PCB (Printed Circuit Board) card board with optical transmission layer and preparation method thereof

Abstract

The invention belongs to the technical field of information photoelectron or optical communication, and particularly discloses a PCB (printed circuit board) card board with an optical transmission layer and a preparation method of the PCB card board. The method comprises the following steps: firstly, removing a coating layer from a single-mode optical fiber to obtain a bare optical fiber only comprising a cladding and a core layer; sequentially carrying out roughening treatment, sensitization treatment and activation treatment to obtain a pretreated bare optical fiber; coating metal on the surface to obtain a treated optical fiber; wrapping the processed optical fiber with a glass fiber sleeve to obtain a protection optical fiber; the protective optical fibers and the glass fiber textile threads are interwoven and laid to obtain stable optical fiber cloth; and immersing in epoxy resin, curing to serve as a semi-cured layer of the PCB, and preparing the PCB card board to obtain the PCB card board with the light transmission layer. The clamping plate prepared by the invention is stable in structure, and the optical fiber is protected by coating, so that the clamping plate is compatible with a traditional PCB (Printed Circuit Board) process, and has the effects of compression resistance and high-temperature protection.

Description

Technical Field

[0001] The present invention relates to the field of information optoelectronics or optical communication technology, and in particular to a PCB card board with an optical transmission layer and a preparation method thereof. Background Art

[0002] With the rapid development of high-performance computers and high-speed communication technologies and the continuous growth of information capacity, the demand for large-capacity, large-bandwidth, high-speed transmission and exchange has become a necessary technology for communication. Traditional electrical interconnection uses copper wires as information transmission channels. In high-speed, high-frequency, and high-interconnection density data processing and transmission systems, problems such as crosstalk and clock skew will occur. These problems are also the bottlenecks of traditional electrical interconnection technology that restrict the rapid development of high-speed communication systems. Optical signals use optical waveguides as carriers and have the advantages of high bandwidth, high density, anti-interference ability, low latency, and low energy consumption. They have become an important technology for high-speed communications.

[0003] In recent years, optical interconnection controlled by IC chips on printed circuit boards has developed rapidly. Optical waveguides are used to replace traditional copper wires to make optoelectronic printed circuit boards, forming a separate optical path layer inside the board. Currently, most optical interconnection solutions are to make separate waveguides or bury optical fibers directly into printed circuit boards (PCBs). PCBs made in this way not only limit the flexibility and functionality of waveguide layout, but also the number of waveguides is very small, which makes it difficult to produce them in large quantities. In addition, when traditional optical waveguides are integrated with PCBs, they are easily affected by high temperature and pressure, resulting in the breakage of waveguide transmission links and high-temperature modification.

[0004] Therefore, how to provide a new PCB card with an optical transmission layer, improve the flexibility and functionality of the PCB card waveguide layout, and avoid the breakage and modification of the waveguide transmission link is a difficult problem to be solved urgently in this field. Summary of the invention

[0005] In view of this, the present invention provides a PCB card board with an optical transmission layer and a preparation method thereof, which solves the problem of limited flexibility and functionality of waveguide layout when making a separate waveguide or directly burying the optical fiber into the printed circuit board; it also solves the problem of easy breakage and high-temperature modification of the waveguide transmission link.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a PCB card with a light transmission layer comprises the following steps:

[0008] 1) removing the coating layer of the single-mode optical fiber to obtain a bare optical fiber containing only the cladding and the core layer;

[0009] 2) performing roughening treatment, sensitization treatment and activation treatment on the bare optical fiber in sequence to obtain a pretreated bare optical fiber;

[0010] 3) coating metal on the surface of the pre-treated bare optical fiber to obtain a treated optical fiber;

[0011] 4) Wrapping the treated optical fiber with a glass fiber sleeve to obtain a protected optical fiber;

[0012] 5) interweaving and laying the protective optical fiber and the glass fiber textile line to obtain a stable optical fiber cloth;

[0013] 6) immersing the stabilized optical fiber cloth into epoxy resin, and obtaining a semi-cured layer with the stabilized optical fiber cloth after curing;

[0014] 7) The semi-cured layer with the stable optical fiber cloth is used as a semi-cured layer of the PCB to prepare a PCB card to obtain a PCB card with a light transmission layer.

