer platform is used to correct the chip or wafer angle θ and chip polarity. The wafer platform can rotate 360 ​​degrees.

[0057] Step S6, Die Bonding: Place the die-bonded PCB (i.e., substrate) into a hot circulating oven and let it stand at a constant temperature for a period of time until the silver paste cures. Remove it afterward (do not leave it for too long, otherwise the LED chip plating will turn yellow, i.e., oxidize, making bonding difficult). If LED chip bonding is involved, the above steps are required; if only IC chip bonding is involved, these steps are omitted.

[0058] In this embodiment, the die-bonding temperature and settling time are typically as follows:

[0059] When using low-temperature silver paste: the curing temperature is generally around 100℃~150℃. If using 100℃, the curing time is 60~90 minutes; if using 130℃, the curing time is about 40~60 minutes; if using 150℃, the curing time is 30~50 minutes.

[0060] When using medium-temperature silver paste: the curing temperature is usually between 150℃ and 200℃. If it is 160℃, it needs to be cured for 30 to 40 minutes; if it is 180℃, the curing time is 20 to 30 minutes.

[0061] When using high-temperature silver paste: the curing temperature is usually above 200℃, generally in the range of 200℃~300℃. At 200℃, curing takes 20~30 minutes; if the temperature reaches above 250℃, curing time of 15~20 minutes is usually sufficient.

[0062] Step S7, attaching the chip: Use a dispensing machine to apply an appropriate amount of red glue (or black glue) to the IC position on the substrate (taking PCB printed circuit board as an example), and then use an anti-static device (such as a vacuum pen or vacuum suction cup) to correctly place the IC on the red glue or black glue.

[0063] Step S8, Post-soldering inspection: Inspect the solidified chip or wafer to ensure its firmness and prevent movement during the die bonding process. Inspection methods can include vibration, air blowing, etc.

[0064] Step S9, Flying Camera Detection: The chip or wafer is detected by flying camera (in machine vision projects, the axis moves continuously when it reaches the shooting position, instantly completes high-speed capture, processing and feedback of results) to ensure that its position is accurate and there are no missing parts;

[0065] Step S10, Drying: Place the substrate with the attached chip into a hot air circulation oven and place it on a large flat heating plate to maintain a constant temperature for a period of time. Alternatively, it can be naturally cured (natural curing takes longer). For temperature settings and market conditions for heat curing, please refer to step S6.

[0066] Step S11, Substrate Operation: The chip or wafer is bonded using a die bonder. The wafer (LED chip or IC chip) is bridged to the corresponding pads on the substrate using metal wires. This is called COB internal lead bonding, which usually takes a long time.

[0067] Step S12, Pre-test: Use a special testing tool (different equipment is used for different types of COB, usually a high-precision regulated power supply) to test the COB board and rework any unqualified boards.

[0068] Step S13, dispensing: Use a dispensing machine to apply an appropriate amount of the prepared AB glue onto the bonded LED chip to encapsulate and protect it. The chip (i.e., IC) is encapsulated with black glue, and then the appearance is encapsulated according to the requirements.

[0069] Step S14, Curing: Place the sealed substrate in a hot circulating oven and keep it at a constant temperature. Different drying times can be set according to requirements to ensure that the adhesive is cured.

[0070] Step S15, Post-test: The packaged substrate is then subjected to electrical performance testing using specialized testing tools;

[0071] Step S16, Substrate unloading: Unload the bonded substrate to complete the operation.

[0072] The LED chip in the above embodiments can also be called an LED chip. An LED chip is a very small solid; its two electrodes are only visible under a microscope. It emits light only after an electric current is applied. In the manufacturing process, besides soldering the two electrodes of the LED chip to expose the positive and negative terminals, it is also necessary to protect the LED chip and its two electrodes. There are two types of LED chip structures: upright and flip-chip.

[0073] In this embodiment, the LED chip with a top-mounted structure is coated with an epoxy resin layer, with sapphire as the substrate underneath and the electrodes on top. The materials from top to bottom are: P-GaN, light-emitting layer, N-GaN, and substrate. Light emitted from the active region of the top-mounted structure is emitted through the P-type GaN region and the transparent electrode. A metal transparent electrode is fabricated on the P-type GaN to stabilize current diffusion and achieve uniform light emission. In the top-mounted structure LED, the EDp and n electrodes are on the same side of the LED, and the current must flow laterally through the N-GaN layer, resulting in current congestion, high local heat generation, and limitation of the driving current. Furthermore, the poor thermal conductivity of the sapphire substrate severely hinders heat dissipation.

