Let’s see together what are the basic notions to know about the tin soldering process: from the necessary tools to the different applications.
Among the various welding processes developed by man, the tin one is one of the most common; technically speaking it seems easy, but in reality it can be more or less complex depending on its applications, which are many.The intrinsic ease of this type of welding is primarily due to its execution dynamics; to solder two metal edges, in fact, it is not necessary to melt them but simply put them together, as in the iron brazing process , and then melt the filler metal directly on the parts to be joined. Tin, in fact, is to be considered more a soft brazing process than a real welding.
A further aspect that contributes to its ease of execution is given precisely by one of the typical characteristics of the filler metal, namely the melting point of tin which is relatively low, just below 232 ° C; consequently, to be melted it does not require the use of complex systems or high amperage currents. Precisely for this reason, however, its applications are limited only to certain specific areas.
Tin for soldering
The definition “tin welding” is used above all for convenience, since this metal is not used in pure form but always combined in an alloy with another metal; moreover, tin-based alloys are technically defined as eutectic , a Greek term that means “easy to melt”.
Until a little less than fifteen years ago the most widespread eutectic alloy was based on lead and tin in the proportion 60/40, but starting from 2006 lead, due to its recognized toxicity, was banned and replaced with a small percentage of copper or silver; the eutectic alloys used nowadays, therefore, are composed of tin and copper or tin and silver in different proportions, depending on the applications.
Tin solder alloys are sold in the form of wire spools of varying thickness; the wire is also cored, like the one used with the wire welder , except that instead of being composed of another metal or element, the core of the tin wires is made up of a deoxidizer, commonly known as solder paste or firm paste.
The latter has the purpose of removing the oxide in the points where the welding is carried out, in order to avoid the risk that the tin at the melting point does not grip the surface to be welded. The paste can also be purchased in jars and applied directly to the parts to be welded.
Whatever the form in which it is used, during the soldering phase the paste evaporates in the form of white smoke that it is advisable not to inhale, so you must take the appropriate precautions to prevent this from happening.
The soldering iron
As mentioned at the beginning of our article, tin welding does not require high amperage currents so the tool used for welding is simple, compact and extremely handy; However, there are three different types depending on the intended use.
Nail welder: it is the simplest model and is equipped with a fairly coarse heating tip, similar to a nail. Being basic, just connect it to an electrical outlet and wait for it to heat up, then you have to bring the tip to the joint to be welded and rub quickly so as to spread the tin on the edges.
Welder with switch: it is an advanced version of the nail welder, similar in design but more powerful, therefore able to reach the melting temperature of the tin more quickly ; it is also equipped with a switch that allows you to turn it off without having to unplug it from the electrical socket. In this way it is possible to take advantage of the gradual cooling of the tip to solder at a congenial temperature and avoid the risk of burning the tin. A further variant is the tin soldering iron for micro-welding , which has a similar shape but reduced dimensions, similar to those of a stylus pen.
Mallet welder: it is identical to the two welders described above, except for the tip which, instead of being a nail, is flat and transversal; this type is especially suitable for performing linear welds on large surfaces, and therefore is ideal for metal laminates.
Gun welder: thanks to its versatility of use it is also known as a generic or ” rapid heating ” welder ; its characteristic, in fact, is to mount a tapered tip that can be used for both spot and linear welding. It is usually heavier and bulky, but also safer to use than other types of soldering irons, as it has a “trigger” to be held down to transmit current to the tip. This type is suitable for welding brass , copper and other metals; using a specific flux it can also be used to weld aluminum with tin . It is especially suitable for welding pipes and profiles, but not suitable for welding that requires high precision.
How to solder with tin
The soldering method of tin requires a standard procedure regardless of the type of soldering iron used and the specific application. The first step, as also occurs in normal electrode and continuous wire welding, consists in carefully cleaning the edges to be joined in order to remove all traces of slag, and then apply a layer of deoxidizing paste (the solder paste).
Holding the tin wire with one hand and the soldering iron with the other, therefore, it is necessary to approach the edges to be joined in order to melt the tin and pour it directly on the joint, and then spread it evenly with the tip of the soldering iron. The movements must be fast enough, as the tin cools quickly and tends to burn very easily if the temperature of the tip is above 270 ° C.
The welding of electronic components, on the other hand, is even more complex and requires a lot of expertise, as the minute dimensions of the components do not allow you to proceed comfortably; it is therefore necessary to try to join the pieces cold in order to make them stay in position and then add drops of molten tin.