| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 98 === Soldering reactions of the high-Pb/Cu at 350°C and the high-Pb/Ni at 400°C were investigated to uncover the massive spalling phenomenon, which was frequently observed in solder joint systems. As a function of solder compositions (99.5Pb0.5Sn, 99Pb1Sn, 97Pb3Sn and 95Pb5Sn, in wt.%) and reaction time (1–240 min), the sequence of events during the massive spalling was observed in step-by-step process which was ever recorded in such detail for this phenomenon. Moreover, the spalling process strongly depended on the Sn concentration in solder. The ternary phase diagram is successfully used in this study to rationalize the massive spalling phenomenon. With the help of diffusion path, a key kinetic diffusion feature of the driving force behind the massive spalling in this study was proposed. A possible mechanism of penetration through triple-junctions of intermetallic grains was proposed to explain the large-scale detachment of intermetallic layer without disintegrating the intermetallic layer into individual grains.
The only intermetallic compound formed in high-Pb/Cu solder reaction was Cu3Sn. However, the type of Ni–Sn intermetallic compounds formed in high-Pb/Ni soldering reaction was directly related to the Sn concentration in solder. When the Sn concentration was 5 wt.%, Ni3Sn4 formed first and followed by the formation of Ni3Sn2. When the Sn concentration decreased to 3 wt.%, Ni3Sn2 formed first and followed by the formation of Ni3Sn. When the Sn concentration became 1 wt.%, only Ni3Sn2 was observed after 240 min. This fascinating concentration dependency can be rationalized by using the Pb–Sn–Ni isotherm. The grain boundaries penetration of pure Ni by molten Pb-rich phase was observed in high-Pb/Ni soldering reactions at 400°C. This suggests that high-Pb solders are not compatible with pure Ni substrates at 400°C or higher temperature.
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