A vacuum acid etching process for circuit board

Abstract

This invention relates to the field of circuit board manufacturing technology and discloses a vacuum acid etching process for circuit boards. The process includes pre-treating a double-sided copper-clad laminate substrate, applying a photosensitive dry film, and then exposing and developing it. The developed circuit board is then conveyed into a closed etching chamber where it is sprayed with acidic etching solution. Simultaneously, a top vacuum is activated to create a dynamic micro-negative pressure, while oxygen-rich air is blown in from the bottom to form a gas-liquid micro-vortex. The discharged acid mist is guided into a gas-liquid condensation and separation device, where it is absorbed by a chloride ion trapping solution to a set threshold before being pumped into the main etching tank. Alternating jet negative pressure suction is then used for initial washing, followed by film removal, acid pickling and neutralization, and drying. This invention improves the uniformity of the etching process by constructing a directional gas-liquid micro-vortex, utilizes a trapping solution to recover acidic gas, maintains the chemical balance of the main tank system, and reduces pollution emissions. Furthermore, the negative pressure suction forcibly displaces residual acid from micropores, thereby reducing the probability of corrosion in subsequent circuits.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, specifically to a vacuum acid etching process for circuit boards. Background Technology

[0002] In the circuit board manufacturing process, acid etching is a fundamental process for achieving pattern transfer and forming a conductive network. It typically involves spraying an etching solution containing copper chloride and hydrochloric acid onto the surface of the copper-clad laminate, causing the copper layer not protected by the dry film to undergo an oxidation-reduction reaction and dissolve.

[0003] In existing acid etching processes, after the etchant is sprayed onto the circuit board surface, the reaction products tend to remain on the board surface and form a fluid boundary layer. This accumulated liquid layer hinders the contact between the subsequent fresh etchant and the underlying unreacted copper surface, reducing gas-liquid mass transfer efficiency. The lack of targeted local oxidation mechanisms in conventional open or semi-closed spray environments results in a slow process of re-oxidizing the monovalent cuprous ions generated in the reaction into divalent copper ions. This makes it difficult to maintain a consistent etching rate in different areas, affecting the etching uniformity of the circuit board surface and the overall reaction efficiency.

[0004] Under spray and heating conditions, the hydrogen chloride component in the acidic etching solution easily volatilizes and generates a large amount of mixed acid mist. Existing equipment treats these waste gases by directly exhausting them and then centrally scrubbing them. This method not only poses the risk of free acid mist escaping and polluting the surrounding environment, but also causes a continuous loss of hydrogen and chloride ions in the etching system. The unintended loss of acidic gases disrupts the chemical balance of the divalent copper ion complex system in the main etching tank. In order to maintain the specific gravity of the tank solution and the etching rate, large amounts of fresh replenishing solution must be added frequently during the production process, resulting in high chemical consumption.

[0005] After etching, circuit boards inevitably retain residual acid, requiring initial water rinsing for cleaning. As circuit boards become increasingly dense and fine-pitched, the gaps between microscopic lines are constantly shrinking. Conventional surface water rinsing spray methods are limited by the surface tension of the water flow and the capillary resistance within the pores, making it difficult for the cleaning medium to penetrate deep into the tiny pores for effective mixing. This makes it difficult to remove the residual acidic components in the deeper areas using conventional rinsing methods. The acidic substances remaining deep in the pores will slowly seep out during subsequent processing or long-term use, easily causing circuit corrosion and even electrical failure. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a vacuum acid etching process for circuit boards, which solves the problems of poor etching uniformity caused by liquid on the board surface hindering gas-liquid mass transfer, loss of effective chemical components and environmental pollution caused by acid mist volatilization and emission, and difficulty in removing deep residual acid in micropores by conventional water washing, thus leading to subsequent circuit corrosion.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a vacuum acid etching process for circuit boards, employing the following technical solution: A vacuum acid etching process for circuit boards includes the following steps: The double-sided copper-clad board is degreased and activated by micro-etching and acid washing, and the surface moisture is dried to obtain the pre-treated circuit board. A photosensitive dry film is pressed onto the surface of the pre-treated circuit board, and after exposure treatment, a circuit board with completed pattern transfer is obtained. The circuit board with the completed pattern transfer is subjected to a developing process to clean the residual developing solution from the board surface, resulting in a developed circuit board. The developed circuit board is conveyed into a fully enclosed etching chamber, where it is sprayed with acidic etching solution. Simultaneously, the top of the etching chamber is evacuated to create a dynamic micro-negative pressure, and oxygen-rich air is blown in from the bottom upwards. The oxygen-rich airflow at the bottom and the micro-negative pressure at the top form a directional gas-liquid micro-vortex. The mixed acid mist gas discharged from the top is introduced into a gas-liquid condensation and separation device, where it is enriched and absorbed using a chloride ion capture solution. When the equivalent hydrochloric acid concentration of hydrogen chloride absorbed by the chloride ion capture solution reaches a set threshold, it is pumped into the main etching tank as a replenishing solution, resulting in the etched circuit board. The etched circuit board is conveyed into the primary water washing section and subjected to a spatial alternating jet negative pressure suction primary washing to obtain the primary washed circuit board. The circuit board after initial washing is washed with water and dried. It is then transferred to a stripping tank to peel off the cured dry film. After acid washing and neutralization, it is finally washed and dried to obtain the finished circuit board.

[0008] By adopting the above technical solution, and through the use of fluid dynamics control and acid mist recovery and reuse mechanisms within the etching chamber, as well as the physical displacement cleaning mechanism in the initial washing section, the effects of improved etching uniformity, maintenance of chemical system balance, and reduction of acidic residue in pores are achieved. The specific reaction mechanism and innovative process are explained step-by-step as follows: Regarding the enhancement of gas-liquid mass transfer at the etching reaction interface, when a circuit board is sprayed with acidic etching solution in an etching chamber, copper is oxidized by divalent copper ions to generate monovalent cuprous ions. Traditional spraying methods create a fluid boundary layer on the board surface, hindering the contact between fresh etching solution and the copper surface. This solution uses top micro-negative pressure suction and bottom oxygen-enriched air blowing to create a bottom-up directional gas-liquid micro-vortex within a sealed chamber. The physical shear force generated by this micro-vortex helps to break down the fluid boundary layer on the board surface, displacing the accumulated reaction liquid and allowing fresh etching solution to quickly contact the unreacted copper surface. Simultaneously, the oxygen-enriched air directly participates in the etching solution regeneration reaction, promoting the re-oxidation of monovalent cuprous ions to divalent copper ions, thereby maintaining the local oxidation capacity of the board surface to a certain extent.

[0009] Regarding the acid mist recovery and in-situ chemical system equilibrium process, relying on a slight negative pressure suction, the volatile hydrogen chloride gas inside the chamber enters the gas-liquid condensation and separation device with the airflow. Condensation liquefies some water vapor, and the airflow then enters the chloride ion capture liquid. The amino components in the capture liquid neutralize the hydrogen chloride, typically fixing the volatile hydrogen chloride into a salt form. When the capture liquid enriches hydrogen chloride to a set concentration threshold, it is directly pumped into the main etching tank. In this process, the enriched liquid not only replenishes the hydrogen and chloride ions consumed during etching, helping to maintain the complexed state of divalent copper ions in the main etching tank, but also reduces the possibility of free acid mist being emitted into the external environment.