[0015] Preferably, the roughening treatment is to immerse the bare optical fiber in a roughening liquid for 10 to 20 minutes, and then keep the temperature at 140 to 160° C. for 8 to 15 minutes to complete the roughening treatment;

[0016] The sensitization treatment is to immerse the roughened bare optical fiber in a sensitizing solution at a temperature of 25 to 35° C. for 8 to 15 minutes to complete the sensitization treatment;

[0017] The activation treatment is to immerse the bare optical fiber after the sensitization treatment into an activation solution at a temperature of 25 to 35° C. for 12 to 18 minutes, and then keep the temperature at 140 to 160° C. for 8 to 15 minutes to complete the activation treatment.

[0018] Preferably, the roughening solution comprises a mixed solution of hydrofluoric acid and fluorosilicic acid; the sensitizing solution comprises a mixed solution of stannous chloride and hydrochloric acid; and the activating solution comprises a mixed solution of palladium chloride and hydrochloric acid.

[0019] Preferably, the method of coating the surface with metal includes chemical plating or ion sputtering;

[0020] The metal type of the surface coating metal includes one or more of copper, nickel and gold;

[0021] The thickness of the surface coating metal is 8-20 μm.

[0022] Preferably, the glass fiber sleeve is obtained by weaving a sleeve with quartz fiber wires;

[0023] The diameter of the quartz fiber line is smaller than the radius of the processed optical fiber; the radius of the sleeve is equal to the radius of the processed optical fiber.

[0024] Preferably, the glass fiber textile yarn in step 5) is woven from glass fibers;

[0025] The diameter of the glass fiber textile line is 90-110% of the diameter of the protective fiber.

[0026] Preferably, the epoxy resin includes one or more of bisphenol epoxy resin, novolac epoxy resin and glycidylamine epoxy resin.

[0027] Another object of the present invention is to provide a PCB card board with a light transmission layer prepared by the preparation method.

[0028] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0029] The PCB card with an optical transmission layer prepared by the present invention contains a semi-cured layer with a stable optical fiber cloth, which can be used for the transmission of high-speed optical signals. The card replaces high-speed electrical signals with optical signals, solving the bottleneck problem of the transmission rate of electrical signals of traditional PCB cards; in addition, the card is interwoven with glass fibers to improve the structural stability of the glass card and the waveguide, and the optical fiber is coated and protected to achieve compatibility with traditional PCB processes, and has the effects of pressure resistance and high temperature protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 It is a schematic diagram of interweaving and laying of the present invention;

[0032] Figure 2 A schematic diagram of a PCB card with a light transmission layer prepared in the present invention. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a PCB card board with a light transmission layer, comprising the following steps:

[0034] 1) removing the coating layer of the single-mode optical fiber to obtain a bare optical fiber containing only the cladding and the core layer;

[0035] 2) performing roughening treatment, sensitization treatment and activation treatment on the bare optical fiber in sequence to obtain a pretreated bare optical fiber;

[0036] 3) coating metal on the surface of the pre-treated bare optical fiber to obtain a treated optical fiber;

[0037] 4) Wrapping the treated optical fiber with a glass fiber sleeve to obtain a protected optical fiber;

[0038] 5) interweaving and laying the protective optical fiber and the glass fiber textile line to obtain a stable optical fiber cloth;

[0039] 6) immersing the stabilized optical fiber cloth into epoxy resin, and obtaining a semi-cured layer with the stabilized optical fiber cloth after curing;

[0040] 7) The semi-cured layer with the stable optical fiber cloth is used as a semi-cured layer of the PCB to prepare a PCB card to obtain a PCB card with a light transmission layer.

[0041] In the present invention, the coating layer is preferably removed by soaking in acetone, and the soaking time is determined according to the thickness of the protective layer and the concentration of acetone until the coating layer is completely removed; the coating layer is generally composed of acrylate or polyimide.

