Characterization of SAC Solder Microstructure Evolution During Thermal Cycling with Statistical and In-situ Methods

摘要

The evolution of Sn grain microstructure during thermomechanical cycling occurs due to grainrnboundary movement, as some single crystal solder joints gradually transform to multicrystals. This processrnhas been documented statistically using polarized light and EBSP mapping by counting the numbers of jointsrnwith different orientations and microstructures in packages with different aging and thermomechanicalrncycling histories. The process by which evolution occurs is was examined assessed by comparing diffractionrnpatterns and peak shifts obtained from in-situ measurements from the full volume of a solder ball at differentrnstages of thermal cycling history using synchrotron radiation. Diffraction patterns were used to identifyrncrystal orientations present in the joint, and peak shape and peak shifts were used to assess changes inrninternal stress in several joints.