Catalyst solution for electroless copper plating

Abstract

The present application relates to a catalyst solution for electroless copper plating. The antioxidant is added into the catalyst solution, even palladium with the medium-concentration dry bath ratio can show excellent catalytic performance, the original solution cannot change along with time, and the service life and plating reliability of dry bath liquid can be ensured for a long time when the catalyst solution is applied to a plating site.

Description

Technical Field

[0001] This application relates to a catalyst solution for electroless copper plating. Background Technology

[0002] Semiconductor chips containing integrated circuits are mounted on printed circuit boards (PCBs) for use in electronic devices. A printed circuit board is formed by stacking unit substrates, namely copper-clad laminates (CCLs), which are thin sheets made of insulating materials such as epoxy resin and have a copper overlay.

[0003] In printed circuit boards (PCBs), to allow current to flow from one side of the substrate to the other, the inner walls of the formed through-holes need to be plated with a metal material such as copper. Since the surfaces of the through-holes on PCBs contain insulators, chemical plating is required for this process.

[0004] Existing technical documents

[0005] Patent documents

[0006] Korean Patent Publication No. 10-1681116 Summary of the Invention

[0007] Technical issues

[0008] This application relates to a catalyst solution that exhibits the same superior performance as a catalyst solution with a high dry bath ratio, even at a medium concentration dry bath ratio. More specifically, this application relates to a catalyst solution that, even at a medium concentration dry bath ratio, does not experience liquid collapse when left for extended periods at room temperature or high temperature, and that ensures long-term dry bath solution lifespan and plating reliability when applied in plating environments.

[0009] Solution to the problem

[0010] In this specification, if the measurement temperature affects the results of any physical property mentioned, unless otherwise specified, the physical property refers to the physical property measured at room temperature. The term "room temperature" means the natural temperature at which the temperature is neither increased nor decreased, typically a temperature in the range of about 10°C to 30°C, or about 23°C or about 25°C. Furthermore, unless otherwise specified in this specification, the unit of temperature is °C. In this specification, if the measurement pressure affects the results of any physical property mentioned, unless otherwise specified, the physical property refers to the physical property measured at atmospheric pressure. The term "atmospheric pressure" means the pressure under natural conditions at which the pressure is neither increased nor decreased, typically about 1 atmosphere.

[0011] This application relates to a catalyst solution. The catalyst solution can be a catalyst solution used for electroless copper plating. The catalyst solution may include a coordination compound containing palladium ions and a first ligand bound to the palladium ions. The catalyst solution may further include a second ligand. The second ligand can act as a dispersing stabilizer between the coordination compounds through electrostatic interactions, preventing palladium particles from precipitating in the solution.

[0012] The palladium ions mentioned above can originate from palladium compounds containing palladium ions. These palladium compounds can include at least one selected from the group consisting of palladium sulfate, palladium chloride, palladium fluoride, palladium bromide, palladium iodide, palladium nitrate, and palladium sulfide. Palladium ions can act as a catalyst in electroless copper plating. In one example, during electroless copper plating, palladium metal from the aforementioned coordination compound can be deposited on the surface of the object to be plated. The palladium metal can be used as a catalyst to reduce copper ions in the plating bath, thereby depositing copper on the surface of the object to be plated. In this way, electroless copper plating can be achieved on the surface of the object to be plated. In one example, the palladium compound can be palladium sulfate.

[0013] The first ligand can be a compound capable of coordinate bonding with a palladium ion. The first ligand can be a compound possessing a lone pair of electrons. In one example, the first ligand may comprise at least one compound selected from the group consisting of pyridine compounds, pyridine alcohols, pyridine amines, and pyridine carboxylic acids. Examples of the aforementioned pyridine compounds include pyridine, pyridine oxide, Borane pyridine, 2-chloromethylpyridine, and 4-trifluoromethylpyridine. Examples of the aforementioned pyridine alcohols include 2-pyridinemethanol, 3-pyridinemethanol, or 4-pyridinemethanol. Examples of the aforementioned pyridine amine compounds include 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, and 4-dimethylaminopyridine. Examples of the aforementioned pyridine carboxylic acid compounds include pyridine-2-carboxylic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-2,6-dicarboxylic acid, and chloropyridine-2-carboxylicacid.