[0042] In the present invention, after the coating layer is removed, the process further includes the steps of ethanol washing and water washing in sequence, the purpose of which is to wash the obtained bare optical fiber.

[0043] In the present invention, the roughening treatment is to immerse the bare optical fiber in a roughening liquid for 10 to 20 minutes, specifically 12 minutes, 14 minutes, 15 minutes, 16 minutes, or 18 minutes; after the treatment is completed, the roughening treatment is completed by keeping it warm at 140 to 160°C for 8 to 15 minutes; the insulation temperature can be specifically 142°C, 145°C, 148°C, 150°C, 152°C, 155°C, or 158°C, and the insulation time can be specifically 9 minutes, 10 minutes, 11 minutes, 12 minutes, or 14 minutes.

[0044] In the present invention, the sensitization treatment is to immerse the roughened bare optical fiber in a sensitizing solution at a temperature of 25 to 35°C for 8 to 15 minutes to complete the sensitization treatment; the treatment temperature can be specifically 26°C, 28°C, 30°C, 32°C, or 34°C; the treatment time can be specifically 9 minutes, 10 minutes, 11 minutes, 12 minutes, or 14 minutes.

[0045] In the present invention, the activation treatment is to immerse the bare optical fiber after sensitization treatment in an activation solution at a temperature of 25-35°C for 12-18 minutes, and then keep it at 140-160°C for 8-15 minutes to complete the activation treatment; the treatment temperature can be 26°C, 28°C, 30°C, 32°C, 34°C; the treatment time can be 13min, 14min, 15min, 16min, 17min; the insulation temperature can be 142°C, 145°C, 148°C, 150°C, 152°C, 155°C, 158°C; the insulation time can be 9min, 10min, 11min, 12min, 14min.

[0046] In the present invention, the roughening solution includes a mixed solution of hydrofluoric acid and fluorosilicic acid, but is not limited to this mixed solution.

[0047] In the present invention, the mixed solution of hydrofluoric acid and fluorosilicic acid is preferably hydrofluoric acid:fluorosilicic acid:water=1:1:3.

[0048] In the present invention, the sensitizing solution includes a mixed solution of stannous chloride and hydrochloric acid, but is not limited to the mixed solution.

[0049] In the present invention, the mixed solution of stannous chloride and hydrochloric acid is preferably obtained by mixing 10 g / L stannous chloride solution with 40 mL / L hydrochloric acid.

[0050] In the present invention, the activation solution includes a mixed solution of palladium chloride and hydrochloric acid, but is not limited to the mixed solution.

[0051] In the present invention, the mixed solution of palladium chloride and hydrochloric acid is preferably obtained by mixing 0.5 g / L palladium chloride with 5 mL / L hydrochloric acid.

[0052] In the present invention, the method of coating the surface with metal includes chemical plating or ion sputtering.

[0053] In the present invention, the metal type of the surface coating metal includes one or more of copper, nickel and gold.

[0054] In the present invention, the thickness of the surface-coated metal is 8 to 20 μm, and specifically can be 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, or 18 μm.

[0055] In the present invention, the glass fiber sleeve is obtained by weaving quartz fiber wires into a sleeve.

[0056] In the present invention, the quartz fiber wire is preferably obtained by drawing quartz fiber, and then winding the drawn fiber into a wire to ensure that the thickness of the wire should be smaller than the radius of the optical fiber; the protective optical fiber obtained by the present invention has excellent tensile strength and good heat insulation effect, and can resist the high temperature and pressure in PCB production.

[0057] In the present invention, the diameter of the quartz fiber line is smaller than the radius of the processed optical fiber; the radius of the sleeve is equal to the radius of the processed optical fiber.

[0058] In the present invention, the glass fiber textile yarn in step 5) is woven from glass fibers, and the diameter of the glass fiber textile yarn is 80-120% of the diameter of the protective fiber, specifically 85%, 90%, 95%, 100%, or 110%.

