Tin plating solution and tin plating method for inkjet printed PCBs

Abstract

This invention discloses a tin-immersing solution for inkjet-printed PCBs, relating to the field of PCB manufacturing technology. The tin-immersing solution comprises the following components in mass concentrations: 3.0-5.0% tin oxide compound; 1.0-3.0% complexing agent; 1.0-2.0% reducing agent; 1.0-3.0% wetting agent; 1.0-3.0% accelerator; and 0.5-1.5% stabilizer. It has the following significant advantages: First, its low viscosity ensures uniform deposition of the tin-immersed layer on the PCB surface and within micropores; second, it has the ability to passivate organic impurities, as the formulation components can passivate residual organic impurities from previous processes, inhibiting their reaction with Sn. 2+ Side reactions occur, ensuring that the increase in TOC before and after the use of the solution is stably controlled at <0.28%; thirdly, the ink adhesion does not decrease after tinning, the tin layer surface is smooth and without defects, and the micropore tinning coverage rate is ≥99.92%, meeting the reliability requirements of high-precision inkjet printed circuit boards.

Description

Technical Field

[0001] This invention relates to the field of PCB manufacturing technology, and in particular to a solder immersion solution and method for inkjet-printed PCBs. Background Technology

[0002] As the core carrier of modern electronic devices, printed circuit boards (PCBs) play a crucial role in interconnecting electronic components and realizing circuit functions. The continuous evolution of electronic products towards miniaturization, lightweighting, high-density interconnection, and fine-line processing places unprecedentedly stringent demands on PCB manufacturing processes.

[0003] Traditional PCB surface treatment processes (such as hot air leveling, organic coating, electroless nickel / immersion gold, immersion silver, and immersion tin) are no longer sufficient to meet the industry's development needs. Especially in the preparation of metal protective layers, the increasingly dense circuitry presents significant challenges in terms of uniformity, stability, and film thickness control. Immersion tin technology forms a tin layer on the copper surface through a chemical displacement reaction, which is crucial for protecting copper traces, preventing oxidation / sulfidation, and ensuring subsequent packaging.

[0004] Meanwhile, PCB inkjet printing technology, with its advantages of high precision, non-contact operation, digitalization, environmental friendliness, and micron-level positioning, is becoming an emerging force in the manufacturing industry, especially in the application of solder mask layers. However, there is a severe shortage of immersion solder solutions and methods specifically adapted to inkjet printing processes. Existing immersion soldering processes are incompatible with the characteristics and requirements of inkjet printing, leading to problems such as poor solder layer adhesion, uneven thickness, and poor flatness after processing, which seriously affect PCB performance and quality.

[0005] Therefore, in order to keep pace with the development trend of electronics and meet the industry's urgent need for high-performance and environmentally friendly immersion tinning processes, it is of great practical significance and urgency to develop dedicated immersion tinning solutions and methods compatible with inkjet printing processes. This is of great value to promoting PCB technology progress and improving the quality and competitiveness of electronic products.

[0006] Existing technologies have developed various tin plating solutions. For example, CN113862650A provides a chemical tin plating solution for 5G signal boards, comprising Agent A (5%-12% tin oxide compounds, 18%-26% reducing agent, 18%-26% citric acid complexing agent, 1%-5% modified cerium chloride solution additive, 8%-10% sodium hypophosphite reducing agent, and water) and Agent B (2%-6% nonionic surfactant APG penetrant, 1%-5% quercetin and thiourea modifier, and water). This solution aims to reduce grain surface energy, promote tin ion replacement reaction, increase coating deposition rate, and reduce tin ion diffusion coefficient, thereby obtaining a tin layer with fine and uniform crystals, improved conductivity, and enhanced durability. CN114908342B discloses a tin-immersion solution containing tin compounds, complexing agents, wetting agents, accelerators, stabilizers, etc., and a method for tin-immersion on circuit boards. Its core innovation lies in replacing the thiourea component in traditional solutions, improving the stability of the solution, significantly reducing ink shedding while ensuring good tin-immersion effect, increasing product qualification rate, enhancing corrosion resistance, and ensuring a smooth tin layer surface.

[0007] However, in the face of the stringent requirements for PCB wiring accuracy and surface treatment brought about by the development of lightweight, high-density, high-frequency and high-speed electronic products, surface tinning, an environmentally friendly lead-free process, is crucial in fine-line PCBs due to its flatness, solder compatibility and cost-effectiveness. However, the inherent problems of traditional tinning processes (such as jetting and immersion) such as high chemical consumption, low coverage of micro-vias / micro-blind vias and poor process stability make it difficult to meet the industrialization needs of high-precision inkjet printing technology.

