LED package structure and packaging method

Abstract

The application is suitable for the technical field of LED packaging, and provides an LED packaging structure, which comprises a substrate and a plurality of light-emitting units arranged on the substrate, wherein each light-emitting unit comprises at least one LED chip, and an ink layer is arranged between the light-emitting units, the ink layer comprises a first part and a second part connected with the first part, the second part is located around the light-emitting unit and extends from the first part to above the light-emitting unit, and the LED packaging structure further comprises a light-transmitting coating layer corresponding to each light-emitting unit and used for preventing the second part from extending to directly above the light-emitting unit, and the light-transmitting coating layer covers the upper surface of the light-emitting unit. The application further provides an LED packaging method. The LED packaging structure and the packaging method provided by the application can prevent the ink from climbing onto the LED chip, have a remarkable effect, are good in practicability and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of LED packaging technology, and particularly relates to an LED packaging structure and packaging method. Background Technology

[0002] In recent years, high-density COB / COG direct-view LED packaging products have been widely promoted in the market. Their flip-chip technology structure meets the requirements for dense packing in ultra-small spaces and is suitable for various packaging substrate materials, gradually becoming the mainstream in the future display market. The substrate material for module packaging is generally a PCB substrate or a glass substrate. To solve the problem of light crosstalk between adjacent pixels and improve ink color consistency and contrast, a black ink layer needs to be prepared on the substrate. There are two main methods: one is to create an ink layer with windows. The ink layer must ensure a large window size. When the ink layer is thicker, the window size becomes larger, exposing more pads and affecting the product's contrast and ink color consistency; the other is to use inkjet printing after die bonding. However, because the ink material used in inkjet printing has extremely low viscosity (good fluidity), ink creep (i.e., ink creeps towards the chip side) occurs after printing onto the substrate surface and then creeps onto the chip surface, such as... Figure 1 As shown, this affects the chip's light emission. Summary of the Invention

[0003] The purpose of this invention is to overcome at least one of the shortcomings of the prior art and to provide an LED packaging structure and packaging method that can prevent ink from creeping onto the light-emitting unit, with significant effect, good practicality and low cost.

[0004] The technical solution of the present invention is: an LED packaging structure, including a substrate and a plurality of light-emitting units disposed on the substrate, each light-emitting unit including at least one LED chip, and an ink layer disposed between the light-emitting units, the ink layer including a first part and a second part connected to the first part, the second part being located around the light-emitting units and extending from the first part upwards from the light-emitting units, the LED packaging structure further including a light-transmitting coating layer corresponding one-to-one with the light-emitting units and used to prevent the second part from extending directly above the light-emitting units, the light-transmitting coating layer covering the upper surface of the light-emitting units.

[0005] As a further improvement to this technical solution, the light-transmitting coating layer includes a front light-transmitting layer located on the upper surface of the light-emitting unit and a side light-transmitting layer located on the side of the light-emitting unit.

[0006] As a further improvement to this technical solution, the light-transmitting coating layer is dome-shaped; the height of the light-transmitting coating layer is less than the width of the light-transmitting coating layer.

[0007] As a further improvement to this technical solution, the second part is located below the upper surface of the light-emitting unit.

[0008] As a further improvement to this technical solution, the ink layer is black, and an irregular curve is formed at the junction of the second part and the side of the light-emitting unit or at the junction of the second part and the light-transmitting coating layer.

[0009] As a further improvement to this technical solution, the material of the light-transmitting coating layer is epoxy resin or silicone resin; and / or, the material of the ink layer is epoxy resin or silicone resin.

[0010] As a further improvement to this technical solution, the hydrophilicity of the light-transmitting coating layer and the ink layer are different.

[0011] As a further improvement to this technical solution, the LED packaging structure also includes a light-transmitting protective layer covering the light-transmitting coating layer and the top of the ink layer.