[0059] In the present invention, the protective optical fiber is used as one of the wires in the interwoven laying and is woven with the glass fiber textile wire (the ratio of the number of protective optical fibers to the glass fiber textile wire is determined according to needs, and can be 1:20-1000, specifically 1:50, 1:100, 1:200, 1:500, 1:800), but the number of overlaps in the interwoven laying needs to be much smaller than that of the glass fiber textile wire (optical fiber reduces crossing) to reduce the number and amplitude of bending of the protective optical fiber.

[0060] In interlaced laying, the optical fiber needs to be properly routed. For optical fibers that turn at 90°, it is preferred to reduce the transverse glass fiber to reserve the transverse direction of the optical fiber turning. The turning angle should have a larger curvature. Figure 1 shown.

[0061] In the present invention, the epoxy resin includes one or more of bisphenol epoxy resin, novolac epoxy resin and glycidylamine epoxy resin.

[0062] The present invention also provides a PCB card board with a light transmission layer prepared by the preparation method, and the schematic diagram of the PCB card board with a light transmission layer is as shown in Figure 2 shown.

[0063] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] Example 1

[0065] The standard single-mode optical fiber was immersed in acetone for 25 minutes until its coating layer was completely removed to obtain a bare optical fiber containing only a cladding layer and a core layer; after removing the coating layer, the bare optical fiber was placed in ethanol for ultrasonic cleaning and then cleaned with distilled water.

[0066] After cleaning, the bare optical fiber is treated with roughening liquid, sensitizing liquid and activating liquid in turn to form an optical fiber with good metal adhesion ability; the roughening liquid is: hydrofluoric acid: fluorosilicic acid: water = 1:1:3, and the treatment time is 15 minutes; after roughening, heat treatment is carried out at 150℃ for 10 minutes. The sensitizing liquid is: stannous chloride concentration is 10g / L, hydrochloric acid concentration is 40mL / L, the temperature is maintained at 30℃, and the treatment time is 10 minutes; the sensitized optical fiber is ultrasonically cleaned with distilled water for 10 minutes. The activation liquid is: palladium chloride concentration is 0.5g / L, hydrochloric acid concentration is 5mL / L, the temperature is maintained at 30℃, the treatment time is 15 minutes, and after activation, heat treatment is carried out at 150℃ for 10 minutes.

[0067] The pre-treated optical fiber is coated on the surface using ion sputtering, and the coating metal is copper. A 10μm thick metal layer is formed on the surface of the optical fiber, which can ensure a certain degree of ductility and a certain degree of compressive resistance, thereby ensuring good transmission performance of the optical fiber.

[0068] The treated optical fiber is sheathed in a tight glass fiber sheath. The glass fiber sheath is drawn from Philihua quartz fiber and then the drawn fiber is wound into a wire to ensure that the diameter of the quartz fiber wire is smaller than the radius of the optical fiber (optical fiber after metal coating treatment); the quartz fiber wire is woven into a sheath with a radius equal to the radius of the optical fiber, and the optical fiber is sheathed in the sheath to obtain a protected optical fiber; the formed protected optical fiber has excellent tensile strength and good heat insulation effect, and can resist the influence of high temperature and pressure in PCB production.

[0069] The prepared protective optical fiber is interwoven with the glass fiber textile line and laid. During the interwoven laying process, the protective optical fiber is woven as one of the lines to form a waveguide transmission pattern and a stable optical fiber cloth.

[0070] The prepared stable optical fiber cloth is soaked in bisphenol epoxy resin to form a semi-cured layer, i.e., a waveguide layer, which is the same as the traditional PCB. The prepared waveguide layer is used as one of the semi-cured layers using the same process as the PCB to be integrated with the PCB process to form a PCB board, as shown in the schematic diagram. Figure 2 shown.

[0071] Example 2

[0072] The standard single-mode optical fiber was immersed in acetone for 25 minutes until its coating layer was completely removed to obtain a bare optical fiber containing only a cladding layer and a core layer; after removing the coating layer, the bare optical fiber was placed in ethanol for ultrasonic cleaning and then cleaned with distilled water.

