Metal interconnection method of through hole electroplating crystal face preferred copper plating layer of printed circuit board
By combining azo-based acid dye compound leveling agents with unidirectional pulse electroplating technology during PCB electroplating, the problems of coating uniformity and crystal phase structure were solved, achieving high-quality copper interconnects, simplifying the production process and reducing costs.
Patent Information
- Application Number
- CN202511490626.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-17
- Publication Date
- 2026-01-02
AI Technical Summary
In existing PCB copper plating processes, the plating uniformity and density are insufficient, resulting in uneven through-hole structure, which affects electrical performance. Furthermore, traditional additive systems are difficult to form high-quality Cu(111) texture directly during the electroplating process, requiring subsequent annealing treatment to control the crystal phase structure, which increases production costs and complexity.
By using a combination of additives containing azo acid dye compounds as leveling agents and a unidirectional pulse electroplating process, the optimal crystal plane growth of copper plating is achieved by optimizing the composition of the electroplating solution and current parameters, directly forming a dense Cu(111) texture and avoiding annealing treatment.
It improves the uniformity and grain size of the copper plating layer in PCB through-holes, enhances the conductivity and mechanical strength of the plating layer, simplifies the production process, reduces costs, and improves the reliability of the interconnect structure.
Smart Images
Figure CN121250488A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic electroplating technology, and specifically relates to a method for metal interconnection of a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board. Background Technology
[0002] With the rapid development of cutting-edge technologies such as 5G communication, artificial intelligence, autonomous driving, and new energy vehicles, more stringent requirements are being placed on semiconductor devices in terms of high-frequency performance, heat dissipation, and long-term reliability. As a key carrier of electronic systems, printed circuit boards (PCBs) not only carry core components such as chips but also provide them with stable and reliable electrical connections, which is fundamental to ensuring the stable operation of electronic devices in complex environments. Electronic components use PCBs to achieve signal transmission and power distribution, thereby completing various complex circuit functions. In the interconnection process of micro- and nano-scale electronic components, electroplating is currently the most mature key technology. Through a cathode electrochemical deposition process, metal ions in the plating solution are reduced and deposited, directly forming the metal and constructing an interconnection structure for electrical signal transmission.
[0003] Currently, PCB copper plating processes commonly use acidic copper sulfate systems as plating solutions, and their composition and process parameters directly affect the plating quality. In actual plating processes, due to the uneven electric field distribution and weak convection within micron-sized via structures, copper ion mass transfer within the vias is limited, easily leading to concentration polarization. This results in a deposition rate at the via opening being much higher than inside the via, causing a decrease in plating uniformity and density, severely impacting the electrical performance of the PCB. To address this issue, the industry mainly optimizes both the plating solution formulation and the process to create super-filled, high-quality interconnect structures: on the one hand, by introducing functional additives to improve plating solution performance; on the other hand, by employing novel processes such as pulse plating to enhance mass transfer and polarization control. The additives currently used are compound systems containing inhibitors, accelerators, and leveling agents. Specifically, inhibitors (such as polyether polymers) suppress the rapid deposition of copper by adsorbing onto the cathode surface; accelerators (such as organosulfur compounds) promote copper ion reduction and improve deep plating capability, and their effect usually depends on the complex formed with Cl⁻ within the pores to lower the reaction energy barrier; leveling agents (such as nitrogen-containing heterocyclic compounds or quaternary ammonium salts) preferentially adsorb onto the high current density pore opening region, inhibiting deposition at that location, thereby improving the overall uniformity of pore filling. These three components coordinate the growth rate of the metal coating at different locations during electroplating, triggering a "rate reversal" phenomenon between the inside and outside of the pore to achieve metal filling from the inside out.
