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How to Prevent Tombstoning During PCB Assembly

Prevent Tombstoning During PCB Assembly

Tombstoning is an undesirable phenomenon that occurs when surface-mount components are partially lifted from a pad and stand upright, resembling a tombstone. The problem can cause circuit boards to fail or display erratic behavior. Thankfully, this defect can be prevented with careful planning and precise manufacturing processes.

Tombstones are caused by an imbalance in pulling forces between the component’s pads. Different metal alloys in solder paste melt at different temperatures, so one side of the component may pull more than the other. This can also occur if the component is attached to pads with different surface characteristics, such as etched or bare copper. Another common cause is an uneven reflow profile, which can result in thermal stresses that shift the component to one end of the board.

In order to minimize the risk of tombstoning, it is important to use a reliable PCB assembly manufacturer. They will employ quality inspection techniques that include visual and automated optical inspection to identify defects like this before they become a problem during production. They will also ensure that their reflow ovens are properly calibrated to match the needs of each board type and component type.

Other causes of tombstoning include mismatched pad sizes, incorrect deposition of solder paste, and poor positioning of the component on the board. The pad size should be the same for both terminals of a surface-mount component, and the space between the pad and the component should be equal as well. Insufficient or inconsistent paste deposition can lead to an imbalance in pulling forces, which could cause one terminal to lift from the pad during reflow soldering.

How to Prevent Tombstoning During PCB Assembly

The thickness of the solder mask can also affect a PCB’s sensitivity to tombstoning. If the mask is too thick and rises above the pads, it can cause them to heat unevenly during reflow. This can result in the thinner area on one side of the component heating up more than the other, causing it to lift from its pad. The resulting tombstone will cause an unconnected electrical connection and can render the entire component useless.

PCB tombstoning is a frustrating and often costly issue, but it can be avoided with good design practices and proper PCB assembly. By evaluating the pad size and shape, ensuring that the footprint construction and routing follow DFM guidelines, and using precise reflow ovens, you can avoid this costly problem. By paying close attention to the small details, you can wipe out tombstoning and prevent it from disrupting your next project.

Tombstoning is a common defect in pcb assembly us where one end of a surface-mounted component lifts off the pad, resembling a tombstone. This issue typically arises during the reflow soldering process and can significantly impact the reliability and performance of the final product. Preventing tombstoning involves a combination of design considerations, process control, and material selection. Here are some key strategies to prevent tombstoning during PCB assembly:


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