Inemi Pb-Free Alloy Characterization Project Report: Part V – The Effect Of Dwell Time On Thermal Fatigue Reliability
Authors: Richard Coyle, Richard Parker, Michael Osterman, Stuart Longgood, Keith Sweatman, Elizabeth Benedetto, Aileen Allen, Elviz George, Joseph Smetana, Keith Howell, Joelle Arnold Company: Alcatel-Lucent, CALCE, Delphi, Nihon Superior Co., Ltd., Hewlett-Packard Co., and DfR Solutions Date Published: 10/13/2013
Abstract: The Pb-Free Alloy Characterization Program sponsored by International Electronics Manufacturing Initiative (iNEMI) is conducting an extensive investigation using accelerated temperature cycling (ATC) to evaluate ball grid array (BGA) thermal fatigue performance of 12 commercial or developmental Sn-based, Pb-free solder alloys. This paper presents the initial findings from a specific subset of the temperature cycling test matrix that focuses on the relationship between alloy performance and temperature cycling dwell time. Results from the literature have shown that an increase in dwell time can produce a significant decrease in the thermal cycling reliability of most Sn-based, Pb-free solders. The iNEMI test matrix contains several thermal cycling profiles that allow dwell time comparisons to be made for different temperature extremes and cyclic temperature ranges (?T). Reliability comparisons are made for Pb-free alloys with Ag content varying from 0.3 to 4 wt. percent and a SnPb eutectic control is included. The failure data are reported as characteristic life ? (number of cycles to 63.2% failure) and slope ? from a two-parameter Weibull analysis. The Weibull statistics confirm that testing with an extended dwell time typically results in a significant decrease in the thermal cycling reliability of the Pb-free solders. The ATC data and failure analyses are discussed in terms of the relationship to dwell time, alloy composition, the initial microstructures and the microstructures as they evolve during temperature cycling.
Pb-free solder, thermal fatigue, dwell time, solder microstructure