A leadless electroplating manufacturing process for NFC products

Abstract

The application provides a leadless electroplating manufacturing process method of an NFC product, comprising the following steps: S1. substrate cutting and drilling; S2. full-plate conduction and initial copper plating; S3. first surface circuit pattern formation; S4. second surface protection; S5. local thickening electroplating; and S6. second surface circuit formation. The application effectively avoids the residual metal protrusion from causing the bubble, poor fitting and open circuit risk in subsequent cover film pressing, and the short circuit risk possibly caused by burr residue.

Description

Technical Field

[0001] This invention belongs to the field of electronic circuit manufacturing technology, and specifically relates to a leadless electroplating process for NFC products. Background Technology

[0002] Near Field Communication (NFC) technology, as a mature short-range wireless communication method, has been integrated into smart cards, electronic tags, smartphones, and various IoT terminals. One of the core components of these devices is the built-in NFC antenna, which is typically fabricated as a fine conductive coil on a flexible or rigid circuit board. During the manufacturing of NFC antennas, specific functional areas, such as pads connecting to the chip or areas requiring enhanced signal coupling, often need to be locally thickened to meet electrical performance, mechanical reliability, or subsequent packaging structural requirements.

[0003] Traditional local thickening processes commonly employ a "wired electroplating" method, which involves creating temporary metal conductive leads on the substrate outside of the patterned circuitry. These leads act as current channels during the electroplating process, guiding the current to the target area requiring thickening. After electroplating, these leads need to be removed. However, because they are on the same layer as the functional circuitry and tightly connected, it is difficult to completely remove them using conventional etching or machining methods, inevitably leaving residues. These residual leads not only occupy valuable wiring space, limiting the development of antenna designs towards smaller and higher densities, but more seriously, they form persistent micro-protrusions on the substrate surface. In subsequent cover film lamination processes, these protrusions can easily lead to incomplete lamination, air bubbles, and potential open circuits; simultaneously, residual burrs may also pose a short circuit risk.

[0004] To eliminate lead residue, existing technologies have made some attempts, such as using more expensive laser ablation techniques to remove leads and developing soluble temporary conductive inks. However, these alternatives either significantly increase production costs and process complexity or face challenges in stability and precision control, making them difficult to apply reliably in large-scale production. More importantly, directly eliminating the conductive leads and attempting to conduct electroplating current solely through the product's own vias will lead to a series of new technical problems: when current passes through the limited vias, it tends to accumulate at the edges, creating an edge effect that results in excessively thick plating, coarse crystals, or even scorching in the area around the via, while the area far from the center of the via has insufficient plating, leading to poor thickness uniformity; localized increases in current density can also exacerbate heat generation, potentially damaging thin substrates; furthermore, compared to wide, flat leads, elongated vias have higher resistance, which may lead to a decrease in electroplating deposition rate and affect production efficiency.

[0005] Therefore, it is necessary to design a leadless electroplating manufacturing process for NFC products. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, a manufacturing process for leadless electroplating of NFC products is provided.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A manufacturing process for leadless electroplating of NFC products includes the following steps: S1. Substrate cutting and drilling: providing an insulating substrate and forming at least one through hole on the insulating substrate; S2. Full board conduction and initial copper plating: The insulating substrate is subjected to hole metallization treatment so that its first surface, second surface and the inner wall of the through hole are covered with a first conductive layer; S3. Formation of the first surface circuit pattern: A first circuit pattern is formed on the first surface, the first circuit pattern including at least one area to be thickened that is electrically connected to the through hole; S4. Second surface protection: A cover layer is provided on the second surface, the cover layer being able to prevent electroplating deposition; S5. Local thickening electroplating: Using the first conductive layer of the second surface as the current feed end, the electroplating current is sequentially conducted through the second surface and the first conductive layer of the inner wall of the through hole to the area to be thickened on the first surface, and the area to be thickened is selectively electroplated to thicken it. S6. Second surface circuit formation: Remove the cover layer of the second surface and form a second circuit pattern on the second surface.

[0008] In step S1, the diameter of the through hole is 0.2mm-0.5mm.

[0009] In step S2, the hole metallization process includes chemical copper plating and electroplating of copper, and the thickness of the first conductive layer is 8μm-20μm.

