Solder (metal)

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When Lot is called an agent metals by soldering connects. The solder consists of a mixture ( alloy ) of different metals. Lead , tin , zinc , silver and copper are used particularly frequently .

The metals to be connected are copper, bronze , brass , tombac , nickel silver , silver, gold , hard lead, zinc, aluminum but also iron . When soldering, heat creates a local melt . After cooling, a mechanical and electrically conductive connection remains. The alloyability of the solder with the metallic work pieces, materials, (electronic) components, wires, pieces of jewelry or other components is the prerequisite for a permanent, solid material connection. The melting point of the respective solder is generally lower than that of the workpieces to be connected.

In the past, many solders contained lead. Since lead is poisonous, since July 2007 it may only be contained and used in the EU in accordance with the RoHS directives in exceptional cases. Exceptional cases are areas in which empirical values ​​about the long-term reliability of the new solder alloys are not yet available and failures due to defective solder joints in safety-relevant areas could lead to serious problems, such as in the brake control of a car, in control systems of aircraft or in critical devices in medicine and Military.


Before soldering, the metal workpieces to be connected should be mechanically and chemically free from paint layers, dirt, oxides and sulfides, as well as degreased. The metal surfaces should be "bare". This enables good and quick wetting of the solder together with a suitable flux on the surfaces and thus significantly supports the soldering. Especially on soft-soldering in the electronics sector, it is also not useful to the surfaces of workpieces or components wires with solder before the actual Zusammenlötung advance nor tin , to reduce the soldering time. During the soldering process, the flux dissolves the oxide layers that are constantly forming on the metal surfaces of the workpieces. At the same time, it protects against renewed oxidation during the soldering process and improves the flowability of the solder, whereby the workpieces to be connected must be heated to the temperature of the liquid solder. This is e.g. B. to be observed with heat-sensitive electronic components, d. H. maximum soldering times must be observed! The heat supply capacity z. B. via soldering iron or gas burner and thus also the soldering temperature must be adapted to the solder in question, the size of the soldering point and its heat dissipation to the workpiece. Because the tensile strength, especially with soft solders, is usually lower than that of the materials to be connected, the solder layer should therefore be as thin as possible when there are high mechanical forces.

A eutectic alloy has a lower melting temperature than the pure substances it forms and melts or solidifies like a pure substance at a fixed temperature (unlike a "normal" mixture), e.g. B. Sn62Pb38 at approx. 183 ° C. This is desirable for electronic soldering.

All non-eutectic alloys have two characteristic temperature points between the beginning of the melt and complete liquefaction (and vice versa), the so-called solidus and liquidus temperatures . So you have a melting / solidification area , which z. B. with plumbing is desirable. The alloy is completely solid below the solidus temperature, pulpy up to the liquidus temperature, and completely liquid above it.

By definition, solders are divided into hard solders and soft solders based on the liquidus temperature of the solder . Solders with softening temperatures below 450 ° C are soft solders with low mechanical strength, while those with softening temperatures above 450 ° C are hard solders (previously also known as blow solders) with high strength.

Hard solders

Hard solders are alloys with a high silver content, nickel silver or brass base, which are usually available in rod, rod, wire, foil and sometimes paste form. Brazing pastes already contain flux , so that a separate addition is no longer necessary, in contrast to the other forms of solder. Flux in paste form is mostly used there.

In contrast to soft solder (based on tin / lead), hard solders are also suitable for mechanically and thermally more heavily stressed metallic connections (especially for normal iron and nickel-containing workpieces, such as hard metal cutting in iron drills, the "stone drills") . Stainless steels with chromium , tungsten and / or molybdenum are, however, often difficult to braze and usually not solderable at all. This makes soldering tests necessary. Otherwise, these materials should be better welded. In contrast to stainless steels, copper-containing material alloys such as bronze, brass, tombac, nickel silver as well as silver and gold can be hard (and soft) soldered very well. Brazed joints sometimes have higher strengths than the base material . Sometimes a flux, e.g. B. based on borax , added. Usually the solder wire is covered with it on the outside. The processing temperatures for hard solders are between 500 and 1000 ° C. As heat sources u. a. Gas torch or industrial laser used.

In the case of oil and gas pipes with copper pipe fittings, if soldering should be carried out, only brazing is permitted. Heating installations are often brazed from a pipe diameter of 35 mm. Drinking water installations may only be brazed from this diameter. Since the water heated by solar collectors can reach temperatures of over 200 ° C, depending on the collector type and system pressure, copper pipes in the solar circuit are also connected by hard soldering in Germany, while in Austria soft soldering is also permitted if it is ensured that the water temperature does not exceed 200 ° C rises.

