Electroless plating solution and use thereof

Abstract

The application relates to a chemical plating solution and application thereof, and the chemical plating solution comprises a metal salt, a reducing agent, a complexing agent and TiN nanoparticles; wherein the TiN nanoparticles are dispersed in the chemical plating solution; the metal salt comprises stannous sulfate and cobalt sulfate. After chemical plating is performed on a PCB, the stannous sulfate and the cobalt sulfate are reduced into a tin-cobalt alloy under the action of the reducing agent and the complexing agent and are deposited onto the surface of a laser ablation layer; the tin-cobalt alloy cooperates with the TiN, is favorable for reducing the energy density of a laser used for laser ablation and improving the edge quality of a circuit; meanwhile, the tin-cobalt alloy can also adjust the composite plating layer to have a proper melting point, is favorable for reducing the probability of circuit edge blurring caused by the flow of the composite plating layer in the laser ablation process, and further improves the quality of a processed circuit.

Description

Technical Field

[0001] This application relates to the field of PCB circuit board technology, and in particular to chemical plating solutions and their applications. Background Technology

[0002] As electronic products gradually become smaller, the line width and spacing of printed circuit board (PCB) lines are constantly shrinking. The traditional pattern transfer process, which involves coating the PCB surface with photoresist and then exposing, developing, and etching, is no longer suitable for the fabrication of fine PCB lines.

[0003] Compared to the above processes, laser ablation offers higher processing precision in fabricating fine PCB circuits. However, there are several issues when directly ablating circuits on a PCB with a laser: the copper layer on the PCB surface has a high reflectivity to light in the 200nm~1000nm wavelength range, requiring a laser with high energy density to effectively ablate the copper layer. However, increasing the laser energy density leads to an increase in the heat-affected zone of the ablation process, reducing the edge quality of the ablated circuits and affecting the fineness of the resulting circuits. Summary of the Invention

[0004] Based on this, this application provides a chemical plating solution that can form a composite plating layer on the surface of the PCB laser ablation layer to improve the absorption rate of the laser, thereby improving the edge quality of the circuit when using a laser with higher energy density.

[0005] The first aspect of this application provides a chemical plating solution comprising: a metal salt, a reducing agent, a complexing agent, and TiN nanoparticles; wherein the TiN nanoparticles are dispersed in the chemical plating solution; and the metal salt comprises stannous sulfate and cobalt sulfate.

[0006] In some embodiments, the electroless plating solution satisfies at least one of the following characteristics:

[0007] (1) The average particle size of the TiN nanoparticles is 20 nm to 50 nm; optionally, the average particle size of the TiN nanoparticles is 25 nm to 35 nm.

[0008] (2) In the electroless plating solution, the concentration of the TiN nanoparticles is 1.0 g / L to 2.0 g / L; optionally, in the electroless plating solution, the concentration of the TiN nanoparticles is 1.3 g / L to 1.7 g / L.

[0009] (3) The concentration of stannous sulfate in the electroless plating solution is 15 g / L to 25 g / L; optionally, the concentration of stannous sulfate in the electroless plating solution is 18 g / L to 22 g / L.

[0010] (4) The concentration of cobalt sulfate in the electroless plating solution is 5 g / L to 15 g / L; optionally, the concentration of cobalt sulfate in the electroless plating solution is 9 g / L to 11 g / L.

[0011] (5) The reducing agent includes sodium hypophosphite and dimethylaminoborane; optionally, in the electroless plating solution, the concentration of sodium hypophosphite is 30 g / L to 40 g / L and the concentration of dimethylaminoborane is 1 g / L to 3 g / L; optionally, in the electroless plating solution, the concentration of sodium hypophosphite is 33 g / L to 37 g / L and the concentration of dimethylaminoborane is 1.5 g / L to 2.5 g;

[0012] (6) The complexing agent includes one of sodium citrate, sodium gluconate or potassium sodium tartrate;

[0013] (7) In the electroless plating solution, the concentration of the complexing agent is 60 g / L to 80 g / L; optionally, in the electroless plating solution, the concentration of the complexing agent is 68 g / L to 72 g / L.

[0014] In some embodiments, the electroless plating solution satisfies at least one of the following characteristics:

[0015] (1) The electroless plating solution further includes a buffer, which includes boric acid and borax; optionally, the concentration of boric acid in the electroless plating solution is 20 g / L to 30 g / L, and the concentration of borax is 10 g / L to 15 g / L; optionally, the concentration of boric acid in the electroless plating solution is 24 g / L to 26 g / L, and the concentration of borax is 11 g / L to 13 g / L.

[0016] (2) The electroless plating solution further includes additives, including thiourea, 2-mercaptobenzothiazole and polyethyleneimine; optionally, in the electroless plating solution, the concentration of thiourea is 0.5 mg / L to 1.5 mg / L, the concentration of 2-mercaptobenzothiazole is 0.1 mg / L to 0.3 mg / L, and the concentration of polyethyleneimine is 5 mg / L to 15 mg / L; optionally, in the electroless plating solution, the concentration of thiourea is 0.8 mg / L to 1.2 mg / L, the concentration of 2-mercaptobenzothiazole is 0.15 mg / L to 0.25 mg / L, and the concentration of polyethyleneimine is 8 mg / L to 12 mg / L;

[0017] (3) The electroless plating solution also includes a dispersant, which includes a nonionic surfactant; optionally, the concentration of the dispersant in the electroless plating solution is 0.1 g / L to 0.3 g / L; optionally, the concentration of the dispersant in the electroless plating solution is 0.15 g / L to 0.25 g / L.

[0018] (4) The pH of the electroless plating solution is 8.8~9.2; optionally, the pH of the electroless plating solution is 8.9~9.1.

[0019] A second aspect of this application provides the application of the chemical plating solution described in any of the above embodiments in the preparation of printed circuit boards.

[0020] In some implementations, the application includes the following steps:

[0021] S1. Perform chemical plating on the printed circuit board using a chemical plating solution including any of the above embodiments to prepare a composite plating layer on the surface of the laser ablation layer of the printed circuit board.

