Method for treating a substrate surface and use thereof

Abstract

The application discloses a substrate surface treatment method and application thereof, and relates to the technical field of substrate surface treatment, in particular to a substrate surface treatment method and application thereof.The method comprises the following steps: pretreating a metal surface of a substrate; performing chemical plating on the pretreated substrate at a predetermined temperature, wherein a plating solution of the chemical plating comprises a nickel salt, a complexing agent, a reducing agent and a MOF additive; and cleaning the metal substrate surface after the chemical plating to complete the metal substrate surface treatment.The technical scheme of the application not only greatly simplifies the process flow of surface treatment, reduces the production cost, improves the stability of the process, but also avoids the black board problem of ENIG technology and the plating leakage, plating penetration and false plating phenomenon of ENEPIG technology, and the PCB after surface treatment has excellent properties such as acid resistance, alkali resistance, high temperature and high humidity resistance, oxidation resistance, good weldability and conductivity, super surface hardness, coating uniformity and the like, can replace ENIG and ENEPIG technology, and can be applied to PCB surface treatment of high-end electronic products.

Description

A substrate surface treatment method and its application Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a substrate surface treatment method and its application. Background Technology

[0002] As the point where the PCB comes into contact with the outside world, the surface treatment layer not only protects the internal circuitry from external corrosion and oxidation, but also bears the responsibility of allowing chips to connect to it, requiring good solder wetting. However, because brittle intermetallic compounds can form between the solder and the surface treatment layer material, the solder joint often becomes the weakest link in the final electronic product. Therefore, research on the materials and performance of the surface treatment layer is extremely important.

[0003] Currently, commonly used PCB surface treatment technologies include: chemical immersion tin, chemical immersion silver, electroplating nickel gold, organic solderability protection film (OSP), chemical nickel immersion gold (ENIG), and chemical nickel palladium immersion gold (ENEPIG).

[0004] Nickel-gold plating technology refers to the technique of applying a layer of metallic nickel or gold onto the copper layer of a PCB using electroplating. Because the nickel plating layer effectively prevents atomic diffusion between the copper substrate and the outer gold layer, and the gold layer is more soluble in solder and has better corrosion resistance, the nickel layer is usually plated first, followed by the gold layer. However, soldering can cause the electroplated gold to become brittle, shortening its lifespan.

[0005] OSP, also known as heat-resistant flux, primarily functions to form a thin film of organic compounds on the copper surface, protecting it from oxidation or sulfidation in the natural environment. During high-temperature soldering, this film is removed by the flux, exposing the copper surface to molten solder, forming a strong solder joint almost simultaneously. Due to its low production cost, simple processing steps, and lack of involvement of toxic or harmful substances, OSP technology has gained widespread application in PCB surface treatment. However, OSP technology has limitations on the number of thermal cycles it can withstand; excessive cycles can lead to aging of the outer layer and decreased solderability.

[0006] ENIG surface finishing technology is widely used in the surface finishing of PCB boards for high-end electronic products due to its excellent conductivity and ability to meet the requirements of high-density packaging. Compared with nickel-gold plating, the ENIG process is more difficult to control, but because the gold layer plated by this technology is very thin and uniform, brittleness is rare. However, ENIG technology also has disadvantages such as high plating temperature, long processing time, high cost, and the presence of highly toxic cyanide in the plating solution. The most serious problem is that nickel corrosion, known as "black disk," often occurs between nickel and gold, leading to plating peeling and detachment of soldered components.

[0007] To address the "black disk" problem in ENIG technology, researchers have developed a new technique called ENEPIG (Enhanced Electroless Nickel-Palladium Ingot) technology, which uses palladium chemically deposited between nickel and gold to prevent direct contact between them. Compared to ENIG surface modification technology, ENEPIG offers superior solder interconnect performance and solder joint reliability. However, due to the high cost of palladium and the weak anti-interference ability of the palladium activation solution in actual production applications, the solution is in a metastable state, easily leading to incomplete plating, over-plating, and false plating. Furthermore, PCB rework after this process is difficult and costly, significantly increasing manufacturing costs.

