Cyanide-free alkaline copper electroplating process suitable for various base materials

Abstract

The invention relates to the technical field of electroplating, in particular to a cyanide-free alkaline copper electroplating process suitable for various substrates, which comprises the following steps: adding a predetermined amount of water into a plating bath, and sequentially adding conductive salt, methionine copper, a complexing agent and a brightener to form a plating solution which comprises 100-150g / L of conductive salt, 35-50g / L of methionine copper, 10-20ml / L of complexing agent and 1-3ml / L of brightener; wherein the complexing agent comprises the following components in percentage by mass: 1% of sodium hydroxide, 33% of dispersing agent NNO and the balance of deionized water. A dispersing agent NNO in the complexing agent can effectively inhibit hydrolytic precipitation of copper ions in the plating solution and can refine crystal grains of a plating layer at the same time; and moreover, the complexing agent can have a synergistic effect with copper salt and conductive salt in the plating solution, so that the uniformity and brightness of a plating layer can be improved, the vaporific defect of a low-current area is effectively improved, and the glossiness and stability of the plating layer are enhanced while the brightness range of the plating layer is expanded.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more specifically to a cyanide-free alkaline copper electroplating process applicable to a variety of substrates. Background Technology

[0002] Under the trend of green transformation in the electroplating industry, cyanide-free alkaline copper electroplating technology has become a core direction to replace traditional cyanide copper plating technology due to its compliance with environmental regulations. Although traditional cyanide copper plating technology was once used due to its strong coating adhesion and excellent coverage, cyanide is highly toxic, posing a serious threat to the health of operators and causing serious environmental pollution, and has now been gradually phased out by the industry. Cyanide-free alkaline copper plating technology is being promoted gradually due to its environmentally friendly advantages, but its technological maturity still needs to be improved, with the core bottleneck concentrated in the design and optimization of the complexing agent system.

[0003] Existing cyanide-free alkaline copper plating processes often use single-type or simply compounded complexing agents. The synergistic effect between these agents and components in the plating bath, such as copper salts and conductive salts, is insufficient, resulting in poor stability and weak resistance to contamination. Long-term use can lead to component imbalance, resulting in decreased plating brightness and uniformity. Furthermore, traditional processes struggle to balance the plating brightness range with the coverage of complex workpieces. Low-current areas are prone to hazy defects, and plating integrity is insufficient for deep holes and irregularly shaped workpieces. Additionally, wastewater treatment in some processes is difficult, leading to high maintenance costs and failing to meet the high precision and stability requirements of high-end manufacturing. Summary of the Invention

[0004] The primary objective of this invention is to provide a cyanide-free alkaline copper electroplating process applicable to various substrates, in order to solve the problems of poor coating uniformity, brightness, and insufficient coverage in the prior art.

[0005] To achieve the objectives of this invention, this invention provides a cyanide-free alkaline copper electroplating process applicable to various substrates, comprising the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form a plating solution. The plating solution comprises 100-150 g / L conductive salt, 35-50 g / L copper methionine, 10-20 ml / L complexing agent, and 1-3 ml / L brightener. The complexing agent comprises, by mass ratio: 1% sodium hydroxide, 33% dispersant NNO, and the balance being deionized water. Electroplating: The plating solution is heated to a predetermined temperature, and the workpiece is placed into the plating solution for electroplating. The current density, the concentration of metal ions in the plating solution, and the temperature are controlled within a predetermined range.

[0006] Preferably, the conductive salt comprises, by mass ratio: 39% sodium carbonate, 10% sodium thiocyanate, 24% sodium gluconate, and 27% sodium chloride.

[0007] Preferably, the brightener comprises, by mass ratio: 15% sodium dodecyl sulfonate, 35% triethanolamine, and the balance being deionized water.

[0008] Preferably, in the electroplating step, the plating bath temperature is controlled at 40-55℃, the plating bath pH is 9-13, and the current density is 0.5-4 A / dm³. 2 The copper ion concentration in the plating solution is 12-35 g / L, and the concentration of free conductive salt is 10-25 g / L.

[0009] Preferably, the steps for determining the concentration of free conductive salts in the plating solution are as follows: Take 1 ml of plating solution sample and dilute it with 50 ml of water, then add 10 ml of 10% (m / v) potassium iodide to the plating solution; Titrate the plating solution with 0.1N silver nitrate until the endpoint. The plating solution will be slightly yellow and turbid. Record the titration volume N1 of silver nitrate and the concentration of free conductive salt C1 (g / L) = 9.8·N1.

[0010] Preferably, the steps for determining the concentration of copper ions in the plating solution are as follows: Take 2 ml of plating solution sample, add 1 g of ammonium persulfate and an appropriate amount of water to the plating solution, shake the plating solution well and place it on an electric furnace to heat to 40°C; Add 10 ml of pH 10 buffer solution and 6-10 drops of 0.1% PAN indicator to the plating solution, and then titrate with 0.1N EDTA to the endpoint. The plating solution changes from blue to green. Record the titration volume N2 of EDTA and the copper ion concentration C2 (g / L) = 3.18·N2.

