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

Abstract

The invention discloses a binding type high-transmittance transparent screen based on a COB technology and a processing method, the transparent screen comprises a base material, more than one driving chip, more than one LED wafer, a positive power line, a negative power line and a signal line, the positive power line, the negative 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, 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 invention, the driving chip and the LED wafer are fixed on the base material in 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] The present invention discloses a transparent screen, in particular a bonded high-transmittance transparent screen based on Mini LED COB direct display technology and a processing method, which can be widely used in outdoor advertising, indoor display, stage performances, museums, exhibition halls, science and technology museums, multimedia teaching, smart windows, indoor partitions, liquid crystal display backlight sources and other fields. Background Art

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

[0003] The substrate of the transparent screen is usually made of transparent materials, such as transparent glass or acrylic, to ensure that light can pass through. At the same time, the LED lamp beads are installed on the transparent substrate. Through special structural design, such as arranging the lamp beads on the edge of the transparent substrate or using hollowing, grid and other forms, the light is blocked to reduce the transparency effect. It is also possible to use a circuit board with a conventional substrate and achieve the transparency effect by hollowing out the substrate.

[0004] Transparent screens can be installed in the windows, entrances or key locations of shopping malls, department stores and brand stores to dynamically display product advertisements, promotional information or brand stories, attract customers' attention, and increase brand awareness and product sales. They can also be seamlessly integrated into architectural elements such as glass curtain walls, windows, and columns to beautify the appearance of buildings, enhance the sense of technology and modernity of buildings, and can be customized according to the style and characteristics of buildings to achieve perfect integration with buildings. Or in museums, science and technology museums, art galleries and other places, they can be used to display pictures and video information of cultural relics, artworks or technological products. The audience can clearly see the details behind the exhibits through the transparent screen, which enhances the interactivity and fun of the exhibition. It can also be used in stage performances, entertainment fields, public spaces and transportation hubs, etc., and has a wide range of uses.

[0005] The transparent screens in the prior art are all made by welding lamp beads on a substrate. On the one hand, the price of the finished lamp beads is relatively high, which makes the price of the entire transparent screen expensive. On the other hand, the packaged finished lamp beads, whether they have a driving function or are simply LED lamp beads, must include a lamp frame and a lampshade structure, which occupy a relatively large space. After welding, they will occupy a larger substrate area, thereby 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 transparent screen in the prior art, which is processed by welding packaged lamp beads on a substrate, which is expensive and has poor light transmittance, the present invention provides a bonded high-transmittance transparent screen and a processing method based on Mini LED COB direct display technology, which fixes the driver chip and LED wafer on the substrate by direct bonding, and can minimize the area of ​​the substrate occupied by the LED and the driver chip.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a bonded high-transmittance transparent screen based on Mini LED COB direct display technology, the transparent screen includes a substrate, one or more driving chips, one or more LED wafers, a positive power line, a negative power line and a signal line, the positive power line, the negative power line and the signal line are respectively fixed on the substrate, the driving chip and the LED wafer are fixed on the substrate, the positive power end of the driving chip is bonded to the positive power line through a metal wire, the ground end of the driving chip is bonded to the negative power line through a metal wire, the signal end of the driving chip is bonded to the signal line through a metal wire, and the LED wafer is bonded to the driving chip through a metal wire.

[0008] A processing method of a bonded high-transmittance transparent screen based on the Mini LED COB direct display technology as described above, the processing method comprises the following steps: Step S1, substrate loading, substrate loading includes the following sub-steps: Step S1-1, substrate feeding: feeding the substrate to be processed into the working position of the die bonding machine; Step S1-2, substrate identification: identifying and judging the substrate; Step S1-3, solder joint identification: identifying solder joints on the substrate; Step S1-4, platform XY correction: adjust the position of the substrate; Step S2: Chip loading, which includes the following sub-steps: Step S2-1, chip feeding: feeding the chips or wafers to be processed, including driver chips and LED wafers; Step S2-2, chip ring identification: identifying the chip ring; Step S1 and step S2 are performed simultaneously or in steps; Step S3, crystal expansion: using an expansion machine to evenly expand the entire LED wafer film / chip film, so that the LED wafers / chips closely arranged on the surface of the film are pulled apart; Step S4, backing glue: backing silver paste on the LED wafer / chip on the expanded crystal ring; Step S5, crystal piercing: placing the crystal expansion ring with the prepared silver paste into the crystal piercing frame, and piercing the LED chip onto the substrate; Step S6, solidifying the crystal: placing the pierced substrate in a thermal cycle oven and keeping it at a constant temperature for a period of time, and taking it out after the silver paste solidifies; Step S7, sticking the chip: use a glue dispenser to apply an appropriate amount of red glue or black glue on the IC position of the substrate, and then use an anti-static device to correctly place the chip on the red glue or black glue; Step S8, post-solidification inspection: inspect the fixed chip or wafer; Step S9, flying camera detection: detecting the chip or wafer by flying camera; Step S10, drying: drying the substrate with the chip attached; Step S11, substrate operation: the die bonding machine performs bonding operation on the chip or wafer; Step S12, pre-test: inspect the COB board and re-repair the unqualified COB board; Step S13, glue dispensing: using a glue dispensing machine to dispense the prepared AB glue onto the bonded LED chips for packaging and protection, and the chips are packaged with black glue; Step S14, curing: placing the sealed substrate into the mold for curing; Step S15, post-test: using a detection tool to perform an electrical performance test; Step S16, discharging the substrate: discharging the bonded substrate to complete the operation.

