Method for electroplating nickel on a bismuth telluride substrate

Abstract

Disclosed is a method for electroplating nickel on a bismuth telluride substrate. In the method, roughening is performed, the bismuth telluride substrate is placed in a roughening solution for roughening treatment to form a porous structure on the surface of the bismuth telluride substrate; chemical plating is performed, the bismuth telluride substrate after step S1 is placed in a chemical plating solution for chemical plating treatment; electroplating is performed, the bismuth telluride substrate after step S2 is placed in an electroplating solution for electroplating treatment to obtain a nickel plating layer. The nickel plating layer obtained by electroplating has high bonding strength and stable process. The bismuth telluride-based thermoelectric device manufactured by the method has higher reliability and longer service life.

Description

Technical Field

[0001] This invention belongs to the field of bismuth telluride electroplating, and in particular, a method for electroplating nickel on a bismuth telluride substrate under operating conditions. Background Technology

[0002] Bismuth telluride is one of the best-performing thermoelectric materials, its main principle being the Seebeck effect, which refers to the directional migration of charge carriers in a semiconductor under temperature differences, generating current. It has already achieved large-scale commercial applications below 200°C. Commercial thermoelectric devices are fabricated by alternating series connection of N-type and P-type thermoelectric arms and soldering them onto metal electrodes. However, direct contact between bismuth telluride and solder can lead to severe interfacial reactions. Therefore, before device manufacturing, a nickel plating layer is needed at the interface between the bismuth telluride and solder as a barrier layer to reduce interfacial reactions and extend the device's lifespan. Due to its good electroplating uniformity and suitability for industrial batch nickel plating, it is used in the processing technology of the bismuth telluride barrier layer.

[0003] The general process of nickel electroplating involves degreasing and acid activation of the workpiece in different solutions, followed by depositing a nickel layer on the workpiece using a nickel plate as the anode and the workpiece as the cathode, after applying a DC power supply. However, the general nickel electroplating process suffers from interfacial bonding strength issues. Bismuth telluride and nickel have different coefficients of thermal expansion (CTE). Bi2Te3 =15μm·m⁻¹·K⁻¹, CTE Ni =12.8 μm·m⁻¹·K⁻¹), and at 200℃ and above, this difference will generate significant internal stress at the interface, causing interface cracking. Furthermore, during device use, thermal shock, external forces, and other factors can also create stress concentration at the interface, making the interface coating more prone to cracking.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a method for electroplating nickel on a bismuth telluride substrate, which improves the bonding force between bismuth telluride and the nickel layer, and ensures that the interface between bismuth telluride and the nickel layer remains stable under extreme environments, thereby optimizing the reliability of bismuth telluride-based thermoelectric generators.

[0006] The objective of this invention is achieved through the following technical solution: a method for electroplating nickel on a bismuth telluride substrate includes:

[0007] Step S1: Roughening is performed by placing the bismuth telluride matrix into a roughening solution for roughening treatment to form a porous structure on the surface of the bismuth telluride matrix.

[0008] Step S2: Perform chemical plating by immersing the bismuth telluride substrate treated in step S1 into a chemical plating solution for chemical plating treatment.

[0009] Step S3: Electroplating is performed by immersing the bismuth telluride substrate treated in step S2 into an electroplating solution to form a nickel plating layer.

[0010] In the method for electroplating nickel on a bismuth telluride substrate, prior to step S1, bismuth telluride substrate preparation and pretreatment are performed, including the following steps:

[0011] Step A: A bismuth telluride-based bulk thermoelectric material is prepared by sintering, zone melting, hot extrusion or powder metallurgy, and then cut to expose the surface of the bismuth telluride to be electroplated to form the bismuth telluride matrix.

[0012] Step B involves degreasing the bismuth telluride matrix by immersing it in solution a at 60±5℃ for 8-10 minutes to remove surface grease. Solution a includes degreasing powder.

[0013] Step C involves washing and drying the bismuth telluride substrate surface with deionized water to ensure a clean surface.