[0022] The composite coating comprises a tin-cobalt alloy and TiN;

[0023] S2. Use a laser to ablate the printed circuit board according to a preset circuit pattern, so that the composite coating corresponding to the laser ablation area is vaporized, exposing the laser ablation layer.

[0024] S3. Etching to remove the laser ablation layer exposed in step S2;

[0025] S4. Stripping the plating to remove the composite plating layer and prepare the desired printed circuit board circuit.

[0026] In some embodiments, in step S1, the atomic percentage of TiN in the composite coating is 6% to 12%; and / or, in step S1, the atomic percentage of cobalt in the composite coating is 8% to 18%.

[0027] In some embodiments, in step S1, the atomic percentage of TiN in the composite coating is 8% to 10%; and / or, in step S1, the atomic percentage of cobalt in the composite coating is 12% to 15%.

[0028] In some embodiments, in step S2, when the wavelength of the laser is 355 nm, the absorption rate of the composite coating to the laser is greater than or equal to 70%; and / or, in step S2, when the wavelength of the laser is 355 nm, the ablation threshold of the composite coating is less than or equal to 0.3 J / cm².

[0029] In some embodiments, in step S1, the conditions for the electroless plating satisfy at least one of the following characteristics:

[0030] (1) The temperature of the electroless plating is 70℃~80℃; optionally, the temperature of the electroless plating is 73℃~78℃;

[0031] (2) During the electroless plating process, the electroless plating solution is continuously stirred at a stirring rate of 100 rpm to 200 rpm.

[0032] (3) The electroless plating time is 10 min to 20 min.

[0033] In some embodiments, step S4 includes: immersing the printed circuit board in a stripping solution to dissolve the composite plating layer;

[0034] The stripping solution includes: nitric acid, hydrogen peroxide and p-hydroxyanisole; and / or, the stripping temperature is 48℃~52℃ and the time is 3min~5min.

[0035] This application provides a chemical plating solution comprising: a metal salt, a reducing agent, a complexing agent, and TiN nanoparticles; wherein the TiN nanoparticles are dispersed in the chemical plating solution; and the metal salt comprises stannous sulfate and cobalt sulfate. After chemical plating on a PCB, stannous sulfate and cobalt sulfate are reduced to a tin-cobalt alloy under the action of the reducing agent and the complexing agent, and deposited onto the surface of the laser ablation layer. The tin-cobalt alloy and TiN work synergistically to reduce the energy density of the laser used for laser ablation and improve the edge quality of the circuit. Simultaneously, the tin-cobalt alloy can also adjust the melting point of the composite plating layer, which helps reduce the probability of blurred circuit edges caused by the flow of the composite plating layer during laser ablation, thereby improving the quality of the processed circuit. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments and examples of this application, and to more completely understand this application and its beneficial effects, the accompanying drawings used in the description of the embodiments or examples will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0037] Figure 1 The UV / Vis spectrophotometer absorption spectra of the composite coating in Example 1, the coating in Comparative Example 1, and the composite coating in Comparative Example 2 are shown. Figure 1 In this context, Wavelength refers to the wavelength of the laser beam; Absorption refers to the laser absorption rate.

[0038] Figure 2 The elemental distribution diagram of the composite coating of the printed circuit board in Example 1 is obtained using a scanning electron microscope.

[0039] Figure 3 The elemental distribution map of the ablation area of ​​the printed circuit board in Example 1 after deplating is obtained using a scanning electron microscope.

[0040] Figure 4 This is a photograph of the circuit diagram of the printed circuit board in Example 1 under an optical microscope.

[0041] Figure 5 This is a photograph of the circuit board image in Comparative Example 1 under an optical microscope. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the accompanying drawings, embodiments, and examples. It should be understood that these embodiments and examples are for illustrative purposes only and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to enable a more thorough and comprehensive understanding of the disclosure of the present application. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. For example, features described or illustrated as part of one embodiment can be combined in a suitable manner in another embodiment to produce new embodiments. Furthermore, numerous details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for descriptive purposes only and is not intended to be limiting of the application.

[0044] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0045] The terms “and / or,” “or / and,” and “and / or” as used herein include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. “Any and all combinations” includes any two related listed items, any more related listed items, or a combination of all related listed items. For example, “A and / or B” includes three parallel options: A, B, and “a combination of A and B.”

[0046] In this application, the terms "multiple", "various", "multiple times", "several", "several", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0047] In this application, "optionally", "optional", and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without".

[0048] In this application, the technical features or solutions described in open-ended language include both closed-ended technical features or solutions consisting of the listed contents and open-ended technical features or solutions that include the listed contents.

[0049] In this application, where the method flow involves multiple steps, unless otherwise explicitly stated herein, there is no strict order restriction on the execution of these steps; they can be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0050] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0051] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0052] To improve the quality of trace edges in PCBs, a sacrificial layer with high laser absorption, such as a pure tin sacrificial layer, can be pre-placed on the surface of the laser ablation layer (copper layer) of the PCB before laser ablation. This reduces the energy density of the laser used for ablation, exposing the underlying copper layer during the ablation process, and then transferring the pattern onto the copper through etching. However, the reduction in laser reflectivity by the pure tin sacrificial layer is limited, the required ablation threshold remains high, and the low melting point of pure tin causes molten tin to flow into adjacent areas during laser ablation, meaning the quality of the pattern edges still needs further improvement.

[0053] Based on this, the first aspect of this application provides a chemical plating solution comprising: a metal salt, a reducing agent, a complexing agent, and TiN nanoparticles; wherein the TiN nanoparticles are dispersed in the chemical plating solution; and the metal salt comprises stannous sulfate and cobalt sulfate.