[0008] Current technical bottlenecks manifest themselves in the following ways: First, poor chemical compatibility. Traditional chemical formulations, based on fluid dynamics, exhibit high viscosity and surface tension, which can lead to uneven spreading of the tin plating solution on the ink curing surface, resulting in "narrowing linewidth" due to edge shrinkage. Second, microstructure coverage defects. For HDI boards with increased aspect ratios and micropores, traditional chemicals lack sufficient diffusion capacity, leading to "cavitation effects" and discontinuous tin layers on the hole walls, jeopardizing electrical reliability. Third, reaction kinetic mismatch. The layer-by-layer deposition characteristics of inkjet printing require chemicals with rapid low-temperature film-forming capabilities. However, existing chemicals rely on high-temperature activation and reduction reactions, increasing the risk of substrate thermal deformation and failing to meet the tin deposition rate requirements for efficient production. Fourth, high sensitivity to organic contamination. The inkjet printing environment easily introduces organic residues, and the strong complexing agents in traditional chemicals readily react with them, accelerating chemical decomposition and significantly shortening bath life.

[0009] While inkjet printing technology has become a core direction in PCB additive manufacturing due to its non-contact and digital pattern positioning advantages, existing immersion solder solutions are severely incompatible with it, hindering its application in precision devices such as 5G RF modules and IC substrates. Therefore, developing a dedicated immersion solder solution with low viscosity, high immersion solder bonding performance, and strong anti-fouling properties, along with a deposition method suitable for inkjet processes, has become an urgent task. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a tin-immersing solution and method for inkjet-printed PCBs, applicable to the tin-immersing process in PCB inkjet printing technology. This tin-immersing solution contains effective components such as stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers. It is a low-viscosity fluid, which helps ensure uniform tin-immersing. Simultaneously, the effective components in the tin-immersing solution passivate organic impurities introduced from other processes, preventing them from reacting with Sn. 2+ Side reactions result in a TOC (Total Organic Carbon) increase of less than 0.28% before and after each batch of the solution is immersed in tin. The ink on the circuit board will not fall off after immersion tinning, the tin surface is smooth, and the micropore coverage rate after immersion tinning is ≥99.92%. It has excellent immersion tinning performance and is suitable for immersion tinning process of inkjet printed circuit boards.

[0011] The stannous compound in this medicine is reactant Sn. 2+ +Cu→Sn+Cu 2+ Provides deposited tin ions, reduces interfacial tension, and promotes uniform deposition; the complexing agent stabilizes Sn. 2+ To prevent hydrolysis, regulate deposition potential, and suppress side reactions; the reducing agent provides the reduction driving force and can controllably release electrons at low temperatures (50-60℃), matching the low-temperature process requirements of inkjet printing; the wetting agent can reduce the surface tension of the solution and enhance the wettability of inkjet ink edges; the accelerator can adsorb onto the copper surface to catalyze the replacement reaction, inducing tin grain refinement and improving the deposition rate; the stabilizer can inhibit Sn... 2+ Oxidized to Sn 4+ This prevents the solution from becoming turbid and, at the same time, adjusts the deposition potential to achieve uniform film formation.

[0012] This invention provides a solder immersion solution for inkjet printing PCBs, comprising the following components by mass concentration:

[0013] Tin compounds 3.0-5.0%;

[0014] Complexing agent 1.0-3.0%;

[0015] Reducing agent 1.0-2.0%;

[0016] Wetting agent 1.0-3.0%;

[0017] Accelerator 1.0-3.0%;

[0018] Stabilizer 0.5-1.5%;

[0019] The stannous compound is selected from one or a mixture of more than one of stannous oxalate (CAS No.: 814-94-8), stannous chloride (CAS No.: 10025-69-1), and stannous methanesulfonate (CAS No.: 53408-94-9);

[0020] The complexing agent is selected from one or a mixture of more of the following: p-hydroxyphenylacetylglycine (CAS No.: 28116-23-6), N-benzyloxycarbonyl-4-hydroxy-D-2-phenylglycine (CAS No.: 26787-75-7), and (S)-3-carboxy-4-hydroxyphenylglycine (CAS No.: 55136-48-6);

[0021] The reducing agent is selected from one or a mixture of more than one of 4-hydroxybenzoyl hydrazine (CAS No.: 5351-23-5), 3-hydroxybenzoyl hydrazine (CAS No.: 5818-06-4), and 3,4-dihydroxybenzoyl hydrazine (CAS No.: 39635-11-5);