[0014] In the method for electroplating nickel on a bismuth telluride substrate, step S1 includes the following steps:

[0015] Step D involves pre-roughening the bismuth telluride matrix by immersing it in solution b at 25±5℃ for 3-5 minutes. The volume fractions of the components in solution b are: dimethylformamide 15-25%, N-methylpyrrolidone 5-15%, ethylene glycol ethyl ether 20-40%, and the remainder being deionized water.

[0016] Step E: Roughening is performed by placing the bismuth telluride matrix into solution C and immersing it at 50±10℃ for 10-15 minutes. The components of solution C are: 410-430 g / L chromium trioxide and 400-410 g / L sulfuric acid.

[0017] Step F involves washing and drying the bismuth telluride substrate surface with deionized water to ensure a clean surface.

[0018] Step G: Neutralization is performed by placing the bismuth telluride matrix into solution d and immersing it at 60±2℃ for 10-15 minutes. The composition of solution d is: hydrochloric acid volume fraction of 25%-30% and sodium sulfite volume fraction of 20-100g / L.

[0019] In the method for electroplating nickel on a bismuth telluride substrate, step S2 includes the following steps:

[0020] Step H involves activation by immersing the bismuth telluride matrix in solution e at 25±5℃ for 10-15 minutes to improve the adhesion of the electroless plating. The composition of solution e is: hydrochloric acid volume fraction 8-12%, colloidal palladium 0.4-0.8 g / L.

[0021] Step I: Accelerate degelling by immersing the bismuth telluride matrix in solution f at 50±5℃ for 10-15 minutes. The composition of solution f is: sulfuric acid 50-150 ml / L.

[0022] Step J: Perform chemical plating by immersing the bismuth telluride substrate in solution g and soaking it at 25±5℃ for 20-30 minutes. The components of solution g are: nickel chloride 30g / L, ammonium chloride 50g / L, sodium hypophosphite 40g / L, sodium citrate 15g / L, and ammonia water 18ml / L.

[0023] In the method for electroplating nickel on a bismuth telluride substrate, step S3 includes the following steps:

[0024] Step K involves acid activation, in which the bismuth telluride matrix is ​​placed in solution h and soaked at 25±5℃ for 5-10 minutes. The composition of solution h is: sulfuric acid 30-50g / L.

[0025] Step L involves nickel electroplating in a solution i at a temperature of 60±5℃. The solution i consists of: NiSO4 280-320 g / L, NiCl2 60-80 g / L, H3BO4 45-50 g / L, nickel electroplating additives, a nickel electroplating current of 1.5±0.5 amperes / dm², and a nickel electroplating time of 40±10 minutes.

[0026] The method for electroplating nickel on a bismuth telluride substrate further includes a water washing and drying step, in which the electroplating solution remaining on the product surface is cleaned with deionized water and then dried to ensure that the plating layer is dry and clean.

[0027] Compared with existing technologies, the present invention has the following advantages: the nickel plating layer obtained by electroplating in this invention has high bonding strength and stable process. Bismuth telluride-based thermoelectric devices manufactured using this method have higher reliability and longer lifespan. Attached Figure Description

[0028] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0029] In the attached diagram:

[0030] Figure 1 This is a flowchart of the electroplating process of the present invention;

[0031] Figure 2 These are electron microscope images of the roughened bismuth telluride substrate surface in the examples;

[0032] Figure 3 This is an electron microscope image of the interface between the nickel layer and the bismuth telluride substrate after a thermal shock test at 300°C in the example.

[0033] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0034] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0035] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0036] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0037] In one embodiment, such as Figures 1 to 3 As shown, a method for electroplating nickel on a bismuth telluride substrate includes, S0, a step of preparing and pretreating the bismuth telluride substrate, which specifically includes the following three steps:

[0038] A. An n-type bismuth telluride sample is prepared by discharge plasma sintering and then cut to expose the surface of the bismuth telluride to be electroplated, thus forming the bismuth telluride substrate.

[0039] B. Degreasing step: Immerse the bismuth telluride matrix in solution a at 60±5℃ for 8-10 minutes to remove surface grease. The components of solution A are: sodium hydroxide 60-80g / L, sodium carbonate 15-20g / L, and trisodium phosphate 30-50g / L.