[0010] Regarding the forced displacement cleaning process of the residual liquid in the micro-pores, after the circuit board enters the primary water washing section, the alternating jet negative pressure suction mechanism begins to intervene. Deionized water jets are injected onto the board surface to dilute the residual acid between the micro-pores and dense circuitry. Then, due to the board surface being in close contact with the micro-negative pressure suction slits, the diluted liquid in the pores is forcibly extracted under the influence of instantaneous high negative pressure, followed by water injection again. This cyclical physical displacement effect of water injection and forced evacuation followed by water injection can partially overcome the surface tension and capillary resistance of the fluid within the micro-pores, removing deep-seated acidic components that are difficult to clean with conventional spraying, thus reducing the risk of acid seepage in subsequent processes.

[0011] Preferably, the chloride ion capturing solution contains the following components by weight percentage: 5% to 10% diethylenetriamine, with the balance being deionized water, and the sum of the weight percentages of each component is 100%.

[0012] By employing the above technical solution, the diethylenetriamine molecule contains multiple active amino groups, possessing a certain acid gas binding capacity, which helps to absorb hydrogen chloride molecules in the gas flow and convert them into the corresponding amine salt. Controlling its concentration within the range of 5% to 10% preserves the required absorption capacity while avoiding the problem of excessive liquid viscosity affecting the gas-liquid contact area.

[0013] Preferably, the preparation method of the chloride ion capturing solution includes the following steps: weighing diethylenetriamine and deionized water separately for later use; adding the weighed deionized water to a mixing vessel equipped with a stirring device and a cooling jacket, starting the stirring, and slowly adding the weighed diethylenetriamine dropwise while continuously stirring to obtain a mixed system; during the dropwise addition process, controlling the cooling water flow rate of the cooling jacket of the mixing vessel to keep the temperature of the mixed system below 40°C; after the diethylenetriamine has been completely added, continuing to stir the mixed system for 30 minutes to obtain a mixed liquid; and naturally cooling the mixed liquid to 25°C to obtain the chloride ion capturing solution.

[0014] By adopting the above technical solution, diethylenetriamine releases heat of solution when dissolved in water. By adding it dropwise and using a cooling jacket to control the temperature below 40°C, the volatilization of organic components or side reactions caused by heat can be reduced, which is beneficial to maintaining the effective concentration and chemical stability of the capture solution.

[0015] Preferably, the acidic etching solution is prepared according to the following components at concentrations: copper chloride dihydrate at a concentration of 300 g / L to 400 g / L, hydrochloric acid at a concentration of 1.5 mol / L to 2.5 mol / L, sodium chloride at a concentration of 30 g / L to 60 g / L, and polyethylene glycol at a concentration of 1 g / L to 5 g / L, with deionized water as the solvent; when performing the acidic etching solution spraying operation, the temperature of the acidic etching solution is 45°C to 55°C, the spraying pressure is 0.2 MPa to 0.35 MPa, and the oxidation-reduction potential is maintained in the range of 500 mV to 560 mV using an online controller.

[0016] By employing the above technical solution, copper chloride dihydrate serves as the primary oxidant, providing the basis for etching; hydrochloric acid provides an acidic environment and inhibits copper ion hydrolysis; sodium chloride provides additional chloride ions, promoting the formation of easily soluble complexes by cuprous ions to leave the copper surface; and polyethylene glycol, as a surfactant, reduces the surface tension of the etching solution, improving its wettability among fine lines. Maintaining the redox potential within a specific range ensures a relatively balanced ratio of divalent to monovalent copper in the etching solution, which is beneficial for maintaining a stable etching rate.

[0017] Preferably, the cabin pressure of the dynamic micro-negative pressure is maintained at -1kPa to -10kPa; the oxygen volume fraction in the oxygen-enriched air is 25% to 40%, and the air flow rate is 10L / (min·m) to 50L / (min·m); the condenser tube temperature of the gas-liquid condensation separation device is maintained at 5℃ to 15℃; and the set threshold for the equivalent hydrochloric acid concentration is 4mol / L to 6mol / L.

[0018] By adopting the above technical solutions and controlling the ratio of slight negative pressure to airflow within the chamber, a suitable vortex field can be formed, reducing the likelihood of crystallization caused by drying the plate surface. Controlling the condenser temperature helps improve the condensation and capture efficiency of hydrogen chloride. Setting a threshold range ensures that the replenishment solution pumped back to the main tank has a corresponding ion concentration, preventing excessive moisture from entering the main tank and causing an imbalance in the etching solution density.

[0019] Preferably, during the initial cleaning of the space-alternating jet negative pressure suction, deionized water is sprayed onto the etched circuit board. The cleaned board surface then adheres closely to the micro-negative pressure suction slit, creating a physical displacement effect of water injection and forced vacuuming followed by water injection through physical displacement. The temperature of the deionized water is 20℃~30℃, and the spray pressure is 0.2MPa~0.3MPa. The distance between the micro-negative pressure suction slit and the board surface is set to 0.5mm~1.5mm, and the instantaneous negative pressure at the slit opening is -20kPa~-40kPa.

[0020] By adopting the above technical solution and controlling the slit spacing and instantaneous negative pressure value, it is possible to generate a suction pressure difference to overcome the capillary resistance of the pores, thereby achieving fluid displacement and separation, while reducing physical damage to the line.

[0021] Preferably, during the degreasing treatment, the degreasing temperature is 50℃~65℃, and the degreasing solution composition used contains the following components by weight percentage: sodium hydroxide 2%~5%, trisodium phosphate 3%~6%, fatty alcohol polyoxyethylene ether 0.5%~2%, with the balance being deionized water, and the sum of the weight percentages of each component is 100%; during the micro-etching acid pickling activation treatment, the micro-etching acid pickling activation temperature is 25℃~40℃, and the micro-etching solution composition used contains the following components by weight percentage: sodium persulfate 8%~15%, sulfuric acid 1%~3%, phosphoric acid 0.01%~0.05%, with the balance being deionized water, and the sum of the weight percentages of each component is 100%.

[0022] By employing the above technical solutions, the degreasing solution uses alkaline substances and surfactants to remove fingerprints and grease from the copper surface. The micro-etching solution utilizes the oxidizing properties of sodium persulfate to form a surface structure with a certain degree of roughness on the copper surface, increasing the physical adhesion between the subsequent dry film and the board surface.

[0023] Preferably, after the photosensitive dry film is laminated onto the surface of the pretreated circuit board, it is vacuum-pressed and then exposed using an ultraviolet light source. The temperature of the laminator rollers is controlled at 100℃~120℃, and the pressure is set at 0.3MPa~0.5MPa. The vacuum degree of the vacuum pressing is -70kPa~-90kPa, and the exposure energy of the ultraviolet light source is controlled at 40mJ / cm². 2 ~100mJ / cm 2 During the development process, the temperature of the developing solution is 28°C to 35°C, the spray pressure is 0.15MPa to 0.25MPa, and the developing solution composition used contains the following components by weight percentage: 0.8% to 1.5% anhydrous sodium carbonate, 0.05% to 0.1% polydimethylsiloxane, and the balance is deionized water, and the sum of the weight percentages of each component is 100%.

[0024] By employing the above technical solution, vacuum lamination helps reduce micro-bubbles on the circuit board surface, allowing the photosensitive dry film to better fill the substrate surface. During the development stage, a sodium carbonate solution of a specific concentration is used to dissolve the unexposed portions of the dry film, and polydimethylsiloxane is used as an antifoaming agent to suppress excessive foam generation in the developer, which could affect development accuracy, thereby achieving pattern transfer.

