I'm designing a product which will Tx/Rx at 2.4GHz, and I've thrown everything at it to guarantee I pass EMC first time (of course after pre-testing with an SDR). Max clock is 32MHz (ouch), but max signal speed is 7MHz, both traces are 5mm long and under solid RF shields on both sides. All 4 layers of the 0.8mm thick, <25mm diagonal board have ground pours via-stitched together across the perimeter of all 4 layers and every IC has at least 2, 0402 capacitors of different values to decouple the s**t out of the 10mW of total operating power of the device.
Obviously I will fail the EMI testing the first time, losing thousands despite everything I try to do.
I got cornered by design limitations and was forced to ground the micro-USB shield because it wouldn't fit otherwise. Obviously as soon as they plug in the USB cable to charge it, the thing will start screaming my mistake across the galaxy as the signals creep in (at least I decoupled all the data and power lines on the USB?) According to reply #1 on
https://www.eevblog.com/forum/projects/usb-shield-ground-connection/ it's actually okay to ground the shield, but the topic of shielding seems to be a matter of opinion. Big device, isolate it, little fella, leave it grounded. It's not too late to change it, but can I just use a special isolated/shielded USB cables during the EMC testing to hide the non-conformity there, or will they use metrology grade micro USB-B connectors? Do they even test for conformity during charging? The charging circuit itself is just a linear circuit without switching, but without a rated PSRR like an LDO would have, I'm afraid that will just be a conduit for stray signals with the grounded shield making things worse.
Gosh I hope they just toss it on the rotary platform and measure the thing instead of actually testing it for its real world compliance. I could just disable operation while charging in software... or just toss in some LDO's to reject noise...
What else have you all done to narrowly get by the EMC tests?
Maybe my suffering with hand-soldering 0402's will lead to effective decoupling
