Acid sulfate system electrocoppering combined additive for PCB through hole conformal electroplating

Abstract

The invention discloses an acidic sulfate system electrocoppering combined additive for conformal electroplating of PCB through holes, and relates to the technical field of electronic electroplating, the combined additive is composed of a bridging agent, an inhibitor, a brightener and a leveling agent, and the mass ratio of the bridging agent to the inhibitor to the brightener to the leveling agent is (40-100): (20-1000): (0.1-20): (0.1-100); the bridging agent is one or a combination of more of sodium chloride, hydrochloric acid, potassium bromide and potassium iodide; according to the acidic sulfate system electrocoppering combined additive for PCB through hole conformal electroplating, inorganic matter providing halogen anions serves as a bridging agent, a polyol or polyether compound serves as an inhibitor, a sulfur-containing compound serves as a brightening agent, an organic compound with a specified structure serves as a leveling agent, and the acidic sulfate system electrocoppering combined additive for PCB through hole conformal electroplating is prepared. And in combination with conditions of specific plating solution concentration, temperature, electroplating current density and the like, uniform electroplating of the PCB through hole is realized.

Description

Technical Field

[0001] The present invention relates to electronic electroplating technology, and specifically to an acidic sulfate system electroplating copper combined additive for conformal electroplating of PCB through-holes. Background Art

[0002] Printed circuit boards (PCBs) play a connecting role in the electronics industry: they not only support various electronic components but also achieve the electrical connection of various components. The development process of printed circuit boards has evolved from the initial single-layer boards to double-layer boards, multi-layer boards, and now into today's high-density arbitrary-layer interconnections. Electroplating copper technology has always been a technical difficulty in the printed circuit manufacturing process. How to ensure the reliability of printed circuit boards under the circumstances of increasingly shrinking volume, gradually enhanced functions, and increasing integration is the core issue of current advanced printed circuit technology. In multi-layer printed boards, realizing interlayer interconnection is the most important topic. Interlayer interconnection mainly includes three forms: through-holes (TH), microvias, and buried vias. Among them, uniform electroplating of through-holes is the key technology for realizing interlayer interconnection.

[0003] In through-hole electroplating, due to the geometric shape limitations of through-holes, there are huge differences in the convection environment and electric field inside and outside the through-holes, which is very unfavorable for the uniform electroplating of through-holes. At the same time, the geometric shape of through-holes causes non-uniform current distribution, and the difference in current intensity poses an even greater challenge to the electroplating uniformity of through-holes, especially those with a high aspect ratio (AR>6:1). Non-uniform through-holes will greatly reduce the reliability of electronic products. Summary of the Invention

[0004] The purpose of the present invention is to provide an acidic sulfate system electroplating copper combined additive for conformal electroplating of PCB through-holes to solve the problem of electroplating uniformity of through-holes in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: an acidic sulfate system electroplating copper combined additive for conformal electroplating of PCB through-holes, the combined additive is composed of a bridging agent, an inhibitor, a brightener, and a leveling agent, and the mass ratio of the bridging agent, inhibitor, brightener, and leveling agent is 40-100:20-1000:0.1-20:0.1-100.

[0006] Further, the bridging agent is one or a combination of more of sodium chloride, hydrochloric acid, potassium bromide, and potassium iodide.

[0007] Further, the inhibitor is one or a combination of more of polyethylene glycol, polypropylene glycol, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0008] Further, the brightening agent is one or a combination of more than one of sodium bis(3-sulfopropyl) disulfide, sodium 3-mercapto-1-propanesulfonate, sodium N,N-dimethyldithiocarbamoyl propane sulfonate, sodium thiazolinyl disulfide propane sulfonate, sodium bis(2-sulfoethyl) disulfide, sodium bis(6-sulfohexyl) disulfide, sodium 3-(benzothiazol-2-ylthio)propane-1-sulfonate, 3-sulfo-isothiourea propionic acid, sodium 2-mercapto-1-ethanesulfonate, sodium 4-mercapto-1-hexanesulfonate, and sodium 2,3-dimercapto-1-propanesulfonate.

