The PCB Assembly Process
Component Procurement
Component procurement is the process of purchasing all of the components needed to assemble the PCB. Components come is various standard packagings, designed to make automated assembly possible; for example Tape & Reel, Tube, and Tray. Standard packaging is also usually supplied with standard component quantities – for example 5000 resistors on a reel; some component distributors do however offer a reeling fee, where they will take a smaller strip of components and load them onto a reel for you (with “leading” and “trailing” empty sections of tape added, which aid in loading the reel into automated assembly equipment). “Bill of Materials” (BoM) output from your PCB Design software can be used to create a list of the components and quantities needed (Proteus has a dedicated Bill of Materials module in the software), which can easily be multiplied up in a spreadsheet for multiple boards.
Machine Feeding
Components (in the standard packagings) are loaded into assembly machine “feeders”, which automatically feed components into the machine as they are used by it. Tape & Reel packaged components consist of a tape with holes for a cog wheel to pull it in on, and a plastic strip stuck on top which holds the components in place inside the strip and then gets peeled off just as the components are needed. Tubes are fed into the machine with vibration feeders, which vibrate the components along and out of the tubes. Trays are usually just opened and placed into the machine at a specific position.
Component Placement
Next, the pasted board goes into one or more “pick and place” machines (the ones which we loaded components into and programmed earlier). These machines use vacuum nozzles to pick components out of the feeders and place them in the correct locations on the board (top machines do this faster than the eye can see!).
