Manufacturing process of ultrathin printed circuit board for MiniLED

Abstract

The invention relates to the technical field of circuit boards, in particular to a manufacturing process of an ultrathin printed circuit board for a Mini LED. The problems that the printed circuit board for the Mini LED is not light and thin enough and poor in quality are solved. The size stability of the circuit board is improved by changing the baking temperature and the baking time and using a lamination technology combining vacuum hot pressing and a flexible mold; the wettability of the surface of the circuit board is enhanced by changing process parameters of low-temperature plasma treatment, and a good welding joint is formed; by preparing the solder resist ink, the acid and alkali resistance, the yellowing resistance and the reflectivity of the prepared circuit board are improved; ultrasonic assistance is introduced in the drilling process, the pulse laser power of micro-etching treatment is changed, and the bonding welding spot quality of the circuit board is improved; by using plasma pretreatment, the copper deposition temperature, the copper deposition time and the current density during copper deposition are controlled, and the manufactured circuit board is lighter and thinner, so that the quality of the circuit board is comprehensively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit boards, and in particular to a process for manufacturing an ultra-thin printed circuit board for MiniLED. Background Art

[0002] MiniLED, also known as sub-millimeter light-emitting diode, is a new type of LED display technology. The basic principle of MiniLED is similar to that of ordinary LED, which is to control the current in semiconductor materials to achieve light emission. It combines the technical characteristics of LED and LCD, and reduces the size of LED pixels to less than tens of microns to achieve a more delicate and clear display effect. In addition, due to the small size of MiniLED, more LED pixels can be integrated on a display panel to achieve higher brightness and higher contrast. At the same time, it has the advantages of low power consumption, long life, high reliability and environmental protection, and can be widely used in various display devices, such as TVs, monitors, mobile phones, tablets, etc. MiniLED is developed to solve the problem that the granularity of traditional LED partition light control is not fine enough. The light-emitting crystals are smaller, and the number of crystals that can be embedded in the backlight panel per unit area is more. More backlight beads can be integrated on the same screen, which is the result of further refinement of LED.

[0003] Printed circuit boards are important electronic components, supporting bodies for electronic components, and carriers for electrical interconnection of electronic components. They are also one of the important components of the electronics industry. Printed circuit boards are composed of an insulating base plate, connecting wires, and pads for assembling and welding electronic components. They have the dual functions of conductive lines and insulating base plates. Printed circuit boards miniaturize and visualize circuits, and play an important role in the mass production of fixed circuits and the optimization of electrical appliance layouts. They can replace complex wiring and realize electrical connections between components in the circuit. They not only simplify the assembly and welding of electronic products, reduce the wiring workload under traditional methods, and greatly reduce the labor intensity of workers, but also reduce the size of the entire machine, reduce product costs, and improve the quality and reliability of electronic equipment.

[0004] Chinese patent CN109862687B discloses a MiniLED flexible printed circuit board and a method for manufacturing the same. The circuit board includes a white substrate layer, one surface of the white substrate layer is provided with a pad array, the other surface is provided with a signal line, and the area outside the signal line is provided with a grid layer formed by crisscrossing copper wires, and the grid layer is provided with copper blocks corresponding to the positions of the pads. The back of the pad array is provided with a grid formed by crisscrossing copper wires, and a solid copper block is provided on the back of the pad array to ensure the flatness of the board surface and the stability of the expansion and contraction of the entire board, thereby ensuring the manufacturing accuracy of the pads, high production yield, avoiding solder mask deviation and subsequent welding deviation, and improving the reflectivity of the flexible circuit board by adopting a white substrate. However, the circuit board produced in this patent is not thin enough.

[0005] Chinese patent CN117177445A discloses a method for manufacturing a high-integration precision circuit board, including: designing a circuit board including an effective area and an auxiliary area, pre-designing the auxiliary area to form a panelized circuit board; performing pre-processing, drilling, full-board electroplating, and baking to form a panelized circuit board; performing plugging and segmented baking to form a plugged circuit board; performing grinding to form a flattened circuit board; performing circuit pattern processing and dehumidification baking to form a circuit pattern circuit board; using electrostatic spraying to make a solder resist ink layer to form a solder resist layer circuit board; performing solder resist pattern production to form a high-integration precision circuit board; by increasing the design of the auxiliary area and performing plugging after full-board electroplating, and using electrostatic spraying to make the solder resist layer, combined with multiple baking in the process to remove internal stress, effectively controlling expansion and contraction, improving the processing accuracy of the circuit pattern and the solder resist pattern, and preventing the problems of incomplete plugging, red hole mouth, and white hole mouth solder resist. However, the circuit board production in this invention adopts the process of first electroplating and then making solder mask. During the solder mask window opening process, ink is easy to remain, which will cause different degrees of pollution to the gold-plated interface of the circuit board. When the contaminated circuit board is subjected to the bonding process, if the bonding interface is not treated or treated incompletely, it will cause problems such as cold soldering, desoldering, and low bonding strength.

[0006] With the rapid development of MiniLED technology, higher requirements are placed on the performance of printed circuit boards, such as thinness, lightness, and high precision. Although the ultra-thin printed circuit boards for MiniLED prepared by existing technologies have made certain progress, there are still some shortcomings. The circuit boards are not thin enough; yellowing, desoldering, and other phenomena may occur, resulting in reduced quality of the circuit boards.

