Flux is a water based paste that contains a cleaning agent, activator, and wetting agent used in soldering to remove oxides from the area to be soldered. A good flux cleans the area to be soldered and allows the melted solder to flow and bond with the metal surfaces. The activator is a specific chemical designed to remove oxides, oil, and dirt.
Commonly there are three types of fluxes for electronics applications: rosin, water-soluble, and no-clean fluxes. These fluxes are selected depending on the need and applications. Fluxes can be made from ammonium chloride, hydrochloric acid, zinc chloride, or rosin.
Water-soluble paste fluxes are applied by brush or dispensed from a syringe into the appropriate area, then heated using conventional methods. A no-clean flux does not require any cleaning after soldering. It is preferable to use the flux that matches the solder wire you are using.
There are three main categories of solder wire: Lead-based, lead-free, and flux-core solder.
Lead based is a type of traditional solder wire with 60/40 (tin/lead) mixture, the most common one available in the market. Its melting point is around 180-190 degrees Celsius. With higher tin concentration, it will have better tensile and shear strengths. You can also find non-corrosive solder wire having 63% tin and 37% lead mixture with good solderability and insulation resistance.
The second type is a lead-free solder wire. Lead affects health and environment and so lead based solder wire is not the ideal solution. Lead-free solder usually contains 99.3% tin and 0.7% copper with higher melting temperature of around 217 degrees Celsius.
The third is solder wire having the flux embedded in the solder wire itself. It does not require additional flux while soldering.
Solder flux from Noel and Glare India are found good enough for hobbyists. Bharti, Amico, TINNZTES, Globomotive, and Kester are some other popular solder wire brands. These brands are being mentioned based on our personal experience and reviews found online and are not necessarily the best ones.