**Abstract**

The formation of defects and imperfections in the soldering process can have many causes, which primarily include a poorly setup technological process, inappropriate or inappropriately used materials and their combinations, the effect of the surroundings and design errors. This chapter lists some examples of errors that can occur in soldering, while review is devoted to selected defects: non-wettability of the solder pads, dewetting, wrong solder mask design, warpage, head-in-pillow, cracks in the joints, pad cratering, black pad, solder beading, tombstoning, dendrites, voids, flux spattering from the solder paste, popcorning and whiskers.

**Keywords:** electronic assembly, soldering, reflow soldering, soldering defects, reliability issues

## **1. Introduction**

A significant change in soldering technology was the transition to lead-free soldering. With this change and the increasing miniaturisation of electrical equipment comes the associated issue of developing suitable alloys, production technology, etc. Over time, soldering has become a very complex process, with many factors affecting the final quality of the solder joints, and thus the product.

The formation of defects and imperfections in the soldering process can have many causes, which primarily include a poorly setup technological process, inappropriate or inappropriately used materials and their combinations, the effect of the surroundings and design errors. This chapter lists some examples of errors that can occur in soldering.

## **2. Non-wettability**

One of the problems is the non-wettability of the soldering pads. During the soldering process, the soldering pads are not sufficiently wetted with the solder alloy (the solder does not create a connection with the entire surface of the soldered area). An example of this defect is shown in **Figure 1**.

This defect may be caused by the soldering pads being too oxidised, the flux not being active enough, insufficient PCB warming, soldering pad contamination as well as, for instance, a poor solder mask coating [1].

**Figure 1.** *Problems with the non-wettability of soldering pads.*
