Electrolyte for low-temperature environment-friendly type citrate system electrocast bright hard gold

Abstract

The application relates to the field of electrochemical deposition and metal material processing, and discloses an electrolyte for low-temperature environment-friendly type citrate system electroformed bright hard gold, which comprises water, 15-25 g / L of gold sulfite in terms of alloy concentration, 60-80 g / L of triammonium citrate, 10-20 g / L of succinic acid, 30-50 g / L of potassium sulfate, 80-100 g / L of potassium dihydrogen phosphate, 0.5-1.5 g / L of a soluble salt of a rare earth element, 0.01-0.05 g / L of a high-molecular polymer containing nitrogen, 1.0-2.0 g / L of saccharin and 10-30 mg / L of 2,2'-dipyridyl, and the pH value is 7.0-7.5. In the process, the workpiece is placed in the electrolyte, the temperature is kept at 38-42 DEG C, and the deposition is carried out by applying a current density of 0.15-0.5 A / dm2. The application overcomes the low-temperature polarization anomaly by compounding the rare earth salt and the polymer, and prepares a bright gold layer with a hardness of 120-150 HV, thereby reducing the energy consumption and simplifying the wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of electrochemical deposition and metal material processing technology, specifically to a low-temperature environmentally friendly citrate system electrolyte for electroforming bright hard gold. Background Technology

[0002] Electroforming is a metalworking process that deposits a gold layer onto the surface of a cathode mandrel or substrate through an electrochemical deposition process. Electroforming can replicate the surface contours of the substrate and impart electrical conductivity, oxidation resistance, and chemical stability to the workpiece.

[0003] In the surface treatment industry, electroforming gold is used in the manufacturing of precision electronic connectors, semiconductor lead frames, and jewelry. Traditional gold electroforming processes mostly use cyanide systems. Due to the toxicity of cyanide, the industry has gradually shifted towards developing cyanide-free systems. Among the existing cyanide-free systems, citrate systems have become a common industrial choice to replace cyanide systems due to their low toxicity and near-neutral operating environment.

[0004] Conventional citrate-based cyanide-free electroforming systems require maintaining the electrolyte at relatively high temperatures in actual production to ensure normal ion conduction and metal crystallization. Higher operating temperatures increase energy consumption and accelerate the decomposition of organic additives in the electrolyte, leading to unstable bath composition and maintenance difficulties. Directly lowering the operating temperature of the conventional system reduces the ion conductivity of the electrolyte, increases cathodic polarization, and causes the growth rate of crystal nuclei to exceed the nucleation rate due to increased mass transfer resistance. Therefore, gold layers deposited under low-temperature conditions in conventional systems exhibit coarse crystals, scorching at workpiece edges, and low Vickers hardness. Current technologies cannot simultaneously meet the demands of reducing operating energy consumption and obtaining high-hardness, high-brightness gold layers in industrial production. Summary of the Invention

[0005] The technical problem solved by this invention is that conventional citrate systems have technical defects such as low ion conductivity, abnormal cathode polarization leading to rough coating crystals, scorching, and insufficient hardness during low-temperature operation, and cannot simultaneously achieve low-temperature operation, high hardness, and surface gloss.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a low-temperature environmentally friendly citrate-based electrolyte for electroforming bright hard gold, employing the following technical solution: a low-temperature environmentally friendly citrate-based electrolyte for electroforming bright hard gold, wherein the low-temperature environmentally friendly citrate-based electrolyte for electroforming bright hard gold comprises water and components of the following concentrations: gold sulfite (alloy concentration) of 15-25 g / L; triammonium citrate: 60-80 g / L; succinic acid: 10-20 g / L; potassium sulfate: 30-50 g / L; potassium dihydrogen phosphate: 80-100 g / L; hardener: 0.5-1.5 g / L, wherein the hardener is a soluble salt of a rare earth element; grain refiner: 0.01-0.05 g / L, wherein the grain refiner is a nitrogen-containing polymer; saccharin: 1.0-2.0 g / L; 2,2'-bipyridine: 10-30 mg / L.

