Solder

The solder is called a metal alloy consisting depending on the application of certain mixing ratios of metals; mainly lead, tin, zinc, silver and copper. They are used to solder suitable metals and alloys such as copper, bronze, brass, red brass, nickel silver, silver, gold, hard lead, zinc, aluminum as well as iron, by a melt surface with these combine or alloy and after cooling solidify. This the solder to alloy with the metallic workpieces, materials (electronic) components, wires, jewelery or other components is a prerequisite for a durable, solid cohesive solder joint. The melting point of the solder is generally lower than that of the workpieces to be joined.

• 3.1 Tin solders
• 3.2 Properties of the solder constituents
• 3.3 Common solder alloys
• 3.4 Weichlotbezeichnungen 3.4.1 Abbreviations used in solders
• 3.4.4 For copper pipe fittings
• 3.4.5 For aluminum
• 3.4.6 Electrical Applications

General

Before soldering the metal to be joined workpieces should be degreased mechanically and chemically free of paint layers, dirt, oxides and sulfides as well. The metal surfaces should be " blank". Thus a good and rapid wetting of the solder to allow the surfaces together with a suitable flux, and thus the soldering substantially supported. Especially for soft - soldering in the electronics sector, it is also still useful to advance even to tin the surfaces of the workpieces or components wires with solder before the actual Zusammenlötung to reduce the soldering time. The flux thereby dissolves during soldering the ever newly forming oxide layers on the metal surfaces of the workpieces. It protects at the same time before further oxidation during the soldering process and to improve the flowability of the solder, whereby the workpieces to be joined must be heated to the temperature of the liquid solder. That is, for example, be observed when heat-sensitive electronic components, that is, there are maximum soldering time observed! The heat capacity eg via soldering iron or torch and thus the soldering temperature must be adapted to the particular Lot, the size of the solder joint and the heat dissipation to the workpiece. Because the tensile strength is usually less than that of the materials to be bonded especially with soft solder, the solder layer at high mechanical forces, therefore, should be as thin as possible.

A eutectic alloy has the lowest melting temperature and melts and solidifies at a fixed temperature as a pure substance, such as Sn62Pb38 at about 183 ° C. This is desirable in electronics soldering.

All non- eutectic alloys have two characteristic points between the starting temperature of the melt and completely liquefied ( and vice versa), called the solidus and liquidus temperature. So you have a Schmelz-/Erstarrungsbereich what is desirable, for example in plumbing solders. Below the solidus temperature of the alloy is completely solid, mushy to the liquidus temperature, about completely liquid.

Solders are distinguished by definition above the liquidus of the solder in brazing alloys and solders. Solders with softening temperatures below 450 ° C are soft solders with low mechanical strength, such are hard solders ( formerly known as shock solders ) with high strength with softening temperatures above 450 ° C.

Brazing alloys

When brazing alloys are called alloys hochsilberhaltiger on nickel silver or brass base, in bar, rod, wire, foil and partly paste form are usually available. Hartlotpasten included flux, so that a separate addition, also as a paste, as the other Lotformen is no longer required.

Brazing alloys are, in contrast to the soft solder ( tin / lead-based ), for mechanically and thermally more stressed metallic compounds (especially for normal iron-and nickel-containing workpieces, such as carbide cutting edges in iron drills, the " rock drills " ). Stainless steels with chromium, tungsten and / or molybdenum, however, are often difficult and usually not brazeable weichlötbar. This makes soldering tests required. Otherwise, these materials should be better welded. For this, in turn, are copper-containing material alloys, such as bronze, brass, red brass, nickel silver and silver, gold very hard (and soft) solderable. Brazed joints have some higher strength than the base material. Sometimes Hartlotdrähten be a flux, such as on Boraxbasis, added. Most of the solder is so wrapped externally. The processing temperatures for brazing alloys are between 500 and 1000 ° C. As a heat source and a gas burner or industrial lasers are used.

In gas lines with copper pipe fittings brazing is prescribed.

