The 70V reverse standoff voltage means it sits across a 70V rail without leakage — the breakdown starts at 77.8V min, so the rail sees no clamping action during normal operation. The single bidirectional channel protects against both positive and negative transients on the same line — useful for AC-coupled or floating signal pairs where polarity isn't fixed.
The DO-214AA (SMB) package sits flush on the board; the copper pad area under the cathode tab sets the thermal resistance, so a solid ground-plane connection helps keep junction temperature down during repetitive surges.