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j777
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I'm designing my first SBC which will (hopefully) run Linux. The board will have the following:
Features:
AT91SAM9XE128 MCU at 180MHz (not in production yet but hopefully soon)
128MB SDRAM
128MB NAND Flash
16MB Serial DataFlash
10/100 Ethernet
33.6 Analog Modem (MultiTech SocketModem)
SD/MMC Slot
Battery Backed RTC
Power:
5VDC Input
1.8V MCU Core
3.3V Everything else
I'd like to design the board using 4 layers so I've been looking for a good 4 layer stack-up. The following stack-up has caught my attention (see figure 3b at http://www.hottconsultants.com/techtips/pcb-stack-up-2.html" ) :
1 - GND
2 - Sig/Pwr
3 - Sig/Pwr
4 - GND
While I'm not an EE expert there are a couple of things that seem to be real positive about this stack-up. For example:
I have 3 questions regarding this stack-up:
1. What are additional pros/cons/gotchas for this stack-up that I should know about?
2. How should the two GND planes be connected? Only stitched together around the edges of the board or connected elsewhere as well?
3. Am I correct in thinking that I should try to keep signals on one of the signal layers rather than switching between layers to provide good return current paths?
Thanks
Features:
AT91SAM9XE128 MCU at 180MHz (not in production yet but hopefully soon)
128MB SDRAM
128MB NAND Flash
16MB Serial DataFlash
10/100 Ethernet
33.6 Analog Modem (MultiTech SocketModem)
SD/MMC Slot
Battery Backed RTC
Power:
5VDC Input
1.8V MCU Core
3.3V Everything else
I'd like to design the board using 4 layers so I've been looking for a good 4 layer stack-up. The following stack-up has caught my attention (see figure 3b at http://www.hottconsultants.com/techtips/pcb-stack-up-2.html" ) :
1 - GND
2 - Sig/Pwr
3 - Sig/Pwr
4 - GND
While I'm not an EE expert there are a couple of things that seem to be real positive about this stack-up. For example:
- GND on the first layer provides a low inductance connection for decoupling capacitors and significantly reduces the number of vias.
- Layout is somewhat easier because no space taken up by vias for GND connections.
- Since I only have 2 supply voltages that have to be distributed around the baord and the 1.8V supply is only for MCU core it's easy to combine power with the signal layers.
- As noted on the above listed website this stack-up performs well from an EMC standpoint.
I have 3 questions regarding this stack-up:
1. What are additional pros/cons/gotchas for this stack-up that I should know about?
2. How should the two GND planes be connected? Only stitched together around the edges of the board or connected elsewhere as well?
3. Am I correct in thinking that I should try to keep signals on one of the signal layers rather than switching between layers to provide good return current paths?
Thanks
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