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. With increasing silver content, the processing temperature decreases. Silver solder to flow more easily than brass solders and are used to connect copper pipe fittings used. We distinguish:

• Silver alloy of cadmium addition ( not for drinking water installations) L- Ag40Cd (40 % Ag, 19% Cu, 21% Zn, 20 % Cd)

Brass solders

Brass alloys are alloys of copper and zinc with small quantities of silver, silicon, tin and manganese. The processing temperature is 800 to 1000 ° C. With increasing copper content, the higher the melting point and strength.

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

Phosphorus solders

Phosphorus solders are alloys of copper and phosphorus (and possibly silver ).

• L- CuP6 ( 93.8 % Cu, 6.2% P)

Brazing alloys for aluminum

• L- AlSi12
• L- ZnAl30

Soft solder joints have, compared to brazed joints often only moderate strength. They are mainly used in the electrical and electronics, in domestic installations and through the stained glass technique in art ( lead glass windows, Tiffany lamps ) application. To craft soldering today electrically heatable and digital in their brazing temperature of about 60 ° C to 420 ° C or analog adjustable and regulated soldering iron be used with replaceable soldering tip of about 5 to 250 watts nominal power. Soft and hard soldering should be done because of the risk of splashing of solder and flux always wearing safety goggles and because of the resulting harmful Flux fumes under an air extractor. Details please see soldering.

Tin solders

The soft solders most commonly used are the tin solders, ie alloys of tin and lead with small amounts of iron, antimony, copper and nickel. The melting point of tin solder is below 330 ° C. During heating the solder to go from a solid to a slurry, and finally in the liquid state. Of particular importance is the eutectic, also called Sickerlot (63% Sn, 37% Pb). At a temperature of 183 ° C, it goes directly from solid to liquid state. Alloys, which are remote from the eutectic, are in favor of a technically desired freezing range between liquidus and solidus also used.

Use of tin solder with a tin content of:

• 20-40 %: Connecting copper pipes, lead wires and sleeves, zinc gutters
• 50 %: Fine soldering of metal sheets
• 60 ... 63 % ( Sickerlot ): Connect and tin of electrical cables, wires, circuit boards
• > 90 %: soldering tin cans

The lowest melting points at about 75 ° C, the so-called Wood's metal, consisting of 50% bismuth ( Bi), 25 % lead (Pb), 12.5 % cadmium ( Cd) and 12.5 % tin (Sn ) and at 62 ° C, the Fieldsche metal, consisting of 32.5 % bismuth ( Bi), 51 % indium (In) and 16.5 % tin (Sn ). The former is highly toxic and harmful to the environment because of the cadmium component, wherein the Fieldsche metal used as a replacement is significantly more expensive due to the Indiumanteils.

So-called cored solder ( Radiolot or Elektroniklot ) have one or more incorporated souls of organic acid-free resins of trees, including rosin, which is often referred to in the trade name as " Flux" and acts as a flux during the soldering process.

Properties of the solder constituents

Because of the good technical controllability and the low melting point contains a number of solders lead. Due to the current legal situation, especially in the EU (among WEEE, RoHS: ie DIR 2002/96/EC and 2002/95/EC DIR ), there is worldwide but strong efforts to replace the lead-containing solders with lead- free. However, these usually have a less universal application and bring in some cases technical problems such as brittleness and whisker with it. For this reason, is not permitted in the manufacture of electronic components for medical technology, security technology, instrumentation, aerospace, railway engineering, fire engineering as well as for military / police use of the use of lead- free solder. In electronic assemblies that are exposed to, for example, extreme temperatures, or where the use of lead is useful for other reasons, such as in metrology, the use of lead solder is left to the discretion of the manufacturer.

