Chemical palladium plating solution as well as preparation method and application thereof

Abstract

The invention relates to the technical field of surface treatment, in particular to a chemical palladium plating solution and a preparation method and application thereof. The chemical palladium plating solution comprises palladium salt, a reducing agent, additives and a solvent, and the additives comprise a stabilizer, an accelerator, a complexing agent and a plating starting agent; wherein the plating starting agent comprises an OPSS type polymer. The chemical palladium plating solution contains the OPSS polymer plating starting agent, and the OPSS polymer has a catalytic effect and can initiate and promote conversion of palladium ions into palladium elementary substances. Through the combined action of the reducing agent, the stabilizing agent, the accelerating agent, the complexing agent, the plating starting agent and other additives, the deposition rate and deposition quality of the palladium plating layer can be effectively controlled, the continuous, uniform and undoped pure Pd plating layer can be formed easily, and the defects of plating leakage, hard spots and the like of the plating layer are prevented.

Description

Technical Field

[0001] This application belongs to the field of surface treatment technology, and in particular relates to a chemical palladium plating solution, its preparation method and application. Background Technology

[0002] The "kilovolt" high-voltage architecture is an inevitable trend for achieving 5-minute rapid power replenishment. With the increasing application of high-voltage, low-loss, and high-power-density SiC and III-V power devices, the voltage withstand capability of IGBTs (Insulated Gate Bipolar Transistors) in electric drive power modules is facing correspondingly higher requirements, constantly challenging the performance and reliability of drive chips. As a core component of the high-voltage platform, the quality of the chip packaging process has a significant impact on its soldering reliability and device lifespan. Currently, chip packaging typically uses ENIG (Chemical Electroless Nickel-Gold) surface treatment technology to ensure soldering reliability. Digital energy companies have a strong demand for this technology, as they need to improve reliability and system verification before pushing it into product applications. However, Au (gold) attacks the Ni (nickel) grain boundaries, causing nickel layer passivation—the "black disk effect"—which severely reduces the wettability of the solder surface.

[0003] ENEPIG (Electrochemical Nickel-Palladium-Gold) surface treatment technology adds a palladium layer between electroplated nickel and immersion gold, isolating the nickel layer from the immersion gold plating solution and preventing corrosion. This helps overcome the black disk effect present in electrochemical nickel-gold treatment. Currently, Pd layers are mainly prepared using electroless palladium plating solutions. However, the high palladium ion concentration in existing electroless palladium plating solutions makes it difficult to control the palladium deposition rate. This results in impurities in the formed palladium layer, making it difficult to form a high-quality pure Pd film. Consequently, chip packaging suffers from problems such as doping, plating gaps, and poor soldering.

[0004] Therefore, it is particularly important to develop a chemical palladium plating solution that can effectively control the deposition rate of palladium coatings and improve the purity of Pd coatings. Summary of the Invention

[0005] The purpose of this application is to provide a chemical palladium plating solution, its preparation method and application, which aims to solve the problem that the deposition rate of palladium in existing chemical palladium plating solutions is difficult to control and that the Pd coating formed is doped with heteroatoms.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] The first aspect of this application provides a chemical palladium plating solution, comprising palladium salt, reducing agent, additives and solvent, wherein the additives include stabilizers, accelerators, complexing agents and plating starters; wherein the plating starter comprises OPSS-type polymers.

[0008] The electroless palladium plating solution provided in this application includes a reducing agent used to reduce palladium ions in palladium salts, achieving autocatalytic deposition of metallic palladium; a stabilizer in the additives to ensure the stability of the plating solution and palladium deposition; an accelerator to ensure stable plating rate; and a complexing agent to buffer the palladium ion concentration, simultaneously ensuring stable plating rate. Furthermore, the plating starter in the additives includes OPSS-type polymers, which have a catalytic effect, initiating and promoting the conversion of palladium ions into elemental palladium, and effectively controlling the deposition rate of the palladium coating, thus facilitating the preparation of undoped pure Pd coatings. The starter also helps form a continuous and uniform palladium coating, preventing defects such as incomplete plating and pitting. The resulting palladium coating does not undergo substitution with Ni or Au, and does not form intermetallic compounds with nickel or gold. Moreover, the Pd coating has high hardness, effectively avoiding the black disk effect of nickel coatings and improving the reliability of application devices.

[0009] As some possible implementations of the electroless palladium plating solution of this application, in the electroless palladium plating solution, the concentration of the palladium salt is 0.1 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 1 mg / L to 100 mg / L, the concentration of the accelerator is 10 g / L to 100 g / L, the concentration of the complexing agent is 1 g / L to 10 g / L, and the concentration of the plating starter is 0.3 g / L to 0.6 g / L. In this case, the concentrations of each component in the electroless palladium plating solution are beneficial for maintaining the stability of the plating solution and extending its lifespan, as well as for adjusting the palladium deposition rate in the plating solution and improving the palladium deposition efficiency. This results in a stable plating rate, minimizing the problem of uneven plating and heteroatom doping in the plating layer caused by excessively rapid palladium deposition, reducing heteroatom doping in the plating layer, and improving the purity and uniformity of the palladium plating layer.

[0010] As some possible implementations of the electroless palladium plating solution of this application, the molar ratio of the complexing agent to the plating starter is (1-20):1; in this case, the activity of the electroless palladium plating solution can be guaranteed, while avoiding the phenomenon of tank turnover caused by continuous overload during continuous production.

[0011] As some possible implementations of the electroless palladium plating solution of this application, the molar ratio of the stabilizer to the complexing agent is 1:(2-20); in this case, the electroless palladium plating solution can simultaneously satisfy the plating solution activity and stability, avoiding phenomena such as incomplete plating and difficulty in starting plating.

[0012] As some possible implementations of the electroless palladium plating solution of this application, the pH value of the electroless palladium plating solution is 5.5-6. Under the condition of pH value 5.5-6, the electroless palladium plating solution has better stability and plating life, and at the same time, it has a better plating rate, which is beneficial to obtaining a high-purity palladium coating.

[0013] As some possible implementations of the electroless palladium plating solution of this application, the additive also includes at least one pH adjuster from hydrochloric acid, nitric acid, sulfuric acid, and ammonia water; these acidic or alkaline reagents can flexibly adjust the pH value of the electroless palladium plating solution to maintain it under suitable pH conditions.

[0014] As some possible implementations of the electroless palladium plating solution of this application, the concentration of the palladium salt in the electroless palladium plating solution is 0.8 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 10 mg / L to 40 mg / L, the concentration of the accelerator is 30 g / L to 60 g / L, the concentration of the complexing agent is 3 g / L to 6 g / L, and the concentration of the plating initiator is 0.3 g / L to 0.6 g / L. In this case, the stability of the electroless palladium plating solution can be better maintained, the plating solution life can be extended, the palladium deposition rate can be better controlled, the palladium deposition efficiency can be improved, the plating solution has a more stable plating rate, the doping of heteroatoms in the coating can be reduced, and the purity and uniformity of the palladium coating can be better improved.

[0015] As some possible implementations of the electroless palladium plating solution of this application, the general structural formula of the OPSS-type polymer is:

[0016] Wherein, n is an integer between 1 and 5, R1 is selected from one of hydrogen atoms, alkyl, unsaturated alkyl, phenyl, and heteroatom groups; R2 is selected from one of straight-chain alkanolamine groups and heterocyclic phenol groups; the OPSS polymer used has a good initiation and catalytic effect on the reaction of palladium ions to palladium element, which can effectively control the deposition rate of palladium coating and is conducive to the preparation of doped pure Pd coating.

[0017] As some possible implementations of the electroless palladium plating solution of this application, the alkyl group is selected from alkyl groups having 1 to 4 carbon atoms.

[0018] As some possible implementations of the electroless palladium plating solution of this application, the unsaturated alkyl group includes at least one of methenoyl, vinyl, and propenyl groups.

[0019] As some possible implementations of the electroless palladium plating solution of this application, the heteroatom groups include at least one of hydroxyl, amino, carboxyl, and amide groups.

