LED chip and its preparation method and LED display module preparation method

Abstract

The present invention provides a manufacturing process for an LED chip and an LED chip. The LED chip includes a light-emitting layer, a substrate, and an electrode; the substrate is arranged between the light-emitting layer and the electrode; the substrate is welded to the first electrode of the initial LED chip; and the second electrode is connected to the side of the substrate away from the first electrode to obtain the LED chip; the substrate strengthens the bottom strength of the LED chip to avoid the bottom being damaged during the connection process with the PCB board; at the same time, the substrate can raise the height of the light-emitting layer on the LED chip, thereby increasing the distance between the light-emitting layer and the PCB board, thereby making it easier to subsequently use a shielding material to shield the exposed portion of the PCB substrate. When the shielding material climbs up when shielding the PCB board, it will only shield the substrate but not the light-emitting layer, thereby improving the display effect of the COB product.

Description

Technical Field

[0001] The present invention relates to the field of LEDs, and in particular to an LED chip and a preparation method thereof, and a preparation method of an LED display module. Background Art

[0002] Due to the increasing market demand for fine-pitch screens, indoor fine-pitch products have become a major technological development area in the display field. Furthermore, as the required pitch becomes smaller and smaller, traditional discrete devices cannot achieve this even at the limits of existing processes. In other words, traditional devices cannot meet the needs of products below P0.7. At this time, COB (Chip On Board) products have gained a foothold in the fine-pitch market due to their low cost, high reliability, high protection, and easy cleaning. However, issues such as ink color consistency, bright lines between modules, and color lines have not been effectively resolved. As a result, the overall COB screen effect is not as good as that of traditional SMD products, which has hindered the market promotion of COB products.

[0003] At present, the thickness of conventional LED chips is about 85μm, of which the light-emitting layer is more than 32 microns. Figure 7 , and the other top thickness is sapphire 31. When using conventional LED chips, the chip's bottom light-emitting layer is relatively fragile during the die bonding process, often resulting in top damage. To ensure ink color consistency and improve contrast, inkjet or black glue is sprayed between chips. However, due to capillary phenomena, the ink or black glue will climb up along the side of the chip while covering the electrode 33. Inconsistent climbing height leads to inconsistent side light emission, affecting the side viewing effect of the COB product. To optimize the COB light output effect, optical structures or optical films are generally added to the light-emitting surface, resulting in an excessively thick COB package surface, which can cause bright lines and color lines between modules. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an LED chip and a preparation method thereof, and an LED display module preparation method, so as to improve the display effect of COB products.

[0005] In order to solve the above technical problems, a technical solution adopted by the present invention is:

[0006] An LED chip comprises a light-emitting layer, a substrate and electrodes;

[0007] The substrate is disposed between the light-emitting layer and the electrode.

[0008] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0009] A method for preparing an LED chip, comprising the steps of:

[0010] soldering a substrate onto the first electrode of the initial LED chip;

[0011] A second electrode is connected to a side of the substrate away from the first electrode.

[0012] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0013] A method for preparing an LED display module, characterized in that it comprises the steps of:

[0014] Connecting the second electrode of at least one LED chip to the lamp surface of the PCB substrate;

[0015] Applying shielding material in the gaps between LED chips;

[0016] The PCB substrate provided with the LED chip is packaged to obtain an LED display module.

[0017] The beneficial effects of the present invention are as follows: after the substrate is welded to the first electrode of the initial LED chip, the second electrode is connected to the other side of the substrate to obtain the LED chip. The substrate strengthens the bottom strength of the LED chip, avoiding the bottom being damaged during the connection process with the PCB board. At the same time, the substrate can raise the height of the light-emitting layer on the LED chip, thereby increasing the distance between the light-emitting layer and the PCB board, thereby making it easier to use the shielding material to shield the exposed PCB substrate portion. When the shielding material rises when shielding the PCB board, it will only shield the substrate but not the light-emitting layer, thereby improving the display effect of the COB product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flowchart of a method for preparing an LED chip according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic structural diagram of an LED chip according to an embodiment of the present invention;

[0020] Figure 3 A schematic diagram of a wafer capable of generating multiple LED chips according to an embodiment of the present invention;

