Is it true that the shape of a PCB is supposed to be rectangular by default? - Page 1
Forum section: electronics / projects

author: dastructhm
author_rank: Contributor
timestamp: September 08, 2022, 03:51:52 am
content: I heard that if you were to design it with shapes like a square, a circle or other irregular shapes, something would go wrong, like EMI?Should I always make rectangular PCB's?

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2022, 04:00:58 am
content: I've never heard this. PCBs are made in all shapes and sizes, a rectangle is the most efficient use of materials but I don't see how it would make any functional difference.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 08, 2022, 04:08:26 am
content: Not sure either. Or at least the question is too generic as is.Sure depending on the shape of the PCB and component density, it may become difficult to route it in a way that makes the most sense EMI-wise, and if the shape is odd, I guess it could be pretty tough compared to a more common rectangular shape. But that's really all you need to consider here. The shape itself doesn't matter, it's the consequences of the shape on routing that could.

author: ataradov
author_rank: Super Contributor
timestamp: September 08, 2022, 04:27:55 am
content: Apart from the answers above, why not think about it for 5 seconds and locate a few PCBs around you or even go to the google and search for PCBs from any famous products? Do you see any trend for them to be rectangular?

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2022, 04:42:08 am
content: Quote from: james_s on September 08, 2022, 04:00:58 ami thought hexagon is the most space efficient..https://slate.com/technology/2015/07/hexagons-are-the-most-scientifically-efficient-packing-shape-as-bee-honeycomb-proves.htmland circle is the least surface tension in 2D...https://en.wikipedia.org/wiki/Surface_tensionQuote from: ataradov on September 08, 2022, 04:27:55 am

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 08, 2022, 05:01:54 am
content: I expect that it will depend on the process how the PCB shape is cut out. In case of the cutting tool it will be easier to produce and fit cutting tool which will cut rectangular shapes (at least in past, hard to say how it is now). In case that you use milling process than the the shape is only question of time.

author: Haenk
author_rank: Super Contributor
timestamp: September 08, 2022, 05:22:18 am
content: That likely dates back quite some time - no water jet or laser cutting available, so a straight cut was the only possible method to break down larger master PCBs. Plus most parts are square, to densly pack them, a square PCB is best. Plus the routing software back then made everything 90 degree. Earlier on, the manual routing for dense tracks was much easier, when doing straight lines.However this does not really matter a lot today - except for the wasted PCB material when doing non-square layouts.

author: Bud
author_rank: Super Contributor
timestamp: September 08, 2022, 05:59:31 am
content: PCBs in cell phones or tablets often have bizzare shapes. They perform fine.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 08, 2022, 06:48:43 am
content: The idea that a PCB is "supposed" to be rectangular, or any other shape, is nonsense.In any project, the mechanical outline of the PCB is usually one of the last things to be defined. The PCB fits the space, whatever shape that happens to be, once the industrial design of the enclosure, mounting points, connectors and any other fixed items has been defined.There are constraints, of course. In low to medium volume, PCBs are typically separated from the panel using a CNC router with a 2mm bit; the bit size defines the minimum internal radius on any corners.In high volume applications it can be worth manufacturing a die which can be used to stamp out individual boards like a cookie cutter. This is why things like PC expansion boards have very rough edges; they've been stamped out of the panel and not cleaned up afterwards.

author: niconiconi
author_rank: Frequent Contributor
timestamp: September 08, 2022, 07:05:01 am
content: Quote from: Haenk on September 08, 2022, 05:22:18 amExactly. There's no real manufacturing obstacle to use curves anymore. The only reason people keep using straight lines today everywhere is that they're still easier to draw and handle on a computer, especially in legacy or entry-level software. You can draw a rectangle with four mouse clicks, but a curve requires more efforts, especially if you want a free-hand Bézier curve.Traces have the same problem. With the advance of computers, you can use arbitrary curves nowadays (ironically, it's a return to the old days when free-hand traces were the norm). For example, I've seen many Altium and PADS layouts and they use curves liberally. In comparison, KiCad still doesn't support curves as its first-class citizen (KiCad 6 finally allowed you to smooth a 45-degree turn to a curve, but it's only a smoothing operation, you still can't draw a native curve), so it's really difficult to draw these shapes, the only workaround is exporting the layout to a 2D CAD, draw the curves, and importing the layout back - which is just not worthwhile the effort, most of the time. In my opinion it's a serious software limitation, but because it's not really a must-have feature, it's not serious enough to motivate someone to contribute code and implement it.If you use autorouters, nearly all of them are designed to work on a grid too, so straight traces are the norm. The only exception is TopoR with an unique free-hand routing algorithm.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2022, 07:41:16 am
content: they didnt need fancy bezier curve software nor laser/water cutter to do curve things back then (if they wanted to)... and i'm pretty sure they were more diligent and persistent with saw and file than we are today...https://www.reddit.com/r/electronics/comments/6pl8nj/interesting_looking_vintage_1980s_pcb/

author: oz2cpu
author_rank: Frequent Contributor
timestamp: September 08, 2022, 07:51:25 am
content: i have been designing PCB's and electronic products my entire life,some times they are funny shapes to fit / solve some special tasks,but YES most of them are rectangular just as you say. so yes that is correctly observed.a rectangular pcb can be milled or V-cut with almost no loss of material,it also most likely fit into most cases, they are also most likely rectangular,but you do see more and more round shaped products, it is not all of them that also contain a round pcbif the pcb is much smaller, it can still be rectangular or square.

