Preparation process of high reflectivity mini LED PCB

Abstract

The application discloses a high-reflectivity Mini LED PCB preparation process, comprising the following steps: solder mask pretreatment, solder mask printing, pre-baking, exposure, development and post-baking; white solder mask ink is used for solder mask printing, and the preparation method of the white solder mask ink is as follows: a photosensitive resin is divided into a first photosensitive resin and a second photosensitive resin, the first photosensitive resin, a photoinitiator A and a 1-2 functionality monomer are uniformly stirred, and the mixture is uniformly sprayed on the surface of titanium white powder, followed by baking and pre-exposure to obtain coated titanium white powder, and the coated titanium white powder is uniformly mixed with the second photosensitive resin, a photoinitiator B, a 3-6 functionality monomer and an additive, and the mixture is ready. The coated titanium white powder is prepared by coating the titanium white powder with the photosensitive resin, and the dispersibility of the titanium white powder in the ink can be improved without adding a dispersant; and the application also reduces the influence of the incorporation of the titanium white pigment on the mechanical anchoring ability of the ink, and improves the adhesion of the ink to the PCB substrate.

Description

Technical Field

[0001] This invention belongs to the field of circuit board technology, specifically relating to a high-reflectivity Mini LED PCB fabrication process. Background Technology

[0002] Mini LEDs (small light-emitting diodes) are small in size and have irregular cutting characteristics. When paired with flexible substrates, they can also achieve high-curvature backlighting. They employ local dimming design and have better color performance. They can be used in commercial large-size displays, as well as in products such as televisions, automotive panels, and gaming laptops. Therefore, Mini LEDs have high reflectivity requirements.

[0003] The main factor affecting the surface reflectivity of Mini LED printed circuit boards is the white solder resist ink layer. Currently, there are two main problems with white solder resist ink:

[0004] 1. Titanium dioxide is a commonly used pigment in white solder resist inks. Due to its small particle size, it is prone to agglomeration and has poor compatibility with organic resins, resulting in poor dispersibility. Although conventional dispersants can improve the dispersibility of titanium dioxide, different dispersants have different effects on the dispersion effect of titanium dioxide, requiring a complicated screening process. It is also necessary to control the compatibility between the dispersant and the system, which makes the process complicated. In addition, the dispersant can also easily affect the surface properties of titanium dioxide, thereby affecting the performance of titanium dioxide.

[0005] 2. Currently, in order to produce high reflectivity Mini LED PCBs, it is usually necessary to increase the amount of white pigment titanium dioxide added to the solder resist ink. With high titanium dioxide content, the mechanical anchoring ability of the resin is easily reduced, resulting in reduced ink adhesion.

[0006] In summary, how to provide a high-reflectivity Mini LED PCB manufacturing process by improving the dispersibility of titanium dioxide in white solder resist ink and reducing the impact of high titanium dioxide content on ink adhesion is an urgent problem to be solved. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-reflectivity Mini LED PCB manufacturing process. This process involves coating titanium dioxide with photosensitive resin to obtain coated titanium dioxide, which exhibits good compatibility with the ink system. It improves the dispersibility of titanium dioxide in the ink without the need for dispersants, and the method is simple and has no adverse effects. Furthermore, this invention introduces cationic photopolymerization reactions on both the coated titanium dioxide and the PCB substrate surface, reducing the impact of titanium dioxide pigment incorporation on the mechanical anchoring ability of the ink, thereby improving the adhesion between the ink and the PCB substrate.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A high-reflectivity Mini LED PCB fabrication process includes the following steps:

[0010] (1) Perform solder resist pretreatment on the PCB substrate (including cleaning and roughening the substrate);

[0011] (2) Use white solder resist ink for solder resist screen printing (screen printing, 32T-51T, 20-30μm printing thickness).

[0012] (3) Pre-baking: 75-80℃×10-40min;

[0013] (5) Exposure: Exposure machine with a wavelength of 365nm, ink surface 300-800mj / cm 2 ;

[0014] (6) Development: The developing temperature is 28-33℃, and the spray pressure is 0.15-0.18MPa;

[0015] (7) Post-baking: 150℃, 60min.

[0016] The raw materials for preparing the white solder resist ink include 30-60 parts of photosensitive resin, 20-50 parts of titanium dioxide (0.01-10μm), 2-10 parts of photoinitiator, 10-30 parts of monomers containing double bonds, and 0-20 parts of additives.

[0017] The photoinitiator comprises photoinitiator A and photoinitiator B in a mass ratio of 1:(8-12), wherein photoinitiator A comprises a free radical photoinitiator with an absorption wavelength range of 380-420nm, and photoinitiator B comprises a free radical photoinitiator with an absorption wavelength range of 320-370nm.

[0018] Preferably, the photoinitiator A is TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide), 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), or ITX (isopropylthioxanthone), and the photoinitiator B is 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone) or 651 (benzoin methyl ether).

[0019] The double-bonded monomers include 1-2 functional monomers and 3-6 functional monomers in a mass ratio of 1:(9-14).

