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The reliability of Ag wedge bonding with various bonding pads for power devices
Keywords: Power devices, Ag wedge bonding, Intermetallic compound
Recent years, with the development of intelligent vehicles, power devices will be widely used. But traditional Si power devices have problems under high temperature. Now, there is a trend toward to use SiC instead of Si in power devices, as SiC has a higher band gap 3.25 eV compared with 1.12 eV of Si. So that SiC power devices can withstand higher temperature and voltage. Also SiC power devices have the advantages of lower parasitic parameters, smaller device size and shorter response time. Wedge bonding with large diameter bonding wire can be used in power devices package. The bonding wire used to be Al, but Al wire has the problem of recrystallization under high temperature and electro migration under high current. So there is a necessary to investigate replaceable bonding wires. The most common alternative wire materials include Ag and Cu. But Cu wire has the problem of under pad damage and oxidation. Our group proposed the application of Ag wedge bonding to power devices as Ag wire has the advantages of electrical resistivity and thermal conductivity. To investigate the reliability of Ag wedge bonding, Ag wires were bonded on Al pad and Ni/Au pad. And then we did shear test after high temperature storage life test (HTSL). Finally we used energy dispersive X-ray spectroscopy (EDS) to do cross-section observation. The results show that, for Al pad, the shear strength has decreased after annealing at 300 with mold packages, cracks and corrosion were observed. For Ni/Au pad, the shear strength has increased after annealing, and no cracks or corrosion were formed. So Ag bonding wire is proposed as an alternative to Al bonding wire for selected metal pads in power devices.
Xing Wei,
Graduate School of Information, Production and Systems, Waseda University
KITAKYUSHU-SHI, Fukuoka
Japan


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