[0008] By employing the above technical solution, the kinetics of the cathode interface reaction are adjusted in the chelation system of triammonium citrate and succinic acid by combining soluble salts of rare earth elements with nitrogen-containing polymers, along with saccharin and 2,2'-bipyridine. This allows for the stable deposition of a high-hardness, low-roughness, bright gold layer at low temperatures of 38-42℃. The working principle and reaction process are as follows: First, establishing complexation equilibrium: Triammonium citrate and succinic acid in the electrolyte act as primary and secondary complexing agents, forming water-soluble metal chelates with rare earth ions in the soluble salts of rare earth elements. Under an environment with a pH of 7.0-7.5, the rare earth ions are masked, preventing hydrolysis and precipitation, thus maintaining electrolyte clarity. Second, regulating cathode polarization: The nitrogen-containing polymers adsorb onto the active sites on the cathode surface through polar groups, hindering the direct discharge of gold complex ions, thereby increasing the electrochemical polarization of the cathode and raising the cathode overpotential. The increase in overpotential compensates for the decline in mass transfer kinetics caused by the decrease in operating temperature and suppresses the hydrogen evolution side reaction. The third step is the recombination and nucleation process: under the action of the cathode overpotential, the discharge reduction process of gold ions transforms from grain growth to three-dimensional nucleation, increasing the nucleation rate and forming a densely crystalline deposit that hinders dendrite growth. The fourth step is solid solution formation and grain refinement strengthening: during electroforming deposition, rare earth ions are adsorbed at grain boundaries and growth steps and co-deposited into the gold lattice, inducing lattice distortion and internal stress strengthening. The internal stress, combined with the grain refinement strengthening induced by the nitrogen-containing polymer, hinders grain boundary slip and dislocation movement, thereby increasing the hardness of the gold layer.

[0009] Preferably, the gold sulfite salt is potassium gold sulfite or sodium gold sulfite; the soluble salt of the rare earth element is one or a combination of cerium ammonium nitrate, cerium chloride, and cerium sulfate; and the nitrogen-containing polymer is one or a combination of polyethyleneimine, polydiallyl dimethyl ammonium chloride, and chitosan. By adopting the above technical solution, the types of components are limited, the chemical compatibility between the substances is ensured, and the quality of gold layer crystallization is optimized.

[0010] Preferably, the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system contains water and the following components at the following concentrations: gold sulfite (alloy concentration: 20 g / L); triammonium citrate: 70 g / L; succinic acid: 15 g / L; potassium sulfate: 40 g / L; potassium dihydrogen phosphate: 90 g / L; hardener: 1.0 g / L; grain refiner: 0.03 g / L; saccharin: 1.5 g / L; 2,2'-bipyridine: 20 mg / L. By adopting the above technical solution, the concentrations of each component are limited, achieving a balance between the complexation masking effect and polarization regulation, resulting in a uniform gold layer.

[0011] Preferably, the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system has a pH value of 7.0-7.5, and further contains ammonia or citric acid to adjust the pH value. By adopting the above technical solution, the electrolyte is controlled within a neutral range, reducing corrosion to the electroforming equipment while ensuring the stability of the complexation system.

[0012] Secondly, the present invention provides a low-temperature environmentally friendly citrate system electroforming bright hard gold process, which adopts the following technical solution: A low-temperature environmentally friendly citrate system electroforming bright hard gold process includes the following steps: placing the pretreated workpiece as the cathode and the pure gold plate as the anode in the electrolyte of the above-mentioned low-temperature environmentally friendly citrate system electroforming bright hard gold; keeping the temperature of the electrolyte of the low-temperature environmentally friendly citrate system electroforming bright hard gold constant at 38-42℃; and applying a cathode current density of 0.15-0.5A / dm² under stirring conditions for electroforming deposition.

[0013] By adopting the above technical solution, the low-temperature environmentally friendly citrate system electroforming bright hard gold process, combined with the above electrolyte components, operates in a low-temperature environment of 38-42℃, reducing energy consumption and decomposition of additives. It controls the cathode current density within the range of 0.15-0.5A / dm², matching the electrochemical discharge rate of gold ions with the low mass transfer rate of the solution, avoiding concentration polarization caused by mass transfer resistance, and avoiding crystal roughness and plating defects.

[0014] Preferably, the pretreatment steps for the pretreated workpiece include: degreasing, acid pickling and activation, and thorough water washing. By adopting the above technical solution, oil stains and oxide layers on the surface of the workpiece are removed, and the adhesion between the gold layer and the workpiece substrate is improved.

