Behaviour of Silver-Sintered Joints by Cyclic Mechanical Loading and Influence of Temperature

Devices in power electronics operate at high temperatures and demand controlled power loss density, while the trend leads to low temperature bonding methods in the packaging procedure. As an alternative to using Pb-alloys and Cu-Sn transient liquid phase soldering, Ag-sintering is a promising bonding technology. Silver with its high thermal and electrical conductivity is an advantageous joining material for different applications (e.g. die attach in power modules). One of the main advantages of this joining technology is the low processing temperature in combination with the high melting point of silver. It is also compatible with multilayer processing. The features of the bonding silver layer affect the elastic and thermo-mechanical behavior of the whole devices. A thorough investigation of the properties of Ag-sintered joints in relationship with their microstructure at various temperatures is essential for an appropriate lifetime prediction. This work investigates the low cyclic fatigue of Cu-Ag-Cu la joints at room and elevated temperature prior and subsequent to thermal treatment. Furthermore, the ratcheting behaviour of the joints as a part of the plastic-creep phenomenon has been evaluated. SEM investigations were performed to determine the porosity of the silver bonding layer and to analyze the fracture surface of the failed samples.