Process for multi-element chemical plating of flexible circuit boards of aluminum foil material

Abstract

This invention relates to the field of flexible circuit board manufacturing technology using aluminum foil materials, specifically to a multi-faceted electrochemical plating process for flexible circuit boards using aluminum foil materials, comprising the following process steps: Step S1, surface treatment: scanning the texture of the flexible circuit board, and imprinting the texture on the substrate using printing technology. The specific process is as follows: using a computer vision camera to scan the existing texture of the flexible circuit board to generate 3D model data; this invention can imprint groove textures on the substrate through printing. The groove structure increases the contact area between the plating layer and the substrate by 40%-60%, and the peel strength of the plating layer is increased from 12-15MPa in the traditional process to 18-22MPa. Furthermore, the groove guides the flow of the electroplating solution, reducing the plating thickness fluctuation from ±5μm to ±1.5μm, and the porosity from 8% to ≤2%.

Description

Technical Field

[0001] This invention relates to the field of aluminum foil flexible circuit board manufacturing technology, specifically to a multi-faceted chemical plating process for aluminum foil flexible circuit boards. Background Technology

[0002] Using aluminum substrate instead of copper substrate as the conductive substrate for circuit boards can significantly reduce costs and make the production process more environmentally friendly, thus finding applications in many fields. However, aluminum substrate circuit boards cannot be soldered to other electronic components using ordinary solder paste because the oxide film formed by the oxidation of aluminum substrate in the air is solder-resistant. Therefore, it is generally necessary to plate an anti-oxidation and easy-to-solder metal substrate on the aluminum surface to ensure the bonding of other electronic components.

[0003] The working principle of flexible circuit boards made of aluminum foil is to use insulating material to isolate the conductive layer of the surface aluminum foil, allowing current to flow along a pre-set path through the various components to perform functions such as work, amplification, attenuation, modulation, demodulation, and encoding. Flexible circuit boards made of aluminum foil are composed of multiple layers of aluminum plates and insulating plates, and can only be made easy to solder using chemical plating.

[0004] To optimize the electroless nickel plating process for flexible circuit boards made of aluminum foil, existing technologies employ techniques such as printing to address the aforementioned issues. However, the specific details of traditional circuit board printing techniques are as follows: Screen printing (applicable substrates: rigid / flexible substrates) Screen printing is the most traditional technique, which uses a screen stencil to press ink onto a substrate to form circuit patterns. The specific process includes steps such as screen stretching and screen exposure. It requires advance preparation of the stencil and control of tension. It is suitable for mass production and has a low cost, but the accuracy of complex patterns is limited.

[0005] Direct imaging printing method (applicable substrates: photosensitive substrates) Direct imaging printing uses photosensitive materials and photolithography to directly image onto a substrate, eliminating the need for a physical template. Precision circuits are formed through ultraviolet (UV) exposure, achieving micron-level accuracy, making it suitable for high-density integrated circuit board manufacturing. However, it places high demands on the substrate material.

[0006] Electron beam printing (applicable substrates: special substrates) Electron beam printing uses an electron beam to etch patterns on the surface of a substrate. It is a high-precision technology suitable for micro-components or ultra-fine lines, but the equipment cost is relatively high.

[0007] Graphic transfer printing method (applicable substrate: multilayer board substrate) The graphic transfer printing method first prints the pattern onto transfer paper, and then transfers it to a substrate through heat or pressure. It is suitable for complex patterns and multilayer circuit boards, but it has high requirements for material compatibility.

[0008] For example, CN110453205A, published on November 15, 2019, describes a chemical nickel plating process for an aluminum foil circuit board. The process includes the following steps: Step 1, alkaline etching; Step 2, two-stage water washing; Step 3, catalyst catalysis; Step 4, two-stage water washing; Step 5, chemical nickel plating; Step 6, two-stage water washing; Step 7, sealing with a sealing agent; Step 8, two-stage water washing; Step 9, drying. Although this patented technology achieves chemical nickel plating through a 9-step process, the single nickel layer structure results in a conductivity of only 5.8 × 10⁻⁶. 6 S / m, much lower than the 5.96×10 of copper. 7 The nickel layer thickness needs to reach 15-20μm to meet the welding requirements, which results in a waste of precious metal resources. The phosphorus-containing chemical nickel reagent used poses a risk of heavy metal pollution and does not comply with RoHS environmental standards.

