Brown solution for printed circuit board as well as preparation method and application of brown solution

Abstract

The invention discloses browning liquid for a printed circuit board as well as a preparation method and application of the browning liquid, and aims to solve the problems that the interlayer binding force of the printed circuit board treated by the existing browning liquid is insufficient, and the oxidation rate is not matched with the film forming rate. The browning liquid takes sulfuric acid as a main etching agent, organic acid as an auxiliary etching agent, hydrogen peroxide as a main oxidizing agent and nitrobenzenesulfonate as an auxiliary oxidizing agent, and is matched with functional components such as a buffering agent and a corrosion inhibitor. During preparation, the temperature is controlled to be 25-30 DEG C, the stirring speed is 200-300 r / min, and the materials are added And treatment is performed for 0.5-2 minutes at the temperature of 30-40 DEG Through component synergy, a browning film is compact and uniform, the peel strength is larger than or equal to 5.7 lb / in, layering and board explosion are avoided under thermal stress, the stability of the browning liquid is good, the browning liquid is suitable for precise manufacturing of high-end PCBs, and practicability and industrial value are both achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical agents for circuit boards, and particularly to a browning solution for printed circuit boards, its preparation method, and its application. Background Technology

[0002] Printed circuit boards (PCBs) are the core interconnect carriers of electronic devices, widely used in high-end electronic equipment, communication equipment, precision instruments, and other fields. As electronic products evolve towards thinner and lighter designs and higher densities, the interlayer bonding strength of multilayer PCBs has become a key indicator determining product reliability, directly affecting the structural stability of equipment during use and preventing failures such as delamination and board bursting under thermal stress.

[0003] Browning is a core process in the manufacturing of multilayer printed circuit boards. Browning solution reacts with the surface of inner copper foil to form a browning film, which can improve the micro-roughness of the copper foil surface to provide mechanical anchoring points, optimize the interfacial compatibility with the prepreg resin, and ultimately ensure interlayer bonding.

[0004] However, while existing browning solutions can complete basic copper-side browning treatment and meet the production needs of ordinary printed circuit boards, they have a significant shortcoming in the interlayer bonding performance, which is the core of high-end multilayer printed circuit board manufacturing. Specifically: Currently, most browning solutions on the market use a simple formula of a single corrosion inhibitor combined with conventional etchants and oxidants. This makes it difficult to precisely control the microscopic roughness of the copper foil surface and the density of the browning film, resulting in insufficient mechanical anchoring between the copper foil and the prepreg, poor interfacial compatibility, and limited adhesion. Furthermore, while some technologies attempt to improve performance through formula adjustments, such as using compound corrosion inhibitors with silane coupling agents, or focusing on optimizing secondary properties such as the thermal stability and copper loading capacity of the browning solution, they fail to address the core pain point of "high adhesion." They cannot resolve the inherent contradiction between "moderate roughening of the copper foil surface to improve the anchoring effect" and "densification of the browning film to ensure adhesion stability," nor can they achieve a breakthrough in adhesion. Ultimately, this leads to insufficient peel strength of printed circuit boards treated with these solutions, making them prone to delamination and board bursting under thermal stress, and failing to meet the structural stability requirements of high-end electronic devices.

[0005] Therefore, developing a browning solution and its application process that is based on high adhesion, can simultaneously achieve moderate roughening of the copper foil surface and densification of the browning film, and is compatible with high-end printed circuit board manufacturing processes is a technical problem that the printed circuit board manufacturing industry urgently needs to solve. Summary of the Invention

[0006] The main objective of this invention is to provide a browning solution for printed circuit boards, its preparation method, and its application. By introducing a specific auxiliary oxidant and working synergistically with other key components at optimized concentrations, a browning film with excellent mechanical anchoring effect and high cohesive strength is formed on the copper surface, thereby improving the interlayer bonding and thermal reliability of multilayer printed circuit boards.

[0007] To achieve the above objectives, the present invention provides a browning solution for printed circuit boards, comprising the following components: a main etchant, an auxiliary etchant, a main oxidant, an auxiliary oxidant, a buffer, a corrosion inhibitor, a surfactant, and deionized water; The auxiliary oxidant is a nitrobenzene sulfonate compound.