[0025] Preferably, the peeling and curing of the dry film is carried out by immersion combined with high-pressure physical spraying. The temperature of the peeling solution is 50℃~70℃, the spraying pressure is 0.2MPa~0.3MPa, and the peeling solution composition contains the following components by weight percentage: 5%~10% potassium hydroxide, 2%~5% monoethanolamine, and the balance is deionized water, and the sum of the weight percentages of each component is 100%.

[0026] By adopting the above technical solution, strong alkali potassium hydroxide is combined with monoethanolamine to penetrate into the interior of the cured dry film, causing it to swell and peel off. Combined with the mechanical force of spraying, the dry film is made to fall off in sheets, reducing the risk of dry film debris re-adhering to the board surface.

[0027] Preferably, the acid washing and neutralization uses a dilute sulfuric acid solution with a sulfuric acid weight percentage of 1% to 3%, and the final washing and drying operation uses a hot air drying system to completely dry the product at a temperature of 100℃ to 120℃.

[0028] By employing the above technical solution, dilute sulfuric acid can neutralize the alkaline substances remaining on the board surface after film removal, delaying the oxidation and discoloration process of the exposed copper surface in an alkaline environment. The final hot air drying removes residual moisture from the board surface, ensuring the finished circuit board is dry for subsequent storage and processing.

[0029] This invention provides a vacuum acid etching process for circuit boards. It has the following advantages: 1. This invention creates a dynamic micro-negative pressure by evacuating air from the top of the etching chamber and simultaneously blowing oxygen-rich air upwards from the bottom, constructing a bottom-up directional gas-liquid micro-vortex within the chamber. The physical shear force generated by this gas-liquid fluid movement helps to break down the fluid boundary layer generated by the reaction on the board surface, allowing fresh acidic etching solution to contact the unreacted copper surface more quickly. At the same time, the blown-in oxygen-rich airflow can directly participate in the reaction, causing monovalent cuprous ions to be re-oxidized into divalent copper ions. Through the combination of fluid dynamics control and localized oxidation, the uniformity and reaction efficiency of the circuit board etching process are improved.

[0030] 2. This invention utilizes top-mounted air extraction to guide the mixed acid mist generated during etching into a gas-liquid condensation and separation device. A chloride ion capturing liquid containing diethylenetriamine is used for neutralization and enrichment absorption. When the capturing liquid absorbs the volatilized hydrogen chloride to a set concentration threshold, it is directly pumped into the main etching tank as a replenishing liquid. This recovery mechanism reduces the emission of free acid mist into the external environment while guiding the escaped hydrogen and chloride ions back into the main etching tank, which helps maintain the chemical balance of the divalent copper ion complex system in the main etching tank and reduces the consumption of conventional fresh replenishing liquid.

[0031] 3. This invention introduces a spatial alternating jet negative pressure suction operation in the primary water washing section after the circuit board is etched. Through the alternating action of deionized water jet injection and instantaneous negative pressure forced vacuuming in micro-slits, a fluid physical displacement effect is formed between the micro-pores and dense lines on the board surface. This pressure difference generated by negative pressure can overcome the capillary resistance and fluid surface tension inside the micro-pores, and displace and remove deep-seated acidic components that are difficult to clean by conventional surface spraying, thereby reducing the probability of circuit corrosion caused by acid seepage in subsequent processes and use. Attached Figure Description

[0032] Figure 1 The Fourier transform infrared spectra of the chloride ion capturing liquid of the present invention before and after in-situ absorption of acid mist. Figure 2 Figure 1 shows the mass transfer enhancement test diagram of the micro negative pressure eddy current system of the present invention. Figure 2 shows the etching rate distribution curve of each test point in the transverse direction of the sample plate, and Figure 3 shows the change curve of dissolved oxygen concentration in the reaction liquid film above the plate surface with time during etching. Figure 3 Figure 1 shows the line graphs of the chemical parameters of the main tank during the continuous etching process of the present invention over time. Figure 2 shows the curve of the free hydrochloric acid concentration in the main tank over time, and Figure 3 shows the curve of the redox potential in the main tank over time. Figure 4 The ion chromatograms of the extract from the plate surface after initial washing are shown in Figure (a), which is the ion chromatogram of the extract from the sample prepared in Comparative Example 4, and Figure (b) is the ion chromatogram of the extract from the sample prepared in Example 2. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a chloride ion capturing solution, including the following steps: (1) Weigh out 50g of diethylenetriamine and 950g of deionized water respectively for later use; (2) Add the deionized water weighed in step (1) to a mixing vessel equipped with a stirring device and a cooling jacket, start stirring, and slowly add the diethylenetriamine weighed in step (1) while continuously stirring to obtain a mixed system. (3) During the dripping process, control the cooling water flow rate of the cooling jacket of the mixing vessel to keep the temperature of the mixing system in step (2) below 40°C. After the diethylenetriamine in step (2) is completely dripped, continue to stir the mixing system for 30 minutes to obtain the mixture. (4) Cool the mixture obtained in step (3) naturally to 25°C to obtain a chloride ion capturing solution with a diethylenetriamine weight percentage of 5%.

[0035] Preparation Example 2: This preparation example provides a method for preparing a chloride ion capturing solution, including the following steps: (1) Weigh out 75g of diethylenetriamine and 925g of deionized water respectively for later use; (2) Add the deionized water weighed in step (1) to a mixing vessel equipped with a stirring device and a cooling jacket, start stirring, and slowly add the diethylenetriamine weighed in step (1) while continuously stirring to obtain a mixed system. (3) During the dripping process, control the cooling water flow rate of the cooling jacket of the mixing vessel to keep the temperature of the mixing system in step (2) below 40°C. After the diethylenetriamine in step (2) is completely dripped, continue to stir the mixing system for 30 minutes to obtain the mixture. (4) Cool the mixture obtained in step (3) naturally to 25°C to obtain a chloride ion capturing solution with a diethylenetriamine weight percentage of 7.5%.

[0036] Preparation Example 3: This preparation example provides a method for preparing a chloride ion capturing solution, including the following steps: (1) Weigh out 100g of diethylenetriamine and 900g of deionized water respectively for later use; (2) Add the deionized water weighed in step (1) to a mixing vessel equipped with a stirring device and a cooling jacket, start stirring, and slowly add the diethylenetriamine weighed in step (1) while continuously stirring to obtain a mixed system. (3) During the dripping process, control the cooling water flow rate of the cooling jacket of the mixing vessel to keep the temperature of the mixing system in step (2) below 40°C. After the diethylenetriamine in step (2) is completely dripped, continue to stir the mixing system for 30 minutes to obtain the mixture. (4) Cool the mixture obtained in step (3) naturally to 25°C to obtain a chloride ion capturing solution with a diethylenetriamine weight percentage of 10%.