[0008] Finally, because ENIG and ENEPIG technologies involve nickel alloy plating, and nickel materials have high resistivity and ferromagnetic properties, they exhibit a large inductance coefficient and relative instability, resulting in high losses during high-speed interconnection. With the rapid development of 5G mobile communication and information storage technologies, the transmission rates required for corresponding electronic products are becoming increasingly demanding. As the carrier of electronic components, PCBs are also evolving towards higher frequencies and speeds. The core requirements for high-frequency, high-speed PCBs are low and stable dielectric constants (Dk) and low dielectric loss factors (Df). Furthermore, because PCBs are used to connect and mount electronic components, the conductivity and signal transmission performance after connection must be considered, thus requiring the lowest possible impedance. Based on these reasons, selecting more suitable surface treatment technologies and plating thicknesses in actual production is of paramount importance for the practical production of high-frequency, high-speed PCBs.

[0009] Electroless plating, also known as autocatalytic plating, is an effective surface modification method to improve the corrosion resistance of metals. Among its various applications, electroless nickel plating is the most widely developed. Ni-P alloys using hypophosphite as a reducing agent exhibit excellent corrosion resistance and good mechanical properties. Researchers have proposed several hypotheses regarding the reaction mechanism and kinetics of Ni-P electroless plating, with the atomic hydrogen evolution theory being a classic theoretical model. This mechanism posits that the reaction involves four steps:

[0010] ①Ni 2+ +H2PO2 - +H₂O→Ni 0 +3H + +HPO3 2-

[0011] ②H2PO2 - +H₂O→HPO₃ 2- +H + +2H

[0012] ③H2PO2 - +H→P 0 +H₂O+OH -

[0013] ④2H→H2

[0014] The current PCB surface treatment process includes the following steps: degreasing → water washing → micro-etching → water washing → acid pickling → water washing → pre-immersion → water washing → electroless nickel plating → water washing → electroless gold plating → water washing. The electroless nickel plating solution mainly consists of a main salt, complexing agent, reducing agent, stabilizer, and pH adjuster. To obtain a sufficiently thick and high-performance gold plating layer on the electroless nickel plating layer, either cyanide-based gold plating solution or cyanide-free gold plating solution can be used. Cyanide gold plating solution has the advantages of excellent stability and the obtained gold plating layer can meet the requirements of the packaging and PCB industries. However, cyanide is a highly toxic substance, the waste liquid is difficult to treat and pollutes the environment, and it is also prone to eroding the solder mask during application. Furthermore, the personal safety of operators cannot be guaranteed. Cyanide-free gold plating solution does not contain highly toxic cyanide, which has a significant advantage in terms of environmental friendliness. However, its plating solution has problems such as nickel substrate corrosion and easy decomposition during the plating process.

[0015] Furthermore, to overcome the "black disk" problem in ENIG technology, a new ENEPIG surface modification technology has been developed in the PCB surface treatment field. This involves sequentially performing electroless palladium plating and electroless gold plating on the nickel-plated layer. ENEPIG surface modification technology not only effectively prevents the "black disk" phenomenon caused by excessive nickel corrosion, but also has significantly lower production costs than traditional ENIG surface modification technology. It offers advantages such as long-term stable storage, strong wire bonding capability, high mechanical strength, good wear resistance, wide application range in complex environments, high compatibility with SAC solder, and high soldering reliability, meeting the technical requirements of various packaging processes such as BGA and CSP / MCP packaging. However, in actual production applications, the palladium activation solution itself has weak anti-interference capabilities, causing the solution to be in a metastable state, which can easily lead to incomplete plating, over-plating, and false plating during the ENEPIG process. Moreover, rework of the circuit boards after this process is difficult and costly, significantly increasing the manufacturing cost of PCBs. Summary of the Invention