[0015] Preferably, the electroforming deposition is powered by a pulse power supply or a DC power supply. When using a pulse power supply, the pulse parameters are: duty cycle 30%-50%, frequency 500-1000Hz. When using a DC power supply, a pre-impregnation treatment is performed before power-on, with a pre-impregnation time of 30-60s. By adopting the above technical solutions, pulse power supply can provide instantaneous overpotential, which is beneficial for refining grains and improving hardness; DC power supply combined with pre-impregnation treatment can form an adsorption layer on the workpiece surface before power-on, ensuring the smoothness of the initial deposition stage.

[0016] Preferably, the stirring method in the stirring conditions is strong stirring with compressed air or cathode movement. The intensity of the strong stirring with compressed air is controlled to produce continuous ripples on the liquid surface without splashing. By adopting the above technical solution, stirring breaks the diffusion layer on the cathode surface, accelerates the transport of complexed ions towards the cathode, and avoids solution splashing.

[0017] Preferably, the substrate material of the workpiece is copper, copper alloy, nickel, or semiconductor lead frame material. By adopting the above technical solution, the applicable range of industrial substrates for the low-temperature environmentally friendly citrate system electroforming bright hard gold process is clarified, adapting to the needs of various substrate materials.

[0018] Preferably, the gold layer on the workpiece surface obtained through the electroforming deposition step has a Vickers hardness of 120-150 HV and a surface roughness Ra ≤ 0.1 μm. By adopting the above technical solution, the final performance indicators achieved by the process are clearly defined, meeting the requirements of precision electronic connectors or jewelry for hardness and appearance.

[0019] This invention provides a low-temperature, environmentally friendly citrate-based electrolyte for electroforming bright hard gold. It offers the following advantages:

[0020] 1. This invention controls the working temperature of the electrolyte between 38 and 42°C, changing the traditional high-temperature operation requirements of the citrate system and reducing energy consumption during production. The low-temperature environment slows down the decomposition rate of organic additives in the electrolyte, maintains the stability of the electrolyte composition, and reduces the daily maintenance cost of the electrolyte.

[0021] 2. This invention overcomes the crystal roughness defect caused by the decrease in ionic conductivity under low-temperature conditions by adding soluble salts of rare earth elements and nitrogen-containing polymers to the electrolyte. The internal stress generated by the co-deposition of rare earth ions and the grain refinement effect caused by the adsorption of polymers combine to achieve a Vickers hardness of 120 to 150 HV for the deposited gold layer, while ensuring the smoothness and brightness of the gold layer surface.

[0022] 3. This invention uses gold sulfite instead of traditional cyanide as the gold source, and combines it with triammonium citrate and succinic acid in a neutral environment to construct a cyanide-free electroplating system. The entire electroplating deposition process involves no highly toxic substances and produces no chlorine gas, improving the operating environment of the production workshop and simplifying the treatment process for electroplating wastewater. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0025] Potassium gold sulfite, CAS No. 71662-32-3, molecular formula K3Au(SO3)2, commercially available electroplating grade purity reagent.

[0026] Sodium gold sulfite, CAS No. 39281-74-8, molecular formula Na3Au(SO3)2, commercially available electroplating grade purity reagent.

[0027] Polyethyleneimine, CAS No. 9002-98-6, is a high molecular weight compound with repeating unit (CH2CH2NH)n. It is a commercially available water-soluble reagent product with an average molecular weight (Mw) of 1800.

[0028] Polydiallyldimethylammonium chloride, CAS No. 26062-79-3, is a high molecular weight compound with repeating unit (C8H16ClN)n. It is a commercially available cationic water-soluble reagent product with a weight-average molecular weight (Mw) of 100,000.

[0029] Chitosan, CAS No. 9012-76-4, is a high molecular weight compound with the molecular formula (C6H11NO4)n. It is a commercially available reagent product with a degree of deacetylation greater than or equal to 85%.

[0030] 2,2'-Bipyridine, CAS No. 366-18-7, molecular formula C10H8N2, commercially available analytical grade reagent.

