[iguffick]

Hi Neeraj,

Sorry, but the internal BGA length is just as important as the external length.
The BGA pins are 1mm apart, so even if they came from very close together on the STM die, there is a 1mm difference getting them to the pad.
The same applies to the tracks placed on the PCB. The extra 1mm to get to the matched BGA pad needs to be taken into account.
It’s the total length the matters not just the length of the external PCB track. The external PCB track length should be adjusted so that the total length matches.
This is critical for both USB and DSI.

For example have a look at STs AN5031 en.DM00389996.pdf page 69 and 76. This shows how ST specify the length difference for the normal BGA packages.

It’s not quite as critical for the external Ethernt PHY RGMII signals, but then the difference between used BGA balls can be up to 5mm.

Can you publish the internal BGA lengths used for bond out please?

Regards,
Ian.

[iguffick]

Hi Neeraj,

Thanks for pointing me at that link. I wouldn’t normally use NC pins. But I like background detail that has been checked to ensure use of pins that are definitely NC. A useful technique to avoid micro-vias or via-in-pad multilayer PCBs.

Regards,
Ian.

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