[0004] Although traditional additive systems can achieve superfilling of vias and meet basic interconnect requirements, the resulting coating has an insufficiently dense crystalline structure, which easily leads to grain boundary dislocations and various defects, severely affecting the reliability of the interconnect structure. Therefore, the ideal high-quality copper interconnect structure for actual PCB products must simultaneously meet two key requirements: first, to achieve defect-free superfilling of vias; and second, to obtain a coating with a regular crystalline structure and dense grains. In actual production, low-temperature annealing is usually introduced after electroplating to regulate the crystalline structure through recrystallization, especially promoting the formation of a preferred orientation texture dominated by Cu(111) crystal planes. This texture has excellent performance and can significantly improve the conductivity, mechanical strength, and corrosion resistance of the coating, thereby enhancing the long-term reliability of the interconnect structure. However, the annealing process also complicates the manufacturing process and increases production costs. Therefore, if a coating with a highly ordered Cu(111) texture and few defects can be directly prepared during the electroplating process, it will help the PCB manufacturing industry achieve cost reduction and efficiency improvement. In recent years, the industry has been committed to developing new leveling agents and combining them with advanced processes such as pulse electroplating. By selecting a leveling agent with specific adsorption-desorption kinetics and matching pulse parameters (such as frequency, duty cycle, forward and reverse current), the filling efficiency and crystal growth orientation within the pores can be optimized simultaneously during electroplating. This technology can directly produce copper plating layers with coarse grains, dense structure, and highly consistent (111) orientation without the need for subsequent high-temperature annealing. This not only avoids problems such as plating expansion and interface cracking that may occur during annealing, but also simplifies the production process, reduces overall production costs, and significantly improves product consistency and reliability.
[0005] In summary, developing leveling agents and compatible electroplating processes that can induce preferential crystal plane growth and directly form microstructured, ordered copper layers during electroplating have become key breakthroughs in advancing PCB electroplating technology. These technologies not only meet the current semiconductor industry's urgent need for highly reliable interconnect structures but also provide crucial support for the upgrading and innovation of the future electronics manufacturing industry, possessing enormous application potential and market prospects. Summary of the Invention
[0006] To address the aforementioned technical problems, this invention provides a method for metal interconnection of printed circuit board through-hole electroplating with preferred copper plating on the crystal surface.
[0007] A method for metal interconnection of through-hole electroplating with preferred copper plating on the crystal surface of a printed circuit board is specifically completed according to the following steps:
[0008] 1. Pre-processing of printed circuit boards containing through-holes:
[0009] The printed circuit board containing through holes is cleaned to obtain a pre-treated printed circuit board containing through holes.
[0010] 2. The pre-treated printed circuit board containing through holes is immersed in an electroplating copper plating solution suitable for filling copper in the through holes of the printed circuit board. The through holes of the printed circuit board containing through holes are electroplated using a unidirectional pulse electroplating process to obtain the electroplated printed circuit board, thus completing a metal interconnection method for electroplating a crystal surface preferred copper plating layer on the through holes of the printed circuit board.
[0011] The copper plating solution for filling through-holes in printed circuit boards described in step two is prepared from copper sulfate pentahydrate, sulfuric acid, chloride ions, and a combination of additives. The combination of additives includes leveling agents, accelerators, and inhibitors. The leveling agent is an azo acid dye compound containing sulfonyl groups, azo groups, hydroxyl groups, and at least three benzene ring structures in its molecule.
[0012] The peak current density of the forward current pulse in the unidirectional pulse electroplating process described in step two is 1.5~2.5A / dm². 2 The pulse duration is 0ms~20ms, the duty cycle is 60%~80%, and the reverse current is 0A / dm. 2 The ratio of forward to reverse energizing time is 4:1.
[0013] Electroplating using the above method can not only achieve super-filling of PCB vias, but also optimize the plating structure, improve the microstructure quality of the electroplated copper layer, and achieve high-quality copper interconnects.
[0014] The beneficial effects of this invention are:
[0015] I. Compared with existing PCB copper plating technology, this invention can effectively improve the uniformity of copper plating layer in PCB through holes and increase the TP value of through holes;
[0016] II. The present invention uses a combination of a novel leveling agent (azo acid dye compound) and a pulse process (unidirectional pulse electroplating process), which has a significant effect on improving the texture coefficient of Cu (111) crystal plane and increasing the grain size, and effectively controls the grain structure.
