We find from our vendors that the difference in cost between 6 layers and 8
layers is pretty insignificant. If you use 8 layers, things get much better:
This gives you a buried capacitance layer (good to very high frequencies)
for the power, and at least 3 of the routing layers are referenced
(impedance-wise and return current mirror-wise) to primo clean ground
planes. The fourth routing layer (third from bottom) is at least some
greater distance from the noisy power plane.
Bay Networks, Inc
At 09:17 PM 12/5/97 +1100, you wrote:
>We are designing a system which is derived from futurebus using the 2mm amp
>connectors. It is a synchronous time slice bus running at 12.5MHz. We are
>planning to distribute the clock from the centre of the backplane with each
>board having its own clock. Signal pins are alternated with ground pins
>across the connector. We are also using Futurebus transceivers for the
>address and data because of the control they provide.
>We are now considering how the backplane is to be laid out. One question is
>layer stackup. We need at least 6 layers. At a first pass we are
>very thick core
>Would you care to comment on these please given that we also need to have
>fairly uniform trace impedances
>I do not want alternating signal/plane layers as we will have some
>difficulties getting the backplanes manufactured.
>Australian Broadcasting Corporation