[0054] The electroless plating solution of this application uses stannous sulfate (SnSO4) and cobalt sulfate (CoSO4·7H2O) metal salts as the main salts. Under the action of a reducing agent and a complexing agent, the metal salts are reduced by the reducing agent, and the Sn in the stannous sulfate... 2+ Co in cobalt sulfate 2+ Simultaneously, the tin-cobalt alloy is reduced to a tin-cobalt alloy and deposited on the surface of the laser ablation layer. The grain boundaries of the tin-cobalt alloy can form multiple scattering in the composite coating, which is beneficial to improving the laser absorption rate. At the same time, TiN nanoparticles can utilize their plasmon resonance characteristics to generate intrinsic absorption of the laser, which is beneficial to further enhance the laser absorption rate. Thus, the synergistic effect of the tin-cobalt alloy and TiN helps to reduce the energy density of the laser used for laser ablation, thereby reducing the damage to the circuit near the ablation area and improving the edge quality of the circuit. In addition, the tin-cobalt alloy can also adjust the composite coating to have a suitable melting point, which helps to reduce the probability of circuit edge blurring caused by the flow of the composite coating during laser ablation.

[0055] In some embodiments, the average particle size of the TiN nanoparticles is 20 nm to 50 nm. In other embodiments, the average particle size of the TiN nanoparticles is 25 nm to 35 nm. An average particle size within this range is beneficial for forming a better scattering structure, further enhancing the absorption rate of laser light, and thus helping to further reduce the energy density of the laser used for laser ablation, improving the edge quality of the circuit. Specifically, the average particle size of the TiN nanoparticles includes, but is not limited to, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any combination thereof. It should be noted that the average particle size of the TiN nanoparticles is obtained by laser particle size analyzer testing, and those skilled in the art can select TiN nanoparticles with appropriate average particle sizes according to actual needs.

[0056] In some embodiments, the concentration of TiN nanoparticles in the electroless plating solution is 1.0 g / L to 2.0 g / L. In some embodiments, the concentration of TiN nanoparticles in the electroless plating solution is 1.3 g / L to 1.7 g / L. Specifically, the concentration of TiN nanoparticles includes, but is not limited to: 1 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, 2 g / L, or any range between the foregoing.

[0057] In some embodiments, the concentration of stannous sulfate in the electroless plating solution is 15 g / L to 25 g / L. In some embodiments, the concentration of stannous sulfate in the electroless plating solution is 18 g / L to 22 g / L. Specifically, the concentration of stannous sulfate includes, but is not limited to: 15 g / L, 17 g / L, 19 g / L, 21 g / L, 23 g / L, 25 g / L, or any range between the foregoing.

[0058] In some embodiments, the concentration of cobalt sulfate in the electroless plating solution is 5 g / L to 15 g / L. In some embodiments, the concentration of cobalt sulfate in the electroless plating solution is 9 g / L to 11 g / L. Specifically, the concentration of cobalt sulfate includes, but is not limited to: 5 g / L, 7 g / L, 9 g / L, 11 g / L, 13 g / L, 15 g / L, or any range between the foregoing.

[0059] In some embodiments, the reducing agent includes sodium hypophosphite and dimethylaminoborane (DMAB). By selecting sodium hypophosphite and dimethylaminoborane (DMAB) as reducing agents, it is possible to promote the growth of Sn. 2+ and Co 2+ While restoring, it promotes Sn 2+ and Co 2+ The uniform dispersion of the two elements in the tin-cobalt alloy improves the uniformity of their distribution, promotes better absorption of laser light in all areas of the composite layer, and thus helps optimize the edges of PCB circuits and improve the quality of the pattern.

[0060] In some embodiments, the concentration of sodium hypophosphite in the electroless plating solution is 30 g / L to 40 g / L, and the concentration of dimethylaminoborane is 1 g / L to 3 g / L. In some embodiments, the concentration of sodium hypophosphite in the electroless plating solution is 33 g / L to 37 g / L, and the concentration of dimethylaminoborane is 1.5 g / L to 2.5 g / L. Specifically, the concentration of sodium hypophosphite includes, but is not limited to, 30 g / L, 32 g / L, 34 g / L, 36 g / L, 38 g / L, 40 g / L, or any range between the two aforementioned. Specifically, the concentration of dimethylaminoborane includes, but is not limited to, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, or any range between the two aforementioned.

[0061] In some embodiments, the complexing agent includes one of sodium citrate, sodium gluconate, or potassium sodium tartrate. Sodium citrate (Na3C6H5O7·2H2O) acts as a complexing agent against Sn. 2+ It has a strong complexing ability, which is beneficial for reducing Sn. 2+ Dissolution; sodium gluconate (C6H) 11 NaO7) is beneficial for complexing Co. 2+ This is beneficial to Co 2+ The deposition of tin-cobalt alloy is facilitated by selecting complexing agents including sodium citrate and / or sodium gluconate, which can promote the formation of an appropriate amount of tin-cobalt alloy in the prepared composite coating, thereby improving the laser absorption rate and increasing the melting point of the composite coating, thus further improving the quality of the pattern.

[0062] In some embodiments, the concentration of the complexing agent in the electroless plating solution is 60 g / L to 80 g / L. In some embodiments, the concentration of the complexing agent in the electroless plating solution is 68 g / L to 72 g / L. Specifically, the concentration of the complexing agent includes, but is not limited to: 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, or any range between the foregoing.

[0063] In some embodiments, the electroless plating solution further includes a buffer, which includes boric acid and borax. In some embodiments, the concentration of boric acid in the electroless plating solution is 20 g / L to 30 g / L, and the concentration of borax is 10 g / L to 15 g / L. In some embodiments, the concentration of boric acid in the electroless plating solution is 24 g / L to 26 g / L, and the concentration of borax is 11 g / L to 13 g / L. By selecting the above-mentioned buffer, boric acid and borax work together to form a stable buffer pair within a pH range of 8.5 to 9.5, which helps maintain the stability of the pH of the plating solution during the electroless plating reaction, thereby improving the quality of the composite plating layer and further improving the quality of the prepared PCB circuit. Specifically, the concentration of boric acid includes, but is not limited to: 20 g / L, 22 g / L, 24 g / L, 26 g / L, 28 g / L, 30 g / L, or any range between the foregoing. Specifically, the concentration of borax includes, but is not limited to: 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, or any range between the two mentioned above.

