Mining EDS-EBSD Data to Study Microstructure of Solder Bump with Completely Unknown Intermetallics

Microstructure characterization of a solder bump especially related to intermetallics (IMCs) formed at the interface of jointing metals is important for understanding the origin of physical and electronic failures. In this paper, we illustrate how to analyze the microstructure of a solder bump with unknown IMCs using simultaneous Energy X-ray Dispersive Spectrometer (EDS) and Electron Backscatter Diffraction (EBSD) detector on a Scanning Electron Microscope (SEM). A recently proposed workflow based on two existing functions in AZtec software, the simultaneous EDS-EBSD mapping and the EBSD Phase ID was used to study the unknown phases in a Sn-based microbump. The analysis started from the EBSD and EDS simultaneous mapping on the microbump with a step size of 0.1 um, and all raw data were saved for further analysis. Using Phase ID, we successfully find three IMCs (hexagonal $\boldsymbol{\eta}$ -Cu6Sn5, orthorhombic Cu3Sn and Ag3Sn), cubic Cu and Ni, and $\boldsymbol{\beta}$ -Sn in the sample. After phase identification, many high-quality EBSD maps including phase distribution map, IPF orientation map, and Kernel average map were reconstructed from the saved raw mapping dataset, which reveals various microstructure information about the microbump. In particular, the IPF map reveals that the Ni-layer has the nano grain size with an average of around 0.7um, and the KAM map indicates that the Ni-layer has the highest strain among different materials with the highest risk for cracking. This analytical approach combined with EDS-EBSD techniques can provide abundant microstructural data for the complex packaging samples with unknown IMCs, such as wire bonding, through-Si via, as well as other interconnectors.