[0014] The second ligand can be a substance with lower volatility compared to the first ligand. In this specification, "substance A has lower volatility than substance B" can mean that the vapor pressure of substance A is lower than that of substance B. In one example, the vapor pressure of the second ligand can be 0.01 mmHg or higher. The upper limit of the vapor pressure of the second ligand can be, for example, 10.00 mmHg or lower. In this specification, vapor pressure can be a value measured at approximately 20°C. In one example, the difference (AB) between the vapor pressure of the first ligand (A) and the vapor pressure of the second ligand (B) can be in the range of 5.00 mmHg to 20.00 mmHg.

[0015] The second ligand differs from the first ligand in that it does not bind to palladium ions (e.g., through coordination bonding). The second ligand can be included in the catalyst solution as a dispersion stabilizer to stably disperse the particles (coordination compounds) formed by palladium ions and the first ligand in the catalyst solution.

[0016] The second ligand can be a compound having a functional group in its molecular structure that can form hydrogen bonds due to its dipole moment. The second ligand can include at least one selected from the group consisting of pyridine alcohols, toluenes, pyridineamines, carboxylic acids, and pyridinecarboxylic acids. More specifically, the second ligand can include at least one selected from the group consisting of pyridine alcohols, toluenes, and pyridineamines. Examples of the aforementioned pyridine alcohols include 2-pyridinemethanol, 3-pyridinemethanol, or 4-pyridinemethanol. Examples of the aforementioned toluenes include toluene, 4-(methylsulfonyl)toluene, toluene-3,4-dithiol, and toluene sulfonic acid. Examples of the aforementioned pyridine amine compounds include 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, and 4-dimethylaminopyridine. Examples of the aforementioned carboxylic acid compounds include 2-methylpyridine-3-carboxylic acid, 1-cyclohexene-1-carboxylic acid, imidazole-2-carboxylic acid, 2-hydroxypyridine-3-carboxylic acid, and 2-aminopyridine-3-carboxylic acid. Examples of the aforementioned pyridine carboxylic acid compounds include pyridine-2-carboxylic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-2,6-dicarboxylic acid, and chloropyridine-2-carboxylic acid.

[0017] The catalyst solution may contain antioxidants. Antioxidants can prevent palladium ions (Pd) from entering the catalyst solution.2+ The antioxidant acts as a precipitate, formed from the oxidation of palladium oxide (PdO2). Specifically, it prevents unstable free radicals generated during the plating process from reacting with palladium ions (PdO2). 2+ This combination of factors contributes to the precipitation of palladium oxide (PdO2). Furthermore, the antioxidant also helps prevent palladium ions (PdO2) from precipitating in the catalyst solution. 2+ The reduction effect. By including antioxidants in the catalyst solution, even with a medium-concentration dry bath ratio catalyst solution, a uniform distribution of palladium ions can be achieved, thereby realizing stable coating performance.