[0020] Preferably, the 1-2 functional monomers are one or any combination of acrylate monomers, vinyl ester monomers, butenolate monomers, and phosphate ester monomers containing 1-2 double bonds;

[0021] Preferably, the 1-2 functional monomers comprise a phosphate ester monomer containing 1-2 double bonds and an acrylate monomer containing 1-2 double bonds in a mass ratio of 1:(1-3). The acrylate monomer containing 1-2 double bonds is one or more of glycidyl methacrylate (GMA), allyl methacrylate (AMA), 1,6-hexanediol diacrylate (HDDA), and tripropylene glycol diacrylate (TPGDA). The phosphate ester monomer containing 1-2 double bonds is one or two of trimethyl 4-phosbutenoate and allyl diethyl phosphate.

[0022] More preferably, the 1-2 functional monomers comprise trimethyl 4-phosbutenoate and glycidyl methacrylate in a mass ratio of 1:(1-3).

[0023] The 3-6 functional monomers are one or any combination of acrylate monomers, vinyl ester monomers, and butenolate monomers containing 3-6 double bonds.

[0024] Preferably, the 3-6 functional monomer is an acrylate monomer containing 3-6 double bonds, and the acrylate monomer containing 3-6 double bonds is one or any of the following: trimethylolpropane triacrylate (TMPTA), 3-ethoxy-trimethylolpropane triacrylate (3EOTMPTA), propoxylated trimethylolpropane triacrylate (POTMPTA), isoprene tetraacrylate, and dipentaerythritol hexaacrylate (DPHA).

[0025] Preferably, the photosensitive resin is an unsaturated polyester, acrylic resin, epoxy resin, or epoxy-acrylic resin. More preferably, the photosensitive resin is epoxy-acrylic resin.

[0026] Preferably, the titanium dioxide is rutile titanium dioxide, and the additives include one or any combination of 0.5-2 parts leveling agent, 2-6 parts antioxidant, 1-3 parts defoamer, 1-2 parts adhesion promoter, and 1-3 parts ultraviolet absorber.

[0027] The method for preparing the white ink includes the following steps:

[0028] The photosensitive resin was divided into two parts by mass ratio of 1:(10-15). The first part of the photosensitive resin, photoinitiator A, and 1-2 functional monomers were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 70-80℃ for 5-10 minutes, and then pre-exposed in a 395nm exposure machine with exposure parameters of 50-200 mJ / cm. 2 The coated titanium dioxide is obtained by mixing it evenly with the second part of photosensitive resin, photoinitiator B, 3-6 functional (double bond) monomer and additives.

[0029] Preferably, the photoinitiator A further includes a cationic photoinitiator 1, and the mass ratio of the 380-420nm free radical photoinitiator to the cationic photoinitiator 1 is 1:(0.5-1).

[0030] Preferably, the pretreatment before solder resist further includes: uniformly spraying a cationic photoinitiator 2 solution onto the surface of the PCB substrate, wherein the spraying amount of cationic photoinitiator 2 is 0.8-3 g / m². 2 The concentration of the cationic photoinitiator 2 solution is 0.5-20%.

[0031] Preferably, the cationic photoinitiator 1 and cationic photoinitiator 2 are any one or more of diaryliodomonium salt, triarylthionium salt (triarylhexafluorophosphate thionium salt), and alkylthionium salt.

[0032] The present invention also provides a developing process in the fabrication process of the high reflectivity Mini LED PCB, wherein the developing solution used includes 0.8-1.8 parts sodium carbonate and 100-150 parts water.

[0033] Preferably, the developing solution further includes 1-4 parts of an amino compound and 1-6 parts of propylene carbonate.

[0034] Preferably, the amino compound is any one or more of nicotinamide ethyl ester, choline acetate, ethanolamine, ammonia, and triethylamine.

[0035] More preferably, the amino compound includes 0.4-1 parts of choline acetate and 0.6-3 parts of nicotinamide ethyl ester.

[0036] Technical effects of the present invention:

[0037] 1. In the preparation of white solder resist ink, the present invention coats titanium dioxide with photosensitive resin and then pre-exposes and cures it with low-energy UV (initial shaping), which can produce coated titanium dioxide with good compatibility with ink system. It can improve the dispersibility of titanium dioxide in ink without adding dispersant. The method is simple and has no adverse effects.

[0038] 2. The white solder resist ink prepared by this invention is prone to a phenomenon of asynchronous curing of the photosensitive resin in the coated titanium dioxide and the photosensitive resin in the ink body during subsequent ink exposure due to the pre-exposure of the photosensitive resin in the coated titanium dioxide. This affects the dispersion of titanium dioxide in the ink and the incomplete curing of the resin. It is also prone to delamination caused by a decrease in interfacial bonding.