[0031] The triammonium citrate, succinic acid, potassium sulfate, potassium dihydrogen phosphate, cerium ammonium nitrate, cerium chloride, cerium sulfate, saccharin, anhydrous ethanol, ammonia, and citric acid involved in this invention are all known commercially available substances that can be identified by their chemical structural characteristics in the art. Whether or not they are disclosed will not result in insufficient disclosure. The purpose of this invention can be achieved by using commercially available conventional analytical grade reagents.

[0032] The pure gold plate, copper, copper alloy and nickel matrix materials involved in this invention are all common metal materials with conventional purity or industrial grade, and will not be described in detail here.

[0033] Preparation Example 1:

[0034] This preparation example provides a low-temperature, environmentally friendly citrate-based electrolyte for electroforming bright hard gold, comprising the following steps:

[0035] Dissolve 70 g / L triammonium citrate, 15 g / L succinic acid, 40 g / L potassium sulfate, and 90 g / L potassium dihydrogen phosphate sequentially in deionized water. After complete dissolution, add potassium gold sulfite (equivalent to 20 g / L), 1.0 g / L cerium ammonium nitrate, 0.03 g / L polyethyleneimine, and 1.5 g / L saccharin. Finally, add 20 mg / L 2,2'-bipyridine, which has been dissolved in anhydrous ethanol beforehand. After mixing thoroughly, adjust the pH to 7.2 with ammonia or citric acid to obtain the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system.

[0036] Preparation Example 2:

[0037] This preparation example provides a low-temperature, environmentally friendly citrate-based electrolyte for electroforming bright hard gold, comprising the following steps:

[0038] Dissolve 60 g / L triammonium citrate, 10 g / L succinic acid, 30 g / L potassium sulfate, and 80 g / L potassium dihydrogen phosphate sequentially in deionized water. After complete dissolution, add sodium gold sulfite (equivalent to 15 g / L), 0.5 g / L cerium chloride, 0.01 g / L polydiallyldimethylammonium chloride, and 1.0 g / L saccharin. Finally, add 10 mg / L 2,2'-bipyridine, which has been dissolved in anhydrous ethanol beforehand. After mixing thoroughly, adjust the pH to 7.0 with ammonia or citric acid to obtain the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system.

[0039] Preparation Example 3:

[0040] This preparation example provides a low-temperature, environmentally friendly citrate-based electrolyte for electroforming bright hard gold, comprising the following steps:

[0041] Dissolve 80 g / L triammonium citrate, 20 g / L succinic acid, 50 g / L potassium sulfate, and 100 g / L potassium dihydrogen phosphate sequentially in deionized water. After complete dissolution, add potassium gold sulfite (equivalent to 25 g / L), 1.5 g / L cerium sulfate, 0.05 g / L chitosan, and 2.0 g / L saccharin. Finally, add 30 mg / L 2,2'-bipyridine, which has been dissolved in anhydrous ethanol beforehand. After mixing thoroughly, adjust the pH to 7.5 with ammonia or citric acid to obtain the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system.

[0042] Reference Figure 1 , Figure 1 Here is a process flow diagram of the present invention:

[0043] Example 1:

[0044] This embodiment provides a low-temperature, environmentally friendly citrate-based electroforming bright hard gold process, including the following steps:

[0045] Take the electrolyte prepared in Preparation Example 1 and keep the electrolyte temperature constant at 40°C. Use a copper substrate that has undergone degreasing, acid washing and activation pretreatment, thoroughly wash it with water, and use a pure gold plate as the anode in the electrolyte. Use a pulse power supply to turn on the compressed air to stir vigorously. Control the stirring intensity to produce continuous ripples on the liquid surface without splashing. Apply a cathode current density of 0.3 A / dm² for electroforming for 2 hours.

[0046] Example 2:

[0047] This embodiment provides a low-temperature, environmentally friendly citrate-based electroforming bright hard gold process, including the following steps:

[0048] Take the electrolyte prepared in Preparation Example 2 and keep the electrolyte temperature constant at 38°C; place the pretreated workpiece as the cathode and the pure gold plate as the anode in the electrolyte; use a DC power supply and perform a pre-immersion treatment before powering on, with a pre-immersion time of 30s; apply a cathode current density of 0.15A / dm² for electroforming deposition under stirring conditions with the cathode moving.