[0009] For example, CN116634696A, published on August 22, 2023, describes the production of flexible circuit boards using aluminum foil with partitioned nickel plating. The chemical nickel plating process includes the following steps: S71, Degreasing: Using a release agent solution to remove organic contaminants from the pads and initially remove oxides; S72, Water washing: Removing residual release agent; S73, Descaling: Using a descaling agent solution to remove residual oxide film from the aluminum foil surface at the pads, forming a micro-etched surface; S74, Water washing: Removing residual descaling agent solution; S75, Zinc immersion: Using a zinc immersion agent to immerse zinc at the pads; S76, Water washing: Water washing to remove residual zinc immersion agent; S77, Nickel plating: Using a nickel plating agent solution to plate nickel at the pads; S78, Water washing: Water washing to remove residual zinc immersion agent; S79, Drying: Drying the washed product. While this patented technology uses partitioned nickel plating to improve precision, it does not address the defects in substrate pretreatment. (1) After zinc plating, the porosity of the zinc layer is >8%, which leads to a 30% decrease in the adhesion of the coating; (2) The residual oxide film at the solder pad position reduces the solder bond strength to only 12-15 MPa; (3) No reagent recovery system was set up, and the amount of plating solution carried out reached 15-20 mL / m².

[0010] It is evident that the existing chemical nickel plating process for flexible circuit boards made of aluminum foil has drawbacks: low conductivity, poor solder adhesion, excessively thick nickel plating layer, wasteful costs, and environmentally unfriendly chemicals.

[0011] Therefore, there is an urgent need to design a diversified chemical plating process for flexible circuit boards made of aluminum foil to solve the above problems. Summary of the Invention

[0012] The purpose of this invention is to provide a multi-faceted chemical plating process for flexible circuit boards made of aluminum foil, so as to overcome the above-mentioned shortcomings in the prior art.

[0013] To achieve the above objectives, the present invention provides the following technical solution: A multi-faceted chemical plating process for flexible circuit boards made of aluminum foil includes the following steps: Step S1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture to generate 3D model data. Customize a high-precision steel printing mold based on the scan data. This process involves laser engraving of the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Heat the aluminum foil substrate to 120-150℃ to soften it, specifically preheating it to 150℃ for 3 minutes to soften it; (3) The mold is pressed by a hydraulic press at a pressure of 50-80MPa to form a groove pattern with a depth of 8-12μm. The pressing process parameters are set as follows: pressure 70MPa, holding time 90 seconds, cooling rate 10℃ / min, and the mold is demolded after being water-cooled to 50℃ after pressing by the hydraulic press. (4) Composite cleaning to optimize groove texture; The residue and oxide layer on the substrate surface are then removed by chemical methods, and the residual chemicals on the substrate surface are removed by water washing. The specific process is as follows: (a) Acid degreasing and water washing treatment: Prepare an acidic degreasing solution to degrease the substrate. The acidic degreasing solution is: H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, wet the substrate with water at room temperature for 30 seconds. During the wetting process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After wetting, pickle the substrate with the pickling solution to remove imprint residue. After pickling, clean the substrate with water using a three-stage countercurrent water wash at a water flow rate of 5L / min. (b) Alkaline etching and water washing treatment: Prepare an alkaline degreasing solution to degrease the substrate. After degreasing, continuously wet the substrate with a water film. During the wetting process, prepare an alkaline etching solution of sodium hydroxide (80g / L). After wetting, perform alkaline etching treatment on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface to form a 15-20° tilt angle at the edge of the groove, with 18° being the best angle. After alkaline etching, use water washing technology to clean the substrate. (c) Pickling and washing treatment: Prepare a phosphoric acid / sulfuric acid (2:1 ratio) mixed solution (pH 2.5) pickling solution, pickle for 45 seconds, and pickle the substrate with the pickling solution to passivate the substrate surface. The roughness of the bottom of the groove is reduced to Ra≤0.3μm. After pickling, the residue on the substrate is neutralized by weak alkali (Na2CO3 0.5% solution). After neutralization, the substrate is cleaned by water washing technology.

[0014] Step S2, Pre-treatment before nickel plating: The surface-treated substrate is placed in a zinc bath for immersion zinc treatment. The immersion zinc process uses a two-stage immersion zinc technology, and the specific steps are as follows: (1) Single zinc immersion: The surface-treated substrate is placed in a zinc bath and immersed for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc immersion: The substrate is placed in the zinc bath again for 20-30 seconds, focusing on filling the pores of the first zinc immersion. The residual zinc solution on the substrate is then recovered using recycling technology, and the residue on the substrate is then removed by washing with water. The specific steps of the recycling technology during the zinc precipitation process are as follows: (1) Rinse the substrate with clean water to remove the zinc liquid from the substrate; (2) The zinc liquid obtained is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, and then the obtained zinc liquid is reintroduced into the zinc pool.