Silver solders

Silver solders are alloys of silver , copper , cadmium and zinc , with small amounts of manganese and nickel . The processing temperature is 600 to 800 ° C. As the silver content rises, so does the processing temperature. Silver solders flow more easily than brass solders and are used to connect copper pipe fittings. A distinction is made between:

  • Silver solder without added cadmium
    • L-Ag34Sn (34% Ag, 36% Cu, 27.5% Zn, 2.5% Sn)
    • L-Ag44 (44% Ag, 30% Cu, 26% Zn)
    • L-Ag55Sn (55% Ag, 21% Cu, 22% Zn, 2% Sn)
  • Silver solder with added cadmium (not for drinking water installations )
    • L-Ag40Cd (40% Ag, 19% Cu, 21% Zn, 20% Cd)
    • L-Ag30Cd (30% Ag, 28% Cu, 21% Zn, 21% Cd)

Brass solders

Brass solders are alloys of copper and zinc with small additions of silver, silicon , tin and manganese. The processing temperature is 800 to 1000 ° C. As the copper content increases, the melting point and strength increase.

  • L-CuZn40 (60% Cu, 39.7% Zn, 0.3% Si)

Phosphor solders

Phosphor solders are alloys made from phosphorus and copper (and possibly with silver).

Hard solders for aluminum

  • L-AlSi12
  • L-ZnAl30

Soft solders

Commercially available soldering tin roll

Compared to hard solder connections, soft solder connections often have only moderate strengths . They are mainly used in electrical engineering and electronics , in house installation and, thanks to lead glass technology, in art ( lead glass windows , Tiffany lamps). For manual soft soldering, electrically heated and regulated soldering irons with a soldering temperature of around 60 ° C to 420 ° C that can be set digitally or analogously with exchangeable soldering tips from around 5 to 250 watts nominal power are used today. Soft and hard soldering should always be carried out with protective goggles due to the risk of solder and flux splashing, and under an air extraction device because of the flux fumes that are harmful to health. For more see soldering .

Tin solders

Solder with flux core

The most frequently used soft solders are tin solders, i.e. alloys made of tin and lead with small amounts of iron , antimony , copper and nickel. The melting point of the tin solders is below 330 ° C. When heated, the solders change from a solid to a mushy and finally to a liquid state. The eutectic, also known as seepage solder (63% Sn, 37% Pb), with a melting temperature of 183 ° C is of particular importance. Alloys that are remote from the eutectic are also used in favor of a technically desirable solidification area between the liquidus and solidus line.

Use of tin solders with a tin content of:

  • 20–40%: Connecting copper pipes, lead cables and sleeves, zinc gutters
  • -0050%: Fine soldering of sheet metal
  • 60–63% (seepage solder): connecting and tinning electrical lines, wires, printed circuit boards
  • 00> 90%: Soldering cans

Wood's metal , consisting of 50% bismuth (Bi), 25% lead (Pb), 12.5% cadmium (Cd) and 12.5% ​​tin (Sn), has the lowest melting points of approx. 75 ° C Field's metal at 62 ° C , consisting of 32.5% bismuth (Bi), 51% indium (In) and 16.5% tin (Sn). The former is highly toxic and environmentally harmful due to the cadmium content , while the Field metal used as a replacement is significantly more expensive due to the indium content .

Tube solders (radio solder or electronic solder ) have one or more incorporated cores made of organic, acid-free tree resins such as B. Rosin , which act as a flux when soldering . In the English-speaking world, these are referred to as flux .

Properties of the solder components

element chem.
significant influence
tin Sn 0232.0 ° C Main component of soft solders
lead Pb 0327.5 ° C Lowering of the melting temperature of the solder; Improvement of the flow properties
Bismuth Bi 0271.3 ° C significant reduction in melting temperature of the solder
antimony Sb 0630.7 ° C increases the tensile strength of the solder; reduces the degree of shrinkage
silver Ag 0961.9 ° C Reduces the alloying of silver from the workpieces or
electronic components to be connected into the solder
copper Cu 1084.4 ° C reduces the alloying of copper from the workpieces to be connected or
electronic components into the solder; extends the service life of copper soldering tips

Because of the good technical controllability and the low melting point, a number of solders contain lead. Due to the current legal situation, especially in the EU (including WEEE, RoHS : i.e. DIR 2002/96 / EG and DIR 2002/95 / EG), there are strong efforts worldwide to replace leaded soft solders with lead-free ones. However, these usually have a less universal area of ​​application and bring z. T. technical problems such as embrittlement and whisker formation with it. For this reason, the use of lead-free solder is not permitted in the production of electronic assemblies for medical technology, security technology, measuring devices, aerospace, rail technology, fire fighting technology and for military / police use . In electronic assemblies that z. B. are exposed to extreme temperatures, or where the use of lead is useful for other reasons, e.g. B. in measurement technology, the use of lead-containing solder is left to the discretion of the manufacturer.

