Non-magnetic printed circuit board and surface treatment EPAG process thereof

Abstract

According to the non-magnetic printed circuit board and the surface treatment EPAG process thereof provided by the invention, a nickel-palladium-gold-free thick plating layer structure of'catalytic nano palladium layer-pure palladium layer-gold layer 'is constructed on the copper surface of the printed circuit board by improving the surface treatment process flow method, so that the magnetic interference of the printed circuit board in a high-frequency signal transmission scene is avoided; secondly, a soaking technology is adopted in the whole process, the technological process of surface treatment of the printed circuit board is simplified, meanwhile, complete reaction is guaranteed through soaking time of the preparation tank, liquid medicine contact uniformity is guaranteed through a filtering / circulating system of the preparation tank, and the reaction environment is stabilized through a temperature control system; therefore, the electroplating uniformity during surface treatment is ensured, the thickness and the plating range of the plating layer are improved, palladium leakage is avoided, the reliability of the printed circuit board is improved, the adhesive force of the plating layer is improved, the service life of a product is prolonged, the signal transmission performance of the printed circuit board is further improved, and the printed circuit board is more suitable for high-frequency and fine-line-distance application requirements.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing, and more specifically, to non-magnetic printed circuit boards and their surface treatment process EPAG. Background Technology

[0002] In the field of printed circuit board (PCB) manufacturing, surface treatment processes for PCBs have undergone long-term development. Traditional technologies, such as electroless nickel-gold and nickel-palladium-gold, have formed mature systems and are widely used in various electronic devices. Electroless nickel-gold and nickel-palladium-gold processes involve depositing a nickel alloy layer on the copper layer of the PCB surface as a transition, followed by a palladium and gold layer, thereby improving the adhesion of the palladium and gold plating and preventing copper diffusion. However, as the electronics industry advances towards high-frequency communication, precision sensing, and high-density integration, magnetic interference and increased signal loss in high-frequency signal transmission scenarios, as well as signal crosstalk during fine-pitch wiring, have become key bottlenecks restricting technological upgrades. Simultaneously, the limited plating thickness of traditional processes makes it difficult to meet the higher requirements of precision electronics for bonding reliability and lifespan.

[0003] Faced with the above problems, improvements to traditional processes are often limited to adjusting the concentration of the chemical solution or optimizing the soaking parameters, failing to address the root cause. In traditional processes, the core of magnetic interference lies in the characteristics of nickel. To ensure plating performance, a nickel-phosphorus alloy layer must first be deposited on the copper surface. However, nickel, as a ferromagnetic metal, spontaneously generates a stable magnetic field and leaves residual magnetism, a characteristic that cannot be eliminated through process fine-tuning. This magnetism not only causes electromagnetic coupling with high-frequency signals, inducing eddy current losses and hysteresis losses, leading to signal energy loss and distortion, but also interferes with surrounding magnetically sensitive elements. Furthermore, the palladium layer in traditional processes is often a phosphorus-containing palladium layer, which, when superimposed on the nickel-phosphorus alloy layer, further enhances the magnetism. Moreover, limited by process conditions such as the palladium bath circulation rate, the plating thickness is difficult to increase, easily leading to problems such as palladium leakage, affecting the overall precision and reliability of the printed circuit board. Even if the thickness is forcibly increased, the characteristics of the nickel layer result in poor uniformity and decreased reliability, failing to fundamentally solve the signal and reliability problems.

[0004] Therefore, it is necessary to develop a non-magnetic, low-loss, thick-plating surface treatment process for printed circuit boards to improve the high-frequency performance, signal integrity, and stability of the treated printed circuit boards, making it suitable for applications in high-density, high-precision, and high-reliability electronic products. Summary of the Invention

[0005] The present invention aims to overcome at least one of the shortcomings of the prior art and provide a non-magnetic printed circuit board and its surface treatment EPAG process.

[0006] One object of the present invention is to provide a surface treatment process for non-magnetic printed circuit boards called EPAG, specifically comprising the following steps: H1: Copper surface pretreatment, which involves cleaning and polishing the copper surface of the printed circuit board, and pretreating the copper surface with copper surface cleaning solution. H2: Copper surface catalysis, using palladium deposition solution to deposit a catalytic nano-palladium layer on the exposed copper surface of the printed circuit board through a displacement reaction; H3: Chemical palladium deposition, used to clean the surface of printed circuit boards, followed by the application of chemical palladium solution to catalyze the palladium nanolayer through an oxidation-reduction reaction; H4: Reduced gold, cleaned copper surface, using immersion gold solution to deposit a gold layer of a certain thickness on the surface of pure palladium through oxidation-reduction reaction; H5: Post-processing involves cleaning and drying the printed circuit board after palladium deposition, and then conducting reliability testing. In steps H1-H4, the process is completed using an immersion process in the preparation tank; the preparation tank is equipped with at least a filtration / circulation system and a temperature control system.

