**8. Solder beading**

The presence of balls of solder alloy next to the package (solder beading) is an error that is easily detectable by optical inspection methods. An example of balls next to the component package is shown in **Figure 12a**. The device's reliability is compromised in the event that the conductive ball becomes free, which can be a potential risk of a fault in the device, for example, it can cause an accidental short circuit. The occurrence of the balls is due to inaccurate deposition of solder paste (either due to solder paste misprint or due to excessive amount of the deposited paste), where particles of the solder alloy get under the package when attaching the component [11]. An example of inaccurate application of solder paste is shown in

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

**Figure 12b**. The solder alloy particles partially agglomerate under the component package during reflow, and the component's package squeezes them out of its side. This phenomenon is illustrated schematically in **Figure 13**. If the error occurs regularly during mass production for a specific group of components, it is necessary

*Schematic representation of the principle of balls forming next to the component's package: (a) solder paste deposited on solder pads (b) mounting the component (c) during reflow particles of solder paste partially* 

*(a) Solder alloy balls occurring next to the component's package. (b) Inaccurate deposition of solder paste with* 

The tombstone effect (or Manhattan effect, drawbridging or the Grabstein effect) is a phenomenon which is characterised by one of the sides of a small SMD component (typically in a 0805, 0603, 0402 and 0201 package) lifting up during

Tombstone effect is caused by an imbalance of wetting forces during the reflow process [12]. This can be caused by unequal amount of solder paste applied to the connecting pads, differently sized soldering pads, eccentrically mounted component, different wettability of soldering pads, a different time of solder melting on each side of the component, etc. or by upward push by solvent vapours from flux during an asymmetric reflow process [13]. The effect of the wetting force, or

The frequency of the tombstone effect is also influenced by the reflow technology used. The feedback from industrial practice says that this effect is more frequent in vapour-phase soldering technology. This has been experimentally verified and presented in the publication dealing with tombstone effect [14, 15]. Currently work is being done on a more detailed explanation of the cause of the higher occur-

to modify the dimensions of apertures in the stencil.

*agglomerate (d) a ball forms next to the component's package.*

reflow. A photo of the tombstone effect is shown in **Figure 14**.

upward push force from solvent vapours, is depicted in **Figure 15**.

rence of the tombstone effect in vapour-phase soldering.

**9. Tombstone effect**

**Figure 12.**

**Figure 13.**

*regard to the solder pads.*

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

**Figure 12.**

*Welding - Modern Topics*

**7. Black pad effect**

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

The black pad effect is a characteristic for Ni/Au surface finishes, where Ni contains higher amount of phosphor. During the Ni/Au surface layer creation, the nickel layer is covered with a thin layer of gold; this plating process may lead to corrosion of the nickel surface. The final Au coating can provide good wetting for the solder alloy, even though it has an oxidised Ni-P layer under it. Another cause of the black pad effect is the solder pads reacting with a lead-free alloy with a higher tin content at a higher temperature (longer reaction time). This reaction produces a thicker layer (rich in phosphorus) on the interface, which has a defective structure (microfractures, microvoids). Due to the black pad effect, the soldered joint is considerably weakened mechanically and ultimately will break the conductive connection between the component's terminal and the soldering pad. This fault is very difficult to detect; thus it may occur on devices that have passed output control tests and have already been sent to market (**Figure 11**).

The presence of balls of solder alloy next to the package (solder beading) is an error that is easily detectable by optical inspection methods. An example of balls next to the component package is shown in **Figure 12a**. The device's reliability is compromised in the event that the conductive ball becomes free, which can be a potential risk of a fault in the device, for example, it can cause an accidental short circuit. The occurrence of the balls is due to inaccurate deposition of solder paste (either due to solder paste misprint or due to excessive amount of the deposited paste), where particles of the solder alloy get under the package when attaching the component [11]. An example of inaccurate application of solder paste is shown in

often have different coefficients of thermal expansion.

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**8. Solder beading**

*Photo of black pad effect after stripping off the immersion gold layer.*

**Figure 11.**

*(a) Solder alloy balls occurring next to the component's package. (b) Inaccurate deposition of solder paste with regard to the solder pads.*

#### **Figure 13.**

*Schematic representation of the principle of balls forming next to the component's package: (a) solder paste deposited on solder pads (b) mounting the component (c) during reflow particles of solder paste partially agglomerate (d) a ball forms next to the component's package.*

**Figure 12b**. The solder alloy particles partially agglomerate under the component package during reflow, and the component's package squeezes them out of its side. This phenomenon is illustrated schematically in **Figure 13**. If the error occurs regularly during mass production for a specific group of components, it is necessary to modify the dimensions of apertures in the stencil.
