The AQY212EHAX: The 4-SMD supplier package designation means the thermal pad is the same as the 4-pin DIP; no exposed paddle, so the on-state resistance of 2.5 Ohms max at 550 mA is the total junction-to-ambient loss, and the board copper does the heat spreading. Pin 1 is marked by a chamfered corner on the package body — orientation is unambiguous under a pick-and-place camera, and the gull-wing leads are co-planar enough for a standard reflow profile without a pre-bake at MSL 1 (the standard moisture sensitivity for this hermetic PhotoMOS construction).
Rated for 550 mA continuous load current at 60 V AC or DC — this is the continuous DC or RMS AC current the output MOSFET can sustain without exceeding the junction temperature at 25 °C ambient. The 2.5 Ohm on-state resistance means a voltage drop of about 1.4 V at full load, so the power dissipation is roughly 0.75 W — the 4-SMD package on a standard FR-4 board with 1 oz copper can handle that without derating up to 60 °C ambient, but above that the current should be linearly derated per the datasheet curve. The SPST-NO (1 Form A) circuit means the output is normally open; apply the input voltage and the output closes, switching AC or DC loads up to 60 V.
Sourced per RFQ — confirmed availability and current pricing at quote time.