[0016] The purpose of this invention is to provide a substrate surface treatment method and its application. Addressing the problems of existing technologies, this technology adds nanoscale metal-organic framework (MOF) additives to the surface treatment solution. Utilizing the autocatalytic effect of nanoparticles, metal ions are reduced and deposited on the substrate surface, forming a dense nanocomposite film. Through the action of nanomaterials, various problems existing in current PCB surface treatment processes are completely solved, while simultaneously improving the coating's acid resistance, alkali resistance, high temperature and humidity resistance, oxidation resistance, solderability, conductivity, and surface hardness. To achieve the above objectives, this invention provides the following technical solution:

[0017] A method for surface treatment of a substrate, the method comprising,

[0018] Pre-treat the metal surface of the substrate;

[0019] The pretreated substrate is subjected to chemical plating at a predetermined temperature, wherein the plating solution for chemical plating includes nickel salt, complexing agent, reducing agent and MOF additive.

[0020] Clean the surface of the metal substrate after chemical plating to complete the surface treatment of the metal substrate.

[0021] Furthermore, the pretreatment of the metal surface of the substrate includes:

[0022] Grinding and polishing the metal surface of the substrate;

[0023] After sanding and polishing, rinse the substrate with water for 20-30 seconds, then clean it with an alkaline cleaning solution at 60℃ for 15-20 minutes.

[0024] After cleaning with alkaline cleaning solution, rinse the substrate with water for 20-30 seconds, then micro-etch it with micro-etching solution at 40℃ for 10-20 seconds.

[0025] After micro-etching, the substrate is rinsed with water for 20-30 seconds and then pickled with 5% sulfuric acid solution at room temperature for 2 minutes.

[0026] After pickling, the substrate is rinsed with water for 20-30 seconds and then activated with a 10 ppm palladium sulfate solution at room temperature for 2 minutes.

[0027] After palladium activation, the substrate is rinsed with water for 20-30 seconds to complete the metal surface pretreatment of the substrate.

[0028] Furthermore, the micro-etching solution is a mixed solution; the mixed solution includes 5% sulfuric acid and 1.5-2% H2O2.

[0029] Furthermore, the pH value of the electroless plating solution is 5.5-6.5.

[0030] Furthermore, the electroless plating temperature is 60-85℃.

[0031] Furthermore, the complexing agent includes one of citric acid, sodium citrate, ammonium citrate, EDTA, lactic acid, glycolic acid, succinic acid, and sodium pyrophosphate;

[0032] The reducing agent includes, but is not limited to, sodium hypophosphite.

[0033] The MOF additive is used to co-deposit with nickel and phosphorus atoms to form a dense nickel-MOF-phosphorus alloy composite film coating. The pH adjuster includes, but is not limited to, ammonia, sodium hydroxide, and potassium hydroxide.

[0034] Furthermore, the amount of nickel salt added is 30–50 g / L;

[0035] The amount of complexing agent added is 50-70 g / L;

[0036] The amount of reducing agent added is 20-30 g / L;

[0037] The amount of MOF additive added is 5-15 g / L.

[0038] Furthermore, the MOF additive has Ni as the central metal ion and is bonded to a two-dimensional layered structure through ligands with delocalized large π bonds.

[0039] The present invention also provides the application of the substrate surface treatment method described above in PCB surface treatment.

[0040] The present invention also provides the application of the substrate surface treatment method described above in the surface treatment of stainless steel substrates.

[0041] The technical effects and advantages of this invention are as follows:

[0042] This invention introduces a nanoscale metal-organic framework (MOF) additive into the surface treatment solution, enabling MOF nanoparticles to co-deposit with nickel metal on the substrate surface, forming a dense nanocomposite film. Through the action of the nanoparticle additive, the performance of the PCB after plating is optimized and improved. Compared with the ENIG and ENEPIG technologies commonly used in high-end electronic products, this project's technical solution replaces the two-layer (Ni+Au) coating of ENIG and the three-layer (Ni+Pd+Au) coating of ENENPIG with a single nickel-based alloy nanocomposite film (Figure 1). This simplifies the pretreatment and plating processes of the surface treatment technology, saves costs, and achieves cyanide-free and environmentally friendly production.

