Beginners and casual modders, keep these in mind. These are mistakes ordered roughly from most common to least common.
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Do we need this? There are excellent videos with audio commentary from professionals for free on the web!
There are excellent videos with audio commentary! But if somebody is deaf and wants to read about it, here it is:
Be careful to remove the old one! Following procedure has been working for me:
An alternate method to use a small butane torch, such as a jet lighter to heat the chip pins. Keep the flame moving and do not linger in one spot. This method is faster than a heatgun and does not require masking of the board or removal of the capacitors, but requires more care to avoid scorching the components or board.
Yet another alternate method for if you only have a soldering iron (nonetheless with a small tip) is to simply flood all the pins with solder so that they're bridged and then, maintaining heat to it, use tweezers to lift that side up off the board, then simply do the same with the other side and finally, clean up all the solder using some copper solder braid to absorb it.
When it comes to resoldering, you can do roughly the same in reverse; first get the chip lined up with the pads and stuck down with masking tape and/or blu-tack then again flood the pins with solder and use solder braid to soak it all up… assuming you do it right there won't be any joins between the pins, but of course, use a magnifying glass to check it, and a scalpel can do wonders if there's a join you just can't get rid of.
If the router is not working and you see a permanent restart on the serial console, check the connections, the memory is quite hard to destroy.