Designing and Building a LED Fixture

[redman88]

use the silver solder its tons better for this kind of detail work

[Hoppy]

Silver solder requires a higher temperature to melt, so that would be potentially damaging to the LEDs. It isn't made for electronic work, to the best of my knowledge.

[691175002]

Solder with a small amount of silver (Aka silver bearing solder) tends to melt more easily and can be remelted and worked more.

I normally do smd soldering with silver bearing solder and at one point I ran out and was forced to try a roll of (rather expensive) rohs leadless crap. I ended up ruining a board before giving up.

That being said, almost anything should work fine for wires to pads.

[chonhzilla]

This is a very impressive wright-up. Great job.

[malaybiswas]

Originally Posted by Hoppy

I thought the solder pads were pre-tinned. They look that way anyway. It isn't really hard to tin them again, but I wish the manufacturer was more clear about that part. Of course, these are not aimed at people like me, more for the real electronic geeks and small business operations.

I admit I'm very nervous about when I will finally push the plug into the wall socket. I can just see 24 small columns of smoke!

they are tinned but they are not uniform or sufficient on each of them. I had problems keeping them soldered and then found a web post that suggested tinning them again. Tried and got good results.

The biggest reason a led might burn is if the polarity gets reversed by mistake. You can align the anodes and cathodes in a certain direction and solder from one side so that you are following a pattern when soldering. I did it that way and being a beginner did not have any mistakes.

Anyways there definitely won't be 24 columns of smoke. LEDs being diodes will break the circuit the first point any one in series burns saving the rest beyond it. Good luck!

[malaybiswas]

Originally Posted by Hoppy

Silver solder requires a higher temperature to melt, so that would be potentially damaging to the LEDs. It isn't made for electronic work, to the best of my knowledge.

Silver solder is specifically used for most led reflow soldering and from what I learned on the web it is recommended. I did my second fixture with silver solder. However normal core solder works fine too.

[Hoppy]

I understand now: from my ancient history, silver solder is a solder specifically formed to melt at a higher temperature and end up much stronger than lead tin solder and is also referred to as hard solder. Silver soldering was very similar to brazing. The silver solder you are referring to is made for electronic wiring and is intended to avoid using the crappy no-lead solder now sold for soldering wires. I will probably just use the 60-40 solder I have, which does contain lead.

Another question: since the LED stars are now virtually cemented to the heatsink, doesn't that require more soldering pencil wattage to get the temperature up? Seems like the heat sink would keep the solder pad too cool.

And, I'm delighted to hear that I will not get 24 columns of smoke, just one

[redman88]

don't use more then a 15 watt soldering iron near those LED's thats why you need the silver solder

[Hoppy]

I will stop by a RadioShack this morning for their 2% silver solder, which seems to get rave reviews from those who buy it. I notice that Frys sells the same composition solder, but only in much larger quantities, so I assume it is the standard stuff.

Question: do you tin the wire and solder pad with this solder the same as with tin/lead solder?

[redman88]

it wouldn't hurt.

[Hoppy]

I plan to do the soldering tomorrow. Today I had to baby sit my 4 yr old grandson for 3 hours - roughly equivalent to fighting two bulls at Barcelona. Not a good time for precision soldering.

[evilc66]

Originally Posted by redman88

don't use more then a 15 watt soldering iron near those LED's thats why you need the silver solder

?????

Higher wattage irons will allow the area to be soldered to be heated up quicker, preventing the LED from being heated. Especially when mounted to a heatsink, low wattage irons will have a hard getting the solder pad heated up fast enough to melt solder without transferring heat to the LED. Obviously, higher wattage irons will require more skill to use.

[redman88]

i can't remeber where i read that but take a look at the data sheet for the LED for the max temp and dwell time

[Hoppy]

Originally Posted by evilc66

?????

Higher wattage irons will allow the area to be soldered to be heated up quicker, preventing the LED from being heated. Especially when mounted to a heatsink, low wattage irons will have a hard getting the solder pad heated up fast enough to melt solder without transferring heat to the LED. Obviously, higher wattage irons will require more skill to use.

Intuitively, this makes sense. Did you notice problems getting the solder pads hot enough when the LEDs are mounted on a heatsink? Again, intuitively I expect that it will be much harder with a low wattage soldering iron. All soldering irons reach the same temperature, but high wattage ones do so faster and can maintain that temperature better when lots of heat is being conducted away. Does this mean my 15 watt iron will be a problem? Drat!!

[redman88]

the main thing is most led's shouldn't be subjected to high temps for more then 2-3 seconds