Laser drilling parameter optimization method

Abstract

The invention discloses a laser drilling parameter optimization method in the technical field of printed circuit board manufacturing. The method comprises the following steps: firstly, coating the surface of a plate with specifically prepared ternary hybrid gel, and curing to form an auxiliary functional layer; then, pre-set initial laser parameters are adopted for trial machining, and pulse energy, defocusing amount and scanning speed are directionally adjusted according to a clear rule according to a real-time evaluation result of the hole diameter, the hole wall and the hole bottom morphology; and the optimal process parameter combination can be quickly converged through iteration of limited times, and stable and efficient batch drilling is carried out accordingly. According to the method, the special coating is combined with systematic parameter adjustment and optimization, the cleanliness, precision and consistency of drilling are remarkably improved, the optimization process is rapid, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board manufacturing technology, specifically relating to a method for optimizing laser drilling parameters. Background Technology

[0002] Laser drilling technology, a key process in modern high-density interconnect printed circuit board manufacturing, aims to achieve high-precision, high-efficiency, and high-quality processing of micro-blind vias. With the rapid miniaturization and high-performance development of electronic devices, circuit board designs are becoming increasingly complex, with ever-increasing layers. The widely used composite substrates containing electrolytic copper foil and low-dielectric-constant resin pose even more stringent challenges to the drilling process. Due to its unique crystalline morphology and surface characteristics, electrolytic copper foil is more prone to molten spatter and re-solidification under laser irradiation compared to rolled copper foil, forming difficult-to-remove copper residues at the via opening and copper nodules on the via walls. This severely affects the reliability of subsequent electroplating and the integrity of signal transmission. Simultaneously, the low-dielectric-constant resin substrate has high thermal sensitivity and is prone to carbonization, delamination, or dielectric degradation under the heat generated by laser processing, requiring extremely high precision in laser energy control. Traditional single-pulse laser drilling processes often struggle to balance efficient copper removal with the protection of the resin substrate when dealing with such heterogeneous composite materials. This results in a series of problems, such as unsatisfactory hole taper, resin residue at the bottom of the hole, or excessive ablation, becoming a technical bottleneck that restricts the improvement of the quality and yield of high-end printed circuit boards.

[0003] To address these challenges, the industry has explored various process optimization approaches, one of which involves coating the material surface with a functional auxiliary layer before drilling. These auxiliary layers aim to alter the initial interaction mechanism between the laser and the material surface, such as enhancing energy utilization by increasing absorption of specific wavelengths of laser light, or removing molten material through vaporization to clean the hole walls. Common auxiliary layer materials include organic polymer films, metal oxide coatings, or simple silane coupling agent treatments. However, existing auxiliary layer technologies exhibit significant limitations when dealing with the specific combination of electrolytic copper foil and low-dielectric resin: many coatings lack sufficient adhesion to the copper foil surface and are easily peeled off under laser impact; their ability to adjust the laser ablation threshold for both copper and resin is limited, failing to simultaneously optimize the removal process of both layers; more importantly, most coatings lack the ability to adsorb and remove fine molten copper particles generated during laser processing, resulting in poor cleaning performance. Therefore, developing a novel composite auxiliary coating that can adhere firmly, precisely control energy distribution, and effectively assist in slag removal has become an important research direction for overcoming the current limitations of laser drilling technology.

[0004] This invention, based on a profound understanding of the shortcomings of existing technologies, proposes an innovative method for optimizing laser drilling parameters and a dedicated key material system. The core of this method lies in the creative preparation and application of a uniquely structured ternary hybrid gel as a laser-assisted layer. This gel is not a simple mixture, but rather, through precise chemical design, it hybridizes inorganic ammonium salt components with specific photothermal conversion and catalytic properties with organosilane components containing different reactive functional groups at the molecular level, forming a network structure that combines structural stability and functional synergy. When this gel is coated onto the area to be drilled, its behavior under laser irradiation is redefined. It not only promotes uniform absorption and transfer of laser energy and effectively suppresses irregular copper sputtering, but also undergoes controllable decomposition at high temperatures, assisting in the removal of residues at the hole edges. In conjunction with this dedicated auxiliary layer, this invention further designs a systematic parameter iterative optimization process. Starting from a validated initial parameter combination, based on real-time detection feedback of hole diameter, hole wall quality, and penetration state, a clear parameter adjustment logic is established, thereby quickly converging to the optimal processing window for the current material and coating system. This method solves two major problems in an integrated way: auxiliary layer material design and process parameter optimization, providing a new and efficient solution for achieving high-quality and high-consistency laser drilling. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for optimizing laser drilling parameters.