[0073] After cleaning, the bare optical fiber is treated with roughening liquid, sensitizing liquid and activation liquid in turn to form an optical fiber with good metal adhesion ability; the roughening liquid is: hydrofluoric acid: fluorosilicic acid: water = 1:1:3, and the treatment time is 20 minutes; after roughening, heat treatment is carried out at 140℃ for 15 minutes. The sensitizing liquid is: stannous chloride concentration is 10g / L, hydrochloric acid concentration is 40mL / L, the temperature is maintained at 35℃, and the treatment time is 8 minutes; the sensitized optical fiber is ultrasonically cleaned with distilled water for 10 minutes. The activation liquid is: palladium chloride concentration is 0.5g / L, hydrochloric acid concentration is 5mL / L, the temperature is maintained at 35℃, the treatment time is 12 minutes, and after activation, heat treatment is carried out at 140℃ for 15 minutes.

[0074] The pre-treated optical fiber is coated on the surface using ion sputtering, with gold as the coating metal. A 15μm thick metal layer is formed on the surface of the optical fiber, which not only ensures a certain degree of ductility, but also has a certain degree of compressive resistance, thus ensuring good transmission performance of the optical fiber.

[0075] The treated optical fiber is sheathed in a tight glass fiber sheath. The glass fiber sheath is drawn from Philihua quartz fiber and then the drawn fiber is wound into a wire to ensure that the diameter of the quartz fiber wire is smaller than the radius of the optical fiber (optical fiber after metal coating treatment); the quartz fiber wire is woven into a sheath with a radius equal to the radius of the optical fiber, and the optical fiber is sheathed in the sheath to obtain a protected optical fiber; the formed protected optical fiber has excellent tensile strength and good heat insulation effect, and can resist the influence of high temperature and pressure in PCB production.

[0076] The prepared protective optical fiber is interwoven with the glass fiber textile line and laid. During the interwoven laying process, the protective optical fiber is woven as one of the lines to form a waveguide transmission pattern and a stable optical fiber cloth.

[0077] The prepared stable optical fiber cloth is soaked in bisphenol epoxy resin to form a semi-cured layer, i.e., a waveguide layer, which is the same as a traditional PCB. The prepared waveguide layer is used as one of the semi-cured layers using the same process as PCB to be integrated with the PCB process to form a PCB board.

[0078] Example 3

[0079] The standard single-mode optical fiber was immersed in acetone for 25 minutes until its coating layer was completely removed to obtain a bare optical fiber containing only a cladding layer and a core layer; after removing the coating layer, the bare optical fiber was placed in ethanol for ultrasonic cleaning and then cleaned with distilled water.

[0080] After cleaning, the bare optical fiber is treated with roughening liquid, sensitizing liquid and activation liquid in turn to form an optical fiber with good metal adhesion ability; the roughening liquid is: hydrofluoric acid: fluorosilicic acid: water = 1:1:3, and the treatment time is 10 minutes; after roughening, heat treatment is carried out at 160℃ for 8 minutes. The sensitizing liquid is: stannous chloride concentration is 10g / L, hydrochloric acid concentration is 40mL / L, the temperature is maintained at 25℃, and the treatment time is 12 minutes; the sensitized optical fiber is ultrasonically cleaned with distilled water for 10 minutes. The activation liquid is: palladium chloride concentration is 0.5g / L, hydrochloric acid concentration is 5mL / L, the temperature is maintained at 28℃, the treatment time is 18 minutes, and after activation, heat treatment is carried out at 150℃ for 15 minutes.

[0081] The pre-treated optical fiber is coated on the surface by chemical plating, and the coating metal is copper. A metal layer with a thickness of 18μm is formed on the surface of the optical fiber, which can ensure a certain ductility and a certain compressive resistance, thereby ensuring good transmission performance of the optical fiber.

