Right angle traces - Page 1
Forum section: electronics / beginners

author: talvor
author_rank: Contributor
timestamp: September 20, 2013, 06:03:29 am
content: Hi, I currently in the process of laying out my first PCB for an 8x8 RGB LED Matrix.I would like to know if using right angle traces is a bad thing? And if so why.ThanksPhillip

author: Psi
author_rank: Super Contributor
timestamp: September 20, 2013, 06:26:00 am
content: It's bad practice.And 45deg just looks nicer.The usual arguments against 90deg tracks are..- They act as an antenna at high frequencies, producing noise and loading your signal (there's some debate about this)- The copper track itself can break off the pcb easier because of the small area right at the corner.In reality it's not going to make any difference if your circuit is simple and slow speed. Like a typical 8bit mcu or 555 timer.But, other engineers who see your design wont be impressed.Best to always do 45deg, you never know when you may need to show your PCB to someone, if its got 90deg tracks you probably wont get offered a job.

author: sleemanj
author_rank: Super Contributor
timestamp: September 20, 2013, 06:26:26 am
content: Quote from: talvor on September 20, 2013, 06:03:29 amFor your 8x8 led matrix purposes;Angles less than or equal to 90 degrees are usually considered to be aesthetically displeasing (they look naff).The sharp angle can create problems with etching, especially if you do it yourself, it's easier to break a trace at a sharp corner.other than that, copper is copper (for your project's purposes).

author: IanB
author_rank: Super Contributor
timestamp: September 20, 2013, 06:29:45 am
content: I think it's the sharp corners that are worse than the angles.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 06:30:35 am
content: Check this out ->NO ! You don't need to worry about 90 degrees corner at PCB traceIf you believe 90 degrees is bad, then never use vias on your board.Also quoting from PCB expert :Right angle bends do not cause signal integrity problems at any practical edge speedRight angle bends also do not cause EMIRight angle bends are NOT acid trapThere is no good technical reason to prevent the use of right angle bends to route traces in a PCB."Vias used to route signal from one layer to another do not have a significant impact on signal quality even with 200 ps edges."

author: talvor
author_rank: Contributor
timestamp: September 20, 2013, 06:39:51 am
content: OK, so right angle bends are a bad idea. Cool, now I get to play around in KiCad for a few more hoursSo where should I put the 2 x 45 degree bends, close to where the 90 degree one is or further along the trace. That is should I be trying to make the straight parts of the trace as equal as possible, or does this not matter.

author: Unknown
author_rank: Unknown
timestamp: September 20, 2013, 07:09:49 am
content: Quote from: Psi on September 20, 2013, 06:26:00 amLow speed is up to a few GHz in this case. That's one fast 555!

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 07:15:22 am
content: You need a nice radius to each bend, to help the electrons take the corner without flying off. They move really fast you know.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 07:21:25 am
content: Quote from: GK on September 20, 2013, 07:15:22 amNot even close, if I'm not mistaken, according to Dr. Howard Johnson at TheAmpHour session, the physical speed of the electron moving inside the conductor is even slower than a walking ant.

author: marshallh
author_rank: Unknown
timestamp: September 20, 2013, 07:29:28 am
content: The only electrical problem with 90 degree bends is at high speed (>100mhz) where the small part of excess copper is a minute parasitic capacitance... if you are working with stuff fast enough to worry about it, you already know the problem. At ghz speeds it becomes a waveguide and that's when you see mitered edges on the bends.45 bends look better though.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 07:35:34 am
content: Quote from: marshallh on September 20, 2013, 07:29:28 amAgain, in the Dr. Howard Johnson session at TheAmpHour, this is also discussed and he said that at the sharp 90 degrees tip at the corner creates the same effect no more than a small lump of solder at the pcb even at ghz signal.

author: marshallh
author_rank: Unknown
timestamp: September 20, 2013, 07:56:45 am
content: Exactly, you'd have to route DDR3-1600 using all right angle bends for it to approach being an issue

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 08:25:18 am
content: Quote from: BravoV on September 20, 2013, 07:21:25 amWhich species of ant? There is a lot of variation you know.

author: DutchGert
author_rank: Frequent Contributor
timestamp: September 20, 2013, 08:32:33 am
content: Quote from: BravoV on September 20, 2013, 07:35:34 amIn my experience Dr's unsually don't know much about production.In the past 90* corners would lead to etching problems and indeed sharp edges come of the board easyer.In your case it's fine to use sharp edges, it's makes you just look like an absoluut n00b.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 08:36:08 am
content: Quote from: GK on September 20, 2013, 08:25:18 amOk .. ok ... I get it, must be this one ...The Atom Ant !!!!!

