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Are there any standards or rules of thumb for panelizing boards when using breakway tabs with holes drilled on the tabs?
Specifically...
1) What is a standard width for the slot around the board outline?
2) How wide should the tab be for a 1.6mm FR-4 PCB?
3) What size drills should be on the tab? Should the drill centers be directly on the PCB outline? Or perhaps the drill diameter should be tangent to the board outline?
4) How closely spaced should the drills be on the tab?
5) Should the drills be on both ends of the tab (PCB side and panel side)? I've seen it done both ways - with drills only on the PCB side, but also done with drills on both ends. Is there a reason to choose one vs. the other?
6) How frequently (in linear inches or linear millimeters) should tabs be placed around a PCB?
And on a related note - when you folks are panelizing boards, do you generally leave the copper on the unused portion of the panel? Or put a cross-hatch or dotted fill? Do you indicate anything special on your gerbers - instructions, specifications, indicating which is the PCB and which is the panel (in case it's not obvious), etc?
Comments are appreciated - just wondering how other people do it. I've winged it so far by loosely copying panelizations that were done by PCB manufacturers on my behalf. But there are a bunch of PCB's being worked on here at the moment and I'd like to learn more about the topic.
- Comments(1)
A****min
Nov 15.2019, 18:15:01
0.5mm holes, 0.75mm apart.
Length depends on panel size and number of tabs - typically 4-8 holes
Slot width 2mm - this is a fairly standard size, below which manufacturers start charging more as they have to run smaller tools more slowly
If I need a final PCB edge with no bumps ( e.g. it needs to slide into a slot in a channel) I offset the rat-bite row into the PCB and bend the ends of the slots to meet the row of holes.
If you are panelising individual PCBs within the panel, so when broken out there is a PCB-shaped hole with the tabs left in the panel you should only rat-bite the PCB edge so it leaves the tabs on the waste.
If you are panelising a set of PCBs such that the slot forms the edges of two adjacent PCBs, you need to rat-bite both edges of the tab. The advantage is better panel utilization, but the disadvantage is that you then have to snap off all the tab remnants after you've broken the PCBs out.