[0022] The wetting agent is one or a mixture of more of the following: trimethylolpropane triglycidyl ether (CAS No.: 30499-70-8), trihydroxypolyoxypropylene ether (CAS No.: 25791-96-2), and tri(propylene glycol) butyl ether (CAS No.: 55934-93-5);

[0023] The accelerator is selected from one or a mixture of more of 6-carboxytetramethylrhodamine (CAS No.: 91809-67-5), 6-carboxytetraethylrhodamine (CAS No.: 162926-23-0), and 5-carboxytetraethylrhodamine (CAS No.: 162926-24-1);

[0024] The stabilizer is selected from one or a mixture of more of the following: 3,3-diamino-4,4-dicarboxybiphenyl (CAS No.: 1799740-97-8), 1,3,5-tris(4′-carboxy-1,1′-biphenyl-4-yl)benzene (CAS No.: 911818-75-2), and 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid (CAS No.: 3365-90-0).

[0025] Preferably, the tin plating solution for inkjet-printed PCBs comprises components of the following mass concentrations:

[0026] Tin compounds 3.0-5.0%;

[0027] Complexing agent 1.0-3.0%;

[0028] Reducing agent 1.0-2.0%;

[0029] Wetting agent 1.0-3.0%;

[0030] Accelerator 1.0-3.0%;

[0031] Stabilizer 0.5-1.5%;

[0032] The remainder is water.

[0033] More preferably, the tin plating solution for inkjet-printed PCBs comprises components of the following mass concentrations:

[0034] Tin compounds 4.0%;

[0035] Complexing agent 2.0%;

[0036] Reducing agent 1.5%;

[0037] Wetting agent 2.0%;

[0038] Accelerator 2.0%;

[0039] Stabilizer 1.0%;

[0040] The remainder is water.

[0041] The above-mentioned method for preparing tin-immersion solution (hereinafter referred to as tin-immersion solution) for inkjet-printed PCBs involves weighing out tin oxide compound, complexing agent, reducing agent, wetting agent, accelerator and stabilizer in water according to the proportions of each component, and mixing them evenly at room temperature to obtain the tin-immersion solution.

[0042] The present invention also provides a method for immersion tin, comprising the following steps: immersion tin stage: immersing an inkjet-printed PCB in the above-mentioned immersion tin solution; the temperature of the immersion tin solution is 50-60℃, and the immersion time is 55-65s.

[0043] Preferably, in the tin immersion section, the temperature of the tin immersion solution is 55±1℃, and the soaking time is 60±3s.

[0044] Furthermore, the immersion tin method of the present invention includes a pre-dip stage before the immersion tin stage: the inkjet-printed PCB is immersed in the pre-dip stage solution; the pre-dip stage solution is composed of the immersion tin solution of the present invention with a mass concentration of 40-70% and the remainder water, the immersion temperature is 40-50℃, and the immersion time is 25-35s.

[0045] Preferably, in the pre-soaking section, the pre-soaking solution consists of 50% of the tin-immersing solution described above in this invention and the remainder water, with a soaking temperature of 45±1℃ and a soaking time of 30±3s.

[0046] Pre-soaking treatment in the pre-soaking section can reduce the introduction of harmful and polluting substances into the immersion tin solution in the immersion tin section, thereby extending the life of the immersion tin solution in the immersion tin section.

[0047] Furthermore, the immersion tin method of the present invention includes a micro-etching stage before the pre-dip stage: a micro-etching solution is sprayed onto the inkjet-printed PCB; the spraying pressure is 1.5 ± 0.5 kg / cm². 2 The spraying time is 30±15s;

[0048] Preferably, the micro-etching solution consists of 5% by mass of Shenzhen Banming Technology Co., Ltd.'s micro-etching solution BTH-2011R and the remainder water.

[0049] Micro-etching the inkjet-printed PCB in the micro-etching stage can remove oxides from the copper surface of the PCB.

[0050] Furthermore, the present invention provides a method for immersion tin, comprising the following steps: S1 micro-etching → S2 water washing → S3 pre-immersion → S4 immersion tin → S5 water washing → S6 drying.

