Two kinds of lead-free solders derived from tin-based nanopowders were fabricated. One was the lead-free solders with Sn-Ag-Cu nanopowders, and the other was nano-sized Cu_6Sn_5 doped Sn-Ag-Cu solders. The lead-free solders with Sn-Ag-Cu nanopowders were synthesized by chemical precipitation with NaBH_4. The isolated particle exhibited a near spherical shape with particle sizes around 5 nm. The primary particle size of Sn-Ag-Cu nanopowders was in the range of 40 nm. Microstructural characteristics of particle growth were evaluated by TEM and FE-SEM. The primary particles after precipitation were (Ag,Cu)_4Sn with a size of 4.9 nm. It was also revealed that (Ag,Cu)_4Sn transformed into (Ag,Cu)_3Sn, when the total amount of Sn contributed from both (Ag,Cu)_4Sn and Sn covering the (Ag,Cu)_4Sn overtook that of (Ag,Cu)_3Sn. The nano-sized CugSn_5 doped Sn-Ag-Cu solder paste was produced by mixing Cu_6Sn_5 nano powder into commercial SnAg solder paste. To realize the effect of Cu_6Sn_5 nano powder doping, the ball shear strength of the joint was further investigated. The fracture behavior of Sn-Ag-Cu solder joints was probed with respect to the fracture surfaces, interfacial morphologies, and ball shear strength. It was demonstrated that the creep strain rate sensitivity of nano-Cu_6Sn_5 doped composite solder was higher than that of commercial Sn-Ag-Cu solder, although the creep hardness of both solders was nearly identical.
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