[0039] Therefore, this invention controls the curing speed of the photosensitive resin in the coated titanium dioxide and the photosensitive resin in the ink matrix by controlling the composition of the photoinitiator and monomers. The photoinitiator includes photoinitiator A (absorption wavelength range of 380-420nm) and photoinitiator B (absorption wavelength range of 320-370nm), and the monomers include 1-2 functional monomers and 3-6 functional monomers. Photoinitiator A and 1-2 functional monomers are used in the coated titanium dioxide, and photoinitiator B and 3-6 functional monomers are used in the ink matrix. This can comprehensively adjust the resin crosslinking speed and achieve synergistic optimization of the highly dispersible titanium dioxide and ink system.

[0040] 3. The 1-2 functional monomers used in the coated titanium dioxide of the present invention are preferably trimethyl 4-phosphobutenoate and glycidyl methacrylate. These monomers not only improve the adhesion of the surface coating layer to the titanium dioxide surface, making the coating layer less likely to fall off and improving the coating stability of the coated titanium dioxide, but also form a rough coating layer on the titanium dioxide surface during pre-curing, promoting the bonding between the rough coated titanium dioxide and the ink system, improving the regional uniformity of the ink layer, and thus improving the uniformity of reflectivity.

[0041] 4. The photoinitiator A in the coated titanium dioxide of the present invention further includes a cationic photoinitiator 1, and the cationic photoinitiator 2 is sprayed onto the surface of the PCB substrate during the solder resist pretreatment, so that cationic photopolymerization reaction exists on both the coated titanium dioxide and the PCB substrate surface. During the reaction, positive ion active centers are generated on both the titanium dioxide surface and the substrate surface. As a result, there is a certain repulsive force between the coated titanium dioxide and the PCB substrate surface, which reduces the bonding between the coated titanium dioxide and the PCB substrate surface. This reduces the influence of titanium dioxide pigment incorporation on the mechanical anchoring ability of ink, thereby improving the adhesion between ink and PCB substrate.

[0042] 5. Since the coated titanium dioxide used in the white ink of this invention is a pre-cured product, it does not undergo cationic photopolymerization in the non-exposed area and therefore does not have repulsive force. This results in some coated titanium dioxide being bonded to the surface of the PCB substrate, increasing the difficulty of development. Furthermore, the substrate surface in the unexposed area also contains an active cationic photoinitiator 2. Under visible light irradiation, the pre-cured product (coated titanium dioxide) is prone to undergo cationic photopolymerization in the presence of cationic photoinitiator 2, further increasing the difficulty of development. Ordinary developer (sodium carbonate) is prone to causing incomplete development.

[0043] Therefore, this invention uses a developer with a specific composition, employing an amino compound to assist sodium carbonate, which can effectively remove ink from unexposed areas. Simultaneously, the developer uses acrylate carbonate and water as a mixed solvent, exhibiting good dissolving effects on both ink and cationic photoinitiator 2, significantly improving the developing effect. The amino compound is preferably choline acetate and nicotinamide ethyl acetate, which can rapidly reduce the activity of cationic photoinitiator 2 and increase the developing speed. Detailed Implementation

[0044] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0045] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0046] Example 1

[0047] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, including the following steps:

[0048] (1) Perform solder resist pretreatment on the PCB substrate (clean and roughen the substrate).

[0049] (2) Use white solder resist ink for solder resist screen printing (32T screen printing, 30μm printing thickness).

[0050] (3) Pre-baking: 78℃×20min.

[0051] (5) Exposure: Exposure machine with a wavelength of 365nm, ink surface 500mJ / cm 2 .

[0052] (6) Development: The developing solution is a sodium carbonate aqueous solution with a mass concentration of 1%, the temperature is 30℃, and the spray pressure is 0.16MPa.

[0053] (7) Post-baking: 150℃, 60min.

[0054] (8) Others (character printing, surface treatment, molding, etc.).

[0055] The raw materials for preparing white solder resist ink include 45 parts epoxy acrylic resin, 35 parts rutile titanium dioxide (0.5μm), 6 parts photoinitiator, 20 parts monomers containing double bonds, 1 part leveling agent (acrylate), 4 parts phenolic antioxidant (1010), and 2 parts silicone defoamer.

[0056] The photoinitiator comprises photoinitiator A and photoinitiator B in a mass ratio of 1:10, wherein photoinitiator A is TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide) and photoinitiator B is 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone).

[0057] The monomers containing double bonds include 1-2 functional monomers (containing 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate in a mass ratio of 1:10) and 3-6 functional monomers (dipentaerythritol hexaacrylate (DPHA)).

[0058] The preparation method of white solder resist ink includes the following steps:

[0059] The epoxy acrylate resin was divided into two parts with a mass ratio of 1:12. The first part of epoxy acrylate resin, photoinitiator A, and 1-2 functional monomers were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 75°C for 7 minutes and pre-exposed in a 395nm exposure machine with an exposure parameter of 100 mJ / cm. 2 To obtain coated titanium dioxide, mix the coated titanium dioxide with the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomer, leveling agent (acrylate), antioxidant (1010) and silicone defoamer evenly.

[0060] Example 2

[0061] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 1 in that the epoxy acrylate resin is replaced with acrylic resin.