[0011] Preferably, the anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and an anode bag is placed over the anode.

[0012] Preferably, in the electroplating step, the plating solution is continuously filtered at a frequency of 4-8 cycles / hour.

[0013] Preferably, in the electroplating step, the brightener is added at a frequency of 180-200 ml / kWh.

[0014] Preferably, the following steps are also included: Before electroplating, activated carbon powder is added to the plating solution, and then the plating solution is filtered to remove organic impurities.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The complexing agent system of the present invention comprises 1% sodium hydroxide, 33% dispersant NNO and the balance deionized water. The dispersant NNO can effectively inhibit the hydrolysis and precipitation of copper ions in the plating solution, and at the same time refine the grain size of the plating layer. With the synergistic effect of the complexing agent and copper salts and conductive salts in the plating solution, the uniformity and brightness of the plating layer can be improved, the haze defects in the low current area can be effectively improved, and the gloss and stability of the plating layer can be enhanced while expanding the bright range of the plating layer.

[0016] 2. The complexing agent of this invention exhibits excellent synergy with the components of the plating solution, which can enhance the plating solution's resistance to impurity contamination, reduce component imbalance problems after long-term use, and ensure the long-term stability of the plating solution. At the same time, this complexing agent system can optimize the dispersion performance of the plating solution, improve the coverage of complex workpieces such as deep holes and irregular shapes, and ensure the integrity of the coating on such workpieces.

[0017] 3. The complexing agent system of the present invention can be applied to the coating adhesion requirements of metal substrates with different potentials. It can stably adapt to substrates with different potentials such as steel, copper, zinc alloy, and aluminum alloy without adjusting the core components of the plating solution, ensuring that the coating and the substrate form a strong bond. At the same time, it reduces the plating solution adjustment process when switching substrates, significantly improving production efficiency.

[0018] 4. This invention adopts a cyanide-free complexation system, avoiding the health and environmental risks caused by cyanide; at the same time, the stability of the plating solution components is improved, reducing the amount of waste plating solution generated, reducing the difficulty and maintenance cost of wastewater treatment, and further adapting to the green transformation direction of the electroplating industry. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Existing cyanide-free alkaline copper plating processes typically use single-type or simply compounded complexing agents, which are usually only compatible with specific substrates, resulting in a narrow range of substrate compatibility. Switching between different substrates often requires adjusting the plating bath composition, severely impacting production efficiency. Furthermore, existing complexing agents lack sufficient synergy with copper salts, conductive salts, and other components in the plating bath, leading to poor stability and weak resistance to impurities. Long-term use can easily result in component imbalance, leading to decreased coating brightness and reduced uniformity.

[0021] Traditional processes also face the challenge of balancing the brightness of the plating layer with the coverage of complex workpieces. Low-current areas are prone to hazy defects, and the plating integrity is insufficient for deep holes and irregularly shaped workpieces. For various metal substrates with significant potential differences, traditional complexing agents are insufficient to meet the plating adhesion requirements, often resulting in inadequate substrate-coating bonding. Furthermore, wastewater treatment in some existing processes is difficult, and maintenance costs are high, failing to meet the high precision and stability requirements of high-end manufacturing.

[0022] To address the above problems, this invention provides a cyanide-free alkaline copper electroplating process suitable for various substrates, comprising the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form a plating solution. The plating solution comprises 100-150 g / L conductive salt, 35-50 g / L copper methionine, 10-20 ml / L complexing agent, and 1-3 ml / L brightener. The complexing agent comprises, by mass ratio: 1% sodium hydroxide, 33% dispersant NNO, and the balance being deionized water. Electroplating: The plating solution is heated to a predetermined temperature, and the workpiece is placed into the plating solution for electroplating. The current density, the concentration of metal ions in the plating solution, and the temperature are controlled within a predetermined range.

[0023] Copper methionine (Cu(Met)2) serves as the main salt in the plating bath, primarily providing copper ions. The dispersant in the complexing agent is NNO (sodium methylene bis(naphthalene)sulfonate, chemical formula C). 21 H 14 Na₂O₆S₂ primarily functions as a dispersant, preventing particle agglomeration and refining crystal grains through physical dispersion and adsorption. Sodium hydroxide provides OH⁻. - Sodium hydroxide is used to adjust the pH, stabilizing the complexation of methionine and copper ions. Furthermore, sodium hydroxide improves the dispersion of the dispersant NNO. Brighteners, as organic additives, can be sulfur- or nitrogen-containing organic compounds that selectively adsorb on the cathode surface, altering the crystal growth pattern of copper deposition. This primarily affects grain morphology and brightness, resulting in a denser and brighter coating.

[0024] In the electroplating process, the cathode is the workpiece, where a reduction reaction occurs, resulting in copper deposition. Methionine copper exists in a complexation-dissociation equilibrium in the plating bath. On the cathode surface, copper ions gain electrons and are reduced to metallic copper, which is then deposited on the workpiece.

