Triangular PCB Cutout Procedure

[Unsanity]

A while back I got a triangular PCB from JLCPCB. The edges are very smooth and square. I have always wondered how a triangular PCB might be cut out in a small volume production (~10 ordered).

Because of how smooth the edges are, I don't think they were v-cut. milled maybe? but then how are all of the edges milled....? I always thought they were partially milled out, then snipped and sanded smooth, but that just seems like to many steps for something that only cost $2  I added a few pictures...

I figured I would shoot this question into the ether and see what others might think.

[bpiphany]

You are likely going to have to pay for a square wherein the triangle fits, but other than that you just submit a triangular outline.

And in the case of JLCPCB's $2 offer, that would be within a 100x100mm square.

And yes their PCBs are delivered with milled outline.

[ataradov]

I would like to see how they actually do work-holding while milling those out. I've ordered 10x15 mm PCBs with milled outline. And I can't imagine a machine that would hold them for the whole perimeter milling.

[Doctorandus_P]

I would like to see how they actually do work-holding while milling those out.

Attached a panel from the purple company that sheds some light on this.
the holes in the corners are probably used for aligning during production, for example between drilling and etching, where the panel has to move between different machines. these holes become more important with multi layer PCB's of course.

For the milling. They probably only clamp the outside perimeter of the PCB during routing, and then start with routing far away from the clamps. and route nearer to the clamps as routing progresses. You could for example only clamp on the left side, and then start with routing on the right side.

[bpiphany]

I don't know if they leave cutoff tabs or not. Anyone care to guess how clean cuts a tool like this gives?
https://www.olamefusa.com/e_dptools.htm

[T3sl4co1l]

Yes, milled.  You can see the start/end marks where there's bumps in the outline.  These are typically within 0.1mm or so, far from a precision fit but largely good enough for something that snaps into a plastic enclosure or whatever.

The default process is a 2mm, probably two flute?, carbide end mill.

Particularly if you're going for a custom fab run, you can ask for more precision, which will involve cutting fewer boards per stack, slower feedrate, sharper tooling, less speed-optimal tool route, etc.  In extreme cases, you might send the parts (or have them subcontract, if they can't do it themselves?) to a machine shop, to do metrology, fixturing and cutting; but below, oh I don't know, maybe 0.02mm, 0.01mm tolerance on a part that size, it's not really going to matter much due to variances in the material itself (expansion vs. humidity and temperature, anisotropy due to the weave, etc.).  So, somewhere between those tolerance margins, is where you can expect some range of, asking for tighter tolerances --> paying more to meet them.

Tim

[langwadt]

Yes, milled.  You can see the start/end marks where there's bumps in the outline.  These are typically within 0.1mm or so, far from a precision fit but largely good enough for something that snaps into a plastic enclosure or whatever.

The default process is a 2mm, probably two flute?, carbide end mill.

definitely carbide, probably diamondcut/"corncob" ala https://www.uniontool.co.jp/assets/img/product/drill_router/pcb_router_rhm.jpg 

[Doctorandus_P]

Although the video has a low resolution, you can see some fraying left where the depaneling tool did it's work.

After a short search of PCB depaneling I found the video below. It is horribly made and there are only a few seconds of vague info, but it looks like a robot arm hold the customer PCB from the top while a router on the bottom cuts off the tabs.



Other youtube video's suggest other machines too. From big hydraulic presses that do a whole manufacturers panel at once to cutting the tabs with lasers.

[ataradov]

Attached a panel from the purple company that sheds some light on this.

This dos not really explain how full perimeter routing is done.

OshPark leaves small annoying tabs as a result of their process. PcbWay sends perfectly routed PCBs with no tab leftovers.

[thm_w]

This dos not really explain how full perimeter routing is done.

OshPark leaves small annoying tabs as a result of their process. PcbWay sends perfectly routed PCBs with no tab leftovers.

Vacuum holds the board down and a router goes around the entire board. Does that not explain it?



Though maybe its more complicated, I've never seen JLC's bare PCB depaneling shown. It would have to be a generic fixture that would be able to hold down all kinds of boards.

[ataradov]

Vacuum holds the board down and a router goes around the entire board. Does that not explain it?

I can see that working on a larger board. May be my intuition is failing me, but I don't see that working on a 10x15 mm board full of vias and though holes.

[langwadt]

Vacuum holds the board down and a router goes around the entire board. Does that not explain it?

