Printed circuit board and its copper plating process

Abstract

This invention discloses a printed circuit board and its copper plating process. The copper plating process of the printed circuit board includes the following steps: providing a substrate: providing a printed circuit board substrate, the substrate defining a region to be protected and a region to be copper plating; applying protective ink: applying a protective ink made of a mildly peelable protective composite material to the region to be protected; curing: curing the applied protective ink to form a protective layer on the region to be protected; copper plating: copper plating the substrate with the protective layer applied to form a copper layer on the region to be copper plating; and peeling: after the copper plating is completed, using a peeling liquid capable of selectively dissolving the structural resin in the composite material, peeling off the protective layer. This invention has the advantages of strong protection and mild peelability.

Description

Technical Field

[0001] This invention relates to the field of printed circuit technology, and in particular to a printed circuit board and its copper plating process. Background Technology

[0002] In the manufacturing process of printed circuit boards (PCBs), chemical copper plating or via metallization (PTH) is a key step in achieving electrical interconnection between multilayer boards. This process deposits a conductive copper layer on the insulating via walls through a series of chemical reactions, laying the foundation for subsequent electroplating thickening. During chemical copper plating and its complex pretreatment steps, temporary protective materials must be used to cover and shield these non-target areas to prevent unnecessary metal deposition or chemical corrosion of the already formed fine copper traces on the substrate surface.

[0003] Currently, the commonly used technical solution in the industry is to apply a protective ink or dry film to the copper traces that need protection. These protective materials need to maintain their structural integrity and adhesion to the substrate throughout the entire copper plating pretreatment process (e.g., sequential steps such as swelling, permanganate treatment, neutralization, degreasing, micro-etching, activation, and acceleration). However, the aforementioned pretreatment process includes various strong acids, strong alkalis, and strong oxidizing chemicals. Traditional protective inks often exhibit insufficient tolerance to these harsh chemical environments, such as swelling, cracking, edge peeling, or even localized dissolution. This not only leads to protection failure and corrosion of the underlying copper traces but may also contaminate the expensive copper plating solution, affecting the stability of the entire production line.

[0004] Therefore, in the field of copper plating process for printed circuit boards, developing a more reliable and easily removable temporary protection process has become an urgent need for the industry. Summary of the Invention

[0005] The main objective of this invention is to propose a copper plating process for printed circuit boards, aiming to solve the technical problem that the temporary protective ink used in the existing copper plating process has insufficient protective ability when facing harsh chemical treatment processes, and that the subsequent stripping process is prone to damaging the substrate and plating layer.

[0006] To achieve the above objectives, the copper plating process for printed circuit boards proposed in this invention includes the following steps:

[0007] Substrate provided: A printed circuit board substrate is provided, the substrate defining an area to be protected and an area to be copper plating;

[0008] Applying protective ink: A protective ink made of a mildly peelable protective composite material is applied to the area to be protected, wherein the composite material comprises:

[0009] Structural resins based on polyvinyl acetal resins;

[0010] Adhesive resins containing phenolic resins and epoxy resins;

[0011] High-performance organic polymers whose main chain contains aromatic rings and / or heterocycles;

[0012] Inorganic fillers whose surfaces are modified by at least one functional group from the group consisting of aniline group, nitrogen-containing functional groups on the main chain or branches, double-bonded functional groups and epoxy groups;

[0013] Curing: The applied protective ink is cured to form a protective layer on the area to be protected;

[0014] Copper plating: A copper plating process is performed on the substrate to which the protective layer has been applied, to form a copper layer on the area to be copper-plated; and

[0015] Stripping: After the copper plating is completed, the protective layer is stripped away using a stripping solution that can selectively dissolve the structural resin in the composite material. The stripping solution contains at least one of the following organic solvents: alcohol solvents, ketone solvents, ester solvents, and halogenated hydrocarbon solvents.

[0016] In one embodiment, after the copper plating step and before the stripping step, the copper plating process further includes:

[0017] Drilling: Drilling is performed on the initial substrate to form at least one hole.

[0018] In one embodiment, after the curing step and before the copper plating step, the copper plating process further includes:

[0019] Drilling: Drilling the initial substrate to form at least one hole;

[0020] The copper plating step further includes: copper plating the inner wall of the hole to form a copper layer on the inner wall of the hole.

[0021] In one embodiment, the protective ink is in liquid or gel state; wherein,

[0022] When the protective ink is applied by at least one of screen printing, stencil printing, spraying, stencil coating, slot coating, and blade coating, the viscosity of the protective ink is between 8 mPa·s and 20000 mPa·s.

[0023] When the protective ink is applied by dispensing, the viscosity of the protective ink is between 20,000 mPa·s and 150,000 mPa·s.

[0024] In one embodiment, the curing step includes:

[0025] At least one drying stage for removing the solvent; and

[0026] A curing stage performed at a temperature higher than that of the drying stage.

[0027] In one embodiment, the drying stage includes a first stage of drying and a second stage of drying performed sequentially, wherein,

[0028] The drying conditions for the first stage are: a temperature of 40°C to 60°C for 3 to 10 minutes;

[0029] The drying conditions for the second stage are: a temperature of 80°C to 100°C for 3 to 10 minutes;

[0030] The curing stage is performed at a temperature of 130°C to 150°C for 30 to 60 minutes.

[0031] In one embodiment, the stripping fluid further comprises water, wherein the weight ratio of the organic solvent to water is between 100:0 and 5:95.

[0032] In one embodiment, the organic solvent is ethanol, and the weight ratio of ethanol to water is between 100:0 and 30:70.

[0033] In one embodiment, the stripping step includes: spraying and / or soaking at a temperature of 20°C to 80°C, selectively combined with ultrasonic oscillation.

[0034] In one embodiment, during the copper plating step, a copper layer is formed both above the protective layer of the area to be protected and on the area to be plated with copper.

[0035] After the copper plating step and before the stripping step, the process further includes:

[0036] Grinding and thinning: The copper layer in the area to be protected is ground to remove the copper layer deposited on top of the protective layer and expose the protective layer.

[0037] In one embodiment, the content of each component in the protective ink is as follows:

[0038] The weight percentage of the structural resin is between 40% and 90%.

[0039] The weight percentage of the adhesive resin is between 5% and 40%.

[0040] The weight percentage of the high-performance organic polymer is between 5% and 50%; and

[0041] The inorganic filler has a weight percentage between 0.5% and 40%.

[0042] The present invention also proposes a printed circuit board, which is prepared using the copper plating process described in any of the above claims.

[0043] The copper plating process for printed circuit boards described in this application utilizes a protective ink. The protective layer formed after curing benefits from the unique composition of the composite material—namely, a high-performance organic polymer containing aromatic rings and / or heterocyclic rings in its main chain and inorganic fillers with specific functional groups modified on the surface. These two components together construct a robust, chemically resistant framework, resulting in a protective layer with excellent chemical inertness, mechanical strength, and structural integrity. Furthermore, during subsequent copper plating processes, especially pretreatment involving a series of strong acid, strong alkali, and strong oxidizing chemical solutions such as swelling, desmearing, neutralization, and activation, this protective layer remains stable, preventing swelling, cracking, or peeling. This provides a perfect, defect-free shield for the area to be protected below and avoids contamination of the chemical bath due to the protective layer dissolving, ensuring the stability and high quality of the entire copper plating process.

[0044] On the other hand, since the core components of the protective ink also include a "structural resin based on polyvinyl acetal resin" as the film-forming matrix, this process can employ a novel stripping strategy in the stripping step. The stripping solution used in this strategy (containing alcohol and / or ketone solvents) does not rely on strong corrosiveness, but rather selectively dissolves the structural resin matrix in the protective layer, causing it to lose its binding force on other insoluble components. This enables rapid and thorough disintegration and removal of the entire protective layer, thereby ensuring that the newly formed, unstable copper plating layer and the sensitive substrate material are not chemically damaged during the stripping process.