[0082] The treated optical fiber is sheathed in a tight glass fiber sheath. The glass fiber sheath is drawn from Philihua quartz fiber and then the drawn fiber is wound into a wire to ensure that the diameter of the quartz fiber wire is smaller than the radius of the optical fiber (optical fiber after metal coating treatment); the quartz fiber wire is woven into a sheath with a radius equal to the radius of the optical fiber, and the optical fiber is sheathed in the sheath to obtain a protected optical fiber; the formed protected optical fiber has excellent tensile strength and good heat insulation effect, and can resist the influence of high temperature and pressure in PCB production.

[0083] The prepared protective optical fiber is interwoven with the glass fiber textile line and laid. During the interwoven laying process, the protective optical fiber is woven as one of the lines to form a waveguide transmission pattern and a stable optical fiber cloth.

[0084] The prepared stable optical fiber cloth is soaked in bisphenol epoxy resin to form a semi-cured layer, i.e., a waveguide layer, which is the same as a traditional PCB. The prepared waveguide layer is used as one of the semi-cured layers using the same process as PCB to be integrated with the PCB process to form a PCB board.

[0085] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0086] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a PCB card with a light transmission layer, characterized in that: The steps include: 1) removing the coating layer of the single-mode optical fiber to obtain a bare optical fiber containing only the cladding and the core layer; 2) performing roughening treatment, sensitization treatment and activation treatment on the bare optical fiber in sequence to obtain a pretreated bare optical fiber; 3) coating metal on the surface of the pre-treated bare optical fiber to obtain a treated optical fiber; 4) Wrapping the treated optical fiber with a glass fiber sleeve to obtain a protected optical fiber; 5) interweaving and laying the protective optical fiber and the glass fiber textile line to obtain a stable optical fiber cloth; 6) immersing the stabilized optical fiber cloth into epoxy resin, and obtaining a semi-cured layer with the stabilized optical fiber cloth after curing; 7) The semi-cured layer with the stable optical fiber cloth is used as a semi-cured layer of the PCB to prepare a PCB card board to obtain a PCB card board with a light transmission layer.

2. The method for preparing a PCB card with a light transmission layer according to claim 1, characterized in that: The roughening treatment is to immerse the bare optical fiber in a roughening liquid for 10 to 20 minutes, and then keep the temperature at 140 to 160° C. for 8 to 15 minutes to complete the roughening treatment; The sensitization treatment is to immerse the roughened bare optical fiber in a sensitizing solution at a temperature of 25 to 35° C. for 8 to 15 minutes to complete the sensitization treatment; The activation treatment is to immerse the bare optical fiber after the sensitization treatment in an activation solution at a temperature of 25 to 35° C. for 12 to 18 minutes, and then keep the temperature at 140 to 160° C. for 8 to 15 minutes to complete the activation treatment.

3. The method for preparing a PCB card with a light transmission layer according to claim 2, characterized in that: The roughening solution includes a mixed solution of hydrofluoric acid and fluorosilicic acid; the sensitizing solution includes a mixed solution of stannous chloride and hydrochloric acid; and the activating solution includes a mixed solution of palladium chloride and hydrochloric acid.

4. The method for preparing a PCB card with a light transmission layer according to claim 3, characterized in that: The method of coating the surface with metal includes chemical plating or ion sputtering; The metal type of the surface coating metal includes one or more of copper, nickel and gold; The thickness of the surface coating metal is 8-20 μm.

5. The method for preparing a PCB card with a light transmission layer according to any one of claims 1 to 4, characterized in that: The glass fiber sleeve is made of quartz fiber wires weaved into a sleeve to obtain a glass fiber sleeve; The diameter of the quartz fiber line is smaller than the radius of the processed optical fiber; the radius of the sleeve is equal to the radius of the processed optical fiber.

6. The method for preparing a PCB card with a light transmission layer according to claim 5, characterized in that: The glass fiber textile yarn in step 5) is obtained by weaving glass fibers; The diameter of the glass fiber textile line is 90-110% of the diameter of the protective fiber.

7. The method for preparing a PCB card with a light transmission layer according to claim 6, characterized in that: The epoxy resin includes one or more of bisphenol epoxy resin, novolac epoxy resin and glycidylamine epoxy resin.

8. A PCB board with a light transmission layer prepared by the preparation method according to any one of claims 1 to 7.

Images