MICROSTRUCTURAL EVOLUTION OF SN-AG SOLDER JOINTS RESULTING FROM SUBSTRATE COPPER DISSOLUTION
Author: Srinivas Chada Company: Marquette University Date Published: 9/12/1999
Abstract: Studies of the effect of Cu substrate dissolution on the microstructure of solder joints were carried out using samples reflow soldered isothermally at various temperatures and times. Light (LM) and scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS) were used to study the microstructural evolution. All samples were found to exhibit highly inhomogeneous, non-equilibrium microstructure. Analysis of some of these samples showed that the Cu concentration, the volume fraction of primary Sn-dendrites and n(Cu6Sn5) intermetallics in the solder increased with reflow temperature and time as a result of Cu dissolution. In addition, the relative amount of eutectic decreased with increasing time and temperature. Sn-Ag-Cu ternary phase diagram along with vertical sections at various constant Cu concentrations was constructed to explain the observed microstructure.