A power-free electroless nickel plating method and device based on two-component time-sharing injection

Abstract

The application discloses a power-free electroless nickel plating method and device based on two-component time-sharing spraying, wherein the nickel salt first plating solution and the reducing agent second plating solution are stored separately; the substrate is activated and kept at a constant temperature of 30-60 DEG C; the double spraying heads spray 1-100 pL microdroplets to the same point of the substrate at different times with an interval of 0.1-10 s; the two solutions are mixed in situ on the substrate surface to generate autocatalytic deposition; and the distance between the spraying head and the substrate is 0.2-1.0 mm; three-dimensional nickel-phosphorus structures are formed layer by layer by controlling the movement and time sequence of the spraying head; and the components are obtained by washing and drying. The two plating solutions are added with 0.5-8 wt% thickening agents, and one or more of the following compounds can be selected and compounded: cellulose derivatives, natural colloids, polymers, fumed silica and the like. The matched device comprises double liquid storage tanks, double independent spraying heads, a temperature-controlled substrate, a time sequence controller and a motion control platform; in-situ plating is realized by time-sharing and fixed-point spraying, an external power supply is not needed, and three-dimensional nickel-phosphorus alloy plating layer components can be accurately prepared.

Description

Technical Field

[0001] This invention belongs to the field of chemical plating additive manufacturing and precision surface treatment technology, specifically relating to a power-free chemical nickel plating method and apparatus based on two-component time-division spraying. Background Technology

[0002] Electroless nickel-phosphorus alloy plating is a deposition method that requires no external power supply and utilizes a reducing agent to catalyze the spontaneous reduction of nickel ions by metal ions on the substrate surface. This technology has advantages such as uniform coating, no current distribution problem, and suitability for complex-shaped workpieces, and is widely used in electronics, aerospace, automotive and other fields. However, traditional electroless nickel plating has the following inherent defects: (1) Poor stability of the plating solution: Electroless nickel plating solution is a thermodynamically metastable system. The nickel salt and reducing agent coexist in the plating solution and are prone to spontaneous decomposition, resulting in a short plating solution life (usually only 4-6 metal turnover cycles MTO). (2) Difficulty in achieving localized deposition: Traditional electroless plating involves immersing the entire workpiece in the plating solution, and the coating is uniformly deposited on the entire surface, which cannot achieve selective and localized 3D printing effects. (3) Uncontrollable deposition rate: Since the reducing agent and nickel salt always coexist, once the deposition is triggered, it continues, making it difficult to achieve "start on demand and stop on demand".

[0003] To address the aforementioned technical problems, this invention proposes a power-free electroless nickel plating method and apparatus based on two-component time-division spraying. The electroless nickel plating solution is divided into a first plating solution and a second plating solution, which are stored separately and sprayed in stages during deposition. Deposition is triggered by the mixing of microdroplets of the first and second plating solutions on the substrate surface, thereby achieving high localization of electroless nickel plating 3D printing without an external power source. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing electroless nickel plating technology, such as the inability to achieve localized deposition and poor stability of the plating solution, and to provide a power-free electroless nickel plating method and apparatus based on two-component time-division spraying.

[0005] S1. Prepare a first plating solution and a second plating solution that are not premixed and store them separately; the first plating solution is a nickel salt component and the second plating solution is a reducing agent component;

[0006] S2. Perform activation pretreatment on the surface of the metal substrate to be plated, and after treatment, keep the substrate temperature constant at 30-60℃.

[0007] S3. A fixed-point, time-division micro-droplet spraying method is adopted, with the spraying distance controlled between 0.2 and 1.0 mm. For the same target point on the substrate, the first plating solution micro-droplets are sprayed onto the substrate first, and after an interval of 0.1 to 10 seconds, the second plating solution micro-droplets are sprayed onto the same point. The two plating solutions are mixed in situ only on the substrate surface, triggering a power-free autocatalytic electroless nickel plating reaction and depositing a nickel-phosphorus alloy coating in situ. The single spraying volume of the first plating solution micro-droplet is 1-100 pL, and the single spraying volume of the second plating solution micro-droplet is 1-100 pL.

[0008] S4. Control the relative motion trajectory between the two-component plating solution and the substrate, the spraying sequence, the layer-by-layer lifting height, the point-by-point scanning, and the layer-by-layer deposition to form a three-dimensional nickel-phosphorus alloy structure on the substrate surface.

[0009] S5. After deposition, the substrate is rinsed with deionized water to remove residual plating solution, and then dried at 80-100℃ to obtain nickel-plated components.