[0007] To this end, a process for manufacturing an ultra-thin printed circuit board for MiniLED is proposed. Summary of the invention

[0008] The purpose of the present invention is to provide a process for manufacturing ultra-thin printed circuit boards for MiniLEDs. The present invention increases the dimensional stability of the circuit board by changing the baking temperature and baking time, and using a lamination technology combining vacuum hot pressing with a flexible mold; by changing the process parameters of low-temperature plasma treatment, the wettability of the circuit board surface is enhanced to form a good welding joint; by preparing solder resist ink, the acid and alkali resistance, yellowing resistance and reflectivity of the circuit board are improved; by introducing ultrasonic assistance during the drilling process and changing the pulsed laser power of the micro-etching treatment, the quality of the bonding solder joints of the circuit board is improved; by using plasma pretreatment to control the copper deposition temperature, copper deposition time and current density during copper deposition, the circuit board is made thinner and lighter, thereby comprehensively improving the quality of the circuit board.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A process for manufacturing an ultra-thin printed circuit board for MiniLED, the steps for preparing the ultra-thin printed circuit board for MiniLED are as follows: cutting a substrate, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating to obtain a copper foil layer; drawing a circuit pattern on the copper foil layer and performing AOI inspection to obtain a circuit pattern layer; performing low-temperature plasma treatment on the circuit pattern layer, coating with solder resist ink, and vacuum pressurizing to obtain a coating layer; laminating, first baking, exposure, second baking, development, and curing the coating layer to obtain a solder resist layer; micro-etching the solder resist layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is a combination of vacuum hot pressing and a flexible mold; ultrasonic vibration is introduced in vacuum hot pressing; vacuum hot pressing is a multi-stage vacuum hot pressing;

[0011] In parts by weight, the raw materials used in the production of solder mask ink include 30-60 parts of polyester resin, 5-15 parts of epoxy resin, 10-20 parts of active diluent, and 5 parts of pigment; the pigment is one of low-pigment carbon black, medium-pigment carbon black, and high-pigment carbon black.

[0012] Preferably, the first baking temperature is 80-100° C. and the time is 10-15 min; the second baking temperature is 100-150° C. and the time is 25-40 min.

[0013] Preferably, the solder resist ink is prepared by the following steps: using an organic solvent to dissolve a photoinitiator and a reactive diluent, and adding a polyester resin, a pigment and an inorganic filler to obtain a mixture one; adding a defoamer and a leveling agent to the mixture one and stirring evenly to obtain a mixture two; adding an epoxy resin and an adhesion promoter to the mixture two, and using a disperser to disperse at high speed to obtain a mixture three; the dispersion time is 10 minutes; using a three-roll grinder to grind the mixture three until the particle fineness reaches 10 μm, and discharging the material to obtain the solder resist ink.

[0014] Preferably, the processing power of the plasma pretreatment is 160W, and the vacuum degree is 46Pa; the discharge power during the low-temperature plasma treatment is 200-800W, and the gas pressure is 0.1-0.5MPa.

[0015] Preferably, the copper deposition current density is 10-30A / dm 2 ; The copper deposition temperature is 30-50℃; The copper deposition time is 5-15s.

[0016] Preferably, the pulse laser power during micro-etching is 220-350W.

[0017] Preferably, the ultrasonic frequency of ultrasonic assisted drilling is 30 kHz and the drilling speed is 120 mm / min.

[0018] Preferably, the lamination steps are as follows: place the coating layer in the middle of the flexible mold, set the initial temperature of the vacuum hot pressing equipment to 85°C, start the vacuum pump, gradually evacuate the vacuum degree in the vacuum chamber to 35Pa, set the pressure to 0.22MPa, maintain for 12min, continue to heat to 140°C at a rate of 1.5°C / min, gradually increase the pressure to 1.5MPa, and turn on the ultrasonic vibration system at the same time, set the frequency to 30kHz, adjust the amplitude to 30μm, maintain for 25min, then continue to heat to the final curing temperature of 200°C at a rate of 1.8°C / min, increase the pressure to 4MPa, keep the ultrasonic vibration system on, continue for 84min, and finally cool to 85°C at a rate of 1.4°C / min, and gradually reduce the pressure to 0.2MPa, turn off the ultrasonic vibration system, and maintain for 12min.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention changes the baking temperature and baking time to evaporate the moisture and volatile organic compounds in the circuit board, thereby reducing the risk of expansion and deformation of the circuit board in a high temperature environment, improving the stability of the circuit board, and helping to eliminate the internal stress generated by the circuit board during the manufacturing process, making the size and shape of the circuit board more stable; in addition, the lamination technology combining vacuum hot pressing with a flexible mold is used to exclude interlayer air in a vacuum environment to prevent the generation of bubbles and improve the interlayer bonding strength. The flexible mold can better fit the ultra-thin sheet material, evenly apply pressure, reduce deformation caused by uneven pressure, and further enhance dimensional stability. The expansion and contraction coefficient of the obtained ultra-thin printed circuit board for MiniLED is 0.8ppm / ℃, and the quality of the circuit board is improved.

