The phase and intermetallic thickness of Cu-Zn5 and Cu5Zn8 has been investigated under liquid state aging using reflow method. Both intermetallics were formed by reacting Sn-9Zn lead free solder with copper substrate. Scanning electron microscope (SEM) was used to see the morphology of the phases and energy dispersive x-ray (EDX) was used to estimate the elemental compositions of the phases. The morphology of the Cu5Zn8 phase was rather flat but when the soldering temperature and time increases, the morphology becomes scallop. Intermetallic thickness measurements show that the thickness of Cu-Zn5 decreases with increasing soldering time and temperature. Whereas, the thickness of Cu5Zn8 intermetallic increases with soldering time and temperature.