Stable chemical palladium plating solution and application thereof

Abstract

The invention discloses a stable chemical palladium plating solution and application thereof, and belongs to the technical field of metal surface treatment. The invention provides a chemical palladium plating solution. The chemical palladium plating solution mainly comprises 1-2g / L of tetraammine palladium sulfate, 1-2g / L of a catalyst, 1-2g / L of a complexing agent and the balance of 0.3 to 1.7 g / L of sodium hypophosphite; 3.6 to 14.4 g / L of ethylene diamine tetraacetic acid disodium salt; glycine with a concentration of 15 to 25 g / L; and 1-2 * 10 <-5 > mol / L of potassium iodate. The invention aims to provide the method for depositing the palladium plating layer with required performance on the surface of the nickel layer by changing the components and parameters of the plating solution, so that the stability of the plating solution in the whole chemical plating process can be maintained, the quality of the palladium layer is improved, and the overall surface performance, especially the corrosion resistance, of the palladium layer is improved.

Description

Technical Field

[0001] The invention relates to a stable chemical palladium plating solution and application thereof, belonging to the technical field of metal surface treatment. Background Art

[0002] Printed circuit boards (PCBs) are the interconnecting substrates for electronic components, typically using copper as a conductor for signal transmission. With the advent of high-end electronic products and the advent of 5G communication technology, PCBs are increasingly oriented towards smaller size, easier packaging, greater multifunctionality, and higher frequency and speed. This places higher demands on the surface stability of copper circuits. To protect copper from oxidation and deterioration, maintain its conductivity, and improve component solderability, surface treatment is required. Currently, electroless nickel / electroless palladium / immersion gold (ENEPIG) is an ideal surface modification technology for copper surfaces. Compared to electroless nickel / immersion gold (ENIG), the introduction of a highly stable Pd layer in ENEPIG effectively prevents excessive Au attack on Ni grain boundaries, providing an oxygen-free Ni surface. This effectively avoids the "black pad" problem and further improves the reliability of lead-free solder / PCB joints. The quality of the Pd layer deposition directly determines the formation of an oxygen-free Ni surface, which in turn affects the surface properties of the coating.

[0003] Chemical plating is essentially a thermodynamically unstable system composed of an oxidant and a reducing agent. In particular, when Pd particles at the edge of the deposited metal layer diffuse into the bulk solution, the Pd particles themselves have strong catalytic activity. If not controlled, the particles will grow further, causing the plating solution to decompose. At the same time, a large amount of waste will be generated, causing environmental pollution. Therefore, the preparation of a palladium plating solution with good stability has become one of the obstacles to the widespread application of the ENEPIG process. The plating solution components and additives can control the deposition rate and nucleation, and are the key to the success of chemical palladium plating technology. Therefore, the present invention is to regulate the plating solution components and maintain the relative stability of the plating solution throughout the entire chemical plating process, thereby improving the deposition quality of the palladium layer and improving the overall surface properties (corrosion resistance) of the coating, thereby providing a reference for the large-scale application of the ENEPIG process. Summary of the Invention

[0004] In order to solve or partially solve the problems existing in existing plating solutions, the purpose of the present invention is to provide a stable chemical palladium plating solution by changing the composition and parameters of the plating solution, which can maintain the stability of the plating solution throughout the entire chemical plating process, improve the quality of the palladium layer, and improve the overall surface properties (corrosion resistance) of the palladium layer.

[0005] To achieve the above object, the present invention adopts the following technical solutions: Firstly, a stable chemical palladium plating solution is provided. The main components of the stable chemical palladium plating solution include: tetraammine palladium sulfate, sodium hypophosphite, disodium ethylenediaminetetraacetate, glycine and potassium iodate.

[0006] Preferably, the main components of the chemical palladium plating solution include: 1-2 g / L of tetraammine palladium sulfate, 0.3-1.7 g / L of sodium hypophosphite, 3.6-14.4 g / L of disodium ethylenediaminetetraacetate, 15-25 g / L of glycine and 1-2×10 -5 mol / L potassium iodate.

[0007] The present invention also provides an application of the stable chemical palladium plating solution in palladium plating on a nickel-plated metal surface.

