Uniqueness and challenges of sintered silver as a bonded interface material

There are numerous attributes of sintered silver (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 the last several years. Sintered silver potentially has a high temperature capability, high electrical and thermal conductivities, its microstructure is in equilibrium, it could predictably respond linearly elastically during thermal cycling, and the time-dependent pore coalescence and pore growth that exists with solders is apparently minimal or even nonexistent. But sintered silver 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 it compared to solder bonding and those are oveniewed here based on the authors' experience with Ag- sintering over the last several years. For sintered-Ag interconnect bonding: it 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 employment of sintered-Ag technology and the exploitation of its attributes for fabricating more reliable, higher- Temperature-capable, and more thermally conductive power electronic modules.