Palladium-nickel alloy electroplating solution, preparation method and application thereof

Abstract

The application relates to the technical field of electroplating liquid and electronic connector terminal surface treatment, and discloses a palladium-nickel alloy electroplating liquid and a preparation method and application thereof, wherein the electroplating liquid comprises palladium ions provided by tetraammine palladium sulfate, nickel ions provided by nickel sulfamate, ammonium sulfamate, ammonium sulfate, a ladder complex release component composed of glycine, sodium citrate, N-(2-hydroxyethyl) iminodiacetic acid disodium, ethylenediamine disuccinic acid trisodium and polyaspartic acid sodium, L-proline, sodium 1,2,4-triazole-3-carboxylate and a micro-area wetting component. Through cooperation of the components, the application can reduce the edge enrichment deposition and grain boundary pore defects of a high-speed connector contact area, and improve the contact stability of a palladium-nickel alloy plating layer.

Description

Technical Field

[0001] This invention relates to the field of electroplating solutions and surface treatment technology for electronic connector terminals, and more specifically, to palladium-nickel alloy electroplating solutions and their application in high-speed connectors. Background Technology

[0002] High-speed connector terminals typically require a wear-resistant, corrosion-resistant, and contact resistance-stable functional plating layer to be formed on the contact area surface of a copper alloy substrate. Palladium-nickel alloy plating, combining the contact stability of precious metals with the hardness and wear resistance of nickel, has been used in electronic connector terminals and related electrical contact components. In the prior art, patent CN101838830B discloses a palladium-nickel alloy electrolyte, which includes a main salt, a complexing agent, additives, a conductive salt, and a pH stabilizer. The palladium salt can be tetraamminepalladium sulfate, the nickel salt can be nickel aminosulfonate, the complexing agent can be glycine, citric acid, or their salts, the conductive salt can be ammonium sulfate, the pH stabilizer is boric acid or pyroborate, and the additives can be thiourea compounds, pyridine sulfonic acid, alkynyl alcohols, etc. This type of solution can obtain bright, dense palladium-nickel alloy plating layers with varying nickel content.

[0003] US Patent 5342504A discloses a palladium-nickel alloy electroplating solution comprising water-soluble palladium salt, water-soluble nickel salt, ammonia, ammonium salt, and 3-pyridine sulfonic acid, used to obtain a uniform and bright palladium-nickel alloy electrodeposited film at a high current density. US Patent 4699697A discloses a high-purity palladium-nickel alloy electroplating solution for electronic components, wherein the electroplating solution contains a palladium-ammonium complex, nickel salt, aromatic sulfonate, ammonium salt, and ammonium sulfate, and forms a palladium-nickel alloy deposition layer with a nickel content of 1%-15% under conditions of pH 6-8.

[0004] Regarding connector terminal structure, patent CN202205928U discloses a linear plug terminal. The electroplated layer of the terminal consists of a nickel layer, a palladium-nickel layer, and a gold layer from the inside out. The mass ratio of palladium to nickel in the palladium-nickel layer is 80%-85%:20%-15%, which is used to reduce the cost of gold-plated plug terminals while taking into account conductivity and wear resistance.

[0005] However, the aforementioned existing technologies primarily focus on the brightness, conventional density, nickel content range, adaptability to higher current densities, or composite plating structures of connector terminals in palladium-nickel alloy plating. For narrow strip-shaped contact areas, arc-shaped contact bumps, or elastic contact beams in high-speed connector terminals, differences exist between the edge and center positions of the contact area in terms of current distribution, fluid flow renewal, and diffusion layer thickness. This can easily lead to uneven metal composition distribution, edge-enriched deposition, grain boundary porosity defects, and contact resistance fluctuations in the palladium-nickel alloy plating within the micro-contact area. Especially without using cyanide, boric acid, pyroborate, 3-pyridine sulfonic acid, thiourea, and alkynyl alcohol brighteners, there is still room for improvement in achieving both palladium-nickel co-deposition stability, micro-area deposition uniformity, and high-speed connector contact reliability in a weakly alkaline, low-free-ammonia system.

[0006] Therefore, when existing palladium-nickel alloy electroplating solutions are used in the tiny contact areas of high-speed connector terminals, it is difficult to simultaneously reduce the enrichment deposition at the contact area edges, grain boundary porosity defects, and contact resistance fluctuations without relying on traditional boric acid / pyridine sulfonic acid / thiourea / alkynyl alcohol systems. Summary of the Invention

[0007] The purpose of this invention is to provide a palladium-nickel alloy electroplating solution, its preparation method, and its application, in order to solve the above-mentioned technical problems.