[0009] The technical solution adopted by the present invention to solve the technical problem further includes: A driver chip and a group of LED wafers constitute a display unit.

[0010] The driver chip is a four-pin driver chip, including a positive power supply terminal, a ground terminal and two signal terminals, both of which have I / O functions, and the two signal terminals are respectively bonded to a signal line through metal wires.

[0011] The driver chip is a three-pin driver chip, including a positive power supply terminal, a ground terminal and a signal terminal. A positive power supply line, a negative power supply line and a signal line are correspondingly arranged on the substrate. Each driver chip signal terminal is bonded to the signal line through a metal wire.

[0012] The driving chip adopts a five-pin driving chip, including a positive power supply terminal, a ground terminal and three signal terminals, and the three signal terminals all have I / O functions, wherein one signal terminal is arranged on one side, and two signal terminals are arranged on the other side. One or two signal lines are arranged between adjacent display units. If one signal line is arranged, one signal terminal is arranged on one side, and the signal terminal is bonded to the signal line through a metal wire. If two signal terminals are arranged on one side, the two signal terminals are respectively bonded to the signal line through a metal wire. If two signal lines are arranged, one signal terminal is arranged on one side, and the signal terminal is respectively bonded to the signal line through a metal wire. If two signal terminals are arranged on one side, the two signal terminals are respectively bonded to one signal line through a metal wire.

[0013] The driver chip adopts a six-pin driver chip, including a positive power supply terminal, a ground terminal and four signal terminals. The four signal terminals all have I / O functions. The four signal terminals are respectively bonded to a signal line through metal wires, two of which are connected to the front-stage driver chip, and the other two signal lines are connected to the rear-stage driver chip.

[0014] A group of LED wafers includes a blue LED wafer, a green LED wafer and a red LED wafer. The blue LED wafer, the green LED wafer and the red LED wafer are arranged in a straight line or a line on the substrate.

[0015] The blue LED wafer, green LED wafer and red LED wafer adopt a common anode driving mode, the anodes of the blue LED wafer, green LED wafer and red LED wafer are respectively bonded to the positive power line through a metal wire, and the cathodes of the blue LED wafer, green LED wafer and red LED wafer are respectively bonded to the corresponding pins of the driving chip through 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 a display unit at the end of each row or column is connected to the signal line of an adjacent display unit in the same group through a switching line.

[0017] The material of the substrate is transparent glass, transparent soft PC or FR4.

[0018] The beneficial effects of the present invention are: the present invention fixes the driver chip and the LED wafer on the substrate by direct bonding, which can minimize the area of ​​the substrate occupied by the LED and the driver chip, improve the light transmittance of the entire product, and reduce the cost of the product. Compared with other packaging technologies, COB technology is inexpensive (only about 1 / 3 of the same chip), saves space, and has mature technology.

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the circuit structure of the present invention.

[0021] Figure 2 for Figure 1 A is a schematic diagram of a local enlarged structure.

[0022] Figure 3 It is a processing flow chart of the present invention.

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

[0024] This embodiment is a preferred implementation mode of the present invention. Other embodiments whose principles and basic structures are the same or similar to those of this embodiment are within the protection scope of the present invention.