[0010] This invention separates and independently stores the nickel salt and reducing agent plating solutions, allowing them to mix and react in situ only on the substrate surface. This avoids premature precipitation in pipelines and containers, significantly extending the service life of the plating solutions. Microdroplets are sprayed sequentially and at timed intervals of 0.1–10 seconds onto the same target point on the substrate, preventing nozzle blockage and achieving selective localized plating. By limiting each spray to 1–100 pL of microdroplets and a close spray distance of 0.2–1.0 mm, precise landing points without dripping or deviation are achieved, resulting in clear micro-area contours. By controlling the three-dimensional movement of the substrate during the spraying of the two-component plating solution, layer-by-layer lifting and scanning is achieved, overcoming the limitations of traditional planar plating and enabling the layer-by-layer deposition of complex three-dimensional nickel-phosphorus alloy structures. Low-temperature autocatalytic deposition at a constant substrate temperature of 30–60°C eliminates the need for an external power source, resulting in low energy consumption and no electroplating electric field risks. Water washing and low-temperature drying ensure a dense and corrosion-resistant coating.

[0011] Preferably, the composition of the first plating solution in step S1 is: nickel sulfate 30-100 g / L, complexing agent CA-A 8-32 g / L, complexing agent CA-B 8-32 g / L, malic acid 8-32 g / L, lactic acid 4-20 g / L, sodium acetate 12-40 g / L, thiourea 1.0-8.0 mg / L, SDS 10-60 mg / L, and thickener 0.5-8 wt%; the pH of the first plating solution is 5.8-6.8. The thickener does not react with any component of the first plating solution. A multi-component organic acid buffer system consisting of a compound dual complexing agent, malic acid, and lactic acid, combined with trace amounts of thiourea stabilizer and SDS surfactant, can stabilize high-concentration nickel salt systems and inhibit nickel ion hydrolysis and precipitation. The thickener increases the viscosity of the plating solution, making it difficult for droplets to spread laterally after spraying, resulting in excellent point-fixed shape retention and ensuring the precision of fine pattern forming. The pH is controlled at 5.8~6.8, which is suitable for in-situ autocatalytic reactions on low-temperature substrates, and the deposition reaction is slow and controllable.

[0012] Preferably, the composition of the second plating solution in step S1 is: sodium hypophosphite 36-100 g / L, thiourea 2.0-12.0 mg / L, sodium acetate 12-40 g / L, thickener 0.5-8 wt%, and the pH of the second plating solution is 6.4-6.8. The thickener does not react with any component of the second plating solution. Sodium hypophosphite, as a self-catalytic reducing agent, will not be deactivated by contact with nickel ions when stored alone; it only releases its reducing power after mixing with the first plating solution, ensuring the smooth precipitation of nickel-phosphorus alloy in situ. The sodium acetate buffer system stabilizes the pH of the second component, and the overall pH of the two plating solutions falls within the suitable chemical plating range after mixing, avoiding acid-base imbalance that could cause deposition stagnation or a loose coating. Trace amounts of thiourea, in conjunction with the first plating solution stabilizer, synergistically inhibit side reactions, refine nickel-phosphorus grains, and improve the density of the coating after mixing. The thickener can constrain the diffusion of the reducing solution, preventing blurring of the coating edges and improving the clarity of the three-dimensional structure edges.

[0013] Preferably, the thickener in the first and second plating solutions is one or more of the following: hydroxyethyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, sodium alginate, gelatin, xanthan gum, guar gum, polyethylene glycol (molecular weight 2000-20000), polyvinyl alcohol (molecular weight 10000-100000), fumed silica, sodium polyacrylate, and carbomer. Various thickeners, such as cellulose, polysaccharides, polymers, and inorganic silica, can be used individually or in combination to adjust the viscosity of the plating solution. All types of thickeners do not interfere with the nickel-phosphorus autocatalytic deposition reaction, inhibiting droplet spreading without reducing coating deposition efficiency. The formulation is flexible and adaptable to the spray molding requirements of different fineness structures.