[0062] Example 3

[0063] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 1 in that the 1-2 functional monomers are glycidyl methacrylate.

[0064] Example 4

[0065] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 1 in that the 1-2 functional monomer is trimethyl 4-phosphobutenoate.

[0066] Example 5

[0067] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 1 in that the 1-2 functional monomers contain allyl diethyl phosphate and glycidyl methacrylate in a mass ratio of 1:2.

[0068] Example 6

[0069] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 1 in that the 1-2 functional monomers contain 4-phosphobutenoic acid trimethyl ester and dipropylene glycol diacrylate in a mass ratio of 1:2.

[0070] Example 7

[0071] Based on Example 1, this example provides a high-reflectivity Mini LED PCB fabrication process. Photoinitiator A includes TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) and cationic photoinitiator 1 (triarylhexafluorophosphate thioonium salt) in a mass ratio of 1:0.7.

[0072] The pretreatment before solder resist application also includes uniformly spraying a 5% cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) solution onto the PCB substrate surface, with a spraying amount of 1 g / m². 2 The solvent in the cationic photoinitiator 2 solution is propylene carbonate.

[0073] Example 8

[0074] Based on Example 7, this example modifies the developing solution in the developing process.

[0075] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, including the following steps:

[0076] (1) Perform solder resist pretreatment on the PCB substrate.

[0077] First, the substrate is cleaned and roughened. Then, a 5% cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) solution is uniformly sprayed onto the substrate surface. The spraying amount of cationic photoinitiator 2 is 1 g / m². 2 The solvent in the cationic photoinitiator 2 solution is propylene carbonate.

[0078] (2) Use white solder resist ink for solder resist screen printing (32T screen printing, 30μm printing thickness).

[0079] The raw materials for preparing white solder resist ink include 45 parts epoxy acrylic resin, 35 parts rutile titanium dioxide (0.5μm), 6 parts photoinitiator, 20 parts monomers containing double bonds, 1 part leveling agent (acrylate), 4 parts phenolic antioxidant (1010), and 2 parts silicone defoamer.

[0080] The photoinitiator comprises photoinitiator A and photoinitiator B in a mass ratio of 1:10. Photoinitiator A consists of TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) and cationic photoinitiator 1 (triarylhexafluorophosphate thionium salt) in a mass ratio of 1:0.7. Photoinitiator B is 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone).

[0081] The monomers containing double bonds include 1-2 functional monomers (containing 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate in a mass ratio of 1:10) and 3-6 functional monomers (dipentaerythritol hexaacrylate (DPHA)).

[0082] The preparation method of white solder resist ink includes the following steps:

[0083] The epoxy acrylate resin was divided into two parts with a mass ratio of 1:12. The first part of epoxy acrylate resin, photoinitiator A, and 1-2 functional monomers were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 75°C for 7 minutes and pre-exposed in a 395nm exposure machine with an exposure parameter of 100 mJ / cm. 2 To obtain coated titanium dioxide, mix the coated titanium dioxide with the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomer, leveling agent (acrylate), antioxidant (1010) and silicone defoamer evenly.

[0084] (3) Pre-baking: 78℃×20min.

[0085] (5) Exposure: Exposure machine with a wavelength of 365nm, ink surface 500mJ / cm 2 .

[0086] (6) Development: The developing temperature is 30℃ and the spray pressure is 0.16MPa.

[0087] The developer solution comprises 1.3 parts sodium carbonate, 2.5 parts amino compound, 3 parts propylene carbonate, and 130 parts water. The amino compound comprises 0.5 parts choline acetate and 2 parts nicotinamide ethyl ester.

[0088] (7) Post-baking: 150℃, 60min.

[0089] (8) Others (character printing, surface treatment, molding, etc.).

[0090] Example 9

[0091] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, including the following steps:

[0092] (1) Perform solder resist pretreatment on the PCB substrate.

[0093] First, the substrate is cleaned and roughened. Then, a 0.5% cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) solution is uniformly sprayed onto the substrate surface. The spraying amount of cationic photoinitiator 2 is 0.8 g / m². 2 The solvent in the cationic photoinitiator 2 solution is propylene carbonate.

[0094] (2) Use white solder resist ink for solder resist screen printing (32T screen printing, 30μm printing thickness).

[0095] The raw materials for preparing white solder resist ink include 30 parts epoxy acrylic resin, 20 parts rutile titanium dioxide (0.5μm), 2 parts photoinitiator, 10 parts monomers containing double bonds, 0.5 parts leveling agent (acrylate), 2 parts antioxidant (1010), and 1 part silicone defoamer.

[0096] The photoinitiator includes photoinitiator A and photoinitiator B in a mass ratio of 1:8. Photoinitiator A consists of 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) and cationic photoinitiator 1 (triarylhexafluorophosphate thioonium salt) in a mass ratio of 1:0.5. Photoinitiator B is 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone).