[0008] To achieve the above objectives, the present invention provides the following solution: On one hand, the present invention provides a palladium-nickel alloy electroplating solution for depositing a palladium-nickel alloy plating layer in the contact area of ​​a high-speed connector terminal. The palladium-nickel alloy electroplating solution is a near-neutral to weakly alkaline aqueous electroplating solution, comprising, by mass concentration: Palladium ions: 8 g / L-16 g / L, wherein the palladium ions are derived from tetraamminepalladium sulfate; Nickel ions: 1.2 g / L - 4.0 g / L, wherein the nickel ions are derived from nickel aminosulfonate; Ammonium aminosulfonate 40g / L-90g / L; Ammonium sulfate 8g / L-35g / L; The stepwise complexation release component is 11 g / L-34 g / L, and the stepwise complexation release component is composed of glycine, sodium citrate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediamine disuccinate and sodium polyaspartate. The nickel deposition buffer component is 0.4 g / L-2.0 g / L, and the nickel deposition buffer component is L-proline; The grain boundary adsorption regulating component is 0.05 g / L-0.35 g / L, and the grain boundary adsorption regulating component is sodium 1,2,4-triazole-3-carboxylate; The micro-wetting component is 0.02 g / L-0.18 g / L, and the micro-wetting component is N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt; The remainder is deionized water; The pH of the palladium-nickel alloy electroplating solution is 6.6-7.6, and the free ammonia concentration is ≤3g / L.

[0009] Preferably, in the stepwise complexation release component, the mass concentration of glycine is 6 g / L-16 g / L, the mass concentration of sodium citrate is 3 g / L-10 g / L, the mass concentration of disodium N-(2-hydroxyethyl)iminodiacetic acid is 1.2 g / L-4.0 g / L, the mass concentration of trisodium ethylenediaminedisuccinate is 0.6 g / L-3.0 g / L, and the mass concentration of sodium polyaspartate is 0.05 g / L-0.50 g / L.

[0010] Preferably, the sodium polyaspartate has a weight-average molecular weight of 1000-3000, and the combined mass concentration of the glycine and sodium citrate is 2.5 to 8 times the combined mass concentration of the disodium N-(2-hydroxyethyl)iminodiacetic acid and the trisodium ethylenediaminedisuccinate.

[0011] Preferably, L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt together constitute the interface stabilization system of the high-speed connector contact area; the interface stabilization system of the high-speed connector contact area is used to reduce the edge enrichment deposition, grain boundary porosity defects, and contact resistance fluctuations of the palladium-nickel alloy plating on the surface of narrow strip contact areas, arc-shaped contact bumps, or elastic contact beams.

[0012] Preferably, under the conditions of temperature 48℃-58℃, pH 6.8-7.3, and current density 4A / dm²-12A / dm², the palladium-nickel alloy electroplating solution deposits a palladium-nickel alloy coating in the contact area of ​​the high-speed connector terminal, and the difference in nickel mass percentage between the edge and center of the palladium-nickel alloy coating is ≤2.5%.

[0013] On the other hand, the present invention also provides a method for preparing the above-mentioned palladium-nickel alloy electroplating solution, comprising the following steps: Nickel aminosulfonate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, a portion of glycine, and a portion of deionized water were mixed and the pH was adjusted to 6.4-7.0 to obtain a nickel complex mother liquor. Mix tetraamminepalladium sulfate, sodium citrate, the remaining glycine, and some deionized water, and adjust the pH to 6.8-7.4 to obtain the palladium complex mother liquor; The nickel complex mother liquor was added to the palladium complex mother liquor, and ammonium aminosulfonate and ammonium sulfate were added to obtain a palladium-nickel base solution. L-proline, sodium 1,2,4-triazol-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt were added sequentially to the palladium-nickel base solution. Deionized water was added and the pH was adjusted to 6.6-7.6 to obtain the palladium-nickel alloy electroplating solution.

[0014] Preferably, when preparing the nickel complex mother liquor, the temperature is controlled at 35℃-45℃ and the stirring time is 30min-80min; When preparing the palladium complex mother liquor, the temperature is controlled at 30℃-45℃ and the stirring time is 20min-60min; After adding L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt to the palladium-nickel base solution, stirring was continued for 30-90 minutes.

[0015] In another aspect, the present invention also provides an application of the above-mentioned palladium-nickel alloy electroplating solution on high-speed connector terminals. Specifically, the copper alloy substrate of the high-speed connector terminal is subjected to degreasing, micro-etching and activation treatment. After forming a nickel barrier layer on the surface of the contact area of ​​the copper alloy substrate, the palladium-nickel alloy electroplating solution is used to deposit a palladium-nickel alloy plating layer on the surface of the nickel barrier layer. The contact area is a narrow strip-shaped contact area, an arc-shaped contact bump, or an elastic contact beam.

[0016] Preferably, when depositing the palladium-nickel alloy coating, an inner wear-resistant zone is first formed at a first current density, and then an outer contact zone is formed at a second current density. The first current density is 7A / dm²-12A / dm², and the second current density is 3A / dm²-6A / dm². The nickel mass percentage content in the inner wear-resistant zone is 16%-22%, and the nickel mass percentage content in the outer contact zone is 8%-15%. A palladium-nickel composition transition zone is formed between the inner wear-resistant zone and the outer contact zone.