[0064] In some embodiments, the electroless plating solution further includes additives, including thiourea (CH4N2S), 2-mercaptobenzothiazole (C7H5NS2), and polyethyleneimine (PEI). In some embodiments, the concentration of thiourea is 0.5 mg / L to 1.5 mg / L, and the concentration of 2-mercaptobenzothiazole is 0.1 mg / L to 0.3 mg / L. In some embodiments, the concentration of polyethyleneimine is 5 mg / L to 15 mg / L. In some embodiments, the concentration of thiourea in the electroless plating solution is 0.8 mg / L to 1.2 mg / L, the concentration of 2-mercaptobenzothiazole is 0.15 mg / L to 0.25 mg / L, and the concentration of polyethyleneimine is 8 mg / L to 12 mg / L. The addition of thiourea and 2-mercaptobenzothiazole helps to inhibit the excessive decomposition of the reducing agent and promote Sn plating. 2+ and Co 2+ The effective reduction of thiourea forms a tin-cobalt alloy; simultaneously, thiourea can selectively adsorb onto the high-energy crystal planes of the formed tin-cobalt alloy, assisting in grain refinement and thus improving the scattering of the tin-cobalt alloy grain boundaries in the composite coating, further enhancing the absorption rate of the composite coating to laser. Polyethyleneimine, as a polymeric adsorbent, can inhibit grain growth through steric hindrance and assist in TiN dispersion. Therefore, by selecting the above additives, it is beneficial to improve the absorption of laser by the composite coating, thereby further improving the quality of the prepared PCB circuit. Specifically, the concentration of thiourea includes, but is not limited to: 0.5 mg / L, 0.7 mg / L, 0.9 mg / L, 1.1 mg / L, 1.3 mg / L, 1.5 mg / L, or any range between the two aforementioned. Specifically, the concentration of 2-mercaptobenzothiazole includes, but is not limited to: 0.1 mg / L, 0.15 mg / L, 0.2 mg / L, 0.25 mg / L, 0.3 mg / L, or any range between the two aforementioned. Specifically, the concentration of polyethyleneimine includes, but is not limited to, 5 mg / L, 7 mg / L, 9 mg / L, 11 mg / L, 13 mg / L, 15 mg / L, or any range between the two mentioned above. This application does not impose any particular limitation on the weight-average molecular weight (Mw) of polyethyleneimine, as long as it achieves the purpose of this application. For example, the weight-average molecular weight (Mw) of polyethyleneimine can be 8000 g / mol to 12000 g / mol.

[0065] In some embodiments, the electroless plating solution also includes a dispersant, which includes a nonionic surfactant. In some embodiments, the dispersant includes polyethylene glycol octylphenyl ether (Triton X-100). The presence of the dispersant helps reduce the aggregation of TiN nanoparticles and promotes the uniform distribution of TiN nanoparticles in the coating, thereby improving the quality of the composite coating. Each region of the composite coating can achieve good laser absorption, thus improving the quality of the prepared PCB circuitry.

[0066] In some embodiments, the concentration of the dispersant in the electroless plating solution is 0.1 g / L to 0.3 g / L. In some embodiments, the concentration of the dispersant in the electroless plating solution is 0.15 g / L to 0.25 g / L. Specifically, the concentration of the dispersant includes, but is not limited to: 0.1 g / L, 0.15 g / L, 0.2 g / L, 0.25 g / L, 0.3 g / L, or a range between any two of the foregoing.

[0067] In some embodiments, the pH of the electroless plating solution is 8.8–9.2. In some embodiments, the pH of the electroless plating solution is 8.9–9.1. By adjusting the pH within the above range, maintaining a weakly alkaline environment of the plating solution is beneficial for the smooth progress of the reduction reaction, thereby improving the quality of the composite coating, increasing the absorption rate of laser light, and thus improving the quality of the prepared PCB circuit. Specifically, the pH of the electroless plating solution includes, but is not limited to, 8.8, 8.9, 9, 9.1, 9.2, or any two of the aforementioned ranges.

[0068] This application does not impose any particular limitation on the preparation method of the electroless plating solution, as long as it achieves the purpose of this application. For example, the electroless plating solution may include the following steps:

[0069] Step 1: Preparation of TiN nanoparticle suspension: TiN nanoparticles and a dispersant are added to deionized water and dispersed until a uniform, stable, black TiN nanoparticle suspension without visible agglomerates is formed. This application does not impose any particular limitations on the dispersion conditions described above, as long as the objective of this application can be achieved. For example, dispersion can be performed under ultrasonic treatment at 300W~500W for 30~50 minutes.

[0070] Step 2, Preparation of the base plating solution: Heat deionized water to 45℃~50℃. While stirring (stirring speed 300℃~500rpm), add the complexing agent and buffer sequentially, stirring until dissolved. Then add the metal salt and continue stirring until the solution is clear and transparent. It is understood that stannous sulfate must be added in the presence of a complexing agent to prevent hydrolysis and precipitation.

[0071] Step 3: Addition of additives and reducing agents: While maintaining the stirring state of Step 2, slowly add the pre-dispersed TiN nanoparticle suspension from Step 1 to the base plating solution, stirring to ensure uniform dispersion. Subsequently, add the reducing agent and additives sequentially, stirring until homogeneous, to prepare the chemical plating solution precursor.

[0072] Step 4, pH Adjustment and Volume Adjustment: Adjust the pH value of the electroless plating solution precursor and adjust the volume. This application does not impose any particular restrictions on the pH adjustment method, as long as it achieves the purpose of this application. For example, when the pH value of the electroless plating solution precursor is lower than the target pH, 20%~25% ammonia solution can be added to adjust the pH to 8.8~9.2; when the pH value of the electroless plating solution precursor is higher than the target pH, 15%~25% dilute sulfuric acid can be added to adjust the pH to the target pH. It should be noted that due to the presence of a buffer in the electroless plating solution, the pH change after adjusting the pH and then adjusting the volume is negligible.

[0073] In some embodiments, in order to improve the uniformity of the composite coating obtained after electroless plating, the prepared electroless plating solution can be left to stand for 1-3 hours until the bubbles disappear and the solution is stable before use.

[0074] The metal salts, reducing agents, complexing agents, TiN, buffers, additives, and dispersants used in this application are all commercially available.

