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BGA escape routing

Quentin Davis
Prodigy 190 points

I'm trying to layout a board with the DM365.  I can't find an example BGA escape routing that uses the 18/8 via size specified in the datasheet.  I've seen examples with 16/8 vias, but not 18/8.  Does TI have any examples they can point me to?  The Spectrum EVA and LeopardBoard both use vias that are smaller than 18/8.

Thanks!

 

Quentin

  • 0
    TI__Intellectual 1670 points

    What page on the DM365 data sheet says that an 18/8 via is possible?  If there is a page like that, it's incorrect. 

     

    I wish it were possible, but there's just no way to route the DM365 ZCE package with large 18/8 rules.  The 0.65mm pitch standard array is not friendly to typical through-hole via sizes like 18/8.  Only the packages with Via Channel(TM) will allow large vias like this at 0.65mm pitch, and the DM365 does not come in a Via Channel package unfortunately.

     

    Please respond with the page number and we'll make sure to change this error.  I wish I had better news.

     

    Good luck with your design!

  • 0 in reply to KevenC
    Prodigy 190 points

    The November 2010 datasheet is the one I'm referencing.

    Page 111: Table 2-26, rows 8 and 9,  says 18/8 vias.

    Page 16: Section 2.7.1:  "Note that micro-vias are not required."

    Page 206: Section 7: "Note that micro-vias are not required."

    Page 206: Section 7.2: "Note that micro-vias are not required for this package."

     

  • 0 in reply to KevenC
    Prodigy 190 points

    How do you recommend to route the DM365?  Is the best to use 16/8 vias?

    Thanks,

    Quentin

  • 0 in reply to Quentin Davis
    TI__Intellectual 1670 points

    Thanks for pointing out the data sheet errors.  I've already forwarded this to the appropriate people to correct the errors.

     

    A 16/8 via is the largest possible via to use for a DM365 design, however there are two problems with this, both of which can be overcome with some extra care:

    1.  A 16/8 via only allows traces in between every other via.  In other words, you can't get a trace in between every via, so this makes layout very tricky.

    2.  A  16/8 via is only manufacturable at certain PCB fabs.  Many of them will allow this for prototyping, but only a few will allow it for production, therefore most 0.65mm pitch designs end up as HDI (High Density Interconnect) designs, meaning they use laser drilled micro vias.

     

    #2 requires asking your PCB fab to see what they can do and seeing if there are any that can do better. 

    #1 can be overcome with a careful layout.  A 16/8 via layout is available at:

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/100/p/114268/408294.aspx#408294

     

    If in doubt, use micro vias.  An HDI design for this part is the norm, and this has the advantage of making the final PCB smaller, so this may be a benefit although it will come with added expense.

    I hope that helps!  Good luck with your design.