[0008] Through the above component design, the core technology leverages the synergistic effect of nitrobenzenesulfonate auxiliary oxidants and main oxidants to solve the problem of mismatch between oxidation rate and film formation rate in existing technologies, significantly improving the interlayer adhesion of printed circuit boards. Specifically, nitrobenzenesulfonate compounds possess suitable oxidation potentials, allowing for precise control of the oxidation degree on the copper foil surface. This not only works in conjunction with the main oxidant to achieve appropriate micro-etching of the copper surface to form anchoring points, but also avoids excessive oxidation that leads to a porous film layer, thus greatly improving the interfacial compatibility between the browning film, copper foil, and prepreg resin.

[0009] In one possible implementation, the concentrations of the browning solution components are as follows: main etchant 40–55 g / L, auxiliary etchant 0.4–0.7 g / L, main oxidant 10–20 g / L, auxiliary oxidant 0.1–0.5 g / L, buffer 5–15 g / L, corrosion inhibitor 5–10 g / L, surfactant 0.4–0.7 g / L, and the balance being deionized water.

[0010] By using the precise concentration ratios described above, the synergistic effect of each component is maximized. A main etchant concentration of 40–55 g / L can form a copper surface with suitable roughness. An auxiliary etchant concentration of 0.4–0.7 g / L further refines the surface morphology. An auxiliary oxidant concentration of 0.1–0.5 g / L is precisely matched with the main oxidant concentration of 10–20 g / L to avoid under-oxidation or over-oxidation. The concentrations of buffers and corrosion inhibitors ensure the stability of the reaction system and reduce corrosion defects on the copper surface.

[0011] In one possible implementation, it further includes a complexing agent of 0.2–0.7 g / L, an electrolyte of 0.02–0.07 g / L, and a cosolvent of 0.1–0.3 g / L.

[0012] By adding complexing agents, electrolytes, and co-solvents, the stability, service life, and compatibility of the browning solution are further improved. Complexing agents form stable complexes with metal ions generated during the reaction, preventing precipitation that could lead to solution failure. Electrolytes optimize the system's conductivity, promoting uniform reaction of components on the copper surface, reducing local concentration deviations, and ensuring stable treatment performance during long-term use, while reducing waste liquid generation. Co-solvents enhance the solubility and system compatibility of organic functional components in the browning solution, such as corrosion inhibitors and surfactants, preventing organic components from precipitating or dispersing unevenly. They also improve the wettability of the browning solution on the copper foil surface of printed circuit boards, ensuring uniform treatment at high-density circuit gaps, reducing interface contamination caused by residues, and indirectly ensuring stable interlayer adhesion.

[0013] In one possible implementation, the primary etchant is sulfuric acid; the secondary etchant is at least one selected from citric acid, tartaric acid, methanesulfonic acid, and phosphoric acid.

[0014] By selecting sulfuric acid as the primary etchant and organic acids as secondary etchants, both etching effectiveness and surface compatibility are balanced. Sulfuric acid has a mild yet highly efficient etching capability, forming a uniform micro-rough surface; organic acids such as citric acid can regulate the etching rate, refine the rough morphology, avoid sharp protrusions that could lead to film cracking, and simultaneously improve the interfacial bonding between the browning film and the resin, thus resolving the contradiction between "roughness" and "film integrity" that is difficult to balance with a single etchant.

[0015] In one possible implementation, the primary oxidant is hydrogen peroxide; the secondary oxidant is at least one of sodium p-nitrobenzenesulfonate, sodium o-nitrobenzenesulfonate, sodium m-nitrobenzenesulfonate, sodium 2,4-dinitrobenzenesulfonate, and ammonium nitrobenzenesulfonate.

[0016] Precise control of the oxidation process is achieved through the combination of hydrogen peroxide and specific nitrobenzenesulfonate auxiliary oxidants. Hydrogen peroxide provides the main oxidation driving force, rapidly oxidizing copper to form cuprous oxide; nitrobenzenesulfonate compounds optimize the oxide layer structure through synergistic oxidation, making the browning film denser, while inhibiting the decomposition of hydrogen peroxide and prolonging its effective action time.

[0017] In one possible implementation, the buffer is at least one selected from tris(hydroxymethyl)aminomethane, ammonium bicarbonate, monoethanolamine, diethanolamine, and triethanolamine. The corrosion inhibitor is at least one of benzotriazole, methylbenzotriazole, carboxybenzotriazole, and 2-mercaptobenzothiazole; The surfactant is at least one of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, polypropylene glycol, polyethylene glycol, and alkylphenol polyoxyethylene ether.