[0021] Figure 4 A schematic diagram of a substrate according to an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of combining an LED chip wafer and a substrate according to an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of a vertical printing method according to an embodiment of the present invention;

[0024] Figure 7A schematic diagram of an LED chip in the prior art;

[0025] Figure 8 Schematic diagram comparing the climbing performance of the LED chip of the prior art and the LED chip of the present invention under the same amount of shielding material;

[0026] Description of labels:

[0027] 1. LED chip; 11. First electrode; 12. Protective layer; 13. Light-emitting layer; 14. Substrate; 141. Solder pad on substrate; 15. Second electrode; 16. Printing red LED chip; 17. Printing green LED chip; 18. Printing blue LED chip;

[0028] 2. Blocking materials. DETAILED DESCRIPTION

[0029] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0030] As described in the background technology, the problem of poor light emission effect of LED chips in the prior art has been discovered by the inventors. This problem is most prominent in the field of Mini LED chips (LED chips with a size between 50 and 200 μm). The reason for this problem is that in order to solve the problem of ink color consistency and improve contrast, inkjet or spraying black glue between chips is a common technical means. However, due to capillary phenomena, the height of the ink or black glue climbing on the side of the chip is different, which will cause adverse effects due to the lateral light emission of the chip. Based on this, the present application proposes an LED chip and its preparation method and packaging method, which can be applied to the field of conventional LED chips and the field of Mini LED chips. Specifically, the substrate is welded before the LED chip is cut. The substrate can raise the height of the light-emitting layer on the LED chip, increase the distance between the light-emitting layer and the PCB board, and avoid ink or black glue blocking the light-emitting layer, thereby improving the contrast and ink color consistency of the COB module display module and improving the display effect.

[0031] Please refer to Figure 2 and Figure 8 , one embodiment of the present invention is:

[0032] An LED chip includes a light-emitting layer 13, a substrate 14, an electrode 15, and a protective layer 12; the substrate 14 is disposed between the light-emitting layer 13 and the electrode 15; the protective layer 12 is disposed on a side of the light-emitting layer 13 away from the substrate 14; the electrode 15 is used to connect to a pad on a PCB; the thickness of the substrate 14 is 5-85 μm;

[0033] In an optional embodiment, the electrode includes a first electrode 11 and a second electrode 15; one end of the first electrode 11 is disposed on a side of the light-emitting layer 13 away from the protective layer 12, and the other end is connected to one side of the substrate 14; the second electrode 15 is disposed on the other side of the substrate 14;

[0034] In an optional embodiment, the substrate and the second electrode are integrated, that is, during the process, it is only necessary to connect the first electrode and the side of the substrate where the second electrode is not provided;

[0035] Please refer to Figure 8 The top light-emitting surface of the LED chip of the present invention has no sapphire. By adding a substrate, the bottom strength of the LED chip is enhanced to avoid the bottom being damaged during the crystal solidification process. At the same time, the light-emitting layer is raised to provide enough climbing space for black ink or black glue, so that it cannot block the light-emitting layer and affect the side light. Removing the top sapphire can provide more operational space for COB surface treatment to optimize its display effect without causing bright lines or color lines between modules due to excessive thickness.

[0036] Based on the same invention concept, please refer to Figure 1-Figure 5 , the present application also provides a method for preparing an LED chip, comprising steps S100 to S500:

[0037] S100, welding a substrate onto the first electrode of the initial LED chip;