[0010] In step S3, the area to be thickened includes several through holes, and the through holes are arranged in a ring or array.

[0011] The multiple through holes arranged in a ring are a concentric multi-ring structure, and the diameter of the inner ring through hole is less than or equal to the diameter of the outer ring through hole. The radial distance between adjacent rings in the concentric multi-ring structure is 1.5 to 3 times the diameter of the hole.

[0012] In step S5, the electroplating solution used for selective electroplating thickening is a sulfate-type acidic copper plating solution. The process parameters for selective electroplating thickening are: current density of 2.5-3.2 ASD, electroplating solution temperature of 20-28℃, and cathode moving speed of 0.8-1.2 m / min.

[0013] In step S5, the thickness of the area to be thickened after electroplating is 30-60 μm higher than that of the adjacent non-thickened area.

[0014] The sulfate-type acidic copper plating solution comprises, by weight, 180-250 parts of copper sulfate pentahydrate, 50-80 parts of sulfuric acid, 30-80 parts of sodium chloride, and 0.5-3.5 parts of an electroplating additive composition.

[0015] The electroplating additive composition is a mixture of brightener, leveling agent and wetting agent in a mass ratio of 1:1:0.05-1:3:0.15. The brightener is a mixture of sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivative in a mass ratio of 1:0.2-1:1.5. The leveling agent is polyethylene glycol and the wetting agent is polyoxyethylene octylphenol ether.

[0016] The preparation method of the brightener includes the following steps: M1. Weigh out sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivatives respectively at a mass ratio of 1:0.2-1:1.5; M2. Dissolve the weighed sodium polydithiopropane sulfonate in deionized water at 40-60℃; M3. Dissolve the weighed polyethyleneimine alkyl salt derivative in deionized water at 20-30℃; M4. Under stirring conditions, slowly add the solution of M2 to the solution of M1, controlling the time to be 20-40 minutes; M5. After mixing, the mixture is kept at 45-55℃ and stirred for 1-2 hours to obtain the brightening agent.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention abandons the design and use of temporary conductive leads in traditional processes, eliminating the hidden dangers caused by lead residue from the source, avoiding the problem of difficulty in completely separating leads and functional circuits due to same-layer etching, and directly solving the risk of open circuit caused by residual metal protrusions in subsequent cover film lamination, which leads to bubbles and poor adhesion, as well as the risk of short circuit caused by burr residue.

[0018] 2. This invention increases the number of parallel channels for current conduction from the second surface to the thickened area by setting multiple through holes in a specific arrangement, especially a concentric multi-ring structure. This optimizes their spatial distribution and helps to distribute the concentrated current more evenly throughout the thickened area. It effectively alleviates the excessive accumulation of current at the edges of a single or a small number of holes, thereby improving the uniformity of the coating thickness in the thickened area. It also reduces the phenomenon of rough coating crystals and scorching caused by excessively high local current density, or insufficient coating caused by excessively low current density, thus improving the overall quality and consistency of the thickened coating.

[0019] 3. The electroplating additive composition of this invention comprises a compounded brightener, leveling agent, and wetting agent. The brightener optimizes the fineness and brightness of the coating crystallization; the leveling agent helps improve the dispersion ability of the plating solution on micro-uneven surfaces, promoting uniform deposition of the coating; the wetting agent reduces the surface tension of the plating solution, enhancing its wetting and covering performance on the substrate surface. This is particularly important in scenarios involving current conduction through densely packed micropores, reducing gas retention within the pores and ensuring unobstructed current channels. The combined effect of the electroplating additive composition, under controlled process parameters such as current density, temperature, and migration speed, enables stable and controllable localized rapid deposition without leads, ensuring the physical and electrical properties of the coating. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of a leadless electroplating manufacturing process for an NFC product according to the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the specific embodiments of this application, the sources of various main raw materials are briefly described as follows: Copper sulfate pentahydrate: Jiangxi Jiangnan New Material Technology Co., Ltd., content ≥99.5%.

[0023] Sulfuric acid: Zhongtiaoshan Nonferrous Metals Group Co., Ltd., industrial sulfuric acid, purity ≥92.5% or ≥98%.

[0024] Sodium chloride: Lianyungang Longtaiwei Food Ingredients Co., Ltd., purity 99% or 99.5%.

