Through-hole or SMT for signal integrity

Jun 19, 2012 2 Replies
A

I am designing a system where point-to-point differential connections (SGMII) are routed via a connector on a backplane. I am wondering whether the SMT or through-hole connector is the better choice wrt signal integrity. With the number of signals we need inner signal layers will be needed. So I either can contact the signal layer from the through-hole connector directly or I have to use vias. Vias have smaller diameter so my power planes are less perforated, but would require more "turns".



For PCI Express on PC mainboards I have seen only through-hole but this might be due to the insertion/extraction force for the heavier add-on cards.



Andreas


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C

are routed via a connector on a backplane.

wrt signal integrity.

directly or I have to use vias.

require more "turns".

be due to the insertion/extraction force for the heavier add-on cards.

It all depends, of course...

IF you are doing blind vias, so you only build the via from your signal layer directly to the surface where you have your SMT connector, and you have characterized the launch of your signal from the trace to the pad to the connector, then THEORETICALLY, you can get better integrity than a TH connector. What is your clock speed on your SGMII bus?

Charlie

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J

are routed via a connector on a backplane.

wrt signal integrity.

directly or I have to use vias.

require more "turns".

be due to the insertion/extraction force for the heavier add-on cards.

SGMII is "only" 625 MHz, so either would work. Surface-mount would have a bit better signal integrity, avoiding some thru-hole pin capacitance, but probably not enough to matter.

We did PCI Express gen 1 (2.5 gbps/lane) with a surfmount connector and some vias in the signal paths. Worked fine.

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John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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