[0043] The technical solution of this invention not only greatly simplifies the surface treatment process, reduces production costs, and improves process stability, but also avoids the black disk problem that is prone to occur in ENIG technology and the phenomena of missed plating, plating penetration, and false plating that are prone to occur in ENEPIG technology. Moreover, the PCB after surface treatment has excellent properties such as acid resistance, alkali resistance, high temperature and humidity resistance, oxidation resistance, good solderability and conductivity, super surface hardness, and coating uniformity. It can replace ENIG and ENEPIG technologies and be applied to the PCB surface treatment of high-end electronic products.

[0044] 1. A surface treatment liquid additive based on nanoscale metal-organic framework (MOF) was designed and synthesized, which reduces the two-layer Ni+Au and three-layer Ni+Pd+Au coatings of the existing ENIG and ENEPIG processes to a single dense Ni-MOF-P alloy composite film coating, simplifying the process flow, eliminating the use of cyanide in the existing gold plating process, and reducing industrial pollution.

[0045] 2. The PCB coating treated with this technology avoids the black disk problem that is easy to occur with ENIG technology and the phenomena of missing plating, plating penetration and false plating that are easy to occur with ENEPIG technology. Moreover, the PCB after surface treatment has excellent properties such as acid resistance, alkali resistance, high temperature and high humidity resistance, oxidation resistance, good solderability and conductivity, super surface hardness and coating uniformity. It can replace ENIG and ENEPIG technologies and be used for PCB surface treatment of high-end electronic products.

[0046] 3. Design and synthesize a surface treatment liquid additive based on nanoscale metal-organic framework (MOF) to give the coating excellent properties such as acid resistance, alkali resistance, high temperature and humidity resistance, oxidation resistance, good weldability and conductivity, ultra-high surface hardness, and coating uniformity.

[0047] 4. Based on the technology of this surface treatment liquid additive, a cyanide-free formula is adopted, and the surface treatment liquid can be recycled by periodically adding nickel ions, hypophosphite ions, and MOF nano-additives. Therefore, it can effectively reduce energy consumption, save costs, reduce industrial pollution, and solve the problems of tin whiskers and rodent bites in the current PCB surface treatment chemical immersion tin technology, as well as the Giaviani phenomenon in the chemical immersion silver technology; solve the problem of deterioration of solderability due to multiple thermal cycles in the organic solderability protective film (OSP) process; solve the "black disk" problem in the chemical nickel immersion gold (ENIG) process; and solve the problems of high cost, incomplete plating, over-plating, and false plating in the chemical nickel palladium immersion gold (ENEPIG) process, and completely replace all existing PCB surface treatment technologies.

[0048] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0049] Figure 1 is a comparison diagram of the coating of the present invention with ENIG and ENEPIG technologies;

[0050] Figure 2 shows the structure of the MOF additive in a specific embodiment of the present invention;

[0051] Figure 3a shows the test points for the thickness of the PCB coating after processing in a specific embodiment of the present invention;

[0052] Figure 3b is an enlarged view of the PCB plating thickness test points after processing in a specific embodiment of the present invention;

[0053] Figure 3c is a topography test image of the processed PCB in a specific embodiment of the present invention;

[0054] Figure 4a shows a PCB treated with this technical solution in a specific embodiment of the present invention, after being immersed in a 5% HCl solution for 0.5 hours without discoloration.

[0055] Figure 4b shows images of the PCB treated with this technical solution in a specific embodiment of the present invention, after being immersed in a 5% NaOH solution for 0.5 hours without any color change.

[0056] Figure 5a is a test diagram of the gold wire on the first surface of the substrate after being treated by this technical solution in a specific embodiment of the present invention.

[0057] Figure 5b is a test diagram of the gold wire bonding on the second surface of the substrate after being treated by this technical solution in a specific embodiment of the present invention.