[0075] The second aspect of this application provides an application of the chemical plating solution described in any of the above embodiments in the fabrication of printed circuit boards. By using the chemical plating solution of this application to perform chemical plating on the PCB, a composite plating layer is formed. The composite plating layer has a high laser absorption rate and a high melting point. After laser ablation, etching, and stripping processes, lines with good edge quality can be fabricated on the PCB.

[0076] After electroless plating of a PCB using the chemical plating solution of this application, a composite coating, namely the aforementioned sacrificial layer, can be formed on the PCB surface. The composite coating includes a tin-cobalt alloy and TiN. The grain boundaries of the tin-cobalt alloy can form multiple scattering in the composite coating, which, in conjunction with the plasmon resonance characteristics of TiN, synergistically enhances the absorption rate of the composite coating to the laser. This helps to reduce the energy density of the laser used for laser ablation, thereby reducing damage to the circuits near the ablation area and improving the edge quality of the circuits. At the same time, the tin-cobalt alloy can also adjust the composite coating to have a suitable melting point, which helps to reduce the probability of blurred circuit edges caused by the flow of the composite coating during laser ablation. Furthermore, while current nickel-based films (such as Ni-P) sacrificial layers can effectively improve laser absorption, they are difficult to remove. Strong oxidizing solutions are usually required to remove the sacrificial layer, leaving behind hard-to-remove residues (black film) on the copper surface, affecting subsequent processes and ultimately impacting the final quality of the circuit. In contrast, the composite coating prepared using the chemical plating solution of this application is easy to remove after laser ablation of the circuit. The copper layer after removal has a smooth surface without any hard-to-remove black film, which facilitates subsequent processes and improves product quality.

[0077] In some embodiments, the application includes the following steps: S1, performing chemical plating on the printed circuit board using a chemical plating solution including any of the above embodiments to prepare a composite plating layer on the surface of the laser ablation layer of the printed circuit board; the components of the composite plating layer include tin-cobalt alloy and TiN; S2, using a laser to perform laser ablation on the printed circuit board according to a preset circuit pattern, causing the composite plating layer corresponding to the laser ablation area to vaporize and expose the laser ablation layer; S3, etching to remove the laser ablation layer exposed in step S2; S4, stripping the plating to remove the composite plating layer and prepare the desired printed circuit board circuit. The composite coating can improve laser absorption and lower the ablation threshold. During laser ablation, even a lower energy density laser can vaporize the composite coating in the ablation area, exposing the underlying copper layer. Combined with the coating's high melting point, it also reduces the thermal impact of the laser on the edges near the ablation area, thereby optimizing the edge quality of the circuit. Furthermore, the composite coating prepared using the chemical plating solution of this application exhibits good adhesion to copper and effectively protects the copper layer in non-laser-ablated areas during etching. After stripping, the copper layer surface is smooth without any difficult-to-remove black film, and the remaining copper layer forms a clearly defined circuit. In addition, the chemical plating solution of this application not only yields high-quality circuits in PCB fabrication but also offers a simple method.

[0078] In some embodiments, prior to the chemical plating in step S1, a pretreatment process for the PCB substrate is included. For example, the pretreatment steps include: immersing the PCB substrate in an alkaline degreasing solution for degreasing and cleaning, then immersing the PCB substrate in a micro-etching solution for micro-etching to roughen the copper surface and enhance the adhesion between the composite plating layer and the copper layer, followed by cleaning. This application does not impose any particular limitation on the micro-etching solution, as long as it achieves the purpose of this application. For example, the micro-etching solution may include 40g / L to 60g / L sodium persulfate and 15ml / L to 25ml / L sulfuric acid. This application does not impose any particular limitation on the depth of the micro-etching, as long as it achieves the purpose of this application. For example, the depth of the micro-etching may be 0.5μm to 1.0μm. In some embodiments, the PCB substrate may also be immersed in a dilute sulfuric acid solution (80ml / L to 100ml / L) to remove the oxide layer on the surface. In some embodiments, the PCB substrate may also be pre-immersed in a solution containing a complexing agent at room temperature for 1-3 minutes to prevent the pretreatment solution from being carried into the chemical plating solution and causing contamination.

[0079] In some embodiments, in step S1, the atomic percentage of TiN in the composite coating is 6% to 12%. In some embodiments, in step S1, the atomic percentage of TiN in the composite coating is 8% to 10%. Specifically, the atomic percentage of TiN includes, but is not limited to: 6%, 7%, 8%, 9%, 10%, 11%, 12%, or any range between the foregoing.

[0080] In some embodiments, in step S1, the atomic percentage of cobalt in the composite coating is 8% to 18%. In some embodiments, in step S1, the atomic percentage of cobalt in the composite coating is 12% to 15%. Specifically, the atomic percentage of cobalt includes, but is not limited to: 8%, 10%, 12%, 14%, 16%, 18%, or any range between the foregoing.

[0081] In some embodiments, the electroless plating temperature in step S1 is 70°C to 80°C. In some embodiments, the electroless plating temperature is 73°C to 78°C. Specifically, the electroless plating temperature includes, but is not limited to: 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, or any range between the foregoing.

[0082] In some embodiments, in step S1, the electroless plating solution is continuously stirred during the electroless plating process at a stirring rate of 100 rpm to 200 rpm. Specifically, the stirring rate includes, but is not limited to, 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm, 200 rpm, or any range between the two aforementioned.

[0083] In some embodiments, the electroless plating time in step S1 is 10 min to 20 min. Specifically, the electroless plating time includes, but is not limited to, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, or any range between the two mentioned above.

[0084] In some embodiments, in step S2, when the wavelength of the laser is 355 nm, the absorption rate of the composite coating to the laser is greater than or equal to 70%; and / or, in step S2, when the wavelength of the laser is 355 nm, the ablation threshold of the composite coating is less than or equal to 0.3 J / cm².