[0015] Step S3, Nickel Plating: Immerse the pretreated substrate in a nickel plating solution and apply appropriate current and voltage. Nickel ions will deposit on the substrate surface to form a uniform nickel layer. The plating solution formula is as follows: Main salt: 25-35 g / L nickel sulfate or 20-30 g / L soluble nickel salt; reducing agent: 10-15 g / L sodium hypophosphite combined with 1-3 g / L dimethylaminoborane; complexing agent: 20-30 g / L sodium citrate or 0.5-10 g / L ethylenediamine; additives: sulfur-containing compounds. Plating parameters: Temperature: Controlled at 80-90℃, with temperature fluctuations ≤ ±2℃; Time: 10-60 minutes, deposition rate approximately 10-15 μm / h.

[0016] Step S4, Copper Plating Pretreatment: After nickel plating, the residual nickel plating solution on the substrate is recovered using recycling technology. The residue on the substrate is then removed by water washing. After water washing, the substrate undergoes activation treatment to enhance the adhesion of subsequent copper plating. After activation, the substrate is further cleaned using water washing technology. The activation treatment steps are as follows: (1) Alkaline etching cleaning: Use an alkaline solution (pH 10-12) to remove the surface oxide layer and residual oil stains to ensure the substrate is clean; (2) Catalysis: Using a nickel salt activator, nano-sized nickel particles are deposited on the aluminum surface to form a passivation layer to block oxidation and enhance the adhesion of subsequent copper plating; (3) Pre-immersion treatment: neutralize residual alkaline solution with acidic pre-immersion solution (pH 4.5-5.0) to avoid plating solution contamination.

[0017] Step S5, Copper Plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the substrate surface to form a uniform copper layer. The copper plating process consists of two steps, as shown below: (1) Pre-plating copper: Cuprous cyanide (20-30 g / L) is used as the main salt and sodium cyanide (30-50 g / L) as the complexing agent. The current density is 1-2 A / dm² and the time is 2-3 minutes to form a dense transition layer. The concentration of free sodium cyanide is controlled to be ≥5 g / L and the pH is 10-12 to prevent the copper layer from being loose or foaming. (2) Thickened acid-copper plating: Plating solution formulation: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), with the addition of brightener (such as sodium polydisulfide dipropane sulfonate 0.01-0.05g / L), temperature 25-30℃, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra≤0.5μm.

[0018] Step S6, Recycling and subsequent processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the copper plating layer on the substrate is protected. Then, the substrate is washed with water using ultrasonic equipment to remove any residue left after the protective treatment, and then sent to a drying device for drying.

[0019] A multi-electrochemical plating process for flexible circuit boards made of aluminum foil is characterized by comprising the following additional process step, which uses any one of the dependent claims 2-4 and 7-9: Step A1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture to generate 3D model data. Customize a high-precision steel printing mold based on the scan data. This process involves laser engraving of the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Heat the aluminum foil substrate to 120-150℃ to soften it, specifically preheating it to 150℃ for 3 minutes to soften it; (3) The mold is pressed by a hydraulic press at a pressure of 50-80MPa to form a groove pattern with a depth of 8-12μm. The pressing process parameters are set as follows: pressure 70MPa, holding time 90 seconds, cooling rate 10℃ / min, and the mold is demolded after being water-cooled to 50℃ after pressing by the hydraulic press. (4) Composite cleaning to optimize groove texture; The process involves removing residues and oxide layers from the substrate surface using chemical methods, followed by washing with water to remove any remaining chemicals. The specific steps are as follows: (a) Acid degreasing and water washing treatment: Prepare an acidic degreasing solution to degrease the substrate. The acidic degreasing solution is: H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, wet the substrate with water at room temperature for 30 seconds. During the wetting process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After wetting, pickle the substrate with the pickling solution to remove imprint residue. After pickling, clean the substrate with water using a three-stage countercurrent water wash at a water flow rate of 5L / min. (b) Alkaline etching and water washing treatment: Prepare an alkaline degreasing solution to degrease the substrate. After degreasing, continuously wet the substrate with a water film. During the wetting process, prepare an alkaline etching solution of sodium hydroxide (80g / L). After wetting, perform alkaline etching treatment on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface to form a 15-20° tilt angle at the edge of the groove, with 18° being the best angle. After alkaline etching, use water washing technology to clean the substrate. (c) Pickling and washing treatment: Prepare a phosphoric acid / sulfuric acid (2:1 ratio) mixed solution (pH 2.5) pickling solution, pickle for 45 seconds, and pickle the substrate with the pickling solution to passivate the substrate surface. The roughness of the bottom of the groove is reduced to Ra≤0.3μm. After pickling, the residue on the substrate is neutralized by weak alkali (Na2CO3 0.5% solution). After neutralization, the substrate is cleaned by water washing technology.

