What are the advantages and disadvantages of using a reflow oven vs a hot air station for prototyping SMD PCB? Do you need an oven or would an air station work?
The advantage of a reflow oven is that it evenly heats everything in a controlled and automated way. Assuming the oven is well calibrated you can precisely reproduce the manufacturers reflow profile, hopefully resulting in reliable soldering and very low probability of damage to components. The disadvantage is usually cost, and that cheap reflow oven often do not precisely track the programmed profile.
The advantage of hand reflow with hot air is that it is fast, doesn't require a reflow oven, and for prototyping can work quite well. The disadvantage is that it is hard to reflow large boards evenly, so except for very small PCBs you will probably end up applying too much heat to some areas and too little to others. Further problems occur with plastic components, which tend to be hard to reflow without melting because you don't have that fine control over temperature. For example, I would not use hot air to reflow a large 10" wide PCB with many surface mount components and plastic connectors, but I have done 1" PCB modules with hot air and found that it worked fairly well because the boards were so small I could evenly heat them.
I have done a lot of at-home assembly of SMD boards. I do a mix of one-offs and 10s of boards, with anywhere from a few to hundreds of components. People vary in which type of assembly they prefer. For me, if there are only a few SMD components on a board, and they're not too fine pitch (e.g. 0603 passives and SOT-23 or SOIC-8 size), I will hand solder them with an iron. Any more than that, and I will get a stencil and reflow. Stencils are quite cheap now, I see no reason to manually dispense paste from a syringe, which I find pretty finicky.
For the actual reflowing, I started with a hotplate. This was OK, but I found it a little touchy, and tended to burn the PCB. I switched to an unmodified, cheap toaster oven, which I have used to do many boards. I used a thermocouple the first few times I did this, and you may want to do that to get a feel for it, but mostly found it unnecessary. I used the following "profile", turning on a stopwatch when I turned on the oven:
- Set oven to 150C
- Wait until 1:30
- Turn off oven
- Wait until 2:00
- Set oven to max
- Wait until solder reflows
- Turn off oven
- Wait 10 seconds
- Open oven
- Wait a few minutes and remove boards
Unless you have especially sensitive components (like WS2812 LEDs, which I have found best to hand-solder), this works really well, is cheap, and easy. Last year I built a temp-controlled reflow oven using the Controleo3. It is more precise, which is important if you have more sensitive components. But, for most hobbyist use, it's overkill.
Ovens are generally easier and are certainly more repeatable. But the cost is significant.
I use a cheap hot air station for prototyping and get good results. It can be tricky to solder leadless components without overheating them. Especially when some pins go to large copper areas (or vias to ground/power planes).
So, I now have a cheap preheater to go with my cheap air station! You heat the entire board to some intermediate temperature, which includes the internal planes and through-vias. Then you only have to supply a little heat from the air station to make the solder flow.
I totally disagree with the statement that oven heats with best control. It really depends on the quality of the oven. Simple Chinese ovens need a lot of attention and setup to get a stable result. We use ovens just because it's a bit faster for a big amount of similar PCBs.