[0051] S1 Micro-etching: Micro-etching is performed on inkjet-printed PCBs to remove oxides from the copper surface. The specific process involves a spray method. The micro-etching solution (the aforementioned micro-etching solution) contains 5% (w / w) of Shenzhen Banming Technology Co., Ltd.'s micro-etching solution BTH-2011R, with the remainder being tap water. The micro-etching tank is 2.0m long, the solution temperature is 25±5℃, the linear velocity is 4.0±0.5m / min, and the spray pressure is 1.0±0.5kg / cm². 2 ;

[0052] S2 Water Wash: The inkjet-printed PCBs that have undergone S1 micro-etching are washed with tap water. The specific process is as follows: spray method; bath solution (tap water) temperature 25±5℃; water washing tank length 1.0m; linear velocity 3.0±0.5m / min; pressure 1.0±0.5kg / cm 2 ;

[0053] S3 Pre-dip: The inkjet-printed PCB that has been washed with water in S2 is pre-dip treated with a bath solution containing the tin-retaining solution of the present invention. The specific process is as follows: an immersion method is adopted; the bath solution in the pre-dip tank uses 50% by mass of the tin-retaining solution of the present invention, and the remainder is tap water; the bath temperature is 45±1℃, the length of the pre-dip tank is 2.0m, and the linear velocity is 4.0±0.1m / min.

[0054] S4 Immersion Tin: The inkjet-printed PCB that has been pre-dipped in S3 is treated with immersion tin using the immersion tin solution of the present invention. The specific process is as follows: an immersion method is adopted; the immersion tin bath uses the immersion tin solution of the present invention, the temperature of the bath solution (the immersion tin solution of the present invention) is 55±1℃, the length of the immersion tin bath is 2.0m, and the linear speed is 2.0±0.1m / min.

[0055] S5 Water Wash: The inkjet-printed PCBs that have undergone S4 tin plating are cleaned with hot tap water. The specific process is as follows: spray method; bath solution (hot tap water) temperature 55±1℃; water washing tank length 1.0m; linear velocity 3.0±0.5m / min; pressure 1.0±0.5kg / cm². 2 ;

[0056] S6 Drying: The inkjet-printed PCBs that have been washed with S5 water are dried. The specific process is as follows: temperature 70±5℃, drying section length 2.0m; linear speed 4.0±0.3m / min.

[0057] The tin-immersing solution of this invention is composed of core components such as tin compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers. It provides a highly stable and high-coverage tin-immersing solution for PCB inkjet printing technology, with the following outstanding advantages: First, its low viscosity ensures uniform deposition of the tin layer on the PCB surface and within micropores; second, it has the ability to passivate organic impurities, as the formulation components can passivate residual organic impurities from previous processes, inhibiting their interaction with Sn. 2+ Side reactions occur, ensuring that the increase in TOC before and after the use of the solution is stably controlled at <0.28%; thirdly, the ink adhesion does not decrease after tinning, the tin layer surface is smooth and without defects, and the micropore tinning coverage rate is ≥99.92%, meeting the reliability requirements of high-precision inkjet printed circuit boards. Attached Figure Description

[0058] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 The results of scanning electron microscopy observation of the tin surface after tin plating in Example 1 are shown below.

[0060] Figure 2 The results of scanning electron microscopy observation of the tin surface after tin plating in Comparative Example 2 are shown.

[0061] Figure 3 The results of scanning electron microscopy observation of the tin surface after tin plating in Comparative Example 5 are shown.

[0062] Figure 4 The image shows the scanning electron microscope observation results of the tin surface after tin plating in Comparative Example 13. Detailed Implementation

[0063] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0064] It should be noted that the contents or concentrations mentioned in the following examples / comparative examples are all mass concentrations.

[0065] The preparation methods of the tin immersion solution in Examples 1-5 are as follows: according to the formula of Examples 1-5, tin oxide compound, complexing agent, reducing agent, wetting agent, accelerator, stabilizer and the balance water are weighed in sequence and added to the reaction vessel. The mixture is stirred and mixed at room temperature for 30 minutes to obtain the tin immersion solution of the corresponding example. The obtained tin immersion solution is sealed and stored for later use.

[0066] Example 1

[0067] The tin immersion solution in this embodiment is composed of the following components:

[0068] The content of stannous compounds is 4.0%, specifically stannous oxalate;

[0069] The complexing agent content is 2.0%, specifically hydroxyphenylacetylglycine;

[0070] The reducing agent content is 1.5%, specifically 4-hydroxybenzoyl hydrazide;

[0071] The wetting agent content is 2.0%, specifically trimethylolpropane triglycidyl ether;

[0072] The accelerator content is 2.0%, specifically 6-carboxytetramethylrhodamine;

[0073] The stabilizer content is 1.0%, specifically 3,3-diamino-4,4-dicarboxylic biphenyl;

[0074] The remainder is water.

