why use curly tracks - Page 1
Forum section: electronics / projects

author: bug13
author_rank: Regular Contributor
timestamp: November 24, 2017, 12:05:18 am
content: Hi guysI come across this today, this is a PCB in a lithium battery for a cordless power tool (this:http://www.ryobi.co.nz/power-tools/products/list/family/brushless)From my quick google search, I can understand that it maybe used to reduce reflection. But I don't understand these curly tracks are required in a lithium battery pack. I mean they don't do high frequency (in GHz range) in these battery right? So why did the design do that?

author: chris_leyson
author_rank: Super Contributor
timestamp: November 24, 2017, 12:22:18 am
content: In this case I don't think there is any particular electrical reason for the curly tracks it's just that the pcb designer prefered to route the board like that, it's probably more to do with aesthetics. A lot of PCB design packages allow you to switch off 45 degree routing and use various curved traces.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 24, 2017, 02:34:34 am
content: Hi,This layout looks 'old school', it may have been done without a CAD system. You can make the artwork with paper tapes and precut pads. This was common 30 years ago, but rare today.Jay_Diddy_B

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 24, 2017, 02:38:49 am
content: Not hard to do, may be easier in some than other EDA packages. Most it's just tedious (e.g., Altium can route with arc segments, but they're harder to adjust).Tim

author: pigrew
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:40:35 am
content: I like how the layout looks. There are some minor advantages to the fabrication process due to etch rates/bias being very slightly different at sharp corners, so things are more uniform if there are no sharp corners.Notice how there are nice teardrops at most of the pads, which decrease the chance of open circuits if the drill alignment is bad.It's my understanding (I have no first hand experience) that sharp corners can cause the conductors to be torn in flexible PCBs.

author: floobydust
author_rank: Super Contributor
timestamp: November 24, 2017, 03:03:29 am
content: You get fewer acid-traps I think and at high frequencies reflections are less with curved traces. A 90 degree elbow is too abrupt.In the very old PCB layout days, it was easier to curve the tape instead of cut'in splice to do a right-angle turn. So old PCBs from the 70-80's were curved traces, then CAD came about and made 90 degree elbows as it was easier to draw.

author: tautech
author_rank: Super Contributor
timestamp: November 24, 2017, 03:26:27 am
content: Looks plain retarded.45's and curves on the same traces ? ?

author: Someone
author_rank: Super Contributor
timestamp: November 24, 2017, 03:33:40 am
content: Quote from: pigrew on November 24, 2017, 02:40:35 amAgree, sharp corners and points do affect etching reliability the teardrops help there too by eliminating internal corners where pads meet traces.Along with impedance/differential matching reflections etc, curves also become important for shaping voltage fields when you get into "high" voltage designs.

author: daqq
author_rank: Super Contributor
timestamp: November 24, 2017, 07:36:20 am
content: I'd say that in a lot of cases while there's no reason to use curly traces, there's no reason NOT to use curly traces. If the aesthetics please the designer there's no reason why to avoid them.Also, the electrons don't shoot out when going too fast and encountering an edge

author: ogden
author_rank: Super Contributor
timestamp: November 24, 2017, 07:56:43 am
content: Quote from: daqq on November 24, 2017, 07:36:20 amAt >= 1GHz frequencies waves of electrons may bounce back, thou charger is not the case. Particular board looks to me as "work in progress" where someone did some corner straightening, but ran out of timeOther option - engineers changed. Designer of last board revision have other style (visual preferences) than one who created it

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 24, 2017, 08:56:10 am
content: Quote from: floobydust on November 24, 2017, 03:03:29 amThere's some fairly high frequency stuff that does fine with 90 degree corners. It's a bit of a myth that this would be an issue, unless you're talking about very high microwave frequencties.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: November 24, 2017, 09:08:26 am
content: They could had cleaned it up a biti am a bit of clean freak with flux residues.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2017, 10:10:26 am
content: Curved tracks can also be more space efficient. Angled corners and zig-zags take up more space than curves when you have a bunch of parallel tracks and space is tight. It certainly takes less space to curve a track around a via.