[0074] In this embodiment, the packaging of the upright LED chip includes the following steps:

[0075] Step S1, Die Expanding: Since the LED chips are still closely packed with a very small spacing (usually about 0.1mm) after dicing, it is not conducive to subsequent processes. A die expander is first used to expand the film bonding the LED chips, stretching the spacing between the LED chips to about 0.6mm. Manual expansion can also be used, but it easily causes problems such as chip loss and waste.

[0076] Step S2, Chip Inspection: Microscopic inspection is usually used to check whether there is mechanical damage and tiny pits on the material surface;

[0077] Step S3, dispensing: Apply silver paste or insulating glue to the corresponding positions on the substrate. For GaAs and SiC conductive substrates, silver paste is used for red, yellow, and yellow-green LED chips with back electrodes. For blue and green LED chips on sapphire insulating substrates, insulating glue is used to fix the chips.

[0078] Step S4, Back Adhesive: Back adhesive is applied by first applying silver paste to the back electrode of the LED using an adhesive preparation machine, and then mounting the LED with silver paste on the back onto the substrate.

[0079] In this embodiment, the selected silver paste should be stored in a freezer. Before use, it must be thawed at room temperature for at least 90 minutes. If it is a large container of silver paste, it needs to be warmed up for at least 3 hours. After warming up, it needs to be divided into smaller containers and refrigerated at -5°C. After the silver paste has warmed up, it should be stirred with a glass rod or stainless steel rod. Before use, the stirring rod should be cleaned with a solution such as acetone.

[0080] Step S5, Die Bonding: The die bonder uses vacuum suction to lift the chip. During suction, a needle under the chip lifts it up, allowing it to be held by the vacuum nozzle. The vacuum nozzle, carrying the chip, is then tilted 90° to the support. The vacuum is released, and a small amount of pressure is applied to press the chip onto the silver paste, completing the chip placement. In this embodiment, after the vacuum nozzle lifts the chip, its position can be adjusted by monitoring its image, allowing for timely addition of silver paste and control of the amount of paste.

[0081] Step S6, Baking: After the crystal bonding is completed, baking is required. The baking conditions are 150℃ and the baking time is 1 hour. After baking, the thrust test should be greater than 70g.

[0082] Step S7, Wire Bonding: The end of the gold wire is ignited and sintered into a gold ball using an electronic igniter. Then, the gold ball and the solder pad are made to move relative to each other by ultrasonic oscillation energy under a certain welding pressure using a welding needle. The energy generated by the rapid friction makes the gold ball and the solder pad achieve ion-level fusion.

[0083] Wire bonding is a key step in LED packaging technology. The main processes that need to be monitored are the shape of the gold (or aluminum) wire arch, the shape of the solder joint, and the tension.

[0084] In this embodiment, the requirements for the bonding wires are that the bonding arch height of each gold wire is appropriate, with no collapsed wires, bent wires, or excess solder wire. The diameter of the solder ball should be greater than twice the diameter of the gold wire and less than four times the diameter of the gold wire. The thickness of the solder ball should be greater than 1.2 times the diameter of the gold wire and less than 2.5 times the diameter of the gold wire. When using 0.8~1.0 mil gold wire, the tensile strength should be ≥5g; when using 1.0~1.2 mil gold wire, the tensile strength should be ≥6g.

[0085] Step S8, Applying phosphor: Ordinary LED chips cannot directly emit white light. In this embodiment, white light can be achieved through the following three methods:

[0086] (1) It uses a combination of red, green and blue LEDs to emit light, i.e., multi-chip white LED;

[0087] (2) Using blue LED chips and fluorescent yellow phosphors, white light is obtained by the complementary colors of blue and yellow light, or by using blue LED chips with red and green phosphors, white light is obtained by mixing the blue light emitted by the chip, the red light emitted by the phosphors, and the green light emitted by the phosphors.

[0088] (3) White light is obtained by using the near-ultraviolet light emitted by the ultraviolet LED chip to excite the three primary color photosensitive powders;

[0089] To ensure production consistency, after applying phosphor, the LEDs should be left to stand for half an hour before being baked in the oven. The baking conditions are: 150℃, baking time 1 to 1.5 hours. After baking, the color temperature of the LEDs will increase and the xy color coordinates will decrease.

[0090] After mixing the powder and adhesive, stir for 15-20 minutes, then vacuum to remove air bubbles. The fluorescent powder must be used within 3 hours. If left for a longer period, it must be stirred again, and after stirring, it must be vacuumed and stored.

[0091] Step S9: Applying adhesive. This involves applying adhesive to protect the LED chip. Several methods can be used:

[0092] (1) Manual dispensing: Manual dispensing and encapsulation requires a high level of skill. The main difficulty is controlling the amount of dispensing, because epoxy will thicken during use. In addition, the dispensing of white LEDs also has the problem of phosphor precipitation leading to color difference in light output.

