Preferred orientation of 30 μm fine pitch Sn2.5Ag micro-bumps studied by synchrotron polychromatic x-ray Laue microdiffraction

Synchrotron radiation white beam x-ray microdiffraction was employed to study grain size and orientation of fine pitch Sn2.5Ag micro-bumps. The indexing of the Laue patterns shows that there is mostly one dominant grain orientation in each micro-bump. Moreover, a statistics study based on the characterization of 72 micro-bumps, shows that the [001] direction, which is the fast diffusion path for Ni/Cu atoms in Sn tends to be parallel to the substrate of the test vehicle. This property remains stable after repeated reflow processes.