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2017, 10:34:31 am
content: There is a topological router called TopoR that routes like that...

author: mikerj
author_rank: Super Contributor
timestamp: November 24, 2017, 11:27:00 am
content: Quote from: tautech on November 24, 2017, 03:26:27 amIt does look odd. I'm wondering if perhaps more than one person worked on this, and one of them couldn't be bothered to radius all the bends.

author: ogden
author_rank: Super Contributor
timestamp: November 24, 2017, 03:30:53 pm
content: Quote from: Mr. Scram on November 24, 2017, 08:56:10 amDepends on what you consider "very high microwave frequency" and how wide are tracks as well. Usually at 1GHz effect is barely measurable, at 5GHz (which is not that high microwave freq at all) and up you shall pay attention on what you are doing. Better just run straight and downconvert your signal to lower frequencies ASAP before corner

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 24, 2017, 04:13:43 pm
content: Quote from: ogden on November 24, 2017, 03:30:53 pmNot a very high microwave frequency, but a very high frequency, or a microwave frequency. The rest has been answered by Dave and others many times over.https://www.eevblog.com/forum/eda/no-!-you-don't-need-to-worry-about-90-degrees-corner-at-pcb-trace/

author: nctnico
author_rank: Super Contributor
timestamp: November 24, 2017, 05:21:46 pm
content: Quote from: T3sl4co1l on November 24, 2017, 02:38:49 amI can imagine it is done to achieve a higher clearance and/or higher density compared to 45 degree routing.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 24, 2017, 05:32:04 pm
content: It looks totally arbitrary to me. Perhaps a new designer recently discovered the corner radius tool and thought it looked cool.Short and misplld from my mobile......

author: chris_leyson
author_rank: Super Contributor
timestamp: November 24, 2017, 05:33:34 pm
content: I wouldn't worry about 90 degree bends either, you can always put a chamfer on the corner to correct the capacitance but it's unlikely I will do any PCB design at 10s of GHz. It's funny, a long time back I read a report from some "EMC consulant" who was advising somebody beacause a logic PCB with a not very fast microprocessor was failing emissions at a few hundred MHz, he said you had to chamfer the 90 degree bends to fix the problem. It was odd because there were no 90 degree bends and he had failed to notice the rather long slots in the grounplane. I think he got paid something like £500/day for that. Also seem somebody go to a great deal of trouble to route an RS485 pair as an HF 120 ohm balanced pair, some people just havn't got a clue. I once routed a Gige ethernet flexi cable with lots of serpentine wiggles and I think I got the mismatch down to 20ps, a complete and utter waste of time but I was bored and it was fun. I suppose curly tracks have their place and they could have been used to get more clearance.

author: imidis
author_rank: Frequent Contributor
timestamp: November 24, 2017, 06:30:27 pm
content: Looks kind of nastalgic

author: IconicPCB
author_rank: Super Contributor
timestamp: November 25, 2017, 02:10:47 am
content: 2N3055 mentioned TopoRHere is a sample of TopoR output generated yesterday.

author: 2N3055
author_rank: Super Contributor
timestamp: November 25, 2017, 09:58:05 am
content: Quote from: IconicPCB on November 25, 2017, 02:10:47 amYep, that is it... TopoR routes surprisingly good, and uses space very efficiently... Looks wierd but it works... Electrons don't mind ..

author: bd139
author_rank: Super Contributor
timestamp: November 25, 2017, 04:44:35 pm
content: I rather like that!

author: pigrew
author_rank: Frequent Contributor
timestamp: November 25, 2017, 07:20:16 pm
content: Quote from: 2N3055 on November 25, 2017, 09:58:05 amI like the curves, but I tend to increase the spacing so that the ground fill can pour between all the tracks. I expect the router has an option to do this. I should try it out.

author: Kilo Tango
author_rank: Regular Contributor
timestamp: November 25, 2017, 07:32:02 pm
content: here's part of a microwave detector running at up to 40GHz.Ken

author: ogden
author_rank: Super Contributor
timestamp: November 25, 2017, 10:02:17 pm
content: Quote from: Kilo Tango on November 25, 2017, 07:32:02 pmAs expected - curved microstrip instead of corner

author: floobydust
author_rank: Super Contributor
timestamp: November 26, 2017, 05:44:00 am
content: A few PCB design docs say curves are only needed >2GHz.