[0025] Please refer to the attached Figure 1 and attached Figure 2 The present invention mainly protects a bonded high-transmittance transparent screen based on Mini LED COB direct display technology. COB, or chip on board, is a technology that directly mounts integrated circuit chips on circuit boards, that is, the bare die of the chip is directly fixed on the circuit board through a specific process, and the electrical connection between the chip and the circuit on the circuit board is achieved through metal wire bonding and other methods. The transparent screen mainly includes a substrate 1, one or more driver chips 2, one or more LED wafers 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 respectively fixed on the substrate 1, the driver chip 2 and the LED wafer 3 are fixed on the substrate 1, the positive power end of the driver chip 2 is bonded to the positive power line 4 through a metal wire 8, the ground end of the driver chip 2 is bonded to the negative power line 5 through a metal wire 8, the signal end of the driver chip 2 is bonded to the signal line 6 through a metal wire 8, and the LED wafer 3 is bonded to the driver chip 2 through a metal wire 8.

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

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

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

[0029] In specific implementation, the driving chip 2 may also adopt a three-pin, five-pin or six-pin design.

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

[0031] The driver chip 2 adopts a five-pin driver chip design, including a positive power supply terminal, a ground terminal and three signal terminals, and the three signal terminals all have I / O functions. One signal terminal is set on one side and two signal terminals are set on the other side. The signal line 6 between adjacent display units can be set as one or two. If one signal line 6 is set, one signal terminal is set on one side, and the signal terminal is bonded to the signal line 6 through a metal wire 8. If two signal terminals are set on one side, the two signal terminals are bonded to the signal line 6 through a metal wire 8 respectively. If two signal lines 6 are set, one signal terminal is set on one side, and the signal terminal is divided into The two signal ends are respectively bonded to the signal line 6 through a metal wire 8. If two signal ends are set on one side, the two signal ends are respectively bonded to a signal line 6 through 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-stage (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-stage (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 front end or the rear end, it is connected to the controller, thereby forming a connection mode of parallel power supply and series communication control.

[0032] The driver chip 2 adopts a six-pin driver chip design, including a positive power supply terminal, a ground terminal and four signal terminals. The four signal terminals all have I / O functions. The four signal terminals are respectively bonded to a signal line 6 through a metal wire 8, two of which are connected to the front-stage (i.e., the display unit set at the front end) driver chip 2, and the other two signal lines 6 are connected to the rear-stage (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 front end or the rear end, it is connected to the controller, thereby forming a parallel power supply and series communication control connection mode. The signal line 6 adopts a redundant design to improve the stability of signal control.

[0033] In this embodiment, a group 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, the green LED chip 32 and the red LED chip 33 are arranged in a "one" shape on the substrate 1. In a specific implementation, the blue LED chip 31, the green LED chip 32 and the red LED chip 33 can also be arranged in a "pin" shape.

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

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

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

[0037] In this embodiment, the display units are arranged on the substrate 1 in rows and columns, or in a matrix arrangement. The spacing between adjacent display units is 5 to 20 times the size of the LED wafer. Two rows or two columns form a group. The signal line 6 of a display unit at the end of each row or column is connected to the signal line 6 of the adjacent display unit in the same group through a adapter line 7, so that the control signals of a group of two rows or two columns of display units 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 a certain display unit and will 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 above-mentioned Mini LED bonding structure can be used in direct display transparent screens. In the field of transparent display screens, "direct display" means that display technology can directly use light-emitting elements as pixels to realize image display without the need for additional backlight and other auxiliary means to illuminate the pixels. Mini LED direct display technology uses Mini LED lamp beads directly as pixels. Based on the electroluminescent effect of light-emitting diodes, when current passes through semiconductor materials, electrons and holes recombine to generate photons, releasing energy to achieve self-luminous display. Each Mini LED can be independently controlled and can achieve local dimming, which can make black more pure, greatly improve contrast, and enhance the three-dimensional sense and depth of the picture. With self-luminous technology, each pixel can emit light independently. Compared with some display technologies that require backlight, it can achieve higher brightness and contrast, making the display picture clearer and more vivid, brighter in the bright part and darker in the dark part. It can achieve pure black display at the pixel level, making the black part of the picture deeper, so that the overall contrast is higher, the display effect is better, and the layering and details of the image are richer. Mini LED direct display technology usually uses a smaller current drive to reduce power consumption. At the same time, since Mini LED itself has good thermal stability and other characteristics, it also increases the service life of the display.

[0040] The present invention can be used in direct display transparent screen terminal products such as vehicle-mounted screens, shopping mall display screens, advertising screens, and number-calling screens. In addition, it can also be used as a backlight module for liquid crystal screens, and its light emission is more uniform and the lighting effect is better.

