Diversified chemical plating process for aluminum foil material flexible circuit board

Abstract

The invention relates to the technical field of aluminum foil material flexible circuit board preparation, in particular to an aluminum foil material flexible circuit board diversified chemical plating process which comprises the following process steps: S1, surface treatment: scanning lines of a flexible circuit board, embossing the lines on a base material through a printing technology, the process specifically comprises the following steps: (1) scanning existing lines of the flexible circuit board by using a computer vision camera to generate 3D model data; groove lines can be embossed on a base material through printing, the contact area of a plating layer and the base material is increased by 40%-60% through the groove structure, the stripping strength of the plating layer is improved to 18-22 MPa from 12-15 MPa of a traditional technology, the groove guides an electroplating solution to flow, the thickness fluctuation of the plating layer is reduced to + / -1.5 micrometers from + / -5 micrometers, the porosity is reduced to be smaller than or equal to 2% from 8%, the line positioning precision reaches + / -10 micrometers, and the plating layer is not prone to falling off. The problem of line offset in the traditional etching process is avoided, and the reject ratio of products is reduced from 15% to below 3%.

Description

Technical Field

[0001] The invention relates to the technical field of preparing flexible circuit boards made of aluminum foil, and in particular to a multi-layer chemical plating process for flexible circuit boards made of aluminum foil. Background Art

[0002] Using aluminum instead of copper as the conductive substrate for circuit boards significantly reduces costs and makes the production process more environmentally friendly, leading to its application in many fields. However, aluminum-based circuit boards cannot be soldered to other electronic components using ordinary solder paste. This is because the oxide film formed by oxidation of the aluminum in air is solder-repellent. Therefore, a layer of anti-oxidation and easily solderable metal substrate is generally plated on the aluminum surface to ensure adhesion to other electronic components. The operating principle of aluminum foil flexible circuit boards is to use insulating material to isolate the surface aluminum foil conductive layer, allowing current to flow through the various components along a pre-set route, completing functions such as work, amplification, attenuation, modulation, demodulation, and encoding. Aluminum foil flexible circuit boards are composed of a multi-layer composite of aluminum and insulating sheets, and can only be easily soldered using chemical plating.

[0003] In order to optimize the electroless nickel plating process for flexible circuit boards made of aluminum foil, existing technologies such as printing are used to solve the above problems. However, the specific details of traditional circuit board printing technologies are as follows: 1. Screen printing method (applicable substrates: rigid / flexible substrates) Screen printing is the most traditional technique, where ink is applied to a substrate using a screen stencil to create a circuit pattern. The process involves stretching the screen and drying it. This requires pre-preparing the stencil and controlling the tension. While it is suitable for mass production and offers low costs, it also limits the precision of complex patterns.

[0004] 2. Direct imaging printing method (applicable substrate: photosensitive substrate) Direct imaging printing utilizes photosensitive materials and photolithography techniques to create images directly on a substrate, eliminating the need for a physical template. Ultraviolet light exposure creates precise circuits with micron-level accuracy, making it suitable for high-density integrated circuit board manufacturing. However, it places high demands on the substrate material.

[0005] 3. Electron beam printing method (applicable substrate: special substrate) 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 circuit scenarios, but the equipment cost is relatively high.

[0006] 4. Graphic transfer printing method (applicable substrate: multilayer substrate) Graphic transfer printing involves printing a pattern onto transfer paper and then transferring it to the substrate using heat or pressure. This method is suitable for complex graphics and multi-layer PCBs, but it requires high material compatibility.

[0007] For example, the chemical nickel plating process for aluminum foil circuit boards with publication number CN110453205A and publication date 20191115 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 sealant; 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 an electrical conductivity of only 5.8×106S / m, which is far lower than the 5.96×107S / m of copper, and the nickel layer thickness needs to reach 15-20μm to meet welding requirements, resulting in a waste of precious metal resources. The phosphorus-containing chemical nickel agent used therein has a risk of heavy metal pollution and does not meet RoHS environmental protection standards.