[0025] Sodium polydisulfide dipropane sulfonate: Hubei Qiansheng Biotechnology Co., Ltd., industrial grade, 95% purity.

[0026] Polyethyleneimine alkyl salt derivatives: Wuhan Bolaite Chemical Co., Ltd., CAS No. 9002-98-6, appearance is a slightly turbid, colorless or pale yellow liquid.

[0027] Polyethylene glycol: Shanghai Lishida Chemical Co., Ltd., products with molecular weights ranging from 600 to 2000.

[0028] Polyoxyethylene octylphenol ether: Shandong Yukang Chemical Co., Ltd., CAS No. 9002-93-1, model OP-10, purity 99%.

[0029] The technical solution of this application is as follows: like Figure 1 As shown, a manufacturing process for leadless electroplating of NFC products includes the following steps: S1. Substrate cutting and drilling: providing an insulating substrate and forming at least one through hole on the insulating substrate; S2. Full board conduction and initial copper plating: The insulating substrate is subjected to hole metallization treatment so that its first surface, second surface and the inner wall of the through hole are covered with a first conductive layer; S3. Formation of the first surface circuit pattern: A first circuit pattern is formed on the first surface, the first circuit pattern including at least one area to be thickened that is electrically connected to the through hole; S4. Second surface protection: A cover layer is provided on the second surface, the cover layer being able to prevent electroplating deposition; S5. Local thickening electroplating: Using the first conductive layer of the second surface as the current feed end, the electroplating current is sequentially conducted through the second surface and the first conductive layer of the inner wall of the through hole to the area to be thickened on the first surface, and the area to be thickened is selectively electroplated to thicken it. S6. Second surface circuit formation: Remove the cover layer of the second surface and form a second circuit pattern on the second surface.

[0030] In step S1, the diameter of the through hole is 0.2mm-0.5mm.

[0031] In step S2, the hole metallization process includes chemical copper plating and electroplating of copper, and the thickness of the first conductive layer is 8μm-20μm.

[0032] In step S3, the area to be thickened includes several through holes, and the through holes are arranged in a ring or array.

[0033] The multiple through holes arranged in a ring are a concentric multi-ring structure, and the diameter of the inner ring through hole is less than or equal to the diameter of the outer ring through hole. The radial distance between adjacent rings in the concentric multi-ring structure is 1.5 to 3 times the diameter of the hole.

[0034] In step S5, the electroplating solution used for selective electroplating thickening is a sulfate-type acidic copper plating solution. The process parameters for selective electroplating thickening are: current density of 2.5-3.2 ASD, electroplating solution temperature of 20-28℃, and cathode moving speed of 0.8-1.2 m / min.

[0035] In step S5, the thickness of the area to be thickened after electroplating is 30-60 μm higher than that of the adjacent non-thickened area.

[0036] The sulfate-type acidic copper plating solution comprises, by weight, 180-250 parts of copper sulfate pentahydrate, 50-80 parts of sulfuric acid, 30-80 parts of sodium chloride, and 0.5-3.5 parts of an electroplating additive composition.

[0037] The electroplating additive composition is a mixture of brightener, leveling agent and wetting agent in a mass ratio of 1:1:0.05-1:3:0.15. The brightener is a mixture of sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivative in a mass ratio of 1:0.2-1:1.5. The leveling agent is polyethylene glycol and the wetting agent is polyoxyethylene octylphenol ether.

[0038] The preparation method of the brightener includes the following steps: M1. Weigh out sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivatives respectively at a mass ratio of 1:0.2-1:1.5; M2. Dissolve the weighed sodium polydithiopropane sulfonate in deionized water at 40-60℃; M3. Dissolve the weighed polyethyleneimine alkyl salt derivative in deionized water at 20-30℃; M4. Under stirring conditions, slowly add the solution of M2 to the solution of M1, controlling the time to be 20-40 minutes; M5. After mixing, the mixture is kept at 45-55℃ and stirred for 1-2 hours to obtain the brightening agent.

[0039] The present invention will be described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited to these examples. Unless otherwise specified, the chemical reagents and raw materials used in the following examples and comparative examples are all conventional commercially available products.

[0040] Example 1

[0041] This embodiment provides a manufacturing process for leadless electroplating of NFC products. First, an S1 substrate is cut and drilled to provide an insulating substrate, and through-holes are formed on this insulating substrate. The diameter of the through-holes is selected to be 0.5 mm.

