Results for “Ag3Sn” | Engineering Papers

DOE OSTI2020

Materials Data on Ag3Sn by Materials Project

Ag3Sn is Magnesium-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. there are two inequivalent Ag sites. In the first Ag site, Ag is bonded to twelve Ag atoms to form AgAg12 cuboctahedra that share corners with six equivalent AgAg12 cuboctahedra, corners with twelve equivalent SnAg6Sn6 cuboctahedra, edges with eighteen AgAg12 cuboctahedra, faces with two equivalent SnAg6Sn6 cuboctahedra, and faces with eighteen AgAg12 cuboctahedra. There are six shorter (2.93 Å) and six longer (3.11 Å) Ag–Ag bond lengths. In the second Ag site, Ag is bonded to nine Ag and three equivalent Sn atoms to form AgAg9Sn3 cuboctahedra that share corners with eighteen equivalent AgAg9Sn3 cuboctahedra, edges with six equivalent SnAg6Sn6 cuboctahedra, edges with twelve AgAg12 cuboctahedra, faces with six equivalent SnAg6Sn6 cuboctahedra, and faces with fourteen AgAg12 cuboctahedra. All Ag–Ag bond lengths are 3.11 Å. All Ag–Sn bond lengths are 3.10 Å. Sn is bonded to six equivalent Ag and six equivalent Sn atoms to form SnAg6Sn6 cuboctahedra that share corners with six equivalent SnAg6Sn6 cuboctahedra, corners with twelve equivalent AgAg12 cuboctahedra, edges with six equivalent SnAg6Sn6 cuboctahedra, edges with twelve equivalent AgAg9Sn3 cuboctahedra, faces with six equivalent SnAg6Sn6 cuboctahedra, and faces with fourteen AgAg12 cuboctahedra. All Sn–Sn bond lengths are 3.11 Å.

36 MATERIALS SCIENCE↗

NASA NTRS2005

Mechanical Properties and Microstructure Investigation of Lead Free Solder

While the electronics industry appears to be focusing on Sn-Ag-Cu as the alloy of choice for lead free electronics assembly, ,the exact composition varies by geographic region, supplier and user. Add to that dissolved copper and silver from the printed circuit board traces and surface finish, and there can be significant variation in the final solder joint composition. A systematic study of the mechanical and microstructural properties of Sn-Ag-Cu alloys with Ag varying from 2wt% to 4wt% and Cu varying from 0.5wt% to lSwt%, was undertaken in this research study. Different sample preparation techniques (water quenched, oil quenched and water quenched followed by reflow) were explored and the resulting microstructure compared to that of a typical reflowed lead free chip scale package (CSP) solder joint. Tensile properties (modulus, 0.2% yield strength and the ultimate tensile strength) and creep behavior of selected alloy compositions (Sn-4Ag-1 X u , Sn-4Ag-OSCu, Sn- 2Ag-1 X u , Sn-2Ag-OSCu, Sn-3.5Ag-O.SCu) were determined for three conditions: as- cast; aged for 100 hours at 125OC; and aged for 250 hours at 125OC. There was no significant difference in Young's Modulus as a function of alloy composition. After an initial decrease in modulus after 100 hours at 125"C, there was an insignificant change with further aging. The distribution of 0.2% strain yield stress and ultimate tensile strength as a function of alloy composition was more significant and decreased with aging time and temperature. The microstructures of these alloys were examined using light and scanning electron microscopy (LM and SEM) respectively and SEM based energy dispersive x-ray spectroscopy (EDS). Fracture surface and cross-section analysis were performed on the specimens after creep testing. The creep testing results and the effect of high temperature aging on mechanical properties is presented for the oil quenched samples. In general the microstructure of oil quenched specimen exhibited a eutectic region of Sn with moderately dispersed Ag3Sn intermetallic, surrounded by a dendritic Sn-rich phase. The SEM images of the fracture surface indicated the presence of a tough shear surface at the initial cavity break area and a break line in the middle of specimen along the failure direction. A hyperbolic-sine creep model was adopted and used to fit the creep experiment data. The effect on the mechanical properties by adding the quaternary element bismuth to the Sn-3.5Ag-0.8Cu alloy was measured and compared with the mechanical properties of the ternary alloys. The results of this research study provide necessary data for the modeling of solder joint reliability for a range of Sn-Ag-Cu compositions and a baseline for evaluating the effects of subsequent quaternary additions.

Wang, Qing↗