[SI-LIST] 18um vs. 36um thick copper (Was: Re: 1 oz vs. 1/2 oz cu)

Hi Greg and others,

Inchauspe, Greg E wrote:
> I'm working on a 18 layer board stack-up and was wondering what the =
>  trade-offs are between going with 1 oz Cu signal layers and =BD oz 
> Cu = signal layers.  All power and ground are 1 oz Cu.

By taking the risk to fire off yet another Metric vs. Imperial thread I
will ask: Do you mean 18um thick copper when saying 1/2 oz Cu and 36um
thick copper while saying 1 oz Cu?

Assuming balanced stack-up, main limitations are with track/gap
requirements. For 0.1mm tracks, usage of 36um copper may be out of
question (depends on manufacturer) or not recommended due lower yields
while for 0.2mm traces there's not much difference. For outer layers,
one also needs to consider effects of plating.

This is from manufacturing point of view. As far as SI is concerned,
inductance of a trace (and thus impedance) will change, again effect
depends on trace width. As you're building stack-up at moment, this
seems not to be a problem. I also assume that increased resistance due
skin effect is not a problem. Thou I may be wrong as I don't know
anything more about your board or considered frequency range.

Regards,
Indrek

-- 
  Indrek Rebane           |      Borthwick-Pignon
  Electronics Engineer    |    Tartu Science Park
  Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
  Fax:   (+372) 7 383 041 |               Estonia
  indrek@xxxxxxxxx        |         www.bps.co.ee


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