Four steps for consistent joint quality in selective soldering (Part I)

In order to ensure reproducible, high-quality solder joints during selective and wave soldering, the solder bath must be continuously monitored in order to detect any impurities that could negatively influence the soldering process at an early stage. The composition of the solder bath should also be checked and, if necessary, the solder alloy “refreshed”.

Various steps are necessary for this, which we present in parts I and II:

1. timely detection of impurities with negative influence on the joint quality

The thermal soldering process in wave or selective soldering not only transports the solder alloy from the solder bath to the component, but also continuously in the opposite direction. In the course of time, the composition and quality of the original alloy is usually changed negatively. Effects such as bridging, wetting problems, reduction of penetration, depositions, etc. are the result. Therefore, timely detection and correction is essential for a consistently high quality. Depending on output, the solder composition should be checked quarterly or at least every six months.

2. checking the entrance of contaminants and their source of origin

Impurities or contaminations are often also introduced into the solder bath by components or printed circuit boards. For example, there are residues from the manufacturing process of printed circuit boards or components, residues of protective coatings and fluxes, alloys from pre-tinning, contacting or metallurgical coatings. Some of these contaminants can cause undesirable effects on assemblies or equipment over time, if not monitored. Also, this is usually accompanied by an increase in oxide formation, which automatically leads to higher maintenance requirements.