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 09:40:50 am
content: Years ago in high school we all had to assemble in the library one afternoon to receive a lecture in electrical safety from some supposed expert that they (school admin) managed to find from who knows where. He was an old fart and shortly after he started yacking, it became quite clear that rather than being an expert on electrical safety, he was a bit of a nutter. Spent the whole time overly enthusiastically trying to scare us, eyes bulging and arms waving and all, with exaggerated examples and stories of real life electrocutions. He concluded his spiel with an account of some bloke who got his fingers in between the joiners of an electrical extension lead - "the electricity shot right up his arm, couldn't take the corner at the top and blew his shoulder right out!". Fair dinkum. Our technical studies teacher Mr Walkley marched out of the room shaking his head. The students thought the whole lecture was totally awesome, of course, except for a few of the girls.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 20, 2013, 10:29:32 am
content: so... this $800 worth of device from Agilent is a bad practice? or they purposely intending to flew some electrons away to make the device within spec?

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 10:49:44 am
content: An absolute poop load of old stuff was layed out exclusively with 90 degree bends - especially digital boards in the '70s full of logic chips. I'm not sure that the manufacturing/etching argument was ever that valid.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 10:54:49 am
content: Quote from: DutchGert on September 20, 2013, 08:32:33 amQuote from: Mechatrommer on September 20, 2013, 10:29:32 amI guess we will have to wait for DutchGert for that, since he boldly claims Howard Johnson and Agilent are bunch of noobs.

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 11:48:21 am
content: The only problem is manufacturability.Acid traps is still a problem, despite what the experts claim it no longer is.Sure, the problem has been solved for run of the mill boards with 8 mil traces... Once you get to hdi boards it becomes a problem again. It all has to do with the thickness of the copper vs the width of the trace. etching a 3 mil trace in 1 ounce copper is borderline. Throw in a sharp corner and the misery begins.Sharp corners also have other problems. The soldermask is easier damaged .That stuff all doesnt maater for your one-off board.. But for industrial production it does as it has an impact on the yield and durability of the end product.

author: Psi
author_rank: Super Contributor
timestamp: September 20, 2013, 11:51:23 am
content: Are there any advantages to a 90deg tracks that you don't get from 45deg ?Other than maybe routing a tight corner slightly easier i cant think of any.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 20, 2013, 11:56:09 am
content: Quote from: Psi on September 20, 2013, 11:51:23 amyou can measure traces length easier with a ruler and one eye.

author: BravoV
author_rank: Super Contributor
timestamp: September 20, 2013, 12:10:36 pm
content: Quote from: Mechatrommer on September 20, 2013, 11:56:09 amYou're right, like in calculating the resistance across the trace in high accuracy, eg. using copper trace as low ohm resistor.

author: DutchGert
author_rank: Frequent Contributor
timestamp: September 20, 2013, 12:30:23 pm
content: Quote from: free_electron on September 20, 2013, 11:48:21 amThis and the fact that using 45* usually leads to shorter traces -> more free space for components or planes: win-winAparrently my RF story was a big load of crap as I just found out.And ofc it simply looks nicer with 45*

author: Psi
author_rank: Super Contributor
timestamp: September 20, 2013, 12:31:08 pm
content: Quote from: BravoV on September 20, 2013, 12:10:36 pmAccuracy would be better measuring that with a low ohm meter.Rather than relying on distance measurements and assumptions about the copper thickness being exactly what it should be.

