Electroless Plating Process And Electrochemical Analysis Of Bismuth Telluride Barrier Layer And Study On Electrical Connection Of Copper

As a green new energy,thermoelectric conversion technology has important application prospects in waste heat recovery and reuse.Thermoelectric devices are the functional modules of thermoelectric conversion technology,and its energy conversion efficiency is the focus of the industry.In the electrical interconnection preparation process of thermoelectric device packaging and manufacturing,the electrical properties of the interface between the thermoelectric material and the metal electrode are the key factors affecting the actual energy conversion efficiency of the device.This topic focuses on the interface electrical connection performance of bismuth telluride-based thermoelectric devices through the composition and structure design of the bismuth telluride contact barrier layer and the optimization of the electroless coating process;the mechanical and electrical connection is realized by the reflow soldering process,and the electrical transport performance of the interface is tested.The research results of the subject are as follows:（1）Ni single-layer,iron-cobalt two-layer and iron-cobalt-nickel three-layer diffusion barrier systems were prepared by electroless plating.The traditional Sn-Pd/Ag activation system was replaced by the BH^4-/Me²⁺(Ni²⁺,Co²⁺,Fe²⁺)pre-plating activation system,which reduced the cost of electroless plating,obtained stable acid and alkaline electroless nickel plating process,alkaline electroless cobalt plating process,and alkaline electroless iron plating process by using aluminum.The average deposition rates of nickel,cobalt,and iron metal thin films were obtained by weighing method to be 5.92μm/h,7.1μm/h and 2.6μm/h,respectively.（2）The deposition mechanism of BH^4-/Me²⁺pre-plating system and electroless nickel,cobalt and iron were studied by electrochemical workstation.The results show that nickel ion has the strongest oxidizing ability,ferrous ion has the weakest oxidizing ability,cobalt ion has an oxidizing ability between the two,and hypophosphite ion has a weaker reducing ability than borohydride ion.The activation effect of BH₄^-/Me²⁺pre-plating system is the best at p H=10.Temperature can affect the reducing ability of hypophosphite ions,ensuring that hypophosphite ions deposit nickel and cobalt films,but still cannot reduce ferrous ions.As the sacrificial anode of the galvanic system,aluminum provides part of the electrons required for the initial reduction of ferrous ions and induces the reduction of ferrous ions by hypophosphite ions.（3）The two-dimensional transient electroless nickel plating simulation was obtained by using Comsol electrical analysis physics.The simulation results show that the suspended substrate can ensure that a relatively uniform metal film is deposited on the surface of each substrate,and the film deposition rate at the edge of the substrate is faster than the deposition rate on the substrate surface.Secondly,the deposition reaction only occurs near and on the surface of the substrate,which verifies the solid-liquid heterogeneous catalysis.Therefore,bismuth telluride was suspended in the bath for electroless coating experiments and barrier layer preparation.（4）"Bismuth telluride-copper"solder samples were prepared by reflow soldering.A method for measuring the contact resistivity of heterojunctions was proposed,and the electrical connection properties of three diffusion barrier systems were obtained.The contact resistivities at room temperature,70℃and 110℃are 32.35μΩ·cm²,26.78μΩ·cm²,52.2μΩ·cm²,respectively.Interfacial microstructural analysis confirmed the multilayer structure of the contact barrier and solder layers,which suppressed elemental diffusion of copper and solder.The interfacial shear strengths of the two parallel samples of the nickel monolayer barrier layer are 3.55MPa and 4.59MPa,respectively.