[0014] The powerless electroless nickel plating apparatus based on two-component time-division spraying to implement the above method includes a first storage tank, a first nozzle connected to the first storage tank, a second storage tank, a second nozzle connected to the second storage tank, a motion control platform, a timing controller, a substrate, and a substrate temperature control platform. The first nozzle and the second nozzle are fixedly mounted on the motion control platform, which drives the first nozzle and the second nozzle to move relative to the substrate. The timing controller is electrically connected to the first nozzle, the second nozzle, and the motion control platform, and is used to control the two nozzles to independently start and stop spraying at different times, adjust the spraying interval sequence of the nozzles, and synchronously control the motion control platform to drive the first nozzle and the second nozzle to generate two-dimensional / three-dimensional displacement relative to the substrate. The spraying target points of the first nozzle and the second nozzle coincide, enabling them to spray plating solution separately to the same target position on the substrate at different times. The substrate temperature control platform is thermally bonded to the substrate and is used to precisely control the substrate temperature, so that the two plating solutions mix in situ after dripping onto the substrate surface, triggering a powerless autocatalytic electroless nickel plating deposition reaction. This invention employs a first storage tank and a second storage tank to hold the first plating solution (nickel salt component) and the second plating solution (reducing agent component) respectively. By using separate tanks for storage and isolating the formulation, the nickel salt component and the reducing agent component are stored separately, preventing contact and premature autocatalytic decomposition during storage. This significantly extends the shelf life of the plating solution and reduces waste of the first and second plating solutions, overcoming the problem of easy failure in traditional premixed chemical plating solutions. By using dual nozzles to independently deliver the plating solution and utilizing a timing controller to link the dual nozzles with the motion platform, the invention precisely controls the sequential spraying of the dual nozzles onto the same target point on the substrate. This provides the hardware foundation for in-situ mixing and reaction on the substrate surface, achieving power-free autocatalytic chemical plating. No external electroplating power supply is required, and the equipment eliminates the need for a rectifier power supply and electrode fixtures. The motion control platform moves the nozzles, abandoning the traditional full-immersion plating mode. It enables targeted, selective spraying of the plating solution, forming a plating layer in a designated area of ​​the substrate, and can also build up a three-dimensional nickel-phosphorus structure layer by layer. This is suitable for irregularly shaped parts and localized reinforcement nickel plating scenarios. Temperature is controlled by a substrate temperature control platform to precisely maintain the substrate reaction temperature, avoid uneven coating deposition rate, pinholes, peeling defects caused by local temperature differences, stabilize the autocatalytic deposition reaction rate, and improve coating uniformity and adhesion.

[0015] Preferably, the first and second nozzles are piezoelectric microdroplet nozzles or thermal bubble microdroplet nozzles. Using piezoelectric or thermal bubble nozzles enables precise, quantitative spraying of micro-droplets at the picoliter level (pL level). The droplet size is uniform, and the amount of adhesive applied at each point is controllable, avoiding edge smudging and excessive thickness of the coating caused by large droplets flowing. This improves the coating accuracy of micro-area patterns and is suitable for the layer-by-layer deposition requirements of fine three-dimensional structures. The spraying response is fast, and start / stop is controllable, facilitating precise control of the landing interval between the two plating solutions to ensure sequential liquid application and in-situ mixing. The nozzles are compact and flexibly arranged, suitable for high-precision three-axis / five-axis platform high-speed point-to-point machining and for localized chemical plating of microstructures and micro-parts.

[0016] Preferably, the motion control platform is a three-axis motion platform or a five-axis motion platform. A three-axis motion platform can achieve three-dimensional linear displacement in X / Y / Z, meeting the requirements for layer-by-layer stacking of planar substrates. It offers moderate equipment cost, simple control, and is suitable for point-to-point nickel plating of conventional flat workpieces. A five-axis motion platform increases rotational freedom, allowing the nozzle to spray at multiple angles, and is suitable for full-surface point-to-point spraying of curved, irregularly shaped, and unevenly textured substrates, breaking through the limitations of planar processing and expanding the ability to form complex three-dimensional nickel-phosphorus components. Using a three-axis or five-axis motion platform enables CNC programmed path navigation, high displacement accuracy, ensuring consistency of the deposition contour for each layer, and improving the dimensional accuracy of the three-dimensional structure.

[0017] Preferably, the substrate is one of an aluminum alloy substrate, a copper substrate, or a stainless steel substrate.

[0018] Preferably, the volume of each spray from the first and second nozzles is 1-100 pL. This invention uses picoliter-level micro-droplets, which can precisely control the supply of plating solution at a single point according to the coating thickness and structural fineness. Thin coatings use small-volume droplets, while thick three-dimensional structures can be sprayed in multiple layers, eliminating the problems of droplet dripping and structural contour distortion.

[0019] Preferably, the distance between the first and second nozzles and the substrate is 0.2-1.0 mm. The close-range spraying range of 0.2-1.0 mm ensures stable microdroplet flight trajectory and target point overlap without deviation, improving positioning accuracy; at the same time, it provides a safety gap so that the nozzles will not touch or scratch the formed three-dimensional nickel-phosphorus structure when scanning layer by layer, significantly improving the yield of finished products.

