# 0603 SMD LED Solder Question



## Lord Homicide (May 11, 2012)

Does it matter if you solder two wires or just one wire to the anode/cathode on a 0603 SMD LED? I've seen both - didn't know what the difference was. 

Wire used: 30 awg kynar


----------



## corey872 (Jan 10, 2010)

Just a standard color / single 0603?

I can't think of any reason why it would need two - unless the circuit it is in would need two for some reason. Even then, given the size of an 0603, you might be better coming off the LED die with one wire, then splitting into two somewhere else! (Edit for clarification: As David_AVD says, you would need one to the anode, one to the cathode... but don't know why you'd need 2 to cathode or 2 to anode, as that is what I interpreted from the original question.)

30awg wire is good for anywhere between 140 and 860 mA, depending on the length of the run, but even at the very low amp / long distance end of the range, 140 mA is much more than the LED would handle.

If it is a bi-color, RGB, or 'color control' LED, then it might have 3 (or more) wires, but not sure those last two are available in an 0603 package... at least not yet!


----------



## David_AVD (Nov 9, 2012)

You need one wire to each of the anode and cathode connections. Using the LED end as a junction is certainly valid but can be fiddly.


----------



## Lord Homicide (May 11, 2012)

The "fairy lights" that you buy in stores have two wires on both sides (the lights my wife bought) and didn't know why. My plan is to buy a quantity of 0603s and attempt to make a light strand.

From there, I am looking to creating custom strands to whatever my application will be. 

It's been a long time since I've wired LEDs and such and have forgotten how to do the math for power source and wire gauge


----------



## corey872 (Jan 10, 2010)

Whew! Far more patient person than I! My last project had four 0603 LEDs on a circuit board and that was enough for me!

As far as the two wires, I can only imagine it might be for looks, durability, mechanical strength or some other factor. On some LED light strings, it seems they don't even use a proper AC>DC converter - they just wire enough LEDs in series for the voltage requirements, then have half 'forward' polarity and half 'reversed'. The string will flicker with the AC input, but apparently a lot of people don't notice or aren't sensitive to the flicker. (I've found I'm not one of those people and a walk through the LED light aisle at the local store might as well be a nausea inducing walk through a funhouse with 1000's of strobe lights going off)

Anyway, for consideration:

Electrically, you'd only need one wire. I usually give ampacity charts a quick browse and there are a gazillion LED calculators available for volt/current/resistor choices. (links below).

If I had to do it, I might consider series/parallel arrangement so if one LED dies, you don't loose the whole string.

Along the same lines, you probably want to choose a LED voltage safely under the input voltage so you don't need a pile of current limit resistors, too.

You might also consider some type of very thin stranded wire vs solid 30awg. The stranded will be much more tolerant of bending and movement than a solid wire.

Wire ampacity:
http://www.powerstream.com/Wire_Size.htm

LED calculator (gives many series/parallel options)
http://led.linear1.org/led.wiz


----------



## Lord Homicide (May 11, 2012)

corey872 said:


> I've found I'm not one of those people and a walk through the LED light aisle at the local store might as well be a nausea inducing walk through a funhouse with 1000's of strobe lights going off


Me too. I know we have the same name but are we kin?


----------



## David_AVD (Nov 9, 2012)

I know the LED strings you're talking about. I have bought them on eBay cheap. There are often 50 LEDs in a string.

The LEDs are all in parallel, so must be the same colour, or must use LEDs of the same chemistry that use phosphor to get the different colours. This is so the forward voltage of the LEDs is all the same.


----------



## corey872 (Jan 10, 2010)

Lord Homicide said:


> Me too. I know we have the same name but are we kin?


If nothing else, we apparently share the same good genetics...at least for eyesight! 

David_AVD - I've seen the lights you mention. 'Fairy light' or 'Fairy LED' seem to be good search terms. On the absolute tiniest ones (equivalent to the 0603 LED which basically looks like a dot of light in thin air) I have only noticed single color. Though I suspect it would be pretty easy to make series strings of solid colors, then weave them together for a multi-color string if needed. The next step up (seems to be a 3mm LED?) you can get RGB or mixed colors. Either way, prices seem to run about 50 cents US per meter.


----------



## David_AVD (Nov 9, 2012)

I've bought both single and mixed colour strings off eBay that use 0603 (or similar) LEDs in parallel. Each LED is blobbed in epoxy to seal and strengthen the joints.


----------



## Lord Homicide (May 11, 2012)

^ how much did a strand cost and how many feet? Looking for about 2200K on the color temp

I would consider clear shrink wrapping the entire length


----------



## David_AVD (Nov 9, 2012)

At the time I paid anywhere from $0.20 to $2.50 AUD per 5m string as they were eBay auctions.

2200K is very warm white. I did get warm and cool white from memory but no idea on the actual CT.


----------

