pcb layout opinions

Discussion in 'General Electronics Chat' started by chrisw1990, Oct 27, 2011.

  1. chrisw1990

    Thread Starter Active Member

    Oct 22, 2011
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    ok.. had differing opinions of the past several months about using right angled tracks, curved tracks and 45degree tracks..
    what are the opinions on which is best? i guess emi/emc would become more apparent in angular tracks?
     
  2. Sparky49

    Active Member

    Jul 16, 2011
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    To some degree, I would presume so.

    But what is the application of the circuit on the pcb? If emi/emc is not of major importance, then you could get away with it. I have played around with various pcbs and found that in most cases, it doesn't matter if the tracks are angular or straight.

    I must say, I've never come across curved tracks. From my point of view, it would make problem-finding a lot harder, as straight, angular tracks are far easier to follow, IMO.

    As for which is best, I'd say 90° tracks are far easier to work with for most hobby purposes, but looking into the more complex circuits in industry, more angular tracks come into their own.

    I'd stick my neck out on the line and say that, in most cases, curved tracks are nonsense.;) There just isn't a need for them.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I don't like 90° turns, so I use 45° turns instead. It makes the board neater, and helps defeat choke points.
     
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  4. chrisw1990

    Thread Starter Active Member

    Oct 22, 2011
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    see, i was talking to some people on my placement, and they said curved tracks were good for RF stuff? like an onboard antenna connection for GPS stuff?

    i agree 45 is neater.. dunno why it just looks awesome when you get your pcb back and its got that sheen in the light as it bounces of the 10way (or however many) bus tracking across the pcb..
     
  5. Sparky49

    Active Member

    Jul 16, 2011
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    Most cases!:p

    Talking of pretty pcbs, have you seen black pcbs with gold lettering and contacts - now they look sexy with all their tracks!
     
  6. chrisw1990

    Thread Starter Active Member

    Oct 22, 2011
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    i like red and white;) sadly green and white is cheapest:(
     
  7. steveb

    Senior Member

    Jul 3, 2008
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    Curved traces are best for high speed circuits. Think about high speed digital lines in modern processor-based PCB designs. The interconnects are basically transmission lines.

    Would you take an RF cable and bend it at right angles, or would you curve it as gently as possible? Right angle traces will cause reflections and losses.

    Ideally, straight traces are best for high speed connections, but if you have to redirect them, then curved is best.
     
  8. nigelwright7557

    Senior Member

    May 10, 2008
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    I start off with 90 degree tracks and once routing is completed I convert to 45 degree where possible to shorten the lengths of the tracks. I also go around minimising the number of vias.
     
  9. colinb

    Active Member

    Jun 15, 2011
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    You are asking the wrong question. Who cares what opinions people hold? Facts are all that matter. So what do we actually know?

    - Who's Afraid of the Big Bad Bend? by Dr. Howard Johnson. First publ. in EDN magazine, May 2000

    - si-list discussion “Right Angle Bends” (long!) from July 2011

    As far I can tell, unless you are pushing the extreme limits of high speed signals with high speed differential pairs and 10 Gbit/s+ data links, the right angle bends cause no measurable electrical effect.

    While you might prefer 45 degree bends for PCB space efficiency and aesthetic reasons, the only substantive reason to avoid 90 degree corners has to do with the etching process and the potential for the corner to form an acid trap (probably only an issue for very narrow traces), and problems with wave soldering processes.
     
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  10. steveb

    Senior Member

    Jul 3, 2008
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    Keep in mind that technology changes fast and 12 years is a long time in "tech-time", if you consider Moores Law and similar trends. The faster you go, the more it matters. In the latest high speed designs, a right angle bend can typically create a few ohms of impedance discontinuity on a 50 ohm impedance trace connection. That implies several percent of reflection. Of course, digital systems are pretty robust and so the system might easily tolerate the degradation of the digital signal, but that doesn't change the fact that a curved trace pretty effectively eliminates the sudden discontinuity and minimizes the chances of problems due to reflections.
     
    Last edited: Oct 27, 2011
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Using any suitable angle generally gives significantly shorter traces, a very real improvement in reducing trace resistance, and also usually gives the ability to make the PCB more dense. Two real benefits.

    Restricting to only 45 degree angled traces gives a very standard looking, "pro" looking result that many people expect.

    I use both systems, for personal stuff and where performance is critical, I use any track angle that makes it better. When I do commercial design generally I stick to 45' traces only, apart from some critical higher current traces.
     
  12. colinb

    Active Member

    Jun 15, 2011
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    I agree that 45° angles are usually the best choice for a number of reasons, but the original question was about which is “best” and whether EMI/EMC was a concern. A lot of superstition has formed around the degree of problems that 90° track angles and I'm just saying you need to look at real measurements and real results before saying that one is technically superior. Let's say 45° is a good rule of thumb but there is rarely a reason to avoid 90° angles if it makes your routing cleaner or easier.

    OK, a board can be “pretty” or “professional-looking” if it has 45° angles perhaps, and I'm all for aesthetically pleasing designs, but let's be honest about why the choices are made: personal preference vs. technical reasons.
     