[0006] In a first aspect, the present invention provides a method for optimizing laser drilling parameters, comprising the following steps: S1. By weight, a multilayer PCB board containing electrolytic copper foil and a low dielectric constant resin substrate is placed in an oven and pre-baked at 78-82℃. 1-5 parts of a mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel are ultrasonically dispersed in a mixed solvent of 95-99 parts of n-propanol and deionized water to obtain a dispersion. The dispersion is coated onto the target drilled area and cured at 108-112℃ to obtain a coated multilayer PCB board. S2. Load the coated multilayer PCB board into the laser drilling machine table and set the initial parameters: pulse energy of 118-122μJ, repetition frequency of 150-200kHz, scanning speed of 780-820mm / s, defocusing amount of +0.1 to +0.2mm, and auxiliary gas of nitrogen, and perform single-pulse drilling. S3. Use an optical microscope and white light interferometer to evaluate the target aperture and copper residue at the aperture opening. If the aperture is too large, reduce the pulse energy. If copper nodules appear on the aperture wall, increase the absolute value of the defocusing amount. If the bottom of the aperture is not sufficiently penetrated, reduce the scanning speed. S4. Repeatedly adjust the parameters until the optimal parameter combination is obtained, and perform batch drilling based on the final parameters. Do not change the gas or lens during the drilling process.

[0007] In the laser drilling process, this invention utilizes a mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel to synergistically regulate laser-material interactions through multiple mechanisms, significantly improving the quality of microhole processing. Under laser irradiation, the coated gel's multi-metal-oxygen cluster components exhibit high selective absorption of specific wavelengths of laser light, preferentially enhancing local energy absorption in the copper foil layer. Meanwhile, the siloxane network forms a thermal buffer layer, inhibiting overheating and carbonization of the resin substrate. This optimized energy distribution positions the laser focus near the material surface, preventing copper layer melting and resin overheating caused by excessive energy concentration. When the defocusing amount is set within a positive range, the gel's thermal buffering effect further alleviates thermal stress in the copper layer, effectively inhibiting copper nodule formation. Simultaneously, the uniform coating ensures uniform laser energy distribution across the hole wall region, reducing residue at the hole opening. During the parameter optimization phase, problems are quickly identified through optical evaluation: when the aperture is too large, the pulse energy is reduced to decrease energy input; when copper nodules appear on the aperture wall, the absolute value of the defocusing amount is increased (i.e., the focal point is closer to the surface) to suppress copper melting; when the bottom penetration is insufficient, the scanning speed is reduced to extend the energy application time. The entire optimization process requires only minor fine-tuning to achieve precise aperture control and smooth, defect-free aperture walls. The molecular-level structure of this gel plays an adaptive regulatory role during drilling, requiring no additional auxiliary consumables, and is fully compatible with commercial laser equipment. This elevates the micro-hole processing precision to the micrometer level, providing an efficient and reliable process foundation for high-density interconnect PCB manufacturing.

[0008] According to a preferred embodiment of the present invention, in step S1, the curing time at 108-112°C is 5-10 min.

[0009] According to a preferred embodiment of the present invention, in step S2, the flow rate of nitrogen is 4-6 L / min.

[0010] According to a preferred embodiment of the present invention, in step S3, the target pore size is 47-53 μm.

[0011] According to a preferred embodiment of the present invention, in step S4, the parameter adjustment is repeated no more than 3 times.

[0012] In this invention, ...

[0013] According to a preferred embodiment of the present invention, the preparation steps of the mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel include: A1. By weight, under nitrogen protection, 30-70 parts of 12-phosphomolybdic acid hydrate and 30-70 parts of 12-tungsten phosphate hydrate are dissolved together in 500-1500 parts of deionized water. The mixture is stirred to obtain a homogeneous solution. Then, ammonia water is added dropwise under ice bath cooling until the pH reaches 6.4-6.6. The mixture is stirred and centrifuged to obtain a solid precipitate. The solid precipitate is washed with anhydrous ethanol and dried under vacuum at 58-62℃ to obtain a mixed ammonium salt powder. A2. Disperse the mixed ammonium salt powder ultrasonically in 1000-3000 parts of anhydrous ethanol, add 50-150 parts of vinyltrimethoxysilane and 50-150 parts of 3-aminopropyltriethoxysilane, add 10-50 parts of hydrochloric acid aqueous solution dropwise under ice bath conditions of 0-5℃, and then transfer to oil bath at 58-62℃ for continuous stirring and reflux to obtain POM-bissilane hybrid sol; A3. Transfer the POM-bissilane hybrid sol to a high-pressure reactor and place it in an oven at 115-125℃ for crystallization treatment. Cool it to room temperature to obtain a gel block. Extract the gel block continuously with anhydrous ethanol using a Soxhlet extractor and then vacuum dry it at 78-82℃ to obtain a dry gel. A4. Grind the dry gel in an agate mortar under argon protection.