[0025] In addition, the plating solution contains sodium hydroxide, making it alkaline at pH, which may lead to the hydrogen evolution side reaction: 2H₂O + 2e⁻. →H₂↑+2OH⁻ However, the hydrogen evolution reaction leads to increased porosity in the coating and increased stress.

[0026] The anode can be made of various materials, such as stainless steel, zinc alloy, iron, copper, and bronze. The oxygen evolution reaction mainly occurs at the anode: 2H₂O → O₂↑ + 4H₂O. + +4e The copper ions in the plating solution are provided solely by the dissolution and dissociation of copper methionine, requiring regular replenishment of the main salt, copper methionine.

[0027] The above process uses copper methionine as the copper source and main salt. Methionine has both amino and carboxyl groups, which form a stable complex with copper ions. The complex structure is stable, and the change in copper ions is relatively gradual when the pH and temperature of the plating solution change, resulting in a long plating solution life. Compared with the traditional cyanide copper plating process, it does not contain cyanide and is safe and environmentally friendly.

[0028] Second, the complexing agent composition has both complexing and dispersing effects, with sodium hydroxide providing OH-. The pH is adjusted so that methionine exists in anionic form, which facilitates the complexation of copper ions. Dispersant NNO, traditionally used in dye dispersants and concrete water-reducing agents, is rarely seen in plating solutions. In this process, NNO mainly functions to disperse, prevent agglomeration, refine grains, and improve the microstructure of the coating. It reduces the impact of suspended matter and particulate impurities, essentially combining the complexing agent and dispersant into one component, simplifying the formulation. The synergistic effect of the complexing agent with copper salts and conductive salts in the plating solution improves the uniformity and brightness of the coating, effectively improves hazy defects in low-current areas, expands the brightness range of the coating, and enhances the gloss stability of the coating.

[0029] Third, the complexing agent exhibits excellent synergy with the components of the plating solution, which can enhance the plating solution's resistance to impurity contamination, reduce component imbalance after long-term use, and ensure the long-term stability of the plating solution. At the same time, this complexing agent system can optimize the dispersion performance of the plating solution, improve its coverage of complex workpieces such as deep holes and irregular shapes, and ensure the integrity of the coating on such workpieces.

[0030] Fourth, the entire electroplating process has a wide parameter window, making it easy to control. The high concentration of conductive salts improves the conductivity of the plating solution, reduces tank voltage and energy consumption, and helps maintain a uniform plating layer even at high current densities.

[0031] Fifth, the complexing agent system of the present invention can be applied to the coating adhesion requirements of metal substrates with different potentials. It can stably adapt to substrates with different potentials such as steel, copper, zinc alloy, and aluminum alloy without adjusting the core components of the plating solution, ensuring that the coating and the substrate form a strong bond. At the same time, it reduces the plating solution adjustment process when switching substrates, significantly improving production efficiency.

[0032] The electroplating process provided in this application results in a coating with stable composition and structure, refined grains, and a smooth and flat surface. Furthermore, the refined grains improve the adhesion of the coating, making it less prone to peeling or flaking, thus achieving a coating with good bonding strength.

[0033] In one embodiment, the conductive salt comprises, by mass ratio: 39% sodium carbonate, 10% sodium thiocyanate, 24% sodium gluconate, and 27% sodium chloride. Sodium chloride provides a large amount of Cl. - and Na + The conductivity contributes the most, and sodium carbonate, sodium thiocyanate, and sodium gluconate also have good conductivity. The plating solution has high conductivity and more uniform current distribution, and can work at higher current densities without causing serious heat generation.

[0034] Furthermore, sodium carbonate forms a buffer system in water: CO3 2- +H2O HCO3 +OH It can stabilize the pH of the plating solution, avoid rapid pH drift due to side reactions (such as hydrogen evolution), provide a suitable alkaline environment for methionine copper complexation, and reduce the risk of Cu(OH)2 precipitation caused by pH fluctuations.

[0035] In addition to improving conductivity, sodium thiocyanate can also be slightly adsorbed at the cathode, refining grains, improving coating uniformity, and enhancing the deep plating capability of the plating solution.

[0036] Sodium gluconate is also an organic complexing agent. It works synergistically with methionine to further reduce the concentration of free copper ions, inhibit the hydrolysis and precipitation of copper ions, improve the stability and lifespan of the plating solution, and enhance the brightness and uniformity of the coating.

[0037] In summary, the synergistic effect of multiple ions in conductive salts results in high conductivity of the plating solution, uniform current distribution, and consistent coating thickness. Conductive salts can also improve pH buffering capacity, enhance the stability of the plating solution, and prevent precipitation. Furthermore, they can assist in complexation, thereby improving the lifespan and reliability of the plating solution.

[0038] In one embodiment, the brightener comprises, by mass ratio: 15% sodium dodecyl sulfonate, 35% triethanolamine, and the balance being deionized water.

