The step that, at least for me, stands out as by far the most difficult in the entire process is the initial chip placement. By that I mean the chip has to be set reasonably close to the ideal even if surface tension helps fine tune it during the reflow. I'm not yet sure just how close "reasonably close" needs to be, but... pretty close.
I have fairly steady hands (probably better than average), and nonetheless my first placement would often not be close enough (based on my guessing of what was close enough). So, I would then nudge it with a pair of tweezers until it finally ended up where I thought was "reasonably close". However, it's very easy to either overshoot or undershoot or accidentally rotate it, all of which leads to more nudging. Now, granted, eventually it gets to where it needs to be, but it can be frustrating at times. Any of this sound familiar?
So, if there are any tips on that part of the process , I'd be interested to hear. In comparison, the rest of it is relatively straight forward. I'm starting to think that making some kind of simple but small x-y table with a fixed vacuum chip holder above it that simply plunges in the z-axis might be the way to go. That way one could literally dial in the chip placement and remove imperfect hand motions from the equation. Yet, I haven't read of others doing that, so there must be easier ways.