[0097] The monomers containing double bonds include 1-2 functional monomers (containing 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate in a mass ratio of 1:9) and 3-6 functional monomers (trimethylolpropane triacrylate (TMPTA)).

[0098] The preparation method of white solder resist ink includes the following steps:

[0099] The epoxy acrylate resin was divided into two parts with a mass ratio of 1:10. The first part of epoxy acrylate resin, photoinitiator A, and 1-2 functional monomers were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 70℃ for 10 minutes and pre-exposed in a 395nm exposure machine with an exposure parameter of 50 mJ / cm. 2 To obtain coated titanium dioxide, mix the coated titanium dioxide with the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomer, leveling agent (acrylate), antioxidant (1010) and silicone defoamer evenly.

[0100] (3) Pre-baking: 75℃×40min.

[0101] (5) Exposure: Exposure machine with a wavelength of 365nm, ink surface 400mJ / cm 2 .

[0102] (6) Development: The developing temperature is 28℃ and the spray pressure is 0.15MPa.

[0103] The developer solution comprises 0.8 parts sodium carbonate, 1 part amino compound, 1 part propylene carbonate, and 100 parts water. The amino compound comprises 0.4 parts choline acetate and 0.6 parts nicotinamide ethyl ester.

[0104] (7) Post-baking: 150℃, 60min.

[0105] (8) Others (character printing, surface treatment, molding, etc.).

[0106] Example 10

[0107] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, including the following steps:

[0108] (1) Perform solder resist pretreatment on the PCB substrate.

[0109] First, the substrate is cleaned and roughened. Then, a 10% cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) solution is uniformly sprayed onto the substrate surface. The spraying amount of cationic photoinitiator 2 is 3 g / m². 2 The solvent in the cationic photoinitiator 2 solution is propylene carbonate.

[0110] (2) Use white solder resist ink for solder resist screen printing (32T screen printing, 30μm printing thickness).

[0111] The raw materials for preparing white solder resist ink include 60 parts epoxy acrylic resin, 50 parts rutile titanium dioxide (0.5μm), 10 parts photoinitiator, 30 parts monomers containing double bonds, 2 parts leveling agent (acrylate), 6 parts antioxidant (1010), and 3 parts silicone defoamer.

[0112] The photoinitiator includes photoinitiator A and photoinitiator B in a mass ratio of 1:12. Photoinitiator A consists of TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide) and cationic photoinitiator 1 (triarylhexafluorophosphate thioonium salt) in a mass ratio of 1:1. Photoinitiator B is 651 (benzoin methyl ether).

[0113] The monomers containing double bonds include 1-2 functional monomers (containing 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate in a mass ratio of 1:14) and 3-6 functional monomers (dipentaerythritol hexaacrylate (DPHA)).

[0114] The preparation method of white solder resist ink includes the following steps:

[0115] The epoxy acrylate resin was divided into two parts by a mass ratio of 1:15. The first part of epoxy acrylate resin, photoinitiator A, and 1-2 functional monomers were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 80℃ for 5 minutes and pre-exposed in a 395nm exposure machine with an exposure parameter of 100 mJ / cm. 2 To obtain coated titanium dioxide, mix the coated titanium dioxide with the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomer, leveling agent (acrylate), antioxidant (1010) and silicone defoamer evenly.

[0116] (3) Pre-baking: 80℃×10min.

[0117] (5) Exposure: Exposure machine with a wavelength of 365nm, ink surface with 600mJ / cm 2 .

[0118] (6) Development: The developing temperature is 33℃ and the spray pressure is 0.18MPa.

[0119] The developer solution comprises 1.8 parts sodium carbonate, 4 parts amino compound, 6 parts propylene carbonate, and 150 parts water. The amino compound comprises 1 part choline acetate and 3 parts nicotinamide ethyl ester.

[0120] (7) Post-baking: 150℃, 60min.

[0121] (8) Others (character printing, surface treatment, molding, etc.).

[0122] Example 11

[0123] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 8 in that the amino compound is nicotinic acid ethyl ester.

[0124] Example 12

[0125] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 8 in that the amino compound is choline acetate.

[0126] Example 13

[0127] This embodiment provides a high-reflectivity Mini LED PCB fabrication process, which differs from Embodiment 8 in that the amino compound is ethanolamine.

[0128] Comparative Example 1

[0129] The difference between this comparative example and Example 1 is that the white solder resist ink is prepared using a common formula and a common method. The raw materials for preparing the white solder resist ink include 45 parts epoxy acrylic resin, 35 parts rutile titanium dioxide (0.5 μm), 6 parts photoinitiator 1173, 20 parts double bond monomer (dipentaerythritol hexaacrylate), 1 part leveling agent (acrylate), 4 parts phenolic antioxidant (1010), and 2 parts silicone defoamer.