[0017] In another aspect, the present invention also protects a high-speed connector terminal, comprising a copper alloy substrate and a nickel barrier layer and a palladium-nickel alloy plating layer sequentially formed on the surface of the contact area of ​​the copper alloy substrate, wherein the palladium-nickel alloy plating layer is formed by deposition of the aforementioned palladium-nickel alloy electroplating solution. The thickness of the nickel barrier layer is 0.8μm-2.5μm; The thickness of the palladium-nickel alloy coating is 0.10 μm-0.70 μm; The palladium-nickel alloy coating includes an inner wear-resistant zone, a palladium-nickel composition transition zone, and an outer contact zone. The mass percentage of nickel in the inner wear-resistant zone is greater than the mass percentage of nickel in the outer contact zone. The outer contact area serves as the outermost contact metal layer of the high-speed connector terminal.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses a stepped complexation release component composed of glycine, sodium citrate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediamine disuccinate, and sodium polyaspartate to form palladium and nickel ions in a weakly alkaline, low-free-ammonia system with varying intensities of complexation release. This reduces the local drift in the palladium-nickel co-deposition ratio during electroplating of the contact area of ​​high-speed connector terminals, thereby improving the consistency of nickel content between the edge and center of the contact area.

[0019] By using L-proline as a buffer component for nickel deposition, the deposition rate variation of nickel during the palladium-nickel co-deposition process is buffered, which helps to reduce the residual tensile stress of the palladium-nickel alloy coating and reduce cracks or increased contact resistance caused by stress concentration in the coating during subsequent insertion and extraction wear.

[0020] By setting sodium 1,2,4-triazole-3-carboxylate as a grain boundary adsorption regulating component, the grain boundary deposition state of the palladium-nickel alloy coating can be adjusted, which helps to reduce grain boundary porosity defects and improve the contact stability of the palladium-nickel alloy coating in humid, hot, sulfur-containing or mixed gas environments.

[0021] By setting N,N-dimethyl-N-dodecyl-3-sulfopropylammonium internal salt as a micro-area wetting component, the wetting state of the narrow strip contact area, arc-shaped contact bump, or elastic contact beam surface of the high-speed connector terminal is improved, which can reduce the enrichment and deposition at the edge position caused by insufficient fluid flow renewal or local current concentration.

[0022] The palladium-nickel alloy electroplating solution of the present invention is free of cyanide, boric acid, pyroborate, 3-pyridine sulfonic acid brighteners, thiourea brighteners, and alkynyl alcohol brighteners. It can achieve uniform composition, reduced porosity, controlled stress, and stable contact resistance in the palladium-nickel alloy plating layer for the contact area of ​​high-speed connector terminals, under conditions that are different from traditional palladium-nickel bright electroplating systems.

[0023] When the palladium-nickel alloy electroplating solution is applied to the terminals of high-speed connectors, a palladium-nickel alloy plating layer suitable for high-speed differential signal transmission contacts can be formed on the surface of the nickel barrier layer. Furthermore, by setting the inner wear-resistant zone, the palladium-nickel composition transition zone, and the outer contact zone, the plating layer can achieve both resistance to insertion and extraction wear and stability of the outer contact. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise stated, all raw materials used in this invention are commercially available. Tetraamminepalladium sulfate is measured by palladium ion mass concentration, and nickel aminosulfonate is measured by nickel ion mass concentration. pH adjustment can be performed using dilute ammonia or aminosulfonic acid. A small amount of dilute ammonia is used to raise the pH, and aminosulfonic acid is used to lower the pH, ensuring the free ammonia concentration does not exceed 3 g / L during the adjustment process. The conductivity of the deionized water is preferably not greater than 5 μS / cm.

[0026] In this invention, palladium and nickel ions serve as the metal sources for the palladium-nickel alloy coating. The palladium ions are derived from tetraamminepalladium sulfate, which is beneficial for maintaining the complexation stability of palladium in a weakly alkaline system. The nickel ions are derived from nickel sulfamate, which is beneficial for providing a suitable nickel ion source for palladium-nickel co-deposition and reducing the impact of chloride ions on coating stress and corrosion reliability. Ammonium sulfamate and ammonium sulfate are used to improve the conductivity of the electroplating solution and, in conjunction with the weakly alkaline pH environment, maintain the stability of the palladium-nickel co-deposition process.

[0027] In this invention, glycine, sodium citrate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, and sodium polyaspartate together constitute a stepwise complexation release component. Glycine and sodium citrate provide a basic complexation environment, maintaining palladium and nickel ions in a depositable state in a weakly alkaline system. Disodium N-(2-hydroxyethyl)iminodiacetic acid and trisodium ethylenediaminedisuccinate regulate the release intensity of the nickel complexed state, reducing the nickel deposition ratio deviation between the edge and center positions of the contact area in the high-speed connector. Sodium polyaspartate improves the local distribution stability of metal ions near the micro-contact area, mitigating local deposition spikes. Through the combined action of these components, the local drift of the palladium-nickel alloy co-deposition ratio at different locations in the contact area can be reduced.

[0028] In this invention, L-proline serves as a nickel deposition buffer component to buffer the deposition rate changes of nickel during the palladium-nickel co-deposition process, reducing the residual tensile stress in the palladium-nickel alloy plating. Sodium 1,2,4-triazole-3-carboxylate serves as a grain boundary adsorption regulating component to adjust the deposition state at the grain boundaries of the palladium-nickel alloy plating, reducing grain boundary porosity defects. N,N-dimethyl-N-dodecyl-3-sulfopropylammonium internal salt serves as a micro-area wetting component to improve the wetting state of narrow contact areas, arc-shaped contact bumps, or elastic contact beam surfaces of high-speed connector terminals, reducing edge enrichment deposition. L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium internal salt together constitute an interface stabilization system for the contact area of ​​the high-speed connector.

