I’m working on a 4 layer PCB breakout for WT41u-E which has both a UART and a USB 2.0 interface (Full speed 12Mbits/s)
I’m thinking about ordering from JLCPCB, see their stackup.
Now the pads on the WT41 looks randomly placed… the USB+ and USB- have an orientation which require the traces to move through the inner module area, otherwise they cross each other (see image)
I’ll be very thankful if you’ll help with the following:
How can I match a 90 ohm impedance on the USB differential pair? The traces start on the first layer, go through an ESD protection IC then through resistors (which should do the matching, according to the WT41 datasheet), then through vias to the forth layer and back to the first and only then they are connected to the USB pads of module…
Is it ok to route the USB traces in the 4th layer? the 4 layers are 1:Signal 2:GND 3:Power 4:Signal
Is it ok to place the VIAs and the traces under the module?
Bonus question - the UART pads are also randomly placed, how bad is it if the traces length are not the same?