[0038] The initial LED chip includes a substrate layer, a light-emitting layer, and a first electrode on the light-emitting layer. The substrate layer serves as the substrate for the light-emitting layer's growth, and its type is determined by the desired emission wavelength. For example, LED chips made of GaN semiconductor materials, such as blue or white LEDs, utilize substrates such as sapphire, SiC, and Si; LED chips made of AlInGaP materials, such as red LEDs, utilize GaAs substrates. In one embodiment, the substrate is a sapphire substrate. This substrate not only boasts mature production technology and high device quality, but also offers excellent stability, enabling high-temperature growth processes. Its high mechanical strength makes it easy to handle and clean, thereby improving the performance of the LED chip. The first electrode serves as a bridge for establishing an electrical connection between the light-emitting layer and the PCB substrate. The number, shape, and material of the first electrodes 11 are not unique; for example, two or three can be present, and the shape can be circular, square, or oval. The material can be Ag, Au, Ni-Au alloy, or ITO (Indium Tin Oxide). Furthermore, the location of the first electrode 11 is not unique; for example, it can be located at the edge of the light-emitting layer or in the center of the layer. In one embodiment, two first electrodes 11 are square electrodes disposed at the edges of the light-emitting layer in the longitudinal direction, thereby enhancing the bonding strength between the chip and the substrate. Specifically, the electrode layer can be formed by evaporation or deposition, and patterned by photolithography and etching to obtain the desired first electrodes 11.

[0039] In an optional embodiment, the preparation process of the initial LED chip includes the following steps:

[0040] A transparent electrode is plated on the epitaxial wafer, a preset pattern is photoetched on the transparent electrode by a photolithography machine, and the preset pattern is etched out, the photoresist is removed, and the platform pattern is photoetched, and dry etching is performed, and then the resist is removed and annealing is performed;

[0041] Deposit silicon dioxide, photoetch a window pattern on the deposited silicon dioxide, etch the silicon dioxide according to the window pattern and perform resist stripping, then photoetch an N-pole pattern and perform pre-cleaning. After pre-cleaning, plate the N / P pole material and strip the excess N / P pole material, and then perform annealing.

[0042] Photolithography of the P-pole pattern, coating and stripping of the film, and then grinding and thinning the substrate layer to obtain the initial LED chip required for S100;

[0043] In this embodiment, the grinding step can be omitted.

[0044] S200 , connecting the second electrode 15 to a side of the substrate 14 away from the first electrode 11 .

[0045] In an optional embodiment, the substrate 14 has a second electrode 15 on a side away from the first electrode 11 ;

[0046] S500: Cutting the LED chips into the desired size.

[0047] The required LED chips are obtained by cutting a whole block of connected substrate and wafer according to the size of a single LED chip.

[0048] Furthermore, after dicing, the chips need to be tested and sorted for subsequent processing. Specific methods for chip sorting can include visual inspection and power-on testing. For example, visual inspection can identify chips with a certain distance between the edge of the light-emitting portion and the edge of the substrate as good, while others as defective, to avoid damage to the light-emitting portion during dicing.

[0049] In one embodiment, step S100 includes the following steps:

[0050] S110 . Planting a metal ball on the first electrode 11 of the initial LED chip to form a soldering pad of the initial LED chip.

[0051] Please refer to Figure 3 , is a schematic diagram of a wafer, on which a plurality of initial LED chips are arranged, each initial LED chip including two first electrodes 11; the metal ball is a metal element or an alloy;

[0052] S120 , soldering the substrate 14 onto the soldering pads of the initial LED chip.

[0053] The substrate 14 is soldered on the pad by eutectic soldering, laser soldering or high-temperature reflow soldering, so that the surface electrodes of the substrate are connected to the chip;

[0054] In an optional embodiment, corresponding pads 141 are provided on the substrate 14 to solder the pads of the LED chip and the pads 141 on the substrate 14 ;

[0055] Please refer to Figure 4 , a plurality of pads 141 are provided on a substrate 14, that is, a substrate can be combined with a plurality of initial LED chips on a wafer;

[0056] In an optional embodiment, the substrate 14 includes a BT resin substrate or a glass substrate;

[0057] In an optional embodiment, the thickness of the substrate 14 is 5-85 μm, and the thickness of the substrate 14 is smaller than its length and width;

[0058] In one embodiment, after step S200 and before step S500, the method further includes step S300: peeling off the substrate layer of the initial LED chip to expose the light-emitting layer 13;

[0059] Specifically, the substrate layer of the initial LED chip is peeled off by laser. Since the chip substrate layer is gallium nitride, the laser can vaporize the gallium nitride, thereby achieving the peeling of the substrate layer and the light-emitting layer, reducing the chip thickness and improving the luminous efficiency.