[0007] In this technical solution, by improving the process flow and methods, a nickel-free palladium-gold plating structure combining a "catalytic nano-palladium layer - pure palladium layer - gold layer" is constructed on the copper surface of the printed circuit board. This avoids magnetic interference in high-frequency signal transmission scenarios and reduces signal loss, making the surface-treated printed circuit board suitable for high-frequency and high-speed applications. Secondly, by using an immersion process for the entire surface treatment of the printed circuit board, the process flow and operation difficulty are simplified. At the same time, the immersion time in the preparation tank ensures complete reaction, the built-in filtration / circulation system ensures uniform contact of the chemical solution, and the temperature control system stabilizes the reaction environment. This ensures the uniformity of electroplating during surface treatment, increases the plating thickness and plating range, avoids palladium leakage, and improves the reliability of the printed circuit board. Specifically, a catalytic nano-palladium layer is precisely deposited on the pretreated copper surface using a palladium-immersion solution through a displacement reaction, laying the foundation for subsequent plating layers. This provides a catalyst for the subsequent palladium-gold plating without introducing other plating components, eliminating magnetic interference on the printed circuit board surface from the source. Subsequently, a chemical palladium solution combined with a redox reaction achieves controllable deposition of pure palladium and gold layers. A filtration / circulation system ensures solution uniformity, and a temperature control system stabilizes the reaction environment. This allows for the reliable deposition of uniform, thicker, and more varied pure palladium and gold layers on the catalytic nano-palladium layer, reducing the risk of palladium leakage, improving plating adhesion and product lifespan, and further enhancing the signal transmission performance of the printed circuit board, making it more suitable for high-frequency and fine-pitch applications.

[0008] Furthermore, in step H2, the circulation rate of the filtration / circulation system is set to 4-8 TO, the temperature control system is set to 20-30℃, the concentration of the palladium precipitation solution is 60±20 PPM, and the time for the printed circuit board to be immersed in the palladium precipitation solution is 3±2 min.

[0009] In this technical solution, by precisely controlling the operating parameters of the filtration / circulation system and temperature control system in the copper surface catalysis process, as well as the concentration of the palladium deposition solution and the immersion time of the printed circuit board, the thickness, uniformity, and density of the catalytic nano-palladium layer are ensured, reducing process defects such as palladium leakage, thus providing a good foundation for subsequent plating. Specifically, a catalytic nano-palladium layer is formed on the copper surface of the printed circuit board through a displacement reaction between the palladium deposition solution and the copper surface. By controlling the concentration of the palladium deposition solution and the immersion time, the displacement reaction is ensured to proceed within limits. Simultaneously, by combining a reasonable solution concentration and immersion time, using the filtration / circulation system to ensure uniform composition of the palladium deposition solution, and maintaining a suitable environment for the reaction by the temperature control system, the displacement reaction is further ensured to proceed smoothly and efficiently. This guarantees the uniform formation of the required amount of catalytic nano-palladium layer on the copper surface, improving the uniformity and density of the catalytic nano-palladium layer deposition, reducing process defects such as palladium leakage, enhancing the catalytic effect of the nano-palladium layer on subsequent chemical palladium deposition, laying a good foundation for the formation of a stable pure palladium layer, and optimizing the process stability of the copper surface catalysis process, reducing product quality differences caused by parameter fluctuations.

[0010] Further, in step H3, the thickness of the pure palladium layer deposition is 0.05-1 μm.

[0011] Preferably, in step H3, 0.5-1% sodium chloride is used as the palladium bath precipitant to prepare the palladium solution in the preparation tank, and the concentration of the palladium solution is 0.6±0.2 g / L. The main components of the palladium solution include palladium dichloride, a reducing agent, a complexing agent, and a stabilizer. Further, the printed circuit board to be plated is immersed in the prepared palladium solution for a redox reaction. The circulation rate of the filtration / circulation system is 13±4 TO, the temperature of the temperature control system is 50-70℃, and the immersion time is 200-400 s.

[0012] In this technical solution, the pure palladium layer deposited on the printed circuit board through the redox reaction has a deposition thickness of 0.05-1μm. Compared with the traditional palladium plating method, the pure palladium layer can be deposited more uniformly with a wider thickness range. This reduces the risk of palladium leakage, improves the adhesion of the plating layer and the service life of the product, and further improves the signal transmission performance of the printed circuit board, making it more suitable for high-frequency and fine-pitch applications. Preferably, to prepare a pure palladium layer with better uniformity and greater thickness, the concentration and core components of the chemical palladium solution were optimized in the chemical palladium deposition step. Simultaneously, the operating parameters of the filtration / circulation system and temperature control system were also optimized accordingly. Specifically, palladium dichloride was used to provide a stable palladium source, and the reducing agent, complexing agent, and stabilizer worked synergistically to ensure the orderly conduct of the redox reaction. At the same time, a higher circulation rate filtration / circulation system maintained a higher solution exchange frequency to ensure solution uniformity, and a higher reaction temperature ensured reaction speed and completeness. This improved the controllability and quality stability of the pure palladium layer deposition, while also enhancing the density, uniformity, and thickness of the pure palladium layer. This ensured the pure palladium layer's ability to block copper diffusion, providing a high-quality substrate for the subsequent gold reduction step. Furthermore, the characteristics of the pure palladium layer prevented magnetic interference on the printed circuit board, improved signal transmission performance, and enhanced product lifespan and application adaptability.

[0013] Furthermore, the gold layer has a deposition thickness of 0.05-1 μm.