[0040] C. The steps of washing and drying: After washing the surface of the bismuth telluride substrate with deionized water, dry it to make the surface of the bismuth telluride substrate clean.

[0041] S1, the roughening process: The bismuth telluride matrix is ​​placed in a roughening solution for roughening treatment to achieve a porous structure on the material surface. This step specifically includes the following steps:

[0042] D. The pre-roughening step: The bismuth telluride matrix is ​​placed in solution b and soaked at 25±5℃ for 3-5 minutes. The volume fraction of each component in solution b is as follows: The volume fraction of each component in solution B is as follows: dimethylformamide 15-25%, N-methylpyrrolidone 5-15%, ethylene glycol ethyl ether 20-40%, and the remainder is deionized water.

[0043] E. The roughening step: The bismuth telluride matrix is ​​placed in solution c and soaked at 50±10℃ for 10-15 minutes. The components of solution C are: 410-430 g / L of chromium trioxide and 400-410 g / L of sulfuric acid.

[0044] F. The steps of washing and drying are as follows: wash the surface of the bismuth telluride substrate with deionized water and then dry it to make the surface of the bismuth telluride substrate clean.

[0045] G, the neutralization step: bismuth telluride matrix is ​​placed in solution d and soaked at 60±2℃ for 10-15 minutes. The components of solution d are: hydrochloric acid volume fraction of 25%-30% and sodium sulfite of 20-100g / L.

[0046] Figure 2 This is an electron microscope image of the bismuth telluride substrate surface after step G. Effective roughening of the bismuth telluride substrate surface creates numerous pores, which significantly increases the contact area between the nickel layer and the bismuth telluride, thereby improving the interfacial bonding strength.

[0047] S2, the electroless plating step: The bismuth telluride substrate treated in step S1 is immersed in an electroless plating solution for electroless plating treatment to improve the conductivity of the bismuth telluride substrate. This step specifically includes the following steps:

[0048] H, the activation step: immerse the bismuth telluride matrix in solution e and soak it at 25±5℃ for 10-15 minutes to improve the adhesion of the electroless plating. The composition of solution e is: hydrochloric acid volume fraction 8-12%, colloidal palladium 0.4-0.8g / L.

[0049] I. The step of accelerating degelling: The bismuth telluride matrix is ​​placed in solution f and soaked at 50±5℃ for 10-15 minutes. The composition of solution f is: sulfuric acid 50-150ml / L.

[0050] J, the steps for chemical plating: bismuth telluride substrate is placed in solution g and soaked at 25±5℃ for 20-30 minutes. The components of solution g are: nickel chloride 30g / L, ammonium chloride 50g / L, sodium hypophosphite 40g / L, sodium citrate 15g / L, and ammonia water 18ml / L.

[0051] S3, the electroplating step: The bismuth telluride substrate treated in step S2 is placed in the electroplating solution for electroplating treatment. This step specifically includes the following steps:

[0052] K, the acid activation step: bismuth telluride matrix is ​​placed in solution h and soaked at 25±5℃ for 5-10 minutes. The composition of solution h is: sulfuric acid 30-50g / L.

[0053] L, the steps for nickel electroplating: nickel plating is performed in solution i at a temperature of 60±5℃. The composition of solution i is: NiSO4 280-320g / L, NiCl2 60-80g / L, H3BO4 45-50g / L. The electroplating additives are purchased from Bigley Company and include nickel plating softener 10-12ml / L, nickel plating brightener 0.1-0.3ml / L, wetting agent 1-3ml / L. The electroplating current for nickel is 2 amperes / dm², and the electroplating time for nickel is 30 minutes.

[0054] Finally, the process also includes a water washing and drying step, where the electroplating solution remaining on the product surface is cleaned with deionized water and then dried to ensure that the plating layer on the product surface is dry and clean.