[0012] The present invention also provides an LED packaging method, comprising the steps of:

[0013] A substrate is provided, on which a plurality of light-emitting units are disposed;

[0014] A light-transmitting coating layer is formed by inkjet printing above the plurality of light-emitting units, and the light-transmitting coating layer covers the upper surface of the light-emitting units;

[0015] A black ink layer is formed by inkjet printing along the gaps between the light-emitting units on the substrate; the ink layer includes a first part and a second part connected to the first part, the second part being located around the light-emitting units and extending from the first part upwards from the light-emitting units;

[0016] A light-transmitting protective layer is formed above the black ink layer and the light-transmitting coating layer.

[0017] The present invention provides an LED packaging structure and packaging method, including a substrate and a plurality of light-emitting units disposed on the substrate. Each light-emitting unit includes at least one LED chip. An ink layer is also provided between the light-emitting units. The ink layer includes a first part and a second part extending from the first part to the side of the light-emitting unit and higher than the first part. The LED packaging structure also includes a light-transmitting coating layer corresponding to each light-emitting unit and used to prevent the second part from extending directly above the light-emitting unit. The light-transmitting coating layer covers the upper surface of the light-emitting unit, which can prevent ink from climbing onto the light-emitting unit. This effectively avoids ink from obscuring or partially obscuring the upper surface of the light-emitting unit (LED chip) and thus affecting the light emission of the LED chip. The effect is significant, practical and low cost. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of an LED packaging structure provided in the background art;

[0020] Figure 2 This is a schematic diagram of an LED packaging structure provided in Embodiment 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of an LED packaging structure provided in Embodiment 2 of the present invention;

[0022] Figure 4 This is a schematic diagram of an LED packaging structure provided in Embodiment 3 of the present invention;

[0023] Figure 5 This is a schematic diagram of an LED packaging structure provided in Embodiment 4 of the present invention;

[0024] Figure 6 This is a schematic diagram of an LED packaging structure provided in Embodiment 5 of the present invention;

[0025] Figure 7 This is a schematic diagram of an LED packaging structure provided in Embodiment Six of the present invention.

[0026] Numbering on the map:

[0027] 1-Substrate; 2-LED chip; 3-Ink layer; 31-First part; 32-Second part; 4-Light-transmitting coating layer; 41-Front light-transmitting layer; 42-Side light-transmitting layer; 43-Light-transmitting filling layer; 5-Light-transmitting protective layer; 6-Boundary. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] It should be noted that the terms "setup" and "connection" should be interpreted broadly. For example, they can refer to direct setup or connection, or indirect setup or connection through centered components or centered structures.

[0030] Furthermore, in embodiments of this invention, terms such as "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" are used to indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, or in a conventional placement or usage state. These terms are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the structures, features, devices, or elements referred to must have a specific orientation or positional relationship, nor that they must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0031] The various specific technical features and embodiments described in the detailed embodiments can be combined in any suitable manner without contradiction. For example, different implementation methods can be formed by combining different specific technical features / embodiments. In order to avoid unnecessary repetition, the various possible combinations of the various specific technical features / embodiments in this invention will not be described separately.

[0032] like Figures 2 to 6As shown, an embodiment of the present invention provides an LED packaging structure, including a substrate 1 and a plurality of light-emitting units 2 disposed on the substrate 1. Each light-emitting unit 2 includes at least one LED chip. The substrate 1 can be a PCB substrate or a glass substrate. Each light-emitting unit 2 can be a monochromatic light chip or an RGB chip. An ink layer 3 is disposed between the light-emitting units 2. The ink layer 3 is formed of ink and is disposed on the substrate 1. The ink layer 3 includes a first part 31 (in this embodiment, the first part 31 is a relatively flat part; in other embodiments, the first part can also be a concave surface, a convex surface, or a rough surface) and a second part 32 connected to the first part 31. The second part 32 is located around the light-emitting unit 2 and extends from the first part 31 upwards from the light-emitting unit 2. The second part 32 is higher than the first part 31 and closer to the light-emitting unit 2 than the first part 31. The LED packaging structure also includes a light-transmitting coating layer 4, which corresponds one-to-one with each light-emitting unit 2. To prevent the second part 32 from moving directly above the light-emitting unit 2, the light-transmitting coating layer 4 covers the upper surface of the light-emitting unit 2. Specifically, the light-transmitting coating layer 4 can cover the upper surface of the LED chip. Due to the extremely low viscosity and good fluidity of the ink, it is easy to climb along the side of the chip. In this embodiment, there is an anti-ink-climbing height difference between the light-transmitting coating layer 4 and the ink layer 3. Specifically, the height of the ink layer 3 is not higher than the height of the light-transmitting coating layer 4. Since the light-transmitting coating layer 4 covers the upper surface of the LED chip, the top of the ink layer 3 is lower than the upper surface of the LED chip, which can prevent the ink from climbing to the upper surface of the LED chip, thereby avoiding the shading or partial shading of the upper surface of the LED chip (ink climbing phenomenon) and causing light blocking. It has good practicality, good anti-ink climbing effect, and helps to reduce the brightness loss of the LED chip. It only requires that the upper surface of the light-emitting unit 2 is covered with the light-transmitting coating layer 4 before the ink layer 3 is prepared. The structure is relatively simple, the preparation cost is low, and it is conducive to widespread application and market promotion.