[0014] Preferably, in step H4, 10-20% ethylene glycol and 2-5% potassium (1-hydroxyethylidene) bisphosphonate are used as the immersion bath preparation agent to prepare the gold immersion solution in the preparation tank. The concentration of the gold immersion solution is 0.8±0.4 g / L. The main components of the gold immersion solution include formaldehyde, potassium gold cyanide, ethylene glycol, methanol, potassium (OC-6-11)-hexacyanoferrate (4-)potassium, N,N'-diisopropylethylenediamine, potassium (1-hydroxyethylidene) bisphosphonate, complexing agent, and stabilizer. Further, the printed circuit board to be plated is immersed in the prepared gold immersion solution for a redox reaction. The circulation rate of the filtration / circulation system is 16±4 TO, the temperature of the temperature control system is 80-90℃, and the immersion time is 500-1000 s.

[0015] In this technical solution, the gold layer deposited on the printed circuit board through the oxidation-reduction reaction has a deposition thickness of 0.05-1μm. Compared with the traditional method, the gold layer can be deposited more uniformly with a higher thickness and a wider thickness range, thereby improving the adhesion of the plating and bonding reliability, increasing the product lifespan, and further improving the signal transmission performance of the printed circuit board, making it more suitable for high-frequency and fine-pitch applications. Preferably, to prepare a gold layer with better uniformity and greater thickness, the concentration and core components of the gold deposition solution were optimized. Simultaneously, the operating parameters of the filtration / circulation system and temperature control system were also optimized accordingly. Specifically, potassium gold cyanide provides a stable source of gold ions, formaldehyde and other components play a reducing role, and complexing agents and stabilizers work synergistically to ensure the orderly progress of the reaction. A high-volume filtration / circulation system ensures uniform solution composition, and a high-temperature control system maintains the appropriate temperature environment required for the reaction. This improves the uniformity and thickness controllability of the gold layer deposition, enhances the density and corrosion resistance of the gold layer, improves the bonding reliability of the printed circuit board, and the synergistic effect of the gold layer and pure palladium layer further strengthens the non-magnetic properties, improves the integrity of high-frequency signal transmission, reduces signal loss, extends the product's lifespan, and enhances its applicability in the field of precision electronics.

[0016] Further, step H1 includes the following steps: H11: Alkaline degreasing, the copper surface of the printed circuit board is cleaned by immersion process using an alkaline degreasing agent, and then the residual alkaline degreasing agent is cleaned off with deionized water. H12: Copper surface micro-polishing, the copper surface of the printed circuit board is micro-polished by immersion process using copper surface polishing solution, and then deionized water is used to clean the residual copper surface polishing solution. H13: Pretreatment: The copper surface of the printed circuit board is pretreated by immersion with copper surface cleaning solution, and then deionized water is used to clean off any remaining copper surface cleaning solution.

[0017] Preferably, in step H11, the immersion time of the printed circuit board in the preparation tank is 3-5 minutes; the concentration of the alkaline degreasing agent is 10±5%; and then the residual alkaline degreasing agent is cleaned off through a three-stage DI water washing process. In step H12, the circulation rate of the filtration / circulation system is 4-8 TO, the temperature of the temperature control system is 30-40℃, the immersion time of the printed circuit board in the preparation tank is 3±1 min, and the concentration of the copper surface polishing solution is 60±10 ml / L; then, the residual copper surface polishing solution is cleaned off through a two-stage DI water washing process. In step H13, the circulation rate of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, and the concentration of the copper surface cleaning solution is 50±10 ml / L; then, the residual copper surface cleaning solution is cleaned off through a two-stage DI water washing process. In the three-stage DI water washing process and the two-stage DI water washing process in step H1, the washing time for each stage is 60-120s.

[0018] In this technical solution, the copper surface pretreatment process is refined into three sub-steps: alkaline degreasing, copper surface micro-polishing, and pretreatment. By precisely matching the soaking time, chemical concentration, and circulation volume of the filtration / circulation system configured for each step, the cleanliness and surface consistency of the copper surface are improved. This thoroughly removes impurities and oxide layers that affect subsequent processes, eliminates the color difference problem of the copper surface, improves the activity and compatibility of the copper surface, and enhances the bonding stability of subsequent processes such as copper surface catalysis and chemical palladium deposition with the copper surface. This ensures the smooth progress of the entire surface treatment process and provides ideal substrate conditions for the high-quality deposition of subsequent pure palladium and gold layers. Specifically, each sub-step employs an immersion process, followed by a rigorous multi-stage countercurrent deionized water washing step. This process progressively dissolves organic contaminants and fingerprints on the copper surface using an alkaline degreasing agent, and removes volatile substances from the green oil layer. A copper surface polishing solution ensures the copper surface is uniform, oxidation-free, and color-neutral. A copper surface cleaning solution provides deep pretreatment while effectively preventing residues of various chemicals on the printed circuit board surface. Through the progressive synergistic effect of each sub-step, a highly clean, uniformly active, and chemically stable copper substrate on the printed circuit board surface is obtained. This significantly reduces the risk of palladium leakage in subsequent catalytic processes due to a poor substrate, ensuring the uniformity, density, and reliable bonding of the subsequent nano-palladium catalytic layer and thick palladium-gold plating. Further preferably, during the multi-stage DI water washing, the deionized water in the preparation tank is aerated and stirred, making the washing process more efficient and thorough.

[0019] Furthermore, after step H2 and before step H3, the following steps are also included: H21: Post-immersion, which uses post-immersion solution to clean the residual palladium deposit solution on the surface of the printed circuit board through an immersion process, and then uses a two-stage DI water washing process to clean the residual post-immersion solution. In step H21, the circulation volume of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, the post-immersion solution is sulfuric acid, and the concentration of the post-immersion solution is 50±10 ml / L. In the two-stage DI water washing process, the washing time for each stage is 20-60 seconds.