[0008] For example, the production of a flexible circuit board made of aluminum foil material with zoned nickel plating, with publication number CN116634696A and publication date 20230822, wherein the chemical nickel plating process includes the following steps: S71, degreasing: using a stripping agent solution to remove organic pollutants at the pad position and preliminarily remove oxides; S72, water washing: removing residual stripping agent; S73, descaling: using a descaling agent solution to remove the residual oxide film on the surface of the aluminum foil at the pad position to form a micro-etched surface; S74, water washing: removing residual descaling agent solution; S75, zinc deposition: using a zinc deposition agent to zincate the pad position; S76, water washing: water washing to remove residual zinc deposition agent; S77, nickel plating: using a nickel plating agent solution to nickel plate the pad position; S78, water washing: water washing to remove residual zinc deposition agent; S79, drying: drying the washed product. Although this patented technology uses zoned nickel plating to improve accuracy, it does not solve the defects of substrate pretreatment: (1) The porosity of the zinc layer after zinc deposition is >8%, resulting in a 30% decrease in the bonding strength of the coating; (2) The residual oxide film at the pad position makes the solder bonding strength only 12-15MPa; (3) There is no reagent recovery system, and the amount of plating solution carried out is 15-20mL / m².

[0009] ‌It can be seen from this that the existing chemical nickel plating process for flexible circuit boards made of aluminum foil has disadvantages such as low electrical conductivity, poor solder bonding, too thick a nickel plating layer, wasteful costs, and environmentally unfriendly chemicals.‌ Therefore, it is urgent to design a diversified chemical plating process for flexible circuit boards made of aluminum foil to solve the above problems. Summary of the Invention

[0010] The purpose of the present invention is to provide a multi-layer chemical coating process for a flexible circuit board made of aluminum foil material to solve the above-mentioned deficiencies in the prior art.

[0011] In order to achieve the above object, the present invention provides the following technical solutions: A multi-layer chemical coating process for a flexible circuit board made of aluminum foil includes the following steps: Step S1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. 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. This process involves laser engraving the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Soften the aluminum foil substrate by heating it to 120-150°C, specifically preheating it at 150°C for 3 minutes; (3) The mold is embossed by a hydraulic press at a pressure of 50-80 MPa to form a groove pattern with a depth of 8-12 μm. The embossing process parameters are set as follows: The pressure is 70MPa, the holding time is 90 seconds, the cooling rate is 10℃ / min, and the hydraulic press is water-cooled to 50℃ for demoulding after embossing; (4) Composite cleaning to optimize groove texture; The residue and oxide layer on the surface of the substrate are then removed by chemical methods, and the residual chemical agents on the surface of the substrate are removed by water washing. The specific process is as follows: (a) Acid degreasing and water washing: Prepare an acidic degreasing solution and degrease the substrate. The acidic degreasing solution is H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, moisten the substrate with water at room temperature for 30 seconds. During the moistening process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After moistening, pickle the substrate with the pickling solution to remove the imprint residue. After pickling, clean the substrate with water washing technology. A three-stage countercurrent water washing is performed with a water flow rate of 5L / min. (b) Alkali etching and water washing: prepare alkaline degreasing solution and degrease the substrate. After degreasing, continuously wet the substrate with a water film. Prepare sodium hydroxide solution (80g / L) alkaline etching solution during the wetting process. After wetting, alkaline etching is performed on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface so that the groove edge forms an inclination angle of 15-20°, with an angle of 18° being the best. After alkaline etching, the substrate is cleaned with water washing technology. (c) Pickling and water washing: prepare a pickling solution of phosphoric acid / sulfuric acid (ratio 2:1) mixed solution (pH 2.5), pickle for 45 seconds, pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the groove bottom to Ra ≤ 0.3 μm. After the pickling is completed, the residue on the substrate is neutralized with a weak alkali. The weak alkali neutralization is selected (Na2CO3 0.5% solution). After the neutralization is completed, the substrate is passivated with a passivation solution. A chromate passivation solution is selected for passivation to form a 0.2 μm passivation film. After the passivation is completed, the substrate is cleaned with water washing technology.

[0012] Step S2. Pretreatment before nickel plating: Place the surface treated substrate into a zinc bath for zinc deposition. The zinc deposition process uses a secondary zinc deposition technology, and the specific steps are as follows: (1) Primary zinc deposition: Place the surface treated substrate into the zinc pool for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc deposition: Place the substrate into the zinc pool again for 20-30 seconds, focusing on filling the pores of the first zinc deposition; The zinc solution remaining on the substrate is recovered by recycling technology, and then the residue on the substrate is cleaned by water washing. 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 solution on the substrate; (2) The obtained zinc liquid is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, which is then reintroduced into the zinc pool.

[0013] 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 surface of the substrate to form a uniform nickel layer. The plating solution formula is as follows: Main salt: nickel sulfate 25-35g / L or soluble nickel salt 20-30g / L, reducing agent: sodium hypophosphite 10-15g / L combined with dimethylaminoborane 1-3g / L, complexing agent: sodium citrate 20-30g / L or ethylenediamine 0.5-10g / L, additives: sulfur-containing compound 0.01-10ppm or sodium tungstate 0.5-1.0g / L; Plating parameters: Temperature: controlled at 80-90°C, with a temperature fluctuation of ≤±2°C. Time: 10-60 minutes, deposition rate about 10-15 μm / h16.