[0037] Examples 1-3: Example 1:

[0038] This embodiment provides a vacuum acid etching process for circuit boards, including the following steps: (1) The commercially available FR-4 double-sided copper-clad laminate was immersed in a degreasing solution for degreasing treatment. The treatment temperature was controlled at 50℃ and the treatment time was 2min. The degreasing solution composition was 2% sodium hydroxide, 3% trisodium phosphate, 0.5% fatty alcohol polyoxyethylene ether, and the remainder was deionized water by weight percentage. After washing with countercurrent water for 1min, it was put into the micro-etching section for acid pickling and activation. The temperature was controlled at 25℃ and the time was 45s. The micro-etching solution composition was 8% sodium persulfate, 1% sulfuric acid, 0.01% phosphoric acid, and the remainder was deionized water by weight percentage. After activation, it was washed with pure water and put into the drying section. The surface moisture was dried under hot air at 100℃ to obtain the pretreated circuit board. (2) A 38μm thick photosensitive dry film is laminated onto the clean copper foil surface of the circuit board obtained in step (1). The roller temperature of the laminator is controlled at 100℃, the pressure is set to 0.3MPa, and the conveying speed is set to 1.5m / min. After lamination, the circuit film is precisely aligned with the circuit board, and after vacuuming to -70kPa and pressing tightly, it is exposed using an ultraviolet light source with an exposure energy controlled at 40mJ / cm. 2 After exposure, let it stand for 15 minutes to obtain a circuit board with completed pattern transfer; (3) The circuit board obtained in step (2) is horizontally conveyed into the developing machine for developing. The temperature of the developing solution is 28°C, the spray pressure is 0.15MPa, the conveying speed is 1.5m / min, and the developing solution composition is 0.8% anhydrous sodium carbonate, 0.05% polydimethylsiloxane, and the remainder is deionized water by weight percentage. After developing, the circuit board is physically blocked and cleaned by three-stage countercurrent water washing and one-stage overflow water washing to remove residual developing solution from the board surface and obtain the developed circuit board. (4) The circuit board obtained in step (3) is smoothly conveyed by horizontal rollers into the fully enclosed etching chamber and subjected to high-pressure spraying of acidic etching solution from the top and bottom. The acidic etching solution consists of copper chloride dihydrate with a concentration of 300 g / L, hydrochloric acid with a concentration of 1.5 mol / L, sodium chloride with a concentration of 30 g / L, and polyethylene glycol with a concentration of 1 g / L, with the remainder being deionized water. The etching process parameters are maintained at a liquid temperature of 45°C, a spraying pressure of 0.2 MPa, and an online controller to maintain the oxidation-reduction potential at 500 mV. Simultaneous micro-negative pressure vortex control and in-situ reflux are performed. Specifically, the top of the etching chamber is evacuated to maintain the chamber pressure at a dynamic micro-negative pressure of -1 kPa. At the same time, oxygen-enriched air with an oxygen volume fraction of 25% is blown upwards obliquely from the air array below the horizontal roller at a flow rate of 10 L / min·m. The oxygen-enriched air at the bottom and the micro-negative pressure at the top form a directional gas-liquid micro-vortex. The mixed acid mist gas discharged from the top is introduced into the gas-liquid condensation and separation device, and the condenser tube temperature is maintained at 5°C. The condensed acidic mixed gas enters the chloride ion capture liquid prepared in Preparation Example 1 for enrichment and absorption and circulation. The concentration change of the capture liquid is monitored in real time using an online concentration meter. When the equivalent hydrochloric acid concentration of the hydrogen chloride absorbed by the capture liquid reaches the set threshold (set to 4 mol / L in this embodiment), the infusion pump is turned on by the control system and pumped into the etching main tank as a replenishing liquid to complete the micro-negative pressure vortex acid etching and in-situ reflux, and the etched circuit board is obtained. (5) The circuit board obtained in step (4) is conveyed into the primary water washing section. During the horizontal movement of the circuit board at a speed of 1.5 m / min, a spatial alternating jet negative pressure suction initial washing is performed. The environment of the primary washing section is normal pressure. Deionized water at a temperature of 20°C is sprayed onto the circuit board through a high-pressure water spray pipe at a pressure of 0.2 MPa. After cleaning, the board surface is then closely attached to the micro-negative pressure suction slit. The distance between the slit and the board surface is set to 0.5 mm. The instantaneous negative pressure at the slit opening is -20 kPa, thereby forming a physical displacement effect of water injection and forced vacuuming and water injection in physical displacement, and obtaining the circuit board after primary washing. (6) The circuit board obtained in step (5) is further subjected to a first-level overflow water wash for physical isolation, and then pure water is used for closed-loop spray circulation cleaning; after cleaning, it is passed through an air knife array, and the excess water on the surface and in the micropores is removed and dried by high-pressure airflow to obtain a dehydrated circuit board. (7) The circuit board obtained in step (6) is transferred into the stripping tank and soaked in a combination of high-pressure physical spray to peel off the cured dry film on the board surface. The temperature of the stripping solution is 50°C and the spraying pressure is 0.2 MPa. The stripping solution composition is 5% potassium hydroxide, 2% monoethanolamine and the remainder is deionized water by weight percentage. After stripping, the circuit board is washed with two stages of physical water to remove the residual stripping residue and alkaline solution on the board surface, and the stripped circuit board is obtained. (8) The circuit board obtained in step (7) is acid-washed and neutralized by spraying with a dilute sulfuric acid solution with a sulfuric acid weight percentage of 1% for 30s; then it is washed with pure water for three stages, and finally dried completely in a hot air drying system at 100℃ to obtain the finished circuit board.

[0039] Example 2:

