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I often see the advice "use a small soldering iron" when soldering rather delicate devices. I think that most times this is actually bad advice. I've had lots of people ask me to take a crack at soldering something after they have made a mess. I usually break out a larger iron.

To solder something you need to get the joint hot enough, or you get a bad joint. To keep the heat from traveling to the semiconductors you want to solder really fast. A small iron that has to sit on the joint for several seconds to heat it to the proper soldering temperature is sending lots of heat into the circuit while you are waiting. With a large iron, already heated up hot, it takes just a quick touch and the joint is up to temperature, the solder is in and you are done.

I did one this weekend. It was a home water sensor with a brass plated rod soldered to a circuit board. It had broken loose from a cold joint by the manufacturer. The owner tried unsuccessfully to solder it back. I simply cleaned up the mess with solder wick, then using a relatively massive 40 watt iron instead of the 25 watt iron he used I soldered it in about 2 seconds flat.
 

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You know it sure does seem like the LEDs are a lot of trouble, and most of that trouble seems to be controlling the current through the LED. Why not just isolate all your lights through a lighting control board. Then feed the lighting control board through a regulated switching DC to DC power supply. That would isolate all the spikes and provide very close regulation of the voltage, and therefore current to the LEDs. This should allow the use of low cost LEDs, as long as heat is not the problem.
 

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On the subject of soldering heat sensitive components. I believe most soldering damage is done by using a soldering iron that is too SMALL, not too big! When you put a small iron against the joint, the joint sucks the heat out of the iron instantly. The iron must then supply more heat until the temperature comes back up and in the meantime heat is flowing into the device and the wire. Your insulation burns back and your device may be damaged. Use a larger iron and it holds enough heat to do the entire job. So when you touch the iron to the joint, the joint heats to the proper temperature instantly the solder melts, and you are done in an instant so the heat doesn't have time to flow. Try it, you won't believe how much better your solder joints will be!

Gary H. Lucas
 
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