[0130] The preparation method of white solder resist ink includes the following steps:

[0131] Mix epoxy acrylate resin, rutile titanium dioxide, photoinitiator 1173 and dipentaerythritol hexaacrylate evenly, then add leveling agent (acrylate), antioxidant (1010) and silicone defoamer and mix evenly.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that the white solder resist ink was prepared using the formulation of Example 1 and a conventional method. The preparation method of the white solder resist ink includes the following steps:

[0134] Divide the epoxy acrylate resin into two parts by mass ratio of 1:12. Mix the first part of epoxy acrylate resin, photoinitiator A, 1-2 functional monomers, and titanium dioxide evenly. Then add the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomers, leveling agent (acrylate), antioxidant (1010), and silicone defoamer and mix evenly.

[0135] Comparative Example 3

[0136] The difference between this comparative example and Example 1 is that photoinitiator B is used instead of photoinitiator A in the raw materials for preparing the white solder resist ink. In this case, photoinitiator A is 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone).

[0137] Comparative Example 4

[0138] The difference between this comparative example and Example 1 is that photoinitiator A is used instead of photoinitiator B in the raw materials for preparing the white solder resist ink. In this case, photoinitiator B is TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide).

[0139] Comparative Example 5

[0140] The difference between this comparative example and Example 1 is that, in the raw materials for preparing the white solder resist ink, a 3-6 functional monomer is used instead of a 1-2 functional monomer, and the 1-2 functional monomer is bispentaerythritol hexaacrylate (DPHA).

[0141] Comparative Example 6

[0142] The difference between this comparative example and Example 1 is that in the raw materials for preparing the white solder resist ink, a 1-2 functional monomer is used instead of a 3-6 functional monomer. In this case, the 3-6 functional monomer contains 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate in a mass ratio of 1:2.

[0143] Comparative Example 7

[0144] The difference between this comparative example and Example 1 is that the coated titanium dioxide does not contain photoinitiator A. Therefore, the preparation method of the coated titanium dioxide includes the following steps:

[0145] The first part of epoxy acrylic resin and 1-2 functional monomers are mixed evenly and sprayed evenly onto the surface of titanium dioxide. Then, it is baked at 75°C for 7 minutes to obtain coated titanium dioxide.

[0146] Comparative Example 8

[0147] The difference between this comparative example and Example 1 is that, in the preparation method of the white solder resist ink, the surface resin of the coated titanium dioxide is not pre-exposed. In this case, the preparation method of the white solder resist ink includes the following steps:

[0148] The epoxy acrylate resin is divided into two parts by mass ratio of 1:12. The first part of epoxy acrylate resin, photoinitiator A, and 1-2 functional monomers are stirred evenly and sprayed evenly onto the surface of titanium dioxide. Then, it is baked at 75°C for 7 minutes to obtain coated titanium dioxide. The coated titanium dioxide is then mixed evenly with the second part of epoxy acrylate resin, photoinitiator B, 3-6 functional monomers, leveling agent (acrylate), antioxidant (1010), and silicone defoamer.

[0149] Comparative Example 9

[0150] The difference between this comparative example and Example 1 is that, in the preparation method of the white solder resist ink, the surface resin of the coated titanium dioxide is completely cured, and the exposure parameter is modified to 500 mJ / cm. 2 .

[0151] Comparative Example 10

[0152] The difference between this comparative example and Example 8 is that the coated titanium dioxide does not contain cationic photoinitiator 1 (triarylhexafluorophosphate thioonium salt).

[0153] Comparative Example 11

[0154] The difference between this comparative example and Example 8 is that, when performing solder resist pretreatment on the PCB substrate, the cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) solution is not used to spray the substrate.

[0155] Comparative Example 12

[0156] The difference between this comparative example and Example 8 is that the amount of cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) sprayed on the PCB substrate before solder resist treatment is 0.4 g / m. 2 .

[0157] Comparative Example 13

[0158] The difference between this comparative example and Example 8 is that the amount of cationic photoinitiator 2 (triarylhexafluorophosphate thioonium salt) sprayed on the PCB substrate before solder resist treatment is 4 g / m. 2 .

[0159] Comparative Example 14

[0160] The difference between this comparative example and Example 8 is that the developing solution does not contain amino compounds.

[0161] Comparative Example 15

[0162] The difference between this comparative example and Example 8 is that the developer does not contain propylene carbonate.

[0163] I. PCB board reflectivity test

[0164] 1. Average reflectance test

[0165] The reflectance of the PCB boards baked after Examples 1-10 and Comparative Examples 1-9 was measured. Five samples were used, and the average reflectance results are shown in Table 1 below.

[0166] Table 1

[0167]

[0168] As shown in Table 1, the reflectivity of the Mini LED PCB boards obtained by the processes in Examples 1-10 of this invention is in the range of 88.52%-93.52%, resulting in high-reflectivity Mini LED PCBs. Among them, the reflectivity of the Mini LED PCB boards obtained by the processes in Examples 1-2 and 7-10 is in the range of 92.04%-93.52%, which is relatively high.

[0169] Compared with Examples 3-6, the white solder resist inks of Examples 1 and 2 of the present invention contain 4-phosbutenoic acid trimethyl ester and glycidyl methacrylate as 1-2 functional monomers, which further improves the reflectivity of the PCB board.