[0085] This application does not impose any particular limitation on the etching method in step S3, as long as it can achieve the purpose of this application. For example, the printed circuit board can be immersed in an etching solution at 50°C to 60°C for 4 to 6 minutes. This application does not impose any particular limitation on the composition of the etching solution, as long as it can achieve the purpose of this application. For example, the etching solution includes 130-150 g / L of copper chloride, 280-300 ml / L of ammonia (25%), 45-55 g / L of ammonium chloride, and the pH value of the etching solution is 7.8-8.2.

[0086] In some embodiments, step S4, the stripping step, includes immersing the printed circuit board in a stripping solution to dissolve the composite plating layer; the stripping solution includes nitric acid, hydrogen peroxide, and p-hydroxyanisole. In some embodiments, by mass percentage, the stripping solution includes: 18%~22% concentrated nitric acid (68% by mass), 4%~6% hydrogen peroxide (30% by mass of ammonia), 0.09%~0.11% p-hydroxyanisole, and the balance being deionized water.

[0087] In some embodiments, the stripping temperature is 48°C to 52°C, and the time is 3 min to 5 min. Specifically, the stripping temperature includes, but is not limited to, 48°C, 49°C, 50°C, 51°C, 52°C, or any range between the two. Specifically, the stripping time includes, but is not limited to, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, or any range between the two.

[0088] The embodiments of this application will be described in detail below with reference to some examples. It should be understood that these embodiments are only for illustrating this application and are not intended to limit the scope of this application. For experimental methods in the following embodiments where conditions are not specified, please refer to the guidelines given in this application first, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0089] In the following examples, the measurement parameters of the raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0090] Atomic percentage tests of cobalt and TiN:

[0091] The cross-section of the coating was analyzed by surface scanning analysis using an energy dispersive spectroscopy (SEM-EDS) instrument equipped with a scanning electron microscope. Four elements, namely tin, cobalt, titanium, and nitrogen, were selected for analysis. The atomic percentages of tin, cobalt, titanium, and nitrogen in the coating were determined, and the atomic percentage of TiN was calculated as: atomic percentage of titanium + atomic percentage of nitrogen.

[0092] Laser absorption rate test:

[0093] Using a Shimadzu UV-3600 plus UV / Vis spectrophotometer, the light absorption spectra of the composite coatings or coatings in the examples or comparative examples were measured in the wavelength range of 200 nm to 1200 nm. Barium sulfate was used as a reference. The UV / Vis absorption spectra of the examples or comparative examples were recorded and measured. Then, the absorbance at 355 nm was read from the graph.

[0094] Laser ablation threshold test:

[0095] The laser ablation threshold refers to the minimum laser energy density at which the material surface begins to be ablated and removed. The ablation threshold of the material is calculated using the following formula:

[0096] .

[0097] Using the least squares method, the square of the ablation diameter of the composite coating or coating in the examples or comparative examples under different pulse number femtosecond laser irradiation was linearly fitted to the logarithm of the laser power. In the linear fitting curve, k=2. The y-intercept b = -2 lnP th ω0 is the focused spot radius, f is the laser repetition frequency, and Pth is the threshold power. The ablation threshold can be calculated. In this scheme, a 355nm ultraviolet picosecond laser with a pulse width of 15ps and a repetition frequency of 100kHz is used for laser ablation threshold testing. The ablation diameter is calculated by observing the morphology and width of the ablation slit using an optical microscope. The ablation diameter is 2ω0, and the value of ω0 is calculated accordingly. Finally, the ablation threshold φ for each material is obtained by fitting the formula. th .

[0098] Graphic quality check:

[0099] Use an optical microscope to inspect the quality of the circuit pattern, measure the line width / line spacing, and observe whether the pattern is complete, whether the edges are clear, whether there are any residues, and whether there are any short circuits or open circuits.

[0100] Example 1:

[0101] The preparation of the chemical plating solution includes the following steps:

[0102] Step 1: Preparation of TiN nanoparticle suspension: Weigh 1.5g of TiN nanoparticles (average particle size 30nm, purity ≥99.9%) and 0.2g of dispersant Triton X-100, and add them to 200mL of deionized water. Disperse under 300W ultrasound for 45 minutes until a uniform, stable, black TiN nanoparticle suspension without visible agglomerates is formed.

[0103] Step 2, Preparation of the base plating solution: Take 600 mL of deionized water and heat it to 50°C. While stirring (stirring speed 500 rpm), add 70 g of complexing agent sodium citrate; then add buffer: 25 g boric acid and 12 g borax, and stir until completely dissolved. Subsequently, slowly add the metal salts: 20 g stannous sulfate and 10 g cobalt sulfate, and continue stirring until the solution is clear and transparent.

[0104] Step 3: Addition of Additives and Reducing Agents: While maintaining the stirring state from Step 2, slowly add the pre-dispersed TiN nanoparticle suspension from Step 1 to the base plating solution, stirring for 15 minutes to ensure uniform dispersion. Then, dissolve 35g of sodium hypophosphite and 2g of dimethylaminoborane, the reducing agents, in 150ml of deionized water, and slowly add them while stirring. Next, add the additives sequentially: 1.0mg thiourea, 0.2mg 2-mercaptobenzothiazole, and 10mg polyethyleneimine. Stir for 5 minutes after each additive is added before adding the next.

[0105] Step 4, pH Adjustment and Volume Adjustment: Adjust the pH of the plating solution to 9.0 using 25% ammonia. Add deionized water to a final volume of 1L, and continue stirring for 20 minutes to ensure all components are thoroughly mixed and homogeneous to obtain the chemical plating solution.

[0106] Let the prepared chemical plating solution stand for 2 hours until the bubbles completely disappear and the solution is stable before use.

[0107] PCB fabrication includes the following steps:

[0108] Pre-treatment process for copper clad laminates:

[0109] Epoxy fiberglass copper clad laminate (referred to as copper clad laminate, FR-4 substrate, copper foil thickness of 18μm) was selected as the substrate, and pretreatment was performed according to the following steps:

[0110] Step 1, Degreasing: Immerse the copper-clad laminate in an alkaline degreasing solution (which includes 50g / L sodium hydroxide, 30g / L sodium carbonate and 30g / L trisodium phosphate) and treat it at 55℃ for 5 minutes to remove the oil stains on the surface of the copper-clad laminate.

