Tin- and lead-based solders have been used in a wide variety of industries for decades. But in recent years, the share of their use has significantly decreased. 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 are taking over so quickly 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 other substances) in the manufacture of electrical and electronic devices. This is due to the requirements of environmental safety and human he alth. 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 today. In many countries, tin-lead solders are used in the transport, military and aerospace industries.
Features and main characteristics of lead-free solders
The main advantage of such compositions is absolute environmental safety. In addition, equipment and machinery made with their use is much easier to dispose of.
The technological feature of these solders is an increased melting point. On average, it is 50 ⁰С higher than that of tin-lead counterparts. 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.
It is impossible not to note such an important characteristic of these solders as high electrical conductivity.
Varieties
For lead-free soldering today, four main types of solders are used, which consist of:
- only from tin (Sn);
- from tin and copper (SnCu);
- from tin and silver (SnAg);
- from tin, silver and copper (SnAgCu).
The last composition is most widely used for soldering because of the balanced price/quality ratio. The main component in the composition is, of course, tin. The percentage of other ingredients varies within different limits and depends on the brand of solder and its application.
Tin solder (Sn-100) is used quite rarely, as it has the highest melting point (232 ⁰С). However, the well-known Japanese company Nihon Superior positions it as one of the best lead-free solders.
There are also special formulations containing bismuth and indium. However, they are designed for highly specialized purposes and are quite rare on the open market.
Copper-containing solders
A special Sn99/3Cu0.7 solder (with 0.7% copper content) was originally 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 joint. Under the POM-07 index, it is produced by the Russian Solder Plant (Novosibirsk). Of the foreign manufacturers of this type of solder, the most famous are Asahi (Singapore), Wyctin B&C (China) and Tamington (USA).
Sn97Cu3 solder (with a copper content of 3%) is used for soldering various products made of copper (especially drinking water pipes), brass, nickel, steel and alloys based on them. Seams made using this composition have increased heat and cold resistance. The main suppliers of this type of solder on the Russian market are the German manufacturers Rothenberger and Brazetec. Among domestic manufacturers, such products are produced by Skat (St. Petersburg).
Silver-containing solders
The addition of silver to lead-free solders increases their fluidity and adhesion to the elements to be joined. Moreover, the greater the percentage of silver in the composition, the higher these indicators (the cost, of course, also increases). Today, manufacturers offer solders with a percentagetin/silver: 97/3, 96, 5/3, 5 (the most popular and most widely used ratio), 96/4 and 95/5. The melting point of such compositions (221 ⁰С) is lower than that of copper-containing products. In addition, they are distinguished by increased reliability of the connection (equipped with their help), and in terms of strength they even surpass lead-containing solders. The most widely represented products on the Russian market are the products of the German company Felder and the American Kester.
Three-component solders
What do electrical parts and radio components solder today at modern enterprises (as well as numerous do-it-yourselfers)? Three-component SnAgCu solders. It is this composition that combines all the advantages of lead-free products, has good performance, low melting point (217 ⁰С) and an optimal price / quality ratio.
The scientific dispute about the ratio of components has been going on for quite some time. To date, the optimal content (both according to manufacturers and reviews of numerous consumers) is considered to be the content in such solder of 95.5% tin, 3.8% silver and 0.7% copper (Sn95 / 5Ag3 / 8Cu0, 7). It is widely used in enterprises for the production of radio-electronic equipment and electrical engineering. In addition, it is quite easy to work with him at home. Quite successfully, such solders cope with old, heavily oxidized parts. In Russia, the products of the famous German manufacturer Stannol are the most popular.
Technology Featuresrations
Technology for the production of work using lead-free solders is practically no different from soldering with familiar components. However, there are a few things to keep in mind.
To the question of what they solder with, the answer is unambiguous: with a soldering iron. However, it is best to use a device with a thermostat. This will allow work to be carried out within the operating temperature range specified by the manufacturer. And it is much less than 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 an ordinary copper tip will last (when using such solders) for a rather short time. It is better to use special steel-coated or chrome-nickel-coated tips.
The choice of flux also plays an important role when working with lead-free solders. Usually, special formulations are used for this (usually more chemically active). The most convenient liquids, gels and pastes that do not require subsequent cleaning of the soldering site.
Otherwise everything is as usual:
- heat up the soldering iron to the required temperature;
- if necessary, clean the soldering points;
- apply flux;
- simultaneously apply a bar of solder and a soldering iron tip to the junction of the elements;
- let the soldered elements cool naturally.
In conclusion
If you don't reallyIf you think about he alth (for yourself and your loved ones), then you can safely use the cheap and affordable POS-40 solder to repair your favorite coffee pot. However, by spending a little more money on safe supplies, you will save a lot on medicines in the future, and maybe even significantly increase your life expectancy. Naturally, the final choice is yours.