[0045] In summary, the process of this invention, by organically combining a specific material with a specific process flow, successfully solves the long-standing technical contradiction between "strong protection" and "non-destructive removal," greatly improving the yield, circuit accuracy, and long-term reliability of the copper plating process for printed circuit boards. Attached Figure Description

[0046] 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.

[0047] Figure 1 This is a schematic flowchart of an embodiment of the copper plating process for printed circuit boards according to the present invention.

[0048] 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

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0051] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0052] This invention proposes a copper plating process for printed circuit boards.

[0053] In embodiments of the present invention, such as Figure 1 As shown, the copper plating process for this printed circuit board includes the following steps:

[0054] S10. Provide a substrate: Provide a printed circuit board substrate, wherein the substrate defines an area to be protected and an area to be copper deposited.

[0055] Here, the printed circuit board substrate can be any board material in the art that requires copper plating, such as rigid epoxy resin glass cloth copper clad board (FR-4), flexible polyimide (PI) substrate, or ceramic substrate, etc., and this application does not make any special limitation on it.

[0056] The area to be protected can be a pre-formed copper circuit pattern, pad, or other functional metal area on the substrate that needs to be protected from subsequent copper plating processes. The area to be copper plating refers to a pre-defined exposed substrate area that needs to be processed by subsequent chemical copper plating or electroplating processes to form new circuit patterns or thicken the existing thin copper layer. In different embodiments of the present invention, the area to be protected can be disposed on only one surface of the substrate, or simultaneously on two opposite surfaces of the substrate; similarly, the area to be copper plating can exist only on one surface of the substrate or simultaneously on two surfaces, and this application does not impose any particular limitation on this.

[0057] S20. Applying protective ink: Applying a protective ink made of a gently peelable protective composite material to the area to be protected, wherein the composite material comprises:

[0058] Structural resins based on polyvinyl acetal resins;

[0059] Adhesive resins containing phenolic resins and epoxy resins;

[0060] High-performance organic polymers whose main chain contains aromatic rings and / or heterocycles;

[0061] Inorganic fillers whose surfaces are modified by at least one functional group from the group consisting of aniline groups, nitrogen-containing functional groups on the main chain or branches, double-bonded functional groups and epoxy groups.

[0062] Specifically, the structural resin based on polyvinyl acetal resins mainly serves as the film-forming matrix, and its molecular characteristics lay the foundation for the entire protective layer to be eventually peeled off by a mild solvent. The adhesive resin, which includes phenolic resin and epoxy resin, provides strong adhesion and cohesive strength to the protective layer through cross-linking reaction after curing. The high-performance organic polymer with aromatic rings and / or heterocyclic rings in the main chain, together with the inorganic filler modified with specific functional groups on the surface, constitutes the chemical-resistant additive, providing the protective layer with a robust protective framework against strong acids (sulfuric acid, hydrochloric acid, nitric acid, hydrogen peroxide, etc.), strong alkalis (swelling, permanganate, sodium hydroxide, potassium hydroxide and sodium ethylenediaminetetraacetate, etc.), high temperature and high pressure.

[0063] In some embodiments, the protective ink is applied to the area to be protected by at least one of screen printing, stencil printing, spraying, stencil coating, slot coating, doctor blade coating, and dispensing.

[0064] For example, the choice of application method can be determined based on the specific physical state (e.g., viscosity) of the protective ink. When the protective ink is in a liquid state with low viscosity (e.g., any value between 8 mPa·s and 20,000 mPa·s), methods that can achieve large-area, uniform coating, such as screen printing, stencil printing, spraying, dot coating, slotted coating, and doctor blade coating, are more suitable. When the protective ink is in a colloidal state with high viscosity (e.g., any value between 20,000 mPa·s and 150,000 mPa·s), dispensing is more suitable to achieve precise and controllable application to specific or irregular areas.

[0065] S30. Curing: Curing the applied protective ink to form a protective layer on the area to be protected.

[0066] Specifically, this curing step can be completed by heating, aiming to transform the liquid ink into a solid film layer with final protective properties. During this process, the solvent in the ink is evaporated and removed, while the thermosetting components in the system (such as phenolic resin and epoxy resin) undergo a cross-linking reaction, thereby giving the protective layer the required mechanical strength, chemical resistance, and strong adhesion to the substrate.

[0067] In some embodiments, to more precisely control the film formation process and avoid defects, the curing step can be designed as a multi-stage procedure. Specifically, the curing step may include at least one drying stage performed at a relatively low temperature, primarily for solvent removal, followed by a final curing stage performed at a temperature higher than the drying stage, primarily for promoting resin crosslinking.

[0068] It is understandable that this staged heating process has clear technical advantages. First, through one or more low-temperature drying stages, the solvent in the ink coating can evaporate at a gradual and controlled rate, effectively avoiding defects such as bubbles and pinholes caused by the solvent boiling inside the film layer due to excessively rapid heating. After the solvent is almost completely removed, raising the temperature to a higher curing stage ensures that the crosslinking reaction of the thermosetting resin proceeds fully and uniformly without solvent interference, thereby obtaining a dense, high-performance final protective layer.

[0069] As a more specific and preferred implementation of the aforementioned staged heating process, the entire heating process can be broken down into three stages executed sequentially:

[0070] First, the first stage of drying is performed. In this stage, the substrate coated with protective ink is kept at a relatively mild temperature of 40°C to 60°C for 3 to 10 minutes. The main purpose of this low-temperature stage is to evaporate and remove most of the low-boiling-point solvents in the ink in a gentle manner, and to allow the ink coating to flow sufficiently, avoiding the formation of bubbles or surface defects due to excessively rapid heating.

[0071] Next, the second stage of drying is carried out. In this stage, the temperature is raised to 80°C to 100°C and maintained for 3 to 10 minutes. The higher temperature helps to further remove residual high-boiling-point solvents from the coating, ensuring that solvent interference is minimized before final curing, thus laying the foundation for the formation of a dense cured network.

[0072] Finally, the final curing stage is carried out. In this stage, the temperature is significantly increased to 130°C to 150°C and maintained for 30 to 60 minutes. This high-temperature stage provides the necessary activation energy for the crosslinking reaction of the thermosetting resins (such as phenolic resins and epoxy resins) in the system, allowing it to proceed fully and rapidly, thereby forming a stable three-dimensional network structure and endowing the final protective layer with excellent mechanical strength, adhesion, and chemical resistance.

[0073] Specifically, precisely defining the temperature and time ranges for each stage of the heating process is crucial to ensuring the quality of the final protective layer.

[0074] In the first stage of drying, the temperature is set between 40°C and 60°C for precise control of the solvent evaporation rate. If the temperature is below 40°C, the evaporation rate of most commonly used organic solvents will be too slow, resulting in low production efficiency; while if the temperature is above 60°C, it may cause the ink coating surface to form a skin too quickly, encapsulating the internal solvent. When the internal solvent finally vaporizes, it will break through the skin, resulting in fatal defects such as bubbles or pinholes on the film layer. Similarly, the duration of 3 to 10 minutes is designed to ensure sufficient time for most low-boiling-point solvents to escape slowly. Too short a time will result in incomplete solvent removal, while too long a time will unnecessarily increase the process time.