[0020] In this technical solution, a post-immersion treatment step is added between the copper surface catalysis step and the chemical palladium deposition step. The post-immersion step's filtration / circulation system parameters, immersion time, chemical concentration, and the washing time of the two-stage DI water washing process are precisely set. Specifically, the post-immersion chemical dissolves and removes residual palladium deposition chemicals from the printed circuit board surface, and a multi-stage countercurrent deionized water washing step further cleans the surface of residual post-immersion chemicals and other impurities. This improves the cleanliness of the copper surface, avoids adverse interference from residual chemicals to the subsequent chemical palladium deposition reaction, and ensures the stability of the pure palladium layer deposition process. It not only significantly blocks the risk of cross-contamination and protects the activity of the nano-palladium catalytic layer, providing a pure and stable starting interface for the subsequent autocatalytic palladium deposition reaction, but also improves the uniformity and density of the pure palladium layer, enhances the adhesion between the pure palladium layer and the copper surface, ensures the quality of the overall plating structure, further optimizes the continuity and reliability of the entire surface treatment process, and lays a good foundation for the smooth progress of the subsequent gold reduction step and the improvement of the gold layer quality. More preferably, during multi-stage DI water washing, the deionized water in the preparation tank is aerated and stirred to make the water washing process more efficient and cleaner.

[0021] Another object of the present invention is to provide a non-magnetic printed circuit board, wherein the surface structure of the non-magnetic printed circuit board is prepared by the EPAG surface treatment process as described in this technical solution. The surface structure of the non-magnetic printed circuit board comprises, from the copper surface of its substrate outwards: a catalytic nano-palladium layer, a pure palladium layer, and a gold layer; The deposition thickness of both the pure palladium layer and the gold layer is 0.05-1 μm.

[0022] In this technical solution, the surface structure of the non-magnetic printed circuit board is prepared by using the surface treatment EPAG process. This constructs a stacked structure consisting of a "catalytic nano-palladium layer - pure palladium layer - gold layer" from the copper surface on the printed circuit board substrate outwards. This not only provides protection and conductivity to the surface structure, avoiding reliability defects caused by exposed copper, but also fundamentally avoids magnetic interference from nickel metal on the printed circuit board surface structure, improving signal transmission integrity. Simultaneously, this surface treatment EPAG process forms a thicker pure palladium layer and a wider range of thickness combinations on the printed circuit board surface, enhancing the bonding stability between the layers and the product's corrosion resistance. This improves the signal transmission integrity of the printed circuit board in high-frequency applications and its operational stability in strong magnetic field environments, while also ensuring the reliability of the printed circuit board, extending its service life, and improving the product's adaptability to high-frequency and fine-pitch applications.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a non-magnetic printed circuit board (PCB) surface treatment process called EPAG. By improving the process flow and methods, a nickel-free palladium-gold plating structure combining a catalytic nano-palladium layer, a pure palladium layer, and a gold layer is constructed on the copper surface of the PCB. This avoids magnetic interference in high-frequency signal transmission scenarios, reduces signal loss, and makes the PCB suitable for high-frequency and high-speed applications. Secondly, by employing an immersion process throughout the PCB surface treatment, the process flow and operational difficulty are simplified. Furthermore, the immersion time in the preparation tank ensures complete reaction, the built-in filtration / circulation system ensures uniform contact of the chemical solution, and the temperature control system stabilizes the reaction environment. This ensures uniform electroplating during surface treatment, increases plating thickness and plating range, avoids palladium leakage, and improves the reliability of the PCB. Specifically, a catalytic nano-palladium layer is precisely deposited on the pretreated copper surface using a palladium-immersion solution through a displacement reaction, laying the foundation for subsequent plating layers. This provides a catalyst for the subsequent palladium-gold plating without introducing other plating components, eliminating magnetic interference on the printed circuit board surface from the source. Subsequently, a chemical palladium solution combined with a redox reaction achieves controllable deposition of pure palladium and gold layers. A filtration / circulation system ensures solution uniformity, and a temperature control system stabilizes the reaction environment. This allows for the reliable deposition of uniform, thicker, and more varied pure palladium and gold layers on the catalytic nano-palladium layer, reducing the risk of palladium leakage, improving plating adhesion and product lifespan, and further enhancing the signal transmission performance of the printed circuit board, making it more suitable for the application requirements of high-frequency and fine-pitch electronic products.

[0024] 2. A non-magnetic printed circuit board (PCB) is provided. The surface structure of the non-magnetic PCB is prepared using the EPAG surface treatment process. This constructs a stacked structure consisting of a "catalytic nano-palladium layer - pure palladium layer - gold layer" from the copper surface on the PCB substrate outwards. This not only provides protection and conductivity to the surface structure, avoiding reliability defects caused by exposed copper, but also fundamentally avoids magnetic interference from nickel metal on the PCB surface structure, improving signal transmission integrity. Simultaneously, this EPAG surface treatment process forms a thicker pure palladium and gold layer with a wider range of thickness combinations on the PCB surface, enhancing the bonding stability between the layers and the product's corrosion resistance. This improves the signal transmission integrity in high-frequency applications and the operational stability in strong magnetic field environments, while also ensuring the reliability of the PCB, extending its service life, and improving the product's adaptability to high-frequency and fine-pitch applications. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the overall process of the EPAG surface treatment process for a non-magnetic printed circuit board according to the present invention.