Since July 2006, however, lead-containing tin solder may no longer be used in electronic devices due to the environmental and health effects (see RoHS DIR 2002/95 / EC). Lead-free tin alloys with copper and nickel are now being used, but these are sometimes patented and quite expensive. Tin alloys with copper and silver are used as an inexpensive alternative, e.g. B. Sn 95.5 Ag 3.8 Cu 0.7 (melting temperature about 220 ° C), outside of Europe people like to replace lead with bismuth. For private applications and for special areas of application (see above) such as However, lead-containing solders may still be used, e.g. aerospace, military and some other special applications.

Since June 2011, with the new RoHS DIR 2011/65 / EU, the exceptions for medical and measurement technology no longer apply. However, there are transition periods until 2019 at the latest.

In the past, solders with a high bismuth content were used as " thermal fuses " in electronic devices because of the very low solder melting temperature of below 100 ° C.

Common solder alloys

Various soft solders. On the left a lead-free tin-silver solder.

The following table lists some common solder alloys and their applications.

alloy Temperature (° C) Remarks application
Solidus Liquidus
Sn42Bi58 138 138 eutectic Low temperature solder
Sn43Pb43Bi14 144 163 Low temperature solder
Sn62Pb36Ag2 179 179 eutectic
Sn63Pb37 183 183 eutectic Standard electronics solder (with lead)
Sn60Pb40 183 191 Standard electronics solder (with lead)
Sn96.5Ag3.0Cu0.5 217 219 Lead-free electronics solder
Sn96Ag4 (Sn96,3Ag3,7) 221 221 eutectic
Sn95Ag5 221 245
Sn99.3, Cu0.7 227 227 eutectic Lead-free electronics solder
Sn99, Ag0.3, Cu0.7 227 227 eutectic Lead-free electronics solder
Sn100 232 232 Pure tin
Sn95Sb5 232 240 Lot with antimony
Sn89Sb10.5Cu0.5 242 263 Lot with antimony
Sn10Pb88Ag2 268 290 Lead solder with a high melting point
Sn10Pb90 275 302 Lead solder with a high melting point
Au80Sn20 280 280 Au 5 Sn-AuSn eutectic Chip bonding
Sn5Pb92.5Ag2.5 287 296 Lead solder with a high melting point
Sn5Pb95 308 312 Lead solder with a high melting point

Soft solder designations

Abbreviations used for soft solders

According to DIN 1707, the following abbreviations are used for soft solders .

  • Group A: lead / tin and tin / lead soft solders
  • Group Ah: Contains antimony
  • Group Aa: low in antimony
  • Group Af: Antimony-free
  • Group B: tin / lead solders with added copper , silver or phosphorus
  • Group C: special soft solders
  • Group D: soft solders for aluminum

Soft solders containing antimony

  • L-PbSn12Sb (12% tin, 0.2-0.7% antimony , remainder lead, 250 ° C solidus, 295 ° C liquidus temperature; cooler construction)
  • L-PbSn30Sb (30% tin, 0.5-1.8% antimony, remainder lead, 186 ° C solidus, 250 ° C liquidus temperature; lubricating solder, lead solder)
  • L-PbSn40Sb (40% tin, 0.5–2.4% antimony, remainder lead, 186 ° C solidus, 225 ° C liquidus temperature; cooler construction)

Low-antimony soft solders

  • L-PbSn8 (Sb) 0( 08% tin, 0.12-0.5% antimony, remainder lead, 280 ° C solidus, 305 ° C liquidus temperature; radiator construction, thermostats)
  • L-PbSn30 (Sb) (30% tin, 0.12-0.5% antimony, remainder lead, 183 ° C solidus, 255 ° C liquidus temperature; thin sheet packing)
  • L-PbSn40 (Sb) (40% tin, 0.12-0.5% antimony, remainder lead, 183 ° C solidus, 235 ° C liquidus temperature; tin-plating, sheet metal packaging, plumbing )
  • L-PbSn60 (Sb) (60% tin, 0.12-0.5% antimony, remainder lead, 183 ° C solidus, 215 ° C liquidus temperature; tin-plating, sheet metal packaging, electrical industry, galvanized sheet metal)

For copper pipe fittings

  • L-Sn50Pb (lead-tin solder)
  • L-SnAg5 (tin silver solder)
  • L-SnCu3 (tin-copper solder)

For aluminum

When soldering aluminum, it should be noted that, as a result of potential differences between the soldering point and the base material, bimetal corrosion can occur in a damp environment. The solder joint should therefore, for. B. be protected with paint .