[0014] Step S4. Copper plating pretreatment: After the nickel plating is completed, the nickel plating solution remaining on the substrate is recovered by a recovery technology, and then the residue on the substrate is cleaned by water washing. After the water washing is completed, the substrate is activated to enhance the bonding strength of the subsequent copper plating on the substrate. After the activation is completed, the substrate is continued to be cleaned using a water washing technology. The activation treatment steps are as follows: (1) Alkaline etching cleaning: Use alkaline solution (pH 10-12) to remove the surface oxide layer and residual oil to ensure the substrate is clean; (2) Catalytic catalysis: Using a nickel salt activator, nano-sized nickel particles are deposited on the aluminum surface to form a passivation layer to prevent oxidation and enhance the bonding strength of subsequent copper plating; (3) Pre-dip treatment: Acidic pre-dip solution (pH 4.5-5.0) neutralizes residual alkali solution to avoid plating solution contamination.

[0015] Step S5. Copper plating: Immerse the pretreated substrate in a copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the surface of the substrate to form a uniform copper layer. The copper plating process is divided into two steps, as shown below: (1) Pre-copper plating: Use cuprous cyanide (20-30g / L) as the main salt and sodium cyanide (30-50g / L) as the complexing agent. The current density is 1-2A / dm² and the time is 2-3 minutes to form a dense transition layer. The free sodium cyanide concentration is controlled to be ≥5g / L and the pH is 10-12 to prevent the copper layer from becoming loose or bubbling. (2) Acid copper plating thickening: Plating solution formula: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), brightener (such as sodium polydisulfide dipropylene sulfonate 0.01-0.05g / L), temperature 25-30℃26, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra ≤0.5μm.

[0016] Step S6. Recovery and subsequent treatment: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper-plated layer of the substrate is protected. The protection treatment is as follows: Immerse in chromate passivation solution for 10-20 seconds to form an anti-oxidation film; Chromate passivation solution: pH 3-4, containing Cr 3+ Concentration 3-5g / L; Then use ultrasonic equipment to wash and remove the residue on the substrate after protection treatment, and then send it to the drying equipment for drying.

[0017] A multi-layer chemical coating process for a flexible circuit board made of aluminum foil includes the following process steps: Step A1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. 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. This process involves laser engraving the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Soften the aluminum foil substrate by heating it to 120-150°C, specifically preheating it at 150°C for 3 minutes; (3) The mold is embossed by a hydraulic press at a pressure of 50-80 MPa to form a groove pattern with a depth of 8-12 μm. The embossing process parameters are set as follows: The pressure is 70MPa, the holding time is 90 seconds, the cooling rate is 10℃ / min, and the hydraulic press is water-cooled to 50℃ for demoulding after embossing; (4) Composite cleaning to optimize groove texture; The composite cleaning process is specifically divided into the following steps: (a) Acid degreasing and water washing: Prepare an acidic degreasing solution and degrease the substrate. The acidic degreasing solution is H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, moisten the substrate with water at room temperature for 30 seconds. During the moistening process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After moistening, pickle the substrate with the pickling solution to remove the imprint residue. After pickling, clean the substrate with water washing technology. A three-stage countercurrent water washing is performed with a water flow rate of 5L / min. (b) Alkali etching and water washing: prepare alkaline degreasing solution and degrease the substrate. After degreasing, continuously wet the substrate with a water film. Prepare sodium hydroxide solution (80g / L) alkaline etching solution during the wetting process. After wetting, alkaline etching is performed on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface so that the groove edge forms an inclination angle of 15-20°, with an angle of 18° being the best. After alkaline etching, the substrate is cleaned with water washing technology. (c) Pickling and water washing: prepare a pickling solution of phosphoric acid / sulfuric acid (ratio 2:1) mixed solution (pH 2.5), pickle for 45 seconds, pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the groove bottom to Ra ≤ 0.3 μm. After the pickling is completed, the residue on the substrate is neutralized with a weak alkali. The weak alkali neutralization is selected (Na2CO3 0.5% solution). After the neutralization is completed, the substrate is passivated with a passivation solution. A chromate passivation solution is selected for passivation to form a 0.2 μm passivation film. After the passivation is completed, the substrate is cleaned with water washing technology.

