Soldering a LED to the 'Wrong' Side of a PCB





Introduction: Soldering a LED to the 'Wrong' Side of a PCB

Electronics Tips and Tricks

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Electronics Tips and Tricks

Why would you want to mount LEDs on the copper side of a single sided board?  How about if you want to mount a board directly behind a front panel with the LEDs showing through holes in the panel.  You can't put them on the usual side because the other components would stop the board fitting flush to the front panel, and you can't solder to the component side because there's no track there (unless you have a plated-through hole PCB).  I have just such a project in mind and this is the solution I came up with.

All you need is a couple of strands from a multi-strand cable; A power cable from a PC strips down nicely.  Put the LED in position and wrap a couple of turns of wire strand around one leg, pushing it down to the PCB with needle-nose pliers or a scalpel.  Feed one free end through the adjacent hole in line with the track and cut off the other end.  Solder the wrapped strand to the LED with a fine-tipped iron - See picture 3.

Turning the board over, hold the wire strand in place with a finger along the line of the track and solder as close as you can to the LED, being careful not to solder over the next hole along.  Cut off the loose end - See picture 4.   Repeat this and the previous step for the other leg and any other LEDs.

You now have LEDs mounted on the 'wrong' side of the board, and can continue adding the other components to the 'right' side.  Drill the front panel to accept the LEDs using a step drill and a scrap piece of matrix board as a measuring guide.  Before you position the board on a metal front panel, make sure that nothing from the PCB will short out.  Make a card spacer drilled the same as the front panel and put over the LEDs as an insulator before securing the PCB.

The final photos show the actual project build and how tightly you can pack LEDs with this method.  There's 7 x 5mm LEDs in a 3/4" (2cm) square which will have additional components filling the rest of the PCB and be mounted directly into an Altoids Smalls box lid. 



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    i'm a total n00b, so bear that in mind when i ask, what is the purpose of the strands from the multi-strand cable?

    Normally you'd mount a LED on the same side as the other components and solder to the back side where the copper tracks are - Easy!

    At the moment I'm making an electronic dice in an Altoids smalls tin and need to get 7 LEDs in the space of a square inch on the top of the box.  I'll have the LEDs poking out through the tin lid but to do this there will have to be  no other components on the same side of the board.
    If I put the LEDs through the board the other way, I can't solder to the copper because the LED covers up the tracks where I want to solder it.

    A single strand of multicore wire is very flexible so this is what I've used to wrap around each LED leg and pass through the board where I can solder it to the copper track so the current gets to the LED.  I can now get the board close to the tin lid as the other components are away from the LEDs.

    Thanks AndyGadget! I'm learning a little at a time... :) This is a cool instructable.

    That is clever. I normally do that with more pain and frustration.

    Nicely done. I usually just surfacemount them.

    Good idea, but I rather just bend the leads around and pulling it through to the other side with pliers, forming a U shape with the leads.

    I thought of that, but none of the LEDS I had (a dozen different types) had wires thin enough to pull through without forcing.  Applying a lot of force would seriously stress the LED and possibly crack it.  Also, you'd lose a stripboard hole on each side of the LED which could be important if you're doing a compact build.

    Just widen the holes slightly so the LED legs go in, then bend them back and pull through enough to solder them. Or sand/cut the upper part of the LED legs so they fit in the original hole.

    I didn't think this was much of an instructable, I'll see if I can find one how to tie a knot, pour a glass of water or get out of bed in the morning. ;-)

    I'd like to see you try that and have a working LED afterwards.
    As for not being much of an Instructable, check out the competition title and the other 256 entries.
    And tying a knot -  Which sort would you like?