Horizontal reducing agent for PCB chemical copper, and preparation method and application thereof

Abstract

The invention relates to the technical field of PCB manufacturing, in particular to a horizontal reducing agent for PCB chemical copper and a preparation method and application thereof. The cutting fluid is prepared from the following raw materials in mass concentration: boric acid, borate, a reducing agent, a processing aid, a composite accelerant and deionized water, the mass concentration of the boric acid is 6-10 g / L, the mass concentration of the reducing agent is 3-6 g / L, the mass concentration of the processing aid is 0.2-0.5 g / L, the mass concentration of the composite accelerant is 2-4 g / L, the borate is used for adjusting the PH value of the solution to be larger than or equal to 7, and the composite accelerant is composed of activated carbon and a nitrogen-containing heterocyclic compound. The PCB is reduced to form a plating layer which is uniform in distribution, high in purity and compact in crystallization through the synergistic effect of the buffer solution of boric acid and borate, the activated carbon in composite promotion and the nitrogen-containing heterocyclic compound, so that the corrosion resistance of the plating layer is higher, and excessive corrosion of hydrochloric acid and nitric acid to the PCB is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of PCB manufacturing, and particularly relates to a horizontal reducing agent for PCB chemical copper, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of electronic product technology, the structure and mounting method of electronic chips have undergone major changes from plug-in pin components to highly integrated circuit modules with ball matrix arrangement soldering points. To comply with this development trend, the resin plug hole process (POFV) has been increasingly widely used in the printed circuit board (PCB) industry, especially in high-layer and large-thickness PCB products. After the POFV board is plugged, in order to ensure the reliability of electrical connection, hole cover plating is required, and chemical copper plating technology is a key technology in this plating process. The steps of the existing chemical copper plating production process are usually as follows: the substrate is sequentially subjected to swelling treatment, deslagging, neutralization, oil removal, acid etching, activation, reduction treatment of reducing agent, and a series of treatments such as chemical copper plating after reduction, and finally a copper-plated product is obtained.

[0003] In the manufacturing process of printed circuit boards, the activation step in the chemical copper plating process plays a decisive role in the quality of the plating layer. Currently, the PCB chemical copper plating field mainly adopts two activation methods, namely ion palladium activation technology and colloidal palladium activation technology. Colloidal palladium activation technology relies on high-concentration hydrochloric acid to stabilize colloidal palladium, while ion palladium activation technology does not require a large amount of hydrochloric acid, has better effect when processing blind hole boards, and has better environmental performance, so it has become the first choice of major PCB manufacturers.

[0004] A reducing solution for PCB chemical copper provided by the prior art is composed of a reducing agent, hydrochloric acid and / or nitric acid, a surfactant, and a chelating agent, with water as the solvent. The PCB is immersed in the reducing solution, heated at a temperature of 35℃ for 35s to obtain a reduced PCB, then the reduced PCB is washed with water, and then placed in a chemical copper plating solution at a temperature of 32℃ for 6min of copper plating treatment, and finally washed with water, dried to obtain a copper-plated product. The PCB treated by the above-mentioned reducing solution greatly reduces the probability of hole cover plating leakage.

[0005] However, the above reducing liquid still has obvious defects in practical application. On the one hand, the use of hydrochloric acid and nitric acid may produce acidic wastewater, which is easy to pollute the environment, and the wastewater treatment in the later stage is more troublesome, and is easy to cause corrosion to the production equipment, shorten the service life of the equipment; on the other hand, although the strong oxidizing property of hydrochloric acid and nitric acid can reduce the hole cover plating rate, it excessively erodes the surface of the palladium catalytic core, resulting in high porosity and uneven plating layer of the chemical copper deposition layer. Such microscopic defects directly lead to the decrease of the corrosion resistance of the plating layer. Therefore, in order to maintain the quality of copper plating, the production line needs to frequently replace the reducing liquid, resulting in the increase of annual maintenance cost. Especially for some small precision PCBs, such as the PCB in the smart watch for children, since the PCB is made of copper foil or epoxy resin material, which is easy to react with strong acid such as hydrochloric acid and nitric acid, and the PCB surface is easy to be corroded to cause cracking and peeling after being immersed in the solution containing strong acid for 35s. Moreover, the aperture of such small PCB is small, and the palladium particles eroded after the excessive erosion of the surface of the palladium catalytic core are peeled off from the hole wall and migrate to the hole or hole cover to cause blockage. SUMMARY