[0018] Step A2. Pretreatment before copper plating: Place the surface treated substrate into a zinc bath for zinc deposition. The zinc deposition process uses a secondary zinc deposition technology, and the specific steps are as follows: (1) Primary zinc deposition: Place the surface treated substrate into the zinc pool for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc deposition: Place the substrate into the zinc pool again for 20-30 seconds, focusing on filling the pores of the first zinc deposition; The zinc solution remaining on the substrate is recovered by recycling technology, and then the residue on the substrate is cleaned by water washing. 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 solution on the substrate; (2) The obtained zinc liquid is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, which is then reintroduced into the zinc pool.

[0019] Step A3. Copper plating: Immerse the pretreated substrate in a copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the surface of the substrate, forming a uniform copper layer. The copper plating process is divided into two steps, as shown below: (1) Pre-copper plating: Use cuprous cyanide (20-30g / L) as the main salt and sodium cyanide (30-50g / L) as the complexing agent. The current density is 1-2A / dm² and the time is 2-3 minutes to form a dense transition layer. The free sodium cyanide concentration is controlled to be ≥5g / L and the pH is 10-12 to prevent the copper layer from becoming loose or bubbling. (2) Acid copper plating thickening: Plating solution formula: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), brightener (such as sodium polydisulfide dipropylene sulfonate 0.01-0.05g / L), temperature 25-30℃26, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra ≤0.5μm.

[0020] Step A4. Recovery and subsequent treatment: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper-plated layer of the substrate is protected. The protection treatment is as follows: Immerse in chromate passivation solution for 10-20 seconds to form an anti-oxidation film; Chromate passivation solution: pH 3-4, containing Cr 3+ Concentration 3-5g / L; Then use ultrasonic equipment to wash and remove the residue on the substrate after protection treatment, and then send it to the drying equipment for drying.

[0021] In another embodiment provided by the present invention, the water washing is performed by three-stage water washing, and the three-stage water washing is a three-stage countercurrent water washing with a water flow rate of ≥5 L / min·m².

[0022] In the above technical solution, the present invention provides a multi-chemical coating process for a flexible circuit board made of aluminum foil, which has the following beneficial effects: (1) The present invention can emboss groove patterns on a substrate through printing. The groove structure increases the contact area between the coating and the substrate by 40%-60%, and the peel strength of the coating is increased from 12-15 MPa of the traditional process to 18-22 MPa. In addition, the groove guides the flow of the electroplating solution, and the fluctuation of the coating thickness is reduced from ±5 μm to ±1.5 μm, the porosity is reduced from 8% to ≤2%, and the pattern positioning accuracy reaches ±10 μm, thereby avoiding the line deviation problem of the traditional etching process, and reducing the product defective rate from 15% to below 3%. At the same time, it also avoids the shortcomings of the traditional printing process and can meet the large-scale production needs of acid- and alkali-resistant circuit board substrates with metal foil as the substrate.

[0023] (2) The present invention changes the existing single chemical nickel plating into a multi-chemical plating, mainly using copper plating to improve the conductivity of the flexible circuit board made of aluminum foil, increase the solder bonding strength, and save resources by reducing the thickness of the plating layer, and change the phosphorus-containing chemical nickel agent into an environmentally friendly chemical nickel agent.

[0024] (3) The present invention can reserve groove marks on the substrate by printing the substrate in advance, which can improve the bonding strength between the coating and the substrate during the subsequent multi-layer chemical coating of the board, thereby enhancing product quality.

[0025] (4) Compared with the original nickel plating process, the present invention can remove excess foreign matter generated in the upstream plate making process of the aluminum foil flexible circuit board, making the welding position cleaner and the coating bonding stronger. At the same time, it can recycle the chemicals brought out from the product surface, reducing the waste of resources, and the product surface is micro-processed, which greatly improves the brightness and aesthetics of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0027] Figure 1 A schematic diagram of the process flow of an embodiment of the multi-chemical coating process for a flexible circuit board made of aluminum foil is provided.

[0028] Figure 2 Another process flow diagram provided for an embodiment of the multi-chemical coating process of a flexible circuit board made of aluminum foil material according to the present invention. DETAILED DESCRIPTION

[0029] In order 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.

