Void formation in Cu-Sn SLID bonding for MEMS

The hermetic sealing of a Micro Electronic Mechanical (MEMS) system is a critical requirement to the functional operation of MEMS devices. Cu-Sn SolidLiquid Inter-diffusion (SLID) bonding is one such encapsulation method of achieving hermetic sealing of MEMS devices. Recently, studies have identified a cause for concern relating to the reliability of SLID bonding. These studies have shown that electroplated (EP) copper is a source of higher voiding propensity. Labelled Kirkendall Voids (KV), which are micro voids that form at the interface of intermetallic compounds (IMC), due to the imbalance of Cu-Sn atom fluxes. KV have been shown to be a serious reliability issue which many studies have shown to seriously degrade the mechanical stability of interfaces. This paper will examine previous studies undertaken into the causes of KV, test whether KV are reproducible while varying EP parameters, and address the question, whether these are really KV?