Flux (metallurgy)

A flux referred to in the field of joining technology manufacturing processes such as the soft and hard soldering, various chemical substances that allow the metallic solder and the parts to be soldered entering into a solid metallic connection. To this end, they remove the resting surfaces to be bonded oxides by chemical reactions. The same applies to oxides which occur under the influence of atmospheric oxygen and heat during the soldering process until or before this occurs. One of the most important properties of the flux is that it reduces the interfacial tension and thus enables better wetting.

Operation

The solder pads are treated with the agent of choice. There follows a heating above the melting point of the solder out.

The flux is reduced ( deoxidized ) when heating the surfaces of the surfaces to be joined, as well as the solder and prevents re- oxide formation by forming a liquid protective layer. A further effect is to reduce the surface tension of the liquid solder.

Selection criteria

Fluxes are different in composition, which depends on the type of parts to be soldered.

  • For the electronics, a flux is necessary which leaves no corrosive residues (such as the organic substance is rosin, the reducing effect on heating ).
  • Stainless steel can be soldered only with special fluxes. For aluminum, there are now alternative soldering, which make the use of fluxes superfluous.
  • For work on highly contaminated joining partners acidic fluxes are used ( soldering fluid based on zinc chloride, separate liquid ). Acidic residues flux must be removed, as this will lead to corrosion of the solder joint.
  • For the soft as the brazing there is flux which take into account the range of temperature in which the soldering is carried out in the composition and melting point.

For all needed flux the request is the same: you need to back oxide-free soldering surfaces or cause Oxidfreiheit.

In special cases, such as when a contamination of the solder joint is to be avoided by residues of the flux necessarily be soldered under protective gas or vacuum without such. This oxidation of the surfaces to be joined during the soldering process is prevented.

Hazard potential

Flux can be corrosive (zinc chloride, ammonium chloride). They may include halogenated hydrocarbons, in order to free the soldering areas of fat. In the application of flux, the data sheet for application and handling as well as the R- and S-phrases should always be followed.

Soldering flux and solder flux left on insulating conductive and hygroscopic residues which can lead to faulty insulation, electric shock and short circuit. Even so these funds are not to be used in electrical / electronics.

Also electronic flux ( flux core solder wire in electronics, tinctures, Lötlacke and rosin ) are harmful to health because they tend near the soldering temperature of flue gases and these vapors can be inhaled. In accordance with current health and safety regulations is to ensure that occurring fumes are not inhaled.

Type designation used in soldering flux

The type - identifier consists of the letter F ( derived from the term flux ), followed by two more letters. The first indicates the material to be soldered: S (heavy metal ), L ( light metal ); the second, the soldering process: H ( brazing ), W ( soldering )

The auxiliaries may be used for both hard and soft soldering.

For brazing

The fluxes used differ according to their effective temperature and the corrosion behavior of the residues.

  • For heavy metals F- SH 1: effective temperature ( 550-800 ) ° C, boron compounds, complex fluorides, generally corrosive residues washable or abbeizbar.
  • F- SH 1 a: effective temperature ( 550-800 ) ° C, boron compounds, complex fluorides, chlorides, corrosive residues washable or abbeizbar.
  • F -S 2: Operating temperature ( 750-1100 ) ° C, boron compounds, are generally not corrosive.
  • F- SH 3: effective temperature ( 1000 to 1250 ) ° C, boron compounds, phosphates, silicates, non-corrosive.
  • F -S 4: Operating temperature ( 600-1000 ) ° C, chlorides, fluorides without boron compounds generally corrosive. Residues washable or abbeizbar.
  • For light metals F -LH 1: Operating temperature ( 500-600 ) ° C, hygroscopic chlorides and fluorides, are generally corrosive. Residues washable or abbeizbar.
  • F -LH 2: Operating temperature ( 500-600 ) ° C, non-hygroscopic fluorides, are generally non-corrosive.

For soft soldering of heavy metals

Cause flux residues, depending on the flux type, different strengths or only minor corrosion. The solid residues on the application of future flux must be carefully removed after soldering. In addition, there are virtually residue- free flux, called No Clean Flux, which are increasingly used in electronics manufacturing. Most fluxes are hygroscopic, therefore, take on humidity and promote corrosion.