[0014] In this invention, the formation of the mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel originates from the ion exchange reaction of phosphomolybdic acid and phosphotungstic acid hydrates under the action of ammonia water and the molecular-level hybridization of the silane precursor. First, phosphomolybdic acid hydrate and phosphotungstic acid hydrate are dissolved in deionized water to form a homogeneous solution. Then, ammonia water is slowly added under ice bath conditions, precisely controlling the pH to a slightly alkaline range, promoting ion exchange between the two heteropolyacids to generate a mixed ammonium salt precipitate containing molybdenum and tungsten mixed metal centers. This precipitate is washed with ethanol and dried under low-temperature vacuum to obtain a structurally homogeneous mixed ammonium salt powder. Next, the mixed ammonium salt is dispersed in anhydrous ethanol, and vinyltrimethoxysilane and 3-aminopropyltriethoxysilane are added. Pre-hydrolysis is carried out in a low-temperature acidic environment, with hydrochloric acid catalyzing the hydrolysis of the silane to generate active silanol groups. These groups combine with the mixed ammonium salt anions through hydrogen bonding and electrostatic interactions to form a preliminary hybrid system. Subsequently, the system was continuously refluxed at a mild temperature to promote the condensation of the siloxane network and the ordered arrangement of polyoxometalate clusters, forming a stable hybrid sol. The sol was then crystallized in a high-pressure reactor to further order the molecular structure, followed by Soxhlet extraction with anhydrous ethanol to remove unreacted small molecules, and vacuum drying to obtain a dry gel. Finally, it was ground into a fine powder under inert gas protection to ensure uniform particle size. The entire process, through precise control of reaction conditions, achieved molecular-level hybridization of inorganic polyoxometalate clusters and organosilanes, constructing a three-dimensional network structure with high light absorption, thermal stability, and interfacial anchoring ability, providing a key material basis for laser drilling.

[0015] According to a preferred embodiment of the present invention, in step A1, the stirring time is 2-4 hours.

[0016] According to a preferred embodiment of the present invention, in step A2, the stirring and reflux time is 24-30 hours.

[0017] According to a preferred embodiment of the present invention, in step A3, the crystallization treatment in an oven at 115-125°C takes 48-50 hours.

[0018] According to a preferred embodiment of the present invention, in step A4, the grinding time is 30-60 minutes.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention revolutionizes the core mechanism of laser drilling by innovatively introducing a ternary hybrid inorganic material based on phosphomolybdic acid, ammonium phosphotungstenate, and bissilane. This material forms a dense and uniform protective layer at the interface between the copper foil and the resin substrate, precisely controlling the absorption distribution of laser energy and the heat conduction path, so that the diameter of the micropore is stably controlled within the micrometer range, and the hole wall is smooth without copper nodules or internal defects.

[0020] (2) The laser drilling parameter optimization process is extremely simple to operate, requiring only initial settings and one or two fine-tuning adjustments to lock in the optimal combination. Specifically, a conventional optical microscope and white light interferometer are used to quickly assess the hole diameter and copper residue status. When the hole diameter is too large, the pulse energy is fine-tuned; when copper nodules appear on the hole wall, the absolute value of the defocus is adjusted; and when the bottom penetration is insufficient, the scanning speed is optimized. The entire convergence process is strictly controlled within three adjustments. No gas, lens, or special consumables need to be changed during the entire drilling process. It is fully compatible with the operating parameter range of commercial laser equipment, significantly shortening the process debugging cycle and eliminating equipment maintenance costs. This highly simplified optimization path enables operators to achieve high-yield mass production without complex training, significantly improving production line response speed and resource utilization.

[0021] (3) This invention is of great value to the manufacturing of high-density interconnect multilayer printed circuit boards. It successfully leaps the micro-hole processing capability from the millimeter level of traditional mechanical drilling to the micrometer level, perfectly adapting to the stringent requirements of ultra-high-density circuits for cutting-edge electronic devices such as 5G communication modules, artificial intelligence chip packaging, and LED displays. By eliminating copper nodules and indentations, the yield of micro-hole processing is improved, while reducing material waste and rework costs. This technology does not require customized raw materials or equipment modification and can be directly integrated into existing PCB production lines, providing key support for the development of the electronics manufacturing industry towards miniaturization and high reliability. It is expected to bring significant economic benefits and market competitiveness in the high-end packaging field. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0023] Example 1 This embodiment provides a method for optimizing laser drilling parameters, including the following steps: Preparation of mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel: A1. In a nitrogen-filled glove box, add 1000g of deionized water to a 2000mL three-necked flask. Under continuous nitrogen purging, add 50.0g of 12-phosphomolybdic acid hydrate solid powder and 50.0g of 12-tungsten phosphate hydrate solid powder sequentially to the flask. Place the flask on a magnetic stirrer and stir at 500rpm for 30min at room temperature until all solids are completely dissolved, yielding a clear homogeneous solution. Then, transfer the flask to an ice bath containing an ice-water mixture to lower the solution temperature to approximately 0-5℃. Under continuous stirring and ice bath cooling, slowly add 25% (w / w) concentrated ammonia solution using a constant-pressure dropping funnel, and monitor the pH value of the solution in real time using a pH meter. When the pH value reaches 6.5, immediately stop adding ammonia solution. Remove the ice bath, allow the reaction system to return to room temperature, and continue stirring at room temperature for 3.0h. The resulting white suspension was transferred to several centrifuge tubes and centrifuged at 8000 rpm for 15 min. The supernatant was carefully discarded. 500 mL of anhydrous ethanol was added to the precipitate, and the mixture was washed with a glass rod and centrifuged again. This washing process was repeated three times. The washed, moist solid was transferred to a petri dish and placed in a vacuum drying oven. It was dried at 60 °C and -0.1 MPa for 12 h to obtain a dried mixed ammonium salt powder, weighing 72.5 g.

