Improved Reliability and Mechanical Performance of Ag Microalloyed Sn58Bi Solder Alloys

Guang Ren,Maurice N Collins

doi:10.3390/met9040462

Abstract

Ag microalloyed Sn58Bi has been investigated in this study as a Pb-free solder candidate to be used in modern electronics industry in order to cope with the increasing demands for low temperature soldering. Microstructural and mechanical properties of the eutectic Sn58Bi and microalloyed Sn57.6Bi0.4Ag solder alloys were compared. With the addition of Ag microalloy, the tensile strength was improved, and this was attributed to a combination of microstructure refinement and an Ag3Sn precipitation hardening mechanism. However, ductility was slightly deteriorated due to the brittle nature of the Ag3Sn intermetallic compounds (IMCs). Additionally, a board level reliability study of Ag microalloyed Sn58Bi solder joints produced utilizing a surface-mount technology (SMT) process, were assessed under accelerated temperature cycling (ATC) conditions. Results revealed that microalloyed Sn57.6Bi0.4Ag had a higher characteristic lifetime with a narrower failure distribution. This enhanced reliability corresponds with improved bulk mechanical properties. It is postulated that Ag3Sn IMCs are located at the Sn–Bi phase boundaries and suppress the solder microstructure from coarsening during the temperature cycling, hereby extending the time to failure.

Highlights

IntroductionSn37Pb (expressing 37 wt.% Pb and the balance is Sn concentration, hereafter) eutectic solder in the electronic industry
The implementation of legislation entitled “Restriction on the use of certain Hazardous Substances (RoHS)” in the European Union in July 2006 marked the beginning of the phasing out of conventionalSn37Pb eutectic solder in the electronic industry
Various SAC alloy systems have been proposed by Japanese (SAC305, short for Sn3.0Ag0.5Cu), EU (SAC387, short for Sn3.8Ag0.7Cu), and US (SAC396, short for Sn3.9Ag0.6Cu) consortiums [8], with the SAC305 alloy widely used by the industry as the most promising candidate for reliable Pb-free solder due to its reliability under thermal cycling [9,10]

Summary

Introduction

Sn37Pb (expressing 37 wt.% Pb and the balance is Sn concentration, hereafter) eutectic solder in the electronic industry. Most major electronics manufacturers have stepped up their search for alternatives to Pb-containing (Sn37Pb) solders (i.e., Pb-free solders). Sn–Ag, Sn–Cu, and Sn–Ag–Cu (SAC) Pb-free eutectic or near eutectic systems have emerged as the front runners in the replacement of Sn37Pb solder [2]. Various SAC alloy systems have been proposed by Japanese (SAC305, short for Sn3.0Ag0.5Cu), EU (SAC387, short for Sn3.8Ag0.7Cu), and US (SAC396, short for Sn3.9Ag0.6Cu) consortiums [8], with the SAC305 alloy widely used by the industry as the most promising candidate for reliable Pb-free solder due to its reliability under thermal cycling [9,10]

Methods

Discussion

Conclusion