[0006] In order to avoid the excessive erosion of hydrochloric acid and nitric acid to the PCB, and improve the corrosion resistance and uniformity of the PCB plating layer, and reduce the porosity of the chemical copper deposition layer, the application provides a horizontal reducing agent for PCB chemical copper, a preparation method and application thereof.

[0007] In a first aspect, by mass concentration, the following raw materials are used: boric acid, boric acid salt, reducing agent, processing aid, composite accelerator, and deionized water; the mass concentration of the boric acid is 6-10 g / L, the mass concentration of the reducing agent is 3-6 g / L, the mass concentration of the processing aid is 0.2-0.5 g / L, the mass concentration of the composite accelerator is 2-4 g / L, the boric acid salt is used to adjust the solution PH value to be greater than or equal to 7, and the composite accelerator is composed of activated carbon and a nitrogen-containing heterocyclic compound. By using the above technical solution, the boric acid and the boric acid salt form a buffer solution system with a PH value greater than or equal to 7, the pH value of the horizontal reducing agent is maintained stable, an appropriate acid-base environment is provided for subsequent chemical copper plating, the stable progress of the chemical copper plating reaction is facilitated, excessive erosion of the PCB in the acidic environment is avoided, and the peeling of palladium particles from the hole wall to block the hole opening of the PCB is avoided. The reducing agent can effectively reduce the palladium catalytic nucleus and promote the deposition of chemical copper. The activated carbon and the nitrogen-containing heterocyclic compound in the composite accelerator can jointly trigger the reduction of copper ions quickly, improve the deposition rate, and reduce the reaction activation energy through coordination catalysis. The borate ions in the boric acid system are adsorbed on the surface of the copper crystal through hydrogen bonding or electrostatic interaction, cooperatively regulate the crystal growth direction with the nitrogen-containing heterocyclic compound, refine the grain structure, cooperatively inhibit the oxidation side reaction in the boric acid system, and improve the corrosion resistance. These raw materials cooperate with each other, so that the horizontal reducing agent can effectively reduce the porosity of the chemical copper deposition layer during the chemical copper plating process, make the plating layer more uniform, and improve the corrosion resistance of the plating layer. Preferably, the nitrogen-containing heterocyclic compound is a thiazolidinethione compound and a pyrimidine compound. By using the above technical solution, the nitrogen-containing heterocyclic compound uses a thiazolidinethione compound and a pyrimidine compound to form a composite accelerator. The thiazolidinethione compound and the pyrimidine compound have a unique heterocyclic structure and electron distribution, reduce the reaction activation energy through coordination catalysis, cooperatively regulate the crystal growth direction with the buffer solution system with a PH value greater than or equal to 7, refine the grain structure, cooperatively inhibit the oxidation side reaction in the boric acid system, improve the corrosion resistance, reduce the frequency of replacing the reducing solution on the production line, reduce the annual maintenance cost, and also avoid the problem of peeling of palladium particles from the hole wall to block the hole opening or hole cover. Preferably, the thiazolidinethione compound is 3-methyltetrahydrothiazole-2-thione, and the pyrimidine compound is 2-piperazinyl pyrimidine. By using the above technical solution, 3-methyltetrahydrothiazole-2-thione accelerates the reduction of the reaction energy barrier through catalysis, 2-piperazinyl pyrimidine ensures the continuous progress of the reaction by stabilizing the copper ion supply, and the two cooperate to improve the deposition rate. The sulfur atom in the 3-methyltetrahydrothiazole-2-thione molecule can be adsorbed on the surface of the copper crystal, selectively inhibit the growth of a specific crystal face, promote the preferential development of a certain crystal face, thereby refine the grain structure, reduce the porosity of the plating layer, and improve the compactness and corrosion resistance of the plating layer. Preferably, the processing aid is composed of a surfactant and a chelating agent.By adopting the above technical solution and adding surfactants, the surface tension of the solution can be reduced, allowing the plating solution to better wet the hole walls and hole caps, resulting in a more uniform plating layer.

