Interfacial reaction and IMCs formation between Sn-0.7Cu solder and Cu substrate during reflow soldering

The interfacial reaction and growth of intermetallic compounds (IMCs) between the eutectic Sn-0.7 wt.% Cu solder and Cu substrate during soldering process were investigated experimentally. The Sn-0.7Cu/Cu couples were fabricated with soldering temperature varied at four levels of 300, 320, 340 and 360°C, while soldering time is varied at five levels between 5 and 90 min. Microstructural analysis is conducted to analyze the IMCs thickness and morphology. Two intermetallic phases were observed during soldering at the interface: η-phase (Cu
₆
Sn
₅
) and ε-phase (Cu
₃
Sn) IMC layers, except for the solder joints which were fabricated at low temperature and/or short soldering time. The thickness of the η and ε IMC phases increase with increasing the soldering temperature and/or soldering time. It's found that the increase in total IMC layer thickness obeys a linear relationship with soldering temperature. And the relationship between X and T was given as X = 0.0866×T - 22.5 by means of linear fitting method.