[0030] Example 1

[0031] like Figure 1 As shown, an embodiment of the present invention provides a multi-layer chemical coating process for a flexible circuit board made of aluminum foil, including the following process steps: Step S1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. 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. This process involves laser engraving the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Heat the aluminum foil substrate to 120-150°C to soften it, specifically preheating it at 150°C for 3 minutes to soften it; (3) The mold is embossed by a hydraulic press at a pressure of 50-80 MPa to form a groove pattern with a depth of 8-12 μm. The embossing process parameters are set as follows: The pressure is 70MPa, the holding time is 90 seconds, the cooling rate is 10℃ / min, and the hydraulic press is water-cooled to 50℃ for demoulding after embossing; (4) Composite cleaning to optimize groove texture; The residue and oxide layer on the surface of the substrate are then removed by chemical methods, and the residual chemical agents on the surface of the substrate are removed by water washing. The specific process is as follows: (a) Acid degreasing and water washing: Prepare an acidic degreasing solution and degrease the substrate. The acidic degreasing solution is H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, moisten the substrate with water at room temperature for 30 seconds. During the moistening process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After moistening, pickle the substrate with the pickling solution to remove the imprint residue. After pickling, clean the substrate with water washing technology. A three-stage countercurrent water washing is performed with a water flow rate of 5L / min. (b) Alkali etching and water washing: prepare alkaline degreasing solution and degrease the substrate. After degreasing, continuously wet the substrate with a water film. Prepare sodium hydroxide solution (80g / L) alkaline etching solution during the wetting process. After wetting, alkaline etching is performed on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface so that the groove edge forms an inclination angle of 15-20°, with an angle of 18° being the best. After alkaline etching, the substrate is cleaned with water washing technology. (c) Pickling and water washing: prepare a pickling solution of phosphoric acid / sulfuric acid (ratio 2:1) mixed solution (pH 2.5), pickle for 45 seconds, pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the groove bottom to Ra ≤ 0.3 μm. After the pickling is completed, the residue on the substrate is neutralized with a weak alkali. The weak alkali neutralization is selected (Na2CO3 0.5% solution). After the neutralization is completed, the substrate is passivated with a passivation solution. A chromate passivation solution is selected for passivation to form a 0.2 μm passivation film. After the passivation is completed, the substrate is cleaned with water washing technology.

[0032] Step S2. Pretreatment before nickel plating: Place the surface treated substrate into a zinc bath for zinc deposition. The zinc deposition process uses a secondary zinc deposition technology, and the specific steps are as follows: (1) Primary zinc deposition: Place the surface treated substrate into the zinc pool for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc deposition: Place the substrate into the zinc pool again for 20-30 seconds, focusing on filling the pores of the first zinc deposition; The zinc solution remaining on the substrate is recovered by recycling technology, and then the residue on the substrate is cleaned by water washing. 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 solution on the substrate; (2) The obtained zinc liquid is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, which is then 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 surface of the substrate to form a uniform nickel layer. The plating solution formula is as follows: Main salt: nickel sulfate 25-35g / L or soluble nickel salt 20-30g / L, reducing agent: sodium hypophosphite 10-15g / L combined with dimethylaminoborane 1-3g / L, complexing agent: sodium citrate 20-30g / L or ethylenediamine 0.5-10g / L, additives: sulfur-containing compound 0.01-10ppm or sodium tungstate 0.5-1.0g / L; Plating parameters: Temperature: controlled at 80-90°C, with a temperature fluctuation of ≤±2°C. Time: 10-60 minutes, deposition rate about 10-15 μm / h16.

[0034] Step S4. Copper plating pretreatment: After the nickel plating is completed, the nickel plating solution remaining on the substrate is recovered by a recovery technology, and then the residue on the substrate is cleaned by water washing. After the water washing is completed, the substrate is activated to enhance the bonding strength of the subsequent copper plating on the substrate. After the activation is completed, the substrate is continued to be cleaned using a water washing technology. The activation treatment steps are as follows: (1) Alkaline etching cleaning: Use alkaline solution (pH 10-12) to remove the surface oxide layer and residual oil to ensure the substrate is clean; (2) Catalytic catalysis: Using a nickel salt activator, nano-sized nickel particles are deposited on the aluminum surface to form a passivation layer to prevent oxidation and enhance the bonding strength of subsequent copper plating; (3) Pre-dip treatment: Acidic pre-dip solution (pH 4.5-5.0) neutralizes residual alkali solution to avoid plating solution contamination.

[0035] Step S5. Copper plating: Immerse the pretreated substrate in a copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the surface of the substrate to form a uniform copper layer. The copper plating process is divided into two steps, as shown below: (1) Pre-copper plating: Use cuprous cyanide (20-30g / L) as the main salt and sodium cyanide (30-50g / L) as the complexing agent. The current density is 1-2A / dm² and the time is 2-3 minutes to form a dense transition layer. The free sodium cyanide concentration is controlled to be ≥5g / L and the pH is 10-12 to prevent the copper layer from becoming loose or bubbling. (2) Acid copper plating thickening: Plating solution formula: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), brightener (such as sodium polydisulfide dipropylene sulfonate 0.01-0.05g / L), temperature 25-30℃26, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra ≤0.5μm.

