There are a number of DIY reflow projects on YouTube. The simplest being merely placing the PCB on a hotplate and watching it, the next step up using the hotplate at the soak temperature (drying the volatiles and activating the flux), then a hot air reflow gun to melt the solder.
Or using a toaster oven by manually changing temperature, and watching the board.
A lot of people seem to have stopped there.
Going further requires programming, so you'll find more reflow oven projects on sites like forum.arduino.cc and here is a recent thread from 2020:
Note that it pretty quickly goes from PID controller to watching a hotplate.
I don't know how good it is, but I see even Amazon is selling soldering reflow ovens, lowest price $239.
I'm one of probably a number of people who have the intent, got many of the parts, but never finished. Convection toaster oven found at a thrift store, 320x240 touchscreen so it can display the temperature profile, Arduino, thermocouple interface and type K thermocouples, SSR.
I actually have two tabletop convection ovens. One is a standard toaster oven, the other is meant to put like a chicken or a small roast in it. Both convection. The roast oven seems better suited to putting the controls inside. The standard toaster oven, I was going to put a box next to it with the electronics in it.
--
Steven Greenfield AE7HD
Steven Greenfield AE7HD