[0170] Compared to Example 1, Comparative Example 1 used a common formulation and method to prepare white solder resist ink, and Comparative Example 2 used the formulation of Example 1 and a common method to prepare white solder resist ink. The results showed a significant decrease in the reflectivity of the PCB board. Comparative Examples 3-7 changed the composition of the photoinitiator and the double-bonded monomer, and Comparative Examples 8-9 changed the exposure method of the coated titanium dioxide. The results in a decrease in the reflectivity of the PCB board in all these cases.

[0171] 2. Reflectivity of different areas of the PCB board

[0172] The reflectivity of the PCB boards baked after Examples 1 and 3-8 was tested. Five different areas (test points) of the same PCB board were randomly selected for reflectivity testing. The results are shown in Table 2 below.

[0173] Table 2

[0174]

[0175] As shown in Table 2, compared with Examples 3-6, the reflectance deviations of different regions of the PCB boards prepared in Examples 1 and 7-8 of this invention are smaller, indicating that their reflectance uniformity is better. This demonstrates that controlling the composition of 1-2 functional monomers in the white solder resist ink can control the reflectance uniformity of the PCB board.

[0176] II. Curing Degree of Solder Resist Ink in Different Areas of the PCB Board

[0177] Fourier transform infrared spectroscopy (FTIR) was used to detect the curing degree of the PCB boards exposed in Examples 1 and 8 and Comparative Examples 3-9 of this invention, and the double bond conversion rate in different ink regions was detected. The results are shown in Table 3.

[0178] Table 3

[0179]

[0180] As shown in Table 3, compared with Comparative Examples 3-9, the double bond conversion rate deviation in different areas of the PCB boards after exposure in Examples 1 and 8 of this invention is smaller, indicating better curing uniformity. This demonstrates that controlling the composition of photoinitiators and double-bond-containing monomers in the white solder resist ink can control the curing effect of the ink.

[0181] III. Performance Test of the Coated Titanium Dioxide of the Invention

[0182] 1. Dispersibility of white solder resist ink

[0183] White solder resist inks were prepared according to the methods of Examples 1, 8-10 and Comparative Examples 1-9 of this invention. The ink dispersion was observed after being left for different periods of time, and the results are shown in Table 4.

[0184] Table 4

[0185]

[0186] As shown in Table 4, the white solder resist inks prepared in Examples 1 and 8-10 of this invention have good dispersion stability. Compared with Example 1, Comparative Examples 1-9 changed the raw materials and preparation methods of the white solder resist inks, resulting in poor ink dispersibility.

[0187] 2. Coating layer adhesion of coated titanium dioxide

[0188] Coated titanium dioxide was prepared according to the methods of Examples 1, 3-8 of this invention. The coated titanium dioxide was placed in a photosensitive resin (epoxy acrylic resin) and stirred at a certain speed for 30 minutes. The peeling of the coating layer on the surface of the titanium dioxide was observed. The results are shown in Table 5.

[0189] Table 5

[0190]

[0191] As shown in Table 5, compared with Examples 3-6, the surface coating layer of the coated titanium dioxide prepared in Examples 1 and 7-8 of this invention did not show obvious peeling, indicating that the adhesion between the coating layer and the titanium dioxide is better. This demonstrates that controlling the composition of 1-2 functional monomers in the white solder resist ink can control the adhesion between the coating layer and the titanium dioxide.

[0192] IV. Adhesion Test of Solder Resist Ink on PCB Board

[0193] The adhesion of the white solder resist inks prepared in Examples 1, 7-10 and Comparative Examples 10-13 was tested using a cross-cut adhesion tester. The results are shown in Table 6.

[0194] Grade 0: The edges of the cut are completely smooth, and there is no peeling at the edges of the grid.

[0195] Level 1: Small pieces peel off at the intersection of the cuts, and the actual damage within the gridded area is ≤5%.

[0196] Grade 2: Peeling occurs at the edges and / or intersections of the incision, covering an area greater than 5% to 15%.

[0197] Level 3: Partial or large-scale peeling occurs along the cut edge, or some grid cells are completely peeled off. The peeled area exceeds [a certain percentage].

[0198] 15%–35%.

[0199] Level 4: Large areas of the cut edge are peeling off, or some squares are partially or completely peeled off, with the area exceeding 35% of the marked area.

[0200] 65%.

[0201] Level 5: Large areas of paint have peeled off at the edges and intersections of the lines, and the total area of ​​paint peeling off is greater than 65%.

[0202] Table 6

[0203]

[0204] As shown in Table 6, based on Example 1, Examples 7-10 introduced cationic photopolymerization reaction on the surfaces of coated titanium dioxide and PCB substrates, which improved the adhesion of white solder resist ink.

[0205] Compared with Example 8, Comparative Examples 10-13 changed the addition of cationic photoinitiator 1 and cationic photoinitiator 2, resulting in a decrease in ink adhesion.

