This is going to be an ongoing series of posts, and I hope that you won't have to wait too long between them. Feel free to directly ask questions or prompt me to expand on any particular topic. Here are the basics: Fluxes are used to remove oxidation not contamination. Always clean the parts being joined by soldering. Use the lowest activity flux that you can. In order from low to high, they are R, RMA, RA and OA. Never use OA flux for hand soldering electronic components on a PCB. Avoid RA unless you have a very good reason to do so (you won't have a good reason most likely). Use eutectic solder formulated at 63/37. Do not use 60/40 solder. I will explain why in a later post called "Heat Control". Pre-solder all components. That means "tinning" wires or leads to be soldered, and also solder cups on connectors. For large projects such as building patchbays that require hundreds of wire tips to be pre-soldered, consider a solder pot. Never solder crimped connectors. Either solder, or crimp, but do not solder a crimped connector under any circumstances. If a crimped connection is failing, replace it by cutting the union off and re-crimping, or soldering. Keep the cleaning sponge on your soldering station slightly damp, and not soaked. The recommendation is to use distilled water to prevent calcium and other chemical contaminants from getting on the soldering iron tip and interfering with the soldering operation. Use a well-regulated soldering iron. Once you touch the iron to the joint, if the iron cannot hold the temperature reasonably well (in other words, it's underpowered and can't supply enough heat) that will interfere with the creation of a proper intermetallic bond. Properly performed hand soldering is a controlled operation. Desoldering however, is an uncontrolled operation, and all desoldered components should be discarded and replaced using heat control techniques. Suspect that all desoldered components may be heat damaged. In practice, this may not be possible, so use extreme caution when desoldering any component that must be reused.