[0036] Step S6. Recovery and subsequent treatment: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper-plated layer of the substrate is protected. The protection treatment is as follows: Immerse in chromate passivation solution for 10-20 seconds to form an anti-oxidation film; Chromate passivation solution: pH 3-4, containing Cr 3+ Concentration 3-5g / L; Then use ultrasonic equipment to wash and remove the residue on the substrate after protection treatment, and then send it to the drying equipment for drying.

[0037] Example 2

[0038] like Figure 2 As shown, an embodiment of the present invention provides a multi-layer chemical coating process for a flexible circuit board made of aluminum foil, including the following process steps: Step A1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. 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. This process involves laser engraving the steel mold with a line width of 45±2μm and a depth of 10μm. (2) Soften the aluminum foil substrate by heating it to 120-150°C, specifically preheating it at 150°C for 3 minutes; (3) The mold is embossed by a hydraulic press at a pressure of 50-80 MPa to form a groove pattern with a depth of 8-12 μm. The embossing process parameters are set as follows: The pressure is 70MPa, the holding time is 90 seconds, the cooling rate is 10℃ / min, and the hydraulic press is water-cooled to 50℃ for demoulding after embossing; (4) Composite cleaning to optimize groove texture; The residue and oxide layer on the substrate surface are removed by chemical methods, and the residual chemical agent on the substrate surface is removed by water washing. The specific process is as follows: (a) Acid degreasing and water washing: Prepare an acidic degreasing solution and degrease the substrate. The acidic degreasing solution is H2SO4 (10%) + surfactant (3%). Soak at 40°C for 2 minutes. After degreasing, moisten the substrate with water at room temperature for 30 seconds. During the moistening process, prepare a mixed pickling solution of nitric acid / hydrofluoric acid (ratio 3:1) (concentration 5%-8%). After moistening, pickle the substrate with the pickling solution to remove the imprint residue. After pickling, clean the substrate with water washing technology. A three-stage countercurrent water washing is performed with a water flow rate of 5L / min. (b) Alkali etching and water washing: prepare alkaline degreasing solution and degrease the substrate. After degreasing, continuously wet the substrate with a water film. Prepare sodium hydroxide solution (80g / L) alkaline etching solution during the wetting process. After wetting, alkaline etching is performed on the substrate with the alkaline etching solution. The sodium hydroxide solution (80g / L) micro-etches the surface so that the groove edge forms an inclination angle of 15-20°, with an angle of 18° being the best. After alkaline etching, the substrate is cleaned with water washing technology. (c) Pickling and water washing: prepare a pickling solution of phosphoric acid / sulfuric acid (ratio 2:1) mixed solution (pH 2.5), pickle for 45 seconds, pickle the substrate with the pickling solution to passivate the substrate surface and reduce the roughness of the groove bottom to Ra ≤ 0.3 μm. After the pickling is completed, the residue on the substrate is neutralized with a weak alkali. The weak alkali neutralization is selected (Na2CO3 0.5% solution). After the neutralization is completed, the substrate is passivated with a passivation solution. A chromate passivation solution is selected for passivation to form a 0.2 μm passivation film. After the passivation is completed, the substrate is cleaned with water washing technology.

[0039] Step A2. Pretreatment before copper plating: Place the surface treated substrate into a zinc bath for zinc deposition. The zinc deposition process uses a secondary zinc deposition technology, and the specific steps are as follows: (1) Primary zinc deposition: Place the surface treated substrate into the zinc pool for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc deposition: Place the substrate into the zinc pool again for 20-30 seconds, focusing on filling the pores of the first zinc deposition; The zinc solution remaining on the substrate is recovered by recycling technology, and then the residue on the substrate is cleaned by water washing. 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 solution on the substrate; (2) The obtained zinc liquid is evaporated using low-temperature evaporation technology to obtain concentrated zinc liquid, which is then reintroduced into the zinc pool.