[0018] In this specification, the dry bath ratio of the catalyst solution refers to the composition ratio when the catalyst solution is first prepared in the electroless plating process, and is particularly related to the concentration of catalyst components such as palladium. In this specification, a medium-concentration dry bath ratio catalyst solution can be a catalyst solution with a palladium concentration in the range of approximately 80 ppm to 160 ppm. In this specification, a high-concentration dry bath ratio catalyst solution can be a catalyst solution with a palladium concentration exceeding approximately 160 ppm. Specifically, the palladium concentration in the aforementioned high-concentration dry bath ratio catalyst solution can be 170 ppm or more, or 180 ppm or more, and can be less than 250 ppm. Although this specification describes that the above-mentioned catalyst solutions, even at medium-concentration dry bath ratios, possess excellent performance comparable to high-concentration dry bath ratios, the scope of the invention is not limited to catalyst solutions with medium-concentration dry bath ratios. When prepared by mixing the components contained in the catalyst solution, the catalyst solution can have a high Pd concentration (e.g., 1,000 ppm or more) (in which case it can also be referred to as a stock catalyst solution). The concentration of the above-mentioned catalyst solution can be adjusted as needed, for example, the concentration can be appropriately adjusted according to the operating environment or plating conditions before use. The scope of the present invention may include not only the catalyst solution in the original liquid state containing the components described in the present invention, but also the catalyst solution after dilution of the catalyst solution in the original liquid state (e.g., including the medium-concentration dry bath ratio catalyst solution and the high-concentration dry bath ratio catalyst solution described above).

[0019] The catalyst solution described above, when subjected to palladium concentrations of 80 ppm to 160 ppm and a volume of 1 L, yielded precipitates with a weight of less than 1 g after being left at room temperature and 70°C for 4 days respectively. In other words, the catalyst solution under the above conditions yielded precipitates with a weight of less than 1 g after being left at room temperature for 4 days, and the catalyst solution under the above conditions yielded precipitates with a weight of less than 1 g after being left at 70°C for 4 days. The weight of the precipitate can be determined by filtering the catalyst solution using 150 mm, No. 2 filter paper from Toyo Roshi Kaisha, Ltd., drying the precipitate at 60°C for 8 hours, and then measuring the weight of the dried precipitate.

[0020] The catalyst solution described above, with a palladium concentration of 80 ppm to 160 ppm and a volume of 1 L, exhibits a weight change rate of less than 1% after being placed at room temperature and 70°C for 4 days respectively. In other words, the catalyst solution obtained after being placed at room temperature for 4 days under the above conditions exhibits a weight change rate of less than 1%, and the catalyst solution obtained after being placed at 70°C for 4 days also exhibits a weight change rate of less than 1%. The weight change rate of the catalyst solution can be calculated using Equation 1 below.

[0021] [Formula 1]

[0022] Weight change rate = (AB) / A × 100%

[0023] A: Initial weight of the catalyst solution; B: Weight of the catalyst solution after being placed at room temperature or 70°C for 4 days.

[0024] The aforementioned antioxidants may comprise at least one compound selected from the group consisting of toluene compounds, acetate compounds, quinone compounds, benzene alcohol compounds, and anisole compounds. In this specification, "A-class compounds" may refer to compounds containing the structure A, or compounds derived from A. Examples of toluene compounds include dibutyl hydroxytoluene. Examples of acetate compounds include disodium ethylenediaminetetraacetate. Examples of quinone compounds include tertbutyl hydroxyquinone. Benzene alcohol compounds may be, for example, phenolic compounds, such as catechol. Examples of anisole compounds include butyl hydroxyanisole.

[0025] When the catalyst solution contains an antioxidant, the antioxidant content in the catalyst solution can be from 0.001 wt% to 1 wt%, or from 0.01 wt% to 0.5 wt%. The weight ratio of the second ligand to the antioxidant in the catalyst solution can, for example, be from 1:0.01 to 1:0.5. If the antioxidant concentration is too high, it may cause oxidation on the substrate (the object to be plated), thereby reducing the amount of Pd that needs to play a catalytic role in the plating process. 2+The number of ions affects the reliability of the plating, so it is preferable to keep their concentration within the above range.

[0026] The catalyst solution may further contain water as a solvent. In one example, the pH of the catalyst solution may be between 11 and 13. When the pH of the catalyst solution is within the above range, it is beneficial to increase the likelihood that the free hydroxyl groups in the catalyst solution will form stable coordination compounds with palladium. The above pH values ​​may specifically be 11 or higher, 11.5 or higher, or 12 or higher, and may be 13 or lower, or 12.5 or lower.

