Solders : Availability & Different Types Of Solder

2.1 Cored wire: A flux cored solder wire is a wire of solder alloy containing some longitudinal cavities along its length which are filled with flux. The flux is solid (or pasty) at room temperature, but when a piece of solder wire is melted the flux is released in liquid form, so that it can perform its cleaning action. The amount of flux is about 1 to 4 mass percent (3 mass % is approximately 20 volume %). Most solder alloys are available as flux-cored solder wire with diameters ranging from 0.25mm to 3 mm for use with a soldering iron. The homogeneity of the distribution of activator and the continuity of the flux cores depend on the processing of the wire, for which one should rely on approved suppliers. The alloy with 60 tin and 40 Pb is widely used for quality work in electronics. Adding silver to the solder reduces the dissolution of silver from the work piece.

2.2 Solder Paste: Solder paste is essentially comprised of metal powder particles in thickened flux, to which special agents are added to maintain its parameters such as viscosity, thixotropy etc. Most solder pastes contain 80 to 90 mass percent of solder metal, which is about 30 to 40 volume percent. Dispensing agents are added to prevent the separation of the heavy metal from the light vehicle. As mentioned, solder paste is available in jars and sachets for use in screen printing/ stencil printing. It is also available in syringes for use in dispensing applications.

2.3 Solder preforms: Preforms are small objects of a given mass, made of solder, which are placed at the place to be soldered. They are available in many metal compositions and soldering flux may or may not be supplied as part of the preform. Various shapes of preforms exist: discs, washers, spheres, foil etc.

2.4 Solder rods: Solder rods are used for preparing solder bath during wave soldering of leaded components.