Yes that's why, to protect the MOSFET.
I wasn't questioning the existence of the zener diode, just it's voltage rating.
I think if you're going to stick with MOSFET-based polarity protection, then you should change to a MOSFET with a higher Vgs and use a higher-value zener diode. You want a zener rated such that it protects the gate of the MOSFET adequately, but does not conduct in reverse bias at normal operating input voltages.
Also I came up with this copper island connected with vias to the other side as an attempt at heatsinking - yes the contact with the device will be poor. KiCAD says it's a total of 628mm2.
The device itself seems like the wrong type of package with no metal underneath just the legs and tab, for anything drawing more than very modest current. I'm coming around to using another regulator, but really I just need 5V up to 1A from an external PSU.
I think you should probably look at using a buck regulator instead for 1A. You can get synchronous regulators that don't need an external diode and switch at high 100's kHz or MHz that only need a small inductor, so you can probably fit it all in the same space on your PCB. Something like an
AP62300.
Even with that copper area, and an input voltage of only 7V, you'd still be massively overloading the NCP1117 with 1A. There is a chart, figure 32, in the NCP1117 datasheet of R
θJA for a given copper heatsinking area, and extrapolating out 600mm
2 still only gives about 80 °C/W. If the regulator is dissipating 2W (7V input, 1A output), that's still a 160 °C temperature rise!