[0024] A2. Add 2000g of anhydrous ethanol to a 5000mL three-necked flask. Weigh 100.0g of the mixed ammonium salt powder prepared in step A1 and slowly add it to the flask with the aid of ultrasonic oscillation. Sonicate for 30min to form a uniform suspension. Add 100.0g of vinyltrimethoxysilane and 100.0g of 3-aminopropyltriethoxysilane to the suspension sequentially. Place the flask in an ice bath and control the liquid temperature at 2℃. With vigorous stirring, slowly add 30.0g of 0.5mol / L hydrochloric acid aqueous solution over 30min using a dropping funnel. After the addition is complete, remove the ice bath and transfer the flask to an oil bath preheated to 60℃. Install a reflux condenser and continuously stir and reflux at 300rpm for 26h under a nitrogen atmosphere to obtain a pale yellow, slightly viscous POM-bissilane hybrid sol.

[0025] A3. Pour all the sol obtained in step A2 into a 200 mL polytetrafluoroethylene-lined container and seal it in a stainless steel high-pressure reactor. Place the reactor in a forced-air drying oven and crystallize at 120°C for 49 h. After treatment, close the oven and allow the reactor to cool naturally to room temperature (approximately 25°C). Open the reactor to obtain a translucent, pale yellow gel block. Transfer this gel block to the extraction sleeve of a Soxhlet extractor, add 400 mL of anhydrous ethanol as the extraction solvent to a 500 mL round-bottom flask, and extract continuously at 85°C for 24 h. After extraction, remove the gel block and place it in a vacuum drying oven at 80°C and -0.1 MPa for 24 h to obtain a brittle, dry gel block.

[0026] A4. Place the dry gel block obtained in step A3 into an agate mortar placed in a glove box filled with argon gas, grind manually for 45 minutes, pass through a 300-mesh sieve to obtain a light yellow fine powder ternary hybrid gel product, seal and store for later use.

[0027] Optimize laser drilling parameters: S1. Take an 8-layer PCB board with dimensions of 100mm × 100mm, containing 18μm electrolytic copper foil and a low dielectric constant resin substrate. Wipe the surface with anhydrous ethanol and place it in a forced-air drying oven at 80℃ for 30 minutes to remove moisture. Weigh 3.0g of the ternary hybrid gel powder prepared above and place it in a 250mL beaker. Measure 97.0g of a mixed solvent consisting of 72.75g of n-propanol and 24.25g of deionized water (volume ratio approximately 3:1) and add it to the beaker. Place the beaker in an ultrasonic cleaner and ultrasonically disperse it for 60 minutes at 40kHz and 300W to obtain a uniform and stable milky white dispersion. Use a slot coating method to uniformly coat the dispersion onto the pre-marked target drilling areas on the PCB board surface, controlling the wet film thickness to 20μm. The PCB board is then transferred to another forced-air drying oven and cured at 110°C for 8 minutes to form a firmly adhered transparent coating, resulting in a coated multilayer PCB board that can be laser drilled.

[0028] S2. Fix the coated PCB board obtained in step S1 onto the worktable of the laser drilling machine, ensuring its surface is parallel to the focal plane of the optical lens. Set the initial processing parameters of the laser as follows: pulse energy of 120μJ, repetition frequency of 180kHz, scanning speed of 800mm / s, defocusing distance of +0.15mm (i.e., the focal point is above the material surface), and the auxiliary gas is high-purity nitrogen, with its flow rate precisely set to 5.0L / min using a mass flow controller. Under these parameters, perform a single-pulse drilling test on the target area.

[0029] S3. After drilling, remove the PCB board. First, use a 200x optical microscope to observe the hole morphology, measure the hole diameter, and check for any copper residue (defined as adherent metal bright spots) at the hole edge. Then, use a white light interferometer to scan the three-dimensional morphology of the hole and evaluate the hole wall roughness and hole bottom condition. The test results are as follows: the hole diameter is 50.2μm, the hole edge is smooth with no visible copper residue; the hole wall is steep and smooth with no copper nodules; the hole bottom is clean, the resin substrate is completely penetrated, and there are no residues.

[0030] S4. Since all evaluation indicators in step S3 (pore size within the range of 47-53μm, with no copper residue, no copper nodules, and sufficient penetration) met the optimal standard on the first attempt, it was determined that no parameter adjustment was needed. The initial parameter combination was thus determined as the final optimized parameters. Based on this set of final parameters, a batch drilling production of 1000 holes was carried out on the same equipment, using the same bottle of nitrogen, and without changing the focusing lens.

[0031] Example 2 The difference between this embodiment and Example 1 is that a mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel is prepared: A1. Under nitrogen protection, add 800 g of deionized water to a 1500 mL beaker. Then add 35.0 g of 12-phosphomolybdic acid hydrate and 65.0 g of 12-tungsten phosphate hydrate sequentially, stirring until dissolved. Under ice bath cooling, adjust the pH to 6.4 by adding ammonia dropwise. After removing the ice bath, continue stirring at room temperature for 2.5 h. Centrifuge the suspension, and wash the precipitate three times with anhydrous ethanol. Dry the solid in a vacuum drying oven at 59 °C for 10 h to obtain a mixed ammonium salt powder.