[0040] This embodiment provides a vacuum acid etching process for circuit boards, including the following steps: (1) The commercially available FR-4 type double-sided copper-clad board was immersed in degreasing solution for degreasing treatment. The treatment temperature was controlled at 58℃ and the treatment time was 3.5min. The degreasing solution composition was 3.5% sodium hydroxide, 4.5% trisodium phosphate, 1.25% fatty alcohol polyoxyethylene ether, and the remainder was deionized water by weight percentage. After washing with 1.5-stage countercurrent water for 1.5min, it entered the micro-etching section for acid pickling and activation. The temperature was controlled at 32℃ and the time was 67s. The micro-etching solution composition was 11.5% sodium persulfate, 2% sulfuric acid, 0.03% phosphoric acid, and the remainder was deionized water by weight percentage. After activation, it was washed with pure water and entered the drying section. The surface moisture was dried under hot air at 110℃ to obtain the pretreated circuit board. (2) A 38μm thick photosensitive dry film is laminated onto the clean copper foil surface of the circuit board obtained in step (1). The roller temperature of the laminator is controlled at 110℃, the pressure is set at 0.4MPa, and the conveying speed is set at 2.2m / min. After lamination, the circuit film is precisely aligned with the circuit board, and after vacuuming to -80kPa and pressing tightly, it is exposed using an ultraviolet light source with an exposure energy controlled at 70mJ / cm. 2 After exposure, the circuit board is left to stand for 22 minutes to obtain the circuit board with completed pattern transfer. (3) The circuit board obtained in step (2) is horizontally conveyed into the developing machine for developing. The temperature of the developing solution is 31°C, the spray pressure is 0.20 MPa, the conveying speed is 2.2 m / min, and the developing solution composition is 1.15% anhydrous sodium carbonate, 0.07% polydimethylsiloxane, and the remainder is deionized water by weight percentage. After developing, the board is physically blocked and cleaned by three-stage countercurrent water washing and one-stage overflow water washing to remove residual developing solution from the board surface and obtain the developed circuit board. (4) The circuit board obtained in step (3) is smoothly conveyed by horizontal rollers into the fully enclosed etching chamber and subjected to high-pressure spraying of acidic etching solution from above and below. The acidic etching solution consists of copper chloride dihydrate with a concentration of 350 g / L, hydrochloric acid with a concentration of 2.0 mol / L, sodium chloride with a concentration of 45 g / L, and polyethylene glycol with a concentration of 3 g / L, with the remainder being deionized water. The etching process parameters are maintained at a liquid temperature of 50°C, a spraying pressure of 0.27 MPa, and an online controller to maintain the oxidation-reduction potential at 530 mV. Simultaneous micro-negative pressure vortex control and in-situ reflux are performed. Specifically, the top of the etching chamber is evacuated to maintain the chamber pressure at a dynamic micro-negative pressure of -5.5 kPa. At the same time, oxygen-enriched air with an oxygen volume fraction of 32% is blown upwards at an angle from the air array below the horizontal roller at a flow rate of 30 L / min·m. The oxygen-enriched air at the bottom and the micro-negative pressure at the top form a directional gas-liquid micro-vortex. The mixed acid mist gas discharged from the top is introduced into the gas-liquid condensation and separation device, and the condenser tube temperature is maintained at 10°C. The condensed acidic mixed gas enters the chloride ion capture liquid prepared in Preparation Example 2 for enrichment and absorption and circulation. The concentration change of the capture liquid is monitored in real time using an online concentration meter. When the equivalent hydrochloric acid concentration of the hydrogen chloride absorbed by the capture liquid reaches the set threshold (set to 5 mol / L in this embodiment), the infusion pump is turned on by the control system and pumped into the etching main tank as a replenishing liquid to complete the micro-negative pressure vortex acid etching and in-situ reflux, and the etched circuit board is obtained. (5) The circuit board obtained in step (4) is conveyed into the primary water washing section. During the horizontal movement of the circuit board at a speed of 2.2 m / min, a spatial alternating jet negative pressure suction initial washing is performed. The environment of the primary washing section is normal pressure. Deionized water at a temperature of 25°C is sprayed onto the circuit board through a high-pressure water spray pipe at a pressure of 0.25 MPa. After cleaning, the board surface is then closely attached to the micro-negative pressure suction slit. The distance between the slit and the board surface is set to 1.0 mm. The instantaneous negative pressure at the slit opening is -30 kPa, thereby forming a physical displacement effect of water injection and forced vacuuming and water injection in physical displacement, and obtaining the circuit board after primary washing. (6) The circuit board obtained in step (5) is further subjected to two-stage overflow water washing for physical isolation, and then pure water is used for closed-loop spray circulation cleaning; after cleaning, it is passed through an air knife array, and the excess water on the surface and in the micropores is removed and dried by high-pressure airflow to obtain a dehydrated circuit board. (7) The circuit board obtained in step (6) is transferred into the stripping tank and soaked in a combination of high-pressure physical spray to peel off the cured dry film on the board surface. The temperature of the stripping solution is 60°C and the spraying pressure is 0.25 MPa. The stripping solution composition is 7.5% potassium hydroxide, 3.5% monoethanolamine and the remainder is deionized water by weight percentage. After stripping, the circuit board is washed with two stages of physical water to remove the residual stripping residue and alkaline solution on the board surface, and the stripped circuit board is obtained. (8) The circuit board obtained in step (7) is acid-washed and neutralized by spraying with a dilute sulfuric acid solution with a sulfuric acid weight percentage of 2% for 45s; then it is washed with three stages of pure water and finally dried completely in a hot air drying system at 110℃ to obtain the finished circuit board.

[0041] Example 3:

[0042] This embodiment provides a vacuum acid etching process for circuit boards, including the following steps: (1) The commercially available FR-4 double-sided copper-clad laminate was immersed in a degreasing solution for degreasing treatment. The treatment temperature was controlled at 65℃ and the treatment time was 5min. The degreasing solution composition was 5% sodium hydroxide, 6% trisodium phosphate, 2% fatty alcohol polyoxyethylene ether, and the remainder was deionized water by weight percentage. After rinsing with countercurrent water for 2min, it was put into the micro-etching section for acid pickling and activation. The temperature was controlled at 40℃ and the time was 90s. The micro-etching solution composition was 15% sodium persulfate, 3% sulfuric acid, 0.05% phosphoric acid, and the remainder was deionized water by weight percentage. After activation, it was rinsed with pure water and put into the drying section. The surface moisture was dried under hot air at 120℃ to obtain the pretreated circuit board. (2) A 38μm thick photosensitive dry film is laminated onto the clean copper foil surface of the circuit board obtained in step (1). The roller temperature of the laminator is controlled at 120℃, the pressure is set at 0.5MPa, and the conveying speed is set at 3.0m / min. After lamination, the circuit film is precisely aligned with the circuit board, and after vacuuming to -90kPa and pressing tightly, it is exposed using an ultraviolet light source with an exposure energy controlled at 100mJ / cm. 2 After exposure, let it stand for 30 minutes to obtain a circuit board with completed pattern transfer; (3) The circuit board obtained in step (2) is horizontally conveyed into the developing machine for developing. The temperature of the developing solution is 35℃, the spray pressure is 0.25MPa, the conveying speed is 3.0m / min, and the developing solution composition is 1.5% anhydrous sodium carbonate, 0.1% polydimethylsiloxane, and the remainder is deionized water by weight percentage. After developing, the board is physically blocked and cleaned by three-stage countercurrent water washing and one-stage overflow water washing to remove residual developing solution from the board surface and obtain the developed circuit board. (4) The circuit board obtained in step (3) is smoothly conveyed by horizontal rollers into the fully enclosed etching chamber and subjected to high-pressure spraying of acidic etching solution from the top and bottom. The acidic etching solution consists of copper chloride dihydrate with a concentration of 400 g / L, hydrochloric acid with a concentration of 2.5 mol / L, sodium chloride with a concentration of 60 g / L, and polyethylene glycol with a concentration of 5 g / L, with the remainder being deionized water. The etching process parameters are maintained at a liquid temperature of 55°C, a spraying pressure of 0.35 MPa, and an online controller to maintain the oxidation-reduction potential at 560 mV. Simultaneous micro-negative pressure vortex control and in-situ reflux are performed. Specifically, the top of the etching chamber is evacuated to maintain the chamber pressure at a dynamic micro-negative pressure of -10 kPa. At the same time, oxygen-enriched air with an oxygen volume fraction of 40% is blown upwards at an angle from the air array below the horizontal roller at a flow rate of 50 L / min·m. The oxygen-enriched air at the bottom and the micro-negative pressure at the top form a directional gas-liquid micro-vortex. The mixed acid mist gas discharged from the top is introduced into the gas-liquid condensation and separation device, and the condenser tube temperature is maintained at 15°C. The condensed acidic mixed gas enters the chloride ion capture liquid prepared in Preparation Example 3 for enrichment, absorption and circulation. The concentration change of the capture liquid is monitored in real time using an online concentration meter. When the equivalent hydrochloric acid concentration of the hydrogen chloride absorbed by the capture liquid reaches the set threshold (set to 6 mol / L in this embodiment), the infusion pump is turned on by the control system and pumped into the etching main tank as a replenishing liquid to complete the micro-negative pressure vortex acid etching and in-situ reflux, and the etched circuit board is obtained. (5) The circuit board obtained in step (4) is conveyed into the primary water washing section. During the horizontal movement of the circuit board at a speed of 3.0 m / min, a spatial alternating jet negative pressure suction initial washing is performed. The environment of the primary washing section is normal pressure. Deionized water at a temperature of 30℃ is sprayed onto the circuit board through a high-pressure water spray pipe at a pressure of 0.3 MPa. After cleaning, the board surface is then closely attached to the micro-negative pressure suction slit. The distance between the slit and the board surface is set to 1.5 mm. The instantaneous negative pressure at the slit opening is -40 kPa, thereby forming a physical displacement effect of water injection and forced vacuuming and water injection in physical displacement, and obtaining the circuit board after primary washing. (6) The circuit board obtained in step (5) is further subjected to three-stage overflow water washing for physical isolation, and then pure water is used for closed-loop spray circulation cleaning; after cleaning, it is passed through an air knife array, and the excess water on the surface and in the micropores is removed and dried by high-pressure airflow to obtain the dehydrated circuit board. (7) The circuit board obtained in step (6) is transferred into the stripping tank and soaked in a combination of high-pressure physical spray to peel off the cured dry film on the board surface. The temperature of the stripping solution is 70°C and the spraying pressure is 0.3 MPa. The stripping solution composition is 10% potassium hydroxide, 5% monoethanolamine and the remainder is deionized water by weight percentage. After stripping, the circuit board is washed with two stages of physical water to remove the residual stripping residue and alkaline solution on the board surface, and the stripped circuit board is obtained. (8) The circuit board obtained in step (7) is acid-washed and neutralized by spraying with a dilute sulfuric acid solution with a sulfuric acid weight percentage of 3% for 60s; then it is washed with pure water for three stages and finally dried completely in a hot air drying system at 120℃ to obtain the finished circuit board.

