Effects of Ultra-High Cooling Rates on the Tensile and Cyclic Stress- Strain Behavior of Nanoscale Solder Materials

S Fardin and MJ Moresalein and M Motalab and A Faiyad and R Paul, JOURNAL OF ELECTRONIC MATERIALS, 54, 6828-6846 (2025).

DOI: 10.1007/s11664-025-12048-6

In recent years, lead-free solder alloys have gained popularity over lead-based ones due to their improved mechanical and electrical properties and non-toxic nature. Our previous studies examined the stress-strain behavior of 96.5Sn3Ag0.5Cu (SAC305) material at the nanoscale under varying cooling rates. This study extends the investigation to pure Sn, Sn-Ag, and SAC305 to compare their relative tensile and cyclic properties. Understanding the mechanical behavior of lead-free solder alloys under ultra-high cooling rates can guide the design of more durable solder joints in microelectronics, automotive electronics, and aerospace applications, where thermal and mechanical stresses are critical factors. The reliability of solder joints in these applications depends on the tensile and cyclic stress-strain behavior of the materials, which is influenced by the solidification rates of the alloys. Therefore, molecular dynamics simulations are used to heat the model at a constant rate, followed by cooling at ultra-high rates (2.5, 10, 50, and 100 K/ps). Exponential cooling is also applied to replicate real-world conditions like air, water, and furnace cooling. A modified embedded atom method (MEAM) potential is utilized for both tensile and cyclic loading simulations. The tensile test is performed at a strain rate of 1 x 109 s-1 until fracture and cyclic loading is analyzed over 10 cycles within a strain range of - 10% to 10%. The results indicate that cooling rates significantly influence mechanical properties, with slower rates (2.5 K/ps and 10 K/ps) showing substantial differences, while the differences between higher rates (50 K/ps and 100 K/ps) are less pronounced. Ultimate strength, Young's modulus, resilience, and thermal expansion decrease with higher cooling rates, while toughness increases. The hysteresis loop area and stress amplitude indicate energy dissipation per unit volume during cyclic loading. Over time, energy loss stabilizes, while stress amplitude decreases with cycles.

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