About 2 layer PCB for industrial application

[gmarocco]

Hy, this september I have started to work for a new company.
The main project has been designed with 2 layer PCB. I have not designed it but I have revised the BOM and I have written the technical manual (in Italian fascicolo tecnico)
 
The project is composed by three boards The simplest board has some LEDS and an I/O expander.

The lower board has a microcontroller with USB connectivity and some transceivers (RS485 and CAN bus).
The most complex board is the third: there are two connectors in order to carry a Raspberry-PI 4 module, a 4 port USB hub and an ethernet connector connected to the Raspberry PI module.
 
All the three boards are 2 layer boards with components on TOP side only. The diffusion of ground is  only on the bottom side.

Although the connections on the bottom side are reduced, there are some big slots in the ground diffusion especially in the most complex board
.
Although the product is running on the lab for several weeks, I have fear regarding the future EMC tests that have to be done.

I have asked why the project has been designed with a 2 layer PCB and the reason the designer has given is the
cost.
I feel more confortable with a 4 layer stack-up like this in order to reduce the changes of the original design
L1 : signals/power with tracks
L2 : solid ground plane
L3: solid ground plane
L4 : signals/power with tracks
 
Unfortunately I have no proof to show that a 4 layer design would be safer concerning EMC stuff.

What is your advice? Have you any suggestions?
 
Thanks in advance.

[T3sl4co1l]

Correct, an inner ground plane design is generally an excellent choice for EMC purposes.

Whether it matters, depends on everything -- testing levels, components, routing and layout, etc.

2-layer boards can be nearly as good as 4-layer, when both sides are poured with ground, and the pours are stitched with vias at regular intervals, with priority given to certain inner or outer corners, trace crossings, and component pins.  As long as traces/buses are always routed over one plane, and openings through both layers are kept to a minimum (pay attention to the negative space around traces, rows of pads, etc., especially where they are crossing!), the EM environment is very similar to that of a 4-layer board.

Of the signals listed, USB is probably the biggest concern, but it's not obvious if it's actually routed on board, or present in a separate module.  If module, there is the different concern, that the connections between modules are well shielded, and that the modules are compatible with the test levels in the first place.  Shielding of USB can vary wildly with quality of connectors and cables; cheap products abound.

Tim

[Benta]

What is your advice? Have you any suggestions?

Yes. Always involve an EMC/EMI lab/consultant as early as possible. These have excellent advice and recommendations on EMC-compliant design and will save you a lot of money later. They usually have an RF lab for measurement, and it's far less expensive than you think.
The labs/consultants I've worked with have cost 5...20k Euro depending on circuit complexity.

And at the end it was worth it. Not just their knowledge of which EU-Directives to apply (this is not so difficult), but which Harmonized Standards (ENxxxxx) come into play was Gold. And don't forget: the ENxxxxx Standards also cost money.

No affiliations, I'm retired. Just my experience.