Soldering/Flux

== Overview ==
Selecting and applying flux correctly improves soldering results. It prevents oxide formation, cleans the surface, and improves solder flow. 
=== Why Use Flux? ===
400px|right|Flux core in solder wire. In soldering, flux serves a threefold purpose: 
Flux removes oxides from the surfaces to be soldered, 
Flux blocks oxygen preventing further oxidation, and
Facilitates amalgamation, which improves the wetting characteristics of the liquid solder. 
Corrosive fluxes require damp sponges or absorbent materials for cleaning after soldering to prevent damage. Acidic fluxes are unsuitable for electrical or electronic soldering.
Several non-corrosive flux types are used in electronics. Flux should be cleaned after soldering a joint.
=== Warning Regarding Flux Usage ===
Numerous decoder manufacturers explicitly advise against applying any flux during soldering.
 Why? Many modellers refuse to take advice and apply an acid flux, such as that from the tins conveniently found in the plumbing section of hardware stores. Another culprit often praised online is the TIX brand flux. Tix contains zinc chloride, which is inappropriate for electrical work. TIX is marketed to gold and silversmiths for soldering jewelry. 
Be aware that many solder preparations are available which contain acids. Solder pastes, as an example.Solder pastes are often sold in syringes at hardware stores. Solder pastes for electrical work are difficult to find as they are often sold in large quantities to manufacturers which have the equipment to properly apply the paste (using a silk screen process) to circuit boards during manufacture. These solders, along with acidic fluxes, are not recommended for use in electrical or electronic applications. The flux cannot be completely removed or neutralized through cleaning. This is particularly true for stranded wire, as the flux will wick into the bundle of wires and travel away from the joint. There is no effective method to clean or neutralize the flux in this situation. Acid flux residues become conductive over time. Given the close spacing of modern electronic devices, the remaining flux residue will become conductive and provide multiple paths for current flow.
If in doubt ask for and read the Material Data Sheet. If the ingredients include: 
* Zinc chloride
* Ammonium chloride 
* Hydrochloric acid
* Phosphoric acid 
* Citric acid or 
* Hydrobromic acid
the flux is acidic and not recommended for electrical work. These aggressive fluxes are meant application with a brush to plumbing, steel, and other materials normally not used in electronics, and at higher soldering temperatures such as with a torch.
=== Can I Use Acid Flux? ===
 A major decoder manufacturer stated the most common cause of decoder failures is Acid Flux. Some manufacturers include a warning regarding flux, and may not honour a warranty return if any flux was used during installation.
 
Acid fluxes used in plumbing and automotive applications are very aggressive, often containing hydrochloric or other acids. Those properties make it very effective, and thus popular with modellers. Acid based fluxes dissolve small wires over time, and their residues are conductive. Therefore, acid fluxes are not recommended for electrical and electronic work. If the flux contains Ammonium Chloride or Zinc Chloride, they are acidic and not appropriate for electrical work.
 A repeat offender is the TIX brand flux which is enthusiastically promoted by model railroaders on web forums and email lists. Do not use TIX for electrical work! There are a number of fluxes recommended by users on the internet, Tix is one, Nokorode is another which should be avoided. 
===Rosin Flux===
The correct flux for electrical work is Rosin Flux. 
Many solders used for electrical purposes are rosin-core. The solder wire has a hollow core filled with rosin flux, which is activated by the heat of the iron. For better results, apply additional flux. Rosin flux can be purchased in liquid or paste form, and there are also various devices available to aid in application from an electronic component store. Solid wire solders (often used for plumbing) also require the use of flux.
 Rosin Core Solder reacts with the lead content, reducing its effectiveness over time. Adding additional flux is necessary. Rosin Core Solder with less than 70% lead content has a three-year shelf life from the “Date of Manufacture.” Flux also has a (typical) three-year shelf life. Check with the manufacturer for details.
