Automated PCB Assembly
Advancements in Automation
At the same time, the disadvantages of pin mounting are also associated with through holes in the printed circuit board (more precisely, with “through metallized holes in the printed circuit board,” as written in GOST R 53386-2009 “Printed boards. Terms and definitions”):
– impossibility of further miniaturization of the printed circuit assembly. Strictly speaking, this is not a disadvantage – rather a limitation, due to which pin mounting can be successfully used in large-scale instrument making, where miniaturization is irrelevant, but cannot be used for mounting a smartphone. However, we emphasize that it was the inability, due to the hole, to reduce the dimensions of mounted components that once became the main reason for the emergence of SMD technology. The driver of this process was computer technology, which was in dire need of miniaturization. Old computers took up a lot of space, sometimes several rooms, so technologies were required to reduce the size of the computer;
– also a disadvantage in particular cases is the restrictions on the routing of conductors on the printed circuit board due to through holes in multilayer boards;
– since now THT and OFA boards are often mixed, that is, made using SMD elements, the manufacturer has to perform several productive cycles for one board: both reflow soldering and selective soldering.
Despite these limitations, the installation of THT and OFA is still relevant. Several decades of use speak in its favor, thanks to which the assembly mechanism is well developed in both manual and automatic modes and there is a variety of assembly equipment and technological equipment.
Typical THT and OFA installation operations are:
– preparing the board for soldering. If the work is performed manually by installers, then this stage can be divided into two technical processes: first, the component leads are prepared, molded and trimmed, then manual installation is carried out (“filling” in professional jargon), after which the board is ready for soldering. If the machine is working, then both the preparation of the board and the installation of the elements occur inside the mounting platform within the framework of a single technical process;
– soldering, which, again, can be carried out either manually or in group automatic soldering mode. The latter can be performed by the so-called solder wave, when molten solder in a special bath creates a continuous flow – a wave, washing the lower part of the printed circuit board with installed lead components. The solder wets the pads and leads of the components and works its way up through the holes to form solder joints. This technology processes absolutely all components on the board, unless special pallets are used to protect certain areas of the underside of the board. Another type of automatic soldering is selective . In this case, we can talk about mini-wave soldering: a small “nozzle” approaches each pin separately and solders it in accordance with the mode specified by the program. This mechanism is reminiscent of hand soldering.