[0039] Sodium dodecyl sulfate is a typical anionic surfactant that can adsorb onto the cathode surface, inhibiting the rapid growth of copper on certain crystal planes and refining the grains, resulting in a brighter, smoother, and more even coating. Furthermore, sodium dodecyl sulfate significantly reduces the surface tension of the plating solution, making it less likely for bubbles to adhere to the workpiece surface and improving the appearance of pitting and pinholes caused by hydrogen evolution reaction at the cathode. The plating solution also more easily penetrates deep holes and crevices, enhancing the ability to achieve deep plating.

[0040] Triethanolamine exhibits slight adsorption on the cathode surface, which enhances cathode polarization, inhibits grain growth, and promotes crystal nucleation—a key factor in obtaining a bright, dense coating. Triethanolamine synergistically enhances adsorption capacity with sodium dodecyl sulfate, improving grain refinement, stabilizing the brightener system, and reducing delamination. Triethanolamine also forms weak complexes with copper ions, resulting in gentler copper deposition and reduced roughness defects. Furthermore, it forms a synergistic complexation system with methionine, making the plating bath more stable.

[0041] In one embodiment, during the electroplating step, the plating bath temperature is controlled at 40-55°C, the plating bath pH is 9-13, and the current density is 0.5-4 A / dm³. 2 The copper ion concentration in the plating bath is 12-35 g / L, and the concentration of free conductive salt is 10-25 g / L. Controlling the electroplating temperature between 40-55℃ avoids excessively low temperatures leading to overly strong copper complexation and insufficient free copper ions, resulting in slow deposition. It also avoids excessively high temperatures causing excessive dissociation of the complex, leading to a rough coating. The 40-55℃ temperature range places the copper ion complexation-dissociation within an optimal range, resulting in ideal deposition rate and grain size. The pH is 9-13, as methionine exists in anionic form under alkaline conditions, exhibiting the strongest binding capacity. The current density is 0.5-4 A / dm³. 2 The process has a wide window of opportunity, strong adaptability, and is easier to control in industrial production. Controlling the copper ion concentration at 12-35 g / L ensures a sufficient deposition rate; the concentration is neither too low (resulting in slow deposition) nor too high (resulting in coarse grains and a rough coating). Controlling the free conductive salt concentration at 10-25 g / L ensures stable conductivity of the plating solution and maintains its pH buffering capacity.

[0042] In one embodiment, the step for determining the concentration of free conductive salt in the plating solution is as follows: Take 1 ml of plating solution sample and dilute it with 50 ml of water, then add 10 ml of 10% (m / v) potassium iodide to the plating solution; Titrate the plating solution with 0.1N silver nitrate until the endpoint. The plating solution will be slightly yellow and turbid. Record the titration volume N1 of silver nitrate and the concentration of free conductive salt C1 (g / L) = 9.8·N1.

[0043] As described above, the conductive salts, by mass ratio, comprise 39% sodium carbonate, 10% sodium thiocyanate, 24% sodium gluconate, and 27% sodium chloride. Among these salts, those that can react with Ag... + The precipitate is Cl. - and SCN - Cl - and SCN - Both are related to Ag + Both produced white precipitates, while CO3... 2- With Ag+ It will generate Ag2CO3, but in the presence of I - In the system, it may be masked or not affect the endpoint observation. Therefore, this titration process is equivalent to measuring free Cl. - and SCN - The total amount.

[0044] The determination process begins by taking 1 mL of plating solution, diluting it with 50 mL of water, and then adding 10 mL of 10% (m / v) potassium iodide (KI) to provide a large amount of I₂. - This allows Ag to reach the titration endpoint. + First with I - The reaction produces AgI, a yellow precipitate, which causes the solution to become slightly yellow and cloudy. This is the color at the titration endpoint. - As an indicator, it indicates that the endpoint has been reached. Titration with 0.1N silver nitrate to the endpoint results in Cl... - and SCN - All have been completely precipitated, and the volume of silver nitrate consumed at this point is recorded as N1 (ml). Because for Cl... - and SCN - In this case, the equivalent concentration equals the molar concentration; therefore, the molar concentration of silver nitrate is 0.1 mol / L, and the number of moles of anions contributing to the titration of the conductive salt is 0.0001N1 (mol). Based on the composition of the conductive salt, the weighted average equivalent mass can be calculated, thereby converting it into the free conductive salt concentration C1, which is a theoretical calculation value. However, considering that other components in the plating bath can interfere with the results, side reactions occurring in the plating bath can also cause interference, and the indicator itself will consume some Ag... + There are also some subjective errors in the determination of the titration endpoint. Based on these factors and multiple experimental corrections, the conductive salt component is equivalently converted into an equivalent salt of 98 g / mol, thus obtaining the free conductive salt concentration C1 (g / L) = 9.8·N1.

