electrical properties of lead solder alloy

Lead Solder Alloys - Applications of metallurgical properties in Electrical ConductivityA report

Material Science Assignment

Group 1 (Roll 1 to 27)Section A, 3rd SemesterDepartment of MechatronicsManipal Institute of TechnologyManipal, INDIA.

Soldering alloys:-

There are many different types of soldering alloys. They depend on the different compositions of the various materials used in the alloy. The main ingredients being lead (major) and silver (minor).Price of the soldering material changes for different compositions. Some alloys are relatively cheap. A spool may cost a few hundreds of Indian rupees while others are much costlier. A Single wrong choice will cost you more money, time and effort. Hence it is a good idea to know the different types of alloys.Therefore various references were developed with respect to the variety of the alloys. The following reference covers solder alloys which feature melting points from about 50C to about 400C, both lead based and lead free. They're also known as soft solders. Most of them are patent free. The information below has been gathered mostly from product data sheets of various manufacturers such as Indium Corp. of America, Alpha Metals (Cookson Group), Stannol and others. The alloys are labeled by their metal percentages, but there also commercial and historical names included. Those commercial alloy numbers are shared widely among manufacturers. For instance, Indalloy 281, Ostalloy 281 and AsarcoLo 281 refer to the same alloy of 58% bismuth and 42% tin. In this case, 281 stands for the melting point in F, but such a number may have a different meaning for other alloys.

Some alloys have single melting point like most other materials. Thus, whenever certain temperature is reached the alloy will completely change its state to liquid. There are also some alloys which wont completely change their composition at a specific temperature. These alloys will be completely solid below a temperature called the solidus temperature. They are in pure liquid phase above a temperature. In between these they lie in a semisolid state. However for ease of soldering it is preferred that the temperatures have minimal difference. . When temperature is between solidus and liquidus, an alloy is in so called plastic state due to some liquid and solid content present at the same time.

Soldering theory:

Solderingis a process in which two or moremetallicitems are joined together by melting and flowing afiller metalinto the joint, the filler metal having a lower Melting ptthan the adjoining metal. Soldering differs fromweldingin that soldering does not involve melting the work pieces. Inbrazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes.

Soldering filler materials are available in many differentalloysfor differing applications. In electronics assembly, theeutecticalloy of 63% tin and 37% lead (or 60/40, which is almost identical in melting point) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications. Some examples of soft-solder are tin-lead for general purposes, tin-zinc for joiningaluminum, lead-silver for strength at higher than room temperature, cadmium-silver for strength at high temperatures, zinc-aluminum for aluminum and corrosion resistance, and tin-silver and tin-bismuth for electronics. As our studies are concerned with electrical applications of soldering given below is an usurp from a text on proper electrical soldering. This will make sure if the component has been properly soldered or not. In case of oxidation of the solder, its electrical conductivity changes due to the dissolution of the removal of all free or most electrons in bonds.

Soldering is quickly heating the metal parts to be joined, then applying a flux and a solder to the mating surfaces. The finished solder joint metallurgically bonds the parts - forming an excellent electrical connection between wires and a strong mechanical joint between the metal parts. Heat is supplied with a soldering iron or other means. The flux is a chemical cleaner which prepares the hot surfaces for the molten solder. The solder is a low melting point alloy of non-ferrous metals.Solder and FluxSolder is a metal or metallic alloy used, when melted, to join metallic surfaces together. The most common alloy is some combination of tin and lead. Certain tin-lead alloys have a lower melting point than the parent metals by themselves. The most common alloys used for electronics work are 60/40 and 63/37. The chart below shows the differences in melting points of some common solder alloys.Tin/LeadMelting Point

40/60460 degrees F (230 degrees C)





Most soldering jobs can be done with fluxcored solder (solder wire with the flux in a "core") when the surfaces to be joined are already clean or can be cleaned of rust, dirt and grease. Flux can also be applied by other means. Flux only cleans oxides off the surfaces to be soldered. It does not remove dirt, soot, oils, silicone, etc.

Physical and Mechanical Properties of Lead Solder Alloys

SolderAlloyMeltingPoint,Csolidus/liquidusDensity,g/cmElectricalResistivity,mThermalConductivity,W/mKTensileStrengthatBreak,kgf/cmTensileElongationatBreak,%BrinellHardness,HB

alloys of tin (Sn) and lead (Pb) with or without silver (Ag)

Sn90Pb10(alloy #118)183 / 2137.55--49040-

Sn63Pb37(alloy #106)183 / 1838.400.145505253717

Sn62.5Pb36.1Ag1.4(alloy #104)179 / 1798.410.14550490-16

Sn60Pb40(alloy #109)183 / 1918.500.153495354016

Sn55Pb45(alloy #113)183 / 2008.68-----

Sn50Pb50orPb50Sn50(alloy #116)183 / 2128.870.158484203514

Pb55Sn45orSn45Pb55(alloy #125)183 / 2279.070.166----

Pb60Sn40orSn40Pb60(alloy #130)183 / 2389.280.171443802512

Pb65Sn35orSn35Pb65(alloy #135)183 / 2479.500.176---12


Pb75Sn25orSn25Pb75(alloy #145)183 / 2689.960.194-2405311


Pb85Sn15orSn15Pb85(alloy #153)183 / 28810.70--330-11

Pb88Sn10Ag02(alloy #228)267 / 29010.750.2032723042-


Pb92.5Sn05Ag2.5(alloy #151)287 / 29611.020.200-295--


Pb97.5Ag1.5Sn01(alloy #165)309 / 30911.280.28723310239

alloys of bismuth (Bi) and/or cadmium (Ca) with tin (Sb) and/or lead (Pb)

