[SI-LIST] Re: 6 Layer PCB
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Jon Bean <jbean@xxxxxxxxxxxxxxxxx>
- Date: Sat, 31 Jul 2010 09:19:41 -0700
Jon, there isn't a single answer. In order to get to a particular
impedance, you need a combination of:
1. Transmission line configuration: microstrip, symmetric stripline, or
offset stripline
2. Material properties of your dielectric: primarily eR.
3. Acceptable range of trace widths.
4. Acceptable range of dielectric thicknesses.
Skinnier traces over thinner dielectric will allow you to pack more
traces per linear inch at a given amount of cross-talk. As microstrips,
they will also emit less. But, they will have more etching variability,
and more skin loss than wider lines of the same impedance. You need to
know what matters to your application and make some decisions.
My first impression here is that you would do well to get a copy of a
good book on signal integrity. For this particular topic, Eric
Bogatin's "Signal Integrity Simplified" is probably a good choice as
Eric does a very nice job of demonstrating "control knobs", ie how over
a limited range changing one parameter such as line width affects
performance parameters such as impedance and loss.
Second, search for "impedance calculator". There are many free
impedance calculators on the WWW. Most are pretty accurate for common
stripline configurations, but many can be pretty far off with
microstrips. Rogers has one of the more accurate calculators for
microstrip. Those will get you reasonably close to a configuration that
works for your needs. Then discuss your proposed stack-up and line
widths with your board fabricator. Virtually all of the better board
fabricators have field solvers that yield precise answers. Your board
fabricator will also be able to help you define a stack-up using
specific materials. If you want repeatable results it is very important
to follow Lee Ritchey's advice on this topic and specify your stack-up
calling out the specific laminates in each layer. Since you aren't an
expert, using a better board house to help you define that stack-up is
probably the easiest and most reliable way to go.
Steve.
Jon Bean wrote:
> Hi
>
>
> Can anyone give me a stack up for a 6 layer pcb of 1.6mm thickness?
>
> I know the layer order I want to use but require the dielectric thickness to
> give 50 ohm signals on the signal layers. Ideally I would like the signal
> width to be no more than 0.2mm on those layers and using ½ oz copper for the
> signals and 1 oz for the planes.
>
>
>
> Top
>
> Gnd
>
> Sig
>
> Sig
>
> Pwr
>
> Bottom
>
>
>
> Thank you
>
>
>
> Jon
>
>
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
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