[0041] Please refer to the attached Figure 3 The present invention adopts a solid crystal machine during processing, which mainly includes the following steps: Step S1, substrate loading, substrate loading includes the following sub-steps: Step S1-1, substrate feeding: feeding the substrate 1 to be processed into the working position of the die bonding machine; Step S1-2, substrate identification: the substrate 1 is identified and judged to ensure the accuracy of the feeding. In this embodiment, the substrate is identified by scanning a code, which is fast and accurate. The scanning code can be a QR code or a bar code; Step S1-3, solder joint identification: identifying the solder joints on the substrate 1 to ensure that there are no missing solder joints, continuous solder joints, or solder joint misalignment. In this embodiment, machine vision can be used for solder joint identification; Step S1-4, platform XY correction: adjust the position of the substrate 1 to ensure the accuracy of the position of the substrate 1. In this embodiment, the accuracy of the XY position is guaranteed to be within ±20 μm; Step S2: Chip loading, which includes the following sub-steps: Step S2-1, chip feeding: feeding the chips or wafers to be processed, including driver chips and LED wafers; Step S2-2, chip ring identification: When loading chips or wafers, the whole tray is loaded, and the chip ring can be identified to ensure that the chip is correct. In this embodiment, the chip ring is identified by scanning code, which is fast and accurate. The scanning code can be a QR code or a bar code; In this embodiment, step S1 and step S2 can be performed simultaneously, and the two do not conflict with each other.

[0042] Step S3, crystal expansion: using an expansion machine to evenly expand the entire LED wafer film / chip film, so that the LED wafers / chips closely arranged on the film surface are pulled apart, and the chip ring also forms a "crystal expansion ring" to facilitate subsequent crystal piercing operations; Step S4, back glue: Place the expanded crystal ring on the back glue machine surface with the silver paste layer scraped, and apply silver paste to the LED wafer / chip. The back glue operation is applicable to the entire LED wafer / chip, and the silver paste application operation is applicable to bulk LED wafers / chips. At the same time, in this step, a glue application machine is also used to apply an appropriate amount of silver paste to the pad position on the substrate; Step S5, crystal piercing: placing the crystal expansion ring with the prepared silver paste into the crystal piercing frame, and piercing the LED wafer onto the substrate with a crystal piercing pen. In this embodiment, the crystal piercing step includes the following sub-steps: Step S5-1, taking out the crystal: taking out the chip or wafer from the chip ring by using the vacuum suction head of the crystal pricking pen. In this embodiment, the vacuum suction head is used for adsorption when taking out the crystal, and the suction pressure of the vacuum suction head is between 30g and 100g; Step S5-2, chip identification: identifying the chip or wafer to determine the polarity of the chip or wafer; Step S5-3, wafer ring angle correction: use a wafer platform to correct the chip or wafer angle θ and the chip polarity, and the wafer platform can rotate 360 ​​degrees; Step S6, bonding: Place the PCB printed circuit board (i.e. substrate) with the pierced crystal in a heat cycle oven and place it at a constant temperature for a period of time, and take it out after the silver paste solidifies (do not leave it for a long time, otherwise the LED chip coating will be baked yellow, i.e. oxidized, causing difficulties in bonding). If LED chips are bonded, the above steps are required, and if only IC chips are bonded, the above steps are omitted.

[0043] In this embodiment, the temperature and standing time of the die bonding are generally as follows: When using low-temperature silver paste: the general curing temperature is around 100℃~150℃. If it is 100℃, the curing time is 60~90 minutes; if the temperature is 130℃, the curing time is about 40~60 minutes; when the curing temperature is 150℃, the curing time is 30~50 minutes.

[0044] When using medium-temperature silver paste: the curing temperature is usually between 150℃~200℃. If it is at 160℃, it takes 30~40 minutes to cure; if it is at 180℃, the curing time is 20~30 minutes.

[0045] When using high-temperature silver paste: the curing temperature is usually above 200°C, generally in the range of 200°C~300°C. At 200°C, it takes 20~30 minutes to cure; if the temperature reaches above 250°C, a curing time of 15~20 minutes usually meets the requirements.