[0020] This invention adopts a strategy of "separate storage of nickel salt and reducing agent, time-sharing spraying, and on-site mixing" to solve the fundamental problems of traditional electroless nickel plating. The beneficial technical effects of this invention include: (1) Significantly improved stability of the plating solution. The nickel salt and reducing agent are stored independently and mixed and reacted in situ only on the substrate surface, which completely solves the problem of water leaching and rapid failure of traditional premixed plating solutions during long-term storage, extends the service life of the plating solution, and reduces raw material loss. The nickel salt plating solution adopts a dual complexing agent + multi-element organic acid composite buffer system, which effectively stabilizes nickel ions and inhibits hydrolysis precipitation. Combined with thiourea and SDS, it refines the coating grains and reduces coating defects. The pH of the reducing plating solution and the nickel salt plating solution are compatible with each other, and the two quickly start a gentle autocatalytic reduction reaction after contacting the substrate. (2) Eliminates nozzle clogging and ensures stable continuous operation of the equipment. Through time-sequenced spraying, the two plating solutions do not come into contact and mix inside the nozzle or pipeline, avoiding nozzle crystallization and clogging from the root, and enabling continuous batch processing for a long time. (3) Enables selective fixed-point plating + three-dimensional additive manufacturing. Unlike traditional immersion and full-surface spraying which can only coat the entire plane, the picoliter microdroplet fixed-point time-division spraying can coat the substrate locally as needed; with the nozzle lifting and scanning layer by layer, it can build up complex three-dimensional nickel-phosphorus alloy three-dimensional structures layer by layer. (4) High forming accuracy and excellent appearance quality of components. With the matching two-component thickening formula, the sprayed droplets are not easy to spread and smudge laterally; the microdroplet volume is limited to 1~100pL and the spraying distance is 0.2~1.0mm, the droplet landing point is accurate without deviation and without dripping, and the edge contour of the three-dimensional structure is clear. (5) Low temperature electrodeposition, green and low consumption. The coating is completed by self-catalytic reaction, without the need for an external electroplating power supply, and the energy consumption is lower; the substrate reacts at a low temperature of 30~60℃, and with the water washing and low temperature drying process, the coating is dense and uniform with fewer pinholes and pits, and the bonding force and corrosion resistance are better. (6) Multi-layer stacking 3D printing can be realized. Through the cycle of layer-by-layer spraying-deposition, multiple depositions can be made at the same location to achieve the manufacturing of three-dimensional structures with controllable thickness. The final thickness can be controlled by repeated printing. (7) At the device level: 1) The timing controller links the dual nozzles and motion control platform, and the hardware accurately matches the time-sharing spraying sequence to automatically complete the scanning and layer lifting actions. 2) The dual nozzle target points overlap with the substrate-specific temperature control platform to build a stable constant temperature reaction field and ensure that the in-situ autocatalytic reaction continues to proceed smoothly. 3) The piezoelectric / thermal bubble microdroplet nozzle and the three-axis / five-axis motion platform are adapted to the processing of micro-fine three-dimensional structures and are compatible with various metal substrates such as aluminum alloy, copper, and stainless steel. The equipment has strong versatility. 4) The device hardware parameters and process parameters are matched one by one. The microdroplet volume and spraying distance are controllable and adjustable, taking into account both processing accuracy and production yield. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the power-free chemical nickel plating device based on two-component time-division spraying as described in this invention.

[0022] The components include: 1. a first liquid storage tank; 2. a first nozzle; 3. a second liquid storage tank; 4. a second nozzle; 5. a motion control platform; 6. a substrate; 7. a substrate temperature control platform; and 8. a timing controller. (Detailed implementation details follow.)

[0023] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. It should be noted that in the system of the present invention, the thickener can be selected from one or more of hydroxyethyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, sodium alginate, gelatin, xanthan gum, guar gum, polyethylene glycol (molecular weight 2000-20000), polyvinyl alcohol (molecular weight 10000-100000), fumed silica, sodium polyacrylate, and carbomer. The following examples only select some types of thickeners. Other single-component, binary, ternary, and multi-component combinations not listed in the examples can achieve the same thickening and anti-stratification effects simply by adjusting the proportions of each component according to the limits specified in this application, and all fall within the scope of protection of this invention.