[0017] This invention provides a method for metal interconnection of a preferred copper plating layer on the crystal surface of a through-hole in a printed circuit board. Attached Figure Description
[0018] Figure 1 The molecular structural formula of Acid Orange 7;
[0019] Figure 2 The images are three-dimensional microscopic images of copper plating on copper foil surfaces. In the figures, a is the plating obtained by the unidirectional pulse electroplating process without leveling agent in Comparative Example 1, b is the plating obtained by the unidirectional pulse electroplating process with the novel leveling agent Acid Orange 7 in Example 1, and c is the plating obtained by the DC electroplating process with the novel leveling agent Acid Orange 7 in Comparative Example 2.
[0020] Figure 3 The figures are metallographic cross-sections of the through holes after electroplating. In the figures, a is the through hole cross-section obtained by the unidirectional pulse electroplating process without leveling agent in Comparative Example 1, b is the through hole cross-section obtained by the unidirectional pulse electroplating process with the novel leveling agent Acid Orange 7 in Example 1, and c is the through hole cross-section obtained by the DC electroplating process with the novel leveling agent Acid Orange 7 in Comparative Example 2.
[0021] Figure 4 The images show the XRD patterns of the electroplated copper coatings obtained in Example 1, Comparative Example 1, and Comparative Example 2. In the images, Comparative Example 1 is without leveling agent and pulsed coating, Comparative Example 2 is with leveling agent and DC current, and Example 1 is with leveling agent and pulsed coating. Detailed Implementation
[0022] Specific Implementation Method 1: This implementation method is a metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole in a printed circuit board, specifically completed according to the following steps:
[0023] 1. Pre-processing of printed circuit boards containing through-holes:
[0024] The printed circuit board containing through holes is cleaned to obtain a pre-treated printed circuit board containing through holes.
[0025] 2. The pre-treated printed circuit board containing through holes is immersed in an electroplating copper plating solution suitable for filling copper in the through holes of the printed circuit board. The through holes of the printed circuit board containing through holes are electroplated using a unidirectional pulse electroplating process to obtain the electroplated printed circuit board, thus completing a metal interconnection method for electroplating a crystal surface preferred copper plating layer on the through holes of the printed circuit board.
[0026] The copper plating solution for filling through-holes in printed circuit boards described in step two is prepared from copper sulfate pentahydrate, sulfuric acid, chloride ions, and a combination of additives. The combination of additives includes leveling agents, accelerators, and inhibitors. The leveling agent is an azo acid dye compound containing sulfonyl groups, azo groups, hydroxyl groups, and at least three benzene ring structures in its molecule.
[0027] The peak current density of the forward current pulse in the unidirectional pulse electroplating process described in step two is 1.5~2.5A / dm². 2 The pulse duration is 0ms~20ms, the duty cycle is 60%~80%, and the reverse current is 0A / dm. 2 The ratio of forward to reverse energizing time is 4:1.
[0028] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the degreasing solution mentioned in step one is composed of a mixture of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium dodecyl sulfate, and water. The concentrations of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, and sodium dodecyl sulfate are 5 g / L to 10 g / L, 15 g / L to 25 g / L, 5 g / L to 15 g / L, 5 g / L to 10 g / L, and 1 g / L to 2 g / L. The other steps are the same as in Specific Implementation Method One.
[0029] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the cleaning described in step one is as follows: First, immerse the printed circuit board containing through holes in a degreasing solution for 5-10 minutes. After removal, rinse with room temperature water for 30-60 seconds. Then, immerse it in 10% sulfuric acid for ultrasonic cleaning for 5-8 minutes. After removal, rinse with room temperature water for 30-60 seconds. Then, immerse it in room temperature water for 1-3 minutes. Finally, remove it and rinse with room temperature water for 30-60 seconds to obtain a pre-treated printed circuit board containing through holes. Other steps are the same as in Specific Implementation Method One or Two.