[0018] By selecting the aforementioned specific functional components, a stable reaction system is constructed and the film performance is optimized. The buffer stabilizes the pH value of the system and avoids fluctuations in the etching rate; the corrosion inhibitor forms an adsorption film on the copper surface to prevent over-etching; the surfactant reduces the surface tension of the browning solution and ensures uniform wetting in the gaps of high-density lines. The three components work synergistically to make the browning film uniform in morphology and have strong adhesion, which is suitable for the precision manufacturing requirements of high-end printed circuit boards.

[0019] A method for preparing a browning solution for printed circuit boards, comprising the following steps: At 25–30°C, under stirring conditions, the main etchant, auxiliary etchant, main oxidant and auxiliary oxidant are added sequentially to deionized water. After stirring until dissolved, buffer, corrosion inhibitor and surfactant are added. After stirring until completely dissolved and mixed evenly, the volume is adjusted to obtain the browning agent.

[0020] The above preparation method ensures that all components of the browning solution are fully mixed and have stable performance. Maintaining a temperature of 25–30°C prevents thermal decomposition of the components. Controlling the order of addition and temperature ensures that all components, especially functional additives, are fully dissolved and mixed sequentially under suitable conditions. This avoids localized precipitation, component decomposition, or reduced efficiency that may result from improper addition, thus yielding a uniform, stable, and reliable browning solution product.

[0021] In one possible implementation, when the browning solution contains a complexing agent, a cosolvent, and an electrolyte, the complexing agent, the electrolyte, and the cosolvent are added together with the buffer, the corrosion inhibitor, and the surfactant during the step of adding the buffer, the corrosion inhibitor, and the surfactant.

[0022] By employing the above method, complexing agents, electrolytes, co-solvents, and functional components such as buffers, corrosion inhibitors, and surfactants are added simultaneously. This avoids localized excessive concentrations or incomplete reactions caused by stepwise addition, while allowing the co-solvent to synergistically interact with the organic functional components in a timely manner, preventing the organic components from being precipitated or unevenly dispersed. Simultaneously, it reduces operational steps and minimizes human error during production. This addition method ensures that all auxiliary components form a stable and synergistic system with the core reactive components, further improving the homogeneity of the browning solution and the repeatability of the treatment effect, guaranteeing batch-to-batch performance stability.

[0023] The application of the browning solution for printed circuit boards in the browning treatment of printed circuit boards.

[0024] Through the above applications, this browning solution can be efficiently applied to the browning process of the inner layer of printed circuit boards. Its unique formula system can quickly form a high-quality browning film with strong adhesion and good thermal stability on the copper foil surface, fundamentally improving the lamination reliability of multilayer printed circuit boards and the service life of the final product.

[0025] In one possible implementation, the process conditions for the application include: immersing the pretreated inner layer of the printed circuit board into the browning solution, treating it at 30-40°C for 0.5-2 minutes, followed by washing and drying.

[0026] The optimized application process conditions described above enable efficient and stable browning treatment. A temperature of 30–40°C is suitable for the reaction rate of each component, and a processing time of 0.5–2 minutes ensures the formation of a browning film of appropriate thickness. This avoids both insufficient treatment leading to poor adhesion and over-treatment causing copper foil loss. The washing and drying steps remove residual chemicals, ensuring the purity of the film layer and improving the yield of printed circuit board products.

[0027] Compared with the prior art, the beneficial effects of this application are as follows: This invention fundamentally solves the inherent contradiction between "moderate roughening of the copper surface and densification of the browning film" in existing browning solutions by using a synergistic system of "main oxidant plus nitrobenzenesulfonate auxiliary oxidant" and precisely proportioned functional components such as main etchant, auxiliary etchant, and corrosion inhibitor, thereby significantly improving the interlayer bonding of printed circuit boards.

[0028] Nitrobenzene sulfonate compounds, with their suitable oxidation potential, work synergistically with hydrogen peroxide to form uniform, micro-rough copper surface anchoring points with the sulfuric acid main etchant, while also refining the surface morphology through the auxiliary etchant. This avoids defects in the film layer caused by excessive oxidation or etching, significantly improving the interfacial compatibility between the browning film and the copper foil and prepreg resin. The peel strength of the treated printed circuit board is stable at over 5.7 lb / in, and there is no delamination or board bursting under thermal stress.