[0075] Example 2

[0076] The tin immersion solution in this embodiment is composed of the following components:

[0077] The content of stannous compounds is 4.0%, specifically stannous chloride;

[0078] The complexing agent content is 2.0%, specifically N-benzyloxycarbonyl-4-hydroxy-D-2-phenylglycine;

[0079] The reducing agent content is 1.5%, specifically 3-hydroxybenzoyl hydrazide;

[0080] The wetting agent content is 2.0%, specifically trihydroxy polyoxypropylene ether;

[0081] The accelerator content is 2.0%, specifically 6-carboxytetraethylrhodamine;

[0082] The stabilizer content is 1.0%, specifically 1,3,5-tris(4′-carboxy-1,1′-biphenyl-4-yl)benzene;

[0083] The remainder is water.

[0084] Example 3

[0085] The tin immersion solution in this embodiment is composed of the following components:

[0086] The content of stannous compounds is 4.0%, specifically stannous methanesulfonate;

[0087] The complexing agent content is 2.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine;

[0088] The reducing agent content is 1.5%, specifically 3,4-dihydroxybenzoylhydrazine;

[0089] The wetting agent content is 2.0%, specifically tris(propylene glycol) butyl ether;

[0090] The accelerator content is 2.0%, specifically 5-carboxytetraethylrhodamine;

[0091] The stabilizer content is 1.0%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid;

[0092] The remainder is water.

[0093] Example 4

[0094] The tin immersion solution in this embodiment is composed of the following components:

[0095] The content of stannous compounds is 3.0%, specifically stannous methanesulfonate;

[0096] The complexing agent content is 1.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine;

[0097] The reducing agent content is 1.0%, specifically 3,4-dihydroxybenzoylhydrazine;

[0098] The wetting agent content is 1.0%, specifically tris(propylene glycol) butyl ether;

[0099] The accelerator content is 1.0%, specifically 5-carboxytetraethylrhodamine;

[0100] The stabilizer content is 0.5%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid;

[0101] The remainder is water.

[0102] Example 5

[0103] The tin immersion solution in this embodiment is composed of the following components:

[0104] The content of stannous compounds is 5.0%, specifically stannous methanesulfonate;

[0105] The complexing agent content is 3.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine;

[0106] The reducing agent content is 2.0%, specifically 3,4-dihydroxybenzoylhydrazine;

[0107] The wetting agent content is 3.0%, specifically tris(propylene glycol) butyl ether;

[0108] The accelerator content is 3.0%, specifically 5-carboxytetraethylrhodamine;

[0109] The stabilizer content is 1.5%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid;

[0110] The remainder is water.

[0111] Based on Example 1, tin-immersion solutions of Comparative Examples 1-12 were prepared; in addition, tin-immersion solution of Comparative Example 13 was prepared.

[0112] Comparative Example 1

[0113] The only difference between Comparative Example 1 and Example 1 is that the components do not contain tin compounds.

[0114] Comparative Example 2

[0115] The only difference between Comparative Example 2 and Example 1 is that the components do not contain a complexing agent.

[0116] Comparative Example 3

[0117] The only difference between Comparative Example 3 and Example 1 is that the components do not contain a reducing agent.

[0118] Comparative Example 4

[0119] The only difference between Comparative Example 4 and Example 1 is that the components do not contain a wetting agent.

[0120] Comparative Example 5

[0121] The only difference between Comparative Example 5 and Example 1 is that the components do not contain an accelerator.

[0122] Comparative Example 6

[0123] The only difference between Comparative Example 6 and Example 1 is that the components do not contain stabilizers.

[0124] Comparative Example 7

[0125] The only difference between Comparative Example 7 and Example 1 is that the concentration of stannous compound in the component is 10.0%.

[0126] Comparative Example 8

[0127] The only difference between Comparative Example 8 and Example 1 is that the concentration of the complexing agent in the component is 6.0%.

[0128] Comparative Example 9

[0129] The only difference between Comparative Example 9 and Example 1 is that the concentration of reducing agent in the component is 4.0%.

[0130] Comparative Example 10

[0131] The only difference between Comparative Example 10 and Example 1 is that the concentration of wetting agent in the component is 6.0%.

[0132] Comparative Example 11

[0133] The only difference between Comparative Example 11 and Example 1 is that the concentration of the accelerator in the component is 6.0%.

[0134] Comparative Example 12

[0135] The only difference between Comparative Example 12 and Example 1 is that the concentration of stabilizer in the component is 3.0%.

[0136] Comparative Example 13

[0137] Comparative Example 13 is the tin immersion solution described in prior art CN114908342B, the composition of which includes: stannous isooctanoate 6.0%; 1-aminocyclobutanecarboxylic acid 6.0%; 2,3-dicyano-6-nitronaphthalene 4.0%; tridecylmethylammonium nitrate 3.0%; dibutyltin maleate 3.0%; the balance being water.