[0008] Preferably, the surfactant is one or more of polyethylene glycol, polyvinyl alcohol, fatty alcohol polyoxyethylene ether, and amine ethoxylate.

[0009] By employing the above technical solutions, using one or more of polyethylene glycol, polyvinyl alcohol, fatty alcohol polyoxyethylene ether, and amine ethoxylates as surfactants can reduce the surface tension of the solution, allowing the plating solution to better wet the hole walls and hole caps. Preferably, the reducing agent is dimethylaminoborane. By employing the above technical solutions, using dimethylaminoborane as the reducing agent in the horizontal reducing agent for PCB electroless copper plating, the directional reduction deposition of copper ions is achieved by providing electrons. Simultaneously, due to its mild reaction characteristics and excellent solubility, the corrosion resistance of the electroless copper plating process is optimized. Preferably, the chelating agent is disodium diaminetetraacetate and / or potassium sodium tartrate. By employing the above technical solutions, disodium diaminetetraacetate can suppress side reactions, prevent spontaneous decomposition or co-deposition of the catalytic plating solution, stabilize the pH of the plating solution, reduce the formation of metal hydroxide precipitates, and refine the coating grains by precisely controlling the copper ion release rate. Potassium sodium tartrate has a low activation energy and a fast triggering speed, reducing copper oxide inclusions in the coating and improving the coating ductility and tensile strength. The combination of the two can enhance their synergistic effect, balancing performance and cost.

[0010] Secondly, the preparation method of the horizontal reducing agent for PCB chemical copper includes the following steps: 1) Weigh a portion of deionized water and boric acid according to the weight concentration, mix them evenly, add borate and stir until completely dissolved and adjust the pH value to ≥7 to obtain a buffer solution; 2) Weigh the reducing agent, processing aid, and composite accelerator according to their weight concentration and add them sequentially to the buffer solution. Mix thoroughly, then add deionized water to make up the volume to obtain a horizontal reducing agent. By adopting the above technical solution, adding boric acid and borate to prepare a buffer solution with a pH value ≥ 7 can provide a suitable reaction environment for subsequent components. Preparing activated carbon, nitrogen-containing heterocyclic compounds, and deionized water to form a composite accelerator can better utilize the performance of the composite accelerator. Adding the reducing agent, processing aid, and composite accelerator sequentially to the buffer solution and adding the remaining deionized water to make up the volume ensures that all components are mixed evenly. The resulting horizontal reducing agent avoids environmental pollution caused by the use of hydrochloric acid and nitric acid, avoids excessive erosion of the palladium catalyst core surface, reduces the porosity and unevenness of the electroless copper deposition layer, improves the corrosion resistance of the coating, and prevents palladium particles from peeling off and accumulating, causing blockage of the orifice or orifice cap. Preferably, the pH value range of the buffer solution is 7-9. By adopting the above technical solution, controlling the pH value of the buffer solution within the range of 7-9 is relatively mild and can avoid adverse effects on the subsequent electroless copper plating process due to excessive acidity or alkalinity. An overly acidic environment may excessively corrode the surface of the palladium catalyst core, leading to high porosity and uneven coating in the electroless copper plating layer; an overly alkaline environment may affect the activity of the reducing agent and other components. Adding a composite accelerator to the buffer solution has minimal impact on pH, providing a stable promoting effect during electroless copper plating. This avoids compromising the overall corrosion resistance of the system due to the acidity or alkalinity of the composite accelerator, thus ensuring the smooth progress of the electroless copper plating process, improving plating quality, reducing the probability of incomplete plating of the hole cap, minimizing microscopic defects, and enhancing the corrosion resistance of the coating.