[0024] Example 1

[0025] An apparatus used in a power-free electroless nickel plating method based on two-component time-division spraying, such as... Figure 1 As shown, the system includes a first liquid storage tank 1, a first nozzle 2 connected to the first liquid storage tank 1, a second liquid storage tank 3, a second nozzle 4 connected to the second liquid storage tank 3, a motion control platform 5, a timing controller 8, a substrate 6, and a substrate temperature control platform 7. The first nozzle 2 and the second nozzle 4 are fixedly mounted on the motion control platform 5, which drives the first nozzle 2 and the second nozzle 4 to move relative to the substrate 6. The timing controller 8 is electrically connected to the first nozzle 2, the second nozzle 4, and the motion control platform 5, and is used to control the first nozzle 2 and the second nozzle 4 to independently open and close the spray at different times, adjust the spray interval sequence, and synchronously control the motion control platform 5 to drive the first nozzle 2 and the second nozzle 4. The two nozzles 4 generate two-dimensional / three-dimensional displacement relative to the substrate 6; the spray target points of the first nozzle 2 and the second nozzle 4 coincide, enabling them to spray plating solution onto the same target position on the substrate 6 at different times; the substrate temperature control platform 7 is thermally bonded to the substrate 6 and is used to precisely control the temperature of the substrate 6, so that the two plating solutions mix in situ after falling onto the surface of the substrate 6, triggering a power-free autocatalytic electroless nickel plating deposition reaction; in this device, the first nozzle 2 and the second nozzle 4 are piezoelectric nozzles, and the volume of each droplet sprayed by the first nozzle 2 and the second nozzle 4 is 100 pL; the distance between the first nozzle 2 and the second nozzle 4 and the substrate 6 is 0.5 mm; the motion control platform 5 is a three-axis motion platform.

[0026] The above-mentioned nickel plating method based on a two-component time-spraying, power-free chemical nickel plating apparatus includes the following steps:

[0027] S1. Prepare a first plating solution and place it in a first storage tank 1. The first plating solution is a nickel salt component. Prepare a second plating solution and place it in a second storage tank 3. The second plating solution is a reducing agent component.

[0028] S2. After performing activation pretreatment on the surface of substrate 6, substrate 6 is placed on substrate temperature control platform 7, and the substrate temperature control platform 7 is used to maintain the substrate 6 at a constant temperature of 45°C.

[0029] S3. Start the timing controller 8, motion control platform 5, first nozzle 2 and second nozzle 4. The timing controller 8 controls the first nozzle 2 and second nozzle 4 to spray micro-droplets at fixed points and time. For the same target point on the substrate 6, the first nozzle 2 is first controlled to spray the first plating solution micro-droplets. After an interval of 5 seconds, the second nozzle 4 is controlled to spray the second plating solution micro-droplets to the same point. The two sets of droplets are mixed in situ on the surface of the substrate 6, and a self-catalytic electroless nickel plating reaction occurs, and a nickel-phosphorus alloy coating is deposited in situ.

[0030] S4. The relative motion trajectory, spraying sequence, and layer-by-layer lifting height of the first nozzle 2 and the second nozzle 4 with the substrate 6 are synchronously controlled by the motion control platform 5. The three-dimensional nickel-phosphorus alloy structure is formed on the surface of the substrate 6 by scanning point by point and depositing layer by layer.

[0031] S5. After completing all deposition processes, remove the substrate 6, rinse the substrate 6 with deionized water to remove residual plating solution, and then dry it at 100°C to obtain the nickel-plated component.

[0032] The components of the first and second plating solutions in this embodiment are shown in Tables 1, 2 and 3. The substrate 6 described in this embodiment is a 1060 aluminum alloy plate. The pretreatment of the substrate 6 surface for activation in step S2 includes the following processes: (1) Alkali etching: 60 g / L NaOH, alkali etching at 50°C for 20 s; (2) Acid pickling and brightening: using 50 vol% HNO3, acid pickling at room temperature for 10 s; (3) First zinc immersion: the zinc immersion solution used is a mixture of 35 g / L ZnO, 350 g / L NaOH, 30 g / L potassium sodium tartrate, and 2 g / L FeCl3, at room temperature for 40 s; (4) Nitric acid zinc stripping: using 50 vol% HNO3, treatment at room temperature for 10 s; (5) Second zinc immersion: the second zinc immersion solution is a mixture of 15 g / L ZnO, 130 g / L NaOH, 30 g / L potassium sodium tartrate, 2 g / L FeCl3, and 2 g / L NaNO3, zinc immersion at room temperature for 50 s.

[0033] In this embodiment, a continuous nickel line with a width of approximately 80-120 μm and a thickness of approximately 1.5-2.5 μm was obtained on an aluminum alloy plate. The deposited layer was dense, with clear edges and no stray deposits. EDS analysis showed that the phosphorus content of the coating was approximately 2.5-3.5%, which is a low-phosphorus electroless nickel plating layer.

[0034] Example 2

[0035] The difference between the device in this embodiment and that in Embodiment 1 is that the first nozzle 2 and the second nozzle 4 are thermal bubble nozzles, with a droplet volume of 1 pL per spray; the distance between the first nozzle 2 and the second nozzle 4 and the substrate 6 is 0.2 mm. The motion control platform 5 is a five-axis motion platform. The substrate 6 is a 1060 aluminum alloy sample after a second zinc immersion treatment, simulating the surface of a heat sink. The components of the first and second plating solutions in this embodiment are shown in Tables 1, 2, and 3.

