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

: Geißler, U.; Schneider-Ramelow, M.; Lang, K.-D.; Reichel, H.


Journal of Electronic Materials 35 (2006), Nr.1, S.173-180
ISSN: 0361-5235
ISSN: 1543-186X
Fraunhofer IZM ()

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 ><111> and <100> orientation. 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 Au8Al3.