Via in Pad Common in Modern PCBs
There are three main types of vias used on PCBs: Through hole (standard vias) buried vias, and via in pad. Each type has different attributes and functions, contributing to the optimal performance of circuit boards or electronic products. However, a via in pad might be necessary when other methods are not suitable due to the size and pin-count of the board. This method increases cost and PCB turnaround time, but it can help reduce the overall inductance of a high-speed circuit.
via in pad, also known as capped vias, is a fabrication process that allows solder paste to be stenciled onto the pads of surface mount devices without the fear of it wicking into a via and shorting out the net. This is especially useful for fine pitch BGAs, where the volume of solder that can be stenciled on to the pads and in the BGA balls is small, making it difficult to escape traces with traditional routing methods.
The key difference between standard plated vias and capped vias is that the latter are filled with epoxy and electroplated over, whereas the former are simply drilled. A PCB fab must then take additional steps to cap and fill these vias, which adds to production costs and increases the chance of mistakes during assembly. The best way to avoid these issues is by using a design tool that has the option of automatically capping and filling these vias, which can be done with most EDA tools.
Is a Via in Pad Common in Modern PCBs?
Adding this feature to your schematic and PCB designs will not only make the job of routing your circuits easier, but it will also help to decrease inductance. By decreasing the trace length and removing solder from the circuit, this method can significantly reduce the amount of inductance that is generated by the circuit board.
Another advantage of capped vias is that they are more tolerant to thermal stress than standard plated vias. This is because the epoxy that is used to fill these vias has a lower coefficient of thermal expansion (CTE) than the laminate on which the circuit board is manufactured. This means that the via will not be pulled out of the pad and into the circuit board during reflow, causing a short.
The primary drawbacks of a via in pad are that it can introduce additional cost and delay to the PCB production process, but it can also increase the risk of thermal stresses on components. To minimize these risks, it is recommended that you use other DFM / DFA techniques to route your circuit board, and only consider via in pad when there is no alternative. If you do decide to use this technology, we recommend that you limit the number of instances and try to make the vias as small in diameter as possible, and that you use blind vias when they are available. In addition, it is a good idea to consider other options like the Dog-bone fanout when possible.