[0042] Next, S2 full board conduction and initial copper plating are performed, and the insulating substrate is subjected to hole metallization treatment, which includes chemical copper plating and electroplating copper, so that the first surface, the second surface and the inner wall of the through hole of the substrate are covered with a first conductive layer, the thickness of which is controlled to be 14μm.

[0043] Then, the S3 first-side circuit pattern is formed. A first circuit pattern is formed on the first surface through pattern transfer and etching processes. This pattern includes a thickened area electrically connected to a via. The thickened area contains several vias arranged in a ring. Specifically, the multiple ring-arranged vias form a concentric multi-ring structure, with the diameter of the inner ring vias being smaller than the diameter of the outer ring vias. In this embodiment, the radial distance between adjacent rings in the concentric multi-ring structure is set to 1.5 times the via diameter.

[0044] Subsequently, S4 second surface protection is performed, in which a peelable dry film is applied to the second surface as a cover layer, which can completely prevent copper deposition on the second surface during the electroplating process.

[0045] The crucial S5 localized thickening electroplating step then begins. Using the first conductive layer beneath the protected second surface as the current feed point, the electroplating current is sequentially conducted through the second surface, the first conductive layer inside the via, and to the area to be thickened on the first surface, thereby achieving localized electroplating thickening of that area. The electroplating solution used in this step is a sulfate-type acidic copper plating solution. By mass, this solution contains 250 parts copper sulfate pentahydrate, 80 parts sulfuric acid, 80 parts sodium chloride, and 3.5 parts of an electroplating additive composition. This additive composition is a mixture of brightener, leveling agent, and wetting agent in a mass ratio of 1:3:0.15. Specifically, the brightener is a mixture of sodium polydithiopropane sulfonate and a polyethyleneimine alkyl salt derivative in a mass ratio of 1:1.5; the leveling agent is polyethylene glycol with a molecular weight of approximately 1000; and the wetting agent is polyoxyethylene octylphenol ether.

[0046] The brightener is prepared as follows: Sodium polydithiopropane sulfonate and a polyethyleneimine alkyl salt derivative are weighed separately. Sodium polydithiopropane sulfonate is dissolved in deionized water at 55°C, and the polyethyleneimine alkyl salt derivative is dissolved in deionized water at 25°C. Under stirring conditions, the former solution is slowly added to the latter solution over 30 minutes. After mixing, the mixture is kept at 50°C and stirred for 1.5 hours to obtain the brightener. The process parameters for selective electroplating thickening are: current density set to 3.2 ASD, electroplating solution temperature set to 28°C, and cathode moving speed set to 1.2 m / min. By controlling the electroplating time, the thickness of the area to be thickened after electroplating is 60 μm higher than that of the adjacent non-thickened area.

[0047] Finally, the second-side circuit formation is performed in S6. The dry film covering layer on the second surface is removed, and the required second circuit pattern is formed on the second surface through conventional pattern transfer and etching processes.

[0048] Example 2

[0049] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: In step S1, the diameter of the through hole is selected as 0.2 mm.

[0050] In step S2, the thickness of the first conductive layer formed after the hole metallization process is controlled to be 8 μm.

[0051] In step S3, the through holes in the area to be thickened are arranged in a concentric multi-ring structure, and the diameter of the inner ring through holes is equal to the diameter of the outer ring through holes. The radial distance between adjacent rings in the concentric multi-ring structure is set to 3 times the diameter of the through holes.

[0052] Step S4 is the same as in Example 1.

[0053] In the S5 local thickening electroplating step, the sulfate-type acidic copper plating solution used contains, by weight, 180 parts copper sulfate pentahydrate, 50 parts sulfuric acid, 30 parts sodium chloride, and 0.5 parts of an electroplating additive composition. The mass ratio of brightener, leveling agent, and wetting agent in the electroplating additive composition is 1:1:0.05.

