A common problem with SMT flatpack components relates to the package resonant frequencies being within the dynamic range of the random vibration Power Spectral Density (PSD). The body of the package provides both the mass and the rotational inertia while the leads, as a group, provide the linear and torsional springs to create several mass-spring resonances with the associated natural frequencies. Please note that the quad SMTs have higher resonances because the leads at the “ends” provide sufficient stiffness to drive the rotational and linear modes above our PSD limiting frequency usually at 2 kHz. As packages become large and heavier with smaller leads due to finer pitch, it is possible the quad flatpacks could present a similar problem in the future. However heat dissipation design from these larger packages may change structural considerations for the better.