What is the most common practice in performing EMC tests for PCB assemblies that will be sold without a housing? In my case it is an FPGA development board. Is it possible to design excessive switching hardware in a way that it passes CE and FCC testing without a metal housing? Or do you usually define a designated case of application with a housing?
You can make single board products with fast electronics pass CE/FCC in plastic or no housing.
It is easier if you:
- keep all cables attached in one end only
- use fewer cables
- specify a specific simple application for the FCC/CE test
- don't have things that stick off the board (display, large connectors etc.)
- make a very low impedance power distribution network (PDN)
- have good filtering on the interfaces off the board
It is very difficult if you have multiple boards (plug-in, stacked, cable connected etc.). Actually I would specify a Faraday cage type box if you have multiple boards.
If you absolutely must include a display - try to get one with LVDS interface.
If you have a radio as part of your design, some of this becomes a bit more complex.
I suspect many go fairly light on the CE/FCC thing and self-certify with limited time spent on measurements. It is highly unlikely anyone will ever sue you for an eval board that is out of FCC/CE spec and most of these boards runs in fairly limited volumes.
Also: I have seen some outfits in China offer to do very cheap CE/FCC marking for you. You get the paperwork - they get some money. Win-win. :-)
We have passed the test for FCC and CE compliance without a metal housing. Thus: Yes it is possible. Sure, the EMC behavior strongly depends on the design inside the FPGA, therefore we defined a typical application. For getting a credible result this typical application should be the worst-case (especially in terms of IO pins and cables).
For all who are planning to do such test: Define your typical application and don't forget to bring several high quality cables and PSUs.