Tin immersion liquid medicine for ink-jet printing of PCB and tin immersion method

Abstract

The invention discloses a tin immersion liquid medicine for ink-jet printing of a PCB, and relates to the technical field of PCB production. The tin immersion liquid medicine comprises the following components in mass concentration: 3.0-5.0% of a stannous compound; 1.0%-3.0% of a complexing agent; 1.0%-2.0% of a reducing agent; 1.0%-3.0% of a wetting agent; 1.0%-3.0% of an accelerant; the liquid medicine has the following prominent advantages: firstly, the liquid medicine has the characteristic of low viscosity, and is in a low-viscosity fluid state, so that a tin immersion layer is ensured to be uniformly deposited on the surface of the PCB and in micropores; 2, the liquid medicine has the capability of passivating organic impurities, and the formula components can passivate the residual organic impurities in the previous process and inhibit the residual organic impurities from generating side reaction with Sn < 2 + >, so that the TOC amplification before and after the liquid medicine is used is stably controlled to be less than 0.28%; and thirdly, the adhesive force of the ink is not attenuated after tin immersion, the surface of a tin layer is flat and has no defect, the micropore tin immersion coverage rate is greater than or equal to 99.92%, and the reliability requirement of a high-precision ink-jet printed circuit board is met.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB production, and particularly to a tin immersion solution and a tin immersion method for inkjet printing PCB. Background Art

[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. With the continuous evolution of electronic products towards miniaturization, lightweight, high-density interconnection, and fine circuits, unprecedentedly stringent requirements have been imposed 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 able to meet the development needs of the industry. Especially in the preparation of metal protective layers, the increasing density of circuits has brought huge challenges in terms of uniformity, stability, and film thickness control. The tin immersion process forms a tin layer on the copper surface through a chemical displacement reaction, which is crucial for protecting copper wires, preventing oxidation / sulfuration, and ensuring subsequent packaging.

[0004] At the same time, PCB inkjet printing technology, with its advantages of high precision, non-contact, digitalization, environmental protection, and micron-level positioning, is emerging as a new force in the manufacturing field, especially in the application of solder mask layers. However, there is a severe shortage of tin immersion solutions and methods specifically adapted to the inkjet printing process. The existing tin immersion processes are incompatible with the characteristic requirements of inkjet printing, resulting in problems such as poor adhesion of the tin layer, uneven thickness, and poor flatness after treatment, seriously affecting the performance and quality of PCBs.

[0005] Therefore, in order to conform to the development trend of electronics and meet the urgent needs of the industry for high-performance and environmentally friendly tin immersion processes, the development of dedicated tin immersion solutions and methods compatible with the inkjet printing process is of great practical significance and urgency, and is of great value for promoting PCB technology progress and enhancing the quality and competitiveness of electronic products.

[0006] Multiple immersion tin plating solution schemes have been developed in the prior art. For example, CN113862650A provides a chemical immersion tin plating solution for 5G signal boards, which includes Agent A (5%-12% stannous compounds, 18%-26% reducing agents, 18%-26% citric acid complexing agents, 1%-5% modified cerium chloride solution additives, 8%-10% sodium hypophosphite reducing agents and water) and Agent B (2%-6% non-ionic surfactant APG penetrants, 1%-5% quercetin and thiourea modifiers and water); this scheme aims to reduce the surface energy of the crystal grains, promote the tin ion replacement reaction, increase the deposition rate of the coating, and reduce the tin ion diffusion coefficient, so as to obtain a tin layer with fine and uniform crystallization, improved conductive strength and service life. CN114908342B discloses an immersion tin plating solution containing stannous compounds, complexing agents, wetting agents, accelerators, stabilizers, etc. and a method for immersing tin on a circuit board; its core innovation lies in replacing the thiourea component in the traditional solution, improving the stability of the solution, significantly reducing the ink peeling while ensuring good tin immersion effect, improving the product qualification rate, and enhancing the corrosion resistance ability to ensure the smoothness of the tin layer surface.

[0007] However, in the face of the stringent requirements for PCB wiring accuracy and surface treatment in the development of electronic products towards lightweight, high density, high frequency and high speed, although the surface immersion tin plating, an environmentally friendly lead-free process, is crucial in fine-line PCBs due to its flatness, soldering compatibility and cost-effectiveness, the inherent problems of the traditional immersion tin plating process (such as jet flow type, dipping type), such as high solution consumption, low coverage rate of micro-holes / micro-blind holes, and poor process stability, make it difficult to meet the industrialization requirements of high-precision inkjet printing technology.