[0029] In this invention, the palladium-nickel alloy electroplating solution preferably does not contain cyanide, boric acid, pyroborates, 3-pyridine sulfonic acid brighteners, thiourea brighteners, or alkynyl alcohol brighteners. The above limitation does not exclude unavoidable trace impurities, but rather refers to the fact that these substances are not actively added as effective functional components during the preparation of the electroplating solution.

[0030] In this invention, the palladium-nickel alloy electroplating solution can be prepared via a stepwise complexation method. First, a nickel complexing mother liquor is prepared, allowing nickel ions to form a stable complex with disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, and a portion of glycine. Then, a palladium complexing mother liquor is prepared, allowing the palladium-amine complex to form a suitable complexing environment for subsequent co-deposition with sodium citrate and the remaining glycine. Next, the nickel complexing mother liquor is added to the palladium complexing mother liquor to form a palladium-nickel base solution, followed by the addition of L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt. This stepwise complexation method helps reduce localized complexation imbalances caused by direct mixing and improves the storage stability of the electroplating solution and the stability of the palladium-nickel ratio during deposition.

[0031] In this invention, the high-speed connector terminal can be a high-speed board-to-board connector terminal, a high-speed backplane connector terminal, a server high-speed connector terminal, an automotive high-speed connector terminal, or a high-speed differential signal connector terminal. The copper alloy substrate can be phosphor bronze, beryllium copper, copper-nickel-silicon alloy, or other copper alloy materials suitable for high-speed connector terminals. The contact area can be at least one of a narrow strip contact area, an arc-shaped contact bump, or an elastic contact beam.

[0032] In application, the copper alloy substrate is first subjected to alkaline degreasing, water washing, micro-etching, water washing, acid activation, and water washing, and then a nickel barrier layer is formed on the surface of the contact area. The thickness of the nickel barrier layer can be 0.8μm-2.5μm. After forming the nickel barrier layer, a palladium-nickel alloy plating layer is deposited on the surface of the nickel barrier layer using the palladium-nickel alloy electroplating solution of the present invention. When depositing the palladium-nickel alloy plating layer, an inner wear-resistant zone can be formed first at a first current density, and then an outer contact zone can be formed at a second current density, where the first current density is greater than the second current density. The palladium-nickel alloy electroplating solution is not changed between the first and second stages, so that a palladium-nickel composition transition zone is formed between the inner wear-resistant zone and the outer contact zone. The mass percentage of nickel in the inner wear-resistant zone can be 16%-22%, and the mass percentage of nickel in the outer contact zone can be 8%-15%.

[0033] In this invention, the difference in nickel mass percentage between the edge and center locations can be determined using scanning electron microscopy (SEM) energy dispersive spectroscopy. The edge location refers to the area within 0.02mm-0.05mm of the side edge of the contact area; the center location refers to the area near the centerline of the contact area's width direction and at least 30% of the contact area's width from both sides. During testing, at least five test points are selected at the edge location and at least five test points are selected at the center location. The nickel mass percentage in the palladium-nickel alloy plating is measured at each point, and the difference between the average nickel mass percentage at the edge location and the average nickel mass percentage at the center location is calculated.

[0034] Pore ​​defects can be evaluated using the ferricyanide test paper method combined with microscopic observation, expressed as the number of pores per square centimeter of palladium-nickel alloy plating surface. Residual tensile stress can be measured using the plating stress sheet method. The increase in contact resistance can be measured using the four-terminal method, with a test current of 100 mA and a test load of 0.5 N, recording the difference between the contact resistance before insertion / removal and after 500 insertion / removal cycles. The test conditions for the increase in contact resistance after mixed gas corrosion are: temperature 40℃, relative humidity 75%, sulfur dioxide concentration 0.2 ppm, hydrogen sulfide concentration 0.01 ppm, nitrogen dioxide concentration 0.2 ppm, chlorine concentration 0.01 ppm, and treatment time 96 h. Example

[0035] This embodiment provides a palladium-nickel alloy electroplating solution, which, by mass concentration, comprises: Palladium ions: 12 g / L, derived from tetraamminepalladium sulfate; Nickel ions: 2.4 g / L, derived from nickel aminosulfonate; Ammonium aminosulfonate 65g / L; Ammonium sulfate 20 g / L; Glycine 10g / L; Sodium citrate 6 g / L; N-(2-hydroxyethyl)iminodiacetic acid disodium salt 2.2 g / L; Trisodium ethylenediaminedisuccinate 1.5 g / L; Sodium polyaspartate 0.20 g / L, the weight-average molecular weight of sodium polyaspartate is 2000; L-proline 1.0 g / L; 0.18 g / L of sodium 1,2,4-triazole-3-carboxylate; N,N-Dimethyl-N-dodecyl-3-sulfopropylammonium inner salt 0.08 g / L; The remainder is deionized water.