[0054] The brightener contained sodium polydithiopropane sulfonate and polyethyleneimine alkyl salt derivative in a mass ratio of 1:0.2. The preparation temperature and mixing time were adjusted accordingly: sodium polydithiopropane sulfonate was dissolved in deionized water at 40℃, and the polyethyleneimine alkyl salt derivative was dissolved in deionized water at 20℃. The mixing time was controlled at 20 minutes, the holding and stirring temperature was 45℃, and the time was 1 hour. The selective electroplating process parameters were: current density 2.5 ASD, electroplating bath temperature 20℃, and cathode moving speed 0.8 m / min. This resulted in the electroplated thickness of the area to be thickened being 30 μm higher than that of the adjacent areas.

[0055] Step S6 is the same as in Example 1.

[0056] Example 3

[0057] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: In step S1, the diameter of the through hole is selected as 0.35mm.

[0058] In step S2, the thickness of the first conductive layer formed after the hole metallization process is controlled to be 20 μm.

[0059] In step S3, the through holes in the area to be thickened are arranged in a concentric multi-ring structure. The radial distance between adjacent rings in the concentric multi-ring structure is set to twice the hole diameter.

[0060] Step S4 is the same as in Example 1.

[0061] In the S5 localized thickening electroplating step, the sulfate-based acidic copper plating solution used comprises, by weight, 215 parts copper sulfate pentahydrate, 65 parts sulfuric acid, 55 parts sodium chloride, and 2.0 parts of an electroplating additive composition. The mass ratio of brightener, leveling agent, and wetting agent in the electroplating additive composition is 1:2:0.1. Specifically, the mass ratio of sodium polydithiopropane sulfonate to polyethyleneimine alkyl salt derivative in the brightener is 1:0.85. In the preparation of the brightener, sodium polydithiopropane sulfonate is dissolved in deionized water at 60°C, and the polyethyleneimine alkyl salt derivative is dissolved in deionized water at 30°C. The mixing time is controlled at 40 minutes, the holding and stirring temperature is 55°C, and the time is 2 hours. The selective electroplating process parameters are: current density 2.8 ASD, electroplating solution temperature 24°C, and cathode moving speed 1.0 m / min. Ultimately, the thickness of the area to be thickened after electroplating is 45 μm higher than that of the adjacent area.

[0062] Step S6 is the same as in Example 1.

[0063] Comparative Example 1 In this comparative example, the similarities to Example 1 will not be repeated. The differences are as follows: When forming the first surface circuit pattern in S3, a temporary metal conductive lead with a width of 0.15 mm was additionally designed and fabricated, extending from the area to be thickened to the edge of the board. During the electroplating thickening in S5, current is fed in through this lead. After electroplating, a conventional etching process is used to attempt to remove the temporary lead. The remaining steps and parameters, including the arrangement of vias, the electroplating solution formulation, and the process conditions, are consistent with those in Example 1.

[0064] Comparative Example 2

[0065] In this comparative example, the similarities to Example 2 will not be repeated. The differences are as follows: In step S3, only a single through-hole is designed and fabricated in the area to be thickened, instead of multiple through-holes arranged in a concentric multi-ring structure. The diameter of this single through-hole is the same as that used in Example 2. The remaining steps and parameters are consistent with those of Example 2.

[0066] Comparative Example 3

[0067] In this comparative example, the similarities with Example 3 will not be repeated. The differences are as follows: In step S3, although multiple through holes are fabricated in the area to be thickened, these through holes are randomly and disordered, not following a ring or array pattern, and are not a concentric multi-ring structure. The spacing between adjacent holes is also uneven. The total number of through holes is approximately the same as in Example 3. The remaining steps and parameters are consistent with those in Example 3.

[0068] Comparative Example 4

[0069] In this comparative example, the similarities to Example 1 will not be repeated. The differences are as follows: In step S5, the electroplating additive composition used contains only brightener and leveling agent, and contains no wetting agent at all. The mass ratio of brightener to leveling agent is maintained at 1:2. The total mass parts of the additive composition added are the same as in Example 1. The remaining steps and parameters are consistent with those in Example 1.

[0070] Comparative Example 5

[0071] In this comparative example, the similarities to Example 1 will not be repeated. The differences are as follows: In step S5, the process parameters for selective electroplating were adjusted. The current density was increased to 4.0 ASD, while the cathode moving speed was reduced to 0.5 m / min. The electroplating solution temperature was kept constant at 24°C. The remaining steps and parameters, including the via structure and electroplating solution formulation, remained consistent with Example 1.

