Solder is obviously a key element in any form of electronics construction where soldering is undertaken. It provides a mechanical and electrical joint that is essential to keep components in place once a circuit has been assembled. While the mechanical strength is important, it is also necessary to ensure that the soldered joint provides a good electrical connection is made between the two connections that require joining. This can only be achieved satisfactorily if the medium, i.e. the solder joining the two conducts electricity well.
A further requirement of the material making the joint is that it must be easy and convenient to use. Solder has the advantage, unlike other mixtures or pure metals that it melts at a relatively low temperature. This means that it is possible to use it in the construction of electronics equipment..
What is solder?
Traditional solder that used to be used for soldering in the electronics industry used to be a mixture of tin and lead. Different types of solder are used for different purposes. Solder is of course used in plumbing. The type of solder used for electronics usually contains 60% tin and 40% lead. This is often known as "60/40" solder. It is what is termed a "Eutectic Mixture". Although this is a chemical term, basically this type of mixture melts at a temperature well below that which might normally be expected.
In additional to the metal constituents flux is also required to ensure that good joints are made. Flux is an acidic mixture that helps remove oxides from the area of the joint and therefore helps the solder flow easily over the joint and form a good bond. The flux can be seen as a brown liquid as a solder is heated, and it sometimes gives off a pungent smoke that can act as a irritant. This is one reason why soldering should always be carried out in a well ventilated area.
For plumbers solder, a separate flux is used, but for electronics solder, it is contained within the solder itself. The solder used for electronics is normally in the form of a wire, and if it is carefully cut small cores of flux can be seen running through the solder. The amount contained is correct for making electronics joints and separate flux should never be used.
Solder sizes
Solder for electronic construction is sold in the form of a thin wire. When soldering, this makes it easy to handle and apply to the place where the soldered joint is to be made. Different sizes of solder are available and a choice will have to be made when buying any. For most applications for electronics soldering, this will make little difference. The thinner wire is much better for fine work. If it is used for normal soldering then the thin solder can be slightly less convenient because longer lengths are used making a normal joint.
The different solders that are produced are generally specified either in Standard Wire gauge (SWG) or America Wire gauge (AWG). For most printed circuit and general soldering work choose 20 to 22 SWG solder (19 - 21 AWG), although for larger joints a thicker solder, possibly 18 SWG (16 AWG) is better.
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