Predicting the Drop Performance of Solder Joints by Evaluating the Elastic Strain Energy from High-Speed Ball Pull Tests TAEHOON YOU, 1 YUNSUNG KIM, 1 JINA KIM, 1 JAEHONG LEE, 2 BYUNGWOOK JUNG, 2 JUNGTAK MOON, 2 and HEEMAN CHOE 1,3 1.—School of Advanced Materials Engineering, Kookmin University, Chungneung-dong, Songbuk-ku, Seoul 136-702, South Korea , 2.—MK Electron Co., Ltd., 316-2 Geumeoh-ri, Pogok-eup, Cheoin-gu, Yongin-si, Kyeonggi Province 449-812, South Korea. 3.—e-mail: heeman@kookmin.ac.kr Despite being expensive and time consuming, board-level drop testing has been widely used to assess the drop or impact resistance of the solder joints in handheld microelectronic devices, such as cellphones and personal digital assistants (PDAs). In this study, a new test method, which is much simpler and quicker, is proposed. The method involves evaluating the elastic strain energy and relating it to the impact resistance of the solder joint by consid- ering the YoungÕs modulus of the bulk solder and the fracture stress of the solder joint during a ball pull test at high strain rates. The results show that solder joints can be ranked in order of descending elastic strain energy as follows: Sn-37Pb, Sn-1Ag-0.5Cu, Sn-3Ag-0.5Cu, and Sn-4Ag-0.5Cu. This order is consistent with the actual drop performances of the samples. Key words: Solder joint, SnAgCu, deformation and fracture, intermetallic alloys and compounds, mechanical properties, elastic properties INTRODUCTION Lead-free solders, particularly Sn-Ag-Cu, are becoming increasingly popular in the electronic packaging industry, due to the environmental con- cerns associated with lead. 1–6 Sn-Ag-Cu solders possess several advantages over conventional Sn-Pb solders. These include higher stiffness and strength, and superior resistance to thermal cycling and fatigue as well as their high microstructural stability. 2,7,8 However, the fact that they are stiffer and more brittle also makes them more prone to brittle failure during impact loading, which is fre- quently encountered in microelectronic packages for handheld electronic devices. 1,9 A number of differ- ent methodologies (e.g., drop impact, high-speed ball shear or ball pull, and tensile bond tests) to simulate and understand the fracture behavior of a solder joint under high-strain-rate loads have been attempted. 5,10 However, among the various existing test methodologies, only the board-level drop test, proposed by the Joint Electron Device Engineering Council (JEDEC), has been widely acknowledged for providing a common test reference for the industry in assessing the drop performance of microelec- tronic solder joints. Nevertheless, the JEDECÕs standard board-level drop test method is generally too costly and time consuming to be viable. 10,11 Furthermore, the data obtained from this technique make it rather difficult to determine the inherent resistance of the solder joint to impact loadings. This is because it is almost impossible to distinguish between the impact responses of the solder mate- rial, the board, and any other packaging materials. In this article, we propose a new method of quantitatively evaluating the impact resistance of a solder joint. The method involves the analysis of the solder jointÕs elastic strain energy during high- speed tensile loading. The solder materialÕs YoungÕs modulus and the fracture stress of the intermetallic- compound (IMC) interfaces under the high-speed pull test conditions are the only measurements required. (Received August 12, 2008; accepted December 4, 2008; published online January 10, 2009) Journal of ELECTRONIC MATERIALS, Vol. 38, No. 3, 2009 Regular Issue Paper DOI: 10.1007/s11664-008-0633-y Ó 2009 TMS 410