I'm designing an electronic product that has a circular housing. There needs to be a PCB inside this form. In order to reduce costs as much as possible for high volume production (5K-10K), what shape PCB would cost the least?

enter image description here

A circle PCB works, but so does an octagon and hexagon. I'd like to know if any of these shapes lead to a lower cost due to how production is done.

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    \$\begingroup\$ A rectangular PCB, if you have enough space left on the board. \$\endgroup\$ – user110971 Sep 18 '19 at 17:13
  • \$\begingroup\$ Logical answer would be a hexagon, since you can stack them together. \$\endgroup\$ – Marko Buršič Sep 18 '19 at 17:14
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    \$\begingroup\$ Ask your PCB vendor. In the typical PCB process the board is routed out of a sheet, with breakouts (I can't remember what they're called) connecting them. Ultimately, you pay for the sheet, and most PCB vendors will want to lay things out in a rectilinear grid (i.e., not with hexagonal packing). \$\endgroup\$ – TimWescott Sep 18 '19 at 17:14
  • \$\begingroup\$ I think your best bet is to get quotes for all of them from a few different pcb fabrication houses. \$\endgroup\$ – narkeleptk Sep 18 '19 at 17:14
  • \$\begingroup\$ Are you panelizing yourself or getting the PCB vendor to panelize? 10K is not really that many, it may not make much difference. \$\endgroup\$ – Spehro Pefhany Sep 18 '19 at 18:37

Panelization and depanelization is not trivial,

When a board is panelized for production, it looks something like (Picture from surfacemountprocess.com)

http://www.surfacemountprocess.com/pcb-panel-design.html .

The intent is to maximize panel usage and minimize the number of cuts (tool touches) needed to separate the board. Ultimately what determines the cost of the board will be how many can fit on a panel, if you require extra tongues and spacing for clean depanelizing, you may pay more.

Also you fit fewer round PCB's on a rectangular panel than square PCB's

Ultimately a circular PCB panel will be something like this, with the red parts being the mouse-bite or routing tongues.

enter image description here

There are roughly 3 or 4 approaches that can be used for de-panelization

1. V Groove approach, only good for straight lines, and rectangular PCB's. A narrow groove is cut into both sides of the board along your outline . Images are taken from Murata MLCC Datasheet https://search.murata.co.jp/Ceramy/image/img/A01X/G101/ENG/GRM1882C2A102JA01-01A.pdf Murata GRM1882C2A102JA01-01A.pdf This V Groove can be broken in a few ways

1.a. Hand breaking which is also known "Snapping"

Murata GRM1882C2A102JA01-01A.pdf

1.b. Cutting Wheel (Paper cutter per @ScottSeidman) Murata GRM1882C2A102JA01-01A.pdf

1.c. A router can also be used (alternate to b)

2. "Mouse-bite" approach. Perforation is placed along the board outline, A router is used to remove all the extra board material, then the board is snapped along the perforation, usually by hand. The edge can be cleaned up with router or by sanding

enter image description here

Both of these approaches put flex the board, and still require a small connecting piece with the board.

3. 100% Routing, requires special jigs to hold the PCB, but the entire circle is routed out of the design

Generally a fabricator will charge extra for router use, but this is such a normal process now-a-days that it may be already in the cost. However total routing (without mouse bites or a small v groove edge), is a large premium. The tradeoff there is no board flex and cleanest edge.

I would echo @ScottSeidman suggestion to approach your fabricator for input on pricing and suggestions.

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  • \$\begingroup\$ Can you please provide links or citations for the top and bottom graphics in your answer? We want to be sure to give credit to their creators. \$\endgroup\$ – Elliot Alderson Sep 18 '19 at 17:58
  • \$\begingroup\$ @ElliotAlderson , Most of it is from Murata datasheets, I have updated references in text and image alt-text \$\endgroup\$ – crasic Sep 18 '19 at 18:14
  • \$\begingroup\$ Note that v-groove panels will typically be without any gaps between PCB's unlike my example photo \$\endgroup\$ – crasic Sep 18 '19 at 19:41

Most of the panelized circular (or similar) PCBs I've seen at Asian factories use a straightforward X-Y array with relatively generous spacing between the circles.

Usually you want to maintain the panelization intact through pick and place assembly and perhaps beyond that to testing and so on, so the board has to be connected well enough it doesn't come apart, and should have panel fiducials and tooling strips compatible with the requirements of your assembly line or assembly house.

You could probably use an X-Y array with a combination of routed and V-groove to get the best of both worlds and avoid those mouse bites entirely.

Anyway, without doing much work, my thought is probably an elongated hex with flattened sides (so really an octagon) in an X-Y array (not packed) with V-groove and routed roughly triangular "holes" is optimal by a small margin. To a first approximation, cost is based on the rectangular area that will totally enclose your PCB if they are panelizing.

V-grooves add a bit of cost but can reduce area by the 'kerf' of the routing tool. Vendors will want to use a relatively large routing tool. Also V-grooves usually are required to be completely across the panel, vertically or horizontally, so they're not suitable for hexagonal packing. It might slightly complicate setup for pick and place if they're not on an X-Y array too, but probably not very significant.

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Depanelizing tools are like specialized pizza cutters that open the V-grooves. They work in straight lines. I suspect, but don't know for a fact, that the circle would add expense.

I also suspect that the more operations, the higher the cost. You want to give the depanelizer a flat edge to work with at all times, so the operator doesn't have to hunt around for the right position.

You might also think of whether there's a clever way to panelize your board to make all the cuts horizontal or vertical.

Other than that, I recommend working with your fabricator. First, start by getting a quote for what you like. It might not be as expensive as you think. If you don't like it, work with them to minimize cost.

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  • \$\begingroup\$ You can change the circular shape to a line near the tabs. The extra cost probably comes from the extra empty space between the boards on the panel. You can pack rectangular PCBs more efficiently. \$\endgroup\$ – user110971 Sep 18 '19 at 17:20

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