[0036] The palladium-nickel alloy electroplating solution has a pH of 7.1 and a free ammonia concentration of 1.6 g / L. The palladium-nickel alloy electroplating solution is free of cyanide, boric acid, pyroborates, 3-pyridine sulfonic acid brighteners, thiourea brighteners, and alkynyl alcohol brighteners.

[0037] In preparation, nickel aminosulfonate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, 5 g / L glycine, and a portion of deionized water were mixed and stirred at 40°C for 50 min. The pH was adjusted to 6.7 to obtain a nickel complex mother liquor. Tetraamminepalladium sulfate, sodium citrate, the remaining 5 g / L glycine, and a portion of deionized water were mixed and stirred at 38°C for 40 min. The pH was adjusted to 7.1 to obtain a palladium complex mother liquor. The nickel complex mother liquor was added to the palladium complex mother liquor, followed by ammonium aminosulfonate and ammonium sulfate to obtain a palladium-nickel base solution. L-proline, sodium 1,2,4-triazol-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt were added sequentially to the palladium-nickel base solution. Deionized water was added, and the pH was adjusted to 7.1. The mixture was stirred for another 60 min to obtain a palladium-nickel alloy electroplating solution.

[0038] The high-speed connector terminals are electroplated using the aforementioned palladium-nickel alloy plating solution. The copper alloy substrate of the high-speed connector terminals is a copper-nickel-silicon alloy, and the contact area consists of arc-shaped contact bumps with a width of 0.45 mm and a length of 1.8 mm. After alkaline degreasing, water washing, micro-etching, water washing, acid activation, and water washing, a 1.5 μm thick nickel barrier layer is electroplated onto the surface of the contact area.

[0039] When depositing a palladium-nickel alloy coating on the surface of a nickel barrier layer, the electroplating temperature was 52℃ and the pH of the electroplating solution was 7.1. First, an inner wear-resistant zone was formed by deposition at a first current density of 9 A / dm², and then an outer contact zone was formed by deposition at a second current density of 4.5 A / dm². The total thickness of the palladium-nickel alloy coating was 0.35 μm. The nickel mass percentage in the inner wear-resistant zone was 18.6%, and the nickel mass percentage in the outer contact zone was 11.4%, forming a palladium-nickel composition transition zone between the inner wear-resistant zone and the outer contact zone. Example

[0040] The difference between this embodiment and Embodiment 1 is that: The concentrations of palladium ions were 10 g / L, nickel ions were 1.8 g / L, ammonium aminosulfonate was 55 g / L, ammonium sulfate was 15 g / L, glycine was 8 g / L, sodium citrate was 5 g / L, disodium N-(2-hydroxyethyl)iminodiacetic acid was 1.5 g / L, trisodium ethylenediaminedisuccinate was 0.9 g / L, sodium polyaspartate was 0.10 g / L (weight average molecular weight of sodium polyaspartate was 1500), L-proline was 0.7 g / L, sodium 1,2,4-triazole-3-carboxylate was 0.10 g / L, N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt was 0.05 g / L, pH was 6.9, and free ammonia concentration was 1.3 g / L.

[0041] When preparing the nickel complex mother liquor, 4 g / L glycine was added; when preparing the palladium complex mother liquor, the remaining 4 g / L glycine was added. The electroplating temperature was 50℃, the first current density was 8 A / dm², the second current density was 4 A / dm², and the total thickness of the palladium-nickel alloy coating was 0.30 μm. After depositing the palladium-nickel alloy coating on the surface of the nickel barrier layer, the total thickness of the palladium-nickel alloy coating was 0.30 μm. The mass percentage of nickel in the inner wear-resistant zone was 17.2%, and the mass percentage of nickel in the outer contact zone was 9.8%, forming a palladium-nickel composition transition zone between the inner wear-resistant zone and the outer contact zone.

[0042] The remaining components, preparation methods, and electroplating steps are the same as in Example 1. Example

[0043] The difference between this embodiment and Embodiment 1 is that: The concentrations of palladium ions were 14 g / L, nickel ions were 3.2 g / L, ammonium aminosulfonate was 80 g / L, ammonium sulfate was 28 g / L, glycine was 14 g / L, sodium citrate was 8 g / L, disodium N-(2-hydroxyethyl)iminodiacetic acid was 3.4 g / L, trisodium ethylenediaminedisuccinate was 2.4 g / L, sodium polyaspartate was 0.35 g / L (weight average molecular weight of sodium polyaspartate was 2500), L-proline was 1.6 g / L, sodium 1,2,4-triazole-3-carboxylate was 0.28 g / L, N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt was 0.14 g / L, pH was 7.3, and free ammonia concentration was 2.1 g / L.

[0044] When preparing the nickel complex mother liquor, 7 g / L glycine was added; when preparing the palladium complex mother liquor, the remaining 7 g / L glycine was added. The electroplating temperature was 55℃, the first current density was 11 A / dm², the second current density was 5.5 A / dm², and the total thickness of the palladium-nickel alloy coating was 0.45 μm. After depositing the palladium-nickel alloy coating on the surface of the nickel barrier layer, the total thickness of the palladium-nickel alloy coating was found to be 0.45 μm. The nickel mass percentage in the inner wear-resistant zone was 20.5%, and the nickel mass percentage in the outer contact zone was 13.2%, forming a palladium-nickel composition transition zone between the inner wear-resistant zone and the outer contact zone.

