This is essentially a very large oven where the parts that have been placed onto the board are soldered in place.
Temperatures inside this 13-stage reflow oven reaches 237C, causing the solder to melt and fusing the parts in place. Each panel is then gradually cooled.
The process has to be carefully controlled: too cold and some of the joints won't form and too hot and some of the more delicate components will fry.
Photo: Nick Heath / TechRepublic