[0027] The catalyst solution may further contain boron and sodium compounds. In this specification, boron compound may refer to a compound containing boron (B), and sodium compound may refer to a compound containing sodium (Na). The aforementioned boron compound can function as a pH buffer in the catalyst solution. The aforementioned sodium compound can function as a pH adjuster in the catalyst solution. In one example, the boron compound may be boric acid (H3BO3), and the sodium compound may be sodium hydroxide (NaOH).

[0028] In the catalyst solution, the weight concentration of sodium compound can be higher than that of boron compound. In one example, the weight concentration ratio of boron compound to sodium compound in the catalyst solution can be in the range of 1:2 to 1:9. When the weight concentration ratio of boron compound to sodium compound is within the above range, it is beneficial to adjust the pH of the catalyst solution to the above range. The above weight concentration ratio can specifically be 1:2 or higher, and can be 1:9 or lower, 1:8 or lower, 1:7 or lower, 1:6 or lower, 1:5 or lower, 1:4 or lower, or 1:3 or lower.

[0029] In one example, the catalyst solution may further contain a wetting agent. For example, the wetting agent may be a polymer of ethylene glycol. In one example, the molecular weight of the wetting agent may be in the range of 400 to 20,000. When the catalyst solution further contains a wetting agent, the content of the wetting agent in the overall catalyst solution may be from 0.0005% by weight to 0.5% by weight.

[0030] In one example, the catalyst solution may further contain a coupling agent. The coupling agent used in the catalyst solution may be one or a mixture of two of silane-based coupling agents, titanate-based coupling agents, and zirconate-based coupling agents. For example, the coupling agent used in the catalyst solution may be at least one of neopentyl(diallyl)oxy, trineodecanonyl zirconate, and neopentyl(diallyl)oxy, trineodecanonyltitanate. The aforementioned coupling agent can enhance the adsorption of palladium ions on the insulating layer of the printed circuit board and can help with uniform adsorption. When the catalyst solution further contains a coupling agent, the content of the coupling agent in the overall catalyst solution may be from 0.001% by weight to 1% by weight.

[0031] In one example, the catalyst solution may further contain an anti-foaming agent. The anti-foaming agent inhibits bubble formation and also improves wettability through dispersion. If bubbles are generated, they may adhere to the surface of the object being plated (e.g., a printed circuit board) after passing through the catalyst solution, leading to foreign matter defects. However, by using the aforementioned anti-foaming agent, such defects can be prevented. The anti-foaming agent may be 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

[0032] This application also relates to a method for preparing the above-mentioned catalyst solution. Unless otherwise specifically stated in the method for preparing the catalyst solution, the content mentioned above regarding the catalyst solution is equally applicable.

[0033] In one example, the preparation method of the catalyst solution described above may include the following steps: adding a palladium compound to water; adding a first ligand compound; adding an antioxidant; adding a boron compound and a sodium compound; and adding a second ligand compound.

[0034] The amount of the palladium compound added to the overall catalyst solution can be from 0.02% by weight to 3.00% by weight. The amount of palladium compound added determines the concentration of palladium ions in the catalyst solution. If too much palladium compound is added, it may lead to an excessively high concentration of the formed coordination compound, thereby forming an insoluble coordination compound. Therefore, it is preferable that the amount added is within the above-mentioned range. Specifically, the above weight can be 0.1% by weight or more, 0.5% by weight or more, 1.0% by weight or more, 1.5% by weight or more, or 2.0% by weight or more, and can be 3.00% by weight or less, 2.8% by weight or less, or 2.6% by weight or less.

[0035] The first ligand compound can form a coordination compound by reacting with palladium ions derived from the decomposition of the palladium compound. In this case, the reaction temperature for forming the coordination compound can be from 50°C to 90°C, and the reaction time can be from 30 minutes to 480 minutes.

