What 18 V standoff means for the board
The 1.5SMCJ18 holds 18 V reverse standoff — the maximum rail voltage it will not start conducting above in the reverse direction.
DO-214AB package and what it changes on the board
With a 150 °C maximum junction temperature and a -50 °C floor, the part covers industrial environments where ambient can swing wide — the margin between junction and ambient is set by the PCB pad geometry, not the diode itself. Single unidirectional channel — this part protects a positive-going transient on a single rail; it does not provide bidirectional or AC power-line protection.
Active sourcing posture
Listed as Active by Diotec Semiconductor — quoted to order through independent distribution against your BOM quantity.