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A Guide to Lead-free SoldersMicrostructural Instability in Solders

A Guide to Lead-free Solders: Microstructural Instability in Solders Chapter 4 In order to serve the function of joining electronic component leads or pads to printed wiring board circuitry, solders are necessarily relatively low melting point alloys. Therefore, they are placed in service at high homologous tempera- ture; usually temperatures exceed 0.3 0.5 T . As we have discussed previously, diffusion processes are therefore very active. As a result, the microstructure of solder alloys will be unstable at normal operating and storage temperatures for electronic equipment. The as-cast structures we discussed in Chapter 3 will coarsen over time after the assembly is completed. Within the joints, the inter- phase spacing between the constituents of the microstructure will increase and secondary phases within the matrix of Sn will increase in size. These changes in turn affect the properties of the solder. 4.1 Effects of Microstructural Coarsening and Aging on Properties of Solder The microstructure in near-eutectic solder influences the mechanical properties and in-service performance of a solder alloy. For example, ductility and creep behavior are influenced by microstructure, which in turn influences the fatigue performance and assembly reliability. Let us begin our discussion with static aging of near-eutectic SnPb, where there is significant experience in characterizing the microstructure and http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png

A Guide to Lead-free SoldersMicrostructural Instability in Solders

Editors: Engelmaier, Werner
A Guide to Lead-free Solders — Jan 1, 2007
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Publisher
Springer London
Copyright
© Springer-Verlag London Limited 2007
ISBN
978-1-84628-309-3
Pages
79 –95
DOI
10.1007/978-1-84628-310-9_4
Publisher site
See Chapter on Publisher Site

Abstract

Chapter 4 In order to serve the function of joining electronic component leads or pads to printed wiring board circuitry, solders are necessarily relatively low melting point alloys. Therefore, they are placed in service at high homologous tempera- ture; usually temperatures exceed 0.3 0.5 T . As we have discussed previously, diffusion processes are therefore very active. As a result, the microstructure of solder alloys will be unstable at normal operating and storage temperatures for electronic equipment. The as-cast structures we discussed in Chapter 3 will coarsen over time after the assembly is completed. Within the joints, the inter- phase spacing between the constituents of the microstructure will increase and secondary phases within the matrix of Sn will increase in size. These changes in turn affect the properties of the solder. 4.1 Effects of Microstructural Coarsening and Aging on Properties of Solder The microstructure in near-eutectic solder influences the mechanical properties and in-service performance of a solder alloy. For example, ductility and creep behavior are influenced by microstructure, which in turn influences the fatigue performance and assembly reliability. Let us begin our discussion with static aging of near-eutectic SnPb, where there is significant experience in characterizing the microstructure and

Published: Jan 1, 2007

Keywords: Fatigue Life; Solder Joint; Artificial Aging; SnPb Solder; Microstructural Instability

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