[0020] As some possible implementations of the electroless palladium plating solution of this application, the linear alkanolamine groups include at least one selected from -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3)2, -CH2NH(CH2OH), -CH2NH(C2H4OH), -C2H4NH(CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH)2, -CH2N(C2H4OH)2, -C2H4N(CH2OH)2, and -C2H4N(C2H4OH)2. In this case, these linear alkanolamine groups all contain hydroxyl groups. Hydroxyl substitution increases molecular polarity, which is beneficial to improving the stability of OPSS-type polymers.

[0021] As some possible implementations of the electroless palladium plating solution of this application, the heterocyclic phenolic groups include at least one of hydroxylated pyridinyl, hydroxylated furanyl, hydroxylated pyrroleyl, and hydroxylated thiopheneyl. In this case, these heterocyclic phenolic groups all contain hydroxyl groups and heterocyclic structures. Hydroxyl substitution can increase molecular polarity, and heterocyclic structures can change the electron cloud distribution, thus being more conducive to improving the stability of OPSS-type polymers.

[0022] As some possible implementations of the electroless palladium plating solution of this application, the plating starter includes at least one of OH-PEG-amide-OPSS, NHS-PEG-amide-OPSS, and NMe2-PEG-amide-OPSS. These OPSS polymers, as plating starters, can better initiate and catalyze the conversion of palladium ions into elemental palladium, effectively control the deposition rate of the palladium coating, improve the deposition purity of the Pd coating, and help form a continuous, uniform, and high-purity palladium coating, preventing defects such as incomplete plating and pitting.

[0023] As some possible implementations of the electroless palladium plating solution of this application, the palladium salt includes at least one of palladium chloride, palladium sulfate, tetraammonium dichloropalladium, tetraammonium palladium sulfate, and tetraammonium palladium hydrochloride. In this case, the palladium plating layer obtained by the palladium salt does not replace Ni or Au, does not form intermetallic compounds with nickel or gold, and the Pd plating layer has high hardness. Therefore, it can effectively avoid the black disk effect of nickel plating, improve the surface encapsulation and other processing effects of electronic devices, and thus improve the reliability of application devices.

[0024] As some possible implementations of the electroless palladium plating solution of this application, the reducing agent includes at least one of formic acid, hydrazine hydrate, hypophosphorous acid, and formaldehyde.

[0025] As some possible implementations of the electroless palladium plating solution of this application, the reducing agent includes formic acid; it is beneficial to improve the purity of the palladium plating layer and to achieve a doped pure Pd plating layer; moreover, it has low toxicity, is green and environmentally friendly, and is more suitable for large-scale industrial production and application.

[0026] As some possible implementations of the electroless palladium plating solution of this application, the stabilizer includes aromatic ring carboxylic acid molecules.

[0027] As some possible implementations of the electroless palladium plating solution of this application, the stabilizer includes at least one of nicotinic acid, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, methyl 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; these aromatic carboxylic acid stabilizers can all improve the stability of the electroless palladium plating solution and increase the plating solution life.

[0028] As some possible implementations of the electroless palladium plating solution of this application, the accelerator includes sodium sulfonate salt.

[0029] As some possible implementations of the electroless palladium plating solution of this application, the accelerator includes at least one of sodium 2-iodobenzenesulfonate and sodium dodecyl sulfonate; these sodium sulfonate accelerators are all beneficial to improving the plating rate and plating solution life, and improving the coating quality.

[0030] As some possible implementations of the electroless palladium plating solution of this application, the complexing agent includes ammonia nitrogen molecules.

[0031] As some possible implementations of the electroless palladium plating solution of this application, the complexing agent includes at least one of dimethylamine, trimethylamine, 9-aminoacridine, and 2-mercaptocytosine; these ammonia nitrogen complexing agents can all regulate the concentration of palladium ions in the plating solution, better controllable and stable palladium plating process, and improve the plating effect and the quality of coating purity, uniformity, etc.

[0032] As some possible implementations of the electroless palladium plating solution of this application, the solvent includes water. This can improve both the safety of the electroless palladium plating solution and its manufacturability.

[0033] Secondly, this application provides a method for preparing a chemical palladium plating solution, comprising the following steps:

[0034] Palladium salt solution, reducing agent solution, and additive solution are prepared separately. The additive solution includes a stabilizer, an accelerator, a complexing agent, and a plating starter. The plating starter includes an OPSS-type polymer.

[0035] In use, the palladium salt solution, the reducing agent solution, and the additive solution are mixed to prepare a chemical palladium plating solution.

[0036] The method for preparing the electroless palladium plating solution disclosed in this application involves separately preparing palladium salt solution, reducing agent solution, and additive solution. These solutions must be prepared and used immediately; they cannot be mixed before production. Mixing the palladium salt, reducing agent, and additives together in advance will cause the plating solution to fail. Before use, the components are thoroughly mixed to obtain a directly usable electroless palladium plating solution. The preparation process is simple and suitable for large-scale industrial production and application. The prepared electroless palladium plating solution contains an OPSS-type polymer plating initiator, which has a catalytic effect and can initiate and promote the conversion of palladium ions into elemental palladium. Through the combined action of the reducing agent, stabilizer, accelerator, complexing agent, and plating initiator, the deposition rate and quality of the palladium coating can be effectively controlled, contributing to the formation of a continuous, uniform, and doped-free pure Pd coating and preventing defects such as incomplete plating and pitting.

[0037] As some possible implementations of the preparation method of the electroless palladium plating solution of this application, the concentration of the palladium salt solution is 15 g / L to 25 g / L, and the pH value is 10.7 to 11. This is beneficial to ensure stability during transportation and storage, and also facilitates the subsequent preparation of an electroless palladium plating solution with appropriate concentration and good stability with other components.

[0038] As some possible implementations of the preparation method of the electroless palladium plating solution of this application, the concentration of the reducing agent solution is 50 g / L to 200 g / L, and the pH value is 5.5 to 5.7. This is beneficial to ensure stability during transportation and storage, and also facilitates the subsequent preparation of an electroless palladium plating solution with appropriate concentration and good stability with other components.

[0039] As some possible implementations of the electroless palladium plating solution of this application, the concentration of the additive solution is 300 g / L to 600 g / L, and the pH value is 6.9 to 7.2. This is beneficial for ensuring stability during transportation and storage, and also facilitates the subsequent preparation of an electroless palladium plating solution with appropriate concentration and good stability with other components.

[0040] As some possible implementations of the electroless palladium plating solution of this application, the concentration of the palladium salt in the electroless palladium plating solution is 0.8 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 10 mg / L to 40 mg / L, the concentration of the accelerator is 30 g / L to 60 g / L, the concentration of the complexing agent is 3 g / L to 6 g / L, the concentration of the plating initiator is 0.3 g / L to 0.6 g / L, and the pH value is 5.5 to 5.7. Under these conditions, the stability of the electroless palladium plating solution can be better maintained, the plating solution life can be extended, the palladium deposition rate can be better controlled, the palladium deposition efficiency can be improved, the plating solution has a more stable plating rate, the doping of heteroatoms in the coating can be reduced, and the purity and uniformity of the palladium coating can be better improved.

[0041] As some possible implementations of the electroless palladium plating solution of this application, the plating bath life of the electroless palladium plating solution is greater than 3 MTO. The plating bath life is high, exceeding that of other currently commercially available products.

[0042] Thirdly, this application provides a palladium plating layer, which is prepared on a growth substrate using the above-mentioned electroless palladium plating solution or the electroless palladium plating solution prepared by the above method, through an electroless plating process.

[0043] The palladium coating of this application is prepared on a growth substrate using the aforementioned electroless palladium plating solution via an electroless plating process. Through the combined action of reducing agents, stabilizers, accelerators, complexing agents, and plating starters in the electroless palladium plating solution, the deposition rate and quality of the palladium coating can be effectively controlled. This results in palladium coatings that are continuous, uniform, and of high purity with no doping, and the coatings are free from defects such as incomplete plating or pitting. The resulting palladium coating does not undergo displacement with either Ni or Au, and the high hardness of the Pd coating effectively avoids the black disk effect of nickel plating, improving the reliability of the applied devices.