[0045] In one embodiment, the step for determining the concentration of copper ions in the plating solution is as follows: Take 2 ml of plating solution sample, add 1 g of ammonium persulfate and an appropriate amount of water to the plating solution, shake the plating solution well and place it on an electric furnace to heat to 40°C; Add 10 ml of pH 10 buffer solution and 6-10 drops of 0.1% PAN indicator to the plating solution, and then titrate with 0.1N EDTA to the endpoint. The plating solution changes from blue to green. Record the titration volume N2 of EDTA and the copper ion concentration C2 (g / L) = 3.18·N2.

[0046] Specifically, first take 2 ml of plating solution sample and add 1 g of ammonium persulfate (NH4)2S2O8. Ammonium sulfate is a strong oxidizing agent that can destroy the complex structure of copper ions and methionine, releasing copper ions. Heating to 40℃ can accelerate the destruction of the methionine copper complex by ammonium persulfate, making the release of copper ions more complete. Add a buffer solution with a pH of 10, which is the pH environment required for EDTA titration. Add 6-10 drops of 0.1% PAN indicator. PAN (1-(2-pyridinium azo)-2-naphthol) is a Cu... 2+ A classic indicator, Cu, at pH 10 2+ It forms a complex with PAN. However, EDTA (ethylenediaminetetraacetic acid) reacts with Cu. 2+ It has a stronger complexing ability and will bind Cu 2+ EDTA can be extracted from PAN and react with Cu. 2+ It forms a very stable 1:1 complex when all Cu 2+ After being complexed with EDTA, PAN regains its own color, indicating that the titration endpoint has been reached, and the volume of EDTA consumed, N2 (ml), is recorded.

[0047] Since 0.1N EDTA is used, the equivalent concentration of EDTA is the molar concentration. Therefore, the molar concentration of EDTA is 0.1 mol / L. The number of moles of EDTA consumed in the titration = concentration × volume = 0.1 mol / L × (N2 / 1000)L = 0.0001N2 (mol). Therefore, the EDTA titration of Cu... 2+ The molar number of N2 is 0.0001 mol, and the molar mass of copper is 63.55 g / mol. Therefore, the mass of copper is 0.0001 N2 × 63.55 = 0.006355 N2 (g). This is the mass of copper in a 2 ml sample of plating solution. Converting this to the copper concentration (g / L) C2 in the plating solution: C2=(0.006355×N2)×(1000 / 2)=3.18·N2 In one embodiment, the anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and an anode bag is placed over the anode.

[0048] High-purity (≥99.95%) oxygen-free electrolytic copper contains almost no impurities such as iron, lead, and zinc, preventing impurities from dissolving into the plating solution during the electroplating process. If the anode contains impurities, it will lead to the accumulation of impurity ions in the plating solution, causing defects such as burrs, pitting, and blackening in the coating. At the same time, it will disrupt the coordination balance between methionine copper and the complexing agent, affecting the stability of the plating solution.

[0049] An oxygen content of ≤0.001% can prevent the formation of oxide particles such as copper oxide and cuprous oxide during anodic dissolution. If these particles enter the plating solution, they will become the core of impurities in the coating, resulting in decreased coating adhesion and poorer corrosion resistance.

[0050] The oxygen-free copper anode dissolves uniformly and can stably release Cu. 2+ The high-purity anode matches the copper methionine complex system in the plating bath, ensuring a uniform deposition rate and preventing issues such as uneven coating thickness and coarse crystals. It also reduces the introduction of impurities, decreases the frequency of plating bath filtration and purification, extends the service life of the plating bath, lowers maintenance costs, and simplifies process control.

[0051] During electroplating, a small amount of insoluble residue, such as trace impurities, oxides, and undissolved copper particles, is generated on the anode surface, known as "anode mud." Anode bags can intercept these residues, preventing them from adsorbing onto the workpiece surface with the plating solution and causing pitting, pinholes, increased roughness, and inclusions in the plating layer. Furthermore, anode bags can slow down the intense convection of the plating solution on the anode surface, preventing localized Cu... 2+ If the concentration is too high or too low, ensure a uniform ion supply to the workpiece surface to improve the consistency of coating thickness and gloss.

[0052] In one embodiment, during the electroplating step, the plating solution is continuously filtered at a frequency of 4-8 cycles / hour.

[0053] During electroplating, trace impurities are continuously generated. Filtering at a frequency of 4-8 cycles / hour can intercept these impurities in real time, preventing them from adsorbing onto the workpiece surface or embedding into the plating layer. This effectively reduces defects such as pitting, pinholes, burrs, and blackening in the plating layer, and is particularly suitable for cyanide-free alkaline copper systems with high purity requirements for the plating solution. Continuous filtration drives the circulation of the plating solution, preventing localized Cu buildup. 2+ To address issues such as excessively high or low concentrations of brighteners and complexing agents, it is crucial to ensure uniform ion supply and additive action across all areas of the workpiece surface, thereby maintaining the uniformity of the plating solution composition and stabilizing the deposition effect.

[0054] For multi-substrate electroplating (such as steel, aluminum, copper alloys, etc.), different substrates have different requirements for the stability of the plating solution components. A uniform plating solution environment can ensure the consistency of the coating thickness, adhesion and gloss of various substrates, thus meeting the core process requirement of "applicable to a variety of substrates".