[0009] Further, the leveling agent is an organic compound containing one or more of structure (I) or structure (II) among others.

[0010] Further, in structure (I) R1 is a heterocyclic structure containing a benzene ring, R2 is -H, -CH3 or -OCH3, and R3 is -H, -CH3 or -OCH3.

[0011] Further, in structure (II) R4 is a heterocyclic structure containing a benzene ring, R5 is -H, -CH3 or -OCH3, and R6 is -H, -CH3 or -OCH3.

[0012] Further, the bridging agent is a mixture of sodium chloride and a co-promoter, and the mass ratio of sodium chloride to the co-promoter is 20 - 50:1.

[0013] Further, the co-promoter is one or more of an organic compound containing a nitrogen heterocyclic structure, alumina nanoparticles, silica nanoparticles, and boron nitride nanoparticles.

[0014] Further, the applicable electronic electroplating conditions are as follows: the electroplating solution contains 20 - 80 g / L CuSO4·5H2O and 180 - 250 g / L H2SO4, the electroplating temperature is 10 - 40 °C, and the electroplating current density is 0.5 - 5.0 A / dm 2 .

[0015] Compared with the prior art, the acid sulfate system electroplating copper combined additive for PCB through-hole conformal electroplating provided by the present invention has a bridging agent connecting copper ions in the electroplating solution to form an electron bridge, thus having the functions of synergistically inhibiting, brightening or leveling agents; the inhibitor inhibits the reduction of copper ions, promotes the uniform adsorption of brightening and leveling agents, and reduces the surface tension of the electroplating solution and improves the wettability of the coating; the brightening agent promotes the reduction of copper ions and reduces the copper nucleation overpotential; the leveling agent has the functions of inhibiting the reduction of copper ions and the consumption during the electroplating process is controlled by diffusion; by using an inorganic substance providing halogen anions as the bridging agent, a polyol or polyether compound as the inhibitor, a sulfur-containing compound as the brightening agent, and an organic compound containing a specified structure as the leveling agent, combined with specific conditions such as the concentration of the plating solution, temperature and electroplating current density, uniform electroplating of PCB through-holes is achieved. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings.

[0017] Figure 1 SEM image of the first group of copper layers provided in Embodiment III of the present invention;

[0018] Figure 2 SEM image of the second group of copper layers provided in Embodiment III of the present invention;

[0019] Figure 3 SEM image of the third group of copper layers provided in Embodiment III of the present invention;

[0020] Figure 4 SEM image of the fourth group of copper layers provided in Embodiment III of the present invention. Detailed Description of the Embodiments

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will further introduce the present invention in detail in conjunction with the drawings.

[0022] Embodiment I:

[0023] Acid sulfate system electroplating copper combined additives for PCB through-hole conformal electroplating. The combined additives are composed of a bridging agent, an inhibitor, a brightener, and a leveling agent. The mass ratio of the bridging agent, inhibitor, brightener, and leveling agent is 40 - 100:20 - 1000:0.1 - 20:0.1 - 100. The bridging agent is one or a combination of sodium chloride, hydrochloric acid, potassium bromide, potassium iodide, etc.; the inhibitor is one or a combination of polyethylene glycol, polypropylene glycol, polyethylene oxide - polypropylene oxide - polyethylene oxide triblock copolymer, etc.; the brightener is one or a combination of sodium polydithiopropanesulfonate, sodium 3-mercapto-1-propanesulfonate, sodium N,N-dimethyldithiocarbamoylpropane sulfonate, sodium thiazolinyl dithiopropanesulfonate, sodium polydithioethanesulfonate, sodium polydithiohexanesulfonate, sodium 3-(benzothiazol-2-ylthio)-propane sulfonate, 3-sulfo-isothiourea propyl sulfonic acid, sodium 2-mercapto-1-ethanesulfonate, sodium 4-mercapto-1-hexanesulfonate, sodium 2,3-dimercapto-1-propanesulfonate, etc.; the leveling agent is an organic compound containing one or more of structure (I) or structure (II) ; In structure (I) R1 is a heterocyclic structure containing a benzene ring, R2 is -H, -CH3 or -OCH3, and R3 is -H, -CH3 or -OCH3; In structure (II) R4 is a heterocyclic structure containing a benzene ring, R5 is -H, -CH3 or -OCH3, and R6 is -H, -CH3 or -OCH3;

[0024] Specifically, the acid sulfate system electroplating copper combined additives for PCB through-hole conformal electroplating are composed of a bridging agent, an inhibitor, a brightener, and a leveling agent. The mass ratio of the bridging agent, inhibitor, brightener, and leveling agent is 40 - 100:20 - 1000:0.1 - 20:0.1 - 100.

