Via-in-Pad

In these years, engineers starting putting vias directly in the SMT pads for BGA, QFN, and other packaged components during the following advantage.

  • It can help with thermal management.
  • It can help with grounding on high-frequency parts.
  • It can allow really close placement of bypass capacitors.
  • It can make routing easier with fine pitch or Big BGAs.

Contract manufacturer doesn’t like to see the vias in pads.

The vias are left open will cause the solder tend to wick down into the via hole. The larger the diameter, the worse the wicking problem can be. it might end up without enough solder left to secure the component, or even a solder bump on the bottom side of the PCB which could interfere with other components or lead short. Some board house capped or partially filled vias, the caps might pop off due to thermal expansion or out-gassing. Internal air bubbles can migrate up, leading to voids in BGA solder joint.

However, if we can’t re-design the boards so the vias are in between the pads, plug or cap the vias at the board house, nor to use microvias that don’t go all the way through the board. ACME PCB Assembly will suggest you the following way.

Best solution: Have your board fabrication house plug the via and then plate copper over it. usually, the board house will plug with metal or a thermally and electrically conductive epoxy before the final plating steps.

Okay, but still a bit of challenge: Use a micro-via that only goes through one layer of the board. this can still cause some problems. the solder can wick down into the via chamber, but we can enlarged slightly stencil apertures to ensure enough solder stays on the pad.

Not suggest, but not too horrible solution: Cap the underside of the board with solder mask, this will usually stop the solder from completely wicking out, but some time the void is big enough to still suck too much solder off of the BGA and leaving it open.

ACME PCB assembly also doing BGA prototype assembly for customer. We are able to work BGA prototype assembly with or without stencil, and save customer’s prototyping cost.

Please contact us 310-715-1898, or email us if you have any question.

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