I’m new to PCB design, in kicad or otherwise so apologies if this is the wrong forum for my question. I’m trying to design a board that will fit inside a g-scale electric train locomotive. I’m modifying an existing board that came with the train. It has an unusual feature in that it has several tiny PCBs mounted to the main/big PCB at a 90 degree angle. The tiny boards are inserted into a little notch routed out of the big board and attached via some sort of adhesive and also soldered together at their respective contacts. The purpose of this is that the tiny boards have LEDs that drop into some little recesses for the rear and front lights of the locomotive. I’ve attached a photo of the board.
My question is whether there’s a best practice for CADing this aspect of the board up in kicad? e.g. all as one design? or design the tiny board seperately? ideally i’d like to make a design that i could send off to be fabricated and fully assembled…but perhaps thats outside the scope of what’s possible for a hobby level project and I would need to figure out how to attach the tiny boards to the big board myself.
Thanks for any guidance you can provide…appreciate it.
The small PCB’s were probably made inside the holes you see in the bigger PCB. this allows SMT placement of the LED’s in one go with the rest of the PCB. And then breaking them out and soldering under the 90 degree angle is probably done separately.
Thanks so much for the replies. Looking at the board with that insight, you are definitely right…the cutout is the exact same shape as the little boards, with one hole per little board leftover after the operation. Is there a “layer” in kicad to indicate cutouts of this nature? Not sure if there is a best practice for such a design element or whether its an unusual scenario that should be discussed directly with the fabricator in terms of how they’d want it to be labeled/marked. Thanks again.
It also appears that the small boards are hand soldered to the main board.
The whole manufacturing process would be:
Make the board
Machine place the LEDs and other parts
Hand remove the small boards
Hand trim the small boards
Hand solder the small boards to the mother board.
Those cutouts are probably done by with a milling tool. Many fabs use the edge cuts also for cutouts. Don’t forget you also need slots to plug the daughter boards into.
You don’t need to adhere to making the daughter boards from cutouts on the motherboard, you could make them on the side of the motherboard, at the expense of more board area. This would be a form of panelisation.
You should discuss specifications and charges with the fabricators.
Edit: I get the impression that you are hoping there is a set of guidelines such as put this and that in such and such a layer then put the magic word oomamaboomba in the BOM and it will be sorted out. I think the best you can hope for are stories from people who have done something similar but essentially your request is bespoke. Do write it up when you get it done though, it should be interesting.
Likely / probably, especially for small series. Setup time, including the time needed to explain to someone what has to be done all have to be paid for.
You can simply draw lines on the Edge.Cuts layer. But do leave tabs to keep the small PCB’s firmly enough attached to the main PCB. The biggest concern here is for routing out the small PCB’s themselves. When routing is almost finished, and they are just kept in place with the last tab, they may have a tendency to break off, which will likely also break the tool. It’s a bit of an artform to balance that properly. Putting them on the side and/or using mousebites are also valid options.
Attempting to snap off a smd mounted sub-board risks a cracked solder joint.
The solder only mounting to the main board is asking for cracks later too. I was taught to never depend on solder for mechanical mounting
We produce a couple of boards that does pretty much what you have shown. We have a big board (30x20,mm) that has 2 smaller boards that break out of it. On the edge are 2 slots and the small boards have a tab which goes in it. We glue the tab into the slot and then solder the pads to create the electrical connection.
We also do one with a wider slot so we can angle the daughter board at 15 degrees to the main board.
Both work well with no problems and are reliable.
It’s not the solder joint that cracks in cases like this, but it is the ceramic body of SMT resistors and capacitors that are brittle enough to break when the PCB gets bent. In this case it’s hardly a problem because the small PCB’s are very thick compared to their size. It can be a problem with V-grooving and separating the PCB’s. In those cases it helps to put the SMT parts in the same orientation as the V-groove direction if they are close to the V-groove.
Sure, solder is not very strong, but it’s not that bad either. These extra PCB’s are very small, and there is a lot of solder.
I would first make a test PCB to test your desired pcb maker for tollerances.
I order at jlcpcb and I learned that a 1.6mm board is 1.55mm. I make PCB boxes which I fixate with solder pads on the inner corners. Not much different from what you want.
I made a test PCB with rectangle cutouts in several widths varying from 1.50mm to 1.65mm. At first I had problems. I made cutouts of 1.70mm. It was so wide that the box was very instable. It was hard to fixate before I get set the final solder joints. With rectangles of 1.54mm they nicely snap into eachother.
And you should also learn about ‘dog bones’. There is no such thing a right inner corner. They all use round milling tools. A dog bone is a special shape which forces the PCB manufactor machines to use smaller milling bits ensuring that there are no annoying curves in the inner corners.
you can make the copper sitck a little better to the board by adding some via on it. that create a small metal link that help to keep the copper in place.
It’s better but it’s still not very strong
You could design a PCB with the little boards on the top edge near the section shown in the picture that is similar to a copper edge connection. Then surround those little boards with small holes to allow you to snap them off. IF there’s no mechanical reason for a slot for them, I’d save that money to pay for the extra snap off holes. Band sander would clean up the edge of the stand out section and the small boards if needed. Solder them to large pads on the main board and add either a Super glue or hot melt glue to hold them up. Again though, IF there’s a repetitive mechanical reason those original boards were fitted into slots, like they’re exposed so the operator could be accidentally and repetitively pushing on them for some reason, then this might not be the best idea. If the original designer was just getting fancy with the cutouts, then adding the small boards to the main board so they could be snapped off rather then routed out would be fast, efficient and probably save money on the board manufacture. The boards stay in place until after the components are mounted of course. Millions of commercial electronic products are made using stand up boards with just a glue or hot melt glue holding them up.
OK, we do versions of this setup ALL the time in our manufacturing. But we approach things slightly differently.
We’ll usually have a “vertical” PCB with a bunch of SMT loaded on one panel, and then a “base” PCB with both SMT and PTH components on it on another panel. We use a combination of milling and v-grooving around the circuits in each panel to make them easy to remove (and so we don’t put any mechanical pressure on SMT components close to the edges of the PCB). If the profile of the circuit isn’t ammenable to v-grooving, we’ll go with mouse-bites. But v-grooving with a pizza-cutter (a professional PCB one, not an actual pizza cutter!) is our preferred method.
We specify the milling using a 1mm trace on a User layer (shows the width and path of the router bit), and the v-grooving using a 0.1mm trace on another user layer. We then include those two layers on the gerber for the board outline, and just inform our PCB fab house that we’ve put the board outline, milling and v-grooving all on that layer in our spec document.
We then insert all the vertical boards into the base boards (still in their panel), add all the PTH components, and run that whole shenanigans through our wave soldering machine. We’ve got pads like in your photo, but on the bottom side of the base board that the corresponding tabs on our vertical board will solder to.
I think the best you can hope for are stories from people who have done something similar but essentially your request is bespoke. Do write it up when you get it done though, it should be interesting.