[0045] The remaining components, preparation methods, and electroplating steps are the same as in Example 1.

[0046] Comparative Example 1 This comparative example illustrates the effect of stepwise complexation release components on the stability of palladium-nickel co-deposition ratio without the addition of trisodium ethylenediamine disuccinate and sodium polyaspartate.

[0047] The difference between this comparative example and Example 1 is that trisodium ethylenediaminedisuccinate and sodium polyaspartate are not added, and the mass concentration of glycine is adjusted to 11.5 g / L and the mass concentration of sodium citrate is adjusted to 8.2 g / L, so that the total mass concentration of the complexing components is close to that of Example 1. The remaining composition, preparation method and electroplating steps are the same as those in Example 1.

[0048] Comparative Example 2 This comparative example illustrates the effect of L-proline on nickel deposition buffering and residual stress in the coating.

[0049] The difference between this comparative example and Example 1 is that L-proline is not added. The remaining composition, preparation method, and electroplating steps are the same as in Example 1.

[0050] Comparative Example 3 This comparative example illustrates the effect of sodium 1,2,4-triazole-3-carboxylate on grain boundary adsorption regulation and pore defects.

[0051] The difference between this comparative example and Example 1 is that sodium 1,2,4-triazole-3-carboxylate is not added. The remaining composition, preparation method, and electroplating steps are the same as in Example 1.

[0052] Comparative Example 4 This comparative example illustrates the effect of N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt on micro-area wetting and edge deposition uniformity of the contact area in high-speed connectors.

[0053] The difference between this comparative example and Example 1 is that N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt is not added. The remaining composition, preparation method, and electroplating steps are the same as in Example 1.

[0054] Comparative Example 5 This comparative example illustrates the deposition uniformity and contact stability of the plating in the contact area of ​​a high-speed connector when using a complexing and brightening system similar to that of a conventional palladium-nickel alloy plating solution.

[0055] The palladium-nickel alloy electroplating solution of this comparative example comprises, by mass concentration: 12 g / L palladium ions, derived from tetraamminepalladium sulfate; 2.4 g / L nickel ions, derived from nickel sulfamate; 65 g / L ammonium sulfamate; 20 g / L ammonium sulfate; 10 g / L glycine; 6 g / L sodium citrate; 20 g / L boric acid; 0.5 g / L 3-pyridinesulfonic acid; and the balance being deionized water. The pH of the palladium-nickel alloy electroplating solution is 7.1.

[0056] This comparative example does not include disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, L-proline, sodium 1,2,4-triazole-3-carboxylate, or N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt. The remaining electroplating steps are the same as in Example 1.

[0057] Comparative Example 6 This comparative example illustrates the effect of stepwise pre-complexation during the preparation of the electroplating solution on the stability of the palladium-nickel base solution and the stability of the plating composition.

[0058] The composition of this comparative example is the same as that of Example 1, except that instead of forming separate nickel and palladium complex mother solutions, tetraamminepalladium sulfate, nickel aminosulfonate, ammonium aminosulfonate, ammonium sulfate, glycine, sodium citrate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, L-proline, sodium 1,2,4-triazole-3-carboxylate, N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt, and deionized water are mixed all at once, the pH is adjusted to 7.1, and the mixture is stirred for 60 min to obtain the palladium-nickel alloy electroplating solution. The remaining electroplating steps are the same as in Example 1.

[0059] Performance testing The performance of the high-speed connector terminals prepared in Examples 1-3 and Comparative Examples 1-6 was tested, and the test results are shown in Table 1.

[0060] Table 1. Test results of palladium-nickel alloy coating performance

[0061] As can be seen from Examples 1-3, after adopting the stepped complexation release component and the interface stabilization system of the high-speed connector contact area of ​​the present invention, the difference in nickel mass percentage between the edge and center of the palladium-nickel alloy plating layer in the contact area is no greater than 2.5 percentage points, the number of pores is no more than 5 per cm², the residual tensile stress is no more than 108 MPa, the contact resistance increase after 500 mating cycles is no more than 3.5 mΩ, and the contact resistance increase after mixed gas corrosion is no more than 5.2 mΩ. These results indicate that the palladium-nickel alloy plating solution of the present invention can adapt to the small size, bending, and edge current concentration environment of the high-speed connector terminal contact area, and can obtain a palladium-nickel alloy plating layer with uniform composition, few pores, controlled stress, and stable contact resistance.

[0062] A comparison of Example 1 and Comparative Example 1 shows that after removing trisodium ethylenediaminedisuccinate and sodium polyaspartate, the difference in nickel mass percentage between the edge and center positions increased from 1.6 percentage points to 4.7 percentage points, with a simultaneous increase in the number of pores and the increase in contact resistance. This indicates that trisodium ethylenediaminedisuccinate and sodium polyaspartate, together with glycine, sodium citrate, and disodium N-(2-hydroxyethyl)iminodiacetic acid, constitute a stepwise complexation release component, thereby improving the local component drift problem during the palladium-nickel co-deposition process.

