Ask Me Anything about BGA Fanout

Join our next Ask Me Anything about BGA fanout where you can ask us questions on:

  • Best practices for BGA fanout
  • Handling high pin-count BGAs
  • Avoiding common pitfalls in routing
  • And much more!

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Please, note that this is not a live event. We ask you to post your questions on the forum before the deadline.

How do you decide between dog-bone fanout and via-in-pad fanout for a design?

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Does Sierra have recommended trace W/S for different BGA pitch sizes?

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When does mixing dog-bone and via-in-pads becomes a problem or a reliability risk ?

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Fanout will be decided depends on space constraints and pitch of the BGA.

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Usually if it’s impedance trace, then we need to maintain exactly same from impedance table from stackup. For other non-critical signal, we can maintain depends on the fanout techniques. Mainly we need to consider minimum trace width and spacing as per copper thickness to meet production capabilities.

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Yes via-in-pad design needs extra care in assembly and processing step will be more in production like filling or capping the via to ensure the pad is functional for soldering but dog-bone structure doesn’t needs all these care in manufacturing.

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If you have via-in-pad somewhere on the board, is there any advantage to using it only there, or is it “once you need it anywhere, you might as well use it everywhere on that board”

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No use via-in-pad wherever needed, it will increase the production cost, turn time and sometimes soldering issues or voids in the pads.

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If you are already using at least one via-in-pad, how does a second (or 400th) increase turn time? Is the filling and planarizing done individually, and the per-hole time is noticeable compared to the setup time?

Similar question for the cost, soldering issues, and voids … is it just that with via-in-pad is less reliable than pad-trace-via and with 400 holes there are 400 places for something to go wrong, or is there some sort of “special attention” needed that gets diluted with too many relevant holes?

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You are right, filling and planarizing is done at one time, so filling one hole or all the holes for that hole size does not matter.
The cost is different for the filling types like Non-conductive fill and plating over, Conductive fill, copper fill etc.,

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