[0033] In some embodiments, the light-transmitting coating layer 4 includes a front light-transmitting layer 41 located on the upper surface of the light-emitting unit 2 and a side light-transmitting layer 42 located on the side of the light-emitting unit 2; specifically, the LED chip can be a front-mounted chip, and the light-transmitting coating layer 4 is printed using an inkjet printing device. The light-transmitting coating layer 4 is formed by printing the inkjet printing process. Specifically, a light-transmitting material can be used as the printing material, and ink is sprayed onto the top of the LED chip to form the front light-transmitting layer 41. The front light-transmitting layer 41 is disposed adjacent to the ink layer 3 (e.g., ...). Figure 2 and Figure 3 As shown), the front light-transmitting layer 41 can be in contact with the ink layer 3 (e.g., Figure 4 and Figure 5As shown, the printing material has fluidity and can flow to the outer periphery of the LED chip to form a side light-transmitting layer 42. The side light-transmitting layer 42 can also be formed by inkjet printing technology. In other embodiments, the LED chip can also be a flip chip. The light-transmitting coating layer 4 can be dome-shaped. The height of the light-transmitting coating layer 4 is less than the width of the light-transmitting coating layer 4, which helps to save material. Of course, the shape of the light-transmitting coating layer 4 is not limited. The top of the light-transmitting coating layer 4 can be flat or other shapes.

[0034] In some embodiments, the second part 32 is located below the upper surface of the light-emitting unit 2. Specifically, as shown in the figure... Figures 2 to 6 As shown, the top of the ink layer 3 is lower than the top of the LED chip. Specifically, when the LED chip is a top-mounted chip, the top of the ink layer 3 is lower than the top of the LED chip, which can further prevent the ink of the ink layer 3 from flowing to the top light-emitting surface of the LED chip. The top of the second part 32 is not higher than the upper surface of the light-emitting unit 2, so as to avoid being blocked by the second part 32 and facilitate the light emission from the side of the LED chip. Due to process reasons, it is not required that all the second parts 32 are below the upper surface of the light-emitting unit 2, as long as most of them (e.g., more than 80%) are below the upper surface of the light-emitting unit 2, the requirements are met. In some embodiments, the ink layer 3 is black, and the ink layer 3 is printed by inkjet printing equipment. In this embodiment, the LED packaging structure is used for direct display products, and the ink layer 3 can be formed by printing with black ink to increase contrast. The junction of the second part 32 and the side of the light-emitting unit 2 or the junction of the second part 32 and the light-transmitting covering layer 4 forms an irregular curve, such as Figure 7 As shown.

[0035] In specific applications, the ink layer 3 is disposed in the gap between two adjacent light-emitting units 2 and at the edge of the light-emitting unit 2 to the substrate 1, such as... Figure 2 and Figure 3 As shown; the thickness of the ink layer 3 ranges from 3μm to 120μm. In this embodiment, the thickness of the ink layer 3 is controlled by controlling the amount of adhesive dispensed from the print head or the number of prints. In this embodiment, the thickness of the ink layer 3 ranges from 5μm to 15μm.

