[Milkymist-devel] Placements

[Andrés Calderón]

On Tue, Mar 23, 2010 at 8:28 AM, Adam Wang <adam at sharism.cc> wrote:
> Hi,
>
>>>2, FPGA's most decoupling capacitors are located underneath fpga (bot side).
>> Does this imply we have to use blind vias? Is the PCB manufacturer OK with
>> that?
>
> Exactly correct. PCB maker here is OK.
>

I do not think are necessary blind vias, we use a Spartan 3 BGA
package with 1mm pitch and 0402 capacitors  without using blind vias:

http://www.emqbit.com/S3_BGA676_ex.png


Regards,

    Andrés Calderón
    Cel:     +57 (300) 275 3666
    Email: andres.calderon at emqbit.com
    Gtalk:  andresfcalderon at gmail.com
    Web:    www.emqbit.com



>> This is not mandatory. Typically J3 would connect to a cable and not be
>> accessible directly from outside the case... and it's only intended for
>> "advanced" users. You can place it wherever it makes your job easier.
>
> Ok.
>
>> * Do you think the SDRAM is close enough to the FPGA? In [1] Micron recommends
>> 2 inch (5cm) total maximum track length for systems that use series
>> termination only. However, I know some designs which works apparently without
>> meeting this requirement, the OLPC XO for example. Are you able to perform
>> IBIS simulations?
>
> Yes, it's close a bit but also knew some designs without meeting.
> I am not able to use IBIS due to not familiar with this field.
>
>> As I said in my first email, serpentine traces won't be needed: we'll use the
>> IODELAYs instead, which do not pose their signal integrity issues.
>
> I've used serpentine traces on DVR system. The length about
> transmission becomes more seriously. However, haven't seen this useful
> IODELAYs feature said, would like face this powerful practically. But
> if insist on using recommends, I can add length.
>
>> * The MicroSD connector should be placed near the JTAG and UART connectors so
>> that it is accessible through a single door when the board is cased. It should
>> not be placed near the board edge. This model opens on the top and the MicroSD
>> card is laid on it by the user (not slided into it) then the connector is
>> closed to make the contacts.
>
> Ok, will place them close and send you again.
> Thanks,
> Adam
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