How do I make a good quality solder joint?

To be honest, I think there are a lot fewer modelers who know how to solder properly than I previously believed. At a past contest, a friend came back and told me how he just had to show some guys how to solder, and the description he made of their efforts was frightening. To top it off, of all the guys at the field, I would have at least expected THEM to know how to do it properly. I've also seen some very bad cold solder joints done by people who claimed to know how to solder.

I'm not saying you can't do it, or that all bad joints will fail. I'm just suggesting that you learn a lot about soldering before you jump in and create a weak link in your servo extensions, or other important component that your plane longevity depends on. A GOOD solder joint is every bit as reliable as a straight wire. A mediocre or poor solder joint is NOT. I'd recommend that you make a trip to Radio Shack, get yourself some good rosin core flux or--better yet, several kinds, so you can learn the differences--a couple spools of various sizes of wire to practice on, and their little book that tells how to solder. Sit down and solder up 10 feet of wire, one inch at a time, with the different kinds of solder...then, if you know your joints are good, think about working on your servo extensions. 

The best solder joint has the minimum amount of solder on it to do the job, and that solder was definitely not melted, then put on the wire. A good solder joint has the solder melted BY the wire, which was heated up by your soldering iron. You don't want it too hot, though, because then the wire insulation melts, and the wire gets stiff. Stiff wire is more prone to vibration failure. The whole key to a good solder joint is getting the wire WET with solder. Just think of Dustin Hoffman describing the solder joint... "It was wet. Yeah, wet. I liked it." 

Flux will assist in the flowing action, but the solder can't flow regardless of the flux if the wire is not hot enough. Rosin core solder is the best all around solder for electrical joints. There are some other formulas that work well too, like no-clean flux. Just make sure that whatever you do, you DO NOT use an acid core solder, or anything designed to solder your copper pipes together. Also, you must let the joint sit absolutely still while it cools. A good joint will look nice and shiny, with the solder flowing smoothly into the wire. If you have an abrupt stop in the solder, then it probably didn't flow properly. rcfaq 

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