[0046] Step S7, sticking the chip: use a glue dispenser to apply an appropriate amount of red glue (or black glue) on the IC position of the substrate (taking the PCB printed circuit board as an example), and then use an anti-static device (a vacuum suction pen or a vacuum suction device can be used) to correctly place the IC on the red glue or black glue; Step S8, post-solidification inspection: inspect the fixed chip or wafer to ensure the firmness of the crystal and prevent the chip or wafer from moving during the crystal bonding process. The inspection method can be vibration, air blowing, etc. Step S9, flying detection: The chip or wafer is detected by flying detection (in machine vision projects, the axis moves to the photo position without stopping, and high-speed capture is completed instantly and processed and the result is fed back) to ensure that its position is accurate and there is no missing; Step S10, drying: put the substrate with the chip bonded to it into a thermal cycle oven and place it on a large flat heating plate to stand at a constant temperature for a period of time, or it can be cured naturally (the natural curing time is longer). For the temperature setting and market of heating curing, please refer to step S6; Step S11, substrate operation: bonding the chip or wafer through a die bonding machine, bridging the wafer (LED die or IC chip) with the corresponding pad on the substrate through a metal wire, i.e., the inner lead welding of COB, which usually takes a long time; Step S12, pre-test: Use special testing tools (different equipment is used for COBs with different purposes, usually a high-precision voltage-stabilized power supply is used) to test the COB board, and return the unqualified boards for repair; Step S13, glue dispensing: Use a glue dispensing machine to dispense an appropriate amount of the prepared AB glue onto the bonded LED die 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; Step S14, curing: placing the sealed substrate in a thermal cycle oven and keeping it at a constant temperature. Different drying times can be set according to requirements to cure the glue. Step S15, post-test: the packaged substrate is subjected to electrical performance test using a dedicated testing tool; Step S16, discharging the substrate: discharging the bonded substrate to complete the operation.

[0047] The LED wafer in the above embodiment can also be called an LED chip. The LED chip is just a small solid. Its two electrodes can only be seen under a microscope. It will emit light only after current is added. In the manufacturing process, in addition to welding the two electrodes of the LED chip to lead out the positive and negative electrodes, the LED chip and the two electrodes also need to be protected. There are two types of LED wafer structures: a positive structure and a flip-chip structure.

[0048] In this embodiment, a layer of epoxy resin is coated on the LED chip of the upright structure, and sapphire is used as the substrate below. The electrode is on the top. The materials from top to bottom are: P-GaN, light-emitting layer, N-GaN and substrate. The light emitted from the active area of ​​the upright structure is emitted through the P-type GaN area and the transparent electrode. A metal transparent electrode is prepared on the P-type GaN to make the current diffuse stably and achieve the purpose of uniform light emission. The EDp and n electrodes of the upright structure LED are on the same side of the LED. The current must flow horizontally through the N-GaN layer, resulting in current crowding, high local heat generation, and limiting the driving current. Secondly, due to the poor thermal conductivity of the sapphire substrate, the heat dissipation is seriously hindered.

[0049] In this embodiment, the packaging of the LED chip with a front-mounted structure includes the following steps: Step S1, crystal expansion: Since the LED chips are still closely arranged with a small spacing (usually about 0.1mm) after dicing, it is not conducive to the operation of the subsequent process. First, use a crystal expansion machine to expand the film bonded with the LED chips so that the spacing of the LED chips is stretched to about 0.6mm. Manual expansion can also be used, but it is easy to cause problems such as chip falling and waste; Step S2, chip inspection: usually using microscopic inspection to check whether there is mechanical damage and tiny pits on the surface of the material; Step S3, glue dispensing: silver glue or insulating glue is applied to the corresponding position of the substrate. For GaAs and SiC conductive substrates, red, yellow, and yellow-green chips with back electrodes, silver glue is used. For blue and green LED chips on sapphire insulating substrates, insulating glue is used to fix the chips. Step S4, back glue: the back glue is to first apply silver glue on the back electrode of the LED using a glue preparation machine, and then install the LED with silver glue on the back on the substrate; In this embodiment, the selected silver glue should be stored in a refrigerator. When used, it must be thawed at room temperature for more than 90 minutes. If it is a large can of silver glue, it needs to be warmed up for more than 3 hours. After the warming is completed, it needs to be divided into small cans and refrigerated in a refrigerator at -5°C. After the silver glue is warmed up, it is stirred with a glass rod or a stainless steel rod. Before use, the stirring rod needs to be cleaned with acetone or other solutions.

[0050] Step S5, crystal bonding: the crystal bonding machine sucks up the chip through vacuum adsorption. During adsorption, there is a needle under the chip that lifts up the chip, which is just sucked by the vacuum suction port. The vacuum suction port with the chip is swung 90 degrees to the bracket, and the vacuum is removed. At the same time, a little pressure is applied to press the chip onto the silver glue to complete the chip placement. In this embodiment, after the vacuum suction port sucks up the chip, the position of the chip can be adjusted by monitoring its image, and the silver glue can be added in time and the amount of glue can be controlled; Step S6, baking: After the solid crystal is completed, baking is required. The baking condition is 150°C and the baking time is 1h. The thrust test after baking should be greater than 70g; Step S7, wire welding: Use an electronic spark stick to ignite the end of the gold wire and sinter it into a gold ball, then use a welding needle to use ultrasonic oscillation energy to make the gold ball and the welding pad produce relative friction movement under a certain welding pressure, and use the energy generated by rapid friction to achieve ionic welding between the gold ball and the welding pad.

