Provided you have good eyesight and steady hands, I've mostly found what happens as you get smaller is:
- Heating becomes easier. There's no large sinks to take the heat away. It's also easier to overheat things.
- You need finer tweezers, and don't drop them because if you do the tips will bend.
- The solder's surface tension does more of the work. It feels a lot more like sticking together things with tiny droplets of glue. Having the correct amount of solder in the right place is critical.
- Solder and flux become two separate things you have to care about individually
- It is easier to burn yourself
- learning how to brace your hand against something in a way that gives you very fine control. One reason soldering with an iron can be difficult is because your hand is so far away from the tip, like trying to write with a pen held by the end.
How are you burning yourself? I've only ever worked with one person who burned himself soldering when working on a SMT PCBs, and it was while desoldering a through-hole connector, when a desoldering station was long past its cleaning interval and it dripped some solder onto a metal ring he was wearing. This was a guy who would lick a soldering iron to see if it was hot and touch the molten solder in the wave solder machine. The Leidenfrost effect goes a long way.
> The solder's surface tension does more of the work. It feels a lot more like sticking together things with tiny droplets of glue. Having the correct amount of solder in the right place is critical.
I believe this is why I have an easier time hand-soldering BGA than QF[np]: I can't screw up solder amount/evenness.
When I started my first job a coworker encouraged me to learn how to solder SMDs and do "microsoldering". Like most people I thought I was going to need high precision and a much steadier hand. Probably like most people that learned I was impressed at how quick I picked it up. I think the hardest thing was learning about part "tombstoning" but that's not that difficult to deal with. I'm not going to say it is easier than soldering through-hole components, but I think for most people the mental barrier is much higher than the actual barrier.
I now highly recommend learning it to anyone doing electronics. It's well worth the (small) time investment and makes things a lot easier, opening lots of doors. Even for a hobbyist you immediately get benefits. Everything becomes more compact, 2 sided boards are much more usable, and, of course, it opens up a lot of repairability (and recycling. Are you really a hobbyist if you aren't desoldering and reclaiming parts?).