A new high performance semiconductor leadframe alloy possessing high strength and good electrical conductivity was recently developed. The nominal composition of the alloy was Cu-1.35Ni-0.132Si-0.036P. High strength is generally obtained at the expense of good electrical conductivity. The achievement of high strength as well as good electrical conductivity is due to the formation of precipitates.
This work is concerned with precipitation kinetics in the new leadframe Cubase alloy. Effects of different solution treatments (1020℃, 900℃, 780℃) and aging conditions (300℃-700℃) on precipitation kinetics were investigated. Double aging peaks appeared due to the formation of two different kinds of precipitates of $Ni_2Si$ and Ni-P. DTA showed that the earlier peak was related to Ni-P, and the later one was due to Ni-Si precipitate. X-ray and TEM showed that the precipitates were $Ni_2Si$ and $Ni_3P$. At the condition of aging 0.8hr at 450℃, $Ni_3P$ compounds were rod-type 30-60 A˚ in length and had the orientation relationship, $(100)_{mat}//(111)_{Ni_3P}$ and $[011]_{mat}//[132]_{Ni_3P}$. After aged 194hr, $Ni_3P$ compounds increased to 200-300 A˚ and disc-like $Ni_2Si$ compounds with 300-400 A˚ in diameter were formed.
As the solution temperature increases, the rate of formation of Ni$_3P$ was accelerated, while that of $Ni_2Si$ was delayed. The apparent activation energy of $Ni_2Si$ was greatly higher than that of $Ni_2P$. For solution treated at 900℃ with different aging temperature, the activation energy of $Ni_2Si$ was 18.96 Kcal/mole, compared with 5.74 Kcal/mole of $Ni_3P$.
Electrochemical property of corrosion potential was also measured at a fixed aging time as a function of aging temperature. Electrical resistivity measurements were also conducted as a function of aging time at different aging temperature. The results showed that precipitation kinetics of $Ni_3Si$ obeyed the equation of Johnson-Mehl, $y = 1-exp(-(t/τ)^n)$, where n was 2.28 (1.5