[0093] (2) Potting and encapsulation: Lamp-LED is encapsulated in the form of potting. The potting process is to first inject liquid epoxy into the LED molding cavity, then insert the welded LED bracket, put it in the oven to let the epoxy cure, and then remove the LED from the mold cavity to form the LED.

[0094] (3) Molding and encapsulation: The welded LED bracket is placed into the mold, the upper and lower molds are closed with a hydraulic press and vacuumed, solid epoxy is placed into the inlet of the injection channel, heated and pressed into the injection channel of the mold with a hydraulic push rod, and the epoxy enters each LED molding groove along the injection channel and is cured.

[0095] In this embodiment, the flip-chip with bump electrodes on the active surface (i.e., the active area) is directly bonded to the substrate wiring layer. Two gold wire ball solder joints are fabricated below the P and N electrodes of the chip using a gold wire bonding machine as electrode lead-out mechanisms. Gold wires connect the outer side of the chip to the Si substrate. The LED chip is flip-chip connected to the silicon substrate through bumps. In this way, the heat generated by the high-power LED does not need to pass through the sapphire substrate of the chip, but is directly transferred to the silicon or ceramic substrate with higher thermal conductivity, and then to the metal base.

[0096] In this embodiment, the packaging of the flip-chip LED includes the following steps:

[0097] Step S1, Bottom Metallization of Bumps (UBM). In this embodiment, the bumps are usually made of lead-tin alloy material and generated by reflow soldering, center action and solder drop. They are usually made of 95% lead and 5% tin by weight, or 97% lead and 3% tin by weight. The reflow soldering temperature is controlled between 330 and 350°C.

[0098] Step S2, chip bumps, can be achieved by vapor deposition or electroplating;

[0099] In this embodiment, forming bumps using evaporated solder includes the following sub-steps:

[0100] Step S1-1: Sputter the silicon wafer on site, remove oxides or use a photomask before depositing metal, and at the same time, make the silicon wafer passivation layer and the surface of the pads rougher to improve the adhesion to UBM.

[0101] Step S1-2, Metal Mask: A patterned molybdenum metal mask is used to cover the silicon wafer to facilitate the deposition of UBM and bump metal. The silicon wafer is sandwiched between the backplane and the metal template, and then manually aligned, with the alignment tolerance controlled within 25μm.

[0102] Steps S1-3, UBM vapor deposition: deposit Cr layer, CrCu layer, Cu layer and Au layer in sequence;

[0103] Step S1-4, Solder vapor deposition: A layer of lead-tin alloy is vapor deposited on the UBM surface. The thickness of the lead-tin alloy is about 100~125μm, forming a frustum-shaped cone. In this embodiment, the lead-tin alloy usually uses 95% lead and 5% tin by weight, or 97% lead and 3% tin by weight.

[0104] Step S1-5, Forming bumps into spheres: The bumps are formed into spheres using reflow soldering.

[0105] In this embodiment, forming bumps by electroplating includes the following sub-steps:

[0106] Step S2-1, silicon wafer cleaning: Remove oxides or perform photomask before metal deposition. At the same time, make the silicon wafer passivation layer and pad surface rougher to improve the adhesion to UBM.

[0107] Step S2-2, UBM Deposition: A typical UBM material layer is TiW-Cu-Au, sputtered onto the entire silicon wafer. The UBM layer provides an average current distribution to facilitate consistent electroplating. When the silicon wafer is covered with TiW, a mask is applied to form microspheres or thumbtack-head structures, and Cu and Au of a certain height are deposited. Generally, when the overall height of the bumps is 85μm to 100μm, the height of the microspheres is 10μm to 25μm.

[0108] Step S2-3, Electroplating of solder: Apply the mask again to electroplat the bumps. After the bumps are formed, the mask is peeled off. In this embodiment, the exposed UBM will be naturally etched away within one to two days.

[0109] Step S2-4, Reflow to form spheres: The bumps are formed into spheres using reflow soldering. In this embodiment, reflow helps to prevent the bumps from being damaged during UBM removal.

[0110] In this embodiment, the ball placement method involves applying laser pulses through an optical fiber to a ball-placement head unit for reflow soldering while placing the ball.

[0111] Step S3: Assemble the bumped chip onto the substrate / board;

[0112] Step S4: Fill the bottom holes of the chip with a non-conductive material. When filling, heat the flip chip and the substrate to 70 to 75°C. Use an L-shaped syringe filled with filler to inject the filler bidirectionally along the edge of the chip. Due to the capillary siphon effect of the gap, the filler is sucked in and flows towards the center. There are obstructions at the edge of the chip to prevent it from flowing out. Alternatively, the substrate can be tilted to facilitate the flow.