[0075] In the second stage of drying, the temperature is raised to 80°C to 100°C. The main purpose is to provide sufficient heat energy to drive the residual, high-boiling-point solvent molecules in the system to detach from the already viscous film. If the temperature is below 80°C, it may not be able to effectively remove the high-boiling-point solvents, and these residual solvents will cause defects in the final curing stage; while the temperature is above 100°C, it may begin to reach the initial reaction temperature of some thermosetting resins, posing a risk of pre-curing. The duration of 3 to 10 minutes represents a balance between ensuring that the solvent is completely removed and avoiding the film being exposed to high temperatures for an extended period.

[0076] In the final curing stage, the temperature is significantly increased to 130°C to 150°C. This is because the cross-linking reaction between the phenolic resin and epoxy resin, which act as the binder in the system, requires this temperature range to be effectively activated and proceed rapidly and fully. If the temperature is below 130°C, the cross-linking reaction will be incomplete, resulting in insufficient mechanical strength, poor adhesion, and poor chemical resistance of the cured protective layer. Conversely, if the temperature is above 150°C, it may cause thermal degradation of the polymer materials (especially the structural resin), leading to a decline in performance. A duration of 30 to 60 minutes ensures that the cross-linking reaction proceeds to completion, forming a dense and stable three-dimensional network structure. Too short a time will result in incomplete curing, while too long a time may lead to over-curing and brittleness of the material.

[0077] It is worth noting that the selection of temperature and time for the first drying stage, second drying stage, and curing stage needs to be adapted to the actual situation and is not limited to a specific range of values. Those skilled in the art should understand that the above parameters can be adjusted within the disclosed range according to specific circumstances to achieve the best process effect.

[0078] For example, when the protective ink uses methyl ethyl ketone (MEK), which has a low boiling point, as the main solvent, to prevent the solvent from boiling too quickly and generating bubbles during the drying stage, the temperature of the first drying stage can preferably be set at a lower level of 40°C to 50°C, and the temperature of the second drying stage can be correspondingly selected at 80°C to 90°C. As another example, when a thicker protective film needs to be prepared, to ensure complete evaporation of the internal solvent, the time for both the first and second drying stages can be extended to near the upper limit of 8 to 10 minutes. Similarly, in the final curing stage, if a highly reactive curing system is used, curing at 150°C for 30 minutes can be chosen to pursue efficiency; conversely, if lower internal stress is desired, a lower temperature of 130°C can be chosen, and the curing time extended to 60 minutes.

[0079] S40, Copper plating: The substrate to which the protective layer has been applied is subjected to copper plating to form a copper layer on the area to be copper-plated.

[0080] The copper plating process described here is a general process step, and it can be any method of depositing a copper layer on a printed circuit board. For example, this process may include a series of chemical pretreatment steps followed by chemical copper plating or electrolytic copper plating. The purpose of the chemical pretreatment steps is to clean and activate the surface of the area to be copper-plated, and may include porosimetry, desmearing, neutralization, and activation. Throughout the copper plating process, the protective layer formed on the area to be protected maintains its structural integrity and chemical inertness, effectively shielding it from chemical solutions and preventing damage to the protected area.

[0081] In some embodiments, in order to obtain a high-quality copper layer on the area to be copper deposited, the copper plating process may specifically include a series of sequentially performed chemical pretreatment and chemical copper deposit and electroplating steps.

[0082] Specifically, firstly, the substrate undergoes a swelling treatment to moderately swell the resin material (such as epoxy resin) to facilitate the penetration of subsequent chemical solutions and the removal of adhesive residue. Next, a residue removal treatment is performed using a strong oxidant to remove microscopic contaminants from the resin surface and to microscopically roughen it, thereby enhancing the physical adhesion of the subsequent copper layer. Then, a neutralization treatment is performed to remove any remaining strong oxidant from the substrate surface. Following this, an ionic palladium activation treatment is conducted, causing a layer of catalytically active palladium metal nuclei to adsorb onto the insulating surface of the area to be copper-plated, providing catalytic centers for chemical copper plating. Finally, chemical copper plating and electroplating are performed, depositing a uniform and continuous conductive copper layer on the activated insulating surface through a self-catalytic reaction, thus completing the construction of a new circuit pattern on the predetermined area to be copper-plated. Throughout all the above steps, the protective layer formed on the area to be protected maintains its integrity, effectively protecting the existing circuit pattern underneath.

[0083] S50. Stripping: After the copper plating is completed, the protective layer is stripped away using a stripping solution that can selectively dissolve the structural resin in the composite material. The stripping solution contains at least one of the following organic solvents: alcohol solvents, ketone solvents, ester solvents, and halogenated hydrocarbon solvents.

[0084] Specifically, the stripping solution does not destroy the entire protective layer through strong corrosion, but rather utilizes its dissolving ability for specific components. Specifically, the stripping solution selectively penetrates and dissolves or swells the structural resin (i.e., polyvinyl acetal resin) that serves as the continuous phase matrix of the protective layer. Once this matrix is ​​destroyed, other insoluble components that were originally fixed by it (such as cross-linked adhesive resins, high-performance organic polymers, and inorganic fillers) lose their structural support and detach from the substrate surface, thereby achieving rapid and thorough stripping of the entire protective layer. To achieve this goal, the stripping solution may contain one or more specific organic solvents, such as alcohol solvents, ketone solvents, ester solvents, and halogenated hydrocarbon solvents. These solvents have excellent dissolving ability for polyvinyl acetal resins, but are relatively mild for the cured epoxy / phenolic network, as well as for metallic copper and the substrate itself, thus ensuring the efficiency and non-destructive nature of the stripping process.

[0085] Regarding the specific chemical composition of the stripping solution, in some embodiments, the stripping solution can be a pure solution or a mixed solution of two or more organic solvents such as alcohols, ethyl acetate, methyl ethyl ketone, cyclohexanone, dichloromethane, and chloroform. Furthermore, to adjust the stripping rate, reduce costs, or improve operational safety, one or more of the aforementioned organic solvents can be mixed with water.

[0086] In some embodiments employing a mixture of water and organic solvent, the weight ratio of organic solvent to water in the stripping solution can be any ratio between 100:0 and 5:95. For example, as specific, non-limiting examples, the weight ratio of organic solvent to water can be 100:0 (i.e., pure organic solvent), 95:5, 70:30, 50:50, 10:90, or 5:95. It is understood that by adjusting the proportion of water in the stripping solution, the swelling and dissolution rate of the polyvinyl acetal resin matrix in the protective layer can be effectively controlled, thereby achieving precise control of the stripping process.

[0087] In some embodiments, when the organic solvent is ethanol, the weight ratio of ethanol to water in the stripping solution is between 100:0 and 30:70. For example, as a specific, non-limiting example, the weight ratio of ethanol to water can be 100:0 (i.e., pure ethanol), 95:5, 70:30, 50:50, or 30:70.

[0088] It is understandable that ethanol is an excellent solvent for polyvinyl butyral (PVB) resin in terms of performance and selectivity. It can efficiently and selectively dissolve the structural resin used as the protective film matrix, while having virtually no dissolving or corrosive effect on cured epoxy / phenolic crosslinked networks, high-performance organic polymers, inorganic fillers, and copper and epoxy resins used as substrates. This high selectivity ensures that the peeling process only damages the structure of the protective film without harming the delicate circuitry or sensitive substrate it protects. This is the key to achieving the core objective of this invention: "gentle and non-destructive peeling."

[0089] Secondly, in terms of environmental, health, and safety (EHS), ethanol has significant advantages over other technically feasible organic solvents (such as halogenated hydrocarbon solvents like dichloromethane and chloroform). Ethanol is far less toxic than halogenated hydrocarbon solvents, is more operator-friendly, and is more readily biodegradable, resulting in a smaller environmental footprint. Furthermore, mixing it with water effectively reduces its overall volatility and flammability, enhancing the safety of the entire process.