[0058] Figure 6a shows a PCB solder surface with 100% tinning after being treated by this technical solution, under the condition that the solder temperature is 255°C, in a specific embodiment of the present invention.

[0059] Figure 6b shows the PCB surface after a constant temperature and humidity aging test at 60°C and 90% humidity for 168 hours in a specific embodiment of the present invention, showing no oxidation or discoloration.

[0060] Figure 6c shows the tin on the PCB surface after a constant temperature and humidity aging test at 60°C and 90% for 168 hours in a specific embodiment of the present invention.

[0061] Figure 6d shows the oxidation and discoloration of the PCB surface coating after salt spray testing in a specific embodiment of the present invention.

[0062] Figure 6e shows the solderability test results of the PCB board after the salt spray test in a specific embodiment of the present invention, indicating that the solderability test results are still good.

[0063] Figure 6f shows the PCB after being processed by this technical solution in a specific embodiment of the present invention. After passing through the reflow oven 5 times, no oxidation or discoloration was found on the coating surface.

[0064] Figure 6g shows the solderability test results of the PCB after passing through 5 reflow ovens in a specific embodiment of the present invention, indicating that the solderability still has good tinning.

[0065] Figure 6h shows the solderability test results of the PCB after being processed by this technical solution in a specific embodiment of the present invention. At 288°C, there were 3 instances of floating solder in 10 seconds, with no pad delamination, bubbling, or peeling. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] To address the shortcomings of existing technologies, this invention discloses a substrate surface treatment method. The method includes: polishing the metal surface of the substrate; rinsing the polished substrate with water for 20-30 seconds, then cleaning it with an alkaline cleaning solution at 60°C for 15-20 minutes; rinsing the cleaned substrate with water for 20-30 seconds, then micro-etching it with a micro-etching solution at 40°C for 10-20 seconds; rinsing the micro-etched substrate with water for 20-30 seconds, then acid-washing it with a 5% sulfuric acid solution at room temperature for 2 minutes; rinsing the acid-washed substrate with water for 20-30 seconds, then activating it with a 10ppm palladium sulfate solution at room temperature for 2 minutes; rinsing the palladium-activated substrate with water for 20-30 seconds, thus completing the metal surface pretreatment. The pretreated substrate is then subjected to chemical plating at 60-85°C, wherein the chemical plating solution includes nickel salts, complexing agents, reducing agents, and MOF additives; rinsing the chemically plated metal substrate surface with a large amount of water for approximately 2 minutes, thus completing the metal substrate surface treatment.

[0068] In one specific embodiment of the present invention, the pH value of the electroless plating solution is 5.5-6.5.

[0069] In one specific embodiment of the present invention, the micro-etching solution is a mixed solution; the mixed solution includes 5% sulfuric acid and 1.5-2% H2O2.

[0070] In one specific embodiment of the invention, the role of the nickel salt is to provide reducible nickel ions for deposition in the solution. Free nickel ions in the solution undergo hydrolysis, leading to solution instability. Therefore, a complexing agent needs to be added to the solution to complex some of the free nickel ions, preventing precipitation and maintaining solution stability. Simultaneously, most complexing agents are weak organic acids, stabilizing the pH of the plating bath while maintaining solution stability. The reducing agent provides electrons for nickel ion deposition, and the molar ratio of nickel ions to hypophosphite also affects the plating rate, phosphorus content, surface properties, and coating color.

[0071] MOF additives are co-deposited with nickel and phosphorus atoms to form a dense nickel-MOF-phosphorus (Ni-MOF-P) alloy composite film, thereby optimizing and improving the performance of the PCB after plating. A pH adjuster is used to adjust the pH value of the solution to ensure the reaction occurs within the specified acid-base range.

[0072] The complexing agent includes one of citric acid, sodium citrate, ammonium citrate, EDTA, lactic acid, glycolic acid, succinic acid, and sodium pyrophosphate; the reducing agent includes, but is not limited to, sodium hypophosphite.

