Selective soldering is similar to wave soldering. It is preferred to wave soldering in the case of mixed-technology printed circuit boards (PCBs) with layout constraints, also where specific components cannot withstand the heat of wave soldering.
It is an automated process that gives the precision of hand soldering with none of its delays and inconsistencies.
In this process, a mobile mini wave solders specific components to the board, without coming in the way of other components.
Stages in selective soldering
The solder pot is first programmed with all the positions on the board that need to be soldered. Other parameters such as solder wave height and speed are set before the main stages begin.
Fluxing: Here flux is applied to the components that need to be soldered (rather than the entire board as in the case of wave soldering).
Preheating: The temperature of the assembly is then raised to the required level for the purposes of activating the flux and ensuring the effective filling of spaces with solder.
Soldering: The mini solder wave moves below the component to be soldered before soldering the leads to the board. The solder pot then lowers and moves to the next area to be soldered.
The effectiveness of selective soldering depends on many factors such as the configuration of machine, the attributes of flux and the choice of nozzle. Nitrogen, specifically nitrogen of high purity, plays an important role in the case of selective soldering. This is because dross formation caused by oxidation can interfere with the solder flowing over the nozzle, which can lead to soldering issues. Moreover, the use of nitrogen extends the lifetime of the nozzles used for soldering, which saves costs. For these reasons and more, selective soldering in nitrogen is the optimal choice.
Nitrogen in selective soldering
The industry preference for nitrogen use in soldering is heavily influenced by the improved process window, as performing the production process in nitrogen compared to air reduces issues such as defect formation. But the cost benefits are important as well, as the savings offset the nitrogen expenses.
A nitrogen environment also improves first pass soldering yields, which translates into cost savings. Therefore, on-site nitrogen generation in particular makes a better case for cost and resource savings.
On-site nitrogen for quality soldering
An on-site nitrogen generator not only gives you control over air purity for soldering purposes (which is critical in ensuring appropriate solder spreading behavior at low temperatures) but also reduces your operating costs (as compared to third-party supply) and ensures you have a constant flow of nitrogen gas when downtime can interrupt production. Generating nitrogen on your own with an on-site nitrogen generator allows safer handling and ensures a lower carbon footprint. Additionally, on-site nitrogen generators, such as those from Pneumatech, are easy to integrate into existing systems.
Pneumatech designs and manufactures both standard and engineered on-site gas generator products. Explore Pneumatech’s full range of nitrogen generators. Or get in touch with us right away.
Reflow soldering is primarily used in surface-mount technology (SMT), notably in fine pitch ball grade array (BGA) components. For this purpose, solder paste, which contains flux suspended with solder, is used.