[0055] In one embodiment, during the electroplating step, the brightener is added at a frequency of 180-200 ml / kWh. Adding the brightener at this frequency precisely maintains its effective concentration, ensuring stable gloss and leveling of the plating layer. This avoids excessively high concentrations that could lead to brittle plating and reduced adhesion, or excessively low concentrations that would prevent leveling and brightening, resulting in defects such as haziness and streaks in the plating layer.

[0056] A fixed brightener addition frequency can avoid brightener concentration imbalance caused by fluctuations in electroplating time and workpiece loading, ensuring that coatings of different batches and substrates can maintain uniform gloss, smoothness and fineness, reducing batch differences and meeting the quality control requirements of mass production scenarios.

[0057] In one embodiment, the process further includes the following steps: Before electroplating, activated carbon powder is added to the plating solution, and then the plating solution is filtered to remove organic impurities.

[0058] Organic impurities are easily introduced during the preparation and pretreatment of the plating solution. These include trace organic byproducts from methionine copper synthesis, organic matter generated from the degradation of NNO dispersant in the complexing agent, and trace amounts of oil residue from workpiece pretreatment. These organic impurities can contaminate the plating solution. Activated carbon, with its extremely high specific surface area and adsorption activity, can specifically adsorb these organic impurities, preventing them from adsorbing onto the workpiece surface or embedding into the plating layer during electroplating. This effectively reduces defects such as haze, blooming, uneven gloss, and decreased adhesion in the plating layer, and is particularly suitable for the cyanide-free alkaline copper system's sensitivity to organic impurities.

[0059] Example 1 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 135g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 15ml / L (prepared by mass ratio: 1% sodium hydroxide + 33% dispersant NNO + balance deionized water); Brightener 2ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole stainless steel workpiece. The stainless steel workpiece is activated with 5% sulfuric acid solution for 30 seconds and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 2A / dm³. 2 The plating solution temperature was 45℃, the pH of the plating solution was 11, the copper ion concentration in the plating solution was 25g / L, and the free conductive salt concentration was 15g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 6 cycles / hour, and the brightener addition frequency is 190ml / KAH.

[0060] Example 2 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 100g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 10ml / L (prepared by mass ratio: 1% sodium hydroxide + 33% dispersant NNO + balance deionized water); Brightener 1ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole zinc alloy workpiece. The zinc alloy workpiece is treated with a weak alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then activated with 10g / L zinc oxide solution for 30 seconds, and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 1 A / dm³. 2 The plating solution temperature was 40℃, the pH of the plating solution was 9, the copper ion concentration in the plating solution was 15g / L, and the free conductive salt concentration was 10g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 4 cycles / hour, and the brightener addition frequency is 180ml / KAH.

[0061] Example 3 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 135g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 15ml / L (prepared by mass ratio: 1% sodium hydroxide + 33% dispersant NNO + balance deionized water); Brightener 2ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole zinc alloy workpiece. The zinc alloy workpiece is treated with a weak alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then activated with 10g / L zinc oxide solution for 30 seconds, and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 2A / dm³. 2 The plating solution temperature was 45℃, the pH of the plating solution was 11, the copper ion concentration in the plating solution was 25g / L, and the free conductive salt concentration was 15g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 6 cycles / hour, and the brightener addition frequency is 190ml / KAH.

[0062] Example 4 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 150g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 50g / L; Complexing agent 20ml / L (prepared by mass ratio: 1% sodium hydroxide + 33% dispersant NNO + balance deionized water); Brightener 3ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole zinc alloy workpiece. The zinc alloy workpiece is treated with a weak alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then activated with 10g / L zinc oxide solution for 30 seconds, and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 4A / dm³. 2 The plating solution temperature was 55℃, the pH of the plating solution was 13, the copper ion concentration in the plating solution was 35g / L, and the free conductive salt concentration was 25g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 8 cycles / hour, and the brightener addition frequency is 200ml / KAH.

[0063] Example 5 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 135g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 15ml / L (prepared by mass ratio: 1% sodium hydroxide + 33% dispersant NNO + balance deionized water); Brightener 2ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole aluminum alloy workpiece. The aluminum alloy workpiece is treated with an alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then etched with a 20g / L sodium hydroxide solution for 1 minute, and then treated with a zincate treatment solution (10g / L zinc oxide + 80g / L sodium hydroxide) for 2 minutes to form a zinc transition layer. After rinsing, it is placed in the tank.

[0064] Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 2A / dm³. 2 The plating solution temperature was 45℃, the pH of the plating solution was 11, the copper ion concentration in the plating solution was 25g / L, and the free conductive salt concentration was 15g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 6 cycles / hour, and the brightener addition frequency is 190ml / KAH.

