| Summary: | 碩士 === 國立交通大學 === 工學院半導體材料與製程設備學程 === 106 === When the packaging industry moves to 3D IC packaging, flip-chip solder joints has been replaced by microbumps for interconnects. The solder height for a flip-chip joint is approximately 70m, and it decrease to about 15 m for a microbump. In addition, the dimension of microbumps will continue to scale down, therefore, the solder height will decrease in the future. However, whether the solder height will affect metallurgical reaction is worthy to investigate.
In this study, we examine the metallurgical reactions of SnAg and Cu or Ni under various solder heights. We fabricated Cu and Ni under-bump-metallization (UBM), and electroplate SnAg solders on them. Then, various solder joints were prepared by jointing the solder bumps on the Cu or Ni UBM. Thus solder joints with 5 m, 10m, 15 m and 20 m thick can be fabricated. Then metallurgical reactions under reflow at 260℃ and solid state aging at 150℃ were performed and thickness of intermetallic compounds was measured. We found that the thickness of the intermetallic compounds was not affected by the solder height. Nevertheless, we observed obvious thermomigration of Cu atoms. Cu atoms migrated toward the cold end, and formed Cu-Sn intermetallic compounds at the Cu/solder interfaces, resulting the thicker Cu-Sn intermetallic compounds on the cold end. In addition, bridging of Cu-Sn intermetallic compounds was observed in the joints with low solder heights. For the Cu/5 m SnAg/Cu and Cu/5 m SnAg/Ni specimens at initial state, the Cu-Sn intermetallic compounds bridged within one minute of reflow. This may cause problems for yield and reliability.
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