[0030] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the electroplating time in step two is 60 to 90 minutes. The other steps are the same as in Specific Implementation Methods One to Three.
[0031] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the mass fraction of sulfuric acid mentioned in step two is 98%. The other steps are the same as in Specific Implementation Methods One to Four.
[0032] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the inhibitor is a high molecular weight polyether compound; the high molecular weight polyether compound is polyethylene glycol; and the molecular weight of the polyethylene glycol is 20,000. The other steps are the same as in Specific Implementation Methods One to Five.
[0033] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the accelerator is a small molecule sulfide; the small molecule sulfide is sodium polydisulfide dipropane sulfonate; and the azo acid dye compound is Acid Orange 7. Other steps are the same as in Specific Implementation Methods One to Six.
[0034] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step two, the concentration of copper sulfate pentahydrate in the electroplating solution suitable for filling copper in through-holes of printed circuit boards is 75 g / L, the concentration of sulfuric acid is 220 g / L to 240 g / L, the concentration of chloride ions is 60 mg / L, the concentration of leveling agent is 10 mg / L to 250 mg / L, the concentration of accelerator is 1 mg / L to 10 mg / L, and the concentration of inhibitor is 150 mg / L to 650 mg / L. The other steps are the same as in Specific Implementation Methods One to Seven.
[0035] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step two, the concentration of copper sulfate pentahydrate in the copper plating solution suitable for filling copper in through-holes of printed circuit boards is 75 g / L, the concentration of sulfuric acid is 240 g / L, the concentration of chloride ions is 60 mg / L, the concentration of leveling agent is 20 mg / L to 160 mg / L, the concentration of accelerator is 1 mg / L to 3 mg / L, and the concentration of inhibitor is 200 mg / L to 400 mg / L. The other steps are the same as in Specific Implementation Methods One to Eight.
[0036] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: the printed circuit board used in step two has a size of 2cm × 5cm, a through-hole diameter of 300μm, and a thickness-to-diameter ratio of 8:1; the Haring bath used for electroplating in step two has a capacity of 1.5L. Other steps are the same as in Specific Implementation Methods One through Nine.
[0037] The beneficial effects of the present invention are verified using the following embodiments:
[0038] Example 1: A method for metal interconnection of through-hole electroplating with preferred copper plating on the crystal surface of a printed circuit board, specifically completed according to the following steps:
[0039] 1. Pre-processing of printed circuit boards containing through-holes:
[0040] First, immerse the printed circuit board containing through holes in the degreasing solution for 5 minutes, then rinse it with room temperature water for 30 seconds, then immerse it in 10% sulfuric acid for ultrasonic cleaning for 5 minutes, then rinse it with room temperature water for 30 seconds, then immerse it in room temperature water for 1 minute, and then rinse it with room temperature water for 30 seconds to obtain the pre-treated printed circuit board containing through holes.
[0041] The degreasing solution mentioned in step one is composed of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium dodecyl sulfate and water, wherein the concentration of sodium hydroxide is 5 g / L, the concentration of sodium carbonate is 20 g / L, the concentration of sodium phosphate is 10 g / L, the concentration of sodium silicate is 5 g / L and the concentration of sodium dodecyl sulfate is 1 g / L.
[0042] 2. At 25°C, the pre-treated printed circuit board containing through holes is immersed in a copper plating solution suitable for filling copper through holes of printed circuit boards. The through holes of the printed circuit board containing through holes are electroplated for 60 minutes using a unidirectional pulse electroplating process to obtain the electroplated printed circuit board.
[0043] The peak current density of the forward current pulse in the unidirectional pulse electroplating process described in step two is 2 A / dm. 2 The pulse duration is 20ms, the duty cycle is 80%, and the reverse current is 0A / dm. 2 The ratio of forward to reverse energizing time is 4:1;
[0044] The copper plating solution for filling through-holes in printed circuit boards described in step two is composed of copper sulfate pentahydrate, sulfuric acid, chloride ions, a combination of additives, and water; the sulfuric acid has a mass fraction of 98%; the combination of additives includes leveling agents, accelerators, and inhibitors.
