Abstract
The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in Cu/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated. Being different from the symmetrical growth during isothermal aging, the interfacial IMCs showed clearly asymmetrical growth during reflow, i.e., the growth of Cu6Sn5 IMC at the cold end was significantly enhanced while that of Cu3Sn IMC was hindered especially at the hot end. It was found that the temperature gradient had caused the mass migration of Cu atoms from the hot end toward the cold end, resulting in sufficient Cu atomic flux for interfacial reaction at the cold end while inadequate Cu atomic flux at the hot end. The growth mechanism was considered as reaction/thermomigration-controlled at the cold end and grain boundary diffusion/thermomigration-controlled at the hot end. A growth model was established to explain the growth kinetics of the Cu6Sn5 IMC at both cold and hot ends. The molar heat of transport of Cu atoms in molten Sn was calculated as + 11.12 kJ/mol at 250 °C and + 14.65 kJ/mol at 280 °C. The corresponding driving force of thermomigration in molten Sn was estimated as 4.82 × 10−19 N and 6.80 × 10−19 N.
Highlights
The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in C is the solute (Cu)/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated
Guo et al.[11] found that the interfacial Cu6Sn5 was much thicker at the cold end whereas the consumption of Cu was much faster at the hot end in Cu/Sn-2.5Ag/Cu solder joints during reflow at 260 °C on a hot plate, due to the rapid migration of Cu atoms under a simulated temperature gradient of 51 °C/cm
When aged at 250 °C, bilayer IMCs with thick scallop-like Cu6Sn5 of 8.45 μ m close to the Sn matrix and thin Cu3Sn of 1.53 μ m close to the Cu substrate formed at both interfaces
Summary
The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in Cu/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated. The formation of interfacial intermetallic compound (IMC) during soldering reaction is essential to realize a reliable metallurgy interconnection between solder and under bump metallizations (UBMs). Guo et al.[11] found that the interfacial Cu6Sn5 was much thicker at the cold end whereas the consumption of Cu was much faster at the hot end in Cu/Sn-2.5Ag/Cu solder joints during reflow at 260 °C on a hot plate, due to the rapid migration of Cu atoms under a simulated temperature gradient of 51 °C/cm. Qu et al.[12] in situ studied the soldering interfacial reactions under a temperature gradient of 82.2 °C/cm at 350 °C using synchrotron radiation real-time imaging technology, and asymmetrical growth and morphology of interfacial IMCs between the cold and hot ends were clearly observed
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