[0026] Figure 2 This is a schematic diagram illustrating the specific process of copper surface pretreatment steps in the EPAG surface treatment process for a non-magnetic printed circuit board according to the present invention.

[0027] Figure 3 This is a schematic diagram of the surface structure of a non-magnetic printed circuit board according to the present invention.

[0028] Figure description: Non-magnetic printed circuit board substrate L10, copper surface L20, catalytic nano-palladium layer L30, pure palladium layer L40, gold layer L50. Detailed Implementation

[0029] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0030] In the description of this invention, it should be noted that the term "TO" refers to the number of times the chemical solution is circulated in the cylinder per hour, and "DOE" refers to the experimental design, which uses experiments to find the optimal process parameters. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "copper-surface catalysis," "chemical palladium deposition," and "reduced gold," etc., should be interpreted broadly. For example, "copper-surface catalysis" refers to the replacement of a copper surface with a layer of catalytic palladium, which acts as a catalyst in the palladium deposition reaction; "chemical palladium deposition" refers to the redox reaction in a palladium bath solution, where palladium ions undergo a reducing agent, resulting in the continuous deposition of palladium on the copper surface of the printed circuit board; and "reduced gold" refers to a redox reaction in which gold ions in the solution are deposited onto the palladium layer surface under the action of a reducing agent. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Example 1 like Figures 1-2 As shown, this embodiment provides a non-magnetic printed circuit board and its surface treatment EPAG process.

[0032] One object of the present invention is to provide a surface treatment process for non-magnetic printed circuit boards called EPAG, specifically comprising the following steps: H1: Copper surface pretreatment, which involves cleaning and polishing the copper surface of the printed circuit board, and pretreating the copper surface with copper surface cleaning solution. H2: Copper surface catalysis, using palladium deposition solution to deposit a catalytic nano-palladium layer on the exposed copper surface of the printed circuit board through a displacement reaction; H3: Chemical palladium deposition, used to clean the surface of printed circuit boards, followed by the application of chemical palladium solution to catalyze the palladium nanolayer through an oxidation-reduction reaction; H4: Reduced gold, cleaned copper surface, using immersion gold solution to deposit a gold layer of a certain thickness on the surface of pure palladium through oxidation-reduction reaction; H5: Post-processing involves cleaning and drying the printed circuit board after palladium deposition, and then conducting reliability testing. In steps H1-H4, the process is completed using an immersion process in a preparation tank; the preparation tank is equipped with at least a filtration / circulation system and a temperature control system.

[0033] Specifically, a catalytic nano-palladium layer is precisely deposited on the pretreated copper surface using a palladium-immersion solution through a displacement reaction, laying the foundation for subsequent plating layers. This provides a catalyst for the subsequent palladium-gold plating without introducing other plating components, eliminating magnetic interference on the printed circuit board surface from the source. Subsequently, a chemical palladium solution combined with a redox reaction achieves controllable deposition of pure palladium and gold layers. A filtration / circulation system ensures solution uniformity, and a temperature control system stabilizes the reaction environment. This allows for the reliable deposition of uniform, thicker, and more varied pure palladium and reduced gold layers on the catalytic nano-palladium layer, reducing the risk of palladium leakage, improving plating adhesion and product lifespan, and further enhancing the signal transmission performance of the printed circuit board, making it more suitable for high-frequency and fine-pitch applications.

[0034] Further, in step H2, the circulation rate of the filtration / circulation system is set to 4-8 TO, the temperature control system is set to 20-30℃, the concentration of the palladium precipitation solution is 60±20 PPM, and the time for the printed circuit board to be immersed in the palladium precipitation solution is 3±2 min.

[0035] Specifically, a catalytic nano-palladium layer is formed on the copper surface of a printed circuit board through a displacement reaction between a palladium precipitation solution and the copper surface. By controlling the concentration and soaking time of the palladium precipitation solution, the displacement reaction is ensured to proceed within limits. At the same time, by combining reasonable solution concentration and soaking time, and by using a filtration / circulation system to ensure the uniformity of the palladium precipitation solution composition, and by using a temperature control system to maintain a suitable environment for the reaction, the displacement reaction is further ensured to proceed smoothly and efficiently. This ensures that the required amount of catalytic nano-palladium layer is formed uniformly on the copper surface, improves the uniformity and density of the catalytic nano-palladium layer deposition, reduces process defects such as palladium leakage, enhances the catalytic effect of the nano-palladium layer on subsequent chemical palladium precipitation, lays a good foundation for the formation of a stable pure palladium layer, and optimizes the process stability of the copper surface catalysis process, reducing product quality differences caused by parameter fluctuations.

[0036] Furthermore, in step H3, the thickness of the pure palladium layer deposition is 0.05-1 μm.

[0037] Preferably, in step H3, 0.5-1% sodium chloride is used as the palladium bath precipitant to prepare the palladium solution in the preparation tank, and the concentration of the palladium solution is 0.6±0.2 g / L. The main components of the palladium solution include palladium dichloride, a reducing agent, a complexing agent, and a stabilizer. Further, the printed circuit board to be plated is immersed in the prepared palladium solution for a redox reaction. The circulation rate of the filtration / circulation system is 13±4 TO, the temperature of the temperature control system is 50-70℃, and the immersion time is 200-400 s.

