Physical metallurgy in lead-free electronic solder development

Abstract

physical metallurgy principles play significant roles in the pursuit of suitable substitutes for traditional lead-based solders in the electronic industry. Phase diagrams, alloy development, solidification, diffusion, wetting, aging, precipitation of second-phase particles, microstructural coarsening, temperature effects, thermomechanical behavior, and creep are among the issues to be considered. This article focuses on the importance of physical metallurgy in these developments. BACKGROUND

Interfacial Intermetallic Growth and Strength of Composite Lead-Free Solder Alloy Through Isothermal Aging

“…4a). EDS analyses of these phases yielded compositions in weight percent of Sn-4.0Ag, Sn-73Ag, and Sn-40Cu, surmised to be (Sn), Ag 3 Sn, and Cu 6 Sn 5 , respectively. The Ag 3 Sn was organized as a fine needle-like phase within the (Sn) matrix.…”

“…2 During the soldering process molten solder wets and reacts with the metallization of the substrate to form a metallurgical bond by the formation of intermetallic compounds. 3 While adequate formation of this intermetallic layer is essential for good bonding, an overly thick layer promotes a brittle failure mode at this interface. 4 The thickening of this layer is due to the constant and inevitable diffusion of Sn from the bulk solder to the substrate primarily during service at high homologous temperatures.…”

Effect of Antimony Additions on Corrosion and Mechanical Properties of Sn-Bi Eutectic Lead-Free Solder Alloy

“…Among the ternary compositions, the Sn-Bi-Zn one was used in making printing wiring boards [1], however all of these eutectic compositions have a melting temperature above 200˚C. Sn-Zn eutectic has a lower melting temperature of 199˚C, but its corrosion behavior and poor wetting ability renders it useless [2]. Among the commercial Pb-free alloys, Sn-58 wt% Bi eutectic alloy may be a favorable alloy specially for electronics and telecommunications.…”

“…Among the commercial Pb-free alloys, Sn-58 wt% Bi eutectic alloy may be a favorable alloy specially for electronics and telecommunications. In fact, this alloy, which has the eutectic temperature of 139˚C, has a higher ultimate tensile stress and shear strength than Sn-Pb eutectic [2,3]. Bismuth has also been used as the alloying element in ternary Sn-Zn-Bi [4] Sn-Ag-Bi [5,6] and Sn-BiCu [7] systems to provide suitable substitutes for Sn-Pb solder alloys.…”

Interfacial Reaction and Morphology Between Molten Sn Base Solders and Cu Substrate

“…During the past decade, increasing efforts have been made to find suitable Pb-free solders as substitutes for the Sn-37(mass%)Pb alloy, and research findings have indicated Sn-base alloys to be promising candidates. [1][2][3][4] Numerous works have also contributed to knowledge of the interfacial reaction between Pb-free solders and substrates such as Cu, Ni and Au such knowledge being important, because the formation and growth of the intermetallic compounds (IMCs) produce a site for easy nucleation of cracks at the interface which may lead to the serious reliability problems.…”