Lighting Solder for diy led

Well here is a crash course (no pun intended) on soldering LEDs.

Basic things I do:

Solder should be lead solder, rosin core, 60/40 (some use 63/37 which is made for electronics) and small (0.032" diameter).

I have a 50 watt adjustable iron which I set to about 35 watts when doing soldering, 50W initially until it can melt solder. When starting, let it heat up and tin the tip right when it gets hot enough to melt it, then use a sponge to wipe off excess. What I do is give the iron a flick towards the floor of the garage to get excess solder off the tip then wipe on the sponge (not a lot, just need to get the excess off, but mainly the rosin). I do this "flick" very often, wipe on sponge less often, I end up with a mess of solder blobs on the floor but it works for me.


Step 1: pre-tinning. Do not mount LEDs to a heat sink before tinning. The point is to get the pad hot enough to accept solder, and having it on a heat sink means more contact time with a hot iron, which heats up not only the pad but the LED. I pre-tin on a piece of cardboard or MDF or plywood. You should have a little solder on the iron tip, then touch it to the pad. The solder should flow onto the pad once the pad it hot enough (I call it "snapping" to the pad, because it wicks on quickly) then I push the solder on to the pad at the junction of the pad and iron tip (usually about 1" worth of solder) and then lift the iron away. For a fraction of second, the solder will "wobble" and then turn from shiny to slightly duller in a flash when it soldifies. That's it - repeat as necessary for all pads you plan on attaching to (and only the pads you are planning to attach wires to). As far as the size of the "blob" - I prefer to make it just big enough that is looks like a 'bead' on top of the pad, versus only a "bump", if that makes sense. This will be clear as to why in step 3.

Step 2: Attach to heat sink. Do whatever you prefer in this step

Step 3: Soldering wires. This is easy, if you have set is up right. I cut all my wires to necessary length and strip about 1/16" off each end ahead of time so that I can do these all quickly. Get your iron hot and tip clean. What you are going to do it sandwich the stripped end of the wire between the iron and the solder point (blob on star pad) to which you wish to make. Take the stripped end of your wire hold it right above the solder blob, then put the iron on the wire for a fraction of a second before you put it on the blob. This 'pre-heats' the wire so that the heat of the wire melts the solder, not the iron. The solder will melt, then you push the wire down into the solder and hold it for a second (should not need to hold it any longer) and then lift iron away. When the iron is in contact with the solder/wire, sometimes you can see the rosin "boiling" around the edge - this is fine (actually it's perfect). When you lift the iron away, you should not see any bare wire, and the solder blob will go shiny-to-dull again like in step 1. If the solder does not cover the wire, but instead the wire looks like it's a "hot dog in a bun" with the solder surrounding it and bare wire showing, then just touch the iron tip to it again for just a fraction of a second so that the solder wicks over the wire. You may have to do this a couple times, quickly. If you have a bubble of solder on the pad from step 1, after you are done the iron will "pull" some of this off, leaving you with a nice dome of solder over your wire. You will now have excess solder on your iron tip. Flick this off, and wipe about every 2nd or 4th connection you make. Repeat for all connections.

As for the wires, they heat up fast and the plastic jacket can sometimes get too hot to hold. This is where working quickly with practice helps. Try not to hold the wires with anything metal like tweezers, pliers, or even your fingernails (pads of fingers only) as all of these will pierce or dent a warmed-up jacket, leaving bare wire exposed.

I used to put the iron on to the solder bubble, and then insert the wire into the molten bubble, and this didn't seem to cause me any issues, but I guess it's not quite the right way to do it, because technically it's a semi-cold joint - but I would hold the wire down with the iron for a second to make sure it was hot enough, so this might still be OK too.

I don't pre-tin wires, though you can if you want. Some suggest that you get a little solder on the tip of the iron then touch to the wire to get it to wick on to it but this is tedious and unnecessary IMO.

The important principle here is that you use the iron to get the copper pad hot and let the solder flow on to it, or using the iron to heat the wire and then making the wire melt the solder - that will give you the proper bond.

Also if you have problems with a solder blob not returning back to a nice round dome or bubble shape (like a bead of mercury) after you remove the iron, but instead you get a sort of craggy little mountain looking glob that just isn't playing nice - just add a bit more solder like you are re-tinning it, clean the tip, then try again.

HTH

Bud

 

Cool! This is the type of stuff I eventually want to have in articles on this site. Glad to help