[0036] The amount of the first ligand compound added in the overall catalyst solution can be from 0.2% to 2.0% by weight. When the content of the first ligand compound is within the above range, it is suitable to form a coordination compound by coordinating with palladium. The above weight can specifically be more than 0.2% by weight, more than 0.3% by weight, more than 0.4% by weight, or more than 0.5% by weight, and can be less than 2.0% by weight, less than 1.5% by weight, less than 1.0% by weight, or less than 0.8% by weight.

[0037] The antioxidant described above can be added in the overall catalyst solution at a rate of 0.001% to 1% by weight. When the weight of the antioxidant is within the above range, it may be more suitable for effectively removing free radicals in the mixed solution. Specifically, the weight of the antioxidant can be 0.01% by weight or more, and 0.5% by weight or less.

[0038] The total weight of the aforementioned boron and sodium compounds can range from 1% to 15% by weight of the total catalyst solution. When the content of boron and sodium compounds is within this range, it may be advantageous in terms of adjusting the pH of the catalyst solution to this range. Specifically, the total weight can be 1% or more, 1.3% or more, or 1.5% or more, and can be less than 15% by weight, less than 13% by weight, less than 11% by weight, less than 9% by weight, less than 7% by weight, less than 5% by weight, or less than 3% by weight.

[0039] The amount of the second ligand added to the overall catalyst solution can be from 0.01% to 0.5% by weight. If the amount of the second ligand added is too high, it may interfere with the coordination bond between the first ligand and palladium. To ensure that the second ligand only forms a stable electrostatic attraction, its content is preferably within the above range. The above weight can specifically be more than 0.01% by weight or more than 0.03% by weight, and can be less than 0.5% by weight, less than 0.3% by weight, or less than 0.1% by weight.

[0040] The method for preparing the catalyst solution may further include a step of adjusting for water after adding the second ligand. This water adjustment step may involve adjusting for the weight of volatile water during the catalyst solution preparation process to ensure a consistent total volume of the final catalyst solution. The pH of the final catalyst solution may be between 11 and 13. Specifically, the pH value may be 11 or higher, 11.5 or higher, or 12 or higher, and may be 13 or lower, or 12.5 or lower.

[0041] This application also relates to the use of the aforementioned catalyst solution. Unless otherwise specifically stated in the description of the use of the catalyst solution, the content mentioned above regarding the catalyst solution is equally applicable. The aforementioned catalyst solution can be a catalyst solution for electroless plating. The aforementioned plating can include copper plating, tin plating, or nickel plating. In one example, this application relates to a method for electroless copper plating using the aforementioned catalyst solution. The aforementioned electroless copper plating method can include: a step of catalytically treating the object to be plated with the catalyst solution; and a step of immersing the object to be plated in a plating solution containing copper ions.

[0042] In the step of catalytically treating the object to be coated with a catalyst solution, the term "catalytic treatment" can refer to contacting the object to be coated with the catalyst solution. There are no particular limitations on the contact method; for example, dipping, spraying, etc., can be used. In this step, palladium metal ions in the catalyst compound can be reduced and deposited as palladium metal on the surface of the object to be coated.

[0043] In the step of immersing the object to be plated in a plating solution containing copper ions, the copper ions can be reduced using palladium metal as a catalyst, thereby causing copper to deposit on the surface of the object. This forms a copper plating layer on the surface of the object. There are no particular limitations on the plating solution containing copper ions; known compositions for copper plating can be used.

[0044] The aforementioned electroless copper plating method may further include a pre-dip step before catalytic treatment of the object to be plated. This pre-dip step can refer to treating the object to be plated with a pre-dip solution, which can be performed by immersing the object to be plated in the pre-dip solution. The pre-dip solution may contain a first ligand component. In the plating process, since the components of the pre-dip solution will enter the catalyst solution, using the same ligand component as in the catalyst solution allows for maintaining a high concentration of the first ligand without disrupting the composition of the catalyst solution, thus offering an advantage.