[0011] Thirdly, the application of the horizontal reducing agent for PCB chemical copper plating involves immersing the substrate to be reduced in the horizontal reducing agent at a temperature of 25℃-35℃ for 30s-40s for reduction treatment. The reduced substrate is then subjected to chemical copper plating. The horizontal reducing agent is any one of the horizontal reducing agents for PCB chemical copper plating as described in claims 1-8. By adopting the above technical solution, existing PCB chemical copper plating reducing solutions using hydrochloric acid and nitric acid easily generate acidic wastewater that pollutes the environment, is troublesome to treat, and corrodes equipment. Furthermore, it can excessively corrode the surface of the palladium catalyst core, resulting in high porosity and uneven plating of the chemical copper deposition layer, reducing the corrosion resistance of the plating layer. This necessitates frequent replacement of the reducing solution in the production line, increasing maintenance costs and even causing blockage of orifices or caps. In contrast, this horizontal reducing agent uses boric acid and borates to form a buffer system, maintaining a suitable pH, avoiding the use of strong oxidizing acids, and reducing environmental pollution and equipment corrosion. By adding reducing agents and composite accelerators to achieve synergistic effects, it can effectively avoid excessive erosion of the palladium catalyst core surface, reduce the porosity of the electroless copper deposition layer during the copper plating process, make the coating more uniform, improve the corrosion resistance of the coating, reduce the frequency of changing the reducing solution on the production line, reduce maintenance costs, and also avoid the problem of clogging of the orifice or cover. Therefore, it can be well applied to electroless copper plating production.

[0012] In summary, this application includes at least one of the following beneficial technical effects: 1. This reducing agent, by mass concentration, consists of boric acid, borate, reducing agent, processing aid, composite accelerator, and deionized water. It maintains a stable acid-base environment by constructing a boric acid buffer system with a pH value ≥ 7, effectively preventing excessive corrosion of PCBs and generating easily treatable wastewater.

[0013] 2. The composite accelerator is composed of activated carbon and nitrogen-containing heterocyclic compounds. In a buffer system environment with a pH value ≥ 7, the activated carbon adsorbs impurities and microparticles, rapidly triggering copper ion reduction and increasing the deposition rate. The nitrogen-containing heterocyclic compounds in the boric acid system can synergistically regulate the crystal growth direction, refine the grain structure, improve the uniformity of PCB plating, and reduce the porosity of the chemical copper deposition layer, thereby reducing the frequency of changing the reducing solution on the production line and lowering the annual maintenance cost.

[0014] 3. This reducing agent avoids the use of hydrochloric acid and nitric acid, and will not cause palladium particles to peel off from the pore wall and accumulate at the pore opening or pore cover due to excessive corrosion by hydrochloric acid or nitric acid, thus preventing blockage. Detailed Implementation

[0015] The present application will be further described in detail below with reference to the embodiments.

[0016] Introduction to some raw materials: 2-Piperazinylpyrimidine, CAS No.: 20980-22-7; 3-Methyltetrahydrothiazolyl-2-thione, CAS No.: 1908-87-8; The activated carbon is coconut shell activated carbon, with a mesh size of 200-300; Polyethylene glycol, manufacturer: Guangzhou Diweisai New Materials Co., Ltd., CAS No.: 25322-68-3; Borates, a mixture of sodium tetraborate and potassium pentaborate; Copper plating solution, manufacturer: Huizhou Ronganda Chemical Co., Ltd., model: CH-968M / A / B. Example

