Analyses of Materials Behavior and Solder Fatigue Test and Prediction Results for Long-Term Thermal Cycling

The major aim of the study is the validation of FE-simulation based prediction of fatigue life and calculated acceleration factors for selected components, which have been tested in a long-term thermal cycling test with loadings close to service conditions, i.e., <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$18{ }^{\circ} \mathrm{C} / 80^{\circ} \mathrm{C}$</tex>, 7.1 hours. Theoretical analyses are made and compared to test cycling (TS <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-40 / 125^{\circ} \mathrm{C}$</tex>, 1 hour) results. Some results related to the test duration of up to 13 years (15,650 field cycles) were reported in [1], in particular for QFP100, FBGA277, and 0201 ceramic chip components. This paper focuses again on FBGA 277 and additionally on QFN packages. More detailed investigations are made on aging of materials, in particular molding compounds. The weakness of the unknown plastic materials properties and neglecting cure shrinkage is overcome by thermal deformation analyses on component level and adjustment by FEA. It is shown that these effects are noticeable for FBGA, but essential for QFN. For example, even the warpage direction at room temperature (RT), calculated without cure shrinkage, are opposite to the measured ones. Additionally, for the FBGA distribution patterns of cyclic creep strains/ dissipation densities across the balls are compared to failure patterns. Anand creep laws including aging from literature [2] have been investigated. It turned out that creep results-based creep laws with 5 to 60 days aging all agree qualitatively with the failure pattern, only the unaged data set does not.