Dendritic and eutectic growth of Sn–0.5 wt.%Cu solders with low alloying Al levels

The dependences of microstructures on the solidification thermal parameters of Sn–0.5 wt.%Cu, Sn–0.5 wt.%Cu–0.05 wt.%Al, and Sn–0.5 wt.%Cu–0.1 wt.%Al alloys are examined. Ranges of sizes and morphologies of microstructural phases have been quantitatively assessed due to the broad spectra of cooling rates and thermal gradients associated with the experiments. Various types of growth relations are proposed to represent the microstructural progresses. Al addition does not change either the matrix primary dendritic spacing or the spacing between Cu₆Sn₅ particles. However, it is shown that the secondary dendrite arm spacing, λ₂, is greatly affected, increasing with the increase in the Al content. Both globular-type and fibrous-type morphologies typify the Cu₆Sn₅ intermetallics located in interdendritic zones.