[0036] In some embodiments, the LED packaging structure further includes a light-transmitting protective layer 5 disposed on top of the light-transmitting coating layer 4 and the ink layer 3. The light-transmitting protective layer 5 can be formed by dispensing or molding. The thickness of the light-transmitting protective layer 5 is 200μm to 400μm.

[0037] In some embodiments, the thickness of the light-transmitting coating layer 4 ranges from 30 μm to 100 μm; specifically, the thickness of the light-transmitting coating layer 4 can range from 30 μm to 80 μm. In specific applications, when the LED packaging structure is applied to a direct-view display product, such as... Figure 5 and Figure 6 As shown, the LED chip includes three RGB chips, and the light-transmitting coating layer 4 may further include a light-transmitting filling layer 43 disposed between two adjacent RGB chips. The front light-transmitting layer 41 is in contact with the light-transmitting filling layer 43. The thickness of the light-transmitting coating layer 4 can be controlled by controlling the amount of adhesive dispensed or the number of prints from the inkjet printer nozzle. In this embodiment, the thickness of the light-transmitting coating layer 4 is 35μm. In one embodiment, to improve display contrast, the light-transmitting protective layer 5 can be a semi-transparent layer. For example, the light-transmitting protective layer can be made of a transparent adhesive material uniformly mixed with a certain proportion of black or gray powder. The proportion of black or gray powder can be adjusted according to design needs. The light-transmitting coating layer 4 is made of transparent material, which can increase the transparent light path above the LED chip and reduce the thickness of the light-transmitting protective layer above the light-emitting unit, thus helping to reduce the brightness loss of the LED chip.

[0038] In some embodiments, the light-transmitting coating layer 4 is made of epoxy resin or silicone resin; in other embodiments, the ink layer 3 is made of epoxy resin or silicone resin; in this embodiment, the light-transmitting coating layer 4 and the ink layer 3 can be made of the same material, which helps to reduce costs.

[0039] In some embodiments, the hydrophilicity of the light-transmitting coating layer 4 and the ink layer 3 are different. Specifically, the light-transmitting coating layer 4 may have hydrophilic factors added to make it hydrophilic, and the ink layer 3 may have hydrophobic factors added to make it hydrophobic. This effectively prevents the ink from obscuring or partially obscuring the upper surface of the LED chip, thereby affecting the LED chip's light emission, and is cost-effective.

[0040] In some embodiments, an LED packaging method is also provided, the LED packaging method being used to package the above-described LED packaging structure, comprising the steps of:

[0041] A substrate 1 is provided, on which a plurality of light-emitting units 2 are disposed. The substrate 1 can be a PCB substrate or a glass substrate; the light-emitting unit 2 includes at least one LED chip.

[0042] A light-transmitting coating layer 4 is formed by inkjet printing above each of the plurality of light-emitting units 2, and the light-transmitting coating layer 4 covers the upper surface of the light-emitting unit 2.

[0043] A black ink layer 3 is formed by inkjet printing along the gap between the light-emitting units 2 on the substrate 1. The ink layer 3 includes a first part 31 and a second part 32. The second part 32 is connected to the first part 31. The second part 32 is located around the light-emitting unit 2 and extends from the first part 31 toward the light-emitting unit 2.

[0044] A light-transmitting protective layer 5 is formed above the black ink layer 3 and the light-transmitting coating layer 4.

[0045] In this embodiment, the method to prevent ink from flowing to the upper surface of the light-emitting unit 2 is as follows: the light-transmitting coating layer 4 is used to prevent the second part 32 from moving above the light-emitting unit 2, and to prevent ink from flowing to the upper surface of the light-emitting unit 2; the light-transmitting coating layer 4 covers the upper surface of the light-emitting unit 2, and an anti-ink-crawling height difference is formed between the light-transmitting coating layer 4 and the ink layer 3; in this embodiment, the light-transmitting coating layer 4 corresponds one-to-one with the light-emitting unit 2; the thickness of the light-transmitting coating layer 4 can be from 30μm to 100μm, and in this embodiment, the thickness of the light-transmitting coating layer 4 is 35μm.