[0008] The specific manifestations of the current technical bottlenecks are as follows: First, the poor adaptability of the solution. The traditional solution formula is designed based on hydrodynamics. Its high viscosity and high surface tension characteristics are likely to cause the uneven spreading of the immersion tin plating solution on the surface of the cured ink, reducing the "line width narrowing" problem caused by edge shrinkage. Second, the micro-structure coverage defect: For the micro-holes of HDI boards with an increasing aspect ratio, the insufficient diffusion ability of the traditional solution leads to the "cavitation effect", resulting in discontinuous tin layers on the hole walls, endangering the electrical reliability. Third, the reaction kinetics mismatch: The layer-by-layer deposition characteristics of inkjet printing require the solution to have the ability to form a film quickly at low temperature. However, the existing solutions rely on high-temperature activation reduction reactions, which not only increase the risk of substrate thermal deformation, but also their tin deposition rate cannot meet the requirements of high-efficiency production. Fourth, high sensitivity to organic pollution: The inkjet printing environment is likely to introduce organic residues, and the strong complexing agents in the traditional solutions are prone to side reactions with them, accelerating the decomposition of the solution and significantly shortening the bath life.

[0009] Although inkjet printing technology has become the core direction of PCB additive manufacturing due to its advantages of non-contact and digital graphic positioning, the existing immersion tin chemical system does not match it seriously, which hinders the application of this technology in precision devices such as 5G RF modules and IC substrates. Therefore, it has become an urgent task to develop a special immersion tin chemical with low viscosity, high tin deposition bonding performance and strong anti-pollution characteristics, and to develop a deposition method suitable for the inkjet process. Summary of the Invention

[0010] Aiming at the disadvantages of the existing technology, the present invention provides an immersion tin chemical and an immersion tin method for inkjet printing PCB, which can be used in the immersion tin process of PCB inkjet printing technology. The immersion tin chemical contains effective components such as stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, stabilizers, etc., and is a low-viscosity fluid, which helps to improve the uniformity of tin deposition. At the same time, the effective components in the immersion tin chemical can passivate the organic impurities brought in by other processes and prevent them from reacting with Sn 2+ side reactions, so that the increase of TOC (total organic carbon) before and after tin deposition in each batch of chemical is < 0.28%, the ink on the circuit board will not fall off after tin deposition, the tin surface is flat, and the micropore coverage rate after tin deposition is ≥ 99.92%. It has excellent tin deposition performance and is suitable for the immersion tin process of inkjet printing circuit boards.

[0011] The stannous compound in this chemical provides tin ions for the reaction Sn 2+ +Cu→Sn+Cu 2+ and can also reduce the interfacial tension to promote uniform deposition; the complexing agent can stabilize Sn 2+ to prevent hydrolysis, adjust the deposition potential and inhibit side reactions; the reducing agent provides a reduction driving force and can controllably release electrons at low temperature (50-60 °C) to meet the low-temperature process requirements of inkjet printing; the wetting agent can reduce the surface tension of the chemical and enhance the wettability of the edge of the inkjet ink; the accelerator can adsorb on the copper surface to catalyze the displacement reaction to induce tin grain refinement and improve the deposition rate; the stabilizer can inhibit the oxidation of Sn 2+ to Sn 4+ prevent the chemical from becoming turbid, and at the same time adjust the deposition potential to achieve uniform film formation.

[0012] The present invention provides an immersion tin chemical for inkjet printing PCB, which comprises the following components in mass concentration: Stannous compound 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 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 methylsulfonate (CAS No.: 53408-94-9); The complexing agent is selected from one or a mixture of more than one of p-hydroxyphenylacetylglycine (CAS No.: 28116-23-6), N-carbobenzoxy-4-hydroxy-D-2-phenylglycine (CAS No.: 26787-75-7), and (S)-3-carboxy-4-hydroxyphenylglycine (CAS No.: 55136-48-6); The reducing agent is selected from one or a mixture of more than one of 4-hydroxybenzohydrazide (CAS No.: 5351-23-5), 3-hydroxybenzohydrazide (CAS No.: 5818-06-4), and 3,4-dihydroxybenzohydrazide (CAS No.: 39635-11-5); The wetting agent is selected from one or a mixture of more than one of trimethylolpropane triglycidyl ether (CAS No.: 30499-70-8), trihydroxy polyoxypropylene ether (CAS No.: 25791-96-2), and tris(propylene glycol) butyl ether (CAS No.: 55934-93-5); The accelerator is selected from one or a mixture of more than one of 6-carboxytetramethylrhodamine (CAS No.: 91809-67-5), 6-carboxytetraethylrhodamine (CAS No.: 162926-23-0), and 5-carboxytetraethylrhodamine (CAS No.: 162926-24-1); The stabilizer is selected from one or a mixture of more than one of 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).

