Have a project underway that may get scaled up to a small production situation in tbe near future. I requires 15, 5mm LEDs mounted radially (inserted from the inside) in a small diameter cylinder (1.5" pvc pipe cap). The unit will be potted after connections are complete. Breadboarded the circuit and it is undergoing stress testing. Next step was to figure out how to actually wire it inside the small available space. As a “rats-nest” is out of the question I figured a PCB was a good start. After a couple of days of teaching myself enough Eagle to be dangerous, I came up with a simple single-side round board I could proto at home or get a couple cheap copies made.
Doable, but after inserting all the LEDs in the housing (leads bent 90deg vertical) I would still have to thread the board down over 30 leads at the same time before soldering.
Came up with the idea that if I could slot the edge of the board, providing an 0.032 slot (same size as the drill for a std 5mm LED package) as below, it would allow me to work the board one lead at a time rather than trying to thread 30 at once.
Now the question… How would you go about slotting the board? From what I have read, the tooling used for milling out an odd shaped board is well in excess of 0.032" in diameter so I shouldn’t expect a fab house to be able to just follow the outline as drawn, without wallowing out the through-holes and pads. I thought this would be an innovative solution to the assembly problem, but am stuck on how to accomplish it. Best solution would be one the fab house could handle, but an after fabrication/before assembly modification would be all right as well. Very little experience in PCB fabrication and modification, so any suggestions are very much appreciated.
A fret saw would make quick work of this, though even for a small run (let’s say, 100+), that may be more time than you’d be willing to invest in doing it.
How, exactly, are the LEDs to be assembled onto the board and mounted in the pipe you’re referring to, and what would be the environment it is used in?
I only ask because for a similar thing where the LEDs had to point outward and we didn’t want to commit to side-emitting SMD components, we had a design along the same lines of your first post, but instead of the regular PTH drills used elongated SMD pads. The LEDs themselves were pre-mounted in the enclosure, the board pushed up underneath, and the leads could be soldered to the pads directly, and the excess clipped off. I wouldn’t generally recommend this because physical stress could relatively easily snap the leads or even pull the pads off the board, but board had nowhere to go and the LEDs were recessed enough so as not to receive any stress unless somebody purposely poked at them with a stick.
Also, slight tip - but not sure how well it would work out in your scenario - when dealing with a component with lots of leads (or just a lot of components with long leads that you want to thread together), clip them altogether diagonally. That way you, ideally, only have to deal with 1 lead at a time as well (reducing the frustration of getting e.g. 9 leads threaded with the 10th bumping just to the side of the drilled hole, having to lift the board, and losing 4 of the earlier threads that it seems you’re trying to avoid)
In my original scenario where I wanted the slots to ease assembly, the LEDs would be inserted in 5mm holes drilled in the housing, with leads preformed to match the radius of the drills on the PCB. The board would be threaded down over the leads and soldered.
Or if slotted, the leads would be slipped through the slots one at a time, soldered, and so on around the board .
After further reflection, it may be possible to insert the board into the housing first, thread the LED leads into the board, then insert LED into the 5mm hole. After all LEDs are threaded through the board and inserted into the 5mm holes, solder the whole board at once. Bit of a reach, but with so few components and all with decent access, might be doable without the slots.
If I do need slots, figured a sawed slot was the way to go on initial run of 5 or 6. If we get into larger numbers guess it will require negotiating with the fab house, or setting up an in-house jig to use an .032 diamond cut bit.
The whole assembly will be filled with potting compound after testing. Exposed marine enviroment. Not submerged, but subject to rain and salt spray. Potting will also serve to secure and seal LEDs and board. Obviously unit will be mounted 180 degrees from assembly position… Solid end up
The polarity problem in the initial single side design was caught and corrected after the OP. Too lazy to post an edited version, but will do that now. Will be using the second 2 sided version to allow for slots if required. Re: ballasting resistors… On the breadboard, with the 317 set up for current regulation, we are running at less than 1% differences string to string. LEDs are from Cree and expect variance to be within spec sheet tolerances. Have a breadboard that’s been running for 500hrs+ at 12.0Vdc to 14.4Vdc input with steady good results. Hoping no changes.
http://i150.photobucket.com/albums/s84/ … oard-3.png
http://i150.photobucket.com/albums/s84/ … d-slot.png
http://i150.photobucket.com/albums/s84/ … oard-5.png
