Reliability of Lead-Free Solders

Published

December 1, 2001

Author(s)

C A. Handwerker, D Noctor, G Whitten

Abstract

In the assessment of the performance of lead-free solders, the most important question is how well these materials perform under conditions of thermomechanical fatigue. Eutectic tin-lead solders have a long history of acceptable performance with an evolving component set. From through-hole components to discrete passives and compliant-leaded devices to BGAs and CSPs, the failure modes of lead-tin solder are reasonably well understood as the thermal and mechanical loading conditions change with component type. It is straightforward then to rank the components in terms of order of failure for eutectic lead-tin. There is no such body of data for lead-free solders. There is a growing amount of data on the mechanical properties of lead-free solders but it is not known how to use these data to develop a reliability model since the failure modes of lead-free solders in use are poorly understood. The recent literature contains many extrapolations of properties to performance that have no basis. For example, it the isothermal creep rate of a lead-free alloy is found to be lower than for eutectic Sn/Pb, the reliability of that alloy is stated to be better than Sn/Pb for all component types. In the NCMS report published in 1997, thermomechanical fatique testing showed no simple relationship between the mechanical properties of the seven down selected alloys and their performance under conditions of thermomechanical fatigue (TMF). Furthermore, the ranking of alloys was found to vary with component type and thermal cycling conditions. This chapter reviews the reliability data for lead-free solders based on TMF testing, the gold test for solder joint reliability. These data come from the NCMS Lead-Free Solders Project, the EU IDEALS project, Flip Chip Technologies, and Sandia National Laboratories. The forms of the data range from Weibull plots comparing lead-free solders with Pb-Sn eutectic to statements of relative performance with no quantitative data. Various consortia have been formed in 1999-2000 to complete the gaps in these previous studies and the types of TMF experiments. Updates and information obtained by these groups can be found at HTTP://www.nemi.org, http://www.leadfree.org, and http://www.lead-free.org.

Citation

Lead-Free Solders

Volume

23

Pub Type

Journals

Keywords

consumer electronics, environmentally conscious manufacturing, lead-free solder, microelectronic assemblies, printed wiring boards, solder

Citation

Handwerker, C. , Noctor, D. and Whitten, G. (2001), Reliability of Lead-Free Solders, Lead-Free Solders (Accessed April 26, 2024)