[0044] As some possible implementations of the palladium coating in this application, the palladium content in the palladium coating is greater than 99.5%; indicating that the palladium coating has high purity and very low impurity content.

[0045] As some possible implementations of the palladium coating in this application, the size of the crystal grains in the palladium coating is less than 100 nm; the metal grains in the palladium coating are fine and dense, and the coating is free from defects such as missed plating, pitting, and nodular structures, resulting in high coating uniformity.

[0046] As some possible implementations of the palladium coating in this application, the palladium coating has a coverage rate of more than 99.5% over the growth substrate; indicating that the palladium coating has a good coverage effect on the growth substrate and there is no missed coating.

[0047] As some possible implementations of the palladium coating in this application, the average thickness of the palladium coating is 0.05 μm to 0.5 μm; the thickness can be selected according to the actual application requirements, and the thickness of the coating can be flexibly adjusted by controlling the chemical plating time.

[0048] As some possible implementations of the palladium coating of this application, the electroless plating process uses a temperature of 55℃~65℃, a pH of 5~7, and a plating rate of 0.02µm / min~0.03µm / min. Under these conditions, the temperature, pH, and plating rate of the electroless plating solution are all conducive to controlling the appropriate reaction rate, controlling the deposition efficiency and effect of palladium in the electroless plating solution, and ensuring the acquisition of a high-purity, uniform, and complete palladium coating.

[0049] As some possible implementations of the palladium coating in this application, the surface of the growth substrate includes at least one of a Ni layer, a Ni-P alloy layer, and a Ni-B alloy layer. In this case, the palladium coating deposited on the surface of the growth substrate can effectively avoid the black disk effect of the nickel coating, thereby improving the reliability of the application device.

[0050] Fourthly, this application provides an electronic device, wherein the encapsulation layer of the electronic device includes the aforementioned palladium plating layer.

[0051] The electronic device of this application includes the aforementioned palladium plating layer in its packaging layer, which is beneficial for improving the packaging effect of the electronic device, ensuring the soldering reliability of the electronic device, and thus improving the performance and reliability of the electronic device.

[0052] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0053] Figure 1 This is a schematic flowchart of the preparation method of the chemical palladium plating solution provided in the embodiments of this application. Detailed Implementation

[0054] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0055] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0056] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0057] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0058] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0059] The term "ENIG" is an abbreviation for "Electroless Nickel / Immersion Gold," also known as electroless nickel gold, immersion nickel gold, or electroless nickel gold. It involves chemically replacing palladium on the surface of copper, then chemically plating a nickel-phosphorus alloy layer onto the palladium core, followed by a substitution reaction to plate a layer of gold onto the nickel surface. Electroless nickel gold immersion gold has two processes: substitution and a hybrid bath of partial substitution and partial reduction. Electroless nickel gold is mainly used for surface treatment of circuit boards to prevent oxidation or corrosion of the copper surface, and is also used for soldering and contact applications.

[0060] The term "ENEPIG" is an abbreviation for "Electroless Nickel Electroless Palladium Immersion Gold," representing electroless nickel-palladium alloy, an upgraded version of immersion gold. By adding a palladium layer between the electroplated nickel and immersion gold, the immersion gold plating solution is shielded from the attack on the nickel layer. Its thickness is typically in the range of 0.05μm to 0.1μm. The palladium layer acts as a barrier against corrosion of the nickel layer by the immersion gold process. Therefore, immersion nickel-palladium alloy overcomes the black nickel defect (i.e., black disk effect) present in immersion gold. Furthermore, immersion nickel-palladium alloy offers highly reliable wire bonding capabilities, excellent reflow soldering performance, and includes switching contact surfaces, enabling it to meet the stringent requirements of high-density and multi-surface packaged chips.

[0061] The term "IGBT" is an abbreviation for "Insulated Gate Bipolar Transistor." By combining the features of a MOSFET and a bipolar transistor, the IGBT becomes a power transistor that possesses the advantages of both devices.

[0062] The term "MTO" is an abbreviation for "Metal Turnover," referring to the metal turnover rate. In electroless nickel plating, MTO refers to the service life of the solution, measured in the amount of main salt added during initial tank preparation. Each time the main salt (typically the amount of salt A added during initial tank preparation) is consumed and replenished, it is called one MTO cycle. 1 MTO = Metal ion count at tank preparation = Nickel added (g / L) * Tank volume. One MTO occurs when the amount of added nickel ions equals the amount added to the tank. During the electroless nickel plating process, hypophosphite and additives decompose to generate many byproducts. These byproducts affect the reaction rate and plating quality. Therefore, the MTO is generally used to calculate the optimal time for the nickel plating tank to be used.

[0063] The term "bonding" refers to wire bonding, chip coating, or bonding. Bonding is a wire bonding method in chip manufacturing, generally used to connect the internal circuitry of the chip to the package pins with gold wires before packaging. After bonding (i.e., after the circuitry is connected to the pins), the chip is typically encapsulated with a black adhesive.

[0064] The term "IMC" is an abbreviation for "Intermetallic Compound," referring to compounds formed between metals or between metalloids (such as H, B, N, S, P, C, Si, etc.).

[0065] The term "black disk effect" refers to a passivation phenomenon in the nickel layer, primarily occurring at the interface between nickel and gold. This occurs because the atomic radius of nickel is smaller than that of gold, resulting in a rough surface grain after immersion gold plating. The gold plating solution penetrates the nickel layer, causing an interfacial reaction and corroding the nickel. The corroded nickel atoms continue to oxidize, forming nickel oxide, which has poor solderability. Because nickel oxide has a dark, black color, it is called a "black disk." This can severely impact IC manufacturing and component connections, such as poor component adhesion to pads, degraded solder joint quality, and even component detachment.

[0066] The term "plating rate" refers to the increase in the thickness of a metal coating per unit time. The plating rate is positively correlated with the rate of the chemical reaction in which metal ions are reduced to elemental metals, and is independent of the plating area. Generally, factors affecting the plating rate include temperature, reactant concentration (e.g., metal ion concentration, reducing agent concentration), the reduction potential of the reducing agent, and other kinetic factors.

[0067] From a market perspective, with the increasing application of high-voltage, low-loss, and high-power-density SiC and III-V power devices, the voltage withstand rating of IGBTs (Insulated Gate Bipolar Transistors) in electric drives is facing higher requirements, and the performance and reliability of driver chips are constantly being challenged. As a core component of high-voltage platforms, the quality of chip packaging greatly affects its soldering reliability and device lifespan. Currently, chip packaging typically uses ENIG (Chemical Electroless Nickel-Gold) surface treatment technology to ensure soldering reliability. However, Au (gold) attacks the Ni (nickel) grain boundaries, causing passivation of the nickel layer—the "black disk effect"—which severely reduces the wettability of the solder surface. Research has found that ENEPIG (Chemical Electroless Nickel-Palladium-Gold) surface treatment technology, by inserting a Pd (palladium) layer between the Ni and Au layers, can achieve the following technical effects: ① Reducing the distance: blocking the diffusion and migration of Ni. During soldering, the high-melting-point Pd forms a barrier layer on the Ni surface, effectively preventing the formation of metal oxides; ② Filler material: Pd has higher hardness, which can significantly reduce the thickness of the Au layer. Therefore, the chemical nickel-palladium-gold surface treatment technology can isolate the nickel layer from the attack of the immersion gold solution, thus preventing the immersion gold technology from corroding the nickel layer and helping to overcome the black disk effect of chemical nickel-gold treatment.

[0068] Currently, Pd layers are mainly prepared by electroless palladium plating using a palladium electroless plating solution. This solution typically contains reducing agents, stabilizers, accelerators, complexing agents, and other additives. Depending on the type of reducing agent, the technical pathways for achieving Pd autocatalytic deposition can be categorized into: hydrazine hydrate system, hypophosphite system, and formic acid system. Among these, the hydrazine hydrate system has a low safety factor, making industrial production control difficult, and its high reduction potential leads to excessively fast Pd deposition rates, which are challenging to control. In the hypophosphite system, P co-deposits with Pd, making it difficult to form high-quality pure Pd films and prone to problems such as doping, plating gaps, and poor soldering. In the formic acid system, the Pd deposition rate is too slow, requiring prolonged plating time or increased precious metal concentration, which is detrimental to cost control.