[0072] Performance Test Results and Analysis

[0073] A series of performance tests were conducted on the products obtained in the examples and comparative examples, respectively. The test items and methods are as follows: Coating thickness uniformity: Using an X-ray fluorescence thickness gauge, the total coating thickness (including the initial copper layer) was measured at five points: the center point and four points (east, south, west, and north) 100 μm from the edge within each area to be thickened. The standard deviation (SD) of the five measurements was calculated to characterize the uniformity of the coating thickness; a smaller standard deviation indicates better uniformity.

[0074] Coating surface quality: The arithmetic mean roughness (Ra) of the surface of the area to be thickened was measured using a stylus surface profilometer. At the same time, the surface morphology of the coating was observed under a 100x optical microscope, and the presence of defects such as scorching, rough crystals, or nodules was recorded.

[0075] Coating adhesion: The cross-cut test is used. A 1mm x 1mm grid is cut into the surface of the area to be thickened, with the cuts reaching the substrate. Then, 3M 600 tape is applied and quickly peeled off at a 90-degree angle. The coating within the grid is observed for any peeling. No peeling is considered a pass.

[0076] Electrical Performance and Reliability: The on-resistance between the area to be thickened (as a simulated pad) and specific lines on the second surface on the back was measured using a precision LCR meter. Additionally, for the completed NFC antenna coil samples, the quality factor (Q value) at 13.56MHz was measured to evaluate antenna performance. Finally, all samples underwent thermal stress testing by being placed in a 150°C oven for 1 hour. After cooling, the plating surface was observed again, and the on-resistance was tested to check for failure phenomena such as blistering, cracking, or a sharp increase in resistance.

[0077] The results were tested, and the specific test results are shown in Table 1.

[0078] Table 1 Analysis of Test Results As can be seen from Table 1, in terms of coating thickness standard deviation and surface roughness, Examples 1 to 3 of the present invention all show excellent performance, with standard deviations between 3.5 and 4.2 μm and Ra values ​​between 0.25 and 0.32 μm, indicating that the coating deposition is uniform and the surface is smooth.

[0079] In contrast, Comparative Example 1, while also employing a porous structure, exhibited slightly higher surface roughness due to the risk of residual temporary lead etching, and microbubbles appeared after thermal stress. Comparative Example 2, using only a single via, had the worst uniformity (standard deviation 9.8 μm) and the roughest surface, indicating that a single channel leads to excessive current accumulation at the orifice, resulting in severe edge effects, causing over-deposition around the orifice while insufficient deposition in areas far from it. Comparative Example 3, although porous, failed to optimize current distribution due to its disordered arrangement, and its uniformity (7.3 μm) was significantly worse than the examples. This confirms the crucial role of concentric multi-ring or regular array arrangements in dispersing current and achieving uniform electroplating, thus realizing the goal of "distributing concentrated current more evenly throughout the entire area to be thickened."

[0080] Regarding electrical performance and reliability, the on-resistance of Examples 1 to 3 of this invention is low and stable, with high Q values, and no abnormalities were observed after thermal stress testing. This demonstrates that by optimizing the hole structure and electroplating process, this invention can achieve low-resistance, high-reliability electrical connections even without wide, flat leads. Comparative Example 5 used excessively high current density and excessively low cathode movement speed, resulting in poor coating crystallization, weakened adhesion, wrinkling after thermal stress, and increased resistance. This reveals the necessity of the process parameter range defined in this invention for ensuring the physical and electrical properties of the coating and avoiding damage to the substrate.

[0081] The effect of the electroplating additive composition was verified by Comparative Example 4. Comparative Example 4 did not use a wetting agent; although its coating uniformity and surface finish were better than Comparative Examples 2 and 3, they were slightly inferior to Example 3. The lack of a wetting agent affected the wetting of the plating solution within the densely packed pores and the expulsion of gas, which may have resulted in slight local current conduction obstruction, thus having a minor impact on deposition uniformity. The additive compositions formulated in Examples 1-3 of this invention work synergistically under their respective process conditions, jointly ensuring the stability of the leadless electroplating process and the excellent coating quality.

[0082] Test results show that Examples 1, 2, and 3 all yielded products with satisfactory performance under different parameter combinations. This invention eliminates the design and use of temporary conductive leads in traditional processes, thus removing potential hazards caused by lead residue. It avoids the problem of incomplete separation between leads and functional circuits due to same-layer etching, effectively preventing residual metal protrusions from causing bubbles and poor adhesion during subsequent cover film lamination, which could lead to open circuit risks, as well as short circuit risks that may be caused by burr residue.

