BGA Bond out lengths

[iguffick]

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.

[Neeraj Kumar Reddy Dantu]

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

[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.

[Tobias]

Is there an update on this question?

• This reply was modified 4 years, 10 months ago by Tobias.

[Neeraj Kumar Reddy Dantu]

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

[Author]

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