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Minimal PCB design

ricferreira , 12-02-2015, 06:40 AM
H i,

Following the high speed design course I am designing a pcb using the IMX6UL. My project should be a very small PCB and I have 2 technical questions.
1) Is it possible to design a pcb with DDR3 on one side and an eMMC just bellow? Like the picture bellow (I don't have the supply circuit yet)

2) In the IMX6UL evaluation board, the signals for the address are routed in different layers (address, RAS, CAS, CS, WE). They have some address in one layer,other address in another. Is this a good approach? Because it makes the design much simpler.

Thank you very much
robertferanec , 12-02-2015, 06:59 AM
Hello @ricferreira

1) I have seen the picture - your PCB is basically only around CPU + 1x DDR3. The main question is, what you are going to do with that PCB? Usually, you also need some connectors and these are going to take some space. Will be there some connectors on your PCB?

Possibly, for inspiration, have a look at our TinyRex - that is one of the smallest things we ever designed. It may give you an idea about what else you may need on your small PCB: http://www.imx6rex.com/imx6-tiny-rex/

2) We also sometimes route ADDR/CMD/CTRL signals on different layers. Just be sure you are careful about what you are doing - for example, you may need to consider the length in VIAs and also length routed on the TOP/BOTTOM layer vs Inner layers.
ricferreira , 12-02-2015, 07:53 AM
Hi @robertferanec

Thank you for your answer!
In fact in the bottom layer of the PCB there is an eMMC. The objective of this pcb will be to be to have a CPU + DDR3 + eMMC + 2 connectors and connect another pcb after with supply and other peripherials.

What you think about the design. Regards
Ricardo F.
robertferanec , 12-02-2015, 12:21 PM
Normally we create the schematic first and then we do 3D model. After that we see if it's going to fit ... usually it doesn't fit

In your PCB, you may have three possible difficulties: decoupling under CPU, space for the 2 connectors, space for the power supplies (chips + inductors + capacitors).
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