The SMT floor is filled with machines that autonomously handle most of the steps in this initial stage of production. The first of these machines is the solder paste printer, which prepares the traced PCB for component placement by spreading a thin layer of conductive solder onto the substrate through a stencil.
The next stop is the component gun, which places up to 10 components per second on each board in a dizzying display of mechanical engineering at its finest.
Components are loaded into the gun on reels, just like bullets in an ammo belt. Keep in mind that each of these resistors or microchips is only a few millimeters across; every reel pictured below contains thousands of parts.
During the reflow soldering process, components placed by the rapid-fire gun are loosely soldered into place so basic testing can be done. If you want a good read on the details of this stage of the process, Wikipedia has a nice article on the subject.
After surface-mounted components are loosely anchored, it's time for the boards to be inspected. The first step of this process is done by hand, with a relatively small group of people performing a visual inspection of each board to ensure that nothing is obviously wrong.
Our tour guide explained that while automation in testing has come a very long way in this industry, there are certain things that humans are simply better at detecting quickly, like a burnt area of a PCB or a component that has been rotated slightly. For this reason, visual inspections are still an integral part of the assembly procedure. Certain machines are used in conjunction with these inspections to minimize defective boards, though.
One of those machines is the optical tester, which takes many pictures of a board and uses specialized optical recognition software to analyze the photos for missing or improperly installed components.
Instead of simply flagging boards as good or bad, the optical tester produces a detailed report of problem areas for a quick diagnosis.
Large testing devices like the Miko-Kings TR-518FE check boards against a given template to ensure that each component is electrically connected.
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