[0083] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A manufacturing process for leadless electroplating of NFC products, characterized in that, Includes the following steps: S1. Substrate cutting and drilling: providing an insulating substrate and forming at least one through hole on the insulating substrate; S2. Full board conduction and initial copper plating: The insulating substrate is subjected to hole metallization treatment so that its first surface, second surface and the inner wall of the through hole are covered with a first conductive layer; S3. Formation of the first surface circuit pattern: A first circuit pattern is formed on the first surface, the first circuit pattern including at least one area to be thickened that is electrically connected to the through hole; S4. Second surface protection: A cover layer is provided on the second surface, the cover layer being able to prevent electroplating deposition; S5. Local thickening electroplating: Using the first conductive layer of the second surface as the current feed end, the electroplating current is sequentially conducted through the second surface and the first conductive layer of the inner wall of the through hole to the area to be thickened on the first surface, and the area to be thickened is selectively electroplated to thicken it. S6. Second surface circuit formation: Remove the cover layer of the second surface and form a second circuit pattern on the second surface.

2. The manufacturing process of leadless electroplating for NFC products according to claim 1, characterized in that: In step S1, the diameter of the through hole is 0.2mm-0.5mm.

3. The manufacturing process of leadless electroplating for NFC products according to claim 1, characterized in that: In step S2, the hole metallization process includes chemical copper plating and electroplating of copper, and the thickness of the first conductive layer is 8μm-20μm.

4. The manufacturing process of leadless electroplating for NFC products according to claim 1, characterized in that: In step S3, the area to be thickened includes several through holes, and the through holes are arranged in a ring or array.

5. The manufacturing process of leadless electroplating for NFC products according to claim 4, characterized in that: The multiple through holes arranged in a ring are a concentric multi-ring structure, and the diameter of the inner ring through hole is less than or equal to the diameter of the outer ring through hole. The radial distance between adjacent rings in the concentric multi-ring structure is 1.5 to 3 times the diameter of the hole.

6. The manufacturing process of leadless electroplating for NFC products according to claim 1, characterized in that: In step S5, the electroplating solution used for selective electroplating thickening is a sulfate-type acidic copper plating solution. The process parameters for selective electroplating thickening are: current density of 2.5-3.2 ASD, electroplating solution temperature of 20-28℃, and cathode moving speed of 0.8-1.2 m / min.

7. The manufacturing process of leadless electroplating for NFC products according to claim 6, characterized in that: In step S5, the thickness of the area to be thickened after electroplating is 30-60 μm higher than that of the adjacent non-thickened area.

8. The manufacturing process of leadless electroplating for NFC products according to claim 6, characterized in that: The sulfate-type acidic copper plating solution comprises, by weight, 180-250 parts of copper sulfate pentahydrate, 50-80 parts of sulfuric acid, 30-80 parts of sodium chloride, and 0.5-3.5 parts of an electroplating additive composition.

9. The manufacturing process of leadless electroplating for NFC products according to claim 8, characterized in that: The electroplating additive composition is a mixture of brightener, leveling agent and wetting agent in a mass ratio of 1:1:0.05-1:3:0.

15. The brightener is a mixture of sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivative in a mass ratio of 1:0.2-1:1.

5. The leveling agent is polyethylene glycol and the wetting agent is polyoxyethylene octylphenol ether.

10. The manufacturing process of leadless electroplating for NFC products according to claim 9, characterized in that, The preparation method of the brightener includes the following steps: M1. Weigh out sodium polydisulfide dipropane sulfonate and polyethyleneimine alkyl salt derivatives respectively at a mass ratio of 1:0.2-1:1.5; M2. Dissolve the weighed sodium polydithiopropane sulfonate in deionized water at 40-60℃; M3. Dissolve the weighed polyethyleneimine alkyl salt derivative in deionized water at 20-30℃; M4. Under stirring conditions, slowly add the solution of M2 to the solution of M1, controlling the time to be 20-40 minutes; M5. After mixing, the mixture is kept at 45-55℃ and stirred for 1-2 hours to obtain the brightening agent.

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