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RM46L852ZWT BGA footprint - PCB routing

baptiste besson
Prodigy 150 points
Other Parts Discussed in Thread: RM46L852

Hi,

I want to design a PCB using RM46L852ZWT (BGA 0.8mm pitch).

- RM46L852 16- and 32-Bit RISC Flash Microcontroller datasheet (p181) indicates  0.45/0.55mm ball size.

- According to In "General hardware design/BGA PCB design" (http://processors.wiki.ti.com/index.php/General_hardware_design/BGA_PCB_design), for a nominal ball diameter of 0.55, nominal land diameter should be 0.4mm.

- I have downloaded dedicated footprint (RM46Lx ZWT BSDL Model --> spnm026.zip) on TI page (http://www.ti.com/product/RM46L852/toolssoftware), and land diameter is 0.55mm.

- With 0.55mm land, it is not possible to route vias between balls for a class 6 PCB so I should use µVias.

 

--> What would be the minimum land size diameter for the footprint of the RM46L852ZWT BGA ? 0.55mm seems to big ! Could it be 0.4mm, that would make easier the placement of fan out vias ?

 

Thank you.

  • 0
    TI__Guru 59540 points

    Hello Baptiste,

    The BSDL file is not a file to use for layout. It is a device modeling tool intended to be used for boundary scan and in circuit testing. If there is mention of a pad size in the file it is the ball size which would match what you are seeing.

    I think what you want instead is the CAD information for the device. It is located on the "Quality and Packaging" tab which is located here: http://www.ti.com/product/RM46L852/quality

    Once on this page look for the CAD/CAE Symbols section to download library symbols and footprint information.

    In regard to the land size to use, this is highly dependent on your application and your needs. Generally speaking, there are industry standards and there are company/application specific standards that are based on your specific industry and application requirements/needs. Please use a best practice approach based on your needs and your project requirements.

  • 0 in reply to Chuck Davenport
    Prodigy 150 points

    Hello Chuck,

    There was a mistake in my previous message. I have downloaded the CAD file where I found the 0.55mm land size diameter.

    But I still don't know which solution to choose as both design guidelines come from TI 

    - CAD file from TI --> 0.55mm

    - General hardware design-BGA PCB design --> 0.4mm

    0.4mm is much easier for fanout pattern but I wonder whhy CAD file is using 0.55mm land pad.

    Baptiste

  • 0 in reply to baptiste besson
    TI__Guru 59540 points

    Hello Baptiste,

    I checked with one of our engineers that usually does the designs on our development kits and such and they have used a 0.36mm land with a 0.46mm solder mask opening.

    I am not certain of the source of the CAD files or the intent of making the landing 0.55mm, but it is provided as a ease of use tool to give customers something to start with. if you have other inputs that state the pad size should be different, please feel free to update the file to suit your needs and application requirements. In the end, the design is yours and you are free to do as you need to do per your own engineering judgment and product requirements.

  • 0 in reply to baptiste besson
    Prodigy 150 points

    Hello chuck,

    Thank you for this answer.

    Regards,

    Baptiste