[0055] Figure 3 This is an electron microscope image of the interface between the nickel layer and the bismuth telluride substrate after a 300°C thermal shock test. The conventional operating temperature of bismuth telluride-based thermoelectric devices is approximately 200°C, but the nickel electroplated layer manufactured in this invention does not fracture under a 300°C thermal shock test. This is of significant value for broadening the application range of bismuth telluride-based thermoelectric materials and enhancing device reliability.

[0056] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for electroplating nickel onto a bismuth telluride substrate, characterized in that, It includes the following steps, Step S1 involves roughening the bismuth telluride matrix by immersing it in a roughening solution to form a porous structure on the surface of the bismuth telluride matrix. Step S1 includes the following steps: Step D: Pre-roughening is performed by placing the bismuth telluride matrix into solution b and immersing it at 25±5℃ for 3-5 minutes. The volume fractions of each component in solution b are: dimethylformamide 15-25%, N-methylpyrrolidone 5-15%, ethylene glycol ethyl ether 20-40%, and the remainder is deionized water. Step E: Roughening is performed by placing the bismuth telluride matrix into solution c and immersing it at 50±10℃ for 10-15 minutes. The components of solution c are: 410-430 g / L chromium trioxide and 400-410 g / L sulfuric acid. Step F involves washing and drying the bismuth telluride substrate surface with deionized water to ensure a clean surface. Step G: Neutralization is performed by placing the bismuth telluride matrix into solution d and immersing it at 60±2℃ for 10-15 minutes. The components of solution d are: hydrochloric acid volume fraction of 25%-30% and sodium sulfite volume fraction of 20-100g / L. Step S2 involves electroless plating, where the bismuth telluride substrate treated in step S1 is immersed in an electroless plating solution for electroless plating. Step S2 includes the following steps: Step H involves activation by immersing the bismuth telluride matrix in solution e at 25±5℃ for 10-15 minutes to improve the adhesion of the electroless plating. The composition of solution e is: hydrochloric acid volume fraction 8-12%, colloidal palladium 0.4-0.8 g / L. Step I: Accelerate degelling by immersing the bismuth telluride matrix in solution f at 50±5℃ for 10-15 minutes. The composition of solution f is: sulfuric acid 50-150 ml / L. Step J: Perform chemical plating by immersing the bismuth telluride substrate in solution g and soaking it at 25±5℃ for 20-30 minutes. The components of solution g are: nickel chloride 30g / L, ammonium chloride 50g / L, sodium hypophosphite 40g / L, sodium citrate 15g / L, and ammonia water 18ml / L. Step S3: Electroplating is performed by immersing the bismuth telluride substrate treated in step S2 into an electroplating solution to form a nickel plating layer.

2. The method for electroplating nickel on a bismuth telluride substrate according to claim 1, characterized in that, Before step S1, bismuth telluride matrix preparation and pretreatment are performed, including the following steps: Step A: A bismuth telluride-based bulk thermoelectric material is prepared by sintering, zone melting, hot extrusion or powder metallurgy, and then cut to expose the surface of the bismuth telluride to be electroplated to form the bismuth telluride matrix. Step B involves degreasing the bismuth telluride matrix by immersing it in solution a at 60±5℃ for 8-10 minutes to remove surface grease. Solution a includes degreasing powder. Step C involves washing and drying the bismuth telluride substrate surface with deionized water to ensure a clean surface.

3. The method for electroplating nickel on a bismuth telluride substrate according to claim 1, characterized in that, Step S3 includes the following steps: Step K involves acid activation, in which the bismuth telluride matrix is ​​placed in solution h and soaked at 25±5℃ for 5-10 minutes. The composition of solution h is: sulfuric acid 30-50g / L. Step L involves nickel electroplating in a solution i at a temperature of 60±5℃. The solution i consists of: 280-320 g / L NiSO4, 60-80 g / L NiCl2, 45-50 g / L H3BO4, and nickel electroplating additives. The electroplating current is 1.5±0.5 amperes / dm², and the electroplating time is 40±10 minutes.

4. The method for electroplating nickel on a bismuth telluride substrate according to claim 1, characterized in that, It also includes a water washing and drying step, in which the electroplating solution remaining on the product surface is cleaned with deionized water and then dried to ensure that the coating is dry and clean.

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