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Solder Reliability

"The Effects of Water Soluble Paste Formulation on the Ball Attach and Ball Shear Failure"

Authors: Li Tianpeng, Jorcelyn Tan Ying Ru, C. D. Breach and A. Hawkins; tpli@kester.com.sg.

Abstract: Solder ball attach of two water-soluble solder pastes, a novel zero halogen material and a halogenated material, was compared in nitrogen and air atmospheres after reflow in a Malcom reflow simulator. Videos of the reflow process showed that both pastes reflowed well in nitrogen. After air reflow, the zero halogen paste exhibited good ball attach capability without defects and minimal degradation, while the halogenated paste showed head-in-pillow defects. Decomposition and weight loss of the pastes in air and nitrogen were studied using thermogravimetric analysis (TGA). The weight loss of the zero halogen paste in air and nitrogen atmospheres was similar, which indicated that the presence of oxygen had a minor effect on the ability of the flux to protect the solder alloy. However, the halogenated paste exhibited significantly greater weight loss in air compared with nitrogen, demonstrating the poorer protection of the solder against oxidation due to the poorer thermal stability of the halogenated flux. Wetting balance results showed that wetting force obtained with the zero halogen paste was very stable with the time, whereas the wetting force obtained with the halogenated paste displayed was unstable wetting force and decreased with time. Ball shear testing was conducted at different shear speed. Failure mode and failure force were analyzed. (International Conference on Soldering and Reliability, May 2014)

"A Case Study of First-Level Die Attach with Nano-Ag Paste"

Authors: Keith Howell, Takatoshi Nishimura, Keith Sweatman, Tetsuro Nishimura and Teruo Komatsu; k.howell@nihonsuperior.co.jp.

Abstract: Since nano-Ag can be sintered at temperatures similar to those used in the reflow of high-lead solders, it has been increasingly considered one of the most promising replacement candidates because, once sintered, the melting point returns to the 961.8[degrees]C of bulk Ag. Joints made with nano-Ag have physical and mechanical properties comparable with those of Ag. That means that joints sintered with nano-Ag have higher reliability at elevated temperature and in thermal cycling, higher electrical and thermal conductivity compared with the conventional high-Pb solders. Data obtained in a successful commercial application of this...

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