[0043] Comparative Examples 1-5: Comparative Example 1: Compared with Example 2, the difference is that in step (4), the oxygen-enriched air blowing operation of the air array below the bottom horizontal roller is turned off, and only the top of the etching chamber is kept evacuated. The rest are the same.

[0044] Comparative Example 2: Compared with Example 2, the difference is that in step (4), the top air extraction operation of the etching chamber is turned off to maintain the normal pressure environment inside the etching chamber; otherwise, they are the same.

[0045] Comparative Example 3: Compared with Example 2, the difference is that in step (4), the gas-liquid condensation separation device and the chloride ion capture liquid enrichment and circulation reflux system are removed, and the mixed acid mist gas extracted from the top of the etching chamber is directly connected to the plant waste gas treatment system for discharge. The rest are the same.

[0046] Comparative Example 4: Compared with Example 2, the difference is that in the primary water washing section of step (5), the forced evacuation operation of the micro-negative pressure suction slit is cancelled, and only the high-pressure jet cleaning of deionized water under normal pressure is retained, while the rest are the same.

[0047] Comparative Example 5: Compared with Example 2, the difference is that in step (4), the chloride ion capturing liquid obtained by Preparation Example 2 that is received by the gas-liquid condensation and separation device is replaced with an equal mass of pure deionized water for the enrichment and circulation of the mixed gas. All other steps are the same.

[0048] Test Examples 1-4: Test Example 1: This test case aims to verify the chemical mechanism and feasibility of the chloride ion capturing liquid of the present invention for in-situ absorption of volatile acid mist.

[0049] Experimental steps: Freshly prepared chloride ion capturing solution and the capturing solution during process operation were selected as test objects. Specifically, 50 mL of the fresh capturing solution obtained in Preparation Example 2 was extracted as a blank reference sample; during the etching process operation of Examples 1, 2 and 3, when the online monitoring system determined that the capturing solution had reached the reflux set point, 50 mL of the circulated capturing solution was extracted from the enrichment tank below the gas-liquid condensation separation device as the absorbed sample.

[0050] The structure of the above samples was characterized using Fourier transform infrared spectroscopy. Before testing, an appropriate amount of sample was uniformly coated onto a potassium bromide pellet and vacuum dried to remove moisture interference. The spectrometer scanning range was set to 4000 cm⁻¹. -1 Up to 400cm -1 The resolution is 4cm. -1 The infrared transmission spectra of fresh and absorbed samples were collected 32 times.

[0051] The total acidity of the above samples was quantitatively determined using an automatic potentiometric titrator. 5.00 mL of the sample was placed in a titration vessel, diluted with 50 mL of deionized water, and titrated using a 1.02 mol / L standard sodium hydroxide solution as the titrant. The initial pH value was recorded, and the equivalent hydrochloric acid concentration in the capturing solution was calculated based on the volume of titrant consumed at the potential jump point of the titration curve.

[0052] Table 1. Acid-base titration test data before and after chloride ion capturing solution absorption. Note: Table 1 shows the titrant consumption volume of the fresh capture solution in Example 2, which represents the blank consumption measured by the instrument. Since the fresh capture solution is strongly alkaline and there is no free acid in the system, this small consumption is background consumption introduced by the deionized water solvent and carbon dioxide from the air; its corresponding equivalent hydrochloric acid concentration can be considered zero. Furthermore, the acid in the captured solution after circulation exists in the bound state of diethylenetriamine hydrochloride; the values ​​in the table are equivalent hydrochloric acid concentrations calculated proportionally from the total acidity titrated.

[0053] in conclusion: Based on the data in Table 1 and the appendix Figure 1 The polyamine chloride ion capturing solution exhibits structural differences before and after absorbing acid mist in a micro-negative pressure vortex system. Figure 1 As can be seen from the infrared spectrum, the fresh capture solution at 3300 cm⁻¹ -1 Up to 3400cm -1 The region contains absorption peaks for the NH stretching vibrations of primary and secondary amines. After cycling through the absorption of volatile acid mist, the intensity of the characteristic peak in this region decreases, down to 2500 cm⁻¹. -1 Up to 3000cm -1 A relatively wide absorption band appears within the range, at 1510 cm⁻¹. -1 A deformation vibration peak was generated nearby. This spectral change is consistent with the structural characteristics of aliphatic amines protonated to form ammonium salts, indicating that hydrogen chloride gas binds to the amino site of diethylenetriamine.

[0054] Based on the titration data in Table 1, the fresh capture solution was initially alkaline, and the equivalent hydrochloric acid concentration approached zero after deducting the blank consumption. After micro-negative pressure operation in Examples 1 to 3, the capture solution became acidic, with equivalent hydrochloric acid concentrations reaching 4.07 mol / L, 5.04 mol / L, and 6.12 mol / L, respectively, meeting the replenishment standards set for each example.

[0055] Test results show that the gas-liquid condensation device combined with polyamine capture liquid can absorb and enrich the volatile acidic substances in the system. The concentration index of the captured liquid after absorption meets the process requirements for reinjection into the main tank as an acidic replenishment liquid.

[0056] Test Example 2: This test case aims to verify the effect of the micro-negative pressure eddy current system on eliminating plate surface liquid and gas-liquid mass transfer.

[0057] Experimental steps: The micro-negative pressure eddy current etching conditions of Example 2 were selected as the test group, while the conventional spraying conditions with micro-negative pressure extraction and bottom blowing turned off were set as the control group. The test object was a standard FR-4 double-sided copper-clad laminate sample with a size of 500mm×500mm and an initial copper foil thickness of 35μm.

[0058] Under the two conditions described above, unidirectional fixed-point etching was performed on the copper-clad laminate samples, with the etching time uniformly set to 60 seconds. During the sample's journey, a miniature optical dissolved oxygen probe fixed inside the main etching chamber at a distance of 3 mm from the sample's surface was used to monitor and record the changes in dissolved oxygen (DO) concentration in the reaction liquid film above the board surface over time.

