Dear Richard,
In general PCB fab house will tweak the thickness of dielectric and resign
thickness to achieve the targeted impedance.They also look at the copper
percentage used at appropriate/adjacent layers to achieve this.To meet the
impedance they fix the material with respect to application used,trace and
copper thickness are fixed at design level by designers and the only option
for fabrication house to tweak the thickness of dielectric used.
This all upto my knowledge and i got the information from my fabrication
house.Let me know if any come across any different points.
Regards,
Praveen
www.convora.co
On Sun, May 29, 2016 at 6:33 PM, Richard Allred <richard.allred@xxxxxxxxx>
wrote:
Greetings,
I am aware that typical PCB manufacturers usually guarantee some impedance
target (+/- 10 or 15%) for high speed traces and that they may use any
number of manufacturing controls to achieve this. The result is that the
only way to know the geometric dimensions of a given sample is to
cross-section it.
What I am interested in is, what kind of variation can be expected in the
effective dielectric properties due to the PCB manufacturers tweaking of
the glass/resin ratio and the geometrical variation? Is anyone aware of a
published study that reports this?
Kind regards,
Richard Allred
www.SiSoft.com
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