author: Rigby
author_rank: Super Contributor
timestamp: September 20, 2013, 01:05:04 pm
content: I'm not very experienced in electronics, but I'm becoming somewhat of an aged fella; experienced in life. One of the very few things that has been constant in my life is the general lack of correctness in "well known" things like this.That is, the more people who "know" something, the less likely it will ever be verified. Knowledge that is taken for granted is never verified. Why would you test it, when everyone "knows" it?Everyone "knows" that XML is far slower to read, write, and parse than plain text. (false.) Everyone "knows" that HTTPS is far slower than HTTP. (false) All sailors "know" that a snapped deck line under tension will cut you in half if it hits you. (false.)I suspect this is one of those things that everyone (or almost everyone) takes for granted and never verifies, trusting the (potentially false) community wisdom over the scientific process that could prove it one way or another.The hallmark of this phenomena is the 100% conviction shown in something that is a potential pain to test. In software development, false community knowledge is rampant.I'd bet that few of you who declared the 90 degree corners a bad idea have access to the RF signal generators, RF leakage detectors, or any of the necessary equipment (whatever that equipment may be) to test this, and those of you that do have access to this equipment wouldn't use it to test something "well known" like this.I'm not arguing with anyone. I can't tell you that any of you are correct or incorrect, because I don't know who is correct here, but I can say that this REEKS of generational knowledge that has never been tested by anyone repeating it today, and that has just as much of a chance to be correct as it does to be incorrect.

author: Psi
author_rank: Super Contributor
timestamp: September 20, 2013, 01:20:34 pm
content: Quote from: mojo-chan on September 20, 2013, 01:05:38 pmThis comes to mind.

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 01:42:20 pm
content: If acids traps are an issue for 90 degree bends, then why aren't they an issue for the inner corners of T junctions? Or do they have to be broadly radius-ed for ultra fine tracks? Most board houses do 6 thou track width minimum. Does anyone not laying out boards with ultra fine tracks (=> 6 thou) need to care?Incidentally, I don't use 90 degree bends, but that is besides the point.

author: c4757p
author_rank: Super Contributor
timestamp: September 20, 2013, 01:59:06 pm
content: I was under the impression that theywereconsidered a potential issue for T junctions, hence why T junctions are occasionally seen with "chamfered"* corners.*Not sure if "chamfer" is really the right term here, but anyway, y'all know what I mean... O0

author: GK
author_rank: Super Contributor
timestamp: September 20, 2013, 02:06:36 pm
content: Well, I've never had a T junction not etch cleanly, even with 6 thou tracks. I could imagine "chamfering" the corners of every T junction on a moderately complex board being a major pain in the arse. Do any layout packages even have the capability to do that automatically? BTW, I've got Altium Designer 13 now

author: c4757p
author_rank: Super Contributor
timestamp: September 20, 2013, 02:20:33 pm
content: No idea. TBH, I've never had anything 8mil and up not etch cleanly at home in my kitchen unless I do something really clumsy. I find it a bit hard to believe that real PCB fabs would have more trouble with simple things like that than I have in my kitchen. But I have heard that.No idea if anything can do it automatically. My instinct is that if anything can do it, Altium can... but I have no idea. One things's for sure - KiCad can't

author: MacAttak
author_rank: Unknown
timestamp: September 20, 2013, 03:26:33 pm
content: I find it interesting that so many people have clearly stated that obtuse angles (and preferably 45 degrees) "look better" than right angles. Yet the preference was exactly the opposite in the other thread that discusses schematic wire routing.On a schematic, everyone wants right angles. On a PCB nobody wants right angles.However the science and reasoning behind either of those stances seems dubious at best but mostly specious?

author: AlfBaz
author_rank: Super Contributor
timestamp: September 20, 2013, 03:55:42 pm
content: Would the sharp edge of a corner be a slightly better antenna thereby promoting coupling to adjacent parallel tracks like those in a multilane bus?

