Study of Electromigration in Flip Chip Solder Joints under Extra High Current Density with Temperature Control
Date Issued
2010
Date
2010
Author(s)
Lin, Yu-Wei
Abstract
To meet the requirement for decreasing packaging size, the electron current density through flip chip solder joints has to increase with every new generation of devices. At this condition, electromigration in flip chip solder joints become a serious issue.
In this research, electromigration in flip chip solder joints under extra high current density (3.5×10^4 ~ 6.0×10^4 A/cm^2) is studied. At such a high current density level, due to Joule heating, the joint temperature is strongly coupled to the applied current density. Accordingly, it is highly desirable to have the capability to decouple the chip temperature and the current density. In this study, a water cooling module with a PID controller was devised for controlling the chip temperature. The configuration of flip chip solder joints used in this research was Ni(2 micron)/Sn2.6Ag/Cu structure.
Without the cooling module, the chip temperature increased rapidly with the applied current. When the current density reached 4.5×10^4 A/cm^2, a rapid failure caused by excessive Joule heating was observed only after 10 min of current stressing. With the cooling module attached, the chip temperature kept constant during current stressing, and the joint exhibited a much longer life (935 h) under 4.5×10^4 A/cm^2. It was successfully demonstrated that the cooling module was able to de-couple the applied current density and the chip temperature.
Since the chip temperature and the current density are successfully de-coupled, the effects of these two parameters can be studied independently. At constant chip temperature test, the failure time for flip chip solder joints increased when the current density decreased. At constant current density test, the mechanism was different when the chip temperature changed.
Subjects
flip chip
electromigration
cooling module
temperature controlled
solder
Type
thesis
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