Here's a paper that shows reflections (Fig. 3, "S11") and insertion loss (Fig. 4, "S12") on coplanar waveguides, when using a sharp 90° bend, a 90° bend with a champfer and the case where the bend is replaced by two successive 45° turns ("final design").<p>The frequency scale spans 10..90 GHz.<p><a href="http://tentzeris.ece.gatech.edu/ECTC09_Rida.pdf" rel="nofollow">http://tentzeris.ece.gatech.edu/ECTC09_Rida.pdf</a>
What I've been taught during my EE studies, is that the main reason to avoid square traces is for EMC reasons, mainly due to reflections due to the hard boundaries. Interesting that the article doesn't touch on that.<p>PCB design/layout is one of the more important factors influencing EMC. Taking it into account early in the PCB design phase saves you a lot of trouble during certification.
There are a lot of good technical arguments raised here but the real reason we don't use right-angle bends on the 90% of PCBs which aren't carrying serious current or running at GHz is that right angles look ugly.
Another important consideration is ease of routing signals during design. Using 45 degree corners in general produces pretty space-efficient routing that makes it easy to cluster signals together as well as move them if necessary during layout.<p>One point the article left out is the risk of traces lifting off of the board. Having less sharp corners seems to reduce the risk of this happening with components that have a mechanical risk of coming off (like USB connectors, or large capacitors).
Square corners seems likely to be less space efficient, which is one consideration of pcb design. Why we don't use round corners or fluid traces might be a better question.
Acid trap was the one I kept hearing, and proved true on my home-etched PCBs. The 90-degree traces would get undercut but the 45-degree ones were fine.<p>To be fair it's less likely to be an issue with more advanced etching processes, but there are still limits. The thicker the copper layer, the wider your minimum track and gap widths become, otherwise the copper traces are excessively undercut.
I don't know about PCB level, but on smaller scales you should avoid making right-angle turns in metal lines because of electromigration [1]. Energetic electrons flowing along the line will crash into the 'wall' at the turn, and will knock the atoms out of place a little bit. Over time, this will lead to 'erosion' of the corner.<p>[1] <a href="https://en.wikipedia.org/wiki/Electromigration" rel="nofollow">https://en.wikipedia.org/wiki/Electromigration</a>
Conclusion:<p>> The reason we don’t see square traces in most PCB designs is simply due to aesthetic convention. If it looks wrong, it is wrong. There is no specific reason why every circuit board design should shy away from 90-degree angles on traces, it’s just something that you shouldn’t do because it looks wrong.
Huh, article says not to worry about traces unless dealing with 100 MHz+ signal lines.<p>Isn't that very common? Hell even the MSP430 is running at 25 MHz these days.<p>And for all the other reasons listed in the article, you should avoid sharp corners. It's lazy to do otherwise when mitred 45 degree bends or curves are so easy to generate in a CAD tool. It's the hardware version of a code smell - the board house (compiler) might not care, but it should be fixed - don't give up freely obtained manufacturing slack because you couldn't set up a trace bend rule.<p>I kind of feel like PCB layout ought to just be done by the antenna engineers for any serious product with wireless comms or high speed I/O.
The image at the top of the article shows a number of traces that look like they're trying to climb a steep hill. I don't know much about PCB design, so my best guess is that those squiggles are trying to match a certain latency. But if 90-degree turns are so meticulously avoided in the industry, why is it okay to do multiple 180-degree turns in quick succession?
Related: looking at the main image, there are lots of places where traces routinely deviate to go around a pad, with an extremely low clearance, needlessly so. The designer probably took a defensive approach: the traces have been routed to leave as much space as possible to easily allow additional traces in the same gap.<p>So to me this pcb is a rough draft, an unoptimized initial version. The optimization obviously wasn't worth any time (and I agree with that), but I think an EDA tool worth its price should take such a design and optimize it. Such details really aren't the job of a designer, but still have the potential to significantly improve a layout.
Um wait, the main reasons for I know about is, that square corners are a huge issue with higher currents, as they tend to burn from the inside out, due to the lower resistance in the corner and non equal flowing of electrons.
I take issue with this article.<p>Electrons do bunch up on sharp corners, as far as high voltage design is concerned.<p>Sharp corners cause inductance when the current has to “turn the corner”. An infinitely sharp edge would have infinite inductance. Think of a charge having momentum, and the H field the result of that momentum. You can’t just change it.<p>This is more troublesome at RF due to the currents crowding at the edges of the line, where the path length is now different for inside and outside radius, irrespective of lumped discontinuities.<p>In the RF world we mitre the bends, and sometimes used swept bends. The swept bends supposedly radiate more than mitered, but have not proven that to myself.<p>The case where you do want sharp, 90 degree bends are on electrically small monopole type antennas. The inductance will compensate for the high capacitive reactance of the antenna.
For simple and slow communication busses on hobbyist boards, sure it probably doesn't matter.<p>But I really can't trust this very superficial attempt to prove a negative with regards to a very complex phenomenon that I do not think he understands, especially since he mentions nothing about inductance, reflections, or impedance changes.<p>Hell, RF experts with decades of experience will still find new corner-cases and issues with PCB layouts when it comes to analog signals.<p>In terms of "actual wisdom" regarding 90 degree traces: Some time ago at my job we had to actually scrap a PCB because of right-angle traces causing too much interference. The end effect was a comb filter on the signal and a ton of emitted RF interference.<p>TLDR: Yes, the phenomenon is real. Do not trust these hand-wavy attempts to dismiss it.
You can fit more in if you avoid 90 degree corners. You have shorter traces too.<p>Also, auto-routing exists so most people aren't handcrafting these corners.
TLDR "conventional" wisdom about square traces having adverse effects on introducing noise for high frequency lines turns out to be negligible. Instead square traces were/are frowned on because of acid pooling from the etching process for making PCBs.