Via in Pad Be Problematic
A via in pad allows designers to connect a signal line directly to a component without using a track. This can save board space and reduce parasitic inductance, especially for high-speed designs and interfaces. However, a via in pad can be problematic in some ways and should only be used when necessary.
One of the most common issues with vias in pads is wicking. If a via is too close to a pad or even inside a pad, it can suck solder away from the pad due to capillary action during reflow soldering. This can result in unconnected leads and bad connections on the pcb.
This is why it is important to always cap a via in a pad with solder mask to prevent this from happening. Also, it is a good idea to use non-conductive epoxy for vias in pads so that any outgassing doesn’t break the solder joint on the back side of the board.
Can a Via in Pad Be Problematic?
Another issue with via in pad is that they can be a source of design rule check errors, particularly when the footprint size does not meet the minimum annular ring requirement. In these cases, the via in a pad can trigger routing and escape problems, which could require a rework of the pcb.
If you are designing a PCB with very small components such as fine-pitch BGAs, the only way to route them is with a via in pad. There is just not enough room on the pads for a trace, and even a through-hole via would wick away solder due to the small volume of stenciled solder between the pads and BGA balls. In addition, the BGA pitch is so small that you cannot fit a via between the pads even with a blind/buried via.
For these reasons, many pcb manufacturers offer to use a via in pad option on their fab lines. While it can cause some design issues, such as a higher manufacturing cost and time, it is a great option for a tight PCB layout with very small components. Just be sure to work with your contract pcb manufacturer to understand how these vias will affect your production process so that you can make informed decisions about whether to use them on your next project.
This will ensure that your production runs go smoothly and your product is made as expected. Thanks for reading! If you have any questions about via in pad or any other topic related to PCB layout and design, please feel free to reach out to me. I look forward to hearing from you! –David H. Fenech, CED, EE, PME, SM is the founder and CEO of DA Electronics in Los Angeles, California. He has over 30 years of experience in the electronics industry. He has a passion for helping engineers solve their complex challenges with simple and cost-effective solutions. He enjoys sharing his knowledge of the industry through writing and speaking engagements. He can be reached at [email protected].
