Effect of solidification parameters on the microstructure of Sn-3.7Ag-0.9Zn solder

Abstract

In this work, Sn–Ag–Zn alloy of eutectic composition (Sn-3.7wt.%Ag-0.9wt.%Zn) was directionally solidified upward at a constant temperature gradient ( G = 4.33 K/mm) in a wide range of growth rates ( V = 3.38–220.12 μm/s) and a constant growth rate ( V = 11.52 μm/s) with different temperature gradients ( G = 4.33–12.41 K/mm) using a Bridgman type directional solidification furnace. The microstructure was observed to be a rod Ag 3Sn structure in the matrix of β–Sn from the directionally solidified Sn-3.7wt.%Ag-0.9wt.%Zn samples. The values of eutectic spacing ( λ) were measured from transverse section of samples. The dependency of eutectic spacing on the growth rate ( V) and temperature gradient ( G) were determined with linear regression analysis. The dependency of λ on the values of V and G were found to be λ = 10.42 V − 0.53 and λ = 0.27 G − 0.48 , respectively. The values of bulk growth were also determined to be λ 2 V = 86.39 μm 3/s by using the measured values of λ and V. The results obtained in present work were compared with the previous similar experimental results obtained for binary and ternary alloys.