[0060] Please refer to Figure 5 , which is a schematic diagram of the wafer and substrate 14 being combined and the substrate layer being peeled off;

[0061] In an optional embodiment, S3 further includes: peeling off the substrate layer of the initial LED chip to expose the light-emitting layer under the substrate layer; the substrate layer may be sapphire;

[0062] In one embodiment, after step S200 and before step S500, step S400 is further included: coating a protective layer 12 with a preset thickness on the light-emitting layer 13;

[0063] Specifically, a predetermined thickness of silicon dioxide is plated on the surface of the light-emitting layer 13 as a protective layer 12. Silicon dioxide is transparent and relatively strong. While protecting the light-emitting layer, it does not affect the transmittance of the light of the light-emitting layer 13, thereby ensuring the light-emitting efficiency of the light-emitting layer.

[0064] Based on the same inventive concept, this application also provides a method for preparing an LED display module, please refer to Figure 6 , the method includes steps S20 to S70.

[0065] S20, connecting the second electrode of the LED chip to the lamp surface of the PCB substrate.

[0066] The LED chip may be an LED chip mentioned in this specification, or an LED chip prepared by an LED chip preparation method mentioned in this specification;

[0067] The PCB substrate acts as a driver for the LED chip, providing the driving voltage for the light-emitting portion. The PCB substrate includes a driving surface for soldering the driver circuit and a lighting surface for soldering the LED chip.

[0068] Specifically, in one embodiment, step S20 includes the following steps:

[0069] S21: Printing solder on the lamp surface of the PCB substrate. The solder can be solder paste or a tin-based alloy. Printing the solder on the lamp surface of the PCB substrate can be done by stencil printing or dispensing with a dispensing machine.

[0070] Furthermore, before solder printing, the process also includes soldering components in the driver circuit to the driver surface of the PCB substrate. These components include integrated circuit (IC) control chips, IC memory chips, resistors, capacitors, connectors, and the like. Specifically, soldering these driver surface components can be accomplished using SMT (Surface Mount Technology) technology.

[0071] S22: Connecting the second electrodes of the LED chips to the lamp surface pads of the PCB board to form an LED chip 1 array.

[0072] The electrical connection between the PCB board and the LED chip is achieved through reflow soldering on the PCB board.

[0073] S30 , applying a shielding material in the gaps of the LED chip 1 array.

[0074] Among them, a high-precision inkjet printer, a mask shielding spraying process, a silk screen process, or a dispensing process can be used to apply the shielding material around the LED chip 1. In one embodiment, a high-precision printing device is used to print the three colors of RGB (red, green, and blue) in sequence longitudinally on the side of the LED chip 1 away from the PCB board, with each LED chip 1 printed with one color. At this time, the shielding material 2 spreads to both sides, covering the pads and solder on the PCB substrate, and climbs onto the substrate of the LED chip 1. Because the light-emitting part of the LED chip 1 is lifted by the substrate, the shielding material 2 will not climb onto the light-emitting part, especially blocking the side of the light-emitting part to affect the light emission of the light-emitting part, thereby ensuring the light emission effect of the LED chip;

[0075] Please refer to Figure 6 , is a schematic diagram of vertical printing, wherein the printed red LED chip 16, the printed green LED chip 17 and the printed blue LED chip 18 are arranged in sequence along the vertical direction;

[0076] In an optional embodiment, the shielding material 2 may be black ink or black glue;

[0077] S50, the packaging glue is covered with the PCB substrate through molding to complete the packaging protection.

[0078] The packaging glue is directly molded by a molding process to complete the packaging of the PCB board provided with the LED chip 1.

[0079] Furthermore, a functional optical film is added to the packaging surface according to specific process requirements;

[0080] In an optional embodiment, the encapsulant is a transparent or melanin-doped epoxy resin; or a transparent or melanin-doped silicone;

[0081] S60: Cut off the process edge of the packaged PCB substrate to obtain a finished display module.

[0082] In one embodiment, the display module is a COB (Chip On Board) module.

[0083] In one embodiment, after step S30 and before step S50, step S40 is further included: lighting the LED chip 1 and aging it for a preset time.