[0013] Preferably, the stannous electroplating solution for inkjet printing PCB consists of components with the following mass concentrations: Stannous compound 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 balance is water.

[0014] More preferably, the stannous immersion solution for inkjet printing PCB consists of components with the following mass concentrations: Stannous compound: 4.0%; Complexing agent: 2.0%; Reducing agent: 1.5%; Wetting agent: 2.0%; Accelerator: 2.0%; Stabilizer: 1.0%; The balance is water.

[0015] The preparation method of the above stannous immersion solution for inkjet printing PCB (hereinafter referred to as stannous immersion solution) is as follows: According to the proportion of each component, weigh the stannous compound, complexing agent, reducing agent, wetting agent, accelerator, and stabilizer in sequence and add them to water, and mix evenly at room temperature to obtain the stannous immersion solution.

[0016] The present invention also provides a stannous immersion method, which includes the following steps. Stannous immersion section: Immerse the inkjet printed PCB in the above stannous immersion solution; the temperature of the stannous immersion solution is 50 - 60°C, and the immersion time is 55 - 65 s.

[0017] Preferably, in the stannous immersion section, the temperature of the stannous immersion solution is 55 ± 1°C, and the immersion time is 60 ± 3 s.

[0018] Furthermore, in the stannous immersion method of the present invention, before the stannous immersion section, there is also a pre - immersion section: Immerse the inkjet printed PCB in the pre - immersion section solution; the pre - immersion section solution consists of 40 - 70% of the above stannous immersion solution of the present invention by mass concentration and the balance water, the immersion temperature is 40 - 50°C, and the immersion time is 25 - 35 s.

[0019] Preferably, in the pre - immersion section, the pre - immersion section solution consists of 50% of the above stannous immersion solution of the present invention by mass concentration and the balance water, the immersion temperature is 45 ± 1°C, and the immersion time is 30 ± 3 s.

[0020] The pre - immersion treatment in the pre - immersion section can reduce the harmful and polluting substances brought into the stannous immersion solution in the stannous immersion section, so as to extend the service life of the stannous immersion solution in the stannous immersion section.

[0021] Furthermore, in the stannous immersion method of the present invention, before the pre - immersion section, there is also a micro - etching section: Spray the inkjet printed PCB with a micro - etching solution; the spray pressure is 1.5 ± 0.5 kg / cm 2 , and the spray time is 30 ± 15 s; Preferably, the micro - etching solution consists of 5% of the micro - etching solution BTH - 2011R of Shenzhen Banming Technology Co., Ltd. by mass concentration and the balance water.

[0022] Micro - etching the inkjet printed PCB in the micro - etching section can remove the oxides on the copper surface of the PCB.