[0008] The technical solution provided by the present invention can have the following beneficial effects: (1) When the present invention performs chemical palladium plating on nickel-plated copper sheets, a main salt and a reducing agent with high stability, non-toxicity, environmental protection and cleanness are used: the main salt is tetraammine palladium sulfate, and the reducing agent is sodium hypophosphite.

[0009] (2) The main complexing agent selected in the present invention is disodium ethylenediaminetetraacetic acid, the auxiliary complexing agent is glycine, which is also a buffer, and the stabilizer is potassium iodate; wherein disodium ethylenediaminetetraacetic acid and glycine can react with Pd 2+ Form a complex to maintain free Pd in ​​the plating solution 2+ The concentration is relatively constant and the pH value of the plating solution is kept within a certain range. The addition of potassium iodate, a stabilizer, effectively improves the stability of the plating solution, allowing the plating solution to constantly precipitate palladium under stable conditions and promote the deposition of Pd 2+ The ordered growth of palladium on the nickel surface improves the quality of the palladium deposit and the overall performance (corrosion resistance) of the coating.

[0010] (3) The stability of the plating solution is significantly improved, the stabilization time is prolonged, and the resulting coating has the best corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a SEM photograph of the palladium coating of Example 1 of the present invention.

[0012] Figure 2 1 is a SEM photograph of the palladium coating of Comparative Example 1 of the present invention.

[0013] Figure 3 1 is a SEM photograph of the palladium coating of Comparative Example 2 of the present invention.

[0014] Figure 4 3 is a SEM photograph of the palladium coating of Comparative Example 3 of the present invention.

[0015] Figure 5 3 is a SEM photograph of the palladium coating of Comparative Example 4 of the present invention.

[0016] Figure 6 5 is a SEM photograph of the palladium coating of Comparative Example 5 of the present invention.

[0017] Figure 7 1 and 2 are the potentiodynamic polarization curves of Example 1 and Comparative Examples 1 to 5 of the present invention.

[0018] Figure 8 (a) Nyquist and (b, c) Bode plots of Example 1 and Comparative Examples 1 to 5 of the present invention. Figure 9 The figure shows a comparison of the stabilization time of the plating solutions prepared in Example 1 of the present invention and Comparative Examples 1 to 5. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0020] Example 1 The main components of the stable chemical palladium plating solution used in this embodiment include: 1g / L tetraammine palladium sulfate, 2g / L sodium hypophosphite, 6.8g / L disodium ethylenediaminetetraacetate, 20g / L glycine and 1×10 -5 mol / L potassium iodate.

[0021] The stable chemical palladium plating solution is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are as follows: (1) The copper sheet was placed in a chemical degreasing solution and reacted at 85°C for 20 minutes to remove lubricating oil, polishing paste and other oil stains on the surface of the copper sheet to ensure the smoothness and flatness of the substrate surface and improve the adhesion between the coating and the substrate; the composition of the chemical degreasing solution was as follows: NaOH: 8 g / L, Na3PO4‧12H2O: 50 g / L, Na2CO3: 50 g / L and Na2SiO3: 5 g / L.

[0022] (2) The copper sheet after chemical degreasing was placed in a micro-etching solution and treated at 20°C for 30 seconds to remove oxides and rust products on the surface of the copper sheet. The composition of the micro-etching solution was as follows: concentrated sulfuric acid: 20 mL / L and Na2S2O8: 100 g / L.

[0023] (3) The micro-etched copper sheet is placed in an acid pickling solution and treated at 20°C for 30 seconds to remove a small amount of oxide generated on the surface of the copper sheet during the chemical degreasing and micro-etching process, so that the matrix structure is fully exposed, which is conducive to the close bonding between the coating and the substrate; the acid pickling solution is concentrated sulfuric acid: 27mL / L.

[0024] (4) The pickled copper sheet is placed in a liquid chemical nickel plating solution and treated at 55°C for 3 minutes for pre-nickel plating to form a pre-nickel plating layer on the surface of the copper sheet, thereby increasing catalytic active sites for subsequent chemical nickel plating. The composition of the chemical pre-nickel plating solution is as follows: 30g / L NiSO4‧6H2O, 25g / L C6H5Na3O7‧2H2O, 10g / L NH4Cl, 12g / L NaH2PO2‧H2O and 2g / L DMAB, pH 10.