[0113] After filling, the oven is heated in stages. When the curing temperature reaches about 130℃, it is maintained for 3 to 4 hours to achieve complete curing. The curing temperature should be low to prevent the PCB from thermally deforming.

[0114] When selecting, minimize stress mismatch and ensure that the Z-direction of the packing and the connection point of the protrusion are matched.

[0115] Insufficient filler can cause the wafer to crack, while excessive filler can overflow beyond the bottom of the chip. The filler amount depends on the accurate calculation of the fill space and the precision of the filler tool.

[0116] The filling temperature, especially the preheating, heating and post-filling heating, has a great influence on its fluidity.

[0117] Filling methods generally involve filling from one side, which results in a longer flow time, and filling from both sides, which can lead to the formation of air pockets inside.

[0118] This invention uses a direct bonding method to fix the driver chip and LED wafer onto the substrate, which can minimize the area occupied by the LED and driver chip on the substrate, improve the light transmittance of the entire product, and reduce the product cost. Compared with other packaging technologies, COB technology is inexpensive (only about 1 / 3 the cost of the same chip), space-saving, and has a mature process.

Claims

1. A bonding type high-transparency transparent screen based on Mini LED COB direct display technology, characterized in that: The transparent screen comprises a substrate (1), one or more driving chips (2), one or more LED crystal units (3), a positive power line (4), a negative power line (5) and a signal line (6), the positive power line (4), the negative power line (5) and the signal line (6) are fixedly arranged on the substrate (1), the driving chip (2) and the LED crystal unit (3) are fixed on the substrate (1), the positive power end of the driving chip (2) is connected with the positive power line (4) through a metal wire (8), the grounding end of the driving chip (2) is connected with the negative power line (5) through the metal wire (8), the signal end of the driving chip (2) is connected with the signal line (6) through the metal wire (8), and the LED crystal unit (3) is connected with the driving chip (2) through the metal wire (8). ​ 2. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: One driving chip (2) and one group of LED crystal units (3) form one display unit.

3. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: The driving chip (2) is a four-pin driving chip, comprising a positive power end, a grounding end and two signal ends, the two signal ends have I / O functions, and the two signal ends are respectively connected with one signal line (6) through metal wires (8).

4. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: The driving chip (2) is a three-pin driving chip, comprising a positive power end, a grounding end and one signal end, the substrate (1) is provided with the positive power line (4), the negative power line (5) and the signal line (6), and the signal end of each driving chip (2) is connected with the signal line (6) through a metal wire (8).

5. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: The driving chip (2) is a five-pin driving chip, comprising a positive power end, a grounding end and three signal ends, the three signal ends have I / O functions, one side is provided with one signal end, the other side is provided with two signal ends, one or two signal lines (6) are arranged between adjacent display units, if one signal line (6) is arranged, the signal end provided on one side is connected with the signal line (6) through a metal wire (8), the two signal ends provided on one side are respectively connected with the signal line (6) through metal wires (8), if two signal lines (6) are arranged, the signal end provided on one side is respectively connected with the signal lines (6) through metal wires (8), and the two signal ends provided on one side are respectively connected with one signal line (6) through metal wires (8).

6. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: The driving chip (2) is a six-pin driving chip, comprising a positive power end, a grounding end and four signal ends, the four signal ends have I / O functions, the four signal ends are respectively connected with one signal line (6) through metal wires (8), two signal lines (6) are connected with a preceding driving chip (2), and the other two signal lines (6) are connected with a subsequent driving chip (2).

7. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 1, characterized in that: The group of LED crystal units (3) comprises one blue LED crystal unit (31), one green LED crystal unit (32) and one red LED crystal unit (33), the blue LED crystal unit (31), the green LED crystal unit (32) and the red LED crystal unit (33) are arranged in a "one" shape or a "product" shape on the substrate (1).

8. The bonding type high-transparency transparent screen based on the Mini LED COB direct display technology according to claim 7, characterized in that: The blue light LED crystal element (31), the green light LED crystal element (32) and the red light LED crystal element (33) adopt a common anode driving mode, the anodes of the blue light LED crystal element (31), the green light LED crystal element (32) and the red light LED crystal element (33) are respectively connected with the positive power line (4) through a metal wire (8), and the cathodes of the blue light LED crystal element (31), the green light LED crystal element (32) and the red light LED crystal element (33) are respectively connected with the corresponding pin of the driving chip (2) through a metal wire (8).

9. The bonding type high-transparency transparent screen based on Mini LED COB direct display technology according to claim 2, characterized in that: The display units are arranged in a matrix on the base material (1), two rows or two columns are a group, and the signal line (6) of the last display unit in each row or each column is connected with the signal line (6) of the adjacent display unit in the same group through the adapter line (7).

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