[0049] Example 3:

[0050] This embodiment provides a low-temperature, environmentally friendly citrate-based electroforming bright hard gold process, including the following steps:

[0051] Take the electrolyte prepared in Preparation Example 3 and keep the electrolyte temperature constant at 42°C. Place the pretreated workpiece as the cathode and the pure gold plate as the anode in the electrolyte. Power the workpiece with a pulse power supply, set the pulse parameters to a duty cycle of 50% and a frequency of 1000Hz, and apply a cathode current density of 0.5A / dm² for electroforming deposition under the condition of strong stirring with compressed air.

[0052] Comparative Example 1:

[0053] Compared with Example 1, the difference is that the isothermal control temperature of the electrolyte is changed to 60°C, and all other aspects are the same.

[0054] Comparative Example 2:

[0055] The difference from Example 1 is that cerium ammonium nitrate is not added to the electrolyte, but all other aspects are the same.

[0056] Comparative Example 3:

[0057] The difference from Example 1 is that polyethyleneimine is not added to the electrolyte; all other aspects are the same.

[0058] Comparative Example 4:

[0059] Compared to Example 1, the difference is that neither cerium ammonium nitrate nor polyethyleneimine is added to the electrolyte, while all other aspects are the same.

[0060] Test Example 1:

[0061] Performance tests were conducted on workpiece samples prepared using the processes of Examples 1 to 3 and Comparative Examples 1 to 4, after cleaning and drying. The surface smoothness, color continuity, and presence of scorching and plating defects were observed visually under natural light. X-ray fluorescence thickness gauges were used to measure the surface center and four corners of the workpiece samples, and the arithmetic mean of these five points was recorded as the plating thickness. A micro Vickers hardness tester was used to perform spot tests on the gold layer cross-section of the workpiece, with a load set to 25 grams and a holding time of 15 seconds. Five different locations were randomly selected for testing each sample, and the arithmetic mean was calculated after removing outliers. A contact surface roughness tester was used to determine the arithmetic mean deviation Ra value of the gold layer surface profile.

[0062] Table 1. Performance test data of electroformed gold layers in the examples and comparative examples.

[0063]

[0064] Table 1 shows that Examples 1 to 3 obtained bright gold layers with a hardness between 124 and 148 HV and a roughness Ra of less than 0.1 micrometers within a temperature range of 38 to 42°C. Comparative Example 4 exhibited edge scorching and rough crystallization at 40°C. This is because the ion mass transfer rate of the conventional citrate system decreases at low temperatures, inducing concentration polarization. The nucleus growth rate exceeds the nucleation rate, leading to dendrite growth and hydrogen evolution side reactions.

[0065] A comparison of data from Example 1 and Comparative Example 2 shows that the Vickers hardness of the gold layer increased from 86 to 136 after the addition of cerium ammonium nitrate to the system. Rare earth cerium ions adsorb at grain boundaries and growth steps during electrodeposition, and are co-deposited into the gold lattice. Doping induces lattice distortion, resulting in a combined effect of solid solution strengthening and grain refinement strengthening, which hinders grain boundary slip and internal dislocation movement, manifesting as an increase in the hardness of the gold layer.

[0066] A comparison of data from Example 1 and Comparative Example 3 shows that after adding polyethyleneimine, the surface roughness Ra decreased from 0.22 μm to 0.06 μm, and no whitening or hazing phenomenon appeared on the surface. The nitrogen-containing polymer possesses polar groups, which adsorb onto the active growth points on the cathode surface. This adsorption behavior increases the electrochemical polarization of the cathode, inhibits grain elongation and growth, and promotes the formation of new crystal nuclei by metal ions. The three-dimensional nucleation process dominates, resulting in a dense microstructure and improved surface smoothness in the deposited layer.

