PCB assembly Assembly and soldering process for printed circuit boards

Surface mounting technology (SMT) is the basis for modern component assembly. In contrast to the through-hole assembly of wired components, SMD components (surface mount devices) have solderable connection surfaces that are soldered directly onto the upper side of the PCB using the reflow soldering process. SMT soldering makes it possible to optimize component assembly in terms of inexpensive and high-quality PCB assembly.

Through-hole reflow (THR) soldering combines the solder connections of through-hole technology, which are particularly stable in mechanical terms, with the production processes of surface mounting, which can be automated efficiently. In the THR process, the solder paste is pressed into the through-contacted holes using the same process equipment. The functional principle of this method is today regarded as being established and has been accounted for in a separate standard, DIN EN 61760-3.

In the case of wave soldering, depending on the assembly method, wired components or connection elements are soldered onto the PCB manually or using pick-and-and-place machines. First, the entire module is wetted with flux on the solder side, then pre-heated, and finally run through a single or double solder wave where it is wetted with the solder. After soldering, the entire module is cooled in order to reduce the thermal load on the PCB again. If only through-hole technology (THT) components are soldered, which by virtue of their design must withstand greater mechanical strain, wave soldering is always the standard method.

In the case of direct connection, the direct connector contacts the corresponding contact pads on the edge of the PCB. As a result, wire-to-board and board-to-board connectors can easily be plugged horizontally onto 1.6 mm thick printed circuit boards without any additional tools. The male connectors are coded at the factory to prevent mismatching. Two spring-loaded engagement catches lock the connectors in place on the PCB. As the soldering process is eliminated, the connection components are not subjected to thermal stress.