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Multi layer PCB board question

Discussion in 'Electronic Basics' started by R.Spinks, Oct 1, 2005.

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  1. R.Spinks

    R.Spinks Guest

    What are the typical methods for determining how many layers a PCB board is.
    Like after you take something apart and see the PCB ... how can you tell if
    it's multi layer and how many layers it is. I tried looking at the side
    profile of the board ... it's FR4 but that's all I can tell by just looking
    at it.
     
  2. John Larkin

    John Larkin Guest

    Hold it up to the light. If all that's indicated is the surface
    traces, it's a 1 or 2-layer. You can usually discern internal planes,
    and most multilayers pretty much block all the light, because they
    have solid internal copper planes.

    The only good way to count layers is to section the board, preferably
    through some vias.

    John
     
  3. In the old days yes but not today's PCBs they make them dark with 4 or more
    layers and may be the way to find out how many
    layers is to read the schematic or diagram.
     
  4. PeteS

    PeteS Guest

    The reason the board is 'dark' with internal layers is you can't see
    through the internal copper. It's common for at least one of the
    internal layers to be a ground plane and at least one other a power
    plane, so virtually all the layer is copper, rendering it impossible to
    view through.

    As John noted, the only real way to know is to section the board at a
    via (or look at the original design fabrication notes which generally
    has a stackup diagram).

    Cheers

    PeteS
     
  5. w2aew

    w2aew Guest

    Many times, the PCB designers will put a "layer key" on the edge of the
    board somewhere. The "key" is simply a layer number, made in copper,
    arranged so that when you look "thru" the board (illuminated from the
    rear), the numbers will appear adjacent to each other. FR-4 is
    moderately translucent, so this generally works for up to many layers
    (depending upon the thickness and materials used). Maybe you'll be
    lucky and the board will have such a "key" designed in.
     
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