BGA Bond out lengths
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- This topic has 4 replies, 3 voices, and was last updated 4 years, 3 months ago by
Neeraj Dantu.
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- June 27, 2020 at 9:34 am #10309
I’m trying to match the lengths of PCB traces for the high speed signals.
But simply matching the external length does not take into account any internal bond-out length difference.
Do you have any data on the BGA bond out lengths for each pin.This is more important for the high speed signals, such as USB & DSI.
But also for matching external Ethernet PHY signals on the normal port pins.Regards,
Ian. - July 2, 2020 at 10:51 am #10332
Ian,
You don’t have to worry about SiP internals. If you match the trace lengths from the SiP balls to the external devices, you should be able to achieve optimal performance.
Best,
Neeraj
- July 3, 2020 at 7:15 am #10334
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. - July 27, 2020 at 9:10 am #10440
- July 28, 2020 at 10:14 am #10449
Ian & Tobias,
We apologize for the delay in getting you a response to this question. Please see below for the requested data for the high speed buses below:
Signal Name Trace Length(um) Differential(um) DSI DSI_D1_N 14889.249 387.191 DSI_D1_P 14502.058 DSI_D0_N 15464.216 927.249 DSI_D0_P 14536.967 DSI_CK_N 15307.686 -410.481 DSI_CK_P 15718.167 USB1 USB1_N 15379.511 559.346 USB1_P 14820.165 USB2 USB2_N 18453.704 572.107 USB2_P 17881.597 Note that all lengths are in microns.
Best,
Neeraj
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