How to Prevent Tombstoning During Electronic Component Assembly

Prevent Tombstoning During Electronic Component Assembly

Tombstoning is a well-known issue that can negatively affect the quality and performance of electronic components. This phenomenon occurs when a surface mount component stands upright on the PCB during the soldering process, giving it the appearance of a tombstone. It is a serious problem that can lead to open circuits and even board failure. Therefore, it is important to understand the causes, prevention, and mitigation of tombstoning.

One of the most common factors that can cause tombstoning is a mismatch between the pad size and solder ball size on a SMT component. When this happens, it can result in a solder ball that is too small to provide sufficient anchoring force for the component. This can cause the solder to wick down the pad and then lift the component from the board.

Another factor that can contribute to tombstoning is the use of different copper thicknesses on the same layer of a electronic component assembly. When this occurs, it may cause uneven heating during the wave soldering process. This can also create a thermal stress that can cause a part to shift and then lift off of the pad during the reflow process.

If a PCB’s pads and terminals are coated with an oxide layer, this can also slow the wetting process. As a result, one side of the pad or terminal can liquefy more quickly than the other, and this can cause the solder to pull that end of the component upward during reflow.

How to Prevent Tombstoning During Electronic Component Assembly

Pad geometry and shape can also impact the likelihood of tombstoning. If the pads of a SMT component are of different sizes or shapes, it can cause an imbalance in the wetting forces on the terminations. This can lead to the component standing upright on the pad.

It is also important to note that the pads of SMT components must be large enough to allow adequate anchoring forces during reflow. This is especially critical for high-aspect ratio SMD packages.

The best way to prevent tombstoning is by using a careful design process and selecting the proper SMD package types. Choosing smaller packages with larger pads can reduce the risk of tombstoning. It is also important to use a gentle ramp rate during reflow, as this can help to mitigate the effect of sudden stresses that can cause components to lift off of the pad.

In addition, it is a good idea to use a PCB finish that can improve wetting. This can include immersion tin, immersion gold, or others based on your design needs. Lastly, it is recommended to use in-line inspection and other process feedback methods to detect and respond to issues like tombstoning before they can cause serious problems. By addressing these issues, tombstoning can be minimized and the overall quality of electronic products manufactured can be improved. This will help to decrease the need for post-soldering rework and other costly production issues. To learn more about how to prevent tombstoning and other assembly issues, contact the experts at APX for additional information.

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