[0023] Furthermore, the present invention provides a tin immersion method, comprising the following steps: S1 micro-etching → S2 water washing → S3 pre-immersion → S4 tin immersion → S5 water washing → S6 drying; S1 micro-etching: Micro-etch the inkjet-printed PCB to remove the oxides on the copper surface; The specific process is as follows: adopting the spraying method, the solution in the micro-etching tank (the above-mentioned micro-etching solution) contains 5% by mass concentration of the micro-etching solution BTH-2011R of Shenzhen Banming Technology Co., Ltd., and the balance is tap water; The length of the micro-etching tank is 2.0 m, the temperature of the solution in the micro-etching tank is 25 ± 5 °C, the linear speed is 4.0 ± 0.5 m / min, and the spraying pressure is 1.0 ± 0.5 kg / cm 2 ; S2 water washing: Wash the inkjet-printed PCB that has undergone S1 micro-etching with tap water. The specific process is as follows: adopting the spraying method; the temperature of the tank solution (tap water) is 25 ± 5 °C, and the length of the water washing tank is 1.0 m; the linear speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S3 pre-immersion: Perform pre-immersion treatment on the inkjet-printed PCB that has undergone S2 water washing with the tank solution containing the tin immersion solution of the present invention. The specific process is as follows: adopting the immersion method; the tank solution in the pre-immersion tank uses 50% by mass concentration of the tin immersion solution of the present invention, and the balance is tap water; the temperature of the tank solution is 45 ± 1 °C, the length of the pre-immersion tank is 2.0 m; the linear speed is 4.0 ± 0.1 m / min; S4 tin immersion: Perform tin immersion treatment on the inkjet-printed PCB that has undergone S3 pre-immersion with the tin immersion solution of the present invention. The specific process is as follows: adopting the immersion method; the tin immersion tank uses the tin immersion solution of the present invention, the temperature of the tank solution (the tin immersion solution of the present invention) is 55 ± 1 °C, the length of the tin immersion tank is 2.0 m; the linear speed is 2.0 ± 0.1 m / min; S5 water washing: Wash the inkjet-printed PCB that has undergone S4 tin immersion with hot tap water. The specific process is as follows: adopting the spraying method; the temperature of the tank solution (hot tap water) is 55 ± 1 °C, the length of the water washing tank is 1.0 m; the linear speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S6 drying: Perform drying treatment on the inkjet-printed PCB that has undergone S5 water washing. The specific process is as follows: the temperature is 70 ± 5 °C, and the length of the drying section is 2.0 m; the linear speed is 4.0 ± 0.3 m / min.

[0024] The stannous plating solution of the present invention is composed of core components such as stannous compounds, complexing agents, reducing agents, wetting agents, accelerating agents, and stabilizers, providing a high-stability and high-coverage stannous plating solution for PCB inkjet printing technology, with the following outstanding advantages: First, it has a low-viscosity property, and the solution is in a low-viscosity fluid state, ensuring uniform deposition of the stannous plating layer on the PCB surface and in the micro-holes; Second, it has the ability to passivate organic impurities. The formulation components can passivate the residual organic impurities in the previous process and inhibit their side reactions with Sn 2+ from occurring, and the increase in TOC before and after the use of the solution is stably controlled at <0.28%; Third, the ink adhesion after stannous plating does not decay, the surface of the tin layer is flat without defects, and the stannous plating coverage rate in the micro-holes is ≥99.92%, meeting the reliability requirements of high-precision inkjet printed circuit boards. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 It is the scanning electron microscope observation result of the tin surface after stannous plating in Example 1; Figure 2 It is the scanning electron microscope observation result of the tin surface after stannous plating in Comparative Example 2; Figure 3 It is the scanning electron microscope observation result of the tin surface after stannous plating in Comparative Example 5; Figure 4 It is the scanning electron microscope observation result of the tin surface after stannous plating in Comparative Example 13. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0028] It should be noted that the contents or concentrations described in the following examples / comparative examples are all mass concentrations.

[0029] The preparation methods of the stannous plating solutions in the following Examples 1-5 are as follows: According to the formulations of Examples 1-5, stannous compounds, complexing agents, reducing agents, wetting agents, accelerating agents, stabilizers, and the balance of water are sequentially weighed and added to a reaction kettle, and stirred and mixed at room temperature for 30 minutes to obtain the stannous plating solutions corresponding to the examples. The obtained stannous plating solutions are sealed and stored for standby.

[0030] Example 1

[0031] The stannous plating solution of this example consists of the following components: The content of stannous compound is 4.0%, specifically stannous oxalate; The content of complexing agent is 2.0%, specifically hydroxyphenylacetylglycine; The content of reducing agent is 1.5%, specifically 4-hydroxybenzohydrazide; The content of wetting agent is 2.0%, specifically trimethylolpropane triglycidyl ether; The content of accelerator is 2.0%, specifically 6-carboxytetramethylrhodamine; The content of stabilizer is 1.0%, specifically 3,3-diamino-4,4-dicarboxybiphenyl; The balance is water.