[0025] The bridging agent is sodium chloride, the brightener is sodium polydithiopropanesulfonate, the inhibitor is polyethylene glycol - 10000, and the leveling agent is an organic compound containing one or more of structure (I) (abbreviated as structure (I)) or structure (II) (abbreviated as structure (II)); In structure (I), R1 is a heterocyclic structure containing a benzene ring, R2 is -H, -CH3 or -OCH3, and R3 is -H, -CH3 or -OCH3; In structure (II), R4 is a heterocyclic structure containing a benzene ring, R5 is -H, -CH3 or -OCH3, and R6 is -H, -CH3 or -OCH3.

[0026] The bridging agent has the function of connecting copper ions in the electroplating solution to form an electron bridge and cooperating with inhibitors, brighteners or leveling agents; when the mass concentration of the bridging agent is lower than 10 mg / L, it is difficult to form an electron bridge; when the mass concentration of the bridging agent is higher than 100 mg / L, a cuprous film is likely to form on the surface of the coating, which is not conducive to the reduction of copper ions to metallic copper.

[0027] The inhibitor has the functions of inhibiting the reduction of copper ions, promoting the uniform adsorption of brighteners and leveling agents, and reducing the surface tension of the electroplating solution and improving the wettability of the coating; when the mass concentration of the inhibitor is lower than 20 mg / L, the copper deposition rate at the orifice of the PCB through-hole is fast, excessive deposition is likely to occur at the orifice, and pores are likely to form in the coating inside the hole; when the mass concentration of the carrier agent is higher than 1500 mg / L, a composite film layer of inhibitor-cuprous-bridging agent is likely to form on the surface of the coating, which is not conducive to the reduction of copper ions to metallic copper, and a large amount of foam is generated during the electroplating process.

[0028] The brightener has the function of promoting the reduction of copper ions and reducing the copper nucleation overpotential. When the mass concentration of the refining agent is lower than 0.1 mg / L, it cannot combine with the bridging agent, accelerating the copper deposition in the middle of the PCB through-hole; when the mass concentration of the brightener is higher than 20 mg / L, the copper deposition in the middle of the PCB hole is strongly inhibited, forming pores.

[0029] The leveling agent has the functions of inhibiting the reduction of copper ions and the consumption during the electroplating process being controlled by diffusion. When the mass concentration of the leveling agent is lower than 0.1 mg / L, it cannot regulate the relative rates of copper deposition in the middle and at the orifice of the hole; when the mass concentration of the leveling agent is higher than 100 mg / L, due to its strong adsorption ability, it is easily incorporated into the deposited copper layer, affecting the physical properties of the copper layer, such as thermal conductivity, electrical conductivity, ductility, etc.

[0030] In summary, when the mass ratio of the bridging agent, inhibitor, brightener and leveling agent is 40-100:20-1000:0.1-20:0.1-100, the electroplating copper composite additive uses an inorganic substance providing halogen anions as the bridging agent, a polyol or polyether compound as the inhibitor, a sulfur-containing compound as the brightener, and an organic compound with a specified structure as the leveling agent, combined with specific conditions such as the concentration of the plating solution, temperature and electroplating current density, to achieve uniform electroplating of PCB through-holes.

