Effect of Electromigration-Induced Joule Heating on the Reliability of Sn-Ag Microbump with Different UBM Structures
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https://doi.org/10.1007/s11664-020-08527-7 Ó 2020 The Minerals, Metals & Materials Society
Effect of Electromigration-Induced Joule Heating on the Reliability of Sn-Ag Microbump with Different UBM Structures KIRAK SON,1 GYU-TAE PARK,2 BYEONG-ROK LEE,3 CHEOL-WOONG YANG,4 JEONG SAM HAN,5 TAE-KYU LEE,6,7 and YOUNG-BAE PARK 1,8 1.—School of Materials Science and Engineering, Andong National University, Andongsi, Gyeongsangbuk-do 36729, Korea. 2.—Amkor Technology Korea Inc, Incheon 21991, Korea. 3.—STATS ChipPAC Korea Ltd, Incheon 22379, Korea. 4.—School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon-si, Gyeonggi-do 16419, Korea. 5.—Department of Mechanical and Robotics Engineering, Andong National University, Andongsi, Gyeongsangbuk-do 36729, Korea. 6.—Mechanical and Materials Engineering, Portland State University, Portland, OR 97201, USA. 7.—e-mail: [email protected]. 8.—e-mail: [email protected]
The effect of current stress-induced Joule heating on two different underbump metallization (UBM) structures in Sn-Ag microbumps was investigated with current stressing at 150°C and a current density of 5 9 104 A/cm2. Both Ni UBM and Cu UBM configuration microbump structures underwent extensive electromigration (EM) testing, with results revealing a longer lifetime with the Cu UBM configuration than the Ni UBM structure. The observed EM failure mechanism in the Ni UBM configuration was identified as a void formation within the bump interconnected Al trace and not due to damage accumulation inside the microbump structure. The intermetallic compound developed inside the microbump was formed and maintained its stability throughout the current stressing period. To identify the main driving force of damage accumulation in the Al trace, the current density and temperature distributions in the Sn-Ag microbumps were analyzed numerically via the finite element method. The simulation results showed higher Joule heating with the Ni UBM than the Cu UBM microbump configuration, along with the bump geometrical contribution of add-on higher Joule heating in the Ni UBM microbump structure. Key words: Under-bump metallization, microbump, intermetallic compound, electromigration, Joule heating
INTRODUCTION With the general trend toward miniaturization and multi-functionalization in current electronic devices, and the popularization of big data along with the aggressive movement in the Internet of Things, the service temperature and power density in integrated circuits are increasing.1,2 Moreover,
(Received June 28, 2020; accepted September 25, 2020)
the shrinkage of Si devices is constantly challenged by Moore’s law, where three-dimensional integrated circuit (3D-IC) technology provides an alternative to maintain the increasing rate of packaging density.3–6 Microbumps in 3D-IC have emerged as an important and critical building block to meet the demands of better performance and higher packaging density.4–8 Currently, the diameters of microbumps are below 20 lm, and due to the size effect, the entire microbump
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