[0017] Example 1 A horizontal reducing agent for PCB chemical copper is obtained by the following method: The composite accelerator is composed of activated carbon and a nitrogen-containing heterocyclic compound in a weight ratio of 1:1; the nitrogen-containing heterocyclic compound is 2-piperazinylpyrimidine. 1) Weigh 45L of deionized water and 300g of boric acid according to the weight concentration and put them into a 50L mixing tank. Mix them evenly, then add a mixture of sodium tetraborate and potassium pentaborate. Stir at 100rpm to completely dissolve the mixture and adjust the pH to 7 to obtain a buffer solution. 2) Weigh 150g of reducing agent, 15g of processing aid and 200g of composite accelerator according to weight concentration and add them to the buffer solution in sequence. Continue stirring until completely dissolved, then add deionized water to make up to 50L. After mixing evenly, the horizontal reducing agent is obtained. The processing aid is composed of polyethylene glycol and disodium diaminetetraacetate in a weight ratio of 1:1; the reducing agent is dimethylaminomethylborane.

[0018] Example 2-3 The difference between Examples 2-3 and Example 1 is that the amount of raw materials used is different, as shown in Table 1. Table 1. Raw material usage (g / L) for Examples 1-3 Raw materials Example 1 Example 2 Example 3 Boric acid 300 500 400 Reducing agent (dimethylaminoborane) 150 300 250 Complexing promoter 200 100 150 Processing aid 15 10 25 Example 4 The difference between Example 4 and Example 3 is that the nitrogen-containing heterocyclic compound consists of 3-methyltetrahydrothiazol-2-thione and 2-piperazinylpyrimidine in a weight ratio of 1:1.

[0019] Example 5 The difference between Example 5 and Example 3 is that in step 1), 45L of deionized water and 300g of boric acid are weighed according to weight concentration and placed into a 50L mixing tank. After mixing evenly, a mixture of sodium tetraborate and potassium pentaborate is added and stirred at 100rpm to completely dissolve the mixture and adjust the pH to 9 to obtain a buffer solution.

[0020] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that borate was replaced with boric acid in equal amounts.

[0021] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that the composite accelerator is activated carbon.

[0022] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that the composite accelerator is a nitrogen-containing heterocyclic compound.

[0023] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that boric acid was replaced with an equal amount of hydrochloric acid (6% by mass).

[0024] Application examples Application Example 1 An application of a horizontal reducing agent for PCB chemical copper plating involves sequentially performing a bulking treatment, removing adhesive residue, neutralizing treatment, degreasing and cleaning, acid etching treatment, and activation treatment to obtain a conductive PCB to be reduced. The conductive PCB to be reduced is then completely immersed in the horizontal reducing agent obtained in Example 1. After reduction treatment at a heating temperature of 30°C for 35 seconds, a copper plating product is obtained. The copper plating product is then immersed in a copper plating solution at a heating temperature of 38°C for 360 seconds to obtain a copper-plated product.

[0025] Application Example 2-10 The difference between Application Example 2-9 and Application Example 1 is that the source of the horizontal reducing agent is different, as shown in Table 2. Table 2 Sources of horizontal reducing agents in Application Examples 1-9 Application example Sources of horizontal reducing agents Application example 1 Example 1 Application example 2 Example 2 Application example 3 Example 3 Application example 4 Example 4 Application example 5 Example 5 Application example 6 Comparative example 1 Application example 7 Comparative example 2 Application example 8 Comparative example 3 Application example 9 Comparative example 4 Performance testing Detection methods / test methods Experiment (1) Perform batch restoration processing according to the restoration method in Application Examples 1-9; Sample: A conductive PCB to be reduced, measuring 20mm×30mm. The PCB is made of copper foil. Each PCB sample has 10 microholes with a diameter of 0.2mm. 100 PCB samples are used as a group, and 9 groups of samples are used. Nine PCB sample groups were immersed in nine different horizontal reducing agents from different sources for reduction treatment to obtain nine copper plating products. After the reduction treatment, 30 copper-plating products were randomly selected from each group. These 30 products were first rinsed in a clean water tank for 1 minute at a flow rate of 1 L / min, then placed in an oven and dried at 50°C for 5 minutes. After being left at room temperature for 30 minutes, the products were observed under a 200x microscope for micropore blockage. If micropore blockage was found in even one of the 30 products in each group, it was considered unqualified. Only when none of the products showed micropore blockage was it considered qualified. Specific data are shown in Table 3.