[0032] Example 2

[0033] The stannous plating solution of this example consists of the following components: The content of stannous compound is 4.0%, specifically stannous chloride; The content of complexing agent is 2.0%, specifically N-carbobenzoxy-4-hydroxy-D-2-phenylglycine; The content of reducing agent is 1.5%, specifically 3-hydroxybenzohydrazide; The content of wetting agent is 2.0%, specifically trihydroxy polyoxypropylene ether; The content of accelerator is 2.0%, specifically 6-carboxytetraethylrhodamine; The content of stabilizer is 1.0%, specifically 1,3,5-tris(4'-carboxy-1,1'-biphenyl-4-yl)benzene; The balance is water.

[0034] Example 3

[0035] The stannous plating solution of this example consists of the following components: The content of stannous compound is 4.0%, specifically stannous methylsulfonate; The content of complexing agent is 2.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine; The content of reducing agent is 1.5%, specifically 3,4-dihydroxybenzohydrazide; The content of wetting agent is 2.0%, specifically tris(propylene glycol) butyl ether; The content of accelerator is 2.0%, specifically 5-carboxytetraethylrhodamine; The content of stabilizer is 1.0%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid; The balance is water.

[0036] Example 4

[0037] The stannous plating solution of this embodiment consists of the following components: The content of stannous compound is 3.0%, specifically stannous methylsulfonate; The content of complexing agent is 1.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine; The content of reducing agent is 1.0%, specifically 3,4-dihydroxybenzohydrazide; The content of wetting agent is 1.0%, specifically tri(propylene glycol) butyl ether; The content of accelerator is 1.0%, specifically 5-carboxytetraethylrhodamine; The content of stabilizer is 0.5%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid; The balance is water.

[0038] Example 5

[0039] The stannous plating solution of this embodiment consists of the following components: The content of stannous compound is 5.0%, specifically stannous methylsulfonate; The content of complexing agent is 3.0%, specifically (S)-3-carboxy-4-hydroxyphenylglycine; The content of reducing agent is 2.0%, specifically 3,4-dihydroxybenzohydrazide; The content of wetting agent is 3.0%, specifically tri(propylene glycol) butyl ether; The content of accelerator is 3.0%, specifically 5-carboxytetraethylrhodamine; The content of stabilizer is 1.5%, specifically 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid; The balance is water.

[0040] Based on Example 1, the stannous plating solutions of Comparative Examples 1-12 were prepared; in addition, the stannous plating solution of Comparative Example 13 was configured.

[0041] Comparative Example 1 Compared with Example 1, the only difference in Comparative Example 1 is that the component does not contain stannous compound.

[0042] Comparative Example 2 Compared with Example 1, the only difference in Comparative Example 2 is that the component does not contain complexing agent.

[0043] Comparative Example 3 Compared with Example 1, the only difference in Comparative Example 3 is that the component does not contain reducing agent.

[0044] Comparative Example 4 Comparative Example 4 is different from Example 1 only in that the component does not contain a wetting agent.

[0045] Comparative Example 5 Comparative Example 5 is different from Example 1 only in that the component does not contain an accelerator.

[0046] Comparative Example 6 Comparative Example 6 is different from Example 1 only in that the component does not contain a stabilizer.

[0047] Comparative Example 7 Comparative Example 7 is different from Example 1 only in that the concentration of stannous compound in the component is 10.0%.

[0048] Comparative Example 8 Comparative Example 8 is different from Example 1 only in that the concentration of complexing agent in the component is 6.0%.

[0049] Comparative Example 9 Comparative Example 9 is different from Example 1 only in that the concentration of reducing agent in the component is 4.0%.

[0050] Comparative Example 10 Comparative Example 10 is different from Example 1 only in that the concentration of wetting agent in the component is 6.0%.

[0051] Comparative Example 11 Comparative Example 11 is different from Example 1 only in that the concentration of accelerator in the component is 6.0%.

[0052] Comparative Example 12 Comparative Example 12 is different from Example 1 only in that the concentration of stabilizer in the component is 3.0%.

[0053] Comparative Example 13 Comparative Example 13 is the tin immersion solution described in the prior art CN114908342B, and its components include: 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 is water.

[0054] The following performance tests are carried out on the tin immersion solutions of the above examples / comparative examples.

[0055] 1) Detect the viscosity of the tin immersion solutions obtained in the above examples / comparative examples; the detection method is the rotational viscometer method, and the instrument model is the Brookfield viscometer ZH1341; the present invention requires that the viscosity of the tin immersion solution is 5-10 mPa·s.

