4-VSSOP package and board-fit note
The AQY221N2TY comes in a 4-VSSOP package (4-SMD, 0.071" body width, 1.80 mm height) — a compact footprint for dense signal-routing boards where through-hole relays would consume too much real estate. Surface-mount termination with SMD (SMT) tab means the relay sits flat on the PCB with no through-hole stubs; the thermal path is through the solder pads, so the board copper area under the device sets the effective power dissipation for the 120 mA load.
On-resistance and RF signal handling
Maximum on-state resistance of 12.5 Ohms is the key insertion-loss figure for this relay — at 120 mA the voltage drop across the contacts is 1.5 V, which matters more for low-voltage analog paths than for digital switching. Rated for AC and DC loads including RF signals (the output type explicitly covers RF), so it switches small RF paths without the mechanical bounce of an electromechanical relay — the PhotoMOS die turns on cleanly in microseconds.