[0069] Based on the above considerations, to alleviate the problem of excessively high palladium ion concentration in existing electroless palladium plating solutions, which makes it difficult to control the palladium deposition rate and results in the formation of impurities in the palladium coating, making it difficult to form a high-quality pure Pd film, and causing problems such as doping, plating gaps, and poor soldering in chip packaging, it is particularly important to develop an electroless palladium plating solution that can effectively control the deposition rate and improve the purity of the Pd coating.

[0070] After in-depth research, this application proposes a chemical palladium plating solution. For ease of understanding, this application is specifically illustrated through the following embodiments. It should be understood that the following embodiments are only used to further illustrate the solution of this application and are not intended to limit the scope of this application.

[0071] Firstly, such as Figure 1 As shown in the embodiments of this application, a chemical palladium plating solution is provided, comprising palladium salt, reducing agent, additives and solvent, wherein the additives include stabilizer, accelerator, complexing agent and plating starter; wherein the plating starter includes OPSS-type polymer.

[0072] Thus, the electroless palladium plating solution provided in this application embodiment includes a reducing agent used to reduce palladium ions in palladium salts, achieving autocatalytic deposition of metallic palladium; a stabilizer in the additives to ensure the stability of the plating solution and palladium deposition; an accelerator to ensure stable plating rate; and a complexing agent to buffer palladium ion concentration, simultaneously ensuring stable plating rate. Furthermore, the plating starter in the additives includes OPSS-type polymers, which have a catalytic effect, initiating and promoting the conversion of palladium ions into elemental palladium, and effectively controlling the deposition rate of the palladium coating, facilitating the preparation of undoped pure Pd coatings. The starter also helps form a continuous and uniform palladium coating, preventing defects such as incomplete plating and pitting. The resulting palladium coating does not undergo substitution with Ni or Au, and does not form intermetallic compounds with nickel or gold. Moreover, the Pd coating has high hardness, effectively avoiding the black disk effect of nickel coatings and improving the reliability of application devices.

[0073] Furthermore, the deposition rate of the plating layer in the electroless palladium plating solution can be equivalent to the Pd reduction rate. According to the principles of reaction kinetics, Pd... 2+ The reaction rate of reduction to elemental Pd is determined by Pd 2+ The reaction rate is determined by key factors such as ion concentration and reducing agent concentration. Generally, the lower the reactant concentration, the slower the reaction rate. However, if the concentration is too low, the reaction cannot overcome the reaction barrier; if the concentration is too high, it will lead to plating failure. The electroless palladium plating solution of this application overcomes the reaction barrier through a plating starter, allowing the reduction reaction to occur smoothly. At the same time, additives such as complexing agents, accelerators, and stabilizers are used to maintain a stable reactant concentration over a long period, which helps to ensure a stable deposition rate and the production life (usage time) of the plating solution. Furthermore, the electroless palladium plating solution formulation designed in this application, through the synergistic effect of its components, can effectively reduce the problem of impurity in the coating caused by the intercalation of organic matter and inorganic anions during the metal deposition process, significantly improving the coating purity and forming a high-quality pure Pd film.

[0074] In some possible implementations, the concentration of palladium salt in the electroless palladium plating solution is 0.1 g / L to 1.2 g / L, the concentration of reducing agent is 10 g / L to 40 g / L, the concentration of stabilizer is 1 mg / L to 100 mg / L, the concentration of accelerator is 10 g / L to 100 g / L, the concentration of complexing agent is 1 g / L to 10 g / L, and the concentration of plating starter is 0.3 g / L to 0.6 g / L. In this case, the concentrations of each component in the electroless palladium plating solution are beneficial for maintaining the stability of the plating solution and extending its lifespan, as well as for regulating the palladium deposition rate and improving the palladium deposition efficiency. This results in a stable plating rate, minimizing the problem of uneven plating and the presence of heteroatoms in the coating due to excessively rapid palladium deposition, reducing heteroatom doping in the coating, and improving the purity and uniformity of the palladium plating layer. Specifically, the concentration of palladium salts affects performance characteristics such as plating rate, coating quality, and bath life. Too low a concentration leads to a slow plating rate, reducing production efficiency; conversely, too high a concentration results in a fast plating rate, causing loose Pd grains, poor bath stability, and reduced bath life. The concentrations of additives such as reducing agents and accelerators affect the plating rate. The concentration range described in this application helps ensure a suitable and stable plating rate. The concentration of stabilizers ensures the stability of the plating solution, which helps improve bath life (MTO). The concentration of complexing agents effectively buffers the palladium ion concentration in the plating solution, ensuring a stable plating rate and a suitable palladium deposition rate. The concentration of the plating initiator better initiates / catalyzes Pd deposition. 2+ →Pd(0) reaction improves palladium deposition efficiency and purity, which is beneficial for obtaining undoped pure Pd coating.

[0075] For example, in the electroless palladium plating solution, the concentration of palladium salt can be any typical but non-limiting point value or a range between any two points, such as 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.78 g / L, 0.9 g / L, 1.0 g / L, 1.1 g / L, 1.2 g / L; the concentration of reducing agent can be any typical but non-limiting point value or a range between any two points, such as 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L; and the concentration of stabilizer can be 1 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 ... The concentrations of the accelerator can be any typical but non-limiting point value or any range between any two points, such as 0 mg / L, 100 mg / L, etc.; the concentrations of the complexing agent can be any typical but non-limiting point value or any range between any two points, such as 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc.; the concentrations of the plating starter can be any typical but non-limiting point value or any range between any two points, such as 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, etc.; and the concentrations of the plating starter can be any typical but non-limiting point value or any range between any two points, such as 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, etc.

[0076] In some possible implementations, the molar ratio of the complexing agent to the plating starter is (1-20):1. In this case, the activity of the electroless palladium plating solution is maintained, while preventing plating tank turnover due to consecutively excessive loads during continuous production. For example, the molar ratio of the complexing agent to the plating starter can be any typical but non-limiting point value or a range between any two points, such as 1:1, 2:1, 3:1, 5:1, 8:1, 9:1, 10:1, 12:1, 14:1, 15:1, 16:1, 18:1, 20:1.

[0077] In some possible implementations, the molar ratio of stabilizer to complexing agent is 1:(2-20). In this case, the electroless palladium plating solution simultaneously satisfies the requirements of plating activity and stability, avoiding phenomena such as incomplete plating and difficulty in initiating plating. For example, the molar ratio of stabilizer to complexing agent can be any typical but non-limiting point value or a range between any two point values, such as 1:2, 1:3, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20.

[0078] In some possible implementations, the concentration of palladium salt in the electroless palladium plating solution is 0.8 g / L to 1.2 g / L, the concentration of reducing agent is 10 g / L to 40 g / L, the concentration of stabilizer is 10 mg / L to 40 mg / L, the concentration of accelerator is 30 g / L to 60 g / L, the concentration of complexing agent is 3 g / L to 6 g / L, and the concentration of plating starter is 0.3 g / L to 0.6 g / L. In this configuration, the stability of the electroless palladium plating solution can be better maintained, the solution life can be extended, the palladium deposition rate can be better controlled, the palladium deposition efficiency can be improved, resulting in a more stable plating rate, reduced heteroatom doping in the coating, and better improvement in the purity and uniformity of the palladium coating.

[0079] In some possible implementations, the pH value of the electroless palladium plating solution is 5.5–6. In this case, the pH value of the electroless palladium plating solution affects the stability, lifespan, and plating rate of the plating solution. Under the condition of a pH value of 5.5–6, the electroless palladium plating solution has better stability and lifespan, and at the same time, it has a better plating rate, which is beneficial for obtaining a high-purity palladium coating.

[0080] In some possible implementations, the additive also contains at least one pH adjuster from hydrochloric acid, nitric acid, sulfuric acid, and ammonia; in this case, the pH of the electroless palladium plating solution can be flexibly adjusted by using these acidic or alkaline reagents to maintain it under suitable pH conditions.