  13. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Could sharp corners have significant effects in circuits operating at higher voltages (kilovolts)? I have seen rounded pads specified to reduce electrostatic stress, so perhaps swept bends would also be required.
     
  14. mixed_signal

    New Member

    Dec 5, 2009
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    In the 1990's board houses liked to limit us to 45 degree angles as they could ensure consistent rates of etchant flowing off the board, and keep line widths under better control, or something to that effect...
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Well to be just "technical" then 90 degree bends are far inferior to 45' bends, the tracks are longer with greater resistance (up to 41% longer in the worst cases) and PCB density suffers greatly with only 90' bends allowed.

    I'm not sure about etching issues but it stands to reason that 90' bends will have RF issues.
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Not even at kilovolts. Best practice is to "chamfer" a 90 degree bend so that it looks like a short 45 degree trace connecting two perpendicular traces.

    For the "straightness" of traces, try to keep them in the same direction on one layer, and in the opposite direction on the other layer (for two layer+ boards), so if it is horizontally aligned on the bottom, try for vertically or diagonally aligned on the top.

    The circular traces, spiral PCB inductors or antennas, etc. are important when you bump into the 700Mhz+ range, especially at 1Ghz (GPS), above 1Ghz, electrons act more and more like light, and will reflect if they see a solid 90 degree bend. With higher frequencies, you also want to keep your traces as short as possible, meaning SMD components are essentially required.
     
  17. t06afre

    AAC Fanatic!

    May 11, 2009
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    http://www.montrosecompliance.org/technical_papers/corners-Japan.pdf
    This is a quite good approach to the problem. For hobbyist DIY PCBs. I would say it does not matter anything. But for a good looking PCB most often the creator have had some plan behind the work, and showed some care about component placement. And that is pluss for the board. Many of the design "rules" or do's and don'ts for PCBs have its origen in industrial production. And for a one of a kind board they are not so important. Like if you can simplify routing your hobbyist board by not place all ICs in the same direction just do it.
    http://www.montrosecompliance.org/technical_papers/corners-Japan.pdf
     
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  18. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I guess I came into this a little late, but I'm going to go ahead and give my 2 cents worth. :D

    I tend to avoid right-angle traces, as they look very unprofessional and sometimes become choke points. I generally use 45° angles, as they look much neater, and there is less of a chance of it causing problems in the circuit. For "T" intersections, I generally add two 45° traces on either side of the trace coming in, so it makes a triangle-shaped junction. It's not absolutely necessary, but it looks neat and works well.

    Der Strom
     
  19. colinb

    Active Member

    Jun 15, 2011
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    Thanks for the real information in the midst of the unsupported opinions that dominate this thread.

    There is no question that you can make more attractive-looking boards when using 45° angles in traces. That's great. Everyone agrees that it's nice to make pretty boards. But don't throw around opinions and assumptions about electrical performance as if they were fact.

    Unless you're one of the relatively few engineers designing circuits with multi-gigahertz signals, you don't have to worry about signal integrity issues with 90° corners. If you are one of those few designers, you will know what you need to do.

    I'll say farewell to this thread with a quote from Mr. Montrose:
    CONCLUSION

    Time domain (signal integrity concerns): There are no measurable reflections from 90 degree, 45 degree or round corners. In theory, and by mathematical analysis, the impedance of a corner will decrease by a calculable amount. This impedance change is not sufficient to be measured with a 3 GHz bandwidth network analyzer. The velocity of propagation of a signal within the transmission line (trace) is oblivious to the discontinuity unless one designs signals in the upper Gigahertz frequency range or use edge rates faster than 15 ps.

    Frequency domain (EMC compliance): Radiated emissions exist, however, measurements up to 1 GHz does not show an increase for 90 degree, 45 degree or round corners that is of any significant amount greater than the level of uncertainty of the measurement equipment. The average radiat ed emissions were approximately 5 dB. The discontinuities within component packages, connector pin -outs, layer jumping of routed traces, vias and common-mode currents within the transmission line will radiate at levels that far exceed any measurable effects from any corner configuration. Corners do not appear as radiated emissions until the upper MHz range . The magnitude of the radiated signal measured is minimal. It is difficult, if not impossible to accurately measure radiated emissions from any trace corner configuration.

    (Mark I. Montrose, RIGHT ANGLE CORNERS ON PRINTED CIRCUIT BOARD TRACES, TIME AND FREQUENCY DOMAIN ANALYSIS)

     
  20. colinb

    Active Member

    Jun 15, 2011
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    Well, was going to say goodbye to this thread, but this is a good “rule of thumb” in terms of making efficient use of board space for trace routing. When the traces all run in the same direction on a layer, space is much more efficiently used.

    Also see ExpressPCB's Tips for Designing PCBs, section Placing Signal Traces. It mentions this strategy and also says “It is a common practice to restrict the direction that traces run to horizontal, vertical, or 45 degree angles.” (Rightly presented as a suggestion, not making claim to its necessity...)
     
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