Re-soldering SMD with SMD rework station

Question

I recently purchased a clone 858D SMD rework station and would like to get familiar with de-soldering and re-soldering SMD chips.

I was able to de-solder fine, but when trying to re-solder I can't seem to get all the legs to solder onto the PCB. My question is, what could be the cause of this?

Here's the steps I took before re-soldering:

1. Added flux to the pads on the PCB
2. Cleaned up/added solder to the pads
3. Add a bit of solder to the legs of the SMD chip

One big thing I noticed is that before re-soldering, the chip didn't sit flat at all on the pads.

This was the PCB before soldering:

The outcome after soldering:

Answer 1

You need to get the PCB up to temperature evenly enough that the solder melts all the way around -- if you don't get all the solder melted all at once, then the solid stuff will always hold the chip up and it'll never work.

For a hot-air station, this means either getting a tip that blows hot air evenly over all of the chip, or playing the tip in an oval around the chip, with some extra attention to the board side (because the board will wick away heat).

It can help a lot to take a piece of tin can and bend a 'U' or 'L' shaped piece that surrounds the chip and sort of holds the hot air in the vicinity of the chip.

An alternative with any sort of package that has legs sticking out like that is to clean the PCB off until the pads are just tinned. Then tack the chip down in two corners, and solder it on leg by leg. If it's too fine a pitch to do that, just get everything soldered, even if you get solder bridges -- then go back and clean off the solder bridges with solder wick. The more magnification you can get when you're doing this, the better.