[0090] Furthermore, from an economic perspective, ethanol and water are bulk chemical raw materials, and their acquisition costs are far lower than those of other special organic solvents. This gives the process of the present invention a significant cost advantage when realizing large-scale industrial production.

[0091] Finally, regarding process controllability, the solubility and peeling rate of the stripping solution can be easily fine-tuned by adjusting the ratio of ethanol to water. For example, for protective films with a high degree of curing or a thicker film layer, a high-concentration ethanol solution can be used to accelerate the peeling speed; while for more sensitive substrates, the proportion of water can be increased to obtain a smoother and more controllable peeling process. This broad and easily adjustable process window allows the present invention to flexibly adapt to different production needs.

[0092] After determining the chemical composition of the stripping solution, in some embodiments, the specific physical operating conditions of the stripping step may include the selection of temperature, operating method, and auxiliary means.

[0093] Specifically, the peeling operation can be performed within a temperature range of 20°C to 80°C (in actual operation, any temperature within this range can be selected as needed, such as 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.). Peeling at lower temperatures (such as near room temperature, close to 20°C) offers advantages such as low energy consumption and safe operation; while appropriately increasing the temperature of the peeling solution (e.g., heating to 80°C) can significantly accelerate the swelling and dissolution rate of the structural resin matrix, thereby greatly shortening the peeling time and improving production efficiency.

[0094] In terms of operation, it can be carried out by spraying and / or immersion. Spraying can use the flow and impact force of the stripping liquid to help remove the protective layer that has been partially dissolved or swollen; while immersion can ensure that the protective layer has a longer contact time with the stripping liquid, which is more effective for thicker or more cured film layers.

[0095] Furthermore, to further enhance the stripping effect, especially for areas with fine circuit patterns, the stripping step can be selectively combined with ultrasonic oscillation. The cavitation effect generated by ultrasound in the stripping solution can produce powerful microscopic agitation, thereby physically assisting in the destruction of the swollen film structure and accelerating solvent penetration and exchange, achieving a faster and cleaner stripping effect.

[0096] In some embodiments of the composite material, the structural resin is a polyvinyl acetal-based structural resin. This structural resin primarily functions as a film-forming substance in the composite material, creating a continuous polymer matrix. It not only provides a carrier for other functional components but, more importantly, lays the technological foundation for the gentle peeling of the entire composite material. This is because polyvinyl acetal resins (especially polyvinyl butyral resins) exhibit good solubility or swelling properties in specific mild organic solvents such as alcohols. When the protective film needs to be removed, the solvent can selectively disrupt or dissolve the structural resin matrix, which serves as the continuous phase, thereby causing the entire film structure to disintegrate and enabling easy peeling.

[0097] Alternatively, the structural resin may be present in the composite material at a weight percentage of 40% to 90%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0098] Specifically, when the content of structural resin is not less than 40%, the amount of structural resin is sufficient to form a complete and continuous polymer network, thereby effectively encapsulating and bonding other functional components (adhesive resin, chemical-resistant additives) together to form a uniform and defect-free protective film. If its content is less than 40%, it may lead to poor film-forming properties, defects in the film layer, or the inability to form a continuous matrix, making it impossible for the matrix to be effectively dissolved during peeling.

[0099] When the content of structural resin is no higher than 90%, sufficient space can be left for other protective components, avoiding dilution of the overall chemical resistance, heat resistance, and mechanical strength of the material due to its excessive proportion, thus ensuring the material's protective capability in harsh environments. Conversely, if it exceeds 90%, the overall protective performance (chemical resistance, heat resistance, and mechanical strength) of the material will be greatly reduced, making it difficult to meet the requirements of practical applications.

[0100] Furthermore, the bonding resin ensures that the composite material adheres firmly to the surface of various substrates such as copper foil, epoxy resin, or glass after curing. Simultaneously, it increases the cross-linking density of the composite material, enhancing its pressure resistance, heat resistance, and chemical resistance, preventing cracking and detachment during harsh processes such as high-temperature and high-pressure treatments. This is because the bonding resin undergoes a cross-linking reaction during curing, forming stable chemical bonds to enhance adhesion to the substrate, and also improving the cohesive strength, hardness, and heat resistance of the entire composite material.

[0101] Specifically, the bonding resin includes phenolic resin and epoxy resin. The epoxy and phenolic resins can be pure substances, mixtures, and compounds of the following materials:

[0102] The epoxy resin material used in this application has an epoxy molecular weight of 2500 g / mol to 6000 g / mol.

[0103] (1) Glycidylamine epoxy resin

[0104] Structural formula:

[0105] The epoxy equivalent is between 93 and 150 g / eq, the hydrolytic chlorine content should be less than 200 ppm, and the viscosity at 25°C should be between 0.5 and 5 Poise.

[0106] (2) Multifunctional o-cresol formaldehyde glycidyl ether type epoxy resin

[0107] Structural formula:

[0108] The epoxy equivalent is between 195 and 230 g / eq, the hydrolytic chlorine at 120℃ is between 470 and 1000 g / eq, the ICI viscosity at 150℃ is between 0.9 and 60 Poise, and the softening point is between 45 and 96℃.

[0109] (3) Phenolic-biphenyl epoxy resin

[0110] Structural formula:

[0111] The epoxy equivalent is between 261 and 280 g / eq, the hydrolytic chlorine content should be less than 100 ppm, the viscosity at 25°C is between 0.1 and 4.5 Poise, and the softening point is between 45 and 75°C. Adding it to PVB and copolymerizing it with its hydroxyl groups can effectively improve the glass strength, Tg, and impact resistance of copper.

[0112] (4) Bisphenol F solid epoxy resin

[0113] Structural formula:

[0114] The epoxy equivalent is between 450 and 1000 g / eq, the hydrolytic chlorine should be less than 300 ppm, the viscosity at 25℃ is less than 1000 poise, and the softening point is between 50 and 88℃.

[0115] Solid bisphenol F epoxy resin is characterized by low viscosity and flexibility. The properties of its cured product are almost the same as those of bisphenol A epoxy resin. When added to PVB and copolymerized with its hydroxyl groups, its corrosion resistance can be effectively improved.

[0116] (5) Isocyanate (MDI) modified epoxy resin

[0117] Structural formula:

[0118] The epoxy equivalent is between 280 and 380 g / eq, the hydrolytic chlorine should be less than 300 ppm, the viscosity at 25℃ is between 0.5 and 3 Poise, and the softening point is between 50 and 88℃.

[0119] Solid bisphenol F epoxy resin is characterized by low viscosity and flexibility. The properties of its cured product are almost the same as those of bisphenol A epoxy resin. When added to PVB and copolymerized with its hydroxyl groups, it can effectively improve the bonding strength and peel strength.

[0120] (6) Naphthol-type epoxy resin

[0121] Structural formula:

[0122] The epoxy equivalent is between 280 and 380 g / eq, the hydrolytic chlorine should be less than 300 ppm, the viscosity at 25℃ is between 0.5 and 3 Poise, and the softening point is between 50 and 88℃.

[0123] It is superior to traditional bisphenol A in terms of curability, heat resistance, and mechanical properties. Furthermore, due to its lower internal stress, it has a higher Tg and better adhesion. When added to PVB and copolymerized with its hydroxyl groups, it can effectively improve the Tg point, bond strength, and peel strength.

[0124] (7) Phenolic epoxy resin

[0125] Structural formula:

[0126] The epoxy equivalent is between 165 and 200 g / eq, the hydrolytic chlorine content is less than 250 ppm, the viscosity at 25°C is between 1.1 and 12.5 Poise, and the softening point is between 25 and 86°C. Because it contains two or more epoxy groups in its molecular structure, when added to PVB and copolymerized with its hydroxyl groups, the resulting product has a high crosslinking density and excellent adhesive strength, heat resistance, and chemical resistance. General PVB is compatible with low molecular weight epoxy resins, while high molecular weight epoxy resins require PVB with a high acetal degree for compatibility.

