This is mostly out of pure curiosity, but when designing a PCB, are there any pros to going with a rounded or circular shape? I can see the obvious con of losing out on surface area for running traces or placing components, but I'm curious if there's any gain to it as well.
Any other information about how the design may be impacted electrically or mechanically is welcome. Like I said, this is mostly out of pure curiosity.
There aren't really any pros and cons for PCB shape without additional context. If you need to fit a board into a circular device, then a circular shape maximizes the area of the board.
The most obvious con, to me, would be yield of boards in a panel. Any non-rectangular shape would leave voids in the panel which you are going to be paying for, but unable to use, in mass production.
Another potential con might be in assembly and testing. Tooling to hold the PCB during testing or assembly may be lower cost with rectangular-shaped boards, because no special considerations or changes need be made. However, as you mass-produce larger quantities, setup for such tooling becomes less significant.
Well, generally speaking, you make a board only round when you have to (or maybe for aesthetics). So an obvious pro is that round boards can fit in places where rectangular boards don't.
Cons of round boards:
Typically (at least in small to moderate quantities) you'll pay for the area of the smallest rectangle your board fits into, so a 100mm round board will cost the same as a 100mm x 100mm board. The former has area of 6940mm^2 if you allow 3mm around the perimeter, the latter 9409mm^2, so you lose more than 1/4 the board space.
It's probably worse than that in practice since components tend to be linear or rectangular and thus don't fit into an area with curved edges without more wasted space. Smaller boards (in relation to component sizes) would be worse.
The shipping weight will be reduced a bit, so there's that.
If you want to use V-score the boards will have to be both routed and scored and the panelization will have the boards using just the same area as if they were squares of the circle diameter (square packing rather than triangular or hexagonal). They will also have small rough flats on some or all of the edges.
There's no particular issue for modern PCB manufacturers to make round (or indeed elliptical) circuit boards without much (if any) additional charge but it may not be the most convenient in general. For some applications such as mounting inside sensor heads (such as the below, image from here) it is necessary unless you can fit everything on a much smaller rectangular board of an area that can be inscribed inside the circular cavity.
If it's just for looks, you can round the corners off and have a board that's a bit more pleasant to handle and perhaps fits inside a housing with curved inside corners such as an Altoids tin (like the Beaglebone Black).
I would like to add to this question from our perspective as a PCB assembly company. So this is regarding the actual manufacturing of your product.
To assemble the bare PCB, all PCBA companies will put your individual PCB into a panel of multiple PCBS. On one hand, this is to reduce the handling times (like buying a carton of 12 eggs instead of individual eggs), on the other hand, this is to make it possible to run the PCB on automated conveyors during assembly. Generally speaking, most companies will want to have a 10mm frame around the panel without components to make sure the PCB can be transported on conveyors and to have sufficient surface area to clamp the panel in the various assembly processes (paste printing, pick-and-place).
Having a round design limits the PCB assembler in how they can connect the individual board to this panel, and it ultimately limits the ways in which the depanelization can happen later. We like to panelize PCBs with V-Cuts instead of tabs (also called catwalks). This is because the panel connection is quite stable during assembly and can quickly be separated with a machine that runs a blade over it to cut the boards out of the panel. If you have a round PCB, there are limited options to connect the PCB with a v-cut. If you add perforated tabs, those might be in the way during your assembly unless the depanelization was done with a very precise milling process.
If you would like to have a round shape overall, I found it best to straighten out the edges of the PCB. You lose a bit of surface for routing, but you ultimately enable your PCB assembly house to chose whatever panelization method best fits your quantity.
Here is an example image I just drew up:
A: Round PCB B: Round PCB with straightened edges C: Example of panel connection with straightened edges
A final consideration is efficient material usage of PCB base material. While this is not such an important consideration with small volumes or double sided standard PCBs, wasting PCB base material can have a punishing effect on your final product price for very high layer counts or special PCBs such as metal core PCB or rigid-flex PCBs where the cost of the base materials are a significant factor of your PCB price.
EDIT - Updated PCB panel based on Spehro Pefhany's comment:
The original question may be referring to rounded or square corners.
Pros: Corners rounded around mounting holes are less likely to get mechanically damaged during box build, or if the PCBAs are dropped accidentally.
Cons: To separate boards during depanelization, PCBAs with rounded corners need to be routed, which is slightly more expensive than V cutting or perforation.
If you require your boards to have smooth edges and prefer routing for separation, I'd opt for rounded corners.