[0036] The above-mentioned nickel plating method based on a two-component time-spraying, power-free chemical nickel plating apparatus includes the following steps:

[0037] S1. Prepare a first plating solution and place it in a first storage tank 1. The first plating solution is a nickel salt component. Prepare a second plating solution and place it in a second storage tank 3. The second plating solution is a reducing agent component.

[0038] S2. After performing activation pretreatment on the surface of substrate 6, substrate 6 is placed on substrate temperature control platform 7, and the substrate temperature control platform 7 is used to maintain the substrate 6 at a constant temperature of 30°C.

[0039] S3. Start the timing controller 8, motion control platform 5, first nozzle 2 and second nozzle 4. The timing controller 8 controls the first nozzle 2 and second nozzle 4 to spray micro-droplets at fixed points and time. For the same target point on the substrate 6, the first nozzle 2 is first controlled to spray the first plating solution micro-droplets. After an interval of 10 seconds, the second nozzle 4 is controlled to spray the second plating solution micro-droplets to the same point. The two sets of droplets are mixed in situ on the surface of the substrate 6, and a self-catalytic electroless nickel plating reaction occurs, and a nickel-phosphorus alloy coating is deposited in situ.

[0040] S4. The relative motion trajectory, spraying sequence, and layer-by-layer lifting height of the first nozzle 2 and the second nozzle 4 with the substrate 6 are synchronously controlled by the motion control platform 5. The three-dimensional nickel-phosphorus alloy structure is formed on the surface of the substrate 6 by scanning point by point and depositing layer by layer.

[0041] S5. After completing all deposition processes, remove the substrate 6, rinse the substrate 6 with deionized water to remove residual plating solution, and then dry it at 90°C to obtain the nickel-plated component.

[0042] In this embodiment, the nickel layer deposited in a designated area of ​​an aluminum alloy heat sink was tested for solderability. The results showed that the surface was completely wetted after immersion in Sn solder at 250°C for 1 second.

[0043] Example 3

[0044] The difference between the device in this embodiment and that in Embodiment 1 is that the first nozzle 2 and the second nozzle 4 are thermal nozzles, each spraying a droplet volume of 50 pL. The distance between the first nozzle 2 and the second nozzle 4 and the substrate 6 is 0.8 mm. The substrate 6 is a copper plate, and its pretreatment process involves polishing with 400# sandpaper, cleaning with acetone, immersion in 5% dilute sulfuric acid, rinsing with pure water, and drying. The components of the first and second plating solutions in this embodiment are shown in Tables 1, 2, and 3.

[0045] The above-mentioned nickel plating method based on a two-component time-spraying, power-free chemical nickel plating apparatus includes the following steps:

[0046] S1. Prepare a first plating solution and place it in a first storage tank 1. The first plating solution is a nickel salt component. Prepare a second plating solution and place it in a second storage tank 3. The second plating solution is a reducing agent component.

[0047] S2. After performing activation pretreatment on the surface of substrate 6, substrate 6 is placed on substrate temperature control platform 7, and the substrate temperature control platform 7 is used to maintain the substrate 6 at a constant temperature of 60°C.

[0048] S3. Start the timing controller 8, motion control platform 5, first nozzle 2 and second nozzle 4. The timing controller 8 controls the first nozzle 2 and second nozzle 4 to spray micro-droplets at fixed points and time. For the same target point on the substrate 6, the first nozzle 2 is first controlled to spray the first plating solution micro-droplets. After an interval of 8 seconds, the second nozzle 4 is controlled to spray the second plating solution micro-droplets to the same point. The two sets of droplets are mixed in situ on the surface of the substrate 6, and a self-catalytic electroless nickel plating reaction occurs, and a nickel-phosphorus alloy coating is deposited in situ.

[0049] S4. The relative motion trajectory, spraying sequence, and layer-by-layer lifting height of the first nozzle 2 and the second nozzle 4 with the substrate 6 are synchronously controlled by the motion control platform 5. The three-dimensional nickel-phosphorus alloy structure is formed on the surface of the substrate 6 by scanning point by point and depositing layer by layer.

[0050] S5. After completing all deposition processes, remove the substrate 6, rinse the substrate 6 with deionized water to remove residual plating solution, and then dry it at 85°C to obtain the nickel-plated component.

[0051] In this embodiment, three-dimensional nickel micropillars with a diameter of approximately 150 μm and a height of approximately 14 μm were obtained on a copper plate. Cross-sectional SEM observation showed good interlayer bonding with no delamination or porosity.

