About DDR3 Length Matching

[MertkanTuna]

Hi ALL;

I am designing a HDI circuit which has two DDR3 ram routed by fly-by. I have a problem in my mind while i am matching RAMs address tracks' length. Some of address tracks were routed from L12 to L3 and another ones from L12 to L10. I always used equal number of through hole vias for layer changing. My question is, should i consider via distance between L3 and L10 (X) when i route address tracks for length matching.

Thanks for your interest.

[robertferanec]

- Yes, length in VIA needs to be considered.

PS: In reality, length matching is based on propagation delay (based on time), but if some specific conditions are met it can be simplified to: make the length of tracks similar/same (based on distance). If you are routing signals what are from the same group and need to be length matched, you need to know what you are doing if you are not going to route them the same way (the same way means, they all go through the same layers).

[MertkanTuna]

For example, let's assume that we started routing from L12 and putting TH Via end of signal, when I route the signal from L10, should i base my distance from L12 to L10 while matching the signal lengths, or should I think the signal travels all TH VIA?

[robertferanec]

Only L12-L10 is important (only the distance the signal needs to travel between the pins)

[Paul van Avesaath]

i calculated that manually once in excel, butif you keep the layerchange the same in your "set " of signals te same, it is ok and you do not need to take that into account.. mind you that was before xSignals.. is that not an option for you to use?

[MertkanTuna]

Thanks, Robert.