[0025] (5) Placing the pre-nickel-plated copper sheet in a chemical nickel plating solution and treating it at 60°C for 60 minutes to perform chemical nickel plating to form a nickel plating layer on the surface of the pre-nickel plating layer; the composition of the chemical nickel plating solution is as follows: 26 g / L NiSO4‧6H2O, 40 g / L C6H5Na3O7‧2H2O, 33 g / L H3BO3: 26 g / L NaH2PO2‧H2O; pH is 8.

[0026] (6) Place the copper sheet after chemical nickel plating in a stable chemical palladium plating solution and treat it at 55°C for 30 minutes to perform chemical palladium plating.

[0027] Example 2 The main components of the stable chemical palladium plating solution used in this embodiment include: 2g / L tetraammine palladium sulfate, 0.3g / L sodium hypophosphite, 14.4g / L disodium ethylenediaminetetraacetate, 15g / L glycine and 2×10 -5 mol / L potassium iodate.

[0028] Example 3 The main components of the stable chemical palladium plating solution used in this embodiment include: 1.5g / L tetraammine palladium sulfate, 1.7g / L sodium hypophosphite, 3.6g / L disodium ethylenediaminetetraacetate, 25g / L glycine and 1×10 -5 mol / L potassium iodate.

[0029] The performance characteristics of the stable chemical palladium plating solutions prepared in Examples 2 and 3 are similar to those in Example 1.

[0030] Comparative Example 1 As a comparison, the only difference between this comparative example and Example 1 is that thiourea is used instead of potassium iodate; The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as those in Example 1.

[0031] Comparative Example 2 As a comparison, the only difference between this comparative example and Example 1 is that acrylic acid is used instead of potassium iodate; The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as those in Example 1.

[0032] Comparative Example 3 As a comparison, the only difference between this comparative example and Example 1 is that sodium thiosulfate is used instead of potassium iodate; The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as those in Example 1.

[0033] Comparative Example 4 As a comparison, the only difference between this comparative example and Example 1 is that lead nitrate is used instead of potassium iodate; The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as those in Example 1.

[0034] Comparative Example 5 The difference between this comparative example and Example 1 is that potassium iodate is not added to the stable chemical palladium plating solution used. The rest is the same as Example 1. The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as Example 1.

[0035] Comparative Example 6 The difference between this comparative example and Example 1 is that no disodium ethylenediaminetetraacetic acid is added to the stable chemical palladium plating solution used. The rest is the same as Example 1. The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as Example 1.

[0036] Comparative Example 7 The difference between this comparative example and Example 1 is that glycine is not added to the stable chemical palladium plating solution used. The rest is the same as Example 1. The chemical palladium plating solution obtained in this comparative example is plated on the surface of the copper sheet by chemical palladium plating, and the specific steps are the same as Example 1.

[0037] Performance Testing The coatings obtained in Example 1 and Comparative Examples 1 to 7 were subjected to the following performance tests: (1) Surface morphology of coating: the results are as follows Figures 1 to 6 As shown, Figure 1 This is the surface morphology of the palladium coating prepared after adding potassium iodate as a stabilizer in Example 1. It can be seen that the surface of the coating is smooth and fine without obvious defects. Figure 2 and Figure 4 The surface morphologies of the palladium coatings of Comparative Examples 1 and 3 are shown. Thiourea and sodium thiosulfate sulfur-containing compounds were added to Comparative Examples 1 and 3, respectively. It can be seen that large corrosion pits exist on the surface of the coatings and the plating leakage phenomenon is serious. Figure 3 This is the surface morphology of the palladium coating in Comparative Example 2. Acrylic acid was added to Comparative Example 2. It can be seen that obvious decomposition products are present on the surface of the coating, which is related to the accelerated decomposition of the plating solution by acrylic acid. Figure 5 This is the surface morphology of the palladium coating obtained after adding lead nitrate in Comparative Example 4. It can be seen that there are obvious decomposition products on the surface of the coating. Figure 6It is the surface morphology of comparative example 5 palladium coatings, and comparative example 5 does not add potassium iodate, from which it can be seen that there is obvious flaky corrosion on the coating surface, and the coating unit cell is thick.Comparative examples 6 and 7 all adopt single complexing agent, and now, the high palladium ion concentration of free state causes palladium deposition rate very fast, and the surface of the palladium coating of gained floats black powder, and poor adhesion, therefore do not further carry out the characterization of scanning electron microscope.Therefore the preferred potassium iodate of the present invention is as stabilizer, can effectively promote the orderly growth of metal palladium, and the potassium iodate adsorbed on nickel surface does not produce the negative effect of leakage plating, and then makes the coating surface smooth intact, uniform and meticulous.

