Abstract
SnAg and SnAgCu alloys are widely used in electronic packaging industry. Recently, Sn’s anisotropic properties have been widely reported. Several researchers reported that the interstitial diffusions of Cu and Ni along c-axis of Sn grains are much faster than along a-axis. Electromigration degradation via IMCs dissolutions and metallization layer consumption will be strongly facilitated if electron flow parallels to c-axis of Sn grain. One of the main objectives of this research is to refine the microstructure of solder joints by minor Ti, Mn, Zn additions. With finer Sn grains and random grain orientations, the electromigration-resistance might be enhanced. Interfacial integrity of SnAg and SnAgCu tin rich solder joints still needs to be improved, too. Growth of Cu3Sn has been linked with Kirkendall voids formation, which is one of the main reasons causing deterioration of tin rich solder joints with Cu substrate. Therefore, the other objective of this research is to improve the interfacial integrity by minor Ti, Mn, Zn additions. Interfacial reactions are studied in order to clarify the effects of different minor addition elements on growths of intermetallic compounds. Sn2.4Ag-X (X=none, 0.2Ti, 0.2Mn, 0.4Zn, 0.2Ti0.4Zn) solder balls were bonded with Cu pads by reflow process, and then thermal aged at 150℃. Cross-sections of samples were meticulously observed by Optical Microscopy with Cross-Polarizers, Electron Backscatter Diffraction (EBSD), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), Field Emission Scanning Electron Microscope (FE-SEM), Field Emission Electron Probe Micro Analyzer (FE-EPMA). The effects of different minor elements will be discussed.
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