Failure Mechanism of the SnAgCu/SnPb Mixed Soldering Process in a Ball Grid Array Structure
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https://doi.org/10.1007/s11664-020-08372-8 Ó 2020 The Minerals, Metals & Materials Society
Failure Mechanism of the SnAgCu/SnPb Mixed Soldering Process in a Ball Grid Array Structure LI-YIN GAO,1,2 XIAN-WEI CUI,3 FEI-FEI TIAN,4 and ZHI-QUAN LIU
1,2,5
1.—Shenzhen Institute of Advanced Electronic Materials, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China. 2.—Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China. 3.—Jiangyin Changdian Advanced Packaging Co., Ltd., Jiangyin 214431, China. 4.—Nanjing Electronic Devices Institute, Nanjing 210016, China. 5.—e-mail: [email protected]
In this study, the influence of different reflow profiles and dosages of SnPb solder paste on the reliability of the SnAgCu/SnPb mixed assembly process was investigated. The interfacial microstructures were carefully examined through scanning electron microscopy, and two failures modes were found. Firstly, when reflowed at 245°C for 95 s, Pb-rich phases were buried within an intermetallic compound (IMC) layer and led to micro-voids and cracks under thermal stress or mechanical stress. However, upon increasing the reflow temperature or time further led to melting the solder ball totally, and the Pb element dissolved into a liquid phase and precipitated into uniform and small granules during the cooling process. Further, among the samples with different dosages of SnPb solder paste, severe shrinkage occurred at the solder joints with the addition of 12 wt.% eutectic SnPb component. Electron backscattered diffraction analysis was conducted in order to determine the mechanism of different shrinkages. The solder ball consisted of several primary Sn grains, and the shrinkage and Pb-rich phase are preferred to appear at the grain boundary. When the solder ball consisted of a single grain, no preferred orientation of the shrinkage and Pb-rich phase were detected. The shrinkage appeared at the final solidification region, which is near the IMC layer. Moreover, the shrinkages connect to each other, and a continuous crack formed on the chip side, leading to the failure. Key words: Mixed soldering, ball grid array, solidification, crack, shrinkage, failure mechanism
INTRODUCTION Lead-free (Pb-free) soldering technology in electronic devices and electronic components packaging is growing technology which is widely used nowadays in consumer electronics. However, in the fields requiring high reliability, such as military equipment, aerospace and medical machinery, the compatibility between Pb-free and Sn-Pb mixed soldering technology is an avoidable issue, since traditional Pb-based soldering still has advantages
(Received March 2, 2020; accepted July 29, 2020)
over the other materials. Therefore, development and assembly of reliable soldering materials with different material combination as a mixed soldering joints has great impact and is still regarded an important subject in electronic industries.1–3 According to the recent literature about soldering materials, the reflow pro
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