발간논문

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Vol.40, No.1, 100 ~ 105, 2002
Title
Welding & Joining : The Effects of Thermal Aging on Fracture Characteristics of Sn - Ag Solder Joint
정아람A Ram Jeong,이백우Baik Woo Lee,정증현Jeung Hyun Jeong,권동일Dong Il Kwon
Abstract
The fracture of eutectic Sn-Ag solder joint by thermal aging was investigated through a pull test and microstructural observation. The joint strength in the pull test decreased with increasing aging time and was saturated for aging time more than 25 hours. The change in joint strength was explained not only by such metallurgical factors as grain growth and intermetallics formation, but also by the mechanical factor of strength mismatch between solder and intermetallics. For aging time less than 25 hours, Cu_6Sn_5 intermetallics formed. Strength mismatch between solder and Cu_6Sn_5 intermetallics reduces joint strength by causing stress concentrations around the intermetallics. Joint strength decreased with the Hall-Petch relationship as solder grains become coarsened with increasing aging time. For aging time above 25 hours, Cu_3Sn intermetallics formation was confirmed. During Cu_3Sn intermetallics formation, voids generally formed. They play an important role in determining the primary failure site. The present study shows that an extended aging time reduces the joint strength and then saturates because all solder joint failure is more strongly determined by local stress concentration around voids than by the stress concentration caused by strength mismatch.
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