[0029] Meanwhile, the addition of complexing agents and electrolytes effectively inhibits the precipitation of metal ions, extends the service life of the browning solution, and reduces waste liquid generation; the targeted selection of buffers, corrosion inhibitors, and surfactants ensures the pH stability of the reaction system, prevents excessive corrosion of the copper surface, and ensures uniform wetting of high-density line gaps, meeting the needs of high-end precision printed circuit board manufacturing.

[0030] The preparation method of this invention optimizes the feeding sequence and temperature conditions to ensure thorough mixing of all components, stable performance, and minimal batch-to-batch variation. The application process is compatible with existing production processes, requiring no equipment modification. The processing temperature of 30–40°C and the processing time of 0.5–2 minutes balance processing efficiency and product qualification rate, ultimately achieving the technical effects of "high bonding strength, high stability, and high adaptability," providing reliable support for the structural stability of high-end electronic devices. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0032] Figure 1 This is a microscope image of the browning film surface in Embodiment 1 of the present invention; Figure 2 This is a microscope image of the browning film surface in Comparative Example 1. The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without a specified manufacturer are all commercially available conventional products.

[0034] This application discloses a browning solution for printed circuit boards, which comprises components of the following concentrations: The main etchant is 40-55 g / L, the auxiliary etchant is 0.4-0.7 g / L, the main oxidant is 10-20 g / L, the auxiliary oxidant is 0.1-0.5 g / L, the buffer is 5-15 g / L, the corrosion inhibitor is 5-10 g / L, the surfactant is 0.4-0.7 g / L, and the balance is deionized water.

[0035] In addition, it also includes complexing agents of 0.2–0.7 g / L, electrolytes of 0.02–0.07 g / L, and cosolvents of 0.1–0.3 g / L.

[0036] The main etchant is sulfuric acid; The auxiliary etching agent is at least one of citric acid, tartaric acid, methanesulfonic acid, and phosphoric acid; The primary oxidant is hydrogen peroxide; The auxiliary oxidant is at least one of sodium p-nitrobenzenesulfonate, sodium o-nitrobenzenesulfonate, sodium m-nitrobenzenesulfonate, sodium 2,4-dinitrobenzenesulfonate, and ammonium nitrobenzenesulfonate. The buffer is at least one of tris(hydroxymethyl)aminomethane, ammonium bicarbonate, monoethanolamine, diethanolamine, and triethanolamine. The corrosion inhibitor is at least one of benzotriazole, methylbenzotriazole, carboxybenzotriazole, and 2-mercaptobenzothiazole; The surfactant is at least one of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, polypropylene glycol, polyethylene glycol, and alkylphenol polyoxyethylene ether. The complexing agent is one or more of the following: disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid, trisodium citrate, and potassium sodium tartrate. The electrolyte is one or a mixture of ammonium chloride, sodium sulfate, and potassium sulfate; The co-solvent is one or a mixture of ethanol, ethylene glycol, propylene glycol, and glycerol.

[0037] Based on the above-mentioned browning solution for printed circuit boards, this application also provides a method for preparing the browning solution for printed circuit boards, comprising the following steps: at 25-30°C, under stirring conditions, a main etchant, an auxiliary etchant, a main oxidant and an auxiliary oxidant are added sequentially to deionized water, stirred until dissolved, and then a buffer, an inhibitor and a surfactant are added, stirred until completely dissolved and mixed evenly, and then the volume is adjusted to obtain the browning agent.

[0038] Furthermore, when the browning solution contains a complexing agent and an electrolyte, the complexing agent, cosolvent, and electrolyte are added together with the buffer, corrosion inhibitor, and surfactant during the steps of adding them.

[0039] Furthermore, based on the aforementioned browning solution for printed circuit boards, this application also provides an application of the aforementioned browning solution for printed circuit boards in the browning treatment of printed circuit boards, wherein the process conditions for the application include: The pretreated inner layer of the printed circuit board is immersed in the browning solution and treated at 30-40°C for 0.5-2 minutes, followed by washing and drying. Specifically, the process steps are as follows: Pre-browning treatment: The inner layer of the printed circuit board is sequentially pickled, washed with water, degreased, washed with water again, and pre-immersed to remove the oxide layer, oil stains and other impurities from the copper foil of the inner layer of the printed circuit board, micro-activate the copper surface, and at the same time avoid the subsequent browning solution from being contaminated by impurities, thus preparing for the subsequent browning process.