[0021] 2. The present invention modifies the printed circuit board by using a low-temperature plasma surface modification process, changes the discharge power and gas pressure during low-temperature plasma treatment, and utilizes the highly active free particles with apparent neutrality generated by air after high-voltage ionization to undergo redox reactions with substances on the surface of the printed circuit board to generate hydrophilic groups, thereby enhancing the wettability of the surface of the printed circuit board. The water contact angle of the obtained ultra-thin printed circuit board for MiniLED is 10.2°, which can ensure that the solder is in close contact with the metal surface to be welded, so that the solder spreads and covers the surface of the metal to be welded, forming a good welding joint, thereby improving the quality of the circuit board.

[0022] 3. The present invention uses polyester resin as the main resin and epoxy resin as the auxiliary resin to prepare solder resist ink. By changing the amount of polyester resin, epoxy resin, active diluent and pigment type, the corrosion resistance, yellowing resistance and general reflectivity of traditional solder resist ink are improved. The reflectivity of the prepared ultra-thin printed circuit board for MiniLED is 96.2%. After immersion in 10% mass% H2SO4 aqueous solution and NaOH aqueous solution for 12 hours, there is no discoloration, falling off and bulging. No color change is observed after irradiation with UV light for 24 hours. The quality of the circuit board is significantly improved.

[0023] 4. The present invention introduces ultrasonic assistance in the drilling process. Ultrasonic vibration can reduce the friction and cutting force between the drill bit and the plate, reduce the roughness of the hole wall, and improve the quality of the bonding solder joints. Good hole wall quality provides a more reliable connection surface for welding. The circuit board is micro-etched by using a laser. By changing the pulse laser power, the pulse laser beam is focused on the surface of the material, so that a very small local high-temperature zone is formed on the surface of the material. In a very short time, the material on the surface of the material quickly melts and evaporates to form a plasma, and the gold-plated layer contaminated on the surface is removed to form a new bonding interface. The lead tension of the obtained ultra-thin printed circuit board for MiniLED is 0.32N, and there will be no problems of cold solder joints and desoldering, which greatly improves the quality of the circuit board.

[0024] 5. The present invention uses plasma to pre-treat the hole wall before copper deposition to activate the hole wall surface, improve its adsorption capacity for copper ions, and achieve better copper deposition effect. By controlling the copper deposition temperature, copper deposition time and current density during copper deposition, local depletion occurs near the electrolyte where the crystal has been generated, thereby inhibiting the growth of the crystal. The resulting copper foil layer has dense, uniform and smooth crystalline particles on the surface, and the copper foil layer has a thickness of 3.3μm. The resulting ultra-thin printed circuit board for MiniLED is thinner and lighter. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a graph showing the lead tension test results of the ultra-thin printed circuit board for MiniLED in Example 45 of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0027] See also Figure 1 The present invention provides a process for manufacturing an ultra-thin printed circuit board for MiniLED, and the technical solution is as follows:

[0028] The substance information involved in the present invention is as follows:

[0029] Polyester resin CAS: 109-16-0; epoxy resin CAS: 24969-06-0; 1,6-hexanediol diacrylate CAS: 13048-33-4; silicon dioxide CAS: 14808-60-7; 2,4-dihydroxybenzophenone CAS: 131-56-6; polydimethylsiloxane CAS: 9016-00-6; ethanol CAS: 64-17-5; leveling agent BYK-3720 was purchased from Guangzhou Haoyi New Materials Technology Co., Ltd.; epoxy phosphate was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; low-color carbon black, medium-color carbon black, and high-color carbon black were all purchased from Anaiji (Shanghai) Pharmaceutical Chemistry Co., Ltd.

[0030] Example 1

[0031] Preparation of solder mask ink: using 30 parts of organic solvent ethanol to dissolve 4 parts of photoinitiator 2,4-dihydroxybenzophenone and 10 parts of active diluent, and adding 30 parts of polyester resin, 5 parts of pigment low-color carbon black and 8 parts of inorganic filler silica to obtain mixture one; adding 1 part of defoaming agent polydimethylsiloxane and 0.8 parts of leveling agent BYK-3720 to mixture one and stirring evenly to obtain mixture two; adding 5 parts of epoxy resin and 0.5 parts of adhesion promoter epoxy phosphate to mixture two, using a disperser for high-speed dispersion to obtain mixture three; the dispersion time is 10 minutes; using a three-roll grinder to grind mixture three until the particle fineness reaches 10 μm, and discharging the material to obtain solder mask ink.

[0032] Preparation of ultra-thin printed circuit boards for MiniLED: cutting, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating of the substrate to obtain a copper foil layer; drawing circuit graphics on the copper foil layer and AOI inspection to obtain a circuit graphic layer; low-temperature plasma treatment of the circuit graphic layer, solder mask ink coating and vacuum pressurization to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is vacuum hot pressing and flexible mold Combined; introduce ultrasonic vibration in vacuum hot pressing; vacuum hot pressing is multi-stage vacuum hot pressing; ultrasonic frequency of ultrasonic assisted drilling is 30kHz, drilling speed is 120mm / min; first baking temperature is 80℃, time is 10min; second baking temperature is 100℃, time is 25min; plasma pretreatment power is 160W, vacuum degree is 46Pa; discharge power during low temperature plasma treatment is 200W, gas pressure is 0.1MPa; micro-etching treatment pulse laser power is 220W; copper deposition current density is 10A / dm 2 ; The copper deposition temperature is 30℃; The copper deposition time is 5s.

