Copper pour or traces?

Discussion in 'Electronic Design' started by Matt, Jan 8, 2007.

  1. Matt

    Matt Guest

    Hello,

    I am laying out a little breakout board that spreads synchro data
    (60/400Hz) throughout a system. This is the first board I have ever
    layed out that I have contimplated using a 2-layer board instead of a
    4-layer board. Because of this, I will not have independent GND/PWR
    planes. Looking around at other 2-layer PCBs, I see that some folks
    like to use a copper pour on the TOP and BOT layers. I am assuming one
    layer is traces+GND and the other is traces+PWR. My questions are
    these:

    1. Is this a sound design (no high frequency and the signals are very
    strong).
    2. From reading, I was convinced to try to use hatching instead of a
    solid copper pour to prevent warping.
    3. If I do use cross hatching what should my grid be if my global
    spacing for all traces, pads, layers, etc. is 8 mils.

    Thank you.
     
    Matt, Jan 8, 2007
    #1
  2. Matt

    John Larkin Guest

    At 400 Hz, practically anything will work.
    Copper pours don't seem to warp boards nowadays, if they ever did.

    John
     
    John Larkin, Jan 8, 2007
    #2
  3. Matt

    Ecnerwal Guest

    However, providing a little relief around the pads can make them easier
    to solder and de-solder (ie, put a hole around the pad, and then tie the
    pad to the pour with 3 or 4 traces, rather than having no pad.) I'll
    often just run a pattern of round holes in the pour rather than a grid
    (resulting in square holes), which in thoery is better for etching
    behavior (less sharp corners) but I'm not sure this is really needed or
    makes any practical difference. However, it keeps me happy, and does not
    seem to detract any.
     
    Ecnerwal, Jan 8, 2007
    #3
  4. Matt

    John B Guest

    Rule 1: Don't assume anything.

    It is unlikely that you will ever find a board with an external power
    plane. Double sided boards will normally have a copper pour on each
    side both of which are connected to GND. Having said that, go back and
    invoke rule 1 above.
    Just use solid copper pours. FR4 will not warp if you have copper pours
    on both sides.
     
    John B, Jan 8, 2007
    #4
  5. Matt

    Joerg Guest

    They used to if you didn't balance the thermal mass between both sides
    from the core layer. In fact, this was the main reason for one of the
    blitz consulting trips. 35 hours was travel time, the remainder was
    finding that warpage was the cause of end test failures, donning the old
    army boots to walk over to a lumber yard (roads too iced up for
    driving), making a frame, running a few boards.
     
    Joerg, Jan 8, 2007
    #5
  6. Matt

    Joerg Guest

    Provided they are somewhat summetrical to the core. Else go back to rule
    1 :)
     
    Joerg, Jan 8, 2007
    #6
  7. Matt

    John Larkin Guest

    We did one board with microwave laminate as the first dielectric, and
    FR-4 for the rest. It looked like a potato chip. It was cool: you
    could lay it on your desk and give it a twirl, and it would spin for
    almost a full minute. It took vise grips to get it out of the card
    cage.

    John
     
    John Larkin, Jan 8, 2007
    #7
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