[0063] A comparison of Example 1 and Comparative Example 2 shows that after removing L-proline, the residual tensile stress increased from 92 MPa to 188 MPa, and the contact resistance increment after 500 insertion / removal cycles increased from 2.8 mΩ to 8.6 mΩ. This indicates that L-proline can buffer the nickel deposition process, reducing the residual stress of the palladium-nickel alloy plating and decreasing the increase in contact resistance after insertion / removal wear.

[0064] A comparison of Example 1 and Comparative Example 3 shows that after removing sodium 1,2,4-triazole-3-carboxylate, the number of pores increased from 3 pores / cm² to 18 pores / cm², and the increase in contact resistance after mixed gas corrosion increased from 4.1 mΩ to 14.2 mΩ. This indicates that sodium 1,2,4-triazole-3-carboxylate can improve the grain boundary adsorption regulation effect of the palladium-nickel alloy coating, reduce grain boundary porosity defects, and improve the stability of the contact interface under corrosive conditions.

[0065] A comparison of Example 1 and Comparative Example 4 shows that after removing the N,N-dimethyl-N-dodecyl-3-sulfopropylammonium internal salt, the difference in nickel mass percentage between the edge and center positions increased from 1.6 percentage points to 5.3 percentage points, and the contact resistance increment after 500 mating cycles increased from 2.8 mΩ to 10.1 mΩ. This indicates that the N,N-dimethyl-N-dodecyl-3-sulfopropylammonium internal salt can improve the micro-wetting state of the narrow contact area of ​​the high-speed connector terminal, reducing contact resistance fluctuations caused by deposition enrichment at the edge positions and subsequent mating wear.

[0066] A comparison of Example 1 and Comparative Example 5 shows that, while a palladium-nickel alloy plating layer can be formed using a glycine / citric acid, boric acid, and 3-pyridine sulfonic acid system similar to that of a conventional palladium-nickel plating solution, the difference in nickel mass percentage between the edge and center positions, the number of pores, the residual tensile stress, and the increase in contact resistance are all significantly greater than in Example 1. This indicates that the present invention does not rely on boric acid, pyroborate, 3-pyridine sulfonic acid-based brighteners, thiourea-based brighteners, or alkynyl alcohol-based brighteners to obtain a palladium-nickel alloy plating layer for the contact area of ​​a high-speed connector. Instead, it achieves plating quality control through a stepwise complexation release of components and an interface stabilization system for the contact area of ​​the high-speed connector.

[0067] A comparison of Example 1 and Comparative Example 6 shows that, in the case where the components are directly mixed without separately preparing nickel-complexing mother liquor and palladium-complexing mother liquor, the difference in nickel mass percentage between the edge and center positions, the number of pores, and the increase in contact resistance are all higher than in Example 1. This indicates that the stepwise formation of nickel-complexing mother liquor and palladium-complexing mother liquor is beneficial for stabilizing the metal complex state in the palladium-nickel base solution, reducing local complexation imbalance during the preparation process and fluctuations in coating composition during continuous deposition.

[0068] The above embodiments and comparative examples demonstrate that the present invention, through the synergistic effect of the step-complex release components and the interface stabilization system of the high-speed connector contact area, can form a palladium-nickel alloy plating with stable nickel content distribution, few pore defects, low residual stress, and small contact resistance fluctuation in the terminal contact area of ​​the high-speed connector without using cyanide, boric acid, pyroborate, 3-pyridine sulfonic acid brighteners, thiourea brighteners, and alkynyl alcohol brighteners.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A palladium-nickel alloy electroplating solution for depositing a palladium-nickel alloy plating layer in the contact area of ​​a high-speed connector terminal, characterized in that, The palladium-nickel alloy electroplating solution is a near-neutral to weakly alkaline aqueous electroplating solution, comprising, by mass concentration: Palladium ions: 8 g / L-16 g / L, wherein the palladium ions are derived from tetraamminepalladium sulfate; Nickel ions: 1.2 g / L - 4.0 g / L, wherein the nickel ions are derived from nickel aminosulfonate; Ammonium aminosulfonate 40g / L-90g / L; Ammonium sulfate 8g / L-35g / L; The stepwise complexation release component is 11 g / L-34 g / L, and the stepwise complexation release component is composed of glycine, sodium citrate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediamine disuccinate and sodium polyaspartate. The nickel deposition buffer component is 0.4 g / L-2.0 g / L, and the nickel deposition buffer component is L-proline; The grain boundary adsorption regulating component is 0.05 g / L-0.35 g / L, and the grain boundary adsorption regulating component is sodium 1,2,4-triazole-3-carboxylate; The micro-wetting component is 0.02 g / L-0.18 g / L, and the micro-wetting component is N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt; The remainder is deionized water; The pH of the palladium-nickel alloy electroplating solution is 6.6-7.6, and the free ammonia concentration is ≤3g / L.

2. The palladium-nickel alloy electroplating solution according to claim 1, characterized in that, In the stepwise complexation release component, the mass concentration of glycine is 6 g / L-16 g / L, the mass concentration of sodium citrate is 3 g / L-10 g / L, the mass concentration of disodium N-(2-hydroxyethyl)iminodiacetic acid is 1.2 g / L-4.0 g / L, the mass concentration of trisodium ethylenediamine disuccinate is 0.6 g / L-3.0 g / L, and the mass concentration of sodium polyaspartate is 0.05 g / L-0.50 g / L.

3. The palladium-nickel alloy electroplating solution according to claim 1, characterized in that, The weight-average molecular weight of the polyaspartic acid sodium salt is 1000-3000, and the combined mass concentration of the glycine and the sodium citrate is 2.5 to 8 times the combined mass concentration of the disodium N-(2-hydroxyethyl)iminodiacetic acid and the trisodium ethylenediaminedisuccinate.

4. The palladium-nickel alloy electroplating solution according to claim 1, characterized in that, L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt together constitute the interface stabilization system of the high-speed connector contact area; the interface stabilization system of the high-speed connector contact area is used to reduce the edge enrichment deposition, grain boundary porosity defects, and contact resistance fluctuations of palladium-nickel alloy plating on the surface of narrow strip contact areas, arc-shaped contact bumps, or elastic contact beams.

5. The palladium-nickel alloy electroplating solution according to claim 1, characterized in that, Under conditions of temperature 48℃-58℃, pH 6.8-7.3, and current density 4A / dm²-12A / dm², the palladium-nickel alloy electroplating solution deposits a palladium-nickel alloy coating in the contact area of ​​the high-speed connector terminal, and the difference in nickel mass percentage between the edge and center of the palladium-nickel alloy coating is ≤2.5%.

6. A method for preparing the palladium-nickel alloy electroplating solution according to any one of claims 1-5, characterized in that, Includes the following steps: Nickel aminosulfonate, disodium N-(2-hydroxyethyl)iminodiacetic acid, trisodium ethylenediaminedisuccinate, sodium polyaspartate, a portion of glycine, and a portion of deionized water were mixed and the pH was adjusted to 6.4-7.0 to obtain a nickel complex mother liquor. Mix tetraamminepalladium sulfate, sodium citrate, the remaining glycine, and some deionized water, and adjust the pH to 6.8-7.4 to obtain the palladium complex mother liquor; The nickel complex mother liquor was added to the palladium complex mother liquor, and ammonium aminosulfonate and ammonium sulfate were added to obtain a palladium-nickel base solution. L-proline, sodium 1,2,4-triazol-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt were added sequentially to the palladium-nickel base solution. Deionized water was added and the pH was adjusted to 6.6-7.6 to obtain the palladium-nickel alloy electroplating solution.

7. The method for preparing the palladium-nickel alloy electroplating solution according to claim 6, characterized in that, When preparing the nickel complex mother liquor, the temperature is controlled at 35℃-45℃ and the stirring time is 30min-80min; When preparing the palladium complex mother liquor, the temperature is controlled at 30℃-45℃ and the stirring time is 20min-60min; After adding L-proline, sodium 1,2,4-triazole-3-carboxylate, and N,N-dimethyl-N-dodecyl-3-sulfopropylammonium inner salt to the palladium-nickel base solution, stirring was continued for 30-90 minutes.

8. The application of the palladium-nickel alloy electroplating solution according to any one of claims 1-5 on high-speed connector terminals, characterized in that, The copper alloy substrate of the high-speed connector terminal is degreased, micro-etched and activated. After forming a nickel barrier layer on the surface of the contact area of ​​the copper alloy substrate, a palladium-nickel alloy plating layer is deposited on the surface of the nickel barrier layer using the palladium-nickel alloy electroplating solution. The contact area is a narrow strip contact area, an arc-shaped contact bump or an elastic contact beam.

9. The application of the palladium-nickel alloy electroplating solution according to claim 8 on high-speed connector terminals, characterized in that, When depositing the palladium-nickel alloy coating, an inner wear-resistant zone is first formed at a first current density, and then an outer contact zone is formed at a second current density. The first current density is 7A / dm²-12A / dm², and the second current density is 3A / dm²-6A / dm². The nickel mass percentage content in the inner wear-resistant zone is 16%-22%, and the nickel mass percentage content in the outer contact zone is 8%-15%. A palladium-nickel composition transition zone is formed between the inner wear-resistant zone and the outer contact zone.

10. A high-speed connector terminal, characterized in that, It includes a copper alloy substrate and a nickel barrier layer and a palladium-nickel alloy plating layer sequentially formed on the surface of the contact area of ​​the copper alloy substrate, wherein the palladium-nickel alloy plating layer is formed by deposition of the palladium-nickel alloy electroplating solution according to any one of claims 1-5; The thickness of the nickel barrier layer is 0.8μm-2.5μm; The thickness of the palladium-nickel alloy coating is 0.10 μm-0.70 μm; The palladium-nickel alloy coating includes an inner wear-resistant zone, a palladium-nickel composition transition zone, and an outer contact zone. The mass percentage of nickel in the inner wear-resistant zone is greater than the mass percentage of nickel in the outer contact zone. The outer contact area serves as the outermost contact metal layer of the high-speed connector terminal.

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