[0127] Furthermore, the phenolic resin material used in this application is mainly used as a curing agent and can be a pure substance, mixture, or compound of the following materials:

[0128] (1) Linear phenol-formaldehyde resin

[0129] Structural formula:

[0130] The free phenol content is <0.6%, the softening point is 96~123℃, the hydroxyl equivalent is between 105~119g / eq, and the electrical conductivity is less than 8us / cm.

[0131] (2) Linear BPA formaldehyde resin

[0132] Structural formula:

[0133] The free phenol content is 1-45%, the softening point is 90-140℃, the hydroxyl equivalent is between 112-130 g / eq, and the electrical conductivity is less than 20 μS / cm.

[0134] Alternatively, the adhesive resin may be present in the protective material at a weight percentage of 5% to 40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%.

[0135] Specifically, when the content of the adhesive resin is not less than 5%, sufficient cross-linking density can be formed, providing strong adhesion between the protective film and substrates such as copper foil and glass, preventing it from peeling off during chemical immersion or high-pressure rinsing. At the same time, it also improves the hardness and heat resistance of the film itself.

[0136] When the content of the adhesive resin does not exceed 40%, excessive development of the cross-linking network can be avoided. Excessive cross-linking makes the film layer too rigid and brittle. More importantly, it severely damages the soluble matrix composed of the structural resin, preventing mild solvents from effectively penetrating and dissolving it, thus resulting in a loss of mild peelability. Therefore, this content range is the key balance point for maintaining the peelability of the material while ensuring adhesion.

[0137] Furthermore, the chemical-resistant additive is composed of a high-performance organic polymer and a surface-modified inorganic filler.

[0138] On the one hand, high-performance organic polymers are polymers whose main chain contains a large number of aromatic rings and / or heterocyclic structures. Here, the main chain refers to the longest and most core skeletal chain that constitutes the polymer. An aromatic ring typically refers to a highly stable planar ring structure such as a benzene ring. A heterocyclic ring refers to a ring structure that contains not only carbon atoms but also other elements such as nitrogen (N) and oxygen (O). This high-performance organic polymer can be composed entirely of aromatic rings or a combination of aromatic and heterocyclic rings.

[0139] Therefore, the presence of aromatic rings and / or heterocycles in the main chain means that, unlike simple, flexible chains like polyethylene composed of carbon-carbon single bonds, the molecular backbone of these high-performance polymers is composed of a large number of highly stable and rigid ring structures directly linked together. This rigid cyclic main chain structure endows them with extremely high chemical inertness and thermal stability, making them a robust chemical barrier in composite materials.

[0140] Alternatively, the weight percentage of high-performance organic polymers in the protective material ranges from 5% to 50%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%.

[0141] Specifically, when the content of high-performance organic polymers is not less than 5%, these highly stable polymers can form effective chemical and thermal barriers in the material, significantly improving the material's ability to resist strong acid and alkali corrosion and high temperatures.

[0142] When the content of high-performance organic polymers does not exceed 50%, it avoids significant increases in cost and processing difficulties caused by excessive dosage. Simultaneously, it prevents excessive content from disrupting the continuity of the structural resin matrix, thereby affecting the final film quality and peel performance. This range ensures optimal chemical and thermal stability while maintaining controllable costs.

[0143] On the other hand, the surface of inorganic fillers is modified with specific functional groups. The inorganic filler itself acts as a physical barrier, effectively improving the mechanical strength, hardness, and pressure resistance of the material, and increasing the penetration pathway of chemicals. More importantly, the modified functional groups on its surface, such as at least one selected from the group consisting of aniline groups, nitrogen-containing functional groups, double-bond functional groups, and epoxy groups, can act as "bridges," enabling the surface of the inorganic filler to form effective physical interactions (such as hydrogen bonds) or chemical bonds with the surrounding organic resin matrix. This strong interfacial bonding ensures that the inorganic filler can be stably and uniformly dispersed and work synergistically with the matrix, thereby maximizing its reinforcing and protective effects.

[0144] In some embodiments, the inorganic filler is selected from at least one of graphite, carbon black, graphene, silicon dioxide, aluminum oxide, aluminum hydroxide, calcium carbonate, magnesium carbonate, magnesium silicate, silicon carbide, titanium carbide, titanium oxide, magnesium oxide, calcium oxide, boron nitride, and aluminum nitride. These fillers can significantly improve the mechanical properties of the composite material (such as hardness, Young's modulus, tensile modulus, and flexural modulus). Among these, the addition of graphite, carbon black, and graphene can enhance the solids content and screen printing capability of the composite material after film formation.

[0145] Alternatively, the inorganic filler may be present in the protective material at a weight percentage of 0.5% to 40%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%.

[0146] Specifically, when the content of inorganic filler is not less than 0.5%, the amount of filler is sufficient to form an effective physical reinforcement network in the material, thereby giving the film excellent surface hardness and resistance to physical scratches, and improving its pressure resistance in processes such as multilayer board lamination.

[0147] When the content of inorganic filler is not higher than 40%, various negative effects caused by excessive filler content (i.e., "overload") can be avoided, such as excessively high slurry viscosity making coating difficult, excessively brittle cured film, and decreased adhesion and peelability due to the relative reduction of polymer matrix. This content range is the ideal range for improving the physical protective performance of materials without sacrificing their processability and core functionality.

[0148] It is understandable that by using a structural resin based on polyvinyl acetal resin as the material matrix, the cured protective film can be quickly and thoroughly peeled off using mild solvents such as alcohols that do not damage the substrate after it has fulfilled its function. This fundamentally avoids the risk of damage to sensitive substrates (such as glass and ceramics) or high-density circuits caused by traditional strong acid and strong alkali peeling processes.

[0149] Meanwhile, the use of a bonding resin containing phenolic resin and epoxy resin ensures strong adhesion between the cured protective film and various substrates such as copper surfaces, epoxy boards, and glass substrates. This effectively prevents edge warping, delamination, or peeling of the protective film during high temperature, high pressure, or chemical immersion processes, guaranteeing the effectiveness and continuity of protection.

[0150] Furthermore, by introducing chemical-resistant additives (especially high-performance organic polymers with aromatic rings and / or heterocycles in the main chain and inorganic fillers with specific functional groups modified on the surface), the composite material of this application can effectively resist the corrosion of chemicals such as strong acids and strong alkalis, and can withstand the high temperature (e.g., 180°C) and high pressure (e.g., greater than 1.8MPa) conditions in processes such as multilayer board lamination, providing comprehensive and stable protection for fine copper circuits.

[0151] Furthermore, by using specific proportions of each component, both protective and peeling functions can be achieved, thus solving the technical problem of the difficulty in achieving both high protection and mild peelability in existing technologies, and obtaining excellent technical results with balanced overall performance.

[0152] In some embodiments, the polyvinyl acetal resin is polyvinyl butyral (PVB) resin, with the following structural formula:

[0153]

[0154] To ensure good film-forming properties and suitable solubility of the material, the molecular weight of the polyvinyl butyral resin used is between 5 g / mol and 10,000 g / mol. As a specific, non-limiting example, the molecular weight of the polyvinyl butyral resin may be 5 g / mol, 100 g / mol, 500 g / mol, 1000 g / mol, 5000 g / mol, or 10,000 g / mol.

[0155] PVB was chosen as the core structural resin because it contains a significant proportion of hydroxyl groups, which enable the polymer to form intermolecular and intramolecular hydrogen bonds, increasing intermolecular forces. Furthermore, due to the presence of hydroxyl groups in its molecular chain, PVB can undergo cross-linking reactions with other thermosetting resins, such as phenolic, urea-formaldehyde, melamine, epoxy, and diisocyanates. By mixing them in appropriate proportions, the brittleness and adhesion of the product can be improved, and bridging reactions can enhance chemical resistance and coating hardness.

