Peter, There is no truth's about the way things are, How something is done is only bound by who is doing it. You can check the archives for info to get you going but it's all up to you. As far as placement order, it all depends on what you are placing Chip On Board with. Normally placed by a Fine Pitch Placement machine therefor placing them after the majority of parts on the board. No rules, just circumstance. Have Fun!