Effects of Be and Co addition on the growth of Sn whiskers and the properties of Sn-based Pb-free solders
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Sun-Kyoung Seo and Moon Gi Cho Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Republic of Korea; and Package Development Team, Semiconductor R&D Center, Samsung Electronics, Hwasung-city, Gyeonggi-do 445-701, Republic of Korea
Dong Nyung Lee Department of Materials Science and Engineering, Seoul National University, Gwanak-gu, Seoul 151-742, Republic of Korea; and R&D Center, Iljin Materials Co., Ltd., Mapo-gu, Seoul 121-716, Republic of Korea
Kyoo-Sik Kang R&D Center, Iljin Materials Co., Ltd., Mapo-gu, Seoul 121-716, Republic of Korea
Hyuck Mo Leea) Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Republic of Korea (Received 14 September 2011; accepted 11 May 2012)
To enhance the reliability of Pb-free solders in high temperature and high humidity conditions, the minor alloying elements of Be and Co are investigated in terms of the growth of Sn whiskers and various properties of Sn-based Pb-free solders. Sn whisker growth is suppressed by adding up to 0.02 wt% Be to Sn-based solders. Adding Be and Co can effectively reduce the undercooling of Sn–1.0Ag–0.5Cu (wt%) solders. And the microstructures of Sn–1.0Ag–0.5Cu–0.02Be solders are similar to those of Sn–1.0Ag–0.5Cu. Furthermore, adding Co to solders increases the microhardness number as a result of the solid solution hardening. Adding Be causes no changes in the morphology or thickness of Cu6Sn5 at the Cu/OSP (organic solderability preservative) under bump metallurgy interface. However, the scallop-like Cu6Sn5 microstructure changes to a flat (Cu,Co)6Sn5 microstructure when 0.05 wt% of Co is added to Sn–1.0Ag–0.5Cu–0.02Be solders. I. INTRODUCTION
Household appliances used to be operated only in the relatively stable environment of the home. However, due to technological advances, there has been a proliferation of mobile devices. Mobile devices are used everywhere in a variety of conditions, including: at the beach or swimming pool, and while hiking, climbing, or jogging, where they may be exposed to high temperatures and humidity. Therefore, mobile devices must be highly durable because of these varied environments and the increased likelihood of accidental impact. Solder alloys, which play a crucial role in mobile devices, must also be stable in high temperature and high humidity and should be able to withstand accidental impact.1,2 Furthermore, in 2006, the EU enacted legislation, Restriction of Hazardous Substances, that prohibits the use of Pb in electronic devices because of health and environmental concerns.3 Consequently, Pb-bearing solder alloys have been replaced with Pb-free solder alloys, specifically, Sn-based Sn–Ag, Sn–Cu, and Sn–Ag–Cu solder alloys.4–6 However, Sn-based Pb-free solders have technical issues a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.182 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
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that must be overcome to ensure the reliability of mobile devices. A major drawback of using
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