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 03:59:31 pm
content: Quote from: c4757p on September 20, 2013, 01:59:06 pmbingo.Code:--- ---\/|yes you still have a sharp 90 degree corner in the valley of the V but... the other side has a loooong trace running away , so even if you get a bit of underetching the out laying corner covers that.now, there is another aspect : length egalisationtake a 32 bit wide bus and have it make a 90 degree corner. the outer trace will be much longer than the inner trace.make the turn with a 45 degree angle and this changes.

author: AlfBaz
author_rank: Super Contributor
timestamp: September 20, 2013, 04:04:22 pm
content: As for proving electrical issues, if I remember, the next time I get on to hyperlinx I might do a few sims and see what, if anything, pops up

author: Unknown
author_rank: Unknown
timestamp: September 20, 2013, 04:15:37 pm
content: Quote from: free_electron on September 20, 2013, 03:59:31 pmThe same will happen with two 45° corners.

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 04:24:56 pm
content: Quote from: alm on September 20, 2013, 04:15:37 pmyes, but with 45 degree corners you can often get away with only one turn.... with 90 degree corners you need two ...

author: WarSim
author_rank: Frequent Contributor
timestamp: September 20, 2013, 06:31:28 pm
content: Quote from: Mechatrommer on September 20, 2013, 10:29:32 amLOL look at the board! Really look and you point will become a joke.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 20, 2013, 07:20:36 pm
content: Quote from: WarSim on September 20, 2013, 06:31:28 pmclarification is much helpful. edit: "much more!" clarification is "much more" helpful.

author: WarSim
author_rank: Frequent Contributor
timestamp: September 20, 2013, 07:46:06 pm
content: Quote from: Mechatrommer on September 20, 2013, 07:20:36 pmAll of the critical paths use obtuse angles on the example given.Several of the 90deg paths required 90deg paths.Some of the 90deg paths functions are not obvious and most likely DC distribution and unlikely require obtuse angles.Only a very few could be argued to be non-critical compromises to fit the pattern.None of the "rules of thumb" have been obviously broken by the board shown.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 22, 2013, 12:20:17 am
content: Quote from: WarSim on September 20, 2013, 07:46:06 pmReally look and you point will become a joke. most 90deg traces can be converted to 45deg. they even "mixed up" 45 and 90 deg for no apparent reason. take for eg the bottom most OP07 the traces out of it is mixed (the 4 parallel traces). give me the pcb file i can convert them all to 45 deg.Quote from: WarSim on September 20, 2013, 07:46:06 pmReally read and you'll understand. i was asking if its a bad practice, regardless of anything in the world, someone argued "90deg is a noob and bad looking". not anything to do with ee or SI, its only MHz range and not fine line less than 4mil i believe as someone working with fine BGA said. so... the rule of thumb as stated by some of the posters IS broken.

author: IanB
author_rank: Super Contributor
timestamp: September 22, 2013, 12:34:39 am
content: No comment needed

author: AlfBaz
author_rank: Super Contributor
timestamp: September 22, 2013, 01:27:39 am
content: So for length matching, would this be a definite no-no?

author: WarSim
author_rank: Frequent Contributor
timestamp: September 22, 2013, 02:45:45 am
content: Quote from: Mechatrommer on September 22, 2013, 12:20:17 amYes most can be converted, I never disagreed with that. I think we have a very different definition of "rule of thumb".The board was presented as an example as an obviously bad board, I disagreed. Then again I did not research the board to determine what was a simple trace or a resistive or inductive element nor a matched pair. Maybe we also disagree on the word obvious also.I disagreed, I said my piece now I stopped caring if you insult someone else's layout designs.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: September 22, 2013, 04:41:57 am
content: I think something is not right here because we are talking about ways to reduce unwanted reflections but most of examples given working in range of frequencies that are waaaaaay below the point when it starts to matter.To my knowledge it only make sense when track with is greater than 1/10 of wavelength which means that for anything less than 400MHz. Even for 900 MHz things like corners don't really matter as much. At frequencies above 4 GHz sharp corners can create reflections. ADS (Advanced Design System) for example offers curved, chamfered and mitered bends and these are separately modeled elements when moved to schematics for simulation. Angle, radius and size of track matters in this case in other words it is not just rounded - geometry has to be right otherwise it can make matters even worth. For frequencies below 200 MHz this kind of details have no effect. Someone had a photo of 200MHz active probe from HP. It is only 200MHz.When I think about this things I always imagine a trough filled with water. Now if you have 10MHz signal on a 4 cm track it is like looking at effect of 1 kilometer long tsunami wave in 1 meter long trough. But when you observe 5mm wave in same trough you will see the reflections in the corner.