[0038] Specifically, palladium dichloride provides a stable palladium source, and the reducing agent, complexing agent, and stabilizer work together to ensure the orderly progress of the redox reaction. At the same time, a filtration / circulation system with a higher circulation rate maintains a high chemical exchange frequency to ensure chemical uniformity, and a higher reaction temperature ensures reaction speed and completeness. By adjusting the deposition time, the deposition thickness is controlled, thereby improving the controllability and quality stability of the pure palladium layer deposition. It also enhances the density, uniformity, and plating thickness of the pure palladium layer, ensuring the pure palladium layer's ability to block copper diffusion and providing a high-quality substrate for the subsequent gold reduction step. In addition, the characteristics of the pure palladium layer prevent magnetic interference on the printed circuit board, improve signal transmission performance, and enhance the product's lifespan and application adaptability.

[0039] Furthermore, the gold layer was deposited to a thickness of 0.05-1 μm.

[0040] Preferably, in step H4, 10-20% ethylene glycol and 2-5% potassium (1-hydroxyethylidene) bisphosphonate are used as the immersion bath building agent to prepare the gold immersion solution in the preparation tank. The main components of the gold immersion solution include formaldehyde, potassium gold cyanide, ethylene glycol, methanol, potassium (OC-6-11)-hexacyanoferrate (4-)potassium, N,N'-diisopropylethylenediamine, potassium (1-hydroxyethylidene) bisphosphonate, complexing agent, and stabilizer. Further, the printed circuit board to be plated is immersed in the prepared gold immersion solution for a redox reaction. The circulation rate of the filtration / circulation system is 16±4 TO, the temperature of the temperature control system is 80-90℃, and the immersion time is 500-1000 s.

[0041] Specifically, the gold layer deposited on the printed circuit board through the redox reaction has a deposition thickness of 0.05-1μm. Compared with the traditional method, the gold layer can be deposited more uniformly with a higher thickness and a wider thickness range, thereby improving the adhesion of the plating and bonding reliability, increasing the product lifespan, and further improving the signal transmission performance of the printed circuit board, making it more suitable for high-frequency and fine-pitch applications. Preferably, to prepare a gold layer with better uniformity and greater thickness, potassium gold cyanide is used to provide a stable source of gold ions, while components such as formaldehyde play a reducing role. Complexing agents and stabilizers work synergistically to ensure the orderly progress of the reaction. A high-volume filtration / circulation system ensures uniform chemical composition, and a high-temperature control system maintains the appropriate temperature environment required for the reaction. The deposition thickness is controlled by adjusting the deposition time, thereby improving the uniformity and thickness controllability of the gold layer deposition, enhancing the density and corrosion resistance of the gold layer, improving the bonding reliability of the printed circuit board, and the synergistic effect of the gold layer and pure palladium layer further strengthens the non-magnetic properties, improves the integrity of high-frequency signal transmission, reduces signal loss, extends the service life of the product, and enhances its application adaptability in the field of precision electronics.

[0042] Further, step H1 includes the following steps: H11: Alkaline degreasing, which uses an alkaline degreasing agent to clean the copper surface of the printed circuit board through an immersion process, and then uses deionized water to clean off any remaining alkaline degreasing agent. H12: Copper surface micro-polishing. Copper surface polishing solution is used to micro-polish the copper surface of the printed circuit board through an immersion process, and then deionized water is used to clean off any remaining copper surface polishing solution. H13: Pretreatment. The copper surface of the printed circuit board is pretreated by immersion with copper surface cleaning solution, and then deionized water is used to clean off any remaining copper surface cleaning solution.

[0043] Preferably, in step H11, the immersion time of the printed circuit board in the preparation tank is 3-5 minutes; the concentration of the alkaline degreasing agent is 10±5%; and then the residual alkaline degreasing agent is cleaned off by a three-stage DI water washing process. In step H12, the circulation rate of the filtration / circulation system is 4-8 TO, the temperature of the temperature control system is 30-40℃, the immersion time of the printed circuit board in the preparation tank is 3±1 min, and the concentration of the copper surface polishing solution is 60±10 ml / L; then, the residual copper surface polishing solution is cleaned off through a two-stage DI water washing process. In step H13, the circulation rate of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, and the concentration of the copper surface cleaning solution is 50±10 ml / L; then, the residual copper surface cleaning solution is cleaned off through a two-stage DI water washing process. In the three-stage DI water washing process and the two-stage DI water washing process in step H1, the washing time for each stage is 60-120s.

[0044] Specifically, the copper surface pretreatment process is broken down into three sub-steps: alkaline degreasing, copper surface micro-polishing, and pretreatment. Each sub-step employs an immersion process, followed by a rigorous multi-stage countercurrent deionized water washing step. The alkaline degreasing agent gradually dissolves organic contaminants and fingerprints on the copper surface and removes volatile substances from the green oil layer. The copper surface polishing solution achieves a uniform, oxidation-free, and color-different state. The copper surface cleaning solution provides deep pretreatment while effectively preventing residues of various chemicals on the printed circuit board surface. Through the progressive synergistic effect of each sub-step, a highly clean, uniformly active, and chemically stable copper substrate on the printed circuit board surface is obtained. This significantly reduces the risk of palladium leakage due to a poor substrate in subsequent catalytic processes, ensuring the uniformity, density, and bonding reliability of the subsequent nano-palladium catalytic layer and thick palladium-gold plating. Further preferably, during the multi-stage DI water washing, the deionized water in the preparation tank is aerated and stirred, making the washing process more efficient and thorough.

