Uniqueness and challenges of sintered silver as a bonded interface material

There are numerous attributes of sintered Ag as a bonded interface between die and substrate or even between substrate and heat sink in power devices. This is attested to by the relatively large number of studies devoted to it in recent years. Sintered Ag potentially has a high temperature capability, high electrical and thermal conductivities, a microstructure in equilibrium, predictable linear elastic response during thermal cycling, and apparently minimal or even nonexistent time-dependent pore coalescence and pore growth that exists with solders. But sintered Ag bonding is a relatively new technology and solid-state sintering science and its application can be unfamiliar to solder/bonding practitioners. There are at least five different aspects of sintered Ag bonding compared with solder bonding. Those are reviewed here based on the authors' experience with Ag sintering over the last several years. Sintered-Ag interconnect bonding is a solid-state process (i.e., no melting); its bond strength is affected by the topography of the mating surfaces; concurrent pressure application during processing can improve bond strength; issues associated with the paste's organic binder burnout and exhaust can arise depending on the interconnect size; and porosity is indigenous to its bulk microstructure, requiring its consideration and possible management. Increased understanding of these unique characteristics will help advance use of sintered-Ag technology and the exploitation of its attributes for fabricating more reliable, higher-temperature-capable, and more thermally conductive power electronic modules.