Soldering is a process by which two metals or alloys are joined together with a third metal or alloy. The third metal or alloy has a much lower melting point compared to the first two metals. Soldering is different from adhesive joining. Adhesives bond by mechanical attraction having to do with mechanical surface properties of the material relative to the adhesive. In the case of solder, there is also a chemical reaction in addition to physical reaction.
Soldering is primarily used to provide a convenient joint to ensure electrical contact or seal against leakage. Solders typically do not provide high mechanical strength, given the soft nature of popular solder materials. Soldering is used extensively in the electronics industry printed circuit boards. It is also used in joining metals in industries such as cutlery, tools, metal box making etc.
|The Inter-metallic Layer|
In order to have a good soldering joint, one must form inter-metallic layers between the solder material and the base metal. Otherwise, the solder simply solidifies over the base metal without forming any bond.
Within each inter-metallic layer, there are actually a number of different compounds formed by the solder materials and the base metal. These compounds are typically quite brittle and will adversely affect the integrity of the solder joint. As the joint is subject to stress, thermal cycles, vibration, or shock, the inter-metallic layers are usually where it starts to fail.
Since the inter-metallic layers are inevitable, it is best to keep it as thin as possible. See the guidelines for tips on minimizing the thickness of the inter-metalic layers.