[0040] Browning treatment: The pre-impregnated inner layer of the printed circuit board is directly immersed in a browning bath containing the browning solution to form a browning film. The operating temperature is 35°C, and the treatment time is 1 minute.

[0041] Post-browning treatment: After browning is completed, wash with water, blow dry and place in a 90℃ oven to dry.

[0042] Example 1 A browning solution for printed circuit boards comprises components of the following concentrations: The main etchant is sulfuric acid with a concentration of 40 g / L; the auxiliary etchant is methanesulfonic acid with a concentration of 0.4 g / L; the main oxidant is hydrogen peroxide with a concentration of 10 g / L; the auxiliary oxidant is sodium m-nitrobenzenesulfonate with a concentration of 0.1 g / L; the buffer is monoethanolamine with a concentration of 5 g / L; the corrosion inhibitor is benzotriazole with a concentration of 5 g / L; the surfactant is polypropylene glycol with a concentration of 0.4 g / L; the complexing agent is disodium ethylenediaminetetraacetate with a concentration of 0.2 g / L; the electrolyte is ammonium chloride with a concentration of 0.02 g / L; the co-solvent is ethylene glycol with a concentration of 0.1 g / L; and the balance is deionized water.

[0043] Its preparation method is as follows: 1. Place 800 mL of deionized water in a corrosion-resistant reaction vessel, control the ambient temperature at 25–30 °C, turn on the stirring device, and adjust the stirring speed to 200–300 r / min; 2. Add the main etchant (sulfuric acid), auxiliary etchant, main oxidant (hydrogen peroxide), and auxiliary oxidant to the deionized water in sequence, stirring for 5-10 minutes after each addition until completely dissolved; 3. Add buffer, corrosion inhibitor, surfactant, complexing agent, electrolyte, and solubilizer in sequence, and continue stirring for 15-20 minutes to ensure that all components are completely dissolved and mixed evenly; 4. Add deionized water to bring the volume to 1L, stir for 5 minutes, and let stand for later use to obtain the target browning solution.

[0044] The browning solution obtained by the above preparation method is used for browning treatment of printed circuit boards. The specific browning treatment process steps are as follows: 1. Pretreatment before browning: The inner layer of the printed circuit board is sequentially subjected to pickling (5% sulfuric acid solution, room temperature treatment for 30 seconds), water washing (rinsing twice with deionized water, 30 seconds each time), degreasing (0.8% sodium hydroxide solution, treatment at 40℃ for 1 minute), water washing (rinsing twice with deionized water, 30 seconds each time), and pre-immersion (mixed solution of 2% benzotriazole and 10% ethylene glycol, room temperature treatment for 30 seconds). 2. Browning treatment: Immerse the pre-impregnated inner layer of the printed circuit board into the browning solution prepared above, control the browning temperature at 35°C, and the treatment time at 1 minute. Use a vertical immersion method and maintain a stirring speed of 50 r / min during the process. 3. Post-browning treatment: Remove the inner layer of the printed circuit board, rinse it three times with deionized water (30 seconds each time), blow the surface moisture with compressed air, and then dry it in a 90℃ oven for 10 minutes to complete the browning treatment.

[0045] Example 2 The difference between this embodiment and Example 1 is that the components and concentrations of the browning agent are adjusted; the preparation method and application process are the same as in Example 1.

[0046] A browning solution for printed circuit boards comprises components of the following concentrations: The main etchant was sulfuric acid with a concentration of 45 g / L; the auxiliary etchant was tartaric acid with a concentration of 0.5 g / L; the main oxidant was hydrogen peroxide with a concentration of 13 g / L; the auxiliary oxidant was sodium o-nitrobenzenesulfonate with a concentration of 0.2 g / L; the buffer was ammonium bicarbonate with a concentration of 8 g / L; the corrosion inhibitor was methylbenzotriazole with a concentration of 7 g / L; the surfactant was fatty alcohol polyoxyethylene ether with a concentration of 0.5 g / L; the complexing agent was disodium ethylenediaminetetraacetate with a concentration of 0.4 g / L; the electrolyte was ammonium chloride with a concentration of 0.04 g / L; the co-solvent was ethylene glycol with a concentration of 0.15 g / L; and the balance was deionized water.