[0138] The following performance tests were conducted on the tin immersion solutions of the above examples / comparative examples.

[0139] 1) Detect the viscosity of the tin immersion solution obtained in the above examples / comparative examples; the detection method is rotational viscometer method, and the instrument model is ZH1341 Brinell viscometer; the present invention requires the viscosity of the tin immersion solution to be 5-10 mPa·s.

[0140] The immersion tin solution of the above examples / comparative examples was used in the immersion tin process of inkjet printed PCB trial production, specifically including the following steps: S1 micro-etching → S2 water washing → S3 pre-immersion → S4 immersion tin → S5 water washing → S6 drying.

[0141] S1 Micro-etching: Micro-etching is performed on inkjet-printed PCBs to remove oxides from the copper surface. The specific process involves a spray method. The micro-etching solution (the aforementioned micro-etching solution) contains 5% (w / w) of Shenzhen Banming Technology Co., Ltd.'s micro-etching solution BTH-2011R, with the remainder being tap water. The micro-etching tank is 2.0m long, the solution temperature is 25±5℃, the linear velocity is 4.0±0.5m / min, and the spray pressure is 1.0±0.5kg / cm². 2 ;

[0142] S2 Water Wash: The PCBs that have undergone S1 micro-etching are washed with tap water. The specific process is as follows: spraying method; bath solution (tap water) temperature 25±5 ℃; water washing tank length 1.0m; linear velocity 3.0±0.5m / min; pressure 1.0±0.5kg / cm 2 ;

[0143] S3 Pre-dip: The PCBs that have undergone S2 water washing are pre-dip treated with a bath solution containing the immersion tin solution of the above examples / comparative examples. The specific process is as follows: immersion method is adopted; the bath solution in the pre-dip tank uses 50% by mass of the immersion tin solution of the above examples / comparative examples, with the remainder being tap water; the bath temperature is 45±1℃, the length of the pre-dip tank is 2.0m, and the linear speed is 4.0±0.1m / min.

[0144] S4 Immersion Tin: The immersion tin solution of the above examples / comparative examples is used to perform immersion tin treatment on the PCB that has been pre-dipped in S3. The specific process is as follows: immersion method is adopted; the immersion tin solution of the above examples / comparative examples is used in the immersion tin bath, the bath temperature is 55±1℃, the length of the immersion tin bath is 2.0m, and the linear speed is 2.0±0.1m / min.

[0145] S5 Water Wash: PCBs that have undergone S4 tin plating are cleaned with hot tap water. The specific process is as follows: spray method; bath solution (hot tap water) temperature 55±1℃; water washing tank length 1.0m; linear velocity 3.0±0.5 m / min; pressure 1.0±0.5 kg / cm². 2 ;

[0146] S6 Drying: The PCBs that have been washed with S5 water are dried. The specific process is as follows: temperature 70±5℃, drying section length 2.0m; linear speed 4.0±0.3m / min.

[0147] 2) Visually inspect whether ink drips off the PCB after tin plating; this invention requires that no ink drips off after tin plating.

[0148] 3) Use a scanning electron microscope to observe whether the tin surface is flat after tin deposition; the instrument model is Hitachi SU3800 scanning electron microscope; this invention requires that the tin surface be flat after tin deposition.

[0149] 4) Calculate the micropore coverage rate after tin plating; the detection method is 3D X-ray microscopy, and the instrument is Rigaku nano3DX X-ray microscope from Rigaku Corporation, Japan; this invention requires a micropore coverage rate of ≥95% after tin plating.

[0150] 5) Detect the TOC (Total Organic Carbon) value of each batch of immersion tin solution; use an M113847 TOC analyzer, and the detection method is to detect the TOC value of the immersion tin solution before and after each production batch, and calculate the TOC increase of the solution in each production batch; this invention requires that the TOC increase of the solution in each production batch be <5%.

[0151] The performance test results of the tin immersion solutions in Examples 1-5 and Comparative Examples 1-13 are shown in Table 1 below:

[0152] Table 1 Performance Test Results

[0153]

[0154] Example 1: Scanning electron microscopy observation results of the tin surface after tin plating. Figure 1 As shown; the scanning electron microscope observation results of the tin surface after tin plating in Comparative Example 2 are as follows. Figure 2 As shown; the scanning electron microscope observation results of the tin surface after tin plating in Comparative Example 5 are as follows. Figure 3 As shown; the scanning electron microscope observation results of the tin surface after tin plating in Comparative Example 13 are as follows. Figure 4 As shown.

