How to Prevent Tombstoning During PCB Assembly Near Me

Prevent Tombstoning During PCB Assembly Near Me

Tombstoning is a problem that occurs when one end of an SMT chip component rises from the pad after the reflow process but remains unattached to the circuit board. It’s an assembly defect that is often associated with poor wetting of the solder paste on the component pads. However, it can also be caused by uneven forces exerted during the reflow process.

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The most common cause of tombstoning is insufficient wetting of the solder paste on the pad. This can be due to the shape of the pad, which may have a radius that does not allow the paste to fully wet. It could also be caused by a large reflow oven that does not distribute heat evenly throughout the batch, causing uneven wetting. Another possible cause of tombstoning is the use of a non-eutectic solder alloy, which has a larger plastic range between solid and molten states than a eutectic alloy. This can lead to one side of the pad melting faster than the other, resulting in the side with less melted solder lifting the component.

How to Prevent Tombstoning During PCB Assembly Near Me

In addition to a good printed circuit board, the best way to prevent tombstoning is to use the right CAD footprint models and follow industry best practices for pad design. The pads on a chip component must be properly sized and the proper gap and overlap should be defined between the pad and the solder paste. It is also crucial to ensure that the copper, solder mask and legend layers are not higher than the pad height. This will ensure that the wetting of the solder paste is optimum.

It is also important to choose the correct paste formulations for your specific application. There are many manufacturers that offer pastes specifically designed to minimize or eliminate tombstoning. The choice of a good contract manufacturer is also very important, as they should have the right CAD tools to create the appropriate footprints and follow best practices for the design of the board. They should also be able to provide the best routing recommendations and a consistent build quality with their automated placement equipment.

Finally, the reflow oven used to reflow the solder should be sized and configured to provide even heating and cooling. A high-quality reflow oven will help to reduce the likelihood of tombstoning by providing adequate time for the molten solder to completely liquefy on both sides of the pad. In addition, the reflow oven should not be over-loaded and should be kept at a stable temperature to prevent the formation of hot spots that can cause tombstoning. Finally, the use of nitrogen in the reflow oven is not recommended as it can contribute to tombstoning by speeding up the melting process.

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