Microstructure and mechanical properties of lead-free solders and solder joints used in microelectronic applications

• Published in: IBM journal of research and development Vol. 49; no. 4.5; pp. 607 - 620
• Main Authors: Kang, S. K., Lauro, P., Shih, D.-Y., Henderson, D. W., Puttlitz, K. J.
• Format: Journal Article
• Language: English
• Published: Armonk International Business Machines Corporation 01.07.2005
• Subjects: Alloys; Crystal structure; Intermetallic compounds; Lead free solders; Mechanical properties; Metal fatigue; Microelectronics; Microstructure; Packaging; Process controls; Solidification; Surface mount technology; Temperature
• ISSN: 0018-8646; 0018-8646; 2151-8556
• DOI: 10.1147/rd.494.0607

The replacement of lead (Pb)-bearing solders used in the electronic industry with Pb-free solders will become a reality in the near future. Several promising Pb-free solders have recently been identified, including Sn-0.7 Cu, Sn-3.5 Ag, Sn-3.8 Ag-0.7 Cu, and Sn-3.5 Ag-4.8 Bi (in wt.% with slight variations in composition). These are all Sn-rich solders with melting temperatures between 210°C and 227°C, and are recommended for various soldering applications, including surface mount technology (SMT), plated-through-hole (PTH), ball grid array (BGA), flip-chip bumping, and others. Although a considerable amount of information on Pb-free solders has been published in the last few years, the database on these new materials is still at an infant stage compared with that for Pb-containing solders. This paper addresses several aspects of the current fundamental materials understanding associated with Pb-free solders and various issues regarding their imminent use in electronic interconnect applications, including microstructure-processing-property relations, mechanical properties, interfacial reactions, and the thermal-fatigue life and failure mechanisms of Pb-free solder joints. [PUBLICATION ABSTRACT]