[0040] Step A3. Copper plating: Immerse the pretreated substrate in a copper plating solution and apply appropriate current and voltage. Copper ions will deposit on the surface of the substrate, forming a uniform copper layer. The copper plating process is divided into two steps, as shown below: (1) Pre-copper plating: Use cuprous cyanide (20-30g / L) as the main salt and sodium cyanide (30-50g / L) as the complexing agent. The current density is 1-2A / dm² and the time is 2-3 minutes to form a dense transition layer. The free sodium cyanide concentration is controlled to be ≥5g / L and the pH is 10-12 to prevent the copper layer from becoming loose or bubbling. (2) Acid copper plating thickening: Plating solution formula: copper sulfate (180-220g / L) + sulfuric acid (50-70g / L), brightener (such as sodium polydisulfide dipropylene sulfonate 0.01-0.05g / L), temperature 25-30℃26, current density 2-4A / dm², time 30-60 minutes, copper layer thickness ≥20μm, surface roughness Ra ≤0.5μm.

[0041] Step A4. Recovery and subsequent treatment: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper-plated layer of the substrate is protected. The protection treatment is as follows: Immerse in chromate passivation solution for 10-20 seconds to form an anti-oxidation film; Chromate passivation solution: pH 3-4, containing Cr 3+ Concentration 3-5g / L; Then use ultrasonic equipment to wash and remove the residue on the substrate after protection treatment, and then send it to the drying equipment for drying.

[0042] In another embodiment provided by the present invention, three-stage water washing is selected for water washing, and the three-stage water washing is three-stage countercurrent water washing, and the water flow rate is ≥5L / min·m².

[0043] In another embodiment provided by the present invention, during step S6 and step A4, the surface of the product is micro-processed during polishing to increase the brightness of the product and beautify the product.

[0044] In Example 1 and Example 2 of the present application, a mold stamping process is used to control alkaline etching to form an 18° tilt angle, which is a 90° straight edge compared to the traditional circuit board printing process. This 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 pickling process enables the surface energy of the stamping group to reach 72dyn / cm, which significantly improves the subsequent plating bonding strength compared to the 38dyn / cm of the traditional group.

[0045] Secondly, although the single processing of the imprint group takes more time, it eliminates the photolithography mask preparation process, and the mass production cost of the circuit board is reduced by 23% (calculated based on 1000m 3 The company claims that the triple post-processing (pickling → alkaline etching → secondary pickling) achieves a groove roughness of Ra ≤ 0.3 μm, which is significantly better than screen printing (usually Ra > 1 μm) and pattern transfer method (prone to burrs). In addition, the aluminum foil heating and softening process (120-150°C) can avoid the risk of tearing the flexible material caused by traditional stamping. The acid / alkaline cleaning process specifically removes stamping residues, ensuring the reliability of the flexible circuit and greatly improving the fidelity of texture reproduction.

[0046] Furthermore, the present application is based on the customization of steel molds through 3D scanning, which can achieve micron-level texture replication, such as biosensor electrodes and other precision structures, such as MEMS fluid channels; and according to experiments, mold imprinting has reliability advantages in the field of precision flexible circuits, and is suitable for small-batch, high-value-added production, and can meet the large-scale production needs of acid- and alkali-resistant circuit board substrates with metal foil as the substrate.

[0047] Finally, the mold embossing process of this application can be complementary to traditional technologies, as shown below: 1. Collaboration with direct imaging Mold embossing to create high-precision grooves → Direct imaging method to deposit conductive materials (such as silver paste) in the grooves, achieving 5μm-level embedded circuits; 2. Alternative electron beam printing scenarios In non-silicon-based flexible circuits (such as wearable devices), die imprinting can achieve similar accuracy at 1 / 10 the cost (12μm vs. 1μm for electron beam); 3. Optimize the pattern transfer yield The inclined groove wall design of the mold stamping can improve the edge breakage problem when the transfer film is peeled off.

[0048] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A multi-chemical coating process for flexible circuit boards made of aluminum foil, characterized in that: The process steps include: Step S1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. The specific process is as follows: (1) Use a computer vision camera to scan the existing flexible circuit board texture, generate 3D model data, and customize a high-precision steel printing mold based on the scan data; (2) Heat the aluminum foil substrate to 120-150°C to soften it; (3) Using a hydraulic press to emboss the mold under a pressure of 50-80 MPa to form grooves with a depth of 8-12 μm; (4) Composite cleaning to optimize groove texture; Step S2. Pretreatment before nickel plating: placing the surface-treated substrate into a zinc bath for zinc precipitation, recovering the residual zinc solution on the substrate using a recovery technique, and then cleaning the residue on the substrate by washing with water; Step S3. Nickel plating: Immersing the pretreated substrate in a nickel plating solution and applying appropriate current and voltage will deposit nickel ions on the substrate surface to form a uniform nickel layer. Step S4. Copper plating pretreatment: After the nickel plating is completed, the nickel plating solution remaining on the substrate is recovered by a recovery technology, and then the residue on the substrate is cleaned by water washing. After the water washing is completed, the substrate is activated to enhance the bonding strength of the substrate for subsequent copper plating. After the activation is completed, the substrate is further cleaned using a water washing technology; Step S5. Copper plating: Immersing the pretreated substrate in a copper plating solution and applying appropriate current and voltage will cause copper ions to deposit on the substrate surface, forming a uniform copper layer. Step S6. Recovery and subsequent processing: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper plating layer of the substrate is protected and then washed with ultrasonic equipment to remove the residue on the substrate after the protective treatment. It is then sent to a drying equipment for drying.