[0038] (2) Deposition rate: Convert weight gain into thickness and calculate using the following formula: Where m0 and m are the mass of the substrate before and after plating (g), is the density of the palladium plating layer (theoretical density 12.0g / cm 3 ), A is the coating area (fixed at 20cm 2 ), t is the plating time (h).

[0039] (3) Plating solution stability: High temperature (80°C) plating solution stability test.

[0040] The test results of Examples 1 to 5 and Comparative Example 1 are shown in Tables 1 to 3.

[0041] Table 1 Comparison of electroless palladium deposition rate and plating solution stability Table 1 is a comparison of the chemical palladium deposition rate and plating solution stability results of Comparative Examples 1-7 and Example 1. It can be seen from Table 1 that Example 1, Comparative Example 1 and Comparative Example 3 are respectively added to the plating solution after potassium iodate, thiourea and sodium thiosulfate, and the chemical palladium deposition rate and the stability of the plating solution are significantly improved. The addition of the stabilizer ensures that the reduction process only occurs on the substrate surface with catalytic activity, rather than in the plating solution away from the substrate; However, Comparative Examples 2 and 4 are added to the plating solution acrylic acid and lead nitrate, and the chemical palladium deposition rate and the stability of the plating solution are reduced. Therefore, it can be concluded that the chemical palladium plating solution provided by the present invention selects potassium iodate, thiourea and sodium thiosulfate as stabilizers, which can effectively reduce the uncontrolled growth of palladium particles in the plating solution and improve the stability of the plating solution. However, a coating with good morphology can be obtained while improving the stability of the plating solution only after adding potassium iodate, and the coating obtained after adding sulfur-containing compounds has obvious leakage plating phenomenon, so potassium iodate is preferably used as a stabilizer. Comparative Examples 6 and 7 both used a single complexing agent. In these cases, the palladium deposition rate was very fast, resulting in a black powder floating on the surface of the resulting palladium-plated layer and poor adhesion. Furthermore, the plating solution was unstable and decomposed during the plating process. Therefore, the samples obtained in Comparative Examples 6 and 7 were not further studied.

[0042] (4) Corrosion resistance: potentiodynamic polarization curve and electrochemical impedance spectroscopy test, Figure 7 and Figure 8 The potentiodynamic polarization curves and Nyquist and Bode plots of the palladium coatings of Comparative Examples 1 to 5 and Example 1 are shown in Tables 2 and 3. The corresponding electrochemical parameters are shown in Tables 2 and 3. It can be seen that the corrosion resistance of Example 1 is better than that of Comparative Examples 1 to 5, indicating that the corrosion performance of the coating is related to the surface morphology.

[0043] Table 2 Comparison of potentiodynamic polarization curve test results Table 3 Comparison of electrochemical impedance spectroscopy test results Combined with Table 1, Figures 1 to 6 , which means that the chemical palladium plating solution provided by the present invention uses potassium iodate as a stabilizer, which can avoid the negative effects such as the addition of acrylic acid promoting the decomposition of the plating solution, and the occurrence of corrosion pits in the coating caused by thiourea, sodium thiosulfate, and lead nitrate, thereby effectively improving the corrosion resistance of the coating.

[0044] In summary, the experimental and test results in Tables 1 to 3 show that the chemical palladium plating solution provided by the present invention uses potassium iodate as a stabilizer to ensure that Pd 2+ The reduction only occurs on the nickel surface, which increases the deposition rate of palladium. The resulting palladium-plated layer is smooth and dense, has no obvious defects, and exhibits excellent corrosion resistance.

[0045] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A stable chemical palladium plating solution, characterized in that: The main components of the stable chemical palladium plating solution include: 1-2 g / L of tetraammine palladium sulfate, 0.3-1.7 g / L of sodium hypophosphite, 3.6-14.4 g / L of disodium ethylenediaminetetraacetate, 15-25 g / L of glycine and 1-2×10 -5 mol / L potassium iodate.

2. Application of the stable chemical palladium plating solution according to claim 1 in palladium plating on nickel-plated metal surfaces.

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