[0045] Furthermore, after step H2 and before step H3, the following steps are also included: H21: Post-immersion, which uses post-immersion solution to clean the residual palladium deposit solution on the surface of the printed circuit board through an immersion process, and then uses a two-stage DI water washing process to clean the residual post-immersion solution. In step H21, the circulation volume of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, the post-immersion solution is sulfuric acid, and the concentration of the post-immersion solution is 50±10 ml / L. In the two-stage DI washing process, the washing time for each stage is 20-60 seconds.

[0046] Specifically, by adding a post-immersion treatment step between the copper surface catalysis step and the chemical palladium deposition step, the post-immersion solution dissolves and removes residual palladium deposition solution from the printed circuit board surface. A multi-stage countercurrent deionized water washing step further cleans the surface of residual post-immersion solution and other impurities, improving the cleanliness of the copper surface. This avoids adverse interference from residual solution to the subsequent chemical palladium deposition reaction, ensuring the stability of the pure palladium layer deposition process. It not only significantly blocks the risk of cross-contamination and protects the activity of the nano-palladium catalytic layer, providing a pure and stable starting interface for the subsequent autocatalytic palladium deposition reaction, but also improves the uniformity and density of the pure palladium layer, enhances the adhesion between the pure palladium layer and the copper surface, and ensures the quality of the overall plating structure. This further optimizes the coherence and reliability of the entire surface treatment process, while laying a good foundation for the smooth progress of the subsequent gold reduction step and the improvement of the gold layer quality. More preferably, during the multi-stage DI water washing, the deionized water in the preparation tank is aerated and stirred, making the washing process more efficient and cleaner.

[0047] Example 2 This embodiment also provides a non-magnetic printed circuit board and its surface treatment EPAG process. The difference between this embodiment and embodiment 1 is that: The pure palladium layer formed in this embodiment has a thickness of 1 μm and the reduced gold layer has a thickness of 1 μm. The printed circuit board with the surface treatment can be used in a magnetic field environment without being affected by the magnetic field, and the signal is stable and without signal loss, making it suitable for high-frequency product applications.

[0048] Specifically, the key to forming a thick plating structure with a pure palladium layer thickness of 1 μm and a reduced gold layer thickness of 1 μm lies in solving the problem of palladium leakage in the copper surface catalysis step and the problems of plating thickness and uniformity in the electroless palladium plating step and the reduced gold step.

[0049] In the copper-face catalysis step, the key factors for solving the palladium leakage problem are the temperature, concentration, and immersion time of the copper-face catalytic solution, as well as the rinsing time in the secondary DI rinsing process after the copper-face catalysis step. Through DOE experiments, the optimal process parameters were determined to be: In step H2, the temperature of the copper surface catalysis process is controlled at 20°C; the concentration of the palladium precipitation solution is 80 PPM; the printed circuit board is immersed in the palladium precipitation solution for 1 minute; after the copper surface catalysis step and before the chemical palladium precipitation step, the printed circuit board with the catalytic nano-palladium layer is rinsed with multi-stage, flowing deionized water, with each stage of DI water rinsing time being 20 seconds and the total water rinsing time being 40 seconds.

[0050] In the electroless palladium plating and gold reduction steps, the key factors for solving the problems of coating thickness and uniformity are the chemical concentration, temperature, and deposition time. Through DOE experiments, the optimal process parameters were determined to be: In the chemical palladium precipitation process in step H3, the temperature of the temperature control system is 62℃; the concentration of the chemical palladium solution is 0.6g / L; and the deposition time is 76min.

[0051] In the gold reduction process in step H4, the temperature of the temperature control system is 82℃; the concentration of the gold deposition solution is 0.8g / L; and the deposition time is 142min.

[0052] Example 3 This embodiment provides a non-magnetic printed circuit board. The surface structure of the non-magnetic printed circuit board provided in this embodiment is prepared using the EPAG surface treatment process provided in Embodiment 1 or Embodiment 2. like Figure 3 As shown, the surface structure of the non-magnetic printed circuit board in this embodiment includes, from the copper surface L20 of its substrate L10 outwards: a catalytic nano-palladium layer L30, a pure palladium layer L40, and a gold layer L50. The deposition thickness of both the pure palladium layer L40 and the gold layer L50 is 0.05-1 μm.

[0053] By employing the EPAG surface treatment process to prepare the surface structure of a non-magnetic printed circuit board (PCB), a stacked structure consisting of a catalytic nano-palladium layer, a pure palladium layer, and a gold layer is constructed outward from the copper surface on the PCB substrate. This not only leverages the protective and conductive functions of the surface structure, avoiding reliability defects caused by exposed copper, but also fundamentally avoids magnetic interference from nickel metal on the PCB surface structure, improving signal transmission integrity. Simultaneously, this EPAG surface treatment process forms a thicker pure palladium and gold layer with a wider range of thickness combinations on the PCB surface, enhancing the bonding stability between the layers and the product's corrosion resistance. This improves the signal transmission integrity of the PCB in high-frequency applications and its operational stability in strong magnetic field environments, while also ensuring the PCB's reliability, extending its service life, and improving the product's adaptability to high-frequency and fine-pitch applications.

