Tin and lead based solders have been used for many decades in a wide variety of industries. But recently, the proportion of their use has decreased significantly. They were replaced by lead-free solders. However, tin remained the main component in their composition. But the lead content is reduced to zero (hence the name).
Legislative initiative or trend of the times
Why is it now that lead-free solders have so quickly begun to gain ground from traditional formulations? The fact is that the EU directive “On the restriction of the use of hazardous substances” (adopted in 2003 and entered into force on July 1, 2006) obliged to limit the use of lead (and five more substances) in the manufacture of electrical and electronic devices. This is due to the requirements of environmental safety and the preservation of human health. And lead belongs to the group of heavy metals, and its vapors are highly toxic.
Although adherents of the usual POS-40 solder should not be upset. It is still produced and sold. In many countries, tin-lead group solders are used in the transport, military and aerospace industries.
Features and main characteristics of lead-free solders
The main advantage of such compounds is absolute environmental safety. In addition, equipment and machinery made with their use are much easier to dispose of.
The technological feature of these solders is the increased melting point. On average, it is 50 ° C higher than that of tin-lead analogues. This somewhat complicates the soldering process and increases the requirements for the equipment used.
According to the generally accepted classification, these compositions belong to soft solders. The tensile strength does not exceed 100 MPa.
One cannot fail to note such an important characteristic of these solders as high electrical conductivity.
Varieties
For lead-free soldering, four main types of solders are used today , which consist of:
- only from tin (Sn);
- from tin and copper (SnCu);
- from tin and silver (SnAg);
- from tin, silver and copper (SnAgCu).
The latter composition is most widely used for soldering due to the balanced price / quality ratio. The main component in the composition is, of course, tin. The percentage of the remaining ingredients varies within various limits and depends on the brand of solder and the area of its application.
Tin solder (Sn-100) is used quite rarely, since it has the highest melting point (232 ° C). However, the well-known Japanese company Nihon Superior positions it as one of the best solders that do not contain lead.
There are also special formulations containing bismuth and indium. However, they are intended for highly specialized purposes and are rarely found on the market.
Copper-containing solders
Initially, special Sn99 / 3Cu0.7 solder (with a copper content of 0.7%) was developed for automated wave soldering of printed circuit boards in the factory. The disadvantages of this composition include the relatively low mechanical strength of the connection. Under the POM-07 index, it is produced by the Russian “Solder Plant” (Novosibirsk). Of the foreign manufacturers of this variety of solders, the most famous are Asahi (Singapore), Wyctin B&C (China) and Tamington (USA).
To solder various copper products (especially drinking water pipes), brass, nickel, steel and alloys based on them, Sn97Cu3 solder (with a copper content of 3%) is used. Seams made using this composition have increased heat and cold resistance. The main suppliers of this variety of solders in the Russian market are German manufacturers Rothenberger and Brazetec. Among domestic manufacturers, such products are manufactured by Skat (St. Petersburg).
Silver-containing solders
The addition of silver to lead-free solders increases their fluidity and adhesion to the connected elements. Moreover, the higher the percentage of silver in the composition, the higher these indicators (the cost, of course, also rises). Today, manufacturers offer solders with a percentage of tin / silver: 97/3, 96.5 / 3.5 (the most popular and most widely used ratio), 96/4 and 95/5. The melting temperature of such compounds (221 ° C) is lower than that of copper-containing products. In addition, they are characterized by increased reliability of the connection (equipped with their help), and even surpass lead-containing solders in terms of strength parameters. The most widely represented products on the Russian market are the German company Felder and the American Kester.
Three-component solders
What is soldering electrical parts and radio components at modern enterprises today (as well as numerous fans who do it with their own hands)? Three-component solders SnAgCu. It is this composition that combines all the advantages of lead-free products, has good performance, low melting point (217 ⁰) and the optimal price / quality ratio.
The scientific debate about the ratio of components has been going on for quite some time. Today, the optimum (both according to manufacturers and reviews of numerous consumers) is considered to be 95.5% tin, 3.8% silver and 0.7% copper (Sn95 / 5Ag3 / 8Cu0.7) in such solder. It is widely used in enterprises for the production of electronic equipment and electrical equipment. In addition, it is quite easy to work with him at home. Quite successfully, such solders cope with old, highly oxidized parts. In Russia, the products of the well-known German manufacturer Stannol are most popular.
Features of soldering technology
The technology of work using solders that do not contain lead in its composition is practically no different from soldering with the usual components. However, some features should be considered.
To the question of what they solder, the answer is unequivocal: with a soldering iron. However, it is best to use a device with a thermostat. This will allow you to work in the range of operating temperatures specified by the manufacturer. And it is much smaller than that of lead-based formulations.
To prevent overheating of parts and minimize thermal contact, it is necessary to choose the optimal shape of the soldering iron tip. In addition, it should be borne in mind that a conventional copper tip will last (when using such solders) for a short time. It is better to use special tips with steel coating or coated with chrome and nickel.
The choice of flux also plays an important role when working with lead-free solders. Usually, special formulations (usually more chemically active) are used for this. The most convenient liquids, gels and pastes in operation that do not require subsequent cleaning of the soldering area.
Otherwise, everything is as usual:
- heat the soldering iron to the required temperature;
- if necessary, we clean the soldering places;
- apply flux;
- at the same time we apply a solder bar and a soldering iron tip to the junction of the elements;
- allow the soldered elements to cool naturally.
Finally
If you don’t really think about health (yours and your loved ones), you can safely use the cheap and affordable POS-40 solder to repair your favorite coffee coffee. However, spending a little more money on the purchase of safe supplies, you will save on medicines in the future, and maybe significantly increase your life expectancy. Naturally, the final choice is yours.