EN ISO 9454

Flux for soldering applications are specified in the standard EN ISO 9454. They are prepared by a four-digit code, which consists of three digits, followed by an optional letter is with the following meaning:

  • A liquid
  • B Festival
  • C paste
  • 2 acids
  • 3 Basisch

Old DIN 8511

According designations Previously, the DIN standard DIN 8511, in a schema of the form F -SW -xx, as usual. This was in 1994 replaced by DIN EN 29454-1 classification. The DIN 8511 followed the following classification:

  • F-SW 11: Liquid. Based on zinc or other metal chlorides of heavy metals and / or ammonium chloride ( sal ammoniac vulgo ) in aqueous solution. Free hydrochloric acid, sulfuric acid, nitric acid or hydrofluoric acid. For heavily oxidized surfaces such as gutters made of pure zinc.
  • F-SW 12: base is zinc chloride, or other heavy metal chlorides and / or ammonium chloride / ammonium chloride. Flux residues are carefully washed off with water. Application as a liquid in Kühlerbau, for plumbing work, among others, copper, dip tinning. As a powder, the cover of solder and tin baths. The solder - flux mixture to Weichverzinnen, such as cast iron, bronze or stainless steel.
  • F-SW 13: base is phosphoric acid or its chemical derivatives. Residues must be removed with suitable cleaning method. Application as a liquid for working on copper, copper alloy or stainless steel.
  • F-SW 21: Effective temperature ( 140-450 ) ° C, zinc and / or ammonium chloride in organic preparation ( eg higher alcohols, fats), limited corrosive for copper and copper alloys.
  • F-SW 22: Effective temperature (200-400 ) ° C, zinc and / or ammonium chloride in organic preparation ( eg higher alcohols, fats ) without ammonium chloride, limited corrosive for copper and copper alloys, drinking water installations.
  • F-SW 23: Effective temperature (200-400 ) ° C
  • F-SW 24: Effective temperature (200-400 ) ° C
  • F-SW 25: Effective temperature (200-400 ) ° C
  • F-SW 26: Effective temperature ( 140-450 ) ° C
  • F-SW 27: Effective temperature ( 140-450 ) ° C
  • F-SW 28: Effective temperature ( 140-450 ) ° C
  • F-SW 31: Effective temperature (200-400 ) ° C, the base is natural or modified resin ( rosin ) without additives. Flux residue may remain on the solder joint. Application in electrical engineering, electronics as a powder to cover Lotbädern. incorporated or as a flux core in the solder wire.
  • F-SW 32: Effective temperature ( 200-300 ) ° C, base, such as F -SW 31, but with organic, halogen-free activation additives, such as stearic acid, salicylic acid, adipic acid, without amines, diamines or urea. Application as a powder, as " soul " in solder wire incorporated. or as a mixture of solder and flux in electrical engineering, electronics, miniature technology ( SMT ) printed circuit boards.
  • F-SW 33: Based on synthetic resins with organic, halogen-free additives activation, but without amines, diamines or urea. Application, such as F-SW 32
  • F-SW 34: base are organic, halogen-free acids and natural resin ( rosin ) without amines, diamines or urea. Incorporated application as a liquid or as a "soul" in the solder in electronics, miniature technology ( SMT ) printed circuit boards.

Comparison of the two standards:

IPC J -STD- 004B, EN 61190-1-1

In the industry increasingly is a classification with the specification, which is published by the IPC, made ​​according to IPC- J -STD- 004B ( largely identical to EN 61190-1-1 ). This specification describes the respective flux with three letters and a number:

It all combinations are possible, such as ROL0, REM1 or ORH0.

Outdated Abbreviations

Occasionally you can find more English / American abbreviations with which the coarse type and activator of flux is described, particularly RA and RMA:

Literature on soldering aid

  • Reinard J. Klein Wassink: Soldering in electronics. 2nd edition. Eugen G. Leuze, Saulgau, 1991, ISBN 3-87480-066-0.
  • Wolfgang Scheel (eds.): Assembly Technology of Electronics. Copying systems, among others, Berlin and others 1997, ISBN 3-341-01100-5.
Shielding gas List of copper alloys
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