Alloying modification of Sn-Ag-Cu solders by manganese and titanium

Effects of Mn and Ti additives on the microstructure and solidification behavior of Sn-1.0Ag-0.5Cu alloys (SAC105), as well as mechanical properties, were investigated in this study. Results show that alloying of Mn and Ti resulted in dramatically reduced undercooling, coarse eutectic structure and extended volume fraction of proeutectic Sn of which the dendritic size was refined. Those thermal and microstructural changes might be ascribed to the formation of MnSn2 and Ti2Sn3 intermetallic compounds (IMCs) which appeared respectively in the Mn-doped and Ti-doped samples. Nanoindentation tests demonstrated that the heterogeneous IMCs produced by alloying were harder and stiffer than the inherent IMCs, Ag3Sn and Cu6Sn5. Worthy of notice is that the elastic modulus of SAC105 alloys decreased with only a minor alloying addition due to the shrunken eutectic regions and coarsened eutectic microconstituents. With a larger quantity of additives, an ascending elastic modulus could be obtained because of the strengthening effect by hard heterogeneous compounds. (C) 2008 Elsevier Ltd. All rights reserved.