rinted Circuit Board (PCB) Soldering
Tombstoning is a common problem that can lead to incomplete solder joints in printed circuit board pcba. This is a very serious issue that must be addressed and prevented at all times to avoid the costly consequences of this defect. The good news is that tombstoning can be prevented in multiple ways, starting right from the design stage of a new PCB project.
A common cause of tombstoning is when a component has an incorrect pad size. This can happen when the original plan for a particular part is altered during the layout or printed circuit board pcba design phase, and this change causes the pads to be too small. When this happens, the solder can’t attach to the pad and it lifts off the end of the component, resembling a tombstone.
Another common cause of tombstoning is uneven thermal capacity between a component’s pads. This can occur if the pads are made of different metal alloys or if one side of the pad is exposed to higher temperatures than the other. The difference in the thermal capacities can cause the wetting process to be out of sync, leading to the part lifting off from the pad.
How is Tombstoning Prevented During Printed Circuit Board (PCB) Soldering?
An easy way to avoid this issue is to use a high-quality stencil printer for your PCB production. This type of equipment ensures that all the solder paste has a uniform amount of coverage over all the pads. It also minimizes variations in the paste volume, ensuring all the pads are properly sized and evenly heated during the reflow process.
Other common causes of tombstoning include a poorly aligned component or bad placement on the PCB. This can occur when a component is not aligned with its pads correctly or when it is placed too close to other components. Poor placement can also cause the pads on a component to heat up and cool down at different rates, leading to the wetting process being out of sync.
Incorrectly sized copper areas on the inner layers of the PCB can also cause tombstoning. This is especially common when the thickness of the copper area is too large for the pad or pads it covers. This can result in a lack of even heating during the wave or manual soldering process, which leads to unbalanced wetting.
Finally, the condition can be caused by a number of other factors that are not directly related to the wetting process, such as oxidation on the pad or component terminals or different weight distributions on the pads. For example, thicker SMD devices are more prone to tombstoning than thinner ones because they have larger terminal surfaces that can be pulled when the solder melts faster on one side than the other. This can also happen if the component is warped, which can create an imbalance in the force exerted on the component when it wets and solidifies. This makes it important to have a well-tuned assembly process and a good understanding of the physics involved.