[0020] Step A2, Pre-treatment before copper plating: The surface-treated substrate is placed in a zinc bath for immersion zinc treatment. The immersion zinc process uses a two-stage immersion zinc technology, and the specific steps are as follows: (1) Single zinc immersion: The surface-treated substrate is placed in a zinc bath and immersed for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc immersion: The substrate is placed in the zinc bath again for 20-30 seconds, focusing on filling the pores of the first zinc immersion. The residual zinc solution on the substrate is then recovered using recycling technology, and the residue on the substrate is then removed by washing with water. The specific steps of the recycling technology during the zinc precipitation process are as follows: (1) Rinse the substrate with clean water to remove the zinc liquid from the substrate; (2) The zinc liquid obtained is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, and then the obtained zinc liquid is reintroduced into the zinc pool.

[0021] Step A3, Copper Plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the substrate surface to form a uniform copper layer. The copper plating process consists of two steps, as shown below: (1) Pre-plating copper: Cuprous cyanide (20-30 g / L) is used as the main salt and sodium cyanide (30-50 g / L) as the complexing agent. The current density is 1-2 A / dm² and the time is 2-3 minutes to form a dense transition layer. The concentration of free sodium cyanide is controlled to be ≥5 g / L and the pH is 10-12 to prevent the copper layer from being loose or foaming. (2) Thickened acid-copper plating: Plating solution formulation: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), with the addition of brightener (such as sodium polydisulfide dipropane sulfonate 0.01-0.05g / L), temperature 25-30℃, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra≤0.5μm.

[0022] Step A4, Recycling and Subsequent Processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the substrate is sent to the drying equipment for drying.

[0023] In another embodiment of the present invention, the water washing is all three-stage water washing, and the three-stage water washing is three-stage counter-current water washing with a water flow rate ≥5L / min·m².

[0024] In the above technical solution, the multi-faceted chemical plating process for flexible circuit boards made of aluminum foil provided by the present invention has the following beneficial effects: (1) The present invention can print grooves on the substrate by printing. The groove structure increases the contact area between the plating layer and the substrate by 40%-60%, and the peel strength of the plating layer is increased from 12-15MPa in the traditional process to 18-22MPa. In addition, the groove guides the flow of the electroplating solution, reducing the plating thickness fluctuation from ±5μm to ±1.5μm, the porosity from 8% to ≤2%, and the product defect rate from 15% to below 3%. It can meet the mass production needs of metal foil and acid and alkali resistant circuit board substrates.

[0025] (2) This invention changes the existing single chemical nickel plating technology to diversified chemical plating, mainly using copper plating to improve the conductivity of flexible circuit boards made of aluminum foil materials, increase the solder bonding force, and save resources by reducing the plating thickness, and changes the phosphorus-containing chemical nickel agent to an environmentally friendly chemical nickel agent.

[0026] (3) By pre-printing the substrate, the present invention can leave groove marks on the substrate, which can improve the bonding strength between the coating and the substrate when the substrate is coated with a multi-electrochemical coating in the subsequent process, thus enhancing the product quality.

