**10. Dendrites**

Dendrites grow due to electrochemical migration when metal ions go into the electrolytic solution at the anode, plating out at the cathode and creating needle- or treelike formations on the PCB substrate (see photos in **Figure 16**) [16]. Electrochemical migration can be defined as the movement of a metal ion in an electrolytic solution between two neighbouring conductors with different electrical potential.

The time required to create dendritic bridges, which cause short circuits between two conductive paths, is determined by several factors including relative humidity,

**129**

**Figure 17.**

*Overview of Selected Issues Related to Soldering DOI: http://dx.doi.org/10.5772/intechopen.91023*

shock tolerance of the whole PCB.

diameter is around 100–300 μm.

**11. Voids**

**11.1 Macrovoids**

nation amount, contamination type, etc. [17–19].

temperature, conductor material, conductor spacing, voltage difference, contami-

The growth of dendrites has become a more serious issue, mainly due to the constant miniaturisation of electronic components (decreasing distance between the cathode and the anode) and the use of newer fluxes (especially no-clean fluxes). Manufacturers use no-clean fluxes to remove the washing process from production and reduce production costs. Despite this, these fluxes, under certain conditions (high humidity, significant temperature changes), are a good basis for creating an electrolytic solution. To prevent the growth of dendrites, it is necessary to thor-

Voids are non-conductive cavities within the soldered joint, and their excessive presence poses a significant reliability risk for the manufactured product, especially in power electronics, where higher currents are present [20]. Voids are formed during the soldering process, their presence in the soldered joint causes the displacement of electrical and thermal paths, the resistance is higher and the temperature stress is non-uniform. This subsequently causes cracks and lowers the mechanical

With the advent of lead-free soldering (new material base, different temperature profiles, different types of fluxes, higher surface tension of solder, etc.), a higher incidence of voids was detected, leading to the lower reliability of soldered

Voids can be classified into several categories [21]. There are macro- and microvoids, shrinkage voids, voids in microvias, Kirkendall voids and pinhole voids (see **Figure 17**).

Macrovoids are the most commonly occurring type of voids. Macrovoids are formed by the evaporation of gases from fluxes and soldering pastes during the reflow process. Macrovoids may occur anywhere in the solder joint, and their

The factors that affect the size of the macrovoids are the solder paste's properties (particle size, composition, melting temperature and oxide content), flux (viscosity,

*Soldered joint and the location of different types of voids. Intermetallic layer contains Kirkendall voids;* 

*pinholes are located on the boundary between the intermetallic layer and the PCB.*

oughly wash (even no-clean fluxes were used) the PCB after soldering.

joints. Increased attention is therefore paid to the voiding issue.

**Figure 16.** *Photo of dendrite.*

temperature, conductor material, conductor spacing, voltage difference, contamination amount, contamination type, etc. [17–19].

The growth of dendrites has become a more serious issue, mainly due to the constant miniaturisation of electronic components (decreasing distance between the cathode and the anode) and the use of newer fluxes (especially no-clean fluxes). Manufacturers use no-clean fluxes to remove the washing process from production and reduce production costs. Despite this, these fluxes, under certain conditions (high humidity, significant temperature changes), are a good basis for creating an electrolytic solution. To prevent the growth of dendrites, it is necessary to thoroughly wash (even no-clean fluxes were used) the PCB after soldering.
