| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 97 === Pb-free solders added with rare earth elements have been widely verified to be able to improve their melting temperature, wettability, strength, ductility, creep resistance. However, most studies for the performance of rare earth doped solders are concerned with the analyses of their basic materials characteristics. The evaluation of reliability for real electronic packaging joints are scarcely reported. Aiming at the application requirements of electronic products, this project will systematically investigate the reliability of BGA packages by dynamic fatigue life test method with Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-0.05Ce, Sn-3Ag-0.5Cu-0.5Ce, Sn-3Ag-0.5Cu-0.5Ce-0.2Zn and Sn-1Ag-0.5Cu-0.06Ni-0.01Ge solder materials. Finite element analysis was also used to estimate the stress concentration phenomenon and probable failure location. The surface finishes for Cu pads on BT substrates include ENIG, ImSn, OSP and NiPdAu. Both the traditional and Halogen-free substrates are employed for FR-4 PCB.
The results show that the Sn-3Ag-0.5Cu-0.05Ce solder joints have similar fatigue lives as the undoped Sn-3Ag-0.5Cu specimens in spite of the various surface finishes such as ENIG, NiPdAu, ImSn and OSP. Dynamic fatigue life tests with thermal effect indicate that lower temperature, higher reliability, and Sn-3Ag-0.5Cu solder has higher fatigue life than Sn-1Ag-0.5Cu-0.06Ni-0.01Ge in all test conditions, but Sn-1Ag-0.5Cu-0.06Ni-0.01Ge has better high temperature fatigue resistance. The results also imply that although adding the Zn elements in the Ce doped solders can inhibit the occurrence of rapid whisker growth, but it cannot assure the improvement of fatigue reliability of its solder joints in real packages.
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