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I would like to cut a small square out of the middle of a large square PCB.

The tricky thing is, I don't want to cut all the way through the board, just about half way. This would create a 1mm-deep square pocket in a 2mm pcb board.

I could do this with my CNC machine easily, but I want to know if something like this could be achieved during circuit board manufacturing. I would hate to have to load hundreds of panels of boards onto a CNC machine; this would raise the cost of manufacturing significantly.

One idea I had was to use fancy programming of the drill that drills holes in the pcb to act like a CNC drill. It would, of course, require changing the drill bit to a special one for milling.

Can anyone who is familiar with these machines (already setup in most Chinese PCB fabrication facilities) foresee a (cheap) way to use them to cut pockets out of a PCB?

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    \$\begingroup\$ Ask the fab..... \$\endgroup\$ – DKNguyen Dec 30 '19 at 4:55
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    \$\begingroup\$ Just out of curiosity, what’s the use case for this? \$\endgroup\$ – jcaron Dec 30 '19 at 12:46
  • \$\begingroup\$ @jcaron Have you seen that Hackaday post about hiding components inside a PCB? I am planning to do something similar. Might post my results Q&A style if it works out... \$\endgroup\$ – Judson Hudson Dec 31 '19 at 6:52
  • \$\begingroup\$ Here’s the link to that post (let me know if I got it wrong). \$\endgroup\$ – jcaron Dec 31 '19 at 7:47
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Yes, it can be done. It's (often) called Z-axis milling. For my usual Chinese supplier it is a standard option and adds USD $100-$150 to a small order of 2mm thick PCBs.

You could also ask for a top layer to be routed through on a multilayer board which might give you better control over the surface finish and maybe thickness.

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  • \$\begingroup\$ Z-axis milling is exactly what I was looking for. \$\endgroup\$ – Judson Hudson Dec 31 '19 at 6:50
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They use something very much like a router or end mill to cut the board outline. They can also make interior cut-outs. So the tool to do this operation is standard equipment.

I've also had controlled-depth milling done but had to be selective about the vendor to be able to get the depth tightly controlled (my project probably needed ~10 um tolerance on the depth). And it will increase cost, because they won't be able to process multiple boards in a stack; they'll have to process each panel individually.

You'll probably need to call a few vendors before you find the right one for your requirements. I also wouldn't count on getting this from a bare-bones Chinese vendor. But you'll never know until you ask.

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  • \$\begingroup\$ Speaking of cheaper Chinese vendors, I've seen JLCPCB take up a few weird challenges like from some hobbyist folks with promising results. \$\endgroup\$ – Polynomial Dec 30 '19 at 5:11
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    \$\begingroup\$ Also, if I were trying to do this and the cut depths were limited to the boundaries of layers, I'd do the cuts in the separate layer pieces before they got laminated. That way I can stack as many panels as I like and I don't have to worry about tightly control depth cutting. Also fairly easy to produce a separate drill file for that pass. \$\endgroup\$ – Polynomial Dec 30 '19 at 5:13
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    \$\begingroup\$ @Polynomial, now I'm wondering why we didn't go that route on my project...Possibly worried about prepreg getting squeezed into the cavity when laminating the outer layer onto the inner ones. \$\endgroup\$ – The Photon Dec 30 '19 at 5:19
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Not a direct answer, but aimed at solving your problem: can't you stack several thin PCBs on top of each other to get the desired effect? E.g. if you want a 1.6 mm thick PCB and a 0.8 mm cut-out, you could just stack one 0.8 mm PCB with a cutout on top of a 0.8 mm PCB without one. Ordering two standard PCBs is also cheaper.

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