[0065] Comparative Example 1 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 135g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 15ml / L (prepared by mass ratio: 34% ethylenediaminetetraacetic acid (EDTA) + balance deionized water); Brightener 2ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole zinc alloy workpiece. The zinc alloy workpiece is treated with a weak alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then activated with 10g / L zinc oxide solution for 30 seconds, and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 2A / dm³. 2 The plating solution temperature was 45℃, the pH of the plating solution was 11, the copper ion concentration in the plating solution was 25g / L, and the free conductive salt concentration was 15g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 6 cycles / hour, and the brightener addition frequency is 190ml / KAH.

[0066] Comparative Example 2 A cyanide-free alkaline copper electroplating process includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form the plating solution; the plating solution includes: Conductive salt 135g / L (prepared by mass ratio: 39% sodium carbonate + 10% sodium thiocyanate + 24% sodium gluconate + 27% sodium chloride); Copper methionine 45g / L; Complexing agent 15ml / L (prepared by mass ratio: 34% sodium hydroxide + balance deionized water); Brightener 2ml / L (prepared by mass ratio: 15% sodium dodecyl sulfate + 35% triethanolamine + balance deionized water); Plating solution pretreatment: Add activated carbon powder to the plating solution and filter to remove organic impurities; Substrate pretreatment: The substrate is a deep-hole zinc alloy workpiece. The zinc alloy workpiece is treated with a weak alkaline degreasing agent (5g / L sodium hydroxide + 10g / L sodium carbonate) for 2 minutes, then activated with 10g / L zinc oxide solution for 30 seconds, and then rinsed and put into the tank. Electroplating: The plating solution is heated, and the workpiece is immersed in the solution for electroplating, with the current density controlled at 2A / dm³. 2 The plating solution temperature was 45℃, the pH of the plating solution was 11, the copper ion concentration in the plating solution was 25g / L, and the free conductive salt concentration was 15g / L. The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and is covered with an anode bag. The continuous filtration frequency is 6 cycles / hour, and the brightener addition frequency is 190ml / KAH.

[0067] Performance testing and results analysis (1) Gloss range and gloss of the coating: Brightness range: Under standard light source D65 conditions, the surface condition of the workpiece after electroplating is recorded by visual observation combined with image acquisition equipment. The percentage of the bright area (area without haze, without pitting, and with uniform color) to the total area of ​​the workpiece is calculated according to the grid partitioning method (each area is 1cm×1cm, and the total number of partitions is ≥50). Coating gloss: The gloss meter with an incident angle of 60° is used for testing. Five evenly distributed effective test points are selected on the surface of the workpiece (avoiding edges and scratch areas). Each point is tested twice and the average value is taken. The final result is the arithmetic mean of all test points (unit: gloss unit, GU).

[0068] (2) Deep hole coverage integrity: Select a standard deep hole workpiece with a hole diameter of 2mm and a hole depth of 10mm. After electroplating, cut along the hole axis and observe the morphology of the coating on the inner wall of the deep hole using a metallographic microscope (magnification of 200x). Calculate the percentage of the continuous coverage area of ​​the coating on the inner wall of the deep hole using image analysis software (conventional image grayscale recognition algorithm).

[0069] (3) Matrix adhesion (cross-cut grade): According to GB / T5270-2024 "Test method for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates", use a cross-cut knife to make a 1mm×1mm grid on the coating surface (cut through the coating to the substrate), apply 3M 600 tape and peel it off quickly perpendicular to the coating surface (peeling speed ≥1m / s). The coating is graded according to the area of ​​peeling off: Grade 1 (no peeling), Grade 2 (peeling area <5%), Grade 3 (peeling area 5%-15%), Grade 4 (peeling area 15%-30%), Grade 5 (peeling area >30%).

[0070] (4) Temperature fluctuation tolerance: The test procedure Nb for "rapid temperature change" in GB / T2423.22-2012 "Environmental testing - Part 2: Test methods - Test N: Temperature change" shall be performed: Test equipment: High and low temperature alternating test chamber (temperature control accuracy ±0.5℃, temperature change rate ≤5℃ / min); Sample preparation: The electroplated workpiece (dry surface, no external damage) is fixed in the sample rack of the test chamber, with a workpiece spacing of ≥2cm (avoid contact); Cyclic procedure: Hold at 35℃ for 2 hours → Increase temperature to 55℃ at a rate of ≤5℃ / min and hold for 2 hours → Decrease temperature to 35℃ at a rate of ≤5℃ / min to complete one cycle, and repeat for a total of 20 cycles; Test items: Detect the proportion of bright areas and adhesion level of the coating, and calculate the gloss change rate (change rate = |gloss after cycle - gloss before cycle| / gloss before cycle × 100%). Result determination: The coating performance is stable: the proportion of bright area decreases by ≤5%, the adhesion level does not decrease, and the gloss change rate is ≤10%; if all conditions are met, it is judged as "stable", otherwise it is "unstable".

