Solder

Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling.

Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined.

Soft solder typically has a melting point range of 90 to 450 °C (190 to 840 °F; 360 to 720 K),[3] and is commonly used in electronics, plumbing, and sheet metal work.

Non-eutectic alloys can have markedly different solidus and liquidus temperatures, as they have distinct liquid and solid transitions.

Non-eutectic mixtures often exist as a paste of solid particles in a melted matrix of the lower-melting phase as they approach high enough temperatures.

It is also available as a room temperature paste, as a preformed foil shaped to match the workpiece which may be more suited for mechanized mass-production, or in small "tabs" that can be wrapped around the joint and melted with a flame where an iron isn't usable or available, as for instance in field repairs.

Lead-free solders have been increasing in use due to regulatory requirements plus the health and environmental benefits of avoiding lead-based electronic components.

[7] Today, many techniques are used to mitigate the problem, including changes to the annealing process (heating and cooling), addition of elements like copper and nickel, and the application of conformal coatings.

Since even small amounts of lead have been found detrimental to health as a potent neurotoxin,[11] lead in plumbing solder was replaced by silver (food-grade applications) or antimony, with copper often added, and the proportion of tin was increased (see lead-free solder).

[12] Lead-tin solders readily dissolve gold plating and form brittle intermetallics.

[14] Lead, and to some degree tin, as used in solder contains small but significant amounts of radioisotope impurities.

Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals.

Lead-free solder typically requires around 2% flux by mass for adequate wetting ability.

Lead-free solder is prohibited in critical applications, such as aerospace, military and medical projects, because joints are likely to suffer from metal fatigue failure under stress (such as that from thermal expansion and contraction).

[19] The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.

Dissolving of process equipment is not common as the materials are usually chosen to be insoluble in solder.

This is manufactured as a coiled wire of solder, with one or more continuous bodies of inorganic acid or rosin flux embedded lengthwise inside it.

Eutectic alloys also solidify at a single temperature, all components precipitating simultaneously in so-called coupled growth.

Premature handling of such joint then disrupts its internal structure and leads to compromised mechanical integrity.

These layers may cause mechanical reliability weakening and brittleness, increased electrical resistance, or electromigration and formation of voids.

The gold-tin intermetallics layer is responsible for poor mechanical reliability of tin-soldered gold-plated surfaces where the gold plating did not completely dissolve in the solder.

[29] Some example interactions include: A preform is a pre-made shape of solder specially designed for the application where it is to be used.