| Co-Investigator(Kenkyū-buntansha) |
SUETSUGU Kenichiro MATSUSHITA ELECTRIC INDUSTRIAL CO.,LTD., 生産技術本部, 主幹技師
INOUE Masahiro OSAKA UNIVERSITY, ISIR, RESEARCH ASSOCIATE, 産業科学研究所, 助手 (60291449)
OKU Taeko OSAKA UNIVERSITY, ISIR, ASSOCIATE PROFESSOR, 産業科学研究所, 助教授 (30221849)
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| Research Abstract |
To understand the mechanism of various types of defect formation in lead-free soldering, the several estimations on lead-free soldered joint were tried by using the microstructural observation, thermodynamic analysis, mechanical test and computer simulation. The following results were obtained :
1. From the. results of microstructural observation with thermodynamic analysis, the formation of large Ag3Sn platelets in Sn-Ag-Cu alloys induces the serious degradation of joining mechanical properties. The optimum composition of Ag is below 3.2 wt% to avoid the formation of large Ag3Sn. The addition of a fourth element to the Sn-Ag-Cu alloy significantly improves the microstructure and undercooling. For Sn-Cu alloy, the addition of Au can improve both strength and ductility up to 0.3wt%Au.
2. From the results of the in situ observation, it is clear that the solidification of a solder fillet or ball is inhomogeneous and locally time dependent. The last portion of solidification frequently forms solidification defects such as cracking. The material parameters such as lead-frame are the most significant factors that affect solidification defect formation. The solidification simulation in various assemblies can reveal the solidification sequence and the location of the last solidification portion.
3. From the results of TEM analysis, the interfaces of Sn-Ag-Cu/Fe, Fe-42Ni, Ni, and Ni-6P were clearly identified and it was revealed that there are the influences of alloying elements and reaction conditions. For the Sn-Ag(-Cu)/Ni-P system without Cu, Ni diffuses to Sn liquid to form the intermetallic layers of Ni_3 Sn_4 /Ni_3 SnP leaving a thick P-rich layer behind by the depletion of Ni, which degrades the interface. In contrast, the addition of Cu to Sn-Ag modified the interface composed of (Cu, Ni)_6 Sn_5 with a thin P-rich layer by preventing Ni diffusion into the interface. This mechanism is expected to extend to the improvement of joint reliability of this reaction system.
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