Prevent Tombstoning During SMT Circuit Board Manufacturing
Tombstoning is a PCB defect that occurs when one side of a component rises up during the soldering process. The condition is caused by different wetting speeds and imbalanced torque. It can also be exacerbated by thermal capacity differences between the welded materials. You can prevent tombstoning by ensuring that the traces that connect to the pads are of equal width and that they are connected in a similar orientation. You can also mitigate variable heat dissipation by assessing the thickness of your PCB’s inner copper layer.
Surface mount components are a popular choice for electronic circuit boards because they have lower mounting costs and are smaller than through-hole devices. However, the fabricated boards must be soldered in order to function. To do this, solder paste is applied to the printed circuit board using stencils. After the solder paste is placed, the fabricated board is heated in a reflow oven. During this process, the heat causes the paste to melt and flow, which then attaches to the component’s leads. The resulting solder connection is called a termination. If the termination is weakened, it will not be able to support the weight of the component.
The most common cause of tombstoning is incorrect pad dimensioning. It’s essential that you double-check your PCB’s layout before production begins to ensure that all of the pad dimensions are correct. You should also ensure that the pads are positioned so that they’re not too close together. This will decrease the likelihood of wicking or solder escape during the reflow process.
How to Prevent Tombstoning During SMT Circuit Board Manufacturing
Another common reason for tombstoning is oxidation of the pad or terminal. Oxidation can increase the wetting time on one side of the terminal, which allows the solder to build up a pulling force and lift the device. This can be prevented by ensuring that the pads and terminals are clean and free of oxidation. In addition, you should avoid using nitrogen in your reflow oven as this can exacerbate the problem.
Changing your PCB’s finish can also help reduce the chance of tombstoning. Traditional hot air surface leveling (HASL) finishes are cheap, but they can make the surfaces uneven, which affects how well solder sticks to them. You can opt for immersion tin, OSP, or immersion gold to achieve a more even finish that’s less prone to tombstoning.
Poor chip placement can also lead to tombstoning. If the PCB has multiple components with the same terminals, the ones that are closer to each other will have a greater chance of melting at the same rate. This may result in them rising at the same time, resembling a tombstone.
Other possible causes of tombstoning include chemical inconsistencies in the solder, the difference between leaded and lead-free alloys, and the thickness of the PCB’s solder mask. This defect is not easy to fix, but it can be prevented with careful planning and a good manufacturing process. By avoiding these problems, you can prevent tombstoning during the smt circuit board.