[0026] Experiment (II) Place the above 9 groups of copper-plating products to be tested after testing at a 45° inclination angle in a loading rack. The loading rack has 9 layers, and 30 copper-plating products of the same group are placed on each layer. The distance between each layer is 5 cm, the distance between adjacent two samples is 1 cm, and the samples of adjacent two layers are placed in a staggered manner. The amount of copper-plating solution is 80 L. When the loading rack with the copper-plating products to be plated is placed in the working tank containing the copper-plating solution, make the copper-plating solution completely submerge all the copper-plating products to be plated; after copper-plating treatment, put it into the water tank and wash it with water for 1 min, the water flow rate is 1 L / min, then put it into the oven and dry it at 50 °C for 5 min, and place it at room temperature for 30 min to obtain the copper-plated products.

[0027] Randomly select 10 copper-plated products from each group for coating uniformity detection. Randomly select two points on the surface of each copper-plated product as the test points, and use a cutting knife to cut the two test points of each copper-plated product at a perpendicular cutting angle, calculate the thickness difference between the two test points of each copper-plated product, and count the number of copper-plated products with a thickness difference < 0.1 mm among the 10 copper-plated products selected for testing in each group; Then randomly select 10 copper-plated products from each group of the above copper-plated products for salt spray testing. The salt spray testing refers to GB / T 2423.18-2012 "Environmental testing - Part 2: Test methods - Test Kb: Salt spray, cyclic (sodium chloride solution)". The concentration of the salt solution is 50 g / L, the pH value of the spray solution is 7, the salt spray deposition rate is controlled at 2.0 mL / (80 cm 2 ·h), the experimental time is 100 h, and observe once every 5 h; in each group of copper-plated products, as long as any one copper-plated product shows corrosion and discoloration within 50 h, it is recorded as unqualified. When all 10 copper-plated products in each group still do not show corrosion and discoloration within 100 h, it is recorded as qualified; then conduct porosity detection on the remaining 10 copper-plated products in each group of the above copper-plated products. The porosity detection refers to the alizarin test in GB / T 17720-1999 "Review of porosity test for metallic coatings". The pH value of the sodium hydroxide, sodium alizarin sulfonate, and glacial acetic acid solution d is 4.2, the experimental time is 1 min. When all 10 copper-plated products in each group meet the porosity ≤ 0.5 pores / cm 2 it is recorded as qualified. When any one of the 10 copper-plated products in each group does not meet the porosity ≤ 0.5 pores / cm 2 it is recorded as unqualified. The specific data is shown in Table 3.

[0028] Table 3 - Experimental data of Application Examples 1-9 Analysis of corrosion, discoloration, and micro-pore blockage detection results: From the data in Table 3, it can be seen that compared with the control group, in Application Examples 1-5, the conductive PCBs were reductively treated with the level reducing agents of Examples 1-5 respectively, and no micro-pore blockage was found in the copper-plating products to be treated after the treatment, and all were qualified. In Application Examples 6-9, the copper-plating products to be treated were reductively treated with the level reducing agents of Comparative Examples 1-4 respectively. Only the micro-pore blockage results of Comparative Examples 2-3 were qualified after the treatment. Micro-pore blockage occurred in all copper-plating products of Comparative Example 1 and 4, and micro-pore blockage occurred in all copper-plating products of Comparative Examples 2 and 3. This shows that the buffer solution system composed of boric acid and borate has a greater impact on micro-pore blockage. Activated carbon and nitrogen-containing heterocyclic compounds are not the reasons for micro-pore blockage. Indirectly, it shows that the buffer solution system composed of boric acid and borate can play a good role in protecting and reducing the PCB, improve the corrosion resistance of the PCB reductive treatment, and effectively prevent the occurrence of micro-pore blockage.