[0033] The lamination steps are as follows: place the coating layer in the middle of the flexible mold, set the initial temperature of the vacuum hot pressing equipment to 85°C, start the vacuum pump, gradually draw the vacuum degree in the vacuum chamber to 35Pa, set the pressure to 0.22MPa, maintain for 12min, continue to heat to 140°C at a rate of 1.5°C / min, gradually increase the pressure to 1.5MPa, and turn on the ultrasonic vibration system at the same time, set the frequency to 30kHz, adjust the amplitude to 30μm, maintain for 25min, then continue to heat to the final curing temperature of 200°C at a rate of 1.8°C / min, increase the pressure to 4MPa, keep the ultrasonic vibration system on, continue for 84min, and finally cool to 85°C at a rate of 1.4°C / min, and gradually reduce the pressure to 0.2MPa, turn off the ultrasonic vibration system, and maintain for 12min.

[0034] Example 2-12

[0035] Referring to the preparation method and parameter conditions of Example 1, the specific differences are shown in Table 1.

[0036] Comparative Example 1

[0037] The preparation method and parameter conditions are the same as those of Example 1, except that lamination is not performed.

[0038] Comparative Example 2

[0039] The preparation method and parameter conditions are the same as those in Example 1, except that no flexible mold is used during lamination.

[0040] Comparative Example 3

[0041] The preparation method and parameter conditions are similar to those of Example 1, except that ultrasonic vibration is not introduced during vacuum hot pressing.

[0042] Comparative Example 4

[0043] The preparation method and parameter conditions are the same as those in Example 1, except that the vacuum hot pressing is a traditional single-stage vacuum hot pressing.

[0044] Example 13 Dimensional stability test

[0045] Example 13 uses the MHY-16096 thermal expansion coefficient tester of Beijing Meihuayi Technology Co., Ltd. to test the dimensional stability of the sample. The test uses the ultra-thin printed circuit board for MiniLED prepared in Examples 1-12 as the sample. The test results are shown in Table 1.

[0046] Table 1 Dimensional stability test of Examples 1-12 and Comparative Examples 1-4

[0047]

[0048] During the baking process, the circuit board will be affected by thermal stress. The appropriate baking temperature can reduce the impact of thermal stress on the dimensional stability of the circuit board, because the thermal expansion and contraction of the circuit board are relatively uniform at this time. As can be seen from Table 1, when the first baking temperature is 90°C, the baking time is 13 minutes, and the second baking temperature is 110°C, and the baking time is 35 minutes, the expansion and contraction coefficient of the obtained ultra-thin printed circuit board for MiniLED is only 0.8ppm / °C, and the dimensional stability is the best at this time, and the circuit board quality is the best. During the baking process, the circuit board will undergo a physical process of thermal expansion and contraction. In Examples 5 and 9, the baking temperature is too high, which will cause the circuit board to expand excessively, and then shrink during the cooling process, thereby changing the size of the circuit board. The length of the baking time directly affects the degree of removal of moisture and volatile organic compounds in the circuit board. In Examples 1-10, the second baking time is insufficient, and these substances cannot be completely removed, resulting in the circuit board still expanding and deforming in a high temperature environment, reducing the quality of the circuit board; in Example 12, the baking time is too long, which will cause the circuit board to be over-baked, and problems such as coking and deformation will occur, thereby affecting the quality of the circuit board. In Comparative Example 1, no lamination process was performed, and the internal stress generated during the production of the circuit board could not be effectively released and balanced. As time goes by or the ambient temperature and humidity change, the internal stress will cause the material to deform, causing the size of the circuit board to change. The flexible mold can better fit the ultra-thin sheet, evenly apply pressure, and reduce deformation caused by uneven pressure. In Comparative Example 2, the flexible mold was not used during lamination, the expansion and contraction coefficient increased, and the quality of the circuit board was poor. Ultrasonic assisted flow and molecular diffusion of interlayer materials are used to enable the bonding material to better fill the interlayer gaps, while improving the uniformity and density of the material. In Comparative Example 3, ultrasonic vibration is not introduced in vacuum hot pressing, which will result in poor dimensional stability of the circuit board. In Comparative Example 4, the vacuum hot pressing is a traditional single-stage vacuum hot pressing, and the circuit board will cause dimensional changes and interlayer stress due to rapid changes in temperature and pressure.

[0049] Embodiment 14

[0050] The solder resist ink was prepared according to the method of Example 1 above.

