Mapping Mechanical Properties of Lead-Free Solder JointsAuthors: Carlos Morillo Ph.D., Jennifer L. Hay and Julie Silk
Company: Center for Advanced Life Cycle Engineering (CALCE), University of Maryland and Keysight Technologies
Date Published: 9/28/2014 Conference: SMTA International
In the present work, a fast technique was used to map the hardness of a SAC 305 solder joint with Au plating. After prolonged isothermal aging, the solder joint is comprised of three constituents: a tin-rich matrix, an interfacial intermetallic (Cu, Ni, Au)6Sn5 and a bulk intermetallic AuSn4. The softest material is the tin-rich matrix, which has a hardness of 0.51 ± 0.07 GPa. The hardness of the bulk AuSn4 intermetallic is 2.12 ± 0.18 GPa. The interfacial intermetallic has extraordinary hardness — greater than 8 GPa. Strain rate sensitivity revealed that the IMC phase has a lower tendency to creep than the tin-rich area. Under uniform plastic strain, the mismatch in hardness between the interfacial intermetallic and surrounding material may increase the local stress intensity factor which drives interfacial fracture.
nanoindentation, mechanical properties, lead-free
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