Temperature dependency of the growth rate of (Cu,Ni)6Sn5 on Cu-xNi substrates

Abstract

Cu6Sn5 is the most common intermetallic compound (IMC) in lead-free solder joints, and is also a promising anode material for advanced lithium-ion batteries. It has been reported that the growth rates of (Cu,Ni)6Sn5 in Sn-based solder alloy/Cu-xNi substrate couples are greatly accelerated compared to the intermetallic layers that form on a pure Cu substrate. Due to the faster growth rates, solidification can progress through a transient-liquid-phase reaction in commercially relevant timeframes. The complete reaction of the liquid Sn in the couple will result in a joint that is stable at high temperatures. Furthermore, the presence of Ni in the intermetallic suppresses the formation of a Cu3Sn layer and stabilises the (Cu,Ni)6Sn5 preventing a polymorphic transformation on cooling along with the associated induced strains. This study investigates the growth rates of (Cu,Ni)6Sn5 in Sn/Cu-xNi couples, where 0 <= x <= 14 wt%, and reports on the effect of temperature on the growth rates at temperatures above the melting point of Sn (231.9°C) between 232°C and 300°C. The results show the highest growth rates occur in the Sn/Cu-6Ni couples, and there is an increase of the (Cu,Ni)6Sn5 growth rate with increasing temperature due to faster diffusion and reaction rates.