Metal-metal bonding process using Ag metallo-organic nanoparticles

We propose a novel bonding process using Ag metallo-organic nanoparticles as a new application of nanotechnologies. The average size of the Ag nanoparticles is around 11 nm, and each particle is covered with an organic shell. Therefore, it has the outstanding feature that each nanoparticle exists independently. However, removal of the organic shell is necessary to bring out characteristics of the nanoparticle. Its decomposition temperature measured by thermal analysis is 573 K or less. In addition, it revealed that the thermal characteristic of the organic shell differed completely from Myristyl alcohol, from which the organic shell was derived. At a low bonding temperature of 573 K at a bonding pressure of 1 or 5 MPa, Cu-to-Cu joining using the Ag nanoparticles was achieved. The shear strength of the joints was 25-40 MPa, which was significantly higher than that made using Ag fine particles of 100 nm in size. That is because the reduction of the particle size to a nano-order improved the sintering of Ag particles and the bondability to Cu. Transmission electron microscope observations revealed that metallurgical bonding could be realized at the interface between the Cu and the Ag layer sintered with Ag nanoparticles. This bonding is suggested to originate from the large surface energy contribution caused by the nano-size particles.