[0067] This method employs a compound of rare earth element soluble salts and nitrogen-containing polymers to alter the reaction kinetics at the cathode interface under low-temperature conditions. The polymers provide the overpotential required for grain refinement, while the rare earth ions provide internal stress reinforcement at the crystal lattice level. Both compensate for the increased mass transfer resistance caused by cooling. This method solves the technical problem of conventional systems being unable to simultaneously achieve low-temperature operation and coating performance, enabling hard gold electroforming under low-temperature conditions.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-temperature, environmentally friendly citrate-based electrolyte for electroforming bright hard gold, characterized in that, The electrolyte for the low-temperature environmentally friendly citrate system electroforming bright hard gold contains water and the following components at the following concentrations: Gold sulfite, with a gold concentration of 15-25 g / L; Triammonium citrate: 60-80 g / L; Succinic acid: 10-20 g / L; Potassium sulfate: 30-50 g / L; Potassium dihydrogen phosphate: 80-100 g / L; Hardener: 0.5-1.5 g / L, wherein the hardener is a soluble salt of rare earth element; Grain refiner: 0.01-0.05 g / L, wherein the grain refiner is a nitrogen-containing polymer; Saccharin: 1.0-2.0 g / L; 2,2'-Bipyridine: 10-30 mg / L.

2. The electrolyte for electroforming bright hard gold using a low-temperature environmentally friendly citrate system according to claim 1, characterized in that, The gold sulfite salt is potassium gold sulfite or sodium gold sulfite; The soluble salts of the rare earth elements are one or a combination of several of cerium ammonium nitrate, cerium chloride, and cerium sulfate. The nitrogen-containing polymer is one or a combination of several of polyethyleneimine, polydiallyldimethylammonium chloride, and chitosan.

3. The electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system according to claim 1, characterized in that, The electrolyte for the low-temperature environmentally friendly citrate system electroforming bright hard gold contains water and the following components at the following concentrations: gold sulfite, with an alloy concentration of 20 g / L; triammonium citrate: 70 g / L; succinic acid: 15 g / L; potassium sulfate: 40 g / L; potassium dihydrogen phosphate: 90 g / L; hardener: 1.0 g / L; grain refiner: 0.03 g / L; saccharin: 1.5 g / L; 2,2'-bipyridine: 20 mg / L.

4. The electrolyte for electroforming bright hard gold using a low-temperature environmentally friendly citrate system according to any one of claims 1 to 3, characterized in that, The electrolyte of the low-temperature environmentally friendly citrate system for electroforming bright hard gold has a pH value of 7.0-7.5, and the electrolyte of the low-temperature environmentally friendly citrate system for electroforming bright hard gold also contains ammonia or citric acid to adjust the pH value.

5. A low-temperature environmentally friendly citrate system electroforming bright hard gold process using the electrolyte of the low-temperature environmentally friendly citrate system electroforming bright hard gold according to any one of claims 1-4, characterized in that, Includes the following steps: The pretreated workpiece is used as the cathode, and the pure gold plate is used as the anode. The workpiece is placed in the electrolyte of the low-temperature environmentally friendly citrate system for electroforming bright hard gold. The temperature of the electrolyte for electroforming bright hard gold using the low-temperature environmentally friendly citrate system is kept constant at 38-42℃. Electroforming deposition was carried out under stirring conditions with a cathode current density of 0.15-0.5 A / dm².

6. The low-temperature environmentally friendly citrate system electroforming bright hard gold process according to claim 5, characterized in that, The pretreatment steps for the pretreated workpiece include: degreasing, acid pickling and activation, and thorough water washing.

7. The low-temperature environmentally friendly citrate system electroforming bright hard gold process according to claim 5, characterized in that, The electroforming deposition is powered by a pulse power supply or a DC power supply. When using a pulse power supply, the pulse parameters are: duty cycle 30%-50%, frequency 500-1000Hz; When using a DC power supply, pre-soaking is performed before powering on, and the pre-soaking time is 30-60 seconds.

8. The low-temperature environmentally friendly citrate system electroforming bright hard gold process according to claim 5, characterized in that, The stirring conditions are described in the form of powerful stirring with compressed air or cathode movement. The intensity of the powerful stirring with compressed air is controlled to produce continuous ripples on the liquid surface without splashing.

9. The low-temperature environmentally friendly citrate system electroforming bright hard gold process according to claim 5, characterized in that, The base material of the workpiece is copper, copper alloy, nickel, or semiconductor lead frame material.

10. The low-temperature environmentally friendly citrate system electroforming bright hard gold process according to claim 5, characterized in that, The gold layer on the workpiece surface obtained through the electroforming deposition step has a Vickers hardness of 120-150 HV and a surface roughness Ra≤0.1μm.

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