100 µF at 4 V — bulk decoupling in a 1206 footprint
In a 1206 (3216 Metric) case, it fits low-voltage rails — 3.3 V, 2.5 V, 1.8 V — where bulk capacitance smooths transient loads or holds up a supply during micro-dropouts.
1.4 Ohm ESR — what it means for ripple and temperature rise
The 1.4 Ohm equivalent series resistance sets the self-heating under AC ripple. For a 100 µF cap on a 100 kHz switching rail with 100 mA ripple current, the internal dissipation is roughly 14 mW — the temperature rise stays negligible inside the -55 to 125 °C operating range. If the ripple current doubles, the power loss quadruples and the cap runs hotter; at that point a larger case or lower-ESR polymer becomes the better fit.