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.