Controlled Synthesis Of Copper-based Micro/nano Materials And Its Application In Microelectronic Packaging

With the rapid development of power semiconductor technology,the demanding for the interconnection of power semiconductor devices are increasing.Copper nanoparticles can be sintered at low temperature and work at high temperature for a long time,which meets the requirements of low temperature sintering and high temperature service.At the same time,copper nanomaterials can be applied to printed electronics.Printed electronics technology is a green manufacturing process that uses printing technology to print various functional conductive inks on bare substrates to prepare conductive circuits and devices.Compared with traditional planar micro-nano processing technology,it has the advantages of low cost,green.flexibility and large area.Conductive ink is the major component of printed electronics.Conductive inks are mainly divided into three types:metal,carbon and organic.Copper-based micro/nano materials are used as substitutes for silver-based materials due to their excellent electrical and thermal conductivity,low price,and low electromigration.However,the poor anti-oxidation performance and harsh sintering process of copper particles limit the application of copper in power semiconductor packaging.It is urgent to prepare copper particles with good oxidation resistance and excellent sintering performance.In this paper,copper particles with different morphologies were prepared by the liquid phase reduction method,and the related properties of conductive inks were explored,which provided an example for the anti-oxidation treatment of conductive inks.(1)Preparation of self-assembled copper particles and the application in printed electronicsIn the experiment,copper hydroxide was used as the copper source,ascorbic acid was used as the reducing agent,and polyvinyl pyrrolidone was used as the protective agent.The dispersed,uniform,internal hollow self-assembled copper particles(2-5?m)were synthetized in large-scale by liquid phase reduction.The growth mechanism was investigated.The copper particles did not suffer significant oxidation after storing for 90 days under ambient conditions,and the anti-oxidation mechanism was investigated via different characterizations.Due to its hollow structure,the particles can be easily transformed into flake structure via ball-milling.The conductivity of the conductive ink after ball milling is about 10 times that of the non-ball milling,and the resistivity can reach 3*10^-5?·cm at 350?.(2)The mixed copper-silver flakes for the application in electronic packagingThe copper flakes were prepared via simple ball-milling,the fillers of ink contained the mixed micron-sized silver flakes and copper flakes,the electrical and shear properties of the ink were investigated.The introduction of silver flakes can greatly improve the conductivity of copper flakes.When the atomic ratio of Ag/Cu was 1:1,the resistivity of the conductive films is 2.8*10^-5?·cm after sintering at 300? for 10 min.The SEM images of the conductive films show that the copper and silver flakes overlapped each other,which promotes the mutual fusion between the particles.The interconnection between copper and silver at the intersectant site through EDS characterization.From the SEM images of the cross-sections of sintered joints of different fillers,with the increase of silver flakes,obvious tensile deformation can be observed at lower temperatures.When the bonding temperature is 300?,the maximum shear strength can reach 38.8 Mpa.(3)Mixed ink of 2D single-crystalline Copper flakes and copper formate complex for the application in printed electronics and the synthesis of copper particles with other morphologyThe copper flakes were prepared with a thickness of 10-50 nm and a lateral size of 2-10?m by liquid phase reduction.The synthesis method is simple and low cost.The conductive properties of copper flakes were investigated and modified them by appropriately adding and copper formate complex.The resistivity of the mixed ink was 1.05*10^-5?·cm after sintering at300?.The copper triangle nanoflakes and copper cubes were prepared by seed-mediated method.