[0051] Preparation of ultra-thin printed circuit boards for MiniLED: cutting, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating of the substrate to obtain a copper foil layer; drawing circuit graphics on the copper foil layer and AOI inspection to obtain a circuit graphic layer; low-temperature plasma treatment of the circuit graphic layer, solder mask ink coating and vacuum pressurization to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is vacuum hot pressing and flexible mold Combined; introduce ultrasonic vibration in vacuum hot pressing; vacuum hot pressing is multi-stage vacuum hot pressing; ultrasonic frequency of ultrasonic assisted drilling is 30kHz, drilling speed is 120mm / min; first baking temperature is 90℃, time is 13min; second baking temperature is 110℃, time is 35min; plasma pretreatment power is 160W, vacuum degree is 46Pa; discharge power during low temperature plasma treatment is 300W, gas pressure is 0.1MPa; pulse laser power for micro-etching treatment is 220W; copper deposition current density is 10A / dm 2 ; The copper deposition temperature is 30°C; The copper deposition time is 5s; The lamination steps are the same as those in Example 1.

[0052] Examples 15-23

[0053] Referring to the preparation method and parameter conditions of Example 14, the specific differences are shown in Table 2.

[0054] Comparative Example 5

[0055] An ultra-thin printed circuit board for MiniLED was manufactured according to the method of Example 14, except that no low-temperature plasma treatment was performed.

[0056] Example 24 Wetting performance test

[0057] Example 24 is a wetting performance test of the sample using the SZ-CAMD3 fully automatic contact angle meter of Shanghai Xuanzhun Instrument Co., Ltd. in accordance with the method in GB / T 30693-2014 "Measurement of Contact Angle of Plastic Film with Water". The test uses the ultra-thin printed circuit boards for MiniLED prepared in Examples 11 and 14-23 as samples, and Comparative Example 1 is designed for comparison. The test results are shown in Table 2.

[0058] Table 2 Wetting performance test of Examples 11, 14-23 and Comparative Example 5

[0059]

[0060]

[0061] It can be seen from Table 2 that when the printed circuit board is treated with plasma under the conditions of constant gas pressure and different powers, as the power increases, the water contact angle on the surface of the printed circuit board first decreases and then slightly increases. After plasma treatment at powers of 400W and 500W, the water contact angle of the printed circuit board is as low as 12.6°, and the wettability is good at this time. It can be seen that appropriately increasing the power can enhance the modification effect and improve the wettability of the printed circuit board; but when the power reaches a certain value, continuing to increase the power does not significantly improve the wettability of the printed circuit board, and may even lead to a deterioration of the wettability. This is because specific functional groups are introduced into the material surface during the plasma treatment process, which play an etching role on the surface of the printed circuit board, forming a cross-linked structure layer or generating surface free radicals. When the power is too high, the high-energy particles in the plasma increase, the etching effect is enhanced, and a part of the grafted functional groups are re-etched, which increases the water contact angle. The increase in gas pressure means an increase in plasma density. The increase in plasma density can significantly improve the cleaning rate and effect of plasma, but the continuous increase in gas pressure will lead to a decrease in particle energy, which in turn affects the etching effect caused by the bombardment of particles on the surface. Therefore, under the condition of constant power, as the air pressure increases from 0.1MPa to 0.6MPa, the water contact angle of the printed circuit board decreases first and then increases. When the power is 400W and the air pressure is 0.3MPa, the water contact angle of the printed circuit board is as low as 10.2°. At this time, the wettability of the printed circuit board is the best, which can ensure that the solder is in close contact with the metal surface to be welded, so that the solder spreads and covers the surface of the metal to be welded, forming a good welding joint, thereby improving the quality of the circuit board. In comparative example 5, when the printed circuit board is not subjected to plasma treatment, the water contact angle is as high as 65°, and the wettability is poor.

[0062] Embodiment 25

[0063] Preparation of solder resist ink: using 30 parts of the organic solvent ethanol to dissolve 4 parts of the photoinitiator 2,4-dihydroxybenzophenone and 12 parts of the active diluent, and adding 30 parts of the polyester resin, 5 parts of the pigment low-color carbon black and 8 parts of the inorganic filler silica to obtain mixture one; adding 1 part of the defoamer polydimethylsiloxane and 0.8 parts of the leveling agent BYK-3720 to the mixture one and stirring evenly to obtain mixture two; adding 5 parts of the epoxy resin and 0.5 parts of the adhesion promoter epoxy phosphate to the mixture two, using a disperser for high-speed dispersion to obtain mixture three; the dispersion time is 10 minutes; using a three-roll grinder to grind mixture three until the particle fineness reaches 10 μm, and discharging the material to obtain the solder resist ink.

[0064] Preparation of ultra-thin printed circuit boards for MiniLED: cutting, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating of the substrate to obtain a copper foil layer; drawing circuit graphics on the copper foil layer and AOI inspection to obtain a circuit graphic layer; low-temperature plasma treatment of the circuit graphic layer, solder mask ink coating and vacuum pressurization to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is vacuum hot pressing and flexible mold Combined; introduce ultrasonic vibration in vacuum hot pressing; vacuum hot pressing is multi-stage vacuum hot pressing; ultrasonic frequency of ultrasonic assisted drilling is 30kHz, drilling speed is 120mm / min; first baking temperature is 90℃, time is 13min; second baking temperature is 110℃, time is 35min; plasma pretreatment power is 160W, vacuum degree is 46Pa; discharge power during low temperature plasma treatment is 400W, gas pressure is 0.3MPa; micro-etching treatment pulse laser power is 220W; copper deposition current density is 10A / dm 2 ; The copper deposition temperature is 30°C; The copper deposition time is 5s; The lamination steps are the same as those in Example 1.