[0045] In step two, the concentration of copper sulfate pentahydrate in the copper plating solution suitable for filling copper through holes in printed circuit boards is 75 g / L, the concentration of sulfuric acid is 240 g / L, the concentration of chloride ions is 60 mg / L, the concentration of leveling agent is 40 mg / L, the concentration of accelerator is 2 mg / L, and the concentration of inhibitor is 250 mg / L.
[0046] The inhibitor is polyethylene glycol with a molecular weight of 20,000;
[0047] The accelerator mentioned is sodium polydisulfide dipropane sulfonate;
[0048] The leveling agent is Acid Orange 7, the structural formula of which is shown below. Figure 1 As shown;
[0049] The printed circuit board used in step two has a size of 2cm×5cm, a through hole diameter of 300μm, and a thickness-to-diameter ratio of 8:1; the Haring tank used for electroplating in step two has a capacity of 1.5L.
[0050] Comparative Example 1: The difference between this example and Example 1 is that no leveling agent was used, and the concentration of the leveling agent was 0 mg / L. That is, the combined additives include both accelerators and inhibitors. All other steps and parameters are the same as in Example 1.
[0051] Comparative Example 2: The difference between this embodiment and Example 1 is that in step two, the pre-treated printed circuit board containing through holes is immersed in a copper plating solution suitable for filling copper in the through holes of the printed circuit board. A direct current electroplating process is used to electroplat the through holes of the printed circuit board for 60 minutes to obtain the electroplated printed circuit board. The cathode current of the direct current electroplating process in step two is set to 3 ADS. Other steps and parameters are the same as in Example 1.
[0052] Figure 2 The images are three-dimensional microscopic images of copper plating on copper foil surfaces. In the figures, a is the plating obtained by the unidirectional pulse electroplating process without leveling agent in Comparative Example 1, b is the plating obtained by the unidirectional pulse electroplating process with the novel leveling agent Acid Orange 7 in Example 1, and c is the plating obtained by the DC electroplating process with the novel leveling agent Acid Orange 7 in Comparative Example 2.
[0053] from Figure 2 It can be seen that the coating roughness of b is higher than that of a and c, indicating that the copper coating obtained in Example 1 has larger crystalline particles, and the process conditions of Example 1 have the effect of increasing the crystallization of the copper coating.
[0054] Figure 3 The figures are metallographic cross-sections of the through holes after electroplating. In the figures, a is the through hole cross-section obtained by the unidirectional pulse electroplating process without leveling agent in Comparative Example 1, b is the through hole cross-section obtained by the unidirectional pulse electroplating process with the novel leveling agent Acid Orange 7 in Example 1, and c is the through hole cross-section obtained by the DC electroplating process with the novel leveling agent Acid Orange 7 in Comparative Example 2.
[0055] from Figure 3 It can be observed that b achieved superfilling in the 300μm diameter through-hole, which is superior to a and b. That is, Example 1 is superior to Comparative Example 1 and Comparative Example 2.
[0056] Figure 4 The image shows the XRD pattern of the copper plating layer obtained by the novel leveling agent Acid Orange 7+ unidirectional pulse electroplating process in Example 1.
[0057] from Figure 4 It can be found that azo acid dye compounds (Acid Orange 7) + pulse electroplating mode (unidirectional pulse electroplating process) are beneficial to the preferred orientation of Cu (111) crystal plane.
[0058] Table 1 shows the main processes and effects of Example 1;
[0059] Table 1
[0060]
[0061] As shown in Table 1, Example 1 can effectively improve the uniformity of the copper plating layer in PCB through holes, increase the TP value of through holes, and improve the texture coefficient of Cu (111) crystal plane. It has a significant effect on increasing the grain size and effectively controls the grain structure.
Claims
1. A method for metal interconnection of through-hole electroplating with preferred copper plating on the crystal surface of a printed circuit board, characterized in that... The method is specifically implemented according to the following steps:
1. Pre-processing of printed circuit boards containing through-holes: The printed circuit board containing through holes is cleaned to obtain a pre-treated printed circuit board containing through holes.