I can see that working on a larger board. May be my intuition is failing me, but I don't see that working on a 10x15 mm board full of vias and though holes.

maybe they stick the whole board on an big piece of thick sticky tape and control the depth to only go part way through the tape

a common trick for milling aluminium is painters tape on the part and then super gluing that to a fixture plate

[Unsanity]

I did see this video where it appears there is no fixturing. It is just cutout and the operator picks it out. I did try to ask JLCPCB customer support but the person I talked to did not seem like he wanted to give that kind of information to me. Maybe I'll try again...

https://youtu.be/42YY7knbBv4?si=lLVUECVDEdq7X4dM]https://youtu.be/42YY7knbBv4?si=lLVUECVDEdq7X4dM]https://youtu.be/42YY7knbBv4?si=lLVUECVDEdq7X4dM

[thm_w]

I did see this video where it appears there is no fixturing. It is just cutout and the operator picks it out. I did try to ask JLCPCB customer support but the person I talked to did not seem like he wanted to give that kind of information to me. Maybe I'll try again...

Yeah it looks like they don't even bother to hold the board down, interesting... That would explain why a bump at the end of the cut is sometimes seen.
Still a small board might be thrown across the room doing this, as ataradov is talking about.

[JLCPCB Official]

Hello ,

Thank you for your inquiry regarding our PCB production process. We usually perform milling the edge of the border twice to eliminate burrs and bumps, whether it's $2 or $200 order .

To ensure consistent quality, we conduct regular inspections and maintenance on our machines, including gong knives.
We appreciate your attention to detail in our services.

[thm_w]

Hello ,

Thank you for your inquiry regarding our PCB production process. We usually perform milling the edge of the border twice to eliminate burrs and bumps, whether it's $2 or $200 order.

To ensure consistent quality, we conduct regular inspections and maintenance on our machines, including gong knives.
We appreciate your attention to detail in our services.

But are you able to tell us how the PCB is held down while the border is being milled? Vacuum? Thanks

[WillTurner]

Tooling holes. If you didn't specify their locations, they were added for you. 

[thm_w]

Tooling holes. If you didn't specify their locations, they were added for you. 

No tooling holes were ever added to my PCBs that I can remember. They add the JLC order number only.

[ataradov]

Here are example PCBs I'm talking about. Green one was made by AllPcb, black is PcbWay.

On this green one you can actually see small protrusion in the top right corner. It clearly has a mill outline,  but the top is not sharp. So, may be it slipped in the holder?

This knob happens to a different degree on may be 1 in 20 boards. PcbWay boards are much better in that respect, but they are also manufactured 2 years after the green ones.

No tooling holes, as you can see. There is not a space for one, even if you wanted to place it. Unless they can use connector holes somehow, but I doubt it.

[JLCPCB Official]

We secure the board's edge with a clamp and then proceed with milling.

Here is about our factory :

[Kean]

I'm not sure if this is the case on PCB milling machines, but some other large bed CNC routers that I've worked with (used for cutting plastic sheet) have a pressure foot around the cutter.  This foot holds down the material surrounding the cut and allows a "vacuum" to remove the debris without sucking up the important parts.

Obviously the foot can't hold down the parts perfectly, so often at the end of an cut path there can be a little movement as the parts come free of the surrounding material, and you get little knobs like those shown on the above photos.  The panel frame is of course clamped along one edge, and the routing paths are optimised to keep as much rigidity in the remaining frame as possible while it moves closer to the clamped edge.

One key thing with the pressure foot was to keep it clean so that it didn't scratch the surface.  Certainly self-lubricating plastics work best for this.

[SiliconWizard]

As shown above - the boards are held down with a vacuum, it's a relatively common approach with automated milling, even. You see that even with woodworking. The bottom plate probably has many tiny holes which allows to get a negative pressure even on small pieces.

[Kean]

As shown above - the boards are held down with a vacuum, it's a relatively common approach with automated milling, even. You see that even with woodworking. The bottom plate probably has many tiny holes which allows to get a negative pressure even on small pieces.

I've used vacuum workholding before for both woodworking and sheet plastic milling, but how does that work with multiple PCB panels in a stack being drilled or routed at once?'
FR4 is not very porous so it isn't going to let any suction through like unsealed MDF does.

[ataradov]

It would be nice to see a closeup video of this. Even with a single panel, the mill has to go below the bottom surface of the PCB, so it would cut into the holding surface.

[free_electron]

vacuum table and sacrifical material