Thanks Wayne for the reply.



We use Polar speed stack for impedance calculations. Our query was basically to more accurately determine the dielectric thickness between the layers which will influence the impedances, especially the differential impedances. The copper thickness and the copper area will have a bearing on that. It is just not ground alone. When there are signals wherein the copper area is less, more resin goes into fill the gaps between the tracks which might reduce the dielectric thickness between the layers. While in a ground layer, as there is nothing to fill, the dielectric thickness would be relatively higher.



Hope this gives a better picture on our concern



Regards



Pradeep





From: Wayne Thayer [mailto:[log in to unmask]]

Sent: Wednesday, May 24, 2017 7:32 PM

To: TechNet E-Mail Forum; Pradeep Menon

Subject: RE: Copper area for impedance calculations



Greetings Pradeep-



What impedance formula are you using? For traveling wave impedance, the common formulas don't have copper area in them. (They do have width and thickness, so you could calculate area, but your context seems to be the copper area on something like a ground plane)



Wayne Thayer



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Pradeep Menon

Sent: Tuesday, May 23, 2017 9:19 PM

To: [log in to unmask]<mailto:[log in to unmask]>

Subject: [TN] Copper area for impedance calculations



Dear All



Wanted a little more clarity on the copper area that is usually considered for inner layers while calculating impedance. Is it copper area in individual circuit or copper area for each layer after panelisation. There can be instances wherein the two can have quite a good difference which may result in dielectric variation and hence the impedance calculations also.



Can you please suggest what is the commonly followed practice.



Rgds



Pradeep

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