[0206] V. Development Effect

[0207] The development was carried out according to the processes of Examples 1, 7-13 and Comparative Examples 14-15 of this invention, and the development was observed. The results are shown in Table 7.

[0208] Table 7

[0209]

[0210] As shown in Table 7, the conventional developer (sodium carbonate aqueous solution) was used in the examples. Although it could achieve clear images without fuzz or residue, the development time was relatively long, requiring 75 seconds. After introducing a cationic photopolymerization reaction into the white solder resist ink in Example 7, the development difficulty was further increased, and both the development effect and the development speed (89 seconds) deteriorated.

[0211] Compared to Example 7, Examples 8-12, using a developer containing amino compounds and propylene carbonate, showed significantly improved development results, producing clearer images without fuzz or residue, and the development speed increased to 45-65 seconds. Examples 8-10, in particular, had a higher development speed of 45-48 seconds.

[0212] Compared with Example 8, Comparative Examples 14-15 changed the composition of the developer, resulting in a decrease in both the developing effect and the developing speed.

[0213] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-reflectivity Mini LED PCB fabrication process, characterized in that: Includes the following steps: Solder resist pretreatment, solder resist silkscreen printing, pre-baking, exposure, development and post-baking; White solder resist ink is used for solder resist screen printing. The raw materials for preparing the white solder resist ink include 30-60 parts of photosensitive resin, 20-50 parts of titanium dioxide, 2-10 parts of photoinitiator, 10-30 parts of monomers containing double bonds, and 0-20 parts of additives. The photoinitiator comprises photoinitiator A and photoinitiator B in a mass ratio of 1:(8-12), wherein photoinitiator A comprises a free radical photoinitiator with an absorption wavelength range of 380-420nm, and photoinitiator B comprises a free radical photoinitiator with an absorption wavelength range of 320-370nm. The double-bonded monomers include 1-2 functional monomers and 3-6 functional monomers in a mass ratio of 1:(9-14); The preparation method of the white solder resist ink includes the following steps: The photosensitive resin was divided into two parts by mass ratio of 1:(10-15). The first part of the photosensitive resin, photoinitiator A, and monomers with 1-2 functionalities were stirred evenly and sprayed uniformly onto the surface of titanium dioxide. Then, it was baked at 70-80℃ for 5-10 minutes, followed by pre-exposure in a 395nm exposure machine with exposure parameters of 50-200 mJ / cm². 2 To obtain coated titanium dioxide, mix the coated titanium dioxide with the second part of photosensitive resin, photoinitiator B, 3-6 functional monomers and additives evenly.

2. The preparation process according to claim 1, characterized in that: The photoinitiator A is 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, or isopropylthioxanthone, and the photoinitiator B is 2-hydroxy-2-methyl-1-phenyl-1-propanone or benzoin methyl ether.

3. The preparation process according to claim 1, characterized in that: The 1-2 functional monomers are one or any combination of acrylate monomers, vinyl ester monomers, butenolate monomers, and phosphate ester monomers containing 1-2 double bonds; The 3-6 functional monomers are one or any combination of acrylate monomers, vinyl ester monomers, and butenolate monomers containing 3-6 double bonds.

4. The preparation process according to claim 1, characterized in that: The photosensitive resin is an unsaturated polyester, acrylic resin, epoxy resin, or epoxy acrylic resin; the titanium dioxide is rutile titanium dioxide; and the additives include one or more of the following: 0.5-2 parts leveling agent, 2-6 parts antioxidant, 1-3 parts defoamer, 1-2 parts adhesion promoter, and 1-3 parts ultraviolet absorber.

5. The preparation process according to claim 3, characterized in that: The 1-2 functional monomers include trimethyl 4-phosbutenoate and glycidyl methacrylate in a mass ratio of 1:(1-3).

6. The preparation process according to claim 4, characterized in that: The photosensitive resin is an epoxy acrylic resin, and the photoinitiator A further includes a cationic photoinitiator 1. The mass ratio of the 380-420nm free radical photoinitiator to the cationic photoinitiator 1 is 1:(0.5-1).

7. The preparation process according to claim 6, characterized in that: The pretreatment before solder resist application includes: uniformly spraying a cationic photoinitiator 2 solution onto the surface of the PCB substrate, wherein the spraying amount of cationic photoinitiator 2 is 0.8-3 g / m². 2 .

8. The preparation process according to claim 7, characterized in that: The cationic photoinitiator 1 and cationic photoinitiator 2 are any one or more of diaryliodomonium salts, triarylthiomonium salts, and alkylthiomonium salts.

9. The preparation process according to claim 1, characterized in that: The developing solution used in the developing process comprises 0.8-1.8 parts sodium carbonate, 1-4 parts amino compound, 1-6 parts propylene carbonate, and 100-150 parts water; The amino compound is any one or more of nicotinamide ethyl ester, choline acetate, ethanolamine, ammonia, and triethylamine.

10. The preparation process according to claim 9, characterized in that: The amino compound includes 0.4-1 parts of choline acetate and 0.6-3 parts of nicotinamide ethyl ester.

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