[0045] In one example, the object to be plated may include an insulator. When the object to be plated is an insulator, conductivity can be imparted by forming a copper plating layer as described above. After imparting conductivity to the surface of the insulator, a copper plating layer can also be further formed by plating.

[0046] In one example, the object to be plated can be the inner wall of a through-hole in a printed circuit board (PCB). A PCB can be a stack of conductive and insulating layers. Specifically, a PCB can be formed by stacking unit substrates of copper-clad laminate (CCL), which are thin sheets made of an insulator with a copper overlay. In a PCB, to allow current to flow from one side of the substrate to the other, a process is required to plate the inner walls of the formed through-holes with a metal material such as copper. Since the surface of the through-holes in a PCB contains an insulator, chemical plating can be used.

[0047] The effects of the invention

[0048] This application, by adding an antioxidant to the catalyst solution, enables even medium-concentration dry-bath ratio catalyst solutions to exhibit the same superior performance as high-concentration dry-bath ratio catalyst solutions. The catalyst solution of this application does not experience liquid collapse when left for extended periods at both room and high temperatures, ensuring long-term dry bath solution lifespan and plating reliability even when applied in plating environments. Attached Figure Description

[0049] Figure 1 The experimental results of Evaluation Example 1 and Evaluation Example 2 are shown.

[0050] Figure 2 The experimental results for evaluation example 3 are shown. Detailed Implementation

[0051] Although this application will be specifically described through the following embodiments, the scope of this application is not limited to the following embodiments.

[0052] Example 1

[0053] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.01 wt% antioxidant (butylated hydroxytoluene), 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total amount with pure water to reach 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0054] Example 2

[0055] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.01 wt% antioxidant (disodium ethylenediaminetetraacetate), 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total amount with pure water to reach 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0056] Example 3

[0057] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.01 wt% antioxidant (tert-butylhydroxyquinone), 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total amount with pure water to reach 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0058] Example 4

[0059] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.01 wt% antioxidant (catechol), 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total amount with pure water to reach 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0060] Example 5

[0061] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.01 wt% antioxidant (butylated hydroxyanisole), 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total amount with pure water to reach 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0062] Comparative Example 1

[0063] A catalyst solution was prepared by sequentially adding 80 wt% pure water, 2.5 wt% palladium sulfate, 0.5 wt% pyridine, 0.05 wt% 3-pyridinemethanol, 0.5 wt% boric acid, 1.1 wt% sodium hydroxide, and 0.05 wt% 3-pyridinemethanol to a beaker, and then adjusting the total volume with pure water to 100 wt%. The pH of the prepared catalyst solution was measured to be 12.3.

[0064] Evaluation Example 1. Evaluation of Liquid Collapse

[0065] The catalyst solutions (catalyst stock solutions) obtained in Examples 1 to 5 and Comparative Example 1 were diluted to prepare high-concentration and medium-concentration catalyst solutions, respectively. Specifically, the palladium concentration in the catalyst solutions (catalyst stock solutions) prepared in Examples 1 to 5 and Comparative Example 1 was approximately 1000 ppm. The ppm values ​​of the palladium concentration mentioned above were calculated and measured based on the mass of the entire solution (according to chemometrics, the theoretical concentration of Pd in ​​the catalyst stock solution is 1000 ppm, and the measured value is between approximately 950 ppm and 1050 ppm. The instrument used for measurement was a PerkinElmer Avio 550 MAX ICP device. At this time, it was assumed that the density of pure water was 1 g / mL). As a high-concentration catalyst solution, 215 mL of the above catalyst solution (catalyst stock solution) was added to approximately 785 mL of pure water to achieve a palladium concentration of approximately 215 ppm. As a medium-concentration catalyst solution, 120 mL of the above catalyst solution (catalyst stock solution) was added to approximately 880 mL of pure water to achieve a palladium concentration of approximately 120 ppm.