[0031] The preparation method of the electroplating copper composite additive for conformal electroplating of PCB through-holes in an acidic sulfate system includes the following steps:

[0032] S1. Take 40-100 g of sodium chloride as the bridging agent and dissolve it in water to obtain a sodium chloride solution; take 20-1000 g of polyethylene glycol-10000 as the inhibitor and dissolve it in water to obtain a polyethylene glycol-10000 solution; take 0.1-20 g of sodium polydithiopropane sulfonate as the brightener and dissolve it in water to obtain a sodium polydithiopropane sulfonate solution;

[0033] S2. Slowly mix the three solutions in S1 and 0.1 - 100 g of the organic compound containing structure (I) or structure (II) as a leveling agent into a clean container, stirring while adding to ensure uniform distribution of each component and avoid excessive local concentration, to obtain a mixed solution; adjust the total volume of the mixed solution to 1 L with water to obtain an additive concentrate;

[0034] S3. Detect the pH value of the additive concentrate and adjust the pH value to 2 - 4 as needed, and confirm whether the final concentrations of each component in the additive concentrate meet the preset ratio;

[0035] S4. Filter the additive concentrate through a fine - pore filter to remove impurity particles, to obtain an acidic sulfate system electroplating copper combination additive for PCB through - hole conformal electroplating.

[0036] The electronic electroplating conditions applicable to the acidic sulfate system electroplating copper combination additive for PCB through - hole conformal electroplating are: the electroplating solution contains 20 - 80 g / L of CuSO4·5H2O and 180 - 250 g / L of H2SO4, the electroplating temperature is 10 - 40 °C, and the electroplating current density is 0.5 - 5.0 A / dm 2 .

[0037] The specific implementation method is that during electroplating, the above - mentioned electroplating copper combination additive is added to the basic electroplating copper solution at a ratio of 1 mL / L. The basic electroplating copper solution is an acidic sulfate electroplating copper solution, which is composed of 20 - 80 g / L of copper sulfate pentahydrate and 180 - 250 g / L of concentrated sulfuric acid, both using water as a solvent.

[0038] Before electroplating, necessary pretreatment is carried out on the PCB board. First, use a degreasing solution composed of 40 g / L of 85% phosphoric acid, 40 g / L of ethylene glycol, and 1 g / L of OP - 10, and treat it in a 50 °C constant - temperature water bath for 15 minutes, during which the degreasing efficiency is improved by stirring. Subsequently, pickling is carried out with 10% sulfuric acid for 1 minute. If flash plating is required, micro - etching treatment is also needed. The micro - etching solution is composed of 4% sulfuric acid and 90 g / L of sodium persulfate, and the treatment time is 1 minute.

[0039] The electroplating copper process uses a constant - current dual - anode electroplating technology. The anode material is selected according to the electroplating type. Phosphor - bronze is used as the anode for through - hole conformal electroplating, while iridium - tantalum - titanium mesh is used for blind - hole filling. The cathode is the PCB board to be electroplated, and the plating solution is mechanically stirred by introducing air to ensure uniform distribution of the plating solution components.

[0040] Example Two:

[0041] Acid sulfate system electroplating copper composite additive for PCB through-hole conformal electroplating. The composite additive consists of a bridging agent, an inhibitor, a brightener, and a leveling agent. The mass ratio of the bridging agent, inhibitor, brightener, and leveling agent is 40 - 100:20 - 1000:0.1 - 20:0.1 - 100. The bridging agent is a mixture of sodium chloride and a co-promoter, and the mass ratio of sodium chloride to the co-promoter is 20 - 50:1. The co-promoter is one or more of an organic compound containing a nitrogen heterocyclic structure, alumina nanoparticles, silica nanoparticles, and boron nitride nanoparticles. The inhibitor is a combination of one or more of polyethylene glycol, polypropylene glycol, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer. The brightener is a combination of one or more of sodium polydithiopropane sulfonate, sodium 3-mercapto-1-propane sulfonate, sodium N,N-dimethyldithiocarbamoyl propane sulfonate, sodium thiazolinyl dithiopropane sulfonate, sodium polydithioethane sulfonate, sodium polydithiohexane sulfonate, sodium 3-(benzothiazol-2-ylthio)-propane sulfonate, 3-sulfanyl-isothiourea propyl sulfonic acid, sodium 2-mercapto-1-ethane sulfonate, sodium 4-mercapto-1-hexane sulfonate, and sodium 2,3-dimercapto-1-propane sulfonate. The leveling agent is an organic compound containing one or more of structure (I) or structure (II) One or more of them; in structure (I), R1 is a heterocyclic structure containing a benzene ring, R2 is -H, -CH3, or -OCH3, and R3 is -H, -CH3, or -OCH3; in structure (II), R4 is a heterocyclic structure containing a benzene ring, R5 is -H, -CH3, or -OCH3, and R6 is -H, -CH3, or -OCH3;