[0027] (4) Compared with the original nickel plating process, the present invention can remove excess foreign matter generated in the upstream board manufacturing process of aluminum foil flexible circuit board, making the welding position cleaner and the plating bonding force stronger. At the same time, it can recover the agent brought out by the product surface, reduce the waste of resources, and perform micro-treatment on the product surface, which greatly improves the brightness and aesthetics of the product. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0029] Figure 1 A schematic diagram of the process flow provided for an embodiment of the multi-functional chemical coating process for a flexible circuit board made of aluminum foil material according to the present invention; Figure 2 This is another process flow diagram provided for an embodiment of the multi-electrochemical plating process for flexible circuit boards made of aluminum foil materials according to the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] Example 1: As Figure 1 As shown in the figure, the present invention provides a multi-faceted chemical plating process for flexible circuit boards made of aluminum foil, which includes the following process steps: Step S1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture to generate 3D model data. Customize a high-precision steel printing mold based on the scan data. This process involves laser engraving of the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Heat the aluminum foil substrate to 120-150℃ to soften it, specifically preheating it to 150℃ for 3 minutes to soften it; (3) The mold is pressed by a hydraulic press at a pressure of 50-80MPa to form a groove pattern with a depth of 8-12μm. The pressing process parameters are set as follows: pressure 70MPa, holding time 90 seconds, cooling rate 10℃ / min, and the mold is demolded after being water-cooled to 50℃ after pressing by the hydraulic press. (4) Composite cleaning to optimize groove texture; The residue and oxide layer on the substrate surface are then removed by chemical methods, and the residual chemicals on the substrate surface are removed by water washing. The specific process is as follows: (a) Acid degreasing and water washing treatment: Prepare an acidic degreasing solution to degrease the substrate. The acidic degreasing solution is: H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, wet the substrate with water at room temperature for 30 seconds. During the wetting process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After wetting, pickle the substrate with the pickling solution to remove imprint residue. After pickling, clean the substrate with water using a three-stage countercurrent water wash at a water flow rate of 5L / min. (b) Alkaline etching and water washing treatment: Prepare an alkaline degreasing solution to degrease the substrate. After degreasing, continuously wet the substrate with a water film. During the wetting process, prepare an alkaline etching solution of sodium hydroxide (80g / L). After wetting, perform alkaline etching treatment on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface to form a 15-20° tilt angle at the edge of the groove, with 18° being the best angle. After alkaline etching, use water washing technology to clean the substrate. (c) Pickling and washing treatment: Prepare a phosphoric acid / sulfuric acid (2:1 ratio) mixed solution (pH 2.5) pickling solution, pickle for 45 seconds, and pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the bottom of the groove to Ra≤0.3μm. After pickling, neutralize the residue on the substrate with a weak alkali (Na2CO3 0.5% solution). After neutralization, clean the substrate with water.

[0032] Step S2, Pre-treatment before nickel plating: The surface-treated substrate is placed in a zinc bath for immersion zinc treatment. The immersion zinc process uses a two-stage immersion zinc technology, and the specific steps are as follows: (1) Single zinc immersion: The surface-treated substrate is placed in a zinc bath and immersed for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc immersion: The substrate is placed in the zinc bath again for 20-30 seconds, focusing on filling the pores of the first zinc immersion. The residual zinc solution on the substrate is then recovered using recycling technology, and the residue on the substrate is then removed by washing with water. The specific steps of the recycling technology during the zinc precipitation process are as follows: (1) Rinse the substrate with clean water to remove the zinc liquid from the substrate; (2) The zinc liquid obtained is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, and then the obtained zinc liquid is reintroduced into the zinc pool.

[0033] Step S3, Nickel Plating: Immerse the pretreated substrate in a nickel plating solution and apply appropriate current and voltage. Nickel ions will deposit on the substrate surface to form a uniform nickel layer. The plating solution formula is as follows: Main salt: 25-35 g / L nickel sulfate or 20-30 g / L soluble nickel salt; reducing agent: 10-15 g / L sodium hypophosphite combined with 1-3 g / L dimethylaminoborane; complexing agent: 20-30 g / L sodium citrate or 0.5-10 g / L ethylenediamine; additives: sulfur-containing compounds. Plating parameters: Temperature: Controlled at 80-90℃, with temperature fluctuations ≤ ±2℃; Time: 10-60 minutes, deposition rate approximately 10-15 μm / h.

[0034] Step S4, Copper Plating Pretreatment: After nickel plating, the residual nickel plating solution on the substrate is recovered using recycling technology. The residue on the substrate is then removed by water washing. After water washing, the substrate undergoes activation treatment to enhance the adhesion of subsequent copper plating. After activation, the substrate is further cleaned using water washing technology. The activation treatment steps are as follows: (1) Alkaline etching cleaning: Use an alkaline solution (pH 10-12) to remove the surface oxide layer and residual oil stains to ensure the substrate is clean; (2) Catalysis: Using a nickel salt activator, nano-sized nickel particles are deposited on the aluminum surface to form a passivation layer to block oxidation and enhance the adhesion of subsequent copper plating; (3) Pre-immersion treatment: neutralize residual alkaline solution with acidic pre-immersion solution (pH 4.5-5.0) to avoid plating solution contamination.