[0052] Example 4

[0053] The difference between the device in this embodiment and that in Embodiment 1 is that the volume of droplets sprayed by the first nozzle 2 and the second nozzle 4 each time is 30 pL. The distance between the first nozzle 2 and the second nozzle 4 and the substrate 6 is 1 mm. The substrate 6 is a stainless steel plate, and the pretreatment method is polishing with 400# sandpaper, cleaning with acetone, soaking in 10% dilute hydrochloric acid, rinsing with pure water, and drying. The components of the first and second plating solutions in this embodiment are shown in Tables 1, 2, and 3.

[0054] The above-mentioned nickel plating method based on a two-component time-spraying, power-free chemical nickel plating apparatus includes the following steps:

[0055] S1. Prepare a first plating solution and place it in a first storage tank 1. The first plating solution is a nickel salt component. Prepare a second plating solution and place it in a second storage tank 3. The second plating solution is a reducing agent component.

[0056] S2. After performing activation pretreatment on the surface of substrate 6, substrate 6 is placed on substrate temperature control platform 7, and the substrate temperature control platform 7 is used to maintain the substrate 6 at 50°C.

[0057] S3. Start the timing controller 8, motion control platform 5, first nozzle 2 and second nozzle 4. The timing controller 8 controls the first nozzle 2 and second nozzle 4 to spray micro-droplets at fixed points and time. For the same target point on the substrate 6, the first nozzle 2 is controlled to spray the first plating solution micro-droplets first. After an interval of 0.1s, the second nozzle 4 is controlled to spray the second plating solution micro-droplets to the same point. The two sets of droplets are mixed in situ on the surface of the substrate 6, and a self-catalytic electroless nickel plating reaction occurs, and a nickel-phosphorus alloy coating is deposited in situ.

[0058] S4. The relative motion trajectory, spraying sequence, and layer-by-layer lifting height of the first nozzle 2 and the second nozzle 4 with the substrate 6 are synchronously controlled by the motion control platform 5. The three-dimensional nickel-phosphorus alloy structure is formed on the surface of the substrate 6 by scanning point by point and depositing layer by layer.

[0059] S5. After completing all deposition processes, remove the substrate 6, rinse the substrate 6 with deionized water to remove residual plating solution, and then dry it at 85°C to obtain the nickel-plated component.

[0060] Comparative Example 1

[0061] Conditions: The thickener was removed from the plating solution composition in Example 1. The first and second plating solutions were premixed at a 1:1 volume ratio to prepare a conventional chemical plating solution (coexistence of nickel salt and reducing agent). The aluminum alloy test piece after the second zinc immersion treatment was immersed in the plating solution and plated for 3 minutes. The result was a uniform nickel layer deposited on the surface of the test piece, with a thickness of about 0.8-1.2 μm and a phosphorus content of about 4.5%. However, after 5 plating cycles (about 0.3 MTO), the plating solution became turbid, and the deposition rate decreased by more than 50%.

[0062] Comparative conclusion: The time-division spraying method of the present invention can achieve a deposition effect comparable to that of traditional electroless plating, but the stability of the plating solution is greatly improved (3 months vs. 1 week), and selective localized deposition is achieved, which is impossible for traditional electroless plating.

[0063] Table 1. Components of the first plating solution in Examples 1 to 4

[0064] Example 1 30g / L 8g / L 8g / L 15g / L 6g / L 25g / L 4mg / L 10mg / L 0.5% 6.6 Example 2 50g / L 15g / L 16g / L 8g / L 4g / L 12g / L 1mg / L 25mg / L 4% 6.8 Example 3 80g / L 20g / L 24g / L 32g / L 20g / L 40g / L 6mg / L 60mg / L 8% 5.8 Example 4 100g / L 32g / L 30g / L 24g / L 15g / L 30g / L 8.0 mg / L 40mg / L 6% 6.4

[0065] Table 2. Components of the second plating solution in Examples 1 to 4

[0066] Example 1 36g / L 5mg / L 20g / L 0.5% 6.5 Example 2 80g / L 2mg / L 12g / L 4% 6.4 Example 3 60g / L 8mg / L 30g / L 8% 6.8 Example 4 100g / L 12mg / L 40g / L 6% 6.6

[0067] Table 3 Thickener components in the first and second plating solutions of Examples 1 to 4

[0068] Example 1 Hydroxyethyl cellulose Hydroxyethyl cellulose Example 2 Sodium alginate Xanthan Gum Example 3 <![CDATA[Fumed SiO₂]]> <![CDATA[Fumed silica]]> Example 4 Sodium polyacrylate and polyvinyl alcohol (molecular weight 10,000-100,000) are mixed in a 1:1 ratio by weight. Sodium polyacrylate and polyvinyl alcohol (molecular weight 10,000-100,000) are mixed in a 1:1 ratio by weight.

