Thin PCB stick manufacturing - Page 1
Forum section: electronics / general

author: leime
author_rank: Newbie
timestamp: April 26, 2019, 01:58:36 pm
content: Hi,I'm trying to manufacture a bunch of LED sticks I designed, which need to have a profile that is as minimal as possible.I've got a couple of single PCB sticks made at different PCB fabs which I then assembled by hand.I got the first iteration single boards from PCBWay and the second iteration from JLCPCB and they both turned out pretty clean, without any signs of breakaway tabs which made me wonder how they managed to produce them.Now I would like to get them assembled at the factory directly as I need around 700 of them.For that I need to panelize the design and I was wondering what the best method for doing that is, particularly because of the unconventional shape of these boards and the board thickness which I would like to be 0.6mm.I already tried a panel design that uses breakway tabs to hold 10 sticks. I ordered 5 unassembled panels as a test at ALLPCB because it was the cheapest I could find that also offers assembly.The panels seem ok, but one of them has some weird bumps on the edges of the board, and when snapping out sticks from the panel there is still ugly residue from the mousebites attached to the sticks. Also, when comparing the sticks with the ones from JLCPCB I notice that the edges are rougher.This makes me hesitant to use this design and order the 700 assembled sticks.That's why I would like to ask some feedback on whether you think this is the best way of producing those sticks.Is there a different way you would panelize this design? Have more or less sticks on a panel? Maybe order unassembled panels from JLCPCB (as they seemed to provide the highest quality) and have them assembled somewhere else?Thanks!

author: Gribo
author_rank: Frequent Contributor
timestamp: April 26, 2019, 02:23:53 pm
content: If you can make the PCB straight all along, you can use V-cut instead of routing.Also, If you can use lower pitch (2mm vs 2.54) connectors, you can reduce the wasted material.Other, similar projects use a more modular approach - shorter sticks with contacts at the end of each stick.

author: IconicPCB
author_rank: Super Contributor
timestamp: April 27, 2019, 07:32:04 am
content: Stagger the ends of the boards such that the areas holding the LEDs are aligned and form a support structure across the panel.this way You can rout out the odd shapes while maintaiing stability of the panel and run V grooving to allow for depaneling post assembly.How many layers in the design?

author: Kean
author_rank: Unknown
timestamp: April 27, 2019, 09:22:23 am
content: The "weird bumps on the edges of the board" would be caused by the PCB flexing during routing as the cutting bit changes direction. Not surprising with such a narrow PCB, let alone with it being thin. JLC must be using a better routing process (speeds & maybe vacuum hold down) to avoid that.You may not want to use V-grooves, as the edge finish also won't be clean. Also they may be a little tricky to separate without damage due to the length unless you use a "pizza cutter" type depanelling device. You may have to check with the PCB house if they'll even V-groove a 0.6mm PCB, as I recall one supplier saying 0.8mm was the minimum for V-groove.What I would suggest is trying to get rid of the "bumps" and wider ends in your design so that the PCBs are straight and easier to route or groove. You may need to go 4 layer for that (if not already). At the ends I'd then just have 4 connecting pads in-line, and then use a separate small breakout PCB to "interpose" from the in-line pads to the 2x2 grid for your connector.

author: Thararot
author_rank: Newbie
timestamp: April 29, 2019, 03:15:31 am
content: I want to find some information from this story.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 29, 2019, 04:31:48 am
content: Yes, that's due to flex in the thin section.If you don't want / can't tolerate bumps on the profile, consider using a combination of rout and v-scored tabs. This way, most of the edge is routed straight and smooth, and the tabs are scored so they break easily and cleanly with minimal burr -- well, less burr than mouse bites anyway. And easier to file off what's left, if you're so inclined.Downside, v-score only works on straight lines. So, on that toothy outline, you could fully score (or tab and score) the straight side, and the teeth could be scored, but the slots between them have to be routed out. But they can be routed out while there's still a lot of meat holding the board to the panel which should help keep things straight.You may also consider flex (or maybe not, I have no idea). Even more flexible, but it's even more tolerant of errors for the same reason. Instead of a very long panel, you could make a sheet with zig-zag cuts and flex the circuit into place.Tim

author: mairo
author_rank: Unknown
timestamp: April 29, 2019, 09:21:07 pm
content: One way to do the depanelize it clean would be to use a laser, but that means that you will need to find an assembly house that has it.Other option is to keep making them unpanelized and come up with some sort of a holding jig that would be used during applying solder paste, pick and place, reflow and AOI. This way however if some boards come with bumbs as shown, they may not fit on the jig , depending how the jig is designed.

author: leime
author_rank: Newbie
timestamp: May 09, 2019, 02:30:11 pm
content: Thanks for all the replies!Quote from: Kean on April 27, 2019, 09:22:23 amIt would indeed be easier if the board was straight all along to allow v-scoring, but I'm aiming to have the profile of the stick to be as minimal as possible in between the LEDs and this would mean that the whole of the board would have to be as wide as the parts that hold the LED. Since it's a personal project, I'm trying to keep the costs down. So I would like to stick to a single, 2 layer PCB.Quote from: mairo on April 29, 2019, 09:21:07 pmI actually didn't realize that there is a laser cutter which I have access to. I've done some testing with it now and it seems to easily cut through this 0.6mm PCB. Now I checkedthis pagewhich says you shouldn't cut through epoxy as it results in a burned mess and creates toxic fumes. This makes me hesitant to use the laser cutter to cut the entire profile of the boards out of the panel, but I feel like cutting off the tabs shouldn't be too much of a problem. So my current plan is to add more tabs in order to reduce the flexing during the routing and use the laser cutter to depanelize the assembled boards by cutting the tabs off.

author: mariush
author_rank: Super Contributor
timestamp: May 09, 2019, 03:28:13 pm
content: Seems to me like you could really tweak your design for v-scoring.Maybe make the width just 1-2 mm wider.move led pads close to other edge so leds will be partially outside the boards when donewith vscore you benefit from having pcb whole, you can use solder paste or whatever and solder leds on whole pcb (for ease of soldering)then break the strips be vscore and your leds will be left partially floating, the vscrore would be under soldered led casewith this layout you may have to stagger the strips,every odd strip would be shifted one led width to one side so that you'd be able to place and solder leds before breaking off strips.change the end connector to 1x4 or 2x2 right angle, or use two 1x2 connectors with some spacing between them ....tighter pitchand will fit on sligthly widened boardyou could have bottom as ground and top carrry voltage and data, could have vias in pads if you want to...and bonus you don't waste so much due to routing, you get more strips in same area... and if board maker puts some texts on pcb chances are you can just throw out that particular strip with text and still have other.

author: mairo
author_rank: Unknown
timestamp: May 11, 2019, 06:07:01 am
content: Quote from: leime on May 09, 2019, 02:30:11 pmUsually there are particular type lasers that are mainly used for this type of work (look at LPKF depanalizing systems). As your board is thin, it could mean that wider variety of laser cutters could be used, but as you said you need to be careful of what fumes it produces during cutting. I think the proper way to have a system like this is would be to have a ventilation system that sucks out the chamber's fumes, then convey them through a correct filter type (based on what chemicals will be present in the fumes) and then via an exhaust pipe to blow them outside.