[0073] The MOF additive is used to co-deposit with nickel and phosphorus atoms to form a dense nickel-MOF-phosphorus alloy composite film coating.

[0074] pH adjusters include, but are not limited to, one of ammonia, sodium hydroxide, or potassium hydroxide.

[0075] In one specific embodiment of the present invention, the amount of nickel salt added is 30-50 g / L; the amount of complexing agent added is 50-70 g / L; the amount of reducing agent added is 20-30 g / L; and the amount of MOF additive added is 5-15 g / L. The MOF additive includes one of Ni3(HITP)2 and Ni3(HHTP)2.

[0076] The present invention also provides the application of the above-described substrate surface treatment method in PCB surface treatment.

[0077] The present invention also provides the application of the above-described substrate surface treatment method in the surface treatment of stainless steel substrates.

[0078] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0079] Example 1:

[0080] Preparation method of MOF additive Ni3(HITP)2

[0081] A solution of nickel chloride (3 g / L) was mixed with a solution of 2,3,6,7,10,11-hexaaminotriphenylhexahydrochloride (HATP·6HCl) ligand (5 g / L) and stirred until dissolved. The mixture was then heated to 60 °C and triethylamine (0.15 g / L) was added to obtain Ni3(HITP)2 additive.

[0082] The chemical pathway for the synthesis of Ni3(HITP)2 is as follows:

[0083]

[0084] Example 2:

[0085] Preparation method of MOF additive Ni3(HHTP)2

[0086] The pH of a nickel acetate aqueous solution (2.5 g / L) was adjusted to 7.5–8.0, and then a hexahydroxytriphenylene (HHTP) ligand solution (2 g / L) was added and stirred. The mixture was then allowed to stand at 70–90 °C for 2–5 h to obtain the Ni3(HHTP)2 additive.

[0087] The chemical route for the synthesis of Ni3(HHTP)2 is as follows:

[0088]

[0089] Combining the above Examples 1 and 2, and looking at the structural schematic diagram of the MOF material shown in Figure 2, the lighter-colored atoms in the figure are nickel atoms. The MOF material of this invention bonds three nickel atoms and two ligand molecules, self-assembling into a perfect hexagonal honeycomb lattice and stacking it into multiple layers. The hexagonal openings in each layer are perfectly aligned, and the gap between layers is 2 nm. The pore size of this material is 1.5 nm. The nickel coordinated by four amino or hydroxyl groups forms a conjugated coplanar structure, and the ligand has a delocalized large π bond. This structure ensures electron transport and therefore exhibits electrical conductivity.

[0090] Example 3:

[0091] PCB surface treatment process flow:

[0092] Alkaline degreasing (60℃ / 15 minutes) → Micro-etching (5% H2SO4 + 1.5% H2O2 / room temperature / 30 seconds) → 5% H2SO4 pickling (room temperature / 120 seconds) → PdSO4 activation (10ppm / room temperature / 120 seconds) → Electroless plating (75℃ / pH 6.0 / 1 hour) → Drying.

[0093] Tests and analyses of the performance of PCBs after plating show that the PCBs treated with this technology have significantly improved acid resistance, alkali resistance, and surface hardness compared to existing technologies.

[0094] As shown in Figures 3a-3c, the coating thickness and SEM test results show that the nickel alloy coating with nanoscale MOF additives has a thickness of 3.9–4.2 μm (Table 1 and Figures 3a and 3b) and a dense surface structure (Figure 3c).

[0095] Table 1. Thickness of nickel alloy coating with nanoscale MOF additives

[0096] Test site Au (μm) Ni-P (μm) 1 0.00 4.2 2 0.00 3.9 3 0.00 4.1 4 0.00 4.2 5 0.00 4.0 6 0.00 4.0 Average 0.00 4.1 Minimum 0.00 3.9 Maximum 0.00 4.2 surface

[0097] The acid and alkali resistance test results show that after immersing the PCB treated with this technical solution in 5% HCl solution and 5% NaOH solution for 0.5 hours respectively, the pad (substrate) did not change color (Figures 4a and 4b). In addition, the results of the gold wire bonding and tensile test on both sides of the pad (substrate) show that the gold wire can be soldered onto the surface of the substrate after plating, and there is residual gold when pushing the gold ball. The broken wire position is qualified, and the tensile strength of the gold wire is greater than 5g. Overall, it meets the test requirements (Figures 5a and 5b).