[0032] A2. Weigh 80.0 g of the powder obtained in step A1 and add it to 1500 g of anhydrous ethanol in a 3000 mL three-necked flask. Disperse the powder by sonication for 30 min. Then add 70.0 g of vinyltrimethoxysilane and 130.0 g of 3-aminopropyltriethoxysilane. Under ice bath conditions at 1 °C, add 20.0 g of 0.8 mol / L hydrochloric acid aqueous solution dropwise. After the addition is complete, transfer the reaction system to a 59 °C oil bath, install a reflux apparatus, and stir and reflux under a nitrogen atmosphere for 25 h to obtain a hybrid sol.

[0033] A3. Pour the sol obtained in step A2 into a polytetrafluoroethylene liner, seal it in a high-pressure reactor, and place it in an oven for crystallization treatment at 118°C for 48.5 h. After natural cooling, a gel block is obtained, which is continuously extracted with anhydrous ethanol in a Soxhlet extractor for 22 h. The gel block is dried in a vacuum drying oven at 79°C for 20 h to obtain a dry gel.

[0034] A4. Under argon protection, grind the dry gel obtained in step A3 for 35 minutes, pass it through a 300-mesh sieve, and obtain the finished gel powder.

[0035] Optimize laser drilling parameters: S1. Take a PCB board of the same specifications and pre-bake it at 79℃ for 30 minutes. Weigh 2.0g of the above gel powder and ultrasonically disperse it in 98.0g of a solvent composed of 65.33g of n-propanol and 32.67g of deionized water to form a dispersion. Apply the dispersion to the target area using slot coating, with a wet film thickness of approximately 18μm. Then, cure the PCB board in an oven at 109℃ for 6 minutes.

[0036] S2. Mount the PCB board cured in step S1 onto the laser drilling machine and set the initial parameters: pulse energy 119μJ, repetition frequency 160kHz, scanning speed 790mm / s, defocusing amount +0.12mm, and nitrogen flow rate 4.5L / min. Conduct a single-pulse drilling test.

[0037] S3. Evaluate the drilling results of step S2 using an optical microscope and white light interferometer: The hole diameter is 48.5 μm, which meets the requirements; there is no copper residue at the hole opening; however, small protrusions (copper nodules) are observed in local locations on the hole wall; the hole bottom is fully penetrated. According to the rule "if copper nodules appear on the hole wall, increase the absolute value of the defocusing amount", the defocusing amount is adjusted to +0.18 mm, with other parameters remaining unchanged, and a second drilling test is performed. The evaluation results show that the hole diameter is 49.1 μm, the hole wall becomes smooth, the copper nodules disappear, and the hole bottom is in good condition.

[0038] S4. After one adjustment in step S3, a qualified hole shape is obtained. The adjusted parameters (pulse energy 119μJ, repetition frequency 160kHz, scanning speed 790mm / s, defocusing amount +0.18mm, nitrogen flow rate 4.5L / min) are determined as the final parameters for batch drilling.

[0039] Example 3 The difference between this embodiment and Example 1 is that a mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel is prepared: A1. Under nitrogen protection, add 1300 g of deionized water to a 2000 mL beaker. Then add 65.0 g of 12-phosphomolybdic acid hydrate and 35.0 g of 12-tungsten phosphate hydrate, stirring until dissolved. Under ice bath cooling, adjust the pH to 6.6 by adding ammonia dropwise. After removing the ice bath, continue stirring at room temperature for 3.5 h. Centrifuge the suspension, and wash the precipitate three times with anhydrous ethanol. Dry the solid in a vacuum drying oven at 61 °C for 14 h to obtain a mixed ammonium salt powder.

[0040] A2. Weigh 120.0 g of the powder obtained in step A1 and add it to 2800 g of anhydrous ethanol in a 5000 mL three-necked flask. Disperse the powder by sonication for 40 min. Then add 140.0 g of vinyltrimethoxysilane and 60.0 g of 3-aminopropyltriethoxysilane. Under an ice bath at 4 °C, add 45.0 g of a 0.3 mol / L hydrochloric acid aqueous solution dropwise. After the addition is complete, transfer the reaction system to a 61 °C oil bath, install a reflux apparatus, and stir and reflux under a nitrogen atmosphere for 28 h to obtain a hybrid sol.

[0041] A3. Pour the sol obtained in step A2 into a polytetrafluoroethylene liner, seal it in a high-pressure reactor, and place it in an oven for crystallization treatment at 124℃ for 49.5h. After natural cooling, a gel block is obtained, which is continuously extracted with anhydrous ethanol in a Soxhlet extractor for 26h. The gel block is dried in a vacuum drying oven at 81℃ for 22h to obtain a dry gel.

[0042] A4. Under argon protection, grind the dry gel obtained in step A3 for 55 minutes, pass it through a 300-mesh sieve, and obtain the finished gel powder.

[0043] Optimize laser drilling parameters: S1. Take a PCB board of the same specifications and pre-bake it at 81℃ for 30 minutes. Weigh 4.0g of the above gel powder and ultrasonically disperse it in 96.0g of a solvent composed of 76.80g of n-propanol and 19.20g of deionized water to form a dispersion. Apply the dispersion to the target area using slot coating, with a wet film thickness of approximately 22μm. Then, cure the PCB board in an oven at 111℃ for 9 minutes.