Bi58Sn42(alloy #281)138 / 1388.560.383195655523

Sn60Bi40(alloy #281-338)138 / 1708.120.345305253524

Bi55.5Pb44.5(alloy #255)124 / 12410.440.43144503815

Sn43Pb43Bi14(alloy #97)144 / 1639.02--45041-

Sn51.2Pb30.6Cd18.2(alloy #181)145 / 1458.45-35440--

alloys of indium (In) with lead (Pb) and/or tin (Sn) and/or silver (Ag)

In70Pb30(alloy #204)165 / 1758.190.19638245--

In60Pb40(alloy #205)173 / 1818.520.24629290--

In50Pb50orPb50In50(alloy #7)184 / 2108.860.287223305510

Pb60In40(alloy #206)197 / 2319.300.33219350--

Pb75In25(alloy #10)240 / 2609.970.375183854810

Pb81In19(alloy #150)260 / 27510.270.38317390--

Pb95In05(alloy #11)300 / 31311.060.33821305526

In52Sn48(alloy #1E)118 / 1187.300.14734120835

In50Sn50orSn50In50(alloy #1)118 / 1257.300.14734120835

In97Ag03(alloy #290)143 / 1437.380.0757355-2

In90Ag10(alloy #3)143 / 2377.540.07867115613

In80Pb15Ag05(alloy #2)149 / 1547.850.13343180585

Pb90In05Ag05(alloy #12)290 / 31011.000.30825405239

Pb92.5In05Ag2.5(alloy #164)300 / 31011.020.31325320--

Sn77.2In20Ag2.8(alloy #227)175 / 1877.250.176544804717

Sn37.5Pb37.5In25(alloy #5)134 / 1818.420.2212337010110

Sn54Pb26In20(alloy #230)136 / 1528.05-----

Sn70Pb18In12(alloy #9)154 / 1677.790.1414537513612

low temperature alloys

In51.0Bi32.5Sn16.5(alloy #19 or Field's alloy)60 / 607.880.522-340-11

Bi50Pb26.7Sn13.3Cd10(alloy #158 or Wood's alloy)70 / 709.580.4311842012015

Bi52Pb30Sn18(alloy #39 or Newton's alloy)96 / 969.600.7501336510016

Bi50Pb28Sn22(alloy #41 or Rose's alloy)100 / 1009.44-----

Phase Diagram of Lead Solder Alloy:

Eutectic Phase Diagram of Tin & Lead

A mixture of lead(Pb) & tin(Sn) is eutectic because these metals are only partially soluble in each other when in the solid state. Lead & tin have different crystal structures(FCC versus BCT) and lead atoms are much larger. No more than 19.2% by weight of solid tin can dissolve in solid lead and no more than 2.5% of solid lead can dissolve in solid tin. The solid lead-tin alloy thus consists of a mixture of two solid phases, one consisting of a lead-rich solid (alpha, -phase) that can dissolve in a maximum of 19.2wt%tin(Sn) at 183C (more at higher temperature), and one consisting of a tin-rich (beta, -phase) that can dissolve in a maximum of 2.5wt%lead(Pb) at 183C (more at higher temperature). For example, above 260C 40wt%;tin in a tin-lead mixture will be a completely intermixed liquid. The liquidus line separates pure liquid phase from phases which can be mixtures of liquid and solid. The solidus line separates mixtures of liquid and solid from pure solid (pure -phase or pure -phase at extremes of concentration). Just below the liquidus line 40wt%tin in a tin-lead mixture will have some solid -phase tin-lead (12wt%tin proeutectic) and the rest a mixture of tin-lead liquid. As temperature drops, the amount of solid -phase tin-lead in the liquid-solid mixture increases, and the percentage of tin in the -phase increases until the temperature reaches 183C and the mixture becomes completely solid partially -phase (19.2wt%tin) and partially -phase (97.5wt%tin) tin-lead mixture, along with some proeutectic solid. A solvus line delineates temperatures below which tin and lead are completely immiscible. Solidification in the alpha proeutectic region consists of layered growth of solid nodules with each layer containing a higher concentration of tin. This layering of increasing concentrations of tin is called coring. Faster cooling results in reduced coring. The word eutectic is derived from Greek roots meaning "easily melted". A eutectic mixture has a eutectic composition for which complete liquefaction occurs at a lower temperature (the eutectic temperature) than for any other composition. For lead & tin the eutectic composition is 61.9wt.% tin and the eutectic temperature is 183C which makes this mixture useful as solder. At 183C, compositions of greater than 61.9wt.% tin result in precipitation of a tin-rich solid in the liquid mixture, whereas compositions of less than 61.9wt.% tin result in precipitation of lead-rich solid.

References:SOLID-LIQUID PHASE DIAGRAMS: TIN AND LEAD http://www.chemguide.co.uk/physical/phaseeqia/snpb.htmlhttp://www.ae.utexas.edu/courses/ase324_huang/Lecture7.pdf

Phase diagrams from http://www.intute.ac.uk/sciences/cgi-bin/search.pl?term1=phase+diagrams&limit=0

electrical properties of lead solder alloy

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