[0059] After etching, the sample was cleaned and dried according to standard procedures. Eleven test points were set at equal intervals from the left edge (0 mm) to the right edge (500 mm) along the transverse centerline perpendicular to the sample's travel direction. The residual copper thickness at each point after the reaction was measured using an X-ray fluorescence thickness gauge, and the actual etching rate of each transverse test point was calculated.

[0060] Table 2. Etching rate test data at various test points in the transverse direction of the copper clad laminate in conclusion: Based on the data in Table 2 and the appendix Figure 2 The use of micro-negative pressure and bottom-blowing airflow altered the fluid state within the etching chamber. Figure 2 As shown in the etching rate distribution curve of (a), under conventional spraying conditions, the etching rate of the control group exhibits a U-shaped distribution along the transverse direction of the board surface, with higher rates at the edges. The rate at the center of the board surface, located at 250 mm, is 16.53 μm / min, indicating that the reaction solution accumulates in the center of the board surface. Under micro-negative pressure eddy current conditions, the etching rates of the test group at various transverse measurement points range from 33.87 μm / min to 35.21 μm / min, with a relatively flat distribution curve and no decrease in rate in the central region.

[0061] The differences in etching uniformity mentioned above reflect variations in the mass transfer resistance of the liquid film. Under normal operating conditions, accumulated waste liquid hinders the contact between the etching solution and the copper surface, resulting in limited reaction in the central region. The gas-liquid vortex generated by micro-negative pressure suction and oblique bottom blowing provides physical shear force to the liquid film on the board surface, which helps to remove the retained reaction products and promotes the contact between fresh etching solution and the copper surface.

[0062] Combination Figure 2(b) shows the dissolved oxygen data. In the control group, the dissolved oxygen concentration in the liquid film was around 2 mg / L. In the test group, after introducing oxygen-enriched air and using a negative pressure vortex, the dissolved oxygen concentration in the liquid film increased to the 8 mg / L range. The increased dissolved oxygen concentration in the system can promote the regeneration and conversion of monovalent cuprous ions to divalent cuprous ions, reduce the adhesion of cuprous chloride on the board surface, and thus improve the overall etching rate and uniformity.

[0063] Test Example 3: This test case aims to compare the effects of different gas phase collection and reflux conditions on the stability of the chemical system in a continuous vacuum etching process.

[0064] Experimental steps: The etching systems described in Examples 2, 3, and 5 were selected as test subjects. Under simulated continuous industrial production conditions, the etching chamber operation programs of each group of equipment were started, and copper-clad laminates were continuously loaded for etching operations. To eliminate interference from the external replenishment system, the automatic acid replenishment program of each group of etching tanks was turned off during the test. The total test cycle was set to 24 hours, with the time when the system started up, reached the set parameters, and the first test board was loaded recorded as hour 0.

[0065] During the 24-hour continuous etching operation, the etching solution in the main tank was sampled at fixed points every 4 hours. Each time, 50 mL of the well-mixed etching solution from the main tank was extracted, and the sample to be tested was placed in a sealed sampling bottle and cooled to room temperature (25°C) before testing.

[0066] The concentration of free hydrochloric acid in the samples at each time point was determined using an automatic potentiometric titrator. During the titration process, the samples were diluted with deionized water and a standard sodium hydroxide solution was used as the titrant. Simultaneously, a portable redox potentiometer equipped with a platinum ring test electrode and a silver / silver chloride reference electrode was inserted into the sampling port of the main tank to measure the redox potential (ORP) values ​​of the system at each time point in real time.

[0067] Table 3. Test data on the variation of chemical parameters in the main tank during continuous production. in conclusion: Based on the data in Table 3 and the appendix Figure 3 Different recycling compensation conditions affect the parameter stability of the etching system. Figure 3 (a) and Figure 3 (b) The data shows that during the 24-hour test period in Example 2, the concentration of free hydrochloric acid in the main tank was between 1.94 mol / L and 2.06 mol / L, and the redox potential was between 527 mV and 535 mV. No significant downward trend was observed in the parameters.

[0068] In Comparative Example 3, due to the lack of a reflux compensation mechanism, the hydrochloric acid concentration in the main tank decreased from 1.98 mol / L to 0.79 mol / L after 24 hours. With the decrease in hydrochloric acid concentration, the redox potential decreased from 528 mV to 392 mV, deviating from the parameter range of conventional etching solutions. The test results show that the volatilization of hydrogen chloride gas increases under a slightly negative pressure environment, and equipping the main tank with a reflux compensation device helps maintain the balance of acidic components.

[0069] Comparative Example 5 used deionized water as the capture medium. Its free hydrochloric acid concentration and redox potential decreased less than those of Comparative Example 3, but the parameters began to decrease after 12 hours, and the hydrochloric acid concentration dropped to 1.08 mol / L after 24 hours. Due to the limited physical solubility of hydrogen chloride gas in water, the absorption efficiency was limited under continuous exhaust conditions. Example 2 used a polyamine-based capture solution to capture hydrogen chloride through chemical action, maintaining the absorption effect during the cyclic enrichment stage and achieving acid replenishment of the main tank etching solution.

[0070] Test Example 4: This test case aims to compare the effectiveness of different initial cleaning processes in removing residual etching solution in the microscopic dead corners of the printed circuit board surface.

[0071] Experimental steps: Printed circuit boards that have completed the initial cleaning step were selected as test objects, specifically samples prepared in Examples 1, 2, 3, and Comparative Example 4 (using conventional pure spray cleaning). The surfaces of these test samples all contain dense blind vias and fine-pitch circuitry. Test blocks measuring 100mm × 100mm were cut from each group of boards.

[0072] Each test block was placed in a clean beaker containing 500 mL of ultrapure water and then immersed in a high-frequency ultrasonic cleaning tank for ultrasonic extraction. The ultrasonic frequency was set to 40 kHz and the extraction time was set to 30 minutes to dissolve the residual chemicals in the micro-grooves and blind pores in the ultrapure water.

[0073] The extract was extracted, filtered through a 0.22 μm microporous membrane, and then injected into an ion chromatograph (IC) for detection. Chloride chromatograms of each sample were recorded, and the residual chloride ion concentration in the extract of each sample was calculated based on the integrated area of ​​the chloride ion peaks.

[0074] Table 4. Test data on residual chloride ion concentration in the extract. in conclusion: Based on the data in Table 4 and the appendix Figure 4Different initial washing processes affect the removal efficiency of residual etching solution within micropores. Table 4 shows that the sample initially washed using conventional pure spraying (Comparative Example 4) had a residual chloride ion concentration of 35.87 mg / L in its extract, corresponding to... Figure 4 (a) shows the conductivity response peak at a retention time of 4.19 min. The residual chloride ion concentration in the extracts of the samples from Examples 1 to 3 ranged from 0.08 mg / L to 0.15 mg / L. Figure 4 (b) No significant signal jumps were observed during the retention period, and the residual chloride ion content was low.

[0075] Conventional spray cleaning relies primarily on water flow energy for surface rinsing. However, in micro-grooves and blind holes, external cleaning fluid cannot easily penetrate to the bottom of the blind holes due to factors such as liquid surface tension and air resistance. This makes it difficult to completely replace the acidic etching solution retained inside the pores, resulting in a high chloride ion content in the sample's extract. These residual conditions can easily lead to subsequent excessive lateral etching (i.e., post-etching).