[0066] The high-concentration and medium-concentration catalyst solutions were placed at room temperature and 70°C for 7 days respectively. The presence of fading and precipitation was observed, and the liquid collapse was evaluated accordingly. The results are shown in Table 1 (no fading and precipitation were rated as "X", and fading and precipitation were rated as "O"). Figure 1The figures show the evaluation results for Example 1 and Comparative Example 1. In Examples 1 to 5, no fading or precipitation was observed in either the high-concentration or medium-concentration catalyst solutions after being placed at room temperature and 70°C for 7 days. In Comparative Example 1, no fading or precipitation was observed in the high-concentration catalyst solution, but fading and precipitation occurred in the medium-concentration catalyst solution after 7 days at room temperature, and again on the 4th day at 70°C. These fading and precipitation phenomena can be explained by the palladium coordination compound transforming into an insoluble form and precipitating, thus causing fading.

[0067] Furthermore, for each of the high-concentration and medium-concentration catalyst solutions, 1 L was left to stand at room temperature and 70°C for 4 days, and the weight of the precipitate was measured. The precipitate was filtered using 150 mm, No. 2 filter paper from Toyo Roshi Kaisha, then dried at 60°C for 8 hours, and the weight of the dried precipitate was measured. In the cases of the high-concentration and medium-concentration catalyst solutions of Examples 1 to 5, and the high-concentration catalyst solution of Comparative Example 1, the weight of the precipitate after standing under the above conditions did not exceed 1 g, while in the case of the medium-concentration catalyst solution of Comparative Example 1, the weight of the precipitate after standing under the above conditions exceeded 1 g.

[0068] Furthermore, for each of the high-concentration and medium-concentration catalyst solutions, 1 L was placed at room temperature and 70°C for 4 days, and the weight change of the solution was measured. The weight change rate of the catalyst solution was calculated according to Formula 1 below. In the cases of the high-concentration and medium-concentration catalyst solutions of Examples 1 to 5 and the high-concentration catalyst solution of Comparative Example 1, the overall weight change rate of the catalyst solution measured after being placed under the above conditions did not exceed 1%, while the medium-concentration catalyst solution of Comparative Example 1 showed a weight decrease after being placed under the above conditions, and its change rate exceeded 1%.

[0069] [Formula 1]

[0070] Weight change rate = (AB) / A × 100%

[0071] A: Initial weight of the catalyst solution; B: Weight of the catalyst solution after being placed at room temperature or 70°C for 4 days.

[0072] Evaluation Example 2. Liquid Life Evaluation

[0073] For the catalyst solutions of Examples 1 to 5 and Comparative Example 1, high-concentration and medium-concentration catalyst solutions were prepared using the same method as in Evaluation Example 1. These catalyst solutions were applied at the plating site, and the lifetime of the liquid (site dry bath solution) was evaluated. The results are recorded in Table 1. Figure 1The figures show the evaluation results for Example 1 and Comparative Example 1. First, the epoxy substrate was degreased and then etched. Subsequently, a pre-immersion treatment using ligand components (pyridine, 3-pyridinemethanol) was performed, followed by treatment with a catalyst solution by immersion at 40°C for 1 minute. Afterward, the catalytically treated epoxy substrate was immersed in a chemical copper plating solution at 35°C for 5 minutes to form a copper plating layer. In Examples 1 to 5, both the high-concentration and medium-concentration catalyst solutions showed no liquid stability issues after 4 weeks of use in a dry bath, and the plating reliability remained normal. In Comparative Example 1, the high-concentration catalyst solution synthesized in the same manner did not show stability or plating reliability issues, but the medium-concentration catalyst solution showed decreased liquid stability (becoming waste liquid) and reduced plating reliability after 2 weeks of use in a dry bath.