[0098] Solderability test results show that, under solder temperature of 255℃ and a tin-floating time of 3 seconds per test, the PCB solder surface treated with this technical solution achieved 100% tinning (Figure 6a). Furthermore, after a constant temperature and humidity aging test at 60℃ and 90% humidity for 168 hours, the PCB surface showed no oxidation or discoloration (Figure 6b), and the solderability test results still showed good tinning (Figure 6c). In addition, PCBs treated with existing surface treatment technologies on the market all exhibited varying degrees of poor tinning after salt spray testing. However, PCBs treated with this technical solution, after a 96-hour salt spray test with 5% NaCl aqueous solution, although the PCB surface plating showed oxidation and discoloration (Figure 6d), the solderability test results still showed good tinning (Figure 6e). To address the limitation of OSP technology on the number of thermal cycles it can withstand, which can lead to aging of the outer sheath and decreased solderability with excessive cycles, this technical solution was applied to PCBs. After five reflow oven cycles, the plating surface showed no oxidation or discoloration (Figure 6f), maintaining excellent solderability (Figure 6g). Thermal stress testing results showed that at 288℃, after three 10-second solder float tests, no pad delamination, blistering, or detachment occurred (Figure 6h). Pull-out testing results showed that when the pull force reached 24.89N, the pads detached without copper-nickel separation. All these results demonstrate that, compared to existing surface treatment technologies, PCBs treated with this technical solution exhibit more stable and superior solderability.

[0099] The high resistivity of nickel material can affect the integrity of signal transmission during high-speed interconnection. The conductivity of the plated PCB was tested. Under the condition of a plating thickness of 1-5 μm, the surface resistivity of the plated PCB was 0.377 μΩ·m, which is less than that of Cu (1.72 μΩ·m) and Ag (1.62 μΩ·m).

[0100] The theoretical basis of this technology is that, in the absence of current, with the aid of sodium hypophosphite as a reducing agent, a heterogeneous surface autocatalytic redox reaction causes metal ions to be reduced and deposited on the surface of the component, forming a dense metal alloy. As shown in Table 2, compared with the performance of existing PCB surface treatment technologies, this technical solution has the following advantages.

[0101] Table 2: Performance Comparison of the Invention Technology and Existing PCB Surface Treatment Technologies

[0102]

[0103] Example 4

[0104] Using 99.95% pure copper as the base material, the copper plate was processed through the following process, and then subjected to NSS neutral salt spray test and CASS acid salt spray test.

[0105] Alkaline degreasing (70℃ / 6 minutes) → Cathodic electrolytic degreasing (5V / room temperature / 90 seconds) → Pickling (room temperature / 30 seconds) → Polishing (room temperature / 30 seconds) → 5% H2SO4 activation (room temperature / 60 seconds) → PdSO4 (10ppm / room temperature / 120 seconds) → Electroless plating (77° / pH7.0) → Dehydration (room temperature / 5 seconds) → Drying → Baking (110° / 15 minutes).

[0106] The NSS neutral salt spray test results showed that PCBs with coating thicknesses of 1.07, 3.05, 5.07, and 10.05 μm remained normal after 864 hours of testing. The CASS acidic salt spray test results showed that PCBs with coating thicknesses of 1.07, 3.05, 5.07, and 10.05 μm were corroded after 48, 72, 144, and 192 hours, respectively, indicating that the PCBs treated with this technology have excellent corrosion resistance.

