Quantitative description of micro-structural changes in lead-free solder alloys

The reliable behavior of solder joints is a well-known key issue for the microelectronic industry. From the technological point-of-view SMT solders guarantee the electrical and mechanical bonding on a printed circuit board. Recently, environmental tendencies turn the attention to lead-free materials, the properties of which still have to be studied. Moreover ongoing miniaturization and increasing functionalities of electronics require an exact knowledge of the material properties. As one aspect that considerably affects the joining capability of solders we concentrate on the experimental and theoretical quantitative examination of micro-morphological changes in solder materials. In particular we investigate the process of phase separation and coarsening for the binary lead-free case study alloy Ag-Cu. We start with the presentation of various experimental investigations and explain how these observations can quantitatively be assessed. Furthermore we present a continuum model, that allows for quantitative simulations of the micro-structural development. Numerical results are presented incorporating external thermo-mechanical loadings. These are compared finally with experimental investigations