**11.4 Microvia voids**

*Welding - Modern Topics*

**11.2 Planar microvoids**

alloy is shown in **Figure 19**.

**11.3 Shrinkage voids**

surface tension, activator, solvent, etc.), components (geometry, shape, terminal oxidation, etc.) and the process (thickness, the shape and the parameters of the solder paste's printed layer, temperature profile) [22–26]. An example of macrovoids in the solder joints of a soldered BGA package on the PCB is given in **Figure 18**.

Microvoids are characterised by their small diameter, less than 25 μm. Their occurrence is typical for Ni/Au, OSP and Ag finishes [27]. There are planar (one plane) on the solder pad/solder alloy interface; due to this, the joint's mechanical strength is significantly reduced. The cause of these voids' formation is not yet fully clarified. An example of planar microvoids on the interface of the solder pad/solder

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

**130**

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

**Figure 18.**

*Macrovoids within the BGA solder joints.*

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