, Volume 38, Issue 12, pp 2770-2779
Date: 12 Sep 2009

Nucleation Control and Thermal Aging Resistance of Near-Eutectic Sn-Ag-Cu-X Solder Joints by Alloy Design

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Elemental (X) additions to Sn-3.5Ag-0.95Cu (SAC3595) solder were developed with minimal (<0.25 wt.%) concentration to avoid pro-eutectic Ag3Sn blades by reducing undercooling (ΔT) and to eliminate thermal-aging-induced embrittlement. Calorimetry and microstructure results on simple Cu/Cu joints identified 0.21Zn, 0.10Mn, and 0.05Al as sufficient to reduce undercooling below that for SAC3595 and to eliminate Ag3Sn blades. A 211°C melting onset for the X = Mn alloys also suggested the discovery of a new quaternary eutectic. Shear testing and microstructure analysis of larger joints showed that 0.05Al and 0.21Zn additions resulted in reduced as-soldered strength (30 MPa), like Sn-0.95Cu, but all joints showed ductile failure at about 30 MPa after 1000 h at 150°C.