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CC3235MODS: Custom PCB board layer questions

Part Number: CC3235MODS

Hi,

we are making our second custom PCB board using CC3235MODS.

The first board, we followed TI example and used 4 layers: Top (1), GND (2), Power (3), Bottom (4).

this works fine.

now, we have second revision that we need to add and route additional signals outside of CC3235MODS.

so we are thinking that we will make a 5 layer board as: Top (1), GND (2), Power (3), Signal (4), Bottom (5).

please note that the Signal layer 4 only used for I2C, CAN differential wires and stayed away from CC3235MODS.

we will follow all the layout guideline for RF signal (pin 31), and the following recommendation.

Can you please kindly confirm if this additional Signal layer (4) is acceptable?

BTW, what is the reason why TI only mention 2 or 4 layer PCB for CC3235MODS?

Thanks and Best Regards,

Henry

  • Hello,

    sorry, we change the configuration to 6 layers as:

    Top

    GND

    POWER 

    GND (still solid GND under CC3235MODS section) => + SIGNAL for I2C and CAN on the other side of the board

    POWER (still solid GND under CC3235MODS section) => + SIGNAL for I2C and CAN on the other side of the board

    BOTTOM

    can you please let us know if this is acceptable for CC3235MODS?

    please let us know the feedback as soon as possible as we are in the routing phase now.

    thanks,

    Henry

  • Henry,

    We recommend a 2 or 4-layer PCB, because using a 6-layer makes optimizing the RF more challenging.

    1. By using a 6-layer PCB, the thickness of the dielectrics between layers become smaller, so your other CPWG parameters must also become smaller. 
    2. If the dielectric thickness between the Top Layer and Layer 2 is too thin, you may need to make the 3rd layer to be the RF GND reference layer by implementing cutouts on the 2nd layer that follow the RF transmission line on the top layer. 

    I recommend working with your board manufacturer first to know what stackups are available for your build. Then designing the RF layout according to the stackup. See what trace width you'll need to use for the transmission line and note if this will drive PCB cost up. Then finally, run ADS RF simulations to ensure your RF circuit is ~50 ohms. 

    BR,

    Seong

  • Thank you Seong for your prompt response.