[0107] Example 5

[0108] Surface treatment technology for 316L stainless steel substrate

[0109] Process flow: Degreasing → Hot water rinse → Cold water rinse → Pickling (5% H2SO4, 2 minutes) → Water rinse → Pre-plating nickel (voltage 10V, current 5-10A / dm²) 2 (30-120 seconds) → Plating (30 minutes) → Deionized water rinse.

[0110] Pre-plating solution: NiCl2·6H2O 240g / L; HCl 120g / L

[0111] Chemical plating solution: Nickel salt 30g / L;

[0112] Complexing agent 50g / L;

[0113] Reducing agent 20g / L;

[0114] MOF additive 10g / L.

[0115] Electrochemical tests on the plated 316L stainless steel substrate showed that, under constant potential of 0.8V, 80℃, and hydrogen gas flow through the anode, the corrosion current density of the plated 316L stainless steel in an electrolyte of H2SO4 (pH=3) + HF (0.1ppm) was 64.97 μA·cm. -2 .

[0116] The contact resistance of the coating was tested using an FT-330 series ordinary four-probe sheet resistance resistivity tester, and the results are shown in Table 3:

[0117] Table 3: Contact resistivity of coatings on metal plate samples under different pressures

[0118]

[0119] The results show that the contact resistance of the 316L stainless steel treated with this technology meets the DOE standard requirements for fuel cells, indicating that the surface treatment layer has good conductivity.

[0120] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for surface treatment of a substrate, characterized in that, The method includes: pretreating the metal surface of a substrate; the metal surface of the substrate is a PCB surface; performing chemical plating on the pretreated substrate at a predetermined temperature, wherein the plating solution for chemical plating includes nickel salt, complexing agent, reducing agent, and MOF additive; the amount of nickel salt added is 30~50 g / L; the amount of complexing agent added is 50~70 g / L; the amount of reducing agent added is 20~30 g / L; the amount of MOF additive added is 5~15 g / L; the MOF additive includes one of Ni3(HITP)2 and Ni3(HHTP)2; the MOF additive is co-deposited with nickel atoms and phosphorus atoms to form a dense nickel-MOF-phosphorus alloy composite film coating; cleaning the surface of the chemically plated metal substrate to complete the surface treatment of the metal substrate, wherein the pH value of the plating solution for chemical plating is 5.5-6.5; the plating temperature for chemical plating is 60-85℃.

2. The substrate surface treatment method according to claim 1, characterized in that, The pretreatment of the metal surface of the substrate includes: grinding and polishing the metal surface of the substrate; rinsing the ground and polished substrate with water for 20-30 seconds, then cleaning it with an alkaline cleaning solution at 60°C for 15-20 minutes; rinsing the substrate with water for 20-30 seconds after cleaning with the alkaline cleaning solution, then micro-etching it with a micro-etching solution at 40°C for 10-20 seconds; rinsing the micro-etched substrate with water for 20-30 seconds, then acid-washing it with a 5% sulfuric acid solution at room temperature for 2 minutes; rinsing the acid-washed substrate with water for 20-30 seconds, then activating it with a 10ppm palladium sulfate solution at room temperature for 2 minutes; and rinsing the palladium-activated substrate with water for 20-30 seconds to complete the pretreatment of the metal surface of the substrate.

3. The substrate surface treatment method according to claim 2, characterized in that, The micro-etching solution is a mixed solution; the mixed solution includes 5% sulfuric acid and 1.5-2% H2O2.

4. The substrate surface treatment method according to claim 1, characterized in that, The complexing agent includes one of citric acid, sodium citrate, ammonium citrate, EDTA, lactic acid, glycolic acid, succinic acid, and sodium pyrophosphate; the reducing agent includes, but is not limited to, sodium hypophosphite; the pH adjusting agent includes, but is not limited to, one of ammonia, sodium hydroxide, and potassium hydroxide.

5. The substrate surface treatment method according to claim 1, characterized in that, The MOF additive uses Ni as the central metal ion and is bonded to a two-dimensional layered structure through ligands with delocalized large π bonds.

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