[0155] As can be seen from the test results of Examples 1-5 in Table 1, the viscosity of the immersion tin solution of the present invention is 6.05-6.22 mPa·s, which has good immersion tin performance. After immersion tinning of inkjet printed PCBs, the ink on the PCB will not fall off, the tin surface is flat, the micropore coverage rate after immersion tinning is ≥99.92%, and the TOC increase before and after immersion tinning of each batch of solution is <0.28%, which meets the requirements of inkjet printed PCB immersion tinning process.

[0156] The difference between Comparative Examples 1-6 and Example 1 is that they lacked one of the following components: stannous compound, complexing agent, reducing agent, wetting agent, accelerator, and stabilizer, respectively. Test results show that the stannous compound provides Sn element for tin deposition and is an essential component in the tin deposition solution formulation; its absence leads to a lack of tin on the circuit board surface. The complexing agent, reducing agent, wetting agent, accelerator, and stabilizer all have a certain impact on the tin deposition reaction; the absence of any one of them will lead to a decrease in the tin deposition effect, resulting in problems such as oil shedding, uneven tin surface, increased solution viscosity, decreased coverage of tin micropores, and increased TOC. This indicates that the excellent performance of the tin deposition solution of this invention is the result of the interaction of its components; the absence of any one component will affect the product's performance.

[0157] The difference between Comparative Examples 7-12 and Example 1 is that the concentrations of stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers in the single components of the tin-immersion solution are all higher than the upper limit of the concentration of the tin-immersion solution of the present invention. The test results show that, compared with Examples 1-5, excessively high concentrations of stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers will not affect the performance of the tin-immersion solution, but excessively high concentrations will increase the cost of the solution. Therefore, the concentrations of each component of the tin-immersion solution of the present invention should not be too high, and good tin-immersion performance of the solution can be guaranteed within the concentration range of the examples.

[0158] Comparative Example 13 uses an existing patented immersion tin solution. The test results show that the immersion tin solution of the present invention has a better bonding effect on printing ink, a smoother tin surface, lower solution viscosity, higher coverage of immersion tin micropores, and a lower increase in TOC of the solution, making it suitable for immersion tinning process of inkjet printed PCBs.

[0159] In summary, the immersion tin solution of this invention is composed of core components such as tin compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers. It provides a highly stable and high-coverage immersion tin solution for PCB inkjet printing technology, with the following outstanding advantages: First, its low viscosity ensures uniform deposition of the immersion tin layer on the PCB surface and within micropores; second, it has the ability to passivate organic impurities, as the formulation components can passivate residual organic impurities from previous processes, inhibiting their interaction with Sn. 2+ Side reactions occur, ensuring that the increase in TOC before and after the use of the solution is stably controlled at <0.28%; thirdly, the ink adhesion does not decrease after tinning, the tin layer surface is smooth and without defects, and the micropore tinning coverage rate is ≥99.92%, meeting the reliability requirements of high-precision inkjet printed circuit boards.

[0160] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A solder immersion solution for inkjet printing PCBs, characterized in that, Components including the following mass concentrations: Tin compounds 3.0-5.0%; Complexing agent 1.0-3.0%; Reducing agent 1.0-2.0%; Wetting agent 1.0-3.0%; Accelerator 1.0-3.0%; Stabilizer 0.5-1.5%; The remainder is water; The stannous compound is selected from one or a mixture of more than one of stannous oxalate, stannous chloride, and stannous methanesulfonate; The complexing agent is selected from one or a mixture of more than one of p-hydroxyphenylacetylglycine, N-benzyloxycarbonyl-4-hydroxy-D-2-phenylglycine, and (S)-3-carboxyl-4-hydroxyphenylglycine; The reducing agent is selected from one or a mixture of more than one of 4-hydroxybenzoyl hydrazide, 3-hydroxybenzoyl hydrazide, and 3,4-dihydroxybenzoyl hydrazide; The wetting agent is selected from one or a mixture of more than one of trimethylolpropane triglycidyl ether, trihydroxypolyoxypropylene ether, and tri(propylene glycol) butyl ether; The accelerator is selected from one or a mixture of more than one of 6-carboxytetramethylrhodamine, 6-carboxytetraethylrhodamine, and 5-carboxytetraethylrhodamine; The stabilizer is selected from one or a mixture of more of the following: 3,3-diamino-4,4-dicarboxybiphenyl, 1,3,5-tris(4′-carboxy-1,1′-biphenyl-4-yl)benzene, and 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid.

