EMI shielding in PCB

Discussion in 'General Electronics Chat' started by ak52, Mar 2, 2015.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Hi again,
    I have seen in many Asus Motherboards (especially the ROG series),they have a special EMI shielded track,
    could someone explain to me if this really is an EMI shield and helps with accurate grounding or is it just a marketing stunt.(The red line in the image)
    Untitled.png
    EMI shields are mostly used to prevent unwanted noises in the audio amplifiers,but if there were any unshielded inductors are nearby, would it ground the excessive EMI radiations from them?
    Any idea on how to implement it?Is it just a thick copper track with ground plane on either side?

    Regards,
    AK
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,060
    3,823
    See this...

    Looks like it is just an LED from the bottom. It indicates physical separation of audio and digital signals.
    http://rog.asus.com/91382012/labels/rog-exclusive/what-is-supremefx-iii/
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Nothing more than a routed cutout in the board with an LED shining through.. Its only purpose is to clearly show that part of the PCB is isolated from the other..
    A marketing gimmic..
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    Ground management, (in this case, ground plane separation) is a very real technique in the area of design called signal integrity. 24 bit audio has a theoretical quantization noise floor of 30 nV (based on 0 dB = 0.5V consumer audio levels). Given the kinds of energy levels running around in a pc, minimizing capacitive coupling is critical to keeping the system noise floor as close to the theoretical limit as possible. The red LEDs are cutesie, but the gap matters. Air gaps routed into pc boards are more common in power supply design, where they are used to contain physically dangerous voltage levels.

    Another thing you might see is a string of closely-spaced vias inside a track. This is called ground stitching, an approximation of a vertical ground shield that extends downward through the pc board. It is a different approach because it conducts noise currents away rather than blocking them with an insulator, but the intent is the same, keeping signals in their places. It also is used to lower te high-frequency impedance of a ground connection. You can see this around the two mounting holes in your photo.

    ak
     
  5. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    yes i figured out the LEDs are present on the back to provide the red color,i din't know that there is a physical separation of the two sections.How is this achieved? its either fill or no fill in most of the PCB design software.If anybody has done this is eagle or orcad please help.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
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    It is done with a CNC router during the pc board fab. You create an assembly drawing describing the track the router bit is to take. Most fab shops have 2 or 3 bit diameters they prefer to use.

    The routing can be done before or after stackup and plating, depending on whether or not you want the insides of the slot plated. For this kind of ground isolation, you wouldn't. But for an obround grounded mounting hole you might.

    ak
     
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