[0156] Specifically, PVB also possesses excellent film-forming properties, transparency, and superior mechanical toughness, providing a robust yet flexible basic framework for composite materials. Furthermore, the PVB molecular chain contains both hydrophobic butyral groups and hydrophilic alcohol hydroxyl groups. This amphiphilic structure gives it excellent adhesion to polar surfaces such as metals (e.g., copper) and inorganic materials (e.g., glass substrates), while also maintaining good compatibility with other organic resins in the system.

[0157] More importantly, the hydroxyl groups on the PVB molecular chain not only provide adhesion but also possess chemical reactivity. These hydroxyl groups can undergo cross-linking reactions with the epoxy and phenolic resins in the bonding resin during the curing process, thus transforming the PVB matrix from an isolated entity into a deeply integrated part of the cross-linked network through chemical bonding. This co-reaction significantly enhances the cohesive strength, heat resistance, and overall structural density of the final protective film, enabling it to better resist high temperatures, high pressures, and chemical corrosion.

[0158] Finally, although PVB participates in the cross-linking reaction, its main chain structure and moderate cross-linking allow the entire system to remain robust while retaining its ability to swell or dissolve in specific mild solvents such as alcohols. Furthermore, by adjusting the ratio of alcohol hydroxyl, acetoxy, and butyral groups in the PVB raw material, its solubility, water resistance, and compatibility with other components can be precisely fine-tuned.

[0159] In some embodiments, to further precisely control the solubility, water resistance, and compatibility with other components of the material, the chemical composition of the PVB resin itself can be selected. Specifically, in polyvinyl butyral resin, the weight percentage of polyvinyl alcohol as the hydrophilic source can be between 11% and 27%, for example, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, and 27%; while the weight percentage of polyvinyl acetate can be between 0% and 8%, for example, 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 8%. By adjusting the proportions of these groups, fine-tuning of the behavior of the final protective film in different solvents and its hydrolysis resistance can be achieved.

[0160] Preferably, in the polyvinyl butyral resin, the weight percentage of polyvinyl alcohol is between 18% and 21%, and the weight percentage of polyvinyl acetate is between 1% and 6%.

[0161] Specifically, the optimal polyvinyl alcohol (polyvinyl alcohol) content aims to achieve the best balance between adhesion, reactivity, and water resistance. Within the broader functional range of this invention (11% to 27%), when the polyvinyl alcohol content is in the lower range (e.g., 11% to 18%), the composite material already possesses good peelability and sufficient adhesion, and exhibits stronger water resistance. When its content is in the higher range (e.g., 21% to 27%), the adhesion and reactivity of the material are further enhanced, and the peeling speed in alcohol solvents may be faster, but the sensitivity to moisture will increase accordingly. In contrast, controlling the polyvinyl alcohol content within the preferred optimal window of 18% to 21% provides excellent adhesion and crosslinking reactivity sufficient to cope with various demanding processes, while maintaining the hydrophilicity of the material at an ideal level. This maximizes its bonding and curing performance without sacrificing water resistance, achieving the most balanced overall effect.

[0162] Similarly, the optimal content of polyvinyl acetate (acetoxy) aims to finely adjust the synergistic effect between the material's hydrophobicity and core functions. Within its wider functional range (0% to 8%), while higher polyvinyl acetate contents (e.g., 6% to 8%) can further enhance the material's hydrolysis resistance, they may slightly dilute the concentration of the alcohol hydroxyl groups, thus having a minor impact on adhesion or reactivity. Controlling its content within the preferred range of 1% to 6% introduces a sufficient amount of hydrophobic groups, significantly optimizing and improving the water resistance and environmental stability of the final protective film, without substantially negatively impacting the core function of the alcohol hydroxyl groups (providing adhesion and reaction sites). Therefore, this range is the best choice for effectively enhancing the material's weather resistance without sacrificing core performance.

[0163] In summary, by limiting the contents of polyvinyl alcohol and polyvinyl acetate to the optimal window of 18%-21% and 1%-6% respectively, PVB structural resin can achieve the best balance in key performance dimensions such as adhesion, reactivity, water resistance and mild solvent solubility.

[0164] In some embodiments, the ratio of phenolic resin content to epoxy resin content in the bonding resin satisfies the following formula:

[0165] Phenolic resin content = (hydroxyl equivalent of phenolic resin / epoxy equivalent of epoxy resin) × epoxy resin content.

[0166] The fundamental reason for using the above formula to determine the amount of the two resins is that it follows the stoichiometric principle in chemical reactions, aiming to achieve an ideal balance in the number of the two core functional groups participating in the reaction, thereby obtaining the curing product with optimal performance.

[0167] Specifically, the curing process of the adhesive resin mainly involves a ring-opening addition reaction between the phenolic hydroxyl groups (-OH) on the phenolic resin molecular chain and the epoxy groups on the epoxy resin molecular chain, forming a highly cross-linked three-dimensional network structure. To ensure the most complete and efficient reaction, theoretically, one phenolic hydroxyl group should react with exactly one epoxy group. Therefore, the ideal feed ratio should be such that the total molar ratio of phenolic hydroxyl groups to epoxy groups in the formulation is as close to 1:1 as possible.

[0168] Here, "Epoxy Equivalent Weight (EEW)" refers to the number of grams of epoxy resin containing 1 mole of epoxy groups, while "Hydroxyl Equivalent" refers to the number of grams of phenolic resin containing 1 mole of phenolic hydroxyl groups. These two values ​​are key parameters for measuring the reactivity of resins.

[0169] Therefore, the essence of the above formula is a mathematical conversion of the chemical equilibrium relationship of "molar number of phenolic hydroxyl groups ≈ molar number of epoxy groups". By using this formula, the amount of phenolic resin containing an equimolar number of reaction sites can be accurately calculated based on the amount of epoxy resin used and its epoxy equivalent.

[0170] Using this stoichiometric method to determine the proportions ensures the full progress of the crosslinking reaction and avoids the presence of a large number of unreacted functional groups in the cured network due to an excess of a certain component. This results in the final cured adhesive resin having the highest crosslinking density, better heat resistance, chemical resistance, and the strongest mechanical strength and adhesion to the substrate.

[0171] In some embodiments, the high-performance organic polymer is selected from at least one of polyimide (PI), poly(p-phenylenebenzodioxazole) (PBO), polybenzimidazole (PBI), benzoxazine, bismaleimide, and bismaleimide triazine.

[0172] The structural formula of liquid polyimide is as follows:

[0173] or .

[0174] The structural formula of liquid poly(p-phenylenebenzodioxazole) is: .

[0175] The structural formula of liquid polybenzimidazole is: .

[0176] The structural formula of benzoxazine is:

[0177] The benzoxazine mentioned in this patent can be copolymerized with epoxy resin to improve the overall heat resistance and mechanical properties (such as hardness) of the composite resin of this invention.

[0178] The following types of benzoxazine (BPA A, BPA F, MDA, DCPD, phenol, DOPO, low-dipolar-moment diamine, double-bond, and ODA types) may be used without limitation.

[0179] Bisphenol A type benzoxazine

[0180] Bisphenol A type benzoxazine is the most common standard type of benzoxazine. It is made by dehydration condensation of bisphenol A, paraformaldehyde, and aniline. It is a yellow solid at room temperature with a melting point of about 70℃. It can self-level when heated to 120℃. G(t) = 300-800s@210℃. The glass transition temperature Tg after curing is ≥170℃. The long-term service temperature is 180-200℃. It has a V1 flame retardant rating, a water absorption rate of <0.2%, and a Rockwell hardness of 120.