[0047] Example 3 The difference between this embodiment and Example 1 is that the components and concentrations of the browning agent are adjusted; the preparation method and application process are the same as in Example 1.

[0048] A browning solution for printed circuit boards comprises components of the following concentrations: The main etchant was sulfuric acid with a concentration of 50 g / L; the auxiliary etchant was citric acid with a concentration of 0.6 g / L; the main oxidant was hydrogen peroxide with a concentration of 16 g / L; the auxiliary oxidant was sodium p-nitrobenzenesulfonate with a concentration of 0.3 g / L; the buffer was tris(hydroxymethyl)aminomethane with a concentration of 10 g / L; the corrosion inhibitor was carboxybenzotriazole with a concentration of 8 g / L; the surfactant was polyethylene glycol with a concentration of 0.6 g / L; the complexing agent was disodium ethylenediaminetetraacetate with a concentration of 0.5 g / L; the electrolyte was ammonium chloride with a concentration of 0.05 g / L; the co-solvent was ethylene glycol with a concentration of 0.2 g / L; and the balance was deionized water.

[0049] Example 4 The difference between this embodiment and Example 1 is that the components and concentrations of the browning agent are adjusted; the preparation method and application process are the same as in Example 1.

[0050] A browning solution for printed circuit boards comprises components of the following concentrations: The main etchant was sulfuric acid with a concentration of 53 g / L; the auxiliary etchant was phosphoric acid with a concentration of 0.65 g / L; the main oxidant was hydrogen peroxide with a concentration of 18 g / L; the auxiliary oxidant was sodium 2,4-dinitrobenzenesulfonate with a concentration of 0.4 g / L; the buffer was diethanolamine with a concentration of 13 g / L; the corrosion inhibitor was 2-mercaptobenzothiazole with a concentration of 9 g / L; the surfactant was polyvinylpyrrolidone with a concentration of 0.65 g / L; the complexing agent was disodium ethylenediaminetetraacetate with a concentration of 0.6 g / L; the electrolyte was ammonium chloride with a concentration of 0.06 g / L; the co-solvent was ethylene glycol with a concentration of 0.25 g / L; and the balance was deionized water.

[0051] Example 5 The difference between this embodiment and Example 1 is that the components and concentrations of the browning agent are adjusted; the preparation method and application process are the same as in Example 1.

[0052] A browning solution for printed circuit boards comprises components of the following concentrations: The main etchant was sulfuric acid at a concentration of 52 g / L; the auxiliary etchant was tartaric acid at a concentration of 0.6 g / L; the main oxidant was hydrogen peroxide at a concentration of 17 g / L; the auxiliary oxidant was sodium m-nitrobenzenesulfonate at a concentration of 0.335 g / L; the buffer was diethanolamine at a concentration of 12 g / L; the corrosion inhibitor was 2-mercaptobenzothiazole at a concentration of 8.5 g / L; the surfactant was polyethylene glycol at a concentration of 0.6 g / L; the complexing agent was disodium ethylenediaminetetraacetate at a concentration of 0.55 g / L; the electrolyte was potassium sulfate at a concentration of 0.055 g / L; the co-solvent was propylene glycol at a concentration of 0.22 g / L; and the balance was deionized water.

[0053] Example 6 The difference between this embodiment and Example 1 is that the components and concentrations of the browning agent are adjusted; the preparation method and application process are the same as in Example 1.

[0054] A browning solution for printed circuit boards comprises components of the following concentrations: The primary etchant is sulfuric acid at a concentration of 55 g / L; the secondary etchant is a mixture of citric acid and phosphoric acid, with citric acid and phosphoric acid concentrations both at 0.35 g / L; the primary oxidant is hydrogen peroxide at a concentration of 20 g / L; the secondary oxidant is ammonium nitrobenzenesulfonate at a concentration of 0.5 g / L; the buffer is triethanolamine at a concentration of 15 g / L; and the corrosion inhibitor is a mixture of benzotriazole and methylbenzotriazole, with benzotriazole concentration at 5 g / L and methylbenzotriazole concentration at 5 g / L. The concentration of benzotriazole is 5 g / L; the surfactant is alkylphenol polyoxyethylene ether with a concentration of 0.7 g / L; the complexing agent is potassium sodium tartrate with a concentration of 0.7 g / L; the electrolyte is a mixture of sodium sulfate and potassium sulfate, wherein the concentrations of sodium sulfate and potassium sulfate are both 0.035 g / L; the co-solvent is a mixture of ethylene glycol and propylene glycol, wherein the concentrations of ethylene glycol and propylene glycol are both 0.15 g / L; and the balance is deionized water.