[0056] The immersion tin solutions of the above-mentioned examples / comparative examples were respectively used in the immersion tin process of the inkjet-printed PCB pilot production, which specifically included the following steps: S1 Micro-etching → S2 Water washing → S3 Pre-impregnation → S4 Immersion tin → S5 Water washing → S6 Drying; S1 Micro-etching: The inkjet-printed PCB that has undergone inkjet printing is micro-etched to remove the oxides on the copper surface; the specific process is as follows: By the spraying method, the solution in the micro-etching tank (the above-mentioned micro-etching solution) contains 5% by mass concentration of the micro-etching solution BTH-2011R of Shenzhen Banming Technology Co., Ltd., and the balance is tap water; the length of the micro-etching tank is 2.0 m, the temperature of the solution in the micro-etching tank is 25 ± 5 °C, the linear speed is 4.0 ± 0.5 m / min, and the spraying pressure is 1.0 ± 0.5 kg / cm 2 ; S2 Water washing: The PCB that has undergone S1 micro-etching is washed with tap water, and the specific process is as follows: By the spraying method; the temperature of the tank solution (tap water) is 25 ± 5 °C, and the length of the water washing tank is 1.0 m; the linear speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S3 Pre-impregnation: The PCB that has undergone S2 water washing is pre-impregnated with the tank solution containing the immersion tin solutions of the above-mentioned examples / comparative examples, and the specific process is as follows: By the immersion method; the tank solution in the pre-impregnation tank uses 50% by mass concentration of the immersion tin solutions of the above-mentioned examples / comparative examples, and the balance is tap water; the temperature of the tank solution is 45 ± 1 °C, and the length of the pre-impregnation tank is 2.0 m; the linear speed is 4.0 ± 0.1 m / min; S4 Immersion tin: The PCB that has undergone S3 pre-impregnation is immersed with the immersion tin solutions of the above-mentioned examples / comparative examples, and the specific process is as follows: By the immersion method; the immersion tin solutions of the above-mentioned examples / comparative examples are used in the immersion tin tank, the temperature of the tank solution is 55 ± 1 °C, and the length of the immersion tin tank is 2.0 m; the linear speed is 2.0 ± 0.1 m / min; S5 Water washing: The PCB that has undergone S4 immersion tin is washed with hot tap water, and the specific process is as follows: By the spraying method; the temperature of the tank solution (hot tap water) is 55 ± 1 °C, and the length of the water washing tank is 1.0 m; the linear speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S6 Drying: The PCB that has undergone S5 water washing is dried, and the specific process is as follows: The temperature is 70 ± 5 °C, and the length of the drying section is 2.0 m; the linear speed is 4.0 ± 0.3 m / min.

[0057] 2) Visually observe whether the ink drops off the PCB after immersion tin; the present invention requires that the ink does not drop off after immersion tin.

[0058] 3) Use a scanning electron microscope to observe whether the surface of the tin is flat after immersion tin; the model of the instrument is Hitachi su3800 scanning electron microscope; the present invention requires that the surface of the tin is flat after immersion tin.

[0059] 4) Calculate the micropore coverage rate after immersion tinning; the detection method is 3D X-ray microscopy, and the instrument model is Rigaku nano3D X-ray microscope of Rigaku Corporation, Japan; the present invention requires that the micropore coverage rate after immersion tinning ≥ 95%.

[0060] 5) Detect the TOC (total organic carbon) value of the immersion tinning solution for each production batch; use the M113847 type TOC detector. The detection method is to detect the TOC value of the bath solution in the immersion tinning tank before the start and after the end of each production batch, and calculate the TOC increase of the bath solution for each production batch; the present invention requires that the TOC increase of the bath solution for each production batch < 5%.

[0061] The performance test results of the immersion tinning solutions of Examples 1-5 and Comparative Examples 1-13 are shown in Table 1 below: Table 1 Performance test results

[0062] The scanning electron microscope observation results of the tin surface after immersion tinning in Example 1 are as Figure 1 shown; the scanning electron microscope observation results of the tin surface after immersion tinning in Comparative Example 2 are as Figure 2 shown; the scanning electron microscope observation results of the tin surface after immersion tinning in Comparative Example 5 are as Figure 3 shown; the scanning electron microscope observation results of the tin surface after immersion tinning in Comparative Example 13 are as Figure 4 shown.

