Chip to chip bonding using micro-Cu bumps with Sn capping layers

초록

The chip to chip bonding technique using a Cu bump capped with thin Sn layers has been frequently applied to 3D chip stacking technology. We studied the effect of the microstructure on the joints. The joints were fabricated by joining micro-Cu bumps capped with Sn-Ag solder with sizes of 10 um X 10 um, 20 um X 20 um, and 30 um X 30 um to Cu pads capped with Sn-Ag solder at 245 °C-330 °C using a thermo compression bonder. Three different types of microstructure were formed in the joints depending on the bonding condition: an Sn-rich phase with Cu6Sn5 in the Cu interfaces, Cu 6Sn5 in the interior with Cu3Sn in the Cu interfaces, and one single Cu3Sn phase. The joint with only the Cu3Sn phase had the highest shear strength. Specimens were aged at 150 °C for up to 1000 h. During aging, the microstructures of all the joints became Cu 3Sn phase only. The shear strength of the joints was very sensitive to the formation of Cu3Sn and microvoids.

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