In-situ isothermal aging TEM analysis of a micro Cu/ENIG/Sn solder joint for flexible interconnects  

作　　者：Jinhong Liu Jianhao Xu Kyung-Wook Paik Peng He Shuye Zhang 

机构地区：[1]State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,150001,China [2]Department of materials science and engineering,KAIST,291 Daehak-ro,Yuseong-gu,Daejeon,305-338,Republic of Korea

出　　处：《Journal of Materials Science & Technology》2024年第2期42-52,共11页材料科学技术（英文版）

基　　金：supported by the opening fund of National Key Research and Development Program of China(No.2020YFE0205300);Key Laboratory of Science and Technology on Silicon Devices,Chinese Academy of Sciences(No.KLSDTJJ2022-5);Chongqing Natural Science Foundation of China(No.cstc2021jcyj-msxmX1002);the Fundamental Research Funds for the Central Universities(No.AUGA5710051221).

摘　　要：Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.

关 键 词：In-situ TEM observation Isothermal aging Micro Cu/ENIG/Sn solder joint Cu_(6)Sn_(5)phase transition 

分 类 号：TG425[金属学及工艺—焊接]