Investigation of microstructural processes during ultrasonic wedge/wedge bonding of AlSi1 wires

The wedge microstructure of AlSi1 wire bonds as well as the interface between the bonding wire and the Cu/Ni/Au metallization layer especially for chip on board (COB) assemblies was investigated by focused ion beam (FIB), transmission electron microscopy (TEM), and microhardness measurements. The as-received wires were characterized by fiber texture of and orientation.1 With increasing ultrasonic (US) power, the results indicate recrystallization of the grain structure and decreasing microhardness inside the bonded wedge contacts. The interface between the AlSi1 wire and the Cu/Ni/ flash-Au metallization layer of the optimized bonds consists of a closed crystalline Au layer. Above this Au layer, a second zone consisting of intermetallic phases was analyzed and identified by electron diffraction as Au^sub 8^Al^sub 3^. [PUBLICATION ABSTRACT]