[0046] Specifically, both the ink layer 3 and the light-transmitting coating layer 4 can be printed using inkjet printing equipment, which is more efficient and lower in cost.

[0047] refer to Figures 2 to 5As shown in the figure, an LED packaging structure provided by an embodiment of the present invention includes a substrate 1, which can be a PCB substrate (FR4 circuit board) or a glass substrate; the packaging structure also includes a plurality of light-emitting units 2 disposed on the substrate 1, each light-emitting unit 2 including at least one LED chip, and an ink layer 3 disposed between the light-emitting units 2. The ink layer 3 is formed of ink and is disposed on the substrate 1. The ink layer 3 includes a first section 31 and a second part 32. The second part 32 is located around the light-emitting unit 2 and extends from the first part 31 upwards from the light-emitting unit 2. The LED packaging structure also includes a light-transmitting coating layer 4, which corresponds one-to-one with the light-emitting unit 2 and is used to prevent the second part 32 from extending directly above the light-emitting unit 2, that is, to prevent ink from flowing directly above the LED chip, thus avoiding direct contact between the ink and the LED chip. The light-transmitting coating layer 4 covers the upper surface of the light-emitting unit 2. The light-transmitting coating layer 4 and the ink layer 3 are hydrophilic. Specifically, the light-transmitting coating layer 4 can be made hydrophilic by adding hydrophilic factors, and the ink layer 3 can be made hydrophobic by adding hydrophobic factors. Hydrophilic factors are molecules with polar groups (polar molecules) that have a strong affinity for water, while hydrophobic factors include alkanes, oils, fats, and most hydrophobic molecules containing oils (non-polar molecules) that can repel water. In another embodiment, the light-transmitting coating layer 4 can be made hydrophobic by adding hydrophobic factors. Layer 4 is hydrophobic, while the ink layer 3 can be made hydrophilic by adding hydrophilic factors. By setting the hydrophilicity of the light-transmitting coating layer 4 to be different from that of the ink layer 3, when the ink climbs to the LED chip and meets the light-transmitting coating layer 4 located on the LED chip, they are immiscible and repel each other. This can effectively prevent the ink from continuing to climb to the upper surface of the light-emitting unit 2 (ink climbing phenomenon), effectively avoiding the ink from blocking or partially blocking the upper surface of the light-emitting unit 2 and thus affecting the light emission of the LED chip. The cost is low.

[0048] In some embodiments, an LED packaging method is also provided, the LED packaging method being used to package the above-described LED packaging structure, comprising the steps of:

[0049] A substrate 1 is provided, on which a plurality of light-emitting units 2 are disposed. The substrate 1 can be a PCB substrate or a glass substrate; the light-emitting unit 2 includes at least one LED chip.

[0050] A light-transmitting coating layer 4 is formed by inkjet printing above each of the plurality of light-emitting units 2. In this embodiment, the light-transmitting coating layer 4 corresponds one-to-one with each of the light-emitting units 2. The thickness of the light-transmitting coating layer 4 can range from 30μm to 100μm. In this embodiment, the thickness of the light-transmitting coating layer 4 is 35μm.

[0051] A light-transmitting protective layer 5 is formed above the black ink layer 3 and the light-transmitting coating layer 4.

[0052] In this embodiment, the method for preventing ink from flowing to the upper surface of the light-emitting unit 2 is as follows: materials with different hydrophilicities are added to the materials forming the ink layer 3 and the light-transmitting coating layer 4, respectively. Specifically, the light-transmitting coating layer 4 can be made hydrophilic by adding hydrophilic factors, and the ink layer 3 can be made hydrophobic by adding hydrophobic factors; or, the light-transmitting coating layer 4 can be made hydrophobic by adding hydrophobic factors, and the ink layer 3 can be made hydrophilic by adding hydrophilic factors. By setting the light-transmitting coating layer 4 and the ink layer 3 to have different hydrophilicities, when the ink rises to the LED chip and encounters the light-transmitting coating layer 4 located on the LED chip, they are immiscible and repel each other. This effectively prevents the ink from continuing to rise to the upper surface of the light-emitting unit 2, avoiding direct contact between the ink and the upper surface of the light-emitting unit 2 (i.e., the LED chip), thus affecting the light emission of the LED chip. This method is low in cost.