[0051] Wire bonding is a key link in LED packaging technology. The main things that need to be monitored in the process are the arch shape of the pressed gold wire (or aluminum wire), the shape of the solder joint, the tension, etc.

[0052] In this embodiment, the requirements for the bonding wires are that the height of each gold wire bonding arch wire is appropriate, there is no collapsed wire, inverted wire, and no excess welding wire. The diameter of the solder ball should be greater than 2 times the diameter of the gold wire and less than 4 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 pulling force is ≥5g, and when using 1.0-1.2 mil gold wire, the pulling force is ≥6g.

[0053] Step S8, applying phosphor: Ordinary LED chips cannot directly emit white light. In this embodiment, white light can be achieved by the following three methods: (1) Using a combination of red, green and blue LEDs to emit light, i.e. multi-chip white light LEDs; (2) Using blue LED chips and fluorescent yellow light powder, the blue light and yellow light complement each other to obtain white light, or using blue LED chips with red and green fluorescent powders to obtain white light by mixing the blue light emitted by the chip and the red and green light emitted by the fluorescent powder; (3) Using the near-ultraviolet light emitted by the ultraviolet LED chip to excite the three primary color light powder to obtain white light; In order to ensure the consistency of production, the phosphor needs to be left for half an hour after being applied before being put into the oven for baking. The baking conditions are: 150°C, and the baking time is 1 to 1.5 hours. After baking, the color temperature of the LED will increase and the xy color coordinates will decrease.

[0054] After mixing the powder and glue, stir for 15 to 20 minutes, then evacuate and remove air bubbles. The fluorescent powder must be used up within 3 hours. If left for a long time, it must be re-stirred. In addition, the mixture must be evacuated after stirring.

[0055] Step S9: dispensing glue to protect the LED wafer. The following methods can be used: (1) Manual dispensing: Manual dispensing packaging requires a very high level of operation. The main difficulty is to control the amount of dispensing, because the epoxy will thicken during use. The dispensing of white light LEDs also has the problem of phosphor precipitation causing color difference in light output.

[0056] (2) Glue encapsulation: Lamp-LED is encapsulated in the form of glue encapsulation. The encapsulation process is to first inject liquid epoxy into the LED molding cavity, then insert the welded LED bracket, put it into the oven to allow the epoxy to cure, and then remove the LED from the cavity to complete the molding.

[0057] (3) Molding package: Place the welded LED bracket into the mold, close the upper and lower molds with a hydraulic press and evacuate them, put the solid epoxy into the entrance of the injection channel, heat it and press it into the mold glue channel with a hydraulic push rod, and the epoxy flows along the glue channel into each LED molding groove and solidifies.

[0058] In this embodiment, the flip-chip structure chip is directly bonded to the wiring layer of the substrate with the chip with bump electrodes on the working surface (i.e., the active area surface) facing downward. Two gold wire ball welding points are made by a gold wire bonding machine under the P pole and N pole of the chip as the electrode lead-out mechanism, and the outer side of the chip and the Si bottom plate are connected with gold wires. The LED chip is flip-chip connected to the silicon base through the 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.

[0059] In this embodiment, the LED chip with flip-chip structure is packaged, including the following steps: Step S1, bottom bump metallization (UBM), in this embodiment, the bump is usually made of lead-tin alloy material, and is generated by reflow soldering, centering effect, and solder drop, etc., usually using 95% by weight of lead and 5% by weight of tin, or using 97% by weight of lead and 3% by weight of tin, and the reflow soldering temperature is controlled between 330 and 350°C; Step S2: Chip bumping can be done by evaporation or electroplating; In this embodiment, forming the bumps by evaporating solder includes the following sub-steps: Step S1-1, sputtering the silicon wafer on site, removing oxides or performing photomasking before depositing metal, and making the silicon wafer passivation layer and pad surface rougher to improve the bonding strength to the UBM; Step S1-2, metal mask: Use a molybdenum metal mask with a pattern to cover the silicon wafer to facilitate the deposition of UBM and bump metal. The silicon wafer is clamped between the backplane and the metal template, and then manually aligned, with the alignment tolerance controlled within 25μm; Step S1-3, UBM evaporation: evaporating a Cr layer, a CrCu layer, a Cu layer and an Au layer in sequence; Step S1-4, solder evaporation: a layer of lead-tin alloy is evaporated on the surface of the UBM, the thickness of the lead-tin alloy is about 100-125 μm, and a frustum shape is formed. In this embodiment, the lead-tin alloy usually uses 95% by weight of lead and 5% by weight of tin, or uses 97% by weight of lead and 3% by weight of tin; Step S1-5, forming bumps into balls: forming the bumps into balls by reflow soldering.