[0074] Evaluation Example 3. Performance Evaluation of Medium-Concentration Pd with Added Antioxidant

[0075] High-concentration and medium-concentration catalyst solutions were prepared using the same method as in Evaluation Example 1 for the catalyst solutions of Examples 1 to 5 and Comparative Example 1. The coating uniformity of the electroless copper plating was confirmed using the above catalyst solutions, and the performance of the medium-concentration palladium (Pd) was evaluated. The results are recorded in Table 1. Figure 2The images show the evaluation results for Example 1 and Comparative Example 1. Specifically, to confirm the uniformity of the electroless copper plating, B / L (backlight) observation of through-holes and Hole Coverage observation of blind holes were performed. Through-hole B / L observation involved cutting the through-hole longitudinally to make its cross-section observable, and then transmitting light through the back of the through-hole to observe the light transmission phenomenon. If the copper plating is uniform, light will not pass through the object under observation; if the copper plating is uneven, light will leak into the gaps (evaluated in order of copper plating uniformity from D0 to D5). Bone Coverage observation confirmed whether the copper plating inside the blind hole was uniformly covered; that is, the plating and unplated areas were identified by examining with an electron microscope. Higher hole coverage (i.e., less unplated area) indicates better plating performance. The electroless copper plating process is as follows: The epoxy board with through-holes was degreased, and then an etching process was performed. Subsequently, the epoxy-based plate was pre-impregnated with a ligand component (3-pyridinemethanol) and then treated with the catalyst solution by immersing it in the catalyst solution at 40°C for 1 minute. Next, the epoxy-based plate was immersed in a chemical copper plating solution at 35°C for 5 minutes to form a copper plating layer. Evaluation results showed that the medium-concentration catalyst solution synthesized according to Examples 1 to 5 exhibited the same performance as the catalyst solution with a high palladium concentration in the dry bath. "Same performance" means that the evaluation result grade was D0 when observing the B / L ratio of the through holes, indicating that the copper plating layer was extremely uniform and that there were no unplated areas when observing the hole coverage of the blind holes. On the other hand, the performance of the medium-concentration catalyst solution prepared by the method of Comparative Example 1 was lower than that of the catalyst prepared with a high concentration (reduced hole coverage).

[0076] Table 1

[0077]

Claims

1. A catalyst solution for electroless copper plating, characterized in that, include: A coordination compound comprising a palladium ion and a first ligand bound to the palladium ion; The second ligand is not bound to the palladium ion mentioned above; and the antioxidant comprises at least one selected from the group consisting of toluene compounds, acetate compounds, quinone compounds, benzyl alcohol compounds and anisole compounds.

2. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The catalyst solution used for electroless copper plating, when placed at room temperature and 70°C for 4 days with a palladium concentration of 80ppm to 160ppm and a volume of 1L, yielded precipitates weighing less than 1g.

3. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The first ligand comprises at least one selected from the group consisting of pyridine compounds, pyridine alcohols, pyridine amines, and pyridine carboxylic acids, and the second ligand comprises at least one selected from the group consisting of pyridine alcohols, toluenes, and pyridine amines.

4. The catalyst solution for electroless copper plating according to claim 1, characterized in that, Antioxidants are used to prevent palladium ions (Pd) from forming in the catalyst solution used for electroless copper plating. 2+ It is oxidized and precipitates as palladium oxide (PdO2).

5. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The weight ratio of the second ligand to the antioxidant is 1:0.01 to 1:0.

5.

6. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The second ligand is included as a dispersion stabilizer to stably disperse the particles formed by palladium ions and the first ligand in the catalyst solution.

7. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The catalyst solution used for electroless copper plating further contains water as a solvent.

8. The catalyst solution for electroless copper plating according to claim 7, characterized in that, The pH of the catalyst solution used for electroless copper plating is between 11 and 13.

9. The catalyst solution for electroless copper plating according to claim 1, characterized in that, The catalyst solution used for electroless copper plating further comprises boric acid (H3BO3) as a boron compound and sodium hydroxide (NaOH) as a sodium compound.

10. The catalyst solution for electroless copper plating according to claim 1, characterized in that, Palladium ions are derived from palladium sulfate.

Images