[0081] For example, the pH value of the electroless palladium plating solution can be any typical but non-limiting point value or a range between any two points, such as 5.5, 5.6, 5.7, 5.8, 5.9, and 6.0. In some specific embodiments, the pH value of the electroless palladium plating solution is 5.7, in which case the electroless palladium plating solution has better performance.

[0082] In some possible implementations, the palladium salt includes at least one of palladium chloride, palladium sulfate, tetraammonium dichloropalladium, tetraammonium palladium sulfate, and tetraammonium palladium hydrochloride. In this case, the palladium coating obtained by the palladium salt does not undergo substitution with Ni or Au, does not form intermetallic compounds with nickel or gold, and the Pd coating has high hardness, thus effectively avoiding the black disk effect of nickel coatings, improving the surface encapsulation and other processing effects of electronic devices, and thereby improving the reliability of application devices.

[0083] In some possible implementations, the general structural formula of OPSS-type polymers is:

[0084] Where n is an integer between 1 and 5, R1 is selected from hydrogen atoms, alkyl groups, unsaturated alkyl groups, phenyl groups, and heteroatom groups; R2 is selected from straight-chain alkanolamine groups and heterocyclic phenolic groups. The OPSS-type polymer used in the plating agent of this application's embodiments reacts with palladium ions to convert into palladium elemental (i.e., Pd). 2+ →Pd(0) reaction) has good initiation and catalytic effects, which can effectively control the deposition rate of palladium coating and facilitate the preparation of doped pure Pd coating. The range of values ​​for n takes into account the synthesis difficulty of OPSS polymers, ensuring the solubility and plating effect of OPSS polymers. If the value of n is too large, the solubility of OPSS molecules will be too poor, and if the value of n is too small, the plating effect will be poor. The hydroxyl substitution in the substituent increases the molecular polarity, and the heterocyclic structure changes the electron cloud distribution, which is beneficial to improving the stability of OPSS polymers.

[0085] In some possible embodiments, the alkyl group is selected from alkyl groups having 1 to 4 carbon atoms. That is, in OPSS-type polymers, R1 can be selected from one of the alkyl groups having 1 to 4 carbon atoms.

[0086] In some possible embodiments, the unsaturated alkyl group includes at least one of methenoyl, vinyl, and propenyl groups. That is, in OPSS-type polymers, R1 can be selected from unsaturated alkyl groups such as methenoyl, vinyl, or propenyl.

[0087] In some possible implementations, the heteroatom group includes at least one of hydroxyl, amino, carboxyl, and amide groups. That is, in OPSS-type polymers, R1 can be selected from heteroatom groups such as hydroxyl, amino, carboxyl, or amide groups.

[0088] In some possible implementations, in OPSS-type polymers, R1 is selected from hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, or an unsaturated alkyl group selected from methanyl, vinyl, and propenyl, or a heteroatomic group selected from hydroxyl, amino, carboxyl, and amide groups. In this case, OPSS-type polymers have better solubility and plating performance.

[0089] In some possible embodiments, the linear alkanolamine groups include at least one selected from -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3)2, -CH2NH(CH2OH), -CH2NH(C2H4OH), -C2H4NH(CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH)2, -CH2N(C2H4OH)2, -C2H4N(CH2OH)2, and -C2H4N(C2H4OH)2. In this case, these linear alkanolamine groups all contain hydroxyl groups. Hydroxyl substitution increases molecular polarity, which is beneficial for improving the stability of OPSS-type polymers.

[0090] In some possible embodiments, the heterocyclic phenolic group includes at least one of hydroxylated pyridyl, hydroxylated furanyl, hydroxylated pyrroleyl, and hydroxylated thiopheneyl. In this case, these heterocyclic phenolic groups all contain hydroxyl groups and heterocyclic structures, wherein hydroxyl substitution can increase molecular polarity, and heterocyclic structures can change the electron cloud distribution, thus being more conducive to improving the stability of OPSS-type polymers.

[0091] In some possible embodiments, the plating starter includes at least one selected from OH-PEG-amide-OPSS, NHS-PEG-amide-OPSS, and NMe2-PEG-amide-OPSS. The structural formula of OH-PEG-amide-OPSS is as follows: The structural formula of NHS-PEG-amide-OPSS is: The structural formula of NMe2-PEG-amide-OPSS is as follows: In the embodiments of this application, these OPSS-type polymers, used as plating starters, can better initiate and catalyze the conversion of palladium ions into elemental palladium, effectively control the deposition rate of the palladium coating, improve the deposition purity of the Pd coating, and help form a continuous, uniform, and high-purity palladium coating, preventing defects such as incomplete plating and pitting in the coating.

[0092] In some possible implementations, the reducing agent includes at least one of formic acid, hydrazine hydrate, hypophosphorous acid, and formaldehyde. In this case, when formic acid is used as the reducing agent, Pd ions in the plating solution first undergo a displacement reaction with the Ni substrate. After a displacement film is formed on the substrate, formate ions undergo catalytic dehydrogenation to produce hydrogen atoms. These hydrogen atoms donate electrons to Pd ions, which are then reduced to metallic Pd. Therefore, the deposited palladium layer has high purity, which helps reduce the introduction of impurity elements. Furthermore, formic acid has lower toxicity compared to other reducing agents, resulting in less environmental impact. However, formic acid has relatively weak reducing power. Hydrazine hydrate has strong reducing properties and can efficiently reduce Pd ions, thereby rapidly depositing a thicker palladium layer. However, palladium plating solutions prepared with hydrazine hydrate have poor stability, a high reduction potential, and excessively fast Pd deposition rates, which are difficult to control. Additionally, the hydrazine hydrate system has a low safety factor, which is not conducive to industrial production management. When hypophosphorous acid is used as the reducing agent, it has good stability in the electroless plating solution, is not easily oxidized, and can deposit a palladium coating with high gloss and a smooth surface. However, phosphoric acid (P) in the hypophosphite system tends to co-deposit with Pd, making it difficult to form high-quality pure Pd films and leading to problems such as doping, intercalation, and poor soldering. Formaldehyde has some reducing properties and can be used in electroless palladium plating processes, but it is highly toxic and poses significant risks to human health and the environment.

[0093] In some possible implementations, the reducing agent includes formic acid. In this case, using formic acid as the reducing agent is beneficial for improving the purity of the palladium coating and achieving a doped pure Pd coating; moreover, it has low toxicity, is environmentally friendly, and more suitable for large-scale industrial production and application. The embodiments of this application utilize the synergistic effect of stabilizers, accelerators, complexing agents, and OPSS-like polymers to effectively enhance the reducing power of formic acid, initiating and promoting the conversion of palladium ions into elemental palladium. Furthermore, it effectively controls the deposition rate of the palladium coating, contributing to the formation of a continuous, uniform, doped pure Pd coating and preventing defects such as incomplete plating and pitting.

[0094] In some possible implementations, the stabilizer includes aromatic ring carboxylic acid molecules. In this case, aromatic ring carboxylic acid molecules, as stabilizers in electroless palladium plating solutions, can form a stable adsorption layer on the surface of the plating solution due to their special chemical structure. This adsorption layer can effectively prevent the disordered reduction of metal ions, thereby maintaining the stability of the plating solution and the uniformity of the plating layer. Furthermore, spontaneous decomposition of the plating solution is a common problem during electroless plating. Aromatic ring carboxylic acid stabilizers can slow down the decomposition rate of the plating solution through their adsorption effect, extending the service life of the plating solution and improving the morphology of the plating layer, making it smoother and denser. Moreover, in electroless palladium plating solutions, aromatic ring carboxylic acid stabilizers can form good synergistic effects with reducing agents, complexing agents, and other components, jointly improving the overall performance of the plating solution.

[0095] In some possible embodiments, the stabilizer includes at least one of nicotinic acid, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, methyl 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; these aromatic carboxylic acid stabilizers can all improve the stability of the electroless palladium plating solution and increase the plating solution life. In some embodiments, the stabilizer includes two or more of nicotinic acid, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, methyl 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. The combination of multiple stabilizers is beneficial for improving the stability and plating solution life of the electroless palladium plating solution.