[0060] In this embodiment, forming the bumps by electroplating includes the following sub-steps: Step S2-1, silicon wafer cleaning: removing oxides or performing photomasking before metal deposition, and at the same time, making the silicon wafer passivation layer and pad surface rougher to improve the bonding strength to the UBM; Step S2-2, UBM deposition: The typical UBM material layer is TiW-Cu-Au, which is sputtered onto the entire silicon wafer. The UBM layer provides an average current distribution to facilitate consistent electroplating. In the case where the silicon wafer is covered with TiW, a mask is applied to deposit a certain height of Cu and Au. Generally, when the overall height of the bump is 85μm ~100μm, the height of the microball is 10μm ~ 25μm; Step S2-3, solder electroplating: applying a mask again to electroplate the bumps. After the bumps are formed, the mask is stripped off. In this embodiment, the exposed UBM will be naturally etched away within one to two days. Step S2-4, reflow into balls: the bumps are formed into balls by reflow soldering. In this embodiment, reflow helps the bumps not to be damaged when the UBM is removed.

[0061] In this embodiment, the ball placement method is to apply laser pulses through optical fibers to a ball placement head unit for reflow soldering while placing the ball.

[0062] Step S3, assembling the bumped wafer onto a substrate / board; Step S4, use non-conductive material to fill the pores at the bottom of the chip. During 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 in both directions along the edge of the chip. Due to the siphon effect of the capillary in the gap, the filler is sucked in and flows toward the center. There are obstacles at the edge of the chip to prevent outflow, and the substrate can also be tilted to facilitate flow.

[0063] After filling, heat up in the oven in stages. When the curing temperature reaches about 130°C, keep it for 3 to 4 hours to achieve complete curing. The curing temperature should be low to prevent thermal deformation of the PCB.

[0064] When selecting, minimize stress mismatch as much as possible and keep the Z direction of the filler and bump connection matched.

[0065] Insufficient fill volume can cause wafer cracking, while excessive fill volume can overflow beyond the bottom of the chip. The fill volume depends on the accurate calculation of the fill space and the accuracy of the fill tool.

[0066] Filling temperature, especially preheating, heating and heating after filling, has a great influence on its fluidity.

[0067] The filling method is generally to fill from one side which will result in a long flow time, and to fill from both sides which will result in internal pores.

[0068] The present invention uses direct bonding to fix the driver chip and LED wafer on the substrate, which can minimize the area of ​​the substrate occupied by the LED and driver chip, improve the light transmittance of the entire product, and reduce the cost of the product. Compared with other packaging technologies, COB technology is inexpensive (only about 1 / 3 of the same chip), saves space, and has mature technology.

Claims

1. A bonded high-transmittance transparent screen based on Mini LED COB direct display technology, characterized by: The transparent screen comprises a substrate (1), one or more driving chips (2), one or more LED wafers (3), a positive power line (4), a negative power line (5) and a signal line (6), wherein the positive power line (4), the negative power line (5) and the signal line (6) are respectively fixedly arranged on the substrate (1), the driving chip (2) and the LED wafer (3) are fixed on the substrate (1), the positive power end of the driving chip (2) is bonded to the positive power line (4) through a metal wire (8), the ground end of the driving chip (2) is bonded to the negative power line (5) through a metal wire (8), the signal end of the driving chip (2) is bonded to the signal line (6) through a metal wire (8), and the LED wafer (3) is bonded to the driving chip (2) through a metal wire (8).

2. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized in that: A driving chip (2) and a group of LED wafers (3) constitute a display unit.

3. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized in that: The driver chip (2) is a four-pin driver chip, including a positive power supply terminal, a ground terminal and two signal terminals, both of which have I / O functions, and the two signal terminals are respectively bonded to a signal line (6) through metal wires (8).

4. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized in that: The driver chip (2) is a three-pin driver chip, including a positive power supply terminal, a ground terminal and a signal terminal. A positive power supply line (4), a negative power supply line (5) and a signal line (6) are correspondingly arranged on the substrate (1). The signal terminals of each driver chip (2) are respectively bonded to the signal line (6) via a metal wire (8).

5. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized in that: The driver chip (2) is a five-pin driver chip, including a positive power supply terminal, a ground terminal and three signal terminals, and the three signal terminals all have I / O functions, wherein one signal terminal is provided on one side and two signal terminals are provided on the other side, and one or two signal lines (6) are provided between adjacent display units. If one signal line (6) is provided, one signal terminal is provided on one side, and the signal terminal is bonded to the signal line (6) through a metal wire (8). If two signal terminals are provided on one side, the two signal terminals are respectively bonded to the signal line (6) through a metal wire (8). If two signal lines (6) are provided, one signal terminal is provided on one side, and the signal terminal is respectively bonded to the signal line (6) through a metal wire (8). If two signal terminals are provided on one side, the two signal terminals are respectively bonded to one signal line (6) through a metal wire (8).

6. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized by: The driver chip (2) is a six-pin driver chip, including a positive power supply terminal, a ground terminal and four signal terminals, the four signal terminals all having I / O functions, the four signal terminals are respectively bonded to a signal line (6) through metal wires (8), two of the signal lines (6) are connected to the front-stage driver chip (2), and the other two signal lines (6) are connected to the rear-stage driver chip (2).

7. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 1 is characterized in that: A group of LED wafers (3) comprises a blue LED wafer (31), a green LED wafer (32) and a red LED wafer (33), wherein the blue LED wafer (31), the green LED wafer (32) and the red LED wafer (33) are arranged on the substrate (1) in a straight line shape or in a line shape.

8. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 7 is characterized in that: The blue LED wafer (31), green LED wafer (32) and red LED wafer (33) adopt a common anode driving mode, wherein the anodes of the blue LED wafer (31), green LED wafer (32) and red LED wafer (33) are respectively bonded to the positive power supply line (4) via a metal wire (8), and the cathodes of the blue LED wafer (31), green LED wafer (32) and red LED wafer (33) are respectively bonded to the corresponding pins of the driving chip (2) via a metal wire (8).

9. The bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to claim 2 is characterized by: The display units are arranged in a matrix on the substrate (1), with two rows or two columns forming a group, and the signal line (6) of a display unit at the end of each row or column is connected to the signal line (6) of an adjacent display unit in the same group via a switching line (7).

10. A method for processing a bonded high-transmittance transparent screen based on Mini LED COB direct display technology according to any one of claims 1 to 9, characterized in that: The processing method comprises the following steps: Step S1, substrate loading, substrate loading includes the following sub-steps: Step S1-1, substrate feeding: feeding the substrate to be processed into the working position of the die bonding machine; Step S1-2, substrate identification: identifying and judging the substrate; Step S1-3, solder joint identification: identifying solder joints on the substrate; Step S1-4, platform XY correction: adjust the position of the substrate; Step S2: Chip loading, which includes the following sub-steps: Step S2-1, chip feeding: feeding the chips or wafers to be processed, including driver chips and LED wafers; Step S2-2, chip ring identification: identifying the chip ring; Step S1 and step S2 are performed simultaneously or in steps; Step S3, crystal expansion: using an expansion machine to evenly expand the entire LED wafer film / chip film, so that the LED wafers / chips closely arranged on the surface of the film are pulled apart; Step S4, backing glue: backing silver paste on the LED wafer / chip on the expanded crystal ring; Step S5, crystal piercing: placing the crystal expansion ring with the prepared silver paste into the crystal piercing frame, and piercing the LED chip onto the substrate; Step S6, solidifying the crystal: placing the pierced substrate in a thermal cycle oven and keeping it at a constant temperature for a period of time, and taking it out after the silver paste solidifies; Step S7, sticking the chip: use a glue dispenser to apply an appropriate amount of red glue or black glue on the IC position of the substrate, and then use an anti-static device to correctly place the chip on the red glue or black glue; Step S8, post-solidification inspection: inspect the fixed chip or wafer; Step S9, flying camera detection: detecting the chip or wafer by flying camera; Step S10, drying: drying the substrate with the chip attached; Step S11, substrate operation: the die bonding machine performs bonding operation on the chip or wafer; Step S12, pre-test: inspect the COB board and re-repair the unqualified COB board; Step S13, glue dispensing: using a glue dispensing machine to dispense the prepared AB glue onto the bonded LED chips for packaging and protection, and the chips are packaged with black glue; Step S14, curing: placing the sealed substrate into the mold for curing; Step S15, post-test: using a detection tool to perform an electrical performance test; Step S16, discharging the substrate: discharging the bonded substrate to complete the operation.

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