[0042] Specifically, the bridging agent has the function of connecting copper ions in the electroplating solution to form an electron bridge and coordinating with the inhibitor, brightener, or leveling agent. When the mass concentration of the bridging agent is lower than 10 mg / L, it is difficult to form an electron bridge. When the mass concentration of the bridging agent is higher than 100 mg / L, a cuprous film is easily formed on the surface of the coating, which is not conducive to the reduction of copper ions to metallic copper.

[0043] The co-promoter plays a key role in the electroplating copper process. It mainly optimizes the chemical environment of the electroplating solution and the adsorption behavior on the electrode surface through the synergistic effect with other additives. It can promote the rapid formation of copper crystal nuclei, improve the morphology and structure of the coating, make the coating finer, more uniform, and denser, thereby improving the brightness and adhesion of the coating. In addition, the co-promoter can also enhance the adsorption ability of other additives on the electrode surface, optimize the current distribution, reduce coating defects and cracks, and significantly improve the electroplating efficiency and coating quality. It is an important component for achieving high-efficiency and uniform electroplating.

[0044] The inhibitor has the functions of inhibiting the reduction of copper ions, promoting the uniform adsorption of brighteners and leveling agents, and reducing the surface tension of the electroplating solution and improving the wettability of the coating; when the mass concentration of the inhibitor is lower than 20 mg / L, the copper deposition rate at the orifice of the PCB through-hole is fast, excessive deposition is likely to occur at the orifice, and pores are easily formed in the coating inside the hole; when the mass concentration of the carrier is higher than 1500 mg / L, an inhibitor-cuprous-bridging agent composite film layer is easily formed on the coating surface, which is not conducive to the reduction of copper ions to metallic copper, and a large amount of foam is generated during the electroplating process.

[0045] The brightener has the functions of promoting the reduction of copper ions and reducing the copper nucleation overpotential. When the mass concentration of the refiner is lower than 0.1 mg / L, it cannot combine with the bridging agent, and the copper deposition in the middle of the PCB through-hole is accelerated; when the mass concentration of the brightener is higher than 20 mg / L, the copper deposition in the middle of the PCB hole is strongly inhibited, and pores are formed.

[0046] The leveling agent has the functions of inhibiting the reduction of copper ions and the consumption during the electroplating process being controlled by diffusion. When the mass concentration of the leveling agent is lower than 0.1 mg / L, the relative rates of copper deposition in the middle and at the orifice of the hole cannot be regulated; when the mass concentration of the leveling agent is higher than 100 mg / L, due to its strong adsorption ability, it is easily incorporated into the deposited copper layer, affecting the physical properties of the copper layer, such as thermal conductivity, electrical conductivity, ductility, etc.

[0047] In summary, when the mass ratio of the bridging agent, inhibitor, brightener, and leveling agent is 40 - 100:20 - 1000:0.1 - 20:0.1 - 100, the electroplating copper combined additive uses an inorganic substance providing halogen anions as the bridging agent, a polyol or polyether compound as the inhibitor, a sulfur-containing compound as the brightener, and an organic compound with a specified structure as the leveling agent, combined with specific conditions such as the concentration of the electroplating solution, temperature, and electroplating current density, to achieve uniform electroplating of PCB through-holes.

