V5 - differential impedances not precise
When calculating the impedance of the above design I noticed that on the top, layer 3 and bottom layers that there appears to be paired tracks in which don’t match the spacing specified on the supplied construction (8.2 thou track & 5 thou spacing). Please could you take a look at Impedance(top).PNG, Impedance(layer 3).PNG, Impedance(bottom).PNG attached and confirm if the highlighted tracks are the paired tracks in which are to be impedance controlled?
Also the construction states that the impedance required is to be 100 Ohms however if we are to followed the supplied files our software is calculating that the impedance would be 89.71 Ohms on the top and bottom track layers and 79.16 Ohms on layer 3. Our software is calculating that in order to meet the 100 ohms impedance required that on the top and bottom track layers we would need to change the finished track widths from 8.2 thou tracking with 5 thou spacing to 7.1 thou tracking with 6.1 thou spacing and on layer 3 we need to change the 8.2 thou tracking with 5 thou spacing to 5.65 thou tracking with 7.55 thou spacing. Please could you verify if we are ok to change these track widths in order to meet the 100 Ohms impedance requirement?
See attached images.
Reported by Graeme Parker <graeme.p@sundance.com> on 6/12/17.
- Erik replied for production: "These lines are not very critical. Please produce the cards using the original Gerber files. There is no need to modify the trace width".