[0029] Analysis of coating uniformity results: The copper-plating products obtained in Application Examples 1-5 were further copper-plated and then subjected to coating uniformity detection. Example 4 was of special grade, and the rest of the examples were all of grade A. This shows that after copper plating of the PCBs treated with the reducing agents of Examples 1-5, the coating uniformity is very high. Especially in Example 4, a nitrogen-containing heterocyclic compound composed of 3-methyltetrahydrothiazole-2-thione and 2-piperazinylpyrimidine was used, and the coating uniformity was better. From the results of Application Examples 6 and 9 being both grade C and the results of Application Examples 7-8 being both grade B, it can be seen that the buffer solution system of boric acid and borate, activated carbon, and the heterocyclic compounds in Handan are all likely to affect the coating uniformity. From the comparison between Application Examples 7-8 and the examples, it can be seen that both activated carbon and nitrogen-containing heterocyclic compounds in the composite accelerator are indispensable. Once one of the substances is missing, the coating uniformity will be reduced. Indirectly, it shows that the buffer solution of boric acid and borate, activated carbon, and nitrogen-containing heterocyclic compounds are all indispensable, and the three need to cooperate to form a uniformly distributed coating.

[0030] Analysis of porosity structure: The porosity detections of the copper-plated products in Application Examples 1-3 and Application Example 5 were all qualified. Although there was one PCB sample in Example 4 that did not meet the porosity ≤ 0.5 holes / cm 2 , it could still greatly reduce the surface porosity of the coating. This shows that when the PCBs treated with the reducing agents of Examples 1-5 were copper-plated, a relatively dense coating could be formed, with low porosity, which is helpful to improve the stability of the coating. The porosity detections of the copper-plated products in Application Examples 6-9 were all unqualified. Compared with Examples 1-5, it shows that the reducing agents of Examples 1-5 have obvious advantages in reducing porosity, indicating that the buffer solution of boric acid and borate, activated carbon, and nitrogen-containing heterocyclic compounds in the composite accelerator are all indispensable, and the three need to cooperate to form a crystalline and dense coating.

[0031] Salt spray test structural analysis: The copper-plated products obtained in Examples 1-5 were further copper-plated and then subjected to salt spray testing. All results were qualified, indicating that the PCBs treated with the reducing agent in Examples 1-5 have good corrosion resistance after copper plating and can remain stable in a salt spray environment. The copper-plated products obtained in Examples 6-9 all failed the salt spray test. This indicates that the buffer solution of borate and boric acid, activated carbon, and nitrogen-containing heterocyclic compounds have a significant impact on the corrosion degree of the coating. In the reduction treatment, the buffer solution of boric acid and borate in the reducing agent, the activated carbon in the composite promoter, and the nitrogen-containing heterocyclic compounds are all indispensable. The three need to work together to form a uniformly distributed, high-purity, and densely crystalline coating, thereby making the coating more corrosion-resistant and able to remain stable in a salt spray environment.

[0032] The role of the boric acid system: In Comparative Example 1, borate was replaced with an equal amount of boric acid, and in Comparative Example 4, boric acid was directly replaced with an equal amount of hydrochloric acid. Both resulted in corrosion and discoloration in the reduced samples, and the copper-plated products failed salt spray and porosity tests. However, Examples 1-5, using borate and adjusted to a suitable buffer system, passed all tests. This indicates that the boric acid system plays a crucial role in the reducing agent, maintaining a stable reducing environment, helping to reduce corrosion, prevent discoloration, improve coating quality, and reduce porosity.

