Any suggestions?

[JerryB]

Gene:

You are correct that it's best to apply a rosin (not "resin") type paste flux to both halves of every solder joint, and to pre-tin both halves. In fact, it is much more important to clean and pre-tin the larger (rail in this case) half than the wire.

I always pre-tin every joint, even on small diameter wires. I just finished assembling the prototype of a small R/C controlled firefighting machine where there were well over 200 18Ga. soldered wire connections, some in very difficult locations. Every joint was pre-tinned and there was not a single failed connection.

Cleaning the joint (especially the rail) is also very important. Use a fine abrasive cloth on the rail. I use a stick such as a bamboo skewer or craft stick to push the abrasive into the corners to make certain the oxidation is removed from all surfaces that are in the join area.

I use alcohol or other light solvent to wipe the join area prior to applying flux and tinning. Chemical (alcohol) cleaning for the wire isn't necessary unless oil or grease contamination is a possibility.

60 / 40 rosin core solder is most commonly used for these applications. Other more exotic solders are useful for specialized materials and situations.

Use a good (not old or eroded) tip in the iron. Clean the tip by dragging it across a damp sponge, then tin the tip. Flux the joint surfaces, heat and apply the solder. Applying the solder to the join surface rather than the tip of the iron will ensure that the join surface is hot enough to melt the solder.

It's not necessary to apply large amounts of solder for pre-tinning. Just coating the surface is good enough. If I get too much solder on an area, I heat it and wipe it off. The pre-tin should appear clean and bright.

I keep a supply of clothespins and other small lightweight clamps near my work station to hold or support the wire near the solder joint. This keeps the parts in contact and helps avoid moving the joint and creating a cold solder join. Add a little more flux to the join surfaces, put the part surfaces together and reheat. Apply just enough solder to create a fillet between the wire and the rail. Let the clamps hold it in place until cool.

Hope this helps.

Happy (Well Connected) RRing,

Jerry