[0111] Step 2, hot water wash: Wash with 55℃ hot water for 1 minute.

[0112] Step 3, cold water wash: Rinse twice with deionized water, 1 minute each time.

[0113] Step 4, Micro-etching: Immerse in micro-etching solution (which includes 50g / L sodium persulfate and 20ml / L sulfuric acid) and treat at room temperature for 1 minute to roughen the copper surface and enhance the adhesion between the composite plating layer and the copper layer.

[0114] Step 5, Rinse with water: Rinse thoroughly twice with deionized water, 1 minute each time.

[0115] Step 6, Activation: Immerse in dilute sulfuric acid solution (100ml / L) and treat at room temperature for 1 minute to remove the oxide layer on the surface.

[0116] Step 7, Pre-immersion: Immerse in a complexing agent sodium citrate solution (20g / L) and treat at room temperature for 1 minute to prevent the pretreatment solution from being carried into the chemical plating solution and causing contamination.

[0117] S1. Immerse the pretreated copper-clad laminate in the prepared electroless plating solution for electroless plating. The plating temperature is 75℃~80℃, and the time is 15 minutes. During the electroless plating process, the plating solution is continuously mechanically stirred at a speed of 200 rpm. After electroless plating, remove the copper-clad laminate, rinse it thoroughly twice with deionized water, and then dry it with hot air at 60℃ for 5 minutes. Thus, a composite coating is prepared on the copper layer surface of the PCB substrate by electroless plating; the components of the composite coating include tin-cobalt alloy and TiN.

[0118] S2. A picosecond ultraviolet laser with a wavelength of 355nm, a pulse width of 15ps, and a repetition frequency of 100kHz is used for laser ablation. The laser parameters are set as follows: energy density 0.3 J / cm², scanning speed 500mm / s. The composite coating is directly scanned according to the preset circuit pattern, causing the composite coating corresponding to the laser ablation area to vaporize and expose the underlying copper layer.

[0119] Calculations show that the ablation threshold of the composite coating in Example 1 is 0.22 J / cm. 2 .

[0120] S3. Immerse the laser-treated PCB in a copper-ammonia alkaline etching solution for etching. The etching solution consists of: 150 g / L copper chloride, 300 ml / L ammonia (25% by mass), 50 g / L ammonium chloride, pH 8.0, and a temperature of 50°C. The etching time is 1.5 minutes. During the etching process, the exposed copper layer is dissolved, while the non-laser-ablated areas (copper circuit areas) still covered by the composite plating are protected.

[0121] S4. Stripping: Prepare the stripping solution, which includes 150 ml / L nitric acid (68% by mass), 50 ml / L hydrogen peroxide (30% by mass), and 1 g / L p-hydroxyanisole. Immerse the etched PCB board in the stripping solution at 50°C for 4 minutes until the Sn / Co / TiN plating is completely dissolved. After stripping, the copper surface is clean and bright, with no black film residue. Remove the board and rinse thoroughly with deionized water, then dry with hot air to remove the composite plating layer and obtain the desired printed circuit board circuitry.

[0122] Comparative Example 1:

[0123] Except for the omission of cobalt sulfate, dimethylaminoborane, TiN nanoparticles, and dispersant Triton X-100 during the preparation of the electroless plating solution, the process was identical to Example 1. After electroless plating of the copper-clad laminate with the electroless plating solution of Comparative Example 1, the coating on the surface of the copper-clad laminate was a pure tin coating.

[0124] Comparative Example 2:

[0125] Except for the omission of TiN nanoparticles and dispersant Triton X-100 during the preparation of the electroless plating solution, the process was identical to that in Example 1. After electroless plating of the copper-clad laminate with the electroless plating solution of Comparative Example 2, the coating on the surface of the copper-clad laminate consisted of a tin-cobalt alloy.

[0126] Table 1

[0127]

[0128] As can be seen from Examples 1 and Comparative Examples 1-2, the electroless plating solutions in these examples include metal salts, reducing agents, complexing agents, and TiN nanoparticles, with the TiN nanoparticles dispersed in the electroless plating solution. The metal salts include stannous sulfate and cobalt sulfate. After electroless plating the printed circuit board, the prepared composite coating includes a tin-cobalt alloy and TiN. During laser ablation, the composite coating exhibits a high absorption rate for 355nm wavelength laser light and a low ablation threshold. In Comparative Example 1, the electroless plating solution does not include cobalt sulfate as a metal salt, dimethylaminoborane as a reducing agent, TiN nanoparticles, or a dispersant. In Comparative Example 2, the electroless plating solution does not include TiN nanoparticles or a dispersant. After electroless plating the printed circuit board, the prepared composite coating exhibits a low absorption rate for 355nm wavelength laser light and a high ablation threshold. This demonstrates that the electroless plating layer prepared using the electroless plating solution of this application can reduce the energy density of the laser used for laser ablation, thereby improving the edge quality of the circuit.

[0129] from Figure 1 It can be seen that, compared with the coating of Comparative Example 1, the laser absorption rate of the composite coating of Comparative Example 2 is improved to a certain extent, while the laser absorption rate of the composite coating in Example 1 is significantly improved compared with both Comparative Example 1 and Comparative Example 2, and the absorption rate in the near-ultraviolet band (355nm) reaches more than 70%.

[0130] from Figure 2 and Figure 3 It can be seen that, before stripping, the Sn, Co, Ti, and N elements are uniformly distributed in the composite coating of Example 1. EDS testing shows... Figure 2 In the composite coating, the atomic percentages of nitrogen (N) are 4.32%, titanium (Ti) are 4.41%, co (Co) are 12.97%, and sn (Sn) are 78.3%; the calculated atomic percentage of TiN is 8.73%. After stripping, Figure 3 In this example, the atomic percentage of Cu is 100%, which demonstrates that the composite coating in Example 1 is easy to remove and leaves no residue.