[0065] Embodiment 26-36

[0066] Referring to the preparation method and parameter conditions of Example 25, the specific differences are shown in Table 3.

[0067] Table 3 Parameters and conditions of Examples 26-36

[0068] Example Polyester resin dosage / part Epoxy resin dosage / part Active diluent dosage / part Pigment Type Embodiment 26 30 5 15 Low pigment carbon black Embodiment 27 30 5 20 Low pigment carbon black Embodiment 28 40 5 15 Low pigment carbon black Embodiment 29 45 5 15 Low pigment carbon black Embodiment 30 60 5 15 Low pigment carbon black Embodiment 31 45 8 15 Low pigment carbon black Embodiment 32 45 10 15 Low pigment carbon black Embodiment 33 45 12 15 Low pigment carbon black Embodiment 34 45 15 15 Low pigment carbon black Embodiment 35 45 12 15 Medium pigment carbon black Embodiment 36 45 12 15 High pigment carbon black

[0069] Example 37 Acid and alkali resistance, yellowing resistance and reflectivity test

[0070] Example 37 is to test the acid and alkali resistance, yellowing resistance and reflectivity of the sample, and the test method is as follows:

[0071] Acid resistance test: Soak the test sample in a 10% mass fraction H2SO4 aqueous solution at room temperature for 12 hours, take it out, wash it with deionized water, air-dry it, and inspect it visually.

[0072] Alkali resistance test: Soak the test sample in a 10% mass fraction NaOH aqueous solution at room temperature for 12 hours, take it out and wash it with deionized water, air-dry it, and inspect it visually.

[0073] The evaluation standards for acid and alkali resistance are as follows:

[0074] ○: The sample does not change, discolor, fall off, or bulge;

[0075] ×: The sample has changed, such as discoloration, falling off, bulging, etc.

[0076] Yellowing resistance test: Use the UV lamp of Shenzhen Lanpulic Technology Co., Ltd. to irradiate the sample for 24 hours for UV aging test to observe whether the sample changes color.

[0077] Reflectivity test: The reflectivity of the sample was tested using the C84-III reflectivity meter produced by Shanghai Meiyu Instrument Co., Ltd.

[0078] The test used the ultra-thin printed circuit boards for MiniLED prepared in Examples 21 and 25-36 as samples, and the test results are shown in Table 4.

[0079] Table 4 Acid and alkali resistance, yellowing resistance and reflectivity test of Examples 21, 25-36

[0080] Example Acid resistance Alkali resistance Yellowing resistance Reflectivity / % Embodiment 21 ○ ○ No color change 88.4 Embodiment 25 ○ ○ No color change 90.5 Embodiment 26 ○ ○ No color change 91.0 Embodiment 27 ○ ○ No color change 91.5 Embodiment 28 ○ ○ No color change 91.8 Embodiment 29 ○ ○ No color change 92.2 Embodiment 30 ○ ○ No color change 91.6 Embodiment 31 ○ ○ No color change 92.5 Embodiment 32 ○ ○ No color change 93.6 Embodiment 33 ○ ○ No color change 94.3 Embodiment 34 ○ ○ No color change 93.1 Embodiment 35 ○ ○ No color change 95.5 Embodiment 36 ○ ○ No color change 96.2

[0081] It can be seen from Table 4 that the solder resist inks prepared in Examples 21, 25-36 have good acid and alkali resistance. The obtained ultra-thin printed circuit board for MiniLED has no change after being immersed in a 10% mass fraction H2SO4 aqueous solution for 12 hours and in a 10% mass fraction NaOH aqueous solution for 12 hours. There is no discoloration, shedding, or bulging phenomenon; and no color change is observed after 24 hours of UV light irradiation. In Example 33, the amount of polyester resin is 45 parts, the amount of epoxy resin is 12 parts, and the amount of active diluent is 15 parts. When low-color carbon black is used as the pigment, the reflectivity of the obtained ultra-thin printed circuit board for MiniLED is the best at 94.3°. At this time, the acid and alkali resistance and yellowing resistance of the circuit board are the best, and the quality of the circuit board is significantly improved.

[0082] Embodiment 38

[0083] A solder resist ink was prepared according to the method of Example 33 above.

[0084] Preparation of ultra-thin printed circuit boards for MiniLED: cutting, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating of the substrate to obtain a copper foil layer; drawing circuit graphics on the copper foil layer and AOI inspection to obtain a circuit graphic layer; low-temperature plasma treatment of the circuit graphic layer, solder mask ink coating and vacuum pressurization to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is vacuum hot pressing and flexible mold Combined; introduce ultrasonic vibration in vacuum hot pressing; vacuum hot pressing is multi-stage vacuum hot pressing; ultrasonic frequency of ultrasonic assisted drilling is 30kHz, drilling speed is 120mm / min; first baking temperature is 90℃, time is 13min; second baking temperature is 110℃, time is 35min; plasma pretreatment power is 160W, vacuum degree is 46Pa; discharge power during low temperature plasma treatment is 400W, gas pressure is 0.3MPa; micro-etching treatment pulse laser power is 230W; copper deposition current density is 10A / dm 2 ; The copper deposition temperature is 30°C; The copper deposition time is 5s; The lamination steps are the same as those in Example 1.

