Conditions and Thermomechanical Stresses

For flip chips on organic substrates with an underfill, a two-part process profile is often used in which the thermal profile associated with solder reflow and attach is modeled in the first part, and the assembly is then simulated to be cooled down to room temperatme. In this case, the entire assembly is assumed to be stress-free at the 

In addition to ATC simulations, field-use simulations can also be performed to assess the long-term reliability of microelectronic pack- 

The mechanical behavior of SAC alloy also depends on the cooling rate during solder reflow and the Ag content in the solder. For example, in Sn-3.8Ag-0.7Cu alloy, when the cooling rate is slow (approximately 0.2 °C/s, or 0.36 °F/s), the volume fraction of AggSn plates and CusSns 

The double power-law creep equation (Eq 8) separates the creep component into climb-controlled and combined climb-glide-controlled. During the field use conditions where the thermal excursions are milder and stresses are lower compared to typical accelerated thermal cycling 

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