So lets' go4it!
First, we need the right Equipment to do this kind of work.
Some kind of hot-air rework-station An soldering-iron station with a normal tip, for desoldering where you need energy and of course desoldering braid: And also a small, chisel formed tip for precise soldering the chips pins: As soldering flux i use cheap RMA-223 with an application needle: As soldering tin, use a small one (0.5mm diameter) but with flux integrated, like this: To inspect the soldering later you should have some kind of a microscope. I use a handheld one and a stationary: Preparation
The key concept is to pull all pins of one side by using a wire, heaten the pins up and lift it up only a bit to separate the pin row from the soldering pads.
So first thing is to prepare a wire. Undrill it from a cable, about 10-15cm length: Shift the wire under the pins of one side: and bend the end to a triangle you can pull at: Now put hotair (use 330 degrees) on the pin row by moving the airgun slowly from left to right and back. Keep a distance of 1-2cm: Apply hot air this way for about a minute until the solder fully melt. Test this by firmly pulling on the wireloop until you can lift the row a few millimeters: Then heat up the other side: If this also is loose, flip the chip off by pulling on the wire: Remove the chip: Next you need to remove the remaining solder from the pads of the board: Apply a little bit of the flux paste to each row of pads to ease desoldering. Use a soldering iron with a normal tip, put the braid on one side of the row, apply the iron on the braid, wait a bit until the braid heats up and melt the solder underneath. Then shift the braid with the irons tip slowly to the other side: Do the same on the other row and clean the pads using alcohol and wipe: After that we solder in the new chip
Place the chip on the pads. Be very precise with aligning. If you found the right position, press it with a finger and put some solder on both sides to fix it, like shown in the picture: To aid soldering the pins, apply a string of flux paste on each row of pins: Now change the soldering tip to the small one. Clean the tip, apply a little bit of soldering tin to the tip and start soldering the pins of each row, one by one. The flux should avoid making tin bridges between two pins. A good way is to put the soldering tip on the pad. This needs a little bit of practice.
Remove the remaining flux again by using alcohol, a short cut paint brush to apply and a wipe to remove:
That's it! Happy repairing
Just advancing the tutorial a bit, time after time. Also, don't overdue and practice on a broken pcb or so.
