**13. Popcorn effect**

During the soldering process, heating the mounted PCB, some components may experience absorbed moisture turning into steam, which may result in damage (delamination, cracking the component's package). The components absorb moisture during their manufacture and storage. It is therefore necessary to dry components that are sensitive to moisture absorption before they are mounted and

**133**

**Figure 24.** *Photos of whiskers.*

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

this defect is very difficult to detect.

*Schematic representation of the popcorn effect.*

**14. Whiskers**

**Figure 23.**

soldered. The popcorn effect is schematically shown in **Figure 23**. With the advent of lead-free soldering, this effect occurs more frequently due to the use of higher soldering temperatures. In some cases, when the package cracks from the PCB side,

Whiskers are electrically conductive and relatively mechanically resistant crystals growing on the surface of some metals. They may grow on the surface of the solder alloys with a high tin content (majority of lead-free solder alloys). It most *Overview of Selected Issues Related to Soldering DOI: http://dx.doi.org/10.5772/intechopen.91023*

*Welding - Modern Topics*

**11.6 Pinhole voids**

slowly into the copper than copper into tin.

**12. Flux spattering from the soldering paste**

source of the stain was flux spattering.

problematic.

surfaces intended for the subsequent electrical testing methods.

a copper solder pad. Tin has a lower diffusion coefficient and thus penetrates more

Pinhole voids arise when a gas leaks from metal soldering pads during the soldering process. These voids have very small dimensions, on average around 1–3 μm. Their appearance is due to substances absorbed by substrates from previous

During the reflow process, the flux may spatter from the soldering paste. If the PCB is cleaned after soldering, flux spattering need not necessarily be considered a problem. If PCB cleaning is not included in the process, then flux residues can not only be the cause of future corrosion, but flux spatter can leave stains on the test

If a flux stain on the test surface gets into sites where the contact test tip is in contact with the test surface, then, due to the non-conducting nature of the flux, the electrical test evaluates the product as a reject, even if the product is fully functional. In addition, these stains are, in most cases, clear and therefore difficult to detect. An example of a photo of the test pads on a PCB is given in **Figure 22** along with an image from an electron microscope, where a dark stain is evident; the

There are various sources of non-conducting stains on the test surfaces, for example, the solder mask, organic coatings, inappropriate materials used when maintaining technological equipment, etc. Diagnosis of the cause can be very

During the soldering process, heating the mounted PCB, some components may experience absorbed moisture turning into steam, which may result in damage (delamination, cracking the component's package). The components absorb moisture during their manufacture and storage. It is therefore necessary to dry components that are sensitive to moisture absorption before they are mounted and

*Test surfaces for electrical testing methods: (a) photo from an optical microscope and (b) photo from an electron* 

*microscope—a dark stain is obvious, and the source of the stain was flux spattering.*

processes. They mostly occur in the case of galvanic copper surface finish.

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**13. Popcorn effect**

**Figure 22.**

**Figure 23.** *Schematic representation of the popcorn effect.*

soldered. The popcorn effect is schematically shown in **Figure 23**. With the advent of lead-free soldering, this effect occurs more frequently due to the use of higher soldering temperatures. In some cases, when the package cracks from the PCB side, this defect is very difficult to detect.
