**11.3 Shrinkage voids**

Shrinkage voids are voids with rough tree-like, branching edges pointing from the joint's surface towards the solder joints' core. They are characteristics for SAC solder

**Figure 18.** *Macrovoids within the BGA solder joints.*

**131**

**Figure 21.** *Microvia void.*

**Figure 20.** *Shrinkage voids.*

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

take them into account during design (**Figure 21**).

**11.4 Microvia voids**

**11.5 Kirkendall (IMC) voids**

alloys. The cause of these voids' formation is the solder solidification process, when the solder shrinks during slow cooling. Their occurrence can be avoided by controlled cooling. It has not yet been proven that these voids have a negative effect on the reliability of soldered joints. An example of shrinkage voids is shown in **Figure 20**.

This type of void arises from gases escaping from the microvia (plated holes with a diameter smaller or equal to 150 μm, used for interconnection of conductive paths between the individual PCB layers) during the soldering process. The solder has inadequate wettability and is not able to penetrate inside a microvia. These voids can greatly affect the reliability of a solder joint; therefore, it is recommended to

Kirkendall voids arise in the intermetallic layer between the solder and the solder pad. They are created when joining two metals with different diffusion coefficients. These voids are most commonly located on the interface between a tin solder and

**Figure 19.** *Planar microvoids.*

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

alloys. The cause of these voids' formation is the solder solidification process, when the solder shrinks during slow cooling. Their occurrence can be avoided by controlled cooling. It has not yet been proven that these voids have a negative effect on the reliability of soldered joints. An example of shrinkage voids is shown in **Figure 20**.