[0044] S2. Mount the PCB board cured in step S1 onto the laser drilling machine and set the initial parameters: pulse energy 121μJ, repetition frequency 195kHz, scanning speed 810mm / s, defocusing amount +0.19mm, and nitrogen flow rate 5.5L / min. Conduct a single-pulse drilling test.

[0045] S3. Evaluate the drilling results of step S2 using an optical microscope and white light interferometer: The hole diameter is 54.3 μm, exceeding the upper limit of 53 μm; the hole opening is clean; the hole wall is smooth; however, there is slight resin residue at the bottom of the hole, indicating incomplete penetration. According to the rules, firstly, due to the requirement of "reducing pulse energy if the hole diameter is too large," the pulse energy was lowered to 115 μJ, with other parameters remaining unchanged, and a second test was conducted. The evaluation results showed that the hole diameter improved to 51.0 μm, but the resin residue problem at the bottom of the hole still existed. Next, according to the requirement of "reducing the scanning speed if the bottom penetration is insufficient," based on the second set of parameters, the scanning speed was reduced from 810 mm / s to 750 mm / s, and a third test was conducted. The evaluation results showed that the hole diameter was 50.2 μm, the resin at the bottom of the hole was completely removed, penetration was sufficient, and the quality of the hole opening and hole wall was good.

[0046] S4. After two adjustments in step S3, a qualified hole shape is obtained. The final parameters (pulse energy 115μJ, repetition frequency 195kHz, scanning speed 750mm / s, defocusing amount +0.19mm, nitrogen flow rate 5.5L / min) are used for batch drilling.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that no mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel coating was applied, and laser drilling parameters were directly optimized. A multilayer PCB board with the same specifications as in Example 1 was pre-baked at 80°C for 30 minutes without any coating treatment. It was directly loaded into the laser drilling machine table. A single-pulse drilling test was performed using the exact same initial laser parameters as in Example 1 (pulse energy 120 μJ, repetition frequency 180 kHz, scanning speed 800 mm / s, defocusing amount +0.15 mm, nitrogen flow rate 5.0 L / min). Immediately after drilling, the hole diameter was evaluated using an optical microscope and found to be 55.8 μm. A distinct, irregular ring of metallic sputtering (copper residue) was present around the hole opening. Further observation with a white light interferometer revealed a rough hole wall surface with numerous nodular protrusions (copper nodules), and an uneven bottom contour with incompletely removed resin residue. Attempts were made to adjust the parameters according to the same rules: first, the pulse energy was reduced to 110 μJ and the aperture was reduced to 52.5 μm, but although the residue at the aperture opening and the copper nodules on the aperture wall were reduced, they were still clearly visible; then, the absolute value of the defocusing amount was increased to +0.25 mm and the experiment was repeated, but the effect on improving the copper nodules was limited, and it also led to an increase in the aperture taper. After multiple adjustments, it was still difficult to find a set of parameters that could simultaneously meet the three key requirements of aperture diameter in the range of 47-53 μm, smooth aperture wall without copper nodules, and clean aperture bottom without residue. The process optimization process was lengthy and the results were unstable.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that a single silane hydrolysate is used as an auxiliary layer. 2000g of anhydrous ethanol and 30.0g of 0.5mol / L hydrochloric acid aqueous solution were added to a 2000mL three-necked flask and stirred until homogeneous. Then, 100.0g of vinyltrimethoxysilane was added. The flask was placed in a 60°C oil bath, a reflux condenser was installed, and the mixture was stirred and refluxed for 6 hours to obtain a clear silane hydrolysate, which was then cooled and set aside. For laser drilling optimization, a PCB board was taken and pretreated as in Example 1. Using the same slot coating process as in Example 1, the above silane hydrolysate was directly coated onto the target drilling area, with a wet film thickness controlled at 20μm. The PCB board was then cured in a 110°C oven for 8 minutes to form a siloxane coating. The coated PCB board was then placed in a laser drilling machine, and single-pulse drilling was performed using the same initial laser parameters as in Example 1. Post-drilling evaluation: The pore diameter was 53.5 μm, slightly exceeding the upper limit; the copper residue around the pore opening was significantly reduced compared to Comparative Example 1, but sporadic attachment points were still visible under a high-powered microscope; the overall pore wall improved, but small, discrete copper nodules were still observed in localized areas (approximately 10% of the pore wall circumference); the bottom penetration was basically complete, but slight heat-affected zone marks were visible on the resin surface. Parameters were adjusted according to the rules: first, the pulse energy was reduced to 115 μJ, resulting in a pore diameter of 50.1 μm; then, the defocusing amount was increased to +0.20 mm to improve the copper nodules. After adjustment, the pore diameter and bottom penetration met the standards, but the localized copper nodules on the pore wall were not completely eliminated, and the repeatability between different pores was only average.