[0054] Obviously, the above embodiments of the present invention are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. The EPAG surface treatment process for non-magnetic printed circuit boards, characterized in that, Includes the following steps: H1: Copper surface pretreatment, which involves cleaning and polishing the copper surface of the printed circuit board, and pretreating the copper surface with copper surface cleaning solution. H2: Copper surface catalysis, using palladium deposition solution to deposit a catalytic nano-palladium layer on the exposed copper surface of the printed circuit board through a displacement reaction; H3: Chemical palladium deposition, cleaning the surface of the printed circuit board, and then using chemical palladium solution to deposit a pure palladium layer of a certain thickness on the catalytic nano-palladium layer through an oxidation-reduction reaction; H4: Reduced gold, cleaned copper surface, using immersion gold solution to deposit a gold layer of a certain thickness on the surface of pure palladium through oxidation-reduction reaction; H5: Post-processing involves cleaning and drying the printed circuit board after palladium deposition, and then conducting reliability testing. In steps H1-H4, the process is completed using an immersion method in the preparation tank; the preparation tank is equipped with at least a filtration / circulation system and a temperature control system.

2. The EPAG surface treatment process according to claim 1, characterized in that, In step H2, the circulation rate of the filtration / circulation system is set to 4-8 TO, the temperature control system controls the temperature to 20-30℃, the concentration of the palladium precipitation solution is 60±20 PPM, and the time for the printed circuit board to be immersed in the palladium precipitation solution is 3±2 min.

3. The EPAG surface treatment process according to claim 1, characterized in that, In step H3, the thickness of the pure palladium layer is 0.05-1 μm.

4. The EPAG surface treatment process according to claim 3, characterized in that, In step H3, the circulation rate of the filtration / circulation system is 13±4 TO, and the temperature of the temperature control system is 50-70℃; the concentration of the chemical palladium solution is 0.6±0.2 g / L, and the main components of the chemical palladium solution include palladium dichloride, reducing agent, complexing agent and stabilizer.

5. The EPAG surface treatment process according to claim 1, characterized in that, In step H4, the gold layer is deposited to a thickness of 0.05-1 μm.

6. The EPAG surface treatment process according to claim 5, characterized in that, In step H4, the circulation rate of the filtration / circulation system is 16±4 TO, and the temperature of the temperature control system is 80-90℃; the concentration of the gold-infused liquid is 0.8±0.4 g / L, and the main components of the gold-infused liquid include formaldehyde, potassium gold cyanide, ethylene glycol, methanol, potassium (OC-6-11)-hexacyanoferrate (4-)potassium, N,N'-diisopropylethylenediamine, potassium (1-hydroxyethylidene)bisphosphonate, complexing agent, and stabilizer.

7. The EPAG surface treatment process according to any one of claims 1-6, characterized in that, Step H1 includes the following steps: H11: Alkaline degreasing, the copper surface of the printed circuit board is cleaned by immersion process using an alkaline degreasing agent, and then the residual alkaline degreasing agent is cleaned off with deionized water. H12: Copper surface micro-polishing, the copper surface of the printed circuit board is micro-polished by immersion process using copper surface polishing solution, and then deionized water is used to clean the residual copper surface polishing solution. H13: Pretreatment: The copper surface of the printed circuit board is pretreated by immersion with copper surface cleaning solution, and then deionized water is used to clean off any remaining copper surface cleaning solution.

8. The EPAG surface treatment process according to claim 7, characterized in that, In step H11, the printed circuit board is immersed in the preparation tank for 3-5 minutes; the concentration of the alkaline degreasing agent is 10±5%; and then the residual alkaline degreasing agent is cleaned off through a three-stage DI water washing process. In step H12, the circulation rate of the filtration / circulation system is 4-8 TO, the temperature of the temperature control system is 30-40℃, the immersion time of the printed circuit board in the preparation tank is 3±1 min, and the concentration of the copper surface polishing solution is 60±10 ml / L; then, the residual copper surface polishing solution is cleaned off through a two-stage DI water washing process. In step H13, the circulation rate of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, and the concentration of the copper surface cleaning solution is 50±10 ml / L; then, the residual copper surface cleaning solution is cleaned off through a two-stage DI water washing process. In the three-stage DI water washing process and the two-stage DI water washing process in step H1, the washing time for each stage is 60-120s.

9. The EPAG surface treatment process according to any one of claims 1-6, characterized in that, The following steps are included after step H2 and before step H3: H21: Post-immersion, which uses post-immersion solution to clean the residual palladium deposit solution on the surface of the printed circuit board through an immersion process, and then uses a two-stage DI water washing process to clean the residual post-immersion solution. In step H21, the circulation volume of the filtration / circulation system is 4-8 TO, the immersion time of the printed circuit board in the preparation tank is 2±1 min, the post-immersion solution is sulfuric acid, and the concentration of the post-immersion solution is 50±10 ml / L. In the two-stage DI water washing process, the washing time for each stage is 20-60 seconds.

10. A non-magnetic printed circuit board, characterized in that, The surface structure of the non-magnetic printed circuit board is prepared using the EPAG surface treatment process as described in any one of claims 1-9. The surface structure of the non-magnetic printed circuit board comprises, from the copper surface of its substrate outwards: a catalytic nano-palladium layer, a pure palladium layer, and a gold layer; The deposition thickness of both the pure palladium layer and the gold layer is 0.05-1 μm.

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