Recent progress in microjoining and nanojoining

Micro-joining and nano-joining have been identified as the key technologies in the construct fabrication such as micro-and nano-mechanical,electronic and medical devices and systems,and their recent progresses are briefly reviewed in this article.For electronic packaging applications,the developed lead-free solders and the two-step loading procedure accompanied with a superimposed ultrasound for copper-wire-bonding were expounded.Typical joining methods including resistance micro-welding,laser micro-welding and brazing for similar and dissimilar wires or pieces used for medical devices were discussed,as well as one-step diffusion bonding with pressing at high temperature for Bi-Sr-Ca-Cu-O superconductive leads.Joining technologies were also introduced,including electron beam irradiating welding,strand wrapping bonding with Double-walled Carbon Nanotube Strands(DWNT) film and brazing,the welding technologies of metal nanoparticles realized through laser irradiation,and the novel process of low-temperature sintering bonding by using Ag,Cu,Ag-Cu and Ag₂O micro/nano-particle pastes for electronic packaging applications.Based on the existing and new processes,the challenges and outlooks in micro-and nano-joining were pointed out.