- Solder won't "take" - grease or dirt present - de-solder and clean up the parts. Or, material may not be suitable for soldering with lead/tin solder (e.g. aluminium).
- Joint is crystalline or grainy-looking - has been moved before being allowed to cool, or joint was not heated adequately - too small an iron/ too large a joint.
- Solder joint forms a "spike" - probably overheated, burning away the flux.
Soldering is a method of joining metal parts using a filler material (SOLDER) which has a melting temperature below 450 °C (842 °F). Soldering is distinguished from brazing by virtue of a lower melting-temperature filler metal; it is distinguished from welding by virtue of the base metal not melting during the joining process.
In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action and to bond to the materials to be joined by wetting action. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique that has been used practically as long as humans have been making items out of metal.
