Advances in Pb-free Solder Microstructure Control and Interconnect Design

Abstract

New electronics applications demanding enhanced performance and higher operating temperatures have led to continued research in the field of Pb-free solder designs and interconnect solutions. In this paper, recent advances in the microstructural design of Pb-free solders and interconnect systems were discussed by highlighting two topics: increasing b-Sn nucleation in Snbased solders, and isothermally solidified interconnects using transient liquid phases. Issues in bSn nucleation in Sn-based solders were summarized in the context of Swenson's 2007 review of the topic. Recent advancements in the areas of alloy composition manipulation, nucleating heterogeneities, and rapid solidification were discussed, and a proposal based on a multi-faceted solidification approach involving the promotion of constitutional undercooling and nucleating heterogeneities was outlined for future research. The second half of the paper analyzed two different approaches to liquid phase diffusion bonding as a replacement for high-Pb solders, one based on the application of the pseudo-binary Cu-Ni-Sn ternary system, and the other on a proposed thermodynamic framework for identifying potential ternary alloys for liquid phase diffusion bonding. All of the concepts reviewed relied upon the fundamentals of thermodynamics, kinetics, and solidification, to which Jack Smith substantially contributed during his scientific career.

Influence of cooling conditions on microstructure and mechanical property of Sn-0.3Ag-0.7Cu lead-free solder

“…By fast cooling condition, IMC in the Sn-rich matrix were more distributed than by slow cooling. This was due to the rapid cooling which promoted fine Ag3Sn particles with spherical morphology dispersed in the Snrich matrix [5].…”

“…Furthermore, growing environmental concerns and related laws and regulations evolve the Restriction of Hazardous Substances (RoHS). This directive has contributed to the development of many lead-free solders to replace the lead-containing solders [5][6][7]. The ternary solder system is the most widely used lead-free solder in the industry, composed of Sn−Ag−Cu (SAC), this solder provides good solderability, high electrical conductivity, and a better mechanical property compared to Sn-Pb solder [7,8].…”