I have a PCB with an RJ45 connector, which naturally requires a 1000 pF/2 kV capacitor connecting chassis GND to system GND.
Unfortunately the PCB was designed with an 0805 package, and I can't find any 2 kV rated 0805 capacitors. I can get one in a 1206 package however, and when I overlaid the 1206 footprint onto the 0805 in EAGLE it seems as though there should be enough overlap to solder the larger capacitor. There are no other signals around the pads, in fact they're both engulfed by same-signal traces.
Will soldering a 1206 high-voltage capacitor onto the 0805 footprint in this manner result in any unintended consequences? I know that this is a bit open-ended, but I'm not even sure where to begin with that line of questioning in terms of what to explore.
For context, this board was a small quantity prototyping run. I just need to prove that an Ethernet signal can pass through this board, and then design the correct footprint size for the manufacturing run. Reordering another prototyping quantity without using these to test and debug would be less than ideal.
Best Answer
You can try to solder the cap but you can also leave it out for initial testing.
A missing cap between chassis and signal ground likely won't cause any Ethernet problems under normal circumstances.
If it does then you likely have problems with the cap in place too.
You can try a capacitor that fits, with smaller voltage rating. Generally you would not have 2kV between chassis and signal ground anyway, or if you need to withstand more than 50V under normal conditions, then it is an indication of something being wrong already.
Sometimes you might already see that connector chassis and signal ground are already connected together via some other route so the AC coupling cap does very little.