|About this Abstract
||Materials Science & Technology 2012
||Green Technologies for Materials Manufacturing and Processing IV
||Pathway of Development for Sn-Ag-Cu (SAC) and SAC+X Pb-free Solders for Broad Application and High Reliability in “Green” Electronic Assembly
||Iver Anderson, Adam Boesenberg, Joel L. Harringa, David D. Hillman
|On-Site Speaker (Planned)
Near-eutectic Pb-free solder alloys that are based on Sn-Ag-Cu (SAC) have been implemented worldwide for electronic assembly as a robust replacement for leaded (Sn-Pb) solders that can become environmental toxins. Eventually, reliability issues appeared in aggressive operating environments and with assembly methods that involve slow cooling. To develop a more universal SAC solder, micro-alloying of Cu-enriched Sn-3.5Ag-0.95Cu (wt.%) solder with Al, Mn, and Zn was developed for controlled heterogeneous nucleation of solder solidification to produce consistent joint microstructures with improved reliability, even with multiple reflows. Calorimetry, microstructure analysis, and X-ray diffraction helped determine coupling between undercooling and joint microstructure development. Globule wetting balance studies of solderability for these SAC3595+X alloys at concentrations between 0.01-0.25wt% established that normal SAC wetting was maintained for Cu substrates. Thermally cycled (-55˚C/+125˚C) BGA joints made with SAC3595+0.21Zn also exceeded avionics standards. Supported by Iowa State University Research Foundation and Nihon-Superior, through Ames Lab contract DE-AC02-07CH11358.