We can write equations and make calculations based on atomic weight & density of pure elements to determine what volume change (%) occurs when for example Au + 4Sn >>> AuSn4 and using intermetallic densities from published sources as shown in Fig. A.
Fig. A – Volume change during formation of solder intermetallic compounds.
Since volume changes during IMC formation, we can expect void formation and interfacial cracking at the IMC/matrix interface as most of these systems show contractions in volume. This may be a contributing factor to thermal fatigue damage found in solder joints on printed circuit board assemblies.