[0063] It can be seen from the test results of Examples 1-5 in Table 1 that the viscosity of the immersion tinning solution of the present invention is 6.05 - 6.22 mPa·s, and it has good immersion tinning performance. After being used for 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 ≥ 99.92%, and the TOC increase before and after immersion tinning of each batch of the solution < 0.28%, meeting the requirements of the immersion tinning process for inkjet printed PCBs.

[0064] The differences between Comparative Examples 1-6 and Example 1 are that they respectively lack a single component of stannous compound, complexing agent, reducing agent, wetting agent, accelerator, and stabilizer. The test results show that the stannous compound provides Sn element for immersion tinning and is an essential component in the immersion tinning solution formula. The lack of stannous compound will result in no tin on the surface of the circuit board. The complexing agent, reducing agent, wetting agent, accelerator, and stabilizer have a certain influence on the immersion tinning reaction. The lack of any one of them will lead to a decline in the immersion tinning effect, problems such as oil dropping, uneven tin surface, increased viscosity of the solution, decreased micropore coverage rate of immersion tinning, and increased TOC increase, indicating that the excellent performance of the immersion tinning solution of the present invention is the result of the interaction of each component, and the lack of any one component will affect the performance of the product.

[0065] The differences between Comparative Examples 7-12 and Example 1 are that the concentrations of stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers in the single component of the immersion tin solution are respectively higher than the upper concentration limits of the immersion tin 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 immersion tin solution, but the excessive concentrations will increase the cost of the solution. Therefore, the concentrations of the components of the immersion tin solution of the present invention should not be too high, and good tin immersion performance of the solution can be ensured within the concentration range of the examples.

[0066] Comparative Example 13 uses an immersion tin solution of an existing patent. The test results show that the immersion tin solution of the present invention has a better binding effect on the printing ink, a smoother tin surface, a lower solution viscosity, a higher coverage rate of tin immersion micropores, and a lower increase in the total organic carbon (TOC) of the solution, and is applicable to the tin immersion process of inkjet printing printed circuit boards (PCBs).

[0067] In summary, the immersion tin solution of the present invention is composed of core components such as stannous compounds, complexing agents, reducing agents, wetting agents, accelerators, and stabilizers, providing a high-stability and high-coverage tin immersion solution for PCB inkjet printing technology, and having the following outstanding advantages: First, it has a low-viscosity characteristic, and the solution is in a low-viscosity fluid state, ensuring uniform deposition of the tin immersion layer on the surface and in the micropores of the PCB; second, it has the ability to passivate organic impurities. The formula components can passivate the residual organic impurities in the previous process and inhibit their side reactions with Sn 2+ so that the increase in TOC before and after the use of the solution is stably controlled at <0.28%; third, the adhesion of the ink after tin immersion does not decay, the surface of the tin layer is smooth and defect-free, and the coverage rate of micropore tin immersion is ≥99.92%, meeting the reliability requirements of high-precision inkjet printing circuit boards.

[0068] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. Immersion tin solution for inkjet printing PCB, characterized in that, Comprising components with the following mass concentrations: Stannous compound 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 stannous compound is selected from one or a mixture of more than one of stannous oxalate, stannous chloride, and stannous methyl sulfonate; The complexing agent is selected from one or a mixture of more than one of p-hydroxyphenylacetylglycine, N-carbobenzoxy-4-hydroxy-D-2-phenylglycine, and (S)-3-carboxy-4-hydroxyphenylglycine; The reducing agent is selected from one or a mixture of more than one of 4-hydroxybenzohydrazide, 3-hydroxybenzohydrazide, and 3,4-dihydroxybenzohydrazide; The wetting agent is selected from one or a mixture of more than one of trimethylolpropane triglycidyl ether, trihydroxy polyoxypropylene ether, and tris(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 than one of 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 immersion tin solution for inkjet printing PCB according to claim 1, wherein, Composed of components with the following mass concentrations: Stannous compound 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 balance is water.

3. The immersion tin solution for inkjet printing PCB according to claim 1, characterized in that, Composed of components with the following mass concentrations: Stannous compound 4.0%; Complexing agent 2.0%; Reducing agent 1.5%; Wetting agent 2.0%; Accelerator 2.0%; Stabilizer 1.0%; The balance is water.