[0096] In some possible implementations, the accelerator includes sodium sulfonate. In this case, sodium sulfonate acts as an accelerator in the electroless palladium plating solution, accelerating the chemical reaction in the solution, allowing Pd ions to be reduced to metallic palladium more quickly and deposited on the substrate surface. This acceleration significantly increases the palladium plating rate, thereby shortening the plating time and improving production efficiency. It can also stabilize the plating solution to a certain extent, preventing adverse reactions such as spontaneous decomposition or precipitation during the palladium plating process, helping to extend the service life of the plating solution and reduce production costs. In addition, by accelerating the palladium plating process, sodium sulfonate helps reduce defects and porosity in the coating, improving the uniformity and consistency of the coating. As an accelerator, the accelerating effect of sodium sulfonate may help refine the grains in the coating, making the coating structure denser and the surface smoother. This not only improves the appearance quality of the coating but also enhances its corrosion resistance and mechanical properties. Furthermore, within an appropriate concentration range, sodium sulfonate can synergistically act with other plating solution components to optimize reaction conditions, making the palladium plating process more stable and efficient.

[0097] In some possible implementations, the accelerator includes at least one of sodium 2-iodobenzenesulfonate and sodium dodecyl sulfonate. These sodium sulfonate accelerators are all beneficial for increasing plating speed and plating bath life, and improving coating quality.

[0098] In some possible implementations, the complexing agent includes ammonia nitrogen molecules. In this case, ammonia nitrogen molecules can undergo a complexation reaction with palladium ions in the plating bath to form a stable complex. This complexation effectively controls the concentration of free palladium ions in the plating bath, preventing palladium ions from being reduced to metallic palladium too quickly, thereby ensuring the controllability and stability of the palladium plating process. In the electroless palladium plating process, if the concentration of free palladium ions in the plating bath is too high, palladium precipitates may form, affecting the stability of the plating bath and the quality of the coating, such as purity and uniformity. By complexing with palladium ions, ammonia nitrogen complexing agents can inhibit the formation of precipitates, control the growth rate and direction of grains in the coating, and make the grain arrangement more orderly. This not only helps to extend the service life of the plating bath but also improves the morphology and structure of the coating, making it smoother and denser. In addition, through the complexation of ammonia nitrogen molecules with palladium ions, the reaction environment in the plating bath can be changed, making it easier for the reducing agent to reduce palladium ions to metallic palladium. This promoting effect can accelerate the palladium plating process and improve production efficiency.

[0099] In some possible implementations, the complexing agent includes at least one of dimethylamine, trimethylamine, 9-aminoacridine, and 2-mercaptocytosine. These ammonia nitrogen complexing agents can regulate the concentration of palladium ions in the plating bath, better controllable and stable palladium plating process, and improve plating effect and coating purity, uniformity, and other quality aspects. In some embodiments, the complexing agent includes two or more of dimethylamine, trimethylamine, 9-aminoacridine, and 2-mercaptocytosine. By using a combination of multiple complexing agents, the concentration of palladium ions in the plating bath can be better controlled, improving plating effect and coating purity, uniformity, and other quality aspects.

[0100] In some possible implementations, the solvent includes water. In this case, using water as the solvent can improve both the safety of the electroless palladium plating solution and the productivity of the plating solution.

[0101] The electroless palladium plating solution provided in this application can be prepared by the method described in the following examples.

[0102] Secondly, embodiments of this application provide a method for preparing a chemical palladium plating solution, as shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0103] S10. Prepare palladium salt solution, reducing agent solution and additive solution respectively. The additive solution includes stabilizer, accelerator, complexing agent and plating starter; wherein the plating starter includes OPSS polymer.

[0104] S20. When using, the palladium salt solution, reducing agent solution and additive solution are mixed to prepare the chemical palladium plating solution.

[0105] The method for preparing the electroless palladium plating solution in this application involves preparing palladium salt solution, reducing agent solution, and additive solution separately. These solutions must be prepared and used immediately; they cannot be mixed before production. Mixing the palladium salt, reducing agent, and additives together beforehand will cause the plating solution to fail. Before use, the components are thoroughly mixed to obtain a directly usable electroless palladium plating solution. The preparation process is simple and suitable for large-scale industrial production and application. The prepared electroless palladium plating solution contains an OPSS-type polymer plating starter, which has a catalytic effect and can initiate and promote the conversion of palladium ions into elemental palladium. Through the combined action of the reducing agent, stabilizer, accelerator, complexing agent, and plating starter, the deposition rate and quality of the palladium coating can be effectively controlled, contributing to the formation of a continuous, uniform, and doped-free pure Pd coating and preventing defects such as incomplete plating and pitting.

[0106] In step S10 above:

[0107] In some possible implementations, the concentration of the prepared palladium salt solution is 15 g / L to 25 g / L, and the pH value is 10.7 to 11. In this case, the palladium salt solution has better stability, which is beneficial to ensure stability during transportation and storage, and also facilitates subsequent preparation with other components to form a chemical palladium plating solution with appropriate concentration and good stability.

[0108] In some possible implementations, the concentration of the reducing agent solution is 50 g / L to 200 g / L, and the pH value is 5.5 to 5.7. In this case, the reducing agent solution has better stability, which is beneficial to ensure stability during transportation and storage, and also beneficial to the subsequent preparation of a suitable concentration and good stability electroless palladium plating solution with other components.

[0109] In some possible implementations, the concentration of the prepared additive solution is 300 g / L to 600 g / L, and the pH value is 6.9 to 7.2. In this case, the additive solution has better stability, which is beneficial to ensure stability during transportation and storage, and also beneficial to the subsequent preparation of a suitable concentration and good stability electroless palladium plating solution with other components.

[0110] In some possible implementations, the solvent in the palladium salt solution includes water. In some possible implementations, the solvent in the reducing agent solution includes water. In some possible implementations, the solvent in the additive solution includes water. In these cases, using water as the solvent improves both the safety of the electroless palladium plating solution and its manufacturability.

[0111] In some possible implementations, the concentration of palladium salt in the electroless palladium plating solution is 0.8 g / L to 1.2 g / L, the concentration of reducing agent is 10 g / L to 40 g / L, the concentration of stabilizer is 10 mg / L to 40 mg / L, the concentration of accelerator is 30 g / L to 60 g / L, the concentration of complexing agent is 3 g / L to 6 g / L, the concentration of plating starter is 0.3 g / L to 0.6 g / L, and the pH value is 5.5 to 5.7. Under these conditions, the stability of the electroless palladium plating solution can be better maintained, the solution life can be extended, the palladium deposition rate can be better controlled, the palladium deposition efficiency can be improved, the plating rate can be more stable, the doping of heteroatoms in the coating can be reduced, and the purity and uniformity of the palladium coating can be better improved.

[0112] In some possible implementations, the palladium salt includes at least one of palladium chloride, palladium sulfate, tetraammonium dichloropalladium, tetraammonium palladium sulfate, and tetraammonium palladium hydrochloride. In this case, the palladium coating obtained by the palladium salt does not undergo substitution with Ni or Au, does not form intermetallic compounds with nickel or gold, and the Pd coating has high hardness, thus effectively avoiding the black disk effect of nickel coatings, improving the surface encapsulation and other processing effects of electronic devices, and thereby improving the reliability of application devices.

[0113] In some possible implementations, the general structural formula of OPSS-type polymers is:

[0114] Wherein, n is an integer between 1 and 5, R1 is selected from hydrogen atoms, alkyl groups with 1 to 4 carbon atoms, or unsaturated alkyl groups selected from methanyl, vinyl, and propenyl, or heteroatomic groups selected from hydroxyl, amino, carboxyl, and amide groups; R2 is selected from -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3)2, -CH2NH(CH2OH), -CH2NH(C2H4OH), -C2H4NH(CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH)2, -CH2N(C2H4OH)2, -C2H4N(CH2OH)2, -C2H4N(C2H4OH)2, or hydroxylated pyridinyl, hydroxylated furanyl, hydroxylated pyrroleyl, and hydroxylated thiopheneyl.