Claims

1. A power-free electroless nickel plating method based on two-component time-division spraying, characterized in that, Includes the following steps: S1. Prepare a first plating solution and a second plating solution that are not premixed and store them separately; the first plating solution is a nickel salt component and the second plating solution is a reducing agent component; S2. Perform activation pretreatment on the surface of the metal substrate to be plated, and after treatment, keep the substrate temperature constant at 30-60℃. S3. A fixed-point, time-division micro-droplet spraying method is adopted, with the spraying distance controlled between 0.2 and 1.0 mm. For the same target point on the substrate, the first plating solution micro-droplets are sprayed onto the substrate first, and after an interval of 0.1 to 10 seconds, the second plating solution micro-droplets are sprayed onto the same point. The two plating solutions are mixed in situ only on the substrate surface, triggering a power-free autocatalytic electroless nickel plating reaction and depositing a nickel-phosphorus alloy coating in situ. The single spraying volume of the first plating solution micro-droplet is 1-100 pL, and the single spraying volume of the second plating solution micro-droplet is 1-100 pL. S4. Control the relative motion trajectory between the two-component plating solution and the substrate, the spraying sequence, the layer-by-layer lifting height, the point-by-point scanning, and the layer-by-layer deposition to form a three-dimensional nickel-phosphorus alloy structure on the substrate surface. S5. After deposition, the substrate is rinsed with deionized water to remove residual plating solution, and then dried at 80-100℃ to obtain nickel-plated components.

2. The method for non-powered electroless nickel plating based on two-component time-division spraying according to claim 1, characterized in that, The composition of the first plating solution in step S1 is as follows: nickel sulfate 30-100 g / L, complexing agent CA-A 8-32 g / L, complexing agent CA-B 8-32 g / L, malic acid 8-32 g / L, lactic acid 4-20 g / L, sodium acetate 12-40 g / L, thiourea 1.0-8.0 mg / L, SDS 10-60 mg / L, thickener 0.5-8 wt%; the pH of the first plating solution is 5.8-6.

8.

3. The method for non-powered electroless nickel plating based on two-component time-division spraying according to claim 1, characterized in that, The composition of the second plating solution in step S1 is as follows: sodium hypophosphite 36-100 g / L, thiourea 2.0-12.0 mg / L, sodium acetate 12-40 g / L, thickener 0.5-8 wt%; the pH of the second plating solution is 6.4-6.

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4. The power-free electroless nickel plating method based on two-component time-division spraying according to claim 1, characterized in that, The thickeners in the first and second plating solutions are one or more of the following: hydroxyethyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, sodium alginate, gelatin, xanthan gum, guar gum, polyethylene glycol (molecular weight 2000-20000), polyvinyl alcohol (molecular weight 10000-100000), fumed silica, sodium polyacrylate, and carbomer.

5. A power-free electroless nickel plating apparatus based on two-component time-division spraying to implement the method of any one of claims 1-4, characterized in that, The system includes a first liquid storage tank, a first nozzle connected to the first liquid storage tank, a second liquid storage tank, a second nozzle connected to the second liquid storage tank, a motion control platform, a timing controller, a substrate, and a substrate temperature control platform. The first nozzle and the second nozzle are fixedly mounted on the motion control platform, which drives the first nozzle and the second nozzle to move relative to the substrate. The timing controller is electrically connected to the first nozzle, the second nozzle, and the motion control platform, and is used to control the two nozzles to independently start and stop spraying at different times, adjust the spraying interval sequence of the nozzles, and synchronously control the motion control platform to drive the first nozzle and the second nozzle to generate two-dimensional / three-dimensional displacement relative to the substrate. The spraying target points of the first nozzle and the second nozzle coincide, enabling them to spray plating solution onto the same target position on the substrate at different times. The substrate temperature control platform is thermally bonded to the substrate and is used to precisely control the substrate temperature so that the two plating solutions are mixed in situ after falling onto the substrate surface, triggering a power-free autocatalytic electroless nickel plating deposition reaction.

6. The power-free electroless nickel plating apparatus based on two-component time-division spraying according to claim 5, characterized in that, The first and second nozzles are either piezoelectric nozzles or thermal nozzles.

7. The power-free electroless nickel plating apparatus based on two-component time-division spraying according to claim 5, characterized in that, The motion control platform is a three-axis motion platform or a five-axis motion platform.

8. The power-free electroless nickel plating apparatus based on two-component time-division spraying according to claim 5, characterized in that, The substrate is one of aluminum alloy substrate, copper substrate, or stainless steel substrate.

9. The power-free electroless nickel plating apparatus based on two-component time-division spraying according to claim 5, characterized in that, The volume of each spray from the first nozzle and the second nozzle is 1-100 pL.

10. The power-free electroless nickel plating apparatus based on two-component time-division spraying according to claim 5, characterized in that, The distance between the first and second nozzles and the substrate is 0.2-1.0 mm.

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