Applying a small amount of flux to the work before soldering significantly improves the results and speeds up the process, especially when soldering track with plastic ties. When heated, the flux activates and facilitates the wetting process, allowing the solder to quickly wick into the joint. Some may argue that adding more flux is unnecessary since solder already has a flux core, but as mentioned earlier, rosin core solders have a shelf life of only a few years. For the average modeler, their solder is likely several years past its best-before date. Adding additional flux won’t harm and could potentially improve the results.
Flux brushes are readily available in many hardware stores, often in packages of a dozen or more. Flux brushes can also be used for sweeping ballast during application and bonding. Electronics stores typically carry various tools for applying flux, in addition to a wide range of solders and fluxes.
==== What Exactly is Rosin Flux? ====
The terms resin and rosin are ambiguous and somewhat interchangeable, with different vendors using different assignments. Generally, fluxes are labeled as rosin if the vehicle they are based on is primarily natural rosin. Some manufactures reserve the "rosin" designation for military grade fluxes based on rosin (R, RMA and RA compositions) and label others as "resin". 
Rosin exhibits excellent flux properties. It’s a glassy solid composed primarily of organic acids, including abietic acid, pimaric acid, isopimaric acid, neoabietic acid, dihydroabietic acid, and dehydroabietic acid. At normal temperatures, rosin is virtually nonreactive and noncorrosive. However, it transforms into a liquid, becomes ionic, and exhibits mild reactivity towards metal oxides when molten. Rosin softens between 60 to 70 degrees Celsius, becoming fully fluid around 120 degrees Celsius. Molten rosin possesses weak acidic properties and can dissolve thin layers of surface oxides from copper without the need for additional additives. For heavier surface contamination or enhanced process speed, additional activators can be incorporated.
There are three types of rosin: gum rosin (derived from pine tree oleoresin), wood rosin (extracted from tree stumps), and tall oil rosin (obtained from tall oil, a byproduct of the kraft paper process). Gum rosin has a milder odor and a lower tendency to crystallize from solutions compared to wood rosin, making it a preferred choice for flux applications. Tall oil rosin has gained popularity due to its enhanced thermal stability, resulting in a reduced likelihood of forming insoluble thermal decomposition residues. The composition and quality of rosin vary depending on the type of tree, location, and even the year. In Europe, rosin for flux is typically obtained from a specific variety of Portuguese pine, while in North America, a North Carolina variant is commonly used.Source: Wikipedia
=== Flux Removal ===
After soldering, use a flux remover and a small brush to clean the area. Flux remover is available in various packages, including aerosols. This is crucial, especially with tracks, as the wheels will pick up the sticky residues and spread them everywhere, causing intermittent operation, particularly at joints that were soldered. These residues will attract and retain dust, moisture, and other contaminants.
Always remove the flux after soldering on a PCB. Over time, the residue can become conductive by attracting dust and other airborne particles. In dense circuit layouts, this can lead to component failures due to short circuits caused by the flux residues.
Several commercial preparations are available for removing flux. Isopropyl alcohol (IPA) and water are effective options. Mixtures of IPA and acetone can also be effective. Refer to the instructions for the recommended solvent to remove the residues. A quick search on the internet will provide numerous possibilities and processes.
If soldering on track, it’s crucial to remove the residual flux afterward. The wheels will pick it up and distribute it all over the track, necessitating extensive track cleaning.
==== "No Clean" Flux ====
Several new flux preparations are now available that prominently display the label message “No Clean.”
Contrary to their label claims, cleaning is still necessary. Residues left behind during soldering on the track will migrate and contaminate the trackwork.
While these fluxes are labeled as “No Clean,” this only applies during the production of electronic devices. The manufacturer is not required to remove flux residue from finished PCBs, as it will not pose a problem in the future. However, for applications such as soldering feeders to trackwork, cleaning is essential and can be easily accomplished using water as a solvent.
=== Videos About Flux ===
==== SoundTraxx Soldering Tips ====
==== What is Flux? ====
Category:Soldering
Category:Electronics
Category:Multifunction Decoder