[0071] Examples 1-5 and Comparative Examples 1-2 used test workpieces with the same shape and size specifications. The above-mentioned tests were performed on each workpiece, and the results are shown in Table 1 below: Table 1 - Comparison of coating performance in each embodiment and comparative example The results are analyzed as follows: (1) The gloss range (90%-95%) and gloss (89-95 GU) of the coatings in Examples 1-5 were significantly better than those in the comparative examples (gloss range 70%-80%, gloss 65-76 GU). In Example 3, the brightener (2 ml / L) and complexing agent (15 ml / L) were synergistically formulated. The sodium hydroxide and NNO in the complexing agent worked synergistically to achieve a gloss range and gloss of 95. Comparative Example 1 used a conventional EDTA complexing agent, while the complexing agent in Comparative Example 2 used an equal amount of sodium hydroxide to replace the dispersant NNO in Examples 1-5. However, the coating quality in Comparative Example 1 and Comparative Example 2 was significantly lower than that in Examples 1-5, indicating that the composition range of the plating solution of the present invention can improve the appearance quality of the coating. The synergistic effect of sodium hydroxide and NNO in the complexing agent can improve the uniformity and gloss of the coating, effectively improve the haze defects in the low current area, and enhance the gloss and stability of the coating while expanding the gloss range of the coating.

[0072] (2) Multi-substrate compatibility: In Examples 1-5, stainless steel, zinc alloy and aluminum alloy were used for electroplating. The plating brightness range, plating gloss, deep hole coverage integrity and substrate adhesion of the three substrate materials are not much different, indicating that the plating solution system of the present invention is suitable for a variety of substrate materials.

[0073] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A cyanide-free alkaline copper electroplating process applicable to various substrates, characterized in that, Includes the following steps: Plating solution preparation: Add a predetermined amount of water to the plating tank, and then add conductive salt, copper methionine, complexing agent, and brightener in sequence to form a plating solution. The plating solution comprises 100-150 g / L conductive salt, 35-50 g / L copper methionine, 10-20 ml / L complexing agent, and 1-3 ml / L brightener. The complexing agent comprises, by mass ratio: 1% sodium hydroxide, 33% dispersant NNO, and the balance being deionized water. Electroplating: The plating solution is heated to a predetermined temperature, and the workpiece is placed into the plating solution for electroplating. The current density, the concentration of metal ions in the plating solution, and the temperature are controlled within a predetermined range.

2. The cyanide-free alkaline copper electroplating process as described in claim 1, characterized in that, The conductive salt comprises, by mass ratio: 39% sodium carbonate, 10% sodium thiocyanate, 24% sodium gluconate, and 27% sodium chloride.

3. The cyanide-free alkaline copper electroplating process as described in claim 1, characterized in that, The brightener comprises, by mass ratio: 15% sodium dodecyl sulfonate, 35% triethanolamine, and the remainder being deionized water.

4. The cyanide-free alkaline copper electroplating process as described in claim 1, characterized in that, In the electroplating process, the plating bath temperature is controlled at 40-55℃, the pH of the plating bath is 9-13, and the current density is 0.5-4 A / dm³. 2 The copper ion concentration in the plating solution is 12-35 g / L, and the concentration of free conductive salt is 10-25 g / L.

5. The cyanide-free alkaline copper electroplating process as described in claim 4, characterized in that, The steps for determining the concentration of free conductive salts in the plating solution are as follows: Take 1 ml of plating solution sample and dilute it with 50 ml of water, then add 10 ml of 10% (m / v) potassium iodide to the plating solution; Titrate the plating solution with 0.1N silver nitrate until the endpoint. The plating solution will be slightly yellow and turbid. Record the titration volume N1 of silver nitrate and the concentration of free conductive salt C1 (g / L) = 9.8·N1.

6. The cyanide-free alkaline copper electroplating process as described in claim 4, characterized in that, The steps for determining the concentration of copper ions in the plating solution are as follows: Take 2 ml of plating solution sample, add 1 g of ammonium persulfate and an appropriate amount of water to the plating solution, shake the plating solution well and place it on an electric furnace to heat to 40°C; Add 10 ml of pH 10 buffer solution and 6-10 drops of 0.1% PAN indicator to the plating solution, and then titrate with 0.1N EDTA to the endpoint. The plating solution changes from blue to green. Record the titration volume N2 of EDTA and the copper ion concentration C2 (g / L) = 3.18·N2.

7. The cyanide-free alkaline copper electroplating process according to any one of claims 1-6, characterized in that, The anode is made of oxygen-free electrolytic copper with a copper content of ≥99.95% and an oxygen content of ≤0.001%, and an anode bag is placed around the anode.

8. The cyanide-free alkaline copper electroplating process according to any one of claims 1-6, characterized in that, During the electroplating process, the plating solution is continuously filtered at a frequency of 4-8 cycles per hour.

9. The cyanide-free alkaline copper electroplating process according to any one of claims 1-3, characterized in that, In the electroplating step, the brightener is added at a frequency of 180-200 ml / KAH.

10. The cyanide-free alkaline copper electroplating process according to any one of claims 1-3, characterized in that, It also includes the following steps: Before electroplating, activated carbon powder is added to the plating solution, and then the plating solution is filtered to remove organic impurities.

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