author: Haenk
author_rank: Super Contributor
timestamp: September 08, 2022, 08:12:30 am
content: Quote from: Mechatrommer on September 08, 2022, 07:41:16 amThat's hand drawn and taped - doing curves looks less crappy than doing a not-so-straight straight line. It gets painful when doing a bus in curves. And is also not really fun to debug a mess of curved connections. This method is fine for handmade simpler designs though.Also note the straight cuts, even when it's not square.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 08, 2022, 10:55:57 am
content: Nah. Unless you're designing a modular system with card slots where you'd use eurocard pcb sizes, it doesnt matter. PCB fabricators used to moan about (charge a lot) for odd shapes, but thats a thing of the past. Let your imagiation run wild.

author: eutectique
author_rank: Frequent Contributor
timestamp: September 08, 2022, 11:07:37 am
content: You might find some new ideas in this video:

author: xrunner
author_rank: Super Contributor
timestamp: September 08, 2022, 11:30:17 am
content: Quote from: Bud on September 08, 2022, 05:59:31 amYep. I've had my Logitech Harmony remote apart many times to clean the keypads. The PCB is shaped just like the outside of the case. Why wouldn't it be if needed to get the maximum PCB area for components?

author: CaptDon
author_rank: Super Contributor
timestamp: September 08, 2022, 11:58:00 am
content: Where do you come up with these pondering questions?? Who ever told you J-Tag wasn't used in production? It is everywhere. As for shapes of PCB's, you could answer that yourself. Look at all the weird shaped objects with printed circuit boards, round CD players, oval radios, toys with all kinds of shapes, circuit boards with big holes in the center with a speaker magnet protruding through. Who told you J-Tag wasn't used or circuit boards should be square or rectangular? Next they will tell you the earth is flat.

author: coppice
author_rank: Super Contributor
timestamp: September 08, 2022, 12:02:24 pm
content: There was a time when most PCBs were assembled as individual boards. These days all but the largest boards are assembled as a sheet of multiple boards which are broken up after assembly and test. The board going through the assembly machines (pasting, PnP, soldering, test probing) usually needs to be a rectangle. The individual boards can be any funky shape you like.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2022, 12:20:46 pm
content: Quote from: CaptDon on September 08, 2022, 11:58:00 am19 posts, 16 topics... looks like we all bots taking the baits and he is the real human

author: reboots
author_rank: Regular Contributor
timestamp: September 08, 2022, 03:51:48 pm
content: Quote from: niconiconi on September 08, 2022, 07:05:01 amI'm surprised to read this. Curved traces was an important feature for me, and so I monitored KiCad's development of it for many years. As of version 6 I am able to natively draw curved traces, switching on the fly between a variety of miter styles. None of the plugins, smoothing operations and other tricks of v5 are necessary. Current version is 6.0.7 on Linux.I did find the default shortcut to switch corner mode cumbersome, so I bound it to 'j' which was undefined in the PCB Editor. This setting is located under Preferences -> Preferences... -> Hotkeys -> PCB Editor -> Track Corner Mode.

author: ataradov
author_rank: Super Contributor
timestamp: September 08, 2022, 04:07:20 pm
content: Quote from: reboots on September 08, 2022, 03:51:48 pmYeah, but editing those traces after they were placed is a pure hell. It is really not worth it except for rounded corners here and there.

author: tooki
author_rank: Super Contributor
timestamp: September 08, 2022, 06:57:03 pm
content: Quote from: ataradov on September 08, 2022, 04:07:20 pmAltium is the same way. Editing them is nightmarish.(I did one board with rounded corners for fun, and to edit, I would convert a track back to mitered, make the changes, and then switch it back to rounded.)

author: reboots
author_rank: Regular Contributor
timestamp: September 08, 2022, 07:35:17 pm
content: Quote from: ataradov on September 08, 2022, 04:07:20 pmI don't find the workflow to be significantly better or worse than with Cadsoft Eagle, where I'll usually rip up and reroute segments of a trace which need to be moved.I'm not claiming Eagle's workflow isgood, just that KiCad is a workable alternative in this respect.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 08, 2022, 08:00:42 pm
content: Eagle is pretty much dead now anyway, isn't it?

author: jpanhalt
author_rank: Super Contributor
timestamp: September 08, 2022, 08:24:32 pm
content: Quote from: SiliconWizard on September 08, 2022, 08:00:42 pmDead? QEII is dead. (I remember her coronation. God save the King.) Eagle 7.x is not. The version I bought still does everything I need it to do, supplemented by its ULP's. Curves and tear drops are easily done, as are imports of DXF centered on whatever axis origin you choose.Is the default board rectangular? Yes, of course. My monitor is also rectangular. I remember when TV screens were round and you watched the neighbor's through a large magnifying glass because in 1947, not many people had them. I wasn't designing PCB's then, nor were many other people alive today.