  • L-SnZn10 (85-92% tin , balance zinc )
  • L-SnZn40 (55–70% tin, balance zinc)
  • L-CdZn20 (75–83% cadmium , balance zinc)
  • L-ZnAl15 (84–86% zinc, balance aluminum )

Earlier aluminum alloys were the most necessary grinding processing with the solder In the tinning of the workpieces as rubbing Lote referred. If "tinning" is applied to the aluminum surface with the friction solder, a normal tin-lead solder, for example, can be used. B. a copper wire can be soldered to the aluminum workpiece as an electrical contact. As a flux , rosin is less suitable due to the higher soldering temperature required here; it evaporates at relatively low temperatures. Therefore, patented special fluxes and, if possible, ultrasonic soldering to tear open the disruptive Al oxide layer that is constantly re-forming, make sense. Flux residues must be removed after soldering.

Alternatively, soft soldering without (toxic) flux (not above 420 ° C) is also useful for joining aluminum. The decisive factor here, however, is that the oxide layer is mechanically destroyed during the soldering process, for example by scratching with a screwdriver. The structure of aluminum changes between 450 ° C and 480 ° C, the soft solder process therefore has no negative influence on the workpiece itself thanks to its lower temperature. When used correctly, there is no distortion on the workpiece, which is why this process is also used for aluminum Proportions of Mg magnesium , Si silicon and others suitable.

Electrical applications

Typical lead-tin-soft solder designations for electronic circuits:

  • L-Sn50PbCu 0(1.2-1.6% copper ; 183 ° C solidus, 215 ° C liquidus temperature)
  • L-Sn60PbCu 0(0.1-0.2% copper; 183 ° C solidus, 190 ° C liquidus temperature)
  • L-Sn60PbCu2 (1.6–2% copper; 183 ° C solidus, 190 ° C liquidus temperature)
  • L-Sn50PbAg (178 ° C solidus, 210 ° C liquidus temperature)
  • L-Sn60PbAg (178 ° C solidus, 180 ° C liquidus temperature)
  • L-Sn63PbAg (178 ° C solidus and liquidus temperature)
  • Fluitin , Stannol and Felder are some brand names for radio and electronic solder .

Typical lead-tin soft solder designations for drag, wave and dip soldering:

  • L-Sn50PbP Cu(0.001–0.004% phosphorus ; 183 ° C solidus, 215 ° C liquidus temperature)
  • L-Sn60PbP Cu(0.001–0.004% phosphorus; 183 ° C solidus, 190 ° C liquidus temperature)
  • L-Sn63PbP Cu(0.001-0.004% phosphorus; 183 ° C solidus and liquidus temperature)
  • L-Sn60PbCuP (0.001–0.004% phosphorus, 0.1–0.2% copper; 183 ° C solidus, 190 ° C liquidus temperature)

According to the RoHS regulations , lead-free solders have only been used in the electronics sector within the EU since 2006/2007 (depending on the EU country), apart from the exceptions mentioned above. These contain nickel or silver. Often copper is added. The melting point is higher (typically 217 ° C… 227 ° C) than classic, lead-containing soft solders.

See also


  • Hans Gramm: The materials. Part 2: Basic terms in materials science, material testing, material standardization, iron and steel. Volume 1: Non-ferrous metals and non-metals (= Deutsche Werkmeister-Bücherei. Group 2: Material science. Volume 1). 3. Edition. Ziemsen, Wittenberg Lutherstadt 1945.
  • Adolf Teml: Electrical engineering (= Friedrich table books. ). 17th, improved edition. (570th – 644th thousand). Fachbuchverlag, Leipzig 1976, p. 92 ff.
  • Reinard J. Klein Wassink: Soft soldering in electronics . 2nd Edition. Eugen G. Leuze, Saulgau 1991, ISBN 3-87480-066-0 .
  • Wolfgang Scheel (Hrsg.): Assembly technology of electronics . Verlag Technik u. a., Berlin a. a. 1997, ISBN 3-341-01100-5 .

Web links

Individual evidence

  1. The professional copper pipe installation, properties · processing · use , p. 20, Deutsches Kupferinstitut
  2. Thermal solar systems , Section 2.7 “Assembly of copper with other materials in closed systems”, Rieke solar systems
  3. Directive 2011/65 / EU of the European Parliament and of the Council of June 8, 2011 on the restriction of the use of certain hazardous substances in electrical and electronic equipment , accessed on August 9, 2017
  4. Qualitek: data sheet Sn42 / Bi58 and Sn63 / Pb37
  5. FELDER GMBH Löttechnik: Product information
  7. Soft soldering of aluminum without flux. Video of the MDR television; Retrieved September 4, 2013.