Development of Microstructure in Eutectic Alloys

The first case is for compositions ranging between a pure component and the maximum solid solubility for that component at room temperature [20°C (70°F)]. For the lead-tin system, this includes lead-rich alloys containing between 0 and about 2 wt% Sn (for the a-phase solid solution) and also between approximately 99 wt% Sn and pure 

Solders are metal alloys that are used to bond or join two or more components (usually other metal alloys). They are used extensively in the electronics industry to physically hold assemblies together they must allow expansion and contraction of the various components, transmit electrical signals, and dissipate any heat that is generated. The bonding action is accomplished by melting the solder material and allowing it to flow among and make contact with the components to be joined (which do not melt) finally, upon solidification, it forms a physical bond with all of these components. 

In the past, the vast majority of solders have been lead-tin alloys. These materials are reliable and inexpensive and have relatively low melting temperatures. The most common lead-tin solder has a composition of 63 wt% Sn-37 wt% Pb. According to the lead-tin phase diagram, Rgure 9.8, this composition is near the eutectic and has a melting temperature of about 183°C, the lowest temperature possible with the existence of a liquid phase (at equilibrium) for the lead-tin system. This alloy is often called a eutectic lead-tin solder. 

Figpre 9.13 Schematic representations of the eqnilibrinm microstrnctnres for a lead-tin alloy of eutectic composition C3 above and below the eutectic temperature. 

Tutorial Video Eutectic Reaction Vocabulary and Microstructures 

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