Abstract
A fluxless bonding technique using eutectic Sn-Bi structure with Au capping layer is presented. Tbis is a new fluxless bonding design that can be performed in ambient air. Microstructure and phase growth mechanism of vacuum deposited Au/Sn/Bi thim films were studied by X-ray diffraction method (XRD) and X-ray Photoelectron Spectroscopy (XPS). It is found that the crystallites of An-Sn intermetallic compounds are randomly distributed in Bi-rich matrix that forms a capping layer. The average size of AnSnl and AuSa cqstallite are 756A and 667& respectively. Solder joints were manufactured in open air at 25OOC process temperature. Ihe resulting joints have only a few voids and have re-melting temperature of 220-225% The joint consists of eutectic Sn-Bi alloy embedded with ribbon shaped AuSn2+AuSa intermetallc layer. The shear strength was measured to be 4.9kg that is almost twice higher than the shear strength of militiuy standard. This new process is valuable for implementing bonding steps which use industrial pick and place machines operating in air or in covered nitrogen
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