Differential Pair Net Length Matching for 4 Pads
I have been doing a best effort to properly research differential pair routing, but I am hung up on couple small details. For background this is a USB 2.0 diff pair with a USB-C port on the top and an RP2040 on the bottom. Next to the connector I have a TPD2EUSB3A ESD IC, and next to the RP2040 are two 27 ohm termination resistors. I have a trace width of 0.18, spacing of 0.12, and height above ground plane 0.2104mm. I may need to tweak this further as I just found that I was using an incorrect copper weight on the inside layer. Zdiff on this version is ~96. That should not affect my questions however.
The main question I have, is when calculating my net trace length for the D+ and D- lines, should I include the jumper between the D+ pads that is underneath the footprints, as the signal would reach the first D+ pad before it hits that trace? Likewise, the jumper for the D- pads is symmetric, so the signal would have the same distance to travel from the start of the fork. Should I use 1/2 the length of the trace between the two D- pads?
Also for trace width and spacing, I need to start somewhere picking either one of these values first to base calculations on. Is there a good rule of thumb or best practice for choosing these values to start with? Right now I am using a trace width equal to the width of the RP2040 pads.
Are there any other glaring issues that stand out with this design? I know I am probably overthinking this for only a USB 2.0 line, but I would like to build proper habits and knowledge early on.
