Characterization of microstructure and crystal orientation of the tin phase in single shear lap Sn–3.5Ag solder joint specimens A.U. Telang, T.R. Bieler * Department of Chemical Engineering and Materials Science, Michigan State University, 2527 Eng Building, East Lansing, MI 48824, USA Received 19 August 2004; received in revised form 7 January 2005; accepted 18 January 2005 Abstract Tin-based solder joints are often near single or multi-crystalline and not polycrystalline, determined by comparing orientations measured using OIM on opposite sides of two solder joints. Comparison with 17 other joints indicated no preferred solidification orientation, though the likelihood for the tin c-axis to be in the plane of the joint is low. Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Lead-free solder; OIM; Texture; Solidification; Single crystal 1. Introduction Soldering is an integral part of electronic assembly where it connects and provides I/O between devices and the printed circuit boards. Lead-tin solders are being replaced by lead-free solders due to environmental concerns and international trade restrictions warranting the eradication of lead from all electronic components by 2006 [1–4]. Consequently, tin based solders such as 96.5Sn–3.5 wt.%Ag or related compositions with ter- nary or quaternary additions have been intensely inves- tigated in recent years [2,5,6]. Characterization of Sn–3.5Ag solder using single shear lap joint specimens revealed that heterogeneous grain boundary sliding and surface relief developed during creep, stress-relaxation, reversed-shear and thermomechanical fatigue (TMF) experiments [7–13]. While microstructural evolution of second phases is easily and commonly characterized with optical and electron microscopy, microstructural evolution in the tin phase is challenging, since the grain boundaries are difficult to identify in the as-solidified microstruc- tures using conventional metallography. Since a large volume fraction of Sn–3.5Ag solders consists of tin, the relationship between the crystallography of tin and deformation and failure processes in the joint con- figuration needs to be understood in order to identify failure mechanisms. Orientation imaging microscopy (OIM) is an ideal tool to obtain crystallographic and microstructural information (mesotexture) from the surface of such joints. The primary goal of this study is to determine the microstructural characteristics and the crystal orienta- tions present in the tin phase of solder joints. Previous studies carried out on one surface/side of single shear lap joints have shown evidence of near single crystals or multicrystals, but not polycrystals. This study evalu- ates the hypothesis that solder joints are nearly single- or multi-crystals, by comparing crystal orientations measured on both sides of two solder joints to deter- mine if they are the same. These measurements are compared with dominant orientations in 17 other sol- der joints, to determine if the solidification texture exhibits trends. 1359-6462/$ - see front matter Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2005.01.043 * Corresponding author. Tel.: +1 517 353 9767; fax: +1 517 432 1105. E-mail addresses: telangad@msu.edu (A.U. Telang), bieler@egr.m- su.edu (T.R. Bieler). www.actamat-journals.com Scripta Materialia 52 (2005) 1027–1031