[0131] from Figure 4 and Figure 5It can be seen that the processed pattern in Example 1 has straight, clean edges without burrs; while the pattern in the comparative example has uneven edges and poor quality. This shows that the pure tin plating in Comparative Example 1 has a low melting point, which causes it to melt and flow during laser etching, affecting the edge quality of the pattern; while the composite plating in Example 1 has high thermal stability and high laser absorption rate, making it suitable for the fabrication of fine circuits.

[0132] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A chemical plating solution, characterized in that, The electroless plating solution includes: metal salt, reducing agent, complexing agent, and TiN nanoparticles; The TiN nanoparticles are dispersed in the electroless plating solution; the metal salts include stannous sulfate and cobalt sulfate.

2. The electroless plating solution according to claim 1, characterized in that, The electroless plating solution meets at least one of the following characteristics: (1) The average particle size of the TiN nanoparticles is 20 nm to 50 nm; optionally, the average particle size of the TiN nanoparticles is 25 nm to 35 nm. (2) In the electroless plating solution, the concentration of the TiN nanoparticles is 1.0 g / L to 2.0 g / L; optionally, in the electroless plating solution, the concentration of the TiN nanoparticles is 1.3 g / L to 1.7 g / L. (3) The concentration of stannous sulfate in the electroless plating solution is 15 g / L to 25 g / L; optionally, the concentration of stannous sulfate in the electroless plating solution is 18 g / L to 22 g / L. (4) The concentration of cobalt sulfate in the electroless plating solution is 5 g / L to 15 g / L; optionally, the concentration of cobalt sulfate in the electroless plating solution is 9 g / L to 11 g / L. (5) The reducing agent includes sodium hypophosphite and dimethylaminoborane; optionally, in the electroless plating solution, the concentration of sodium hypophosphite is 30 g / L to 40 g / L and the concentration of dimethylaminoborane is 1 g / L to 3 g / L; optionally, in the electroless plating solution, the concentration of sodium hypophosphite is 33 g / L to 37 g / L and the concentration of dimethylaminoborane is 1.5 g / L to 2.5 g; (6) The complexing agent includes one of sodium citrate, sodium gluconate or potassium sodium tartrate; (7) In the electroless plating solution, the concentration of the complexing agent is 60 g / L to 80 g / L; optionally, in the electroless plating solution, the concentration of the complexing agent is 68 g / L to 72 g / L.

3. The electroless plating solution according to claim 1 or 2, characterized in that, The electroless plating solution meets at least one of the following characteristics: (1) The electroless plating solution further includes a buffer, which includes boric acid and borax; optionally, the concentration of boric acid in the electroless plating solution is 20 g / L to 30 g / L, and the concentration of borax is 10 g / L to 15 g / L; optionally, the concentration of boric acid in the electroless plating solution is 24 g / L to 26 g / L, and the concentration of borax is 11 g / L to 13 g / L. (2) The electroless plating solution further includes additives, including thiourea, 2-mercaptobenzothiazole and polyethyleneimine; optionally, in the electroless plating solution, the concentration of thiourea is 0.5 mg / L to 1.5 mg / L, the concentration of 2-mercaptobenzothiazole is 0.1 mg / L to 0.3 mg / L, and the concentration of polyethyleneimine is 5 mg / L to 15 mg / L; optionally, in the electroless plating solution, the concentration of thiourea is 0.8 mg / L to 1.2 mg / L, the concentration of 2-mercaptobenzothiazole is 0.15 mg / L to 0.25 mg / L, and the concentration of polyethyleneimine is 8 mg / L to 12 mg / L; (3) The electroless plating solution also includes a dispersant, which includes a nonionic surfactant; optionally, the concentration of the dispersant in the electroless plating solution is 0.1 g / L to 0.3 g / L; optionally, the concentration of the dispersant in the electroless plating solution is 0.15 g / L to 0.25 g / L. (4) The pH of the electroless plating solution is 8.8~9.2; optionally, the pH of the electroless plating solution is 8.9~9.

1.

4. The application of a chemical plating solution as described in any one of claims 1 to 3 in the preparation of printed circuit boards.

5. The application according to claim 4, characterized in that, The application includes the following steps: S1. The printed circuit board is chemically plated using a chemical plating solution comprising any one of claims 1 to 3, thereby preparing a composite plating layer on the surface of the laser ablation layer of the printed circuit board. The composite coating comprises a tin-cobalt alloy and TiN; S2. Use a laser to ablate the printed circuit board according to a preset circuit pattern, so that the composite coating corresponding to the laser ablation area is vaporized, exposing the laser ablation layer. S3. Etching to remove the laser ablation layer exposed in step S2; S4. Stripping the plating to remove the composite plating layer and prepare the desired printed circuit board circuit.

6. The application according to claim 5, characterized in that, In step S1, the atomic percentage of TiN in the composite coating is 6% to 12%; and / or, in step S1, the atomic percentage of cobalt in the composite coating is 8% to 18%.

7. The application according to claim 6, characterized in that, In step S1, the atomic percentage of TiN in the composite coating is 8%~10%; and / or, in step S1, the atomic percentage of cobalt in the composite coating is 12%~15%.

8. The application according to claim 5, characterized in that, In step S2, when the wavelength of the laser is 355nm, the absorption rate of the composite coating to the laser is greater than or equal to 70%; and / or, in step S2, when the wavelength of the laser is 355nm, the ablation threshold of the composite coating is less than or equal to 0.3J / cm².

9. The application according to claim 5, characterized in that, In step S1, the conditions for the electroless plating satisfy at least one of the following characteristics: (1) The temperature of the electroless plating is 70℃~80℃; optionally, the temperature of the electroless plating is 73℃~78℃; (2) During the electroless plating process, the electroless plating solution is continuously stirred at a stirring rate of 100 rpm to 200 rpm. (3) The electroless plating time is 10 min to 20 min.

10. The application according to any one of claims 5 to 9, characterized in that, In step S4, the plating removal step includes: immersing the printed circuit board in the plating removal solution to dissolve the composite plating layer; The stripping solution includes: nitric acid, hydrogen peroxide and p-hydroxyanisole; and / or, the stripping temperature is 48℃~52℃ and the time is 3min~5min.

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