If you are looking for professionally made surface mount PCBs, there is no doubt they are soldered in reflow oven. SMT components are too sensitive and small to be soldered by hand. This is why they are baked in ovens with controlled temperature profile. If you are going to build such oven, there is no problem with – you can get away dirty cheap. All you need is regular oven new or used and temperature controller. There is no big difference what type of oven you are going to use, the most important thing is that there were electric heating element. More important part is the controller. You can find many reflow oven controllers that can be successfully used. You can always build one, but why waste time on building tools if there are many options already available.
We suggest to take a look at time proven projects like ControlLeo2. This is a second version of successful project which was also in Kickstarter. ControlLeo is really simple device with powerful features like four controllable outputs for heaters and fans, algorithm takes care of better heat distribution in oven including eliminating hot spots. Controller can log control data to computer once connected. Controller is based on Atmega32u4 with Arduino Leonardo bootloader. Controller is equipped with LCD display, two buttons, buzzer. It is capable of reading temperature with k-type thermocouple like MAX31855. Controlleris placed in to nice plastic enclosure that can be fixed on top of oven.