Burned nanos?

Hey guys
I think I just burned 2 Nanos.
I'm using a 30W soldering Iron and had to resolder the pins of one and solder the pins of a new one.
Now they don't work. One allows for code upload but won't turn on, other seams to have a short circuit.
Could have I burned the circuits due to a 30W soldering iron?
Also used a little of flux on the pins, can flux pass energy and make bridges?

if it uploads code, it MUST turn on. do you mean that it can be powered by USB, but not VIN or 5V? Did you check your power pins to make sure they're actually making contact with the solder rings? You may have a cold-solder that isn't making good contact.

Can you post a picture?

It doesn't turn on with VIN, USB or 5V. When I upload the code, the on led is off but it blinks like accepting the code.
I just bought a new power station, it will probably solve the problem next time. But I really wanted to save these pour bastards...

Get a soldering iron that allows you to control the temperature.

Rosin flux is an insulator.

You should NOT have to use flux, if you use proper rosin-core (electronics) solder.

If you have used flux made for reflow soldering then you're still ok.
If it was plumbers flux, then throw everything that was in contact with it away.