[0048] The preparation method of the electroplating copper combined additive for conformal electroplating of PCB through-holes in an acidic sulfate system includes the following steps:

[0049] S1. Weigh sodium chloride and the co-promoter according to a mass ratio of 20 - 50:1, add sodium chloride and the co-promoter to deionized water, stir evenly until completely dissolved, and ensure the co-promoter is uniformly dispersed in the solution by ultrasonic dispersion or mechanical stirring to obtain the bridging agent solution; weigh polyethylene glycol and add it to deionized water, stir evenly until completely dissolved to obtain the inhibitor solution; use sodium polydithiopropane sulfonate as the brightener and dissolve it in water to obtain the brightener solution;

[0050] S2. Slowly mix the three solutions in S1 and the organic compound containing structure (I) or structure (II) as a leveling agent into a clean container, stirring while adding to ensure uniform distribution of each component and avoid local high concentration, to obtain a mixed solution; adjust the total volume of the mixed solution to 1 L with water to obtain an additive concentrate; the mass ratio of the bridging agent, inhibitor, brightener and leveling agent in the additive concentrate is 40-100:20-1000:0.1-20:0.1-100;

[0051] S3. Detect the pH value of the additive concentrate and adjust the pH value to 2-4 as needed, and confirm whether the final concentrations of each component in the additive concentrate meet the preset ratio;

[0052] S4. Filter the additive concentrate through a fine pore filter to remove impurity particles to obtain an acidic sulfate system electroplating copper composite additive for PCB through-hole conformal electroplating.

[0053] The electronic electroplating conditions applicable to the acidic sulfate system electroplating copper composite additive for PCB through-hole conformal electroplating are: the electroplating solution contains 20-80 g / L CuSO4·5H2O and 180-250 g / L H2SO4, the electroplating temperature is 10-40 °C, and the electroplating current density is 0.5-5.0 A / dm 2 .

[0054] The specific implementation method is that during electroplating, the above electroplating copper composite additive is added to the basic electroplating copper solution at a ratio of 1 mL / L. The basic electroplating copper solution is an acidic sulfate electroplating copper solution, which is composed of 20-80 g / L of copper sulfate pentahydrate and 180-250 g / L of concentrated sulfuric acid, both using water as a solvent.

[0055] Before electroplating, necessary pretreatment is carried out on the PCB board. First, use a degreasing solution composed of 40 g / L of 85% phosphoric acid, 40 g / L of ethylene glycol and 1 g / L of OP-10, and treat it in a 50 °C constant temperature water bath for 15 minutes. During this period, stir to improve the degreasing efficiency. Subsequently, pickle with 10% sulfuric acid for 1 minute. If flash plating is required, micro-etching treatment is also required. The micro-etching solution is composed of 4% sulfuric acid and 90 g / L of sodium persulfate, and the treatment time is 1 minute.

[0056] The electroplating copper process uses a constant current dual anode electroplating technology. The anode material is selected according to the electroplating type. Phosphor bronze is used as the anode for through-hole conformal electroplating, while iridium tantalum titanium mesh is used for blind hole filling. The cathode is the PCB board to be electroplated, and the plating solution is mechanically stirred by introducing air to ensure uniform distribution of the plating solution components.

[0057] Example three:

[0058] Please refer to Figures 1 - 4, on the basis of Embodiment 1 and Embodiment 2, this embodiment provides a technical solution: the influence of electroplated copper composite additives on the microstructure of electroplated copper layers.

[0059] Prepare four groups of PCB substrates. The first group uses a basic electroplated copper solution (without additives), the second group uses an electroplated copper solution with commercial additives added, the third group uses an electroplated copper solution with the additives of Embodiment 1 of the present invention added, and the fourth group uses an electroplated copper solution with the additives of Embodiment 2 of the present invention added.

[0060] The electroplating conditions are a temperature of 25 °C and a current density of 2.5 A / dm 2 , and the electroplating time is 30 minutes; after electroplating is completed, a scanning electron microscope (SEM) is used to observe the surface morphology of the copper layer.

[0061] Please refer to Figure 1 , the surface morphology of the copper layer of the first group of basic electroplated copper solution is observed by a scanning electron microscope (SEM), and it shows relatively rough characteristics. Specifically, the grain size of the copper layer is relatively large, the shapes of these grains are mostly irregular polygons, and there are obvious boundaries between the grains. This relatively large grain size and irregular grain morphology result in the overall roughness of the copper layer surface, and this rough surface morphology may have an adverse impact on subsequent electronic component installation and electrical performance.

