Металдарды қосуға арналған қорытқыш (Metaldardy qosuğa arnallğan qorytqış)

Alloy used to join metal pieces
the material

Solder (/UK/'/s//ɒ//l//d//ə//, /'/s//ə//ʊ//l//d//ə/; NA: '/s//ɒ//d//ər/) is a fusible metal alloy used to create a permanent bond between metal workpieces. 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. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics. Soft solder typically has a melting point range of , and is commonly used in electronics, plumbing, and sheet metal work. Alloys that melt between are the most commonly used. Soldering performed using alloys with a melting point above is called "hard soldering", "silver soldering", or brazing. In specific proportions, some alloys are eutectic — that is, the alloy's melting point is the lowest possible for a mixture of those components, and coincides with the freezing point. 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. In electrical work, if the joint is disturbed while in this "pasty" state before it fully solidifies, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non eutectic solder can be exploited in plumbing, as it allows molding of the solder during cooling, e. g. for ensuring watertight joint of pipes, resulting in a so called "wiped joint". For electrical and electronics work, solder wire is available in a range of thicknesses for hand soldering (manual soldering is performed using a soldering iron or soldering gun), and with cores containing flux. 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. Alloys of lead and tin were commonly used in the past and are still available; they are particularly convenient for hand soldering. Lead free solders have been increasing in use due to regulatory requirements plus the health and environmental benefits of avoiding lead based electronic components. They are almost exclusively used today in consumer electronics. Plumbers often use bars of solder, much thicker than the wire used for electrical applications, and apply flux separately; many plumbing suitable soldering fluxes are too corrosive (or conductive) to be used in electrical or electronic work. Jewelers often use solder in thin sheets, which they cut into snippets.

The word solder comes from the Middle English word soudur, via Old French solduree and soulder, from the Latin solidare, meaning "to make solid".

The European Union Waste Electrical and Electronic Equipment Directive and Restriction of Hazardous Substances Directive were adopted in early 2003 and came into effect on July 1, 2006, restricting the inclusion of lead in most consumer electronics sold in the EU, and having a broad effect on consumer electronics sold worldwide. In the US, manufacturers may receive tax benefits by reducing the use of lead based solder. Lead free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead free replacements for conventional 60/40 and 63/37 Sn Pb solder have melting points from 50 to 200 °C higher, though there are also solders with much lower melting points. Lead free solder typically requires around 2% flux by mass for adequate wetting ability. When lead free solder is used in wave soldering, a slightly modified solder pot may be desirable (e. g. titanium liners or impellers) to reduce maintenance cost due to increased tin scavenging of high tin solder. 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). Although this is a property that conventional leaded solder possesses as well (like any metal), the point at which stress fatigue will usually occur in leaded solder is substantially above the level of stresses normally encountered. Tin silver copper (Sn Ag Cu, or SAC) solders are used by two thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead free solder alloy family is based on the reduced melting point of the Sn Ag Cu ternary eutectic behavior (217 °C (423 °F)), which is below the 22/78 Sn Ag (wt.%) eutectic of 221 °C (430 °F) and the 99.3/0.7 Sn Cu eutectic of 227 °C (441 °F).

Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or silver are the most common. In silversmithing or jewelry making, special hard solders are used that will pass assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders vary in hardness, designated as "enameling", "hard", "medium" and "easy". Enameling solder has a high melting point, close to that of the material itself, to prevent the joint desoldering during firing in the enameling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint desoldering while additional sites are soldered. Easy solder is also often used for repair work for the same reason. Flux is also used to prevent joints from desoldering. Silver solder is also used in manufacturing to join metal parts that cannot be welded. The alloys used for these purposes contain a high proportion of silver (up to 40%), and may also contain cadmium.

Flux is a reducing agent designed to help reduce (return oxidized metals to their metallic state) metal oxides at the points of contact to improve the electrical connection and mechanical strength. The two principal types of flux are acid flux (sometimes called "active flux"), containing strong acids, used for metal mending and plumbing, and rosin flux (sometimes called "passive flux"), used in electronics. Rosin flux comes in a variety of "activities", corresponding roughly to the speed and effectiveness of the organic acid components of the rosin in dissolving metallic surface oxides, and consequently the corrosiveness of the flux residue. Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water soluble flux, which can be removed with deionized water and detergent, instead of hydrocarbon solvents. Water soluble fluxes are generally more conductive than traditionally used electrical / electronic fluxes and so have more potential for electrically interacting with a circuit; in general it is important to remove their traces after soldering. Some rosin type flux traces likewise should be removed, and for the same reason. In contrast to using traditional bars or coiled wires of all metal solder and manually applying flux to the parts being joined, much hand soldering since the mid 20th century has used flux core 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. As the solder melts onto the joint, it frees the flux and releases that on it as well.

The solidifying behavior depends on the alloy composition. Pure metals solidify at a certain temperature, forming crystals of one phase. Eutectic alloys also solidify at a single temperature, all components precipitating simultaneously in so called coupled growth. Non eutectic compositions on cooling start to first precipitate the non eutectic phase; dendrites when it is a metal, large crystals when it is an intermetallic compound. Such a mixture of solid particles in a molten eutectic is referred to as a mushy state. Even a relatively small proportion of solids in the liquid can dramatically lower its fluidity. The temperature of total solidification is the solidus of the alloy, the temperature at which all components are molten is the liquidus. The mushy state is desired where a degree of plasticity is beneficial for creating the joint, allowing filling larger gaps or being wiped over the joint (e. g. when soldering pipes). In hand soldering of electronics it may be detrimental as the joint may appear solidified while it is not yet. Premature handling of such joint then disrupts its internal structure and leads to compromised mechanical integrity.