Large Via in Pad

Bittele, a turnkey PCB assembly specialist, knows a great deal about Design for Manufacturability, especially where it concerns large vias in pads. We understand the versatility of via in pad design, as well as the risks involved with it; surface mount component assembly can become a serious challenge in HDI circuit board design, where solder may wick away from a component’s contact and cause a poor solder joint. However, a new set of problems arise from the use of large vias in pads.

The ideal use for large vias in pads is for heat dissipation of SMT semiconductor chips, especially those that withstand higher current than other components on the PCB. Typically, such components will have a wide surface area on the underside of the component’s package, meant for soldering onto a grounded pad on the board for the sake of heat dissipation. In those cases, large vias in pads can be arranged in a grid pattern, as through-hole vias, to not only increase the surface area of the heat-dissipating pad but to allow for heat to escape from the opposite side of the board, which also helps in cooling.

However, large vias in pads are not ideal for SMT component pads, especially those meant for semiconductors with a fine-pitch footprint and BGA components. If a via’s diameter is 0.25mm (10 mils) or larger, it would be best to move that via out from the pad and onto a different location of the PCB, or else the via will interference with solder adhesion. If it is not possible to move the via away from the pad, it would be best to reduce the diameter of the via, so that it can be moved further from the component’s footprint or treated with a filler material. Otherwise, the solder will flow away from the component, into the via and cause a poor solder joint, which will lead to a failure during functional testing.

The final issue to consider is the number of components prone to heat up in the circuit board, with respect to the board’s warp and twist tolerance. If there are too many large vias in pads, the PCB will become more prone to damage if bent. In those cases, it is best to avoid using components that rely on vias for heatsinking when possible, or else to consider a thicker board material. Of course, as with any other project involving vias in pads, PCB fabrication costs and lead time will increase, depending on the complexity of circuit board production, type of material and technical requirements involved in treating vias in pads. However, this will vastly improve the quality of the final product and ensure correct functionality.

For further information on how to better adjust your PCB designs, or for any other inquiries about our services, please contact us; our team of experts is more than happy to assist you.

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