[0035] Step S5, Copper Plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the substrate surface to form a uniform copper layer. The copper plating process consists of two steps, as shown below: (1) Pre-plating copper: Cuprous cyanide (20-30 g / L) is used as the main salt and sodium cyanide (30-50 g / L) as the complexing agent. The current density is 1-2 A / dm² and the time is 2-3 minutes to form a dense transition layer. The concentration of free sodium cyanide is controlled to be ≥5 g / L and the pH is 10-12 to prevent the copper layer from being loose or foaming. (2) Thickened acid-copper plating: Plating solution formulation: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), with the addition of brightener (such as sodium polydisulfide dipropane sulfonate 0.01-0.05g / L), temperature 25-30°C, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra≤0.5μm.

[0036] Step S6, Recycling and Subsequent Processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the substrate is sent to the drying equipment for drying.

[0037] Example 2: As Figure 2 As shown in the figure, the present invention provides a multi-faceted chemical plating process for flexible circuit boards made of aluminum foil, which includes the following additional process steps: Step A1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture to generate 3D model data. Customize a high-precision steel printing mold based on the scan data. This process involves laser engraving of the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Heat the aluminum foil substrate to 120-150℃ to soften it, specifically preheating it to 150℃ for 3 minutes to soften it; (3) The mold is pressed by a hydraulic press at a pressure of 50-80MPa to form a groove pattern with a depth of 8-12μm. The pressing process parameters are set as follows: pressure 70MPa, holding time 90 seconds, cooling rate 10℃ / min, and the mold is demolded after being water-cooled to 50℃ after pressing by the hydraulic press. (4) Composite cleaning to optimize groove texture; The process involves removing residues and oxide layers from the substrate surface using chemical methods, followed by washing with water to remove any remaining chemicals. The specific steps are as follows: (a) Acid degreasing and water washing treatment: Prepare an acidic degreasing solution to degrease the substrate. The acidic degreasing solution is: H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, wet the substrate with water at room temperature for 30 seconds. During the wetting process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After wetting, pickle the substrate with the pickling solution to remove imprint residue. After pickling, clean the substrate with water using a three-stage countercurrent water wash at a water flow rate of 5L / min. (b) Alkaline etching and water washing treatment: Prepare an alkaline degreasing solution to degrease the substrate. After degreasing, continuously wet the substrate with a water film. During the wetting process, prepare an alkaline etching solution of sodium hydroxide (80g / L). After wetting, perform alkaline etching treatment on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface to form a 15-20° tilt angle at the edge of the groove, with 18° being the best angle. After alkaline etching, use water washing technology to clean the substrate. (c) Pickling and washing treatment: Prepare a phosphoric acid / sulfuric acid (2:1 ratio) mixed solution (pH 2.5) pickling solution, pickle for 45 seconds, and pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the bottom of the groove to Ra≤0.3μm. After pickling, neutralize the residue on the substrate with a weak alkali (Na2CO3 0.5% solution). After neutralization, clean the substrate with water.

[0038] Step A2, Pre-treatment before copper plating: The surface-treated substrate is placed in a zinc bath for immersion zinc treatment. The immersion zinc process uses a two-stage immersion zinc technology, and the specific steps are as follows: (1) Single zinc immersion: The surface-treated substrate is placed in a zinc bath and immersed for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc immersion: The substrate is placed in the zinc bath again for 20-30 seconds, focusing on filling the pores of the first zinc immersion. The residual zinc solution on the substrate is then recovered using recycling technology, and the residue on the substrate is then removed by washing with water. The specific steps of the recycling technology during the zinc precipitation process are as follows: (1) Rinse the substrate with clean water to remove the zinc liquid from the substrate; (2) The zinc liquid obtained is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, and then the obtained zinc liquid is reintroduced into the zinc pool.

[0039] Step A3, Copper Plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the substrate surface to form a uniform copper layer. The copper plating process consists of two steps, as shown below: (1) Pre-plating copper: Cuprous cyanide (20-30 g / L) is used as the main salt and sodium cyanide (30-50 g / L) as the complexing agent. The current density is 1-2 A / dm² and the time is 2-3 minutes to form a dense transition layer. The concentration of free sodium cyanide is controlled to be ≥5 g / L and the pH is 10-12 to prevent the copper layer from being loose or foaming. (2) Thickened acid-copper plating: Plating solution formulation: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), with the addition of brightener (such as sodium polydisulfide dipropane sulfonate 0.01-0.05g / L), temperature 25-30℃, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra≤0.5μm.

[0040] Step A4, Recycling and Subsequent Processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the substrate is sent to the drying equipment for drying.

[0041] In another embodiment of the present invention, the water washing is all three-stage water washing, and the three-stage water washing is three-stage counter-current water washing with a water flow rate ≥5L / min·m².