[0115] In some possible implementations, the plating starter includes at least one of OH-PEG-amide-OPSS, NHS-PEG-amide-OPSS, and NMe2-PEG-amide-OPSS. These OPSS polymers, as plating starters, can better initiate and catalyze the conversion of palladium ions into elemental palladium, effectively control the deposition rate of the palladium coating, improve the deposition purity of the Pd coating, and contribute to the formation of a continuous, uniform, and high-purity palladium coating, preventing defects such as incomplete plating and pitting.

[0116] In some possible implementations, the reducing agent includes formic acid. In this case, it is beneficial to improve the purity of the palladium coating and to achieve a doped pure Pd coating; moreover, it has low toxicity, is green and environmentally friendly, and is more suitable for large-scale industrial production and application.

[0117] In some possible implementations, the stabilizer includes at least one of nicotinic acid, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, methyl 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; these aromatic carboxylic acid stabilizers can improve the stability of the electroless palladium plating solution and increase the plating solution life.

[0118] In some possible implementations, the accelerator includes at least one of sodium 2-iodobenzenesulfonate and sodium dodecyl sulfonate. These sodium sulfonate accelerators are all beneficial for increasing plating speed and plating bath life, and improving coating quality.

[0119] In some possible implementations, the complexing agent includes at least one of dimethylamine, trimethylamine, 9-aminoacridine, and 2-mercaptocytosine; these ammonia nitrogen complexing agents can regulate the concentration of palladium ions in the plating bath, better control the controllability and stability of the palladium plating process, and improve the plating effect and the quality of the coating purity and uniformity.

[0120] In some possible implementations, the plating life of the electroless palladium plating solution is greater than 3 MTO. The electroless palladium plating solution in this application exhibits a high plating life, exceeding that of other currently commercially available products. The electroless palladium plating solution remains stable for a longer period, is less prone to decomposition or precipitation, and compared to other plating solutions, has better resistance to changes in external conditions (such as temperature, humidity, and light), maintaining a stable plating effect under different environments. This is more conducive to forming a uniform and dense coating on the substrate surface, ensuring consistent coating thickness regardless of the substrate's shape.

[0121] Thirdly, embodiments of this application provide a palladium plating layer, which is prepared on a growth substrate using the above-described electroless palladium plating solution or the electroless palladium plating solution prepared by the above method, through an electroless plating process.

[0122] The palladium coating in this embodiment is prepared on a growth substrate using the aforementioned electroless palladium plating solution via a chemical plating process. Through the combined action of reducing agents, stabilizers, accelerators, complexing agents, and plating starters in the electroless palladium plating solution, the deposition rate and quality of the palladium coating can be effectively controlled. This results in palladium coatings that are continuous, uniform, and of high purity with no doping, and the coatings are free from defects such as incomplete plating or pitting. The resulting palladium coating does not undergo displacement with either Ni or Au, and the high hardness of the Pd coating effectively avoids the black disk effect of nickel plating, improving the reliability of the applied devices.

[0123] In some possible implementations, the electroless plating process uses a temperature of 55°C to 65°C, a pH of 5 to 7, and a plating rate of 0.02 μm / min to 0.03 μm / min. Under these conditions, the temperature, pH, and plating rate are all conducive to controlling the appropriate reaction rate of the electroless palladium plating solution, controlling the deposition efficiency and effect of palladium in the solution, and ensuring the acquisition of a high-purity, uniform, and complete palladium coating.

[0124] For example, the temperature conditions of the electroless plating process can be any typical but non-limiting point value or a range between any two points, such as 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, and 65℃; the pH conditions can be any typical but non-limiting point value or a range between any two points, such as 5, 5.5, 5.7, 5.9, 6.0, 6.5, and 7; and the plating rate can be any typical but non-limiting point value or a range between any two points, such as 0.02 μm / min or 0.03 μm / min. In some specific embodiments, the temperature conditions of the electroless plating process are 60℃; the pH value is 5.7; the atmosphere is air; the plating rate is 0.02 μm / min to 0.03 μm / min; and the time can be adjusted according to the final required Pd film thickness, with longer times resulting in thicker films.

[0125] In some possible implementations, the surface of the growth substrate includes at least one of a Ni layer, a Ni-P alloy layer, and a Ni-B alloy layer. In this case, the palladium plating deposited on the surface of the growth substrate can effectively avoid the black disk effect of the nickel plating, thereby improving the reliability of the application device.

[0126] In some possible implementations, the palladium content in the palladium coating is greater than 99.5%. In the embodiments of this application, the palladium content in the palladium coating is greater than 99.5%, indicating high purity and extremely low impurity content. High-purity palladium coatings can more effectively resist oxidation, corrosion, and wear, protecting the substrate material from environmental factors. High-purity palladium coatings typically have higher hardness and wear resistance, capable of withstanding greater mechanical stress and frictional wear, thus extending service life. Furthermore, high-purity palladium coatings have stronger adhesion to the substrate material, lower contact resistance, and better welding performance, facilitating subsequent processing and connection, which is beneficial for signal transmission and energy consumption reduction in electronic products.

[0127] In some possible implementations, the size of the crystal grains in the palladium coating is less than 100 nm. In this case, the finer the crystal grains in the palladium coating, the denser the coating. This indicates that the palladium coating in the embodiments of this application has fine and dense metal grains, and the coating is free from defects such as incomplete plating, pitting, and nodular structures, resulting in high coating uniformity.

[0128] In some possible implementations, the palladium coating covers the growth substrate with a coverage rate greater than 99.5%, indicating that the palladium coating has a good coverage effect on the growth substrate and there are no missed coatings.

[0129] In some possible implementations, the average thickness of the palladium coating is 0.05 μm to 0.5 μm. The thickness of the palladium coating in the embodiments of this application can be selected according to actual application requirements. The coating thickness can be flexibly adjusted by controlling the electroless plating time; the longer the electroless plating time, the thicker the coating. For example, the thickness of the palladium coating can be any typical but non-limiting point value or a range between any two points, such as 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm.

[0130] Fourthly, embodiments of this application provide an electronic device, wherein the encapsulation layer of the electronic device includes the aforementioned palladium plating layer.

[0131] The electronic device in this application embodiment includes the palladium plating layer mentioned above, which is beneficial to improving the packaging effect of the electronic device, ensuring the welding reliability of the electronic device, and thus improving the performance and reliability of the electronic device.

[0132] In some possible implementations, palladium plating is applied to integrated circuit packaging / surface treatment scenarios such as power integrated circuits using electroless Pd plating.

[0133] Example

[0134] The following description uses specific embodiments. These embodiments are exemplary and are only used to explain this application, and should not be construed as limiting the application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0135] Examples 1-9

[0136] Examples 1 to 9 of this application provide a chemical palladium plating solution, and the components and formulations of each chemical palladium plating solution are shown in Table 1 below:

[0137] The preparation of each electroless palladium plating solution includes the following steps:

[0138] After preparing palladium salt solution, reducing agent solution, and additive solution including stabilizer, accelerator, complexing agent and plating starter, respectively, the palladium salt solution, reducing agent solution and additive solution are mixed together before use to obtain electroless palladium plating solution.

[0139] Comparative Example 1

[0140] This comparative example provides a chemical palladium plating solution, the composition and formulation of which are shown in Table 1 below:

[0141] Its preparation includes the following steps:

[0142] After preparing palladium salt solution, reducing agent solution, and additive solution including stabilizer, accelerator and complexing agent separately, the palladium salt solution, reducing agent solution and additive solution are mixed together before use to obtain electroless palladium plating solution.

[0143] Table 1

[0144]

[0145]

[0146] To verify the advancements of the electroless palladium plating solutions in this application, the plating life of the electroless palladium plating solutions prepared in the above embodiments and comparative examples were tested. The test results are shown in Table 2 below:

[0147] The palladium plating solutions prepared in the above embodiments and comparative examples were then chemically plated onto a nickel layer on an aluminum substrate under the same conditions and steps to form a palladium plating layer on the nickel layer surface. The palladium plating layers prepared in each embodiment and comparative example were tested as follows:

[0148] 1. Thickness test: For each group of experiments, the thickness of the substrate was measured at five points on the four sides and the center, and the average thickness of each palladium coating was calculated.

