Please help! I’ve just received the emitter on a board and the driver, but my soldering is pretty rubbish. I can never manage to achieve a clean look, although it works. But I am sure that a ugly soldering isn’t particularly resistant and it’s prone to crack itself off. At least, that is my intuition.
I have Pb tin, a soldering iron that can vary the temperature up to 520°C, some German flux from Felder Löttechnik simply called Lōtfett (DIN EN 29454.1, 3.1.1.C).
How do I do exactly? Flux on what? Tin applied where, please? At what temperature, aiming at what?
One thing I noticed, that the very tip of the iron it never seem to be hot, while the sides or the tips are more effective.
Which kind of tip, a flat one, not too big, I’d imagine, right?
I really don’t want to have a botching job done on my only torch, can someone kindly help, please?
It would be really, really appreciated.
Around 330 °C should be fine, but this depends on many things. I would suggest using rosin flux (it’s like lube,if you’re in doubt, use more). With Pb-based solder, it shouldn’t be a big deal.
Clean the soldering tip by applying plenty of solder and then flicking or brushing it off. Do the same for the solder pads: once they become dull or non-shiny, apply new solder and remove it until the old, crusty solder is flushed away.
I also have some 0.6mm soldering wire with rosin core, I think I will use that.
Moreover, I researched my German flux but it’s very acidic and leaves residuals, it’s more for copper pipes in plumbing and that’s partly why my soldering was always a botching job.
Also, if you solder to the MCPCB, don’t press it against the host or it will suck away all the heat. Slightly lift it off with a toothpick and soldering will be much easier.
I have very bad solder joints (iron tip is super spent and the new tips I got are not copper and conduct heat horribly), but have found some ways to avoid joints that are bad enough to be non-functional.
(1) Pre-tin everything you possibly could. That includes the MCPCB solder pads (do it before putting it in the light), driver wires, everything.
(2) If the liquid solder surface is balling up, forming a film, or otherwise having poor adhesion and cohesion: use flux! Lots of it, just the flux from the solder wire core won’t be enough. Also prepare alcohol to clean it up afterward. Alcohol is also great for removing old thermal paste.
(3) Whatever temperature your soldering iron states is not going to be the real-world temperature at the tip. Lots of factors, from the high surface-to-volume ratio at the tip to suboptimal thermal path between heating element and tip, can pull the tip temperature under. Really crank up the heat when needed, a short duration of high temp is much more effective than a long duration of low temp.
Looks like a SFT70 3000K with 6V 5A driver, fantastic combination!
I like to solder most stuff hot and fast.
I also recommend a flux that has minimal splatter, especially when soldering mcpcbs, as you don’t want spatter getting on the emitter.
As mentioned above, tin the mcpcb pads and led wires.
I will put a small amount of flux on the wires and pads first.
Then tin them with solder around 725f.
If the mcpcb happens to be installed in the head or on a pill, and it’s not easy to remove, I will crank the heat up to 775-800f.
Put a small amount of solder on the iron tip, hold the tinned wire against the solder blob on the mcpcb pad at the exact angle you want it, and lightly press straight down gently mushing them together.
If your iron is hot enough, you can be in and out in under a few seconds.
If you can solder everything with the led NOT touching the mounting surface, you can get in and out in 1-2 seconds, if the iron is hot enough.
Pay attention to the angle of the wires to be sure they won’t hinder the reflector, and pay special attention that the soldered ends will not hit it once installed.
Super important! I’ve built a few lights that didn’t turn on for this reason. I like to put kapton/electrical tape over the solder joints for peace of mind, but even duct tape or any other tape is better than nothing!
On a related note: if you have a low-current protected battery, try that first after you assemble the light; the protection circuit will catch any potential shorts and save you from frying a driver. I have some 2014-era protected cells that are barely usable due to age, yet I keep them around for precisely this purpose.
A somewhat tangential note: make sure you’re getting solder from a reputable place.
I once bought SnPb solder wire under the brand “Trisonic”. It doesn’t melt under the temperatures that melt my regular SnPb solder or even pure Sn solder, and I couldn’t quite figure out why. At some point I noticed that the color of the solder wire seemed more grey than normal, and it made me suspect that the so-called SnPb solder wire was, with high probability, pure lead, and therefore completely unusable.
Good advice here so far, would echo good advice on thermally isolating the MCPCB to reduce heat being sucked away into the flashlight host, and to watch the shorts on the back of the reflector when re-assembling.
One thing I’d add is get some good tweezers or whittle down a wooden chopstick with an inverted v shape at the end to hold the wires down while you solder then remove the iron.
The LED leads are my biggest headache, the cable coating gets soft with temperature and is easily damaged by most of my tweezers. I’ve actually got a cheap and nasty pair I damaged… I sanded off the sharp burs then bent the tips back on themselves to form broad surfaces to push wires down with.
General soldering advice, it’s best to not let the joint move while it solidifies.
Also be careful of “mixing” solder types, I’ve had headaches in the past where I’ve modified a PbSn joint with Pb-free and no matter what I tried, I couldn’t get a shiny joint.
Great points @gravelmonkey . I use a pair of 5" curved hemostats to hold the wire in place, because as you stated, you definitely don’t want them moving around, especially as the solder cools.
To prevent damage to the wire from tweezer pinching, it helps a lot if you use a good quality silicone wire.
That stuff is pretty durable and I have yet to damage the insulation on decent quality stuff.
I have had good luck with this brand over the years. You can get it on Amazon
I will be in the hunt for rosin flux, as just the rosin core flux solder I have certain won’t work, I tried in the past alone with sad and depressing results.
I had bought a while ago in a Chinese bazar a set of solder wire and rosin flux that I opened yesterday, and damn, that thing has nothing of the flowing nature the word “flux” inherently suggests. It looks like rock solid, pine amber. I really don’t want trying to mix it up with some solvent (I have pine turpentine for example, that may work), because almost surely it won’t be like a proper paste, I don’t have anything small enough to heat up on the hob that small quantity I have, and… I am already not that experienced, I reckon that flux is such an important piece of the puzzle here. I need to get the real thing, that here isn’t very much popular, it seems.
Thanks @delphi for the video series, I will watch it!
@gravelmonkey, I want to find a way to actually hold securely the wires I need to solder, as I don’t have three hands, and the soldering area is really deep in
@QReciprocity42 I will put some electrical isolation, but in any case the parabolic curve of the C8 reflector is so steep that I doubt anything will touch:
