The 1.5SMCJ51C: With a minimum breakdown of 56.7 V, the device sits well below the clamping ceiling at normal operating voltage, so leakage in the off state stays negligible at the rated junction temperature of -50°C to 150°C.
DO-214AB SMC package and thermal margins
The DO-214AB (SMC) is a surface-mount package — the cathodic tab solders directly to the PCB plane, which is the primary thermal path for the clamping event; layout copper area under the tab determines the effective junction-to-ambient thermal resistance.