author: BravoV
author_rank: Super Contributor
timestamp: September 22, 2013, 07:11:00 am
content: Quoting Dr. Howard Johnson on his article on "Who's Afraid of the Big Bad Bend?" ...QuoteRead it yourself the complete writing here ->Who's Afraid of the Big Bad Bend?Before anyone deny Mr.Johnson's argument, please, at least provide your own professional proof or "publicly" written research/experiments etc to counter his writing, otherwise, personally I will keep "blindly" trust Mr.Johnson.

author: free_electron
author_rank: Super Contributor
timestamp: September 22, 2013, 07:12:05 am
content: Quote from: AlfBaz on September 22, 2013, 01:27:39 amThat would be a no-no, but not for signal integrity reasons. It's a no-no for manufacturability. Especially when using small geometries. If the amplitude vs repetition distance ratio is large then you will get etching problems ( amplitude is how tall the matching weave is compared to the opening between the tracks and width of track.) For a dense weave you need either chamfered or rounded turns.Signal integrity is not affected. It is purely a processing problem. The sharp corners are prone to resist peeling when they scrub the boards . After developing the boards are scrubbed with brushes. Sharp outside edges can get damaged. Either lifting the resist or ripping it off.During etch the outward facing corner gets attacked from both sides. This gives an underetchIf the resist was te lift during etch (we are spray etching under high pressure these days) this can give thickness variations and all kind of other problems that will cause the board to be rejected during inspection. The trace is not necessarily et hed open, it is irregular , the corner is slanted and visual inspection will fail this board as a reject. This cost money for the board fab.So they dont like this.Again, if you are doing 8 mil traces it is ok , but start messing around at 4 mil and below and the board house will contact you and request bot to do this, or they will increase the price as the yield goes down.As for Mr Johnsons statement .. It is 15 years old... The world has moved on . Notice how he talks avout 8 mil traces ? Take a look at a board as made for a smartphone or a tablet. The logic board for the ipad uses 2 mil traces ... There aint a lot of room for etching variations there...I believe johnson actually revised that statement a couple of years ago. I need to look it up , i have the coursebook at home.

author: BravoV
author_rank: Super Contributor
timestamp: September 22, 2013, 07:22:13 am
content: Quote from: free_electron on September 22, 2013, 07:12:05 amGreat, really eager to see that revisions.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 22, 2013, 07:31:53 am
content: Quote from: WarSim on September 22, 2013, 02:45:45 amok i get it, you have a serious misunderstanding here, you cant differentiate a statement and a question mark. you've not met sarcastic type of statement yet cheers

author: GK
author_rank: Super Contributor
timestamp: September 22, 2013, 01:26:29 pm
content: Quote from: IanB on September 22, 2013, 12:34:39 amLike I said in reply #17, though that board is really high tech, with 74LS chips rather than just 74's.

author: AlfBaz
author_rank: Super Contributor
timestamp: September 22, 2013, 01:47:57 pm
content: Quote from: free_electron on September 22, 2013, 07:12:05 amThanks for the insight FE

author: AlfBaz
author_rank: Super Contributor
timestamp: September 23, 2013, 01:40:38 am
content: Quote from: AlfBaz on September 20, 2013, 03:55:42 pmRan some quick simulations4/4mil track space 2ns rise times, same layer stackup, 2 tracks on top layerThe drive ends of the tracks start far away in one instance the approach is 45 deg the other 90, run together for about 0.4" and then seperateThe 45 degree approach, with a longer parallel run required 240mV threshold setting to avoid coupling indication90 degree approach, with a shorter parallel run required 450mV threshold setting to avoid coupling

author: AlfBaz
author_rank: Super Contributor
timestamp: September 23, 2013, 01:54:04 am
content: EMI simulation also revealed higher emissions with the right anglesfor the pics belowRA = Right anglesNRA = No right anglesEdit: in the pics below, ignore the lines at the top, they're different emission limits for various standards