Creep of thermally aged SnAgCu-solder joints
ABSTRACT The creep behaviour of Sn96.5Ag3.5- and Sn95.5Ag3.8Cu0.7-solder was studied specifically for its dependence on technological and environmental factors. The technological factors considered were typical cooling rates and pad metallizations for solder joints in electronic packaging. The environmental factors included microstructural changes as a result of thermal aging of solder joints. Creep experiments were conducted on three types of specimens—flip–chip joints, PCB solder joints and bulk specimens. flip–chip specimens were altered through the selection of various under bump metallizations (Cu vs. NiAu), cooling rates (40 K/min vs. 120 K/min), and thermal storage (24 h, 168 h, and 1176 h at 125 °C). PCB solder joints were studied by using a copper pin soldered into a thru-hole connection on a printed circuit board having a NiAu metallization. Bulk specimens contained the pure alloys. The creep behaviour of the SnAg and SnAgCu solders varied in dependence of specimen type, pad metallization and aging condition. Constitutive models for SnAg and SnAgCu solders as they depend on the reviewed factors are provided.
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ABSTRACT: The creep behavior of Sn-3.0Ag-0.5Cu (SAC305), Sn-3.4Ag-1.0Cu-3.3Bi (SAC-Bi), and Sn-3.4Ag-4.8Bi (SnAg-Bi, all wt.%) was studied in constant-stress creep tests from room temperature to 125°C. The alloys were tested in two microstructural conditions. As-cast alloys had a composite eutectic-primary Sn structure, while in aged alloys the eutectic regions were replaced by a continuous Sn matrix with coarsened intermetallic (Cu6Sn5 and Ag3Sn) particles. After aging, Bi in SAC-Bi and SnAg-Bi was found as precipitates at grain boundaries and grain interiors. The creep resistance of of-cast SAC305 was higher than that of as-cast Bi-containing alloys, but after aging the SAC305 had the lowest creep resistance. The creep strain rates in SAC-Bi and SnAg-Bi were much less affected by aging. The apparent activation energy for creep was also changed more for SAC305 than for the other two alloys. The creep behavior of SAC-Bi and SnAg-Bi can be understood by considering the solubility of Bi in Sn. The difference in creep behavior between as-cast and aged SAC-Bi is greatly reduced when room-temperature test results are excluded from analysis. This suggests that the strongest influence on creep in these alloys is due to Bi solute interaction with moving dislocations during deformation.Journal of Electronic Materials 01/2012; 41(2). · 1.64 Impact Factor
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ABSTRACT: The heterogeneous microstructure of solder could be obtained when cooling rate of the solder joint was not even, which would affect the corrosion behavior of solder during service. The ambient temperature would also affect the corrosion behavior of solder joint. In this paper, the effects of microstructure and temperature on the corrosion behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated. The various microstructures of SAC305 lead-free solder were obtained by cooling specimens in air and furnace. Compared to the fine-fibrous Ag3Sn phase inside the commercial SAC305 solder, platelet-like Ag3Sn formed as cooling speed decreasing. The polarization behavior of SAC305 solders in 3.5 wt.% NaCl solution was not significantly affected by various microstructures, but sensitive to temperature.Journal of Materials Science Materials in Electronics 01/2012; 23(1). · 1.49 Impact Factor
- Soldering and Surface Mount Technology 01/2014; 26(4):214-222. · 0.82 Impact Factor