2. The pre-treated printed circuit board containing through holes is immersed in an electroplating copper plating solution suitable for filling copper in the through holes of the printed circuit board. The through holes of the printed circuit board containing through holes are electroplated using a unidirectional pulse electroplating process to obtain the electroplated printed circuit board, thus completing a metal interconnection method for electroplating a crystal surface preferred copper plating layer on the through holes of the printed circuit board. The copper plating solution for filling through-holes in printed circuit boards described in step two is prepared from copper sulfate pentahydrate, sulfuric acid, chloride ions, and a combination of additives. The combination of additives includes leveling agents, accelerators, and inhibitors. The leveling agent is an azo acid dye compound containing sulfonyl groups, azo groups, hydroxyl groups, and at least three benzene ring structures in its molecule. The peak current density of the forward current pulse in the unidirectional pulse electroplating process described in step two is 1.5~2.5A / dm². 2 The pulse duration is 0ms~20ms, the duty cycle is 60%~80%, and the reverse current is 0A / dm. 2 The ratio of forward to reverse energizing time is 4:
1.
2. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The degreasing solution mentioned in step one is composed of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium dodecyl sulfate and water, wherein the concentration of sodium hydroxide is 5 g / L to 10 g / L, the concentration of sodium carbonate is 15 g / L to 25 g / L, the concentration of sodium phosphate is 5 g / L to 15 g / L, the concentration of sodium silicate is 5 g / L to 10 g / L, and the concentration of sodium dodecyl sulfate is 1 g / L to 2 g / L.
3. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The cleaning process described in step one is as follows: First, immerse the printed circuit board containing through holes in the degreasing solution for 5 min to 10 min, then take it out and wash it with room temperature water for 30 s to 60 s, then immerse it in 10% sulfuric acid for ultrasonic cleaning for 5 min to 8 min, take it out and wash it with room temperature water for 30 s to 60 s, then immerse it in room temperature water for 1 min to 3 min, and then take it out and wash it with room temperature water for 30 s to 60 s, thus obtaining the pre-treated printed circuit board containing through holes.
4. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The electroplating time mentioned in step two is 60 min to 90 min.
5. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The sulfuric acid mentioned in step two has a mass fraction of 98%.
6. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The inhibitor is a high molecular weight polyether compound; the high molecular weight polyether compound is polyethylene glycol; the molecular weight of the polyethylene glycol is 20,000.
7. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The accelerator is a small molecule sulfide; the small molecule sulfide is sodium polydisulfide dipropane sulfonate; and the azo acid dye compound is Acid Orange 7.
8. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... In step two, the copper plating solution for filling through-holes in printed circuit boards contains copper sulfate pentahydrate at a concentration of 75 g / L, sulfuric acid at a concentration of 220 g / L to 240 g / L, chloride ions at a concentration of 60 mg / L, leveling agent at a concentration of 10 mg / L to 250 mg / L, accelerator at a concentration of 1 mg / L to 10 mg / L, and inhibitor at a concentration of 150 mg / L to 650 mg / L.
9. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 8, characterized in that... In step two, the copper plating solution for filling through-holes in printed circuit boards contains copper sulfate pentahydrate at a concentration of 75 g / L, sulfuric acid at a concentration of 240 g / L, chloride ions at a concentration of 60 mg / L, leveling agent at a concentration of 20 mg / L to 160 mg / L, accelerator at a concentration of 1 mg / L to 3 mg / L, and inhibitor at a concentration of 200 mg / L to 400 mg / L.
10. The metal interconnection method for electroplating a preferred copper plating layer on the crystal surface of a through-hole of a printed circuit board according to claim 1, characterized in that... The printed circuit board used in step two has a size of 2cm×5cm, a through hole diameter of 300μm, and a thickness-to-diameter ratio of 8:1; the Haring tank used for electroplating in step two has a capacity of 1.5L.