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Getting started with BGA decoupling

Remco Poelstra
Intellectual 985 points
Other Parts Discussed in Thread: TMS320C6748

Hi,

I'm working on a custom board with the TMS320C6748.

I've read all hardware guides that I could find and I thought it would be best to start my layout with decoupling the DSP.

But I've no idea where to start. The power and ground balls seem to be placed more or less random on the inner balls of the package and I don't see how I could combine two balls per via to make enough place for the capacitors (0402). I always get stuck at a ball/via combination which blocks a capacitor somewhere or I decouple 1V3 and 3V3, but then block any decoupling to a 1V8 ball.

Did I miss some structure in the ball assignment?

Are there some recommendations on how to start actual placing the capacitors? Or is there some guide line on which balls could share a via?

Thanks in advance.

 

Kind regards,

 

Remco Poelstra

  • 0
    TI__Expert 4760 points

    Hi Remco Poelstra,

    Hope you have gone through all the design guidelines provided in the general hardware design/ BGA PCB design.

    http://processors.wiki.ti.com/index.php/General_hardware_design/BGA_PCB_design

    I recommend you to please go through the LCDK C6748 & LogicPD C6748 SOM module PCB board file for decoupling capacitor placement and implement the same in your design.  

    Regards

    Antony

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  • 0 in reply to Antony Samsunil
    Intellectual 985 points

    Hi,

    Thanks for your response.

    I hope I've read them all indeed. I've tried to find them all.

    If there is no specific system in the ball allocation, then I'll just copy the LCDK design.

    I noticed that on the LCDK, pairs of balls with the same signal which are close together are only connected to their own shared via, but not to nearby pairs/vias. Wouldn't that improve the inductance?

    Regards,

    Remco Poelstra

  • 0 in reply to Remco Poelstra
    TI__Expert 4760 points

     

    Hi Remco Poelstra,

    Which capacitor package do you prefer? 0202 package is the preferred for 0.8 mm pitch BGA for placing the decoupling capacitor beneath the BGA.

    You’re correct the most recommendation for 0.8mm pitch is sharing balls, But it depends upon design tradeoffs layout constraints (cost,assy,fab,etc..!!) and the cost you will be able to tolerate.

    C6748 LCDK is the only reference design we have for the proof of concept

    Regards

    Antony

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