LED Via in Pad

Vias in pads can be tremendously useful for PCB designs where space is at a minimum, heat dissipation is required or where inductance control is paramount. Here at Bittele, a key part of our turnkey PCB assembly services is our Design for Manufacturability and Design for Assembly services. And we understand the challenge of via in pad design for small-profile components (such as LED and passive components) because of the many PCB assembly issues to consider, including the vias’ diameter measurements, SMT component assembly and the presence of untreated vias, where solder may wick away from a component’s contact and cause a poor solder joint.

If, for example, a small-footprint surface mount LED will be installed, consider the footprint of the LED, with respect to the placement of vias in pads. If the PCB is not an HDI board design, it is highly recommended to move any vias to a different location on the board, so that they will not interfere with soldering the LED onto the board. However, if the board is an HDI board, consider placing the via off-center on the pad and away from the LED’s contact, to maximize solder adhesion between the pad and the LED.

The placement of vias can also be impacted by their diameter. If the via is a laser-drilled micro via, then the via can be placed on a pad may, where it will not impact solder adhesion severely. But if the via’s diameter is 0.25mm (10 mils) or larger, it will be more difficult to position the via within the pad, causing interference with solder adhesion. The result: the solder will wick itself into the via and away from the LED’s contact, causing a poor solder joint and failure during functional testing.

Aside from reducing the diameter of vias or placing them outside of SMT pads, the key solution to this problem is to treat all vias in pads with a filler material, before plating the surface of each via closed. Depending on the PCB design, the filler material can be conductive (to allow for greater current flow between layers in high current applications) or non-conductive (which is typical of low-current applications). In either case, the LED will properly adhere to the PCB, resulting in a clean connection and proper functionality.

PCB fabrication costs and lead time, however, will increase because of the increased complexity of production, material and technical requirements involved with via in pad treatment. Despite this, especially in instances where HDI PCB design cannot be avoided, this will vastly improve the quality of the product and ensure proper functionality. But in the case where high-density design is not necessary, cost reductions and quicker lead times can be achieved through the placement of vias elsewhere on the PCB.

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 are more than happy to assist you.

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