[0085] Examples 39-44

[0086] Referring to the preparation method and parameter conditions of Example 38, the specific differences are shown in Table 5.

[0087] Comparative Example 6

[0088] An ultra-thin printed circuit board for MiniLED is manufactured according to the method of Example 38, except that no micro-etching treatment is performed.

[0089] Comparative Example 7

[0090] An ultra-thin printed circuit board for MiniLED is manufactured according to the method of Example 38, except that ultrasonic assistance is not introduced during the drilling process.

[0091] Example 45 Bonding solder joint quality test

[0092] Example 45 uses the SG-3042 universal tensile testing machine of Suzhou Jinge Testing Equipment Co., Ltd. to test the quality of the bonding solder joints of the sample. The test uses the ultra-thin printed circuit boards for MiniLED prepared in Examples 33 and 38-44 as samples, and Comparative Example 2 is designed for comparison. The test results are shown in Table 5.

[0093] Table 5 Bonding spot quality test of Examples 33, 38-44 and Comparative Examples 6-7

[0094]

[0095]

[0096] From Table 5 and Figure 1 It can be seen that when the pulsed laser power is relatively low, the solder joint area cannot be fully melted or etched, resulting in poor solder joint formation, such as reduced lead wire pull. In Examples 33, 38-41, as the pulsed laser power increases, the material in the solder joint area can be more fully melted, which helps to form a smoother and more uniform solder joint surface, thereby improving the quality and reliability of the solder joint and increasing the lead wire pull. However, in Example 44, when the power is too high, it will cause excessive melting or even ablation of the solder joint area, forming an excessively large molten pool or sputtering residue, destroying the morphology of the solder joint surface, but reducing the solder joint quality, affecting the final bonding effect, and resulting in reduced lead wire pull. In Example 41, when the pulsed laser power of the micro-etching treatment is 400W, the quality of the solder joint of the obtained circuit board is the highest, the lead wire pull is 0.32N, and there will be no problems such as cold solder joints and desoldering, which greatly improves the quality of the circuit board. In Comparative Example 6, the circuit board was not micro-etched, the lead wire pull was only 0.06N, and the solder joint quality was poor. Ultrasonic vibration can reduce the friction and cutting force between the drill bit and the plate, reduce the roughness of the hole wall, and improve the quality of the bonding solder joints. Good hole wall quality provides a more reliable connection for welding. In Comparative Example 7, ultrasonic assistance was not introduced during the drilling process, and the quality of the bonding solder joints was reduced.

[0097] Embodiment 46

[0098] A solder resist ink was prepared according to the method of Example 33 above.

[0099] Preparation of ultra-thin printed circuit boards for MiniLED: cutting, ultrasonic-assisted drilling, plasma pretreatment, copper deposition, and electroplating of the substrate to obtain a copper foil layer; drawing circuit graphics on the copper foil layer and AOI inspection to obtain a circuit graphic layer; low-temperature plasma treatment of the circuit graphic layer, solder mask ink coating and vacuum pressurization to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain an ultra-thin printed circuit board for MiniLED; lamination is vacuum hot pressing and flexible mold combined; ultrasonic vibration is introduced in vacuum hot pressing; vacuum hot pressing is multi-stage vacuum hot pressing; the ultrasonic frequency of ultrasonic assisted drilling is 30kHz, and the drilling speed is 120mm / min; the first baking temperature is 90℃, and the time is 13min; the second baking temperature is 110℃, and the time is 35min; the processing power of plasma pretreatment is 160W, and the vacuum degree is 46Pa; the discharge power during low-temperature plasma treatment is 400W, and the gas pressure is 0.3MPa; the pulse laser power for micro-etching treatment is 300W; the copper deposition current density is 12A / dm 2; The copper deposition temperature is 30°C; The copper deposition time is 5s; The lamination steps are the same as those in Example 1.

[0100] Examples 47-54

[0101] Referring to the preparation method and parameter conditions of Example 46, the specific differences are shown in Table 6.

[0102] Comparative Example 8

[0103] The preparation method and parameter conditions are similar to those of Example 46, except that no plasma pretreatment is performed before copper deposition.

[0104] Example 55 Copper foil layer thickness and surface morphology test

[0105] In Example 55, the thickness of the copper foil layer was measured using a thickness gauge CHY-S produced by Jinan Sanquan Zhongshi Experimental Instrument Co., Ltd., and the surface morphology of the copper foil layer was tested using an Apreo field emission scanning electron microscope produced by Thermo Fisher Scientific. The copper foil layers in Examples 41, 46-54 were used as samples in the test, and the test results are shown in Table 6.