However, since July 2006 allows for problems with complete recycling of lead-bearing solder no longer be used in electronic equipment ( RoHS see DIR 2002/95/EC ), now it is a lead-free tin alloys with copper and nickel. As a budget alternative to these expensive patented tin alloys are used with copper and silver, for example Sn95.5Ag3.8Cu0.7 (melting temperature about 220 ° C). Outside Europe do you replace the lead by like bismuth. For private applications and for certain (see above) as well as application areas for lead-acid batteries, however, solders containing lead may continue to be used.

Stark bismuth solders were due to the very low solder melt temperature ( below 100 ° C), formerly known as " thermal fuse " is used in electronic devices.

Common solder alloys

The following table lists some common solder alloys.

Weichlotbezeichnungen

Abbreviations used in solders

For soft solders according to DIN 1707, the following abbreviations are used.

• Ah Group: Antimony sustainable
• Group Aa: antimony poor
• Group Af: antimony - free
• Group C: Special soft solders
• Group D: Soft solders for aluminum

• L- PbSn12Sb (12% tin, 0.2-0.7 % antimony, lead residue, 250 ° C solidus, 295 ° C liquidus; Kühlerbau )
• L- PbSn30Sb (30 % tin, 0.5-1.8 % antimony, lead residue, 186 ° C solidus, 250 ° C liquidus; Schmierlot, lead solder )
• L- PbSn40Sb (40 % tin, 0.5-2.4 % antimony, lead residue, 186 ° C solidus, 225 ° C liquidus; Kühlerbau )

• L- PbSn8 (Sb ) (8% tin, 0.12-0.5 % antimony, lead residue, 280 ° C solidus, 305 ° C liquidus; Kühlerbau, thermostats )
• L- PbSn30 (Sb ) (30 % tin, 0.12-0.5 % antimony, lead residue, 183 ° C solidus, 255 ° C liquidus, thin sheet packs)
• L- PbSn40 (Sb ) (40 % tin, 0.12-0.5 % antimony, lead residue, 183 ° C solidus, 235 ° C liquidus; tinning, sheet packings, plumbing )
• L- PbSn60 (Sb ) (60 % tin, 0.12-0.5 % antimony, lead residue, 183 ° C solidus, 215 ° C liquidus; tinning, sheet packings, electrical industry, galvanized steel sheets )

For copper pipe fittings

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

For aluminum

When soldering of aluminum is to be noted that electrochemical corrosion can occur in humid conditions due to potential differences between the solder joint and the base material. The solder joint should be protected, for example with varnish.

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

Previously aluminum solders were also referred to as rubbing solders by the grinding processing usually necessary with the solder when tinning In the workpieces. Applying a " tin " on the aluminum surface with the Reibelot, then, for example, a copper wire can be soldered to the aluminum workpiece as an electrical contact with a standard tin-lead solder. As a rosin flux is necessary here because of higher soldering temperatures less suitable it evaporates even at relatively low temperatures. Here special patented flux and when an ultrasonic soldering to tear the ever fast again newly forming, disturbing Al- oxide layer therefore are possible sense. Flux residues must be removed after soldering.

Alternatively, for connecting aluminum is also the soldering without (toxic ) flux (not over 420 ° C) is useful. The key here is, however, that the oxide layer is mechanically destroyed during the soldering process, for example by scraping with a screwdriver. The microstructure of aluminum varies between 450 ° C and 480 ° C, the solder process has therefore due to lower temperature no negative influence on the workpiece itself thus no distortion at the work piece When correctly applied, therefore, this method is also suitable for aluminum with proportions of magnesium Mg, Si, silicon and other suitable.

Electrical applications

Typical lead-tin Weichlotbezeichnungen for electronic circuits:

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

Typical lead-tin Weichlotbezeichnungen for towing, surge and dip soldering:

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

According to RoHS regulations come within the EU in the field of electronics since 2006/2007 (depending on the EU country ) only, except for the above exceptions, lead-free solders are used. These are nickel - or silver-bearing. Copper is often added. The melting point is higher ( typically 217 ° C. .. 227 ° C ) than for classical, lead-containing solders. Therefore RoHS compliant solders are more difficult to process (See further under RoHS).