High temperature MEMS packages: die-attach solutions for LiNbO3 under low bonding pressures

A survey of high temperature die-attach solutions for lithium niobate (LiNbO3) single crystals was conducted and based on that three promising approaches; i.e. eutectic solder, silver sinter-paste and silver-loaded conductive adhesive; were proposed and investigated. A relatively low pressure span (0–4 MPa) was employed, aiming to mitigate the risk of fracture in the brittle die. The mechanical properties of the corresponding die-attach assemblies was examined by a die-shear tester and the reliability of the joints was assessed after isothermal aging at 300 °C. The micro-structural integrity of the bonding was also analyzed by cross-sectional microscopy. The results revealed that silver sinter paste die-attach possesses superior shear strength in comparison to the two other techniques. Cross-sectional failure analysis also indicated a ductile fracture mode throughout the bonding layer for silver-paste and adhesive joints, whereas in soldered assemblies a brittle fracture mode along the interfacial intermetallic compound layer was predominant.