[0062] Please refer to Figure 2 , after electroplating with the electroplated copper solution with commercial additives added in the second group, the surface morphology of the copper layer has been improved to a certain extent. Compared with the basic electroplated copper solution, the grain size has decreased, and the shapes of the grains tend to be more regular, but there is still a certain degree of non-uniformity. The commercial additives have improved the surface flatness of the copper layer to a certain extent. However, overall, the surface of the copper layer is still not smooth enough, and the uniformity of the grain distribution still needs to be improved.

[0063] Please refer to Figure 3 , after electroplating with the additives of Embodiment 1 of the present invention in the third group, the surface morphology of the copper layer shows significant improvement. The SEM observation results show that the grain size of the copper layer is significantly reduced, the shapes of the grains are more uniform, showing an approximately circular or regular polygon morphology, and the boundaries between the grains are clearer. The roughness of the copper layer surface is significantly reduced, and the copper layer surface is more flat. This fine and uniform grain structure not only improves the surface quality of the copper layer but also may have a positive impact on the physical properties (such as conductivity and ductility) of the copper layer.

[0064] Please refer to Figure 4, after electroplating using the additive of Example 2 of the present invention in the fourth group, the surface morphology of the copper layer is further optimized. Compared with Example 1, the grain size is further reduced, the shape of the grains is more regular, and the distribution is more uniform. The surface of the copper layer shows a high degree of flatness. Such a highly uniform grain structure and extremely low surface roughness endow the copper layer with excellent properties in terms of microstructure, providing better guarantee for subsequent installation of electronic components and electrical performance.

[0065] Example 4:

[0066] Based on Example 1 and Example 2, this example provides a technical solution: the influence of the electroplated copper composite additive on the thickness uniformity of the electroplated copper layer.

[0067] Study the influence of different additive formulations on the thickness uniformity of the copper layer in the PCB through-holes, especially on the thickness distribution of the copper layer at the hole mouth, hole wall and hole bottom of the through-hole, so as to evaluate the effect of the additive in improving the electroplating uniformity of the through-hole.

[0068] First, prepare a PCB substrate with standard through-holes, with a hole diameter of 0.5 mm, a hole depth of 3.0 mm, and a thickness-to-diameter ratio of 6:1. The first group uses the basic electroplated copper solution (without additive); the second group uses the electroplated copper solution with a commercial additive; the third group uses the electroplated copper solution with the additive of Example 1 of the present invention; the fourth group uses the electroplated copper solution with the additive of Example 2 of the present invention. Each group contains 5 PCB samples with standard through-holes to ensure the repeatability and reliability of the experimental results.

[0069] After electroplating is completed, take out the PCB samples, rinse them with deionized water, and dry them for standby. Use a mechanical cutting device to cut some samples along the center line of the through-hole to facilitate subsequent measurement of the copper layer thickness. Use an X-ray fluorescence spectrometer (XRF) or a scanning electron microscope (SEM) to measure the copper layer thickness at different positions in the through-hole. The measurement positions include the hole mouth (0.1 mm away from the hole edge), the hole wall (1.0 mm away from the hole edge), and the hole bottom (the center position at the bottom of the hole). Measure 3 times at each position, and take the average value as the copper layer thickness at that position. The specific experimental results are as follows in the table:

[0070] Group Thickness of Copper Layer at Hole Opening (μm) Thickness of Copper Layer on Hole Wall (μm) Thickness of Copper Layer at Hole Bottom (μm) First Group 3.5 2.0 1.0 Second Group 3.0 2.2 1.5 Third Group 2.5 2.3 2.0 Fourth Group 2.2 2.4 2.3

[0071] The thickness of the copper layer at the first group of orifices is significantly higher than that of the hole wall and the hole bottom, and the thickness distribution is extremely uneven. The too-thin copper layer at the hole bottom may lead to unreliable electrical connection. Compared with the basic electroplated copper solution, the commercial additive in the second group improves the thickness uniformity of the copper layer to a certain extent, but the thickness difference between the orifice and the hole bottom is still large, and the thickness of the copper layer at the hole bottom is still insufficient to meet the high-reliability requirements. In the third group, the additive of the present invention significantly improves the thickness uniformity of the copper layer in the through hole. The thickness difference of the copper layer at the orifice, the hole wall and the hole bottom is significantly reduced, and the thickness of the copper layer at the hole bottom reaches 2.0 μm, which can meet the high-reliability requirements. The additive of the second embodiment of the present invention further optimizes the thickness uniformity of the copper layer. The copper layer thicknesses at the orifice, the hole wall and the hole bottom are almost the same, and the thickness distribution is extremely uniform, showing excellent conformal electroplating performance.

