The choice of the alloy depends primarily on the properties of the base metal and application. The selection of the solder alloy is also dependent on the method of application. Solder can be supplied as solid wire, flux cored wire and pastes. The pastes can be supplied in a tub or in some instances a syringe so that the process can be automated.

When selecting an alloy for soldering components factors such as melting point, plastic range, speed of wetting, ability to wet, flow and bond to different metals and also appearance after soldering must be taken into consideration.

Of all the many solders, tin-lead is regarded to be the largest single group of alloys used. When referring to tin/lead solders, the tin content is customarily given first. For example 40/60 refers to 40 percent tin and 60 percent lead by weight. Most metals can be joined with these alloys. In today's industry more and more companies are now looking at eradicating lead from the soldering operation due to its poisonous nature. There is now an extensive range of lead free alloys available to be used, which can replace lead bearing alloys.

Tin-lead solders are compatible with almost all base types of base-metal cleaners, fluxes, and heating methods. Increasing the tin content produces better wetting and flow characteristics. When less tin is used, greater care should be exercised in surface preparation of the metals to be joined as any contamination of the surface to be soldered may impede the flow of the solder. It is imperative that all surfaces to be soldered are thoroughly cleaned from all grease and oxides.

As soon as any heat is applied to the work piece a new oxide begins to form. This will prevent the chemical action of solder. Flux is designed to break this oxide down enabling soldering to be carried out successfully. In general use an acid–type flux for industrial applications is recommended and a rosin–type for electrical connections. Regardless of which flux is used soldering cannot be performed in the open air without the use of a suitable flux.

LEAD CONTAINING SOLDER ALLOYS

LEAD FREE SOLDER ALLOYS

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