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What is preferred way to panelise a Metal Core PCB (MCPCB) - V-scoring or Tab-routing?

The engineering challenge I am facing is that the boards are meant for production (1,000 qty in the initial stage) and unfortunately the most economical SMT Assembly house that I am in touch with cannot depanelise the boards for us.

So the option is either to move onto a more equipped assembler (they are twice as expensive(!)) or depanelise the PCBs on my own.

Some notes on the board design:

  1. It only has LEDs. No resistors or capacitors.
  2. The LEDs are 2.3 mm away from the board edge.
  3. Overall PCB thickness is 1.6 mm.
  4. Boards are rectangular, mostly.
  5. PCB is 25.5 mm x 21.25 mm.
  6. Panel is 5 x 8.

Considering the above, is it a better option to V-Score or Tab-route? What method will allow me to minimize board stresses?

And furthermore, what is the recommend way to depanelise a MCPCB (goal being cost-effectiveness & minimized stress on the components?)

Note: I understand that at a higher volume, I will need a better and more automated way to handle this. However, for now, I am mostly concerned about the 1,000 quantity. I am also open to the idea of redesigning the board.

An idea that I had after typing this question: I should design the panel to be tab-routed. After assembly, I could use a manual milling machine to break apart the PCBs. Will a milling machine cause stress on the components/PCB?

I have access to several milling machines and cheap labour. This is not a big issue.

enter image description here

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    \$\begingroup\$ Interesting question. Have you asked your MCPCB manufacturer? They'd probably know. I'd guess tab-routing is much preferable to v-grooving. \$\endgroup\$ – Connor Wolf Aug 9 '15 at 18:30
  • \$\begingroup\$ @ConnorWolf Haha! The MCPCB manufacturer's first suggestion is to give them the Assembly business. I would love to, but they are out of the country and heavy duties make it unfeasible! But I will ask, nonetheless. \$\endgroup\$ – Saad Aug 9 '15 at 18:58
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    \$\begingroup\$ Manually de-panelising 1000 boards of any sort of substrate is a huge task. I've done 80 FR4 boards before and that took several hours, so doing 1000 would be days of work. Just my thoughts. \$\endgroup\$ – Tom Carpenter Aug 9 '15 at 19:00
  • \$\begingroup\$ @TomCarpenter Even if I use a manual router/milling machine? I also have access to a CNC. \$\endgroup\$ – Saad Aug 9 '15 at 19:02
  • \$\begingroup\$ I can see 2 problems with the milling machine approach because of the metal substrate. (1) you would need to be incredibly careful about cleaning the boards as you'll produce lots of very small pieces of metal which could easily get underneath components and short something. (2) for the metal you may need to use some form of lubrication for the bits which could be difficult to clean off. I've not worked with metal substrate before, so that is just a guess. \$\endgroup\$ – Tom Carpenter Aug 9 '15 at 19:09
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All MCPCB panels I have seen have used a combination of routing and v-scoring (see picture). Small drills are too brittle to drill mouse bites in aluminum.

V-score must be on both sides.

enter image description here

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  • \$\begingroup\$ How do you break the PCBs apart? Shear them or route? \$\endgroup\$ – Saad Aug 9 '15 at 19:34
  • \$\begingroup\$ I break them apart from the panel with my fingers, see picture. There used to be 10 boards on it originally. V-scored tab is plenty weak when not too long. \$\endgroup\$ – Oleg Mazurov Aug 9 '15 at 19:36
  • \$\begingroup\$ This is encouraging! Can you let me know the length of the tab and also the thickness of your PCB? I'm just a bit worried that breaking them apart using my hands may cause me to inadvertently put pressure on the LEDs. \$\endgroup\$ – Saad Aug 9 '15 at 19:46
  • \$\begingroup\$ The tab measures 6.65 mm, total board thickness measures 1.56 mm. You need to understand this arrangement - stars will break off a panel in pairs. You first apply pressure to the tab in the middle. On the other hand, I can't even bend the "margins", let alone separate it from the rest of the panel with my bare fingers. \$\endgroup\$ – Oleg Mazurov Aug 9 '15 at 20:10
  • \$\begingroup\$ Ah. I see now. This is brilliant. Since my PCB is square I'll have to put in a complete cut at the top and bottom. I just may need to somehow make this in 5 x 8 format or something like that with a higher degree of panel utilisation. Any thoughts? \$\endgroup\$ – Saad Aug 9 '15 at 20:21
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My preference would be to V-score. You can then either use a jig to break the boards apart or, if your volume justifies the cost, purchase a purpose-built de-panalize machine.

We don't have one of those specialized machines, so we use a simple jig. This is nothing more than an old hacksaw blade that has been sharpened along the edge opposite the teeth. The blade is held in a vise and the sharpened edge accurately finds and holds into the V-score. A small amount of pressure is all that takes to snap the board.

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Use vcut. I did, worked very nice. I would put two boards back to back,so that not straight side for both of them would be towards outside. Also probably it would be nice to add 5mm margins on right and left for the conveyor.

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