Silver nanopaste: Synthesis, reinforcements and application

To meet the requirement of bonding power chips in microelectronic packaging, low temperature sintering silver (Ag) nanopaste appears to be the most interesting choice in several new attachment technologies. This opportunity is mainly attributed to its high electrical and thermal conductivities of the sintered joint, and its low elastic modulus and process temperature. Over the past decade, in order to improve the mechanical properties, electrical conductivity and thermal conductivity of sintered Ag nanopaste, the formulas for preparing Ag nanopaste were improved, and other materials also have been added into it to make a reinforced matrix. In this review, the material characteristics of Ag nanopaste under low temperature sintering are elucidated, including the progress in the synthesis of Ag nanoparticles, the preparation methods of Ag nanopaste and bonding performance of low temperature sintered Ag nanopaste. The effects of adding different types of reinforcing groups into Ag paste on the bonding properties of sintered Ag joints are discussed, such as carbon reinforced matrix, metal reinforced matrix and other reinforced materials. The recent applications of low temperature sintered Ag joints in power chips are summarized. In addition, the feasibility of preparing Ag nanopaste while adding additional enhancers will be discussed at the end of the paper.