[0149] 2. Purity test: The palladium content in the palladium coatings prepared in each example and comparative example was tested;

[0150] 3. Coverage test of the substrate: Observe the palladium plating layer formed on the surface of the nickel layer using an optical microscope (OM) or a scanning electron microscope (SEM) to determine whether the underlying layer is exposed;

[0151] 4. Plating speed test: The unit of plating speed is μm / min. You can convert it. A plating speed that is stable at around 0.3 μm / min is considered excellent. Too fast a speed can easily cause the plating tank to flip over, while too slow a speed will affect production efficiency.

[0152] 5. Stability index test: Stability is represented by MTO. The larger the MTO, the better the stability index.

[0153] 6. Color difference index test: visual inspection;

[0154] The test results are shown in Table 2 below:

[0155] Table 2

[0156]

[0157] As shown in Table 2, the electroless palladium plating solution prepared in this embodiment has a plating life greater than 3 MTO, indicating a high plating life. The palladium content in the palladium coating is greater than 99.5%, reaching approximately 99.9%, indicating high purity and extremely low impurity content. Furthermore, the palladium coating has small crystal grains, resulting in fine and dense metal grains, free from defects such as missed plating, pitting, and nodular structures, and exhibiting high coating uniformity. The thickness difference between the test points on the four sides and the center is small, indicating uniform coating. The palladium coating covers the substrate with a coverage rate greater than 99.5%, demonstrating good coverage of the growth substrate and no missed plating. However, in Comparative Example 1, without the plating starter from this embodiment, the plating life was significantly reduced to 1 MTO, and problems such as missed plating, poor coating uniformity, poor coverage (only 95%), and low palladium purity (only 99.5%) were observed.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The protection scope of this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A chemical palladium plating solution, characterized in that, It includes palladium salts, reducing agents, additives, and solvents, wherein the additives include stabilizers, accelerators, complexing agents, and plating starters; wherein the plating starters include OPSS-type polymers.

2. The electroless palladium plating solution as described in claim 1, characterized in that, In the electroless palladium plating solution, the concentration of the palladium salt is 0.1 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 1 mg / L to 100 mg / L, the concentration of the accelerator is 10 g / L to 100 g / L, the concentration of the complexing agent is 1 g / L to 10 g / L, and the concentration of the plating starter is 0.3 g / L to 0.6 g / L. And / or, the molar ratio of the complexing agent to the plating starter is (1-20):1; And / or, the molar ratio of the stabilizer to the complexing agent is 1:(2-20); And / or, the pH value of the electroless palladium plating solution is 5.5 to 6.

3. The electroless palladium plating solution as described in claim 2, characterized in that, The additive also contains at least one pH adjuster from hydrochloric acid, nitric acid, sulfuric acid, and ammonia water; And / or, in the electroless palladium plating solution, the concentration of the palladium salt is 0.8 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 10 mg / L to 40 mg / L, the concentration of the accelerator is 30 g / L to 60 g / L, the concentration of the complexing agent is 3 g / L to 6 g / L, and the concentration of the plating starter is 0.3 g / L to 0.6 g / L.

4. The electroless palladium plating solution according to any one of claims 1 to 3, characterized in that, The general structural formula of the OPSS-type polymer is: Where n is an integer between 1 and 5, R1 is selected from one of hydrogen atoms, alkyl, unsaturated alkyl, phenyl, and heteroatom groups; R2 is selected from one of straight-chain alkanolamine groups and heterocyclic phenol groups; And / or, the palladium salt includes at least one of palladium chloride, palladium sulfate, dichlorotetraammonium palladium, tetraammonium palladium sulfate, and tetraammonium palladium hydrochloride; And / or, the reducing agent includes at least one of formic acid, hydrazine hydrate, hypophosphite, and formaldehyde; And / or, the stabilizer includes aromatic ring carboxylic acid molecules; And / or, the accelerator includes sodium sulfonate salt; And / or, the complexing agent includes ammonia nitrogen molecules; And / or, the solvent includes water.

5. The electroless palladium plating solution as described in claim 4, characterized in that, The alkyl group is selected from alkyl groups having 1 to 4 carbon atoms; And / or, the unsaturated alkyl group includes at least one of methenoyl, vinyl, and propenyl groups; And / or, the heteroatom group includes at least one of hydroxyl, amino, carboxyl, and amide groups; And / or, the straight-chain alkanolamine group includes at least one of -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3)2, -CH2NH(CH2OH), -CH2NH(C2H4OH), -C2H4NH(CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH)2, -CH2N(C2H4OH)2, -C2H4N(CH2OH)2, and -C2H4N(C2H4OH)2; And / or, the heterocyclic phenolic group includes at least one of hydroxylated pyridyl, hydroxylated furanyl, hydroxylated pyrroleyl, and hydroxylated thiopheneyl.

6. The electroless palladium plating solution according to any one of claims 1 to 3 or 5, characterized in that, The reducing agent includes formic acid; And / or, the stabilizer comprises at least one of nicotinic acid, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, methyl 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; And / or, the accelerator includes at least one of sodium 2-iodobenzenesulfonate and sodium dodecyl sulfonate; And / or, the complexing agent includes at least one of dimethylamine, trimethylamine, 9-aminoacridine, and 2-mercaptocytosine; And / or, the plating starter includes at least one of OH-PEG-amide-OPSS, NHS-PEG-amide-OPSS, and NMe2-PEG-amide-OPSS.

7. A method for preparing a chemical palladium plating solution, characterized in that, Includes the following steps: Palladium salt solution, reducing agent solution, and additive solution are prepared separately. The additive solution includes a stabilizer, an accelerator, a complexing agent, and a plating starter. The plating starter includes an OPSS-type polymer. In use, the palladium salt solution, the reducing agent solution, and the additive solution are mixed to prepare a chemical palladium plating solution.

8. The method for preparing the electroless palladium plating solution as described in claim 7, characterized in that, The concentration of the palladium salt solution is 15 g / L to 25 g / L, and the pH value is 10.7 to 11. And / or, the concentration of the reducing agent solution is 50 g / L to 200 g / L, and the pH value is 5.5 to 5.7; And / or, the concentration of the additive solution is 300 g / L to 600 g / L, and the pH value is 6.9 to 7.2; And / or, in the electroless palladium plating solution, the concentration of the palladium salt is 0.8 g / L to 1.2 g / L, the concentration of the reducing agent is 10 g / L to 40 g / L, the concentration of the stabilizer is 10 mg / L to 40 mg / L, the concentration of the accelerator is 30 g / L to 60 g / L, the concentration of the complexing agent is 3 g / L to 6 g / L, the concentration of the plating starter is 0.3 g / L to 0.6 g / L, and the pH value is 5.5 to 5.7; And / or, the plating bath life of the electroless palladium plating solution is greater than 3 MTO.

9. A palladium plating layer, characterized in that, A palladium plating layer is formed on a growth substrate by using a palladium plating solution prepared according to any one of claims 1 to 6 or a palladium plating solution prepared according to any one of claims 7 to 8, through a chemical plating process.

10. The palladium coating as described in claim 9, characterized in that, The palladium coating contains more than 99.5% palladium. And / or, in the palladium coating, the size of the crystal grains is less than 100 nm; And / or, the palladium coating has a coverage of more than 99.5% over the growth substrate; And / or, the average thickness of the palladium coating is 0.05 μm to 0.5 μm; And / or, the temperature conditions of the electroless plating process are 55℃~65℃, the pH conditions are 5~7, and the plating rate is 0.02um / min~0.03um / min; And / or, the surface of the growth substrate includes at least one of a Ni layer, a Ni-P alloy layer, and a Ni-B alloy layer.

11. An electronic device, characterized in that, The encapsulation layer of the electronic device includes a palladium plating layer as described in any one of claims 9 to 10.

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