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Why Are There No Right Angle Traces?

Discussion in 'General Electronics' started by BM, Jun 27, 2003.

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  1. Tom Woodrow

    Tom Woodrow Guest

    Had to do that on a 6-layer board once.

    Hand taping was so much fun. Actually I enjoyed
    it most of the time. I even thought in 4x for a
    long while after I laid out my last tapeup PCB.

    Tom Woodrow
    www.dacworks.com
     
  2. Frank Miles

    Frank Miles Guest

    [snip]

    Ah, but at least with tape you can bevel those nasty right-angle corners,
    virtually eliminating the minor TDR glitch.

    -frank
    --
     
  3. John Larkin

    John Larkin Guest

    Yeah. I had to drive down to Mountain View to Lorry Ray Photography,
    the only people I could trust to shoot everything right. Then I had to
    call to see when it would be done, and drive down again to pick up the
    film. And we were always losing film. Their camera was basicly two
    rooms with a lens mounted in the wall between them... they could shoot
    1:1 D-size art, accurate to a couple of mils. Out of business now,
    along with those bastards at Bishop Graphics.

    John
     
  4. John Larkin

    John Larkin Guest

    Nobody I knew liked the color stuff. We did 4 pieces of pin-aligned
    clear mylar: padmaster, top traces, bottom traces, and silkscreen;
    occasionally we did a 4-layer, with the plane art cut out of rubylith.
    Lorry Ray would sandwich layers to shoot the film, and would do tricky
    stuff to make ground planes and solder masks from the padmaster art...
    they could expand, contract, and, or, all sorts of stuff
    photographically.

    We'd make assembly and fab drawings by exposing the mylars directly
    onto sepia paper. By playing with layer exposure times, you could make
    cool faded-layer composites, even burn the title blocks in while you
    were at it.

    John
     
  5. Fast Eddy

    Fast Eddy Guest

    I was told it was because the electronicals would fly off the edge of the
    track
    due to the speed they are travelling.

    Rather like a car on a racetrack going really fast and coming to a corner
    and sliding off.


    You may have to clean out the box that the circuit is in because of the mess
    it will make.

    PS you will need a good eye cos you can't see them too well, but they are
    there somewhere.


    Edward B Tweedel
    Oxford
    UK
     
  6. John Larkin

    John Larkin Guest

    That was Dum.

    John
     
  7. Pat Quinn

    Pat Quinn Guest

    Here are my 2 cents:

    1) across diagonals, you can pack traces closer
    2) current density in the corner is fairly low, thus it is only
    semi-functional metal
    3) breakdown voltage will be lower off of sharp edges
    4) a square corner will lower the impedance of a controlled-impedance
    line at the corner and may lower signal integrity

    -pq
    Portland, Oregon
     
  8. It may very well have to do with the reason that fillets are used
    whenever connecting to pads.

    When I was first learning PC board layout 30 years ago, I was taught
    that this reduces the problem of solder bridges when wave soldering.
    This made sense to me, and so I still always use fillets when
    connecting to pads.

    I suspect that this is the same reason that right angle turn on PCB
    laysouts should be avoided, in that they attract the formation of a
    solder bridge that could very well short to other nearby conductors.

    Harry C.
     
  9. Eric Immel

    Eric Immel Guest

    Don'cha hate it when electrons spill everywere? ;)

    I seem to recall, through a FeCl3 haze, something about acute angles
    causing undercuts in the etching process.

    EI
     
  10. Bob Pownall

    Bob Pownall Guest

    On 12/26/2010 4:33 PM, Phil Hobbs wrote:
    Fill patterns (a.k.a. dummy patterns) are also used for some critical
    etch levels, if isolated lines etch at a different rate than dense lines.

    Bob Pownall
     
  11. Guest

    If there is some significant voltage on the trace relative to other
    traces, a high filed strength is at the corner, which could cause a
    flashover.

    With high frequency signals or signals with sharp edges, the trace
    should be treated as a transmission line, when the trace is longer
    than about 10 % of the wavelength. In the worst case, the corner can
    cause a reflection and the trace leaving at 90 degrees can act as a
    stub, even if the transmission line is terminated properly. With a
    smooth curvature, the trace works properly as a single transmission
    line.
     
  12. Joerg

    Joerg Guest


    Unless you are dealing with a hi-rel design. Right angles are prone to
    stress tears. Ideally there should be no angles at all.

    I sure wish that was so. Sometimes when I advised engineers to set the
    CAD to round all corners and do teardrop entries at connectors and such
    they responded that their CAD couldn't do that. At least not without
    some model-making efforts.

    Gimmee my Rubylith back :)
     
  13. Joerg

    Joerg Guest


    One of several reasons is board flexing. Every board flexes unless you
    epoxy the whole thing onto a chunk of granite. Think of it this way: Why
    are bush pilots drilling holes at both ends of a metal surface tear?

    Yep, vias, too. Which is why I'll never understand why so many layouters
    leave the CAD at a very small default for via size and trace width. Not
    on my boards ...
    The process itself does that already, to some extent. But it is still a
    very small radius. Why expose something to more stress than necessary,
    especially if the remedy costs zero cents?

    The first layouter I worked with in my career was a very attractive
    red-haired lady, and she drove a Corvette.

    Connectivity, romance, hmm ... :)
     
  14. Guest

    IOW, you checked but didn't get clearance.
     
  15. Guest

    No one was on board.
     
  16. Joerg

    Joerg Guest

    But one became like a wild boar? :)
     
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