**6. Cracks: pad cratering**

Cracks occur not only in the soldered joints, but also in the components and PCB. Due to mechanical, thermal and combined stress, the material is under tension, which results in cracks forming in the weakest spot, together with a release of the tension [3].

The location of the cracks depends on many factors (the materials used, the type of soldering technology, the package, the PCB material, geometric factors, etc.) [4, 5]. **Figure 8** shows an overview of crack failures occurring in a PCB assembly.

An example of a crack in the site of the intermetallic alloy on the interface between the BGA package's terminal and the ball of solder alloy is shown in the microsection in **Figure 9**. Due to their minimum dimensions, these errors are difficult to detect using X-ray inspection.

Another example of a crack is pad cratering where a crack is formed within the PCB under the soldering pad (see **Figure 10**). This defect does not manifest during a functional electrical test, and it is not even possible to detect it with the nondestructive methods for the output check.

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**Figure 10.**

A pad cratering defect can be compounded by the use of lead-free solder alloys, where the higher temperatures used for lead-free solder alloys cause greater tension in the materials used [6, 7]. In addition, the lead-free solder alloys are significantly stiffer than tin-lead eutectic solder alloys; therefore, they transfer greater stress

under the package pads during a mechanical stress [8].

*Microsection of a BGA terminal soldered to a PCB with a pad cratering defect.*

*A longitudinal crack between the solder joint and the BGA package's terminal.*

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

*Overview of crack failures occurring in a PCB assembly.*

**Figure 8.**

**Figure 9.**

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

*Welding - Modern Topics*

**Figure 6.**

**Figure 7.**

the reflowed solder alloy on the solder pad no longer joins with the reflowed BGA solder alloy ball. The Head-in-Pillow effect in connection with the temperature profile

Cracks occur not only in the soldered joints, but also in the components and PCB. Due to mechanical, thermal and combined stress, the material is under tension, which results in cracks forming in the weakest spot, together with a release of

of soldering technology, the package, the PCB material, geometric factors, etc.) [4, 5]. **Figure 8** shows an overview of crack failures occurring in a PCB assembly. An example of a crack in the site of the intermetallic alloy on the interface between the BGA package's terminal and the ball of solder alloy is shown in the microsection in **Figure 9**. Due to their minimum dimensions, these errors are dif-

The location of the cracks depends on many factors (the materials used, the type

Another example of a crack is pad cratering where a crack is formed within the PCB under the soldering pad (see **Figure 10**). This defect does not manifest during a functional electrical test, and it is not even possible to detect it with the non-

is shown in **Figure 6**, together with a photo of a microsection in **Figure 7**.

*Head-in-pillow effect in connection with the temperature profile.*

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**6. Cracks: pad cratering**

*Photo of a microsection of the head-in-pillow effect.*

ficult to detect using X-ray inspection.

destructive methods for the output check.

the tension [3].

**Figure 8.** *Overview of crack failures occurring in a PCB assembly.*

#### **Figure 9.**

*A longitudinal crack between the solder joint and the BGA package's terminal.*

#### **Figure 10.** *Microsection of a BGA terminal soldered to a PCB with a pad cratering defect.*

A pad cratering defect can be compounded by the use of lead-free solder alloys, where the higher temperatures used for lead-free solder alloys cause greater tension in the materials used [6, 7]. In addition, the lead-free solder alloys are significantly stiffer than tin-lead eutectic solder alloys; therefore, they transfer greater stress under the package pads during a mechanical stress [8].

Static or cyclic mechanical stress or thermal cycling can lead to the cracks spreading and the consequent failure of the device [9]. Stress can affect a mounted PCB even without external influences; this is called residual stress (tension that remains in the material even though the cause of stress has been removed). The source of the residual stress is primarily the manufacturing process in which many stress factors affect the components [10]. This primarily concerns the soldering process, where the elevated temperature leads to the fixation of components that often have different coefficients of thermal expansion.
