Multi-PCB design with MCU?

[asrock70]

I would like to design something like an industrial thermostat, a control unit, a timer recorder in one. In short, something like see the picture . Not so sophisticated, but at the same time an order of magnitude cheaper than the one in the picture.
Front TFT + 4 buttons
back 4x digilt input, 4x digital output, 4x rele control, 4x 19bit thermocouple input 2xanalog input, 1x analg outpit , 1x ethernet, 1x USB and power up to +24V
internal any MCU for example STM32F7
On a PCB size of 100x100 mm, I don't see a bigger problem in that, but it is too big, the ideal size would be approximately 50 x 50 .

I can't fit on one PCB and I'll have to use two to three on top of each other.
I have no experience and I have a few questions / concerns

1. Ethernet connector and solution
I want to have a processor on a board with an LCD and RJ45. must be the other way around on the last PCB with connectors. If I use MAC in MCU and PHY IC at the connector it means RMII at 50 MHz passing through up to two Pin headers and an estimated 50mm track on the PCB (two layer)
If use external MAC on SPI, will have to go the same way up to 80MHz 4PIN SPI .
Will it not be a problem either in terms of EMC or in general operation?

2. How to connect boards?
My first idea is several classic pinheader with 2.54mm spacing for example 2x10 PIN 2pcs
but maybe there are better connectors today?

 

[KlausST]

Hi,

a panel mount enclosure like above?

One idea: Front with display keys, microcontroller on one pcb. On the backside of the front PCB simple connectors "backplane syle"
To the backside (connectors) 1 or more PCBs right angled to the front PCB.
Maybe the enclosure has PCB mounting guides

Instead of key you could use the cheap TFTs with touch inluded.

Klaus

 

[asrock70]

Thank you for the reaction
That occurred to me as well, but it is a less mechanically stable solution without guide rails .
I don't completely reject it yet, though
- worse mechanical stability, without frame enough to fart
- if there are three boards, there will be one connector in the middle of the back
+ positive is on the board would go only the necessary signals

I'm probably old school, but the button is a button.

I have more ready to design individual blocks (digital I/O, Analog I/O, thermocouples,, powersupply etc.) , but because i don't know how to mechanically bind and lay it out i don't know if to use an external MAC or just a PHY for LAN i don't even know if to use a 64 or 100 pin MCU.

Most recently, I'm hesitant to use 8-bit TFT or SPI bus, but I'll base that on a special thread.
My biggest concern is probably about the extreme PHY on RMII over two ridges