[0084] The preset time is not unique and can be determined based on the specific type of LED chip, for example, 4 hours or 5 hours. Specifically, after soldering and before packaging, the LED chips are illuminated and aged for the preset time. This can screen out LED chips with poor luminous performance and perform de-crystallization and repair, which is beneficial to improving the reliability of the display module.

[0085] In summary, the present invention provides a manufacturing process and LED chip of an LED chip, wherein a substrate is welded on the first electrode of the initial LED chip, and a second electrode is connected to the side of the substrate away from the first electrode. At the same time, the substrate layer of the initial LED chip is peeled off to expose the light-emitting layer, and a protective layer is provided on the light-emitting layer to reduce the overall thickness of the initial LED chip to obtain the required LED chip. By adding a substrate to the bottom of the initial LED chip close to the first electrode, the strength of the bottom of the LED is enhanced, thereby avoiding the bottom top damage during the solid crystal process when connected to the PCB board. Even if the substrate is damaged, it can still protect the light-emitting layer and will not affect the light emission of the light-emitting layer. At the same time, the substrate raises the height of the light-emitting layer relative to the PCB board, providing sufficient climbing space for the black ink or black glue set when blocking the bottom of the PCB board, so that it cannot block the light-emitting layer and affect the side light emission. At the same time, removing the top sapphire substrate layer can provide more operational space for COB surface treatment to optimize its display effect and avoid the problem of bright lines and color lines between modules due to excessive thickness.

[0086] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown sequentially as indicated by the arrows, these steps are not necessarily executed sequentially in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times. The order of execution of these steps or stages is not necessarily sequential, but can be executed in rotation or alternation with other steps or at least a portion of steps or stages in other steps.

[0087] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing an LED display module, characterized in that: Including steps: Connecting the second electrode of at least one LED chip to the lamp surface of the PCB substrate; A shielding material is applied in the gaps between the LED chips; the shielding material does not rise onto the light-emitting layer of the LED chip to block the side of the light-emitting layer and affect the light emission of the light-emitting layer; Encapsulating the PCB substrate provided with the LED chip to obtain an LED display module; The LED chip includes a light-emitting layer, a first electrode and a substrate; One side of the light-emitting layer is connected to one end of the first electrode, and the other end of the first electrode is connected to one side of the substrate; A second electrode is provided on the other side of the substrate.

2. The method for preparing an LED display module according to claim 1, wherein: The LED chip further includes a protective layer; The protective layer is arranged on a side of the light emitting layer away from the substrate.

3. The method for preparing an LED display module according to claim 1, wherein: The method for preparing the LED chip comprises: soldering a substrate onto the first electrode of the initial LED chip; A second electrode is connected to a side of the substrate away from the first electrode.

4. The method for preparing an LED display module according to claim 3, wherein: After welding the substrate on the first electrode of the initial LED chip, the method further comprises: peeling off the substrate layer of the initial LED chip to expose the light-emitting layer; A protective layer with a preset thickness is plated on the light-emitting layer.

5. The method for preparing an LED display module according to claim 3, wherein: Before welding the substrate on the first electrode of the initial LED chip, the method further includes: Planting a metal ball on the first electrode to form a soldering pad for the initial LED chip; The specific steps of welding the substrate onto the first electrode of the initial LED chip are as follows: The substrate is soldered on the solder pad.

6. The method for preparing an LED display module according to claim 3, wherein: The step of welding the substrate onto the first electrode of the LED chip comprises: A BT resin substrate or a glass substrate is welded on the first electrode of the initial LED chip.

7. The method for preparing an LED display module according to claim 3, wherein: The step of welding the substrate onto the first electrode of the initial LED chip is as follows: The substrate is welded on the first electrode of the initial LED chip by eutectic welding, laser welding or high-temperature reflow welding.

8. The method for preparing an LED display module according to claim 4, wherein: The step of stripping the substrate layer of the initial LED chip comprises: The substrate layer of the initial LED chip is lifted off by laser.

9. The method for preparing an LED display module according to claim 4, wherein: The step of coating a protective layer of a preset thickness on the light-emitting layer comprises: Silicon dioxide with a preset thickness is plated on the light-emitting layer.

10. An LED display module, characterized in that: The LED display module is obtained by the method for preparing the LED display module according to any one of claims 1 to 9.

Images