Inemi Pb-Free Alloy Characterization Project Report: Part Vi – The Effect Of Component Surface Finish And Solder Paste Composition On Thermal Fatigue Of Sn100c Solder Balls
Authors: Richard Coyle, Richard Parker, Babak Arfaei, Keith Sweatman, Keith Howell, Stuart Longgood, and Elizabeth Benedetto Company: Alcatel-Lucent, Universal Instruments, Nihon Superior Co., Ltd., Delphi, Hewlett-Packard Co. Date Published: 10/13/2013
Abstract: The Pb-Free Alloy Characterization Program sponsored by the 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 findings from a specific subset of the alloy and temperature cycling test matrix that addresses thermal fatigue performance of the proprietary Sn-Cu alloy, SN100C. Two different BGA components fabricated with SN100C solder balls were assembled with either matching SN100C solder paste or SAC305 solder paste and thermal fatigue was assessed using several different temperature cycling profiles. The study identifies subtle effects that the solder paste composition and the BGA component surface finish have on the microstructures of the final assemblies. The thermal cycling results indicate that the addition of Ag from the SAC305 solder paste produces a moderate increase in fatigue life. Thermal cycling under extended dwell times results in a decrease in fatigue reliability for the samples assembled with SN100C paste as well as those assembled with SAC305 paste. The thermal cycling results are discussed in terms of the possible effects of inadvertent microalloying additions from the solder paste and surface finish.
Pb-free solder, thermal fatigue, dwell time, solder microstructure, microalloying