[0053] The present invention provides an LED packaging structure and packaging method, including a substrate 1, an ink layer 3 formed of ink disposed on the substrate 1, and a light-transmitting coating layer 4 covering the LED chip and used to prevent the second part 32 from extending above the light-emitting unit 2; the second part 32 is located around the light-emitting unit 2 and extends from the first part 31 upwards to the light-emitting unit 2, and is covered by the light-transmitting coating layer 4 on the upper surface of the light-emitting unit 2, or the light-transmitting coating layer 4 and the ink layer 3 have different hydrophilicity, which can prevent ink from climbing to the light-emitting unit 2 (ink climbing phenomenon), effectively avoiding ink from blocking or partially blocking the upper surface of the light-emitting unit 2 (LED chip) and thus affecting the light emission of the LED chip, with significant effect, good practicality and low cost.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An LED packaging structure, comprising a substrate and a plurality of light-emitting units disposed on the substrate, wherein each light-emitting unit includes at least one LED chip, characterized in that, An ink layer is also provided between the light-emitting units. The ink layer includes a first part and a second part connected to the first part. The second part is located around the light-emitting unit and extends from the first part to the top of the light-emitting unit. The LED packaging structure also includes a light-transmitting coating layer that corresponds one-to-one with the light-emitting unit and is used to prevent the second part from extending directly above the light-emitting unit. The light-transmitting coating layer covers the upper surface of the light-emitting unit. The light-transmitting coating layer is formed by inkjet printing, and the light-transmitting coating layer is formed before the ink layer. The light-transmitting coating layer and the ink layer have different hydrophilicity. The second part of the ink layer is located below the upper surface of the light-emitting unit. The LED packaging structure also includes a light-transmitting protective layer covering the light-transmitting coating layer and the top of the ink layer. The light-transmitting protective layer is a semi-transmitting layer containing black or gray powder, and the light-transmitting coating layer is made of a transparent material.

2. The LED packaging structure as described in claim 1, characterized in that, The light-transmitting coating layer includes a front light-transmitting layer located on the upper surface of the light-emitting unit and a side light-transmitting layer located on the side of the light-emitting unit.

3. The LED packaging structure as described in claim 1, characterized in that, The light-transmitting coating layer is dome-shaped; the height of the light-transmitting coating layer is less than the width of the light-transmitting coating layer.

4. The LED packaging structure as described in claim 1, characterized in that, The ink layer is black; the ink layer is formed by inkjet printing process; an irregular curve is formed at the junction of the second part and the side of the light-emitting unit or at the junction of the second part and the light-transmitting coating layer.

5. The LED packaging structure as described in claim 1, characterized in that, The material of the light-transmitting coating layer is epoxy resin or silicone resin; and / or, the material of the ink layer is epoxy resin or silicone resin.

6. The LED packaging structure as described in claim 1, characterized in that, The thickness of the light-transmitting protective layer is 200μm to 400μm, and the thickness of the light-transmitting coating layer is 30μm to 100μm.

7. An LED packaging method, characterized in that, Including the following steps: A substrate is provided, on which a plurality of light-emitting units are disposed; A light-transmitting coating layer is formed by inkjet printing above each of the multiple light-emitting units, and the light-transmitting coating layer covers the upper surface of the light-emitting units; A black ink layer is formed by inkjet printing along the gaps between the light-emitting units on the substrate; the ink layer includes a first part and a second part connected to the first part, the second part being located around the light-emitting units and extending from the first part toward the light-emitting units above the light-emitting units, the light-transmitting coating layer having a different hydrophilicity from the ink layer, and the second part of the ink layer being located below the upper surface of the light-emitting units; A light-transmitting protective layer is formed above the black ink layer and the light-transmitting coating layer. The light-transmitting protective layer is a semi-transmitting layer containing black or gray powder, and the light-transmitting coating layer is made of a transparent material.

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