[0049] Example 3 The difference between this comparative example and Example 1 is that a physically mixed ammonium salt and silane powder are coated. 50.0 g of commercially available ammonium 12-phosphomolybdate powder and 50.0 g of commercially available ammonium 12-phosphotungstenate powder were weighed and initially mixed in a mortar. Then, 100.0 g of vinyltrimethoxysilane liquid and 100.0 g of 3-aminopropyltriethoxysilane liquid were measured. The two liquids and the mixed ammonium salt powder were added together to a wide-mouth bottle and manually stirred with a glass rod for 30 min, resulting in a moist, clumped, and uneven physical mixture. For laser drilling optimization, the PCB board pretreatment was the same as in Example 1. An attempt was made to prepare a dispersion: 3.0 g of the above physical mixture was weighed and added to 97.0 g of the same n-propanol / water mixed solvent as in Example 1, and the mixture was strongly magnetically stirred and sonicated for 60 min. The mixture could not be stably dispersed and quickly separated into layers, with a silane oil phase on top and an ammonium salt precipitate on the bottom. The upper suspension was barely coated onto the PCB board, resulting in a highly uneven coating. After curing at 110℃ for 8 minutes, the surface exhibited a mottled appearance. Drilling was performed using the same initial laser parameters as in Example 1. The post-drilling evaluation results were extremely poor: the pore diameter fluctuated drastically between 48 μm and 56 μm at different locations; the pore openings were severely contaminated, with a large amount of black carbides and metal particles adhering to them; the pore walls were abnormally rough, with copper nodules even more severe and denser than in Comparative Example 1; the pore bottom morphology was irregular, with excessive ablation and unpenetrated areas. Any parameter adjustments to the system were ineffective under these conditions, making it impossible to obtain a satisfactory pore shape.

[0050] In accordance with national and industry standard testing specifications, a series of standardized tests were conducted on the synthesis methods described in Examples 1-3 and Comparative Examples 1-3.

[0051] Immediately after laser drilling, the performance of the holes to be tested was evaluated. All tests were conducted in an environment with a temperature of 23℃±2℃ and a relative humidity of 50%±10%. For each test group, 10 independent holes were randomly selected for the following measurements: Aperture Measurement: Using a high-magnification optical microscope equipped with digital image analysis software, the maximum and minimum diameters of each hole were measured at 200× magnification. The arithmetic mean was taken as the measured aperture diameter of the hole, in micrometers (μm). The average of the measured aperture diameters of 10 holes was calculated to obtain the "average aperture diameter"; the standard deviation of these 10 values ​​was calculated to obtain the "aperture standard deviation".

[0052] Orifice copper residue assessment: The orifice edge regions of the above 10 orifices were observed under the same optical microscope. The number of orifices with any adhering residue having a typical metallic luster was recorded. The orifice copper residue incidence rate is expressed as “number of orifices with residue / total number of orifices observed (10)”.

[0053] Measurement of hole wall roughness: Use a white light interferometer to perform three-dimensional topography scanning on the above 10 holes. In the middle section of the hole wall of each hole, select an area with uniform height and no significant features, and measure the arithmetic mean roughness (Ra) of its surface profile in nanometers (nm). Calculate the average value of the Ra values of the 10 holes to obtain the "average hole wall roughness Ra".

[0054] Evaluation of hole bottom penetration state: Use a white light interferometer to scan the bottom topography of the above 10 holes. By analyzing the cross-sectional profile curve of the bottom area, determine whether the resin substrate has been completely removed and a clear and continuous bottom interface has been formed. Record the number of holes with any visible resin residue or signs of incomplete material removal (i.e., insufficient penetration). The incidence of insufficient penetration at the hole bottom is expressed in the form of "number of unpenetrated holes / total number of observed holes (10)".

[0055] Statistics of batch production pass rate: For the groups entering batch drilling production, during continuous production, one sample is taken every 100 holes, and a total of 10 samples are taken. Evaluate 10 holes in each sample according to the above methods 1 to 4. A hole is judged to be qualified if it must simultaneously meet the following conditions: the measured hole diameter is between 47 μm and 53 μm; there is no copper residue at the hole opening; the Ra value of the hole wall is less than 500 nm; the hole bottom is completely penetrated. The batch production pass rate is the percentage of the total number of qualified holes in all measured samples to the total number of measured holes (100).

[0056] The above performance test data are shown in Table 1.

[0057] Table 1 Performance test results

[0058] As can be seen from the above, the ternary hybrid gel coating and system parameter optimization method adopted in Examples 1 - 3 of the present invention comprehensively and effectively solve the key technical problems existing in laser drilling compared with Comparative Examples 1 - 3.

[0059] First, for the problem of poor hole diameter consistency, the average hole diameters of Examples 1 - 3 are 50.2 μm, 49.1 μm, and 50.2 μm respectively, all accurately falling within the target range of 47 - 53 μm, and the standard deviation of the hole diameter is only 0.8 - 1.2 μm, showing extremely high processing repeatability; while the hole diameter deviations of Comparative Example 1 (without coating) and 3 (physical hybrid coating) are as high as 2.8 μm and 4.5 μm respectively, indicating that the laser action is unstable and it is difficult to control the hole diameter accuracy without an effective auxiliary layer.

[0060] Secondly, regarding the issues of copper residue at the orifice and copper nodules on the orifice wall, the copper residue incidence rate in Examples 1-3 was 0 / 10, and the average orifice wall roughness Ra value was as low as 320-345 nm, proving that the prepared ternary hybrid gel can effectively suppress the melting and splashing of copper under laser action and promote its clean removal, forming a smooth orifice wall. In contrast, the copper residue incidence rate in Comparative Example 1 reached 80%, and the orifice wall Ra value was 950 nm. Although Comparative Example 2 (single silane layer) showed some improvement, it still had 20% residue and a roughness of 610 nm, while Comparative Example 3 was completely ineffective.

