Effect of the microstructure orientation on tensile properties of Sn-Ag-Cu solder

With the miniaturization of the solder joint, the dependence of the property on the microstructure orientation has become increasingly notable. In this work, a lead-free Sn3.8Ag0.7Cu solders with certain microstructure orientation were processed by the Bridgman method in a horizontal furnace. After tensile tests at different strain rates, it was found that the tensile strengths of the materials were strongly dependent on the growth direction. The strength of the sample with a gauge perpendicular to the growth direction was much lower than that parallel to the growth direction. While the radial Cu₆Sn₅ and Ag₃Sn IMCs were distributed uniformly around the equiaxed tin grains perpendicular to the growth direction, the well-arranged needle shaped IMCs were oriented along the growth direction. At an applied tensile strain of 20%, the cross-slip lines were found throughout the polished surface and then impinged to the IMCs, resulting in the breaking of the IMCs. The variation of the tensile property with microstructural orientation may be attributed to the modification of the mobile slip system and the interaction of the slip lines with the IMC phase.