[0033] The role of activated carbon and nitrogen-containing heterocyclic compounds in composite accelerators: Comparative Example 2 used only activated carbon as the composite accelerator, and Comparative Example 3 used only nitrogen-containing heterocyclic compounds as the composite accelerator. Although the reduced samples did not show corrosion or discoloration, their effects on improving coating uniformity, corrosion resistance, and density were poor. However, Examples 1-5, which used composite accelerators composed of activated carbon and nitrogen-containing heterocyclic compounds, showed better performance in all tests, with almost all results meeting the standards. This indicates that activated carbon and nitrogen-containing heterocyclic compounds work synergistically in the composite accelerator; neither can be dispensed with. Together, they promote the reduction reaction, improve the reduction effect, and thus reduce porosity and improve the corrosion resistance of the coating.

[0034] In summary, the reducing agents in Examples 1-5 exhibit excellent performance in reducing corrosion, preventing discoloration, reducing the porosity of copper-plated products, and improving the corrosion resistance of the coating. Furthermore, the boric acid system, the activated carbon in the composite accelerator, and the nitrogen-containing heterocyclic compound work synergistically to ensure the good performance of the reducing agent.

[0035] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A horizontal reducing agent for PCB chemical copper plating, characterized in that, The solution is composed of the following raw materials by mass concentration: boric acid, borate, reducing agent, processing aid, composite accelerator, and deionized water; the mass concentration of boric acid is 6-10 g / L, the mass concentration of the reducing agent is 3-6 g / L, the mass concentration of the processing aid is 0.2-0.5 g / L, the mass concentration of the composite accelerator is 2-4 g / L, the borate is used to adjust the pH of the solution to ≥7, and the composite accelerator is composed of activated carbon and nitrogen-containing heterocyclic compounds.

2. The horizontal reducing agent for PCB chemical copper according to claim 1, characterized in that, The nitrogen-containing heterocyclic compound is the thiazothione compound and / or the pyrimidine compound.

3. The horizontal reducing agent for PCB chemical copper according to claim 2, characterized in that... The thiazothione compound is 3-methyltetrahydrothiazo-2-thione, and the pyrimidine compound is 2-piperazinylpyrimidine.

4. The horizontal reducing agent for PCB chemical copper according to claim 1, characterized in that, The processing aid consists of surfactants and chelating agents.

5. The horizontal reducing agent for PCB chemical copper according to claim 4, wherein the surfactant is one or a combination of more than one of polyethylene glycol, polyvinyl alcohol, fatty alcohol polyoxyethylene ether, and amine ethoxylate.

6. The horizontal reducing agent for PCB chemical copper according to claim 1, characterized in that, The reducing agent is dimethylaminoborane.

7. The horizontal reducing agent for PCB chemical copper according to claim 1, characterized in that, The chelating agent is disodium diaminetetraacetate and / or potassium sodium tartrate.

8. A method for preparing a horizontal reducing agent for PCB chemical copper as described in any one of claims 1-7, characterized in that, Includes the following steps: 1): Weigh out a portion of deionized water and boric acid according to the weight concentration, mix them evenly, then add borate and stir until completely dissolved and adjust the pH value to ≥7 to obtain the buffer solution; 2): Weigh the reducing agent, processing aid and compound accelerator according to the weight concentration and add them to the buffer solution in sequence. Mix well and then add deionized water to make up the volume to obtain the horizontal reducing agent.

9. The method for preparing a horizontal reducing agent for PCB chemical copper according to claim 7, characterized in that, The pH range of the buffer solution is 7-9.

10. An application of a horizontal reducing agent for PCB chemical copper, characterized in that, The substrate to be reduced is placed in a horizontal reducing agent and immersed in it at a temperature of 25℃-35℃ for 30s-40s for reduction treatment. The reduced substrate is then subjected to chemical copper plating treatment. The horizontal reducing agent is a horizontal reducing agent for PCB chemical copper plating as described in any one of claims 1-8.

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