[0181] Bisphenol F type benzoxazine

[0182] Bisphenol F type benzoxazine is a tough benzoxazine produced by the dehydration condensation of bisphenol F, paraformaldehyde, and aniline. It is a yellow solid at room temperature with a melting point of about 60°C. It can self-level when heated to 120°C, with a G(t) of 200-700s@210°C. The glass transition temperature Tg after curing is ≥170°C. It has a V1 flame retardant rating and better toughness than bisphenol A type benzoxazine, making it suitable for the preparation of composite materials.

[0183] MDA type benzoxazine

[0184] MDA type benzoxazine is a high heat-resistant benzoxazine, made by dehydration condensation of diaminodiphenylmethane, paraformaldehyde, and phenol. It is a brownish-yellow solid at room temperature with a melting point of about 90℃. It can self-level when heated to 120℃, with G(t) = 200-600s@210℃. The glass transition temperature Tg after curing is ≥200℃, the long-term service temperature is 200-220℃, the flame retardant rating is V1, and the residual carbon content in a nitrogen atmosphere is >50%@800℃. It is suitable for the preparation of products in high-temperature environments.

[0185] DCPD type benzoxazine

[0186] DCPD type benzoxazine is a low-dielectric benzoxazine, produced by the dehydration condensation of dicyclopentadiene diphenol, paraformaldehyde, and aniline. It is a yellow solid at room temperature with a melting point of about 90℃. It can self-level when heated to 120℃, with G(t) = 1000-3000s@210℃. The glass transition temperature after curing is Tg ≥ 150℃. It has a V1 flame retardant rating. The dielectric constant Dk of dicyclopentadiene type benzoxazine is < 3.0, and the dielectric loss Df is < 0.0095. Its excellent dielectric properties make it suitable for use in the field of copper-clad laminates for communication applications.

[0187] Phenolic benzoxazine

[0188] Phenolic benzoxazine is produced by the dehydration condensation of phenol, paraformaldehyde, and aniline. It is one of the simplest monocyclic benzoxazines. Due to its steric hindrance and small molecular structure, it has a melting point of about 40°C, low viscosity after melting, low curing temperature, and a glass transition temperature (Tg) ≥ 130°C after curing. It has a long-term service life, a V1 flame retardant rating, and is suitable for solvent-free low-viscosity systems, such as RTM molding.

[0189] DOPO type benzoxazine

[0190] DOPO type benzoxazine is a flame-retardant benzoxazine, produced by the dehydration condensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, benzoxazine, paraformaldehyde, and phenol. It is a yellow solid at room temperature with a melting point of about 90℃. It can self-level when heated to 120℃. The glass transition temperature (Tg) after curing is ≥150℃. It has a V0 flame retardancy rating, a phosphorus content >9.0%, and low smoke density. It is also halogen-free and can be used alone as a flame-retardant matrix resin or as a phosphorus-containing curing agent for epoxy resins. It can be applied to halogen-free flame-retardant composite materials and copper-clad laminates.

[0191] The structural formula of bismaleimide is: .

[0192] The bismaleimide referred to in this patent can be copolymerized with epoxy resin to achieve synergistic effects through the formation of an interpenetrating network structure, thereby improving the overall heat resistance and mechanical properties (such as hardness and toughness) of the composite resin of this invention. Modified bismaleimide is preferred, and it can be, but is not limited to, diaminodiphenylmethane (DDM) modified bismaleimide, biphenyl-containing bismaleimide, isopropylparaben-containing bismaleimide, PI modified bismaleimide, and cyanate ester modified bismaleimide.

[0193] The structural formula of bismaleimide triazine can be found in reference to bismaleimide.

[0194] The above materials have high chemical resistance, high Tg point and good film-forming properties.

[0195] Specifically, because the molecular backbone of these polymers consists of the aforementioned extremely stable aromatic and heterocyclic rings, with extremely high chemical bond energies and a dense structure, they exhibit strong inertness to corrosive chemicals such as strong acids and strong alkalis. Introducing them into composite materials can significantly improve the chemical resistance of the composites.

[0196] Secondly, a high Tg point (glass transition temperature) signifies excellent thermal stability. Tg measures the temperature at which a polymer transitions from a rigid glassy state to a soft, elastic state. These high-performance polymers, due to their rigid backbone structure, have very high Tg points because their molecular chains are difficult to move. This ensures that the composite material does not soften, deform, or degrade in performance during high-temperature processes (e.g., 180°C) such as multilayer lamination, maintaining its robust protective capabilities.

[0197] Finally, these materials possess the ability to disperse in solvents and ultimately form a continuous, dense protective phase in the composite material. They are not merely inert powder fillers, but rather can integrate well with other resin components to jointly construct a defect-free, uniform protective film.

[0198] In some embodiments, the composite material of this application further comprises at least one additive selected from leveling agents, dispersants, and defoamers. These additives can further improve the processing performance of the composite material when it is prepared into ink or dry film, as well as the appearance quality of the final film layer (e.g., leveling, defoaming, etc.). Those skilled in the art can select appropriate amounts of additives according to specific application requirements and process conditions to achieve optimal process applicability and film-forming effect.

[0199] In other embodiments, the copper plating process can employ a full-plate electroplating method. In this method, the copper layer is formed not only in the areas to be plated but also deposited on top of the protective layer over the areas to be protected. This process approach simplifies the process control requirements for selective copper plating.

[0200] The advantage of this approach is that it eliminates the need for complex graphical selective control of the electroplating process, simplifies the management of the electroplating bath and current density distribution, and can sometimes even help achieve a more uniform coating thickness across the entire plate, thereby improving production stability and efficiency.

[0201] In this process path, since a copper layer is deposited simultaneously on top of the protective layer in the area to be protected, the process of this application further includes a grinding and thinning step after the copper plating step and before the stripping step. This grinding and thinning step specifically involves grinding the copper layer in the area to be protected to remove the copper layer deposited on top of the protective layer and re-expose the protective layer, thereby preparing it for the subsequent stripping step.

[0202] Specifically, the thinning process typically involves using mechanical grinding equipment, such as precision grinders or polishers, and fine abrasive media (such as abrasive belts, brushes, or pads) to treat the surface of the printed circuit board under precisely controlled pressure and speed. The goal of the operation is to stop precisely at the moment when the protective layer is fully exposed, which can be achieved by setting a fixed grinding time or by using an online thickness monitoring system.

[0203] It is understandable that the grinding and thinning step removes excess copper layer covering the protective layer, exposing the underlying protective layer. This is a crucial prerequisite for subsequent stripping steps; otherwise, the protective ink completely covered by the metal layer will not be able to contact the stripping liquid. Secondly, the grinding process planarizes the entire substrate surface, eliminating microscopic height differences that may be caused by electroplating. This provides a highly flat reference surface for subsequent processes (such as solder mask coating or component mounting), which is particularly beneficial for the manufacture of high-density or high-frequency circuit boards.

[0204] In some embodiments, prior to the stripping step, the copper plating process of this application further includes:

[0205] Drilling: Drilling is performed on the initial substrate to form at least one hole.

[0206] Specifically, the drilling step aims to create via structures on the initial substrate to achieve electrical interconnection between different conductive layers, according to the requirements of the circuit design. In the drilling step, for larger through-holes, high-speed mechanical drill bits can be used for mechanical drilling; while for tiny blind or buried vias in high-density interconnect boards, higher precision techniques such as laser drilling can be used.