4. The preparation method of the immersion tin solution for inkjet printing PCB according to any one of claims 1-3, characterized in that, Weigh the stannous compound, complexing agent, reducing agent, wetting agent, accelerator, and stabilizer in sequence according to the component ratios, add them to water, and mix evenly at room temperature to obtain.

5. A method for stannate immersion, characterized in that, Including the following steps, stannous deposition section: Immerse the inkjet-printed PCB in the stannous deposition solution for inkjet-printed PCB as described in any one of claims 1 - 3; the temperature of the stannous deposition solution for inkjet-printed PCB is 50 - 60°C, and the immersion time is 55 - 65 s.

6. The immersion tin method according to claim 5, wherein In the stannous deposition section, the temperature of the stannous deposition solution for inkjet-printed PCB is 55 ± 1°C, and the immersion time is 60 ± 3 s.

7. The method for immersing tin according to claim 5, wherein Before the stannous deposition section, there is also a pre-immersion section: Immerse the inkjet-printed PCB in the pre-immersion solution; the pre-immersion solution is composed of 40 - 70% by mass of the stannous deposition solution for inkjet-printed PCB as described in any one of claims 1 - 3 and the balance of water, the immersion temperature is 40 - 50°C, and the immersion time is 25 - 35 s.

8. The method for immersion tin according to claim 7, characterized in that, In the pre-immersion section, the pre-immersion solution is composed of 50% by mass of the stannous deposition solution for inkjet-printed PCB and the balance of water, the immersion temperature is 45 ± 1°C, and the immersion time is 30 ± 3 s.

9. The method for immersing tin according to claim 7, characterized in that, Before the described impregnation section, there is also a micro-etching section: spraying and inkjet printing the PCB with a micro-etching solution; the spraying pressure is 1.5 ± 0.5 kg / cm 2 , and the spraying time is 30 ± 15 s.

10. A tin immersion method, characterized in that, Including the following steps: S1 Micro-etching → S2 Water washing → S3 Pre-dipping → S4 Tin immersion → S5 Water washing → S6 Drying; S1 Micro-etching: Micro-etch the inkjet-printed PCB; the specific process is as follows: adopt the spraying method, the solution in the micro-etching tank contains 5% micro-etching solution by mass concentration, and the balance is tap water; the length of the micro-etching tank is 2.0 m, the temperature of the solution in the micro-etching tank is 25 ± 5 °C, the linear speed is 4.0 ± 0.5 m / min, and the spraying pressure is 1.0 ± 0.5 kg / cm 2 ; S2 Water washing: Wash the inkjet printed PCB after S1 micro-etching with tap water. The specific process is as follows: Spray method is adopted; The bath solution is tap water, with a temperature of 25 ± 5 °C, and the length of the water washing tank is 1.0 m; The linear speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S3 Pre-dipping: The inkjet-printed PCB after S2 water washing is pre-dipped with the bath solution containing the tin immersion solution for inkjet-printed PCB as described in any one of claims 1-3. The specific process is as follows: The immersion method is adopted; the bath solution in the pre-dipping tank uses the tin immersion solution for inkjet-printed PCB as described in any one of claims 1-3 with a mass concentration of 50%, and the balance is tap water; the bath solution temperature is 45 ± 1 °C, the length of the pre-dipping tank is 2.0 m; the line speed is 4.0 ± 0.1 m / min; S4 Tin immersion: The inkjet-printed PCB after S3 pre-dipping is subjected to tin immersion treatment with the tin immersion solution for inkjet-printed PCB as described in any one of claims 1-3. The specific process is as follows: The immersion method is adopted; the tin immersion tank uses the tin immersion solution for inkjet-printed PCB as described in any one of claims 1-3, the bath solution temperature is 55 ± 1 °C, the length of the tin immersion tank is 2.0 m; the line speed is 2.0 ± 0.1 m / min; S5 Water washing: The inkjet printed PCB after S4 immersion tinning is washed with hot tap water. The specific process is as follows: Spray method is adopted; The bath solution is hot tap water with a temperature of 55 ± 1 °C, and the length of the water washing tank is 1.0 m; The line speed is 3.0 ± 0.5 m / min, and the pressure is 1.0 ± 0.5 kg / cm 2 ; S6 Drying: The inkjet-printed PCB after S5 water washing is dried. The specific process is as follows: The temperature is 70 ± 5 °C, the length of the drying section is 2.0 m; the line speed is 4.0 ± 0.3 m / min.

Images