Specimens of the prepared solder balls and solder/copper joints after the liquid reaction were mounted in resin for observation and characterization of their microstructure. The specimens were cross-sectioned perpendicularly by carefully grinding toward the centre – using emery paper with a progressively smaller grit size, followed by polishing with 0.5 μm alumina suspension. Etching was performed in a dilute solution of 2 vol.% concentrated hydrochloric CAY10505 (HCl) to provide a contrast between the IMC and the solder matrix. A scanning electron microscope (SEM, Philips XL 40 FEG) with a back-scattered electron imaging mode was used to observe the microstructural morphology of the solder matrix and IMC. An energy dispersive X-ray (EDX) spectrometer (EDAX International, model DX-4) was used to characterize the chemical composition and phase. Image analysis software (ImageJ) was used to measure the matrix interphase spacing of the prepared solders and the interfacial IMC thickness of the joints after undergoing liquid reaction for various time spans. The average thicknesses of the interfacial IMC layers were evaluated as the quotient of the IMC area, divided by the interface length, according to the microstructure images.