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PCB design: Is silkscreen on ground plane okay?

Discussion in 'CAD' started by Andy C, Feb 24, 2007.

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  1. Andy C

    Andy C Guest

    Hi all,

    I'm doing my first PCB design. I'm an EE, but I am not familiar with many
    of the practical aspects of PCB fab. I have IPC-2221 and a couple of other
    documents like it, and have done some searches, but so far I haven't found
    an explicit answer to this question.

    I have a two-layer PCB for which the bottom layer is devoted to signal
    traces and the top to ground plane, with a few signal traces on top. I'd
    like to have a silkscreen layer to help with stuffing the board, but I'm
    not sure if it's kosher to have a silkscreen layer on top of a ground
    plane. Is this okay, or do board houses frown on this?

    Thanks in advance,
    Andy
     
  2. James Beck

    James Beck Guest

    I don't see why it would be any different from any other silkscreen job.
    Hell, it is probably quite a bit smoother than the surface of most
    boards they have to screen.


    Jim
     
  3. Hal Murray

    Hal Murray Guest

    I'm doing my first PCB design. I'm an EE, but I am not familiar with many
    Is this a fancy/expensive board? (microwaves) If so, then
    ask your board house, hire a consultant, or ask your colleagues.

    If it's a low cost board, then I wouldn't expect any problems.
    (I've done it.) If there would be a problem, the board house
    should mention it on their web page or design guide.
     
  4. Hal Murray

    Hal Murray Guest

    That brings up an interesting point. Assuming you are working on
    a 2 layer board and one of them is a ground plane, how do you decide
    if the ground plane goes on top or the bottom? I'm also assuming
    that most of the parts go on the top.

    My first reaction was to put the ground plane on the bottom so the
    pads from the chips on top don't cut holes in the ground plane.

    Signals that are easy to route won't need any vias and/or won't
    cut up the plane as much.
     
  5. This is a +/- 120 Volt DC voltage regulator taking about +/- 130 Volts DC
    in. The board has radial-lead electrolytics on the top that have these
    voltages on their non-grounded pins. If the main traces were on top, the
    radial-lead electrolytics could end up resting on these high-voltage
    traces. Though it may not be a problem in practice, the thought of this
    made me paranoid. There doesn't seem to be any insulation spec that I can
    find for the top side of the radial-lead electrolytics. So I thought it
    best for safety reasons to not allow the bodies of these parts to rest on
    high-voltage traces on the top of the board. Perhaps I'm overreacting, but
    let's just say I have "respect" for high voltages.
    This being a DIY project, all my parts are through-hole types, so they'll
    have pads on top and bottom. But I agree - with lots of surface-mount
    parts, putting the ground plane on the bottom would be much better.

    Andy
     
  6. This is a DIY effort, so I'm in this by myself. It's not a microwave board
    or anything terribly exotic. But there are some voltages over 100 V
    involved - see my other reply.
    Thanks. I will check the web pages of the board house.

    Andy
     
  7. Andy C

    Andy C Guest

    Oops - had to fix the default setting of my newsreader :).

    Andy
     
  8. Andy C

    Andy C Guest

    Thanks!

    Andy
     
  9. qrk

    qrk Guest

    No problem doing this. It prints nicer since you'll have very few
    traces on top.
     
  10. PeteS

    PeteS Guest

    My rule is that there *will* be silk on each surface components are
    loaded on.

    Now, it is often the case that _all_ the silk information can not be
    placed (on dense designs) but at least some information should be on the
    silk for each loaded layer.

    Cheers

    PeteS
     
  11. FrankW

    FrankW Guest

    No problem putting silkscreen on copper.
    Just keep it well away from any pads that are to be soldered
    Cheers
     
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