Soldering/Solder

== Selecting Solder ==
The most prevalent solder alloy is tin/lead (Sn/Pb). However, the lead component is being phased out due to its toxicity, particularly its oxides. These solders with another metal are labeled “lead-free.”
The ratio of the alloy is crucial, as it not only determines the melt point but also the freeze point. For electrical applications, the most commonly used solders are 60/40 and 67/37. The 60/40 alloy is slightly more affordable, while the 63/37 solder is easier to work with. The difference lies in the 63/37 alloy being eutectic, meaning its freeze and melt points are nearly identical. Consequently, the plastic range of the 60/40 alloy is significantly larger. While this may not be a concern during production soldering, it becomes advantageous when soldering with an iron due to the 63/37 alloy’s very small plastic range, which facilitates the creation of a strong and heat-resistant joint. However, if the work being soldered undergoes plastic deformation during the soldering process, a cold solder joint can result.
The price difference between the two alloys is not substantial, and the additional expense of the 63/37 alloy is justified for certain applications. Additionally, a solder containing a small amount of silver (Ag) is desirable for specific purposes, as it enhances the joint’s strength and resistance to heat.
=== Flux Core. ===
 For electrical soldering, the only type of flux to use is Rosin Flux. Most solders sold for the purpose have a rosin core. Light gauge solders may not incorporate rosin flux, as the wire is too small. For these solders an additional flux is required.
=== Gauge ===
Solder comes in various forms, like bars and wire. Wire solder’s gauge matters. Heavy gauge isn’t suitable for electrical work as it can overfill the work. Light gauge is better for electrical work, especially when soldering fine wires to small pads or together, as it allows more control over solder usage. For most purposes, the amount needed is small, especially if the result should be inconspicuous.
thumb|Rosin core solder
== Components of Solder ==
Most solders for electronic and other purposes are an alloy of lead (Pb) and tin (Sn). Some solders also contain Silver (Ag), and others are lead free.
The solder used for electrical work is a tin/lead alloy. Tin has a melting point of 232° Celsius, and lead melts at 325.5° C. When alloyed 60/40 (SnPb) the melting point is 188° C. The most common solder alloy used for electronic/electrical work is 63/37 SnPb, which is a eutectic solder, meaning its melt/freeze point is 183° C, it also has the lowest melting point found in Tin/Lead alloys. This is a preferred alloy. 
Some solders contain Silver (Ag) which is used to reduce the erosion of gold or silver plating, or for joints which have to withstand higher temperatures. Some silver solders are also used with integrated circuits during manufacturing to solder microprocessors and other ICs to the PCB. Silver solders require more heat, and make a stronger joint as well.
Soldering, brazing, and welding are techniques used to join metals together. Of the three, soldering is arguably the weakest. It is strong enough for the needs of Digital Command Control wiring.
=== Lead Free and Lead Solders ===
Avoid mixing the two solder alloys. Using Leaded solder on a joint previously soldered with a lead-free alloy introduces problems, and the reverse is true as well.
=== What is Solder? ===
Solder, an alloy primarily composed of tin (Sn) and lead (Pb), is used for electrical connections. However, due to environmental concerns, the lead component is gradually being phased out as it accumulates in landfills and can contaminate groundwater supplies.
The melting point of solder varies depending on the ratio of tin to lead. Lead-free solders exhibit higher melting points compared to traditional solders.
Pure tin melts at 232°C, while lead melts at 328°C. An alloy containing 63% tin and 37% lead is known as eutectic, having a melting and freezing point of 183°C — the lowest temperature achievable with a combination of tin and lead. Interestingly, the melting point of solder is lower than the melting point of either component alone. The higher the percentage of lead, the higher the melt point; conversely, adding tin lowers the melting point.
A 60/40 alloy has a working range of 183-238°C. Another alloy, Sn43Pb43Bi14, has freeze/melt temperatures ranging from 144-163°C.
Some solders incorporate silver (Ag), which has a significantly higher melting temperature. Additionally, certain formulations include other metals. It is essential to use tin/lead solders exclusively for electrical connections. Silver-based solders are preferred for applications requiring strength, such as track work and soldering switch rails to the throwbar when constructing turnouts. However, silver solder is not suitable for electrical purposes due to the high heat generated, which can melt solder alloys commonly used for electrical work. For instance, connecting wires to a heating element or using a shunt (a device for measuring large currents) are examples of applications where silver solder is justified.
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A 60/40 or preferably 63/37 tin/lead solder should be used for electronics, and only Rosin Flux core solders. Solder is available in a solid wire, or with a rosin (flux) core. Solid wire solder requires flux, or it will not work. For electrical work, a rosin core solder is preferred. 
A 60/40 solder is slightly cheaper than 63/37 solders. For volume soldering, the cost difference may matter.
Rosin flux removes surface oxidation, enabling clean metal bonding. Clean the work after soldering with a flux remover.
 Rosin Core Solder, such as those alloys in the table below, and related fluxes, have a shelf life of three years from Date of Manufacture. Review the manufacturer's specification sheet for their recommended shelf life.
=== Solder Alloys for Electrical and Electronic Applications ===
Alloy 	Freeze/Melt, °C	Eutectic	Comments 	Sn 	Pb 	Ag
Sn60Pb40 	183/190 	No 	Sn60, ASTM60A, ASTM60B. Common in electronics, most popular leaded alloy for dipping. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. Slightly cheaper than Sn63Pb37, often used instead for cost reasons as the melting point difference is insignificant in practice. On slow cooling gives slightly duller joints than Sn63Pb37. 	60 	40 	-
Sn63Pb37 	183 	Yes 	Sn63, ASTM63A, ASTM63B. Common in electronics; exceptional tinning and wetting properties, also good for stainless steel. One of the most common solders. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. Sn60Pb40 is slightly cheaper and is often used instead for cost reasons, as the melting point difference is insignificant in practice. On slow cooling gives slightly brighter joints than Sn60Pb40.	63 	37 	-
Pb92Sn5.5Ag2.5	286/301 	No 	For higher-temperature applications. 	5.5	92 	2.5
Sn62Pb36Ag2 	179 	Yes 	Sn62. Common in electronics. The strongest tin-lead solder. Appearance identical to Sn60Pb40 or Sn63Pb37. Crystals of Ag3Sn may be seen growing from the solder. Extended heat treatment leads to formation of crystals of binary alloys. Silver content decreases solubility of silver, making the alloy suitable for soldering silver-metallized surfaces, e.g. SMD capacitors and other silver-metallized ceramics. Not recommended for gold. General-purpose. 	62 	36 	2
Pb97.5Ag1.5Sn1	309 	Yes 	Ag1.5, ASTM1.5S. High melting point, used for commutators, armatures, and initial solder joints where remelting when working on nearby joints is undesirable. Silver content reduces solubility of silver coatings in molten solder. Not recommended for gold. Standard PbAgSn eutectic solder, wide use in semiconductor assembly. Reducing protective atmosphere (e.g. 12% hydrogen) often used. High creep resistance, for use at both elevated and cryogenic temperatures. 	1 	97.5	1.5
;See note above regarding shelf life of solders.
(Reduced version of the table found on Wikipedia) 
One source (http://www.tpub.com/neets/book4/12n.htm) indicates that soldering is more than just melting-there is a chemical change that occurs as well.
Category:Soldering
Category:Wiring
Category:Electrical
Category:Electronics
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