Size-controllable Synthesis And Sintering Application Of Organic Coated Copper Nanoparticles

The third-generation semiconductor materials can achieve excellent properties.Compared with traditional semiconductor materials,the third-generation semiconductor materials have the working characteristics of high temperature,high integration,high voltage,high power density,high heat dissipation,etc.These bring new challenges and demands to the chip interconnecting materials with high performance,low cost,reliability under extreme conditions,and long-term stability.Nano-metallic materials can be sintered at low temperature and service at high temperature.The properties of sintered nano-metallic materials are similar to those of bulk metals.These make the nano-metallic material a better material for new micro-nano scale interconnection than the traditional interconnection materials such as solder paste and conductive adhesive.Compared with precious metals such as nano-gold and nano-silver,nano-copper particles(Cu NPs)has very broad application prospects in future chip interconnections in key areas such as power electronic,microwave radio frequency,optoelectronics,etc.due to its“high performance and low cost”characteristics.At present,the use of Cu NPs as a new interconnect materials for low-temperature sintering of chips has become a hot research topic in industry.In this paper,Cu NPs was synthesized by liquid phase redox method in absolute ethanol solvent using Cu(OH)₂ as the copper source,ascorbic acid as the reducing agent and polyvinylpyrrolidone(PVP)as the protective additive.The effects of reaction solvents,protective additives,reaction time,temperature,molar ratio of copper source to reducing agent and the dosage of protective additive were studied.The suitable experimental conditions for synthesis of Cu NPs with narrow size distribution,mono-dispersibility and high purity were obtained.By adjusting the dosage of PVP,the average size of Cu NPs can be tuned in the range from 100 nm to 245 nm.Transmission electron microscope(TEM),fourier transform infrared spectrometer(FT-IR),thermogravimetry(TG)were also used for further detecting the surface structure,component and thermal properties of as-synthesized Cu NPs.The anti-oxidation capacity of Cu NPs were studied by storage experiment under the environment of constant temperature and humidity.This paper performed electrodeposition experiments to explore the nucleation and growth mechanism of nano-copper with and without PVP coating.The electrolyte was prepared with the same component of the synthesis system of Cu NPs.An electrochemical workstation with a rotating disk electrode was employed.By selecting an appropriate organic supporting electrolyte in anhydrous ethanol solvent and taking effective pre-treatment measures,cyclic voltammetry and chronoamperometry electrochemical experiments were carried out.It was found that the addition of PVP did not change the overpotential required for the reduction of copper ions to nano-copper,nor did it change the deposition mechanism during the reduction of nano-copper.The addition of PVP can suppress the reduction of copper ions,reduce the reaction rate and nucleation rate when the copper ion is reduced to copper,and make the nucleation and growth process of copper closer to the theoretical curve of instant nucleation.This is an important reason for the refinement of copper particles prepared with PVP additive.Finally,the as-synthesized Cu NPs were formulated into copper paste to characterize the sintering properties.The effects of copper powder mass fractions and sintering temperatures on the sintering performance of the copper paste were studies.The mechanical properties of copper paste sintered at different temperature were tested and analyzed.