[0055] Comparative Example 1 Compared with Example 1, this comparative example is identical in composition except for the absence of the auxiliary etchant. The preparation and application processes are the same as in Example 1.

[0056] It is used to verify the effect of auxiliary etchants on the morphology and adhesion of copper surfaces.

[0057] Comparative Example 2 Compared with Example 1, this comparative example is identical in composition except for the absence of the auxiliary oxidant (nitrobenzene sulfonate). The preparation and application processes are the same as in Example 1.

[0058] Comparative Example 3 Compared with Example 1, this comparative example is identical in composition except for the absence of a surfactant. The preparation and application processes are the same as in Example 1.

[0059] Comparative Example 4 Compared with Example 1, this comparative example differs only in that the mass concentration of the auxiliary etchant (methanesulfonic acid) is 1.0 g / L (exceeding the 0.4-0.7 g / L range specified in this invention), while the other components are the same, and the preparation and application processes are the same as in Example 1.

[0060] It is used to verify the criticality of concentration ranges.

[0061] Comparative Example 5 Compared with Example 1, this comparative example differs only in that the mass concentration of the auxiliary oxidant (sodium m-nitrobenzenesulfonate) is 1.0 g / L (exceeding the 0.1-0.5 g / L range specified in this invention), while the other components are the same, and the preparation and application processes are the same as in Example 1.

[0062] It is used to verify the importance of the concentration balance of oxidizing components.

[0063] Comparative Example 6 Compared with Example 1, this comparative example differs only in that the mass concentration of the surfactant (polypropylene glycol) is 1.2 g / L (exceeding the 0.4-0.7 g / L range specified in this invention), while the other components are identical, and the preparation and application processes are the same as in Example 1.

[0064] It is used to verify the effect of surfactant concentration on adhesion.

[0065] Performance testing: The browning solutions provided in Examples 1-6 and Comparative Examples 1-6 were used to perform browning treatment on the printed circuit boards, resulting in treated printed circuit boards. The browning mold formed on the boards was then tested using the following methods and standards: Browning film appearance: The surface morphology of the browning film on the inner layer of the PCB is observed under a microscope to determine whether the film layer is uniform and dense. The standard is "dense structure and uniform morphology is good, loose structure and uneven morphology is poor, and intermediate is average".

[0066] Browning film adhesion test: A 1-ounce copper-thickness PCB inner layer board (100mm×200mm) that has been browned and dried is hot-pressed with a TG175 polypropylene semi-cured sheet under the conditions of a pressing temperature of 190℃, a pressing pressure of 19kgf / cm², and a pressing time of 60min.

[0067] The interlaminar peel strength of the composite board was determined using a tensile testing machine (test speed 50 mm / min) in accordance with IPC-TM-650 No.2.4.8 standard.

[0068] Meanwhile, in accordance with the IPC-TM-650 No.2.6.8 standard, the laminated composite board was subjected to 5 thermal cycle impact tests (-40℃ for 30 min, 125℃ for 30 min, with rapid switching) to observe whether delamination or board bursting occurred, and to comprehensively evaluate the bonding stability.

[0069] The test results are as follows: Based on the test results, combined with the attached Figure 1 Microscopic images of the browning film surface in Example 1 show that Examples 1-6 all exhibit excellent performance in terms of good browning film appearance, peel strength greater than 5.0 lb / in, and no delamination or delamination due to thermal stress. Specifically, the oxidation-film formation rate is precisely matched between nitrobenzene sulfonate-based auxiliary oxidant and hydrogen peroxide, sulfuric acid and organic acid-based etchant form a uniform micro-rough surface, buffer and corrosion inhibitor stabilize the reaction system, complexing agent and electrolyte improve the stability of browning solution, and surfactant ensures film density; thus verifying the effectiveness of the technical solution.