[0106] Table 6 Copper foil thickness and surface morphology test of Examples 41, 46-54 and Comparative Example 8

[0107] Example <![CDATA[Current density / A / dm 2 > Copper deposition temperature / ℃ Copper deposition time / s Copper foil thickness / μm Surface morphology Embodiment 41 10 30 5 4.5 Dense and uniform Embodiment 46 12 30 5 4.2 Dense and uniform Embodiment 47 18 30 5 4.0 Dense and uniform Embodiment 48 25 30 5 4.2 Dense and uniform Embodiment 49 30 30 5 4.8 Loose and thick Embodiment 50 18 40 5 3.9 Dense and uniform Embodiment 51 18 50 5 4.2 Dense and uniform Embodiment 52 18 40 8 3.3 Dense and uniform Embodiment 53 18 40 12 3.5 Dense and uniform Embodiment 54 18 40 15 3.7 Dense and uniform Comparative Example 8 12 30 5 5.4 Loose and thick

[0108] It can be seen from Table 6 that in Examples 41, 46-49, when the current density is relatively low, the nucleation rate of the copper grains is lower than the growth rate, and the resulting copper deposit is composed of dispersed, irregularly shaped coarse crystals; as the current density gradually increases, local depletion will occur near the electrolyte where the crystals have been generated, inhibiting the growth of the crystals. The resulting copper crystals are dense, small, and uniform, and the thickness of the copper foil layer gradually decreases; however, when the current density increases to a certain extent, the depletion of the electrolyte near the cathode intensifies, hydrogen evolution occurs, and the crystalline particles on the surface of the copper foil layer become loose and coarse, and the flatness of the coating deteriorates. In Examples 51 and 54, excessively high copper deposition temperatures or long deposition times will also cause the crystalline particles on the surface of the copper foil to gradually become coarser. In Example 52, the current density is 18A / dm 2 When the copper deposition temperature is 40°C and the copper deposition time is 8s, the thinnest copper foil layer is 3.3μm, and the circuit board is also the lightest and thinnest. Plasma is used to pre-treat the hole wall before copper deposition to activate the hole wall surface, improve its adsorption capacity for copper ions, and make the copper deposition effect better. In Comparative Example 8, no plasma pre-treatment is performed, the copper deposition effect is poor, and the thickness of the copper foil layer increases.

[0109] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for manufacturing an ultra-thin printed circuit board for MiniLED, characterized in that: The steps for preparing the ultra-thin printed circuit board for MiniLED are as follows: cutting the substrate, ultrasonic assisted drilling, plasma pretreatment, copper deposition, and electroplating to obtain a copper foil layer; drawing the circuit pattern of the copper foil layer and AOI inspection to obtain a circuit pattern layer; low-temperature plasma treatment, solder mask ink coating and vacuum pressurization of the circuit pattern layer to obtain a coating layer; lamination, first baking, exposure, second baking, development and curing of the coating layer to obtain a solder mask layer; micro-etching of the solder mask layer to obtain the ultra-thin printed circuit board for MiniLED; the lamination is a combination of vacuum hot pressing and flexible mold; ultrasonic vibration is introduced in the vacuum hot pressing; the vacuum hot pressing is a multi-stage vacuum hot pressing; In parts by weight, the raw materials for producing the solder resist ink include 30-60 parts of polyester resin, 5-15 parts of epoxy resin, 10-20 parts of active diluent, and 5 parts of pigment; the pigment is one of low-pigment carbon black, medium-pigment carbon black, and high-pigment carbon black.

2. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The first baking temperature is 80-100° C., and the time is 10-15 minutes; the second baking temperature is 100-150° C., and the time is 25-40 minutes.

3. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The solder resist ink is prepared by the following steps: using an organic solvent to dissolve a photoinitiator and the active diluent, and adding the polyester resin, the pigment and the inorganic filler to obtain a mixture one; adding a defoamer and a leveling agent to the mixture one and stirring evenly to obtain a mixture two; adding the epoxy resin and the adhesion promoter to the mixture two, and using a disperser to disperse at high speed to obtain a mixture three; the dispersion time is 10 minutes; using a three-roll grinder to grind the mixture three until the particle fineness reaches 10 μm, and discharging the material to obtain the solder resist ink.

4. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The processing power of the plasma pretreatment is 160W, and the vacuum degree is 46Pa; the discharge power of the low-temperature plasma treatment is 200-800W, and the gas pressure is 0.1-0.5MPa.

5. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The copper deposition current density is 10-30A / dm 2 ; The copper deposition temperature is 30-50°C; The copper deposition time is 5-15s.

6. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The pulse laser power during the micro-etching process is 220-350W.

7. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The ultrasonic frequency of the ultrasonic assisted drilling is 30 kHz, and the drilling speed is 120 mm / min.

8. The process for manufacturing an ultra-thin printed circuit board for MiniLED according to claim 1, characterized in that: The lamination steps are as follows: placing the coating layer in the middle of the flexible mold, setting the initial temperature of the vacuum hot pressing equipment to 85°C, starting the vacuum pump, gradually evacuating the vacuum degree in the vacuum chamber to 35Pa, setting the pressure to 0.22MPa, maintaining for 12min, continuing to heat to 140°C at a rate of 1.5°C / min, gradually increasing the pressure to 1.5MPa, and simultaneously turning on the ultrasonic vibration system, setting the frequency to 30kHz, adjusting the amplitude to 30μm, maintaining for 25min, and then continuing to heat to the final curing temperature of 200°C at a rate of 1.8°C / min, increasing the pressure to 4MPa, keeping the ultrasonic vibration system on for 84min, and finally cooling to 85°C at a rate of 1.4°C / min, while gradually reducing the pressure to 0.2MPa, turning off the ultrasonic vibration system, and maintaining for 12min.

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