2. The multi-chemical coating process for flexible circuit boards made of aluminum foil according to 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: Prepare an acidic degreasing solution to degrease the substrate. After degreasing, moisten the substrate with water. Prepare a nitric acid / hydrofluoric acid mixed pickling solution during the moistening process. After the moistening is completed, the substrate is pickled with the pickling solution to remove the imprint residue. After the pickling is completed, the substrate is cleaned with water washing technology; (b) Alkali etching and water washing: prepare an alkaline degreasing solution and degrease the substrate. After degreasing, continuously wet the substrate with a water film. Prepare a sodium hydroxide solution alkaline etching solution during the wetting process. After wetting, the substrate is etched with the alkaline etching solution. The sodium hydroxide solution micro-etches the surface, forming an inclination angle of 15-20° at the edge of the groove. After the alkaline etching is completed, the substrate is cleaned with water washing technology. (c) Pickling and water washing: A phosphoric acid / sulfuric acid mixed solution is prepared as a pickling solution, and the substrate is pickled with the pickling solution to passivate the substrate surface and reduce the roughness of the groove bottom to Ra ≤ 0.3 μm. After the pickling is completed, the residue on the substrate is neutralized with a weak base. After the neutralization is completed, the substrate is passivated with a passivation solution. After the passivation is completed, the substrate is cleaned with water washing technology.

3. The multi-chemical coating process for flexible circuit boards made of aluminum foil according to claim 2, characterized in that: The zinc precipitation process in step S2 adopts secondary zinc precipitation technology, and the specific steps are as follows: (1) Primary zinc deposition: Place the surface treated substrate into the zinc pool for 40-60 seconds to form a basic zinc layer; (2) Secondary zinc deposition: Place the substrate into the zinc pool again for 20-30 seconds, focusing on filling the pores of the first zinc deposition.

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

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

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

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

8. The multi-chemical coating process for flexible circuit boards made of aluminum foil according to claim 7, characterized in that: The protection process in step S6 is as follows: Immerse in chromate passivation solution for 10-20 seconds to form an anti-oxidation film; Chromate passivation solution: pH 3-4, containing Cr 3+ Concentration 3-5g / L‌.

9. The multi-chemical coating process for flexible circuit boards made of aluminum foil according to claim 8, characterized in that: The water washing is performed by three-stage water washing, and the three-stage water washing is a three-stage countercurrent water washing, and the water flow rate is ≥5L / min·m².

10. A multi-layer chemical coating process for flexible circuit boards made of aluminum foil, characterized in that: The method comprises the following another process step, which uses any one of claims 2 to 4 and claims 7 to 9 as dependent claims: Step A1. Surface treatment: Scan the texture of the flexible circuit board and emboss the texture on the substrate using printing technology. The specific process is as follows: (1) Heat the aluminum foil substrate to 120-150°C to soften it; (2) Using a hydraulic press to emboss the mold under a pressure of 50-80 MPa to form grooves with a depth of 8-12 μm; (3) Composite cleaning to optimize groove texture; Step A2. Pretreatment before copper plating: Place the surface treated substrate into a zinc bath for zinc precipitation, and recover the residual zinc solution on the substrate by recycling technology, and then clean the residue on the substrate by washing; Step A3. Copper plating: Immerse the pretreated substrate in a copper plating solution and apply appropriate current and voltage. Copper ions will be deposited on the surface of the substrate to form a uniform copper layer. Step A4. Recovery and subsequent processing: After the copper plating is completed, the residue on the substrate is cleaned by water washing. After the water washing is completed, the copper-plated substrate is polished. After the polishing is completed, the residue on the substrate is removed by water washing. After the water washing is completed, the copper plating layer of the substrate is protected and then washed with ultrasonic equipment to remove the residue on the substrate after the protective treatment. It is then sent to a drying equipment for drying.

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