Here, the equipment and methods of the manufacturers differ a little, but not fundamentally. First of all, the solderpaste or applied the flux to the bare board. In this process, this is used, for example, to applied with a kind of tampon over laser-cut masks or injected with a nozzle. Some areas can also be coated with solder paste later in the SMT machines if the shape is too special, or if the so-called no-flow method for underfill is to be used.
In the fast no-flow process, in contrast to the capillary underfill, the flux is also used for the underfill and later cured in the reflow furnace. The capillary underfill by means of a guided injection needle (whereby the injected adhesive pulls under the component like a sponge due to the capillary effect) would only be possible after the SMT process and also a cleaning of the boards in the intermediate process after the SMT process and a subsequent curing.
In addition to the small SMD resistors, capacitors or semiconductors, larger components are also applied in the SMT process, which one would not even suspect.
Even larger and above all sensitive components are applied in the Chip Mounter. These machines are then also suitable for the "heavy guys" such as GPU Packages (BGA) or memory. In this case, e.g. with the right equipment, the no-flow underfill. Can, but does not have to.
Then we go to the "bakery". For reflow soldering ("remelter soldering") a hot air furnace is almost always used. In contrast to the later wave soldering, here the already provided with soldered areas of the board or components. There is no additional transfer of lot.
And for all those who like to "bake" defective graphics cards in the domestic oven, I have the right temperatures for free as a package. But please don't just imitate it if all hope isn't really lost!
Afterwards, the quality of the boards is tested using various methods. This is done as a 2D/3D procedure up to complex X-ray systems. Unfortunately, not everything could be photographed here, because every manufacturer has his secrets. But some things are already.
If errors are found, it is necessary to rework or, if necessary, sort them out.
The final check of neuralgic soldering points takes place before the semi-finished board is handed over to the Manual Insertion Line (manual assembly line).
Often enough, manufacturers, in any industry, also use a buffer between SMT and manual assembly to, for example, fluctuations in production, absences due to defects, etc. to be able to compensate. Nothing is more expensive than when all assembly lines and systems need to be stopped.
But not everything can be really machine-loaded and fully automated. Of course there are exceptions (Asus), but even in these factories both exist (still) in peaceful coexistence.
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