Highlights

W.J.Plumbridge

Long term mechanical reliability with lead-free solders

Keywords

Reliability, Reliability management, Solders, Modelling

Abstract

The decision to move to lead-free solders has been made, but processing and performance challenges remain. This paper considers the transition in terms of performance, with particular emphasis on long term, high reliability applications. Comparison of key mechanical properties indicates generally beneficial outcomes of the transition to lead-free alloys, although there is a lack of understanding surrounding anomalous observations, such as the effects of the bismuth. The lower melting point of Sn-Zn-Bi alloys, together with their comparable mechanical properties, provide further impetus to address their shortcomings during processing. Some lead-free alloys, such as Sn-0.5Cu, are susceptible to tin-pest formation following prolonged exposure below 13 C, and this possibility remains for the more concentrated Sn-3.8Ag-0.7Cu alloy.

1. Introduction

The die is cast! Lead-free solders are being introduced at different rates across the world. Japan is ahead; for Europe, 1 July 2006 has been set as the deadline for the transition, and the US is making rapid progress towards this goal. The alloys likely to be the initial replacements for Sn-37 Pb are Sn-0.5 Cu, Sn-3.5 Ag and Sn-3.8 Ag-0.7 Cu or slight variations of them. More uncertainty and debate exists around zinc and bismuth-containing systems (Richards et al.,