[0070] Comparative Examples 1-3, lacking key components such as auxiliary etchant, auxiliary oxidant, and surfactant, yielded the results shown in the attached figures. Figure 2 The micrograph of the browning film surface shown in Comparative Example 1 shows that the browning film has a loose structure, a peel strength of less than 3.0 lb / in, and exhibits cracking or slight cracking. This confirms that the above components are the core components for refining the copper surface morphology, balancing the oxidation rate, and ensuring the film density. The system composed of these three components and other components is indispensable and directly determines the level of adhesion.

[0071] Comparative Examples 4-6 showed that the concentrations of the auxiliary etchant, auxiliary oxidant, and surfactant exceeded the mass concentration range specified in this invention, which disrupted the synergistic balance of the components in the browning solution. As a result, the peel strength was less than 5.0 lb / in and the adhesion was weakened. This demonstrates that the concentration range specified in this invention is a necessary condition for achieving optimal performance.

[0072] In summary, this invention achieves synergistic effects among its components by optimizing the composition of the browning solution, precisely controlling its concentration range, and optimizing the application process, thus ensuring high adhesion of the printed circuit board. This technology effectively solves the problem that existing browning solutions cannot meet the high adhesion requirements of high-end printed circuit board products, demonstrating clear technological innovation and industrial application value.

[0073] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this application, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0074] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A browning solution for printed circuit boards, characterized in that, It includes the following components: main etchant, auxiliary etchant, main oxidant, auxiliary oxidant, buffer, corrosion inhibitor, surfactant, and deionized water; The auxiliary oxidant is a nitrobenzene sulfonate compound.

2. The browning solution for printed circuit boards according to claim 1, characterized in that, The concentrations of the browning solution components are as follows: main etchant 40-55 g / L, auxiliary etchant 0.4-0.7 g / L, main oxidant 10-20 g / L, auxiliary oxidant 0.1-0.5 g / L, buffer 5-15 g / L, corrosion inhibitor 5-10 g / L, surfactant 0.4-0.7 g / L, and the balance is deionized water.

3. The browning solution for printed circuit boards according to claim 2, characterized in that, It also includes complexing agents (0.2–0.7 g / L), electrolytes (0.02–0.07 g / L), and cosolvents (0.1–0.3 g / L).

4. The browning solution for printed circuit boards according to any one of claims 1-3, characterized in that, The main etchant is sulfuric acid; the auxiliary etchant is at least one of citric acid, tartaric acid, methanesulfonic acid, and phosphoric acid.

5. The browning solution for printed circuit boards according to any one of claims 1-3, characterized in that, The primary oxidant is hydrogen peroxide; the secondary oxidant is at least one of sodium p-nitrobenzenesulfonate, sodium o-nitrobenzenesulfonate, sodium m-nitrobenzenesulfonate, sodium 2,4-dinitrobenzenesulfonate, and ammonium nitrobenzenesulfonate.

6. The browning solution for printed circuit boards according to any one of claims 1-3, characterized in that, The buffer is at least one of tris(hydroxymethyl)aminomethane, ammonium bicarbonate, monoethanolamine, diethanolamine, and triethanolamine. The corrosion inhibitor is at least one of benzotriazole, methylbenzotriazole, carboxybenzotriazole, and 2-mercaptobenzothiazole; The surfactant is at least one of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, polypropylene glycol, polyethylene glycol, and alkylphenol polyoxyethylene ether.

7. A method for preparing a browning solution for printed circuit boards, used to prepare the browning solution for printed circuit boards according to any one of claims 1-6, characterized in that, Includes the following steps: At 25–30°C, under stirring conditions, the main etchant, auxiliary etchant, main oxidant and auxiliary oxidant are added sequentially to deionized water. After stirring until dissolved, buffer, corrosion inhibitor and surfactant are added. After stirring until completely dissolved and mixed evenly, the volume is adjusted to obtain the browning agent.

8. The preparation method according to claim 7, characterized in that, When the browning solution contains a complexing agent, an electrolyte, and a co-solvent, the complexing agent, co-solvent, and electrolyte are added together with the buffer, corrosion inhibitor, and surfactant in the step of adding them.

9. The application of the browning solution for printed circuit boards as described in any one of claims 1-6 in the browning treatment of printed circuit boards.

10. The application according to claim 9, characterized in that, The process conditions for the application include: immersing the pretreated inner layer of the printed circuit board into the browning solution, treating it at 30-40°C for 0.5-2 minutes, and then washing and drying it.

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