2. The tin plating solution for inkjet-printed PCBs according to claim 1, characterized in that, It consists of components with the following mass concentrations: Tin compounds 4.0%; Complexing agent 2.0%; Reducing agent 1.5%; Wetting agent 2.0%; Accelerator 2.0%; Stabilizer 1.0%; The remainder is water.

3. The method for preparing the immersion tin solution for inkjet-printed PCBs as described in claim 1 or 2, characterized in that, According to the proportions of each group, weigh out the stannous compound, complexing agent, reducing agent, wetting agent, accelerator, and stabilizer in sequence, add them to water, and mix them evenly at room temperature to obtain the final product.

4. A method for immersion tin, characterized in that, The process includes the following steps: Immersion soldering: The inkjet-printed PCB is immersed in the immersion soldering solution for inkjet-printed PCBs as described in claim 1 or 2; the temperature of the immersion soldering solution for inkjet-printed PCBs is 50-60℃, and the immersion time is 55-65s.

5. The tin-immersion method according to claim 4, characterized in that, In the aforementioned immersion tin section, the temperature of the immersion tin solution used for inkjet printing PCBs is 55±1℃, and the immersion time is 60±3s.

6. The tin-immersion method according to claim 5, characterized in that, Before the immersion tin stage, there is a pre-dip stage: the inkjet-printed PCB is immersed in the pre-dip stage solution; the pre-dip stage solution consists of immersion tin solution for inkjet-printed PCBs with a mass concentration of 40-70% as described in claim 1 or 2 and the remainder water, the immersion temperature is 40-50℃, and the immersion time is 25-35s.

7. The tin-immersion method according to claim 6, characterized in that, In the pre-immersion section, the solution consists of 50% of the immersion tin solution used for inkjet printing PCBs and the remainder water. The immersion temperature is 45±1℃ and the immersion time is 30±3s.

8. The tin-immersion method according to claim 7, characterized in that, Before the pre-impregnation stage, a micro-etching stage is also included: the PCB is printed using inkjet printing with a micro-etching solution sprayed on it; the spraying pressure is 1.5 ± 0.5 kg / cm². 2 The spraying time is 30±15s.

9. A method for immersion tin, characterized in that, Includes the following steps: S1 Micro-etching → S2 Water washing → S3 Pre-immersion → S4 Tin immersion → S5 Water washing → S6 Drying; S1 Micro-etching: Micro-etching of inkjet-printed PCBs; the specific process is as follows: a spray method is used, the micro-etching tank solution contains 5% micro-etching solution by mass concentration, and the remainder is tap water; the micro-etching tank is 2.0m long, the micro-etching tank solution temperature is 25±5℃, the linear velocity is 4.0±0.5m / min, and the spray pressure is 1.0±0.5kg / cm. 2 ; S2 Water Wash: The inkjet-printed PCBs that have undergone S1 micro-etching are washed with tap water. The specific process is as follows: a spray method is used; the bath solution is tap water, the temperature is 25±5℃, the length of the washing tank is 1.0m; the linear velocity is 3.0±0.5m / min, and the pressure is 1.0±0.5kg / cm. 2 ; S3 Pre-immersion: The inkjet-printed PCB that has been washed with water in S2 is pre-immersed in a bath containing the tin-retaining solution for inkjet-printed PCBs as described in claim 1 or 2. The specific process is as follows: an immersion method is adopted; the bath solution in the pre-immersion tank uses 50% by mass of the tin-retaining solution for inkjet-printed PCBs as described in claim 1 or 2, with the remainder being tap water; the bath temperature is 45±1℃, the length of the pre-immersion tank is 2.0m, and the linear velocity is 4.0±0.1m / min. S4 Immersion Tin: The inkjet-printed PCB that has undergone S3 pre-dip treatment is immersion tinned using the immersion tin solution for inkjet-printed PCBs as described in claim 1 or 2. The specific process is as follows: an immersion method is adopted; the immersion tin bath uses the immersion tin solution for inkjet-printed PCBs as described in claim 1 or 2, the bath temperature is 55±1℃, the length of the immersion tin bath is 2.0m, and the linear velocity is 2.0±0.1m / min. S5 Water Wash: The inkjet-printed PCBs that have undergone S4 tin plating are cleaned with hot tap water. The specific process is as follows: spraying method; the bath solution is hot tap water at a temperature of 55±1℃; the washing tank is 1.0m long; the linear velocity is 3.0±0.5m / min; and the pressure is 1.0±0.5kg / cm². 2 ; S6 Drying: The inkjet-printed PCBs that have been washed with S5 water are dried. The specific process is as follows: temperature 70±5℃, drying section length 2.0m; linear speed 4.0±0.3m / min.

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