[0072] By comparing the experimental results of the four groups, it can be clearly seen that there are obvious thickness non-uniformity problems in the through-hole electroplating with the basic electroplated copper solution and the commercial additive, especially the too-thin copper layer at the hole bottom, which is difficult to meet the high-reliability requirements. The additives of the present invention (Embodiment 1 and Embodiment 2) significantly improve the thickness uniformity of the copper layer in the through hole, especially the increase in the thickness of the copper layer at the hole bottom, making the copper layer thickness distribution of the entire through hole more uniform.

[0073] The additive of Embodiment 2 shows the best performance in terms of the thickness uniformity of the copper layer. The copper layer thicknesses at the orifice, the hole wall and the hole bottom are almost the same, which can effectively solve the problem of non-uniform through-hole electroplating in traditional electroplating and provide reliable technical support for the manufacture of high-density multilayer PCBs.

[0074] Only some exemplary embodiments of the present invention have been described above by way of illustration. Undoubtedly, for those of ordinary skill in the art, without departing from the spirit and scope of the present invention, the described embodiments can be modified in various different ways. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. Acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating, characterized in that: The combined additive consists of a bridging agent, an inhibitor, a brightener and a leveling agent, and the mass ratio of the bridging agent, the inhibitor, the brightener and the leveling agent is 40-100:20-1000:0.1-20:0.1-100.

2. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 1, characterized in that: The bridging agent is a combination of one or more of sodium chloride, hydrochloric acid, potassium bromide and potassium iodide.

3. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 1, characterized in that: The inhibitor is a combination of one or more of polyethylene glycol, polypropylene glycol, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

4. The acid sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 1, characterized in that: The brightener is a combination of one or more of sodium polydisulfide propane sulfonate, sodium 3-mercapto-1-propane sulfonate, sodium N,N-dimethyldithioformamide propane sulfonate, sodium thiazoline disulfide propane sulfonate, sodium polydisulfide diethane sulfonate, sodium polydisulfide dihexane sulfonate, sodium 3-(benzothiazole-2-mercapto)-propane sulfonate, 3-sulfur-isothiourea propyl sulfonic acid, sodium 2-mercapto-1-ethane sulfonate, sodium 4-mercapto-1-hexane sulfonate, and sodium 2,3-dimercapto-1-propane sulfonate.

5. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 1, characterized in that: The leveling agent comprises structure (I) or structure (II) One or more organic compounds.

6. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 5, characterized in that: The structure (I) Wherein R1 is a heterocyclic structure containing a benzene ring, R2 is -H, -CH3 or -OCH3, and R3 is -H, -CH3 or -OCH3.

7. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 5, characterized in that: The structure (II) Wherein R4 is a heterocyclic structure containing a benzene ring, R5 is -H, -CH3 or -OCH3, and R6 is -H, -CH3 or -OCH3.

8. The acid sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 1, characterized in that: The bridging agent is a mixture of sodium chloride and a synergistic accelerator, and the mass ratio of the sodium chloride to the synergistic accelerator is 20 to 50:

1.

9. The acidic sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to claim 8, characterized in that: The synergistic promoter is one or more of an organic compound containing a nitrogen heterocyclic structure, aluminum oxide nanoparticles, silicon dioxide nanoparticles, and boron nitride nanoparticles.

10. The acid sulfate system copper electroplating combination additive for PCB through-hole conformal electroplating according to any one of claims 1 to 9, characterized in that: The applicable electronic electroplating conditions are: the electroplating solution contains 20-80g / L CuSO4·5H2O and 180-250g / L H2SO4, the electroplating temperature is 10℃~40℃, and the electroplating current density is 0.5~5.0A / dm 2 .

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