in the G400-S docs, it is written that no traces or vias should be present under the module. Fine.
But does it apply to both the top and bottom layers or only to the top layer ?
And should that keep-out area be a copper or non-copper area ? (on both sides)
Only on the top layer. This is not recommended but you can run traces under as we certainly do in our designs.
The concern comes in short circuits between the module and the circuit under it, which would be a problem in high vibration or extreme temperatures. So unless you are making something high end, it should not be a big concern, yet not recommended.
If you have to and use via’s make sure they are tented so that they are fully covered in resist. This will reduce the chance of a short.
By the way, you do do realise that there needs to be 2 cutouts in the board for the G400-S components that are placed on the underside and they are not simply keep out areas?
Thank you !
I do not want to “ignore” the recommendations, do not worry. I was just wondering if there would be any reason to not route on the bottom layer under the G400. I was thinking at EMI, for example, or things like that.
@ Dave : I will not use vias under the G400 and yes, I do realise that there are the two cutouts
But there is still enough space between them to route some tracks on the bottom layer. This is always good to have on a 2-layers board…
I used to insert a polycarbonate sheet between the EMX and our custom PCBs to isolate vias and it work really well. Moreover, if for some reason SOM becomes out of order ( some customer does not do not know what means respect polarity!!) I just have to heat the board (with a gun heater to remove painting) and the polycarbonate sheet melt with some bubble which separate easily the some from the PCB
Routing on the bottom layer should be OK. I refrain these days from calling it the solder side although it still tends to be called that as SMD means the topside is also the solder side.
These days I tend to use 4 layer boards as the inner ground plane gives me that extra protection from stray signals if there happen to be any.