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Some beginner board layout questions

Discussion in 'Electronic Design' started by Colin Howarth, Apr 4, 2010.

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  1. Hi,

    I've just upgraded Eagle to the non-profit license, so I can now (in
    theory :) do 4-layer boards.

    1. If I have a ground layer and I have one part as an analogue ground
    plane and another as a digital ground plane (two adjacent rectangles)
    how and where should they be connected?

    2. Given that I have a ground plane, should I still do copper pouring in
    the signal layers (and connect them to ground)?

    3. This probably isn't relevant for my first project (guitar-computer
    interface: differential signal, 192 kHz, 24 bit ADC with pre-amp and
    USB/FW), but which is the cleaner solution for, say, a single signal
    crossing: 2 vias with a trace on the bottom signal layer, or a zero ohm
    SMD with the other signal passing under it?

    4. One of the circuits I am copying/modifying has a 1uF / 63V
    electrolytic decoupling capacitor (directly in the signal path) before
    any amplification. Wouldn't a plastic (polyethyleneterephthalate) one be
    better, from a noise point of view?

    5. Is it OK/possible/desirable to place a via on an SMD pad (e.g. for
    resistors & capacitors to ground)?

    6. I suppose it's better not to route signals underneath opamps (from a
    noise point of view)? What if the path then has to become a fair bit
    longer? Is there a rule of thumb here?

    Thanks for any answers!


  2. Hmmmm. That's so odd. They don't come across as an evil company. More
    the opposite in fact with their pricing structure, OSX and Linux
    support, free "support" and encouragement of hobbyists.

    I don't envisage much sharing of libraries myself, other than up and
    downloading libs to/from their website, which I suppose should be OK.

    That said, thanks for the warning. The story you linked does sound
    monstrously unfair.

  3. Joerg

    Joerg Guest

    They aren't, it's IMHO a great company. In about 5 years I never ran
    into any file corruption problems. Just make sure never to use schematic
    parts and such from people that loaded a hacked Eagle onto their PCs.

    Best of all: No dongles that break off on a bumpy airplane ride and they
    let you legally install a 2nd copy for the road on you laptop. Now which
    other CAD company can rival that?

    As for the ground split I (strongly) second John's opinion: Don't do that.

    Caps in series: In the high fidelity audio world ceramics are usually
    not the ticket when in the signal path, and neither are electrolytics. A
    good film cap is best. At least use a smaller film cap in parallel if
    you have to use an electrolytic.

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