SMT soldering process
There are several stages required to solder SMDs to boards. However there are two basic methods of soldering that are used. These two processes require the board to be laid out with slightly different PCB design rules, and they also require the SMT soldering process to be different. The two main methods for SMT soldering are:
Wave soldering: This technique for soldering components was one of the first ones introduced. It entails having a small bath of molten solder which is flowing out causing a small wave. The boards with their components are passed over the wave and the solder wave provides the solder to solder the components. For this process, components need to be held on place, often by a small dot of glue so that they do not move during the solder process.
Reflow soldering: This is by far the preferred method these days. Within the PCB assembling, the board has solder applied through a solder screen. Components are then placed onto the board and held in place by the solder paste. Even before soldering it is sufficient to hold the components in place provided the board is not jolted or knocked. The board is then passed trough an infra-red heater and the solder is melted to provide good joint for electrical conductivity and mechanical strength.
The soldering process is an integral element of the overall PCB assembling process. Typically board assembling quality is monitored at each stage and the results fed back to maintain and optimise the process for the highest quality output.
Accordingly the soldering techniques required for electronics assembly are honed to meet the needs of SMDs and the processes used.