[0207] It is understood that, because the protective layer formed by the protective ink of the present invention after curing has considerable mechanical strength and hardness, it can provide effective mechanical support for the copper foil on the substrate surface during drilling. Furthermore, this can greatly suppress the "burrs" or streaks caused by the metal's ductility when the drill bit exits the copper foil, thereby obtaining cleaner and more regular drilling quality, laying a good foundation for subsequent hole metallization and the reliability of the overall circuit.

[0208] In other embodiments, the copper plating process further includes, after the curing step and before the copper plating step:

[0209] Drilling: Drilling holes in the initial substrate to form at least one hole;

[0210] Accordingly, the copper plating step also includes: copper plating the inner wall of the hole to form a copper layer on the inner wall of the hole.

[0211] Specifically, the collaborative working logic of this process path can be described as follows: First, steps S10-S30 are performed to cure the protective ink applied to the area to be protected on the substrate, thereby forming a robust protective layer with high chemical resistance. Next, before performing copper plating, the substrate with the protective layer formed is drilled to form at least one hole.

[0212] Building upon this, the subsequent copper plating step not only processes the existing copper-to-be-plated areas on the substrate but also the inner walls of the newly formed holes from the drilling process. Therefore, through this copper plating step, a conductive copper layer can be deposited on the inner walls of the holes, achieving plated-thickness (PTH) of the holes.

[0213] It is understandable that by adopting this "curing first, drilling second, and plating third" process sequence, the cured protective layer can provide effective mechanical support for the copper foil on the substrate surface during drilling, helping to suppress burrs at the hole openings. Simultaneously, in the subsequent copper plating step, it acts as a plating resist, ensuring that copper plating occurs precisely and selectively only in the areas to be copper-plated and on the newly formed hole walls. Furthermore, this process sequence can precisely form a conductive copper layer on the inner walls of the holes without affecting the protected areas on the main surface of the substrate.

[0214] As can be seen from the above embodiments, the protective ink used in this process forms a protective layer after curing, which benefits from the unique composition of the composite material—namely, the "high-performance organic polymer with aromatic rings and / or heterocyclic rings in the main chain" and the "inorganic filler with specific functional groups modified on the surface." These two components together construct a robust chemical-resistant framework, resulting in a protective layer with excellent chemical inertness, mechanical strength, and structural integrity. Furthermore, during subsequent copper plating processes, especially when subjected to a series of pretreatment steps involving strong acids, alkalis, and oxidizing chemicals such as swelling, descaling, neutralization, and activation, the protective layer remains stable, without swelling, cracking, or peeling. This provides a perfect, defect-free shield for the area to be protected below and prevents contamination of the chemical bath due to the dissolution of the protective layer, ensuring the stability and high quality of the entire copper plating process.

[0215] On the other hand, since the core components of the protective ink also include a "structural resin based on polyvinyl acetal resin" as the film-forming matrix, this process can employ a novel stripping strategy in the stripping step. The stripping solution used in this strategy (containing alcohol and / or ketone solvents) does not rely on strong corrosiveness, but rather selectively dissolves the structural resin matrix in the protective layer, causing it to lose its binding force on other insoluble components. This enables rapid and thorough disintegration and removal of the entire protective layer, thereby ensuring that the newly formed, unstable copper plating layer and the sensitive substrate material are not chemically damaged during the stripping process.

[0216] In summary, the process of this invention, by organically combining a specific material with a specific process flow, successfully solves the long-standing technical contradiction between "strong protection" and "non-destructive removal," greatly improving the yield, circuit accuracy, and long-term reliability of the copper plating process for printed circuit boards.

[0217] The present invention also proposes a printed circuit board, which is prepared by the copper plating process of the printed circuit board of any of the above embodiments. Therefore, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be repeated here.

[0218] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A copper plating process for printed circuit boards, characterized in that, include: Substrate provided: A printed circuit board substrate is provided, the substrate defining an area to be protected and an area to be copper plating; Applying protective ink: A protective ink made of a mildly peelable protective composite material is applied to the area to be protected, wherein the composite material comprises: Structural resins based on polyvinyl acetal resins; Adhesive resins containing phenolic resins and epoxy resins; High-performance organic polymers whose main chain contains aromatic rings and / or heterocycles; Inorganic fillers whose surfaces are modified by at least one functional group from the group consisting of aniline group, nitrogen-containing functional groups on the main chain or branches, double-bonded functional groups and epoxy groups; Curing: The applied protective ink is cured to form a protective layer on the area to be protected; Copper plating: A copper plating process is performed on the substrate to which the protective layer has been applied, to form a copper layer on the area to be copper-plated; and Stripping: After the copper plating is completed, the protective layer is stripped away using a stripping solution that can selectively dissolve the structural resin in the composite material. The stripping solution contains at least one of the following organic solvents: alcohol solvents, ketone solvents, ester solvents, and halogenated hydrocarbon solvents.

2. The copper plating process for printed circuit boards as described in claim 1, characterized in that, After the copper plating step and before the stripping step, the copper plating process further includes: Drilling: Drilling is performed on the initial substrate to form at least one hole.

3. The copper plating process for printed circuit boards as described in claim 1, characterized in that, The copper plating process, following the curing step and preceding the copper plating step, further includes: Drilling: Drilling the initial substrate to form at least one hole; The copper plating step further includes: copper plating the inner wall of the hole to form a copper layer on the inner wall of the hole.

4. The copper plating process for printed circuit boards as described in claim 1, characterized in that, The protective ink is in liquid or gel form; wherein... When the protective ink is applied by at least one of screen printing, stencil printing, spraying, stencil coating, slot coating, and blade coating, the viscosity of the protective ink is between 8 mPa·s and 20000 mPa·s. When the protective ink is applied by dispensing, the viscosity of the protective ink is between 20,000 mPa·s and 150,000 mPa·s.

5. The copper plating process for printed circuit boards as described in claim 1, characterized in that, The curing step includes: At least one drying stage for removing the solvent; and A curing stage performed at a temperature higher than that of the drying stage.

6. The copper plating process for printed circuit boards as described in claim 3, characterized in that, The drying stage includes a first-stage drying and a second-stage drying performed sequentially, wherein... The drying conditions for the first stage are: a temperature of 40°C to 60°C for 3 to 10 minutes; The drying conditions for the second stage are: a temperature of 80°C to 100°C for 3 to 10 minutes; The curing stage is performed at a temperature of 130°C to 150°C for 30 to 60 minutes.

7. The copper plating process for printed circuit boards as described in claim 1, characterized in that, The stripping fluid also contains water, wherein the weight ratio of the organic solvent to water is between 100:0 and 5:

95.

8. The copper plating process for printed circuit boards as described in claim 5, characterized in that, The organic solvent is ethanol, and the weight ratio of ethanol to water is between 100:0 and 30:

70.

9. The copper plating process for printed circuit boards as described in claim 1, characterized in that, The stripping step includes: spraying and / or soaking at a temperature of 20°C to 80°C, selectively combined with ultrasonic vibration.

10. The copper plating process for a printed circuit board as described in any one of claims 1 to 9, characterized in that, In the copper plating step, a copper layer is formed both above the protective layer of the area to be protected and on the area to be plated with copper. After the copper plating step and before the stripping step, the process further includes: Grinding and thinning: The copper layer in the area to be protected is ground to remove the copper layer deposited on top of the protective layer and expose the protective layer.

11. The copper plating process for a printed circuit board as described in any one of claims 1 to 9, characterized in that, The content of each component in the protective ink is as follows: The weight percentage of the structural resin is between 40% and 90%. The weight percentage of the adhesive resin is between 5% and 40%. The weight percentage of the high-performance organic polymer is between 5% and 50%; and The inorganic filler has a weight percentage between 0.5% and 40%.

12. A printed circuit board, characterized in that, Prepared using the copper plating process as described in any one of claims 1 to 11.

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