Need some soldering advice for beginners

Here are a few observations…

• Underfill is the bane of micro-soldering iDevices. Everyone develops their own method so you’ll have to experiment but consider that most underfill softens up at about 125-150C. That is lower than the melting point of leaded solder (and also non-lead solder) so the trick is to get the are of the board to that temperature without going over the melting point of the solder. That way you can scrape away the visible underfill before removing the IC. For the cleanup underneath the IC, the same temperature guidelines apply. Look at videos from multiple techs online to see a good variety of techniques (and tools) and experiment. You’ll note some folks use hot air, others use a pre-heater or combine the two.
• If your solder is just clumping to the board, that means the board isn’t at the right temperature…it needs to be hotter. This is kind of like freezing rain (but sorta different ;-), the water freezes immediately on a cold surface. This will usually happen on pads or areas under an IC that are a large ground plane. They require more heat than little-bitty pads that are essentially connected to nothing more than a tiny trace or via.
• FPC are not orientation sensitive.

It’s good that you are experimenting with iCloud boards. Try various temperatures and nozzles (for hot air) and tips for your soldering iron. In the end, it’s all about heat transfer. Once you get the area under work at the proper temperature (and no more), you’re technique will improve dramatically. The flip side is to avoid getting too much heat otherwise you will cause lots of collateral damage.