[0042] In another embodiment of the present invention, during steps S6 and A4, the surface of the finished product is micro-treated during polishing to improve the product's brightness and enhance its appearance.

[0043] The first and second embodiments of this application, through the mold imprinting process, can controllably form an 18° tilt angle through alkaline etching, which can make the stress distribution of the copper layer more uniform, reduce the risk of stress concentration during subsequent metallization, and increase the bending life by 19-22 times; and the triple acid pickling process enables the surface energy of the imprinted group to reach 72dyn / cm.

[0044] Secondly, although the imprinting process takes longer per cycle, it eliminates the photolithography mask preparation step, reducing the mass production cost of circuit boards by 23% (calculated based on a batch size of 1000m²). At the same time, the triple post-processing (acid washing → alkaline etching → secondary acid washing) achieves a groove roughness of Ra≤0.3μm. Furthermore, the aluminum foil heating and softening process (120-150℃) avoids the tearing risk of flexible materials caused by traditional imprinting. The acid / alkaline cleaning process specifically removes imprinting residues, ensuring the reliability of flexible circuits and greatly improving the fidelity of texture replication.

[0045] Furthermore, this application, based on the customization of steel molds using 3D scanning, can achieve micron-level texture replication, such as precision structures like biosensor electrodes, and MEMS fluid channels. Experiments show that mold imprinting has reliability advantages in the field of precision flexible circuits, is suitable for small-batch, high-value-added production, and can meet the needs of mass production of circuit boards with metal foil as the substrate and acid and alkali resistant substrate.

[0046] Finally, the mold embossing process of this application can complement traditional technologies, as detailed below: In conjunction with direct imaging: high-precision grooves are created by die imprinting → conductive materials (such as silver paste) are deposited in the grooves using direct imaging to achieve 5μm-level embedded circuits; Alternative to electron beam printing: In non-silicon-based flexible circuits (such as wearable devices), die imprinting can achieve similar accuracy (12μm vs electron beam 1μm) at 1 / 10 of the cost. Optimize pattern transfer yield: The inclined groove wall design of the mold imprint can improve the edge breakage problem when the transfer film is peeled off.

[0047] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A multi-faceted chemical plating process for flexible circuit boards made of aluminum foil, characterized in that, The process includes the following steps: Step S1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture to generate 3D model data, and customize a high-precision steel printing mold based on the scan data; (2) Soften the aluminum foil substrate by heating it to 120-150℃; (3) The mold is pressed by a hydraulic press at a pressure of 50-80MPa to form a groove pattern with a depth of 8-12μm; (4) Composite cleaning to optimize groove texture; Step S2, pretreatment before nickel plating: The surface-treated substrate is placed in a zinc bath for zinc immersion treatment, and the residual zinc liquid on the substrate is recovered by recycling technology. Then, the residue on the substrate is cleaned off by water washing. Step S3, nickel plating: Immerse the pretreated substrate in a nickel plating solution and apply appropriate current and voltage. Nickel ions will be deposited on the substrate surface to form a uniform nickel layer. Step S4, Copper plating pretreatment: After nickel plating is completed, the residual nickel plating solution on the substrate is recovered by recycling technology, and then the residue on the substrate is cleaned by water washing. After water washing, the substrate is activated to enhance the adhesion of the substrate to subsequent copper plating. After activation, the substrate is cleaned by water washing technology. Step S5, copper plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will be deposited on the substrate surface to form a uniform copper layer. Step S6, Recycling and Subsequent Processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the substrate is sent to the drying equipment for drying.

2. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 1, characterized in that, The composite cleaning process in step S1 is specifically divided into the following steps: (a) Acid degreasing and water washing treatment: Prepare an acidic degreasing solution to degrease the substrate. After degreasing, wet the substrate. During the wetting process, prepare a mixed acid pickling solution of nitric acid / hydrofluoric acid. After wetting, pickle the substrate with the pickling solution to remove imprint residue. After pickling, clean the substrate with water washing technology. (b) Alkaline etching and water washing treatment: Prepare an alkaline degreasing solution to degrease the substrate. After degreasing, continuously wet the substrate with a water film. During the wetting process, prepare an alkaline etching solution of sodium hydroxide. After wetting, perform alkaline etching treatment on the substrate with the alkaline etching solution. The sodium hydroxide solution micro-etches the surface, so that the edge of the groove forms an inclined angle of 15-20°. After alkaline etching, use water washing technology to clean the substrate. (c) Pickling and washing treatment: Prepare a phosphoric acid / sulfuric acid mixed pickling solution, and use the pickling solution to pickle the substrate to passivate the substrate surface. The roughness of the bottom of the groove is reduced to Ra≤0.3μm. After pickling, the residue on the substrate is neutralized by weak alkali. After neutralization, the substrate is cleaned by water washing technology.

3. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 2, characterized in that, The zinc plating process in step S2 employs a two-stage zinc plating technique, and the specific steps are as follows: (1) Single zinc immersion: The surface-treated substrate is placed in a zinc bath and immersed for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc immersion: The substrate is placed in the zinc bath again for 20-30 seconds, focusing on filling the pores of the first zinc immersion.

4. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 3, characterized in that, The specific steps of the recovery technology during step S2 zinc immersion process are as follows: (1) Rinse the substrate with clean water to remove the zinc liquid from the substrate; (2) The zinc liquid obtained is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, and then the obtained zinc liquid is reintroduced into the zinc pool.

5. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 4, characterized in that, The plating solution formula in step S3 is as follows: Main salt: Nickel sulfate 25-35 g / L or soluble nickel salt 20-30 g / L; reducing agent: Sodium hypophosphite 10-15 g / L combined with dimethylaminoborane 1-3 g / L; complexing agent: Sodium citrate 20-30 g / L or ethylenediamine 0.5-10 g / L; additives: sulfur-containing compounds 0.01-10 ppm or sodium tungstate 0.5-1.0 g / L. Plating parameters: Temperature: Controlled at 80-90℃, with temperature fluctuations ≤ ±2℃; Time: 10-60 minutes, deposition rate approximately 10-15 μm / h.

6. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 5, characterized in that, The activation process in step S4 is as follows: (1) Alkaline etching cleaning: Use an alkaline solution with pH 10-12 to remove the surface oxide layer and residual oil stains to ensure the substrate is clean; (2) Catalysis: Using a nickel salt activator, nano-sized nickel particles are deposited on the aluminum surface to form a passivation layer to block oxidation and enhance the adhesion of subsequent copper plating; (3) Pre-immersion treatment: Use an acidic pre-immersion solution with pH 4.5-5.0 to neutralize the residual alkali solution and avoid plating solution contamination.

7. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil as described in claim 6, characterized in that, The copper plating process in step S5 consists of two steps, as shown below: (1) Pre-plating copper: Using 20-30 g / L cuprous cyanide as the main salt and 30-50 g / L sodium cyanide as the complexing agent, with a current density of 1-2 A / dm² and a time of 2-3 minutes, a dense transition layer is formed. The concentration of free sodium cyanide is controlled to be ≥5 g / L and the pH is 10-12 to prevent the copper layer from becoming loose or foaming. (2) Thickened acid-copper plating: Plating solution formulation: 180-220g / L copper sulfate + 50-70g / L sulfuric acid, with 0.01-0.05g / L sodium polydisulfide dipropane sulfonate brightener added. Temperature: 25-30℃, current density: 2-4A / dm², time: 30-60 minutes, copper layer thickness: ≥20μm, surface roughness Ra: ≤0.5μm.

8. The multi-faceted chemical plating process for flexible circuit boards made of aluminum foil according to claim 7, characterized in that, All water washing uses a three-stage water washing process, and the three-stage water washing is a three-stage counter-current water washing process with a water flow rate ≥ 5L / min·m².

9. A multi-faceted chemical plating process for flexible circuit boards made of aluminum foil, characterized in that, The following is another process step, which uses any one of the dependent claims 2-4 and 7-8: Step A1, Surface Treatment: Scan the texture of the flexible circuit board and imprint the texture onto the substrate using a printing technique. The specific process is as follows: (1) Soften the aluminum foil substrate by heating it to 120-150℃; (2) The mold is pressed under a pressure of 50-80MPa by a hydraulic press to form grooves with a depth of 8-12μm; (3) Composite cleaning to optimize groove texture; Step A2, Pre-treatment before copper plating: The surface-treated substrate is placed in a zinc bath for zinc immersion treatment, and the residual zinc liquid on the substrate is recovered by recycling technology. Then, the residue on the substrate is cleaned off by water washing. Step A3, copper plating: Immerse the pretreated substrate in the copper plating solution and apply appropriate current and voltage. Copper ions will be deposited on the substrate surface to form a uniform copper layer. Step A4, Recycling and Subsequent Processing: After copper plating is completed, the residue on the substrate is cleaned by water washing. After water washing, the copper-plated substrate is polished. After polishing, the residue on the substrate is removed by water washing. After water washing, the substrate is sent to the drying equipment for drying.

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