[0076] The embodiment employs a spatial alternating jet negative pressure suction process, which alternately applies cleaning fluid jets and negative pressure suction to localized areas of the board surface. The negative pressure suction helps overcome fluid resistance within the pores, extracting the retained etching solution, and then physically displacing it with water flow. Test data shows that this process can reduce the residual acidic components within complex microstructures, thereby reducing the risk of post-etching caused by etching solution residue after removal from the main tank.

Claims

1. A vacuum acid etching process for circuit boards, characterized in that, Includes the following steps: The double-sided copper-clad board is degreased and activated by micro-etching and acid washing, and the surface moisture is dried to obtain the pre-treated circuit board. A photosensitive dry film is pressed onto the surface of the pre-treated circuit board, and after exposure treatment, a circuit board with completed pattern transfer is obtained. The circuit board with the completed pattern transfer is subjected to a developing process to clean the residual developing solution from the board surface, resulting in a developed circuit board. The developed circuit board is conveyed into a fully enclosed etching chamber, where it is sprayed with acidic etching solution. Simultaneously, the top of the etching chamber is evacuated to create a dynamic micro-negative pressure, and oxygen-rich air is blown in from the bottom upwards. The oxygen-rich airflow at the bottom and the micro-negative pressure at the top form a directional gas-liquid micro-vortex. The mixed acid mist gas discharged from the top is introduced into a gas-liquid condensation and separation device, where it is enriched and absorbed using a chloride ion capture solution. When the equivalent hydrochloric acid concentration of hydrogen chloride absorbed by the chloride ion capture solution reaches a set threshold, it is pumped into the main etching tank as a replenishing solution, resulting in the etched circuit board. The etched circuit board is conveyed into the primary water washing section and subjected to a spatial alternating jet negative pressure suction primary washing to obtain the primary washed circuit board. The circuit board after initial washing is washed with water and dried. It is then transferred to a stripping tank to peel off the cured dry film. After acid washing and neutralization, it is finally washed and dried to obtain the finished circuit board.

2. The circuit board vacuum acid etching process according to claim 1, characterized in that, The chloride ion capturing solution contains the following components by weight percentage: Diethylenetriamine 5%–10%, with the balance being deionized water, and the sum of the weight percentages of all components being 100%.

3. The circuit board vacuum acid etching process according to claim 2, characterized in that, The preparation method of the chloride ion capturing solution includes the following steps: Weigh out diethylenetriamine and deionized water separately for later use; The weighed deionized water was added to a mixing vessel equipped with a stirring device and a cooling jacket. Stirring was started, and the weighed diethylenetriamine was slowly added dropwise while stirring was in progress to obtain a mixed system. During the dropwise addition process, the cooling water flow rate of the cooling jacket of the mixing vessel is controlled to keep the temperature of the mixture below 40°C. After the diethylenetriamine has been completely added, the mixture is stirred for another 30 minutes to obtain a mixed solution. The mixture was naturally cooled to 25°C to obtain the chloride ion capturing solution.

4. The circuit board vacuum acid etching process according to claim 3, characterized in that, The acidic etching solution is prepared according to the following concentrations of components: The following are the ingredients: copper chloride dihydrate with a concentration of 300 g / L to 400 g / L, hydrochloric acid with a concentration of 1.5 mol / L to 2.5 mol / L, sodium chloride with a concentration of 30 g / L to 60 g / L, and polyethylene glycol with a concentration of 1 g / L to 5 g / L, with deionized water as the solvent. During the acid etching solution spraying operation, the temperature of the acid etching solution is 45℃~55℃, the spraying pressure is 0.2MPa~0.35MPa, and the oxidation-reduction potential is maintained in the range of 500mV~560mV using an online controller.

5. The circuit board vacuum acid etching process according to claim 1, characterized in that, The cabin air pressure of the dynamic micro-negative pressure is maintained at -1kPa to -10kPa; The oxygen volume fraction in the oxygen-enriched air is 25% to 40%, and the air flow rate is 10 L / (min·m) to 50 L / (min·m). The temperature of the condenser tube of the gas-liquid condensation separation device is maintained at 5℃~15℃; The threshold value for the equivalent hydrochloric acid concentration is set at 4 mol / L to 6 mol / L.

6. The circuit board vacuum acid etching process according to claim 1, characterized in that, When performing the spatial alternating jet negative pressure suction initial cleaning, deionized water is sprayed onto the etched circuit board. The cleaned board surface then closely adheres to the micro-negative pressure suction slit, forming a physical displacement effect of water injection and forced vacuuming and re-injection in physical displacement. The temperature of the deionized water is 20℃~30℃, and the injection pressure is 0.2MPa~0.3MPa; The distance between the micro-negative pressure suction slit and the plate surface is set to 0.5mm to 1.5mm, and the instantaneous negative pressure at the slit opening is -20kPa to -40kPa.

7. The circuit board vacuum acid etching process according to claim 1, characterized in that, During the degreasing treatment, the degreasing temperature is 50℃~65℃, and the degreasing liquid composition used contains the following components by weight percentage: Sodium hydroxide 2%–5%, trisodium phosphate 3%–6%, fatty alcohol polyoxyethylene ether 0.5%–2%, with the balance being deionized water, and the sum of the weight percentages of all components being 100%; During the micro-etching and acid-washing activation process, the activation temperature is 25°C to 40°C, and the micro-etching solution composition used contains the following components by weight percentage: Sodium persulfate 8%–15%, sulfuric acid 1%–3%, phosphoric acid 0.01%–0.05%, with the balance being deionized water, and the sum of the weight percentages of each component is 100%.

8. The circuit board vacuum acid etching process according to claim 1, characterized in that, After the photosensitive dry film is pressed onto the surface of the pretreated circuit board, it is vacuum-pressed and then exposed with an ultraviolet light source. The temperature of the roller of the laminating machine is controlled at 100℃~120℃, and the pressure is set at 0.3MPa~0.5MPa. The vacuum level for vacuum compression bonding is set to -70kPa to -90kPa, and the ultraviolet light source exposure energy is controlled at 40mJ / cm². 2 ~100mJ / cm 2 ; During the development process, the developer temperature is 28°C to 35°C, and the spray pressure is 0.15 MPa to 0.25 MPa. The developer composition used contains the following components by weight percentage: The components are 0.8%–1.5% anhydrous sodium carbonate, 0.05%–0.1% polydimethylsiloxane, and the balance is deionized water, with the sum of the weight percentages of each component being 100%.

9. The circuit board vacuum acid etching process according to claim 1, characterized in that, The peeling and curing of the dry film is performed using a combination of immersion and high-pressure physical spraying. The temperature of the peeling solution is 50℃~70℃, and the spraying pressure is 0.2MPa~0.3MPa. The peeling solution composition used contains the following components by weight percentage: Potassium hydroxide 5%–10%, monoethanolamine 2%–5%, and the balance is deionized water, and the sum of the weight percentages of each component is 100%.

10. The circuit board vacuum acid etching process according to claim 1, characterized in that, The acid pickling and neutralization process uses a dilute sulfuric acid solution with a sulfuric acid weight percentage of 1% to 3%, and the final washing and drying operation uses a hot air drying system to completely dry the product at a temperature of 100℃ to 120℃.

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