[0061] Furthermore, regarding the issue of insufficient penetration to the bottom of the pores, the insufficiency rate in Examples 1-3 was 0, proving that the optimized parameter combination can ensure that energy is effectively transferred to the underlying resin; while in Comparative Examples 1 and 3, 30% and 60% of the pores, respectively, had penetration problems.

[0062] Finally, regarding process stability and mass production feasibility, the mass production pass rate of Examples 1-3 reached over 98.0%, demonstrating the method's ability to quickly converge to a robust process window. In contrast, the pass rate of Comparative Example 2 was only 92.0%, and Comparative Examples 1 and 3 failed to achieve stable mass production due to excessive quality fluctuations. In summary, this invention, through the synergistic effect of precisely designed hybrid gels and optimized directional parameters, systematically solves the bottleneck of achieving high precision, high cleanliness, high consistency, and high reliability in laser drilling technology on high-performance PCB materials, significantly surpassing the technical level of existing uncoated or simple coating processes.

Claims

1. A method for optimizing laser drilling parameters, characterized in that, Includes the following steps: S1. By weight, a multilayer PCB board containing electrolytic copper foil and a low dielectric constant resin substrate is placed in an oven and pre-baked at 78-82℃. 1-5 parts of a mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel are ultrasonically dispersed in a mixed solvent of 95-99 parts of n-propanol and deionized water to obtain a dispersion. The dispersion is coated onto the target drilled area and cured at 108-112℃ to obtain a coated multilayer PCB board. S2. Load the coated multilayer PCB board into the laser drilling machine table and set the initial parameters: pulse energy of 118-122μJ, repetition frequency of 150-200kHz, scanning speed of 780-820mm / s, defocusing amount of +0.1 to +0.2mm, and auxiliary gas of nitrogen, and perform single-pulse drilling. S3. Use an optical microscope and white light interferometer to evaluate the target aperture and copper residue at the aperture opening. If the aperture is too large, reduce the pulse energy. If copper nodules appear on the aperture wall, increase the absolute value of the defocusing amount. If the bottom of the aperture is not sufficiently penetrated, reduce the scanning speed. S4. Repeatedly adjust the parameters until the optimal parameter combination is obtained, and perform batch drilling based on the final parameters. Do not change the gas or lens during the drilling process.

2. The laser drilling parameter optimization method according to claim 1, characterized in that, In step S1, the curing time at 108-112℃ is 5-10 minutes.

3. The laser drilling parameter optimization method according to claim 1, characterized in that, In step S2, the nitrogen flow rate is 4-6 L / min.

4. The laser drilling parameter optimization method according to claim 1, characterized in that, In step S3, the target pore size is 47-53 μm.

5. The laser drilling parameter optimization method according to claim 1, characterized in that, In step S4, the parameters are adjusted no more than 3 times.

6. The laser drilling parameter optimization method according to any one of claims 1-5, characterized in that, The preparation steps of the mixed ammonium salt-vinyltrimethoxysilane-3-aminopropyltriethoxysilane ternary hybrid gel include: A1. By weight, under nitrogen protection, 30-70 parts of 12-phosphomolybdic acid hydrate and 30-70 parts of 12-tungsten phosphate hydrate are dissolved together in 500-1500 parts of deionized water. The mixture is stirred to obtain a homogeneous solution. Then, ammonia water is added dropwise under ice bath cooling until the pH reaches 6.4-6.

6. The mixture is stirred and centrifuged to obtain a solid precipitate. The solid precipitate is washed with anhydrous ethanol and dried under vacuum at 58-62℃ to obtain a mixed ammonium salt powder. A2. Disperse the mixed ammonium salt powder ultrasonically in 1000-3000 parts of anhydrous ethanol, add 50-150 parts of vinyltrimethoxysilane and 50-150 parts of 3-aminopropyltriethoxysilane, add 10-50 parts of hydrochloric acid aqueous solution dropwise under ice bath conditions of 0-5℃, and then transfer to oil bath at 58-62℃ for continuous stirring and reflux to obtain POM-bissilane hybrid sol; A3. Transfer the POM-bissilane hybrid sol to a high-pressure reactor and place it in an oven at 115-125℃ for crystallization treatment. Cool it to room temperature to obtain a gel block. Extract the gel block continuously with anhydrous ethanol using a Soxhlet extractor and then vacuum dry it at 78-82℃ to obtain a dry gel. A4. Grind the dry gel in an agate mortar under argon protection.

7. The laser drilling parameter optimization method according to claim 6, characterized in that, In step A1, the stirring time should continue for 2-4 hours.

8. The laser drilling parameter optimization method according to claim 6, characterized in that, In step A2, the stirring and reflux time is 24-30 hours.

9. The laser drilling parameter optimization method according to claim 6, characterized in that, In step A3, the crystallization treatment in an oven at 115-125℃ takes 48-50 hours.

10. The laser drilling parameter optimization method according to claim 6, characterized in that, In step A4, the grinding time is 30-60 minutes.

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